chemistry of hydration of portland cement

7/30/2019 Chemistry of Hydration of Portland Cement

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Research and Development Laboratoriesof the

Portland Cement Association

RESEARCH DEPARTMENTBulletin 153

Chemistry of Hydration ofo Portland Cement

ByL. E. Copeland, D. L. Kantro, and George Verbeck

R epr in ted fr om Ohemistryof GementP r oceed in gs of t he F on rt h I nt er na t ion a l S ymposium

Wa shingt on , D . C ., 1960, held a t t heNa tion al B urea u of S ta nda rds (U .S . D epa rt men t of C omm er ce)

Mon ogr a ph 43, Vol. I , S ession N , P a per I V-3, 429-465


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CHEMISTRY OF HYDRATION OFPORTLAND CEMENT

ByL. E. Copeland, D. L. Kantro, and George Verbeck

P ORTLAND G 13ME NT AS SOC IATI ONRESEARCH . 4ND DEVE I .OPMEhTT LABORATORIE S

5420 Old Or cha rd Roa dSkok ie , I l li noi s


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Paper IV-3. Chemistry of Hydration of PortlandCement*L. E. Copeland,D. L. Kantro, and GeorgeVerbeck

SynopsisTh e r es ul ts of r ecen t i nv es tig a ti on s h a ve pr ov id ed ev id en ce f or t he pr es en ce of s ev er a la lum in at es a nd s ulfoa lu min at es in h ar den ed por tla nd cem en t pa st es . F or s om e of t hes e,l it tl e ev id en ce f or t h ei r pr es en ce h a d b een ob ta in ed pr ev iou sl y. S om e in di ca t ion s h a ve a ls ob een ob ta in ed a s t o t he n a tu re of t he i ron -b ea r in g h yd ra t es .I nfor ma tion a s t o t he w at er con ten ts of t he va rious hy dr at es for med ca n be obt ainedf or cer ta i n d ry in g con di tion s b y s ta t is ti ca l a n aly sis of n on ev apor a bl e w a t er d at a a s a f un ct ionof t he compos it ion pa r amet er s of t he cem en t.Al on g w it h X-r a y a n d s ta t is ti ca l r es ul ts , f ree-l im e d at a ob ta in ed b y X-r a y q ua n tit a ti vea na lysis ca n be combined w ith the oxide composit ion of a cement so tha t a n est ima tedcom pos it ion of a h yd ra ted pa st e of t ha t cem en t ca n be ca lcula ted . M os t of ou r con cept sa bout t he r at e of h ydr at ion of cem ent in pa st es or con cr et e h ave been ba sed on t he r at e ofin cr ea se of st ren gt h, h ea t of h yd ra tion , a nd fixed w a ter . I nfer en ces con cer ni ng t he r at es ofh yd ra t ion of t he in div id ua l compon en ts h a ve b een m a de f rom con si der a ti on s of r a te of ch a ng ein h ea t of h yd ra tion , a nd in r ela t ed ph ys ica l a nd ch em ica l pr oper ties of t he h yd ra tion pr od -uct s. D irect mea surement of t hese la tt er ra tes show tha t t he inferences a re not a lw aystrue. Recen t da ta a re pr esen ted on t he hea ts of h ydr at ion of t he d iffer en t AS TM t ypes ofcements a t a ges from 3 da ys to 13 yea rs a t 0.40, 0.60, a nd 0.80 w ater-cement ra tio. Thesig nifica nt in flu en ce of w a ter -cem en t r at io on t he r at e of h yd ra t ion of cem en t ca n be in ter -pr et ed in t er ms of ph ys ica l pa ra met er s of t he h yd ra tin g pa st e. Th e effect of t em per at ur esin the ra nge of 4.4 to 110 C on the ra te of hydra tion of cement ca n be expressed by theArrhenius equa t ion .As a fir st a ppr oxim at ion , t he in tr insic h ydr at ion ch ar act er ist ics of cem en ts ca n beexpr essed in t er ms of t he com posit ion s of t he cem en ts, by lea st sq ua res a na lyses of h ea tevolut ion a nd ch em ica lly com bin ed w at er . S econ da ry ch anges of t he hy dr at ed ca lciuma lum in at e a re in dica ted . S om e a spect s of t he r oles of gy ps um , a lka lies, gla ss con ten t, a ndig ni ti on l os s of t he or ig in a l cem en t on h ea t ev ol ut ion a r e con si der ed .

R6sum6L es r&d ta t s d e r eoh er ch es r 6cen tes on t fou rn i d es pr euv es d e la pr 6s en ce d e plu sieu rsa lu min at es et s ulfoa lu min at es cla ns I es pfit es d e cim en t por tla nd d ur cies . P ou r cer ta in esd en tr e elles , cet te pr&en ce n 6t ait ju sq uh pr 6s en t q ue peu 6vid en te. D es in dica tion s on tW 6ga lem en t obt en ues q ua nt A l a n at ur e d es h yd ra tes fer rif~ r es .P ou r cer ta in es con dit ion s d e s 6ch age, on peu t obt en ir d es in for ma tion con cer na n t I est en eur s en ea u des diff&en ts h ydr at es for m6s, a U m Oyen dune a na lyse st at ist iq ue desd on n6es d e lea u n on -&a por able en fon ct ion d es pa ra m?d res d e la com posit ion d u cim en t.Avec les r&u lt a ts d es r ay on s X et st at ist iq ues , les d on n6es d e ch au x I ibr e obt en ues pa ra na ly se q ua nt it at ive d es r ay on s X peuv en t &t re com bin 6es a ux com pos it ion s oxy des d u ncim en t d e fa gon t elle q ue lon peut ca lculer un e com pos it ion es tim 6e d un e pa te h yd ra t6ede ce cim ent . La plupa rt de n os con cept s sur la vit esse dh ydr at at ion d u oim en t cla ns lespit t es ou cla ns le b&on ont W ha s& sur la vit esse de la ugmenta tion de la resist a nce, lach a le ur d h y dr a t a ti on , e t I ea u t ix 4e. D es d educt i on s oon ce rn a n t I es v it es se s d h y dr a t a ti ond es compos a nt s i nd iv id ua ls on t &4 t ir ies A p a rt ir d e con si der a ti on s s ur la v it es se d e ch a ng e-m en t cla ns la ch aleur dh ydra ta tion , et cla ns les propr i6t 6s physiq ues et chim iq ues, S Yr a ppor t an t, d es pr od ui ts d h yd ra t a ti on . L a m es ur e d ir ect e d e ces d er ni ~ res v it es ses in di qu eq ue I es d ed uct ion s n e s en t pa s t ou jou rs v ra ies .P r&en ta t ion es t fa it e d e d on n&es r 6cen tes s ur l es ch a leu rs d h yd ra t a ti on d es d if f6r en tst ypes de cimen ts selon les n or mes AS TM ~ des iges a lla nt de 3 jour s i 13 a ns a un r appor tea u-cim en t d e 0.40, 0.60, et 0.80. I .in flu en ce s ign ifica tive d u r appor t ea u-cim en t s ur lav it es se d h y dr a t a ti on du cime nt p eu t &t r e in t er pr 6t 6e en f on ct ion d e p a ram~ t r es p hy si qu es d e

la p&t e q u i s h yd ra t e. L 4q ua t ion Ar r hen iu s peu t expr im er leff et d es t emper a tu res a lla n t d e4.4 & 110 C s ur la vit es se d h yd ra ta tion d u cim en t.C omme pr em ih re a ppr oxim at ion , on peu t expr im er les ca ra ct ~ ris tiq ues in tr in s~ q uesd h yd ra t a ti on d es cimen ts en f on ct ion d es compos it ion s d es cimen t: , pa r a n al ys es a u x &ca r tsm oi nd res q ua dr a ti qu es d e l4v ol ut ion d e la ch a leu r et d e lea u ch im lq uem en t combi n6e. L esch a ng em en ts s econ da ir es d e la lumin a te d e ca lci um h yd ra t i s en t in di qu&. C er ta in s a s pect sd u r ble d u g yps e, d es a lca lis , d e la t en eu r en v er re, et d e l a per te a u feu d u cim en t or ig in al s url . 6volut i on de l a cha leu r sen t cons id6r&.Zusammenfassung

D ie E rgebn is se d er n eu es ten F or sch un g h aben gezeigt , d afl m eh rer e Alum in at e u ndS ulfoa lu min at e in geh iir tet en P or tla nd zem en tm as sen v or ha nd en s in d. E in ige d ies er s in dfr iih m n icht iden tifizier t w or den , un d m an ha t such sch on et wa s iiber den C ha ra kt er derei se nh a lt ig en Hy dr a t e a u sf in di g ma ch en k onn en .*Fourthnternat ionalym~ miumm theChemistryf Cement ,Washington,,C .,1960, CmtributonfmmtheResearch an dDevelopreenL abora toriesof theP ortlan dCementAssociat ion,kokie,111.

429


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Man k a nn d en Wa s se rg eh a lt d er v er SChi ed en en Hy dr a t e f ur g ew i ss e Trock nun gs be di n-g un gen m it H il fe ei ncr s ta t i. st is ch en An a ly se, b ei d er d a s n ich tv er dampf un gs f a h ig e Wa s sera h Funk ti on d er Zu sammen s et z un gs pa r amet er d es Zemen t es a u sg ed i-i ick t w i rd , b cs t immen .D umb ei ne K ombirmt ion ci cr R on tg en beu gu n gsmes su ng en , d er s ta t is ti sch en Pmmd ta t eu nd d cr Wcr t e fl w f rei en K a lk , w ie s ie d ur ch q ua n ti ta t iv e R bn tg en st ru kt ur bes timmu ng ener hfd ten w er clen , u nd s uch d er Oxy dzu sa mm em et mn gen ka nn m an ein e s ch lit zu ngs weis eZu sammen set zu ng d er h yd ra t is ier ten P a st e ei nes s ol ch en Zem en ts er rech nen . D ie m ei st enu ns er er I deen i ib er d ie H yd ra t a ti on sg es ch w in dig keit d es Zem c+ n t s in P a s ten od er i n B et onwu rd en dur ch ei n S t ud iw n d er Gw chw in d ig ke it d er F es t ig kei ts zu n a hmcm , d er H y dr a t a t ion s.w a rm e u nd d es geb un den en Wa ss er s er ha lt en , D ie H yd ra t a ti on sg es ch w in dig kei ten d erei nz eln en Ver bi nd un gen w ur den v on B et r ach tu ng en , d ie s ich m it d en H yd ra t a ti on sw it rm e-v er fm der un gen b efa s sen , u nd s uch m it v er w a nd ten ph ys ik al is ch en u nd ch em is ch en E ig en -s ch a f t e n d er H y dr a t a ti on s pmdukt e, i nt er - u n d ex tr a pol ier t . Aber cfirekteMessungendieserVeranderungenhaben geze ig t , d a l ? sol che In te r-und Ext rapol ie rungenmanchmal m I r r t t i -mern lei t en konnen .Die let z t , en Messungender I I yd ra t a t i onswarmendcr versch iedcnenASTM-Type n d erZem en te, d ie z wi sch en 3 Ta gen u nd 13 , J a hr en a lt w a r cn , u nd m it Wa s ser /Zem en tv er ha lt .n is scn 0, 40, 0,60 u nd 0,80 a n gem a ch t w or den w a ren , w er den er or ter t . D er b ed eu tu ng sv ol leE i nf lu l? d es \Va s se r/Zemen t ve rh%t ni ss es a u f d ie H y dr a t a t ion sg es chw in d ig kei t d es Zemen t ska ,n n ,n it H ilfe d er pby sika lis ch en P a ra met er d er h yd ra tis ier en den lMa ss e a us ged rt icktw er deu . D er Temper a tu refi ek t ka n n z wi sch en 4,4 u nd 110 C f ir d ie Zem en th yd ra t a ti on sg e-s chw in di gk ei t v erm it t ek t d er Ar r he ni us G l ei chu ng a u sg ed ri ick t w er d en .I n er st er An na h emng ks nn d ie k or per ei gen e H yd ra t a ta t ion sk en ug rof le a ls f hmkt ion d er%em en tz us ammem et zun gen a us ged mckt w er den , w en n m an d ie Met hod e d er klein st enQu ad ra t e a u; d k! Wa rm een tw icklun g u nd d as ch em is ch gebu nd en e Wa ss er a nw en dct . D ash yd ra t is ier te I


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I t ha d been surmised by a number of invest i-ga tors t ha t t he 3:2 ca lcium silica te h ydr at e of t het ober mor it e series, t ha t is, C SH (I ), w as t he m or elikely pr odu ct for med in t he h ydr at ion of por tla ndcements. Tha t thk is t he ca se a rises from thefa ct tha t it is thk composit ion of solid w hich is ineq uilibr ium w it h a sa tura ted Ca (OH )~ solut ion[4]. I f C J 3H (I I) w ere t o form, it w ould pre-suma bly be a meta st a ble product . As fa r ba cka s 1938, t he 3:2 ca lcium silica t e hydra t e w a sconsidered to be t he product of t he hydra tion oft he silica te pha ses of port la nd cement . Forexa mple, Ressey [5] a rr ived a t t his con clusion ont he ba sis of f ree ca lcium h yd rox id e d et ermin a tion son h ydr a ted pa st es.S tein our , in h is 1952 r ev iew [4], poin ts ou t t ha tt he m ost pr oba ble r ea ct ion pr odu ct of t rica lciuma lumm at e, a t lea st init ia lly , is t he t et ra ca lciuma lumjna te hydra te, , C+ H IS . The cubic ca lciuma lumma te, C3AH0, I f I t forms a t a ll, forms on lyslow ly. He point s out a lso t ha t t he hexa gona lhydra te tha t forms ha s a t t imes been report ed a sa n int ergrow th of a dica lcium a lum ina te h ydra tea nd t he tet r a ca lcium a lumina te hydra te, sucht ha t t he overa ll Ca O: A1,OS ra t io of t he pha sei s 3. 0.I n t heir discussion of S tein our s pa per, Nursea nd Ta ylor [6] cit e evidence from X-ra y diffr a c-t ion for t he presence of C ,AH,?. They. a lso cit eX-r ay ev id en ce for t he cubic C ,AH ,, but in asm ucha s t heir obs er va t ion s w er e on a 22-y ea r -old speci-men , t hey concluded t ha t t he cubic hydra te w ast he r gsn lt of a slow con ver sion of t he t et ra ca lciuma l umma te h y dr a t e.There ha ve been a number of invest iga tions ofca lcium a lumin ofer rit es a n d f er rit es , a n d ca lciumferr it e hydra t es ha ve been pre a red which a refna logous t o some of t he ca cmm, a lumina t ehydra t es. The ca lcium fer rit e hydra t es formsolid solut ion s w it h t he cor responding ca lciuma lum in at e hydra tes, but lit tle exper im en ta l da ta

ha d been found tha t t hese solid solut ions occurin h ydr at ed por tla nd cem en t pa st es.One problem tha t ha s received a grea t a mountof a tt ent ion for m any yea rs from cem en t chem ist sis tha t of t he sulfoa lumina tes, a nd, t o a lesserex ten t, s ulfofer rit es . Th es e complex compou nd sa rise from the intera ct ion of t he a ppropr ia t ecomponen t of clinker w it h gypsum, a dded a s ar et ar der . I n gener al, eit her of t wo ca lcium sulfo-a lumina tes ma y form, t hese being t he ca lciummonosulfoaluminate, C ,A.Ca SO,.12H ,0, a ndet t rin git e, C 3A.3C a S0,.31H ,0. Th es e compou nd sa re a lso know n a s the low sulfa te a nd h igh sulfa tesulfoa lum in at e, r es pect iv ely . As w a s poin ted outby S tein our [4], eq uilibr iu m s tudies s uch a s t hos ema de by J ones [7] indica te tha t et t ringit e formsdur in g t he ea rly st ages of r ea ct ion, but a s fur therhydra t ion of C ,A t a kes pla ce, the low sulfa t esulfoa lumina t e w ill form a t t he expense of theet t r ingit e. Once a ll of the SO, ha s been used fort hk rea ct ion, fur t her hydra t ion of a lumina t eshould lea d t o a solid solut ion of t et r a ca lciuma lu min at e h ydr at e a nd ca lcium m on os ulfoa lum i-na te. H ow ever , a t t he t ime of S teinours review ,n o direct obser va tion of eit her sulfoa lumina te incem en t pa st es h ad been m ad e, a nd a ny con clus ion sdra w n w er e st rict ly by infer en ce. The et tr in git eobserved in cra cks a nd pores in old concret e orha rdened pa ste w as considered to be formed byseconda ry rea ct ion due t o exposure. Morerecen t ly simila r observa tions w ere m ade on oldm or ta r exposed t o a ir [8].Th e ca lcium su lfofer rit es cor res pon din g t o t helow -s ulf at e a n d h ig h-s ulf at e s ulf oa ~ umin a tes h a vebeen prepa red individua lly [9]. The a na logy oft he sulfofer rit es t o the sulfoa lumina tes both inconst it ut ion a nd beha vior ha s been point ed out .H ow ever , n o ident ifica tion of eit her of t he sulfo-fer rit es a s a rea ct ion pr oduct of cem ent , gypsum ,a nd w a ter u nder or din ar y con dit ion s of h yd ra t ioncou ld be m a de.

Methods of Investigation of the Chemical Reactions Occurring During theHydration of Portland CementThe q ua lit at ive a nd q ua nt it at ive infor ma tion Ta y lor [10] s epa r a ted s ev er a l f ra ct ion s f rom fin elycon cer ning t he hydr at ion pr ocesses of por tla nd ground pa stes by cen t r ifuging t he ma t eria l incement ha ve been obt ained in severa l d ifferen t bromoform a nd bromoform-benzene mixt ures.

w a ys. In genera l, how ever , rega rdless of w ha t Tur rizia ni [11] u sed a s ed im en ta t ion a ppa ra t us intechniq ue is being used , t he cement pa st e ma y be w hich the suspending a gent w as a myl a lcohol.t rea ted in eit her of t wo w ays. The observa tions S evera l fra ct ions of differen t , finenesses w erema y be ma de on the pa st e a s a w hole or t he pa ste obt ain ed a nd division of t hese int o subfr act ionsma y be broken dow n into fra ct ions such tha t one by t he specific gra vit y techniq ue using bromo-or more of these fra ct ions ma y be enr iched w it h f orm -ben zen e m ixt ur es w a s t hen per formed .r es pect t o cer ta in of t he h ydr a tion pr od uct s. Th e s epa r a tion m et hod s h a ve cer ta in d iff icu lt iesN ur se a n d Ta y lor [6] d es cr ib e a m et h od w h er eb y a ssocia ted w ith t hem. I t ha s not yet been pos-the pa ste is ground to a pow der a nd t hen ground sible to sepa ra te a fr a ct ion consist ing of a singlein a suit able liq uid su ch t ha t a s us pen sion of fin est hydra t ion product , nor ha s it been possible t opa rt icles is for med. The suspension is r em oved sepa ra te a fra ct ion w hich cont ained a ll of a givenf rom t h e coa r se f ra ct ion a n d cen tr if ug ed t o r ecov er subst ance t ha t occur s in t he pa st e, e.g., if a givent h e f in e f ra ct ion . fr a ct ion is show n t o be enr iched w ith respect t oD iffer en ces in specific gr avit y of va rious con - t he iron-bea rin g com pon en t, it st ill w ill not con -s tit uen ts h av e a ls o been us ed t o effect s epa ra t ion . t ain a ll of t he ir on -bea ring ph ases in t he origina l431


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pa ste. Fina lly , t here is t he dist inct possibilit ytha t, t he product s of hydra tion ma y bc a lt ered byt he sepa ra tion pr ocess. Nurse a nd Ta ylor foun dC ,AH , in some of t heir fra ct ions, but a tt ach lit tleimport a nce to t he result since the sample wa shea ted a t on e st age of t he pr oced ur e.P erha ps the most fruit ful invest iga tions madeof hydra t ed cement pa stes, either whole ordivided, a re those using X-ra y diffra ct ion tech-niques. Most of the X-ra y examina t ions ofcement pa stes ma de up t o t he present t ime ha vebeen by t he Debye-S cherrer film t echnique.H ow ever , t he recent developm en t of t he diffr ac-tometer now permit s grea ter resolut ion a nd re-vea ls import ant det ails heret ofore unknow n. I tw a s w it h appa ra t us of this t ype tha t Ka nt ro,C ope la n d, a n d Ander son [12] exa mined a group ofwell-hydra ted port la nd cement pa stes of va riouscomposit ions. Although port ions of these pa steswere ground a nd dried, no t rea tment wa s given

them to muse a ny unknown pha se a lt era t ion,Fully hydra ted pa stes w ere used so tha t clinkerline: w ould not in terfere w ith the lines of t heva rious hydra tes. The hydra ted pa stes wereexammed both in sa tura ted condit ion a nd in &-iedcondit ion. The sa tura t ed specimens were sma llrect a ngula r slices removed from the cent ers of thepa st ,e cylinders a nd polished smooth. The sur-fa ces obt a ined cont a ined no holes due to a irbubbles ina smuch a s the pa stes w ere prepa red bya va cuum-mixing technique [13] so tha t no a irwa s ent ra ined. provisions were made to keep thespecimen sa tura ted during the ent ire X-ra yobservation. The rema inder of the pa ste wa sg rou nd t o pa ss a 200-m esh s ieve a nd dr ied eit herover Mg(CIO~ )z.2-4Hz0 or over ice a t 78 C(see below ). These dried pow ders w ere pa ckedin sma ll sa mple holders a nd t heir diffra ct ionpa t t erns observed in the usua l ma nner . Somed ry pow d er s pecim en s w er e bl ou gh t t o eq uilibr iuma t ot her r ela tlve h um idit ies pr ior t o X-r ay exa mi-na t ion. This wa s a ccomplished by pla cing thesa mple in a desicca tor over a n a ppropr ia te sa tu-r at ed sa lt solut ion , eva cua t in g t he desicca t or , a nda llow ing the sa mple to st a nd under t hese condi-t ions for a t lea st 2 w eeks.One of the difficult ies encount ered by ma nyin ves tig at or s a t tempt in g t o id en tif y t he h yd ra t ionpr oduct s of por tla nd cem en t by X-r ay ddfr act iont ech niq ues is the a lt era t ion or decomposit ion ofcer t a in of tb e hydra t ion product s a s the result ofdrying.I~ nes of some subst a nces dk.a ppea r a nd othersshift t o new posit ions. In view of this t ype ofbeha vior , observa tions of both w et a nd dry sa m-ples pr odu co m or e useful in for ma t ion t ha n eit hert ype of observa tion a lone. The a ssignment of adiffr a ct ion line to a pa rt icula r ma teria l is oft encomplica t ed by t he pr es en ce of a s econ d s ubs ta n ceha ving a line in t he same vicinit y . However,w hen t he w ater content of t he pa ste is cha nged,such t ha t som e of t he lines ma y shift w hile ot hersdo not , t he ident ifica tion of a pa rt icula r hydr at em port la nd cement pa st e ma y be ma de not only

on the ba sis of t he presence of lines a t cert a ind-spa cings, but a lso on the ba sis of t he shift s t helines ha ve when the pa st e is wet t ed or dried.Likew is~ , t he la ck of a line shift serves a s a usefuliden tif y mg f mt ur e m s om e ca ses.Th erm ogr avirnet ric a nd different ia l t herma la na ly sis t ech niq ues h a ve been a pplied t o h yd ra t edpor tla n d cem en t pa st es . Ta y lor [10] u sed t hermo-gra vim.et ric a na lysis t o sh ow t he r ela tionship oft he w eigh t loss-t empera tur e curve of a port la ndcem en t pa st e t o t hos e of va rious subst ances w hichma y be hydra tion pr oduct s. H ow ever , no definit econclusions m ay be dra w n from t he cement pa st eda ta , a lt hough t hey do indica te t he t ype of r esultt o b e e xpe ct ed .R ecen tly Tu rr iz ia n i [11] u sed d iff er en tia l t her -ma l a na lvsis (DT A) in a n invest iga t ion of t hehydra tio~ product s of por thmd c~ mcnt . Thism et hod, h ow ever , like t her mogr avim et ric a na ly -s is, in it s pr es en t s ta t e of d ev elopm en t s uf fer s f romcert a in short comings. P rima ry a mong these ist ha t a num ber of possible cem en t hydra tion pr od-uct s h av e en dot her m so close t o t he sa me posit iontha t , a s Turrizia ni point s out , . thech ar act er iza tion of t he in dividua l com pon en ts ofthe mixture is pra ct ica lly impossible. How -ev er ,. by obs er vin g sa mples u nder r epr oduciblecon dlt lon sj on e ca n oft en d er ive in for ma t ion fr omt he r ela t iv e amplit ud es of cer ta in pea ks .U nt il r ecen tly , m os t of t he in ves tig at ion s ca r riedou t w it h t he elect ron m icr os cope h a ve b een lim it edto the study of hydra t ion product s formed in ala rge excess of w at er . S uch st udies a re subject t ot h e d if fi cu lt ies in v er if yin g t h e i nd ica t ion s r el a ti vet o cement pa ste ment ioned by S t einour [4].S urfa ce replica t echniq ues a re n ow being used t os tu dy t h e s tr uct ur e of h a r de ned pa s tes , a n d met h od sof sa mple prepa ra tion a re being developed tha tm ay per mit on e t o st udy t he subst an ces pr od ucedw hen cement hydra tes a s a pa ste. S elect ed a reaelect ron diffr act ion in con ju nct ion w it h elect ronmicr oscopy pr omises t o be a m ost useful t ool. I t sgrea test disa dva nt age is t he ina bilit y t o cont rolt he or ien ta tion of t he ext rem ely sm all cr yst a llit efound. E vent ua lly elect ron diffra ct ion pa tt e~ nsof cr yst als w it h kn ow n com posi~ ion s w ill pr ow det he informa tion necesia ry t o ma ke cert a in t heident ifica t ion of t he product s of hydra t ion ofcement.

Although elect ron-opt ica l invest iga tions of thestoichiomet ry of port la nd cement hydra t ion fa llw ith in the rea lm of th is discussion, they ha ve, forthe most pa r t , been omit t ed, ina smuch a s t heen tir e field of elect ron -opt ica l in vest iga tion s incem ent chemist ry is discussed elsew her e in t hissymposium. C hemica l a na lysis ha s a nd a lw ays w ill pr ovidea gr ea t dea l of necessa ry inform at ion in t he st udyof cement hydra tion product s. One of the tech-niques of chemica l a na lysis w idely used is t hedet ermina tion of free ca lcium hydroxide. Theq ua nt it at ive a na ly sis for fr ee ca l~ ium h ydr oxideby mea ns of X-ra ys [14] provides a n oxccllentmeans for determining t he a mount of cryst a lline

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ca lcium hydroxide present in a given pa ste. I fam or ph ou s ca lcium h yd roxid e is a lso pr es en t [15],needless t o sa y, it is not det ect ed by t he met hod.All fr ee ca lcium h yd roxi de, b ot h cr ys ta llin e a n damor ph ou~ , m ay be d et er min ed by solven t ext ra c-t ion t echmques. The Fra nke met hod [16] usinga mixt ur e of isobut yl a lcohol a nd et hyl a cet oa ce-t at o a s t he ext ra ct ion solvent ha s been modifiedr ecen t ly [17, 18] s o t h a t t h e t ot a l ca l ci um hyd r ox id eext ra cted ma y be correct ed for t he a mount ofca lcium oxide r em oved from ot her subst ances inthe mixture, provided this decomposit ion ha spr oceed ed slow ly r ela t ive t o t he r at e of solut ion offree ca lcium hydroxide. I f the decomposit ion isr apid, h ow ever } n o such cor rect ion ca n be m ade,a n d it is im pos sible t o d ist in gu is h b et w een ext r act -a ble a nd fr ee ca lciu m h yd roxide by t his t ech niq uealone.I t t herefor e is quit e a dva nt ageous t o compa reresult s of X-ra y a nd solvent ext ra ct ion ca lciumh yd roxid e d et ermin a tion s in or der t o obt a in u sefu linforma tion a bout t he hydra ted cement pa st esystem. Some result s obt a ined by this methodw ill be d iscussed in a la ter sect ion .The int erpret at ion of the da ta obta ined by t hem et hod s descr ibed a bove in q ua nt it a tive or sem i-q ua nt it at ive t er ms requir es t ha t ot her ch emica lda ta be a va ila ble. Among these a re the oxidecomposit ion of t he or igin a l cem en t, t he compou nd

com posit ion of t he or igin al cem en t a nd t he bou ndw at er con tent of t he h ydr at ed pa st e.The oxide a na lyses may be obt a ined by con-vent iona l a na ly t ica l t ech niques. Th e pot ent ia lcompound composit ion of the cement ma y t henbe ca lcula ted a ccording to t he met hod of B ogue[19]. Th e d et ermin a tion of t he a ct ua l compos it ionof t he cement ma y be ca rried out by mea ns ofX-ra y qua nt it at ive a na lysis [20, 2 I]. This a ga in,like the X-ra y free lime det ermina tion, 1s a nin ter na l st a nd a rd m et h od .The bound wa ter cont ent or noneva pora blew at er con ten t of h ydr at ed cemen t pa st e is a some-w ha t a rbit ra ry va lu e, depen din g u pon t he eq uilib-rium w at er va por pressure t o w hich t he ma ter ia lw a s dried. Alt hough ma ny methods of dryingha ve been devised in the pa st only two w ill beconsider ed in t he ensuin g discussions a nd t hesew ill be descr ibed here. The t wo met hods differma inly in the desicca nt used, a nd hence in theeq uilib rium v a por pr ess ur e. One of the desic-ca nt s is a mixture of magnesium perchlora tedihydra te a nd tet ra hydra te, w hich produces a nequilibrium va por pressure of 8 w Th e ot her is icea t t he t empera ture of dry ice ha ving a n equilib-r ium vapor pressure of ji y . The method ofva cu um d ry in g specim en s t o t he )4 p l evel h as been

descr ibed in deta il by C opela nd a nd H ayes [22].The Hydration Products of Portland Cement

The CalciumSilicateHydrateTh e result s obt ained fr om pa tt er ns of bot h w eta n d d ry cer hen t pa st es [12] i nd ica t e t ha t a ca lciu msilica t e h yd ra t e of t h e t ob ermor it e t ype is pr es en t,in a pw em en t w it h t he result s r epor ted by Ta ylor[10], On ly t hr ee d iffr act ion m axim a a re obser vedfor this substa nce. B erna l, J effery , a nd Ta ylor[23] r epor t on ly t w o lin es for t he pr od uct s of h yd ra -t ion of CJ 5 a t room tempera ture. These w ere a t3.07 a nd 1.83 A. More recent ly? B runauer ,C opela nd, a nd B ra gg [24] r eport ed h nes a t 3.03,2.82, a nd 1.83 A from t he product s of the hydra -t ion of C ,S a s pa ste a t room tempera ture. I t ispossible tha t t he 2.82 A line wa s missed in theolder w ork beca use it is a pea k superimposed on

t he broa d high a ngle shoulder of t he 3.o3 A line,a nd a s a result , w ould be difficult ly det ecta bleby a Debye-Scherrer technique. B runauer ,Ka nt ro, a nd Copela nd [15] ha ve found tha t t heca lcium silica te hydr at e pr oduced by t he h ydr a-t ion of C ,S a s w ell a s t ha t by C3S shows the sa meth ree d if fr a ct i on l ines .The X-ra y diffra ct ion pa tt erns of hydra tedpor tla nd cemen t pa st es h ave cer ta in ch ar act er -ist ic~ in common w it h t how of h ydr at ed C .S snclC ,S . The sa me t hree lines a scr iba ble t o ca lciumsilica te h ydr at e in t he pa st es of t he pur e silica tecom pou nd s a lso a ppea r in cemmt pa st e pa t ter ns.Th e ch ar act er ist ics of t hese lin es in cem en t pa st epa t t erns a re much the same a s in the ca lcium

silica te pa st e pa tt ern. There is a broa d humpw ith a maximum in the vicinity of 3.o5 A. Thispea k is quit e a symmet ric, just a s in the ca ses ofC ,S a nd C,S , fa lling off rela tively sha rply on thelow a ngle side a nd much more gra dua lly on thehigh a ngle side. In the wet slab pa t t erns, t heprincipa l ca lcite line, a t 3.03 A [25], is super-im posed on t his pea k.The line found a t 2.82 A in ca lcium silica tehydra t e pa t terns a ppea rs shift ed to 2.78 A incement pa st e pa t terns. This shift is due t o thepr esen ce of lines fr om ot her hydr at ion product sa t a bout t he same spa cin g. Am on g t he subst a ncescon tr ibut ing t o t he 2.78 A pea k is et tr in git c, w it ha line a t 2.77 A [26]. This line, however , wouldn ot be pr esent in dr y pow der pa tt erns. Alt hought he et tr in git e pa t ter n disa ppea rs w hen t he sampleis dr ied, t he 2.78 A line does not shift ba ck to2,82 A. Th e low sulfa te sulfoa lumina te ha s a lin ein the vicinit y of 2.78 A [27, 28, 29]. Thus, t hepersistence, on drying, of t he 2.78 A line in sub-st ances sh ow ing n o low sulfa te sulfoa lumina te,but on ly et tringit e, a s w ell a s in subst ances sh ow -in g t he simult aneous pr esen ce of bot h indica test ha t sulfoa lumina tes a re not solely respon siblefor t he sh ift . . .The 2.78 A line in cement pa stes a ppea rs t o besomew ha t st ron ger t ha n t ha t of t he 2:82 A lin e inpa st es of hydra ted ca lcium silica tes. The sha peis a lso somew ha t different a nd is t ha t sha pe to beexpect ed if a lin e fr om a w ell-cr yst a llized h yd ra t e

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w er e su per im posed u pon t he 2.82 A t obermor it eline.The 1.82 A t ob ermor it e l in e is ea s il y d is tin gu is h-a ble. The line a ppea ring here is fa r t oo st rong t obe a ccou nt ed for a s t he low sulfa t e sulfoa lu min at eline found by Midgley [27,, 28] a t 1.82 A, whileF ra t in i, S ch ippa , a n d Tu rr lz la n i [29] d o n ot r epor ta low sulfa te sulfoa lumma te line a t t his spa cing.iTo know n hydra tion product ot her t ha n t ober-morite ca n give a line st rong enough t o a ccountfor t he 1.82 A s pa cin g obs er ved ,I t ca n be seen from the a bove discussion tha tt he same ca lcium silica te h ydr a te lin es a ppea r in gin pa tterns of hydra ted pa stes of CJ 3 a nd C2S a refou nd in t he pa t ter ns of h ydr a ted por tla nd cem en tpa st es. Alt hough t hese lin es t en d t o ch ar act er izet his h yd ra t e a s a t obermor it e t ype, t hey con st it ut ea set of da ta t oo mea ger in t hemselves t o give a nyinforma tion a s t o t he composit ion of this pha se.Th ere a re indica tion s fr om ot her t echniq ues a sw ell t ha t t he ca lcium silica te hydr at e in por tla ndcement pa st es is of t he t ober mor it e t ype, e.g., t het herm ogr avimet ric cur ves of Ta ylor [10] a nd t hediffer en tia l t her ma l da t a of a n um ber of in vest iga -tors, most recent a mong t hese being Turrizia ni[1 1]. F in ally , G a ze a nd R ober tson [30] h ave id en -t ified t obermorite crysta ls a s t he product of hy-dra tion of a foa med mixt ure of por t la nd cementa n d a sb est os, u sin g a n elect r on m icr os cope. Thepr esen ce of t ober morit e in t his la tt er exa mple is

not conclusive tha t it is the product of ordina rypa s te h y dr a t ion , h ow ev er .The ca lcium silica te hydra te which forms inpor tla nd cement pa st es pr oba bly cont ains sma lla mount s of impurit ies, prima rily a lumin a. I t w asshown by Ka lousek [31] tha t a luminum can besubst it ut ed for silicon in t he t ober mor it e la tt icew it hout t he subst a nce loein g it s or igin al iden tit y.Composit ions cont a ining a s much a s 4 to 5 per-cent A1*03 were prepa red hydrotherma lly . Asimila r sit ua tion ma y exist in por t la nd cementpa stes dur ing hydra tion a t room tempera ture.Other substa nces such a s a lka li ma y a lso ent erin to t he silica t e s tr uct ur e [32].The CalciumSulfoaluminates

I n t he pr eced in g pa r a gr a ph s, sever a l r efer en cesw er e m ade concer ning t he presen ce of eit her t helow sulfa te G alciurn sulfoa lumina te, t ,hc high sul-fa t e ca lcium sulfoa lumina te, or both , X-ra y dif-fra ct ion lines of both subst a nces ha ve been ob-served in hydra ted pa stes, somet imes sepa ra telya n d s om et im es s im ul ta n eou sl y, Ta ble 1 list s theX-ra y diffr a ct ion d-spa cings observed w ith w etsla bs of severa l cement pa st es. Ta ble 2 list sd-spa cings observed w ith dr ied ground cementpastes.The t wo st ronga st et tringite lines, a t 9.73 a nd5.61 A [26] occur in posit ions n ot int er fered w it hby ot her possible pr ~duct s of cemen t hydra t ion .I t ca n be seen in ta ble 1 tha t w henever t he 9,73 Alin e a ppea rs in a h ydr at ed cemen t, t he 5,61 A linea lso a ppea rs. In most cement pa stes w here t hey

appea r , ~ hese lines a re w ea k and the other et -t rmgke hnes a re propor t iona tely w ea ker so a s tobe obscured by norma l ba ckground va ria tion.H ow eve~ , in t hose pa tt erns w her e t he 9.73 A lineis more int ense, some of t he w ea ker lines such a s4.69 a nd 3.48 A ca n be dist inguish ed. Th e r at herst rong line occurr ing a t 3.88 A is somew ha t ob-scured by a ca lcit e lin e. H ow ever , a s t his ca lcit eline is w ea k rela tive t o t he pr incipa l ca lcit e lin e,a t 3.o3 A, t he 3.88 A lin e foun d in a ll cem en t pa st epa tterns show ing 9.73 a nd 5.61 A lines is ea silyseen to be t oo st rong t o be a ccount ed for only a scalcite..4s ca n be seen fr om t able 1, t he et tr in git e linesa re found in pa st es w hich ha ve been cured forlong per iods of t ime. Thus t he da ta for 10-yea r-old pa st es m ad e fr om cem en ts of va r ious com posi-t ion s in dica t e t he pr es en ce of a s ig nifica n t q ua n tit yof et trmglt e, except for t hose pa st es ma de fromcements high in C,A. How ever , in pa stes of onehigh C,A cement , 15754, sa mples of w hich ha vebeen prepa red under a va riet y of condit ions, noet t ringite is found except in t he youngest pa steobserved, onc which wa s hydra t ed for only 6months . Thus it w ould a ppea r tha t t his cementbeha ves in t he ma nner descr ibed by Ta ylor [10],in tha t et t ringite forms a t ea rly a ges, a nd thendisa ppea rs. Ta ylor su ggest ed t ha t t he disa ppea r-a nce of et t ringite ma y be due to the forma tion oft he low sulfa te sulfoa lumina te, w hich then dis-solved in t he C IAH ,~ ph ase t o for m a solid solut ion .On t he ot her h an d, et tr in git e h as been obser vedin some cem en ts, such a s t hose m ent ion ed a bove,even a fter long per iods of curing. This t ype ofbeha vior is in a greement w ith tha t observed byTur rizia ni [11], w ho fou nd t his m at er ia l in pa st esm ad e fr om four cliffer en t cem en t com posit ion s,a nd h ydr a ted a t t wo d iffer en t w a ter -cem en t r at ios,a t a ges from 7 da ys t o 6 yr.C on sid er a bly less success h as been h a d in y ea r spa st in id en tifyin g t he low sulfa t e su lfoa lum in at ein por t la nd cement pa stes by X-ra y diffra ct iont echniques. Turrizia ni [11] wa s una ble t o findevidence for monosulfoa lumina te in a ny of hiss pecim en s o~ -er t he w h ol e r a ng e of compos it ion s,w at er-cement r at ios,, a nd t imes invest iga ted. H econcluded tha t if t his ma teria l does form, it doesso only a t a very slow ra te. D iffra ct ion pa tternsfor t he compound C, A. Ca SO,. 12H ,0 ha ve beenrepor ted by Midgley [27, 28] a nd R-a t i n i, S t i hi ppa ,a nd Tur rizia ni [29]. Th e r esu lt s a re in r ea son ablygood a greemen t, Th e principa l diffr act ion pea ksfor this ma t er ia l a re a t 8.9 a nd 4.45 A. The 8.9A lin e ha s been obser ved in cert ain of t he w et sla bpa tt erns, t he da ta for which a re given in ta ble 1.The 4.45 A line a ppea rs in every one of t hese a sw ell, but in a ddit ion, in pa tterns in w hich t he 8.9A ,line does not a ppea r. As w ill be se~ n la ter,this a rises from the fa ct tha t a st rong hne froma nother pha se a lso a ppea rs a t 4.4 A. The otherlin es of t he ca lcium mon os ulfoa lumin a te a r e eit h ert oo w ea k t o be det ect a ble in view of t he difficult lyd ist in gu ish a ble 8.9 A lin e, or els e ot her s ubst a ncesha ve lines a ppea ring in t he sa me loca tions, such

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TABLE 1 . X-r a uBpecimm c-88 c-54.

Cement . . . . . . . . . . . . . 16;34 15734Tow. . . . . . . . . . .. . . .Nominal W/C. . . . .. .40 ;5Age . . . . . . . . . . . . . . . . . 11yT 11yrSpao ings, A . . . . . . . . . . . . . . .. . . . . . . . . .. . . .. . . . . . . . . . s 97.8 7.8

. . . . . . . . . . . . . . . .6,09 5,064,94 4,92l---------- l . . . . . . . -......... ........4.41 438. . . . . . . . . . 4,274,69 4,CA3.88 3.863.79 3.78

3,433.35 3.353,31 3,30. . . . . .. . . . . . . . . .. . .3.12 3,113.05 3,042.972.88 2,88.......... .........2.62 2.6.32.94 2.3s2. M 2.622.50 2.ml2.47 2.452,43 2.422.37 . . . . . . . . .2,312,29 2,292,27 2,262.14 . ..i. i6..2102.07 ;:2.011.96 1.961,932 1.9291,912 1.9121.881 1.8751.826 1.8191.799 1.7961.722 1.7141,690 1.683

I----------........,1,6$XI 1,658L 629 1.635.....................

~C-87157.54,io7YI

.......7.8. . . . . . .. . . . . . .6,094.93.......4.434.274,623.863.77

. . . . . . .3.34

. . . . . . .3,123,052.88. . . . . . .2.78. . . . . . .2,632.592.342.562,462,432.372,312,292.272,1!3. . . . . . .2,102.Si32.021.971.9311.9121.8791.8241.7991.7231.689L W51.64([email protected]

pacingc-7615154,657V. . . . . . . .8.9. . . . . . .7.7. . . . . . .5,094.93. . . . . . .4,494.394,023.873.77. . . . . . .3.453.353.31. . . . . . .3,123.05. . . . . . .2.582.842,78. . . . . . .2.0s2.692.532,492.472.432.362,292.272.192.142,102.01. . . . . . .1.9311.9121.8791.8241,7991,7191,6901,6s01.638. . . . . . .

hudra tedcementwet s l aband rewet ted samole da tac-75 . C-06-K

115;54 15:34.65 .707rI nmo.......... .........9.0 9.07.8 7,8...iv...,...:i......... ........4,48 . .. . . . . . .4.40 4.414, Za . . . . . . . . .4,02 . ..i.k..3.66 3.783.67 . ..i.%..3.42 . . . . . . . . ........ .........3.32 3.323.12 3,123.04 3.052.97 . ..j.ii..289. . . . . . . 2.822.78 2.78. . . . . . . 2,692.63 2.632,38 2,592.54 ---i:ig... . . . . . .2,46 . ..i.ii..2.422.36 . . . . . . . . .2.29 2,202.26 2.272.m 2.192.14 2.142.10 2.112.07 2,072.01 2,011,96 1.96L 930 1.9321,875 . . .i .6ji .1,823~ ;:; 1,7991.7191,688 1.6901,656 1,8621,638 1,0-351---------

. Shoulder m str ong peak. E xwt d.spa.ing not C@ aimb Badly obscured by stro~3 peak. Spacing cannot be est imated.tha t a ssignment of t he diffra ct ion ma ximum t o apa r ticu la r s ubs ta n ce w ou ld b e q ues tion a ble.H ow ever, t he low sulfa te sulfoa lumina te linesdo not beha ve in t he sa me w ay a s et t ringit e, w hent he ma teria l is dried . Instea d, the ba sa l reflec-t ions shift t o low er d-spa cings, w hile t he ot herlines show no significa nt cha nge. Robert s [33]poin ts out t ha t upon dr yin g ov er a nh ydr ous C aC lz,t he low sulfa t e s ulfoa lum in at e ba sa l spa cin g con -t ra ct s from 8.9 to 8.2 A. When this ma t eria l isdried in C Oz-free a ir a t 115 or in zxzcuo a t roomt empera ture t o the ha lf-micron level, the 8.9 Aline, a ssigned 001 by lh-a t ini, S chippa j a ndTurr izia ni [29], cont ra ct s t o 8.2 A, a nd t he line a t4.45 A,, a ssign ed 002, cont ra ct s t o 4.1 A [34]. Th e8.2 A hne a ppea rs m t he pa tt erns of those pa st esfor which t he w et sla b pa t t ern show ed t he 8.9 Aline. In t he pa st , t he 8.2 A line ha s been a t -t ributed to t he tet ra ca lcium a lumina te hydra te[10], but t he fa ct tha t it a ppea rs on ly in pa tt ernsof ma teria l w hich, w hen dr y, show s t he low sulfa te

c-se-o16;64.57:1#8,77,8. . . . . .6.665.114.92

. . . . . . .4.394.273,m............3,453.34.......3.123.052.982.88. . . . . .2,792.692,632.692.342.492,462,432.36. . . . . .2.292,262.m2.142.102.021.961.9301.9121.8791.8231.7981.7231.6881.6621.6521,6A81,607

c-o-c C-33-1 C-38-1 . C-31-1. LT~ Iyz 15# 154;7

.70 .e47lY :0 ~w :0; -!(09.89.0 . . . . . . . . . . . . 8,8 0.0S 6 . . ..i.i . . . . . . . ..i.i . . . . . 8,37,8 7.87,4 7:4 7.4 . . . . . . . .6,6$ 6.64 Si.$ 5,64.5 , 08 .$6. 6.084,04 4,94 4,92. . . . . . . . . . 4.72 4.72 4,724.46 . . ..i.i . . . . . . . ..i.G . . . . . . . . . . .. . . . .4.41 4.41. . . . . . . . . . 4.26 . . . . .. . . . . . . 4.264.02 4.04 . . ..i.ti . . . 4.02s 88 3,88 3.883.81 . . . .3.ii . . . . . . . .5.6+ . . . . 3,81. . . . . . . .3.54 3.48 3,48 3.49........ ............ ............ ........3,36 3.36 3.38 3,353.31 . . . . . . . . . . . . 3.32 3.313.12 3.12 3,12 3.123.65 3.05 3.05 3,05

l----------l------------l----------. Dried sample, mwetted in a satarated atmosphere.

c-32-113669B.I?Qy Sm

7.86.64...........4.024.72

...........4.294,023,683,693,493.36...........3,263,123,05...........2.842.78. . . . . . . . . . .2,322.662,512.452,41...........2,29...........2,212,162.102.062.011.971.9321.9121,8791,8361.801...........1.6891,6651,634

eulfoa lum ina te line, indica tes t ha t it is t his eub-et a nce w hich is r espon sible for t he lin e. L ikew ise,the 4.15 A line in dr ied pow der pa tt erns a ppea rson ly w hen t he 8.2 A line does. Tha t the 4.4 Aline does not disa ppea r in dry pow der pa tt ernsis due to t he fa ct tha t a nother ma teria l, nota ffect ed by dr yin g, con tr ibut es t o it .Th e l in es of l ow s ulf a te s ul foa l um in a t e a pp ea r in gin dry powder pa t t erns a re st rong a nd sha rp,indica ting tha t a significa nt a moun t of t he ma -teria l is present in t he pa ste. This is t rue evenfor t hose pa st es w hose w et sla b pa tt er ns ga ve lows ulfa t e s ulfoa lumin a te lin es w h ich w er e v er y w ea k.The wea kness of the lines in w et pa stes is due tot h e ef fe ct of ca r bon a t ion .D r ied s pecim en s of s ev er a l of t he pa st es in clu dedin t ables 1 a nd 2 w ere br ought t o eq uilibr ium w it hv a riou s r ela t iv e h um id it ies . No s ig nif ica n t ch a n gesw ere observed a t humidit ies below 28 percent .H owev er , in pa t t er n s of l ow s ulf a te s ul f oa l um in a t e-b ea r in g s ampl es , e qu il ib ra t ed a t h ig her h um id it ies ,

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TABLE 2. X-rau d-snacinoshudr ated cement dried powder data. . -SPdmm I C-,5

?7:;!!::::::::::::15754Nomina l lV/C_ . . . . . ,:5Age . . . . . . . . . . . . . . . . 7 YrSPaCirlgs, A... . . . .. 827.75.47. S .064,924,414093,893623313123,042,92288278,-..-i:ii...2 532.492.462.432.352.312.262.082,011.931,881,821,801.721.691.651,641.61

c-4915754;55 m8.27,9

5,48JV54,414 103.923,323,123.0528827827026302,602.532462.432.352.302.262,102,052,011.931.891,821.801.721.691,651.641.60

c-61-c C-33-1 c-33 C-33-1 C-31 C-32-1 C-32 1562211.6610Y,7.87.45.47. 5.064.924.41

3.863,32

1;:;7 I;wy 15~{9B 15:#lB.s4 .60 .60;0jr iz 10yl 7 yr8.2 . . . . . . . . . . . . . . . . . . . . . ..-1 7.7 l------------l ------------l ------------

1562211.80? yr. . . . . . . .7.87.35.435.064.924.394.al3.893663.35

--l 7-92 1------------1 ------------1 ----,-,:2.862.77 II ;:: l----2:6j----l...5:i3........i.6i...-... .5.ii . . . ..?.E........ .......2...I.......46, 2:68, . . . . .2.432.35

2.052 (I21.931.891.821.801.711.691.661,64

-----------1--------162l------------l-"---"------l----------"-l"-----------s Shoulde r on s trong ~ak . Exac t d .spwtng not ce rta in. ~Bably obscured by strong peak. Sprwing cannot be est imatedt he 8.9 A line a ppea red. I t show ed only a s ash ou lder on t he 8.2 A pea k a t 28.8 per cen t r ela t ivehumidit y, w a s a bout equa l in intensity w it h thesh rin kin g 8,2 A pea k a t 33 per cen t r ela t ive h um id-i(y , a nd a t 42 per cent r ela tive h umidit y, t he 8.2 Apeak wa s a sma ll shoulder on the 8.9 A peak.Tlw sc fea tures a rc illust ra t ed in figure 1, Ath ig her h um id it ies , t h e pa t ter ns a ppea r ed q uit e liket h c w et sla b pa tt erns, except t ha t n o significa ntmnount of ca rbon at ion h ad occurr ed. As a result ,t he low su lfa t e s ulfoa lu rn in a tc lin es w er e of in ten -sit ies com pa ra ble t o t hose of t he lin es in t he dr iedpowder pa tterns. Tha t is, t hey w ere st rong a ndsha rp. B cca uw of this, it w as ea sy t o dist inguishthe 4,45 A snlfoa lumina te line from a 4.4o A lined ue t o a n ot her ph a se (S CCb elow ). Th is r es olu tionis illust ra ted in figure 1. Furt hermore, it ca n beseen from result s in ta bles 1 a nd 2 a nd in figure 1t ha t w hile t he 4.1 A lin e in t he dr y ma teria l shift sto 4.45 A in the w et ma teria l, the line a t 4.o Area ppea rs a s w ell w hen t he sa mple is rew et ted.This cor responds t o t he lin e r epor ted a t 3.99 A byMidglcy [27, 28] a nd a t 4.02 A by F ra t in i, S ch ippa ,a n d Tu rr iz ia n i [29],Thus in figure 1, idea lized pa tterns in the 9 Aa nd 4 A regions a re show n f& pa st es cont ainingthe dry form of low sulfa te sulfoa lumina tc, t hew et form, a nd a n in termedia te ca se (33 percenth um idit y) in w hich bot h for ms a ppea r sim ult a ne-ously, Th e differ ences bet ween w et sla b a nd r c-wet t ed powder pa t terns show tha t low sulfa t e

sulfoa lumina te rea cts w ith CO, iust as doesCa(OH),. -.Th e ct tringit e lin es a ppea rin g in w et sla b pa t-t erns a t 9.8 a nd 5.6 A a rc a bsent in the dr iedpow der pa tt er ns of t hese pa st es. Rew et ting t hesepa st es a t humidit ies up t o 47 percent ha s no sig-n ifica nt effect on t he d iffr act ion pa t ter n. Rcw ct -t ing a t 100 percent rela tive humidit y ca uses t heet tr in git e lin es t o r et ur n. No significa nt a mountof ca rbon at ion occu rr ed w it h t hese r cw et ted sam-ples, a nd yet t he ct tr ingite lines w ere of compa -ra ble int ensit ies t o those in the origina l w et sla bpa t ter ns w her ein con sider ably m or e ca rbon at ionoccurred. Thus, if C OZ rea cts w it h ct t ringit o, itdoes so sufficient ly slow ly so a s not t o a ffect t heX-r ay obse rv a t ions.The low sulfa t e sulfoa lumina t e is found inpa stes ma de from cement s high in C,A, but notin those ma de from cement s low in C8A. On theot her h an d, et tr in git e is t he on ly sulfoa lum in at efound in pa stes ma de from cements low in C,A,w hile lit tle if a ny of it is fou nd in pa st es of cem en tsh ig h in C $A.On c of t he cement s low in C ,A discussed a boveis of especia l in terest in on e respect , h ow ever . I ft he low s ulfa t e s ulfoa lumin a te w er e t o h a ve formedinst ea d of et tr in git e, n ot enough A1Z03 w ould bepresent in the cement t o rea ct w it h a ll t he SO~ .U nder t hese circumst ances, it is possible tha t asulfofer rit c m igh t for m. Ma lq uor i a nd C ir illi [35]h a ve pr epa r ed ca lcium sulfofcr rit es a na logou s t o

436


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d- sr.c.ang, 40 70 46 4.5 4.4 4.3 4,2 41 4.0 3.9 3.81I . ~~y. 33% R,H.--- 47,. , 00% ,.! !

1!

L # / \89,0{1 ,2,.De.arees 2 e

FIGURE 1. C alcium mono,su l foakwru ina te i nes in X-ray pa t t e rnsof port landcemen t p ast e a t d i f fer en t r el a ti v e humidities .t he ca lcium sulfoa lumina tes w hich a re found inhydra ted por t la nd cement pa stes. The X-ra ydiffr act ion pa tt erns of t hese sulfoferr it es a re, ingen er al, v er y m uch like t hos e of t heir sulfoa lum i-n a te a n alog s. Ae a r esult , t he sulfoferrit e com -pounds, w ere t hey presen t in port la nd cementpa stes, w ould not be read i ly d is t in gui sh ab le f r omt heir a lumina te count erpa rt s. H ow eve~ , t here isevidence tha t t he iron-bea ring pha se m cementhydra tes in a unique ma nner not involving S O,.Th is w ill be discus sed in t he n ext sect ion .TheCalciumAluminate and Calcium FerriteHydrates

The ca lcium a lum ina te a nd ca lcium ferr it e h y-dr at es h ave been r epor ted a s exist in g in h yd ra t edcement s in t wo different form s: cubic a nd hexa g-ona l. The cubic hydra tes a re represen ted by thecom poun ds C ~ AH e a nd C tF Ht ; -t he h exa gon al h y-dr at es a re r epr es en ted by t he com poun ds C ,AH ,$a nd CJ ?H ,,. I t w a s shown by ea rher invest iga -tors such a s Wells, C la rke, a nd McMurdie [36]tha t C$AH , is t he st a ble ca lcium a lumina te hy-dra te in conta ct w ith solut ions sa tura ted w ithr espect t o ca lcium hy dr oxide. On t he ot her ha nd,in none of the discussions of t he st oichlomet ryof the hydra t ion of port la nd cement is muchevidence given for t he presence of t he cubic t r i-ca lcium a lumina te hydra te. On t he ba sis of evi-cleny,, ~ la ble a t t he t ime, S t einour [4] st a t edin it ia l forma t ion of C 1AH 13 in clin kera nd w at er pa ste seems much more proba ble tha nforma t ion of cubic C3AH ,. . I t is not impos-sible, h ow ev er , t ha t t he cubic h exa hy dr at e m ig htform la t er . In recen t X-ra y invest iga t ions ofport la nd cement pa st es, Ta ylor [10] a nd la ter

Turrizia ni [11] report only t he h exa gona l t ct ra -ca lcium a lumin a te h yd ra t e, C 4AH ,~ ; t hey ob ser vedn o cu bic t riw dcium a lumin a te h yd ra t e in t he pa st es .In t he discussion t o follow w c sha ll reviewevidence t ha t bot h cubic a nd h exa gona l hydra tesa re present in ha rdened pa st es a nd t ha t t he cubicpha se a t lea st is a solid solut ion of severa l sub-st ances. We sha ll discuss first t he cubic a nd t hent h e h ex a gon a l h yd ra t es .I t ca n be seen from the da t a in t a bles 1 a nd 2tha t a g rou p of lin es a ppea r s d is tin ct ly in pa t ter nsof a ll cement pa stes except t he TYP O IV cement,which is quit e low both in AlZ03 a nd in I eZO~ ,a nd even in pa tt erns of this cement pa st e t here 1sevidence of t hese lines. This group of linesa PP ea rs a t 5.07, 4.40, 3.32, 2.26, 2.01, a nd 1.72A, cor respon ding t o six rela tively st rong C,AH ,lines r eport ed a t 5.14, 4.45, 3.37, 2.30, 2.04, a nd1.75 A by Midgley [27, 28], a nd a t 5.13, 4.45,3,36, 2.30, 2.04, a nd 1.75 A by B ur dese a nd G a llo[37]. Th e lin es for t he a na logou s ir on com poun d,C a FH ,, a r e r epor ted a t 5.20, 4.54, 3,40, 2.33, 2.07,a nd 1.77 A by Flint , McMurdie, a nd Wells [38]a nd a t 5.18, 4.50, 3.41, 2.33, 2.07, a nd 1.77 Aby B nrdese a nd G a llo [37]. More complet ed-spa cing da ta for t hese ma t eria ls a re given int able 3. The repor ted C SAH ,5lines a re a ll h ighertha n those observed in the hydra t ed cementpa st es, a nd t he C ~ FH O lines a re fa rt her r em ovedfr om t he obser ved lines. The spa cings observedin cement pa stes w ould not be t hose expect edfrom C ,AH @, C,F H,, or a solid solut ion of t he t wo.B ur dese a nd G a llo [37] a lso report spa cings fora Partially deh ydr at ed cubic t rica lcium fer rit e,C ,F H,. Th ese spa cings a re 5.07, 4.38, 3.32, 3.10,2.78, 2.53, 2.27, 2.01, a nd 1.72 A in very gooda gr eem en t w it h t hos e obser ved in cem en t pa st es,

437


12/44

TABLE 3. d-spacings reported for t ricalc ium aluminate and fe r r i t e h yd rat es and cor respond ing spac ing s in some representative

hkl [38] .21122032141YI420332422431521440611,532620444640633,552,721642651,732800840

C,AH, [38]5.16(VS)4.47(M)3.37(M)3.15(M)2,81(M)2 56(VW)2 46(w)2.30(VS)2.22(VW)Z 04(S)1.99(VW)~ ;3[vy)1,71(W)1,63(M)1,60(VW)1.57(w)1.40(W)

S,AH, [27,286.14(S)4 45(M)3.37(M)3.15(M)2.82(MS)2,57(w)2.47(M W)2.30(VS)2,23(VW)2,04(S)1.99(VW)1.82(VW)1.75(MW)1.71(W)1 68(M)1.WI(M)1.57(VW)1.41(Ms)

hydrated cement pastesC,AH, [371 c, AII,.,, [44] C ,FH, [38]5.13(MS) 5,03(VW)4.45(M) 4 39(VW)3.36(Mw) 3.30(VW)3.15(W) 3.09(VW)2. 81(MS) 2. 77(VW)2.2.2.2.2.2.i1117:[$, ,. .. ..i.6i(.wj . . . ......... ................1,57(w) I

s Numbers in brackets ref er to l ite ra ture .i ted a t end o f text.b Probably present , but overlapped by l ine f rom some other component .

a s ca n be seen in ta ble 3. The lines a t 3,10 a nd2.78, of cour se, a re over la pped by st ron g lines ofC a(OH ), [39] a nd t he ca lcium silica te hydra te,respect ively , (I t is to be point ed out here a ga int ha t t he st rengt h of t he 2.78 A line is fa r t oo grea tt o be a ccounted for on t he ba sis of a ny a lumina teor ferr it e. ) The compound CIFHZ, how ever , isobt ained by dehydr at ion of C $FH@ at 250 C [40].I t is difficult t o ima gine tha t a species norma llyfor med by deh yd ra t ion a t r ela t ively h igh t em per -a tures should form a t room tempera ture in asa t ur at ed a qu eou s sy st em , un less som e ot her su b-st a nce w er e dissolved in it t o st a bilize it . Stabili-za t ion of solid ph a ses u nd er con dit ion s fa r r em ov edfr om eq uilibr ium is n ot a n un usu al ph en om en on ,especia lly in cemen t ch emist ry; on e mer ely n eedconsider t he ca se of P -C&. H owever , the moreusua l exa mples, such a s L?-C 2S ,do n ot in volve a na q ueou s s olu t ion pha s e.From the khet ic da ta present ed in a nothersect ion of t his discu ssion , it w ou ld a ppea r t ha t t heferr it e pha se in port la nd cement hydra tes w ithn o sign ifica nt ch a nge in A/F r at io of t he r em ain in gunhydra ted ma teria l. H ence, one might a ssumetha t t he product of hydra t ion ma y be a solidsolut ion of a ferr it e a nd a n a lumina te such tha tt he A/F r at io of t he solid solut ion is t he sa me a s itw as in t he origina l ferr it e pha se, Thus, if t heor igina l ferr it e pha se ha d a n A/F ra tio of unit y,t hen the hydra tion product in quest ion w ouldpresuma bly be a n equimola r solid solut ion of aCJ ? hydra te a nd a C,A hydra te, t he pha se ha vingt he over a ll com posit ion C 3AFHZ. On t he ba sisof a st at ist ica l a na lysis of noneva pora ble w aterda t a a s a linea r funct ion of the composit ionpa ra meters of a group of 27 cement s (t he wa terda t a bein g obt a in ed fr om a gr ou p of w ell-h ydr a tedcement pa st es) ~ t he w at er cont ent of such a ph aseis ca lcula ted t o be 6 moles per mole of COAF;tha t is, t he pha se ha s t he composit ion C3AFH ,.This w ork, a nd the ca lcula tions lea ding to thisr esu lt , w ill be d iscu ssed in det a il in a la t er sect ion .H ow ever, it is int erest ing to not e tha t t he w at er

: m[r$3 46(w)3.19(s)2.63(s)2.72(VW)2.60(M)2,50(VW)2.33(M)

1,77(M)L 73(w)1.70(VS)1.62(VW)1.59(w)1.43(M)

C ,FH, [37]5 13(MS)4.50(s)3.41(Mw)3.19(MS)2.65(Ms)2.72(VW)2.61(M W)2.51(w)2.33(MS)2.26(w)2.07(s)2.02(w)1.84(WW)1.77(M)1,74(VW)1.71(VS)1.w(w)

C , FE , [37]I

c-75 C-3>15.07(M) 5.09 5.064.38(M W) 439 4.393,32(W) 3iy 3if;3.1O(MS)2.7s(Ms) (h) (b)2.53(M) 2.53 2.532,44(WW) 2,43 2.442,27(W) 2.27 2.27. .. . . .. . . . . ...-. -- . ... ---- . . . . ..2.01(s) 2.01 2.011.98(W) 1.96 . . . . . . . . . . . .1.79(VW) /yz :;21.72(M)1. 70(VW) . . ..i.66.. . . . . . . .. . . .. . .1.66(VS) 1.66............... ..........1 55(w) IF==

result s obta ined a re such a s t o indica te tha t nopure ferr it e pha se ca n form, a nd tha t solid solu-t ion w it h a n a lu min at e is pr oba bly n ecessa ry .The composit ion C ,AFH , ca n be considered t ocorrespond to a solid solut ion of C3FH2 w ith a na lumina te of composit ion C SAH 4. Th e la tt ice ofC~ AHb shrinks in a regula r ma nner a s w a t er isr em oved [41, 42, 43] but t he la t tice r em ain s cubica s long a s t he H/A ra tio is grea ter tha n 1.5. Onem igh t expect a com posit ion C SAH ~ t o h a ve a lm ostexa ct ly t he same la t t ice pa rameter a s C~ FHZ.I ndeed, t his a ppea rs t o be t he ca se, since B urdesea nd G allo repor t t he la tt ice consta nt of C~ FH Z t obe 12.39 A, a nd Kober ich [44] gives the la tt iceconst a nt of C3AHS ,75 a s 12.37 A. The X-ra yd -spa cin gs r epor t ed for t his m a ter ia l a r e m r ea s on -a bly good a greement w it h those of C3FH~ a ndthose found in pa tterns of hydra ted pa st es a s ca nbe seen in t able 3.The est ima t ion of the composit ion of thisfer rit e-a lumin a te solid s olu tion ph a se is st ill a fir sta ppr oxima tion . Th e ma ter ia l is m or e likely t o bea silica -cont aining member of t he hydroga rnetseries. The est ima t ed wa ter content w ould beexpect ed t o be low beca use it is repla ced by silicaa s w as described by Flint , McMurdie, a nd Wells[38]. Thus, if t he est ima ted la tt ice spa cing of12.38 A is t aken int o con sider at ion, a nd it is st illa ssumed tha t t he A/F ra tio of t he ma teria l is 1.0,t hen the ma teria l corresponds to a hydroga rneth a vin g a com posit ion in t he vicin it y of C ,AF S,H ,.Th e lin es a scr ib ed t o t he pr opos ed solid s olu tionpha se appea r in wet sla b a s well a s dry powderpa t t erns, a s is indica ted by the da ta in ta bles 1a nd 2. How ever , in a lmost a ll pa t terns, wet ordry, t he 5.07 A line is pa rt ly obscured by the4.9o A ca lcium hydroxide line [39]. In manyca ses a sh ou lder a ppea rs su fficien tly d ist in ct ly sotha t a rea sona ble est ima te of the d-spa cing a t5.07 A ca n be ma de. In a few other ca ses, how -ever , t he shoulder is not a s dist inct , a nd a bouta ll t ha t ca n be sa id for such ca ses is t ha t there isa line present , t hough fa ir ly well hidden by the

438


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7[

6C

5[

I(

C-75 We?S1b?,.,., ,57s4 Tyo,l )7Y , , o ld

\

c .66. w ,? SlabCmcm.;:,;54

L

.


14/44

which wa s dried to the ha lf-micron level. Thepa tt ern of t he dr ied pure compound show ed norr pprecia blc shift in line posit ions from t hose int he w et ea mple pa tt er n [34], a nd w a s in r ea son ablygood a greement w ith t he spa cings report ed byTurrizia ni a nd S chippa [45, 46] a nd by B ut tle~ ,D ent G la sser , a nd Ta ylor [48], The ca rboa lum l-n at e lin e in dr ied sa mples, a nd in r ew et ted sa mplesa s w ell, is w ea k, ind~ ca ting tha t not much of thema teria l is present . Tha t lit t le, if a ny , CO, ha sent ered the dried pa stes is indica ted by the fa ctt ha t t he pr in cipa l ca lcit e lin e is n ot obser va ble.B ut t ler , Dent G la sser , a nd Ta y lor presentdia grams of pa t t erns of C ,AH,, a ft er va riousdrying t rea tment s. These pa t t erns indica t e ashift in the ba sa l reflect ion in t he same w a y a sw a s fou nd for t he r non osulfoa lum in at e. Whenhea ted to 105 C , the C ,AH ,, line a t 8 A shift edto 7.8 A. D rying a t 105 C is roughly equiva lentto t he va cuum drying condit ion described byCopela nd a nd Ha yes [22]. How ever , w henCdH ,~ is dr ied in va cuo a t room tempera ture[34], t he ba sa l line shift s from 8.4 A, the w etst at e pos it ion [45], t o 7.8 A ov er a rela t]vely sh or tper iod of t ime. Cont inued drying for a muchlonger per iod of t ime (21 da ys) led t o only asma ll w eight 10SS r ela t ive t o tha t in the first 3da ys, but t he ba sa l reflect ion shift ed t o 7.4 A,in a gr eement w it h t he va lue report ed by Robert s[33]. X-ra y pa tt erns of this ma teria l revea ledon ly t he 7.8 A lin e un less specia l pr eca ut ion s w er e

t a ken to elimina t e a ll t ra ces of wa t er va por ,this being done by pa ssing a dry nit rogen st rea mover the eample while t he pa t t ern w a s beingobt a ined. Hence, it a ppea rs tha t very lit t lew at er need be t a ken up by t he w ell-dried CIAH l~before t he ba sa l reflect ion shift s.from 7.4 A to7.8 A, so tha t in ma ny ca ses, t he line observeda t 7.8 A ma y represent eit her ca rboa lumina te,C ,AH ,,, or both . The reversibilit y of t he hydra -t ion-dehydra tion process in C ,A hydra te w a sa lso noted by Robert s, H ow ever, t here is a lw aysa sma ll amount of COZ in a ny pa st + most ofw hich w a s present in the cement pr ior to hy-dra t ion. I f a ll this COZ were in t he form ofca rboa lumina te, t here w ould, in most ca ses, notbe enough present such tha t a ll of t he tet ra ca l-cirrm a lumina te hydra te pot ent ia lly in t he pa st ew ould be in the form of ca rboa lumina te.

The diffra ct ion ma xinlun, otmcrved a t 7.8 Ais not a strong, sha rp pea k, but ra ther a low ,br oa d hump, This spa cing is t he ba sa l r eflect ionof t he pseudohexa gona l cryst al [48], rega rdlessof w hich of the tw o compounds it represent s.

The fa ct t ha t t his reflect ion is poorly developedindica t es tha t t he cryst a ls ma y be quite sma lla nd disordered, a condit ion somewha t a kin totha t of the CSH(I ) produced by rea ct ion ofCaO a nd S iO, a t room tempera t ure. (Theca lcium silica te h ydra te pr oduced by t he hy dra -t ion of C&, of course, show s no ba sa l reflect ionwh a t ev er [15, 24].)Th er e is s om e ev id en ce t ha t t et ra ca lcium f er rit ehydra te ma y a lso ha ve a diffra ct ion line a t 7.8A, Va rious in vest iga tor s h av e r epor ted d iffer en tba sa l r eflect ion s for C ,F HZ, pr esum ably beca useea ch invest iga ted ma teria l w it h a different m ois-ture cont ent . G reening a nd Seligma nn [47}found the ba sa l spa cing to be 8.2 A for ma teria lin t he sa tura ted st a te. Wa ta na be a nd Iw a i[49] repor t a va lue of 7.96 A for somew ha t drierma teria l. Ta ylor [50] ha s X-ra y da t a for ahydra t e of t he composit ion C4FH ,0 which in-cludes a ba sa l reflect ion of 7.8 A. However ,even this ma teria l w ould presuma bly lose w ateron furt her dry in g t o t he )Lp level, a nd a e a result ,un der go fur th er la yer con tr act ion . Th is w ou ldr esult in a dow nw a rd shift of t he ba sa l r eflect iont ow ard t he 7.4 A va lue repor t ed for dr ied tet ra -ca lcium a lumma t e h ydr at e. There is no in for-ma t ion a va ila ble a t present a s t o how ra pidlyt his d ried fer rit e h ydr at e w ou ld pickup m ois tur e.In some of t he dried powder pa t t erns, ot herlin es of t he h exa gon al ca lcium a lum in at e h ydr at ea re seen. The most import a nt among t hese isa t 3.9 A, t he 002 r eflect ion . Th e ca rboa lur nin at eha s no line a t 3.9 A, but ra ther , one a t 3.8 A.This la t t er spa cing a ppea rs in many wet sla bpa tt erns, a long w ith a linea t 3.9 Aca used by thepresence of ca lcit e. I n the dry pow der pa tt erns,no ca lcit e lines a ppea r , a nd no line a t 3.8 A.H ow ever , a sma ll lin e a ! 3.9 A is found indica tingt ha t t he hydr at ed a lumma te 1s prlma rrly C,AH ,S .The spa cing a t 3.9 A is a lso one found w it hC ,P I I,, [50]. Lines a ppea r a t 2.46 a nd 2.10 Ain t he dr ied pow der pa t t erns, but these a lsocont ain cont ribut ions from ot her compound?,s uch a s ca l cium mon os ul foa l um in a t e. Th e s im i-la rit y of t he pa tt ern of this la tt er compound w iththa t of t et ra ca lcium a lumina te hydra te is quit ema rked, w ith t he except ion of t he loca t ions oft h e b a sa l r ef le ct i on s .There rema ins t he dist inct possibilit y t ha t t hecem ent pnst ~ pa tt ern lines a tt ribrrt ecl t o r ncm o-sulfoa lumina te a re in t rut h those of a solid solu-t ion of this ma t eria l w ith t he tet r a ca lc~ r rrna lumina te hydra te, but this w ould not obvia tet he fa ct tha t t he evidence obta ined indica tes t hepr esen ce of t his la tt er m at er ia l by it self.

The Dependence of Water content on Cement CompositionNoneva por able w at er da ta ha ve been obt ained D evelopment La bora tories. Th e oxide com posi-on a group of cemente hydra t ed for t imes up to13 yr [51, 52], lhe cement s used w er e t hose pr e- t ions a nd t he pot ent ia l com poun d composit ionspa red for use in t he Long Time S tudy project of these cements w ere published by Lercb a nda t t he P ort la nd C em ent Associa tion Resea rch a nd Ford [53].

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T .,, ,. ,7 ,,I t w as a ssumed ma t D ot n noneva pora me w atera nd surfa ce a rea w ere dependen t on linea r func-t ion s of t he cem en t compos it ion pa r am et er s.Thus:w ./c= k l(a l it e) + k ~ (b eli te ) +k ,(C ,A) + k ,(F ,,l + k ,(C a SO, ) (1)w her e t he k, a re const ant s a nd w n,lc i s t he non-eva pora ble w at er con tent in gra ms of w at er perper gra m of cement . The qua nt it ies (a lit e) a nd(belit e) refer t o the Ca S a nd C,S pha ses a s theyoccur in por tla n.d cem en t, ea ch con ta in in g m in orq ua nt it ies of ot her oxides , pr im ar ily Al,Og, a s h asbeen discussed by J effery (in t he ca se of a lit e)[54], a nd in some recent publica t ions on thequa nt it a t ive a na lysis of port la nd cements bymea ns of X-ra ys [20, 21]. The symbol F,, repre-sent s t he fer rit e solid solut ion ph as e. All cem en tcom pound q ua nt it ies m ay be expressed in gra msper gr am of cem en t.I t w a s shown in t he qua nt it a t ive cementa na ly sis w or k t ha t t he compos it ion s obt a in ed fr omX-ra y a na lysis did not differ significa nt ly fromt hose obt ained from t he pot ent ia l compound ca l-cula tion devised by B ogue [19] except in t he ca seof C~ A. The Ca A v a lues w ere low er in t he X-ra ydet er min at ion beca use of t he .41,0, in t he a lit e a ndbelit e ph as es ; t he a lit e ph a se w a s cor res pon din glyhigher beca use of this A1,O,. Ina smuch a s t hefer rit e solid solut ions ha d A/F ra tios nea r unit yfor the most pa rt , t he X-ra y a nd potent ia l va luesw er e in g ood a gr eem en t.F or t he purposes of t he ca lcula tions, it provedexpedient to use P Otent ia l ra ther tha n X-ra yva lues beca use X-ra y va lues w ere not a va ila blefor a ll of the cement s. S ince t he Al,Oa in thea lit e a nd belit e pha ses proba bly beha ves duringt he hydra tion process in much the sa me ma nnera s t ,be AJ ZO~in C jA., it is likely t ha t n o s ig nif ica n terror is int roduced by the use of potent ia l da ta ,E xpressed in terms of the potent ia l compoundcompos it ion s, eq (1) b ecomesw n/c= a l(C 3S ) + Q (C S) + a S (C SA) +a1(ClAF)+a 5(CaS OJ (2)w here the a t a re a ga in const ant s in t he equa tion.S ince t he qua nt it y w ./c in eq (2) is a linea rfunct ion of t he pot ent ra l com poun d q ua nt it ies,w hich, m t urn, a re linea r funct ions of t he oxides

Am W,!C&dry ing ~.13m 0.4{,P),6?4,Yr 0.8,(,P) 0.8$,D)

6?4


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6.5-yea r-old pa ste hydra ted a t a w ater : cementra t io of 0.6, a nd 0,974 for pa stes of t he samea ge hydra t ed a t a w a t er : cemen t ra t io of 0.8.Th ese la tt er va lues, h ow ever , m ust be con sid er eda s ma ximum va lues, ina smuch a s t here is usu-a lly som ew ha t m ore w a ter in t he ca lcium silica tehydra te pha se tha n the tw o moles per mole ofS iO, indica ted by t he tw o eqs (4) a nd (5),, [15].F or 8-M d ried C $ a nd C 2S pa st es, t he st olchio-m et ric eq ua t ion s a r e [15]:2C ,S + 5.8H = C ,S ,H ,.,+ 3 CH (6)2C,S + 3.8H = C$,H 2,, + C H. (7)

These equa tions predict the va lues of a l a nda z t o be 0,229 a nd 0.199, respect ively . The va l-ues obt a ined indica te tha t for pa stes hydra teda t w a t er : cement ra t ios of 0.4, a ft er 1 yr , t heC,S is over 95 percent hydra ted a nd a ft er 6}; y r ,it is complet ely hydra ted. The C2S is not so w ellhydra ted, how ever , being, on the a vera ge, 81.4,87.6, a nd 98.2 percent hydra ted a t 1, 6)4, a nd 13yr , respec t ive ly .Ina smuch a s t he cements used in t he lea stsq ua res a na ly sis a re of w id ely differ en t com posi-t ions, it must be point ed out tha t such a t rea t-men t is va lid only for rela tively w ell-hydra tedpa st es, w her ein t he effect of d epen den ce of h ydr a-t ion ra t e on cement composit ion is no longerimportant ,I nterpret at ion of t he a lumina te, ferr it e, a ndsulfa t e n on eva por able w a ter r esult s is m or e diffi-cult . In t he first pla ce, t here a re severa l possi-ble pr oduct s of hydr at ion, a nd a s ha s been sh ow n,evidence ha s been obta ined for the presence ofsome of t hem . Others ma y be present for w hichno evidence ha s a s yet been obta ined , As ca nbe s een fr om t he st a nda rd er ror s, t he lea st sq ua respa ra met ers for the fer rit e a nd sulfa te a re fa r lesscert a in t ha n a re the C$ a nd CJ 3 pa ramet ers .F ur th er mor e, w hile t her e is n o sign ifica nt d iffer -ence betw een t he 4- a nd 5-pa ramet er C$ a ndC,S result s, t he other pa ra meters a re st ronglya ffect ed . The cont ribut ion of the sulfa te in the5-pa ra met er ca lcula tion is a beor hed pr im ar ily bythe a lumina t e a nd fer rit e pa rameters in t he4-p a r amet e r ca l cu la t i on .The lea st squa res result s ma y be expressed interms of oxides, a ccording to eq (3). The pa ra m-eters ma y t hen be conver t ed t o melee of wa terper mole of oxide. When this is done, t he result sfor h alf-m icron dried sa mples a t a w at er : cem entra tio of 0.8, rounded to w hole numbers (exceptin the ca se of S i02) a re H/C= 1, H/S= 0,5,H/A= 5, H/F= 5, a nd 11/S0,= 2. These va l-ues ma y be used t o predict t he w a ter cont ent sof t he va rious possible product s of hydra tion.For inst a nce, a ca lcium silica te hydra te w it h aC/S ra tio of 3/2 would ha ve the composit ionC,S ,H ,, just a s w as indica ted from the pot ent ia lcompou nd pa r amet er s a nd t he st oichlom et riceq ua tions for t he hy dra tion of t he pur e silica tes,Tet ra ca lcium a lum ina te h ydr at e w ould h ave t hecom posit ion C 4AH g, w hich is t o bc com pa red w it h

the composit ions report ed by Robert s [33] fort et ra ca lcium a lumin a te h yd ra t es d ried u nd er v ar i-ous condit ions. Robert s gives H/A va lues of 11for ma teria l dr ied over solid Na OH or a nhydrousCaC lz, a nd va lues of 7 for ma ter ia l dr ied overP ,O, or a t 120 C .The ca lcium ferr it e hydra t e ca se is not sosimple, A tet ra ca lcium fer rit e hydra te w ouldh ave a n eg at ive w a ter con ten t, w hich is, of cour se,a bsurd. H ow eve~ , if t he a lumina tes a nd f er rit esw er e in s olid s olu tlon , ph ys ica lly pos sible, a n d n otun rea son able, w a ter con ten ts a re pr edict ed .The predicted w a ter content s of t he sulfo-a lumina tes a re, a s w as point ed out a bove, quit eun cer t sin . Th e w a ter -t o-oxid e r at ios giv en a bov elea d t o t he composit ions C,A.Ca SO,.7H a ndC,A.3Ca S0,.5H . Lerch, Asht on, a nd B ogue [55]foun d w at er cont ent s for t hese ma teria ls, dried a t110 C , t o be 6H a nd 7H, respect ively . Rober t srecent w ork [33] indica t es a va lue for t he lowsulfa te sulfoa lumina te of a bout 8H . I f the lea stsqua res H/S 02 va lue w ere 1 inst ea d of 2, thep redi ct e d compos it i on s of the sulfoa lumin a tesw ould be C3A.Ca SOi.8H a nd C~ A,.3Ca S04.8H .Thus, on t he ba sis of experiment al evidence, ita ppea rs t ha t t he H /SOl r at io sh ould bc s om ew her ebetw een 1 a nd 2, B ot h t hese va lues fa llw ell w ithin t he uncer t a int y limit s det erminedst art is t ical ly .Th e ev id en ce f rom t he lea st s qu ar es ca lcu la t ion scombined w it h t he evidence obt a ined from theX-r a y d if fr a ct ion s tu diee pr ov id es a s tr on g in dica -t ion tha t the a lumina in C IA rea ct s in . a differen tma nner from tha t , in the fer rit e pha se. Thecements low in C3A show n in t a bles 1 a nd 2 bothconta in et t r ingit e. On the other ha nd, t hosecements high in CSA w hen hydra ted con ta inedt he low sulfa te sulfoa lurnina te. Thus, it a ppea rstha t on ly when t he A/F ra t io in t he cement isr el a ti ve ly h ig h, d oes t h e l ow s ulf a te s ulf oa l um in a t eform. S teinour point s out , in his recent discus-sion of t he set ting of por t la nd cement [56], t ha tw hen the mola r A/F ra tio in a cement is less t ha n1.0, no ret a rder is needed. He a lso a t t r ibutesfla sh set t o t he forma tion of a hexa gona l ca lciuma lumina te. U nder the condit ions obt a ined w itht he use of t he high C~ A cements w hose composi-t ions a re given in t able 5, t he pr esence of gypsumTfimm 5, Ozick umzpm


17/44

pr ev en t s t he f orma t ion of t he h ex a gon a l a lumin a te(pr es um ably t et ra ca lcium a lu min at e h yd ra t e) byt he forma tion of the sulfoa lumina te. The firstsulfoa lum in at e t o for m is et tr in git e, a ppa ren tly ,since of t he X-ra y pa tt er ns of pa st es fr om cem en t15754, only tha t of t he youngest observed , a6-m on th old s pecim en , s how ed et tr in git e. Ta ylor[10], t oo, st udying a norma l por t la nd cement ,observed init ia l forma tion of et t r ingit e, w it hsubsequent disa ppea ra nce. I t is int erest ing t onot e t ha t a hexa gon al ph ase ult im at ely does form ,t his h ow ev er bein g t he low s ulf at e s ulf oa lumin a te.The mola r A/F ra tios in t he t wo cement s, 15754a nd 15497, in w hich t he m on osu lfoa lum in at e d oesf orm a r e 4.37 a n d 3.15, r es pe ct iv el y.On t he other ha nd, the low sulfa t e sulfo-a lumina te does not form in cements 15622 a nd1.5669 in w hich no significa nt a mount of C3A ispresen t . The mola r A/F ra t ios in these tw o ce-ment s a re 1.45 a nd 1.59, respect ively , or , w hencorrect ed for t he a lumina in the silica te pha ses,0.81 a nd 1.34. I t w ould a ppea r fr om t hese r esult stha t no significa nt a mount of a lumina from thefer rit e pha se en ters int o a sulfoa lum ina te a e lon ga s en ou gh a lum in a is a va ila ble fr om ot her s our cest o combine w it h a ll of t he SOS presen t t o form a tlea st t he h ig h su lfa te sulfoa lum in at e.

F lin t a nd Welle [57] obs er ved t ha t w hile C ,AH ,wa s suscept ible to a t t a ck by sulfa t e, hydro-g ar net s con ta in in g eit her ir on or s ilica w er e q uit eresist ant . I t w ould a ppea r fr om t hese considera -t ions t ha t t he m ola r ra tio of nonfer rit e a lum in a t oSO, in a given cement w ould serve a s a n indica -t ion a s t o w hich s ulfoa lu min at e for ms ult im at ely .Thus, t he high C ,A cement s, w hich con ta in t helow sulfa te sulfoa lumina te for t he m ost pa rt h aveSO, to nonferr it e A1,O, ra t ios of 0.7 a nd 0.6,r espect ively , w hile t he low C 8A cem ent s, w hichcont a in the high form for t he most pa rt ha ver a tios 1.2 a n d 3-.9.I t is t her efor e a lso likely t ha t n o sulfofer rit es. .for m in por tla nd cem en t pa st es , a t lea st of cem en tsw ith in the w ide composit ion ra nge covered byt hose w hose X-ra y da ta a re given in t ables 1 a nd 2,a nd whose composit ions a re given in t a ble 5.F urt herm or e, t he lea st sq ua res coefficient s dis-cussed a bove a lso indica te t ha t t here is no sulfo-fer rit e, in t ha t such a com poun d, eit her high for mor low form , could not h ave a n ega tive ca lcula tedw at er cont en t , physica lly a bsurd. Of course, asolid eolut ion of sulfoa lum in at e a nd sulfofer rit eis possible a s fa r a s t he lea st squa res considera -t ions go just a s in the ca se of a lumina tes a ndferrites.

II . Kineticsof theHydration of PortlandCementL. E. CopelandandD. L. Kantro

IntroductionThe purpose of t his sect ion of t he pa per is tor ev iew ou r kn ow led ge of t he kh et ics of h ydr at ion .Mecha nisms of hydra t ion ma y a t t imes bem en tion ed but a discussion of mecha nism s is n oth p ri nc ip a l obje ct i ve .The first kinet ic studies of t he hydra t ion ofpor tla n d cem en t w er e con cer ned w it h d et ermin in gt he st rengt h of concr et e a nd m ort ars a s a fun ct ionof t ime of cur ing. U seful informa t ion ca n beobta ined from such st udies, but t heir va lue fort heoret ica l purposes is limlted beca use t he de-

velopment of st rength in ooncret e a nd mort ar isinfluenced b ma ny fa ctors ot her tha n t he ra te of[ydra tion o the cement in t he mix, Know ledgeof t he ra t es of hydra t ion of cement is just onestep tow a rd underst a nding the mecha nism ofhydra tion a nd the development of st rengt h, butit is a n impor t a nt one.Three genera l met hods ha ve been used instudying t he kinet ics of hydra tion of por t la ndc~mmt : (1) m icr os copic m am ir mt ion of h m-d mw dnea t cem en t pa st es a ft er know n cur ing t imes, (2)obser va t ion s of ch an ges in t he ph ysica l a nd ch em -ica l pr oper ties of h ar den ed pa st es a s a fun ct ion oft im e, a nd (3) X-r ay diffr act ion a na lysis of un hy -dr at ed cem en t in h ar den ed pa st es.

I n gen er al, t he m icroscopic st udies ca n be, a ndin some, ca ses h ave been, in ter pr et ed t o suppor tMicha ehs t heory of the ha rden ing of por t la ndcement in tha t the unhydra ted clinker pa rt iclesa re foun d em bed ded in a gel w hich h as n o st ruct ur ev is ible in t he lig ht m icr os cope. Th e pr es en ce ofa ll four ma jor pha ses ha s been observed in thesepa r ticlesev en a f ter 20 y r.Th e m ea su rem en t of sever al ph ys ica l a nd t hem -ica l propert ies of pa stes a e a funct ion of cur ingt imes ha s been ma de. In some ca ses inferencescon cer nin g t he r at es of h yd ra t ion of t he in dividua lcom pon ent of cem en t h ave been dr aw n fr om t hesemea surement s. I t w ill become evident tha t someof t hes e in fer en ces a r e n ot ju st if ied .I n r ecen t y ea rs n ew t ech niq ues h av e been d ev el-oped. One of t hese, X-ra y diffra ct ion, offersa bout our best t ool for mea sur ing direct ly t her at es of h yd ra t ion of t he in div id ua l ph as es in por t-la nd cement . At t he presen t t ime the exper i-men ta l er ror is la rge when compa red w it h t heexper im en ta l er ror of st a nda rd ch em ica l m et hod sof a n aly sis , b u~ s ig nifica n t r es ult s ca n b e obt a in ed .Fur ther exper ience w it h the method w ill bringim pr oved result s. P erha ps ot her n ew t ech mq uesca n a lso be a pplied t o t he pr oblem s.

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Direct Microscopic ObservationsMos t of t he m icr os copic exam in a tion s h a ve b eenm ade on polis hed s ect ion s, or som et im es u pon t hinsect ions, of ha rdened pa stes. B ut Anderegg a ndH ubbell [58] ch os e t o d ev elop a d if fer en t t ech niq uefor t heir w ork. They fir st pa ssed cem ent t hrougha n a ir sepa ra tor to obt ain severa l fra ct ions of ce-ment w it h pa r t icles w ith a , na r row size ra nge.Th ey t hen pr epa r ed pa st es of t hes e s iz ed f ra ct ion s,w ,J c= O.4, a nd cured t hem in conta ct w ith a sma llqua nt it y of w a t er . At ea ch of severa l select ed

a ges a .sm !ll fr agment w as broken fr om ea ch pa st ea nd dr ied m a n ov en t o st op t he h ydr at ion r ea ct ion sbyremoving t he w at er . Ea ch fra gment w as t henground unt il microscopic evidence show ed t her na t or ia l t o be s ubd iv id ed in to sma ll a n d u nif ormlyslz~ d pa rt icles. S pecimens for microscopic ex-a mina tions w ere prepa red by pla cing these pa r-t icles on a microscope slide in a n oil w ith arefra ct ive index of 1.67. Thus it w as possible forthem to tell w hether or not a pa rt icle w a s hy-dr at ed by it s r efra ct ive index, for if it is hydra tedit s refra ct ive index is low er tha n t ha t of t he oila nd vice versa . They coun t ed thousa nds of pa r-t icles (w eight ing t he count by the size of t hepa rt icles) a nd det erm ined t he volum e fr act ion ofhydra ted cement from the number of hydra ted~ hey obt a ined the w eigh t fra ct ion hydra ted bya rt icles r ela tive t o t he t ot al n um ber of pa rt icles .using t he densit ies of t he un hydra ted cem ent a ndof t he com plet ely h yd ra t ed cem en t.To ch eck t heir r esult st h ey det er rn in ed t he fr ac-t ion of cement hydra ted in sa mples prepa red bymixing complet ely hydra ted cement w ith unhy-dra ted cement in know n proport ions. They re-por t ed r esul t s a c cu r a t e t oabou t2. 5p er cent .They proceeded t hen to ca lcula te t he dept h ofpenet ra tion of t he w ater int o cement pa rt icles.To do this they a ssumed tha t the sha pe of t heor igina l cement pa rt icles w as t he sa me a s tha t oft he unhy dr at ed pa rt icles rema in in g in t he pa st e,a n d m a de m icr os copic m ea s ur em en ts t o d et ermin et he size a nd sha pe of a g~ ea t ma ny cement pa r-tmles. Typica l result s, given in t a ble 6, w ereest ima t ed for a cement w ith a known pa rt iclesize dist ribut ion using t heir result s on dept h ofpenet ra tion of w aier in sized fr act ions of clinkerpa rt icles. They n ot ed t ha t t heir Type II I cem enta ppea red to hydra te no more ra pidly tha n didt hem Type I cement .Thes e exper imen t s w e re r epe a te d [59] u si ng p ur ecompounds a nd mixt ures of pure compounds.P ure C2S hydra ted much more slow ly tha n didpure C ,S , w hich hydra ted much more slow ly t ha ndid pure C,A. The a ddit ion of 10 percent C ,AFt oeit her C$or C,S ca used t hemixt ure to hydra temuch more ra pidly tha n eit her componen t of them ixt ure w ould hy dra te w hen pure.B r ow nmiller [60] ex am in ed polis hed s ect ion s ofn ea t cem en t pa st es cu red f or v ar iou s t im es . Fromthis exa mina t ion he est ima ted tha t a bout }{ oft he cem cnt rem ained un hydr at eda t t he en d of t hefirst da y. H e compa red t he sizes of the pa rt icles

visible in the polished sect ions w ith t he sizes oft he pa rt icles of or ig in al cem en t a nd est im at ed t ha ta 60Y pa r ticle d ecr ea s ed in s iz e t o a bou t 45Wd ur in gthe first da y , tha t t he depth of penet ra t ion wa sa bout 7}4~ . At 7 da ys a pproxima tely 80 percentof the cement ha dhydra ted, a nd a t 28 da ys a bout85 percen t . Cements tha t w ere h igh in CJ 5 a ndC ,A w ere a lmost complet ely hydra ted a t t he endof 7 da ys. He concluded tha t a s hydra t ion pro-ceeds t here is a uniform decrea se in the size ofthe cement pa rt icles, a nd st a ted, There is nom icroscopic evidence of t he cha nneling of w at erin to t he in ter ior of cem en t pa rt icles t o select ivelyh yd ra t e a n y s in gle m a jor con st it uen t t .TABLE 6, Dep th of p en et r at i on of w a ter i n cl i n k - particles

a nd the degreeof hydra tion of a t ypica l por t la nd cemen tTime Depth of pen..(days) Percenttmtion (J.) hydrated

24+ g:: 422s 5190 so

H ow ever, h e did observe t ha t differ ent pha sesa t the bounda ry of a pa rt icle dld not hydra te a tt he sa me ra tes: e.g., C$ hydra tes more ra pid lyt ha n C ,S , a nd som e int erst it ia l ma teria l hydra tesv er y s low ly in deed .Rexford [61] used thin sect ions. He point edout tha ~ a ccura te ra tes of hydra t ion from suchmicroscopic exa mina tion w ere very difficult t oob La in ; one needs to exa mine ma ny fields a ndm ea s ur e a ccu ra t ely w it h a Wen tw or t h m icr om et erst age. H e confirm ed B row nmillcr s conclusionst ha t hydr at ion pr oceeded fr om t he bounda ries ofcemen t pa rt icles inw ards tow ards the cent er a t acompa r a tiv ely u niform ov er a ll r a te, w h ich a ff ect eda ll the const ituent s of tha t pa rt icle more or lesssimultaneously. He st a ted furt her , No indica -t ion of com plet ed h ydr at ion of a ny on e com pou ndw a s ev er obs er ved a lt hough in cipien t s elect ivit yw a s oft en visible a roun d t he per iph er y of a cem en tp a r ti cl e. H is conclusions w ere ba sed upon t heexamina t ion of ha rdened pa stes cured up t o 6mont hs, a nd upon exa mina tion of concret e up t o20 YrS old . -Wa rd [62] exa mined t hin sect ions a nd ca me tos om ew h a t d if fer en t con clu sion s, H e des cr ibedt wo kinds of gel, one of w hich he ca lled a groundmass gel tha t w as int er rupted by unhydra tedclin ker gr ain s, ca lcium h yd roxid e cr yst als, a nd bysma ll cha nnels, a nd por es. S ma ll cryst alline pa r-t icles of low bm ef rin gen ce w er e s ca t ter ed t hr ou gh -out t his gel. As the pa ste a ged, a clea r gelww:wed iOexude from the gr~ ~nd ma ss Or tOpr ecipit a te m t he v oids a nd ch an nels .

He observed tha t C,S a nd C ,AF were slow t ohydra te a nd tha t ma ny cement ra ins w eresha tt er ed dur ing t he hydra tion. H?e iden t i fi edthe fra gment s a s C jS . He concluded t ha t ea ch444


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clin ker gra in does not h ydra te i n such a ma nnera s to develop a n i,n~ ividua l coa ting of hydra tew it h subs eq uen t u mt mg of t hes e coa tin gs .The overa ll ra t e of hydra t ion of cement ob-s er ved in t hes e m icr oscopic st udies a gr ees q ua li-t at ively w it h expect at ions ba sed upon t he ra te ofst rength development . Anderegg a nd H ubbellt a cit ly a ssumed a mecha nism of hydra tion tha tw as support ed la ter by t he indepen den t observa -t ion s of B r ow nm iller a nd of R exfor d. I n a ns wer in ga crit icism of their pa per, Anderegg a nd Hub-

bell show tha t t hey w ere a wa re tha t this a ssump-t ion w a s n ot un iver sa lly a ccept ed , but a rg ued t ha t: it is t rue. Act ua lly , it is support ed by t he t heoryof ha rden ing a dva nced by Micha elis, just a sB row nmiller interpret s his result s t o suppor tM ich a el is ~ h e or y .There is a sma ll d ifference betw een the com-posit ion s of t he fin ely g rou nd pa rt a nd t he coa rser

pa rt of a cement , but if hydra tion proceeds by am or e or less uniform dim inut ion in t he size of t hecem en t gr ains, t hen t he finer fr act ion w ould dis-a ppea r first -proba bly dur in g t he first da y. Aft er

t ha t t im e t he com posit ion of t he unh ydra ted resi-due should cha nge on ly slow ly if a t a ll.Wa rd crit icized t he a bove view s. He w rot e ofa n a ppa ren t increa se in t he a mount of C$ in t heh ar den ed pa st es a nd s ugg es ted t ha t t he in dividua lpha ses rea ct sepa ra tely , t hen a t a fa vora ble con-cent ra t ion a gen era l pr ecipit at ion of gel occurs.B ut bo~ h con cept s ca n be cor rect . Th e m ech an is mproposed by Wa rd could a ccount for the init ia lset ting of cem en L but by fa r the grea test a mountof cemen t could be hydra ted a s B row nmiller a ndRexford ha ve described it . I t is cer t a inly t ruet ha t if cemen t gra ins w ere sha tt ered by hydra -t ion. this must ha ve occurred before t he pa stehardened.Wa rd observed sha tt ering of C ,S gra ins in ob-s er vin g t he h ydr at ion of t he pu re com pou nd un dert he microscope. He not ed tha t his pure C ,Sshow ed a t endency to dust a nd suggested tha tperha ps t he sha t t ering w a s the result of t he@= XY conversion . Is it possible t ha t w a ter couldlea ch a soluble st a bilizing a gen t out of t he C ,Spha se in por t la nd cement , ca using t he sa me con-ver sion w it h sh at ter in g of t he cem en t gr ain ?

Kinetics From Changes in Physical and Chemical PropertiesHeatof Hydration

Man y w or ker s h a ve d et ermin ed t he h ea t of h yd ra -t ion of por t ,la n d c emen t a s a f un ct ion of t ime of cu ri ng .Wood s, S t ein ou r, a n d S t a rk e [63, 64]w e re a b le t o cor -r ela t e s uch h ea t s of h yd ra t ion w it h t he d ev elopm en tof st rengt h in mor t a rs, a nd a lso found a good cor-rela t ion betw een the ra t e of development t ofst rengt h a nd t he composit ion of t he cement .Their prima ry mot ive w as development of lowhea t cement , a nd t herefore it w a s essent ia l t ot heir pur pose t o find a r ela tion ship bet ween h ea tof hydra t ion a nd composit ion of cement . Forthis t hey employed t he met hod of lea st squa res,a ssuming tha t a t a ny given a ge ea ch percent ofea ch cem en t compou nd m a kes a f ixed con tr ib ut iont o t he h ea t ev olu tion i nd epen den t of t he pr opor t ionof t he compound in t he cement . They w ere Suc-cess ful in a ccom plish in g t heir object iv e. Otherw or ker s ha ve genera lly follow ed t heir exa mple.Da vis, Ca rlson, Troxell, a nd Kelly [65] ma desim ila r s tudies of h ea t s of h ydr at ion , a nd Ver becka nd F ost er [51] published init ia l result s of a n ex-t ensive invest iga tion w hich is con t inuing. Thela tt er a ut hors in cluded t he effect s of gy psum a ndbot h gy psum a nd gla ss in t heir com put at ions.B y com pa rin g t he m a gn it udes of t he r espect ive(cont ribut ions of ea ch of t he com pon en ts t o t hehea t of hydra tion, it ca n be infer red t ha t t he ra tesof hydra tion of the ma jor component s ha ve theorder C3A, C ,AF3 C ,S , C ,S . This order a greesw it h tha t obt a ined by compa ring t he ra tes of hy-dra tion of t he pure componen t s. The cont ribu-t ion of ea ch componen t t o t he hea t of hydra tionof complet ely hydra ted cement pa st e is, w it hinexperiment al er ror , t he hea t of hydra tion of t hepure componen t .

Appa rent ly no one working w ith hea ts of hy-dra t ion ha s done more t ha n draw qua lit a t ivecon clusions con cer nin g ra tes of hy dr at ion of t heindividua l component

chemistry of hydration of portland cement

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