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NRC D

AJP-01-97

1/24/97

COVERSHEET NRCRECORDSCENTERm

TMl-2 181 HSM

CONDITION OF TMI CANISTERS (1/24/97)

T-234-2G

7203

S/N 152463 LMITCO LEITER AJ PALMER TO JO CARLSON LEGACY 1997

ITT it lo. T-2~~-2& DSC

NO TRANSMITIAL SHEET ATIACHED COVER SHEET SCANNED FOR RETRIEVAL AND ADMINISTRATIVE PURPOSES - NOT A TECHNICAL VALIDATION OF RECORD

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LOCKHEED

Lockheed Martin Idaho Technologies Company

INTERDEPARTMENTAL COMMUNICATION

Date: January 24, 1997

To: J. 0. Carlson, MS 3114

From: A. J. Palmer, MS 3765 Al/ pJ __ _ Subject: CONDffiON OF TMI CANISTERS - AJP-01-97

Reference 1 makes the assertion that the condition of the TMI-2 fuel canisters is not as described in the performance specification (Reference 2) and this different condition has necessitated a heated drying system to condition the canisters prior to storage. In order for this conclusion to be valid, both of the following points must be true.

1. The condition of the canisters was not correctly described in the performance specification. 2. If the canisters were configured as described in the performance specification, they could

have been dried without heating.

These points are addressed below.

Condition of Canisters Not Correctly Described

Prior to a recent test on a spare TMI fuel canister, VECTRA drilled a small (:a=l/2 inch) hole into the side of the canister and reported that the LICON inside was of a pasty consistency. Because the performance specification states the LICON is a low density "concrete", Reference 1 argues that a pasty consistency of the LICON constitutes a different condition.

This argument will be examined from two directions. First, was the material found in the drill hole representative of the LICON elsewhere in the canister? Second, is the consistency of the LICON a critical parameter in describing the condition of the canisters?

The LICON in the canister in question had been saturated with water as part of a previous testing program at the INEL and the process of drilling into the LICON coupled with the excess water may have combined to form a paste. In other words, the paste material could have been a combination of the abraded LICON and water, not a representation of the overall condition of the LICON.

The binder in LICON is calcium alurninate cement Reference 1 implies that the only use of calcium alwn.inate cement is as a refractory and that it should have been firedt to remove waters of hydration prior to use. This is incorrect Calcium aluminate cement can and has been used for structural applications after a room temperature cure (Reference 6, attached). According to References 3 and 6, calcium aluminate cement should be cured at temperatures in excess of 95F to produce the most stable crystalline structure, however it will cure at temperatures as low as 40F (see for example Figs. 2, 9 of Reference 3). According to Table V of Reference 3, when

t The word "cured" is used in Reference l, but the context implies a firing operation.

QA RECORD

J. 0 Carlson January 24, 1997 AJP-01-97 Page 2

cured above 95F, the hydration products are 3Ca0* Al203*6B20 + Al20:3*3H20. When cured at temperatures below 95F (as was likely done in the case of the TMI canisters), the hydration products are Ca0*Ah0:3*10H20 and 2Ca0*A120:3*6H20 + Al203*3B20 (gel). In summary, there is no supporting evidence in the literature that the LICON in the canisters should be anything other than a solid.

On the other hand, if for some unexplained reason the material observed in drilling the sample port represents the condition of the LICON in some or all of the TMI-2 fuel canisters; the important issue is not whether the LICON is a rigid solid versus a paste, but rather the amount of water in the LICON. Reference 1 states that 120 lb of water was removed from the LICON by heating at 600F. According to Reference 3 (attached), heating to this temperature would have removed all the pore water plus much of the water of hydration. The performance specification states that the LICON contains 80 - 130 lb of free water plus 20 - 50 lb of pore water for a maximum total of 180 lb. Thus the amount of water removed in VECTRA's heating test is well within the limits set forth in the performance specification.

Canisters Could be Dried Without Heating if LICON Were Solid

Whether a solid or paste, LICON retains a great deal of water. As part of the tests conducted in Reference 4 (see Appendix E), a small solid cube of LICON was soaked in water overnight and then heated in successive steps to 700F. During this process the cube lost 0.33 glee water. This corresponds to 80 lb for the 4 cu-ft occupied by the LICON. Further evidence for the amount of water that is retained by soaked solid LICON is found in Reference 4 Table A.1, where the LICON annulus of a previously heated and dried canister was reflooded and found to retain 110 lb of water.

Whether a solid or paste, LICON is extremely difficult to dry. This is because the water is dispersed throughout a porous matrix. The matrix both impedes heat transfer required to vaporize the water and the migration of the vapor out Reference 5 (selections attached) contains a procedure used by researchers at Oak Ridge National Laboratory to dewater (remove unbound water) from Portland cement, a porous media very similar to the LICON. These researches found that even while holding a vacuum at 250C, a time period of 24 hrs was required to remove the free water, indicating the time required to dewater concrete while under vacuum at room temperature would be impractically long.

The point to be made here is that whether the LICON is in a paste or solid form, a heated drying system is required to dry the canisters such that a 3 Torr vacuum can be held for 30 minutes. This point could be verified by taking one of three spare fuel canisters at the INEL, sampling the LICON to ensure that it is in the solid state, and then after filling it with simulated debris, soaking and dewatering; attempt to dry the canister by vacuuming with no heat addition.

References:

1. P. J. Weishaar, NNS, to M. C. Stone, LMITCO; "LITCO Subcontract C95-180274 dated November 27, 1995; Notification of Constructive Change", lOOOQ-LE-044N, January 21, 1997.

,,

3

J. 0 Carlson January 24, 1997 AJP-01-97 Page 3

2. Performance Specification, ICPP Interim Storage {ISS) for the Long Term Storage of TMI-2 Fuel Project, Subcontract No. C95-180274, Rev. 1, May 1995.

3. G. MacZura, et al., Refractory Cements, Aluminum Company of America, February 1983.

4. A. J. Palmer, A. E. Arave, Dzying Tests Performed on TMI-2 Fuel Canisters, LITCO, INEL-94-053, December 1994.

5. L. R. Dole, et al., Cement-Based Radioactive Waste Hosts Formed Under Elevated Temperatures and Pressures cFUET AP Concretes) for Savannah River Plant High-Level Defense Waste, ORNl/fM-8579, March 1983.

6. A CI Manual of Concrete Practice, Part 1, Guide to the Selection and Use of Hydraulic Cements - Appendix, ACI 225R-91, American Concrete Institute, 1994.

Attachments: As stated

A. J. Palmer, Staff Engineer Mechanical, Civil, and Industrial Engineering

cc: R. C. Hill, MS 3765 R. J. Norris, MS 9208

Refractory Cements GEORGE MAcZURA, LEROY D. HART, RAYMOND P. HEILICH, AND JOSEPH E. KOPANDA

Aluminum Co. of America, Alcoa Technical Center Alcoa Center, PA 15069

Calcium aluminate (CA) or high Al20 3 cements (HAC) continue to be the most important hydraulically setting cements used for bonding refractory castables (concretes) because they develop high strength within 6 to 24 h after placement. This early strength development enables high temperature processing units to be put back on stream with minimum turnaround time, thus providing a favored cost' performance ratio.

Relative to conventional refractories, castables con­tinue to gain in popularity because of the following advan­tages listed adequately by Bakker':

• Quick installation and low construction costs; • Possibility of fully anchored construction; • Reduced and simplified furnace maintenance; • Thermal conductivity one-half to one-third that of

fired brick, permitting thinner linings or improving thermal efficiency;

• Good thermal-shock resistance; • No joints (monolithic); • Prefired shapes need not be stocked; • Ready availability; and • Greater flexibility in design. Portland-cement concretes have limited refractory

applications. Unlike CA cements, they do not retain their integrity when subjected to prolonged periods of high heat, cyclic heating and cooling, and other deleterious conditions of corrosion and erosion present in high temperature indus­trial processes. Portland-cement binders are rarely used for applications >650°C (> 1200°F) and perform poorly when thermally cycled in the presence of moisture to temperatures >425°C (>800°F). 2

In the U. S., limited use of CA cements as refractory­concrete binders began in the 1920s after first being mar­keted in France in 1918. 3 Initially, most refractory concretes were mixed on the job site, similar to portland concrete. In the late 1940s and early 1950s, specially formulated, dry cement-aggregate mixes (castables) became more available

Table I. Typical Chemical-Analysis Ranges of Raw Materials

with a subsequent increased interest in their properties. Until the early 1950s, commercially available HAC

contained large amounts of iron oxide and Si02 as impuri­ties. These oxides limited the cements to relatively low temperature applications. Calcium-aluminate cements of higher purity, introduced during the 1950s, were rapidly accepted. They expanded the use of refractory castables for higher temperature applications. As a result, interest in ther­mal properties and performance of HAC-bonded refractory concretes was renewed in both the U. S. and Europe. 1

The refractories industry adopted tests used by the portland-cement industry for characterizing these binders. Refractory-concrete testing was standardized by casting 230-by-114-by-65- or .76-rnrn (9-by-4.5-by-2.5- or 3-in) brick shapes to take advantage of the American Society for Testing and Materials (ASTM) procedures for evaluating firebrick. In 1973, ASTM Committee C-8 on Refractories began recognizing that the 20° to 30°C (70° to 85°F) curing temperatures previously adopted were not appropriate for characterizing the properties of HAC because of the meta­stable compounds formed at these temperatures. Standard practices were developed to use the ability of refractory concrete to be cast into a variety of shapes required for determining hot-strength properties. Thus, the necessity for expensive diamond cutting of specimens from cast brick shapes was eliminated along with test varations emanating from structural alterations that occur during wet-sawing of castable specimens.

The present paper identifies the predominant CA phases responsible for developing hydraulic bonds at ambi­ent temperatures. It sets out the resultant hydrated phases that provide the basis for HAC technology useful to the refractory industry. It emphasizes the correct use of curing, drying, and firing procedures to obtain optimum castable performance and to avoid structural defects relating to the transition of hydrated phases and gels. Permeable crystalline phases are then developed that maximize structural stability and ensure safe heating of large cross sections.

High Al20 3 Cement Manufacture

Raw Materials The sinter or clinker process is the predominant method

for manufacturing HAC in the U. S. Relatively pure lime­stone (Table I) is used as the lime source for producing all

CaO source Calcined Dried bauxites Oxide Limestone Ah01 Domestic Foreign

constituents (%) (%) (%) (%)

AI203 0.2-0.3 99.0 49-56 50-63 Cao 54-55 <0.1 0.1-0.6 0.01-0.03 Si02 0.4-0.6 <0.1 5-13 0.25-9.0 Fe20i 0.2-0.3 <0.1 3.5-7.5 0.9-18.0 MgO 0.2-0.4 <0.1 Na20 0.3-0.5 <0.5 LOI* ( I 100°C) 41-43 <1.0 27-31 27-34

•Loss on ignition. s

Table II. Composition of CA-Cement Binders

Type

Low purity lntennediate purity High purity

•Total iron as Fe,01

39-50 55-66 70-90

Oxide composition range

Fe,01 • CaO (%) (%)

7-16 1-3

0.0-0.4

35-42 26-36

9-28

SiO, (%)

4.5-9.0 3.5-6.0 0.0-0.3

Table Ill. Typical Mineralogical Phase" Assemblages in CA Cements

Relative Cement purity

hydration Low Intermediate High rate (39o/o-50% Al,01) (55':70-66% AhO,J (70o/o-90% Al10 1)

Fast CA CA CA (4A3S C12A1 C12A1 C12A1 CA2 CAz CA2 C C

Slow C2S C2S C.iAF C.AF C,AS C2AS

Nonhydrating CT CT A A A

•C=CaO; A=Al,01; S=SiO,; S=S01 ; F=Fe,01; T=TiO,.

CA cements. Calcined Al20 3 is used to manufacture high purity CA cements, whereas low iron, low Si02 bauxite is the preferred Alz03 source for intermediate and low purity HAC. Typical raw-material analyses are given in Table I.

Although South American bauxites have been the pri­mary source for U. S. manufacture, domestic bauxite sources of slightly lower purity can be used when enriched with calcined Al.03• There are adequate resources of lime­stone, calcined Alz03 , and domestic bauxite having the purity listed in Table I to make the U. S. self-sufficient with regard to the manufacture of all three purity grades-low, intermediate, and high-of HA.

Commercial HAC is categorized in Table II according to purity and Ah03 content. The low purity cements are manufactured from bauxites containing } 18% Fe20 3 and :}9% Si02 . These impurities limit refractory-concrete ser­vice to = 1425°C ( =2600°F). Lo'-" iron (2-4% Fe20 3) and low (5-7%) Si02 bauxites are sintered with limestone to manufacture the intermediate purity cements. This type of cement is generally used in concretes having a service limit of <1650°C ( <3000°F). Impurities totaling <2% in the high purity cements permit use to service limits of = 1870°C ( ==3400°F), depending on the refractoriness of the aggregate in the mix.

Production Bauxite requires preliminary crushing and drying

before being ground with crushed limestone to a fineness of == 10% residue on a 200-mesh sieve, whereas the nominal 100- to 325-mesh calcined Bayer Al20J requires no process­ing prior to concurrent grinding with the crushed limestone. The proportioned dry raw mix is either fed as ground or as an agglomerate into a rotary kiln, similar to that used in the manufacture of portland cement. The product is sintered at 1315° to 1425°C (2400° co 2600°F), cooled, and then ground

to cement fineness together with any additives, i.e., cal­cined Ah.03 to obtain the desired Al20 3 content, gypsum or other materials to control the set, and fillers and plasticizers for workability improvement. 4

i'vfineralogical Phase Assemblages Table III lists the typical compound constituents of

commercial HAC according to their relative reaction rates with H20. They form the hydrated cement phases re­sponsible for developing strength after curing the concrete in a humid environment. Economics demand rapid relining of process vessels. Short curing times of 6 to 24 h after place­ment have become commonplace prior to dryout and heatup of the units.

Monocalcium aluminate (Ca0·Al20 3 or CA*) is the main active ingredient in all HAC. It hydrates sufficiently fast to satisfy the short turnaround demands of industry. Minor cementitious constitutents such as C 12A7 , CA2 , and C..A3S* contribute to the strength development of high Ah01 cements during the short curing periods allotted by industry. Fast set is prevented by restricting free lime to a low level (<0.3% C*). All of these compounds react with H20 to form the same CA hydrated phases which provide the fundamental basis for CA-cement technology.

The remaining compounds listed in Table ID are inert or react very slowly with H20 at ordinary temperatures. They make an insignificant contribution to the hydration and strength development of refractory concretes, except during extended curing times such as iri greenfield installations.

•Cement chemistry notations are used: C=CaO; A=Al,01; H=H,0; S=SiO,; 5=S01; F=Fe,01; T=TiO,.

13 75

Working time Caltab 20

12 60 c #- ·e ~ 11 45 '

(1)

E ai --;; 10 Cl 30 C: ;:: ..>::

~

0

9 1 5 3:::

a ..._ _ __. __ ..1..-_--L--.l.......-...l-----'--...1.1 o 0

32 20 68

40 60 ·c 50 86 1 04 1 22 1 40 1 58 °F

Mixing temperature

Fig. 1. Casting H 20 required for ball-in-hand consistency.

Calcium-Aluminate-Cement Technology High Al20 3 castables require only 24 h to develop

70-80% full strength when properly cured, in contrast to 28 days for normal portland-cement concretes. The dried and fired strengths developed in refractory concretes are critically dependent on use of 1) the correct amount of tem­pering H20 required by the specific method of placement to assure installation of a sound lining having minimum struc­tural defects, 2) proper curing conditions to ensure develop­ment of the desired hydrated phases to maximize structural integrity, and 3) controlled uniform heating schedules.

The above requirements have a sequential effect on the service life and performance of a refractory-concrete lining bonded with HAC; that is, the strength degradation resulting from structural defects caused by improper placement will be amplified by the use of poor curing practices and of nonuniform and excessively rapid heating. The net result can be a premature shutdown resulting from catastrophic thermomechanical lining failure.

The processing variables which must be controlled dur­ing installation and initial heatup of HAC-bonded castable concretes are material, equipment, and H20 temperatures; H20 content; mixing intensity and time; placement method; curing time, temperature, and humidity; surface character­istics of the working face; and heating rate and schedule.

MPa ,,......-,---...---.-~--,---,-----~

15 C•llab 20 Conditioned and mi1ed 11 curing temoeraturt ..

= } 0 10

5

a Oried. tnl lired 11 OO"C IAST,.. 258- 701 ., 0 ...___....__,__--1 _ __.._.....,_ _ _.__...J..._J...........J

0 32 50

20 68

40 eo 80 ·c 86 104 122 144 158 176 "F

Conditioning/curing temperature

ksi kg/cm2

2.5

150 2.0

1.5 100

1.0

50

0.5

. Fig. 2. Comparative mechanical-strength properties.

MPa ksi k91cm2

2.5

~ "' 15

.. L 2.0 :5 C.

10 ~ = 0 J 100 1.5

" :,

I ~ 3 ,:, 0 E i 1.0 ,:,

5 t J 50 0 • Cured 24h I · 90"1, RH) u

J • Cried 11o·C·24h • Orted. tast tired , ,oa~c.sn 0.5 4 No dry,ng. slow !ited 1 1 oo•c -Sn

0 '---.L--J._--J---1---L--L--L-...L--o 20 40 so 80 ·c 32 50 58 86 104 122 140 158 176 °F

24h Curing temperature

Fig. 3. Comparative mechanical-strength properties.

Temperature is the most important variable requiring control during the installation of refractory-concrete linings because it influences the sensitivity of these materials to all processing steps; that is, mixing, placement, curing, and heatup. It has a significant effect on the extent that cement bonding phases develop and on the sensitivity to explosive­steam spalling on initial heating.

Although fortuitous, the ambient temperatures of 18° to 27°C (65° to 80°F) most comfortable to humans coincide with the temperature range exhibiting the greatest change in hydration products, setting time, and strength development. A change of only 5. 6°C ( 10. 0°F) in curing temperature in this range will produce significant changes in bond structure and physical properties. Unquestionably, the service life and performance of refractory-concrete installations are directly related to the effort put forth in controlling temperature at the desired levels during all installation processing steps.

Influence of Temperature on Mixing, Placement, and Strength Development

The critical influence of temperatures (materials, H20, and mixing environment) on ball-in-hand tempering H20 on the time available for mixing and placement of a 20% high purity HAC-bonded tabular Aii03 castable are shown in

Medium Major (.,AJ

CA .. c ::, 0 E Minor II

ID .? • * .. :I Trace II &. Cl.

c Zero ~ detection o

--:-:: : :-:;-- ' CAH 10 1 " , : ' )

' I / .-11AH3

: 'X: ; \ ,/· '-.I I ,,./•'' ,, •• ••''•'''./'\

r· ················· ·, ' ,, . .-, .. ·' __ ....__

20 40 60 eo·c 32 50 68 86 104 122 140 158 176 'F

Cure temperature Mixed at 22-24'C, Cured 24 hours a!>90% RH

Fig. 4. X-ray analysis of cured Caltab 20 concrete. 7

Cure 0 temperature

20 40 60 00 ·c 50 68 86 104 122 140 158 176°F

Fig. 5. Principal hydration phases of CA-25.

Fig. l. 5 The sharp reduction in working time occurring between 21 ° and 27°C (70° and 80°F) suggests the reaction rate of the HAC is changing rapidly in the temperature range normally associated with laboratory ambient temperatures. lt is imperative, therefore, that the preconditioning and ambient room temperatures be specified exactly with close tolerances on any referee tests conducted between two laboratories.

Conditioning, mixing, and placement temperatures in the 4° to 21 °C (40° to 70°F) range are the most favorable for providing low H20 requirements and consistently long working times which favor the formation of flaw-free cast specimens. Thus, it would seem that mechanical-strength properties should be maximized when compared with speci­mens formed with materials conditioned and processed at higher temperatures which provide less working time for placement. However, this has not proven to be the case as shown in Fig. 2.

Dried and l 100°C (2010°F) fued, 25-mm ( 1-in) bars exhibit maximum cold modulus of rupture (MOR) values when preconditioned, mixed, and cured at 32°C (90°F). The drop-off in dried and fired strengths when processed at temperatures >32°C (>90°F) may be explained by the probability of an increase in formation flaws which enlarge sufficiently on drying and firing to restrict the strength development on heating. Figure 3 supports this premise. Preconditioning, mixing, and casting the specimens at 22° to 24°C (72° to 75°F) favored the formation of test speci­mens having fewer defects as evidenced by the higher fired strengths obtained on the specimens cured at the higher temperatures. ·

The sharp drop in dried and fired strengths occurring in Figs. 2 and 3 for specimens cured at :S21 °C ( :S70°F) corre­sponds precisely with the occurrence of CAH 10* as the only

90 100 110

·c 4 10 15 21 27 32 3a 43 Ambient curing temperature

Fig. 6. Effect of curing temperature on properties of tabular-Al2 0 1 castable bonded with 15% CA-25 ce-ment.

crystalline cementitious phase in the concrete after curing 24 h (Fig. 4). High Al20 3 cements technology'-~ 14 also con­firms the presence of Ah03 gel as a bonding phase. The gel phase becomes sufficiently crystalline at >27°C (>80°F) to become detected by X-ray diffraction as gibbsite (a-AH/').

Literature cites that a strength loss occurs as the meta­stable hexagonal CAH 10 * phase dehydrates through the hexagonal C1AH3* transition phase into the stable cubic C3AH6* as schematically illustrated in Fig. 5. Table IV further clarifies the hydration products of HAC developed after curing and/or dehydration products obtained during heating. Beside the Ah03 gel developed at the lower tem­peratures in combination with CAHIO,* additional gel forms on heating as a decomposition product of CAH10* along with C2AH3. *

The low permeability obtained at temperatures <21 °C ( <70°F) shown in Fig. 615 is ascribed to the Al20 3 gel formed after curing. The increased permeability obtained at the higher curing temperatures corresponds to the crystalli­zation of the Al20 3 gel and to significantly better explosion resistance as demonstrated by the survival of undried, cured, 64-mm (2.5-in) test cubes subjected to a 1650°C (3000°F) chamber without explosion. The control of ambient curing temperatures is a desirable method for averting explosive spalling of refractory castables.

Calcium Aluminate Hydrate Crystal Morphology and Properties

The loss in strength of hardened HAC paste and castable refractories accompanying the conversion of the hexagonal phase, CAH 10, * into the cubic phase, CJAH6, * can best be appreciated by considering the morphological and volume changes accompanying this conversion. The CAH10* crystallizes into hexagonal prisms as shown in the

Table IV. Effect of Temperature on Hydration-Reaction Products of CA Cements Curing temperature

("C)

<21 21-35 >35

("F)

<70 70-95 >95

*C=CaO; A=Al,01; H=H,O.

Hydration products of CA phase•

CAH10+ Alz03 gel C2AH8 +AHJ (gel)1

C3AH6+AHi (crystalline)

'Gel crystallizes between 27° and 32°C (Bl" and 90°F) as detected by X-ray diffraction.

Fig. 7. Scanning electron micrograph showing CAH, 0

crystals (bar= 2 ,um).

scanning electron microscope (SEM) photomicrographs of a fractured CAH 10* specimen (Fig. 7). 16 These crystals trans­form into chin, hexagonal C2AH8* plates during conversion to the somewhat spherical, cubic C3AH6* crystal shown in Fig. 8.

The trapezohedral-type C3AH6* crystals are = 10 times the size of the residual CAH, 0* crystals. le is apparent that part of the strength loss in converted, hydrated HAC results from the reduced specific surface of the material and the voids occurring around the large cubic crystals. 16 These voids occur as the result of a nominal 50% volume change on conversion of CAH,0 * to the denser C3AH6* and a-AH3 * as noted in Table V. The gross restructuring and high shrink­age of the bonding matrix on conversion of the low density CAH 10* phase formed at <21 °C ( <70°F) explain the loss in mechanical strength on drying and firing HAC cascables cured at low temperatures.

Figure 9 shows that dried and fired strengths of castables bonded with intermediate purity cement are also maximum on curing at temperatures >30°C (>85°F) and minimum at lower temperatures. The fallacy in predicting cascable performance based on cured strengths obtained by using portland-cement test conditions is apparent.

Effect of Castable H10 Requirement on HAC Hydration The H20 content used during application is determined

by the consistency required to achieve proper placement. Even the higher H20 levels required for placement by cast­ing is not sufficient to achieve complete hydration of the HAC binder in high strength, castable compositions when cured at lower temperatures. Table VI lists the H20 require­ment for completely hydrating an 18% CaO, high purity HAC when forming the different hydration products at the various curing temperatures. Complete hydration cannot be achieved in castables bonded with 20-30% high purity

Fig. 8. Scanning electron micrograph showing C3 AH6

crystals (bar= 4 ,um).

cement when using 9-9.5% H20 to obtain a good ball-in­hand consistency and curing at <21 °C ( <70°F).

Ball-in-hand consistency for this cement when tested neat is 20-22% by the standard Vicat consistency test. This is not sufficient H20 to completely hydrate this 18% CaO cement even when curing at the higher temperatures. Hydration would be even less complete because of insuffi­cient placement H20 when using the higher lime cements, which require proportionately more H20 to achieve com­plete hydration.

The effect of additional H20 in excess of the ball-in­hand consistency on HAC hydration is illustrated in Fig. IO. The curves identified by the lower H20 additions represent the ball-in-hand consistency requirements when precon­ditioning and testing at 21° and 27°C (70° and 80°F). Increasing the H20 addition to 30% markedly increases the temperature rise as a result of more complete hydration in spice of the additional mass contributed by the extra H20. The larger areas under the curves for the greater H20 addi­tions confirm that 40-50% more hydration has taken place.

Figure IO further illustrates the extreme sensitivity of the hydration rate to ambient room temperatures by com­paring the rise in temperature between the 21 ° and 27°C (70° and 80°F) tests. This 6°C (I0°F) difference in temperature results in a 150% increase in hydration products of the neat HAC. Increased hydration reactivity obtained with in­creasing temperature also prevails in castable compositions as indicated by the decreasing amount of unhydrated CA phase at >21°C (>70°F) shown in Fig. 4. The greater hy­dration efficiency occurring at curing temperatures > 21 °C (>70°F) must also contribute to the increased dried and fired strengths developed under these processing conditions.

At ambient temperatures near 30°C (86°F), the heat of hydration normally increases the curing temperature of 102-mm (4-in) dense linings to the desirable level, thus

Table V. Effect of Temperature on Hydration-Reaction Products of CA Cements

Physical properties

Curing temperature

(°CJ ("Fl

<21 <70 21-35 70-95 >45 >95

Hydration products of CA phase•

CAH 10

C2AHa+AH3 (gel)1

C3AH6+AH 3 (crystalline)

Densi7-(g/cm)

1.72 1.95, 2.42 2.52, 2.42

Solid volume change from CAH,a•

(%)

-37 -53

•C=CaO; A=A!iO,; H=H10. 'Gel crystallizes between 27° and 32°C (81° and 90°FJ as detected by X-ray diffraction.

50

18h • 220"F ..c 6800 0, ,:

~ 6000 "' " > 5200 "'

Intermediate purity cement 1· Cement: CFB ~ 1 :4 lvoi.l 40

24h cure

a. 4400 E 0 U 3600

~h-1600"F

: f 2800 ! I I I I I

"F 40 70 1 00 1 30

·c 4 21 38 54

160

71 24h Curing temperature

j 30

\<g/cm 2

500

= Cl ,:

" 400;

" >

"' "' 300 ~

j 200

a. E 0 u

Fig. 9. Effect of curing temperature on compressive:strength.

ensuring a safe heatup and maximum refractory strength development.

Drying and Firing HAC Castables The fast heating schedules previously specified17 for

heating HAC-castable brick specimens to temperature prior to testing had been adopted from ASTM procedures for evaluating firebrick. The nominal l l00°C (2000°F) average gradient specified between room temperature and 425°C (800°F) is normal for gas-fired furnaces; however, it is too drastic for brick-size specimens of HAC castables. Bakker1

determined that heating rates >0.047°C/s (>300°F/h) lower the strength of brick specimens while increasing the variability (Fig. 11).

Further work by ASTM Committee C-8 resulted in the recommendation of maximum heating rates for brick and smaller specimens that can be used without significantly affecting fired-strength properties (Table VII). The

'F 140 135 130 125 120 115 110 105

·c r,~-,~.-~.-~-r-~,---,~--,-, 60

136"F •• ' \ l58"C), ,

Cylinders 50 mm]

: \80"F 127"C) I I 30~, H20

I \ 100 mm I 116"F (47"C)

I I"""' / 80"F (27"Cl

I I 2J.Jlllo:, H20

55

50

45

,00 t 95 90 85 80 75

93"F/ / {34"C)

I

,}~:!:_. 70"F {21 "Cl _ ,.,:'.,·(29'C)' 30w, H20 ,

.,-'.70"F (21 "C)

40

35

30

25 70 20.4~, H20

65 5 6 7 8 9 10 11 12

Hydration time - h

Fig. 10. Effect of temperature and casting H 20 on hydration- temperature rise of neat CA cement.

psi MPa kg/cm2

>000 l 70

900 9 ,.. 4.5 ~ 2.S•J.O 1n. Brick .. "

] 6.0 :i 60 c.

C. = = 800 I 0 0 .. 5.0 " ::,

,oo f 50 1 3 -0 -0 0 0 ::. ::E·

600

J4·o 40

F·/h 100 300 500 700

c·th 56 167 278 389 Heating Rate

Fig. 11. Effect of heating rate on strength of a gunned 50%-Al201 concrete after heating at ll00°C (2000°F) ( 1 psi ""'6. 9 kPa) (Ref. 1).

Table VI. Effect of Temperature on Hydration-Reaction Products of CA Cements Hydration H,O requirement on dry-weight

basis. high purity CA cement ( 18% CaO)

Castables

Curing temperature Neat 20% JO% Hydration products cement cement cement

("C) ("F) of CA phase• (%) (%) (%)

<21 <70 CAH10 58 11.6 17.4 21-35 70-95 C2AH8 + AH3 (gel) t 32 6.4 9.6 >45 >95 C3AH6 + AH3 (crystalline) 23 4.6 6.9

•C=CaO; A=AhO,; H=H20. . 'Gel crystallizes between zr and 32°C (81 • and 90"F) as detected by X-ray diffraction.

Table Vil. Standard Recommended Practice* for Firing Refractory-Concrete Specimens

Cross section of specimens

(mm) (in)

114 by 76 114 by 65 51 by 51 25 by 25

•Ref. 24(b). 'To 8I6°C (1500°F).

4.5 by 3 4.5 by 2.5

2 by 2 l by l

Maximum heating race'

(°C/ s) (°F /h)

0.015 100 0.015 100 0.047 300 0.106 700

lO

Temp ·c 11

0

20

40

60

100

200-350

600-1000 A

1000-1300

1 400-1 650

24h Cure, > 90'\'o R.H. Tabul., Temp

"F

N

"' I ' I >< I I I I I I I I I I I I l ___ l

Unl'lydrated cement

CA

C·C, 2A7

A---,.--C ~ CA CA

I

grog

32

50

68

86

104

122

140

158

212

392-622

1112-1832

CA2 1832-2372 r-A------~ CAo 2552-3002

I Fig. 12. Hydration and dehydration of Caltab 20.

0.106°C/ s (700°F /h) maximum rate for dried 25-rnrn (I-in) bars favors the use of smaller specimens for evaluating HAC castables because of the shorter evaluation time involved. However, the largest castable aggregate diameter to be tested in 25-mm (1-in) specimens cannot exceed 8 mm (0.33 in). 18

Even faster heating rates can be used with 25-mm (I-in) bars made with tabular Ali03 and bonded with high purity cement (Fig. 3). The dried, fast-fired specimens were heated at a maximum rate of 0.339°C/s (2200°F /h) in the dehydration range. It is interesting to note that the slow heating rate, which reduced the total time required for heat treating by eliminating the 24-h drying step, actually pro­duced significantly lower strengths when heated at a rate of 0.025°C/s (167°F /h) in the dehydration range after curing at temperatures of :$32°C (:$90°F).

Although the aforementioned rate was stow with regard to firing, the drying rate was faster than the rate that occurs with the nonnal placement of specimens into a preheated dryer. Recent ruggedness tests on test procedures19 show that significant (>95% confidence) strength loss occurs

~ .

Tyler Mesh S,ze 325 200 100 48 28 14 a 4 1.0 Dia .. ,-m 10 ,,44, 74 149 298 595119023804760

99.9 , , ,.,

10 100 1000

-< -;

1 1

J ,j

SM Equivalent spherical particle dia. - µ.m

Fig. 13. Continuous particle-size-distribution curve for maximum de:isity (Ref. 21).

when cured specimens are dried at a rate >0.008°C/s (>50°F/h). The significance was even greater for 51-mm (2-in) bars. The ASTh1 recently approved modification of procedures 19 to limit the drying rate of cured specimens to 0.008°C/s (50°F /h).

Dense 102-mm (4-in) refractory linings, cured {24 h at 30° to 38°C (86° to 100°F) with fol'ms in place and/or covered with an impervious membrane to maintain a humid environment for hydration and then air-cured 24 h with the surface exposed at 30° to 38°C (86° to I00°F), should be able to be heat-treated to 510°C (950°F) within 15 h. This can be accomplished by heating the hot face uniformly at 0.008°C/s (50°F/h) to 150°C (300°F) and then increas­ing the rate to O.Ol2°C/s (75°F/h) with a 1-h hold at 315°C (600°F).

Figure 12 schematically shows the hydration and dehy­dration of a 20% high purity cement-tabular Alz03 castable with increasing temperatures. The phases occurring at any specific temperature can be identified by moving horizon­tally across the chart. Reactants and resultant products can be identified by following connecting lines, beginning at the top of the chart.

Although 510°C (950°F) is more than adequate for de­composing hydrated phases in:$ lQ2-rnm (:S4-in) linings, it is not sufficient when hydrothermal phases-C4A3H3 and AH* - are formed within thicker linings due to the hydro­thermal pressures developed during curing, according to Farris and Masaryk20 (Table VIII). Controlled heating for thicker linings should be maintained at 620°C (1150°F).

Table Vlll. Thennal-Decomposition Temperatures for CA-Cement Bond Phases in Dried Concrete*

Temperarure range Peale-reaction temperature

Compound' (·C) ("F) ("C) ("F) I AH3 210-240 410-464 ==230 446 ...

/

C3AH6 240-370 464-698 ==315 600 C3AHu * 465-482 869-900 ==470 878 AH 480-565 896-1049 ==525

I r~a---------·-· C4A3H3 565-620 1049-1148 ==600 CaC03 650-790 1202-1454 ==745 1373

*Ref. 20. 'C=CaO; A=Al,01; H=H:O. 'Questionable-when this peak occurs. X-ray results generally indicate the presence of C,,A ..

I

'

f(

Table IX. Aggregates Used in Dense Refractory Concretes

ConstlCuems

S:O, Al,O, Fe,O, TiO: CoO MgO Cr,O, .\Jbl,es Pyrometnc -cone Bulk specific Open porosity Aggregate (%) (%) (%) 1%1 (%) 1%) (o/o) (%) ~qmvalent gravity 1%)

Calcined fireclay 40-50% Al10J 45-55 40-50 0.5- l.5 l .0-2 0 O. l-0.2 0.05-0. l 0 5-l 5 30-34 2.4-2.6 3-10

Calcined Alabama bauxite

60% Al:OJ 34.9 60.6 l.3 2.5 0.07 70%Al:Oi 25.9 70 l l.l 2.9 .05

Calcined South American bauxite

80-90% Al:Oi 7.0 87.5 2.00 3.25 Trace High purity, sintered

or fused .~l:Oi 2:99% AhOJ .06 99.5 .06 Trace Trace

Philippine chrome ore 5.5 31.0 15.5 .5 •Sintered. 'Fused.

Standard Aggregate for HAC Evaluation Portland cement is normally evaluated neat or as a

mortar with closely sized standard sand. The previously discussed problems associated with H20 requirements pre­clude the use of neat HAC testing. The instability of quartz sands at temperatures> 1095°C (>2000°F) deters its use in HAC evaluations for obtaining fired-strength properties.

Table IX lists various refractory aggregates that might be considered for HAC evaluation. Only fused and tabular aluminas have adequate refractoriness and are sufficiently chemically inert to be considered as standard aggregates for evaluating the bonding characteristics of all HAC types. Properties of aggregates that markedly affect setting proper­ties of HAC are soluble salts, colloidal fines, particle-size distribution, amount of porosity, and pore size. 1 Except for the larger amount of open porosity in the coarser white fused-AlzO, grain, both aggregates can be sufficiently con­trolled to have no effect on setting time.

Evaluation of HAC in castable formulations requires that the variation in particle size of the aggregate be minimized. This can be accomplished by using closed aggregate sizes to approximate the ideal continuous size distribution designed for maximum packing by Furnas21 and Anderegg22 (Fig. 13). The ideal distribution will be matched at one less than the number of size fractions used. It follows

kg/cm2 ksi MPa

J50 ~---------------,

" 300 :i } 250

~ 200 ::, 3 " t 50 a E -,, 100 0 u so

0 Unshoclced sttenqth · 2.5 cm bats

390 kg/cm 2 ~ Stren,gth af1er a !ihock cycles IL.I 60-816-60'C

140 ~ 3.0

2.0

1.0

/ oL....L_,_·~·/J....l_-'--'-'---'-.W....L-JL...Ju......J...:...u..--"-..:.,_.O

816 Firing temp. 'C 1800 1650 816 1800

~~~;n~rog - ---'T-"ab;:cu;.;.:la'-r __ 15 Wt.,. HCA

1650

Fused

JO

25

20

15

10

5

~o

Fig. 14. Thermal-shock-damage resistance of tabular­and fused-Al 20J castables bonded with high purity CA cements.

0.12 0.1 l 37-38 2.7-2.8 3-7 .03 \3 38-39 2.85-3.0 4-10

Trace Tr:i.ce 38 3. 12-20

Trace 07 3.4-3.6* 0 ~* .J

3.7-3.9t 5.0' 16.0 31.5 3.9

then that the ideal distribution will be more closely matched as the number of sized components increases.

The thermal-shock-damage resistance represented by the transverse-strength depreciation of tabular- and fused­Al20, castables bonded with l5 wt% high purity cement after eight shock cycles is illustrated in Fig. 14. The unusu­ally high, unshocked, cold MOR obtained on tabular-Ah01

specimens fired at 1800°( (3270°F) would suggest the presence of a glassy bond. However, the retained strength after thermal shocking is highest for these specimens, sug­gesting the occurrence of a sintered, rather than a glassy, CA6* bond.

The CA-bonded tabular castable exhibits higher strengths than the equivalent white fused aggregate castable for each test condition. Apparently, when the bend strength of the cementitious bond exceeds =6900 kPa ( = 1000 psi), the castable strength becomes limited by transgranular frac­ture through the coarse ( 4-8 mesh) white fused grain. The larger white fused particles contain rather large contiguous

SEM fracture surface L-..J 50 micron Fig. 15. Scanning electron micrograph of fracture surface (bar = SO µ.m) of white fused alumina grain. ·

12..

SEM fracture surface <----J 50 micron Fig. 16. Scanning electron micrograph of fracture surface (bar = SO µ.m) of tabular alumina grain.

open pores (Fig. 15) which reduce particle strength to <50% of equivalent-size tabular particles.

The better thermal-shock-damage resistance of tabular is ascribed to I) the <5-15-µ.m closed pores (Fig. 16) which are thought to act as crack arrestors, 2) better me­chanical bonding to the rougher tabular fractured surfaces, and 3) more efficient use of the CA bond compared with white fused A}i03 wherein some of the HAC is lost in the large open pores of the coarse grain (Fig. 15) and ineffi­ciently used.

The rather large open pores occurring in white fused Al20 3 are further illustrated in Fig. 17. This 8-14-mesh particle had to be turned 90° to the horizontal to observe the continuous "pipes" after sprinkling the particles onto the flat SEM mount. Besides limiting the strength values of the castables, this type of porosity provides a source of vari­ability in castable H20 requirements.

A sintered tabular-Ah03 aggregate also performs ade­quately for hot MOR evaluations as shown in Fig. 18. 23

Tabular-Alz03 castable compositions of differing coarseness exhibit 1370°C (2500°F) hot MOR values equivalent to the best 90% Alz03 fired refractory brick cited in the literature. The increased hot strength that occurs with increasing aggre-

• , .. , •

"

... J.s r===£miiin::;:===----=:-----, lrila•- ..... M.llt • T'flef 1ft9sl\ FwN J.O

2.5

2.0

1.5

1.0

0.5

0 ~

-4 I -I I 1 • I 21 I -48 Ae1,.c1or1" - -~tC-.-1('1.)

J 1$ 20 25 I 20 25 I 25 ! JO ) 25 -

~ nn n~

98.8 95.8 94.8 95.S 9,.s 94.8 93.7 94.8 50 SO 80 90 gg

Ah,ffHna Content {"Ji,)

MPa ll9/cm2

20 r 15 150

10 ~ 100

I J:o

Fig. 18 Hot (1370°C (2S00°F)) modulus of rupture (1 psi= 6.9 kPa).

gate size at the 25% cement level confums the importance of increasing the aggregate size to improve hot strength.

Now that ASTM.has established meaningful tests 19 ·24

based on CA cement technology, further advances will be possible in meeting the future challenges for refractories in process industries. The excellent thermal-shock-damage resistance and high 1370°C (2500°F) hot MOR obtained on the HAC-bonded tabular-A120 3 compositions explain why these systems are performing so well in industry, as illus­trated in the high Al20i snorkel being used to de-gas top­quality steel (Fig. 19).

We conclude that industry will obtain improved service life and performance from refractory concrete or castable linings as field installations continue to move toward adopt­ing and utilizing practices based on HAC technology de­scribed herein, rather than on portland-cernent technology.

References 'W. T. Bakker, "Properties of Refractory Concretes"; pp. l l-5i in

Refractory Concrete (Amer. Coner. lnsr. Pu.bl. No. SP-57). American Concrete Institute, Detroit, MI, 1978.

'Refractory Concrete (Amer. Coner. Inst. Pu.bl. No. 547R-79). American Concrete Institute, Detroit, MI, 1978.

'W. H. Gitzen, L. D. Hart, and G. MacZura, "Properties of Some Calcium Aluminate Cement Compositions," J. Am. Ceram. Soc., 40 [51 158-67 (1957).

'T. D. Robson; pp. 9-27 in High Alumina Cements and Concretes. John Wiley & Sons, Inc., New York, 1962.

'Guy V. Given, Leroy D. Hart, Raymond P. Heilich, and George MacZura, "Curing and Firing High Purity Calcium Aluminate-Bonded Tabular Alumina Castables," Am. Ceram. Soc. Bu.LI., 54 [8] 710-13 (1975).

°T. W. Parker; pp. 485-529 in Proceedings of the Third International Symposium on the Chemistry of Cement. Cement & Concrete Association, London, 1952.

" .. (B)t

··~ ., (C)

Fig. 17. Scanning electron micrographs of white fused Al 20l: (Al bar= [ '1 333 µ.m; (BJ bar=200 µ.m; (CJ bar=50 µ.m.

Fig. 19. High Al20 1 snorkel used to de-gas top-quality steel.

'F. M. Lea and C.H. Desch, The Chemistry of Cement and Concrete. Edward Arnold & Co., London, 1957.

'L. S. Wells and E.T. Carlson. "Hydration of Aluminous Cements and [ts Relation to the Phase Equilibria in the System Lime-Alumina-Water," J. Res. Nat. Bur. Stand., 57 [6] 335-53 ( 1956).

'E.T. Carlson, "Some Observations on Hydrated Monocalcium Aluminate and Monostrontium Aluminate," J. Res. Nat. Bur. Stand., 59 [21107-11 (1957); RP 2777; Ceram. Abstr., 1957, October, p. 277i.

'E.T. Carlson. '"The System Lime-Alumina-Water at !°C," J. Res. Nat. Bur. Stand., 61 [I] 1-11 (1958); RP 2877; Ceram. Abstr., 1960, January, p. ?.lb.

"Samuel J. Schneider. ''Effect of Heat-Treatmenc on the Constirut:;in and Mechanical Properties of Some Hydrated Aluminous Cements ·· J Am Ceram. Soc., 42 [4] 184---93 (1959). · · ·

"A. C. C Tseung and T. G. Carruthers, "Refractory Concretes Based on Pure Calcium Alurrunate Cement," Trans. Brit. Ceram. Soc. 62 305-20 ( 1963). ' '

'1P. K. Mehta, "Retrogr~~sion in Hydraulic Strength of Calcium

Alu!I)~nate Cement S~crures._ Miner. Process .. 2 [LL] L6-19 (1964). H. G. Midgley, 'Tne :Vlineralogy of Set High Alumina Cement."

Trans. Brit. Ceram. Soc .. 66 [4] 161-87 (1967). ''W. H. Gitzen _and L. D. Hart, "Explosive Spalling of Refractory

Castables Bonded w1th Cllcium Aluminate Cement," Am. Ceram. Soc. Bull .. 40 [3] 503-07, 510 (1961).

10 P. K. Mehta and George Lesnikoff. "Conversion of CaQ·A[eO,iOH,O to 3Ca0·Al,01·6H,O." J. Am. Ceram. Soc .. 54 [4J 210-12 ( 1971).

""Modulus of Rupture of Castable Refractories," ASTM Designation C 268. 1982 Annual Book of ASTM Standards, Part 17. p. 217. Americ:in Socie~ for Testing and Materials, Philadelphia. PA.

' "Making and Curing Concrete Test Specimens in the Laboratory:· ASTM Designation C l 92. 1981 Annual Book of ASTM Standards. Part 14, pp. 133-42. American Society for Testing and Materials. Philadelphia. PA.

19"Preparing Refractory Concrete Specimens by Casting," . .\ST~! Designation C 862. 1981 Annual Book of ASTM Standards. Pm 17. pp. 938-44. Americ:in Society for Testing and Materials. Philadelphia, PA.

"'R. E. Farris and J. S. '.'vlasaryk, "'.'vlineralogy of Curing and Drying of a Refractory Concrete··; p. 277 in Ceramic Processing Before Firing. John Wiley & Sons, lnc .. New York. 1978.

21 C. C. Furnace, ··Grading Aggregates: !," Ind. Eng. Chem., 23 [91 1052-58 ( 1931).

nF. 0. Anderegg, "Grading Aggregates: II," Ind. Eng. Chem., 23 [9] 1058-64 (1931).

"R. P. Heilich, G. MacZura, and F. J. Rohr, "Precision Cast 97-97% Alumina Ceramics Bonded with Calcium Aluminate Cement," Am. Ceram. Soc. Bull .. SO [6] 548-54 (1971).

''(a) "Determining the Consistency of Refractory Concretes," pp. 930-35 in Ref. 19.

(b) "Firing Refractory Concrete Specimens," pp. 947-49 in Ref. 19. (c) "Preparing Rdractory Concrete Specimens by Cold Gunning,"

pp. 975-76 in Ref. 19.

ACI MANUAL OF CONCRETE PRACTICE

PART 1-1994

Part 1 contains current committee reports and standards concerned with:

Materials and General Properties of Concrete

New editions of each part of the AC/ Man­ual of Concrete Practice are issued annually and include the latest ACI standards and committee reports.

american concrete institute BOX 19150. REDFORD STATION DETROIT. MICHIGAN 48219

I

I

I

I

I

IS

. I

i

I . ~ -

Heat of hydration The hydration of HAC can produce large amounts of heat during

the first 24 hr. Provisions for dissipating this heat should be consid­ered, especially in thick sections of concrete, e.g., those greater than 150 mm (6 in.) in thickness.

Setting characteristics HAC frequently has quite different setting characteristics from

portland and blended cements. When tested according to standard needle penetration tests (Vica, or Gillmore), different HAC's provide a wide range of ,etting times as shown in Table A. l. In addition, the period between initial and final set is generally much shorter than with portland cements.

The slump cone should not be used for determining the work<1bil­ity characteristics of HAC. Because some HAC's lose slump rather quickly, special care may be required in mixing, handling, placing, and finishing. Other HAC's will remain workable longer than many portland cements. The manufacturer of the particular product under consideration should be consulted in this regard.

Strength HAC's give a much more rapid strength gain than portland ce­

ments (sec Table A. l). Although HAC is capable of producing mor­tars and concretes with very high early strengths, the strength may fall significantly at later ages if the water-cement ratio and curing tem­perature are not controlled as specified. This is associated with the conversion to the stable hydrate of the metastable calcium aluminate hydrates which for~ first, at temperatures below about 24 C (75 F). The rate at which the conversion occurs and its effect upon the strength (and permeability) increases with the amount of water avail­able above the critical water-cement ratio, the curing temperature (above about 30 C), the relative humidity, and the time of exposure. The residual strength after complete conversion depends on the orig­inal water-cement ratio of the concrete. Because of the possibility of conversion, the use of HAC in load-bearing concrete structures should either be avoided or anticipated strength retrogression calcu­lated when engineering the structure.

Resistance to chemical attack HAC concretes are resistant to a number of aggressive acidic agents

that attack portland-cement concretes. HAC was originally devel­oped to resist attack by sulfates in soil, seawater, and industrial waste waters. Experience has shown that HAC concretes are more resistant

to sulfate attack than concretes made with ASTM Type V portlar.d cement. Mortars and concretes made with HAC and suitable aggre­gates are more resistant to mild acids and acid industrial waste li­quors than those made with portland cement. HAC has been used successfully for lining fossil fuel power plant stacks to resist mild sul­furous and sulfuric acid solutions. They have also been used in the following types of manufacturing plants to resist specific aggressive agents shown (see ACI 350R):

Types of plants

Ammunition

Breweries Corn products plants

Dairies, ice cream plants Milk product plants Sugar mills and refineries Tanneries

Distilleries Chocolate plants Fertilizer plants Meat packing plants

Waste water plants and sewers

Water and waste water

I Aggressive agents

Nitric, sulfuric, and other acids Dilute organic acids Dilute sulfurous acids, starch, sucrose Dilute lactic acid, brine Dilute lactic acid Can juice, molasses Dilute tannic acid, dilute chromic and organic acids Dilute organic acids Cocoa butter Dilute ammonium sulfate Dilute organic acids, blood, brine Hydrogen sulfide and sulfuric acid Chemicals used in processes

As a general guideline, the use of !-!AC for resistance to acidic so­lutions is limited to applications where the pH is not less than 3.5 to 4.0. However, whenever possible, and particularly when a new appli­cation is encountered, it is recummended that a trial section be in­stalled.

Resistance to high temperatures If resistance to temperatures higher than about 300 C (570 F) is

needed, the properties of both the cement and the aggregate must be considered. For the most demanding applications, HAC is combined with selected refractory aggregates to produce refractory concretes suitable for use at temperatures up to 1870 C (3400 F). ACl SP-57 and ACl 547R provide more information on refractory concretes us­ing hydraulic-cement binders.

I

225R-28 MANUAL OF CONCRETE PRACTICE

Journal, PCA Research and Development Laboratories, V. I, No. I, Jan. 1959, p. 38.

Powers, T. C.; Copeland, L. E.; Hayes, J.C.; and Mann, H. M., "Permeability of Portland Cement Paste,'' AC! JOURNAL, Proceed­ings V. SI, No. 3, Nov. 1954, pp. 285-298.

Richartz, W., "Effect of Storage on Properties of Cement," Ze­ment-Kalk-Gips (Wiesbaden), V. Z (English Version), 1973, pp. 67-74.

Ritchie, T., "Efnorescence," Canadian Building Digest (01tawa), No. 2, Feb. 1960, 4 pp.

Robson, T. D., High Alumina Cemen1s and Concretes, John Wiley & Sons, New York, 1962, 263 pp.

Roy, D.M., and Goto, S .. "The Effect of Water Cement Ratio and Curing Temperatures on the Permeability of Hardened Cement Paste," Cement and Concrete Research, V. 11, 1981, pp. 575-579.

Schroder, F., and Vinkeloe, R., "Blase Furnace Slag Cement," Proceedings, 5th [nternational Symposium on the Chemistry of Ce· ment, C.:ment and Concret: Association of Japan, Tokyo, 1969, Part 4, p. 186.

Shalon, Rahel, "Report on Behaviour of Concrete in Hot Cli­mate," Materials and StruC/ures, Research and Tes1ing (RILEM, Paris), V. 11, No. 62, Mar.-Apr. 1978, pp. 127-:31.

Short, N.L., and Page, C.L.. "Diffusion of Chloride lons Through Portland and Blended Cement Pasces," Silicates /ndustriels (Mons), V. 47, No. :o, Oct. 1982, pp. 237-240.

Smolczyk, H.G .. "Stace of K.1owledge on Chloride Diffusion in Concrete," Betonwerk und Fertigteil-Technik, No. 12, Wiesbaden, 1984, pp. 837-843.

Taylor. H. F. W., Editor, The Chemistry of Cemen1s, Academic Press, London, 1964, V. I, 460 pp., and V. 2,442 pp.

Ta)lor, Walter H., Concrete Technology and Prac1ice, American Elsevier Publishing Co., New York, 1965, 650 pp.

Thiesen, K., and Johansen, V., "Prehydracion and Strength De· velopment of Cement," Bulletin, American Ceramic Society, Y. 54, 1975, pp. 787-791.

Tuthill, Lewis H., "Resistance of Cement to the Corrosive Action of Sodium Sulfate Solutions," AC! JOURNAL, V. 8, Procudings V. 33, Nov.-Dec. 1936, pp. 83-106.

U.S. Bureau of Reclamation, Concrete Manual, Revised 8th Edi­tion, Denver, 1981. pp. 8-12.

Verbeck, George J., and Foster, Cecil W., "Long-Time Study of Cement Performance in Concrete: Chapter 6-The Heats of Hydra­tion of the Cements," Proceedings, ASTM, V. 50, 1950, p. 1244.

Verbeck, G. J., "Field and Laboratory Studies of the Sulfate Re­sistance of Concrete," Performance of Concrete-Resistance of Concrere to Sulfate and 01her £nYironmen1al Conditions, Thorvald­son Symposium, University of Toronio Press, 1968, pp. 113-124.

Walker, S1an1on; Bloem, D. L.; and Mullen, W. G., "Effects of Temperature Changes on Concrete as Jnnuenced by Aggregates,"

Table A.1 - Chemical composition and property ranges for high-alumina cements

Low purity Intermediate purity High purity

A I ,O,, percent 39 - so 54 • 66 70 · 90

Fe,O., percent 7 • 16 I • 3 0.0 - 0.4

Cao. percent 35 · 42 26 • 36 9 • 28

SiO,, percent 3 • 9 3 • 9 0 • 0.5

Wagner surface, m'/kg 140 • 180 160 • 200 > 220

Blaine surface, m'/kg 260 • 440 320 - 1000 360 • 1150

Setting time

Vicar initial (hr:min) 13:00 • 9:00 [ 3:00 - 9:00 I O:JO • 6:~-

Minimum compressive strength (ASTM C 109, 50-mm [2-in.l cubes), MPa (psi)

I day 7 days =r~;;~: ::::::: ;::

ACI JOURNAL, Proceedings V. 48, No. 8, Apr. 1952, pp. 661-679. Whiting, D .. and Stark, 0., "Control of Air Content in Con­

crete," NCHRP Report No. 258, Transportation Research Board Washington. D.C .. May 1983, 84 pp. '

Woods, Hubert, Durabilily of Concrete Construction, AC! Mon­ograph No. 4, American Concrete lns1i1u1e/[owa State University Prcs.s, Detroit. 1968. 187 pp.

Woods, H.; S1einour, H. H.; and Starke, H. R., lndusrrial and Engineering Chemisrry, V. 24, 1932, pp. 1207-1214.

APPENDIX - HIGH-ALUMINA CEMENTS Manufacture and properties

High-alumina cements (HAC), also known as calcium-aluminate cements or aluminous cements, are hydraulic cements obtained by pulverizing a solidified melt or clinker that consists pretlominantly of hydraulic calcium aluminates formetl from proportionetl mixtures of aluminous and calcareous materials (Lea. 1970; Robson. 1962). They are generally dividetl into three groups based on the alumina and iron oxide contents (see Table A. l). The cements of higher alumina con­tent are suitable for higher temperature applications. No standard specification for HAC exists in the Unitetl S1a1es.

The density of HAC generally ranges from 2.90 to 3.25 Mg/m' (g/cc). The higher ,aJues renect larger amounts of iron oxide in melted low-purity cements and free alumina in high-purity cements.

The colors of HAC's range from dark gray to white, depending mostly on the amount and oxidation state of iron oxide and the man­ufacturing process. The more iron oxide present either as ferrous or ferric o,cide. or both, in the cement, the more intense the color.

All three groups of high-alumina cement are manufactured throughout the world and are commercially available in North and South America. They are considerably more e,cpensive than ordinary portland cements, ranging from appro,cimately J to 4 times more for the low-purity products to 6 10 8 times more for the hi;:h-purity products. Because of their high cost, intermediate and high-purity high-alumina cements are rarely, if ever, used for other than refrac­tory applii:ations.

Potential users of high-alumina cements should contact the manu· facturer of ,he product under consideration for information on mix­ture proportioning. aggregate selection, handling, placing, and cur· ing requirements. [1 is essential that they be aware of the possible conversion of the hydration products from high-strength, metastable hexagonal products to stable cubic products of lower strength (Rob­son, 1962).

Influences of admixtures Chemical admixtures used with portland and blended cements may

not be satisfactory for use with HAC. While some will behave in a similar manner, the dosages required may differ greatly. Other ad­mixtures may be of li1tle value, be harmful, and act in an opposite fashion when used wi1h HAC. ln addition. the various types of HAC may produce different results. Whenever possible. trial batches should be made with the intended cement and technical advice should be sought from the manufacturer of the admixture or the cement. AC! 547 contains a list of various generic additives and admixtures and their effects on HAC.

Influence of the environment Curing temperatures during the first 24 hr innuence the strength

development of HAC concretes. Temperatures below 24 C (75 F) produce a high inicial strength that will generally increase within 6 monchs and then retrogress because of compound conversion to val· ues approaching the one-day strength. Initial curing temperatures above 32 C (90 F) may provide lower 24-hr strengchs in HAC, but re· trogression of strength with time is minimized.

Curing compounds are effective in scaling the concrete .\urface temporarily to prevenc water evaporation. Curing compounds should be applied as \oon as pos.;iblc after completing finishing operations. Fog spray curing ~hould begin only after ini1ial set i.; observed on the concrete surface.

Potential usen of hi11h-alumina cemen1s should obtain further in· formation on curing methods from the manufacturer of the produo;t

j

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DISCLAIMER

This report wu prepaml u u account or work spolUORld by an agency or the United Slal,:.s ~t. Neither the United States GoYernmenl nor auy agency lhcr«>(, nor any or lheir em~y,ees. makes 111y warn.nty, exp= or implied, or usunes any legal liability or responsi­bility for the accuncy, completeneu, or usefulness of any infonnation, apparatu.s, ::,rod11ct, or proo:s:s disclosed., or 1eprcsents that ils use would not infringe privately owned righls. Refer• cna: hetcin lo any spccif"'ic commercial product, process, or scrvioc by trade name, trademark, O RNL / nt-8 S 7 9 m111u!a<:1.1U1:t, or otherwise docs not necessarily constitute or imply its endonement, rccom· Dis t . Cate~ 0 r y UC- 7 Q IDClkL&tioe, or faYOring by the United States Government or any agency thereof. The views alki °"'nioas of aulhon expressed herein do not ne:,:ss.arily stale: or rc:nc:cl those of the: United Sutes Go~nunenl or any agency thereof.

CHE:1ICAL TECHNOLOGY DIVISION O::!!L/T'.i--8 5 7 9

NUCLEAR WASTE PROGRAMS

ORNL Fixation of Waste i~ Concrete (Activity No. AP OS 25 10 0, ONL-WH02)

CEMENT-BASED RADIOACTIVE WASTE HOSTS FOR.'1ED UNDER ELEVATED TE:1PERATURES AND PRESSURES ( FUETAP CONCRETES) FOR

SAVANNAH RIVER PLANT HIGH-LEVEL DEFENSE WASTE

L. R. Dole G. c. Rogers M. T. Morgan* D. P. Stinton ** J. H. Kessler s. M. Robinson J. G. Moore *

*Retired. **Metals and Ceramics Division.

Date Published • March 1983

Prepared by the OAK RIDGE NATIONAL LABORATORY

Oak Ridge, Tennessee 37830 operated by

UNION CARBIDE CORPORATION for the

U.S. DEPARTMENT OF ENERGY Under Contract No. W-7405-eng-26

T _.,. ~. .. ,. .....

17 ·.H•r,

7

2.2 PROCESSING OF SR? WASTES

A major advantage of f·UETA? as a radioactive waste di.sposal alterna­

tive i.s its ease of processing. As illustrated i.n Fig. 1, calci.ned

solids are blended in a drum or cani.ster with the cementi.tious mix and a

minimum amount of water. TI-le m1x 1s then soli.difi.ed by curing at 85 to

2CO"C and 0.1 to 1.5 MPa. To obtain samples cured at lOC°C, molds are

closed and brought to temperature via a 1.5-h heatup i.n an autoclave.

The specimens are cured far 24 h, then removed from the autoclave, and

cooled to room temperature. Tne soli.difi.ed material ts dewatered by

heating at 2so·c for up to 24 h in order to mtn1m1ze gasi.fi.cation by

long-term radi.olysis or heat. Samples wi.th volumes less than 4 Lare

removed from the mo 1_d before dewatering, but the 4- to 75-L specimens

are dewatered wi.th only one end exposed. Tne dewatering is accompli.shed

in a 2so·c oven with rough vacuum for 24 h. Laboratory-scale studi.es

have shown that more than 80% of the total unbound water loss occurs in

the first 6 h, and there i.s no apparent diffusi.on lag i.n the water

releas~. Tilis treatment removes all of the unbound and a small amount

of tte hydrated water, leavi.ng a hard, ceramic-like solid contai.ni.ng -2

wt% water (Table 3). Followi.ng the dewatering step, the cani.ster (or

drum) i.s simply capped and stored.

The generalized flowsheet was modifi.ed (Fig. 2) to meet requirements

specifi.ed by the SRP process evaluation tear.1 on May 7, 1981. Tnis new

flowsheet requires that 2 t of dry solids be added to a full charge of

water and set regulator in a ri.bbon mi.xer within 2 h. Prior to initial

blending, the transfer boom would be set to transfer to an abort/recycle

.... - a rra::_a.:,sm;;f'IMJ.

z I r: r ens nn 2trscrrt 55 9 555 m·sar NV ta•• "

10

Table 3. Results of dewatering the SRP FUETAP concretes

----------Weight

Temp. Time loss Volatiles losta Water remaining (°C) (h) (%) (%) ( wt % ) b

250 5 12.34 67 3.0 24 13.08 71 2.2 48 13.29 72 2 • ()C

400 5 14.91 81 d

24 15.08 82 d

900 24 16.97 92 d

ainitial grout !l'ade up to contain 15 wt% H20. Other ingredie,1ts of the mix normally lose 3.41% of their total weight on heating 24 hat 9oo·i::.

bPercentages are approximate. CRepresents removal of all unbound water, as well as a small amount

of hydrate-water. 0xass spectrometry indicates that decomposition of hydrates,

nitrates, and carbonates occurs at temperatures )400°C.

sink; however, after blending had proceeded to the point w'here an accep­

table product could be made, the transfer boom would be moved to the

normal position to discharge into canisters positioned on a four-place

lazy Susan. Eight to ten hours after the canister had heen filled, it

would be transferred by cranes and a trolley to the curi.ng-dewateri.ng I

cell. Here the canister would be connected to a vacuum off-gas treat-

ment manifold, and th~ connections would be tested for leaks. After the

noncondensable gas had been removed, the vacuum off-gas system would be

turned off and the concrete would be cured by heating the canister at 85

to 2oo•c for 12 to 16 h. Then, the vacuum off-gas system would be

turned on and the temperature increased to 2Jo·c for 14 to 18 h.

l (o