cement-lateritic gravels mixtures microstructure and strength characteristics

9
Cement-lateritic gravels mixtures: Microstructure and strength characteristics Younoussa Millogo a , Mohamed Hajjaji b, * , Raguilnaba Ouedraogo a , Moussa Gomina c a Laboratoire de Physico-Chimie et de Technologie des Mate ´riaux (LPCTM), UFR/Sciences Exactes et Applique ´es, Universite ´ de Ouagadougou, 03 B.P. 7021 Ouagadougou 03, Burkina Faso b Equipe de Physico-Chimie de Mate ´riaux Naturels et Phe ´nome `nes d’Interfaces, De ´partement de Chimie, Faculte ´ de Sciences Semlalia, Universite ´ Cadi Ayyad, Boulevard Prince My Abdellah, B.P. 2390, Marrakech, Morocco c Laboratoire CRISMAT UMR 6508 CNRS/ENSICAEN, 6 Bd Mare ´chal Juin, 14050 Caen Cedex 4, France Received 15 December 2006; received in revised form 11 July 2007; accepted 23 July 2007 Available online 4 September 2007 Abstract Microstructure of cement-lateritic gravels mixes, containing up to 8 wt% cement, was investigated by means of X-ray diffraction, infrared spectrometry, differential thermal analysis, scanning electron microscopy and energy dispersive spectrometry. Also, strength characteristics of the mixtures were measured. The results show that cement admixtures resulted in the formation of 1.4 nm-tobermorite, ettringite, iron oxyhydroxide, portlandite and calcite. The increasing amount of tobermorite, due to the increase of the cement content, was attended with a noticeable reduction of particles segregation. In addition, its marked crystallization, observed for the high curing time (28 days), contributed to the improvement of the mechanical strength. As regards the application aspect, the results show that cement amended lateritic gravels are convenient for base course construction. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Lateritic gravels; Cement mixes; Microstructure; Mechanical strength; Base course 1. Introduction Lateritic soils are widespread materials in tropical and subtropical African countries. They are required for road construction. However, the road sections built with raw lateritic soils are the subject of deterioration because of rain erosion and traffic intensification [1–5]. The viability of roads consisting of lateritic soils is pro- ven to be dependent on the chemical and mineralogical compositions as well as the mechanical characteristics of these raw materials [4]. To improve the latter properties, additions of lime, cement, ash fly, silica fume and vegetable fibres were tested [2,3,5–10]. If the physical parameters of amended argillaceous lateritic soils from some West Afri- can countries have been evaluated, a little attention is paid to the investigation of their microstructure as well as to the study of the lateritic gravels of Burkina Faso, which are lean clay materials [2,3,5,6,9–11]. This work is devoted to the study of the microstructure and the determination of strength characteristics of cement modified lateritic gravels from Burkina Faso. The potential use of these amended materials for road construction is discussed. 2. Materials and experimental procedures 2.1. Materials The mineralogical and chemical compositions of the concerned lateritic gravels, taken from Sapouy (Burkina Faso), are given in Table 1. The values of some physical properties of these materials are gathered in Table 2. Com- ments on these characteristics are reported elsewhere [12]. 0950-0618/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2007.07.019 * Corresponding author. Tel.: +212 24 43 46 49; fax: +212 24 43 74 08. E-mail address: [email protected] (M. Hajjaji). www.elsevier.com/locate/conbuildmat Available online at www.sciencedirect.com Construction and Building Materials 22 (2008) 2078–2086 Construction and Building MATERIALS

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Cement-Lateritic Gravels Mixtures Microstructure and Strength Characteristics

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Page 1: Cement-Lateritic Gravels Mixtures Microstructure and Strength Characteristics

Available online at www.sciencedirect.com Construction

www.elsevier.com/locate/conbuildmat

Construction and Building Materials 22 (2008) 2078–2086

and Building

MATERIALS

Cement-lateritic gravels mixtures: Microstructureand strength characteristics

Younoussa Millogo a, Mohamed Hajjaji b,*, Raguilnaba Ouedraogo a, Moussa Gomina c

a Laboratoire de Physico-Chimie et de Technologie des Materiaux (LPCTM), UFR/Sciences Exactes et Appliquees,

Universite de Ouagadougou, 03 B.P. 7021 Ouagadougou 03, Burkina Fasob Equipe de Physico-Chimie de Materiaux Naturels et Phenomenes d’Interfaces, Departement de Chimie, Faculte de Sciences Semlalia,

Universite Cadi Ayyad, Boulevard Prince My Abdellah, B.P. 2390, Marrakech, Moroccoc Laboratoire CRISMAT UMR 6508 CNRS/ENSICAEN, 6 Bd Marechal Juin, 14050 Caen Cedex 4, France

Received 15 December 2006; received in revised form 11 July 2007; accepted 23 July 2007Available online 4 September 2007

Abstract

Microstructure of cement-lateritic gravels mixes, containing up to 8 wt% cement, was investigated by means of X-ray diffraction,infrared spectrometry, differential thermal analysis, scanning electron microscopy and energy dispersive spectrometry. Also, strengthcharacteristics of the mixtures were measured. The results show that cement admixtures resulted in the formation of 1.4 nm-tobermorite,ettringite, iron oxyhydroxide, portlandite and calcite. The increasing amount of tobermorite, due to the increase of the cement content,was attended with a noticeable reduction of particles segregation. In addition, its marked crystallization, observed for the high curingtime (28 days), contributed to the improvement of the mechanical strength. As regards the application aspect, the results show thatcement amended lateritic gravels are convenient for base course construction.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Lateritic gravels; Cement mixes; Microstructure; Mechanical strength; Base course

1. Introduction

Lateritic soils are widespread materials in tropical andsubtropical African countries. They are required for roadconstruction. However, the road sections built with rawlateritic soils are the subject of deterioration because ofrain erosion and traffic intensification [1–5].

The viability of roads consisting of lateritic soils is pro-ven to be dependent on the chemical and mineralogicalcompositions as well as the mechanical characteristics ofthese raw materials [4]. To improve the latter properties,additions of lime, cement, ash fly, silica fume and vegetablefibres were tested [2,3,5–10]. If the physical parameters ofamended argillaceous lateritic soils from some West Afri-can countries have been evaluated, a little attention is paid

0950-0618/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.conbuildmat.2007.07.019

* Corresponding author. Tel.: +212 24 43 46 49; fax: +212 24 43 74 08.E-mail address: [email protected] (M. Hajjaji).

to the investigation of their microstructure as well as to thestudy of the lateritic gravels of Burkina Faso, which arelean clay materials [2,3,5,6,9–11].

This work is devoted to the study of the microstructureand the determination of strength characteristics of cementmodified lateritic gravels from Burkina Faso. The potentialuse of these amended materials for road construction isdiscussed.

2. Materials and experimental procedures

2.1. Materials

The mineralogical and chemical compositions of theconcerned lateritic gravels, taken from Sapouy (BurkinaFaso), are given in Table 1. The values of some physicalproperties of these materials are gathered in Table 2. Com-ments on these characteristics are reported elsewhere [12].

Page 2: Cement-Lateritic Gravels Mixtures Microstructure and Strength Characteristics

Table 1Chemical and mineralogical compositions (in wt%) of the concerned lateritic gravels

Chemical composition: SiO2 Al2O3 Fe2O3 MgO CaO MnO Na2O K2O TiO2 CuO L.O.I.

56.19 10.10 16.09 0.05 3.24 1.68 2.01 0.07 1.39 0.11 8.14

Mineralogy: Kaolinite Quartz Goethite Hematite Rankinite Balancea

26 42 15 3 6 8

a Constituted mainly of illite and organic matters.

Table 2Geotechnical and mechanical characteristics of the used lateritic gravels

Particles size distribution (wt%) Atterberg limits (%) Blue methylene value Modified proctor California bearing ratio

< 2 mm(Skeleton)

<0.425 mm(Mortar)

<80 lm(Fine particles)

<2 lm(Clays)

wLa wP

b PIc MBVd

(g/100 g)OMCe (%) MDDf

(kN/m3)CBRg (%)

28 18 10.5 5 22.5 12 10.5 0.17 6.6 21.7 43

a Liquid limit.b Plasticity limit.c Plasticity index.d 100 g is the sample weight.e Optimum moisture content.f Maximum dry density.g CBR at 95% of MDD.

Y. Millogo et al. / Construction and Building Materials 22 (2008) 2078–2086 2079

The used cement (Portland (CPA 45)) is supplied byDiamond Cement in Burkina Faso. Its mineralogical andchemical compositions and some of its physical character-istics are gathered in Table 3.

2.2. Experimental procedures

The studied mixtures consisted of cement (up to 8 wt%)and lateritic gravels. For samples preparation, the abovementioned materials were oven-dried at 105 �C for 24 h,manually mixed, for preventing the grain size change,and stored in hermetic plastic bags in order to ovoid mois-ture contamination.

The plasticity index (PI) and the methylene blue value(MBV) of the mixtures were evaluated according to theNF P94-051 [13] and NF EN 933-9 norms [14], respec-tively. The optimum moisture content (OMC) and the

Table 3Chemical and mineralogical compositions (in wt%) and some physical proper

Chemical composition: SiO2 Al2O3 Fe2O3 MgO CaO

20.12 5.73 4.06 1.18 64.82

Mineralogy: C3S C

55.70 1

Physical properties: Specific gravity (g/cm3)

3.02

a Free lime.

maximum dry density (MDD), and the California BearingRatio (CBR) of mixes were determined in conformity withthe NF P94-093 [15] and NF P94-078 [16] standards,respectively. For the CBR measurements, differently trea-ted samples were punched with a universal press (SEDI-TECH apparatus). The grain size distribution wasrealized by dry sieving as well as by sedimentation, accord-ing to the NF P18-560 [17] and NF P94-057 [18] standards,respectively. The former method was used for the classifica-tion of coarse particles (>80 lm in size), when the secondone was applied for tiny grains (<80 lm).

The mechanical tests were realized on cylindrical test-pieces of mixtures, which were moulded in CBR mouldsat the optimum Proctor modified, and kept in room tem-perature for 7, 14 and 28 days. They were performed witha universal press and carried out according to the NF P18-406 [19] norm for the compressive strength and the NF

ties of the used cement

P2O5 SO3 Na2O K2O F.La I.Rb L.O.I.

0.39 2.68 0.08 0.17 0.80 0.28 0.27

2S C3A C4AF

5.68 8.31 12.34

Apparent density (g/cm3) Setting time (h)

1.06 3

Page 3: Cement-Lateritic Gravels Mixtures Microstructure and Strength Characteristics

10 20 30 40 50 60 70

QQ

2θ°

2θ°

T

T

C

K

Q

Q

ET

G

K

HHGG

Q

QQ

QQ

KK

K

K

K

K

I

I

II

Inte

nsi

ty(a

.u.)

IT

E

C

K

RR

(a)

(b)

10 20 30 40 50 60 70

R

R

R

R

QR

RR

P

KP

T

T

C

C

E

EG

QQ

Q

K

QQ

Q

Q

QQQ

KK

KK

II

I

I

I

Inte

nsi

ty(

a.u

.)

I

G H

CP

(c)

(d)

Fig. 1. X-ray diffraction patterns of the lateritic gravels (a) and cementamended samples (b: 2, c: 3 and d: 8 wt% cement). K: kaolinite; I: illite; Q:quartz; G: goethite; H: hematite; T: tobermorite, E: ettringite; P:portlandite; and C: calcite.

0 200 400 600 800

CH(d) (c)

(b)

(a)

Kaolinite dehydroxylation

G

T+E

Dehydration

End

o

T(°C)

Quartz transformation (α to β)

Fig. 2. Thermograms of the basic raw material (a) and its cement mixes(b: 2, c: 3 and d: 8 wt% cement). G: goethite; C: calcite; CH: portlandite; E:ettringite; and T: tobermorite.

2080 Y. Millogo et al. / Construction and Building Materials 22 (2008) 2078–2086

P18-408 [20] standard for the tensile strength. As concernsthe compressive strength determination, the test-pieceexperienced an increasing load until rupture. Knowingthe ultimate load (Fmax, kN) and the average cross-sectionarea of the test piece (S, cm2), the magnitude of the com-pressive strength (MPa) is determined according to therelation: (10Fmax)/S. For the tensile strength, the loadingrate was 0.05 MPa/s and the magnitude, in MPa, wasfound by the formula: (0.637P)/(d · h), where P (106 N)is the applied charge, d (m) and h (m) are the diameterand the height of the cylindrical test-piece.

The nature of crystalline phases in the prepared sampleswas identified by means of a Philips X’Pert MPD diffrac-tometer equipped with a copper Ka radiation (Ka =1.5418 A). The infrared examinations were done on discsconsisting of 1 mg of cement-lateritic gravels samples,taken from the above-mentioned mixtures, and 150 mg ofpotassium bromide (KBr). They were performed by meansof a Nicolet 510FT-IR spectrometer, operating in the range4000–400 cm�1. The thermal changes of the mixes were evi-denced by means of a Labsys–Setaram apparatus, func-tioning at a heating rate of 10 �C/min and under N2

atmosphere.The microscopic examinations were done on carbon-

coated pieces taken from the above-mentioned cylindricalsamples, using a Jeol JSM 5500 scanning electron micro-scope, equipped with a Falcon EDAX analyser. The ele-mental quantitative analyses were performed withoutstandards (ZAF method). The maximum resolution wasaround 3.5 nm.

3. Results and discussion

3.1. Mineralogical and microstructural characterization

As can be derived from the X-ray diffractograms ofFig. 1, cement additions gave way to the formation ofettringite, calcite and portlandite (CaO Æ H2O or CH). Ascompared to CH, the two former compounds occurred inlow cement content samples. X-ray reflections assignableto 1.4 nm-tobermorite became evident with the increaseof the cement amount. To evidence the eventual presenceof amorphous compounds, mixes of cement-lateritic grav-els were subjected to thermal and IR spectroscopy analy-ses. As regards the thermal results (Fig. 2), theendothermic effects at around 80, 350, 530 and 567 �Care linked to dehydration water, loss of crystallizationwater of goethite, deshydroxylation of kaolinite and tothe transformation of quartz a to b, respectively. The weakthermal effect at 150 �C is assignable either to CSH (CaO ÆSiO2 Æ H2O) type tobermorite and ettringite [21–24], whenthe one at 385 �C is attributable to the deshydroxylationof portlandite. Concerning the infrared investigations(Fig. 3), the spectra displayed bands relevant to quartz,kaolinite, goethite and hygroscopic water. Bands associ-ated with calcite and carbon dioxide are also present. Itis worth noting that the marked intensification of the broad

band at 3400 cm�1, which is commonly attributed tohydration water, may be taken as an indication of the pres-ence of CSH (tobermorite), which presence is revealed bythe band at 670 cm�1 [25,26].

Page 4: Cement-Lateritic Gravels Mixtures Microstructure and Strength Characteristics

10030050070090011001300150017001900

Abs

orba

nce

(a.u

.)

(a)

(b)

(c)

(d)

H2O

C

Si-O (K)

Al-Al-OH (K)

C

Si-O(Q)

Si-O(K)

Si-O-Si K

GT

2000220024002600280030003200340036003800

Wavenumber (cm-1)

Wavenumber (cm-1)

Ab

sorb

ance

(a.u

.)

Al-Al-OH

H2O+T

CO2

(d)

c

(b)

(a)

Fig. 3. Infrared spectra of the lateritic gravels (a) and mixes containing 2 (b), 3 (c) and 8 wt% cement (d).

Y. Millogo et al. / Construction and Building Materials 22 (2008) 2078–2086 2081

It may be noticed that the endothermic effect relevant tothe deshydroxylation of kaolinite experienced a slightdecrease with cement additions. This is likely linked tothe pozzolanic reaction involving clay minerals [10].

Segregated particles of quartz (Fig. 4a; Zones A and B)and kaolinite (Fig. 4b; Zone C) were identified in cement-free samples. However, in lower cement content samples,agglomerated particles developed (Fig. 4c) and an iron oxy-hydroxide, looking like FH3 (Fe2O3 Æ 3H2O), was discrimi-nated (Fig. 4c; Zone D) [27]. The agglomeration seems tobe the consequence of flocculation, which resulted of thecation exchange of compensating charges of the basicmaterial and Ca2+ ions, deriving from cement hydration[10]. Small particles, which consisted mainly of calciumand sulphur, were distinguished (Fig. 4d; Zone E). Appar-ently, these correspond to ettringite (C=S ¼ 1:77), whichcould be developed from the aqueous reaction betweengypsum and C3A (3CaO Æ Al2O3). The increase of the

cement content led to the occurrence of sulphur–calcium-rich zones constituting of portlandite and/or calcite,ettringite, and tobermorite (Fig. 4d; Zone F) [28,29]. Refer-ring to some authors [26,30,31], the latter CSH could beoriginated from the hydration of the components of cement(C3S and C2S (2CaO Æ SiO2)), but its partial formationfrom the pozzolanic reaction involving clay minerals andportlandite is plausible. For higher cement content (e.g.,8 wt% cement) (Fig. 4e and f, Zones G and H), ettringiteis rarely encountered. Based on reported results [32], itappears that the reaction between SO2�

4 ions, provided bygypsum, and C3A for forming ettringite became less signif-icant as compared with the fixation of SO2�

4 on CSH phase.The sulphate fixation should be favoured because of thealkalinity of the medium (pH 11.41). On the other hand,it may be remarked that as a result of higher cement con-tent, precipitates of tobermorite became abundant(Fig. 4f; Zone H).

Page 5: Cement-Lateritic Gravels Mixtures Microstructure and Strength Characteristics

Fig. 4. Typical SEM micrographs and EDS analyses relevant to the concerned samples. (a, b): lateritic gravels; (c) : 2 wt% cement; (d): 3 wt% cement;(e, f): 8 wt% cement.

2082 Y. Millogo et al. / Construction and Building Materials 22 (2008) 2078–2086

3.2. Physical characteristics

As can be deduced from the grain size distributioncurves of Fig. 5, the amounts of skeleton (<2 mm), mortar

(<0.425 mm) and fine particles (80–2 lm) increased byabout 1.7-fold as a result of cement additions. In contrast,the amount of the clay-sized fraction (<2 lm) experienceda slight decrease, likely because of its implication in the

Page 6: Cement-Lateritic Gravels Mixtures Microstructure and Strength Characteristics

Fig. 4 (continued)

Y. Millogo et al. / Construction and Building Materials 22 (2008) 2078–2086 2083

above-mentioned processes, namely agglomeration andpozzolanic reaction. As a consequence of the reduction ofthe clay fraction, the plasticity index and the methyleneblue value decreased (Fig. 6).

Cement additions also have an effect on the optimummoisture content and the maximum dry density (Fig. 7).The evolution of the former property is linked to anincreasing cement affinity for water. In fact, the raising of

Page 7: Cement-Lateritic Gravels Mixtures Microstructure and Strength Characteristics

10 1 0.10

20

40

60

80

100 0 ; 2 ; 3 ; 4 ; 6 ; 8 wt.% cement

Per

cen

tag

e p

assi

ng

(w

t.%

)

Particle size (mm)

Fig. 5. Particle size distribution curves relevant to the concerned samples.

0 2 4 6 8

9.5

10.0

10.5

PI

Cement content (wt.%)

0.08

0.12

0.16

MBV

PI (%) MBV(g/100g)

Fig. 6. Variations of the plasticity index (PI) and methylene blue value(MBV) vs. cement content.

0

6.5

7.0

7.5

8.0

8.5

Cement content (wt.%)

OM

C (%

)

OMC

2.10

2.12

2.14

2.16

2.18

MD

D (

g/c

m3)

MDD

2 4 6 8

Fig. 7. Variations of the optimum moisture content (OMC) andmaximum dry density (MDD) against cement additions.

0 4

150

300

450

600

Cement content (wt.%)

CB

R (

%)

a

b

2 6 8

Fig. 8. Evolution of California Bearing Ratio (CBR) of 4 days waterimmersed samples (freshly prepared (a) and 3 days dried (b)) as a functionof cement content.

0 2 4 6 8

2

4

6

7 days 14 days 28 days

Co

mp

ress

ive

stre

ng

th (

MP

a)

Cement content (wt.%)

Fig. 9. Effects of cement additions and curing time on the evolution of thecompressive strength of lateritic gravels samples.

2084 Y. Millogo et al. / Construction and Building Materials 22 (2008) 2078–2086

cement content should be accompanied by an increasingwater demand for the dissociation of portlandite. Asregards the variation of MDD, it is believed that because

of the aggregation phenomenon due to cement additions,the volume of particles increases and consequently MDDdecreases. On the other hand, it may be noticed that theobtained values for OMC (7.2–8.2%) and MDD (2.16–2.1 g/cm3) lay in the required ranges for base course mate-rials [3].

The variation of CBR versus cement content is reportedin Fig. 8. The CBR increasing is due to the continuousdevelopment of tobermorite, which is known as a cementi-tious compound. On the other hand, the higher values ofCBR, relevant to the water immersed fresh specimens,may be interpreted in terms of an uninterrupted processof cement hydration. Corollary, for water immersed drysamples, such process could not keep on since the requiredsetting time of cement is around 3 h. The observed evolu-tions of CBR are inconsistent with the results reported inreference [2]. The discrepancy may be linked to the

Page 8: Cement-Lateritic Gravels Mixtures Microstructure and Strength Characteristics

0 40.0

0.1

0.2

0.3

0.4

7 days 14 days 28 days

Ten

sile

str

eng

th (

MP

a)

Cement content (wt.%)2 6 8

Fig. 10. Variation of the tensile strength of different aged samples againstcement admixtures.

Y. Millogo et al. / Construction and Building Materials 22 (2008) 2078–2086 2085

difference in the clay minerals amounts: because of theirlower contents, the clay minerals pozzolanic reactions inthe concerned lateritic gravels are less quantitative as com-pared with those happened in clay-rich laterite used byMessou [2].

The variations of the compressive and tensile strengthsof differently cured samples as a function of cement contentare shown in Figs. 9 and 10, respectively. The observedincrease of both strengths is chiefly attributed to the forma-tion of tobermorite, which crystallization is timedependent.

Since the compressive strengths are in the range 1.45–3.1 MPa and the CBR values are higher than 160%, thestudied cement-lateritic mixtures are suitable for basecourse construction [3].

4. Concluding remarks

Cement additions to lateritic gravels led to the forma-tion of a homogeneous microstructure and improved themechanical strength. These positive impacts are mainlyrelated to the development of 1.4 nm-tobermorite, whichderived principally from cement hydration. Likely becauseof their minor amounts, the adverse effect of calcite andportlandite on the mechanical properties was insignificant.On the other hand, basing on the reported data relevant tothe use of lateritic gravels in road construction [3], the mea-sured physical magnitudes allow to conclude that the con-cerned cement amended lateritic gravels are convenient forbase course manufacture. For economic considerations, assmall a quantity as 2 wt% is sufficient for this kind ofconstruction.

Acknowledgements

Thanks to the ‘‘Laboratoire National du Batiment et desTravaux Publics du Burkina Faso’’ and the ‘‘Agence Uni-

versitaire de la Francophonie (A.U.F.)’’ for their financialsupport. The authors are grateful to Profs Thomas Armbr-uster (University of Bern; Switzerland), Karfa Traore andAbdelkader Outzourhit as well as to Aziz Khalfaoui, andRachid El Moutamanni for their helps.

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