A Preliminary Investigation of Strength Development in Jamaican Red Mud Composites

8/2/2019 A Preliminary Investigation of Strength Development in Jamaican Red Mud Composites

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A Preliminary Investigation of StrengthDevelopment in Jamaican Red Mud CompositesJunior N. Gordon, Willard R. Pinnockh* & Marcia M. MoorehBuilding Research Institute, Old Hope Road, Kingston 10, JamaicaDepartment of Chemistry, University of the West Indies, Mona CampusKingston 7 Jamaica(Received 5 June 1996; accepted 26 July 1996)Abstract

The 2%day s t rength of 50 mm cubes of com po-sit es formed by the addition of various amounts ofhy drated lime, condensed silica fum e and lime-stone to Jamaican red mud is investigated. Theaim is to produce a red mud composite suitablefor use as a construction mat erial, w ithoutemploy ing Portland cem ent as binder The identi-ties of compounds formed in the composites arededuced from X RD scans, in combination w ithDTG and elect ron micrography w here appropri-ate. The strongest composit e found in this prelimi-nary study has compressive st rength in th e range15-18MPa at 28 days, w ith the strength increas-ing slow ly wit h age to a maxim um so fal; in therange 18-22 MP a at 122 day s. The st rengthdevelopment is observed to be associated w ith theformation of strat lingite, and possibly also w ithth e format ion of complex carbonat es such ashy drogrossular This compos it e com pares fav or-ably, in terms of compressiv e st rength anddurability w ith the one other composite reportedin the literature, w hich is formed similarly fromred mud w ith additiv es, not including Portlandcement. 0 1997 Elsevier Science Limited

INTRODUCTIONThe possibility that Bayer-process waste, redmud, could be used to advantage as a compo-nent of construction material has beensuggested as one way of utilizing the enormous*Author to whom correspondence should be addressed atBureau of Standards, 6 Winchester Road, Kingston IO,Jamaica. 371

quantities of this waste that are generated eachyear by the alumina and alumina-related indus-tries in Jamaica. Added impetus has beenprovided for- further investigation of this possi-bility by the recent apparent shortage of someconstruction materials such as sand, the rela-tively high cost of Portland cement, and thechronic island-wide shortage of housing.2

In order to encourage large-scale use of exist-ing stocks of red mud in the short term, thebuilding material required, in our view, is onethat must be less expensive than concrete. Itmust also be adequately strong and haveweather-resistant characteristics at least com-parable to that of conventional concrete.Ideally, also the process of fabrication should besimple enough that the desired strength anddurability can be achieved in self-help-typeoperations.

With these constraints in mind, several possi-bilities seem to us to be worth considering.These range from the use of red mud simply asa replacement for sand in Portland cement mor-tars to its use in materials in which there is noPortland cement and binding is derived fromcompounds formed by the reaction of compo-nents of the mud with selected additives. In thispreliminary work we have sought to investigatethe latter possibility because of the potential itoffers for the development of low cost materialsand high red mud utilization.

CHEMICAL BASIS FOR ADMIXTURESUSEDThe most common use of industrial waste in thefabrication of construction materials appears to


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372 J. N. Gordon. W . R. Pinnok, M. M. Moore

be that of slags and fly-ash in mortars in whichthey are activated by various means to reactwith added or free lime to produce cementi-tious compounds.- Slags and fly-ashes, whichare used this way usually contain siliceousmaterial in a reactive form, so that they reactwith lime at ambient temperature to producecalcium silicates, which eventually hydrate toproduce calcium silicate hydrates which are thecompounds responsible for binding in Portlandcement concrete. The reaction of the siliceousmaterial with lime, known as the pozzolanicreaction, may be represented as follows:

The optimum molar ratio between lime andsilica is said to be nearer to 2:l in practice,rather than 3:2 as suggested above, affirmingthe well-known fact that the real reaction issomewhat more complicated than the equationsuggests.7 Jamaican red mud is not comparableto any of these wastes in terms of its silica con-tent, as the typical mineral oxide composition ofmud (in Table 1) indicates. That from operationA (one location where bauxite processingoccurs) represents mud derived from the pro-cessing of a typically boehmitic bauxite, whilethat from operation B (another location whereprocessing occurs) represents mud from a moregibbsitic bauxite. Iron is known to be present inred mud mostly as haematite and goethite,while alumina is present mostly as gibbsite andboehmite. The silica present in mud is believedto exist mainly as quartz or bayer sodalite, whilethe titanium exists as the minerals anatase andilmenite. Jamaican red mud is fairly caustic,with the pH of pastes being typically in therange 11-13. Except for the residual NaOH leftafter the final washing in the plant, the compo-

Table 1. Equivalent mineral oxide content of two typicalJamaican red mudsMineraloxide 5%Composition

SiOzTiOzAl203Fe&CaONa,OLOIf+Loss on ignition.

Operation OperationA B8.0 3.06.0 7.0

16.4 16.542.3 49.59.1 5.54.6 2.310.2 11.6

nents of red mud are usually considered to berelatively inert and unreactive.

Despite its apparent inertness and obviouslack of reactive silica, the idea of utilizing thepozzolanic reaction to bind red mud mixturesseemed to be a feasible and potentially low costalternative for the very simple reason that themud is highly caustic and the reaction is favoredin a high pH environment. The admixturesrequired would be hydrated lime, with either flyash, bagasse ash, or silica fume; and all of theseare readily available, or can be produced orimported at relatively low cost.

A further possibility for the production ofcementitious compounds, is that revealed byour previous work, which suggests thathydrated lime will react with the alumina left inred mud to produce calcium aluminates (CAand possibly C5A3). These also hydrate to pro-duce cementitious compounds, in reactionswhich are fairly well known from the fact thatthey are responsible for the strengths of highalumina cement mortars. The reaction of limewith alumina is considered to be a type of poz-zolanic reaction as well.

In this preliminary investigation the strengthsimparted to red mud mortars by admixtures ofhydrated lime and condensed silica fume areexamined. Limestone is employed as a catalystin the later experiments. The aim is to producecementitious compounds through either type ofpozzolanic reaction, while incorporating asmuch mud as possible in the mixtures.

EXPERIMENTAL MATERIALS ANDMETHODSThe hydrated lime used in these experimentswas that available commercially and sold locallyas white lime. The condensed silica fume usedwas that which is sold commercially by a Floridabased company. This is itself a waste productfrom the ferrosilicon industry, and so is a rela-tively inexpensive imported item. It is used herebecause it is known to be highly reactive in thefinely divided state in which it is available, thatis, as a paste with ~53% water. The mud usedhere was that obtained from operation B. Thiswas dried beforehand, crushed and sieved toparticle sizes less than 250 pm. The limestoneused initially was similarly crushed and sieved toparticle sizes less than 250 pm. Tables 2 and 3


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Preliminary investigation of strength development 373

Table 2. Equivalent mineral oxide composition ofmaterials usedMineral oxide 950Red mud* % Limesto ne % Silica fumeSiOZ 3.9 2.4 97A1203 16.4 0.2 1.5Fe203 48.5 0.4 -Na,O 1.7 0.2 -&oCaO 6.2 5:.: 0.lMgO - 1:o -TiOz 6.7LOI 13.1 42.3 G*Composition of mud actually used.

summarize some relevant properties of thesecomponents.

The optimum mass ratio of hydrated lime tosilica fume, for the formation of calcium sili-cates, was determined from semi-quantitativeexamination of the XRD of the productsformed from various mixtures of hydrated limeand silica fume, for excess hydrated lime. Theratio was found to be nearly 2:l by mass, and sothis ratio was maintained between the two,throughout our investigations, except in thosecases where it was desired deliberately to havehydrated lime in excess. The water:solids ratiowas kept near to O-4 in all cases, because of ourfinding that this represented a good balancebetween workability of the mixture and shrink-age of the product during curing.

The materials were used in various combina-tions, to form 50 mm cubes by blending theingredients together with a hand-held electricalblender, and then packing the mixture into themoulds, following the procedure recommendedin ASTM Standard C109-93. The cubes weredemoulded after 24 h and were allowed to curein a humid environment for 28 days. Compres-sive strengths were performed on threespecimen cubes of each composite at28 +2 days, and the strength is taken as themean of these three results. Strength testingwas done on a Controls C901/Z Universal Test-ing Machine, using a loading rate ofO-3 MPa s-. Some measure of the weather

Table 3. Particle size distribution of some materials used

resistance of the stronger composites wasassessed by determining the weight loss andwater absorption which resulted from wet/drycycling. This was done simply by soaking thecubes in water at ambient temperature, thendrying them at 110C over alternate 24 hperiods and determining the mass of the cubeafter each step. XRD, scanning electronmicrography, and thermal gravimetry (TGA/DTG) were employed where they were thoughtto be appropriate, to give information on thephases present.

RESULTS AND DISCUSSIONTable 4 gives the data obtained for the 2%daycompressive strengths of cubes formed in thefirst set of experiments, which involved theaddition of (a) hydrated lime to red mud and(b) condensed silica fume to red mud. Thestrengths obtained can be seen to be lower thanthose obtained for cubes made from red-mud-only pastes. With the mud used in thisexperiment, the strength of red-mud-only cubeswas 4.2 _+0.5 MPa. In the case of the addition ofhydrated lime, the decrease in strength is likelyto be due to the reaction of lime with aluminagel, as is discussed in our previous paper. Thisremoves the incipient binder and replaces itwith calcium aluminate hydrates, which undergoconversion at ambient temperature leading tothe reduction in strength observed. With con-densed silica fume as the only admixture, thereappears to be no significant change in thechemistry of the mixture as the XRD scansremain nearly identical to that obtained frommud-only cube samples.

In our next series of experiments, hydratedlime and condensed silica fume were addedtogether to red mud in the various proportionsshown in Table 5, to investigate the possibilitythat these would combine in the high-pH redmud matrix to form calcium silicate hydrates.The 2%day compressive strengths obtained areagain seen to be less than the strength obtained

Material 250 pm 150 pJ?l Percent retained on sieve90 lun 75 pm 45 pmLimestone 68.8Red mud I: 63.5Silica fume is used in the form supplied, that is, as a paste.

77.5 80.4 93.473.0 77.0 81.4


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374 J. N. Gordon, W ! R. Pinnok, M. M. Moore

Table 4. Compressive strengths of composites of: (a) red mud and hydrated lime; and (b) red mud and condensed silicafume70 Red mud 70 Hydrated lime % Silica fume Compressivestrength

OfPa)100 - - 4.2(;& 5 - 1.390 llz - 1.485 - 2.280 20 - 2.070 30 - 1.950 50 - 2.1

(!?I -95 - : 2.03.2:P - 115 :.:80 20 2.8

Mean of three ( f 0.5 MPa).

for red-mud-only cubes in most cases. X-ray dif-fractograms for (a) red mud with noadmixtures, (b) red mud mixed with hydratedlime and (c) red mud mixed with hydrated limeand condensed silica fume, shown in Fig. 1, sug-gest that the hydrated lime has again reactedwith alumina gel to produce calcium aluminatehydrates. Some of these show up as compoundswith d-spacings of around O-332 nm in both (b)and (c), but also with a d-spacing of around0.740 nm in (b). The desired reaction betweenthe condensed silica fume and hydrated lime isnot occurring, partly, it seems, because thehydrated lime-alumina reaction is occurringmore readily and is using up the availablehydrated lime.

In an effort to reduce this occurrence ournext series of experiments was done with redmud which was treated beforehand withhydrated lime, by making it into a paste withwater and 30% hydrated lime. This mixture was

Table 5. Compressive strengths of composites madefrom mixtures of red mud, hydrated lime and condensedsilica fume% Redmud % Hydratedlime 70 Silicaf um e

Compressivestrength t

Wa)100 lo582 1270 2055 30

Mean of three ( f 05 MPa).

5 4.22.96 4.910 2.415 3.2

kept in a moist state for 14 days before it wasallowed to dry out under lab conditions. Thispre-treated mud was then blended with limeand silica fume in the proportions used in theearlier series and made into cubes as before.The compressive strengths obtained after28 days moist curing are shown in Table 6.

These show that the pre-treatment doesmake a difference, with the strength of the com-posites increasing with increasing proportions oflime/silica in the composite. The diffractogramfor the strongest of these composites is shownin Fig. 2. where it is compared to that obtainedwhen hydrated lime and silica are added, withno pre-treatment. This comparison shows upthe presence of new reflections at O-419, 0.438and O-469 nm that were not present in the pre-vious case, and there are also new reflections at0.376 and 0.384 nm. The absence of significantcalcium hydroxide reflections at O-262 and atO-485 nm suggests that all of the added lime hasreacted. Reflections near O-740 nm indicate thatsome calcium aluminate decahydrate (CAHio)has been formed and is still unconverted evenafter 28 days.

Even though it is difficult to interpret thenew reflections unambiguously in terms of newcompounds formed, it is quite clear that reac-tions are occurring, which use up the addedhydrated lime. The compressive strength testsshow that significant improvement in thestrength of red mud composites is achieved bythe addition of relatively large quantities ofhydrated lime, and suggests that some reaction


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Preliminary investigation of strength development 37.5

Ii HC ,366 nm G .413nm.303 InA 4n C- CalciteH- HaematiteG- Goethite

Fig. 1.+---- Angle20 (Cu K,)

between hydrated lime and condensed silicafume is now taking place. Unfortunately thisresult is not particularly useful for the applica-tion we have in mind, because even thoughhydrated lime is a relatively inexpensive additiveunder normal circumstances, the cost is nottrivial when it constitutes as much as 30% ofthe composite.

The possibility that limestone could be usedto advantage as an admixture to the compositeformed by red mud, hydrated lime, and con-densed silica fume, was next investigated on thebasis of the finding of Alexander that calciumcarbonate has a catalytic effect on the lime-silica reaction. This also turns out to be quite anattractive proposition from the economic point

Table 6. Compressive strengths of composites made withred mud pre-treated with hydrated lime, then mixed withcondensed silica fume and hydrated lime as indicated% Red % Hydrat ed % Silica Compressivemud lime .fime strengthsWPaJ

85 1079 1470 2055 30

Mean of three ( AO.5 MPa).

5 4.27 4.910 6.015 7.2

of view, because limestone deposits can befound in abundance in close proximity to mostJamaican red mud storage lakes. Table 7 givesthe compressive strengths of cubes made frommixtures containing red mud, hydrated lime,condensed silica fume and limestone.

Significant increases in strengths can be seenin Table 7, and the strengths are generally bet-ter than those obtained even by pre-treating themud with hydrated lime. The composite show-ing the highest compressive strength at 28 daysturns out to be one containing equal quantitiesof red mud and limestone, blended with a 2:lmix of hydrated lime and condensed silica fume.Comparisons of the strengths of composites #6and #7 with that of composite #4, in Table 7,suggest that the red mud does play some role inthe binding achieved in the composite with thehighest strength.

XRD analysis of a sample of the compositewith the highest strength is shown in Fig. 3, andagain reflections are seen in the region betweenO-419 and O-483 nm, as in the case of the pre-treated mud composite. Again, it is true thatthere are so many possibilities and so manyoverlapping reflections in this region that pre-cise and unambiguous interpretation is difficult.Majumdar et al. have inferred the presence of


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376 J. N. Gordon, W R. Pinnok , M. M. Moore

+--- Angle 28 (Cu &)Fig. 2.

Table 7. Compressive strengths of composites made of red mud, hydrated lime, condensed silica fume and limestoneComposite % Red % Hyd rated % Silica % Limestonenumber mud lime Compressivefume strength tWW

: :: 77 3.5.5 69.5 12.644.5 13.13 20 14 I 59 14.64 39.5 14 7 39.5 16.75 19 14

4.96 - 14 : 79 13.07 32

2!175 8.5 14.5 14.389 21.5 21:56.5 40 13.96.5 50.5 11.2

I: 53.53.5 21.57 14.5 18.5 6.015.5 7.212 12 61 18 9 10.2Mean of three (f@5 MPa).

C- CalciteS StrathgiteA- Hydr ogrossular

t Angle 28 (Fe&)Fig. 3.


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Prelim inary nv estigation of strength development 377

stratlingite (&ASH,) as the predominant stableend product associated with strength develop-ment in fairly similar mixtures as we have here.It is observed by these workers that stratlingiteis formed very slowly, so that its presence isdetectable by XRD only after about 28 days.The presence of small amounts of stratlingite inour composite would account for the low inten-sity reflections observed around 0.627, O-419and 0.286 nm in the XRD scan, and suggestthat similar strength-giving compounds arebeing formed in our composite. Though therole of the limestone is intended to be catalytic,it seems likely that the carbonate ion does takesome part in the reactions occurring in thiscomposite. XRD reflections at 0500, O-325,0.303 (masked by calcite), and at O-271 nm sug-gest the formation of some hydrogrossular(Ca3A12 (Si04,C03,0H)3), and so suggest thatthe involvement of the limestone/carbonate ionis more than simply catalytic.

A DTG scan of a sample of composite #4,shown in Fig. 4, shows a weak endothermbetween 186 and 200C where stratlingite isknown to dehydrate/dehydroxylate partially*and so is quite consistent with the proposal thatstratlingite is present. The microstructure of thematerial, shown in Fig. 5(b), indicates thepresence of thin needle-like crystals, whichappear to be interwoven in a mat-like formationin some areas, while some less abundant platy

t (AWIAT)

crystals, similar to those identified as stratlingiteby Majumdar and Singh, also appear to bepresent. The microstructure of the composite isclearly very different from that of dried mud,shown for comparison in Fig. 5(a), where thestructure can be seen to be almost totally amor-phous.

Water absorption tests carried out on thematerial of composite #4 gave percentagewater absorption in the range 22-29% over 10wetting and drying cycles, with mass loss beingabout 2% overall after 10 cycles. The density ofthe composite is 2.0 +0-l kg rne3. The 28-daystrength was found to be reproducible withinthe range 15-18 MPa with limestones from dif-ferent sources, all crushed to have grain sizedistributions similar to that given in Tables 2and 3. Long-term studies of the strength of thiscomposite show a much slower increase in thestrength in the period beyond 28 days. Thisstudy has lasted so far, only up to 122 days, asshown in Fig. 6, where each data point repre-sents the mean of four or five strength tests.This finding of slow increase in the long-termstrength is again quite consistent with the pro-posal that the strength is associated with theformation of stratlingite, as its formation hasbeen fairly well-documented to continue rela-tively slowly even up to and beyond five years,in blends of blast furnace slag with high aluminacements.

0 100.

200 300 400 500 600Temperature/ C -+

Heating Rate 2C minFig. 4.


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378 J. N. Gordon, W R. Pinnok , M. M. Moore

This composite compares favorably with theone other red mud composite, containing noPortland cement, which we have found reportedin the literature. Ikeda14 has reported compres-sive strengths as high as 20 MPa (after 91 days)

in composites containing gypsum and Portlan-dite added to Australian red mud. He foundhowever, that the surfaces of his cubes were nothard, and that the strength decreased as theyadvanced in age beyond 91 days. The strengthof our composite is still increasing even after122 days, and it seems likely that the strengthwill continue to increase as the compositeincreases in age.

CONCLUSION

Fig. 5.

Fig.0

6.

I I I I I I20 40 60 80 I I)0 120

Curing time/da y\

It appears from these results that it is indeedpossible to fabricate, from red mud, materialswhich have both the strength and durability thatare likely to make them useful in the construc-tion industry. Strengths in the range 18-22 MPaare attainable (at 122 days) with relatively inex-pensive and readily obtainable additives, whichdo not include Portland cement. Thesestrengths are not yet comparable to the com-pressive strengths obtained with Portlandcement mortars, which we have found to havestrengths in excess of 50 MPa at 28 days, in50 mm cubes cured under the same conditions.However, it is likely that with better under-standing of the strength-giving processesoperating in these composites, the mix of com-ponents can be optimised to produce higherstrengths.

The indication from XRD is that the strengthis associated with the formation of stratlingite(C2ASHH) in a way that is similar to thatobserved in high alumina cements blended withblast furnace slags. The XRD data suggest thatthe formation of complex carbonates might alsocontribute to the strength of these composites.

The possibility that strengths can beimproved by using mixes of components closerto those found in high-alumina cement/slagblends will be investigated in future work. Thepossibility that a local pozzolanic material, suchas bagasse ash, may be used in place of con-densed silica fume is also to be investigated.

ACKNOWLEDGEMENTSThe authors wish to thank the InternationalDevelopment Research center (IDRC) of Can-ada for financial support, through a grant to theJamaica Bauxite Institute. Thanks are due tothis Institute, the Jamaica Building Research


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Preliminary investigation of strength development 379

Institute (now closed), the Jamaica Bureau ofStandards, and the Department of Chemistry,University of the West Indies, for use of facili-ties. The help and advice of Profs J. Smith,H.N. Tran and D. Barham of the Departmentof Chemical Engineering and AppliedChemistry, University of Toronto, are alsogratefully acknowledged.

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UNIDO, Pilot scale testing of representative samplesof bauxite residues for profitable utilization in build-ing materials industry. Report on Project NoSI/JAM/81/802, UNIDO, 1983.MacCarty, S. H., A self-help approach to low-costhousing construction. The Jamaican Bauxit e Inst itu teJ., 10 1992) 70-76.Slota, R. J., Utilization of water glass as an activatorin the manufacture of cementitious materials fromwaste products. Cement and Concrete R es., 17 (1987)703-708.Moukwa, M., Cobalt furnace slag: a latent hydraulicbinder. Cement and Concrete R es., 20 (1990) 253-258.Majumdar, A. J., Singh, B. & Edmonds, R. N., Hydra-tion of mixtures of cement fondu, aluminous cement

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and granulated blast furnace slag. Cement and Con-crete Res., 20 (1990) 197-208.Fraay, A. L., Bijen, J . M. & de Haan, Y. M., Thereactivity of fly ash in concrete: a critical examination.Cement and Concrete Res., 19 (1989) 235-246.Diamond, S., C/S mole ratio of C-S-H gel in amature C2S paste as determined by EDXA. Cementand Concrete Res., 6 (1976) 413-416.Davis, C. E., Mineralogy of Jamaican bauxites. J. ofthe Geological Society of Jamaica, Special Issue, Proc.of Bauxite Symp. II (1993) 6-20.Pinnock, W. R. & Gordon, J. N., Assessment ofstrength development in Bayer process residues. J. qfMaterial Science, 27 (1992) 692-696.American Society for Testing and Materials, Standardtest method for compressive strength of hydrauliccement mortars. Cl 09-93. ASTM 04.01, 1994.Alexander, K. M., Activation of pozzalanic materialby alkali. Aust ralian J. of Applied Sciences, 6 ( 1955)224-229.Mm-at, M., Hydration reaction and hardening of cal-cined clays and related materials, I. Preliminaryinvestigation on metakaolinite. Cement and ConcreteRes., 13 (1983) 259-266.Majumdar, A. J. & Singh, B., Properties of somehigh-alumina cements. Cement and Concrete Res., 22(1992) 1101-1114.Ikeda, Ko, A new type of pozzolanic cement utilizingred mud and fly ash. In Proc. 8th Int . Congr onC$n$t4y qf Cement 1986, Vol. 6, Rio de Janeiro, pp.

A Preliminary Investigation of Strength Development in Jamaican Red Mud Composites

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