compaction delay versus properties of cement-bound

EFFECTS OF COMPACTION DELAY ON THE PROPERTIES OFCEMENT-BOUND LATERITIC SOILS

By

U. N. OkonkwoDepartment of Civil Engineering

Michael Okpara University of Agriculture, Umudike.E-mail: [email protected]

ABSTRACT

This study is an investigation into the effect of 0 to 3 hours compaction delay with half anhour intervals on soil-cement mixes 3,5,8; and 1, 3, 5 percent cement contents by weight ofdry soils, for yellow and red lateritic soils respectively. The tests carried out on the cementstabilized soils were the Compaction test (Standard Proctor), the Unconfined CompressiveStrength (UCS), the California Bearing Ratio (CBR) test and Durability test. The resultsobtained indicated that compaction and strength characteristics decreased with increase incompaction delay for both lateritic soils. For yellow and red lateritic soils 5% and 3% cementcontent respectively were sufficient and compaction delay must not be more than 2 hours.They are good in stabilized form for sub-base and base of light trafficked ro ads with redlateritic soil more economical.

KEYWORDS: Lateritic soils, Stabilization, Compaction delay, California Bearing Ratio,Unconfined Compressive Strength, Maximum Dry Density, and Optimum Moisture Content.

1.1 INTRODUCTIONSoil stabilization techniques for roadconstruction are used in most parts of theworld although the circumstances andreasons for resorting to stabilization varyconsiderably. In industrialized, denselypopulated countries, the demand foraggregates has come into sharp conflictbetween agricultural and environmentalinterests. In the less developed countries andin remote areas the availability of goodaggregates of consistent quality at economicprices may be limited. In either case thesefactors produce an escalation in aggregatecosts with maintenance costs. The upgradingby stabilization of materials thereforeemerges as an attractive proposition. Kogbe(1975) stated that in pre-cambian times,Nigeria consisted of uplifted continental

landmass made up of basement sediments.This resulted in the formation of lateriticsoils which are of relatively good quality forroad construction works.

The addition of adequate percentageof Portland cement to a soil can significantlymodify the properties of the mixtureproduced, independent of the soil used.However, excessive addition of cementbecomes uneconomical. The importance ofcement stabilization of lateritic soils has beenemphasized in the past (Bulman, 1972; Ola,1974; and Portland Cement Association,1959). It is important to note that it isdifficult to estimate precisely the adequateamount of cement required in soil-cementmix. However, the Nigerian GeneralSpecifications (1997) established the usualrange of cement requirements for various

5

6 U.N. OKONKWO

AASHTO group classifications of soils inNigeria. Hence, possible trial cement contentadopted for the red and yellow lateritic soilswere 1%, 3%, 5%; and 3%, 5%, 8%respectively by weight of the dry soil.

Construction specification commonlyrequires that compaction and final shaping should be carried out as soon as possible aftermixing/placing is completed, but usually thisnot the case. Sometimes, there is a delaybetween mixing/placing and compactionbecause of some unforeseen circumstanceslike machine breakdown, injury to workers inthe field, among others. Some researchers(Osinubi, 1998; Obeahon, 1992; Osinubi andKatte, 1991) have worked on elapsed timeafter mixing with lateritic soils. In mostcases, the works were focused on modifiedlateritic soils. Besides, soils havepeculiarities of structures and variations inbehavior at mixing operation. This may bethe case even when they have similarplasticity index but may depend on the sizeand strength of their aggregates (Osinubi,1998). Thus, the objective of this work is toinvestigate the effect of 0-3 hours delay incompaction with half an hour intervals on theproperties of soil-cement mixtures of twolateritic soils with emphasis on their strengthand compaction characteristics.

1.2 MATERIALS AND METHODSThe materials used were ordinary Portlandcement which was the stabilizer for the twolateritic soil samples. The soil samples werecollected by the method of disturbedsampling from two spots of deposits inRigyar Zaki, Ungogo local government area,Kano state of Nigeria. The BS 1377; 1990

was used for the preliminary tests. TheStandard Proctor was used for thecompaction test and the clay mineralidentification was done using the plasticitychart developed by Casagrande , data inMitchell (1976). The results weresummarized in table 1.

The test specimens were prepared byfirst thoroughly mixing dry predeterminedquantities of pulverized soil and Portlandcement in a mixing tray to obtain a uniformcolour. The amount of water required wasdetermined from moisture-densityrelationships for soil-cement mixtures. Thetests were also carried out as specified by BS1924: 1990 for Unconfined CompressiveStrength, California Bearing Ratio andDurability tests. Specimens for unconfinedcompressive strength were wax cured asspecified by Nigerian general specifications(1997). The California Bearing Ratio wasmodified so as to conform to Nigeriangeneral specification (1997), which stipulatesthat specimens should be wax cured for sixdays un-soaked and immersed in water for 24hours before testing. The resistance of loss instrength [durability] was determined as aratio of the Unconfined CompressiveStrength [UCS] of specimen wax-cured for 7days, de-waxed top and bottom, and laterimmersed in water for another 7 days to theunconfined compressive strength of specimenwax-cured for 14 days as specified by BS1924: part 2: 1990.

TABLE 1: SUMMARY OF THE PROPERTIES OF LATERITIC SOILS

NIGERIAN JOURNAL OF TECHNOLOGY, VOL. 28 NO.2, SEPTEMBER 2009

7EFFECTS OF COMPACTION DELAY ON THE PROPERTIES OF CEMENT-BOUND LATERITIC SOILS

Soil Property Red LateriticSoil

Yellow LateriticSoil

Liquid limit (%)Plastic limit (%) % passing BS No. 200 sieveAASHTO classificationMajor clay mineralMaximum Dry Density (Mg/m )3

Optimum Moisture Content (%)Unconfined Compressive Strength (KN/m )2

California Bearing Ratio (un-soaked % )Drying Shrinkage (%)Resistance to water erosion (mm)Moisture Absorption (%)

30.320.035A-2-4(0)Illite1.8811.816973.0842.3323.25

31.019.239A-6(1)illite1.9212.019683.4321.4422.62

1.3 RESULTS AND DISCUSSIONCompaction CharacteristicsFigure 1 shows the relationship between theMaximum Dry Density [MDD] of thecement-bound lateritic soils and compactiondelay after mixing. It was glaring that theMDD decreased with increase in elapsedtime after mixing. As soon as the water wasadded to the soil-cement mix, hydrationreaction kicks off. This resulted in thebonding of the particles in the loose state anddisruption of particles was required to

increase the density of the soil.Consequently, some of the hardening effectof the cement will be lost and in addition,part of the compactive effort was directed inovercoming the cementation. Thus, the MDDdecreased with increase in compaction delayand it is dependent on the rate of hydration ofthe cement. According to Shetty (2005), therate of hydration is very rapid at the initialstage but reduces with time.

It canalso bededuced

t h a t M D Dreduced from1.92Mg/m and3

1.88Mg/m to3


8 U.N. OKONKWO

1.85Mg/m and 1.81Mg/m at no cement3 3

content to 3% and 1% cement contentrespectively for yellow and red lateritic soils,these indicate that for a given level ofcompaction, a stabilized soil has a lowerMDD than that of the unstabilized soil[Sherwood, 1993]. The reduction in theMDD can be attributed to the reactionbetween cement and the fine fraction aspozzolanic components in which they formclusters like coarse aggregates. These clustersoccupied larger spaces thus increasing theirvolume and in consequent decreasing theMDD.

In further addition of the stabilizingagent [cement] at 8% and 5% for yellow andred lateritic soils respectively, the MDDincreased because the clusters formed werestrongly bonded and behaved more as coarseparticles and it was as a result of excesscement. These disagree with the normal trendof continuous reduction of MDD withprogressive addition of stabilizing agent asstated by Sherwood [1993].

Figure 2 represents the relationshipbetween Optimum Moisture Content [OMC]

of the cement-bound lateritic soils andcompaction delay after mixing. It wasdiscovered that the OMC of the lateritic soilsdecreased steadily with increase incompaction delay. This was because thehydration reaction kicks off rapidly at theaddition of water and continues to decreasewith time, thus the demand for water in thesystem also reduced continuously.

In the corollary of the decrease inMDD at the introduction of stabilizing agentought to be an increase in the OMC[Sherwood, 1993]. However, these wereupsets from the trend. The decrease in OMCat no stabilizing agent to that of 3% and 1%cement content of the yellow and red lateriticsoils respectively was probably due to lack ofwater in the system which caused a self-desiccation condition and as a result loweredhydration. If there is no free flow of waterwithin the soil-cement mix, the hydrationreaction uses up the water until too little willbe left to lubricate the soil particles andrelative humidity decrease within the mix[Osinubi, 1998].

S t r e n g t hCharacteri

sticsT h e



Unconfined Compressive Strength [UCS],California Bearing Ratio [CBR] andDurability are measures of strengthproperties of the cement-stabilized lateriticsoils. The UCS and CBR of yellow lateriticsoil rose from 196KN/m and 8% at no2

cement content to 1410KN/m [7 days] and2

140% respectively at 3% cement content andalso that of the red lateritic soil rose from169kN/m and 7% at no cement content to2

1215kN/m [7 days] and 129% respectively2

at 1% cement content. It is obvious that therewas an appreciable improvement in strengthproperties of both lateritic soils at a littleaddition of cement but the red lateritic soilgave a more positive response to the additionof cement. This was as a result of the higherpercentage of fine fractions in the yellowlateritic soil because gravel and sand arealmost inert in the hydration reaction fromwhich strength develops. Therefore, they

have little or no contribution to thedetermination of the quantity of stabilizerrequired. In other words, soils with higherpercentage of fine fractions will likelyrequire higher stabilizer content.

In figures 3, 4 and 5 showed thatstrength properties decreased with increase incompaction delay for both lateritic soils. Thiswas because, as soon as water was added tothe soil-cement mix, the cement began tohydrate and it was therefore desirable tocompact as soon as mixing was completed.When this was not done, not only that someof the hardening effects of the cement wouldbe lost but in addition extra compactive effortwill be required to break down the cementedbonds that have been formed. Both of theseeffects together will lead to serious loss instrength.

Considering the minimum

conventional values of UCS at 7 days for

cement stabilized soils which are 750-1500,

1500-3000, 3000-6000 kN/m for sub-base,2

base [lightly trafficked roads], base [heavily

trafficked roads] respectively in evaluating

the strength of the soil specimens. The 7 days

UCS values for both yellow and red lateritic


10 U.N. OKONKWO

soils at no compaction delay with cement

content of 5% and 3% were 1520kN/m and2

2210kN/m respectively, showed that only2

the sub-base and base requirements for light

trafficked roads were met. Judging by the

180% value of CBR of mix in place

condition as recommended by the Nigerian

General Specification [1997], the 5% and 3%

cement content for yellow and red lateritic

soils recorded CBR values of 208% and

192% respectively at no compaction delay

which indicated that both lateritic soils met

the requirement for the mixes. The durability

requirement for soil-cement mixes was not

satisfied for both lateritic soils. This was

because the resistance to loss in strength

which were determined by comparing 14

days old cured specimen with 7 days curing

and 7 days soaking in water were more than

20% allowable loss in strength. The high loss

in strength may be because of high water

absorption of the clay mineral



1.4 CONCLUSIONSThe following conclusions were drawn afterthis work has been carried out:1. Addition of 3% and 1% cement

content for the yellow and redlateri t ic soi ls respect ively,appreciably improved their strengthproperties.

2. Though the durability requirementwas not satisfied for both lateriticsoils, they can still be adopted forsub-base and base of light traffickedroads because Kano experiences lessrainfall, so alternate cycles of wettingand drying will be reduced.

3. 5% and 3% cement content will beadequate for yellow and red lateriticsoils respectively.

4. The red lateritic soil will be moreeconomical to be adopted as amaterial for stabilization because ofless cement content requirement.

5. The compaction and strengthcharacteristics decreased withincrease in compaction delay.

6. At 5% and 3% cement content for

yellow and red lateritic soilsrespectively, not more than 2 hourscompaction delay should be allowedbecause in most values of strength at2 hours time elapsed between mixingand compaction not more than 20%losses were experienced in theirstrength properties.

REFERENCES

AASHTO (1986): “Standard specificationsfor transportation materials and method ofsampling and testing” 14 edition, Americanth

Association of State Highway andTransportation Officials, Washington D C,USA.

BS 1377 (1990): “Method of testing soils forengineering purpose” British StandardInstitute, London, U.K.

BS 1924 (1990): “Method of test forstabilized soils” British Standard Institute,London, U.K.


12 U.N. OKONKWO

Bulman J. N. (1972): “Soil stabilization inAfrica” Transport and Road ResearchLaboratory Report, LR476, Crowthorne,U.K.

Kogbe C. A. (1975): “Preliminaryinterpretation of gravity measurements in themiddle Niger basin area, Nigeria” Geology ofNigeria, The Elizabethan Publishing.

Mitchell J.K. (1976): “Fundamentals of soilbehaviour” John Willy & Sons, Inc., NewYork, USA.

Nigeria General Specifications (1997):“Bridges and road-works” Federal Ministryof Works, Lagos.

Obeahon S.O. (1992): “Effect of elapsed timeafter mixing on the properties of modifiedlaterite” M. Eng thesis submitted to theDepartment of Civil Engineering, AhmaduBello University, Zaria, Nigeria.

Ola S.A. (1974): “Need for estimated cementrequirement for stabilization of laterite soils”

Journal of Transp. Engrg., ASCE, 100(2);379-388.

Osinubi K.J. (1998): “Influence ofcompaction delay on properties of cementstabilized lateritic soil” Nigerian Journal ofEngrg., 6(1), 13-25.

Osinubi K.J. and Katte V.Y. (1991): “Effectof elapsed time after mixing on grain size andplasticity characteristics of soil-cementmixes” NSE Technical Transactions, 34 (3),38-46.

Portland Cement Association (1959): SoilCement Laboratory Handbook, Chicago,Illinois, USA.

Sherwood P.T. (1993): “Soil stabilizationwith cement and lime” State-of-the-artreview, Dept. of Transport, TransportResearch Laboratory. U.K.

Shetty M.S. (2005): “Concrete technology-theory and practice” S.Chand & CompanyLtd, Ram Nagar, New Delhi, India.


compaction delay versus properties of cement-bound

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