sieve indicates that lime or a combination LCF will bethe best additive for StabilizationSOIL-CEMENT STABILIZATIONIn general, there are three types of soil-and-cementmixtures as follows:lPlastic soil-cement is a hardened mixture of soiland cement that contains, at the time of placing, enoughwater to produce a consistency similar to plasteringmortar. It is used to line or pave ditches, slopes, and otherareas that are subject to erosion. It also maybe used foremergency road repair by mixing high-early-strengthcement into the natural material in mudholes.lCement-modified soil is an unhardened orsemihardened mixture of soil and cement. Whenrelatively small quantities of portland cement are addedto granular soil or silt-clay soil, the chemical andphysical properties of that soil are changed. Cementreduces the plasticity and water-holding capacity of thesoil and increases its bearing value. The degree ofimprovement depends upon the quantity of the cementused and the type of soil. In cement-modified soil, onlyenough cement is used to change the physical propertiesof the soil to the degree desired. Cement-modified soilsmay be used for base courses, subbases, treated sub-grades, highway fills, and as trench backfill material.. Compacted soil-cement, often referred to assimply soil-cement, is a mixture of pulverized soil andcalculated amounts of portland cement and water that iscompacted to a high density. The result is a rigid slabhaving moderate compressive strength and resistance tothe disintegrating effects of wetting and drying andfreezing and thawing. The remainder of our discussionof soil-cement is directed towards this type ofsoil-and-cement mixture.MATERIALS FOR SOIL-CEMENTSoil, portland cement, and water are the three basicmaterials needed to produce soil-cement. Low cost isachieved mainly by using inexpensive local materials.The soil that makes up the bulk of soil-cement is eitherin place or obtained nearby, and the water is usuallyhauled only short distances.The word soil, as used in soil-cement, means almostany combination of gravel, sand, silt, and clay, andincludes such materials as cinder, caliche, shale, laterite,and many waste materials including dirty and poorlygraded sands from gravel pits.The quantities of Portland cement and water to beadded and the density to which the mixture must becompacted are determined from tests. The water servestwo purposes: it helps to obtain maximum compaction(density) by lubricating the soil grains and it is necessaryfor hydration of the cement that hardens and binds thesoil into a solid mass. Properly produced soil-cementcontains enough water for both purposes.The cement could be almost any type of portlandcement that complies with the requirements of the latestASTM (American Safety for testing and Materials),AASHTO(American Association of State Highway andTransportation Officials), or federal specifications.Types I (normal) and IA (air entrained) portland cementsare the most commonly used.The water used in soil-cement should be relativelyclean and free from harmful amounts of alkalies, acid,or organic matter. Water fit to drink is satisfactory.Sometimes seawater has been used satisfactorily whenfresh water has been unobtainable.Practically all soils and soil combinations can behardened with portland cement. They do not need to bewell-graded aggregates since stability is attainedprimarily through hydration of cement and not bycohesion and internal friction of the materials. Thegeneral suitability of soils for soil-cement can be judgedbefore they are tested on the basis of their gradation andtheir position in the soil profile. On the basis ofgradation, soils for soil-cement construction can bedivided into three broad groups as follows:1. Sandy and gravelly soils with about 10- to35-percent silt and clay combined have the mostfavorable characteristics and generally require the leastamount of cement for adequate hardening. Glacial-andwater-deposited sands and gravels, crusher-runlimestone, caliche, lime rock and almost all granularmaterials work well if they contain 55 percent or morematerial passing the No. 4 sieve and 37 percent passingthe No. 10 sieve. Stones over an inch or two in diameterare undesirable. Exceptionally well-graded materialsmay contain up to 65-percent gravel retained on the No.4 sieve and have sufficient fine material for adequatebinding. These soils are readily pulverized, easilymixed and can be used under a wide range of weatherconditions.2 Sandy soils deficient in fines, such as somebeach sands, glacial sands, and windblown sands, makegood soil-cement although the amount of cementneeded for adequate hardening is usually slightly greaterthan with the soil in Group 1 above. Because of poor18-5
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