Chemicalstabilization has different way to be used. Material to beused can beselected depending on soil type and condition ofconstruction site. For example, Lime is not good stabilizer for silts, granularmaterials and soils with sulphate contents greater than 0.3 percent.
Actually,lime is helpful material for clay-bearing and highly cohesive soil whereas flyash is being used for granular or poorly cohesive soil. Many materials can be used like, lime ,cement, fly ash and asphalt. That different chemicals can enhance the strength, compressibility, hydraulic conductivity, swelling potential andvolume changing. 1.1.
1 Soil Stabilization with Lime:Lime is a white caustic alkaline substance consisting of calcium oxide”CaO”, which is obtained by heating limestone and which combines with waterwith the production of much heat. It is very effective chemical in modifyinghigh plastic clayey soil which can be used alone or by mixing it with anotherchemical component like cement, fly ash or bitumen. It is used mainly forstabilizing subgrade. Lime stabilization will be done by changingthe nature of adsorbed layer and providing pozzolanic action. As a result, thehigh plasticity index of the soil will be reduced. Also, the optimum watercontent will be increased and decreasing in the maximum compacted density ofthe soil. Therefore, less compaction will lead to the maximum compacteddensity.
It found that lime can increase the soil strength and durability whenit added to the soil as ( Fig. ) shows. There is an advisable percentage oflime to gain that good improvement from it, from 5-8% for plastic soil. 1.1.
2 Soil Stabilization with Cement 5:The soil stabilized withcement is known as soil cement which done due to cementing action. Cementing isthe result of chemical reactions of cement with siliceous soil during hydrationreaction. There are some factor affecting soil-cement such as nature of soilcontent, conditions of mixing, compaction, curing and admixtures used. Inaddition, depending on the soil type, the amount of cement will differ asfollow:Gravels – 5 to 10% Sands– 7 to 12% Silts – 12 to 15%, and Clays – 12 – 20%In general , Cement stabilization givebetter strength and improve quality of soil.
Other additives can be mixed withcement to enhance the soil like Lime, calcium chloride, sodium carbonate,sodium sulphate and fly ash. In fact, the type of cement which used for stabilizationusually is ordinary Portland cement. calculation of required cement amount isdiscussed following:If the layer of soilhaving surface area of A (m2), thickness H (cm) and dry density rd (tonnes/m3),has to be stabilized with p percentage of cement by weight on the basis of drysoil, cement mixture will be = 100*P/(100+p)and, the amount of cement required for soil stabilization is given byAmount of cement required, in tonnes = 1.
1.3 Soil Stabilization with Bitumen: Asphalt is a dark bituminous substance that is found in natural bedsand is also obtained as a residue in petroleum refining and that consistschiefly of hydrocarbons. Asphalts and tars are bituminous materials which areused for stabilization of soil.
This stabilization method can be defined as thetreatment of naturally occurring neoplastic or moderately plastic soil withliquid asphalt at normal temperatures to improve the load-bearing qualities ofthe soil.That Bituminous materials can impart cohesion and reduced water absorptionwhen added to a soil.