Guide To Cement Modified Soil Cms PDF Download

Cement modification of subgrade has been widely practiced for the past few decades. Recently, cement has become a more economical binder to modify in-situ subgrade soil since other binders, such as fly ash, have become less available and therefore their prices have increased significantly. In addition, a much higher percentage of fly ash needs be used, when compared with cement to achieve the same subgrade strength and stiffness. In general, cement-modified subgrade is prone to develop shrinkage cracking, which can eventually reflect through asphalt pavement layers to the surface after construction. For some subgrade soils, a high cement content is needed to meet the unconfined compressive strength requirement without jeopardizing durability. A higher cement content will result in higher shrinkage cracking potential. To overcome this problem, a microcracking technology has been developed and adopted in the field. This technology involves re-compaction of cement-modified soil (CMS) with a roller, 24 to 48 hours after initial compaction, to induce microcracks in the CMS and minimize the potential for large shrinkage cracks. Microcracking of CMS is not expected to significantly reduce the strength and stiffness of CMS, but it is expected to increase its hydraulic conductivity and reduce the potential for large shrinkage cracks. Unfortunately, the procedure to simulate microcracking of CMS in the laboratory and to evaluate its effect on properties of CMS has not been established yet. This report documents the development of such a procedure and discusses the effect of microcracking on the properties (strength and modulus) of CMS specimens. The developed procedure utilized unconfined compression (UC) tests to generate microcracks in specimens. To generate microcracks, the loading stress level was found to be equal to the unconfined compressive strength of the CMS specimen. The laboratory results showed that microcracking increased the hydraulic conductivity of the specimen and reduced its electrical resistivity when the specimen was saturated. The Light Weight Deflectometer (LWD) tests conducted in the field showed that adding cement increased the subgrade modulus. However, after applying three passes of roller compaction to generate the microcracks in the CMS in the field, the subgrade modulus dropped to approximately 40% of its original value on average.