Development of Laboratory Procedure for Evaluating Microcracking Technology on Cement-Modified Soil Subgrade

Cement modification of soils has been widely practiced for the last few decades. Recently, cement has become a more economical binder to modify in situ subgrade soil because other binders, such as fly ash, have become less available and therefore their prices have gone up 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. However, cement-modified subgrade may have an issue with shrinkage cracking, which can eventually reflect through the 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, microcracking technology has been developed and adopted in the field. This technology involves recompaction of cement-modified soil (CMS) with a roller 24–48 h 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 permeability and reduce the potential for large shrinkage cracks. Unfortunately, the procedure to simulate microcracking of CMS in the laboratory and evaluate its effect on properties of CMS has not been established yet. This note documents the development of such a procedure and discusses the effect of microcracking on the properties (strength and modulus) of CMS specimens.