Advances in design of cement stabilized pavement subgrades

By blending subgrade soils with small amounts of cement, vast improvements can be realized, particularly when considering materials of poor or marginal quality. In its history of use, however, soil-cement construction has been plagued by shrinkage cracking and durability problems.;Traditional design of pavement bases and subgrades has since been influenced by the use of strength-based designs that produce rather high strengths, which comes at the expense of shrinkage cracking. Although the introduction of durability design concepts have accounted for some amount of success in the attempt to control durability problems, design engineers tend to shy away from protocols involving durability because of the intensity of the laboratory tests involved. Studies have also been done in recognition of the existence and negative effects of shrinkage in soil-cement technology, but it has not been incorporated in protocols involving soil-cement mixture designs.;In light of addressing the problem of shrinkage and durability issues in soil-cement subgrades, the first of two objectives of this thesis proposes to develop a protocol that balances the effect of durability, strength and shrinkage. In development of the protocol, a series of cement contents, namely, 3%, 4% and 5% was used for the assessment. Multiple subgrade samples were tested using the above series to determine the durability, strength and shrinkage performances at each level. Such protocol was designed on the basis of empirical-mechanistic optimization of the cement content while maximizing the required effects of the variables including durability, strength and shrinkage, within predetermined limits. Beyond these limits performance was viewed as marginal. Since this demonstration allowed an optimal cement content to be determined, balanced conditions could be realized, hence the premise around which the protocol was designed.;During construction of soil-cement, it is required that construction traffic and other equipment stay off the subgrade course for at least seven days, at which time the cured material is estimated to be strong enough to be loaded with traffic without running the risk of failure through rutting or other distortions. The second objective proposes to assess the adequacy of allowing construction traffic on the processed subgrade prior to seven days, which would subsequently account for a reduction in traffic delay cost. For this assessment, three days laboratory tests were conducted and analyzed against their 7-day counterparts by means of statistical analysis. Such analysis determined that there was no significant difference between the 3-day data and that of the 7-day, thus recommending that the subgrade course could be opened to traffic 4 days earlier than normal (after 3 days), and thus accounting for sizable delay cost savings.