Moisture movement in cement-stabilized base materials

The aggregate base layer is the main load-bearing member in many pavement structures in Texas. If the locally available aggregates are viewed as marginal quality, they are frequently stabilized with cement to improve their properties. The amount of cement used with a base material is generally selected based on the unconfined compressive strength of the treated layer. When reduced levels of stabilization are used, there is a concern that the material property improvements may not be permanent and that the benefits of stabilization will “disappear” after a few years in service. It is well known that a primary factor influencing the long-term performance of cement-stabilized base materials is moisture.; Joint research studies in Texas and Finland proposed the use of a new test procedure, the Tube Suction Test (TST), to evaluate the moisture susceptibility of untreated base materials (Saarenketo and Scullion, 1995). In this research the TST was evaluated on four commonly used base materials stabilized with low levels of cement in the state of Texas. The ultimate proposal is that this test can be used together with current strength tests to ensure that future base materials will have not only adequate initial strength but also be resistant to long term moisture damage. Concern with the TST is that the engineering significance of parameters measured, the surface dielectric constant, is not known. No fundamental studies have been conducted to relate this property to the factors influencing pavement performance.; The primary goal of this research effort is to gain an understanding of the significance of TST results on the physical, chemical and engineering properties that influence long term pavement performance of both treated and untreated base materials.; A controlled laboratory study was conducted in which different amounts of cement were used to stabilize a limited number of aggregate materials that are commonly stabilized with cement and used as base or subbase layers for road construction in the state of Texas. This study evaluated both the strength and moisture changes in these marginal materials. Advanced micro-analysis tools such as electron microscopy, X-ray diffraction, and other new advanced analytical techniques were evaluated to determine if they can show the changes in the amount of pore water before, during and after conducting the tube suction test. These tools were also used to study the chemical changes in cement-stabilized materials and to identify the precipitates that are observed on some samples after completion of TST.