Department of Civil Engineering Institute of Technology recently carried out a study into the Impact of moisture intrusion on durability of lime stabilized subgrades.
They found the following conclusions can be drawn.
- Observations in the study show that the inherent water holding capacity and high-water affinity of Calcium Silicate Hydrate to be a reason for moisture damage in lime treated soil in addition to known factors like increase in pore water pressure and decrease in effective stress. Since C-S-H phases are the primary strength contributor to lime stabilized soil, it is possible that any change in physicochemical properties of C-S-H phases during exposure to moisture have an impact on the strength and therefore on durability of lime stabilized layers.
- Suction potential of lime treated soil was found to increase with increase in curing time possibly due to the progressive formation of C-S-H phase. C-S-H is known to have a high affinity for water due to a highly porous nature and a high specific surface area. Even though suction properties of lime treated soil was found to increase with curing time, water absorption in these layers were found to decrease with curing. This is possibly due to inherent strength gain restricting the matrix from any volumetric changes associated with water absorption.
- Even though 8 percent lime treated soil (C-S-H II) was found to have a higher amount of pozzolanic reaction product when compared to 5 percent lime treated soil (C-S-H I), the strength of both were found to be similar during early curing periods (7 days) possibly due to excess lime present in 8 percent lime treated soil.
- It was observed that the extent of moisture damage in a lime stabilized subgrade is significant during initial curing periods. Further study is needed to determine a way to reduce the initial time span within which the lime stabilized subgrade is vulnerable to moisture damage. A possible option may be using some type of admixture to hasten the rate of strength gain.
- In this study it was observed that the strength loss after soaking was because of a combined effect of increase in pore water pressure and due to the precipitated C-S-H phases absorbing and holding on to external water. Further study is needed to determine the extent to which each of the causes individually contributes to the total strength loss and how lime stabilization with its potential for cost saving can be improved in performance.