Effect of different C-S-H phases on the moisture-induced damage in lime-stabilised soil

What is it about?

Durability is a major concern for all stabilized materials as it can reduce the structural capacity of pavement layers. One of the primary factors influencing the long-term performance of stabilized subgrade layers is moisture. The structural properties of these engineered materials start to deteriorate with the ingress of external water. The detrimental effect of soaking depends on the level of pozzolanic reaction achieved by the stabilized layer prior to water intrusion. Although the affinity for water is reduced after stabilisation, some amount of water is held within the matrix by the precipitated Calcium Silicate Hydrate (C-S-H) phases due to their inherent water adsorption capacity. The extent of damage will, in turn, depend on the type and concentration of different cementitious phases due to the structural, compositional and morphological differences. This study tries to determine the type of hydrated cementitious phase that is more resilient to moisture induced damage. Results indicate presence of C-S-H II phase to be beneficial for durability of lime treated soil as compared to C-S-H I phase.

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Why is it important?

The amount of lime required to treat a problematic soil, referred to as the optimum lime content, is usually obtained using the Eades and Grim pH test. Addition of the optimum lime content ensures long-term strength gain by pozzolanic reaction, besides satisfying the initial amount of lime required for cation-exchange, flocculation and agglomeration of the clay particles (modification of soil). Adding different amounts of lime to a soil not only affects the rate of strength gain, but also the type of cementitious C-S-H phase formed. The type of C-S-H phase formed by adding a certain amount of lime depends on the clay minerals present and the amount of lime added. An attempt was made to comprehend the effect of different hydrated C-S-H phases on the inevitable moisture-induced strength loss in lime-treated subgrade soil. The findings of the study provide some fundamental understanding of the observed behaviour of soil treated with different amounts of lime. Results indicate the presence of C-S-H II phase to be beneficial for durability of lime-treated soil when compared to C-S-H I phase. Hence adding lime content sufficient to form C-S-H II phase (which may be greater than the optimum lime content), may make the lime-treated subgrade soil more resilient to moisture-induced damage.

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