Long-term characteristics of a stabilized expansive clay exposed to environmental-driven processes

Abstract

Understanding the impact of climatic conditions on the long-term performances of soils stabilized with lime and cement is of crucial importance. Most of the available studies on durability solely rely on laboratory investigations to assess the effects of exposure to environmental-driven processes such as wetting and drying, leaching, etc. In this context, a research embankment built in 2010 with an expansive soil stabilized with 4% quicklime and a mix of 2% quicklime and 3% cement was sampled in 2021. A comprehensive experimental campaign was conducted using these samples to evaluate the performance of materials 11 years after the construction of the structure. The studies were completed by microstructural and physico-chemical investigations to understand the mechanisms that might explain changes in performance over time.The analysis of the hydro-mechanical properties of the soil sampled between the edge and the interior of the embankment was first performed. The results indicated that the material taken near the surface had a mechanical behavior equivalent to the untreated soil, demonstrating a total loss of the benefit brought by lime/cement addition. Towards the internal part of the embankment, the mechanical performance progressively increased. Physico-chemical investigations showed that on the edge of the backfill significant part of the calcium was leached 11 years after the construction. This was associated to a drop of pH, and to the formation of calcite. The microstructure was also significantly altered on the edge of the embankment compared to the internal part of the structure. Based on these results, a new mechanism of soil deterioration driven by climatic conditions was proposed. Water circulation and carbonation, associated to a significant reorganization of the microstructure were identified as the main phenomena responsible for the degradation of the treatment effects. This study showed that embankment slopes built with lime and cement stabilized expansive clay must be protected from weather-driven processes to limit any associated degradation.