Heat alters the engineering behavior of soils. Marl soils are highly-erodible sedimentary deposits composed of clay minerals and calcium carbonate. Clay minerals and calcium carbonate in marl soils considerably influence the engineering behavior of such soils. Soils can be exposed to heat for a variety of reasons leading to changes in the physical, mechanical, and microstructural properties, in particular the engineering properties of marl soils. In the design of geo-environmental projects, the results of soil mechanics, especially the permeability coefficient, directly influence the design outcomes. Accordingly, this study aimed at evaluating the effect of heat treatment on the engineering behavior and permeability coefficient of marl soils from a microstructural perspective. To this end, the marl soil was heated to 25–900°C for 2 h. The changes in the engineering properties of marl soils at different temperatures were studied by macrostructural (gradation, Atterberg limits, loss-on-drying, Unconfined Compressive Strength (UCS) and permeability) and microstructural (XRD and SEM) investigations. The results were suggestive of the considerable effect of heat treatment on the engineering behavior of marl soils, as the compressive strength of marl soils increased by 100 folds, and the permeability coefficient reduced by about 6 times at 700°C.

Marl soils, with their low bearing capacity, are widely distributed around the world. Stabilising by way of lime or cement additives is common for these soil types to enhance their performance against heat exposure. Hence, this study investigates the microstructural properties of marl soils that have been stabilised with lime additives under high temperature with special consideration of dihydroxylation temperature. In this regard, marl soils have been first stabilised with 2, 4, 6, 8 and 10 wt% lime and then heated at 100, 200, 300, 500, 700 and 900°C. Various geotechnical properties have been investigated by unconfined compression strength (UCS) test, Atterberg limits, pH variations and microstructural x-ray diffraction. The results revealed that at temperatures lower than the dihydroxylation temperature, increasing the lime percentage was accompanied by an increase in UCS. However, at higher temperatures, increasing the lime content decreased the UCS. The addition of 4% lime at ambient temperature increased the UCS to 1.7 MPa, and 3.75 MPa at 500°C.