The variations on thermal conductivity and structures of silty clay modified by waste fly ash and oil shale ash after freeze–thaw cycles

Abstract

This study was to present changes on the thermal conductivity and structures of silty clay (SC) modified by waste fly ash (FA) and oil shale ash (OSA) after freeze–thaw (F-T) cycles, and discuss the thermal insulation capacity of modified silty clay (MC) and its main influencing factors. Firstly, the thermal conductivity of SC and MC at different moisture contents and dry density was measured after different numbers of F-T cycles. Secondly, the experimental study was conducted to analyze variations on the structure of MC after different numbers of F-T cycles. The test results of thermal conductivity show that: 1) the thermal conductivity of SC and MC decreases with the number of F-T cycles, and they would be constant after 20 F-T cycles; 2) the thermal conductivity of MC ranging from 0.765 to 1.134 W/m/K is lower than that of SC ranging from 1.277 to 1.747 W/m/K, indicating that MC possesses a certain thermal insulation characteristic. The structure analysis shows that: 1) during F-T cycles, the change trends on the micro-structure parameters, macropores and particle size of MC are different; 2) among the many factors which could cause variations on the thermal conductivity of MC during F-T cycles, the variation on macropores could be the main factor.