Laboratory investigation of the strength, stiffness, and thermal conductivity of fly ash and lime kiln dust stabilised clay subgrade materials

Abstract

The effectiveness of Class-C fly ash (FA) (ASTM C-618) and lime kiln dust (LKD) used in clay pavement base materials stabilisation has been investigated in this research. Proctor compaction test, unconfined compression test, and non-destructive test (Briaud compaction device (BCD) modulus and thermal conductivity) were carried out on the chemically modified soil. Test specimens were reconstituted by static compaction, constructed at optimum water content, and tested at various curing periods. Test results revealed that the addition of Class-C FA up to 20 wt% could effectively increase the dry unit weight from 16.8 to 17.4 kN/m3 (105.0 to 108.3 pcf), improve the unconfined compressive strength (UCS, which increased from 181.2 to 497.2 kPa at the end of 28 days of curing), and raise the BCD modulus up to 40 MPa. The LKD was also found to be a good stabiliser for weak soil, which could raise the UCS and stiffness under relatively small mixing rations (4 and 8 wt%), but the dry unit weight decreased as the LKD mixing ratio increased. The thermal conductivity, however, decreased as the curing time and stabiliser mixing ratio increased. Parallel and series models were employed to understand the upper-and-lower bound of the mixtures' thermal conductivity. A thermal strength coupled empirical model which is based on the non-destructive testing results was developed to predict the UCS gain over curing time. The thermal conductivity and BCD modulus were also incorporated into a novel compaction quality check model. Based on the observed test data and regression analysis, both models were found to yield good results, indicating that they are robust tools for predicting the UCS and dry unit weight of chemically treated pavement base materials.