Effects of mellowing sulfate-bearing clay soil stabilized with wastepaper sludge ash for road construction

The main objective of this research was to investigate the effect of mellowing on the swelling properties of stabilized Lower Oxford Clay (LOC), a sulfate-bearing clay soil that has caused concern in the past due to expansion upon stabilization. Two stabilizers were used, quicklime and a more sustainable stabilizer — wastepaper sludge ash (WSA), an industrial by-product used on its own and in combination with either quicklime (CaO) or ground granulated blastfurnace slag (GGBS). Quicklime was used on its own as a control. Compacted cylinders of LOC stabilized with the various stabilizers were made either mellowed (compacted 3 days after mixing with stabilizer) or unmellowed (compacted immediately after mixing with stabilizer). The linear expansion of the stabilized cylinders during moist curing and subsequent soaking was monitored for a total of 100 days. The results obtained showed that the linear expansion of unmellowed stabilized LOC was significantly reduced, and thus in terms of swelling potential, mellowing was not beneficial in the LOC system investigated. The results observed also suggest that there are technological, economic as well as environmental advantages of utilizing WSA and similar industrial by-products, in the stabilization of sulfate-bearing and other clay soils, as an alternative to the traditional stabilizers of lime and/or Portland Cement. ► Sulphate bearing clay soil, Lower Oxford Clay (LOC) was stabilized with CaO, Wastepaper sludge ash (WSA) and slag (GGBS), by-product from industrial waste. ► The effects of mellowing on the strength and swelling properties of stabilized soil were studied. ► For sulfate bearing clay soils, mellowing can be a significant disadvantage due ti increased swelling potential accompanied by the reduction in strength.