Weak subgrade layers can decrease the designed service life of pavements significantly, and building of thicker top layers may be required. Weak local soil can be turned into an effective material by chemical soil stabilization. Class C fly ash (CF), class F fly ash (FF) and Portland cement (PC) have been used for soil stabilization. Fly ash has been used by the concrete industry, and its popularity in industry sometimes causes temporary shortages. PC is known to be the most expensive stabilizer among other stabilizers. In this research, lime sludge (LS) was investigated as an alternative stabilizer due to the benefits of using waste materials and the uncertain future of fly ash and PC. For this purpose, LS was used alone and with other stabilizers for soil stabilization, and unconfined compressive strength (UCS), freeze-thaw (F-T), wet-dry (W-D) tests and swelling test under F-T were conducted.

The UCS test results of the specimens cured up to 90 days showed that LS can be used alone to increase the strength of soil. The UCS test results of 7-day cured specimens pointed out LS can be mixed with CF and FF for further increase in strength. Using LS and PC together decreased the effect of PC because of a low pH environment. F-T test results of 7-day cured specimens showed that relatively higher strength losses were observed in the open system compared to the closed one. In addition, test results showed that there were no considerable benefits of using LS either alone or with other stabilizers on F-T durability. According to the W-D test results, the use of LS decreased the performance of PC and caused failures. Swelling test results under F-T showed that although the use of LS decreased the performance of other stabilizers, an optimum amount of LS (around 12%) could be used alone to reduce the swelling.