Effect of purity of lime on strength and durability of soil-lime mixes

Indian Roads Congress (IRC) as per IRC:SP:20-2002 and Ministry of Road Transport and Highways Specifications for Road and Bridge Works as per Clause 402.2.2 specifies that lime of 70% purity should be used for soil stabilization to get the desired results. However, it has been observed that lime of such purity is generally not available. In case lime of such specification is arranged from specific mines, the cost of the same works out to be even more than the ordinary Portland cement. It may make the cost of the project prohibitive. To evaluate the effect of purity of lime on strength and durability characteristics of different soils, three types of soils generally available in the country were chosen. The soils considered for the study are fine grained soils, i.e. silty soil, black cotton soil and clayey soil. The study was conducted with laboratory grade lime and commercially available limes from different locations. The purity of laboratory grade lime was 87% and of commercial lime "I" & "2" was 50% and 17% respectively. To assess the strength and gain and durability of soil-lime-mixes, the laboratory experiments were planned to compare the effect of lime of different purities on stabilized soils in terms of unconfined compressive strength (UCS) and durability. It was observed that lime of low purities with certain percentage and curing periods also satisfy the UCS criteria for use in sub-base/base layer of pavement. However, when the durability tests were carried out on three type of soils stabilized with limes of different purities, it was found that silty soil stabilized with lime of different purities could withstand the durability cycles with certain percentage of lime, but clayey soils and black cotton soils stabilized with laboratory grade lime and lime of less purity could not withstand durability test. The findings of the study indicate that the criterion of 70% purity of lime can be relaxed for silty type of soil for the purpose of lime stabilization.