Influence of Rubber and Mineral Admixtures on Selected Swelling Properties of Red Clay

Swelling and shrinking of soils is considered to be one of the main reasons of building damages. This problem concerns practically all fine soils in plastic or semi-solid consistency and becomes very intense in the case of montmorillonite or smectite clays. Reduction of soil expansiveness can be obtained by various methods: e.g. surcharge greater than swelling pressure or stabilization with additives such as lime, cement or polymers. In the last decades engineers have become interested in the use of waste materials in geotechnics, and thus such materials like fly ash, furnace slag or scrap tyre rubber are also now considered as valuable and eco-friendly admixtures that might be used to reduce expansiveness of soils. This paper presents a study on the influence of mineral and rubber admixtures on expansive properties of clay: swelling pressure p(s) and free swelling coefficient V-p. The experiments were conducted on red Triassic clay from Patoka in Poland mixed with rubber powder (0.1 - 1.0 mm) or granulate (1 - 5 mm). The rubber content applied was 10% by weight. Results revealed that admixture of rubber reduced the expansiveness of clay: p(s) decreased by 57% and 63% and V-p by 11% and 57% when coarser and finer rubber fraction was used, respectively. In order to check whether the observed decrease in swelling properties resulted from compressive characteristics of rubber, additional specimens were prepared in which the rubber grains were replaced by sand or gravelly sand in the same proportion by weight and by volume. It turned out that the mineral additives can reduce the expansiveness of Red Clay even more effectively than rubber, proving that in this method of stabilization the mechanism of replacement plays more important role than the lower stiffness of the added grains. However, independently of the type of the additive, better results can be obtained when grading of the admixed material is finer.