Panu Promputthangkoon and Bancherd Kanchanachetanee

pp. 579 - 587

Abstract

This research attempts to overcome the two problems of low-quality soil and a growing number of discarded tyres by
mixing low-CBR soil with recycled tyre chips. The compound soil-tyre chips was then stabilised by Portland cement with the
aim of using them as a new material in road construction in order to reduce the occurrence of shrinkage cracks. To achieve
the purposes of this research three standard geotechnical testing programmes were employed: (1) modified compaction tests,
(2) California Bearing Ratio tests (CBR), and (3) unconfined compression tests. The modified compaction test results proved
that for the mixtures having very low tyre chips and cement content, the behaviour is very complex. It was also observed that
the greater the percentage of rubber added the lower the global density. However, this is predictable as the specific gravity
of the rubber is much lower than that of the soil. For the relationship between the optimum moisture content (OMC) and the
cement content, it was observed that there is no clear pattern.
For the specimens having no cement added, the CBR for unsoaked specimens was observed to be greater than that for
soaked specimens. However, when the cement was introduced the CBR test showed that the resistance to penetration for the
soaked specimens was significantly greater, indicating the effects of cement added on the strength. In addition, it was found
that the CBR values for both soaked and unsoaked specimens gradually increased with the increase of cement content.
Lastly, the unconfined compressive strength progressively increased with the increased percentage of cement.