OPTIMISATION OF USED SHREDDED TYRES AS FINE AGGREGATE REPLACEMENT FOR 15 MPA CONCRETE

The exponential growth in the random disposal of used tyres and the increased environmental threats that come with it is becoming a very serious concern in most developing countries especially those in Africa. This research investigated the use of waste tyres from landfills in Namibia as fine aggregate replacement for sand for 15 MPa concrete. Seven different concrete mixed designs containing 2%,4%, 6%, 8% and 10% percentage of shredded tyres was used to replace the same percentage of sand. Six mixed designs were pre-treated using sodium hydroxide (NaOH) solution while the seventh mixed design was untreated shredded rubber tyres at 4%. Destructive Compressive, tensile and flexural strength tests on the rubber tyres modified concrete was done. A non-destructive method of testing on rubber tyres modified concrete was also done. Using the 0% rubber as the control sample, results of compressive and tensile s t r e n g t h s decreased as the rubber tyre content increased while the flexural strength indicated no decrease as the rubber tyre content increased. On pre-treating the rubber tyre, results indicated that the strength of interfacial transition zone as well as the compressive and tensile strengths result improved compared to the unwashed rubber tyre modified concrete. Results of the flexural strength revealed no increase or decrease in results, when comparing the treated with the untreated rubber tyre content.