INVESTIGATING THE MARSHALL STABILITY REQUIREMENTS OF ASPHALT CONCRETE MIX WITH GROUND SCRAP TYRES AS AGGREGATE

Ground scrap tyres can be used in asphalt mixtures either as a binder modifier (wet process) or as a fine and/or coarse aggregate replacement (dry process). To evaluate the effect of rubber-bitumen interaction on the dry processed mixtures, a laboratory investigation was conducted on a range of dense graded dry process with 4.75mm, 2.36mm and 0.600mm particle size rubber modified asphalt mixtures containing 0 (control), 2, 4 6, 8 and 10% ground rubber by aggregate mass. The mixtures were subjected to Marshall Stability test. The stability, flow, percentage air void, unit weight, voids in mineral aggregate, and specific gravity were determined. The results indicated that, in general, as the rubber percentage increase, the stability, unit weight and specific gravity value decrease. In addition, as the rubber content increase, the flow of specimen also increases. The result also showed that as the rubber content increases the percent air voids and VMA increase for 4.75mm RPS and 2.36mm RPS, while for 0.600mm RPS the reverse was the case. Generally as regards the Marshall Stability tests, the rubber modified specimens remained intact after failure. Such behavior will be beneficial for a pavement that requires good impact resistance properties. The use of 10% 4.75mm, 4% 2.36mm or 4% 0.600mm RPS by weight of aggregate mass in asphaltic concrete is recommended for medium traffic volume pavements.