The effect of Reclaimed Asphalt Pavement and crumb rubber on mechanical properties of Roller Compacted Concrete Pavement

A limited number of works have been done on the effect of waste materials such as the Reclaimed Asphalt Pavement (RAP) and crumb rubber on the performance of Roller Compacted Concrete Pavement (RCCP). Although the focus of the majority of these investigations is on identifying mechanical properties of mixes containing waste materials, the judgment about the effectiveness of these waste materials on improving mechanical properties of the mixes is suspicious and questionable. Considering that the traditional methods mainly highlight the flexural and compressive strengths of these concrete mixtures, the present study is conducted to investigate the effect of waste material incorporated RCC mixes with RAP or crumb rubber, as the partial replacement of aggregates, on mechanical properties of concrete pavements by measuring absorbed energy and toughness of these mixes. By putting this method into practice, the 56 RCCP mixtures with different mix designs and waste material contents from 25% to 100% RAP and 5% to 25% crumb rubber were constructed in the laboratory. Next, these mixtures were examined to determine the efficacy of incorporating these waste materials in concrete pavements. Three 70 × 70 × 240 mm3 beam specimens were fabricated for each mix combination for conducting a 4-point beam test. The results reveal that the compressive and flexural strengths of RCC specimens are slightly (around 5%) improved by using 5% rubber content. In contrast, a high decrease in compressive and flexural strength of specimens observed while increasing RAP content. Nevertheless, as mentioned earlier, these conventional laboratory tests could not provide a proper criterion for determining optimal mix combination. Therefore, a secondary test was conducted for measuring absorbed energy and toughness of mixes, which are promising criteria for RCC specimens with the waste material combination. The results show an increasing trend in toughness and energy absorbency of waste incorporated specimens. Hence, energy absorbency concept was highlighted by developing several relationships using Analysis of Variance (ANOVA) and regression analysis. The regression results indicate that incorporating up to 10% rubber and 50% RAP could be cost effective and beneficial to prolong pavement's life through increasing toughness and energy absorbency of the mixes.