Effects of recycled concrete aggregates on properties of asphalt concrete: Fid-Bau Portal

Effects of recycled concrete aggregates on properties of asphalt concrete

Paranavithana, Sumeda / Mohajerani, Abbas

With the growth in world population, the amount of waste generation is increasing at an alarming rate. The number of remaining disposal sites is decreasing causing a blowout in the cost of waste disposal. To counter this trend, considerabel effort is being put into recycling waste. Recycled concrete aggregates (RCA) are produced by crushing demolished concrete elements. RCA differ from fresh aggregates due to the cement paste attached to the surface of the original natural aggregates after the process of recycling. This highly porous cement paste and other contaminations contribute to the lower particle density and higher porosity, variation in the quality of the RCA and the higher water absorption. This paper presents some of the results of an investigation on the possible application of RCA in asphalt concrete. It was found that all the volumetric properties (except the percentage of air voids), resilient modulus and creep values of asphalt specimens containing RCA as coarse aggregates were relatively lower compared with the values found for similar specimens made with only fresh aggregates. Some of these measured properties were within the acceptable recommended limits, for the RCA sample used in this study.This paper has presented some of the experimental results obtained in an investigation of the effect of recycled concrete aggregates (RCA) on the properties of asphalt. Properties of asphalt containing RCA as coarse aggregates and asphalt containing only fresh aggregates (control mix) were analysed. It was found that the bulk density, voids in mineral aggregates, voids filled with binder and film thickness in the compacted asphalt specimens, containing RCA, were lower than those for the control mix. And the air voids were higher for specimens containing RCA. The resilient modulus of asphalt containing RCA decreased with the increase in binder content and these values were significantly lower than the corresponding control mix values. This could be due to the addition of low strength mortar together with the use of relatively lower quality aggregates in the mix. However, those values were within the acceptable limits recommended by the Austroads Pavement Research Group. The resilient modulus increased with the increasing level of compaction. The experimental results found for unbound RCA, used in this study, were compared with those found for fresh crushed basalt aggregates. Due to the highly porous, low dense cement mortar attached onto RCA particles, the particle densities of RCA were relatively much lower and the water absorptions of RCA were much higher. Stripping potential of RCA was found to be significantly higher and RCA samples tested were of greater variation in strengths under wet and dry conditions. The results found in this study are encouraging, however, further investigation is required to examine the findings in this research using different samples of recycled concrete aggregates and to investigate the application of current mix design methods for asphalt mixtures containing RCA.