Volumetric stability of concrete using recycled concrete aggregates

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Recent studies show that many pavements built in the United States of America using recycled concrete aggregate (RCA)-based concretes have experienced high amount of shrinkage cracking. Fresh and hardened concrete properties of RCA-based concretes are linked to the porosity and absorption capacity of the RCA aggregate. In this study, detailed evaluation of the porosity and absorption capacity using petrographic techniques of the selected aggregates was performed. This paper presents a study performed to evaluate the volumetric stability of RCA-based concretes using two types of locally manufactured RCA and one virgin aggregate type to assess the effect of recycling operations on the concrete performance. Concrete mixtures with water to cement ratio (w/c of 0.42 were prepared using the selected virgin aggregates and RCA. Fresh concrete properties such as slump and air content were assessed in addition to hardened concrete properties at 28 days such as compressive strength, flexural strength, and elastic modulus. One-dimensional shrinkage of the virgin aggregate and RCA-based concretes was also measured using sealed and unsealed specimens stored at 50% RH to assess drying and total shrinkage respectively. The difference between the sealed and unsealed prisms gave an indication of the drying shrinkage potential of both the RCA-based and virgin aggregate concretes. Restrained shrinkage behavior and its associated cracking susceptibility was evaluated using the ring test as per AASHTO PP 34. Petrographic studies showed that RCA-based aggregates exhibited high amount of porosity. In the volumetric stability evaluation, it was observed that the shrinkage behavior of RCA-based concretes was linked to the porosity and the amount of existing unhydrated cement material on the RCA through the use of scanning electron microscopy. For the same w/cm, it was observed that the RCA concretes containing slag components exhibited higher values of shrinkage strains in comparison with RCA concretes that were originally limestone aggregates. © 2009 Woodhead Publishing Limited.

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Brittle Matrix Composites 9