مقاومت و دوام بتن حاوی ترکیبات بتنی بازیافت شده Strength and durability of concrete containing recycled concrete aggregates

1. Introduction Coarse aggregates (CA) occupy the major share of concrete with respect to its volume. Several countries are currently facing shortage of natural aggregates and rely on imports to meet their demands. Rapid development and necessity for large scale infrastructure have resulted in indiscriminate and exploitation of natural rocks to meet the soaring demand for aggregates. Unplanned quarrying results in severe environmental degradation and also releases huge quantities of dust into the surroundings. Vibrations, pollution of air and water sources and landslides are some other impacts of unplanned quarrying. This calls for the adoption of greener construction technologies employing the use of artificial aggregates or recycled aggregates. Crushed concrete aggregates (CCA) are recycled aggregates obtained by crushing concrete waste from demolition sites, rejected precast members, laboratory specimens etc. Much of the construction and demolition wastes generated in India are currently dumped in landfills or low lying areas. Hence, utilization of crushed concrete aggregates derived from concrete waste is a value addition process and an eco-friendly alternative approach. The Indian Standard IS: 383 [1] permits the use of up to 20% recycled concrete aggregates in reinforced concrete constructions of grade M25 and below. The primary objective of this study is to identify the maximum aggregate replacement percentage for obtaining a strong and durable CCA concrete and to develop prediction models to estimate the strength parameters of CCA concrete. The influence of the variables on nine control concrete mixes was studied. The novelty in this paper is the development of empirical models to predict the mechanical properties of CCA concrete based on a wide range of test data and the detailed investigation on the durabilityproperties of CCA concrete. The usefulness of the proposed prediction models in the mix design of the concrete containing CCA aggregate is discussed in this paper.