Hindawi Publishing Corporation Advances in Materials Science and Engineering Volume 2013, Article ID 636034, 8 pages http://dx.doi.org/10.1155/2013/636034 Research Article Towards Better Understanding of Concrete Containing Recycled Concrete Aggregate Hisham Qasrawi and Iqbal Marie Civil Engineering, Faculty of Engineering, e Hashemite University, Zarqa 13115, Jordan Correspondence should be addressed to Hisham Qasrawi; hisham qasrawi@yahoo.com Received 20 May 2013; Revised 27 August 2013; Accepted 27 August 2013 Academic Editor: Amit Bandyopadhyay Copyright © 2013 H. Qasrawi and I. Marie. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. he efect of using recycled concrete aggregates (RCA) on the basic properties of normal concrete is studied. First, recycled aggregate properties have been determined and compared to those of normal aggregates. Except for absorption, there was not a signiicant diference between the two. Later, recycled aggregates were introduced in concrete mixes. In these mixes, natural coarse aggregate was partly or totally replaced by recycled aggregates. Results show that the use of recycled aggregates has an adverse efect on the workability and air content of fresh concrete. Depending on the water/cement ratio and on the percent of the normal aggregate replaced by RCA, the concrete strength is reduced by 5% to 25%, while the tensile strength is reduced by 4% to 14%. All results are compared with previous research. As new in this research, the paper introduces a simple formula for the prediction of the modulus of elasticity of RCA concrete. Furthermore, the paper shows the variation of the air content of RAC. 1. Introduction he average world production of concrete in our rapid developing industrialized world is about 6 billion tons per year [1] which has an adverse impact on the environment. Since earth is the source of the aggregates (either natural or crushed), then obtaining these amounts would have an adverse efect on the environment. Furthermore, demolishing concrete structures and dumping the concrete rubbles would aggravate the problem. herefore, recycling construction material plays an important role to preserve the natural resources and helps to promote sustainable development in the protection of natural resources; thus reduces the disposal of demolition waste from old concrete [2]. Hence, recycling concrete wastes becomes important in getting rid of the demolished concrete, which accumulates with time. For example, the amounts of demolished buildings in Europe amount to around 180 million tons per year [3]. Old concrete and masonry that have “reached the end of the road” can be recycled and used not only as aggregate for new concrete, but also for a number of other applications in construction [4]. For example, since 1982, the ASTM deinition of coarse aggregate has included crushed hydraulic cement concrete, and the deinition of manufactured sand includes crushed concrete ines [4]. Similarly, the U.S. Army Corps of Engineers and the Federal Highway Administration encourage the use of recycled concrete as aggregate in their speciications and guides [5]. Several references [3–12] have presented literature survey and research results in the ield of the use of recycled aggregate, concrete, and masonry and their efect on maintaining the environment. Based on these references, the advantages of using recycled aggregate in concrete can be summarized as follows. 1.1. Environmental Considerations. SBM [12] provided brief environmental considerations regarding the use of concrete, quoted in their own words: “In this time of increasing atten- tion to the environmental impact of construction and sus- tainable development, Portland cement concrete has much to ofer: (1) it is resource eicient-minimizing depletion of our natural resources; (2) it is inert, making it an ideal medium in which to recycle waste or industrial byproducts; (3) it is energy eicient, it is superior to wood and steel; (4) it is durable, continuing to gain strength with time; and inally (5) it is recyclable, fresh concrete is used on an as-needed