Indian Journal of Engineering & Materials Sciences Vol. 17, December 2010, pp. 449-462 Recycled aggregate concrete (RAC) methodology for estimating its long-term properties Jorge de Brito & Ricardo Robles Instituto Superior Técnico (IST), Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Lisbon, Portugal Received 12 January 2009; accepted 13 October 2010 In this paper, a methodology for prediction of long-term properties of recycled aggregate concrete is presented, based on an extensive literature review of international experimental campaigns on this type of environment-friendly concrete. The methodology presented is based on the previous determination of the main properties of the aggregates (density and water absorption), primary and recycled, coarse and fine, and alternatively the 7-day compressive strength of concrete made with those aggregates. The methodology is validated, based on a graphical analysis of the most important properties of hardened concrete (compressive strength, modulus of elasticity, splitting and flexural tensile strength, shrinkage, creep, water absorption, and carbonation and chloride penetration depth). It is concluded that the methodology can predict the long-term performance of recycled aggregate concrete as compared with an equivalent conventional concrete and that this prediction can be used to adapt structural design to this material. Keywords: Recycled aggregates, Structural concrete, Performance early prediction, Sustainable materials The construction industry is one of the economic sectors that are more responsible for consuming natural resources and generating waste. Within the sector the activities related to the use of concrete, from production to demolition, play a paramount role. According to the North American organization, the Strategic Development Council 1 , around 6000 million tons of concrete is produced every year, which is equivalent to 1 ton per inhabitant of this planet. To guarantee these levels of concrete consumption equivalent quantities of materials are needed that, in “traditional” processes, are limited and non-renewable natural resources, such as sand, gravel and other aggregates, mostly from stone quarries. On the other hand, the demolition of structures also causes a considerable environmental impact. Masood et al. 2 estimated that concrete demolition waste in the European Union and the United States of America has reached 100 million tons per year. The destination of this waste is presently one of the greatest difficulties and worries of the construction sectors, given the high costs of dumping and transportation and the scarcity of appropriate sites for receiving these materials. The use of aggregates from construction and demolition waste (CDW) in pavement beds is the most usual way of reusing this material. Even though considered as a valid reuse technique, it is not the best economic valorization of this resource and it is considered by many researchers to be a down-cycling process that depreciates the capacities of the material. But the production of structural concrete with recycled aggregates (RA), however, offers great potential and recycles the materials viably and effectively. This paper summarizes the knowledge acquired through past experimental research with recycled aggregate concrete (RAC) performed by researchers from various countries and statistically and graphically processing the published data 3 , aiming at correlating the RAC properties with the properties of the RA used to replace primary aggregates (PA). The data collected is then systemized and some of the results in the field of structural concrete are interpreted. This paper describes the methodology adopted in the data processing that leads to the estimation of the long-term behavior of RAC. A parallel study was performed using experimental results from Portuguese researchers 4 . The graphical analysis of the results of the experimental campaigns followed a sequence of steps in which the absolute values of the properties of the recycled aggregate concrete (RCA) mixes were converted into values relative to those of a reference concrete (i.e. a concrete mix without any recycled aggregates, designated RC) with the same size distribution of aggregates, workability (slump value
Recycled aggregate concrete (RAC) methodology for estimating its long-term properties
May 19, 2023
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