Motivations for adopting recycled concrete as an aggregate source include the preservation of natural resources, effective utilization of the growing waste stream and financial and energy savings. Currently the practice of using RCA in South Africa is infrequent and the use of recycled concrete as an aggregate source in structural concrete application is rare. To make RAC feasible, its properties must be related to the properties of concrete that does not utilize the recycled aggregates. In response to this need, this dissertation was undertaken to investigate the feasibility of using RCA as a viable alternative to NA in the production of concrete manufactured in a conventional ready-mix concrete plant. Aggregate properties and hardened and fresh concrete properties of RCA concrete were studied and compared with the associated properties of NAC. Results indicated that RCA is a viable alternative to NA in the production of concrete. Furthermore, it was confirmed that the properties of RCA dictate the hardened properties of concrete and that RCA from certain sources limited the resulting possible strengths of concrete produced from it.
University of Stellenbosch Page 12 Many studies dealing with the physical and mechanical properties of RCA and their durability performance have been carried out in the world. As far as the author could establish, the first research on RCA in South Africa was done at University of Cape Town in 1984 by Frick. Another study was done at the same university in 2004 by Benjamin. Studies from the University of Pretoria by Kearsley and Mostert, (2010) also show a better performance of RCA in concrete. But there are no guidelines for using RCA in concrete. However, there are few studies that attempt to forecast future trends of RCA when used in structural concrete and this study aims to fill this gap.
1.11. BRIEF CONCLUSION
The world population and the demand for construction materials are increasing at the same tempo. In order to meet the present demand, there is also an increase in the demolition of old structures and their replacement by new ones. As a result, huge amounts of C&DW waste are coming from old structures. It was common practice in many countries to dump this waste on landfill sites, which occupied large areas of these countries. From the middle of last century, research has been carried out to find a way to utilize these waste materials in construction work. This practice not only saves our environment but also saves costs and energy in many ways. But as the present environment has changed largely by changing human activities, people were forced to change their way of thinking such as to reuse old materials and many countries are now reusing C&DW in many fields. Total replacement of NA by RCA may not be suitable for all kinds of construction work but a certain amount of RCA will be suitable for new construction as it does not significantly change the properties of the final product.
University of Stellenbosch Page 13
CHAPTER - 2
LITERATURE REVIEW AND BACKGROUND OF RECYCLED
CONCRETE AGGREGATE
2.1. INTRODUCTION
The literature review presents the current state of knowledge and examples of successful uses of alternative materials in concrete technology and in particular the use of RCA as a coarse aggregate fraction in non-structural and structural concrete. It also presents a review of available literature on RCA properties including particle size distribution, density and water absorption and identifies the need to investigate porosity and possible chemical contamination of the aggregate.
A comparison between conventionally-used aggregate in concrete technology and RCA is made, based on basic engineering properties. Furthermore, accounts of data, opinions and experience gained from successful applications of RCA as coarse aggregate in concrete production are presented, and characteristics of RAC are compared with those of NAC. An analysis of differences between NAC and RAC is presented in a range of physical, mechanical and acoustic properties.
Present articles on RCA indicate that concrete from demolition work has been crushed and re- used economically especially in large urban areas. The increasing cost of carting the rubble to a distant dumping site and the high cost of new aggregates make the recycling of old concrete a viable proposition. It is crushed and screened, and a proportion of new materials may be added to obtain the required grading. Some articles suggest that slightly lower strength may be obtained from concrete made with RCA than from similar concrete made with fresh aggregates, but this can be allowed for in the design. The applications of recycled aggregate in the construction arena are very wide. There are many tests based on the use of recycled aggregate that have been carried out all over the world during the last few decades. The main aim of that testing of the recycled aggregate is to determine the strength characteristic and whether the recycled aggregate is suitable for use in the construction arena. The research reports on RCA show good performance in many fields including that of structural concrete. Successful research has been achieved in many countries in Europe, UK, USA, Australia, China and Japan. There is little research on RCA in South Africa which might be the reason RCA is not popular for use in structural concrete. However those few researches show good performance of RCA when compared with NA in a certain strength class.
University of Stellenbosch Page 14 This chapter presents literature reviews on the effects of various factors on the recycled aggregate based on research from those countries mentioned previously. The background information reviewed in this chapter formed the basis for a formulation of the hypothesis and objectives of this research project. Some of the literature reviews on recycled aggregate are shown below.