Mechanical behaviour and durability performance of concrete containing recycled concrete aggregate

[摘要] ENGLISH ABSTRACT: A major challenge for our society is the protection of the environment. Some of the importantissues are the reduction in the consumption of energy and natural raw materials, as well as theincrease in consumption of waste materials. At present these topics are getting considerableattention as part of sustainable development programs. The use of recycled concrete aggregates(RCA) from construction and demolition waste (C&DW) in construction, as alternative to virgin(natural) aggregates, has strong potential. The use of RCA preserves natural resources andreduces the space required for the disposal of RCA in landfill. It is estimated that 16 thousandmillion (billion) tons of concrete (and 25 billion tons of aggregate) were used in 2010. Of the 2-3billion tons of C&DW which are produced worldwide every year, South Africa contributes 5-8million tons. This amount is increasing rapidly every year. Significant amounts of demolishedconcrete find their way to landfill sites. A solution for excess waste production would be theutilization of RCA together with an improvement in the final quality of RCA. It might be animportant breakthrough for our society in our attempt towards sustainable development.Worldwide, infrastructure has developed a great deal since the beginning of the twentiethcentury. Much of the core infrastructure, including roads, bridges, water systems, and sewers,was put in place during the first half of that century. Aggregates used as construction materials,as for instance in road pavements, or as an ingredient of concrete, are important components ofinfrastructure. Urbanization involves reduction of natural aggregate (NA) resources, butenvironmental concern and the rising cost of NA is the reason that recycled materials fromdifferent sources (like roads, buildings) are being used more and more with NA in newconstruction work.Environmental awareness is increasing in every country for many reasons and sustainabledevelopment is demanded of all industries, including the building and construction industries. Bynature, construction is not environmentally friendly, and sometimes it also changes the behaviorof nature in many ways. Recycling is one of the most important ways to minimize the waste thatcomes from different sources, thereby avoiding repetition of, and additional environmentallyhazardous practices. It may create new wealth by diminished transport and production costs andsparing of landfill site space and cost. It has the potential to extend the life of natural resourcesby adding a source of material, thereby reducing environmental interference and impacting onnearby construction sites, all of which improve sustainability of our natural resources.Much research on the uses of RCA has been performed during the last few decades. In fact, mostof them showed that the strength class of recycled aggregate concrete (RAC) is adequate for useas structural concrete although volume changes in and durability performance of RAC incomparison with natural aggregate concrete (NAC) are still being debated and researched. Someresearchers found that the durability of concrete produced with RCA is inferior, but others havefound it to be sufficient for use in structural concrete. The fact that an insufficient number of studies have been carried out on the durability aspects, has limited the use of RCA as material forroad construction.The aim of this study is to determine the suitability of using the RCA in structural concrete basedon its strength, stiffness, dimensional stability and durability. Three types of RCA designatedRCA1, RCA2 and RCA3 in this study, were taken from three different sources. These materialswere tested to establish their mechanical characteristics for use as aggregates in concrete. In theexperimental program RCA was used at replacement percentages of 0%, 30% and 100% to(partially) replace NA in order to study its suitability as aggregate in concrete, and to what levelof NA replacement its behavior is satisfactory for structural application.A single compressive strength class was studied, due to the limited time. By performing tests ofcompressive strength, Young's modulus, creep, shrinkage, and durability performance, it hasbeen found that selected types of RCA show a real possibility for use as aggregate in concrete.When concrete with a RCA replacement of 100% was compared with NAC100% there was asmall decline in strength, but when concrete with a RCA replacement of 30% was compared withNAC100% the results showed almost equal strength. A slight reduction in durabilityperformance was found for RAC30% compared with NAC100%, but similar dimensionalstability performance in terms of specific creep and drying shrinkage was measured forRAC30% and NAC100%. Based on detailed experimental results obtained from this thesisproject, a number of recommendations have therefore been made for RCA characteristics thatwill be used in concrete mixes also taking into account the quality of RCA. Some suggestions areproposed based on the mechanical properties and durability of the concrete. In the finalconclusions, future studies on RCA properties are suggested, which would help us in increasingour knowledge in the application of RCA, and which may lead to the optimal production ofstructural concrete in a sustainable way. In general the use of RCA in concrete is feasible andgood quality RCA at 30% replacement of NA may be suitable for any kind of structural concrete.

[发布机构] Stellenbosch University