This paper reviews the effect of incorporating recycled aggregates, sourced from construction and demolition waste, on the carbonation behaviour of concrete. It identifies various influencing aspects related to the use of recycled aggregates, such as replacement level, size and origin, as well as the influence of curing conditions, use of chemical admixtures and additions, on carbonation over a long period of time. A statistical analysis on the effect of introducing increasing amounts of recycled aggregates on the carbonation depth and coefficient of accelerated carbonation is presented. This paper also presents the use of existing methodologies to estimate the required accelerated carbonation resistance of a reinforced recycled aggregate concrete exposed to natural carbonation conditions with the use of accelerated carbonation tests. Results show clear increasing carbonation depths with increasing replacement levels when recycled aggregate concrete mixes are made with a similar mix design to that of the control natural aggregate concrete. The relationship between the compressive strength and coefficients of accelerated carbonation is similar between the control concrete and the recycled aggregate concrete mixes.

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Carbonation behaviour of recycled aggregate concrete

Laboratory tests are performed to investigate the effects of a new method of mixture proportioning on the creep and shrinkage characteristics of concrete made with recycled concrete aggregate (RCA). In this method, RCA is treated as a two component composite material consisting of residual mortar and natural aggregate; accordingly, when proportioning the concrete mixture, the relative amount and properties of each component are individually considered. The test variables include the mixture proportioning method, and the aggregate type. The results show that the amounts of creep and shrinkage in concretes made with coarse RCA, and proportioned by the new method, are comparable to, or even lower than, those in similar concretes made entirely with natural aggregates. Furthermore, it is demonstrated that by applying the proposed “residual mortar factor” to the existing ACI and CEB methods for calculating creep or shrinkage of conventional concrete, these methods could be also applied to predict the creep and shrinkage of RCA-concrete.

Creep and drying shrinkage characteristics of concrete produced with coarse recycled concrete aggregate

This paper presents a review of the literature published so far on the use of fine aggregates from construction demolition waste used as a partial or total replacement of fine natural aggregates in concrete production. The review presents the initial works on this subject and an overview of the existing regulations. It goes on to describe the production, treatment and properties of the fine recycled aggregates (FRA). The most suitable mixing techniques for concrete with this type of aggregates are then discussed. The properties of these concrete mixes are analysed in detail, after which a few examples of structures with this type of concrete are described and compared. The acquisition of fine natural aggregates and the dumping of the fine fraction of construction and demolition waste are two serious environmental problems that can be solved simultaneously by using FRA in concrete production, a subject that is lagging behind the use of the corresponding coarse fraction.

Concrete with fine recycled aggregates: a review

Prediction of the shrinkage behavior of recycled aggregate concrete: A review

Recycled aggregates may make an important contribution toward decreasing the adverse consequences of the production and the dumping of construction and demolition waste (CDW) on the environment. The results of the experimental research work carried out at Lisbon’s Instituto Superior Tecnico and Laboratorio Nacional de Engenharia Civil are presented in this article. Normalized laboratory tests to assess the performance of standard mortars were used to demonstrate the technical feasibility of recycling the waste produced by the ceramics industry and from the demolition of red-clay bricks or tiles to produce mortars with less/no consumption of natural aggregates. Results are very promising up to a replacement ratio of sand with ceramic waste of at least 20%. The paper presents useful data for the ceramics industry, builders and mortar manufacturing companies in terms of minimizing the impact of CDW and using eco-efficient materials.

Recycled Red-Clay Ceramic Construction and Demolition Waste for Mortars Production

Quality of concrete with recycled aggregate is generally lower than that of virgin aggregate. The main reason is that, recycled aggregate with its higher water absorption property has more porous mortar matrix around than that of the virgin aggregate and hence develops an inferior bond. In order to improve the quality of recycled aggregate concrete, an innovative method is proposed in this paper. High quality recycled aggregate concrete (HiRAC) can be obtained through a decompression and rapid release (DC-RR) procedure applied after normal mixing of concrete with recycled aggregate. Through the DC-RR procedure, the quality of transition zone between aggregate and cement matrix can be dramatically improved. In this paper, experimental studies are described on the effectiveness of DC-RR procedure on some of the mechanical and physical properties of recycled aggregate concrete. It was found that, by applying the DC-RR procedure, compressive strength of recycled aggregate concrete can be increased by about 20%; creep and carbonation depth can be reduced by about 20% and 30%, respectively.

H Tamura

Papers

High Quality Recycled Aggregate Concrete (HiRAC) Processed by Decompression and Rapid Release