Abdelgadir Abbas

Flexural Performance of Steel-Reinforced Recycled Concrete Beams

A new method of mixture proportioning is used to investigate the flexural performance of reinforced concrete beams made with coarse recycled concrete aggregate (RCA). In this method, RCA is treated as a two-phase material comprising residual mortar and natural aggregate; therefore, when proportioning the mixture, the relative amount and properties of each phase are considered separately. Several reinforced concrete beams are built and tested using concrete mixtures designed by the new method and their deflection; cracking, yielding, and ultimate moments; crack spacing; cracking patterns; and failure modes are studied. The results show that at both the serviceability and ultimate limit states, the flexural performance of beams made of RCA-concrete proportioned by the new method is comparable to that of beams made of conventional natural aggregate concrete; and the general flexural theory and current code provisions for flexural design are applicable, without alteration, to the reinforced recycled concrete beams.

Proposed Method for Determining the Residual Mortar Content of Recycled Concrete Aggregates

Recycling concrete from demolition of existing structures and using it as recycled concrete aggregates (RCAs) in structural-grade concrete have significant economic and environmental benefits. Currently, only a small portion of the concrete waste is reused in building construction, while most of it is used as either pavement base course or sent to landfills for disposal. The lack of confidence in the material properties of the concrete produced with RCAs is generally the main reason for its under-utilization in structural concrete. It has been demonstrated in the literature that the amount of residual mortar attached to the original (or “virgin”) aggregate particles is one of the factors affecting the material properties of RCAs. Therefore, before using RCAs in new concrete, it is crucial that the residual mortar content (RMC) is determined accurately; however, currently there is no standard procedure to determine this quantity. In this paper, an experimental method is proposed to determine the RMC of RCAs. The method comprises a combination of mechanical and chemical stresses that disintegrate the residual mortar and destroy the bond between the mortar and the natural aggregates. The mechanical stresses are created through subjecting RCA to freeze-and-thaw action, while the chemical degradation is achieved through exposure of the RCA to a sodium sulphate solution. The results of the proposed test procedure are validated by means of comprehensive image analysis. With the proposed approach, the attached residual mortar can be adequately removed, and the residual mortar content can be determined.

Environmental Benefits of Green Concrete

Of the approximately 11 million tonnes of annual solid concrete and demolition waste (C&D) in Canada, concrete accounts for about 52% by weight. However, most of this concrete is used as highway base or sent to landfills for disposal; only a very small portion of the concrete waste is reused in building construction. Considering the fact that usable natural aggregate (NA) supplies are diminishing, there will be a high demand for recycled concrete aggregates (RCA) to be used in the so called ldquogreen concrete (GC)rdquo. Using recycled concrete as aggregate will help reduce the total cost of concrete production because aggregates need not be hauled from remote locations, but obtained locally. The combination of RCA with significant quantities of fly ash or slag as replacement for Portland cement is particularly attractive from both economic and environmental perspectives. GC will reduce the demand for natural resources, the associated energy consumption, and green house gas (GHG) emissions required to produce aggregates and cement. These reductions can be considered as one of the construction industrys major contributions to Canadas GHG emission reduction objective. Although there are some guidelines/specifications established by different countries such as the UK and Japan, currently, there are no established guidelines for producing GC in Canada. This paper presents the environmental and economic benefits of increasing the use of GC in the construction industry and highlights the objectives of an ongoing research by the authors on GC.