Abstract
Concrete waste from the construction industry has significantly increased in the last decade, causing serious environmental issues. The employment of concrete waste within the construction sector would help preserve natural resources and ensure proper solid waste management. Hence, the work presented in this thesis aims at assessing the potentials of waste concrete elements for the production of construction materials. The study was conducted in two phases.
In Phase I, new models for predicting the compressive strength, splitting tensile strength, and elastic modulus of recycled concrete containing non-treated and treated coarse recycled concrete aggregates (CRCAs) were developed using an empirical approach. Validation of the models using independent data sources from the literature gave realistic predictions. The proposed models may be employed to convert standard strength grades of conventional concrete made with natural coarse aggregate (NCA) to the equivalent grades for recycled concrete made with CRCA. The performance of standard models for application to predict the elastic modulus of CRCA concrete was also evaluated in Phase I. Five (5) well-known models, as described in ACI 318 (2008), BS 8110 (1997), CSAA 23 (1994), EC2 04 (2004), and SABS 0100 (1992) design codes, were evaluated. The findings showed that the various standard models need modification in order to be applicable to CRCA concrete. The changes need to take into consideration the partial substitution of NCA with CRCA, as CRCA concrete is usually designed by partially replacing NCA with CRCA.
Phase II of the study was done to evaluate the effect of ground granulated blast furnace slag (GGBFS) and fly ash (FA) on cement masonry mortar containing waste concrete powder (WCP), along with their economic and environmental benefits. Mortars were
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made using a binder-to-sand ratio of 1: 3. The cement was substituted with WCP at 0%, 15%, 30%, 40%, 60%, 75%, and 100% levels. Based on the compressive strength results obtained, a mortar mixture made with 40% cement and 60% WCP was selected for further study. Mortars were then prepared by replacing the content of cement with GGBFS or FA at 0%, 5%, 10%, 15%, 20%, and 25%. It was found that the mechanical properties of the mortars were enhanced when GGBFS and FA were used up to 15% and 10%, respectively. From the experimental results, the produced mortars could be utilized for masonry mortar types M, S, N, and O. Also, using WCP, GGBFS, and FA led to significant reductions in the cost and environmental factors of the mortars. Hence, the produced mortars provided the specified strength requirements as well as environmental and economic gains, making them sustainable.
In conclusion, the findings from this study would help to create awareness about the utilization of waste concrete elements, particularly CRCA and WCP, for the production of construction materials.