Recycled Materials in Portland Cement Concrete

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CAIT project no.: FHWA NJ 2000 003

Fiscal Year: 1996/1997

Status: Final

Rutgers-CAIT Author(s): Ali Maher, Patrick J. Szary, Farhad Ansari and Guan Yong Zhang, University of Illinois at Chicago, Allyn Luke, NJIT

External Author(s): Robert Baker, NJDOT



This report pertains to a comprehensive study involving the use of recycled materials in Portland cement concrete. Three different materials were studied including crushed glass (CG), street sweepings (SS), and recycled concrete (RC). Blast furnace slag was also considered as a cementitious additive for enhancing the durability characteristics of the mixture. This research was performed and completed earlier. Four reports were submitted covering literature survey, mix details and experimental results for the recycled materials in the study. However, in these studies, the NJDOT class A concrete was substantially modified in order to establish an optimize mixture. The optimized mixture was used in conjunction with the recycled materials. This was done due to the fact that the researchers were aware of the deleterious effects of the recycled constituents on the Class A mix. However, NJDOT project engineers indicated that despite the outcome, they would like the experiments to also encompass standard class A concrete in conjunction with the recycled materials. The project was extended at no additional cost and a second series of experiments were performed with mixtures that included class A concrete as a base material. The bulk of this report pertains to these results. The research phase corresponding to class A mixtures is designated as Phase-A, and the earlier research with optimized proportions corresponds to Phase-B. Representative results from the earlier study (Phase B) for the crushed glass and recycled concrete are also given for completeness.

Based on the results of this study, it is recommended that street sweepings shall not be used with any type of concrete mixture due to its variability. Crushed glass and recycled aggregate concrete shall be used with optimized cementitious mixtures and not standard class A concrete. These recommendations are mainly based on the decreased durability attributes of such materials. Even with the optimized cementitious mixtures, the reduction in compressive strength as a function of curing age for crushed glass concrete points at uncertainty regarding the long term load bearing characteristics of such material. It is recommended that the crushed glass concrete not be used in structural and load bearing applications. Recycled concrete can be used for secondary applications and it possesses enhanced durability attributes in optimized, cementitious mixtures.