Properties of RCA concretes mixed with cement paste dissociation agent

Abstract

Due to environmental regulations, difficulty in quality control, and decrease in strength properties, the use of recycled concrete aggregate (RCA) has been limited to nonstructural application, despite its economical and eco-friendly benefits. The attached residual mortar (RM) in the RCA unfavorably affects basic aggregate material properties such as density, absorption, porosity, etc. Meanwhile, a cement paste dissolution agent (CPDA) in concrete mix is known to help dissolving the RM within limits and enhance the mechanical properties of RCA concrete. Thus, our study aims at assessing the effect of the CPDA on mechanical strength and drying shrinkage properties of RCA concrete. Two experimental series were carried out. For a first series, a total of three mixes were prepared for typical paving concrete with 100% replacement of the natural coarse aggregate with the RCA. The CPDA ranging from 0-5% by mass of cement has been utilized in the RCA mixes. Test results showed that the addition of 2.5% of CPDA as chemical admixtures in the RCA concrete mixes helps improvement of compressive strength, flexural strength, and elastic modulus properties. Next, a total of nine mixes were proportioned by th the conventional ACI volume mix design and the EMV mix design for typical PC culvert. In the second test series, spray coating the RCAs with CPDA solution for two days before mixing helps decreae of drying shrinkage.