Specimen size effect on compressive and splitting tensile strengths of sustainable geopolymeric recycled aggregate concrete: Experimental and theoretical analysis

The use of industrial solid wastes (e.g., slag, fly ash) and recycled concrete aggregate (RA) to manufacture geopolymeric recycled aggregate concrete (GRAC) has been proved as a sustainable and environment-friendly approach for the concrete industry, and has received an extensive prospect. Understanding the specimen size effect of GRAC is fundamental and essential in the entire design and analysis of concrete components and structures. This paper presents an experimental study on the specimen size effect on compressive and splitting tensile strengths of GRAC, with the influence of RA replacement ratio and water-to-binder (w/b) ratio emphasized. A total of 168 GRAC cubes with four different specimen sizes (70.7, 100, 150 and 200 mm) are tested. The results show that the compressive and splitting tensile strengths of GRAC decrease with increasing RA contents due to the increased amount of defects, with the decreasing amplitudes of about 4%-30.4% for compressive strength and 2.96%-34.91% for splitting tensile strength, respectively, except that their size effect becomes more apparent. While the strengths and specimen size effect degrees of GRAC all decrease with the increase of w/b ratio. Based on Weibull's, Bazant's and Capinteri's size effect laws (SELs), analytical models for SELs of compressive and splitting tensile strengths of GRAC are respectively established. The comparison results indicate that the Bazant's SEL is more suitable for the cubic compressive strength of GRAC, while the splitting tensile strength using Weibull's statistical SEL achieves the most accurate prediction results. Moreover, conversion factors are suggested for the transformation of the compressive and splitting tensile strength measurements of GRAC. Finally, a life cycle assessment method is conducted to evaluate the carbon emission potential of GRAC, which is proven to be a green and low-carbon construction material with an over 60% carbon reduction compared to cement-based plain concrete.