Factorial Design for Studying the Properties of Recycled Aggregate Concrete Exposed to Aggressive Media

Abstract

Recycled Aggregate Concrete (RAC) mixes (1.15: 2.3: 4.6) cement: fine aggregate (sand): coarse aggregate (demolition concrete waste), water / cement (0.5), and 50 % demolition aggregates were prepared according to standard procedure. The resistance of the recycled aggregate concretes towards chemicals was investigated throughout the attack of (Acid: acetic Acid HAC, and salt: Sodium Chloride NaCl) solutions. The test was carried out based on adopted experiments designed using Response Surface Methodology (RSM). A 2-operating parameter central composite design was adopted to study the impact of concentration of the HAC and NaCl solutions (0.1-0.45) Molar, and immersion period (0.57-6.9) day of the (RACs) specimens on weight loss, compressive strength and density. The results obtained confirmed that weight loss increases, but both compressive strength and density decreases after the aggressive solutions attack, however HAC seemed more aggressive. The decrease in compressive strength was (2.8-42) % and (3.2-10.8) %, while the decrease in density was (0.72-2.05) % and (0.6-1.8) % for the samples immersed in HAC and NaCl solutions respectively. The mathematical models presenting the effect of concentration of the aggressive media and immersion duration on weight loss, compressive strength and density were estimated, and the effects were optimized and modeled.  The Analysis of Variance (ANOVA) revealed that an optimum compressive strength (37.8 and 34.8) MPa is obtained for the RACs immersed for 0.56 day at 0.1 Molar HAC and NaCl respectively.