Influence of Ceramic Wastes as a Recycled Coarse Aggregate with Different Maximum Sizes on the Concrete

Natural raw resources needed for concrete construction are continuously being depleted as a result of infrastructure development that is increasing. As a result, waste material substitutes are highly favored because they adopt a sustainable strategy.

In this study, the possibility of substituting natural coarse aggregates with coarse aggregate made from ceramic wall tiles with three different maximum aggregate sizes (12.5, 19, and 25 mm) in three partial replacement levels of natural coarse aggregate by (25, 50, and 75%) was investigated.

Concrete's hardened density, compressive and splitting tensile strengths, ultrasonic pulse velocity, water absorption, and volume of permeable pores were all tested experimentally.

Results indicated that with the increment of the maximum aggregate size, each of the hardened densities, the compressive and splitting tensile strengths and the rate of water absorption diminished while pulse velocity enhanced, regardless of the substitution rate of ceramic aggregate. However, for all maximum aggregate sizes, the mixture containing 25% ceramic coarse aggregate showed a small improvement in mechanical properties. Compared to the reference mixture, which had compressive strengths of 29.31, 38.73, and 47.13 MPa at 7, 28, and 90 days for the 12.5 mm maximum aggregate size, the improvement ratios were 8.9%, 3.7%, and 2.7% at 7, 28, and 90 days, respectively. Moreover, because of increased heterogeneity, internal bleeding, and the development of microcracks in the larger coarse aggregate sizes, concrete with lower ceramic coarse aggregate sizes has a stronger bond than that of the latter. Results also indicated that the mechanical performance of concrete mixtures having ceramic aggregate slightly improved with 25% ceramic coarse aggregate, then lowered in the mixtures with 50% and 75%, consecutively, at all ages. Concrete using ceramic aggregate displays a poor transition zone because of the improper binding between the paste and the coarse ceramic aggregate caused by the aggregate's porcelain texture. Additionally, the water absorption of concrete mixtures containing ceramic aggregate increased with the increase in the percentage of ceramic coarse aggregate.

The employing of ceramic waste aggregate was shown to contribute to sustainable development and a cleaner environment by producing sustainable concrete from the recycling of ceramic wastes. Each of the hardened density, compressive strength, splitting tensile strength, and water absorption of concrete mixtures decreased and the pulse velocity enhanced as the maximum aggregate size increased. The mechanical properties decreased at all ages in the mixtures containing 50 and 75% of the aggregate, whereas they slightly increased in the mixture containing 25% of the aggregate.