Mechanical and transport properties of concrete incorporating recycled crushed clay bricks as coarse and fine aggregates.

Recycling crushed clay bricks as both coarse and fine aggregates has shown promising potential for producing eco-friendly concrete, helping to reduce the industry's environmental footprint while promoting the sustainable reuse of waste materials. However, the inherent variability of these aggregates can lead to inconsistent concrete performance, emphasizing the need for a thorough investigation to assess their suitability for construction applications. For this purpose, a number of concrete mixtures incorporating crushed clay bricks as coarse and/or fine aggregates were produced and tested in this study. Specifically, four mixtures incorporating crushed clay coarse aggregate (CCCA) and another four incorporating crushed clay fine aggregate (CCFA), each at replacement levels of 25%, 50%, 75%, and 100% (by volume). Additionally, one mixture was fully developed using both CCCA and CCFA. For comparison, a control mixture containing 100% natural coarse and fine aggregates was also tested. The properties evaluated for all the developed mixtures included slump, dry density, water absorption, sorptivity, compressive strength, splitting tensile strength, flexural strength, abrasion resistance, impact resistance, ultrasonic pulse velocity, and Schmidt rebound hammer. All results were statistically analyzed to assess the effect of CCCA and/or CCFA on the test outcomes and their significance. The results indicated that replacement levels of CCCA up to 25% and CCFA up to 50% could offer a viable alternative to conventional natural aggregates, while minimizing the deterioration of concrete properties. At any same replacement level, CCFA generally outperformed CCCA, except in abrasion resistance, where CCCA mixtures exhibited better performance. As for the sorptivity, the CCFA improved the capillary structure of concrete leading to lower water ingress, while the CCCA resulted in larger capillary pores and higher sorptivity values compared to the control mix. Under impact loading, replacing more than 25% of the aggregates with either CCCA or CCFA resulted in a significant reduction in the energy absorption capacity of the specimens, thus limiting their suitability for applications exposed to high impact loads. However, combining both CCCA and CCFA at full replacement levels can effectively produce sustainable semi-lightweight concrete with strengths above 25 MPa, making it suitable for various structural applications, although its suitability for environments requiring high abrasion and impact resistance is limited. The findings also suggest that non-destructive tests such as the Schmidt hammer and UPV tests can be used for assessment, with the Schmidt hammer test providing more reliable results for evaluations and estimations. Statistical analysis showed that CCCA, CCFA, and their interaction significantly affected most concrete properties. However, their use resulted in higher variability than natural aggregates, especially in splitting tensile strength, abrasion, and impact energy tests. While CCCA reduces embodied energy compared to natural coarse aggregates, the use of CCFA increases it, though CCFA remains a sustainable alternative for natural sand, aiding in resource conservation.