Synergistic Effects of Composite Expired Cement Fly Ash Cold-bonding Aggregates and Mineral Admixtures on Mechanical and Drying Shrinkage Performance of Sustainable Self-compacted Concrete

In this study, the combined effects of Expired Cement (EC) fly ash lightweight aggregate (ECFLA), silica fume (SF), and fly ash (FA) were utilized as sustainable alternatives for self-consolidating lightweight concrete (SCLC). The ECFLA was produced by a cold bonding pelletization process using 20% EC and 80% FA mixed by weight in a tilted pan and moisturized with water. A total of 12 mixtures were prepared in four groups; the control group the natural aggregate was replaced with partial and full ECFLA coarse aggregates at 0%, 50%, and 100% levels. Also, 20% FA, in the second group and 10% SF third group were in a binary blend replacement of cement, the fourth group, ternary blend was used with the mentioned admixtures. The mechanical properties of SCLC, including compressive, flexural, and splitting strengths as well as elastic modulus, were evaluated. Furthermore, the drying shrinkage behavior of the mixtures was monitored over a 90-day drying period. The results revealed that the density of structural lightweight concrete reached 1830 kg/m3 with full replacement of normal concrete with ECFLA. Moreover, the compressive strength indicated a decrease of approximately 16.3% and 23% with 50% and 100% replacement of ECFLA, respectively than the reference mixture with normal aggregate at 28 days. However, the negative effects of ECFLA in SCLC can be improved with binary and ternary mineral admixtures.