Engineering properties and bond strength of cementless scc with recycled aggregate activated by slaked lime and Na2SiO3

Today, the use of artificial and natural pozzolans (such as silica fume (SF), blast furnace slag (BFS), fly ash (FA), and trass) and construction demolition waste instead of cement and aggregates, respectively, which constitute concrete, offers an important alternative in terms of sustainability and the environment. Within the scope of this thesis study, the effect of the hybrid activator ratio (Na₂SiO₃/(Na₂SiO₃+SK)), the quantity and combination of binder on the fresh and hardened concrete properties of cementless SCC containing recycled aggregate with a hybrid activator (slaked lime and Na₂SiO₃) was investigated. For this purpose, the amount of slaked lime (SL) was kept constant at 67% of the total binder in all cementless SCC mixtures, and the variable parameters were selected as the Na₂SiO₃/(Na₂SiO₃+SL) ratio as 0.15, 0.20, and 0.25 and the amount and combination of binder materials (single, binary, and ternary blends). A total of 12 mixtures were designed, consisting of 3 series of Na₂SiO₃/(Na₂SiO₃+SL) ratios and 4 different mixtures of varying binder material quantities and combinations, along with a Control SCC mixture containing recycled aggregate for comparison purposes. Slump-flow, T500, and L-box of the workability tests as well as setting time tests, were performed for all designed SCC mixtures. Subsequently, compressive strength and flexural strength tests were conducted on samples produced from all mixtures for 7, 28, and 90 curing days, while the modulus of elasticity test was performed using 28-day samples and the capillary water absorption test using 90-day samples. Additionally, a total of 13 beams large-scale beams with lap-spliced reinforcing bar details, consisting of Control and 12 cementless SCC beams, were produced and subjected to four-point bending. As a result, the fresh concrete properties of all mixtures met the slump-flow SF2 (660-750 mm) and L-box (H2/H1≥0.80) criteria recommended by EFNARC. In terms of hardened concrete properties, it was determined that binary blended mixtures with a Na₂SiO₃/(Na₂SiO₃+SK) ratio of 0.15 exhibited the best performance. Furthermore, bending tests conducted on large-scale beam specimens revealed that the highest bond strength values were obtained from binary blended mixtures with a Na₂SiO₃/(Na₂SiO₃+SK) ratio of 0.15. Keywords: Hybrid alkali activator, Binder combination, Recycled agregate, Cementless self-compacting concrete, Large-scale beam with lap-spliced bar, Bond strength