Development and Performance Evaluation of One-part Alkali-activated Binders, Mortars and Engineered Composites

Abstract

<p>The main objective of this experimental research was to develop alkali-activated engineered composites (AAECs) with comparable performance to that of conventional engineered cementitious composites (ECCs). The use high cement content in ECCs for uniform fiber distribution encouraged the development of cement-free binders using alkali-activation technology. Alkali activated binders (AABs) were developed through activation of high calcium industrial wastes comprising of fly ash class C (FA-C), fly ash class F (FA-F) and ground granulated blast furnace slag (GGBFS) as precursors by calcium-based solid form reagent combinations (calcium hydroxide, sodium silicates, sodium metasilicate and sodium sulfate) using a one-part dry mixing technique under ambient conditions. The influences of mono/binary/ternary combinations/proportions of precursors, dosages of reagents, reagent component ratio, and the fundamental chemical ratios (SiO /2l O2,3Na O2SiO , 2aO/SiO , an2 Na O/Al2O ) p2e3ent in the precursorsand reagents on workabilityandcompressivestrength havebeeninvestigatedto suggest suitable AAB mix compositions for further development of alkali-activated mortars and strainhardening AAECs by subsequent additions of silica sand and PVA fiber, respectively. The binary (FA-C and GGBFS) composites obtained higher 56-day compressive strengths (between 48 MPa and 52 MPa) than their ternary (FA-C, FA-F and GGBFS) counterparts. The lower fracture and crack tip toughness of the binary mortars compared to their ternary counterparts facilitated the development of higher flexural strength (ranging from 5.3 MPa to 11.3 MPa) for binary composites. The tensile stress relaxation process was relatively gradual in binary composites owing to the formation of a more uniform combination of reaction products C-S-H/C-A-S-H compared to the combined formation of amorphous N-C-A-S-H/N-A-S-H and crystalline C-A-S-H binding phases with traces of C-S-H in the case of ternary composites. The self-healing performance of composites incorporating reagent-2 (calcium hydroxide: sodium sulfate = 2.5:1) was superior to their counterparts with reagent-1 (calcium hydroxide: sodium metasilicate = 1:2.5) in tensile strength and strain capacity recovery. These composites demonstrated complete recovery of or enhanced/greater tensile strength and strain capacities than their virgin counterparts at 365 days. The developed green cement-free AAECs with satisfactory performance indices (based on stress, energy, tensile and flexural ductility) demonstrated their potential for applications in construction industries.</p>