Abstract
Alkali-activated mortars (AAMs) are developed incorporating binary/ternary combinations of industrial wastes comprising of fly ash class C (FA-C), fly ash class F (FA-F) and ground granulated blast furnace slag (GGBFS) with alkaline reagents and silica sand. The use of high calcium precursors, calcium-based powder form reagents, dry mixing method, and ambient curing with performance characterization based on chemical ratios and fracture properties are some novel aspects of the study. The mechanical (dry density, compressive strength, ultrasonic pulse velocity, elastic modulus, fracture/crack tip toughness and fracture energy), durability (shrinkage/expansion and mass change in water and ambient curing conditions, water absorption and freeze-thaw resistance) and microstructural (SEM/EDS and XRD analyses) characteristics of eight AAMs are investigated. The binary (FA-C + GGBFS) mortars obtained higher compressive strengths (between 35 MPa and 42.6 MPa), dry densities (between 2032 kg/m3 and 2088 kg/m3) and ultrasonic pulse velocities (between 3240 m/s and 4049 m/s) than their ternary (FA-C + FA-F + GGBFS) counterparts. The elastic modulus and fracture toughness for mortars incorporating reagent 2 (calcium hydroxide: sodium sulphate = 2.5:1) were up to 1.7 and five times higher than those with reagent 1 (calcium hydroxide: sodium metasilicate = 1:2.5). This can be attributed to the additional formation of C-S-H with C-A-S-H/N-C-A-S-H binding phases in mortars with reagent 2. Ternary mortars exhibited comparatively lower shrinkage/expansion and initial sorptivity indices than their binary counterparts due to the lower geopolymerisation potential of fly ash class F that facilitated the reduction of matrix porosity. All mortar specimens demonstrated 100% or more relative dynamic modulus of elasticity after 60 freeze-thaw cycles, indicating the damage recovery and satisfactory durability due to probable micro-level re-arrangement of the binding phases. This study confirmed the viability of producing cement-free AAMs with satisfactory mechanical and durability characteristics.
Highlights
The alkali-activated materials or geopolymers are developed by enhancing the reaction process of industrial waste products or geological materials rich in silica and alumina content, such as fly ash, slag and metakaolin, through alkaline reagents, along with the incorporation of fine aggregates [1,2]
This paper addresses the above-mentioned research gaps by presenting a study on the development and comprehensive evaluation of novel silica sand incorporated high calcium based activated mortars (AAMs) mixes
The mechanical properties of the developed mortars are evaluated in terms of dry density, compressive strength, ultrasonic pulse velocity (UPV), elastic modulus, fracture toughness, crack-tip toughness, and fracture energy
Summary
The alkali-activated materials or geopolymers are developed by enhancing the reaction process of industrial waste products or geological materials rich in silica and alumina content, such as fly ash, slag and metakaolin, through alkaline reagents, along with the incorporation of fine aggregates [1,2]. The influence of mix composition (proportion of precursors, concentration and silica modulus of alkali solutions, liquid to binder ratio) on fracture energy characteristics of GGBFS/FA-based concrete was investigated in a recent study [11]. The development of AAMs with adequate fracture properties for producing novel flowable fibre reinforced alkali-activated engineered cementitious composites (AAECCs) having strain hardening, multiple microcracking, strength and durability characteristics comparable to traditional cement-based. The performance of the developed mortars has been assessed in terms of mechanical (dry density, compressive strength, elastic modulus, fracture toughness, crack tip toughness and fracture energy), durability properties (drying shrinkage in water and ambient/air curing regimes, sorptivity and freeze-thaw resistance) and microstructural characteristics through scanning electron microscopy (SEM), coupled with energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The influence of the addition of silica sand on shrinkage/expansion and mass change characteristics of mortars are compared to their paste (without silica sand) counterparts
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