Engineering properties of strain hardening geopolymer composites with hybrid polyvinyl alcohol and recycled steel fibres

Abstract

Strain hardening geopolymer composite (SHGC) is an alkali-activated material reinforced with randomly dispersed short fibres, which exhibits high ductility and strain hardening and multiple cracking behaviour. This paper presents an experimental study on the effect of hybrid polyvinyl alcohol (PVA) and recycled tyre steel (RTS) fibres on engineering properties of fly ash-slag based SHGC cured at ambient temperature, including flowability, setting time, drying shrinkage, compressive strength and flexural behaviour in terms of stress-deflection response, first-crack strength and flexural strength, flexural toughness and toughening mechanisms. Four mix proportions of specimens with various volume fractions of hybrid PVA and RTS fibres including 1.5% PVA, 2% PVA, 1.75% PVA + 0.25% RTS and 1.5% PVA + 0.5% RTS were considered. The results indicated that the hybridisation of PVA fibre with RTS fibre led to a significant reduction in flowability, setting time and flexural strength of SHGC. However, the resistance to drying shrinkage and compressive strength of SHGC were greatly improved. Moreover, all specimens exhibited the expected deflection hardening behaviour with multiple stable microcracks formed over the tensile face of specimens under four-point bending. The addition of RTS fibre resulted in reduced crack widths in specimens where over 90% of cracks had a width of smaller than 60 μm. The mixture containing 2.0 vol% PVA fibre can be regarded as the optimal mixture for SHGC considering the strengths and deflection (or strain) hardening behaviour.

Effect of recycled tyre polymer fibre on engineering properties of sustainable strain hardening geopolymer composites

“…Regarding the effect of PVA fibres, the reduction in spread diameter caused by the addition of 1.0% PVA fibre was limited, only 7.28% lower in comparison with P0R0. Nevertheless, the higher dosages of PVA fibre (1.5% and 2.0%) reduced the spread diameter of SHGC by 18.62-22.10%, which is in agreement with previous studies on FAbased [15] and FA-GGBS based [37] SHGC. There exists a critical fibre dosage, where fibre clumping or balling tends to occur when the incorporated fibre dosage exceeds it [70].…”

“…11c). A similar phenomenon was reported in [37,80] that the original cubic shape of SHGC was maintained after the compressive failure owing to the bridging capacity of the fibres. Compared to the plain matrix mixture, the compressive strength of SHGC is lower while its ultimate compressive strain may be higher [79] that needs to be confirmed by measuring the longitudinal strain of the specimen during the compressive loading.…”

“…The reduced compressive strength of SHCC caused by the fibre incorporation become more obvious with the reducing water-to-binder (w/b) ratio, as reported by Yu et al [79] who observed a reduction of 14.30% in compressive strength when 2.0% PVA fibre was added into the plain mixture with a w/b ratio of 0.2. Besides, Wang et al [37] found that the compressive strength of SHGC with 2.0% PVA fibre was about 9.70% and 7.30% lower than that containing 1.5% PVA fibre at 7 d and 28 d, respectively.…”

“…It was stated that combining 1.5% PVA fibre and 0.5% RTS fibre in SHCC can achieve the optimal engineering properties [36]. Regarding the usage of recycled fibres to replace PVA fibres in SHGC, only one relevant study [37] can be found, which investigated the effect of RTS fibres on the engineering properties of SHGC and noted that RTS fibres are favourable for the improvements of drying shrinkage resistance and compressive strength although the flexural strength is weakened after the incorporation of RTS fibres. It is worth mentioning that besides the above-mentioned benefits, incorporating RTS fibres in SHCC or SHGC can also significantly enhance the sustainability of the composites.…”

Contribution of Interfacial Bonding towards Geopolymers Properties in Geopolymers Reinforced Fibers: A Review

“…With an emanation rate of roughly 700-900 kg per ton, cement has the highest carbon emissions. Several studies have attempted to reduce cement content in concrete blends by partially or completely replacing cement with mineral admixtures or mechanical by-products, with the goal of reducing concrete CO 2 outflows [5][6][7].…”