Influence of Discrete Basalt Fibres on Shrinkage Cracking of Self-Compacting Ambient-Cured Geopolymer Concrete

Short basalt fibres (BFs) have recently gained significant interest in the building materials sector due to their superior mechanical characteristics and cheaper manufacturing cost than other fibre types. Drying shrinkage and the early-age cracking of concrete are the root cause of many durability issues in the long run. Including small dosages of fibres within concrete composites has been shown as an effective technique to minimise drying shrinkage rates and reduce the crack widths developed due to plastic shrinkage cracking. Nevertheless, limited research studies have investigated the influence of short and long BFs with different dosages on the drying shrinkage rates and early-age cracking of geopolymer composites. In the present study, self-compacting geopolymer concrete (SCGC) using fly ash and slag as the binder is mixed with anhydrous sodium metasilicate powder as an alkali-activator. The study aims to investigate the influence of short (12 mm), long (30 mm) and hybrid-length (1:3 (short/long)) BFs with 1%, 1.5% and 2% dosages on the drying shrinkage properties and plastic shrinkage cracking of SCGC. The study results showed that adding BFs to SCGC reduces the drying shrinkage rates compared to plain SCGC, and SCGC reinforced with a 2% dosage of hybrid-length BFs recorded the lowest drying shrinkage rate. Two methods were used to measure crack widths: manual measurement (crack width gauge) and image analysis. No plastic shrinkage cracks were identified in mixes reinforced with 12 mm (1.5% and 2% dosages), 30 mm and hybrid-length BFs.