Sustainable development of mortar with carbon fibre repair using granite dust and nano-silica for mechanical properties improvement

The Malaysian economy has experienced consistent annual growth, particularly in the construction sector, due to increasing demand for residential, commercial, and infrastructure developments. This demand has led to a significant rise in the consumption of concrete and mortar, thereby intensifying the use of essential raw materials such as sand and cement. However, the excessive exploitation of these natural resources has raised serious environmental concerns, including sand scarcity and elevated carbon dioxide emissions from cement production. In response to these challenges, this study aims to explore sustainable alternatives by incorporating granite dust (GD) as a partial sand replacement and nano-silica (NS) as a partial cement replacement in mortar mixtures, as well as evaluating the effectiveness of carbon fibre reinforced polymer (CFRP) wrapping for repair applications and mechanical performance improvement. The incorporation of GD offers cost efficiency and environmental benefits by reducing dependence on natural sand, while NS may contribute to strength development through packing and pozzolanic effects. Mortar specimens were prepared with GD and NS replacements ranging from 0% to 30% and 0% to 2.5%, respectively, and tested for compressive strength at 3, 7, and 28 days. Material characterization was conducted through X-ray fluorescence (XRF), particle size analysis using a Zetasizer, moisture content evaluation, and Scanning Electron Microscopy (SEM). The results indicate that the inclusion of GD and NS, both individually and in combination, generally improved the compressive and flexural strength of mortar compared to control specimens. The GD15+NS1 mixture exhibited the highest compressive strength of 52.63 MPa after 28 days of curing, which may be associated with densification and improved packing. It was found that a mortar mixture that contains 15wt.% granite dust and 1wt.% nano-silica (GD15+NS1) exhibited the highest compressive strength of 52.63 MPa at 28 days curing. Further investigation involving modified mortar patching and CFRP wrapping on cracked specimens demonstrated not only recovery of structural performance but also enhancements surpassing those of uncracked specimens. The results showed that the cracked specimen repaired with modified mortar patching and CFRP wrapping has flexural strength of 13.42 MPa when compared to the strength of undamaged mortar specimen of 3.20 MPa. These findings suggest that the combination of GD, NS and CFRP reinforcement offers potential for enhancing mortar properties and may present a potential approach for both new construction and rehabilitation projects, aligning with current efforts toward resource conservation and improved structural durability.