Sustainable and cost-effective repair material: the role of reactive SiO2 in alkali-activated binders

This study looks at how reactive SiO 2 contributes to high-performance alkali-activated binders (HPAAB), which provide an eco-friendly and affordable option compared to commercial repair materials (CRM). A total of 11 mixtures were investigated: one control mixture composed of high-calcium fly ash (HFA) without reactive SiO 2 additive, and 10 modified mixtures, each incorporating one type of reactive SiO 2 material—either fine, medium, or large nano-SiO 2 at dosages of 1, 2, and 3%wt, or rice-husk ash (RHA) at a dosage of 2%wt. Each mixture included only one type of reactive SiO 2 additive. A 10-molar sodium hydroxide solution combined with a sodium silicate solution was employed as the liquid activator. Experimental evaluations were carried out to assess the setting time, compressive strength, bonding strength, and the interface zone between the repair material and normal concrete substrate. Test results indicated that adding 2% nano-SiO 2 and 2% RHA notably enhanced the mechanical properties and bond quality of the HPAAB paste. This enhancement was attributed to the generation of additional reaction products within the matrix, thus resulting in performance comparable to those of CRMs. Additionally, a cost and life-cycle analysis indicated that HPAABs, especially those incorporating RHA, were more cost-effective and exhibited up to 23 times lower CO 2 emissions compared to CRMs. Although the role of reactive SiO 2 in alkali-activated binders is well established, the novelty of this work offers HPAAB-based repair materials with optimized reactive SiO 2 contents. These materials have demonstrated potential as effective alternatives for concrete repair and rehabilitation, offering enhanced bonding performance, greater cost efficiency, and a reduced carbon footprint in comparison to CRMs. These results provide valuable insights for advancing the application of alkali-activated binders in the construction industry.