Nano-SiO2 coating and silane modified bamboo cellulose nanofibers for alkali-activated slag mortar with recycled aggregate: Performance enhancement and mechanism

Alkali-activated slag mortars with recycled fine aggregate (AASRMs) have attracted high concern due to their promising properties, low carbon emissions, and solid waste utilization. However, high shrinkage made the AASRMs susceptible to cracking, limiting their application in construction industry. This study intends to use green bamboo cellulose nanofibers (CNFs) as reinforcement to overcome the problem. Two CNFs surface modifications including nano-SiO2 coating and KH590 silane were adopted to improve the dispersibility of CNFs and their compatibility with AASRM matrix. Fourier transform infrared spectroscopy, thermal gravimetric analysis, Zeta potential, and scanning electron microscopy were adopted to characterize the CNF modification. The results showed that adding CNFs evidently improved the mechanical strengths, and reduced the chemical and dry shrinkages of AASRMs. CNF to modifications improved their dispersibility within the matrix, strengthened the fiber/matrix interface bonding, and refined the pore structure of the mortars, enhancing the overall performance of AASRMs. Particularly, the incorporation of 0.3 wt% nano-SiO2- and KH590-modified CNFs into AASRMs enhanced the 28-day flexural strength by 15.5 % and 18.3 %, respectively, compared to the control without CNFs. Moreover, these modifications significantly reduced the 14-day dry shrinkage by 49.9 % and 37.1 %, with nano-SiO2 proving more effective than KH590 in mitigating dry shrinkage. This study offers an effective and green strategy for enhancing the performance of AASRMs by using renewable materials, being beneficial for their large-scale application as sustainable building materials.