Experimental study on long-term impermeability of recycled aggregate concrete mixed with crystalline admixture and waste glass powder

The impermeability of recycled aggregate concrete (RAC) presents challenges for underground engineering, particularly concerning its larger pore. Combining crystalline admixture (CA) with waste glass powder (WGP) offers a feasible solution to enhance impermeability. To understand the collaborative mechanism of CA and WGP in improving RAC impermeability and establish an accurate mixture ratio, we conducted compressive strength tests and a series of permeability tests on WGP and CA modified recycled aggregate concrete (WRC). These tests involved different CA contents (0%, 1%, and 2%) and varying WGP replacement rates (0%, 10%, 20%, and 30%). Our findings indicated that when the WGP substitution rate exceeds 10%, the strength of the WRC decreases by approximately 23%. In contrast, the overall decline is about 5% when the CA content increases from 0% to 2%. Therefore, the WGP emerges as the primary factor influencing the compressive strength of WRC. Meanwhile, The WGP and CA play a major role in enhancing the short-term and long-term impermeability of WRC, respectively. Additionally, When the WGP substitution rate increases from 0% to 30% on same CA content, the RC increases by approximately 2%, indicating that elevated WGP content enhances the effectiveness of CA. Finally, the optimal combination to improve the impermeability of WRC is 10% WGP substitution and 1% CA content. Microscopic tests analyses show that under the influence of CA and WGP, C-S-H gel, C-A-S-H gel, and Ettringite are produced inside the WRC, effectively blocking pores and cracks, thus improving the specimen's impermeability. This research not only holds the potential to elevate impermeability but also offers a solution to the issue of waste glass accumulation, contributing to global sustainable development.