Sustainable synthesis of hydrophobic waste glass powder for enhanced water and frost resistance in mortar

Abstract

Most durability issues in cement-based materials stem from water intrusion, which can be mitigated by hydrophobic materials with excellent waterproofing properties. This study proposes a green wet chemical method using stearic acid (SA) and waste glass powder (WGP) to synthesize hydrophobic WGP (HWGP). The effect of SA dosage on the water contact angle of HWGP was investigated, and the optimal SA dosage for preparing HWGP was determined through TG analysis. XRD, FTIR, XPS, and TEM tests revealed the synthesis mechanism of HWGP. The effects of HWGP on mortar's mechanical properties, water and frost resistance were also studied, and the optimal dosage of HWGP for preparing hydrophobic mortar was determined. The results show that 8 % SA is optimal for preparing HWGP, and its water contact angle is 132.2°. The synthesis occurs through reactions between SA and Na⁺, Ca²⁺, and Si-OH groups, with the long carbon chains of SA grafted onto WGP, forming a hydrophobic layer about 4 nm thick. As HWGP content increases, compressive strength initially increases and then decreases, while water and frost resistance improve significantly. The optimal dosage for preparing hydrophobic mortar is 15 % HWGP, where compressive strength decreases by only 6.9 %, flexural strength increases by 12.5 %, and water contact angle increases by 91.2°. Additionally, initial and secondary water absorption rates decrease by 79.4 % and 92.2 %, respectively, total water absorption amount over 8d decreases by 64.9 %, and frost resistance improves by 70.9 %.