Influence of HPMC and VAE on the Properties of Geopolymer Mortar

The delamination of building facades creates a critical demand for inorganic adhesive mortars with high long-term adhesion. Geopolymer (GP) represents an eco-friendly alternative to Portland cement (PC). However, the effect of polymer additives, commonly used in cement-based adhesive mortars, on GP mortar remains insufficiently studied. This study examines the effects of hydroxypropyl methylcellulose (HPMC) and vinyl acetate-ethylene (VAE) polymer on the workability, mechanical properties, durability, and microstructure of GP mortar. Results show that an optimal HPMC content (0.4 wt%) improves the fluidity, compressive strength, and adhesive strength of GP mortar, approximately 6%, 16%, and 20%, respectively. These enhancements are attributed to the incorporation of uniformly distributed microbubbles in the mortar matrix. Beyond this optimal content, however, HPMC impairs flowability and adhesion due to its thickening effect. In contrast, VAE addition significantly enhanced adhesive strength by approximately 28%, albeit at the cost of a 17% reduction in compressive strength, resulting from the retardation of the alkali activation process. This gain in adhesion is associated with the formation of a continuous polymer film that establishes both physical interlocking and chemical bonding with the GP matrix. Furthermore, HPMC improved the durability of the GP mortar, while VAE did not contribute to this aspect. These insights offer valuable guidance for designing high-performance GP-based adhesive mortars suitable for building applications.