Upcycled geopolymer concrete incorporating GFRP waste powder: Sulfate resistance and machine learning-based strength prediction

The expansion of renewable energy technologies has led to increased glass fiber reinforced polymer (GFRP) waste, posing environmental challenges. This study upcycles end-of-life GFRP powder as a supplementary precursor in geopolymer concrete (GPC) to promote circularity and carbon reduction. Three GPC systems—GFRP-based, ground granulated blast furnace slag (GGBS)-based, and a hybrid mixture—were evaluated for sulfate resistance and durability. The hybrid system containing 30 wt.% GFRP powder showed minimal mass gain (1.70% and 1.27%) and limited strength loss (3.53% and 6.22%) after 180 days of exposure to 5% and 10% sulfate solutions, respectively. Enhanced performance stemmed from microstructural densification, reduced calcium leaching, and optimized silica-alumina reactivity. Microstructural analysis confirmed reduced gypsum precipitation and a consolidated aluminosilicate network. Machine learning models predicted residual strength, with multilayer perceptron (MLP) yielding R 2 = 0.93. These results highlight GFRP waste upcycling as a sustainable, low-carbon route for durable, data-driven green infrastructure. • Hybrid GPC (30 % GFRP) showed 3.53% strength loss after 180 d in 5% Na 2 SO 4 . • Hybrid GPC (30 % GFRP) showed 6.22% strength loss after 180 d in 10% Na 2 SO 4 . • Synergistic silica-calcium interaction enhances hybrid GPC durability. • MLP-ANN achieves R 2 =0.93 for predicting hybrid GPC compressive strength.