This study presents a comparative durability assessment of Engineered Geopolymer Composites (EGCs) against a Engineered Cementitious Composite (ECC) under prolonged sulfuric acid (H₂SO₄) attack. This work addresses a critical gap by systematically comparing the strain-hardening performance and degradation mechanisms of lightweight fiber-reinforced composites under aggressive chemical exposure. Four lightweight mixtures—three EGCs with varying slag/fly ash contents (S-EGC: 100% slag; FAS-EGC: 50% slag; FA-EGC: 100% fly ash) and one lightweight ECC control—were fabricated using expanded glass granule (EGG) aggregates and immersed in a 5% H₂SO₄ solution for up to 120 days. Before exposure, the incorporation of slag significantly enhanced pre-exposure mechanical properties; S-EGC showed the highest ultimate strength, while the FAS-EGC mixture provided the best balance of strength and ductility, achieving a tensile strain capacity of 3.21%. The lightweight EGCs demonstrated superior acid resistance compared to the lightweight ECC. After 120 days of exposure, the S-EGC composite retained the highest residual compressive strength (81.59%), while the ECC retained significantly less. Significantly, all exposed EGC and ECC specimens maintained their multiple cracking and deflection-hardening behavior, retaining approximately 50% of their total deflection capacity after four months. Microstructural analysis confirmed that the superior resistance of S-EGC is attributed to its stable, cross-linked alumino-silicate polymer structure. These findings confirm that lightweight slag-based EGCs are a highly durable and ductile sustainable alternative for structural applications in aggressive environmental settings, such as wastewater treatment infrastructure and chemical plants.

This study evaluates the performance of slag-based alkali-activated mortar (AAM) under ambient curing, focusing on the effects of 2% nano-alumina, sodium hydroxide (NaOH) molarity (12, 14, and 16 M), and sodium silicate-to-sodium hydroxide (SS/SH) ratios (1.5 and 2.5). Fresh and mechanical properties, including flowability, compressive strength, and flexural strength, were investigated. Durability was evaluated by measuring water absorption and sorptivity, and by assessing compressive and flexural strengths of AAM after 28 days of exposure to 5% sulfuric acid, 5% magnesium sulfate, and 3.5% sodium chloride solutions. Additionally, General Linear Model Analysis of Variance was conducted to assess the effects of NaOH molarity (12–16M) and 2% nano-alumina on the fresh, mechanical, and durability properties of alkali-activated mortar. Results indicate that NaOH molarity and SS/SH ratio significantly influence workability and strength. The optimal mix (12 M, SS/SH = 2.5 with nano-alumina) achieved a balanced improvement in workability and compressive strength. While flexural strength generally increased with molarity, higher concentrations did not always yield proportional benefits. The addition of nano-alumina greatly increased matrix densification through the filling of micro voids, reducing water absorption and sorptivity with improved mechanical performance and chemical resistance of alkali-activated materials. A manifest synergistic effect of nano-alumina amount and sodium hydroxide molarity was determined, with optimal mixes — namely those with 2% nano-alumina at 12–16 M and at the alkali ratio of 1.5 — showing superior compressive and flexural strength and improved durability against aggressive exposures to sulfuric acid, magnesium sulfate and sodium chloride. While high nano-alumina content marginally decreased workability, it increased cohesion in the mixes which also confirmed its effectiveness as an important ingredient in high-performance mix design. Overall, the interaction between NaOH molarity and nano-alumina plays a key role in enhancing AAM performance, highlighting its potential as a sustainable and durable alternative to conventional cement-based materials.