Mechanical, hygrothermal, and durability performance of Eco-fiber Clay Ash Blocks (EFCAB) as an alternative circular economy-based wall material in humid tropical climates

Reducing embodied carbon in wall materials is increasingly important for humid tropical regions, where conventional fired clay bricks are widely used but require energy-intensive kiln firing and are vulnerable to moisture-related degradation. This study evaluates Eco-Fiber Clay Ash Blocks (EFCAB), an unfired interlocking block made from fly ash, clay, and water hyacinth fiber, as a laboratory-scale alternative wall material within a circular-economy framework. Three mixtures were prepared with a constant 10% water hyacinth fiber content and varying fly ash-clay ratios: V1 (40% fly ash, 50% clay, 10% fiber), V2 (35% fly ash, 55% clay, 10% fiber), and V3 (30% fly ash, 60% clay, 10% fiber). Conventional fired clay bricks were used as the control. Mechanical, hygrothermal, capillarity, wet-dry durability, and simplified cradle-to-gate embodied carbon analyses were conducted. The results show that V1 achieved the highest average compressive strength of 10.7 MPa compared with 8.0 MPa for the control. The same mixture also showed the highest dry density, lowest porosity, reduced water absorption, lower capillarity coefficient, and lower thermal conductivity. After 25 wet-dry cycles, V1 experienced a 4.5% reduction in compressive strength, while the control experienced a 12.5% reduction. One-way ANOVA indicated that mixture composition significantly influenced compressive strength (F = 34.53, p < 0.001, eta squared = 0.87). The embodied carbon calculation is presented as a simplified scenario-based estimate rather than a full ISO-compliant life cycle assessment; under the stated assumptions, V1 showed a potential reduction of approximately 66% compared with fired clay bricks. The findings indicate that EFCAB has promising laboratory-scale performance for non-load-bearing or low-rise wall applications in humid tropical contexts, although long-term exposure, microstructural validation, full-scale wall tests, fire resistance, shrinkage behavior, and code-based certification remain necessary before practical implementation.