Hibiscus extract–epoxy surface treatment for artificial lightweight aggregate concrete

This study explores the effect of partially substituting epoxy resin with hibiscus extract (30–50% by mass) as a surface treatment for artificial lightweight aggregate (ALWA) and ALWA concrete. Cold-bonding agglomeration was employed to manufacture reference ALWA and concrete with properties meeting ASTM, EN, and AIN standards. Incorporating a hibiscus extract–epoxy resin solution reduced water absorption while enhancing compressive and flexural strengths of treated ALWA and concrete compared to untreated counterparts. Microstructural analyses (Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy) confirmed the superior performance of treated samples, revealing the formation of secondary calcium silicate hydrates, calcium aluminate hydrates, and polymeric phases arising from the reaction between residual fly ash and the hibiscus extract–epoxy resin. These compounds filled pores, smoothed surfaces, and densified the microstructure, thereby improving overall aggregate and concrete performance.