Utilization of garlic peel ash as a partial replacement for cement in construction materials

Abstract

Portland cement production is one of the main sources of CO₂ emissions, representing a significant environmental challenge. Supplementary Cementitious Materials (SCMs) have emerged as a promising alternative to mitigate the environmental impact associated with cement manufacturing, while also enhancing the properties of concrete and mortar. In this context, the aim of this study is to evaluate the effect of garlic peel ash (GPA) as a supplementary cementitious material in mortar. Portland cement was partially replaced with GPA at levels of 10%, 20%, and 30% by weight, and the resulting mixtures were evaluated in terms of rheological behavior, setting time, physical properties, mechanical strength, and microstructural characteristics. Isothermal calorimetry revealed that the incorporation of 10% GPA did not hinder the initial hydration reactions but extended the dormant period, likely due to the presence of SO₃ and Cl. The setting time increased proportionally with GPA content, which may be beneficial for workability, provided mechanical performance is maintained. Mortar consistency decreased with higher GPA levels, indicating the need for mixed adjustments. Density remained stable across mixtures, while water absorption and porosity increased for the 20% and 30% replacements. The 10% GPA composition achieved statistically equivalent compressive strength to the reference control, attributed to the packing effect, nucleation from CaCO₃, and alkali activation. Scanning electron microscopy (SEM), x-ray diffraction (XRD), and mercury intrusion porosimetry (MIP) analyses confirmed the formation of hydration products and highlighted the role of GPA in promoting ettringite and reducing CH content. These results suggest that a 10% replacement of cement with GPA can maintain mortar mechanical performance while contributing to sustainability in construction. However, due to its relatively high chloride (2.35%) and sulfate (8.24%) contents, the use of raw GPA in reinforced concrete should be avoided because of potential durability and reinforcement of corrosion concerns. Further studies on appropriate pre-treatment strategies may enable its future application in reinforced concrete.