Investigating concrete durability: The impact of natural pozzolan as a partial substitute for microsilica in concrete mixtures

Abstract

The structural foundations in southern Iran face a formidable challenge due to extensive corrosion. To enhance concrete strength and durability, the construction industry in this region typically incorporates micro silica at a rate of 8% by weight of cement. Nonetheless, given that a significant amount, around 70%, of the concrete expenses in these projects can be attributed to micro silica, and the cost of natural pozzolan in proximity to project sites amounts to only 10% of the price of micro silica, the primary goal of this study is to investigate the durability of concrete incorporating both micro silica and natural pozzolan. The aim is to potentially replace a portion of the micro silica with natural pozzolan while maintaining the required durability and strength of the concrete as specified in the project requirements. To achieve this, eight different concrete mix designs were proposed and subjected them to assessments of compressive strength and various durability standard tests, including water absorption, resistance to rapid freezing and thawing, water permeability, chloride migration coefficient, electrical resistivity, and electron microscopy (Scanning Electron Microscopy (SEM)/Energy Dispersive X-ray Spectroscopy (EDS)/MAPPING). The obtained results indicated that the concrete sample containing 4% micro silica and 12.5% natural pozzolan exhibited similar characteristics to the project's mix design with 8% micro silica in terms of the durability and distribution of permeable spaces within the material. In addition, concerning the pozzolanic reaction, one kilogram of micro silica is nearly comparable to three kilograms of natural pozzolan. Moreover, despite the non-uniform nature of the concrete environment, the EDS and MAPPING results, obtained through random sampling of study points, closely mirrored trends observed in other controlled experiments.