Pakistani bentonite in mortars and concrete as low cost construction material

Abstract

A Pakistani bentonite, in “as is” (21 °C) and “heated” (150 °C, 250 °C, 500 °C, 750 °C and 950 °C) conditions, was incorporated in mortar cubes, concrete cylinders and concrete beams as a partial substitute for Ordinary Portland cement (OPC) and studied in detail. Results showed that OPC mortars and concrete containing 20% “as is” and 25% “heated to 150 °C” bentonite could be used as low-cost construction materials. They will also reduce energy consumption, preserve natural resources and solve environmental problems related to cement production as well as augment the durability and life cycle of the concrete structures. The X-ray diffraction patterns showed that bentonite possessed both crystalline and amorphous phases. The strength activity indices (SAI) after 7 and 28 days were higher than 75% for “as is” and “heated” bentonite, except for the 950 °C samples, which was below the ASTM C618 specified limit of 75%. The maximum SAI was shown by “150 °C heated” bentonite. The compressive strength data also showed similar results for OPC mortar cubes and concrete cylinders containing “150 °C heated” bentonite. When compared with the control mixture, the compressive strength values were the same as for mortar containing 25% bentonite as replacement of OPC. However, these values decreased in concrete initially and started to gain strength remarkably after 28 days. Resistance to sulphate attack and water absorption tests on mortar cubes soaked in 2% magnesium sulphate and 5% sodium sulphate solutions demonstrated consistent improvement as the bentonite content in them was increased. The modulus of rupture of all concrete beams decreased as the OPC substitution level by bentonite increased from 20% to 40%. Bond strength of OPC mortar containing 20% “as is” and 25% “heated to 150 °C” bentonite in brick prisms was almost the same as that of control mixture.