Evaluating Superplasticizer Compatibility With Portland Pozzolana Cement CEM II/B-P in Production of High Performance Concrete

Abstract

Portland Pozzolana Cement CEM II/B-P has potential advantages over Portland Cement CEM I when used to produce concrete. The incorporation of up to 35% natural pozzolana reduces the amount of clinker used in cement production, hence raw materials, CO2 emission, and the energy demand. Moreover, the pozzolana reacts with Ca(OH)2 produced by the hydration of Portland cement thereby mitigating alkali-aggregate reactions, destructive reactions with sulphates and acids, and carbonation shrinkage. In addition, additional C-S-H from the reaction of pozzolana and Ca(OH)2 increases the long term strength and densification of the pore structure leading to improved durability. This research explores the effect of seven locally available superplasticizers in the production of free-flowing high performance concrete with a Portland pozzolana cement CEM II/B-P 32.5N. Compressive, flexural tensile, water absorption and electrical resistivity tests were also carried out on hardened concrete. Four Superplasticizers achieved high initial slump in excess of 200 mm on fresh concrete. However, workability reduced rapidly leading to stiffening within 30 minutes. Such concrete would not allow sufficient time for transportation, placement and finishing, and therefore has limited application. Cube crushing strength in excess of 60 MPa and good indications of durability were obtained at 28 days. In order to unlock the inherent benefits, further research on improving the flow retention of the concrete is necessary.