Effect of superplasticizers on concrete durability indexes

Abstract

Use of durability index (DI) is one of the several approaches that have been used or advanced through various test methods for the purpose of evaluating the durability of concrete mixtures. In South Africa, use of DI's has developed through testing and research over the past years. A consortium of three tests of oxygen permeability index (OPI), water sorptivity and chloride conductivity are employed. This paper presents an investigation conducted to determine the effect that superplasticizers may have on durability indexes of concrete. Concrete mixtures of strengths ranging from 30 to 50 MPa were cast using two types of commercially available superplasticizers, herein referred to as GL and RSP. The admixtures were of different chemical bases with RSP being a sulphonated naphthalene superplasticizer while GL was a polycarboxylate ether superplasticizer. The tests conducted were compressive strength, oxygen permeability and water sorptivity. It was found that use of GL increased the compressive strength of concrete by about 10 MPa over the strengths of mixes made using RSP. Correspondingly, GL had an adverse effect on durability performance, as it decreased the OPI and increased the sorptivity indexes. The results implied the possible coarsening of the pore structure of the hardened concrete which could have resulted from the use of GL. Results also showed that the influence of chemical admixtures on hardened concrete properties and durability characteristics of high strength concretes may be less significant for high strength concretes