Influence of Types of Chemical Admixture and Their Dosages on Properties of Ready Mix Concrete

Abstract

An experimental investigation was carried out to study the effects of types of chemical admixture, increased dosage of admixture, two-stage dosage of admixture, sand to total aggregate volume ratio (s/a), cement content (cc) and fresh concrete temperature on fresh and hardened properties of ready mix concrete. For conducting the investigation, six different types of concrete mixtures were prepared using different types of chemical admixtures, different dosages of admixtures; varying s/a ratio (0.4 and 0.45), cement content (340 kg/m3 and 380 kg/m3); and controlling temperature of fresh concrete. Chemical admixtures such as water reducer based on lignosulphonate; and superplasticizers based on naphthalene sulphonate, organic polymer, second generation polycarboxylic ether, modified polycarboxylic ether, sulphonated naphthalene polymer and synthetic polymer were collected from the local market. Each mixture was subjected to prolonged mixing; slump readings were recorded at 15 minutes intervals to assess the fresh behavior of concrete. A total of 297 cylindrical concrete specimens of diameter 100 mm and length 200 mm were made with the mixtures for assessing the hardened properties of concrete. The specimens were tested for compressive strength, splitting tensile strength, Young's modulus and ultrasonic pulse velocity (UPV). Results indicate that sulphonated naphthalene polymer based superplasticizer and second generation polycarboxylic ether based superplasticizer show best performances in both fresh and hardened states of concrete. The compressive strength of concrete increases with the increase of admixture dosage, when the dosage of admixture is within the range recommended by manufacturer. Applying dosage of chemical admixture in two stages imparts better workability to concrete than applying the same dosage of admixture at the beginning of mixing process. UPV through concrete with admixture is higher compared to UPV through concrete without admixture. For a given water to cement ratio (W/C), workability of concrete increases with the increase of cement content. Workability of superplasticized concrete can be improved by reducing the temperature of fresh concrete during the mixing process.