Estudo da influência de aditivos redutores de água em concretos da construção civil

Abstract

Water-reducing admixtures for concrete are high efficiency dispersants that promote viscosity reduction of suspensions, minimizing the amount of water used to hydrate the cement. However, besides rheological characteristics of the that system, the additives influence the hydration process of the cement, with consequent formation of a microstructure differentiated and with excellent properties, thus allowing for the attainment of less porous concretes with elevated mechanical resistance and greater durability.Once adsorbed to the surface of the concrete particle, the molecular functional groups of these additives create charges that promote deflocculation by electrostatic repulsion or may simply cause deflocculation by creating physical barriers through the long polymer chains phenomenon known as steric effect.Nonetheless, a series of occurrences caused by incompatibility between additive and cement are being reported, since the interaction process between them is still not consolidated. There is, in many cases, the incompatibility between cement and additive is detected, a rigorous evaluation of unique combinations is warranted considering the type and brand of both cement and additives, given that different interactions between them can occur. In this work, It was investigated the effect of a last generation water reduced additive on the properties of concrete in fresh and hardness status, dosed with cement CP II E-32. The properties of concrete analyzed were: determination of rebatement (Slump Test), determination of the initial setting time, final setting time and open time (Vicat method) and mechanical resistance after 7, 14 e 28 days. The dosages of concretes involved combinations between two cement types, three dosages of superplastificizer additives (0,2%, 0,4%, 0,6%), and specific amount of water to each dosage of additive. Our results show that the superplasticizer additive has strong influence in the final characteristics of the concrete, given its presence increases the workability time frame of the investigated formulations, both with Cauê and Holcim cements. The additive enabled low water dosages for cement hydration, resulting in better mechanical properties and plasticity. Comparing both cement brands, formulations with Holcim cement performed better. Analysis of variance confirmed the strong influence of the cement type – as well as the level of additive in the formulations – in the mechanical properties of the product. Cauê cement showed greater hydration time, what in the construction site becomes an advantage in terms of concrete application and desification. On the other hand, the greater plasticity and mechanical resistance obtained with Holcim cement makes it more attractive in terms of construction time, as current construction markets demand constructions delivered faster.