DETERMINAÇÃO DO TEMPO DE TRANSIÇÃO SUSPENSÃO-SÓLIDO (TEMPO ZERO) EM MICROCONCRETOS DE ALTA RESIST̂ENCIA CONTENDO POLÍMERO SUPERABSORVENTE E NANOSSÍLICA

The autogenous shrinkage is a phenomenon that occurs due to the appearance of tensile stresses in capillary pores. Inherent in the hydration process, not depending on external interference. In High Strength Concretes (HSC), autogenous shrinkage is most pronounced, due to the refinement of the microstructure, high cement content, the use of mineral additions and low water/cement ratio, which hinder the transport of curing water. In this context, superabsorbent polymers (SAP) stand out for their ability to reduce or even eliminate the autogenous shrinkage, because they absorb large amounts of water, which is subsequently released within the paste, avoiding auto desiccation and the appearance of tensile stresses (internal curing). However, PSA can reduce the mechanical resistance, which can be compensated by adding nanoparticles such as nanosilica (NS). In this work, was evaluated the effect of these additions in suspension-solid transition time, or Setting Time (T0). The setting time determines the time at which the material starts to behave as a solid, with the formation of a sufficiently rigid mineral skeleton to oppose the volumetric variations that happen in the paste, which can lead to cracking, compromising the esthetics, durability, and security of concrete structures. The determination of T0 was done by the ultrasonic test, which measures the speed of propagation of an ultrasonic wave in the material, and is taken as the point in time when a sudden change in this speed. Nine blends were made containing PSA and NS, where it was verified that the addition of PSA increases the value of T0, while the NS causes a reduction in this value