Determination of time zero in high strength concrete containing superabsorbent polymer and nano-silica

Abstract

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 concrete, autogenous shrinkage is most pronounced, due to the refinement of microstructure, the high cement content, presence of mineral addictions and low water/cement ratio, which interfere in the transport of water curing. In this context, Superabsorbent polymers (SAP) stand out for their ability to reduce or eliminate the autogenous shrinkage, because they absorb large amounts of water, which is subsequently released into the matrix, avoiding self-desiccation and the onset of tensile stresses (internal curing). However, studies show that SAP can reduce the mechanical strength, which can be compensated by addiction of Nano-silica (NS). In this paper, the effect of these additions in Time Zero (T 0 ) was evaluated. T 0 determines the time at which the material starts to behave as a solid, with the development of a rigid mineral skeleton to oppose the volumetric variations that occurs in the paste, which can lead to cracking, compromising esthetics, durability, and structures safety. The ultrasonic pulse velocity test performed the T 0 , which measures the velocity of propagation of an ultrasonic wave through the material and is taken as the time when a sudden change occurs at this velocity. Nine blends were made containing SAP and NS, where it was found that SAP addition increases the T 0 (up to 11%), while NS decrease its value (in 55%).

Performance of cementitious mortars containing hydrogel–nanoclay hybrid nanocomposite

“…These results agree with Cunha et al [77], where fresh-state densities for 0.2 − 0.3% of SAP (poly(acrylic acid)-polyacrylamide) with a w/c ratio = 0.40 was 2.24 g•cm − 3 , and with Esteves et al [78], where the corresponding value for mortars that contain SAP (acrylamide/acrylic acid copolymer) with 0.2% w/wt. cement ratio was ~ 2.25 g•cm − 3 .…”

“…Cunha et al [77] obtained a comparable result that they attributed to the augmented air content caused by the presence of entrapped air bubbles formed in the matrix when the curing water was released. This was considered to affect the mechanical properties.…”

Effect of Superabsorbent Polymer on the Mechanical Performance and Microstructure of Concrete

“…Furthermore, a study of the evolution law and the effect of time-varying damage by different internal curing agents on the macro and micro properties of concrete was discussed. The evolution law and prediction model of the concrete with SAP were also studied by [15][16][17]. The effect of SAP on the transition zone of the steel fiber interface in concrete and related properties was discussed by [9,10].…”

“…It has been ascertained from the above research results that the effect of SAP on concrete strength was controversial [13,18], and the frost resistance and durability of concrete can be effectively improved by SAP [19][20][21]. The autogenous shrinkage and dry shrinkage of concrete were reduced, and the tensile creep of the concrete could also be improved by 50% [15,16,22]. In addition, scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP), and thermogravimetric analyzer (TGA) methods were adopted to discern the effect of SAP on the microstructure of concrete [14,23,24].…”

Effect of Hydrogel Nanocomposites on the Fresh and Hardened Properties of Cementitious Pastes

“…[19] Thus, the internal curing (IC) is a very promising technique that can provide additional moisture to the concrete, aiming more effective cement hydration with low self-drying. [24,25] It is established that the final properties of a cementitious matrix depend directly on the perfection and the time in which its healing process was performed. [26] In this way, the use of polymers and hydrogels as IC agents into inorganic matrices is an alternative to avoid the shrinkage of these cement-hybrid matrices without modifying or even improve their mechanical properties.…”