Application of Nano-silica Particles to Improve the Mechanical Properties of High Performance Concrete Containing Superabsorbent Polymers

Abstract

Autogenous shrinkage is a phenomenon that affects the High Performance Concrete (HPC), mainly due to its refined microstructure, the high cement content, the low w/c ratio and the presence of mineral additions. This is closely associated to the hydration process, not depending on any external interference. The internal curing with Superabsorbent Polymer (SAP) is reported as the most effective mitigating strategy, whereas that it provides the necessary water for hydration, preventing the appearance of tensile stresses that may generate autogenous shrinkage and consequently the cracking of structural elements. The use of SAP increases the porosity of the concrete, mainly because the unconnected voids leaved inside the material and the additional water added for SAP absorption, which would reduce mechanical strength. In this work was used the Nano-silica (NS) particles to compensate this effect. Nine micro concretes with different amounts of SAP and NS were produced. For this work, the mechanical strength was evaluated and the autogenous shrinkage was determined from Time Zero (T0) until 28 days. The results indicate that SAP was efficient for the mitigation of autogenous shrinkage (reduction of 84% for the 0.3% content of SAP), while the addition of NS increases the mechanical properties (there was an improvement in the compressive strength of about 10% for the 2% content of NS). The concrete containing SAP and NS were very promising, since the beneficial action of SAP in mitigation of autogenous shrinkage was not impaired by the presence of NS, while the NS maintained the mechanical strength values of the mixtures containing both SAP and NS additions approximated of the values of the reference.