Laboratory Study On The Properties Of High Performance Concrete With Nano-SiO₂

Generally, High Performance Concrete (HPC) is manufactured by reducing water to cementitious materials ratio, adding some kinds of mineral admixtures and some chemical agents. The aim of this article is to experimentally analyze the properties of HPC with Nano-SiO₂ (NS).This paper presents some properties such as workability, mechanical properties, autogenous shrinkage, chloride permeability resistance, frost resistance of HPC with NS. Meanwhile, the influences of Super Retarder (SR) and Air Entraining Agent (AEA) on concrete workability,mechanical properties are studied here. The apparatus for autogenous shrinkage of concrete is the same as the one brought forward by An M Z et al. The chloride permeability resistance and the frost resistance are separately tested according to ASTM C 1202-97, ASTM C 666-97 (A). The microscopic structure of paste and the interfacial transition zone have been observed by scanning electronic microscope (SEM), and the compositions at different ages are analyzed with X-Ray. Finally, a new approach (BP Network) to predicting the durability factor of concrete has been proposed here.The results, in general showed that: the addition of NS can decrease the slump and the slump flow, improve the early age compressive strength, but has little effect on the later age strength. The autogeous shrinkage of concrete strain is augmented, but the chloride permeability resistance and frost resistance can be largely improved with the addition of NS. The results from X-Ray and SEM showed that NS can obviously improved the interfacial transition zone between aggregate and paste, which can be evidence to the influences of NS on concrete properties. The addition of AEA can increase the slump but can decrease the slump flow; the compressive strength and the autogenous shrinkage are deceased but the chloride permeability resistance and the frost resistance are increased with the addition of AEA, especially the frost resistance. Super-Retarder can decrease the early strength of concrete, but has little effect on the later strength. The durability factors of concrete predicted with the BP Network are comparatively similar to the test values. The difference between the test values and the prediction values are in the range of 5%.