Effects And Mechanisms Of Surface Treatment On Hardened Cement-Based Materials With Colloidal Nano SiO₂ And Its Precursor

Extend the durability of concrete is very important when it comes to the cost we faced to repair the concrete in use every year. It has been well-recognized that the densification of the surface of hardened cement-based material will result in a significant improvement of the quality of the entire structure. In general, improving the quality of the surface and coating on the surface of concrete are the best way. The fine particle size and the high pozzolanic reactivity make nano-SiO₂ be the most potential materials using in the surface of cement-based materials, and tetraethyl orthosilicate silane?TEOS? with a good densification effect and a good cementitiousness is regarded as the hot issue in the surface-treatment agent field. However, the effect and mechanism of TEOS on the surface of cement-based materials still need further study. In order to analyze the effect and mechanism of CNS and TEOS on the surface of cement-based materials, the transport property and microstructure of the samples surface treated by TEOS and CNS were compared. Then macro-properties, micro-properties and the mechanism of TEOS and other common used surface treatment agent were also compared to further study the advantage and drawbacks of TEOS. What's more, the study can be used to choose right surface-treatment agent when treating with different samples.The first part of the paper was comparing the transport property and pore structure when TEOS and CNS treated on the surface of cement-based materials. The results show that both CNS and TEOS can decrease the transport property of cement-based materials. For the samples with a w/c ratio of 1.0, the water absorption ratio of the samples surface treated by CNS and TEOS decreased by 20% and 32.6% with regard to the control samples. The vapor transmission ratio decreased by 18.9% and 42.2%. The pore distribution shows that CNS was expertized in blocking the pores larger than 0.1 mm while TEOS can decrease pore volume and pore size. Based on the results, we choose TEOS for further study.The effect of TEOS and common used surface treatment agent on the transport property, compressive strength, sulfate resistance and microstructure were analyzed. The results showed that, TEOS owns the ability to decrease the transport property of 28 days aged cement-based materials. Na2SiO3 reduced both 1 day and 28 days aged samples while silane deceased the water absorption ratio to a great extend but own little effect on the vapor transmission coefficient. TEOS and silane have the negative effect on the compressive strength and sulfate resistance ability when they were used on the 1 day aged samples. However, TEOS enhanced the compressive strength and sulfate resistance ability of the 28 days aged samples. The calorimetry test was done to analyze the effect of various surface-treatment agent on the hydration of cement. The results turned out that, TEOS and silane hindered the hydration process of cement-based materials obviously, and the acceleration effect of Na2SiO3 on the hydration process was also clearly. In the microstructure aspect, TEOS increased the porosity of early aged samples and decreased the porosity of old aged samples. All the microstructure results were correlated with the macro properties.At lase, XRD and TG were used to analyze the effect of CNS, TEOS and common used surface treatment agent on the mineralogy of cement-based materials. The results showed that CNS and TEOS have the pozzolanic reactivity and TEOS was stronger than CNS. Na2SiO3 and Silane consumed CH. IR and XPS were used to study the effect of CNS, TEOS and common used surface treatment agent on the gel structure of cement-based materials. The results showed that CNS, TEOS and Na2SiO3 reacted with CH and the products was C-S-H. Silane reacted with CH through cross linking.CNS and TEOS made it possible to enhance the durability of cement-based materials, and the work also can be used to furfure study the effect of nano-SiO₂ on other application.