Papers by Keyword: Water Repellent Treatment

Abstract: Anti-permeability, durability even strength of cement-based composites are closely related with the material pore structure. Polyvinyl alcohol (PVA) fiber reinforced strain hardening cement-based composites (SHCC) are provided with high ductility and multi- micro-crack propagation mode. Due to fibers adding, much more interface and tiny fracture had been drawn into SHCC, although it has some advantages such as high tensile strength, ductility and energy consumption under seismic load or other cyclic force. Water repellent treatment can improve the anti-permeability of SHCC. Investigations have been made through Mercury injection experiment to reveal influence on microstructure of PVA-SHCC by silane water repellence. Results show that, the pore structure of SHCC can be fined by inside water repellent agent. That is, water repellent infiltrate through the relative big hole or defect of cement paste and react with the alkali substance. Then the resultant colloids reduce the big hole, pore or fracture and reform the pore structure of the cement paste. Because the fine pore structure can prevent air, water and ions defuse into interior of cement-based composites, water repellent treatment is benefit to increase anti-permeability of high ductile SHCC.

Abstract: Polymers are often applied in concrete for multiple purposes and aims. For instance, surface impregnation of concrete with silanes is a reliable technology to protect cement-based materials from ingress of aggressive solutions into the materials. An alternative method is to add silane emulsion into fresh concrete or mortar to produce integral water repellent materials. In this contribution integral water repellent concrete was prepared by adding 1 %, 2 %, 3 %, 4 % and 6 % of silane emulsion. The influence of silane emulsion on the compressive strength, porosity and pore size distribution, water capillary suction and chloride penetration have been investigated. The results indicate that addition of silane emulsion moderately reduced compressive strength of concrete. With 3 % of silane emulsion the reduction is about 10 %. The addition of silane emulsion hardly has influence on pore size distribution. Silane does not block the capillary pores, but only forms a hydrophobic film on the walls of capillary pores. Addition of silane emulsion reduces water capillary suction significantly. The reduction rate is higher than 89 %. Even the surface of integral water repellent concrete is abraded off 7 mm, the material still demonstrates high water repellency because the entire volume is hydrophobic. In addition, chloride penetration also can be reduced substantially.

Abstract: Water repellent treatment (WRT) has proved to be effective to prevent porous materials from water penetration and consequently can improve the durability of structures. In this contribution, three types of mortar, which are pre-carbonated and non-carbonated, had been water repellent treated by silane gel with usage of 400 g/m2, to investigate into the influence of WRT on carbonated and non-carbonated mortar. Results indicate that carbonation reaction increased the compressive strength of all three types of mortar. Silane gel penetrated to a comparatively higher depth for the carbonated mortar. WRT reduced the absorbed water and capillary absorption coefficient greatly, both for non-carbonated mortar to 2 % ~ 7 % and for carbonated mortar to 22 % ~ 66 %, compared with non-treated ones. WRT is still a feasible method for porous materials with some carbonation to prevent from water penetration. However, the efficiency of WRT on reducing capillary absorption became much lower compared with the non-carbonated mortar. Capillary absorption curves of non-WRT mortar, both carbonated and non-carbonated, could be well fitted by a hyperbolic function of square root of time. For the treated mortar, the absorption curves could be described as a linear equation before carbonation, but an exponential function when the mortar carbonated.