Papers by Author: F.H. Wittmann

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: By now, it is well-known that concrete will lose strength after exposure to elevated temperature. In this case, the damaged concrete is extremely vulnerable with respect to ingress of water and aggressive compounds. Therefore the potential for the protection of concrete from excessive ingress of water after exposure to high temperature, as for instance in an accidental fire, has been investigated. So far, surface impregnation of concrete with silane has been proved to be beneficial to reduce water penetration. In this contribution, surface impregnation with silane was applied on concrete exposed to elevated temperature. The efficiency of surface impregnation with respect to absorption of water and salt solutions by concrete with different levels of damage induced by elevated temperature has been investigated in particular. Results indicate that the increased water absorption of damaged concrete can be reduced significantly by surface impregnation. A reduction of more than 90 % can be achieved. The effective chloride barrier established by surface impregnation can help to extend the service life of fire-exposed concrete structures.

Abstract: Reinforced concrete structures may be exposed to an aggressive environment. In this case combined mechanical and environmental actions may act simultaneously and their synergetic influences have to be taken into consideration. In this contribution results of tests on two different types of concrete and mortars are presented and discussed. Capillary absorption of not carbonated and carbonated concrete has been determined. The influence of mechanical load on capillary suction has been studied separately. A moderate compressive load reduces the coefficient of capillary suction, while capillary suction is enhanced by higher mechanical loads as micro-cracks are formed. Chloride diffusion has been measured by means of the diffusion cell test. The diffusion coefficient observed in carbonated concrete is roughly speaking one order of magnitude higher than the value measured on not carbonated concrete.

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.