Permeability, concrete

Crete surface to the bulk of the concrete. Permeability is high (Figure 1.6) and transport processes like, e. g., capillary suction of (chloride-containing) water can take place rapidly. With decreasing porosity the capillary pore system loses its connectivity, thus transport processes are controlled by the small gel pores. As a result, water and chlorides will penetrate only a short distance into concrete. This influence of structure (geometry) on transport properties can be described with the percolation theory [8] below a critical porosity, p, the percolation threshold, the capillary pore system is not interconnected (only finite clusters are present) above p the capillary pore system is continuous (infinite clusters). The percolation theory has been used to design numerical experiments and apphed to transport processes in cement paste and mortars [9]. 

Actually, a vast number of experiments show that there is no precise correlation between the crack width (as long as they remain below 0.5 mm) and the risk of corrosion. This risk will depend on factors such as environmental conditions (in particular the humidity) and the properties of the concrete (permeability and... 

The splash/tidal zone of bridges and walls represent cylindrical columns immersed in water. These structures involve entry in two dimensions. Chloride ions enter concrete by adsorption at the surface, which is given by an empirical equation. The effective chloride diffusion coefficient is derived from concrete permeability, water/cement ratio, and concrete resistivity. When concentration reaches a critical value in the vicinity of steel, corrosion begins. As shown in Fig. 12.6, a boundary layer exists adjacent to the concrete... 

For application to hardened concrete we need quantitative data on its penetration vs. concrete cover and concrete permeability. 

There were attempts to relate the permeability of concrete to the properties of interfacial transition zone. However, the unambiguous results were not obtained. According to Roy [142], the constraction of interfacial transition zone surface does not play important role in concrete permeability, while Valenta [143] has quite opposite opinion. This problem will be discussed in Chap. 6 where the construction and properties of interfacial transition zone will be presented [144], In the light of the studies by Richet and Oliver [145] it is evident that the porosity of inteifacial transition zone in traditional concretes (w/c = 0.5 or more) has a significant influence on the permeability of concrete this permeability is a hundred times higher than in the case of cement paste and rises with the size of aggregate (Fig. 5.68). However, the effect of the transition zone on the diffusion of ions is not so evident, because the locally increased water content in this zone, decrease the w/c ratio in cement matrix outside it, which consequently limits the diffusion, thus a total effect can be negligible [145],... 

The rate of carbonation depends on concrete permeability, then it decreasing with low w/c ratio, and with cement content increase. Therefore, the rate of caibon-ation is inversely proportional to the strength of concrete. 

Mineral admixtures can be used to reduce concrete permeability. These are typically fly ash, microsilica, or blast furnace slag and are also addressed by TRB [42], and by ASTM Committee C09 on Concrete. 

A fourth category of air voids is caused by air entrapped during compaction. These voids, called bug holes, are usually larger and have no beneficial influence on freeze-thaw resistance. An excessive volume of entrapped air considerably increases the concrete permeability and decreases its strength therefore it should be considered as inadmissible. 

T.L. Anderson, J.A. Coleman, and N.S. Berke, Processed mineral additive for reducing concrete permeability and increasing strength, US Patent 8 568 527, October 29, 2013. 

Evaluating relative concrete permeability by surface air flow ... 

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