Effect of surface treatment on carbonation of concrete -- the influence of concrete moisture diffusion

     Concrete internal humidity conditions on its carbonation development influence, no pressure head in the water can only be in the form of vapor through the surface processing layer, the presence of water repellency change the concrete internal moisture diffusion process, and also changed the carbonization of the concrete development.

      Due to permeable coating in concrete pore surface to form a water repellent layer prevents the penetration of moisture, the concrete surface layer dry degree is high, lack of CO2 with Ca (OH) 2 or calcium silicate gel water neutralization reaction, this part of the concrete generally do not occur carbon. Laboratory of surface treatment was determined using phenolphthalein solution after concrete carbonation depth of the results, as shown in figure 5.8. From figure 5.8 (a) can be seen, surface treatment, concrete specimen showed three colors, the first layer is pink, indicating that after surface treatment, silane infiltration of concrete surface layer and the layer without carbonization; because the surface is dry, CO2 gas can easily pass through the surface treatment layer reaches the concrete internal and internal concrete with water carbonation, carbonation reaction is here to, partial carbonization zone on the second floor in drops of phenolphthalein no color change; due to the deeper parts of the concrete also beautiful, oh and carbonization, drops phenolphthalein is pink, the third floor. In Figure 5.8 (b), the test piece was two color; the near surface of the carbide zone no color change, the internal non carbide area was pink.

      Heinrichs based on the diffusion coefficient of CO2 in concrete, the carbonation reaction rate and the diffusion performance of concrete, the carbonation process of the concrete is analyzed. Fig. 1 the results of carbonation analysis for 5.9 years, 5 years and 10 years for the surface treated and untreated concrete (silane penetration depth of 10mm). Because the silane treatment layer is very dry CO2 diffusion rate in the layer is very fast, carbonation reaction from the surface treatment layer behind the region began to carry out. The greater the penetration depth of silane in the surface treatment, the deeper the carbonization at the beginning. Due to the existence of the water repellent layer and concrete wet diffusion is a slow process, concrete internal high moisture content, pore water delayed the migration of CO2 in concrete, carbonization reaction speed so slow, although so because of the initial carbide frontier, concrete carbonization depth may be higher than that without surface treatment of concrete, the numerical analysis assuming that the penetration depth is deep, and did not consider the carbonation reaction is the release of water, so the conclusion and further test.