Effects Of Concrete Surface Treatments On Permeability Of The Surface Layer Of Concrete

Concrete permeabilty has a very c lose relations hip with its durab ilty. Water canenter the cement-based materals auto matically under presure or capillary forces,leading to cracking and deterioration under the freezing and thawing action. Chlorideion d issolved in the water will e nter the cement-based materia ls and cause corrosionof the re inforecment. On the other hand, carbondioxide in the atmosphere will reactwith the calc ium hydroxide of the surface layer concrete, which will lead to thecorrosion of steel bar as well. So the permeability of concrete is an importantmacroscopic property of concrete. Plenty o f research has been done on the concretepermeab ility and methods to improve the permeability of concrete. But all theseresearch was based on laboratory methods. There was little test for the in-situconcrete. It has been confirmed that s urface treatme nt can be the most s imple methodto improve the inpermeability of the surface concrete. When the specimens had beentreated on56thday, the calc ium hydroxide content and pore structure of motarspecime ns which had the same w/c with the concrete in5mm depth fro m surface weremeasured.In this paper, the effect of the fluoride silicate and silicate treatme nt on thestrength and surface hardness of concrete was stud ied. The Autoc lam test method thatcould be used in-s itu was used to test the gas permeability and water permeability.The effect of these two kinds of surface treatme nts on water absorbtion andcarbonation depth was investigated.Results showed that the28d compressive strength of specime ns after surfacetreatment had little d ifference, but the strength of concrete by fluorosilicate treatme ntwas improved to some extent. Water glass treatment had less impact on the concretesurface hardness, while this condition had significantly improved after the sodiumfluoride pretreatment. So the major role in improving the hardness of the surface wasfluoride silicate.Sodium silicate were better on air-inpermeability and the Autocla m airpermeab ility index had a liner re lationship with the carbonatio n depth o f thece ment-based materia ls. These two surface treatments were all conduc ive to thewater-inpermeability of concrete. The d ifference in treatment effect was that thefluoro-silicate worked in the prior28days, while the effect of sod ium s ilicate was more obvious a fterwards. Autoc la m water permeability index had an exponentia lrelationship with the water porosity of the cement-based materials.It was shown that calc ium fluoride ma gnes ium s ilicate and water glass treatmentcaused the reduction o f the ca lcium hydroxide content, while the ca lc ium hydroxidecontent would increase after sodium fluoride pretreatment. The pore structure analys isshowed that the two types of treatment a gent would decrease the porosity, a long withthe macro-pore and the capillary pore which would affect the permeability ofce ment-based materia ls. There fore, the mecha nis m of these two categories treatme ntagents in reduc ing the permeability of the ce ment-based materia ls is by reduc ing thecontent of macro-pore and capillary pore.