Study On Aging Mechanism Of Silane-impregnated Cement-based Materials

Silane impregnation treatment is a widely used durability protection measure.So far,the study on the long-term degradation of hydrophobicity of silane impregnated cement-based materials is limited,which makes it impossible to quantitatively design and evaluate the life of the anti-corrosion system of silane-cement-based materials.The mechanism of degradation was studied by experiments on hardened cement paste,mortar and concrete with water cement ratio of 0.5 impregnated by triethoxyisobutylsilane.Infrared spectroscopy（IR）,pyrolysis gas chromatography-mass spectrometry（PGC-MS）,water vapour sorption isotherm（WVSI）,gas permeability,capillary water absorption were used to study the effect of photo-oxidation aging and alkali-immersion.The following conclusions are reached:（1）IR and PGC-MS can characterize the alkyl structure of silane and evaluate the content of silane in the sample.There are some differences in silane content between the two methods,but both results showed that the content and structure of silane did not change significantly during the photo-oxidation aging process.The content of silane which can be extracted decreased during the first 14d of alkali-immersion,but the subsequent change of silane content was not significant,and the structure of silane did not change.（2）The adsorption process of cement-based materials can be divided into three stages.The desorption mass increases significantly in the range of 40%-30%relative humidity,which may be caused by"ink bottle effect"of pore structure.Silane impregnation has no significant effect on the adsorption/desorption at low humidity,but inhibits the condensation of water vapor at humidity higher than 50%.There was no significant change in the hydrophobic effect of silane during photooxidation aging.The hydrophobic effect of silane treatment did not decrease,but increased slightly during soaking process,which was reflected in the decrease of adsorption capacity,the increase of k₁ value in the 30%-40%relative humidity range,and the change of desorption and hysteresis curves.（3）Silane impregnation has little effect on the gas permeability of mortar and concrete specimens,and there was no significant change in the permeability of mortar and concrete specimens during the aging process.Silane impregnation greatly reduces the capillary water absorption of mortar and concrete.The water absorption curve of the impregnated specimens has new characteristics compared with the non-impregnated specimens,showing a linear relationship with t^0.5 in the early stage and with t later.The water absorption of mortar increased slightly during photo-oxidation aging and alkali-immersion,possibly due to the changes of the solid matrix during aging process;the water absorption of concrete specimens increased in the early stage,but did not change significantly later.Decrease in impregnation depth was not observed during the two aging processes.（4）Long-term exposure reduced the impregnation effect and the impregnation depth.The hydrophobicity of the surface of a specimen exposed for 13 years diminished,and silane disappeared.The hydrophobicity can be recovered after grinding.The carbonation front is beyond the depth of impregnation,but there still exists a certain alkalinity in the impregnated layer.