Carbonation depth model and carbonated acceleration rate of concrete under different environment

Abstract

Effects of temperature, relative humidity and CO2 concentration on carbonation depth of concrete were investigated, and the variation laws of concrete carbonation depth under coupling effects of environment factors were also studied. A novel prediction model of carbonation depth including component materials and environment factors was proposed on basis of the measured data. The distributions of the relative content of products in concrete, i.e., Ca(OH)2, calcium–silicate–hydrate and hydrated–calcium–aluminate, and pH value were determined through dimensionless processing. Also, the time-dependent curves of concrete carbonation depth were simulated, and a novel method to evaluate the carbonated acceleration rate or time similarity rate of concrete carbonation depth between simulated and natural environment was proposed. The results show that the effects of temperature, relative humidity, CO2 concentration on the carbonation depth are significant, and there are exponential function, power function and polynomial function between carbonation depth of concrete and temperature, CO2 concentration and relative humidity, respectively. The similarities and differences of carbonation depth of concrete under the coupled effects of environmental factors can be found in the characteristic of 3D camber figure and the isopleth of projection plane. Phase composition, hydration products and microstructure of concrete change significantly before and after carbonation. The XRD spectrum and ESEM images reveal that the dominant carbonation product is calcium carbonate. Temperature and CO2 concentration affect the crystal form and practical size of carbonated products, respectively, and the relative humidity changes the compactness of micro structure, quantity of micro pore and cross-sectional characteristic. In addition, the activation energy of carbonation in concrete was also calculated.