Abstract
The carbonation of concrete is the prime deterioration factor in reinforced concrete (RC) structures. During carbonation, the atmospheric CO2 penetrates the concrete and lowers its alkalinity. The problem in predicting carbonation is difficult to address, and a reliable probabilistic carbonation assessment is required to consider different variables such as the concrete quality, the chemistry of the reinforcing steel, and the quality of finishing materials. In the present study, we have used different finishing materials on concrete to minimize the effects of carbonation with a field survey and accelerated conditions. In one experiment, the measurement of the thickness of the concrete cover and the application of the finishing materials were done on-site, whereas, in the other experiment, these were done under accelerated conditions. The carbonation depth and the coefficient of silk wallpaper (SWP) were reduced by half in an accelerated 5% CO2 experiment compared to the plain ordinary Portland cement (OPC), owing to the external physical barrier that reduces the penetration of CO2 through the pores of the concrete. We found that carbonation did not reach the embedded rebar even after 100 years when SWP finishing material was used. The probability model predicted that 51 years would be required for OPC and water paint (WP) to reach a 30% onset of corrosion initiation through accelerated carbonation, while SWP would require 200 years.
Highlights
The replacement of cement with low calcium fly ash, coal fly ash, and green concrete composites is a sustainable process that reduces CO2 emissions and imposes high compressive strength and fracture toughness owing to their high pozzolanic activity and microstructure [1,2,3]
High volume fly ash (HVFA) causes a harmful effect to the concrete structures which induces the corrosion of embedded steel reinforcement due to carbonation [4,5]
The carbonation prediction equation, announced by the Architectural Institute of Japan (AIJ) [26], is one in which the carbonation coefficient (A), can be predicted by the carbonation depth (C), which is proportional to the square root of the elapsed time (t) (Equation (8))
Summary
The replacement of cement with low calcium fly ash, coal fly ash, and green concrete composites is a sustainable process that reduces CO2 emissions and imposes high compressive strength and fracture toughness owing to their high pozzolanic activity and microstructure [1,2,3]. Atmospheric CO2 penetrates into the concrete and lowers its alkalinity [12] This causes the corrosion of the reinforcing bars by destroying the passive films surrounding them [13,14]. The atmospheric CO2 reacts with water or OH− ion and forms H2CO3 (carbonic acid), as presented in Equation (2). The corrosion of reinforcing bars causes expansion owing to the increase in the volume of the corrosion products, leading to the cracking and spalling of concrete that lowers the strength and decreases the durability of RC structures [20,22]. Jiang et al [24] predicted the carbonation depth of concrete bridges in China under changing climatic conditions and traffic loads by considering different parameters. The probability model can perform the predictions while saving time and manpower
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