Abstract
In this paper, the carbonation depths of glazed hollow bead insulation concrete (GHBC) and normal concrete (NC) at different carbonation ages are tested. The microstructure of GHBC and NC before and after carbonation were observed and compared by mercury intrusion porosimetry (MIP), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD). The results showed that NC had better carbonation resistance than GHBC, and GHBC had a carbonation depth of 1.61 times than that of NC at 28 days accelerated carbonation experiment. The microstructural analysis showed that with the decrease of porosity of the samples, the carbon content and CaCO3 content increased after carbonation. The porosity of NC decreased from 14.36% to 13.53%, the carbon content increased from 4.42% to 5.94%, and the CaCO3 content increased from 18.5% to 56.0%. The porosity of GHBC decreased from 22.94% to 20.71%, the carbon content increased from 4.97% to 5.31%, and the CaCO3 content increased from 70.0% to 82.0%. The above results showed that carbon reacts with hydration products 3CaO·SiO2, 2CaO·SiO2, and Ca(OH)2 to produce a large amount of CaCO3 which causes a large amount of pores to be filled and refined hence the porosity and pore size were reduced leading to increase in the compactness of the material. From the results obtained, the carbonation depth prediction formula of glazed hollow bead insulation concrete was developed, and carbonation life was predicted.
Highlights
Carbonation refers to the infiltration of carbon dioxide in the air into concrete, which reacts with the alkaline substances in the concrete (C-S-H, ettringite, and unhydrated cement etc.,) to form silicate and water
It can be seen from the figures: (1) The changes regularity of the carbonation depth of normal concrete (NC) and glazed hollow bead insulation concrete (GHBC) is the same
Tinhcerecaasrebdo,ntahteioncarrabtoenwataiosnthdeefpatshtegstrawdiuthalilny 3indcaryeas,sefodllwowhielde tbhye3catorb1o4ndataiyosn, arantde gradubaelclyamdeecflreaat saefdte.rT1h4e dcaayrbso. nTahtiiosnwraastebewcaasustheeCfOas2tersetacwtsithwiinth3Cdaa(yOs,Hf)o2llaonwdedhybdyra3tetod 1c4aldciauyms, and became flat after 14 days. This was because CO2 reacts with Ca(OH)2 and hydrated calcium silicate to form CaCO3 in the concrete, which blocks the internal pores of the concrete hinders the CO2 diffusion channel and weakens the carbonation reaction
Summary
Carbonation refers to the infiltration of carbon dioxide in the air into concrete, which reacts with the alkaline substances in the concrete (C-S-H, ettringite, and unhydrated cement etc.,) to form silicate and water. At the later stage of carbonization, concrete causes coagulation shrinkage and crack expansion. Carbonation and decalcification of C-S-H lead to an increase of porosity, and the carbonization process continues. Carbonation leads to a decrease in the pH value of concrete. The passivation film formed on the surface of the steel in a high alkalinity environment is destroyed, which causes the chloride ions adhering to the concrete to be converted into free chloride ions. Carbonation is an important factor that causes durability problems in concrete structures and reducing service life
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