In this study, the effect of temperature on macroperformance and microcharacteristic of carbonized concrete was investigated. The carbonation depth, compressive strength, and surface strain of concrete under different simulated environments for 28 d were measured. XRD and ESEM-EDS analysis were conducted to present the phase composition, types of hydration products, and microstructure characteristics of samples before and after carbonation. The results showed that the effects of temperature on carbonation depth, strain, and compressive strength were significant. There was a linear relation between temperature and carbonation depth as well as compressive strength of concrete. The effects of environment factors on concrete surface strain after carbonation manifested as the strain value and the slope of linear segment of strain curve. Significant differences of phase composition and hydration products were observed before and after the carbonation, which mainly manifested as attenuation and disappearance of diffraction peaks of hydration products. Temperature affects the crystal form of the carbonation products.
Concrete carbonation is a neutralization reaction between carbon dioxide (CO2) penetrated into concrete from surrounding atmosphere and the alkaline hydration products (e.g., calcium hydroxide) in concrete [
The objective of this study is to investigate the effect of temperature on concrete carbonation. Macroperformance (i.e., compressive strength, carbonation depth, and strain) and microcharacteristics (i.e., composition phase, microstructure, and carbonation products) of carbonized concrete under different temperature were measured.
P·O 42.5 Portland cement was provided by China Building Materials Academy. River sand (i.e., fine aggregate) and continuous grading limestone gravel (i.e., coarse aggregate) with a grain size of 5∼20 mm were collected. Tap water which met the JGJ63-2006
Mix proportion of concrete (kg·m−3).
Composition materials | Cement | Fly ash | Fine aggregate | Coarse aggregate | Water | Water reducer | |
---|---|---|---|---|---|---|---|
Concrete strength grade | C20 | 195 | 128 | 785 | 1045 | 178 | 1.8 |
C30 | 270 | 125 | 780 | 1050 | 172 | 1.9 | |
C40 | 350 | 122 | 710 | 1052 | 162 | 2.25 |
According to GBT 50082-2009
Testing condition.
Items | Temperature (°C) | Relative humidity (%) | CO2 concentration (%) |
---|---|---|---|
1 | 10 | 70 | 20 |
2 | 20 | 70 | 20 |
3 | 30 | 70 | 20 |
Test instruments mainly included Quanta-200 environment scanning electron microscope (ESEM) made by FEI Company (USA), BD-86 X-ray diffraction (XRD) produced by Rigaku Company (Japan), WAW-DP Universal tester was provided by Shanghai Sansi Co. Ltd. (China), and the environmental simulation test system was made by Wuhan Jinyatai Instrument Co., Ltd. (China). Moreover, the imc data acquisition system with sixteen channels was provided by Integrated Measurement and Control Co. (Germany).
Due to temperature accelerating the carbonation rate, the effect of different temperatures (i.e., 10°C, 20°C, and 30°C) on concrete compressive strength after carbonation for 28 d was investigated. Figure
Curves of concrete compressive strength with temperature.
Figure
Macroperformance of carbonized concrete can also be represented by carbonation depth. Hence, the influence on concrete carbonation depth was measured, and Figure
Carbonation depth profiles of concrete with temperature.
Figure
Due to the carbonation that reacted from concrete surface to the inside, the change of concrete surface can be used to represent the characteristic of concrete carbonation. Using C20 as an example, the influence of temperature on concrete surface strain was investigated. The prism concrete specimens were used to measure the surface strain according to Section
Strain curves of concrete surface with carbonation temperature.
As seen from Figure
In order to investigate the characteristic of carbonation, the microcharacteristic of carbonized concrete was studied. Figure
XRD spectrum of samples under different carbonation conditions.
Figure
Microstructure, morphology, and carbonation product of samples under different temperatures were also measured, as shown in Figure
ESEM-EDS spectrum of samples under different temperatures. (a) Noncarbonation. (b) 10°C. (c) 20°C. (d) 30°C.
Figure
The effect of environmental temperature on concrete carbonation was investigated. The experimental results showed the carbonation depth and compressive strength of concrete manifested as a linear relationship with temperature. Concrete carbonation depth increased with the increase of temperature, but the compressive strength of concrete after carbonation decreased with the strength grade of concrete. This was because CO2 transmission coefficient and chemical reaction coefficient may increase with temperature. The effects of temperature on concrete surface strain after carbonation manifested as the strain value and the slope of linear segment of strain curve. Phase composition, hydration products, and microstructure of concrete changed significantly before and after the carbonation. Such changes were mainly manifested by disappearance and weakening of diffraction peak of some hydration products. XRD and ESEM spectral analysis revealed that the carbonation product was mainly calcium carbonate. Temperature affected the crystal form of carbonation products. Polyhedral spherical vaterite was major carbonation products at 10°C and 20°C, whereas aragonite was the major carbonation products at 30°C.
The data used to support the findings of this study are available from the corresponding author upon request.
All the authors declare that they have no conflicts of interest.
This study was funded by the National Natural Science Foundation of China (grant nos. 51778632, U1434204, and 51408614), National Keypoint Research and Invention Program of the Thirteenth (grant no. 2016YFC0701705-1), and China Postdoctoral Science Foundation (grant nos. 2016M600675 and 2017T100647). The authors have received the research grants from the Basic Research on Science and Technology Program of Shenzhen (JCYJ20170818143541342 and JCYJ20180305123935198) and Natural Science Foundation of Hunan Province of China (2017JJ3385).