Abstract
Excessive emissions of carbon dioxide can lead to greenhouse effect thus destroying the ecological balance. Therefore, effective measures need to be taken to reduce the emission of carbon dioxide. In this study, the influence of carbon dioxide curing on the mechanical strength and NaCl freeze-thaw deterioration of reactive powder concrete (RPC) with the assembly unit of sulphoaluminate cement and ordinary Portland cement was investigated. The ratio of sulphoaluminate cement ranged from 0% to 100% by the total mass of cement with the curing age ranging from 1 d to 28 d. The mechanical strength of RPC with 50% ordinary Portland cement and 50% sulphoaluminate cement containing the polypropylene fibers ranging from 1% to 4% by volume of RPC were investigated. Moreover, the following mass and mechanical strength loss rates, the carbonation depth, the chloride ion migration coefficient and the relative dynamic elastic modulus (RDEM) during NaCl freeze-thaw cycles were determined. Finally, the scanning electron microscope (SEM) and X-ray diffraction were applied in investigating the carbonation process of RPC. Results showed that the addition of sulphoaluminate cement could improve the mechanical strength of RPC at low curing age (lower than 7 d). However, when the cuing age reached 7 d, the sulphoaluminate cement demonstrated negative effect on the mechanical strength. Moreover, the carbon dioxide curing led to increases in the mechanical strength and when ordinary Portland cement was added the enhancing effect was more obvious. Furthermore, the carbon dioxide curing could effectively improve the resistance of NaCl freeze-thaw cycles and increase the carbonation depth. Finally, the increasing dosages of polypropylene fibers were advantageous to the mechanical strength and the resistance of NaCl freeze-thaw cycles. From the researching results of the microscopic performance, the carbon dioxide curing could improve the compactness of hydration products and reduce the content of calcium hydroxide especially at the curing age of 3 days.
Highlights
Excessive emissions of carbon dioxide will destroy the atmospheric ozone layer and cause the greenhouse effect leading to increases in the temperature and affecting the living environment of human beings
Rostami [15] found that the compressive strength of cement paste cured in 8% carbon dioxide for 20 h was 40% higher than that obtained by normal hydration
This paper aims to study the influence of carbon dioxide curing on the mechanical strength and resistances of NaCl freeze-thaw cycles
Summary
Excessive emissions of carbon dioxide will destroy the atmospheric ozone layer and cause the greenhouse effect leading to increases in the temperature and affecting the living environment of human beings. The research of application of carbon dioxide in cement concrete buildings has been reported for several years [7,8]. This viewpoint was firstly put forward in 1970s and has become a research hotspot recently. Ahmad found that the compressive strength of cement concrete cured in carbon dioxide for 1 day was 35–40% higher than that of cured in the standard curing environment [13,14]. Qin et al [16] pointed out that the carbon dioxide curing can effectively improve the compressive strength and chloride ion permeability of cement paste with limestone powder, fly ash and ground granulated blast-furnace slag
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