Abstract
In order to develop a simple and effective activation method of low calcium fly ash concrete (FAC) and to understand their basic properties, the present paper experimentally investigates the influences of the volume of fly ash (FA), the dosage of the activator (AC) and the water to binder ratio (w/b) on the hydration, setting times and the crack-resistance properties of activated FACs. Results verify that increasing FA can effectively reduce the hydration heat of the FA-cement system and increase the setting time of FACs, as well as indicate that FA can delay the occurrence of the initial crack and reduce the maximum width and total area of cracks in these concretes through a new quantitative test. The curing time of concrete affects the hydration heat of FA paste with/without AC. When the curing time of FAC increases, the decrease in amplitude of hydration heat reduces gradually. Additionally, it was found that the used ACs can effectively stimulate the activity of FA in Portland cement (PC) systems, which reduces their setting time slightly. However, high dosages of ACs also accelerate the development of early cracks in the FACs, as well. According to the study, the combined activator (10% CaO + 1.5% Na2SO4) was suggested as the most effective way to promote FA-PC concrete for obtaining acceptable properties at early stages. Besides, the existing calculation model for predicting the setting times of FACs was examined and modified to be more suitable to FACs activated by 10% CaO + 1.5% Na2SO4. The proposed model was verified and can evaluate the experimental results well.
Highlights
With the development of the economy worldwide and the large production of fly ash (FA), as a by-product of various industries, such as thermal power stations, FA has been concerned as one of the potential alternatives of conventional cementitious materials (i.e., mainly Portland cement (PC))or a part-replacement material of PC to propel eco-concrete since the 1930s
A part-replacement material of PC to propel eco-concrete since the 1930s. This is attributed to the fact that a number of researchers have attempted to solve/reduce to a large degree an unavoidable problem caused by the manufacturing of PC: its large amount of carbon dioxide (CO2 ) emission
The cementitious materials used in this study include Portland cement (PC) and fly ash (Chinese standard, Type II, low-calcium level, Kaifeng Thermal Power Plant, Kaifeng, China), whose physical properties and chemical compositions are listed in Table 1, respectively
Summary
A part-replacement material of PC to propel eco-concrete since the 1930s. This is attributed to the fact that a number of researchers have attempted to solve/reduce to a large degree an unavoidable problem caused by the manufacturing of PC: its large amount of carbon dioxide (CO2 ) emission. The application of FA in concretes can improve the greenhouse effect of Earth’s atmosphere caused by the large amount of the emission of CO2 via reducing the utilization of PC in concretes and decrease natural environment pollution by decreasing the floating of FA in the air to. Sci. 2016, 6, 224 decrease the danger to humans and other lives. It has been reported that FA can improve the workability and durability properties of concrete and reduce the construction cost of reinforced concrete (RC) structures [1]
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