Research On The Hydration Kinetics Of Composite Cementitious Material System At Low Temperature

In our cold regions, winter time is longer. So the tight deadline schedules have left less time for construction of the concrete works. This will greatly delay the project. In addition, long-term low-temperature environment also poses a potential threat to the quality of the project. In this context, researching fly ash, silica fume and other industrial waste is particularly important realistic significance for hydration characteristics of cementing material at low-temperature. Although our country has made great progress and experience in the field of construction of cryogenic technology, but the quantity of researches in this area is relatively few. This system is far from providing theoretical guidance for winter construction.At low-temperature, molecule in the concrete has low activity; the rate of cement hydration reaction is slow. It restricted the development of mechanical properties. To improve this situation, we usually mixed with an appropriate amount of mineral admixture and additives during the construction. Although promoting the hydration reaction of cement, it makes hydrated environment more complex. At this time, how composite cementing system hydrates at low-temperature, what impact on cement hydration when admixture is added. This is not only a problem about low concrete, but also an important issue to solve winter construction.In order to guide the construction of concrete effectively at low-temperature and the comprehensive utilization of mineral admixtures, this article tested bond hydration water content of composite cementing system at low-temperature; changes in temperature of hydration reaction and the other indicators respectively by simultaneous thermal analyzer and hydration calorimeter. And through processing and transforming test data, this article studied the low-temperature curing system(0 ℃,-5 ℃,-10 ℃) and the influence of mineral admixtures content(fly ash:0,10%,20%,30%, silica fume:0,2%,5%,8%) on the degree of hydration of early composite cementing system; hydration rate of composite cementing system’s early induction; the variation of the second exothermic peak; kinetics parameters of composite cementing system’s early induction.Through simultaneous thermal analyzer, the paper tested the water content of the bond water composite cementing systems, and considered the influence of the degree of hydration of cementing composites by the low temperature curing of different systems and different dosage of mineral admixtures on the early time. The results show that:It produces an inhibition effect for the early hydration composite binder system by reducing the temperature the early hydration and this inhibition effect will be decreased with decreasing the temperatures. It produces a catalytic role for hydration of cementing composite cryogenic by using silica fume on the early time. It produces an inhibition effect by flying on low hydration of cementing composite material system on the early time, and the inhibitions will be increased apparently with increasing fly ash content of this. In the complex silica fume and fly ash composite cementing systems, the promotion of silica fume composite binder system is clear on hydration inhibition.This paper tests the hydration temperature change of composite cementitious through hydration micro-calorimeter,studys the relationship between different temperatures, different mineral admixtures dosage and composite cementitious hydration heat induction rate secondary exothermic peak.The results shows:As the temperature decreases, the hydration induction period will be extends, hydration secondary exothermic peak delays,the highest heat release rate of the secondary exothermic peak decreases.With the increase of mineral admixture,the hydration induction period will be extends,hydration secondary exothermic peak delays. With the increase of silica fume,the highest heat release rate of the secondary exothermic peak improves. With the increase of the yield of fly ash,the highest heat release rate of the secondary exothermic peak decreases.In the composite cementitious system complexed silica fume and fly ash,the promoting role of silica fume is obvious than the inhibition role of fly ash in composite binder system hydration.By analyzing the heat release rate curve of hydration and choosing the Krstulovic-Dabic hydration heat release model, effect of different temperature and mixing amount of fly ash and silica fume on dynamics parameters such as reaction order, reaction rate constant and procedure transition point was studied. The results showed that, as temperature fell, the reaction order increased, while reaction rate constant reduced and procedure transition point was lagged. Apart from this, with adding of admixtures, the reaction order increased, as well as reaction rate constant of process I. Specifically, adding of silica fume led to an increase of reaction rate constant of process NG and D, and brought the procedure transition point forward, whereas the adding of fly ash lowered the reaction rate constant of process NG and caused a lag of procedure transition point of D procedure.In short, the temperature on the hydration process composite binder system played a inhibition. Increased silica fume will promote hydration process and increased production of fly ash will inhibit the hydration process. In both complex composite cementitious material doped silica fume system, promoting is greater than hydration of fly ash on hydration inhibition.