| In order to meet the requirements of winter construction,anti-freezing admixture is widely used in winter construction.The use of anti-freezing admixtures can reduce the waste of resources and energy,as well as the irreversible frost damage caused by sub-zero temperature.Nowadays,large doped inorganic salt anti-freezing admixture is the most widely used.This kind of admixture will inevitably cause the long-term durability of concrete loss.Finding small doping anti-freezing admixtures that do no harm to the longterm performance is imminent.In this paper,the influence of three low-content anti-freezing admixtures on the development law of compressive strength and hydration process of portland cement were studied.The mechanism of these three low-content anti-freezing admixtures was obtained.And the three reagents were used in combination to explore their influences on performance of concrete,so as to design a composite anti-freezing admixture.The results show ethylene glycol,sodium thiocyanate and sodium oxalate can all be used as low-doping anti-freezing admixtures under the condition of-5℃.The mechanism of anti-freezing admixtures can be considered from both increasing early strength and lowering freezing point.Among them,ethylene glycol play an early and strong role mainly by promoting cement mineral dissolution,promoting C3 S reaction and accelerating AFt to AFm conversion or the second reaction of C3 A.The addition of ethylene glycol can significantly reduce the freezing point of the cement paste,so that the cement at sub-zero temperature can sustainably hydrate.Sodium thiocyanate can promote the reaction in the acceleration period to obtain early strength.But its effect on freezing point reduction is small.Sodium oxalate accelerated the hydration of early cement by promoting the precipitation of ions in the early stage of induction.Sodium oxalate only reduced the freezing point to 2℃.So,it’s effect on freezing was general.Three anti-freezing admixtures with low content were used together,and the influences of each component on concrete performance was determined by orthogonal test.The key to strength development of concrete under negative temperature is to reduce freezing point of pore solution and promote hydration of Portland cement.Sodium thiocyanate,as an accelerator,promotes the hydration at low temperature,even at subzero temperature mainly by shortening the induction period.Therefore,sodium thiocyanate plays a leading role in the initial hydration reaction of cement.With the prolonging of the pre-curing time,ethylene glycol,as an organic antifreeze,can reduce the freezing point at late age.While,sodium oxalate only plays an auxiliary role in promoting the strength growth.This paper analyzed the mechanism of three kinds of anti-freezing admixtures with low content.The influence of each component on concrete performance were studied.An idea for the design of antifreeze with low content was provided.The final anti-freezing admixtures formulation was: 0.5% ethylene glycol,0.5% sodium thiocyanate and 0.6% sodium oxalate. |
