Effect Of Antifreeze Admixture On The Properties Of The High Perfomance Concrete Used In Passenger Dedicated Lines

In the severe cold regions, the construction period is delayed significantly by the cold weather, also the life of projects declines as the setting concrete has been frozen in water or salt water. If the temperature drops under zero in the early age, the hydration of concrete will stop and strength will also stop increasing. The more water stayed inside of the concrete, the more frost stress cased by the ice, and resulted in the greater damage of concrete. Study found that, as so long as the temperature of fresh concrete keeps above zero for some time, the concrete reach the critical strength of concrete to frost, the temperature of recover from, the strength of the concrete strength will sustainably increase and achieve 95% of the design strength, So it's essential to add antifreeze admixture in the negative temperature concrete.In this paper the compound frost salts (CH3OH, Ca(NO₃)₂, Ca(NO₂)₂ and CaCl₂) and end product antifreeze admixtures (PCA, PCB) adding in concrete with super plasticizer and high volume fly ash in the actual project, the air content of the fresh concrete and the mechanical properties, the permeability, frost resistance of the hardened concrete are researchedStudies show that the composite addition of antifreeze salts CaCl₂ increased air content of concrete mix, but it impact differently in the two composite salt of concrete mix. The addition of the fly ash reduces the air-entraining property of the concrete, with the substitution of fly ash increases, the air content of the concrete mix decreased.The adding of CaCl₂ in the subzero concrete have double-sided effect on the internal structure of the concrete. The Addition of CaCl₂ increases the early strength of concrete and the development of the internal pore structure, at the same time changes the internal pore structure of concrete, when the dosage of CaCl₂ was 75%, the mechanical properties; frost salts and durability of concrete are better than others, two effects balance to achieve the best results. The same amount of fly ash to replace the cement, of the early strengths develop the slowly, the freeze conservation in the subzero concrete increases, which is harmful for the subzero salt concrete. With the substitution of fly ash increases, the mechanical properties and durability of negative temperature concrete reduce gradually. In contrast, the mechanical properties and durability of the concrete with the same dosage of fly and the same amount of CaCl₂ or the Ca(NO₃)₂ salts are better than that of the Ca(NO₂)₂ type.The mechanical properties and durability of concrete of the adding PCB are better than that of the PCA antifreeze admixture used in practical engineering, which is inconsistent with the standard on the antifreeze test results .For choosing end products of antifreeze admixture, we can't be based solely on testing standards to evaluate the performance index of the merits of antifreeze admixture. We should take the accommodation of the antifreeze admixture, other admixtures and mineral admixtures into account.