Aiming at the adverse effects of low temperature environment on concrete, the effects of sodium nitrate on concrete strength at different temperatures were studied. The results show that the strength of concrete can be greatly improved at - 5 ℃ and - 10 ℃ when polycarboxylic acid water reducer is combined with sodium nitrate, and the excellent content of sodium nitrate is 0.27% of cementitious material.

混凝土在冬季施工中，由于气温低，水泥水化作用减弱，新浇筑的混凝土强度低，容易出现多种混凝土病害，影响建筑工程的质量，在气温降低到一定程度时，混凝土强度甚会发生不增长，给混凝土施工带来一系列的问题。

During concrete construction in winter, due to the low temperature, the weakening of cement hydration and the low strength of newly poured concrete, it is prone to a variety of concrete diseases and affect the quality of construction projects. When the temperature decreases to a certain extent, the concrete strength will not even increase, which will bring a series of problems to concrete construction.

目前冬季施工一般采用在混凝土中添加早强剂来缓解低温对混凝土造成的不良影响，早强剂大体分为无机盐早强剂和有机物早强剂，其中无机盐早强剂主要包括：氯化盐，碳酸盐，硝酸盐，硫代硫酸盐，硅酸盐，铝酸盐等，有机类早强剂主要有：三乙醇胺，二乙醇胺，甲酸钙，乙酸钙，尿素，草酸等。本论文主要研究无机早强剂NaNO3对混凝土性能的影响。

At present, early strength agents are generally added to concrete in winter to alleviate the adverse effects of low temperature on concrete. Early strength agents are generally divided into inorganic salt early strength agents and organic early strength agents. Inorganic salt early strength agents mainly include chloride, carbonate, nitrate, thiosulfate, silicate, aluminate, etc. organic early strength agents mainly include triethanolamine, Diethanolamine, calcium formate, calcium acetate, urea, oxalic acid, etc. This paper mainly studies the effect of inorganic early strength agent NaNO3 on the properties of concrete.

一、实验部分

1、 Experimental part

1.实验原料

1. Experimental raw materials

所用硝酸钠为分析纯，减水剂为自制质量分数为40%的聚羧酸减水剂液体，水泥为声威P·O42.5水泥。

The sodium nitrate used is analytical pure, the water reducing agent is polycarboxylic acid water reducing agent liquid with self-made mass fraction of 40%, and the cement is Shengwei P · o42.5 cement.

2.实验仪器

2. Experimental instruments

混凝土试验用搅拌机为无锡建仪仪器机械有限公司HJW60型搅拌机。

The mixer for concrete test is HJW60 mixer of Wuxi Jianyi Instrument Machinery Co., Ltd.

3.混凝土强度检测

3. Concrete strength test

根据国标GB/T50107-2010《混凝土强度检验评定标准》对混凝土强度进行检测。

The concrete strength is tested according to the national standard GB / t50107-2010 standard for inspection and evaluation of concrete strength.

二、实验与讨论

2、 Experiment and discussion

硝酸钠在-5℃下对混凝土强度的影响

Effect of sodium nitrate on concrete strength at - 5 ℃

将不同质量的硝酸钠与聚羧酸减水剂复配使用，按照表1配合比制备混凝土并装入试模，放置于温度为-5℃冰柜中冷冻，7天后取出拆模，继续在标准养护条件下养护28天，分别对冷冻7天和冷冻后继续标准养护28天的试块强度进行检测。

Mix sodium nitrate of different quality with polycarboxylate superplasticizer, prepare concrete according to the mix proportion in Table 1, put it into the test formwork, place it in the freezer with the temperature of - 5 ℃, remove the formwork after 7 days, continue to cure under standard curing conditions for 28 days, and test the strength of test blocks frozen for 7 days and after freezing for 28 days.