养护温度对赤泥基路用胶凝材料性能及微观结构的影响

Effects of Curing Temperature on Properties and Microstructure of Red Mud-based Road Cementitious Material

赤泥基路用胶凝材料可代替水泥应用于道路半刚性基层建设。山东省属暖温带季风性气候,全年气温波动大。在半刚性基层施工期间,不同月份导致赤泥基路用胶凝材料养护温度不同。基于2006—2023年山东(济南)温度变化特征确定养护温度为1℃、4℃、10℃、16℃、20℃、25℃、28℃,通过万能试验机和^(1)H低场核磁共振分析仪研究养护温度对赤泥基路用胶凝材料抗压强度及微观结构的影响规律,并利用X射线衍射、热重测试分析、ICP-OES揭示养护温度对赤泥基路用胶凝材料性能演化的作用机理。结果表明,养护温度升高会促进赤泥基路用胶凝材料抗压强度发展,养护温度为28℃时7 d抗压强度达到21.15 MPa,相较于养护温度为1℃时提升67.41%,且当养护温度不低于20℃时,在整个养护阶段强度发展率大于1 MPa/d。养护温度的提升会优化结石体孔结构分布,养护7 d后,随温度升高结石体的凝胶孔、过渡孔占比从37.82%提升到80%以上,毛细孔占比从62.18%下降到15%左右。赤泥基路用胶凝材料水化产物主要为(C,N)-A-S-H凝胶,其对强度发展起重要作用,养护温度的提升会促进赤泥Si/Al元素溶出,从而提高(C,N)-A-S-H凝胶的生成量。月均温度低于10℃时不宜进行道路施工,月均温度在10~20℃时可延长赤泥基胶凝材料养护时间促进其强度发展。

Red mud-based road cementitious material can be used instead of cement in the construction of semi-rigid road bases.Shandong Province has a warm temperate monsoon climate with significant fluctuations in temperature throughout the year.Different months result in different curing temperatures for the cementitious material.This work focused on the influencing law and underlying mechanism of variation of curing temperature on the compressive strength and microstructure of red mud-based road cementitious material.The curing temperatures applied in the experiment was changed amongst 1℃,4℃,10℃,16℃,20℃,25℃,and 28℃,which was determined based on the actual temperature data in Shandong(Jinan)from 2006 to 2023.The instruments used in strength test and microstructure observation were a universal testing machine and a ^(1)H low-field nuclear magnetic resonance analyzer,and the means utilized for revealing the underlying mechanism of curing temperature variation-induced performance evolution included X-ray diffractometry,thermogravimetry,and ICP-OES.It could be concluded that an increase in curing temperature would promote the development of compressive strength of red mud-based road cementitious material.The cementitious material cured at 28℃achieved a 7-day compressive strength of 21.15 MPa,67.41%higher than that achieved under the curing temperature of 1℃.When the material was cured at a temperature of≥20℃,its whole-curing-stage strength development rate was higher than 1 MPa/d.Increasing the curing temperature would result in optimized pore structure distribution of the stone body.After 7 days of curing,with the increase of curing temperature,the proportions of gel pores and transition pores in the stone bodies increased from 37.82%to higher than 80%and the proportion of pores decreased from 62.18%to about 15%.The main hydration product of red mud-based road cementitious material is(C,N)-A-S-H gel,which plays an important role for strength development.Higher curing temperatures are conducive to the dissolution of Si/Al elements in red mud,thus increasing the production of(C,N)-A-S-H gel.For the application of red mud-based cementitious material to road engineering,it is recommended not to perform road construction when monthly average temperature is below 10℃,and to extend the curing time to accelerate strength development when monthly average temperature is within 10—20℃.