不同类型盐碱对不同水泥基材料收缩性能的影响

Influence of Different Alkali Sulfates on Shrinkage Properties of Cement-based Materials with Different Mineral Compositions

通过分别外掺Na_(2)SO_(4)(Na碱)和K_(2)SO_(4)(K碱)将低热硅酸盐水泥、中热硅酸盐水泥和普通硅酸盐水泥总碱含量均调节至0.8%和1.2%,探究了不同类型盐碱对不同水泥基材料自收缩和干燥收缩的影响,并基于微量热技术、孔结构分析技术和核磁共振技术,揭示了不同类型盐碱对不同水泥基材料自收缩和干燥收缩的影响机制。研究表明:①盐碱促进了不同水泥基材料的收缩。在相同盐碱含量下,低热硅酸盐水泥具有较低的自收缩率,普通硅酸盐水泥自收缩率最大,但普通硅酸盐水泥干燥收缩最小,中热硅酸盐水泥干燥收缩最大;②在不同水泥基材料中,K碱的促进作用高于Na碱,并随碱含量的增加而增加,当碱含量为0.8%时,K碱的促进作用为Na碱的1.1倍以上,当碱含量为1.2%时,K碱的促进作用为Na碱的1.3倍以上。微观试验表明,K碱较Na碱对水泥基材料收缩具有更高的促进作用,其机制在于K碱能更大程度促进水泥水化,提高影响收缩的<50 nm的孔含量,并与Al原子向水化硅酸钙(C-S-H)链中转移有关。

In this study,Na_(2)SO_(4)(Na alkali)and K_(2)SO_(4)(K alkali)were added to adjust the total alkali content of low-heat Portland cement(LHPC),medium-heat Portland cement(MMPC)and ordinary Portland cement(OPC)to 0.8%and 1.2%.The effects of different alkali sulfates on autogenous shrinkage and dry shrinkage of cement-based materials with different mineral compositions were investigated.The mechanism of different alkali sulfates affecting the autogenous shrinkage and drying shrinkage of different cement-based materials was also revealed via microcalorimetry,mercury intrusion porosimetry(MIP)and nuclear magnetic resonance(NMR).Results indicate that 1)alkali sulfates promote the shrinkage of different cement-based materials.At the same content of alkali sulfate,LHPC has a low autogenous shrinkage rate and OPC has a high autogenous shrinkage rate;but as for drying shrinkage,OPC has the smallest rate and MHPC has the largest rate.2)In different cement-based materials,the promotion effect of K alkali is higher than that of Na alkali and such promotion effect intensifies with the rise of alkali content.When alkali content is 0.8%,the promotion effect of K alkali is more than 1.1 times that of Na alkali;when alkali content reaches 1.2%,the promotion effect of K alkali is over 1.3 times that of Na alkali.Microscopic test also manifested a larger promotion effect of K alkali than Na alkali:K alkali promotes the hydration of cement,enhances the content of pores with a size smaller than 50 nm,and is related to the transfer of Al atoms into C-S-H chain.