速凝剂主要组分对水泥水化及力学性能的影响

速凝剂是喷射混凝土施工中重要的材料之一,偏铝酸钠(Na Al O2)和硫酸铝(Al2(SO4)3)作为有碱和无碱速凝剂的主要组分(以下分别简称NA和AS),对喷射混凝土性能影响显著。通过化学结合水测试、热分析、压汞测试及强度测试,研究了偏铝酸钠和硫酸铝对水泥水化程度、水化产物类型、硬化浆体孔结构及力学性能的影响。结果表明:NA和AS提高了水泥早期水化速率,降低了浆体内部总孔隙率和最可几孔径,提高了硬化水泥浆体1d的抗压强度,并分别生成以3CaO·Al2O3·Ca SO4·12H2O和3CaO·Al2O3·3CaSO4·32H2O(以下分别简称AFm和AFt)为代表的早期特征水化产物。1 d以后,NA和AS均减缓水泥水化速率及孔结构细化程度,对抗压强度发展产生不利影响,28 d后,掺入NA和AS水泥浆体内部无害孔数量少于空白组,有害孔和多害孔数量多于空白组,抗压强度相对于空白组均产生一定程度的倒缩。掺入AS的硬化水泥浆体无害孔,有害孔和多害孔含量介于空白组和NA之间,对于抗压强度的折减程度要低于NA。

Influence of Accelerator Main Components on Hydration and Mechanical Properties of Portland Cement

Accelerator is one of the important materials in shotcrete construction.Sodium aluminate and aluminum sulfate,as the main components of alkali and non-alkali accelerators,which are referred to NA and AS respectively,have significant influence on the properties of shotcrete.The effects of sodium aluminate(NA)and aluminum sulfate(AS)on the hydration degree,hydration product,pore structure and mechanical properties of Portland cement paste were investigated using non-evaporative water test,thermos gravimetric analysis,mercury intrusion porosimetry(MIP)and strength tests.The results show that NA and AS increased the early hydration rate of cement,reduced total porosity and most probable pore size in the paste,improved the compressive strength of hardened cement paste at 1 d and generated early characteristic hydration products 3CaO·Al 2O 3·CaSO 4·12H 2O and 3CaO·Al 2O 3·3CaSO 4·32H 2O,which are referred to AFm and AFt respectively.After 1 day,NA and AS both slowed down the hydration rate and pore structure refinement of cement,which produce adverse impact on the development of compressive strength.After 28 days,the number of harmless pores in the hardened cement paste mixed with NA and AS was less than that in the blank group and the number of harmful pores and multiple harmful pores was more than that in the blank group.The compressive strength of NA and AS cement paste decreased to a certain extent compared with blank group.The content of harmless pores,harmful pores and multiple harmful pores in the hardened cement paste mixed with AS is between blank group and NA,while the compressive strength reduction degree is lower than NA.