Evolutions in the properties and microstructure of cement mortars containing hydroxyethyl methyl cellulose after controlling the air content

Hydroxyethyl methyl cellulose (HEMC) is generally mixed into cement mortars to improve physical properties. However, the air entrainment effect of HEMC may bring some unsatisfactory performances. The way to control the air content of cement mortars is expected to offset these unsatisfactory properties. The results show that opposite to that without controlling the air content, the mid-late flexural strengths increase with the amount of HEMC through controlling the air content. The decrease of compressive strength is significantly alleviated through controlling the air content. Whether controlling the air content or not, the tensile bond strength is significantly improved by the incorporation of HEMC, and is somewhat higher by controlling the air content. The drying shrinkage values significantly increase with the amount of HEMC, and is apparently alleviated through controlling the air content. Whether controlling the air content or not, the early hydration degree of cement pastes with HEMC is retarded, but is slightly higher by controlling the air content. Additionally, the porosity of cement mortars shows a gradual increase trend with the amount of HEMC. In cement mortars with controlling the air content, the large capillary pores increase but macro pores show limited changes with the amount of HEMC. However, through controlling the air content, both the porosity and the contents of macro pores, medium capillary and large capillary pores are much lower. Obviously, the improvement of performances of cement mortars with controlling the air content may be mainly attributed to the decrease of porosity and the optimization of pore structure.