Investigation on the performance of hydroxyethyl methyl cellulose modified cement mortars with Portland cement-calcium sulfoaluminate cement binders

Abstract

Dry-mix mortars with Portland cement and calcium sulfoaluminate cement (PC-CSA) binders are gradually applied in many fields due to their various excellent properties. Hydroxyethyl methyl cellulose (HEMC) is commonly used as an agent in the dry-mix mortars to further improve performance. Herein, the purpose of this study is to investigate the performance of HEMC-modified cement mortars with PC-CSA binders. The results show that HEMC has great effects on the properties and hydration of the cement mortars with PC-CSA binders. HEMC improves the water retention ability, decreases the consistency and fluidity to bring the flowability reduction, and increases the air content consequently to decrease the bulk density. Meanwhile, HEMC somewhat extends the setting time. With the HEMC content increasing, HEMC obviously decreases the flexural and compressive strengths. However, HEMC can improve the tensile bond strength, especially at the high HEMC content. HEMC decreases the drying shrinkage, regardless of its content. HEMC retards the hydration process of the PC-CSA binders, and affects the formation of ettringite (AFt) and calcium hydroxide (CH). HEMC delays the transformation of AFt to monosulfoaluminate (AFm) and decreases the consumption of CH at later age, and the preferred orientation growth of CH is also declined. Moreover, HEMC increases the macro-capillary pores and macro pores, but decreases the meso-capillary pores.