What are the effects of the addition amount of hydroxypropyl methyl cellulose on the properties of mortar?

Hydroxypropyl methyl cellulose HPMC can significantly improve water retention of mortar, and the lower dosage of hydroxypropyl methyl cellulose HPMC can significantly improve the water retention of mortar. When the content is 0.02%, the water retention rate increases from 83 % rose to 88%; when the dosage was 0.2%, the water retention rate reached 97%. At the same time, the low content of HPMC also significantly reduced the stratification and bleeding rate of the mortar, which indicates that HPMC can not only improve water retention of mortar, but also significantly improve the cohesion of mortar, which is very beneficial to the uniformity of the mortar construction quality.

However, hydroxypropyl methyl cellulose HPMC had a certain degree of negative effect on the flexural and compressive strength of mortar. With the increase of HPMC dosage of hydroxypropyl methyl cellulose, the flexural strength and compressive strength of mortar decreased gradually. At the same time, hydroxypropyl methyl cellulose HPMC can improve the tensile strength of mortar. When the content of hydroxypropyl methyl cellulose HPMC is less than 0.1%, the tensile strength of mortar increases continuously with the increase of HPMC content. After the dosage exceeds 0.1%, the tensile strength does not increase significantly. HPMC can also significantly increase the compressive shear bond strength of mortar. Adding 0.2% HPMC can increase the bond strength of mortar from 0.72MPa. increased to 1.16MPa.

Studies have shown that hydroxypropyl methyl cellulose HPMC can significantly prolong the drying time of mortar and significantly improve slip resistance of mortar, which is very beneficial for tile fixed construction. Without HPMC, the bond strength of mortar after drying for 20min decreased from 0.72MPa to 0.54MPa. After adding 0.05% and 0.1% HPMC, the bond strength of the mortar after drying for 20min was 0.8MPa and 0.84MPa, respectively. The slippage of mortar without HPMC was 5.5mm. With the increase of HPMC content, the slippage decreased continuously. When the content of HPMC was 0.2%, the slippage of mortar dropped to 2.1mm. The significant reduction in slippage provides a technical guarantee for thin-layer construction such as tile fixing.

In addition, hydroxypropyl methyl cellulose HPMC can effectively inhibit the formation of plastic cracks in mortar, which can significantly reduce plastic cracks. When the content of HPMC is low, the crack index decreases significantly with the increase of the content of HPMC. When the content of HPMC is 0.1% and 0.2%, the relative crack index of the mortar is 63% and 50%, respectively. When the content of HPMC exceeds 0.2%, Mortar plastic cracks are no longer significantly reduced.