Functions of HPMC in Dry Mix Mortar

Functions of HPMC in Dry Mix Mortar

In dry mix mortar, adding a little HPMC can significantly improve the performance of wet mortar. It can be seen that HPMC is a major additive that affects the construction performance of mortar.

● Water Retention

Water retention is an important property of HPMC. The viscosity, dosage, environmental temperature and molecular structure of HPMC have a greater impact on its water retention performance. Under the same conditions, the higher the viscosity of HPMC, the better the water retention; The higher content, the better the water retention. Generally, a small amount of HPMC can greatly increase the water retention rate of the mortar. When the content reaches a certain level, The trend of the water retention increasing slows down; as the ambient temperature increases, the water retention of HPMC usually decreases, but some modified HPMC also have better water retention under high temperature conditions; HPMC with lower substitution degree has better water retention performance.

● Thickening and Thixotropy

HPMC gives the wet mortar excellent viscosity, can significantly increase the bonding ability of the wet mortar and the base, and improve the sag resistance of the mortar. It is widely used in plastering mortar, facing brick bonding mortar and external wall insulation system. The thickening effect of HPMC can also increase the anti-dispersion ability and homogeneity of freshly mixed materials, prevent material delamination, segregation and bleeding, and can be used in fiber concrete, underwater concrete and self-compacting concrete.

The thickening effect of HPMC on cement-based materials comes from the viscosity of HPMC solution. Under the same conditions, the higher the viscosity of HPMC, the better the viscosity of the modified cement-based material, but if the viscosity is too large, the fluidity and operability of the material will be affected. Self-leveling mortar and self-compacting concrete, which require high fluidity, require a very low viscosity of HPMC. In addition, the thickening effect of HPMC will increase the water demand of cement-based materials and increase the output of mortar.

● Air-entraining Effect

HPMC has obvious air-entraining effect on fresh cement-based materials. HPMC has both hydrophilic groups (hydroxyl group, ether group) and hydrophobic group (methyl group, glucose ring). It is a surfactant with surface activity and air-entraining effect. The air-entraining effect of HPMC will produce a “ball” effect, which can improve the working performance of freshly mixed materials, such as increasing the plasticity and smoothness of the mortar during operation, which is conducive to the paving of mortar; it will also increase the output of mortar and reduce Mortar production cost; but it will increase the porosity of the hardened material and reduce its strength and elastic modulus and other mechanical properties.

● Retarding

HPMC will prolong the setting time of cement paste or mortar and delay the hydration kinetics of cement, which is beneficial to increase the operating time of freshly mixed materials, improve the consistency of mortar and the loss of concrete slump over time, but it may also delay construction schedule.

Based on above functions of HPMC, HPMC also have other properties in different kind of dry mix mortar products, like sag resistance, increase the workability, Adjust the setting time and increase the bonding strength, and etc.