Analysis of the Effect of Hydroxypropyl Methyl Cellulose HPMC on the Properties of Cement Mortar

The effect of hydroxypropyl methylcellulose (HPMC) dosage on the performance of mortar. HPMC can significantly improve the water retention of mortar. A lower dosage of HPMC can significantly improve the water retention rate of mortar. When the dosage is 0.02%, the water retention rate decreases from 0.02% to 0.02%. 83% increased to 88%; when the dosage was 0.2%, the water retention rate reached 97%. At the same time, low dosage of HPMC also significantly reduces the mortar delamination degree and bleeding rate. This shows that HPMC can not only improve the water retention of mortar, but also significantly improve the cohesion of mortar, which is important for the uniformity of mortar construction quality. Very beneficial. However, HPMC has a certain negative impact on the flexural strength and compressive strength of mortar. As the HPMC content increases, the flexural strength and compressive strength of the mortar show a gradually decreasing trend. At the same time, HPMC can improve the tensile strength of mortar. When the HPMC content is within 0.1%, as the HPMC content increases, the tensile strength of the mortar continues to increase. When the content exceeds 0.1%, the tensile strength is no longer obvious. Adding HPMC can also significantly increase the pressure-shear bonding strength of mortar. Adding 0.2% HPMC can increase the bonding strength of mortar from 0.72MPa to 1.16MPa. Studies have shown that hydroxylactamyl cellulose HPMC can significantly extend the service life of mortar. The cooling time significantly reduces the slippage of the mortar, which is very beneficial for ceramic tile pasting construction. Without HPMC, the bonding strength of the mortar after cooling for 20 minutes dropped from 0.72MPa to 0.54MPa. After adding 0.05% and 0.1% HPMC, the bonding strengths of the mortar after cooling for 20 minutes were 0.8MPa and 0.84MPa respectively. When HPMC is not added, the slippage of the mortar is 5.5mm. As the HPMC content increases, the slippage continues to decrease. When the HPMC content is 0.2%, the slippage of the mortar drops to 2.1mm. The significant reduction in slippage is the reason for the ceramic tile adhesion. The thin-layer construction provides technical support. In addition, hydroxypropyl methylcellulose HPMC can effectively inhibit the formation of plastic cracks in mortar and significantly reduce plastic cracks. When the HPMC content is low, the crack index decreases significantly as the HPMC content increases. When the HPMC content is 0.1% and 0.2%, the relative crack index of the mortar is 63% and 50% respectively. When the HPMC content exceeds 0.2%, The plastic cracks of the mortar are no longer significantly reduced.

Effect of hydroxypropyl methylcellulose HPMC viscosity and fineness on mortar properties Viscosity and fineness are important indicators that affect the performance of HPMC. Research shows that the water retention effect of HPMC increases as its viscosity increases, but when the viscosity exceeds 40,000 MPa-s, the water retention effect increases only to a limited extent as the viscosity increases. The higher the viscosity, the greater the molecular weight of HPMC, and the solubility will be reduced accordingly. It will not greatly improve the water retention of the mortar, but it will have a negative impact on the strength and workability. Taking comprehensive considerations into account, it is more appropriate to use cellulose ether with a viscosity of 40000 MPa's in cement mortar. As the HPMC particles gradually become finer, the water retention of the mortar also increases to a certain extent. Fineness affects the solubility of HPMC. Coarse HPMC dissolves very slowly in water and is not suitable for use in dry-mixed mortar (some domestic products are flocculent, which is not only difficult to disperse and dissolve in water, but may even agglomerate). In dry-mixed mortar, HPMC is dispersed among cementitious materials such as aggregates, fine fillers, and cement. Only sufficiently fine powder can avoid caking when water is added and mixed. When HPMC is dissolved and agglomerated by adding water, it is very difficult to disperse and dissolve again. HPMC with a coarser particle size is not only wasteful, but also reduces the local strength of the mortar. When such dry-mixed mortar is constructed over a large area, the curing speed of the local mortar may be significantly reduced, and uneven hydration of the cementing material may occur. of cracking. For spray mortar using mechanical construction, due to the short mixing time, the requirements for HPMC fineness are higher. Therefore, after comprehensive consideration, the particle size of red vitamin ether used in cement mortar should be less than 80um. It can be seen that hydroxylactamyl cellulose HPMC is an efficient water-retaining agent for dry-mix mortar. It can improve the mortar bleeding rate and layering degree. decreases, thereby improving the cohesion and sag resistance of the mortar. Although HPMC slightly reduces the flexural and compressive strength of the mortar, it can significantly increase the tensile strength and bonding strength of the mortar. The appropriate dosage of HPMC in dry-mixed mortar is 0.1%-0.3%. In addition, HPMC can effectively inhibit the formation of plastic cracks in mortar and reduce the plastic cracking index of mortar. The water retention of mortar increases as the viscosity of HPMC increases, but when the viscosity exceeds 40,000 MPas, the water retention no longer increases significantly. The fineness of HPMC also has a certain impact on the water retention rate of mortar. When the particles are finer, the water retention rate of mortar is improved. Typically the particle size of HPMC used in cement mortars should be less than 80μm.