Questions about You Should Know about HPMCMarch 23rd 2023
The application of RDP to mortar is actually a modification of ordinary mortar, also known as polymer modified cement mortar. Through polymer modification, the weaknesses of traditional cement mortar such as brittleness and high modulus of elasticity are improved; giving the cement mortar better flexibility and tensile bond strength to resist or retard the generation of cracks in cement mortar
The abrasion resistance of modified mortar is related to the type of RDP and the ratio of aggregates to cement. In general, the increase in polymer-cement ratio and the increase in wear resistance are mainly due to the presence of a certain amount of surface polymers on the wear surface, which act as a bonding agent. The net-like structure formed by the polymers penetrates through the holes and cracks in the cement mortar and improves the bond between the aggregate and the cement hydration products, thus increasing the wear resistance.
Cracking of materials is mainly caused by tensile damage. Cracking occurs when the tensile stress exceeds its own tensile strength value. Therefore, a high tensile strength value is required to resist cracking.
The tensile strength of polymer modified mortar tends to increase and then decrease with the increase of polymer to cement ratio, indicating the existence of an optimum fit range. Therefore, the main way to improve the compressive strength is to adjust the ratio of lime to sand and water to cement.
The bonding ability of RDP cement mortar is much better than that of ordinary cement mortar, which is mainly due to the bonding ability exhibited by the properties of the polymer. The bond strength increases with increasing dosage, but there is an optimum dosage range and cost considerations.
High bond strength inhibits shrinkage to some extent and stresses from deformation are easily dispersed and released, so bond strength is very important to improve crack resistance. Especially for those porous substrate surfaces, it can improve the water resistance and freeze-thaw resistance of the substrate.
The moisture permeability of building materials is of great importance. Building materials that can be waterproof and permeable to water vapor are expected in many settings. Polymer modified mortar has low water absorption and improved water resistance, but still has some water vapor permeability, which decreases with the increase of polymer content. It is also possible to compound some hydrophobic materials to improve its overall performance.
In polymer-modified mortar, the polymer-filled reticulated film structure closes the pores and cracks in the cement mortar and reduces the porosity in the hardened body, thus improving the impermeability, water resistance and frost resistance of the cement mortar. Therefore, VAC can also be used except where there is no water resistance requirement. VAC is usually used in gypsum-based products and putty powders that do not contain cement.