mortar additive hpmcMay 11th 2023
As we all know, the theory of cement’s complete hydration theory requires 26% of the cement’s mass, and the actual water consumption of the mortar greatly exceeds the moisture required for the cement’s hydration in the mortar, which is mainly to meet the needs of construction. The strength of cement stone is mainly related to the water-cement ratio. The larger the water-cement ratio, the greater the porosity of the cement stone, the lower the strength of the cement stone, and the lower the mortar strength. Therefore, as long as the water retention performance of the masonry mortar guarantees the operability of the mortar and the water required for cement hydration in the mortar.
If the water retention of masonry mortar is too good, then the actual moisture retained in the mortar will be greater, the true water-cement ratio of the mortar will be greater, the actual strength of the mortar will be lower, and the bond strength with the block will be correspondingly lower. In addition, the water retention of the mortar is too good, and the water is not easily absorbed by the block material, which will also affect the bonding of the cement slurry to the block material, and will prolong the setting time of the mortar, thereby affecting the masonry speed and increasing the difficulty of construction. Therefore, the water retention index of masonry mortar should correspond to the block material.
If the pore structure of the block material is open, and the block material is easy to be penetrated by water, such as sintered bricks, the water retention of masonry mortar can be lower, only 80% or more can be used, such as masonry with traditional mortar Sintering ordinary bricks is very effective.
If the pore structure of the block material is closed, the porosity is high, the block material is not easy to be penetrated by water, or the block material is not allowed to be wetted by water during construction, then the water retention of masonry mortar should be improved to meet the mortar Moisture required for medium cement hydration. For example, in the construction of autoclaved lime-sand bricks, if masonry mortars with a water retention rate of 80% are used to build lime-sand bricks, the mortar’s water retention is low and the mortar water is easily absorbed by the lime-sand bricks, causing cement hydration in the lime joints The required moisture is seriously insufficient, making the cement hydration unable to proceed normally, reducing the true strength of the mortar and the bonding strength between the mortar and the lime-sand bricks. This is also one of the reasons for the easy cracking of the masonry with traditional mortars. Therefore, the water retention of the mortar used for masonry bricks should be controlled above 88%.
However, if we increase the water retention of the mortar of the masonry bricks to more than 95%, it will be difficult to absorb the water in the mortar joints, the actual strength of the mortar will be reduced, and the bond strength between the mortar and the bricks will also be reduced. The water retention of the mortar is too good, and the brick is not easy to adhere to the mortar and stabilized during the masonry, and the height of the masonry is limited.
Therefore, the water retention of hydroxypropyl methylcellulose in masonry mortar is not as high as possible, and there should be a suitable water retention range for different block materials.