Hydroxypropyl methylcellulose has an important role in mortar, that is, water retention. Mortar with poor water retention is easy to segregate during transportation, and water is easy to lose. When it is spread on the surface of porous materials, most of the water is easy to be absorbed. Change the performance of the mortar, so as to affect the normal hardening of the mortar and the bonding between the block materials, thereby reducing the strength of the masonry. The water retention of mortar is expressed by layering degree.
The test method for the degree of stratification of the mortar is as follows: put the freshly mixed mortar mixture into a stratification tester with an inner diameter of 15 cm, a height of the upper part of 20 cm, a height of the lower part of 10 cm and the bottom row, and measure its sedimentation. Then let it stand for 30 minutes, remove the 20 cm of mortar above, re-mix the remaining 10 cm of mortar, measure the sinking degree and other values, then the layering degree of the mortar can be easily calculated by us.
The mortar with good water retention has a small degree of delamination. Generally, it is required to take 1-2 cm as the negative delamination degree. The mortar with a delamination degree greater than 2 cm has poor water retention and is easy to segregate. The construction operation does not restore the mortar with a delamination degree close to zero. , strong water retention, no layering up and down, but this phenomenon is often caused by too much cementitious material or too fine sand, so the mortar is prone to drying shrinkage cracks, especially not suitable for plastering mortar.
01. Effect of water retention performance of hydroxypropyl cellulose on mortar:
The water retention of mortar refers to the ability of mortar to retain water. Mortar with poor water retention is prone to bleeding and segregation during transportation and storage, that is, water floats on the top, and sand and cement sink below. It must be re-stirred before use.
All kinds of bases that require mortar for construction have certain water absorption. If the water retention of the mortar is poor, the ready-mixed mortar will be absorbed as soon as the ready-mixed mortar comes into contact with the block or base during the application of the mortar. At the same time, the outer surface of the mortar evaporates water into the atmosphere, resulting in insufficient moisture in the mortar due to dehydration, which affects the further hydration of the cement, and at the same time affects the normal development of the mortar strength, resulting in strength, especially the interface between the hardened mortar and the base layer. becomes lower, causing the mortar to crack and fall off. For the mortar with good water retention, the cement hydration is relatively sufficient, the strength can be developed normally, and it can be better bonded to the base layer.
Ready-mixed mortar is usually built between water-absorbing blocks or spread on the base, forming a whole together with the base. The impact of poor water retention of mortar on project quality is as follows:
1. Due to the excessive loss of water from the mortar, it will affect the normal coagulation and hardening of the mortar, and reduce the bonding force between the mortar and the surface, which is not only inconvenient for construction operations, but also reduces the strength of the masonry, thereby greatly reducing the quality of the project.
2. If the mortar is not well bonded, the water is easily absorbed by the bricks, making the mortar too dry and thick, and the application is uneven. When the project is implemented, it not only affects the progress, but also makes the wall prone to cracking due to shrinkage;
Therefore, increasing the water retention of mortar is not only beneficial to construction, but also increases the strength.
02. The traditional method of improving the water retention of mortar
The traditional solution is to water the base, but it is impossible to ensure that the base is evenly moistened. The ideal hydration goal of cement mortar on the base is: the cement hydration product penetrates into the base along with the process of the base absorbing water, forming an effective “key connection” with the base, so as to achieve the required bond strength.
Watering directly on the surface of the base will cause serious dispersion in the water absorption of the base due to differences in temperature, watering time, and watering uniformity. The base has less water absorption and will continue to absorb the water in the mortar. Before the cement hydration proceeds, the water is absorbed, which affects the penetration of cement hydration and hydration products into the matrix; the base has a large water absorption, and the water in the mortar flows to the base. The medium migration speed is slow, and even a water-rich layer is formed between the mortar and the matrix, which also affects the bond strength. Therefore, using the common base watering method will not only fail to effectively solve the problem of high water absorption of the wall base, but will affect the bonding strength between the mortar and the base, resulting in hollowing and cracking.
03. The role of efficient water retention
The high water retention performance of mortar has many advantages:
1. The excellent water retention performance makes the mortar open for a longer time, and has the advantages of large-area construction, long service life in the bucket, and batch mixing and batch use.
2. Good water retention performance makes the cement in the mortar fully hydrated, effectively improving the bonding performance of the mortar.
3. Mortar has excellent water retention performance, which makes the mortar less prone to segregation and bleeding, and improves the workability and constructability of the mortar.