Hydroxypropyl methylcellulose (HPMC) mainly plays the role of water retention, thickening and improving construction performance in cement, gypsum and other powder materials. Excellent water retention performance can effectively prevent the powder from drying and cracking due to excessive water loss, and make the powder have a longer construction time.
Carry out the selection of cementitious materials, aggregates, aggregates, water retaining agents, binders, construction performance modifiers, etc. For example, gypsum-based mortar has better bonding performance than cement-based mortar in a dry state, but its bonding performance decreases rapidly under the condition of moisture absorption and water absorption. The target bonding strength of the plastering mortar should be reduced layer by layer, that is, the bonding strength between the base layer and the interface treatment agent ≥ the bonding strength between the base layer mortar and the interface treatment agent ≥ the bond between the base layer mortar and the surface layer mortar Strength ≥ the bonding strength between surface mortar and putty material.
The ideal hydration goal of cement mortar on the base is that the cement hydration product absorbs water along with the base, penetrates into the base, and forms 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 cement hydration and the penetration of 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.
Effect of cellulose ether on compressive and shear strength of cement mortar.
With the addition of cellulose ether, the compressive and shear strengths decrease, because the cellulose ether absorbs water and increases the porosity.
The bonding performance and bonding strength depend on whether the interface between the mortar and the base material can be stably and effectively realized “key connection” for a long time.
Factors affecting bond strength include:
1. The water absorption characteristics and roughness of the substrate interface.
2. The water retention capacity, penetration capacity and structural strength of the mortar.
3. Construction tools, construction methods and construction environment.
Because the base layer for mortar construction has certain water absorption, after the base layer absorbs the water in the mortar, the constructability of the mortar will be deteriorated, and in severe cases, the cementitious material in the mortar will not be fully hydrated, resulting in strength, special The reason is that the interface strength between the hardened mortar and the base layer becomes lower, causing the mortar to crack and fall off. The traditional solution to these problems is to water the base, but it is impossible to ensure that the base is evenly moistened.
Post time: May-06-2023