What is the application of hydroxypropyl methylcellulose ether in machine blasting mortar?

The mechanized construction of mortar has been tried and promoted for many years in China, but no substantial progress has been made. In addition to people’s skepticism about the subversive changes that mechanized construction will bring to traditional construction methods, the main reason is that under the traditional mode, the mortar mixed on site is likely to cause pipe plugging and other projects during the mechanized construction process due to problems such as particle size and performance. Faults not only affect the construction progress, but also increase the construction intensity, which breeds workers’ fear of difficulties and increases the difficulty for the promotion of mechanized construction.

In recent years, with the establishment of large-scale dry-mixed mortar factories all over the country, the quality and stability of mortar have been guaranteed. However, dry-mixed mortar is processed and produced by factories. In terms of raw materials alone, the price must be higher than that of on-site mixing. If manual plastering is continued, it will have no competitive advantage over on-site mixing mortar, even if there are countries Due to the “ban cash” policy, the new dry-mixed mortar factories are still struggling to make ends meet, and eventually go bankrupt. What’s more, there is a shortage of migrant workers in many first-tier cities such as Beijing, Guangzhou, Shenzhen and other places, and the labor cost of construction is getting higher and higher, which promotes the perfect combination of mechanized construction and dry-mixed mortar.

Brief introduction to the comprehensive performance of machine-sprayed mortar Compared with the traditional on-site mixed mortar, the biggest difference of machine-sprayed mortar is the introduction of a series of admixtures such as hydroxypropyl methyl cellulose ether that can optimize the performance of the mortar, so that the freshly mixed The mortar has good workability, high water retention rate, and still has good working performance after long-distance and high-height pumping. Its biggest advantage lies in its high construction efficiency and good quality of mortar after molding. Since the mortar has a relatively large initial velocity during spraying, it can have a relatively firm grip with the substrate, which can effectively reduce the phenomenon of hollowing and cracking. occur. After continuous tests, it is found that when preparing machine-sprayed plastering mortar, use machine-made sand with a maximum particle size of 2.5mm, a stone powder content of less than 12%, and a reasonable gradation, or a maximum particle size of 4.75mm and a mud content of less than 5%. When the water retention rate of the freshly mixed mortar is controlled above 95%, the consistency value is controlled at about 90mm, and the 2h consistency loss is controlled within 10mm, the mortar has good pumping performance and spraying performance. performance, and the appearance of the formed mortar is smooth and clean, the slurry is uniform and rich, no sagging, no hollowing and cracking.

Discussion on composite additives of machine sprayed mortar The construction process of machine sprayed mortar mainly includes mixing, pumping and spraying. On the premise that the formula is reasonable and the quality of raw materials is qualified, the main function of the machine sprayed mortar compound additive is to optimize the quality of the freshly mixed mortar and improve the pumping performance of the mortar. Therefore, the general machine sprayed mortar compound additive is composed of water retention agent and pumping agent. Hydroxypropyl methyl cellulose ether is a water-retaining agent with excellent performance. It can not only increase the viscosity of mortar, but also can significantly improve the fluidity of mortar and reduce segregation and bleeding under the same consistency value. happened. The pumping agent is generally composed of air-entraining agent and water reducing agent. During the stirring process of the freshly mixed mortar, a large number of tiny air bubbles are introduced to form a ball effect, which can reduce the friction resistance between aggregate particles and improve the pumping performance of the mortar. During the spraying process of machine-sprayed mortar, the micro-vibration caused by the rotation of the screw conveying pump can easily cause the mortar in the hopper to stratify, resulting in a small consistency value in the upper layer and a large consistency value in the lower layer, which will easily lead to pipe blockage when the machine is running, and the uneven quality of the mortar after molding is prone to shrinkage and cracking. Therefore, when designing composite additives for machine-blasted mortar, some stabilizers should be properly added to slow down the delamination of mortar.

When the staff were doing machine-sprayed mortar experiments, the amount of compound additives was 0.08%. The final mortar had good workability, excellent pumping performance, no sag phenomenon during the spraying process, and the maximum thickness of one spraying could reach 25px.

When the staff were doing machine-sprayed mortar experiments, the amount of compound additives was 0.08%. The final mortar had good workability, excellent pumping performance, no sag phenomenon during the spraying process, and the maximum thickness of one spraying could reach 25px.

Machine spray plastering mortar experimental formula (M10)

Experimental data of machine sprayed plastering mortar

Common problems and solutions of machine sprayed mortar:

1. Questions about electricity

Machine spraying equipment belongs to high-power electrical equipment. When connecting to electricity, firstly, it is necessary to check whether there is any defect or leakage in the cable, and secondly, it is necessary to pay attention to whether the ground wire is properly handled, and whether the forward and reverse rotation of the motor is normal. If there is any abnormality, it is necessary to cut off the power supply in time for rectification and repair.

2. Questions about plugging

Blockage is mainly caused by the following aspects. (1) There are large particles in the mortar, which causes jamming at the screw pump or spray gun nozzle, causing the mortar to silt and block the pipe; (2) There is no pre-rinsing of the pipeline, so the consistency value is getting smaller and smaller during the pumping process of the mortar. (3) The consistency value of the mortar is too small, and the overload of the rotor will cause heat to cause the mortar to harden and block the pipe; (4) The operation is unskilled, for example, during the spraying process, only the pumping valve is opened, but not opened the air pressure valve thus leads to blockage.

When operating, it must be operated in strict accordance with the regulations, and the equipment must be cleaned in time after each use. In case of pipe blockage, it is necessary to dredge the pipe in time, and it is forbidden to let the mortar condense in the pipe for a long time.

3. Questions about construction safety

Safety responsibility is more important than Mount Tai. Machine spray equipment belongs to small and medium-sized mechanical equipment, but it still has certain dangers due to the need for certain pressure during the pumping process. Especially in high-rise construction, special attention should be paid to the safety of construction personnel. Therefore, it is necessary to place the spraying equipment in a reasonable position during construction, and the operators must cooperate with each other tacitly. It is strictly forbidden to point the spray gun at anyone to prevent physical injury or property loss caused by human factors.

The perfect combination of mechanized construction of mortar and dry-mixed mortar is an inevitable trend in the development of the dry-mixed mortar industry in the future. However, at present, people in China do not have enough awareness of mechanized construction. Most dry-mixed mortar factories do not have a clear understanding of the performance and technical characteristics of machine-sprayed mortar, and there are no skilled workers on the market who can skillfully operate machine-sprayed equipment. many. Therefore, the comprehensive promotion of mechanized construction also needs the strong support of the government and the joint efforts of people with lofty ideals engaged in the construction industry!