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 the 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.
Brief introduction to the comprehensive performance of machine sprayed mortar
Compared with the traditional mortar mixed on site, 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 workability of the newly mixed mortar is good. , 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 for 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 methylcellulose ether is an excellent water-retaining agent, which can not only increase the viscosity of mortar, but also 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 will easily cause the mortar in the hopper to be stratified, 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 After molding, the quality of the mortar is not uniform and prone to drying shrinkage and cracking. Therefore, when designing composite additives for machine blasting mortar, some stabilizers should be properly added to slow down the delamination of mortar.
In the machine-sprayed mortar experiment, the dosage of the composite additive was 0.08%. The resulting mortar had good workability, excellent pumping performance, no sagging during the spraying process, and the maximum thickness of one spraying could reach 25px.