The mortar spraying machine can use P.O 42.5 cement, fly ash, stone powder, sand and additives and other raw materials. Among them, the material with the highest performance and the best economical efficiency for the machine blasting mortar is sand.
The commonly used sand of mortar spraying machine is desalination sand, river sand, mountain sand, machine-made sand and so on. When desalination sea sand and river sand are used in machine-blasted mortar, the ready-mixed mortar prepared has better workability and working performance due to its good particle gradation and fineness modulus, but it needs to be sieved before use Sub-processing to prevent the shell content in sand from being too high has an impact on the water retention, strength and workability of ready-mixed mortar. The characteristics of mountain sand, machine-made sand and tailings sand are large water demand, difficulty in sizing, bulky weight, rough particle surface, sharp polygons, and poor gradation. The particle morphology is polarized. On the one hand, large particles are prone to make the mortar have poor water retention, heavy particle feeling, more sand holes on the wall, pitted surface, and more ground ash. The stone powder has the functions of lubrication, thickening and filling, which can reduce the yield value of the mortar mixture and increase the plastic viscosity, which indirectly improves the workability of the mortar. , Causing problems such as early cracking and short setting time, which is not suitable for construction.
The mortar spraying machine should use medium-graded sand with a fineness modulus between 2.3 and 2.7 and a zone II with good particle morphology. The maximum particle size should not exceed 4.75mm. When the machine-made sand is used for plastering mortar It should not exceed 2.36mm, so the sand must be sieved when the mortar is sprayed (the diameter of the sieve is 5mm). A good gradation can make the porosity and total surface area of the sand smaller, so the amount of cement slurry required is less, and the density, strength and workability of the mortar can also be improved. When the amount of sand is large and the ratio of mortar to sand is low, the volume shrinkage of the mortar is small and the probability of plastic cracks is small, but it should be noted that too little cementing material will also cause the mortar sand to feel heavy and prone to bleeding and astringency.
If the sand gradation is poor and the particle morphology is poor, the performance of the mortar will be greatly affected. When the sand fineness modulus is too small or the stone powder content is too high, its specific surface area increases, and the more slurry needed to wrap it. When the mortar consistency is the same, the mortar prepared with fine sand requires more cementitious material than the mortar prepared with medium and coarse sand, which increases the cost of mortar preparation and increases the risk of plastic cracking; in addition, the change of water-cement ratio will cause Problems such as reduced mortar strength and poor workability. When the sand fineness modulus is too large or the sand particles are poorly graded and the proportion of coarse particles (commonly known as "sand head") is high, the rebound of the mortar particles sprayed on the wall is greater, if the coarse particles of floor ash are used to repair the wall The surface will cause the wall to be scratched unevenly when it is troweled, which will affect the troweling efficiency of the troweler.
