1 Overview
The current concrete pipe mainly includes prestressed concrete pipe, concrete pipe and reinforced concrete pipe. The reinforced concrete pipe is mainly used in highways and the pipe making method mainly includes centrifugal, suspension roller type, vertical extrusion and vertical vibration. Compared with other pipe making process it has the advantages of high strength of pipe external pressure, heavy external load, no leaking, high compactness, good permeability, long durability.
 |
| concrete pipe machine |
2 Pipe Forming Process
The suspension roller type pipe making process utilize the suspension roller driven by the motor drive the mould with the friction of roller and concrete pipe mould. And then with the centrifuge produced by the mould revolving, the concrete mixer will adhere to the inner wall of mould evenly. With the increase of material, the pipe wall will get thicker. When the concrete thickness excesses beyond the mouth of pipe, the mouth will leave the suspension roller. At this moment, the concrete in the pipe inner wall with contact with revolving roller directly. The mould revolves relying on the friction. Meanwhile, the overhang roller will roll press repeatedly. With the increase of thickness of concrete, the pressure on the pipe wall is heavier, the less time will take to compact the concrete and form the smooth surface.
3.1 Stiff concrete, compacted pipe wall, the pipe body can bear higher load.
3.2 The feeding time is short, as well as molding time, the production efficiency is high.
3.3 The waste of concrete is less, no waste cement slurry, no pollution.
3.4 The intensity of high frequency produced during pipe forming process is lower.
3.5 The operative technique is difficult and if can't controlled appropriately the problems such as anti-permeability is not good, the pipe body is not smooth, the pipe wall is quite thick and the slump of pipe wall.
4 Quality Control
4.1 Raw Materials
Cement: the cement should conform to the national standard, and the cement strength grade should not be less than the concrete pipe design strength grade.
Reinforcing bar: the quality of bar should meet the national standard. The bars should be examined by batch when entering the workyard.
Ballast: the quality of ballast should meet the standard of nation. The content of needle shape ballast no more than 15%, the sand content no more than 1%, clay lump content no more than 0.5%, maximum size of ballast no more than 1/3 thickness of pipe wall as well as 3/4 clear distance of circumferential reinforcing bar.
Sand: the quality of sand should accord with national standard. The silt content should not be more than 3%. If the concrete pipes are made of sea sand, the chlorine salt content can't be more 0.1%. when entering the workyard they should be examined by batch.
Additive: the quality of additive should conform to the national standard. The concrete pipes should not be mixed with concrete additive which have corrosive effect on reinforcing bars.
4.2 Mix Ratio
The mixture ratio is the important factor affecting the concrete strength. the concrete used in concrete pipes with hanging roller method is different from general concrete. With the method of suspension roller making pipes, the harsh concrete is necessary. Water cement ratio is generally controlled in 0.3~0.36 or so. Vebe Consistometer is controlled in 20~50s or so. More specific mix ratio differs according to requirements of design strength of concrete pipe. So, it should be confirmed in test room with test mix.
The mould is an important factor affecting the appearance of concrete pipe. The dimension of every part of the mould is in allowable range, there is no obvious gap in the both ends and joints; the connection of all parts should be tight and reliable. The mould should be made from the steel plate with certain rigidity. The dimension allowance meets the quality requirement; the whole rigidity can meet the construction requirements. The inner surface is clean, no rust.
