1 Improper operation can easily lead to blockage of the pipe
1.1 The operator is inattentive
The operator of the concrete pump should concentrate on the pumping construction and always pay attention to the reading of the pumping pressure gauge. Once the reading of the pressure gauge suddenly increases, they should immediately reverse the pump for 2 to 3 strokes. . If the reverse pump has been carried out and the pump is being pumped for several operation cycles, the blocked pipe has not been eliminated, and the pipe should be disassembled and cleaned in time, otherwise the blocked pipe will be more serious.
1.2 Improper selection of pumping speed
When pumping, the choice of speed is critical, the operator cannot blindly map fast, and sometimes haste is not enough. When pumping for the first time, due to the large resistance of the pipeline, it should be pumped at a low speed at this time. After the pumping is normal, the pumping speed can be appropriately increased. When there is a sign of pipe blockage or the slump of a certain truck of concrete is small, it should be pumped at a low speed to eliminate the blocked pipe in the bud.
1.3 Inappropriate control of residual material quantity
When pumping, the operator must observe the remaining material in the hopper at any time, and the remaining material should not be lower than the stirring shaft. If the remaining material is too small, it is easy to inhale air and cause the pipe to be blocked. The material in the hopper should not be piled up too much, and should be lower than the guardrail, so as to clean up the coarse aggregate and oversized aggregate in time. When the slump of a certain truck of concrete is small, the remaining material can be lower than the mixing shaft and controlled above the "S" pipe or the suction port to reduce the mixing resistance, swing resistance and suction resistance. This method is only applicable to "S" valve series concrete pumps.
1.4 The slump is not suitable for easy plugging of pipes
If the slump of concrete is too small, improper measures should be taken. When it is found that the slump of a bucket of concrete is too small and cannot be pumped, the concrete should be released from the bottom of the hopper in time. Never add water to the hopper to stir.
1.5 Excessive downtime
During the shutdown period, the pump should be turned on every 5 to 10 minutes (the specific time depends on the temperature of the day, the slump of concrete, and the initial setting time of concrete) to prevent pipe blockage. It is not advisable to continue pumping for the concrete that has been initially set after the downtime is too long.
1.6 The pipes are not cleaned
After the last pumping is completed, the pipeline is not cleaned, which will cause the pipeline to be blocked during the next pumping. Therefore, after each pumping, the conveying pipeline must be cleaned according to the operating procedures.
5 Pipe blockage caused by unqualified pumping concrete
The concrete used for pumping must meet the requirements of pumping concrete. Not all concrete can be used for pumping. Unqualified pumping concrete will aggravate the wear of the concrete pump and often cause pipe blockage and pipe burst.
5.1 Concrete slump is too large or too small. The size of concrete slump directly reflects the fluidity of concrete, and the conveying resistance of concrete decreases with the increase of slump. The slump of pumped concrete is generally in the range of 8 to 18 cm, and for long-distance and large-height pumping, it is generally required to be strictly controlled at about 15 cm. If the slump is too small, it will increase the delivery pressure, increase the wear of the equipment, and cause the pipe to be blocked. If the slump is too large, the concrete is easy to segregate under high pressure, causing the pipe to be blocked.
5.2 The sand content is too small and the coarse aggregate gradation is unreasonable. According to the source, fine aggregate can be divided into: river sand, artificial sand (ie, machine-made sand), sea sand, and mountain sand. Among them, river sand has the best pumpability, and machine-made sand has the worst pumpability. Fine aggregate can be divided into coarse sand, medium sand and fine sand according to particle size, among which the pumpability of medium sand is the best. Coarse aggregates can be divided into pebbles and crushed stones according to their shape. Pebble is more pumpable than crushed stone. The maximum particle size of the aggregate is also related to the minimum diameter of the conveying pipeline. The maximum particle size of the pebble should be less than 1/3 of the diameter, and the maximum particle size of the crushed stone should be less than 1/4 of the diameter, otherwise it will easily cause the pipe to be blocked. Due to different materials, there is an optimum value for the content of fine aggregate (that is, the sand content) and the gradation of coarse aggregate. Under normal circumstances, the sand content should not be too low, it should be greater than 40%, and the content of large particle size coarse aggregate should not be too high. Reasonable selection of sand content and determination of aggregate gradation are crucial to improving the pumping performance of concrete and preventing pipe blockage.
5.3 The amount of cement is too little or too much. In pumping concrete, cement plays the role of cementing and lubricating. At the same time, cement has good water retention properties, so that concrete is not easy to bleed during the pumping process, and the amount of cement also has an optimal value. If the amount of cement is too small, the It seriously affects the suction performance of concrete, and at the same time increases the pumping resistance, the water retention of concrete becomes poor, and it is easy to bleed, segregate and block pipes. Under normal circumstances, the content of cement per cubic meter of concrete should be greater than 320kg, but it should not be too large. Too much cement will increase the viscosity of the concrete, resulting in an increase in conveying resistance. In addition, the amount of cement is also related to the shape of the aggregate. The larger the surface area of the aggregate, the more cement slurry that needs to be wrapped, and the larger the cement content accordingly. Therefore, a reasonable determination of the amount of cement is also very important to improve the pumpability of concrete and prevent pipe blockage.
5.4 The selection of admixtures is unreasonable. There are many types of admixtures, such as: air-entraining agent, water-reducing agent, superplasticizer, retarder, pumping agent, etc. According to the strength requirements of concrete and the variety of cement, reasonable selection of admixtures can improve the performance of concrete. Pumping performance plays an important role. Unreasonable admixtures will deteriorate the pumpability and fluidity of the concrete, resulting in blocked pipes.
6 Pipe blockage caused by too little mortar or unqualified mix ratio
6.1 The amount of mortar is too small. Because the mixing host, concrete truck mixing tank, hopper, pipeline, etc. must absorb part of the mortar when pumping for the first time, if the amount of mortar is too small, part of the conveying pipeline will not be lubricated, resulting in blockage. The correct amount of mortar should be calculated as about 0.5m3 of mortar per 200m pipeline, and about 0.2m3 of mortar for the mixing host, hopper, concrete truck mixing tank, etc. Therefore, the amount of mortar must be calculated before pumping. Too little mortar will easily block the pipe, and too much mortar will affect the quality of concrete or cause unnecessary waste.
6.2 The mortar mix ratio is unqualified. The mix ratio of mortar is also critical. When the pipeline length is less than 150m, use 1:2 cement mortar (1 part cement/2 parts mortar); when the pipeline length is greater than 150m, use 1:1 cement mortar (1 part cement/1 part mortar), cement Too little dosage can also cause blockage.
7 Blocking pipes caused by temperature changes
In summer, the temperature is high, and the pipeline is exposed to strong sunlight, and the concrete is easy to be dehydrated, which will lead to the blockage of the pipeline. Therefore, the pipeline should be covered with wet straw bags or other cooling supplies. In winter, insulation measures should be taken to ensure the temperature of the concrete.