Pump truck construction, it is inevitable to encounter such materials, this and the distance of the mixing station, as well as the number of mixing trucks are related, some good, mixing trucks are sufficient, waiting in line for unloading, that basically the pump truck does not need to stop, do not need intermittent positive and negative pump operation, to prevent concrete solidification and pipe blocking.
However, this situation is relatively few, most of the cases are the pump truck stop, waiting for the new mixing truck to come to unload, in the waiting process, if the pumping operation is not carried out for a long time, then it is prone to the problem of blocking the pipe after starting the pump again. In order to prevent the problem of pipe blocking, the general pump master will tell you that there should be a gap (10-20 minutes, the longest is not more than 30 minutes) for positive and negative pumping operations, so that the concrete in the pipeline and hopper can flow to avoid pipe blocking. Most of the people who have operated the pump truck should have such an experience, so the problem comes? Does this really work? How often should the positive and negative pump operation effectively avoid tube blockage? If the pump is always positive and negative, will the concrete never block the pipe?
Today we're going to take a closer look at how concrete sets and how we can take a more effective approach to pipe clogging.
Concrete is a mixture of cement, fly ash, sand, stone, additives and water, referred to as concrete, water and cement and fly ash formed paste wrapped in the sand, stone surface, play a lubricating role, additives adjust the strength of concrete, setting time and hardening time. According to the national standard requirements: the initial setting of ordinary Portland cement shall not be earlier than 45 minutes, and the final setting shall not be later than 12 hours. That is to say, the ordinary concrete begins to set after 45 minutes of mixing, and completes the hardening and solidification within 12 hours.
In fact, the hardening process of concrete is a chemical reaction between cement and water, and its hydration products have gelling properties, and the cement slurry gradually thickens and loses plasticity, and gradually develops into a hard cement stone. This chemical process is irreversible, the specific setting and hardening time is affected by the quality of cement and additives, stirring and pump operation have little effect on the concrete setting process. However, mixing can make the inside of the concrete more uniform, the more full the mixing, the better the mixing, the stronger the strength of the concrete after the later hardening, the better the quality.
Since the reverse pump of the pump truck can not delay the condensation process of concrete, why also play the reverse pump of the gap? And if you don't, will it really block the pipe?
Let's talk more about the condensation and hardening process of concrete: the condensation of concrete is actually the condensation of cement, and the condensation begins to form small particles, or attached to the stone and sand above, if the positive and negative pump operation is not carried out at this time, then the condensate will become larger and larger, and eventually lead to large chunks of condensate completely blocking the pipeline.
Another level of consideration, especially for the pump boom to hit high-rise buildings, the whole boom pipe is upward, if the shutdown state is too long, the large stone in the concrete will roll down slowly due to the influence of gravity, and the diluted cement mixture will be passively squeezed upward, which forms the stratification of concrete, that is, the often said segregation phenomenon. Once there is segregation, it is natural to plug the pump.
Therefore, in the process of pumping trucks and other materials, the continuous positive and negative pumping is actually to prevent concrete segregation and organization of the concrete that has been initially set to continue to travel bulk condensation. Why does the master require a maximum of 30 minutes of positive and negative pump once? This is a summary of experience, only suitable for general circumstances, the concrete setting time and the quality of cement, the proportion of water, and additives are related, as the pump truck construction party certainly can not be very accurate on the relevant data to calculate the best positive and negative pump time, so it can only be estimated according to experience, the national requirement is 45 minutes without condensation, This is the standard that all concrete must meet, taking into account the travel time of the mixing truck, so everyone's experience is initially set at the latest 30 minutes positive and negative pump once, basically can meet most of the working conditions, some of the more conservative master, it is controlled within 20 minutes positive and negative pump once, after all, the tube is not a joke, Really plugging up the rescue and removal of the pipe work or their own work, so can be conservative as far as possible conservative.
See here, you do not understand, why the pump truck in the process of waiting for material, need to constantly positive and negative pump reasons? Understand the principle of concrete condensation, to help you better use the pump truck, with fine pump truck!
Finally, a bit of an aside, if you keep repeating the same concrete, is it 12 hours later you will completely block the pump truck?
Obviously not, in fact, if you continue to cycle the concrete, the concrete will eventually become a pile of cement slurry, completely lost the coagulation effect, the kind of condensed small pieces of concrete will be pressed into powder by ultra-high pressure, the stone will continue to friction and S-tube cutting, large petrochemical small, small petrochemical. If you are interested and really bored, you can try it!