Anyone who has ever pumped concrete will have encountered, at some point, problems with pump line blockages. They are a part and parcel of the job, especially in the beginning when operators are learning the ropes. So learning what cause them is a first order on the agenda for any operator. The good news is that most blockages can all be traced back to 3 main causes:
- Problem with the mix (think batter recipe)
- Problem with the pipe line (think capacity & maintenance)
- Operator error (think proper handling)
1) MIXING ISSUES:
Problem: Insufficient mixing
Insufficient mixing of the concrete can result in segregation or separation of heavier particles moving to the bottom of the concrete.
Solution: Ensure proper coating of cement grout and lubrication of the mix. Also avoid overworking cement that is prone to bleeding.
Problem: Concrete Bleeding
Concrete can sometimes bleed, meaning that the aggregates (solid components) do not evenly retain the mixing water. This could come from the sand not being well graded and the water flowing through the tiny channels or floats to the surface of fresh material (since water is the lightest of all the mix constituents).
Solution: Use a different sand, more cement, entrained air or fly ash to reduce bleeding. Avoid remix the bleed water during the finishing of the surface. Instead wait until it has evaporated. Make sure that the evaporation is not faster than the rate of bleed, otherwise plastic shrinkage cracking could happen.
Problem: Premature setting
If, for some reason, the temperature on the site is high on that day or the pumping is delayed due to site issues or traffic, your concrete can set too quickly. This means that the mix could become too thick to pump, not fill the chambers and as a result put undue pressure on the equipment.
Solution: Plan ahead. Check the weather for the week, make sure everything is ready on the site to avoid delays, use the proper mix for the job and if all else fails, use ad mixers (for cold or hot weather).
2) PROBLEM WITH THE PIPE LINE
Sizing the system for the job is essential to avoid common problems. Here are some common pitfalls:
You have insufficient pump capacity and motor horsepower to push the concrete through the entire pipeline.
The aggregate you use is too large for your line so you will need to switch to a larger diameter to solve the problem.
Did you forget to properly clean your pipes on your last job?
This will most likely result in blockages where the old concrete hardened, not to mention causing segregation and bleeding. Don’t cut corners, even if it means working overtime!
Are your couplings, gaskets and weld collars are in working conditions? If not, you risk grout loss. Not good!
How many short and sharp bends do you have in your pipeline? Do you have reductions in your pipeline’s diameter? Bends, on the one end, increase the pressure while reductions, on the other, slow the flow. But both increase the risk of blockages wherever they occur. So now you know: check and recheck your line.
3) OPERATOR ERROR
Novice concrete pump operators may not know that hoses and pipes should only be removed and not added once the pour is in progress. Adding a new hose with dry internal walls could cause a blockage.
Then, there is poor handling of flexible hoses that can result in kinking and rock jam where the kink occurred. This is a double whammy, because not only will you halt or delay the job trying to clear the jam but the constricted aggregate in the line will contribute to wear and tear of the hose leading to an eventual hose rupture.
So make sure you have the right equipment for the job and that it is in good working condition. Using more cement or a larger diameter pipe will increase the cost of the job. So plan your work and work your plan. It will save you money on manpower and equipment cost over time.