Concrete pump pipe blockage would be a great headache for a jobsite, as it will cause much delay in construction process. In modern construction, concrete pumping plays an important role, especially in large-volume projects. It provides high efficiency and fast speed.
Pipe blockages is the most common problem in concrete pumping operation. Once plugs, it will wast time, increase building costs and even compromise the quality of the concrete works.
Why does the blockage happen? Is it the concrete mix? The responsibility of pump operator? The weather issue? The truth is, it’s often a combination of all factors. This guide explore the possible causes of concrete pump blockages issues and offer possible solutions to all these problems. Precautions and systematic measure should be taken to prevent emergency. This will help keep the pipeline clear and avoid burst.
Causes of Concrete Pump Pipe Blockage
We should have a thorough understanding of the mechanics behind the blockage issues. Actually, the blockages are not unpredictable. They usually come from the four key areas: materials, equipment, operation, and environment.
First causes from the concrete mix
If the concrete mix is not suitable for pumping, it will cause pipe blockages, usually the first cause. We should examine the physical properties of the mix very carefully.
The Slump Sweet Spot
If the slump is not suitable, its workability will become low, which is a major problem. If the slump is too small, dry and sticky, it will cause the friction resistance of the pipe increase greatly. And this will cause much more wearing down on the pipeline system. And conversely, if the slump is too high, the concrete inside the pipe will probably become segregation under high pumping pressure.
Rule: Generally speaking, pump concrete slump should be controlled between 12cm and 18cm. For high-rise or long-distance pumping, choose 15cm.
Care about the Aggregate Size
If the coarse aggregate size is too large relative to the pipe diameter, it is of great possibility that jamming will happen. Choose the right size.
The Ratio: if concrete will be pumped under 50 meter high, it is suggested that the crushed stone size should not exceed exceed 1/3 of the pipe diameter, and river gravel (pebbles) should not exceed 1/2.5. As pumping height increases, the ratio much become less.
Shape: avoid stones of flat or needle-like shapes. Keep the ration of such shape of particles less than 10%, as these stones will cause excessive drag along the pipeline inside.
Cement Content Issue
cement is both binder and lubricant. If the cement is 300kg/m³, it would be very difficult to suck the mix into the pipe effectively, and this will cause bleeding and segregation.
Admixture Compatibility
the air content should not exceed 4% of the concrete in the pump. If use additives improperly, like using too much air-entraining agents or superplasticizers, it will reduce the pumpability of the mix.
Equipment and Pipeline Configuration
Beside paying attention to the mix context, we should also care about the pipe delivery system. If the pipe system is not good enough, even the best concrete mix will bring clog.
Poor Pipeline Layout
We should always keep in mind that the golden rule of concrete pump pipe layout is “shortest distance, fewest elbows”.
Critical Error: Please do not connect a 90-degree bend directly to the pump’s outlet cone. Installing at least 5mm of straight pipe before the first bend.
Vertical Pumping: When pumping concrete straight up, the horizontal ground pipe length should be at least 1/4 of the vertical height, and no less than 15m. This will help reduce the clog possibilities.
Leakage Issue
If pipe joints aren’t sealed tight, there will be leakage of grout (cement paste). When the paste leaks out at a clamp, only the aggregate remains. This will create an instant rock jam.
There are some common causes of leakage problem, including worn seals, loose clamps, or excessive gaps between the spectacle plate and the cutting ring.
Insufficient Pressure
Another cause from the pumping system is the pressure. If the pump truck has not enough pressure rating for the distance or height required, the concrete will block in the pipeline.
The Human Factor: Operational Errors
The operator’s technique plays a great role in keep the pump working properly and ensure a good flowing condition of the concrete.
Ignoring the Gauges
Pump operators should focus highly on the pressure gauge. When pressure increase suddenly, it indicates a forming blockage in the pipes. If the operator misses this and fails to reverse the pump immediately, the block will form.
Speed Kills
If the operator works impatiently and does not control the speed, which would cause blocks. When starting concrete pour, resistance is high. Operator must pump at low speed until the flow become normal. If the mix looks dry (low slump), operator should slow down immediately.
Hopper Level
If the concrete level in the hopper is below the mixing shaft, the system will suck air. This “air lock” is a also cause of the concrete pump pipe blockages. Conversely, if the hopper is filled with much mix, it is impossible to remove oversized aggregate.
Downtime Management
Concrete has a shelf life. If pumping stops for more than 30 minutes (even less in summer), the concrete begins to set. This will definitely increase the rise of blockage inside pipeline.
Pro Tip: During delays, cycle the pump (reverse-forward) every 5-10 minutes to keep the material moving.
Environmental Constraints
Extreme Temperature conditions
In summer, hot pipes can dehydrate the concrete. This will cause the concrete becoming stiffened and get blocked more likely. In winter, freezing temperatures is also a problem. It can affect flow and setting times.
Job-site Restrictions
For tight jobsite, there is always need of long, winding pipe, and also too many bends. This will significantly increase friction inside the pipe. And in the meanwhile, this will increase pipe blockage risk.
Possible Preventive Solutions to Concrete Pump Pipe Blockage
We might need a holistic approach to prevent pump pipeline blockages. We would suggest to pay attentions to the aspects of mix design, equipment maintenance, and strict site management.
Optimizing the Concrete Mix
- The Recipe: try best to keep a water-cement ratio of 0.4–0.6, and keep a sand ratio of 38%–45%. The sand ratio is critical. It should be high enough to make sure there is enough mortar surrounding the coarse aggregate to reduce friction.
- Fly Ash: it is highly suggested to add 10-15% fly ash into concrete mix below C25 strength. This can significantly improve pumpability. However, use carefully in winter.
- Aggregate Control: Use different size of stones, not only one size of stones. Mixing in 30-40% of 10-20mm stone and 10-20% of smaller chips. This will create a better lattice for flow.
Equipment Setup and “Priming”
- Lubrication is Needed: it would be quite risky to pump concrete into a dry line. Firstly, it is highly necessary to first pump water. And then pump lubricating mortar (1:1 or 1:2 cement-sand ratio). This is to coat the inner walls. Please make sure calculate the enough volume of lubricating mortar, which is needed to coat the entire length of the pipe.
- The Anti-Backflow Setup: For high-rise pumping, use enough length of horizontal pipe. These pipes length should be at least 15% of the vertical length. Crucially, please install a shut-off valve in the horizontal section. This will prevent concrete from flowing backward when the pump stops.
- Thermal Protection: In summer, cover pipes with wet straw bags or burlap. This will keep them cool. In winter, please wrap them in insulation.
Operational Discipline
- Speed Control: Start slow. Only increase speed once the flow is established. If you see signs of a blockage or a “dry” truckload, drop the speed immediately.
- Continuity: Keep the pump running. If the concrete supply is slow, please lower the pumping speed. It is better than stop the pumping and then start again. If you are waiting for a truck, lower the flow rate, or periodically reverse-pump to keep the mix alive.
- Cleaning: It sounds obvious, but pipes must be thoroughly cleaned after every use. Hardened residue often cause the startup blockages.
Emergency Response – What to Do When Pump Pipe Jams
In case blockages happen. How you do next will determines whether you are down for 10 minutes or 4 hours.
The “Reverse Pump” Technique
This is the first step we suggest.
- Watch the Gauge: As soon as the pressure reading spikes, stop pumping forward.
- The Maneuver: Immediately switch to reverse pumping for 2-3 strokes, then switch back to forward pumping.
- Repeat: Cycle this a few times. This measure is often enough to solve a minor blockage and suck it back into the hopper.
Locating the Blockage
If the measure of reverse pumping does not work, you need to find the plug.
- The Sound Test: Walk along the line and tap the pipe with a hammer.
- Clear Line: You will hear a crisp sound and the “swishing” noise of concrete moving.
- Blocked Line: You will hear a dull, heavy thud. The sound is “dead”.
- Hotspots: Focus your search on elbows, tapered sections, and the very end of the pipeline.
Safe Removal and Cleaning
Concrete under pressure is dangerous.
- Relieve Pressure: Before touching a clamp, ensure the internal pressure is zero. You can do this by reverse pumping or carefully loosening the bolts on a clamp. Do not remove them fully. And then tap the clamp to release pressure gradually.
- The Clean-Out: Once safe, dismantle the blocked section. Remove the concrete manually using appropriate tools. If the concrete has hardened, you may need high-pressure water jets or mechanical drills.
Conclusion
We need to take preventive measures to tackle pump pipeline blockage problem. We need to take into consideration of many aspects, not just focus on one issues. Provide training for operators to make sure a optimized material mixes, smart pipe system layout, and disciplined operation of the pump and how to solve the problem of blockage if happens.
