The construction industry is in boom again. The rush has seen new equipment, new technologies put into action, executing voluminous work within pressing deadlines. This surprisingly has proved to be the best and the most exhaustive test ground for the awesome lineup of equipment. Technologies and equipment have either been scrapped or utilized fully to achieve the set targets.
One such equipment, which has stood this test of time, is the concrete pump. The advent of large projects made the use of the concrete pumps almost mandatory. Unfortunately, the understanding of the technology, especially with respect to the pump selection criteria, has not been large spread. It is quite important to select the correct type and size of concrete pump for a specific project. Largely speaking, the information required before purchase of a pump includes type of project, concrete placement quantity, concrete mix design – slump / aggregate size, vertical & horizontal placement distances from pump and site constraints Let us see how the above points influence the selection of the pump.
Type of Project
Project type can be specified as dam, building, tunnel, bridges, etc. This information helps in the decision of the type of pump to be selected. When the project involves high-rise building or long distance pumping, the stationary pump is more suitable. For mobility, the pump is either trailer mounted or truck mounted, depending on shifting requirements.
When large amount of concrete is to be placed at one place (raft), a mobile boom placer becomes the ideal choice. In addition to its ability to pump concrete at a high rate, it can be easily shifted from site-to-site with no pipeline removal or laying constraints. This ease of mobility has made it a favorite of RMC suppliers worldwide.
Concrete Placement Quantity
The volume of concrete to be placed has to be worked out based on the project scope. A total ‘thinking through’ approach is required in this case. This encompasses the consideration of concrete production, conveying, placement and possible stoppage time.
Concrete pump manufacturers specify the concrete pump output normally in terms of cubic meters per hour, maximum theoretical output. It is important to note that the actual output of the pump will always be less than the specified theoretical output. The actual output depends on many factors like the filling efficiency, type of concrete mix, the delivery distances, etc. Hence, it is necessary to select the maximum theoretical output of the pump more than the actual rate at which the pumping is planned. Enough considerations should also be given in calculating the time for stoppages at site, which are due to pipeline assembly/dismantling at point of discharge, truck mixer change time and time taken in compacting the concrete.
Concrete Mix Design – Slump / Aggregate Size
The pump requires ‘pumpable concrete’ (ref. DIN 1045). To select a concrete pump it is important to know the slump of the concrete & the maximum aggregate size used.
More slump means the concrete is easy to flow and hence less pressure would be required. Accordingly, a low slump reading would require a considerably higher pressure for pumping.
The maximum size of aggregates in the concrete mix decide the size of the pipeline. The size of the pipeline is another constituent in deciding the pump pressure.
Vertical and Horizontal Distance
The vertical and horizontal distance across which the concrete has to be pumped is one of the most important criteria for deciding the pressure and power requirements of the pump.
The concrete pressure is the property of the pump by virtue of which the conveying distances can be determined. Longer the pumping distances, more is the pressure required for pumping.
It is important to note here that the maximum concrete pressure depends upon the hydraulic pressure generated by hydraulic pump and the ratio between concrete delivery piston and the hydraulic piston. The hydraulic pressure can be applied on the rod side or the head side of the concrete pump piston. The smaller pumps usually have only the rod side connection. However, the bigger pumps have additionally a head side connection provision. The head side connection generates more concrete pressure, however with a corresponding cut in the concrete output. Hence, while selecting a concrete pump it is important to ensure that the maximum specified concrete pressure is more than that required at a particular job site.
Site Constraints
The customer may need a diesel engine as prime mover or an electrical prime mover depending upon the site conditions. For example, in remote areas, diesel engine is the obvious choice, since electric supply is not available. Whereas for a project located inside the city, an electric motor may be preferred. The electric motor also helps in reduction of air and noise pollution, though its running cost may prove to be more as compared to a diesel engine, based on present fuel costs.
A Word on Power Requirements
Above inputs help in firming up the pump type, capacity (m3/hr), pipeline size, concrete mix (slump & aggregate size) and the horizontal and vertical placement distances.
The pump manufacturers usually collect the above details to finally work out the pressure and power requirements of the pump, for the specific project. A typical method of arriving at suitable pressure and power requirements is the use of a concrete pressure performance nomograph.
Apart from concrete pressure and output, the power requirement is another important issue, which is often overlooked. A concrete pump may have been designed for required concrete pressure and output, but if it does not have sufficient power, then it cannot perform the task for which it is designed.
Concrete pump manufacturers mention the maximum theoretical output and maximum concrete pressure in their specification. However, it is important to note that both these parameters cannot be met simultaneously. For this reason, a performance curve for a concrete pump is always given, along with other specifications. It should be kept in mind that with higher prime mover capacity better performances can be achieved for machines having similar output and pressure specifications.
Pump Use
Having selected the pump using above guidelines, it is still not certain to give the best results! Its performance will largely depend on the competence of the operator running the pump.
As mentioned earlier, operator training has become a prime concern especially with the introduction of modern technology equipment. Emergency breakdowns of equipment have resulted in substantial loss of time and money for construction companies. New developments have brought in new trends, pushing forth the demand for a skilled workforce. Moreover, proper training also brings in safety awareness and helps in reduction of site accidents.
A few points are highlighted below, which ensure better performance and life of the concrete pump.
Understanding of Pump Parts: The pump manufacturer’s ‘Operation & Maintenance Manual’ explains in detail the pump parts, especially the working of hydraulic system and valve system. These need to be studied in detail and understood, even before the pump is installed.
Pumpability of Concrete: Concrete, either site-mixed or RMC, needs to be checked for its pumpability prior to pumping. The checking procedure has to be set, to avoid recurrent pumping failures.
Pump and Pipeline Installation: The pump is required to be installed firmly on leveled ground. The pipeline installation is critical and the pipeline has to be properly secured to avoid vibrations being transferred to the pump.
Start Up: Oil level, lubrication chart and daily visual inspection, as per the supplier’s instruction manual, are a must. Initial blockages of the pump can be easily avoided by meticulously following a schedule of cement slurry lubrication, prior to the actual concrete pumping.
Pump Cleaning: Thorough cleaning of the pump and pipelines, after use, is of utmost necessity to avoid traces of residual concrete. The residual concrete may lead to major blockages during next pumping operation. Some pumps have effective reverse pumping and water cleaning system features built-in.
Pump maintenance: At some site locations in India, the concrete used is very abrasive and hence causes abnormal wear of the pump parts. Hence, it is important to regularly monitor the condition of the wear parts. Routine maintenance and visual checks, by trained personnel, help in keeping the uptime high.
Safety: Working with concrete pumps can be quite dangerous if proper safety norms are not followed. The hydraulic systems used have a pressure in excess of 350 bar. Even the smaller concrete pumps have concrete pressure in the range of 50 to 100 bar. Another oft seen safety hazard arises with the use of boom placers, with respect to overhead electric cables and obstructions in the vicinity.
To Sum-up:
The concrete pump has proved its usefulness and withstood the challenges of the local working conditions. In fact, presently it is impossible to think of infrastructure/housing projects without a battery of concrete pumps in operation!
However, the days are still to come when construction companies can breathe a sigh of relief over the reduction in non-performance and emergency breakdowns of the equipment. A step towards this is the understanding of the selection criteria of the equipment and a thrust on proper operator training.
The post The Construction Industry and Technologies Equipment News – April 2011 appeared first on EPC World.