We know there have bends and reducers in concrete pumping system to reach concrete to desired height and or distance. Hoses and elbows remain in system produce turbulence inside line. A well-designed mix having proper quantity of mortar will not produce any problem in the system whereas a poorly-graded concrete mix lean in cement paste produce plug and hence produce problem in pumping.
In locating plug we have to first inspect reducer incorporated in the system. In safe opening of coupling, it is recommended to relieve pressure in concrete placing line applying few reverse strokes in pumping.
Pump operators often have tendency to add water to facilitate pumping; it should keep in mind that only contractor or selected representative of him can add water as excess water produce many problem both in pumping system and gaining strength and developing durability of concrete.
Excess water not only results excessive shrinkage in concrete and reduction in strength by increasing water/cement ratio but also results segregation. Segregation is nothing but breaking down of concrete in its constituent components producing a heterogeneous mix. Usually lighter mortar with sand becomes separated from heavier rock which produce serious problem in pumping system.
Modern concrete batching plants are very efficient and usually produce consistent products; however sometimes problems occur-the possible cause may be missing of certain components or poured aggregate may be different from other areas of stockpile.
An abrupt variation of pumping pressure for a particular load from other loads is said “problem” load. In many cases, problem load blended with another one/more loads results satisfactory pumping operation and hence can be utilized.
Pump should be placed as near as possible to placing area and it is recommended to start placing from furthest point from pump location which permits to grout entire placing line before commencing of placing of concrete.
What is pump primer?
Primer for concrete pump is designed to lubricate or coat pump system which facilitates smooth flow of concrete and help to stay concrete hydrated. Properly designed primer can efficiently reduce wear on pumping system and help to handle concrete mixes that are difficult to pump.
While priming, it should keep in mind that primer has to be pumped into placing line and valve ahead of concrete which keep slurry from being mixed with concrete in hopper. If primer pumped into system is discharged on forms, problem may arise; where available, primer port should be used on machine.
While taking sample for testing, the sample should be taken from concrete that are placed normally; not from the system by stopping pumping and allow to drop sample for test specimen. A free fall of concrete into test container must not be allowed. In case of fiber reinforced concrete, it should remember that concrete of both steel and synthetic fiber can be pumped if designed properly.When lightweight aggregate (coarse aggregate) is used in concrete must be soaked in bunkers or stockpiles before use. Usually sprinkling period of at least 3-5 days is recommended. It is important to ensure uniform & complete saturation.