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I agree with Eng. Appi Reddy Kothapally who has elaborated concisely, I just add the few in this regard.
1- The concrete mix should be properly designed with optimum quantity of water to make a cohesive mix. Such concrete will not exhibit any tendency for segregation.
2-Field quality control must be maintained while handling, transporting, placing & compacting and finishing concrete.
3-If at any stage segregation is observed, then remixing should be done to make the concrete again homogeneous.
4-Admixtures, such as pozzolanic materials or air entraining agent should be used to avoid segregation. Air entrainment permits a reduction of the mixing water with no loss of slump which increases workability and decreases segregation and bleeding.
5-Concrete should not be allowed to fall from greater heights. It should be placed as near its final position as possible.
Segregation said to happen when fine particles are not available uniformly in the concrete mass. These fine particles helps in smooth pumping of concrete. Fine particles holds water (moisture) and CA together before commencement of hardening process. Fine particles i.e. cement, Flyash, FA and water (including admixture) together decides whether the concrete cohesive or not. Also note that uniform mix always gives reliable concrete strength at various places of an RCC member.
First place cement mortar in the concrete pump of 1:3 proportion or more rich mortar mix (based on the type of mix to be pumped) to wet the pump and pipe line.
Due to certain practical constraints, placing of concrete from greater than 1.5M is inevitable while using concrete pumps. Such as columns of bridges (metro rail projects), it is best to use SCC (Self Compacting Concrete) to avoid segregation. Long distance (in height also) pumping of concrete is possible with SCC.
TO AVOID CHOCKING OF PUMP & PIPELINES use flyash in concrete mix which creates flow-ability duet to its ball bearing effect among aggregates and makes concrete flowing against all odds like hot weather, early setting of cement, CA too angular, coarse sand, etc .
To avoid segregation during pumping ready mix concrete is to keep the hose as close as possible to the concreting surface (Maximum 1.5m)
