Now-a-days very often concrete not produced in-site and very frequently they are transported by any type of hauler and pumped to desired elevation and distance. So we have to design a concrete mix that can be pumped easily and efficiently. Pumpability is nothing but an ability of mix to be pumped.
Pumpability depends on combination of followings:
a. Properties of concrete
b. Capacity of pump and diameter of pipeline
-Height of placement
-Distance to be covered by pump
-Angle and number of bends
-Continuity of pumping and pumping rate
Regarding properties of concrete, the important properties are
• Ratio of aggregate size (maximum) to diameter of pipeline
We know bleeding is harmful to concrete construction. Too much bleeding leads unpumpable mix. Bleeding can be reduced by applying in mix
• More cement
• Pulverized fuel ash
• Fine sand
• Water reducing agents
Again when concrete becomes excessively cohesive, especially when high percentage of cement is added, excessive friction is generated within pumping system and mix becomes unpumpable. In this case, making more slump concrete may increase pumpability. Remarkable improvement is observed, when aggregate content of 10 mm size in the mix reduced in 20 mm size aggregate, especially when 10 mm particles are flaky considerably.
The general recommendations of making concrete pumpable are as follows:
a. [(Weight of cement)+(Weight in fine aggregate)] > 1.75 X (Free water)
The aggregate of size less than 300 micron is only considered
Cement content in concrete mix is more than 300 kg/m3.
b. Slump of mix greater than 50 mm (75 mm is target slump)
c. (Fine aggregate content) > 1.05 X (FA content of well designed concrete mix not considering pumpability)
d. [Nominal (maximum) aggregate size] ≤ 1/5 X (Pipeline diameter)
Say, if pipeline diameter 100mm, the maximum aggregate size should be 20 mm.