Pumping of concrete is economical if the quantity of concrete required is more than about 1150 m3 or uninterrupted supply of concrete is needed over a long period as at the beginning of each period of pumping the pipes have to be lubricated by mortar (at the rate of about 0.25 in3 per 1000 m length of 150 mm diameter pipe) and also at the end of the operation considerable effort is needed for cleaning the pipes.
The pumping system consists of the following components:
Concrete mixed in the mixer is discharged into this hopper, from where it is discharged at the site by the pump through pipe.
Nowadays several types of pumps such as direct acting, horizontal piston type with semi- rotary valves set etc. are available.
The pump is consisted of the following component parts:
(a) Inlet valve
(b) Outlet valve
(d) Rubber cup
After mixing, the concrete is discharged into the hopper, and pump started. In the suction stroke, the inlet valve is open as shown in Fig.10.5 (a) and delivery valve remains closed. During delivery stroke inlet valve closes and delivery valve opens as shown in Fig.10.5 (b). As shown in the Fig., the diameter of the piston is somewhat less than the diameter of the cylinder.
At the working end of the piston, rubber cups are attached, which check the wastage in the cylinder. At the other end, this piston works in bushes. These bushes are lubricated by the water flowing through empty space between the cylinder and the piston. This water also dissolves the cement paste leaking through rubber cups. Hence the danger of setting the cement paste is reduced. In this way the pump is kept safe from damage. The whole assembly is set in such a way that every part of it can be opened and inspected as per need and the damaged part replaced.
Usually concrete can be pumped along a straight and level pipe line for a distance of about 300 to 450 m and upto 40 m vertical height using a single pump. Any rise of 30 cms is equivalent to 2.4 m on the level ground and a right angled bend is equivalent to about 12 m. Hence for a bend of 90° a horizontal distance of 12 m and for 22 ½° bend 3 m horizontal distance should be reduced. No sharp bends should be attached in a concrete pipe line. In between bends straight pipe should be attached.
Pipe lines for concrete are usually made of mild steel tubes in 3 m sections with special joints for quick assembly and release. Bends and short lengths are also available. The size of pipes varies from 11.25 cms to 20 cms inside diameter. The diameter of pipe should be at least three times the maximum size of aggregate used.
Types of Concrete Pumps:
Squeeze Type Concrete Pump:
In recent times much improvements and refinements have been incorporated in the modem concrete pumps. During 1963 squeeze type concrete pump was developed in U.S.A. In this pump concrete placed in a collecting hopper is fed into the flexible pipe by rotating blades. The flexible pipe is connected to the pumping chamber. In the pumping chamber a vacuum of about 600 mm of mercury is created. This vacuum ensures the shape of the pipe cylindrical except when squeezed by the roller.
This ensures the continuous flow of concrete. Two rotating rollers progressively squeeze the flexible pipe and move the concrete into the delivery pipe Fig.10.6 shows the action of a squeeze pump. Often squeeze pumps are lorry mounted and concrete may be delivered through a folding boom.
Most widely used modern pump is the hydraulic piston pump. Though the specifications of modern and original mechanically driven pumps differ, but the concept of working is the same.
A concrete pump consists of three parts namely:
(a) Concrete receiving hopper,
(b) Value system, and
(c) Power transmitting system.
Types of Modern Concrete Pumps:
There are three main types of concrete pumps.
(2) Static or trailer,
(3) Mortar or screed pump.
Type of Valves:
The valve system is the most important part of any concrete pump.
Following are the main type of valves:
(a) Squeeze type valves
(b) Rotating or sliding gate valves
(c) Flapper valves
(d) Hollow transfer tube valves
(e) Rock valves
Hollow transfer tube valves are most commonly used. Rock valve are also widely used valves.
Problems in Pumping of Concrete:
The most common problem of pumping concrete is blockage. If the pump is mechanically sound, the failure of concrete to emerge at the end of the pipe line is called blockage. The increase in the pressure shown by the pressure gauge of the pump is the indication of the blockage of the pipe line. Most blockages take place or occur at the tapered sections of the pump end.