Concrete pumps

Sometimes concrete is pumped through a steel pipe line. This method is particularly advantageous in lining tunnels or when it is necessary to place concrete in locations which are not easily accessible to conventional mixing.

The concrete can be pumped up to about 1,200 ft horizontally, depending on the size of the pump and pipe and the slump of the concrete.

Immediately after concrete is placed, it should be compacted by hand pudding or a mechanical vibrator to eliminate voids.

General information

Prior to excavating rock, it is necessary to loosen it in order that the excavating equipment may handle it. The loosening is done by drilling holes, filling htem with explosives, and discharging the explosives.

Definition of Terms

Percussion drill

This is a drill which breaks into small particles by the impact from repeated blows.

Abraison drill

This dirll grinds rock into small particles through the abrasive effect of a bit that rotates in the hole.

Belt Conveyors

These are used to convey, handle and transport materials such as sand, cement, aggregates, concrete, earth, etc. The materials are transported with a continuous flow at comparatively high speeds. The belt conveyors are, therefore, found to possess high capacities. The use of belt conveyors is justified for short distances only. But they can be adopted forlong distance, if the quantity of material to be handled is great enough to justify the initial cost of the belt conveyor system.

A belt conveyor consists of the following parts:

1. Continuous belt : This should be of required size, grade and type, depending upon the nature of the material to be transported. The belt should be strong enough to resist the maximum tension likely to be developed.

2. Idlers: These are the supports of the continuous belt. Depending upon the nature of work, the idler of proper type and size should be selected and while determining the power required to drive the belt conveyor, the friction between the belt and idler surface should be considered.

3. Driving Unit: This should be of proper capacity and it should be capable of driving a fully loaded belt conveyor without any difficulty.

4. Pulleys: The belt conveyor is driven through the system of pulleys, which may be installed, either at the head or tail or at nay intermediate position. The number of pulleys will be decided by the load to be transported. The pulleys maybe operated by suitable power such as electric, diesel engine etc.

(2) Feeder conveyors: These conveyors operate in seires with end discharge transfer points, The feeder belt conveyors are operated over an easily installed track system so tht the feeder train can be retracted or extended without interrupting concrete placement. These conveyors are used to transport large volume of concrete and special attention should be paid to the discharge end of the train for the spreading of concrete.

(3) Spreading conveyors: These conveyors may be in the form of radial spreaders or side discharge conveyors. In case of radial spreaders, the placing area is decided by the cantilevered support which swings the dischage end through an arc, usually 180o to 360o. These conveyors are also provided with the arrangement of extending and retracting the placing conveyor to a substantial distance. These conveyors can be set up quickly and they cause minimum obstruction or congestion in the placement area of concrete. These conveyors are of course not suitable for the rectangular placements of concrete. In case of side discharge conveyors, the concrete is discharged over the side of the belt with a travelling plow or diverter and thus, a straight ribbon of concrete, which is ideal for mechanical finishing, is obtained. The diverter is provided with a wiper blade to remove the concrete from the belt. The side discharge conveyors of span upto about 30m are used for large projects such as dams, bridge decks, etc. These conveyors usually operate horizontally so that the belt can be loaded heavily.

The above classification of concrete belt conveyors is based on the function which each of them performs most successfully. Each type of conveyor has some limited ability to reach, lift,. Carry or spread. Hence, in case of large projects, the economic aspect of placing concrete with belt conveyors is carefully studied and then only, suitable belt conveyor or combination of belt conveyors is recommended.