It is found that materials of concrete with help of machine is more efficient and it produces concrete of better quality in a short time. The mixtures of various types and capacities are available in market. They are may eir be of tilting type or non tilting type.

It should however be remembered that action of corrosion become more intensive when it is combined with adverse effects of external and internal stresses. Cracks usually progress or advanced more rapidly where shearing stresses are greatest.

In Guniting, surface to be treated is cleaned and washed. The nozzle is generally kept at a distance of about 750 mm to 850 mm from surface to be treated and velocity of nozzle values from 120 m/sec to 160 m/sec.

Here, fine aggregate or sand is eliminated and such concrete has been adopted for cast in situ external load bearing walls of single and multi storey houses, small retaining walls, damp proof sub base material, etc.

The shrinkage of cement concrete occurs as it hardens. This tendency of cement concrete can be minimised by proper curing of concrete.

In summer, usual mistake made while placing concrete is addition of extra water to mixture as well as finish concrete surface. Such an extra water resistance strength and or properties of concrete.

Similarly higher water content increases workability. But it is not useful for chemical action. The excess water evaporates living pores in concrete. Thus increase water cement ratio lowers strength of concrete.

In Compaction factor test, concrete is allowed to fall in a lower cylindrical mould of 150 mm diameter and 300 mm height through into vertical placed conical Hopper. The surplus concrete appearing about top of mould is removed with a trowel. The weight of concrete in mould is n found out.

The mixing by hand is allowed in case of small works on unimportant work were small quantity of concrete is required. For important work, if hand mixing is to be adopted, it is advisable to use 10% more cement than specified.

This is due to fact that sand and pebbles or crushed rocks, forming bulk of cement concrete, to extent of about 80% to 90%, usually available at moderate cost. The form work, which is of Steel or timber, can be used over and over again or for or purposes after it is removed.