Introduction to Under Water Concreting

Placing concrete under water is a specialized subject and should be avoided whenever practical to do so . Where concrete works have to be constructed below water level as in the case of marine works, deep foundations of bridges etc; one of the two courses may be adopted. Either water may be excluded temporarily from the site by using cofferdams, caissons, pumps, dewatering equipment OR Concrete may be placed in water using special methods.Whilst concrete will set and harden under water its placing presents several problems. The most difficult is the prevention of segregation and loss of cement. Formwork except for simpler forms of construction, is difficult to place accurately and in all cases must be anchored firmly. In view of these difficulties, underwater concreting in generally confined to mass un-reinforced work and consideration should always be given to use of pre-cast block for the whole work or as permanent formwork. 

 General Requirements

• Concrete should not be placed underwater when the temperature of water is below 4°C.
•  It requires a very workable concrete with slump as high as 7" and cement content upto 650 Ibs/cuyd. 
• Placing is done in caissons, confer dam or forms. 
• Foundation clean up is required using hydraulic jets or pumps. 
• Concrete must not be placed in running water. 
• Concrete must not be allowed to fall in water. 
• Concrete should not flow horizontally by more than 10 ft.