WORK IN EXTREME WEATHER CONDITIONS (UNDER-WATER CONCRETING).

Concreting under special conditions and work in extreme weather conditions, during hot or cold weather, the concreting should be done as per the procedure set out in IS:7861(part-1) and part-2. of 1975 . UNDER WATER CONCRETING:-- When it is necessary to deposit concrete under water, the methods, equipment materials and proportions of the mix to be used shall be submitted to and approved by the engineer incharge before the work is started. In no case shall such concrete be considered as"Design mix concrete "The concrete shall contain at least ten percent more cement than that required for the same mix placed in the dry, the quantity of extra cement varying with conditions of placing. The volume or mass of the course aggregate shall be not less than one and a half times, nor more than twice that of the fine aggregate. The materials shall be so proportioned as to produce a concrete having a slump of not less than 100 mm, and not more than 180 mm. Coffee dams or forms shall be sufficiently tight to ensure still water, if practicable, and in any case to reduce the flow of water to less than 3metre per minute through the space into which concrete is to be deposited. Coffer dams or forms in still water shall be sufficiently tight to prevent loss of mortar through the walls. Dewatering by pumping shall not be done while concrete is being placed or until 24 hours thereafter. Concrete shall be deposited continuously until it is brought to the required height. While depositing, the top surface shall be kept as nearly level as possible and the formation of seams. avoided. The methods to be used for depositing concrete under water shall be one of the following (a) Tremie (b) Drop bottom bucket (c) Bags (d) Grouting.