# Civil Engineering - Building Materials - Discussion

Discussion Forum : Building Materials - Section 1 (Q.No. 5)
5.
Pick up the correct statement from the following:
For thin structures subjected to wetting and drying, the water cement ratio should be 0.45
For mass concrete structures subjected to wetting and drying, the water ratio should be 0.55
For thin structures which remain continuously under water, the water-cement ratio by weight should be 0.55
For massive concrete structures which remain continuously under water, the water cement ratio by weight should be 0.65
All the above.
Explanation:
No answer description is available. Let's discuss.
Discussion:
20 comments Page 1 of 2.

Amit Karn said:   10 years ago
The water-cement ratio is a measure of the amount of water used in a concrete mixture relative to the amount of cement. The water-cement ratio is important because it affects the strength, durability, and workability of the concrete. Different types of structures and environments may require different water-cement ratios to achieve optimal results.

For thin structures subjected to wetting and drying, such as walls and bridges, the water-cement ratio should be around 0.45. For mass concrete structures subjected to wetting and drying, such as dams and foundations, the water-cement ratio should be around 0.55.

For thin structures that remain continuously under water, such as slabs and beams, the water-cement ratio should be around 0.55. For massive concrete structures that remain continuously under water, such as piers and abutments, the water-cement ratio should be around 0.65.
(1)

Sanju said:   6 years ago
@All.

As we see in the IS Code-10262, it,s clear that the W/C ratio is fixed based on the experience (d/mix done earlier if any for that area) and trail mix for the particular Gr of concrete. It also depends on the workability (i.e, the reqd. Slump).

W/C ratio normally increases for the higher Gr. of Concrete. The Selection of Gr.of concrete basically depends on the factor like- (a) Types of structure (b) Location of structure (i.e, exposure condition) )to be constructed (c) Strength required for the Concrete.

So, confirming the W/C ratio without considering the above factors is not practically acceptable.
(1)

Gundo said:   10 years ago
The cement:mortar ratio is important in prac engineering work because cement features, precast or not, need a specific ratio to suit its specific function. Say for instance you're building a brick wall which has an opening; your c:m ratio (the first number represents one "part" cement in my country, and the latter represents aggregates such as sand, stones etc) between the bricks which a situated above the opening must be in such a way that it is stronger than the cm of the surrounding bricks.

Arti said:   9 years ago
As the material is thin it will not require much water, even in dry as well in wet condition because it will have the tendency to fulfill its water requirement, but in case of mass concrete it will need enough water for its hydration whether in dry or wet condition, its because it is thick.
(1)

Zach said:   6 years ago
That 0.65 is way too more. For massive structures, we will keep w/c ration very less. Because as w/c ratio increases strength decreases. Just google for WC ratio vs strength, you will get the graph to understand. And for underwater structures, we always try to make WC less.
(2)

Ravi Teja trendy said:   10 years ago
The reaction of cement with water is exothermic and releases lot of heat. This heat is very high in case of mass concrete structures which in turn results in failure.

So high W/C ratio is used for both workability during construction and serviceability during operation.

Khatri, Tejinder said:   8 years ago
Any one please elaborate why there is a need of higher w/c ratio in case of underwater concreting?

Since the structure is already under water so the heat of hydration that gets generated will be taken care of by the curing water itself.

Please correct me if I am wrong.