Characteristics of Strength of Concrete in Actual Structure

There are various factors that affect the strength of concrete in actual structure. The characteristics of strength of concrete in actual structure are determined by the following factors:

1. Grade of Concrete
The grade of concrete is the most important factor that affects the strength of concrete. The strength of concrete is directly proportional to the grade of concrete. The higher the grade of concrete, the higher will be the strength of concrete.

2. Quality Control
Quality control plays an important role in determining the strength of concrete. Proper quality control measures such as the use of quality raw materials, proper mixing, and curing of concrete can result in high strength concrete.

3. Water-Cement Ratio
The water-cement ratio is the ratio of the weight of water to the weight of cement used in the concrete mix. The strength of concrete is inversely proportional to the water-cement ratio. The higher the water-cement ratio, the lower will be the strength of concrete.

4. Age of Concrete
The strength of concrete increases with the age of concrete. The concrete gains strength with time due to the hydration of cement.

5. Testing Method
The testing method used to determine the strength of concrete also affects the strength of concrete. Different testing methods such as compressive strength test, flexural strength test, and split tensile strength test can result in different values of strength.

Conclusion
In actual structure, the characteristic strength of concrete is taken as 0.85 fck. This value is obtained by multiplying the characteristic strength of concrete (fck) by a factor of 0.85. This factor takes into account the variation in strength due to various factors such as quality control, water-cement ratio, age of concrete, and testing method. However, in certain cases, the characteristic strength of concrete may be taken as 0.67 fck or even 0.447 fck depending on the design requirements and the level of confidence required.

Ans is (c)

characteristics strength is 0.67fck