When formulating the requirements of a concrete specification, the characteristi

Question

When formulating the requirements of a concrete specification, the characteristic strength of concrete is used to represent the strength of the concrete. What does the characteristic strength of concrete represent? O a The characteristic strength of concrete is the actual strength of the concrete used to construct a concrete structure o b. The characteristic strength of concrete incorporates statistical variations of strength and ensures the strength in the concrete structure with a certain level of confidence OC. The characteristic strength of concrete will be greater than the mean strength of concrete o d The characteristic strength of concrete is much easier to achieve in the field than the mean strength of concrete QUESTION 2 Which key feature will lead to the sudden failure of a prestressed concrete beam due to the action of chloride-induced corrosion? o a. The formation of considerable rust stains b. The occurrence of large areas of general corrosion CThe occurrence of localised areas of pitting corrosion o d. The spalling of the concrete QUESTION 3 A concrete mix containing steel fibres, when tested for workability, showed zero slump. Which key feature is responsible for the observation of zero slump in the concrete mix containing the steel fibres? a. The concrete mix is very dry and contains an insufficient amount of water and is not workable b The slump test is not a good measure of workability of fibre reinforced concrete ? C. The absorption característics of the steel ibre reinforced concrete mi is di erent to a normal concrete mo and hence, the concrete m od. The addition of steel fibres to the concrete mix has made the concrete mix stiff and, therefore, the concrete mix has flash set has become dry

Explanation / Answer

1) option B is the correct answer

Actually characterstics strength is the probablistic concept which is the strength value with usually 95% of confidence limit.Therefore we can say that charecterstic strength of concrete represents which incorporates the statistical variations of strength and ensures the strength of concrete structure with certain level of confidence.

2) option C is the correct answer

Chloride-induced corrosion widely prevail in civil infrastructure around the globe. In the case of prestressed concrete structures, the corrosion mainly pitting corrosion of prestressing strands can lead to a sudden failure due to higher stress levels in the steel.Threfore key feture for failure of prestressed concrete beams due to chloride induced corrosion is the occurence of localised areas of pitting corrosion

3) option C is the correct answer

The reason of lower slump is that adding steel fibers can form a network structure in concrete, which restrain mixture from segregation and flow. Due to the high content and large surface area of fibers, fibers are sure to absorb more cement paste to wrap around and the increase of the viscosity of mixture makes the slump loss.Therefore the reasonn for zero slump in the concrete mix containing the steel fiber is the absorption charecterstics of the steel reinforced concrete mix is different to a normal concrete mix and hence the concrete mix has become dry.

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