Mild and Moderate Exposures in Concrete

Introduction:
In concrete construction, the exposure conditions determine the requirements for the minimum cement content. The exposure conditions are categorized as mild, moderate, severe, and very severe, depending on the aggressiveness of the environment in which the concrete will be placed. In this case, we need to determine the minimum cement content for mild and moderate exposures when using 20mm down coarse aggregates.

Mild Exposure:
Mild exposure refers to conditions where the concrete is protected from severe weathering and aggressive agents. Typically, mild exposure conditions include indoor environments, such as residential buildings, offices, and schools. The minimum cement content for mild exposure is lower compared to more aggressive conditions.

Moderate Exposure:
Moderate exposure refers to conditions where the concrete is exposed to some degree of weathering and aggressive agents, but not as severe as in severe or very severe exposures. Examples of moderate exposure conditions include exterior building facades, parking structures, and non-industrial environments. The minimum cement content for moderate exposure is higher than for mild exposure but lower than for severe or very severe exposures.

Determining the Minimum Cement Content:
To determine the minimum cement content, the code of practice or design guidelines should be consulted. In this case, according to the given information, the minimum cement content per cubic meter of concrete for 20mm down coarse aggregates should not be less than 300 kg. This means that for both mild and moderate exposures, the minimum cement content should be 300 kg/m³ or more.

Conclusion:
In conclusion, when using 20mm down coarse aggregates, the minimum cement content per cubic meter of concrete must not be less than 300 kg for both mild and moderate exposures. It is important to consider the exposure conditions to ensure the durability and performance of the concrete in its intended environment.