10.11 : Hot Weather Concreting

Concreting at elevated temperatures accelerates the hydration process, leading to quicker setting but potentially reducing the long-term strength of the concrete structure. Additionally, low air humidity fosters rapid moisture loss from the concrete, resulting in reduced workability, pronounced plastic shrinkage, and a higher likelihood of crazing.

Mitigating the heat increase in concrete can be economically achieved by shading aggregate stockpiles to prevent heating from solar radiation, burying water pipes, and painting exposed pipes and tanks white to reflect heat. Lowering the cement content in the mix can reduce the total heat released from hydration; in this case, the decrease in workability due to less cement content can be compensated by selecting aggregates with low absorption rates and minimal impurities. Adjusting workability and setting time is also possible through the application of set-retarding admixture. Incorporating ice into the mixing water helps to control the temperature. It is crucial, however, to ensure the ice is completely dissolved during the mixing process.

It is advisable to place the concrete within 45 to 60 minutes after mixing on dampened formworks and during the cooler evening hours. Post-placement, it is crucial to ensure the evaporation rate does not exceed 0.25 kg/m²per hour on the concrete surface. To protect the concrete from excessive daytime heat, it should be covered. During dry conditions, wetting the concrete can provide dual benefits of cooling and promoting effective curing.