Concreting in Hot Weather
The qualities of concrete and the mixing, transportation, and placement of concrete materials during construction are affected by environmental elements, particularly hot weather conditions. Therefore, understanding how these variables can compensate in various ways to maintain high-quality standards and avoid concrete issues.
Hot weather is any combination of the following conditions that tend to degrade the quality of freshly mixed or hardened concrete by speeding up the rate of moisture loss and cement hydration or caused by other adverse effects:
- High ambient temperature
- High concrete temperature
- Low relative humidity
- High wind speed, and
- Solar radiation
Malaysia's climate is classified as equatorial due to its proximity to the equator, which means it is hot and humid across the year. Malaysia receives an average annual rainfall of 250 centimeters (98 in) and an average daily temperature of 21°C to 32°C.
In the majority of Malaysia's locations, hot weather problems are a regular occurrence. The highlands, on the other hand, have cooler temperatures. Nevertheless, the associated climatic factors of strong winds, low relative humidity, and solar radiation can coincide, particularly in tropical climates. Additionally, hot weather conditions can result in a rapid rate of moisture evaporation from the newly placed concrete's surface, as well as an accelerated setting time. However, by and large, high relative humidity mitigates the effects of high temperature.
Due to the potential for damage to freshly placed concrete, hot weather should be considered when planning concrete projects. An increase in concrete temperature can increase water demand, which increases the water-cementitious material ratio, resulting in decreased strength and durability. In addition, increased temperatures tend to accelerate slump loss and result in the loss of entrained air.
Temperature also plays a significant role in concrete setting time: at higher temperatures, concrete sets more quickly, necessitating faster finishing operations. Concrete that is prematurely cured at high temperatures will not be as strong as concrete that is cured at temperatures in the range of ≈24°C. High temperatures, high wind speeds, and low relative humidity can have a detrimental effect on fresh concrete in two ways: the rapid evaporation rate can cause plastic shrinkage before the concrete sets or early-age drying shrinkage cracking. Consequently, unless proper curing methods are used, the evaporation rate depletes the surface water required for hydration.
Thermal cracking can occur due to rapid temperature changes, such as those experienced when concrete slabs or walls are placed on a hot day followed by a cool night. Additionally, elevated temperatures promote cement hydration, increasing the likelihood of thermal cracking in thicker structural members. The secret to effective hot weather concrete work is to be aware of the factors influencing concrete and plan accordingly.
According to proven local recommendations, adjust concrete mixture composition and proportions, such as water-reducing and retarding admixtures. Additionally, extended-set control admixtures may be used for long-haul deliveries or in extremely hot environments. Modifying concrete mixtures to reduce the amount of heat generated during cement hydration, such as using supplementary cementitious materials, i.e., blended cement with a low heat option, or fly ash and slag cement, potential problems associated with high concrete temperature can be avoided.
It is critical to plan concrete delivery to avoid interruptions and delays during placement and finishing. Trucks should be able to discharge immediately, and there should be sufficient personnel on hand to place and handle the concrete. When feasible, avoid placing and finishing concrete during the hottest part of the day. To facilitate finishing, avoid sprinkling water on the surface of slabs. In extreme temperature conditions or when working with large concrete sections, the temperature of the concrete can be lowered by introducing chilled water or ice in the mixing water.
Chilled water can cool the concrete by up to 6oC; ice can cool it up to 12oC. Other measures, such as sprinkling and shading the aggregate, are used by the ready mixed concrete producer to lower the temperature of the concrete. Liquid nitrogen can be injected into concrete mixers to achieve more significant reductions in concrete temperature. This requires additional setup costs and appropriate safeguards to prevent blade and mixer drum damage. If low humidity and strong winds are forecasts, windbreaks, sunscreens, mist fogging, or evaporation retardants may be required to prevent plastic shrinkage cracking in slabs.