Admixtures for Hot Weather
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The summer time effects of wind, temperature, and air humidity can collectively have a detrimental impact on the performance of concrete. Higher temperatures cause a faster rate of water evaporation and cement hydration, thereby stiffening concrete earlier and increasing the risk of plastic cracking occurring.
- If possible, sprinkle cool water on forms, steel and subgrade before placing
- Schedule mixer trucks to avoid waiting time
- Organise the job in advance, quickly place the concrete, and have sufficient workers to avoid delays
- After pouring, protect exposed surfaces from drying out through wind breaks, sunshades, fog sprays and approved curing membranes
- After finishing, consider a curing membrane, plastic sheeting or water sprays and strength development
- Use retarding admixtures to extend setting times
- Consider early morning or evening placement
Admixtures for Hot Weather
The laying of concrete in hot weather places extra demands on the concrete worker. The ideal conditions for concrete curing are between 10-30 C. The addition of extra heat and/or wind can have a detrimental effect on the finished product because of rapid moisture loss. Concrete develops its properties of durability, wear resistance, permeability and strength over time. To develop these qualities, the hydration must be prolonged. Prolonged hydration requires adequate moisture as well as an even temperature range. The excessive loss of moisture can cause shrinkage cracking. These problems can be controlled through the use of Admixtures.
These are designed to retard setting times so that the concrete worker has enough time to finish the surface of the concrete. It is also useful for maintaining concrete slump during long haul times to construction sites. Retarders temporarily stop the chemical action of hydration but after the planned delay hardening develops at an accelerated rate.
Water Reducing Retarders
Water reducing admixtures improve important properties of concrete in both its plastic and hardened condition. When wet the handling properties can be greatly improved without the addition of extra water. In hardened concrete the properties of the concrete are improved because of the more effective dispersion and hydration of cement. The retarding portion of the admixture delivers similar properties to the detail outlined above. Sika BV40R and BV45R are examples of admixtures which provided both reducing and retarding properties.
Superplasticisers provide substantial improvements in workability and flowability without increased water, this allows for a lower need of vibration. Ideal applications include slender components, columns and beams with congested reinforcement, situations where concrete discharge is difficult and applications requiring fast and efficient placement of concrete. Sikament 1000R is an admixture which provides all these benefits as well as set retardation.
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DISCLAIMER: Allied Concrete has endeavoured to present the best possible information. However we accept no responsibility for the application of the principles discussed.