To develop a high strength concrete it is important to ensure that it is cured at the right temperature: Not too hot, and not too cold. If newly placed concrete is allowed to get too hot or too cold there will be a reduced performance of the concrete with cracking, increased permeability, friability with reduced strength and reduced durability.
During curing, concrete generates heat. This is a byproduct of the curing process.
High Temperatures: If the ambient temperature is high when the concrete is placed, and the temperature is not controlled during placement and on initial curing, then the concrete will dry faster, the thermal stresses will create thermal cracking, it will have increase permeability with decrease strength as well as weaker friable surface. Many manufacturers specify the maximum temperature that concrete should be laid. This is very important during summer in Australia. To cool the concrete down:
- Concrete can be watered down with a fine mist to ensure the concrete does not overheat and to reduce water loss.
- Cooled concrete can be laid. This concrete is made using chilled water or ice in the mixture, or using cooled aggregate.
- The times for placement can be done at night to ensure the early strength is achieved before being subjected to high temperatures
Cold Temperatures: Where temperatures are cool, the concrete will take longer to cure and dry. If the freshly placed concrete freezes then the strength of the concrete and permeability of the concrete will be reduced. This is important in winter, particularly in areas in Victoria, Tasmania, ACT and NSW. Where temperatures are below 5°C, then the concrete can be made using warm or hot water. The concrete must be protected from freezing until it has reached a strength of 3.45MPa
To ensure that you have attained the right temperatures in the placed concrete it is important to monitor the temperature in the concrete, not just the surface, or the ambient temperature. The internal temperature of the concrete can be monitored by using a temperature logger. The logger will record the temperature at regular intervals and store it in the memory. Temperature loggers that are small and easy to set up and download the results are available from our online store. The Thermocrons can be buried into the concrete during laying, with the read wires attached. The data can then be downloaded using TCSpy, or the reader connected to a laptop.