Despite being one of the most versatile construction materials on the planet, concrete requires specific conditions to reach its full strength and performance potential.
With 23°C considered the ideal mix temperature to optimise the hydration process, the Australian Standard AS1379: Specification and Supply of Concrete stipulates that concrete temperatures should be between 5°C and 35°C at the point of delivery to ensure correct curing and strength development. Furthermore, it also recommends that additional precautions are taken to protect the mix if the ambient temperature falls below 10°C or goes above 30°C.
While the major issue with cold-temperature concrete in Australia tends to be increased setting times and the additional costs associated with delays, the issues surrounding hot-weather concrete can be far more serious – and a significantly greater challenge – especially given that temperatures above 30°C are a common occurrence across much of the country during the summer months. Elevated temperatures can also be a major challenge for concreting and shotcreting in mining and underground construction environments.
In short, the elevated temperatures accelerate the hydration process, which in turn reduces the setting time of the concrete or shotcrete. As water evaporates from the mix, it loses slump and workability, reducing the time available to place and finish the concrete. This can lead to poor compaction and surface appearance, plastic shrinkage cracking, thermal cracking, and, perhaps most seriously, a significant reduction in ultimate strength and durability.
Importantly, these issues cannot be overcome by simply adding more water to improve the workability of the mix. While it may increase the slump and workability in the short term, adding water decreases the strength, increases permeability, and ultimately affects the durability of the concrete.
With that in mind, Master Builders Solutions has developed a range of specialist admixtures to help you get the most from your concrete in hot conditions.
Innovative Admixtures for Hot Weather Concreting
These innovative products exhibit several benefits to combat the challenges of hot weather concreting and shotcrete, depending on the mix being used and the type of application.
MasterSure 1008: This new generation slump-retaining aid incorporates an innovative super retention formulation that provides extended slump retention, particularly in hot climates. It is ideal for project work with strict tolerances on the workability of concrete arriving at the site, making it perfect for piling and precast applications where on-site pours can be delayed.
MasterSet RT 122: This admixture retards the setting time of the concrete to facilitate placing and finishing. It provides great flexibility for set time requirements and can be used for all types of applications.
MasterRoc HCA 20: At the extreme end of the hydration control scale, this product is specifically designed for batched wet or dry shotcrete mixes. MasterRoc HCA 20 provides ultimate control of the cement hydration processes, allowing the mixes to remain fresh for up to 3 days without loss of quality, even in elevated temperatures. It is also commonly used in remote areas of Australia where concrete can be transported for up to 3 hours before discharging, offering a solution to both producers and contractors to ensure the concrete arriving at the site is of top quality.