Australia might be the sunburnt country, but winter time presents a range of new challenges for concrete and construction crews as the mercury plummets bringing rainfall and cold temperatures. When preparing and pouring concrete, extra precautions should be taken to minimise the effects of low temperatures and rain on concrete setting times.
Specialised concrete products such as Holcim’s Rapidcrete™ also offer a solution to cold weather concreting, cutting wait times and increasing workability with a range of strength grades customised to the requirements of each job. Industry leaders have also responded to the challenge with standardised recommendations for working with concrete in cold weather, including Cement Concrete & Aggregates Australia’s guide to Cold Weather Concreting. In this article, we present the latest recommendations for cold weather concreting.
The definition of cold weather – for concreting
The Australian Standard 1379: Specification and Supply of Concrete stipulates that concrete temperatures should be between 5°C and 35°C at the point of delivery. Precautions are recommended once the air temperature falls below 10°C. These additional measures are intended to ensure an acceptable minimum concrete temperature at the time of delivery, and to accommodate increased setting times.
The risk of concreting in cold weather
Low ambient air temperatures have an impact on the way concrete behaves, mostly due to a reduced rate of cement hydration. This results in slower setting times, which along with an increased evaporation time of excess water, can delay concrete finishing operations and increase construction and labour costs. Measures to speed up this process such as adding cement or sand mixtures to absorb moisture on the slab surface are not recommended, and could compromise the quality of the finish leading to weakness, flaking and poor wear resistance.
Precautions to take when pouring concrete in cold weather
Further steps can be taken to ensure a good quality finish when concreting in temperatures below 10°C. These measures include placing concrete as soon as possible after mixing to minimise any drop in temperature, and protecting the concrete from the cold by using hot air blowers and a temporary enclosure of tarpaulins. In very cold environments, Insulated formwork can be used to protect the concrete from freezing, and stripping of formwork should be delayed to protect the concrete from frost. Insulation blankets and coverings can aid curing, particularly where insulated formwork is used. Following removal of formwork, the concrete can be covered with plastic sheeting or tarps.
Holcim’s solution for cold weather concreting
At Holcim, we understand the frustration of the delays and increased construction costs resulting from cold and wet weather conditions. Which is why we developed Rapidcrete™. Rapidcrete™ increases workability and early strength, cutting wait times by up to 50 per cent. This is enabling construction and concreting crews to improve productivity, allowing for a flexible response to changing weather conditions, and helping to increase the number of pour days during the cold and wet winter months. The fast setting time of Rapidcrete™ allows for concrete pouring even on wet weather days, with the ability to pour in the morning before any predicted rain or storms in the afternoon. This versatility allows crews to respond dynamically and proactively to changing weather conditions, optimising resources, reducing labour costs and helping to manage project budgets and timelines.
The custom-designed concrete product can also help prevent additional expenses such as vandalism of wet concrete, or repairs and maintenance of compromised concrete poured in cold weather. The performance of Rapidcrete™ can be further enhanced by following a few simple steps during the preparation and pouring stages. This includes limiting slumps to the nominated value, not adding any additional water on-site, protecting the slab base from water and ice, and removing any excess surface water.
Rapidcrete™ is available in three different varieties suitable for most applications, except those that require a bleed, such as stencilled, dry shake coloured or patterned concrete.
What is the right Rapidcrete™ mix for your job?
As a professional you know what you need and what your clients need – an efficient, high quality outcome. Achieve it every time by choosing the optimum Rapidcrete™ product for each application.
Temperature at Last Load
|Rapidcrete™ 1||7-8 hrs||6-7 hrs||5-6 hrs||4-5 hrs|
|Rapidcrete™ 2||6-7 hrs||5-6 hrs||4-5 hrs||3-4 hrs|
|Rapidcrete™ 3||5-6 hrs||4-5 hrs||3-4 hrs||2-3 hrs|
*Set times are approximate only and may vary by +/- 1 hour (depending on climatic conditions).
Please check product availability in your local area.