Climate-improved concreteat lower temperatures

Concrete, which is one of the world's most used due to its properties such as strength, durability, malleability, etc., has a negative characteristic, which is its climate impact, or rather it is concrete's most important component, cement, which has a negative climate impact during its manufacturing process. Today, climate-improved alternatives to the traditional gray concrete have been developed, which means that some cement is replaced with slag (GBBS) or fly ash (FA) and thus the concrete has a lower climate impact. A disadvantage of the climate-improved concrete is that it has a lower strength development at lower temperatures. The purpose of the work is to investigate which measures are most effective to be able to cast green concrete at lower temperatures and still achieve the set requirements regarding strength and form tearing. Investigation is done through the HETT22 software, which is a forecasting tool for simulating the temperature and strength development of the concrete in different types of construction elements. The simulations take place at an air temperature of -5 °C and a wind speed of 7 m/s with five different concrete recipes to find which amount of slag is suitable for the given construction part with different combined and optimized measures. The results of the simulations showed that the form tearing time increases with a higher percentage of slag content in the concrete mixture and may risk early freezing. In the case of measures with, for example, too high a power or too thick insulation, there is a risk of exceeding the maximum temperature of 60°C in the construction. With properly balanced and taken measures, it is possible to cast with a slag content of up to 40% and still achieve a strength of 6 MPa during 18 hours for wall elements and 28 MPa during 100 hours for joists