Frost Resistance of Alkali-Activated Concrete—An Important Pillar of Their Sustainability

Sustainable development of concrete construction requires sustainable materials or sustainable binders. Specifically, alkali-activated materials (AAMs) are an interesting and wide group of materials. They have good strengths and are considered environmentally friendly materials because secondary materials are consumed during the preparation of AAMs. The durability of AAMs is also excellent. One of the most important parts of durability is frost resistance. The frost resistance of alkali-activated materials is usually very good. However, some studies showed opposite properties and poor frost resistance. The reason for this may be a different composition of the activator. The content of alkalis is often considered the main characteristic of alkali-activated materials. However, SiO2 content can play an important role too. This paper discusses the different results for the mechanical properties and frost resistance of different compositions of alkali activators made of sodium water glass with a silicate modulus modified with potassium hydroxide. The role of the activator content and the water-to-cement ratio in this phenomenon is discussed. The results of this article show that the strengths of AAMs are significantly affected by the curing method. Water curing reduced some of the strength of the specimens compared to foil-covered specimens. Frost resistance depends on the method of curing and on the composition of the activator; some concretes with high strengths showed very low frost resistance.