## 1 Introduction  
The present investigation focused on the behaviour of concrete with addition of Ground Granulated Blast-furnace slag (GGBS). GGBS, or slag, can be present in concrete as a separate material added in the mixer, or blended in the Portland cement: either as CEM II/A-S or CEM II/B-S (with up to 35% of GGBS of the total binder content) or as CEM III (also called Blast Furnace slag cement, containing 36% to 95% of GGBS of the total binder content) [1].  
GGBS is often used in concrete to improve certain properties, both in fresh and hardened states. GGBS is frequently used in the production of low heat cement. Ternary systems composed by Portland cement, slag and silica fume have also been used in the production of high-strength concrete. However, the main application of GGBS as a supplementary cementitious material is in concrete structures placed in marine environments, due to its proven influence in reducing chloride ingress in concrete. Other beneficial effects of GGBS in concrete consist of protection against sulphate attack and alkali-silica reaction, also widely reported [2].  
However, some concerns have been raised regarding the durability of concrete with addition of GGBS in freezing environments, especially when de-icing salts are used. Although in the past years there is a new development by integrating anhydrous sodium acetate into concrete for protection against harmful impact of de-icing salt [3], for conventional concrete structures, the use of de-icingsults may result in a type of frost attack in concrete called surface scaling. In this type of frost attack, small chips of the cement paste are removed from the concrete surface, exposing the aggregate. The continuation of this mechanism may lead to severe consequences in the structures as the thickness of the protective layer above the reinforcement is reduced, opening an easier path for chloride to reach the steel reinforcement, promoting the initiation of corrosion and consequent loss of load capacity [4].  
Several investigations report reduced salt-frost resistance of concrete with additions of GGBS, when compared to that of Portland cement concrete, especially when large additions of GGBS are used. However, this conclusion is not consensual; even though laboratory tests usually result in a poorer performance, many researchers have found that, in field exposure, the resistance of concrete with additions of slag is comparable to that of Portland cement concrete [2].  
The research reported herein aimed at investigating the properties of concrete containing additions of GGBS, especially regarding its salt-frost resistance. The use of GGBS in concrete in Sweden is regulated by the Swedish Standard SS 13 70 03 [5], which is the Swedish adaptation of EN 206-1. In this standard, the addition of GGBS is limited to 50 weight-% of CEM I for exposure classes XF1-3, and 25 weight-% of CEM I in exposure class XF4. One of purposes of this study was to investigate whether it is possible to produce GGBS concrete with adequate salt-frost scaling resistance using higher amounts of GGBS than those allowed by SS 13 70 03 [5].  
Therefore, air-entrained concrete mixes with an equivalent water/cement ratio of 0.45 and with different percentages of replacement of Portland cement by GGBS were produced and tested. Besides the salt-frost scaling resistance, the compressive strength and resistance against chloride migration were also studied. The influence of the air entrainment and curing temperature on the properties of the hardened GGBS concrete has also been investigated.