## 2 Laboratory Study  
### Mix Design  
The aim of the laboratory study carried out during this research was to evaluate the effect of the replacement of Portland cement by GGBS on the properties of fresh and hardened concrete, with emphasis on its salt-frost scaling resistance and chloride ingress. Air entrained concrete mixes were produced and tested with different amounts of replacement, namely 0%, 25%, 50% and 100% of GGBS by weight of CEM I. It should be noticed that, if not otherwise stated, the addition of GGBS in this paper is referred to the percentage of the cement (CEM I) weight, in accordance with [5]. As the main binder commonly used in Sweden for infrastructural concrete structures for reducing the risks of thermal cracking, alkali-silica reaction and sulphate attacks, a moderate heat, low-alkali, sulphate-resistant Portland cement was used: _Cementa Degerhamn Anlaggningscement_ (CEM I 42.5 N MH/SR/LA), produced by _Cementa_ AB. The coarse aggregates used were Swedish natural and crushed stone, _Tagene_ (4-8 mm and 8-16 mm). The fine aggregates used were _Sijsand_ (sea sand, 0-4 mm) and _Hol_ (0-8 mm). The Ground Granulated Blast Furnace Slag used was _Slagg Bremen_, imported from _Holcin Deutschland A.G._ The GGBS complies with all the specifications required by EN 15167-1 [6], and was added separately in the mixer. Four mixes with different GGBS contents were produced, namely:  
* Mix 1: 0% GGBS, reference;
* Mix 2: 25% GGBS (which is the maximum amount of GGBS allowed for XF4 exposure class according to SS 13 70 03 [5]). This corresponds to an addition of 20% GGBS of the binder weight (i.e., a CEM II/A-S);
* Mix 3: 50% GGBS. This corresponds to an addition of 35% GGBS of the binder weight (i.e., a CEM II/B-S);
* Mix 4: 100% GGBS. This corresponds to an addition of 50% GGBS of the binder weight (i.e., a CEM III/A). The equivalent water/cement ratio used was 0.45 for all the mixes, which is the maximum allowed in SS 13 70 03 [5] for exposure class XF4. In the calculation of the equivalent water/cement ratio for mixes with GGBS, an efficiency factor of 0.6 was considered, which is the highest k-factor allowed for GGBS added in the mixer together with CEM I, according to SS 13 70 03 [5]. This k-factor, or efficiency factor, is a measure of the relative contribution of the addition to the strength of concrete, compared to an equivalent mass of Portland cement. The efficiency factor concept is based on the fact that, since the hydration of the GGBS is slower than the hydration of Portland cement, if CEM I is replaced by slag on a one-to-one basis, the strength at early ages will be lower. Since the compressive strength of concrete is highly dependent on the water/cement ratio, it follows that one way to achieve higher strength at early ages when using GGBS is to decrease the ratio of water/(cementitious material) content, i.e., the mass of GGBS used will be higher than the mass of Portland cement that it is replacing [7]. This means that \(x\) kg/m\({}^{3}\) of GGBS is equivalent to \(kx\) kg/m\({}^{3}\) of Portland cement, to achieve the same compressive strength as Portland cement concrete at a given age (usually 28 days), and the total equivalent cement content is C + \(kS\), being C the mass of cement and S the amount of slag. Therefore, instead of using the water/cement ratio or water/binder ratio, the equivalent water/cement ratio ((\(w\)/\(c\))) is used, which is given by Equation (1):  
\[\left(w/c\right)_{eq}\ =\frac{w}{c+0.6\ S} \tag{1}\]  
where \"\(w\)\", \"\(c\)\" and \"\(S\)\" are, respectively, the weight of water, cement and slag per unit volume. All concrete mixes were air entrained. The air content was targeted at 4.5% \(\pm\) 0.5%. The targeted air content for each mix was achieved using a synthetic surfactant type of air entraining agent by Sika, SikaAer-S (1:10). SikaAer-S is produced by Sika Sverige AB in Sweden.