*2.1. Binder Composition*

Supplementary cementitious materials are powder additions used as a replacement for clinker (in some cases referred to as Portland cement) with the aim of reducing the carbon footprint of cement while still preserving sufficient cement or concrete properties. The SCM can be blended directly into cement during its production or later during concrete production. The origin of SCM is mostly from various industries' waste streams, which, with or without treatment, are changed into secondary raw materials that are beneficially used in cement or concrete production. The most widely used SCMs are fly ash (FA), ground-granulated blast furnace slag (SL), and silica fume (SF). More alternative types are

calcined clay, ground glass, pumice, or rice husk ash. Nowadays, the trend is highly focused on existing and new SCMs because of the emphasis on the reduction of CO2 emissions, the use of environmentally friendly materials, the circularity of materials through the reuse of waste from various industries, and the reduction of landfilling.

The most important property of SCM is the content of the amorphous (glassy) phase, which is reactive under certain conditions and contributes to the strength and other properties of the binder. Other properties influencing the reactivity of SCMs are fines, the shape of particles, chemical composition, replacement level, and the water/cementitious materials ratio. Another reason why it is essential to keep testing the potential of new materials that could become SCMs is due to the closure of thermal power plants that produce the by-product FA, which is presently the most common SCM on the market.

Reactivity is a factor that sorts SCMs into inert, latent hydraulic, or pozzolanic types based on their chemical reaction principle. For example, the reactivity of SCMs could be improved by the addition of a sulphate constituent (gypsum) and a carbonate constituent (lime). The reactivity of individual SCMs is possible to analyze using various test methods. There are tests specifically for FA and SL described in ASTM and EN, but they are based only on the comparison of strength properties to the reference mix. Other methods, such as the Chapelle test, the Frattini test, the strength activity index test, and the SCM dissolution test, have been introduced. Those methods are useful, but they are not able to distinguish whether the SCM is pozzolanic or latently hydraulically reactive (see Figure 1. Therefore, isothermal calorimetry and thermogravimetry analysis, or "rapid, relevant, and reliable" test methods, were introduced [3].

**Figure 1.** Characteristic of various SCMs: (**a**) ternary phase diagram showing SiO2, Al2O3, and CaO amounts for various SCMs [4]; (**b**) results from isothermal calorimetry and thermogravimetry analysis on various types of SCMs and their classification. Key to SCM types: fly ash (FA), ground granulated blast furnace slag (SL), silica fume (SF), calcinated clay (CC), ground lightweight aggregates (GLWA), quartz (Q), ground limestone (LS), basic oxygen furnace slag (BOFS), municipal solid waste incineration fly ash (MSWIFA), ground pumice (P), ground glass (GG), and basalt fines (BF) [4].

There are two main standards for the utilization of SCMs: directly in cement, later during concrete production, or both to be followed in Europe. The amount of SCMs used as a replacement for clinker is regulated by standard EN 197-1, "Cement—Part 1: Composition, specifications, and conformity criteria for common cements" [5]; and standard EN 197-5:2021, "Cement Part 5: Portland-composite cement CEM II/C-M and composite cement CEM VI" [6]. Only EN197-1 [5] is mentioned in the standard for concrete, EN206, "Concrete—Specification, Performance, Production, and Conformity" [2], and therefore, the maximum replacement of clinker in concrete is approximately 35% (this can

vary for individual countries by the national annex). If the SCMs are added during concrete production, EN206 [2] shall be followed, where in the section "5.2.5 Use of Additives", it is specified the maximal proportions of FA, SF, and SL to cement. The k-value concept is regulative, and if the amount of SCM in question exceeds the limit value, an excessive amount is considered an additive of type I (mineral filler).

All these regulations must be followed, so it is challenging for industry to abide by them and still produce concrete with a low carbon footprint. The demonstration series of mixes contains fly ash, silica fume, and limestone powder in various proportions to cement (see Table 3).


**Table 3.** Binder composition in kg and % per 1 m3 of concrete.

The most common method for evaluating CO2 connected to concrete produced in a given concrete plant is the EPD. This certificate allows concrete producers around Europe to compare their concrete in terms of carbon footprint. A detailed description of EPD is described in the following Section 3.

#### **3. Environmental Product Declaration for Low Carbon Concrete**

The environmental impact in terms of CO2 associated with the production of lowcarbon concrete is calculated in an EPD consisting of four major sections: CO2 related to raw materials (A1) and their transportation (A2), concrete production (A3), and delivery of the final product (A4), concrete, to the construction site where it is used (A4). Stages A1, A2, and A3 belong to the product stage, and stage A4 is part of the construction installation stage [1]. The use of SCMs can help reduce CO2, which is predominantly related to Stage A1. In general, limestone powder and SCMs such as fly ash or microsilica have a significantly lower CO2 footprint connected to their production than Portland cement. The EPDs for the demonstration series were created in two different concrete plants in Northern Norway, Nordland Betong (NB) and HGB Betong AS (HGB). The difference in carbon footprint connected to individual mixes is related to the A2 stage, as all input materials are the same besides aggregates; see Table 4.

**Table 4.** EPD calculations for demonstration series in two different concrete productions.


#### **4. Areas for Utilisation of LCC in Northern Periphery and Arctics**

Different countries in the Northern Periphery and the Arctic have different national regulations and recommendations for LCC, but all of them are aligned with European standards, particularly EN197-1 [5] and EN206 [2]. Individual concrete types are regulated by a classification system that sorts concretes in low-carbon concrete classes defined by kg CO2—eqv. per 1 m<sup>3</sup> of concrete. LCC can be designed for all concrete strength classes, and the emitted CO2 varies for each class. The exposure classes defined in EN 206 [2] further describe the properties of concrete, and if the LCC fulfills those, it can be used for any application. Nevertheless, based on extensive research, we know that LCC suffer in harsh conditions, and their use is even more limited than in countries with a warmer climate. Recommendations and regulations for LCC classification for Norway, Sweden, Iceland, and Finland follow.

#### *4.1. Norway*

For Norway, the system is described in the Norwegian Concrete Association's publication NB 37, "Lavkarbonbetong" [7]. In this publication, it is clearly explained that the production of LCC is more feasible in the southern part of Norway than in the northern part, mainly due to input material transportation. Northern Norway has only one realistic supplier of cement: Norcem in Kjøpsvik. The nearest supplier apart from this is Norcem Brevik (near Oslo). Therefore, CO2 footprint that concrete producers from Northern Norwegian use is 616 kg CO2/ton compared to southern producers, which are using Norcem Brevik with 573 kg CO2/ton [8]. Classification system in NB 37 sorts of concrete in 4 LCC classes and compare them to industrially produced concrete (Industry reference [7]). The following Table 5 presents a system for the classification of LCC in Norway. There are already discussions that The Norwegian Public Roads Administration will impose requirements for low carbon at B in the concrete structures.

**Table 5.** NB's No. 37 overview of greenhouse gas emissions to the low-carbon classes compiled with the industry reference [7].


2) Possible level for some projects, but with several restrictions in the standard work, and limited availability. Feasibility must be clarified in each individual project.
