# High-Durability Concrete Using Eco-Friendly Slag-Pozzolanic Cements and Recycled Aggregate
## 1 Introduction  
### Eco-Efficient Cement Production  
The demand for concrete--the world's most used construction material--continues to remain at a high level notwithstanding recent global economic fluctuations. In doing so, the concrete industry acts as one of the main contributors to CO\({}_{2}\) emissions accounting for approx. 5 to 7% of global anthropogenic CO\({}_{2}\) emissions (see [1; 2; 3; 4]), whereby Portland cement production accounts for approx. 90% of the quoted share [5]. The rapid increase in the recent global cement production is driven by China, which produced 2.35 gigatos of cement in 2015. This corresponds to 55% of the global amount of cement produced, contributing approximately 13 to 15% of China's total CO\({}_{2}\) emissions. In the future, due to population growth, cement production worldwide is projected to increase between 12% and 23% by the year 2050 [6].  
Such production quantities would lead to a global emission, depending on the author, of approximately 1.3 to 1.8 billion tons of CO\({}_{2}\) per year [2,7]. Further, CO\({}_{2}\) emission during cement production is derived from two sources, having a similar share: (1) Process-related CO\({}_{2}\) accounting for the energy demand by the use of fuels and electric energy mainly for drying, grinding, and mostly from clinker burning; (2) the emission of embodied CO\({}_{2}\) (ECO\({}_{2}\)) during CaCO\({}_{3}\) decomposition during heating, when the chemically bound CO\({}_{2}\) from the carbonate rock is degassing [2,5]. Summed up, the amount of generated CO\({}_{2}\) per kilogram of produced clinker varies between 0.65 and 1.0 kg CO\({}_{2}\) per kg clinker [8, 9, 10, 11] depending on the fuel type and the basis of electricity production. The process-related global CO\({}_{2}\) emission of concrete has been estimated at approximately 83 kg CO\({}_{2}\) per ton by [12], while ECO\({}_{2}\) accounts for an additional amount of approximately 95 to 135 kg/ton, varying depending on the specific concrete design [5, 13, 14], adding up to the generation of roughly 200 kg CO\({}_{2}\) per ton of concrete.  
In view of the importance of these issues, measures have been taken to reduce the environmental implications of cement and concrete production by using various strategies. The options range from customized concrete mixing design and plant technology possibilities toward energy saving [15] to carbon capture strategies [16, 17]. As a very central point with regard to embodied CO\({}_{2}\), the usage of alternative raw materials with the absence of carbonates in their mineral content is effective. This means the reduction in the portion of Portland cement replacing the clinker by alternative binder compositions (e.g., fly ash, furnace slag, or natural pozzolans) producing blended or--when using more than one blending material--so-called composite cements [18, 19, 20]. A current strategy in this context is the substitution of clinker by waste-based cementing materials, i.e., [19, 21]. In the present article, the approach of slag-pozzolanic cements (CEM V) according to [22] is pursued.