## 1 Introduction  
Concrete, and subsequently Portland cement, is one of the commodities whose demand is ever increasing. According to the 2050 projections of CEMBUREAU, developing countries and emerging markets such as India and China are expected to need almost six billion tonnes of cement by the year 2050 [1]. Taking into consideration that production of cement is a major cause for carbon dioxide emissions, accountable for about 5-8% of anthropogenic CO\({}_{2}\) emissions worldwide, concrete and cement research has been focusing on the production of low Portland cement formulations using supplementary cementitious materials, such as limestone, fly ash, ground granulated blast furnace slag and silica fume. Although the present research is focused and based on European Standards it should be noted that a global shift towards performance based rather than prescriptive specifications (composition based formulations) can be observed. In fact, particularly with respect to fly ash addition, the American Concrete Institute suggests a maximum limit of 35% of fly ash addition in binary compositions while the need for admixtures is stressed [2]. Still, this limitation can be considered very conservative according to the National Ready Mixed Concrete Association, claiming that prescriptive specifications limit the opportunities to reduce the environmental impact of concrete. According to research carried out the greatest occurrence in specifications is the restriction to the quantities of Supplementary Cementitious Materials (SCMs) (85% occurrence) [3]. The general consensus, therefore is to aim at specific performance, e.g., to limit the cement content, maximize the use of SCM, target specific strengths, curing time, slump, water-to-cementitious materials ratio in order to design the desired cement blend and concrete mix. This will effectively extend the allowable limits of the \"code prescribed permissible\" amounts of SCMs in concrete mixes, creating a gap in the current knowledge on low carbon footprint formulations containing more than two constituents. Furthermore, the evolution of nanotechnology, has not only rendered monitoring of matter, at a scale marginally above the atomic, possible, but has also revolutionized cement science, producing novel cements and concretes of superior strength and durability [4; 5]. Under the European Union FP7 project (FIBCEM), various nanoparticles (commercially available or produced by the project partners) were tested in cementitious matrices at the University of Bath, in an effort to produce low carbon footprint cements [6; 7; 8; 9; 10]. For this, the amount of Portland cement (PC) had to be limited and supplementary cementitious materials had to be added, forming blended cementitious matrices. Although the value of hybrid binders is greatly appreciated [11] and an extensive number of studies have been carried out in an effort to understand possible synergies between constituent materials such as fly ash and limestone in ternary blends [12] or to determine the reactivity of pozzolanic materials [13] in blended cements, there is still limited research on the synergies and material reactivities in very low PC content cementitious matrices. That is to say, research presented to date, investigates the synergistic effect of constituent materials for up to 20% PC replacement [14] or even higher PC replacement rates (55% PC and 35% fly ash and silica fume) but having a very low water to binder ratio (0.17) [15]. Qualitative characteristics of the hydration products resulting from the binary combinations of PC with either fly ash (FA) or silica fume (\(\upmu\)S) or limestone (LS) have been studied in greater detail by [PERSON] et al. [16]. Although there are many publications on binary systems, i.e., studies on various contents of FA or \(\upmu\)S or LS Portland cements, there is limited published research on ternary and above systems.