Low Carbon Concrete Admixtures (LCCAs) are the newest class of admixtures developed for reducing the carbon footprint and improving the sustainability of concrete. Their formulation involves multiple chemicals for enhancing the degree of hydration (DoH) and the compressive strength of cementitious binders at both early and longer curing times. In the present work, the fundamentals of LCCAs are disclosed. Secondary nucleation, augmented pozzolanic reaction, enhanced silicate and aluminate phases dissolution and limestone trigger are the levers which, separately or synergistically, determine the LCCAs effectiveness with blended cements. The mechanism of each controlling factor has been described by the review of the previous literature and studied by the execution of new experimental tests and a statistical analysis approach. Experimental measurements include time resolved XRD hydration kinetics and compressive strength testing of mortars with and without LCCAs. The wide range of chemical-physical processes involved and the possibility to combine the different ingredients in various proportions offer the possibility to formulate a range of products specifically designed for blended cements, which are believed to further expand both in number and composition in the coming years.