Reduction of CO₂ Emission by Using Low Carbon Concretes with Accelerating Admixtures

A major part of the CO2 emitted by the concrete industry comes from the production of cement clinker and covers 5–8% of the world’s CO2 emissions. As the development of long-term solutions for CO2 reduction may take several decades, the need of immediate actions is required. One possible solution can be the replacement of the cement clinker with the ground granulated blast furnace slag. However, due to the high level of slag in low carbon concretes the setting time and early-strength of the concrete can be decreased. Therefore, it is important to ensure a reasonable early-strength development of low carbon concretes for application in the construction industry. This study aims to investigate the effect of several accelerating admixtures to boost the early-strength development of low carbon concretes. The amount of each accelerating admixture required to enhance the hydration rate of CEM III/A and CEM III/B cements to the levels of CEM II/B cement was determined based on the heat development curves. The defined amount of each accelerating admixture was used to cast concrete samples and determine their compressive strength at the early (15, 24, 39, and 48 h) and later (7, 28, and 91 days) stages of hardening. The compressive strength of the low carbon concretes was evaluated with the ultrasound pulse velocity, rebound hammer, and standardised compressive strength tests.