Optimizing the sustainability of concretes for prefabrication
In this study, the sustainability of a concrete mix design for precast elements was improved. The objective had been to reduce the cement content to the minimum allowed by the standards without negatively affecting the properties (strength, consistence). One of the main problems in reducing the cement content is that the early strength (6h - 1 day) required for stripping can frequently no longer be achieved. To counteract this, ultrafine GCC (ground calcium carbonate, high-quality powdered limestone) was used which, through its effect, can compensate the loss of early strength. In this way, the CO2 footprint of the concrete could be reduced by more than 10 %, at comparable cost.
Outlook: As of 2025, with the publication of the new Annex ND to concrete standard SN EN 206:2013+A2:2021, further steps for optimizing concrete are now possible in Switzerland. In particular, the cement contents and the w/c ratio will no longer be specified. In this way, the early strength can be increased without inevitably also leading to a higher 28-day compressive strength and/or excessive concrete strengths. Excessive concrete strengths are often not desired and favor, for example, edge spalling. With the addition of fine or coarse limestone powders, the packing density of concrete and with that the concrete properties can be optimized in a targeted manner.
