Eco-friendly concretes with reduced water and cement content – Mix design principles and application in practice

The major environmental impact of concrete is caused by the CO2-emission during the cement production. Great potential for the reduction of the impact is seen especially for concretes with normal strength. The use of superplasticizer and high reactive cements as well as the optimization of the particle size distribution and the reduction of the water content allows a significant reduction of the Portland cement clinker in the concrete. Essential is the addition of mineral fillers (e.g. limestone powder) to provide an optimal paste volume. In addition the already practicable substitution of the cement clinker by secondary raw materials like fly-ash or furnace-slag is an appropriate opportunity but limited by the availability of these resources. eral test series the fresh and hardened concrete properties of water and cement reduced concretes were investigated, especially the workability, the strength development, the design relevant mechanical properties as well as durability aspects like carbonation. It was shown that concretes with cement contents lower than 125 kg/m3 were able to meet the usual required workability, strength (app. 40 MPa) and mechanical properties. The carbonation depth of concretes with 150–175 kg/m3 of cement was equal or lower than the depth of the conventional reference concretes for exterior structures. The ecological advantages were identified, using the environmental performance evaluation. A reduction up to 50% in environmental impact compared with the conventional concrete and a reduction of more than 65% by using blast furnace cement was calculated. The application in practice was verified conducting full-scale tests in a precast and ready-mix concrete plant. The special requirements on workability and early strength were fulfilled with a cement content of 150 kg/m3.