Moien Rezvani

Eco-Friendly Concretes With Reduced Water and Cement Content: Mix Design Principles and Experimental Tests

The major environmental impact of concrete is caused by CO 2 emissions during cement production. Great potential for reducing the impact is seen especially for concretes with normal strength. The use of superplasticizers and highly reactive cements as well as an optimization of particle-size distribution and reduction in water content allow a significant reduction in Portland cement clinker in the cement and 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 secondary raw materials like fly ash or furnace slag for cement clinker is an appropriate option that is, however, limited by the availability of these resources.

Shrinkage of Mortar Samples Made of Limestone-Rich Cements

Shrinkage in concrete structures may lead to cracks which reduce the durability of concrete against aggressive mediums. In prestressed concrete elements shrinkage results in a significant loss of prestressing forces. Limestone-rich cements with limestone contents beyond the values of DIN EN 197-1 were developed in order to reduce the influence of cement production on environment. In this paper the shrinkage behavior of mortar and concrete samples made of limestone-rich cements up to 70 wt.% with different water/cement-ratios was analyzed. The results indicate that shrinkage of such cements is strongly dependent on the amount, chemical and physical properties and the mineral components of limestone. The mortar samples made of such cements had shown both higher or lower shrinkage than reference samples made of pure Portland cement (CEM I 52,5 R) depending on the used limestone type. Specific surface area measured by BET-method seems to play a key role on the shrinkage behavior by controlling the disjoining pressure between hydration products. Meanwhile, it was found that in contrary to reference samples the prolonged curing in water does not influence the shrinkage of specimens made of limestone-rich cements significantly.