Tilo Proske

Segregation of Coarse Aggregates in Self-Compacting Concrete

A major requirement on self-compacting concrete (SCC) is the resistance to any kind of separation. In the presented studies the segregation behavior of aggregates was analyzed systematically. The rheology of selfcompacting mortars was dealt with at first. Following, the segregation of particles of different size, shape and density in various mortars was examined. The aim was to find an analytical relation to estimate the risk of sedimentation, using the characteristics of the particles and those of the mortars. The classification of the aggregates according to their potential segregation is rather simple. But the description of the segregation resistance of the mortar is much more difficult. It is not possible to evaluate a mortar solely based on the rheological properties. The mixture composition must always be considered as well. Tests on concrete samples were conducted additionally to determine the influence of the overall system of SCC on the sedimentation of the aggregates.

Formwork Pressure of Concretes with high Workability

In the last 15 years the application of high-workability concretes has increased significantly. Such concretes have a spread value larger than 55 cm according to DIN EN 12350-5 (2000) and are classified into the consistency classes F5, F6 (vibrated concretes) and Self-Compacting Concretes (SCC) according to DIN EN 206-1 (2001). Using SCC a mechanical compaction is not necessary anymore.

Formwork Pressure of Highly Workable Concrete – Experiments Focused on Setting, Vibration and Design Approach

The presented investigations were conducted at the Institut fur Massivbau and contributed to a joint research project including several German research institutes [1]. A number of experimental tests on highly workable concretes were carried out. Small scale material analyses as well as measurements of the formwork pressure on large specimens were carried out. Based on the test results an analytical model for the calculation of the concrete pressure on vertical formwork was developed. The analytical model takes into account the time dependent material parameters of the fresh concrete, the specific properties of highly workable vibrated concretes and self-compacting concretes (SCC) as well as operation aspects. A proposal for the design of formwork, based on the experimental tests and the semi-probabilistic safety concept was developed. It was found that even for highly workable concretes, the design load is often lower than the hydrostatic concrete pressure.

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.