High performance concretes with Dyckerhoff Mikrodur® technology
Today, high performance concrete can also be manufactured without silica fume with modern cement technology. Dyckerhoff is manufacturing ultrafine cement constituents separately from Portland cement clinkers and granulated blast-furnace slag for 15 years. In the course of recent years, these ultrafine Mikrodur particles are increasingly used for controlling the cement properties. The Dyckerhoff Premium Cements are cements with extraordinary performance that meet the specifications of the relevant standards, e.g. regarding the development of strength and the resistance to aggressive media. The improvement of cement through Mikrodur is based on a densely packed structure of reactive constituents. The combination of high-quality standard cements and ultrafine cement particles enables a targeted adjustment of properties through granulometric optimization. With Veridur®, for example, high performance bright-coloured fair-faced concrete can be manufactured. At the Lufthansa Aviation Center at Frankfurt airport, uniformly coloured columns of high performance concrete C 60/75 and normal concrete C 45/55 were erected. With Velodur®, early-strength ready-mixed concretes for repairing traffic areas can be produced. However, Variodur® offers the widest range of application. For instance, the natural draft cooling tower for the E.ON power station, Kraftwerk Datteln, Germany, currently under construction is erected with Variodur 30 CEM II/B-S 52.5 R. The extremely dense structure of the hardened cement paste here obviates the need for a coating to protect the structure from the aggressive constituents of the flue gas. The high durability is achieved with ultrafine blast-furnace slag particles whose content depends on the ultimate requirements made on the structure.
"Hollandse Brug" is the name of the bridge that connects the A 6 Amsterdam Expressway with the city of Almere on the Flevolandpolder in Holland that was founded as recently as in 1975. The reinforced-concrete bridge of 350 m length has been provided with a new bridge slab made with a special concrete with Variodur 50 CEM III/A 52.5 N-HS/NA. The repair measure provides for a concrete slab of 17 cm thickness for the existing bridge construction that will be coated with 8 mm epoxy resin for additional surface protection. The requirements made on the concrete after 48 hours, with a blast-furnace slag content of at least 50 % in the cement, were a high tensile-bond strength and an early compressive strength of > 35 MPa as well as a residual moisture of < 2.5 % for installing the epoxy-resin coating. In addition, a high resistance to freeze-thaw with de-icing salt (exposure class XF4), low-shrinkage setting and absence from cracks was specified. The combination of these properties is impossible to achieve with conventional cements.
But durability and resistance to wear are not the only properties that distinguish the Premium Cement Variodur 50 CEM III/A 52.5 N-HS/NA. A particularly interesting area of application is high performance mass concrete that is virtually impossible to be produced with conventional cements. The concrete-technological achievement in constructing the foundation of the KranhausPlus in Cologne (Germany) was in particular the development of a high performance concrete of consistency F5 in which the heat that develops due to the hydration of the cement could be kept as low as possible in order to prevent in this way the occurrence of possible thermal stresses and cracks in the structure. The temperature taken in the core of the foundation measuring 24 m x 10 m x 1.60 m after 48 hours was 56°C, the difference to the rim zones amounting to less than 15 K.
In continuation of the Mikrodur technology, cement mix designs have now been developed that unlike the known binder composition for UHPC contain no silica fume. The new Nanodur conception comprises particle-graded binders made from cement manufactured in accordance with the standards, ultrafine cement components and nanostructured synthetic silica from various production processes.