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2015|16 Annual Report Fraunhofer IGB

10 4 MCure – ADVANCED TECHNOLOGY FOR EFFICIENT REPAIR OF CONCRETE STRUCTURES Chen Zhao, Ali Imran Javaid, Simone Mack, Siegfried Egner Concrete repair and curing Large numbers of concrete structures such as bridges, tunnels, dams, and harbors have reached a state, or will do in the long term, where repair is necessary. This is due to a variety of disintegration mechanisms in the concrete, excessive loads or poor workmanship. According to CON REP NET, over 50 percent of Europe’s annual construction budget is spent on rehabilitation and refurbishment projects, in particular for the repair of damaged concrete structures [1]. This has generated a requirement for technology that will result in more durable and effective repairs to concrete structures. In addition to concrete repairs, efficient curing of concrete is also important in the production of finished parts The curing of concrete is strongly dependent on the course of the process temperature and thereby on the ambient temper- ature. This limits work in colder climates on a seasonal basis. Therefore, the M ure pro ect has developed a scientifically novel system for the stimulation of the curing process that is independent of the outside ambient temperature. It is based on the use of microwaves and is characterized by low energy consumption and high temporal efficiency Curing process Optimized curing of concrete and achievement of the desired strength re uires the maintenance of a specific moisture con- tent and corresponding temperature profile in the concrete for a period of time after placement and surface finishing The combined effect of heat, or the internal changes in tempera- ture, and duration of curing on the development of strength is referred to as “maturity”. This increases rapidly over the first hours of the curing process, after which it slows down significantly and lasts for an indefinite period Optimum strength is achieved in concrete with high tempera- ture curing. The magnitude of the increase in temperature and its duration re uires precise control over a specific cycle Such a rapid rise in temperature can only be achieved through the use of an external energy source, e.g. microwaves, and requires precise sensor technology, controlled by operating algorithms. Reliable processing of concrete under unfavorable weather conditions is currently only possible for precast con- crete parts with the use of steam heating. Curing fresh concrete with microwaves The curing process can be accelerated with the use of micro- waves, that mainly interact with the moisture in the concrete. The moisture contents in the concrete are highly polar due to the high electronegative nature of oxygen and the electro- positive nature of hydrogen The electric field produced by the microwaves induces oscillations whilst travelling through the materials with a bipolar molecular structure. During this process, the moisture is vaporized and migrates to the surface of the material via diffusion. The curing process starts with the direct interaction between the water molecules and microwaves and partly also with the heat generated inside the concrete. This results in the development of a more rapid effect during the first phase of curing When curing concrete, the priority is not to achieve maximum speed of vaporization, but to generate temperatures that are sufficiently high relative to ambient temperature to promote 1 CHEMISTRY bondstrengthinMPa repair material Five Star Monomix Monopour PC6 OPC Mortar 3 0 1 0.5 1.5 2 2.5 34,6 °C 2.46 0.63 38,7 °C 1.8 0.71 37,6 °C 1.69 0.82 38,2 °C 2.15 1.14 microwave cured normally cured 104