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Research & Development
New inspection techniques, New material applications, New applications of process residues.
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Research and development
In an era characterized by a commitment to minimizing environmental impact, by a need to avoid time-consuming inspection and analysis work and by a determination to put residual substances to practical use, research is no luxury.
KEMA’s research addresses all sorts of highly relevant issues. Is it possible, for example, to develop non-destructive inspection techniques, which provide immediate feedback on the condition of a concrete structure without compromising its integrity? And how can one tell whether a repair of a concrete structure will stand the test of time?
Can one recycle concrete effectively by recovering usable materials from it? What further scope is there for utilizing fly ash as an aggregate? Concrete containers for the storage of radioactive materials not only have to provide effective protection, they also need to last a very long time.
KEMA is actively searching for answers to all these questions, and many others besides. We do not work in isolation, but cooperate closely with research partners across Europe, with concrete producers and construction companies and with the end-users of concrete structures.
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New inspection techniques
How can you determine the quality of a concrete structure or repair without compromising its integrity? Both the makers and managers of installations dependent on concrete would dearly like to know. KEMA is accordingly working with several other companies to come up with an answer. Development of an instrument for the non-destructive validation of concrete repairs is being supported by CRAFT, part of the European Commission’s technology stimulation program. Through the program, Brussels aims to assist small and medium-sized enterprises (SMEs) in the production sector, which lack adequate facilities for research and development. Interest in non-destructive validation techniques for concrete stems from dissatisfaction with the methods presently available. These techniques mean damaging the very concrete whose integrity is under examination, necessitating repairs that take time, labour and expensive scaffolding. And when the repairs are complete, you still can’t be certain about the quality of the structure as a whole. Not surprisingly, therefore, finished product quality can be somewhat variable.
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Portable ultrasound scanner
Although concrete is widely thought of as a maintenance-free construction material, bitter experience often shows that this is not the case. Fortunately, effective repairs to concrete structures are nowadays relatively straightforward. The durability and quality of a repair is determined by the composition of the concrete mix, the standard of the advice and the skill of the repairer. As a means of verifying the quality of concrete repairs, Europe’s small and medium-sized enterprise sector, supported by the European Commission, has developed a non-destructive scanner for checking the adhesion of concrete repair layers. A non-destructive means of establishing whether a new layer of concrete is firmly attached to its substrate is a boon, doing away with the need to keep scaffolding available. Using the scanner, it is also possible to perform more tests in a shorter space of time, thereby enhancing the reliability of the findings. Prerequisite for the new technique was that it should be as good as the established methods at determining the extent (area) of any non-adhesion. The decision was made to use ultrasound – an established technology that in the context of other applications had already proven itself reliable, simple and relatively cheap. Developers were given the remit of creating a device capable of detecting non-adhesion in repair layers ten to sixty millimeters thick, when used at an angle to the repaired substrate within a defined arc. It was also important that the scanner should not be significantly affected by the presence of steel reinforcement. Furthermore, it had to be user-friendly and suitable for use by relatively inexperienced personnel. Finally, the cost of the scanner had to be low enough for it to sell at no more than EUR 7,000. Realization entailed an extensive test program. Factors such as the curing rates of fourteen different BETEC repair mixtures were investigated, as well as the influence of variations in the repair methodology (injection and pouring), composition, cement type, grain size distribution (zero to sixteen millimeters), layer thickness and additive use. Test blocks with and without steel reinforcement were then created, complete with artificial adhesion anomalies. Once trials had been completed using a total of eleven transducers (sensors), the findings were used to design a laboratory prototype. Dubbed the Concrete Averaging Detection Device (CADD), the prototype was duly put together by KEMA. With a number of special software features and utilizing mean data from two sensors to compensate for the influence of steel reinforcement, the CADD has shown that non-adhesion between a concrete repair layer and its substrate can be detected with ease. A second prototype has now been produced for practical validation of the scanner. The Concrete Ultrasonic Bonding Evaluator (CUBE), as it is known, is currently undergoing field tests at numerous locations in various European countries.
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Accelerated degradation test
Concrete that is in contact with an aggressive medium such as groundwater is liable to degrade over time as a result of the following processes: - gradual dissolving of the calcium carbonate and hydration products due to the diffusion of calcium ions into the surrounding materials
- interaction of calcium carbonate with hydration products and with corrosive components.
Degradation of concrete due to these mechanisms is very gradual. Consequently, to assess how well concrete will last, it is necessary to use accelerated degradation techniques. The starting point for testing is a mortar or concrete test piece. This block is placed in a test rig, so that it is in contact with water or a solution contained in two drums (see figure above). Each drum contains an electrode, and the two electrodes are connected by a power source and an ammeter. Using this test rig, a voltage can be applied to the test piece. The electric current causes calcium ions to migrate towards the cathode at an accelerated rate. After a period in the rig, the test piece is studied by means of: - image analysis
- porosimetry
- XRD-analysis
What the analysts look for is a relationship between the quality of the test piece and the amount of dissolved calcium. In addition, an acceleration factor is determined – this is the ratio between the amount of dissolved calcium at a given potential gradient and the amount dissolved under electrically neutral conditions.
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New applications of process residues
The development of applications for process residues, the identification of residue storage options and the enhancement of constructional value call for a solution-driven approach to the estimation of environmental impact and economic viability. Coal combustion residues, such as fly ash and bottom ash, plus waste incineration residues, blasting grit and construction waste all pose their own problems. Problems for which KEMA develops structural solutions, with reuse and practical utilization as the dominant themes. The preferred applications and immobilization techniques center on concrete and related materials. KEMA’s Residue Management & Building Quality Team also places great emphasis on the development of refinement techniques, with a view to extending the range of possible uses and facilitating low-cost disposal.
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Fly ash for high grade concrete
Within the concrete industry, demand for uniformly fine-grained aggregate is growing fast. Using such aggregates, it is possible to make high-grade concretes that are twice or three times as strong as the conventional alternatives, and are also easier to work with. The material most commonly used for the purpose is micro-silica, with particles in the range of roughly 0.1 to one micron. Micro-silica is scarce, however. So not only is it expensive, but rising demand is likely to lead to shortages.
Power plants firing pulverized coal produce fine ash, known as fly ash. Because it is very similar to micro-silica in terms of its composition and properties, fly ash would appear to be an ideal alternative in many respects. Unfortunately, however, the particle size is too large – typically between ten and two hundred microns.
Working for the electricity generating companies, with support from the Ministry of Economic Affairs, KEMA has developed a procedure for reducing the particle size of fly ash. This "micronizing" process, as it is known, is the subject of a patent application. Micronization uses a granular milling technique to produce ‘ultra-fine fly ash’ with an average particle size of about 1.5 microns – easily bettering the results of any rival process. Tests have shown that concrete of strength class B105 or higher can be made using ultra-fine fly ash aggregate.
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Fly ash in bricks
Fly ash from the combustion of pulverized coal is a valuable raw material, widely used in the manufacture of building materials. Its use as an additive by the brick industry is opening up new disposal channels for power plant operators. However, fly ash is only suitable for this application if the leaching requirements laid down in the relevant environmental protection decree (the so-called ‘BSB’) can be met. Furthermore, questions have arisen concerning the accuracy of the ‘decay factors’ worked out by the National Institute of Public Health and the Environment (RIVM). These factors are meant to define the relationship between behavior under laboratory conditions and behavior in the field.
The BSB’s leaching requirements are based on the soil immission level over a period of a hundred years. This is determined by a standardized laboratory test. In a field test program the leaching from five sections of brick wall --four single-skin sections and one cavity wall section-- has been examined. The bricks used have been made from two different clay mixes – those in two sections of wall contain 20 per cent fly ash by mass. The dampness of the wall surfaces and the leaching water volumes are measured on a semi-continuous basis and periodic analyses are performed on the leaching water.
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Radon from building materials
Fly ash from the combustion of pulverized coal is a valuable raw material, widely used in the manufacture of building materials. In line with the Dutch government’s Radon Policy Statement, standards are being developed to regulate the radiological properties of building materials. One of the properties to come under scrutiny is ‘radon exhalation’ – the release of the radioactive inert gas radon from a building material. And it appears that the use of fly ash can reduce radon exhalation.
Radon is formed by the disintegration of radium, itself a radioactive decay product of uranium-238. It is found in all minerals and construction raw materials. Being gaseous, radon is able to escape from solid materials. The radon concentration inside a typical building is attributable largely to gas emerging from the ground; only about a third comes from the construction materials. The amount of radioactivity diffusing into the interior of a building over a given period of time is termed the level of "exhalation". Of the background radiation dose received by the average Dutch resident (believed to be about 2.5 millisieverts per year), building materials account for 0.7 millisieverts per year, with 0.4 millisieverts per year attributable to radon exhalation. The remainder of the building-material related exposure involves gamma radiation.
The radon activity of fly ash is greater than that of cement or grit. As a result, the use of fly ash in building materials increases gamma radiations levels slightly. On the other hand, research suggests that the levels of radiation from radon are lower. This is because radon exhalation is strongly influenced by a building material’s structural parameters, upon which fly ash can have a positive effect.
Research has shown that radon exhalation from a building material with a smaller average pore size is less than that from a similar material with larger pores. Armed with this knowledge concerning the relationship between structure and radon exhalation, it is possible to improve the mix of substances used in the manufacture of construction materials to reduce radiation levels. And fly ash has an important role to play in this context.
For more information, please contact us.
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