Reproducible sample preparation in the drying oven
Scanning electron microscopy brings it to light: Depending on the ideal mixture, concrete as a building material is small-pore and compact, and thus resilient towards humidity, frost or chemical substances.
The “cement-bound building materials” team of the German BAM, the Berlin Federal Institute for Materials Research and Testing, conducts research into new concrete formulae, in particular for the repair of concrete. Before numerous material tests are performed, the samples are conditioned in a cooled incubator IPP, a drying oven and a CTC climatic test chamber from Memmert. AtmoSAFE was introduced into the fascinating world of building materials by Dr.-Ing. Hans-Carsten Kühne.
Drying and conditioning test samples
A mortar prism must prepare for the worst at the Federal Institute for Materials Research. In order to test properties such as compression strength, bending tensile strength and elasticity, forces of several tons may be exerted on the test samples at times. To determine the pore size, mercury is injected at high pressure, and to determine the frost resistance, the samples are exposed to extreme fluctuations in temperature over several days. The list of the various material tests is long and often defined by European and national standards. However, one condition must always be fulfilled: the test samples are conditioned before every material test, so that the results can be compared. The temperature and humidity requirements for conditioning are precisely defined for standard tests and must be documented accordingly.
How does conditioning in the temperature control chamber work? Staff at the “cement-bound building materials” task group use the Memmert UFE 500 drying oven to dry mortar and concrete prisms at 105 °C until they reach a constant mass. In the cooled incubator IPP, the test samples are compared with a tolerance of 1 Kelvin with temperatures in the calorimeter, a piece of test equipment in which the specific heat generation during the hydration of the binding agent is subsequently determined. The CTC climatic test chamber on the other hand is used for standard sample storage in which the test samples are exposed to a temperature of 23 °C at a relative humidity of 50% for 28 days, or even longer for measuring length changes, respectively.
Hans-Carsten Kühne demands the same high-quality standards from all of his devices, but with a wink says that Memmert has a problem, since its appliances last too long. Quite a few Memmert veterans are to be found on the historic premises of the BAM Berlin - still working flawlessly. “First and foremost, the appliances need to be absolutely reliable, and must quickly return to setpoint temperature after a power failure”, Kühne responds to the question about what his requirements are. Particularly in material testing of building materials, the robustness, load capacity of grids and easy cleanability play an important role. Many of the employees in the task group also appreciate the possibility of remote programming and controlling the appliances over the network.
About the BAM
The BAM Federal Institute for Materials Research and Testing has a long tradition in the science city Berlin. At the same time that Robert Koch, Rudolf Virchow and Paul Ehrlich were active, Adolf Martens established material testing as a science. In his honour, a certain ferromagnetic structure in metals was named Martensite. The State Material Testing Office, founded by Martens in 1871, ultimately evolved into what today is the BAM. Its tasks are the advancement of safety in technology and chemistry, the implementation and evaluation of physical and chemical testing of materials and facilities, including the provision of reference procedures and reference materials, the promotion of knowledge and technology transfer in the areas of activity of the BAM, the collaboration in the development of legal regulations, e.g. in defining safety standards and limit values, and the consultation of the German Federal government, the economy and national and international organisations in the field of material technology and chemical industry. www.bam.de
An overview of focus topics
- Materials research
- Material test
- Concrete, mortar, cement
- Test specimens
- Drying and conditioning
- Sample storage
- Drying oven
- Climatic test chamber
- Cooled Incubator
Picture credit: BAM, Memmert, sxc.hu (Gergerger7)
The quality of concrete can be seen when comparing microstructures. Porous and permeable to liquids in the first, compact and without pores in the second picture. © BAM
Hans-Carsten Kühne in front of concrete parts in a natural stone look
With a customised test assembly, the frost resistance of concrete as a building material is tested in the Memmert TTC temperature test chamber economically and with absolutely standard-compliant temperature cycles.