Analysis and Testing of Construction and Coating Materials
In the BAW's chemistry and corrosion laboratory, the BAW staff analyse and evaluate the composition, suitability and/or quality of construction and coating materials as well as other materials by applying special physical and chemical testing methods.
Fourier transform infra-red spectroscopy (FTIR spectroscopy) is an analytical method for the definition and study of anorganic/organic molecule groups (Picture 1). By producing infra-red spectrums with typical absorption bands, the molecular character and the composition of materials (construction materials elastomeres, coatings) can be deduced. Examples of such investigations are:
- the identification of coating materials for quality assurance (finger print)
- the verification of composition or hardening reaction problems in coating materials and the examination of carbamate formation in amine hardeners of epoxy resin coatings
- determining mineral phases in concrete and masonry salts
- determining the corrosion products and deducing the source of the corrosion
FTIR spectroscopy thus permits fast and high-quality analysis of construction materials in general and of coating materials in particular.
Thermal Analysis with an Assembly for Concurrent TGA and DTA
The assembly for concurrent thermogravimetric analysis (TGA) and differential thermal analysis (DTA) is used to obtain information on decomposition temperatures, physical processes (melting, phase transition) and on the presence of specific components of the concrete (e.g. portlandite, ettringite and calcite; see Picture 1 for example). Further applications include:
- determination of the residual solvent content in coating samples
- thermal gravimetric analysis of concrete specimens, elastomers and corrosion products
- detection of mixing or hardening problems in two-component coatings
The TGA analysis allows increases in the informative value and the verification of other test results.
Headspace Gas Chromatography (HS-GC)
This chromatographic analysis method is used to screen for specific, volatile substances in a polymeric matrix. Thus it is possible, even after the polymer has hardened, to determine whether non-complying or incompatible solvents were used when applying coatings to steel and hydraulic steel structures. The question regarding the cause of failure of the corrosion protection can thus be clarified. The method can also be used for:
- the detection of toxic alkyloximes and aromates in alkyd resins
- multiple headspace extraction (MHE) to quantify residual solvent contents
- the development of profiles (finger print) for various diluting agents and solvent mixtures
Atomic Absorption Spectrometry - AAS
This spectroscopic analysis method is used to quantitatively determine various elements contained in different materials. It is possible, for example, to establish the composition of steel, alloys and corrosion products. The analysis of binders in concrete specimens thus includes the characterisation of the binder (cement type), taking into account the carbon and sulphur content, and the quantitative determination of the composition of old concrete. The Picture 2 shows a ternary diagram (CaO - SiO2 - Al2O3) depicting the classification of binders.
Using the incident light microscope it is possible to analyse the morphology and structure of material specimens, at a magnification of up to 500X. The structure of applied layers, the succession of the individual layers and any faults (blisters, inclusions, pinholes, etc.) can thus be determined, especially in coating samples. Based on computer-aided image analysis it is also possible to determine other characteristics such as the material strengths of the individual layers or the size of underfilm corrosion surfaces. Metallographical structure investigations (structure, texture, particle size) are also carried out using a reflected light microscope. In special cases, such as the determination of mineral phase and structure, thin sections with a transmitted light microscope (polarising microscope) will be used.