Chemistry Laboratory Overview
The Chemistry Laboratory conducts fundamental studies of highway materials to understand both failure mechanisms and superior performance. New standard test methods are developed to improve and facilitate the chemical analysis of highway materials and to characterize and quantify new or alternative sustainable materials. The Laboratory also assists with forensic investigations of premature failures of pavements and other highway structures.
Chemical characterization entails both sample preparation and analysis. Traditional wet chemistry techniques are used to modify paving and concrete materials and to prepare and condition samples for further testing and analysis. The chemical results are often tied to physical test results from the Binder, Bituminous Mixtures, or Concrete Laboratories, to compile a chemico-physico perspective and evaluate its effect on performance. The Chemistry Laboratory complex includes a traditional chemistry laboratory for wet chemistry and sample preparation, and two laboratories dedicated to instrumentation.
This laboratory has all the necessary equipment for preparation of samples and standards for various analyses of liquid and solid samples. The laboratory houses traditional equipment including glassware, fume hoods, a muffle furnace, centrifuge, aggregate mill, and ovens. More specialized equipment includes a nitrogen gas purged desiccator and glove box to provide an inert atmosphere for the study of ASR (alkali silica reaction) gels, and other cementitious materials. Additionally, the lab is equipped with a particle size analyzer and equipment used to prepare fused beads for x-ray fluorescence (XRF) analysis.
Figure 1. Nitrogen glove box and desiccator to prevent carbonation of different cementitious materials.
Figure 2. Example of platinum crucibles and prepared fused pellets of specimens for elemental analysis using x-ray fluoresce spectroscopy.
These laboratory house a wide variety of state-of-the-art analytical equipment for detailed investigations of highway materials ranging from the atomic to the macro-scale. This equipment includes:
- An environmental scanning electron microscope (ESEM) enables researchers to investigate morphological differences and chemical compositions of minerals, cementitious materials, metals, and coatings used in highway construction. It is fitted with an energy dispersive x-ray fluorescence accessory enabling elemental analysis and mapping of samples.
- A Fourier transform infrared (FT-IR) spectrometer and microscope used for chemical analysis of materials including asphalt binders and hydrated silica gels in cementitious samples.
- An x-ray diffractometer (XRD) used for the analysis of cement, concrete, fly ash, and aggregates, and for studying the kinetics of cement hydration.
- A dispersive Raman spectrometer and microscope used to study aggregates, nanomaterials, and alkali-silica reaction (ASR) gels.
- An inductively coupled plasma (ICP) spectrometer for the analysis of solutions. Typically, these are asphalt binders, ASR gels, and concrete pore solutions.
- An energy dispersive x-ray fluorescence spectrometer (XRF) used to determine the elemental composition of cement, aggregates, and asphalt binders.
- A wavelength dispersive x-ray fluorescence spectrometer (WDXRF) used for the analysis of aggregates and samples related to alkali silica reaction (ASR) gel research.
- A glow discharge spectrometer for the analysis of metals.
- Three handheld spectrometers, FT-IR, XRF, and Raman, for the analysis of construction materials in the field.
- A Thermogravimetric Analyzer (TGA) used to study the effect of temperature on samples.
Figure 3. Lapped and polished specimen of a grout-cement paste bond used to study the microstructure in the interfacial region using the ESEM. This type of specimen is used to understand how the distribution of porosity, sand particles and specific mineral phases such as portlandite and ettringite influence the mechanical performance of the bond.
Figure 4. Attenuated total reflectance FT-IR spectrometer coupled with a state-of-the-art FT-IR microscope.
Figure 5. X-ray diffractometer performing quantitative powder diffraction analysis of fly ash and other supplementary cementitious materials.
Figure 6. Synthetic sodium silica gel being analyzed using the Raman spectrometer to understand the effect of alkalis in the silicate polymerization of the gel.
Figure 7. ICP spectrometer and auto sampler analyzing the ion concentrations of concrete pore solutions expressed from different cement binary mixes.
Figure 8. XRF spectrometer sample changer bed loaded with asphalt mix samples used to detect the presence of waste engine oil residues.
The technology and data generated in this laboratory as well as the expertise of staff are being used by State transportation agencies to enhance the durability of highway materials and to reduce operating costs. The lab also assists Federal and State agencies in forensic investigations of premature highway failures.
The Chemistry Laboratory is currently performing research into new test methods to determine the propensity of aggregates to form alkali silica reaction (ASR) gels if used in concrete. The fundamental information gained from the research is key to developing new testing standards and field procedures to evaluate the adequacy of the original paving materials and ensure the optimal mechanical performance and durability of the final mix design. Research is being conducted in the following areas:
- Fundamental research into the mechanism of ASR with specific emphasis on the role of calcium and identifying important parameters for a reliable test method to predict reactivity of aggregates.
- Develop test methods for the use of handheld XRF, FT-IR, and Raman spectrometers for the field analysis of highway materials. Methods recently developed are for the determination of silica in limestone aggregates and titanium dioxide pigment in thermoplastic road marking paints.