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.
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 laboratory for sample preparation and wet chemistry, and a laboratory dedicated to instrumentation.
Sample Preparation Laboratory
This laboratory has all the necessary equipment for preparation of samples and standards for various analyses of liquid and solid samples. Specific equipment includes a nitrogen desiccator and glove box to prepare samples free of carbonation, a vacuum oven, muffle furnace, vibratory disc mill, centrifuge, ovens, an automatic fused bead preparation system, and a manual hydraulic pellet press.
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 fly ash specimens for elemental analysis using x-ray fluoresce spectroscopy.
This laboratory houses a wide variety of state-of-the-art analytical equipment for detailed investigations of highway materials ranging from the nano- 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.
- A Fourier transform infrared (FT-IR) microscope to map the distribution of carbonation and amorphous silica hydrated 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 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 X-ray fluorescence spectrometer (XRF) used to determine the elemental composition of cement, aggregates, and asphalt binders.
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 fly ash-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 in four principal areas associated with pavement materials: concrete durability, sustainability, bond performance of grout/repair materials, and quality assurance of asphalt binders. 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 also ensure the optimal mechanical performance and durability of the final mix design. In particular, 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 under development are for the determination of silica in limestone aggregates and titanium dioxide pigment in thermoplastic road marking paints.
- Correlation between microstructure and bond performance of grouts and/or repair materials currently used in the construction industry. This particular project is in collaboration with the Structures Laboratory.
- Develop a field test method for the early detection of corrosion on bridges made from weathering steel.