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39 C h a p t e r 4 This chapter presents conclusions on the applicability of por- table spectroscopic devices to conducting QA/QC for com- mon construction materials. In addition, the chapter briefly discusses the deliverables of the project, followed by sugges- tions for further research. applicability of portable Spectroscopic equipment to Field evaluation of Construction Materials The primary objective of this project was to identify the most practical applications of spectroscopic techniques to a wide range of materials commonly used in transportation infrastructure. To identify the needs for spectroscopic test- ing among the SHAs and to develop feasibility criteria, the SHRP 2 coordinators from 50 states were surveyed and a workshop with experts from both SHAs and the industry was held. A list of construction materials and desired testing and equipment parameters were developed to rank the fea- sibility of the spectroscopic techniques for laboratory and field evaluation. Two potential outcomes for spectroscopic testing were identified: (1) verification of the chemical composition (if provided by the manufacturer) or determination of the sig- nature spectrum for pure materials and compounds and their components, and (2) detection and, if possible, quantifica- tion of additives and contaminants in a material. The spec- troscopic techniques evaluated by the project team in the laboratory testing phase (Phase 2) included ATR FTIR spec- troscopy; size-exclusion GPC; NMR; XRF; and XRD. The materials analyzed were epoxy coatings and adhesives, traffic paints, portland cement concrete with chemical admixtures and curing membranes, asphalt binders, emulsions, and mixes with polymer additives. On the basis of the laboratory experiments, portable ATR, XRF and Raman instruments were recommended for field evaluation. The field phase of the project confirmed that a compact ATR FTIR spectrometer was the most successful device to finger- print all pure chemical compounds (i.e., epoxies, waterborne paints, polymers, and chemical admixtures) and to detect addi- tives or contaminants with concentration of 0.4 wt% and higher in complex mixtures (i.e., portland cement concrete, asphalt binders, emulsions, and mixes). In addition, ATR was successful in quantifying polymer additives in asphalt binders and waterâsolvent content in paints at concentrations >0.5 wt%, based on developed calibration curves. ATR generally did not require sample preparation and the major source of error was sample heterogeneity, given the very small amount of material used for analysis. Thus sampling procedures should ensure that the chosen sample and the surface exposed to the infrared beam are representative of the bulk material. On the basis of the field results, the project team found that a handheld XRF instrument may be used to conduct QA/QC of epoxy coatings and traffic paints based on the concentra- tion of major metals in the pigment (Ti or Zn). In other words, the Ti content may be used as an indicator to determine the purity and quality of the paint, whether it has been thinned out with solvent or mixed with other materials. XRF results are a function of the water content of the material, which needs to be taken into account when establishing QC criteria under lab settings. It is recommended that QC criteria for approved material brands are developed by state laboratories, given that manufacturer specifications are typically too broad and not specific to the physical state of the material. Raman analysis was successful in fingerprinting pure, non- opaque liquid samples both in the lab and in the field. How- ever, some safety issues were identified, specifically potential damage to the operatorâs eye by open laser light. In addition, the price of the Raman instruments available on the market considerably exceeds the target cost established in this project ($75,000 as compared with the maximum target cost of $25,000). Therefore, portable Raman instruments are not recommended for use at field conditions. Conclusions and Suggested Research
40 Finally, spectroscopic evaluation of construction materials is a challenging task, especially when dealing with non- uniform materials or additives at small concentrations. In such cases, more work is needed beyond this project to develop robust and universal procedures. project Deliverables Electronic Spectral Library A library of spectra for pure materials was created. This library can be used for the identification of those materials in the field. The database will supplement the standards developed under this project and can be potentially available online for QA/QC specialists. The electronic copy of the spectral library is located at www.trb.org/Main/Blurbs/167279.aspx. Draft AASHTO Standards During the laboratory and field spectroscopic experiments, generic testing procedures with sampling and data analysis guidelines were developed for the ATR, Raman, and XRF applications to liquid and solid material samples. The most successful generic procedures were expanded to the draft AASHTO standard specifications as follows: ⢠Identification of water-reducing, -accelerating, and -retarding chemical admixtures in fresh portland cement concrete by attenuated total reflection infrared spectrom- eter; and ⢠Standard method of test for determination of titanium content in traffic paints by field-portable X-ray fluores- cence spectroscopy. The AASHTO standards provided in Appendix C are des- ignated for the QA/QC personnel and research and material divisions in the SHAs. They can be added to their special pro- visions or construction specifications. Field Operation Manuals On the basis of the experience collected throughout this proj- ect as well as the feedback received during the field phase, the research team prepared two separate field operation manuals for ATR and XRF instruments. These manuals target techni- cal personnel designated by a transportation agency for the spectroscopic testing. The manuals will help the testing per- sonnel to undertake correct steps during spectroscopic test- ing and will provide more concise instructions as opposed to typical generic manuals provided by the manufacturers. Further research A limited range of portable spectroscopic instruments was evaluated in this study because of time and budget con- straints. For instance, neither truly handheld FTIR nor portable time-domain NMR devices were available to the research team. However, the research team believes that the former device can be potentially used on construction sites, especially for the analysis of asphalt and concrete products, while the latter device can allow for the elucidation of practi- cally any organic material structure. In addition, portable gas chromatographs can potentially yield success in evaluation of contaminants and polymer additives in asphalt products. Therefore, further research is suggested with use of handheld FTIR, portable time-domain NMR instruments, and porta- ble gas chromatographs, especially when their costs become more affordable to SHAs. Finally, the research team antici- pates that Raman instruments will be upgraded to prevent thermal emission and operator hazard, which will facilitate their use in construction applications.
