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1One of the goals of the second Strategic Highway Research Program (SHRP 2) is to develop new methods and materials for preserving, rehabilitating, and reconstructing the aging U.S. transportation infrastructure. A growing concern among transportation authorities is that quality assurance/quality control (QA/QC) procedures routinely used in highway construc- tion are time-consuming, expensive, and not always reliable. Accordingly, the SHRP 2 R06B project had as main objective to identify and evaluate handheld spectroscopic equipment for in situ analysis of commonly used construction materials. The first phase to address this objective (Phase 1) was to identify the QA/QC needs for spectroscopic testing among the state highway agencies (SHAs), to determine which spectroscopic techniques can address these needs and to develop appropriate feasibility criteria. To this end a survey was con- ducted among the SHRP 2 coordinators from 50 states and a workshop was held with experts from both SHAs and industry. As a result, a list of construction materials and desired testing and equipment parameters (e.g., sample preparation, test duration, reliability, training effort, and equipment price) was developed to rank the applicability of the spectroscopic techniques for laboratory and field evaluation. Two potential outcomes of spectroscopic testing were identified: (1) verification of the chemical composition (if provided by the manufacturer) or determination of the signature spectrum for pure materials and com- pounds and (2) detection and, if possible, quantification of additives and contaminants in a mixture. The spectroscopic techniques evaluated by the project team in the laboratory included Fourier transform infrared (FTIR) spectroscopy, size-exclusion chromatography (SEC), nuclear mag- netic resonance (NMR), X-ray fluorescence (XRF), and X-ray diffraction (XRD). The materials list included epoxy coatings and adhesives, traffic paints, portland cement concrete (PCC) with chemical admixtures and curing compounds, asphalt binders, emulsions, and mixes with poly- mer additives. The most promising combinations of techniques and materials were evaluated by a comprehensive literature review, in combination with the experience of the research team as well as the survey and workshop results. Accordingly, each combination of material and method was ranked in terms of its probability of success and selected for evaluation under laboratory conditions. The laboratory testing phase (Phase 2) indicated that three methods were most promising for field application: FTIR, XRF, and Raman. A compact FTIR spectrometer working in the attenuated total reflectance (ATR) mode was the most successful device to fingerprint pure chemical compounds (i.e., epoxies, waterborne paints, polymers, and chemical admixtures) and to detect additives or contaminants in complex mixtures (i.e., PCC, asphalt binders, emulsions, and mixes). ATR analysis requires no special sample preparation and a very small sample amount. This renders the sampling process as the limiting step in ensuring that the collected spectrum is representative of the bulk material. ATR also enables the quantification Executive Summary
2of polymer additives in asphalt binders and determination of the water or solvent content in paints. Portable XRF was determined to be suitable for QA/QC of paints and epoxies on the basis of their metal content (Ti or Zn). The main factor affecting the accuracy of the XRF method is the calibration method used for analysis, especially for lighter elements (P, S, and Ca). Finally, fingerprinting of paints, curing compounds, and chemical admixtures to PCC was found to be feasible using a portable Raman analyzer developed by Real-Time Analyzers, Inc. (RTA), a member of the research team. Raman analysis is similar to ATR analysis in that it requires a small sample and thus sample variability is the main source of uncertainty asso- ciated with both techniques. Following the completion of the laboratory experiments, an additional survey of the 50 SHAs was conducted to confirm the relevance of the recommended materialâmethod combinations to the needs of material testing professionals. The survey results reflected a strong need (average need ranking score of 3 out of 5 [see Figure ES.1]) for the majority of the proposed field tests (see Table ES.1). Figure ES.1. Summary of average field need survey scores per SHA.
3Table ES.1. Summary of SHA Survey for Field Evaluation Needs Material Category Spectroscopic Method Objective Average Score Structural coatings and pavement markings ATR FTIR Raman XRF Verification of chemical composition 3.05 ATR FTIR Raman XRF Verification of presence of solvents/diluents 2.73 Epoxy adhesives ATR FTIR Verification of chemical composition 2.68 Chemical admixtures for PCC ATR FTIR Verification of presence of admixture in fresh/ cured PCC mix 2.65 Curing compounds for PCC ATR FTIR Raman Verification of chemical composition/degree of cure (water content) 2.76 Polymer-modified asphalt binders, emulsions, and mixtures ATR FTIR Verification of type/class of polymer modifier 3.45 ATR FTIR Determination of polymer content 3.52 Antistripping agents ATR FTIR Verification of presence/type 3.55 Reclaimed asphalt pavement (RAP) ATR FTIR Determination of RAP content in HMA 3.05 Mean average score 2.97 SD of mean 0.40 A series of field trips to various construction projects was performed in the final phase of the project (Phase 3) to verify the feasibility of field QA/QC procedures for the chosen materialâ method combinations. Overall, field tests confirmed the applicability of most methods and pro- duced results similar to the laboratory phase. Specifically, the compact ATR FTIR spectrometer, handheld XRF instrument, and RTAâs Raman analyzer were employed successfully to analyze the composition of both simple and complex organic compounds, such as epoxy coatings and adhe- sives, curing compounds, and waterborne traffic paints. Furthermore, ATR allowed for the iden- tification of chemical admixtures in freshly mixed PCC samples and provided their concentrations when they were higher than 0.5 wt%. Verification of polymer presence in asphalt binders and emulsions was also possible using the ATR FTIR spectrometer. Although the identification of polymer in hot-mix asphalt (HMA) presented a challenge, the fast binder extraction procedure in the field using dichloromethane solvent appeared to be a feasible alternative for the direct evaluation of polymer-modified HMA. Generic testing procedures with sampling and data analysis guidelines were developed during the project for the ATR, Raman, and XRF applications to selected materials. The most successful generic procedures were expanded to draft AASHTO standard specifications as follows: (1) method for fingerprinting chemical admixtures in freshly mixed PCC by portable ATR FTIR and (2) method for determining the metal content in paints by portable XRF. The target audiences for the AASHTO standards are QA/QC personnel and research and material divisions in SHAs. In addition to the standards, a library of spectra for the tested materials was created, which can be used for the identification of these materials in the field. Finally, field operation manuals were developed for ATR and XRF instruments to supplement the standards. These manuals target the field personnel who will conduct spectroscopic testing; however, the variability in the available instruments requires that the specific technical manual of each instrument should be also consulted.
4It should be noted that because of time and budget constraints, a limited range of portable spectroscopic instruments was evaluated in this study. For instance, neither handheld FTIR nor portable time-domain NMR devices were available for the research team. However, the research team believes that the former can be potentially used on construction sites, especially for the analysis of asphalt and concrete products, whereas the latter can allow for the elucidation of practically any organic material structure. In addition, portable gas chromatographs can poten- tially 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 portable gas chromatographs. Spectroscopic evaluation of construction materials will be always a challenging task, espe- cially when dealing with nonuniform materials or additives at small concentrations. In such cases, more work is needed beyond the scope of this project to develop robust and universal procedures.
