The chemical composition and morphology of alkali–silica reaction (ASR) products is of great importance in studying the reaction mechanism and assessing the effectiveness of mitigation techniques. Epoxy-impregnated, polished thin sections were prepared from an in-service concrete pavement to examine ASR products that originate from chert particles in the fine aggregate. Both hydrous and anhydrous thin-section preparation techniques were used to investigate the influence of sample preparation on the results. Two distinct morphologies of ASR products were observed in the voids adjacent to the chert particles: a bladed crystalline type and a glassy amorphous type. The chemical compositions of the reaction products were determined with a scanning electron microscope via quantitative X-ray energy dispersive spectrometry. Both the chemical composition and morphology were influenced by sample preparation, with hydrous preparation resulting in leaching and degradation. It is recommended that, when conducting studies to assess the ASR mechanism and the effectiveness of mitigation techniques, anhydrous sample preparation be used.

An approach is described that is used to identify to what degree Michigan’s concrete pavements are affected by materials-related distress (MRD) and to determine what distress mechanisms are at work. The approach taken includes a network-level visual assessment and detailed visual inspections, field sampling, and laboratory analyses on 14 selected projects to determine the distress mechanisms. It is concluded that although the majority of Michigan’s concrete pavements are unaffected by MRD, a significant percentage of the concrete pavement network have distress manifestations consistent with the occurrence of MRD. These manifestations included staining in the vicinity of joints and cracks, D-cracking, joint-crack deterioration, progressive map cracking with exudate, scaling, and corrosion of embedded steel. Each pavement section was visually assessed and then tested using a falling weight deflectometer. Field air permeability measurements were also made, and core samples were removed from the pavement to be analyzed in the laboratory. It was found that the presence of MRD affected both the mechanical and the microstructural properties of the pavement concrete. Further, the laboratory analysis determined that a number of MRD types are at work in some of Michigan’s concrete pavements, including aggregate freeze-thaw deterioration, corrosion of embedded steel, and alkali-silica reactivity. This work also found that dedolomization of certain carbonate aggregates and sulfate attack may pose a problem. With this knowledge, the Michigan Department of Transportation is better able to address the cause of distress when selecting repair options and to prevent MRD from affecting future concrete pavements.