11 Jul 2024

Sliver Spall Mitigation: Field Investigation, Laboratory Study, and Mixture Proportioning Analysis

Abstract: A combined field and laboratory study was conducted to identify factors contributing to sliver spall of concrete pavements and recommend avenues for prevention. In this study, spall density maps of eight airfields were created, and cores were taken for petrographic analysis. A companion laboratory study evaluated nondestructive testing equipment for identifying concrete prone to sliver spalling. Concrete mix designs with good and poor performance were analyzed for trends in mixture proportioning and aggregate gradation. Spall density mapping indicated sliver spalling was more likely to occur on longitudinal joints and that the distress was not solely a material or mixture design-related issue. The laboratory study concluded that surface resistivity measurements were able to differentiate edge-finishing techniques (normal versus overworked, mortar-rich edge) after seven days of curing. An analysis of particle packing theory and mixture proportioning trends showed there was substantial overlap in the gradations for good and poor performing pavement. Thus, acceptable mixture designs can produce poor quality pavement if not constructed properly. The main contributors to early age sliver spalling of concrete airfield pavement occur during pavement construction.

3 Feb 2022

Observation of Crack Arrest in Ice by High Aspect Ratio Particles during Uniaxial Compression

Abstract: In nature, ice frequently contains dissolved solutes or entrapped particles, which modify the microstructure and mechanical properties of ice. Seeking to understand the effect of particle shape and geometry on the mechanical properties of ice, we performed experiments on ice containing 15 wt% silica spheres or rods. Unique to this work was the use of 3-D microstructural imaging in a -10ºC cold room during compressive loading of the sample. The silica particles were present in the ice microstructure as randomly dispersed aggregates within grains and at grain boundaries. While cracks originated in particle-free regions in both sphere- and rod-containing samples, the propagation of cracks was quite different in each type of sample. Cracks propagated uninhibited through aggregates of spherical particles but were observed to arrest at and propagate around aggregates of rods. These results imply that spherical particles do not inhibit grain boundary sliding or increase viscous drag. On the other hand, silica rods were found to span grains, thereby pinning together the microstructure of ice during loading. These results provide insights into mechanisms that can be leveraged to strengthen ice.