The use of nuclear methods for compaction control is increasingly problematic for state highway agencies. Regulatory and safety issues have prompted agencies such as the New Mexico State Highway and Transportation Department to look for nonnuclear alternatives for compaction control. A laboratory evaluation of one such commercially available device, known as the GeoGauge, is described. The GeoGauge measures soil stiffness, arguably a more viable engineering parameter than moisture—density measurement. The GeoGauge was found to measure soil stiffness as advertised. Results relating moisture, density, and stiffness were found to be consistent with earlier research on compaction and mechanical strength of soils. However, because of the dynamic nature of the measurement obtained with the GeoGauge and associated boundary constraints, the ability to obtain a target value for stiffness in the laboratory has proved to be elusive. Because of the promising nature of the GeoGauge technology, and because it measures a true engineering mechanical property, a paradigm shift may be necessary for its implementation in field compaction control. Future specifications for compaction using this technology may require specific controls of moisture and compaction equipment with stiffness monitoring via the GeoGauge.
The research experiments reported were conducted at the Materials Research Center, ATR Institute, University of New Mexico, at the request of the Research Bureau, New Mexico State Highway and Transportation Department (NMSHTD). The purpose was to determine the amount of additives required for mitigation of alkali-silica reactivity (ASR) based on screening tests. Fly ash additives routinely used in New Mexico and a new material—lithium nitrate—proposed by the Strategic Highway Research Program were evaluated. The work was motivated by continuous problems with early deterioration of concrete structures due to alkali-silica reactivity. The work was based on the use of acceptance criteria established by NMSHTD for expansion due to ASR, as measured in screening tests. Recommendations resulting from this research do not consider all aspects of the behavior of concrete mixtures and structures. The additive recommendations are based on reduction in mortar-bar expansion during accelerated tests.
A full-scale experimental pavement was constructed to compare low temperature cracking performance of asphalt concrete containing two types of styrene block copolymers and an ethylene-based polymer each at two levels of concentration in a relatively soft asphalt cement. The experiment was designed to compare field performance with observed behavior in the laboratory. Samples of all binders and mixtures were collected during construction and laboratory tests were conducted using actual materials placed in the field. Mixture tests were limited to Marshall, resilient modulus, and ASTM D4867 moisture sensitivity. Results indicate a high resistance to water damage and relatively high Marshall stabilities for all mixtures evaluated. Marshall test results were highly variable and no apparent differences between materials could be resolved using Marshall parameters. Resilient modulus was conducted at three temperatures, but small differences in this property were not conclusive regarding effects of polymer modification on temperature susceptibility of the mixtures. Variability in resilient modulus measurements was high for certain mixtures. Experience gained in the laboratory and field during design and construction of this experimental pavement has provided information regarding recommended practices when using certain polymer modifiers during construction of asphalt concrete. For example, conventional viscosity-temperature relationships developed with capillary viscometers were misleading regarding establishment of mixing and compaction temperatures. The predicted temperatures were higher than required for mixing and compaction of the polymer modified mixtures. This experience suggests that new techniques should be developed for establishing appropriate mixing, laydown and compaction temperatures for polymer modified asphalt mixtures.
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