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We present a proof-of-principle study about the use of a sensor for the nondestructive monitoring of strength development in hydrating concrete. The nondestructive evaluation technique is based on the propagation of highly nonlinear solitary waves (HNSWs), which are non-dispersive mechanical waves that can form and travel in highly nonlinear systems, such as one-dimensional particle chains. A built-in transducer is adopted to excite and detect the HNSWs. The waves are partially reflected at the transducer/concrete interface and partially transmitted into the concrete. The time-of-flight and the amplitude of the waves reflected at the interface are measured and analyzed with respect to the hydration time, and correlated to the initial and final set times established by the penetration test (ASTM C 403). The results show that certain features of the HNSWs change as the concrete curing progresses indicating that it has the potential of being an efficient, cost-effective tool for monitoring strengths/stiffness development.
A common problem in cold regions is the penetration of frost into susceptible subgrade soils. This study investigated the application of bottom ash in comparison with polystyrene boards as an insulation layer at a test road in Edmonton, Alberta, Canada. The adjacent normal section was used as the control section. All sections were instrumented at various depths to monitor temperature variation. On the basis of temperature measurements in the base and subgrade layers from October 2012 to June 2013, frost depth and freezing and thawing periods were analyzed for each section. R-values for thermal resistivity were calculated for each layer, considering its thickness and thermal properties, and were used for justifying and comparing the temperature trends. R-values were established at 1.4 and 16.7 m2 • °C/W for the bottom ash and polystyrene board, respectively. The base layer in the polystyrene section experienced higher temperatures in the summer and lower temperatures in the winter in relation to the bottom ash and control sections. On the basis of temperature measurements at depths of 1.61 to 3.27 m, the subgrade in the polystyrene section showed the lowest variation in temperature with respect to time and depth, followed by the bottom ash and then the control section. This behavior indicated that the insulation layers obstructed the heat transfer between the surface and the lower layers. The use of polystyrene boards and bottom ash as insulation materials decreased the frost depth by at least 40% and 28%, respectively, compared with the control section.
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