No abstract

A space-borne bridge displacement monitoring technology was demonstrated on a major highway bridge in Cornwall (Ontario, Canada) over a 15-month period. Two major challenges had to be overcome and solutions were identified and implemented. The first challenge related to the proper selection and analysis of satellite imagery to optimize the number and signal quality of point targets on the bridge for adequate movement detection and analysis. The second challenge was the comparison and validation of independent sets of data having different measurement methods, reference baselines, and distributions in space and time. The key findings include: (i) the regression analysis of interferometric synthetic aperture radar (InSAR) data from the satellite produced the best coherence when fitted against the following three independent variables: height, ambient temperature, and time; (ii) the bridge railings appeared to be excellent natural reflectors with their sharp edges and regular spacing along the bridge, showing a return of over 3,000 clear point targets to the satellite; (iii) the InSAR displacement thermal sensitivity data was found to compare very well to numerical modeling thermal data. The results show great promise and value in applying satellite-based technology for the remote monitoring of highway and railway bridges to alert engineers of excessive movement and, in turn, will help optimize preventive maintenance management, extend structural lifespan, minimize traffic disruptions due to late repair, and ensure structural integrity.

The effect of calcium carbonate nanoparticles (nCaCO 3 ) on the hydration of ordinary Portland cement (OPC) blended with metakaolin was studied through comparison with OPC, OPC plus metakaolin and OPC plus nCaCO 3 control samples. Isothermal conduction calorimetry measurements showed that the hydration of the ternary OPCmetakaolin-nCaCO 3 blend had pronounced early secondary phase hydration activity compared to the controls. X-ray diffraction and thermogravimetric analysis identified the phases as calcium aluminosulfates, with both ettringite and monosulfate forming more quickly in the ternary blend than in the other samples. The presence of the nCaCO 3 also enhanced the formation of C 3 A . CaCO 3 . 12H 2 O in both blends that contained it. The presence of the secondary phases or the nCaCO 3 itself was associated with a significant reduction in strength in the ternary blend as compared to the OPC-metakaolin binary blend. The results suggest that caution is needed in the development of concrete with nanoparticle additions in order to avoid detrimental combinations of nanoparticles, OPC and supplementary cementing materials.