Short-term Mechanical Strength Prediction of Ultra-High Performance Concrete using Noncontact Synthetic Aperture Radar Imaging

摘要

In recent decades, the use of ultra-high performance concrete (UHPC) has been widely accepted by the construction industry for buildings and bridges. The exceptional properties of UHPC on strength (18 ksi 35 ksi) and durability (freezc-thaw resistance, abrasion resistance, chloride ion penetration resistance) have made it a popular construction material for durable and sustainable civil infrastructure systems. The objective of this paper is to investigate the shortterm mechanical strength development of UHPC specimens using a noncontact synthetic aperture radar (SAR) imaging sensor. UHPC cubes and cylinders were designed and manufactured for nondestructive strength monitoring and kinematic and rheological characterization. Change in moisture content and distribution inside UHPC cylinders was monitored by a laboratory 10-GHz SAR imaging sensor inside a microwave anechoic chamber at UMass Lowell. Hydraulic permeability of UHPC specimens was measured by their bulk electrical resistivity using a concrete resistivity meter (ASTM C1876). The rate of water uptake (absorption or sorptivity) was characterized by an apparatus used to measure the water absorption rate of both the concrete surface and interior concrete (ASTM C1585). Early stage shrinkage behavior of UHPC specimens during the first seven days was also measured using a shrinkage cone. Level of cement hydration in UHPC specimens was quantified by the loss of free water inside UHPC and remotely measured by the SAR imaging sensor. Mechanical strength development in UHPC specimens was monitored by following ASTM C109/C109M. From our preliminary result, it is found that change in SAR amplitude and amplitude distribution can be correlated to the level of strength development.