MONITORING THE GPR RESPONSE OF CURING CONCRETE

摘要

Ground penetrating radar (GPR) is becoming an increasingly popular method for locating embedded targets in concrete. It provides rapid surveying of a concrete slab, and requires access to only one side of a slab. The basic principle of operation is to transmit a broadband high-frequency electromagnetic (EM) pulse into the concrete and detect the reflected pulse. The intensity of the reflected pulse is primarily controlled by the attenuation related to the electrical conductivity losses in concrete while the travel time is controlled by the EM wave velocity in concrete. When concrete is initially poured, it has a high free water content which causes both high attenuation and low velocity. As curing occurs, hydration removes free water and locks it into the concrete structure resulting in an increase in velocity and a decrease in attenuation. In this paper we present the results of GPR imaging of a concrete slab at regular intervals, from immediately after pouring to an apparent fully cured state. The monitoring period was 5 months. As part of the data analysis, velocity and attenuation were estimated as a function of time. The change of these properties indicates the state of water in the curing process and suggests that GPR can provide a useful in situ non-destructive technique for monitoring curing in concrete structures.