Non-destructive Evaluation of Damage in Concrete with Applications in Shallow Foundations

Non-destructive testing;Shallow foundations

Fartosy, Sabahadvisor:Basu, Dipanjan ; advisor:Cascante, Giovanni ; affiliation1:Faculty of Engineering ; Cascante, Giovanni ; Basu, Dipanjan ;

University of Waterloo

关键词: Non-destructive testing;    Shallow foundations;    Doctoral Thesis;   

Others  :  https://uwspace.uwaterloo.ca/bitstream/10012/13926/3/Fartosy_Sabah.pdf

瑞士|英语

来源: UWSPACE Waterloo Institutional Repository

【 摘 要 】

The most widely used material for civil infrastructure is reinforced concrete. The concretedeteriorates over time because of several reasons, and therefore, inspection of concrete isnecessary to ensure its compliance with the design requirements. Decision makers often haveinsufficient data to implement the appropriate corrective measures in the face of infrastructurefailure. Better assessment methods are essential to obtain comprehensive and reliableinformation about the concrete elements. Although, different methods exist to inspect concretemembers, there is no comprehensive technique available for condition assessment of concreteof shallow foundations. To ensure the integrity of shallow foundations during construction andduring its service life, it is necessary to monitor their conditions periodically. To achieve thisgoal a new NDT methodology is developed to reliably evaluate the conditions of new shallowfoundations without changing their future performances.Recently, there is a trend to overcome coupling issues between the transducers and the objectunder investigation, by installing sensor networks in concrete to assess its integrity. Althoughmany NDT approaches are designed to evaluate the integrity of concrete structural elements,shallow foundations, which are concrete elements embedded in soil, have received lessattention. The challenging aspect of characterizing shallow foundations is limited accessibilityfor in-service foundation inspections because of structural restrictions. Even when accessibilityis possible, the NDT methods (ultrasonic pulse velocity, UPV) used may producemeasurements with high uncertainties because of inconsistent coupling between the transducerand the surface of the material being tested.In the current research project, a new NDT procedure is developed based on design of new transducersembedded at the base of lab-scale concrete foundation models, and these transducers are waterproof andused as receivers. The transducers consist of radial-mode piezoceramics that can detect waves fromdifferent orientations. The developed methodology relies mainly on two methods to emit thetransmission pulse; either using a direct contact method by gluing the transducer to the concrete surfaceor using a plastic tube partially embedded in concrete and filled with water. The first procedure is usedwhen the accessibility to the top surface of the foundations is possible; otherwise, the second option isemployed to reach the concrete surface of foundations. The new methodology can be used in differentstages: during construction of foundations to monitor the uniformity and quality of the concrete, andduring in-service life to periodically assess the condition of the foundations, specifically after an eventthat may cause severe damage in concrete such as earthquake and overloading. To verify theapplicability of the methodology, unreinforced and reinforced shallow foundation lab-scale concretemodels were tested in the laboratory under uniaxial compression loads. In this work, all ultrasonicmeasurements are averaged 16 times to ensure the consistency of the results and to eliminatehigh frequency noise. The average coefficient of variance obtained is less than 3.5%; which isconsidered acceptable in this type of measurements (typical measurement error ~5%). Also,different tests were repeated more than three times by removing and putting back all theultrasonic transducers to enhance the statistical significance of the results.The main contributions of the research presented in this thesis are: Characterization of low and high frequency transducers using laser vibrometer tocharacterize their responses for better ultrasonic measurements. Characterization of a single fracture growth in a homogenous material based on wavevelocity and wave attenuation. Characterization of cement-based materials using ultrasonic pulse velocity and laservibrometer methods. Evaluation of freeze/thaw damage and monitoring progressive damage in concretespecimens subjected to uniaxial compression load using ultrasonic pulse velocity andlaser vibrometer methods. Fabrication of thirty-six new radial ultrasonic transducers to embed in concrete modelsfor quality control purposes and to monitor progressive damage using new transmissionpulse methodology.