Now showing 1 - 3 of 3
  • Publication
    Assessment of ultrasonic signals to determine the early age properties of concretes incorporating secondary cementitious materials
    Secondary cementitious materials (SCMs) such as ground granulated blast-furnace slag (GGBS) are used in increasing quantities in concrete practice internationally. While these materials offer benefits such as reduced CO2 and a more dense microstructure, they also have drawbacks in terms of slower initial gain of strength. There are significant financial implications associated with this, as it can lead to delays in the construction process. Key to overcoming this challenge is the development of a methodology to assess the early-age stiffness development in concretes manufactured using GGBS. This paper presents the results of a study into the application of ultrasonic sensors to assess the early age concrete stiffness. A novel wavelet-based approach is used to overcome the difficulties associated with wave reflections and classical wave theory is used to determine the concrete small-strain stiffness based on P and S wave velocities. It was found that the results are largely in agreement with those obtained using standard strength testing, suggesting potential practical applications of this method.
      1396
  • Publication
    Examination of a novel wavelet based approach for bender element testing
    Accurate determination of shear wave arrival time using bender elements may be severely affected by a combination of near field effects and reflected waves. In most cases, the nearfield effect masks the first arrival and it makes its detection difficult in the time domain. Nevertheless the arrival of a shear wave creates a detectable singular point. This paper tests a recent approach for the assessment of shear wave arrival time by analysing the output signal in the time-scale domain using a multi-scale wavelet transform. Indeed, one can follow the local maxima lines of the wavelet transform modulus across scales, to detect the location of all singularities leading to detection of the first arrival.
      1043
  • Publication
    Wavelet analysis of bender element signals
    (Institution of Civil Engineers/Thomas Telford Publishing, 2012-03-01) ; ;
    Accurate determination of shear wave arrival time using bender elements may be severely affected by a combination of near field effects and reflected waves. These may mask the first arrival of the shear wave, making its detection difficult in the time domain. This paper describes an approach for measuring the shear wave arrival time through analysis of the output signal in the time-scale domain using a multi-scale wavelet transform. The local maxima lines of the wavelet transform modulus are observed at different scales and all singularities are mathematically characterised, allowing subsequent detection of the singularity relating to the first arrival. Examples of the use of the approach on typical synthetic and experimental bender element signals are also supplied, and these results are compared to those from other time and frequency domain approaches. The wavelet approach is not affected by near field effects and instead is characterised by a relatively consistent singularity related to the shear wave arrival time, across a range of frequencies and noise levels.
      1427ScopusĀ© Citations 20