Cold temperature effect on the acoustic activity emitted in various concrete mixtures under special monitoring conditions

Kamel, Omar A. (2023) Cold temperature effect on the acoustic activity emitted in various concrete mixtures under special monitoring conditions. Masters thesis, Memorial University of Newfoundland.

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Abstract

Concrete mixtures with different microstructures and mechanical properties release different acoustic activity when they undergo cracking. This thesis aimed to investigate the effect of sub-freezing temperature (-20℃) on the waveforms of the acoustic emission (AE) in various concrete mixtures under flexural moment and abrasion forces. The study included many variables such as different coarse-to-fine aggregate ratios (C/F) (2.0 and 0.7), crumb rubber (CR) contents (0%, 10%, 20%, and 30%), rubber particle sizes (4.5 mm CR and 0.4 mm powder rubber), water-cement ratios (W/C) (0.4 and 0.55), fiber materials (polypropylene synthetic and steel), synthetic fiber lengths (19 mm and 38 mm), and volumes (0.2% and 1%), and sample temperatures (25℃ and -20℃). Samples from thirteen concrete mixtures were cast and tested under abrasion and monotonic fourpoint flexure moments, along with attaching piezoelectric AE sensors to monitor the AE activity throughout testing. Characteristics of AE signals such as the number of hits, signal amplitudes, cumulative signal strength (CSS), and wave rise time were collected and underwent various AE parameter-based analyses to correlate damage progression to the variation in the AE waveform. The results supported the ability of AE analysis to highlight abrasion damage progression and to detect the onset of micro- and macroflexural cracks at both temperatures. Compared to 25℃, cooling down samples’ temperature to -20℃ was found to decrease the values of the number of hits, CSS, severity (Sᵣ), and historic index (H (t)) and to increase b-values for the waves emitted under abrasion and flexure. Noticeably, the reduction in samples’ temperature decreased the emitted number of hits, CSS, Sᵣ, and H (t), and increased b-values till the onset of the first flexural macro-crack regardless of mixture composition. In addition, increasing CR content (up to 30%) decreased wave signal amplitudes significantly at 25℃ and was less noticeable at -20℃, which manifested the attenuation phenomenon at both temperatures. Eventually, the study developed user-friendly damage charts to estimate ranges of abrasion mass loss and wear depth and to classify the collected AE events, whether associated with flexure micro- or macro-cracks, exclusively considering temperature effect.

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