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International Concrete Abstracts Portal

Showing 1-5 of 58 Abstracts search results

Document: 

20-172

Date: 

July 1, 2021

Author(s):

S. E. S. Mendes, R. L. N. Oliveira, C. Cremonez, E. Pereira, E. Pereira, P. O. Trentin, and R. A. Medeiros-Junior

Publication:

Materials Journal

Volume:

118

Issue:

4

Abstract:

Blast-furnace slag (BFS) has been increasingly used in cement production and has shown great influence on the electrical resistivity of concrete. The objective of this paper is to compare the theoretical values of electrical resistivity obtained through a mathematical model with experimental values for concrete with BFS. Reference concrete mixtures with ordinary portland cement were also studied. Results indicate higher electrical resistivity and smaller porosity for concretes with CEM III/A. The electrical resistivity of the CEM III/A concrete does not have a well-defined correlation with the water-binder ratio (w/b) or with the compressive strength, unlike CEM I concretes. The correlation between calculated and experimental resistivity requires a correction factor for the CEM III/A concretes. In this study, the correction factor was obtained empirically by reducing the theoretical tortuosity of concrete by 15%. Therefore, the model should be used in cements with BFS with the application of a correction factor.

DOI:

10.14359/51732597


Document: 

20-013

Date: 

May 1, 2021

Author(s):

H. N. Alnuaimi, S. Sasmal, U. Amjad, A. Nikvar-Hassani, L. Zhang, and T. Kundu

Publication:

Materials Journal

Volume:

118

Issue:

3

Abstract:

Cement paste is the primary constituent of concrete that keeps all other constituents together and gives concrete its strength. During curing, the cement is developed as a binder by going through various chemical reactions. In the present study, ultrasonic testing is carried out on concrete samples during curing in transmission mode. The acoustic signals are generated using lead zirconate titanate (PZT) transducers which are excited by a sweeping frequency signal. Nondestructive testing and evaluation were carried out at various stages of curing for concrete with two different watercement ratios (w/c). The obtained signals were processed to analyze the change in signal characteristics during the different stages of curing. It was found that the nonlinear ultrasonic technique called the side band peak count (SPC) index, which is derived from the frequency spectra, exhibits a clear distinction among various concrete specimens at different stages of curing. Linear ultrasonic parameters, however, do not show such consistency. Therefore, the nonlinear ultrasonic technique provides an easy and effective way for monitoring the degree of concrete curing.

DOI:

10.14359/51730412


Document: 

18-345

Date: 

July 1, 2020

Author(s):

Ashutosh G. Dabli, Abhay N. Bambole, and Kamalkishor M. Bajoria

Publication:

Materials Journal

Volume:

117

Issue:

4

Abstract:

The use of strain relief method is one of the most direct methods for determination of in-place stresses. In this method, a hole is drilled in the concrete member and the change in strain in the vicinity of the hole, on the surface of the member, is measured by means of electrical resistance strain gauges (ERSG). This change in strain due to drilling is used to assess the in-place stress in the member using constitutive relationship and calibration coefficient. This paper presents the experimental application of incremental hole drilling method (IHDM) in concrete under uniaxial stress. A small hole of 25 mm diameter and 40 mm deep was drilled incrementally to estimate the in-place stress in an axially loaded column with minimum damage. Dry drilling was used to eliminate the effect of swelling due to moisture (water) during the drilling. The experimental strain released was then correlated with an analytical solution using the theory of elasticity and finite element method (FEM). The excellent agreement of experimental results with analytical and numerical values of strain released suggests that IHDM can be conveniently used to evaluate in-place stresses in columns.

DOI:

10.14359/51724612


Document: 

19-177

Date: 

March 1, 2020

Author(s):

Piotr Wiciak, Giovanni Cascante, and Maria Anna Polak

Publication:

Materials Journal

Volume:

117

Issue:

2

Abstract:

The ultrasonic pulse velocity (UPV) method is commonly used as a nondestructive testing (NDT) method in civil engineering and is the ASTM standard for the relative evaluation of concrete quality. However, its limitations due to specimen dimensions or the frequency content of the transmitter excitation are not well understood. The only ASTM recommendation related to the specimen dimension is that the length should be larger than one wavelength. In this study, an experimental program is designed to specifically address the current gap in the understanding of transducer coupling and geometric effects on UPV testing. A state-of-the-art laser vibrometer and numerical simulations are used to evaluate a group of 30 specimens to give a comprehensive range of dimension-to-wavelength ratios. This study shows the response of the ultrasonic transducers in terms of the actual displacements, which indicate their complex character instead of the single pulse response typically assumed. In addition, to improve the reliability of the UPV test, the minimum specimen length-to-wavelength ratio should be greater than 4, instead of 1 as typically recommended, and the diameter-to-wavelength ratio should be greater than 3 instead of 1. If the new set of recommendations is not fulfilled, the error of the UPV measurements can reach up to 20%.

DOI:

10.14359/51722399


Document: 

18-565

Date: 

January 1, 2020

Author(s):

Julie Ann Hartell and Hang Zeng

Publication:

Materials Journal

Volume:

117

Issue:

1

Abstract:

Based on a 10-year climate survey for Oklahoma City, OK, three exposure regimens were devised: cyclic high temperature exposure, cyclic freezing-and-thawing exposure, and cyclic wetting-and-drying exposure. A total of four different test methods were compared to determine the extent of damage induced by the exposure mechanisms. Two standard nondestructive methods—ultrasonic pulse velocity and resonant frequency—were compared along with compression load testing. It was found that resonant frequency testing was more sensitive to microcrack formation. All methods discerned a change in properties after 30 cycles of freezing-and-thawing exposure. Interestingly, all three exposure regimens demonstrated a similar extent in degradation after 90 exposure cycles; however, high temperature and wet-dry cyclic exposure induced further damage than freezing-and-thawing-induced damage. Moreover, acoustic emission (AE) monitoring was performed during mechanical loading. A simple AE parameter-based evaluation confirmed the presence of material distress as that found for the destructive and nondestructive evaluation.

DOI:

10.14359/51719078


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