Wave Dispersion Behavior in Quasi-Solid State Concrete Hydration

Abstract

This paper aims to investigate wave dispersion behavior in the quasi-solid state of concrete to better understand microstructure hydration interactions. The quasi-solid state refers to the consistency of the mixture between the initial liquid-solid stage and the hardened stage, where the concrete has not yet fully solidified but still exhibits viscous behavior. The study seeks to enable a more accurate evaluation of the optimal time for the quasi-liquid product of concrete using both contact and noncontact sensors, as current set time measurement approaches based on group velocity may not provide a comprehensive understanding of the hydration phenomenon. To achieve this goal, the wave dispersion behavior of P-wave and surface wave with transducers and sensors is studied. The dispersion behavior with different concrete mixtures and the phase velocity comparison of dispersion behavior are investigated. The analytical solutions are used to validate the measured data. The laboratory test specimen with w/c = 0.5 was subjected to an impulse in a frequency range of 40 kHz to 150 kHz. The results demonstrate that the P-wave results exhibit well-fitted waveform trends with analytical solutions, showing a maximum phase velocity when the impulse frequency is at 50 kHz. The surface wave phase velocity shows distinct patterns at different scanning times, which is attributed to the effect of the microstructure on the wave dispersion behavior. This investigation delivers profound knowledge of hydration and quality control in the quasi-solid state of concrete with wave dispersion behavior, providing a new approach for determining the optimal time of the quasi-liquid product. The criteria and methods developed in this paper can be applied to optimal timing for additive manufacturing of concrete material for 3D printers by utilizing sensors.

Keywords: P-wave; analytical solution; hydration; inhomogenous medium; sensors; surface wave; wave dispersion; wave scattering.

Figure 1

Schematic of wave propagation in an inhomogeneous effective medium.

Figure 2

Setup for testing (a) contact P-wave and (b) noncontact surface wave.

Figure 3

Overall testing configuration of both P-wave and surface wave.

Figure 4

Raw data obtained from (a) surface wave experiment with 80 kHz impulse, five minutes after mixing concrete and (b) the raw data of P-wave S1 and S2. The ∆t is calculated from the first peak of each sensor.

Figure 5

Comparison of wave speeds in concrete specimen during hardening process using different scanning times. The wave speed in the 30-min scanning data is faster than the 10-min data due to the ongoing hydration process of the concrete.

Figure 6

The phase velocity of P-wave experimental data analysis. (a) phase velocity with six different scanning time, (b) the boxplot of different time cases, and (c) the comparison between analytical solution and experimental data.

Figure 6

The phase velocity of P-wave experimental data analysis. (a) phase velocity with six different scanning time, (b) the boxplot of different time cases, and (c) the comparison between analytical solution and experimental data.

Figure 7

The phase velocity of surface wave experimental data analysis. The phase velocity with six different scanning times.