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Concrete is one of the most common construction materials used in rigid pavement, bridges, roads, highways, and buildings. Compressive strength is one of the most important properties of concrete, which determines its quality. This study aims to present the use of a new surface dielectric method to estimate concrete compressive strength. Six concrete mixtures were produced with compressive strengths ranging from 30 to 60 MPa. Compressive strength and strength development were determined during 28 days of curing. All concrete mixes were tested using the ASTM standard. The dielectric properties, ultrasound velocity, and rebound number of all concrete mixes were also measured at each day of curing. The results obtained from the proposed dielectric method in predicting the compressive strength of concrete were compared with the rebound hammer and ultrasonic velocity that are frequently used to evaluate the compressive strength of concrete. The dielectric method shows a higher square correlation coefficient than the other two methods. The results also indicate that combined more than one method of nondestructive techniques will lead to higher prediction and could help to reduce some errors associated with using a certain method alone. The result indicate that the finding of this study could lead to help in reducing the time of evaluating concrete during construction and could also provide tools for practicing engineer to take decision faster with more confidence level on quality of concrete. Doi: 10.28991/cej-2021-03091645 Full Text: PDF

This paper presents a new method of dielectric capacitance cell as a proposed device for measuring the impedance of pure sand artificially contaminated with four heavy metals. Dielectric constant and loss factor of clean and contaminated sand at various levels were calculated from the measured sand impedances. The advantages and benefits of using the proposed dielectric capacitance cell were its low cost, simple calculation, calibration procedures, portable and lightweight, and easy to modify the electrodes to suit testing in the field. Pure sand was saturated with water artificially polluted in the lab with Pb, Cd, Fe, and Zn at heavy metal contents 0, 7.5, 15, 22.5, and 30 mg/kg of sand. The dielectric properties of polluted sand were evaluated at a frequency range from 100 kHz to 1000 kHz. The polluted sand exhibit different dielectric constants and loss factors from the unpolluted sand. The results also indicate that the dielectric constant decreases with increasing pollution level for all heavy metals. This may attribute to the polarization mechanism change with existing heavy metal. The loss factor of sand increases with the increasing pollution level. This may be explained by the increase of ionic conductivity of pore water with heavy metal in the sand. Sand polluted with heavy metal with higher resistivity and density possess a higher dielectric constant and lower loss factor than other polluted metals. Evaluation of the dielectric characteristics of polluted sand could have the potential to monitor heavy metal pollution. Even with promising results obtained with the proposed dielectric device, it is necessary to explore several other factors affecting the measurements such as sand water content, soil texture, and type of soil. Also, testing polluted soil near industrial pollution is needed.

In this study, a method for determining the setting time and the porosity of fly ash-based geopolymer binders (FAGPBs) has been established. This method permits a real-time monitoring of the geopolymerisation and hardening progressions. A parallel plate capacitor cell technique was used to determine the dielectric constant e r ' and dielectric loss factor e r ' ' of fresh and hardened mixes. Equivalent model-circuits of the measurement system were developed, and the accuracy of the system was verified. The dielectric properties were monitored at different ages until 56 days over a frequency range of 0.1–60 MHz. The alkaline solution to fly ash ratio, sodium silicate to alkaline solution ratio, and sodium hydroxide solution molarity were varied to study their effects on the dielectric properties. It was found that dielectric properties can provide valuable information when measured in the frequency range of 10–25 MHz. In this range, the dielectric values responded well to the variations with age and with mix properties. The relationships between the dielectric properties and the different physical states and constituent materials of FAGPBs could be used for quality control applications. The e r ' and e r ' ' time plots were effectively utilized to determine the setting time and the rate of geopolymerisation of FAGPBs. Measurements showed a strong correlation between e r ' and porosity; the e r ' values decreased 2.3-fold over a porosity range of 3–15%. The proposed regression models can be further used in determining the porosity of FAGPBs at a high accuracy level.

This paper presents a new dielectric sensor which could be used for assessment and evaluation of soil pollution in the field. The new device determines the dielectric properties of soil from the measured soil impedances. The dielectric properties used as indirect method to estimate type and pollution content in soil. The new device was calibrated and validated for accurate measurement of soil dielectric properties in the frequency range of 1 kHz to 30 MHz. The new proposed dielectric sensor was used to measure the dielectric properties of clean and contaminated soil. The measured dielectric properties of soil using the proposed sensor could be used to estimate soil moisture content, hydrocarbon diesel and salinity in sand soil. The results also show that the dielectric properties of clay soil were higher than the dielectric properties of san due to existing bound water in clay minerals. Further testing is necessary to evaluate the effects of other parameters such as temperature and various type of soil prior to adopt the sensor for field testing.

In this paper, the near- and far-field microwave methods used in this study indicate that the microwave reflections and dielectric properties are useful parameters for the detection of chloride in concrete material. Furthermore, the amount of chloride present in concrete at the time of mixing can also be determined. The reflection coefficients, dielectric constant and loss factor in the X-band microwave frequencies increase with increasing chloride content in concrete materials and can be used to monitor the hydration process. A linear relationship between the microwave properties of concrete and chloride content were established.

Most available methods for determination of water quality in water bodies such as rivers, lakes, and reservoirs are based on the collection of water samples from water bodies and subsequent laboratory analysis. While these methods are standard and could provide accurate measurements and evaluation of water quality, they are costing and time consuming and do not provide the continuous monitoring and assessing of water quality. In this paper, low frequency dielectric cell is developed for determination the water quality. The proposed method was used to measure the dielectric properties of water. The method was calibrated and validated by measuring dielectric properties of standard materials such as Teflon. The measured dielectric properties of water were used to determine several water quality parameters such as salinity, temperature, turbidity. The proposed method has advantages in compare with the available techniques for water quality including simple, low cost, safe, possible to be continuous and online method, and can be used for in-situ as in the lab. Dielectric constant and loss factor of water decrease with increasing frequency. The rise of water temperature caused an increase in loss factor and a decrease in dielectric constant. The dielectric constant increases with increasing water salinity while it decreases with increasing the turbidity of water. Further investigation is needed to determine the effect of other water quality indices on the dielectric properties of water prior to use the proposed system in practical application.

Generally the methods were used to characterize soil contamination include collecting samples of soil then analyzing them to recognize contaminates in the laboratory. Commonly, this method of characterizing the contamination of a soil system is the only one agreeable to regulatory societies. However, sample analysis in the lab faces important problems such as soils sampling is really time consuming and costly, sampling is not constant with time and the samples be able to contaminate through sampling and carrying to the lab. Thus several geophysical techniques have been developed which used the dissimilarity in the soil physical properties after soil contamination. Dielectric technique shows high conceivable for characterization diesel contaminated soil. Further use of this technique; rely upon the availability of information about the dielectric properties of the contaminated soil. In this study, the effects of induced by a diesel presence in an unsaturated soil, on the complex dielectric properties were sought. It has been shown experimentally that the diesel presence in an unsaturated soil is traduced by an increase of both dielectric constant and loss factor. A comparison with the existing results in this study and in the literature for saturated soils shows an opposite effect on the complex dielectric properties. The importance of the influence induced by the diesel on the dielectric properties of an unsaturated soil was noticed and compared to a saturated soil. On the basis of the theoretical dielectric mixture models, a justification to these opposite behaviors and their importance has been presented and various models for the two cases have been developed.

Introducing steel fiber to concrete materials enhances the performance of concrete structures in terms of their flexural strength, impact load resistance and limited crack propagation. The fiber concrete performance depends on the fiber content, dispersion and orientation. No standard method is currently available to evaluate these three parameters, especially in situ. This paper describes the feasibility of using a surface electromagnetic sensor as nondestructive radio wave test system to determine the concentration, dispersion and orientation of steel fibers in the concrete. The system needs to contact the concrete material and requires only one face of the concrete material for testing. The surface electromagnetic sensor can slide on the fiber concrete surface and measure the dielectric properties at various locations to assess the fiber distribution. In addition, the sensor can rotate to polarize the electric field to various angles and evaluate the fiber orientation. The mean and standard deviation of the measured dielectric properties increase with increasing fiber content and fiber dispersion. The results indicate that the dielectric properties are maximal when the fiber is oriented in the direction of the electric field and minimal when perpendicular. A simple linear model was established to determine the fiber content and flexural strength from the measured electromagnetic properties.

Soil contamination with petroleum hydrocarbons has become one of the most serious problems due to its negative repercussion on ecosystems. For this reason, different analytical techniques have been developed to evaluate the quantity and the quality of organic pollutants using electrochemical techniques, and a geophysical methods have been developed which utilizes the contrast caused by the contaminant on physical properties of the soil dielectric methods shows high potential for characterization kerosene contaminated soil and determination of the level of contaminant. The potential of dielectric measuring techniques for soil characterization has not been fully explored. For this purpose, dielectric measurements, in the frequency range from 100 kHz to1000 kHz, were carried out in sandy soil samples, contaminated with solutions of kerosene, at different concentrations. The differences of the dielectric behavior with contaminant content suggest that the monitoring of complex dielectric constant has the potential to quantify contaminants.

The paper deals with dielectric properties of concrete and the effect of frequency, curing time and water to cement (w/c) ratio, concrete compression strength, steel fibre concrete and moisture content on the dielectric properties. The concrete dielectric properties such as transmission coefficients, reflection coefficients, dielectric constants and loss factors; were investigated using microwave nondestructive testing (MNDT) tech- nique. The MNDT system consists of transmit and receive horn lens antennas, a vector network analyzer, mode transitions, and a printer. The horn lens antennas are used for minimizing diffraction effects due to the edges of the sample. Electromagnetic waves at micro- wave frequency range 7.0-13.0 GHz using free-space microwave method was used for measuring dielectric properties of concrete. Concrete specimens were prepared using different w/c ratios and different com- pressive strengths. Concrete dielectric properties were measured and correlated with compressive strength and w/c ratio of concrete, curing time. The experimental results indicate that microwave non-destructive tech- nique has correlated well with to determine the compressive strength and w/c ratios of concrete. The results also show the potential to be used to determine the percentage of fiber. This technique is easy to adapt for in situ measurements.

The existence of moisture in concrete is a major cause of damage to the concrete structure, so there is an increasing need for nondestructive detection and monitoring of moisture content in concrete. Microwave nondestructive testing (MNDT) techniques have advantages over other NDT methods (such as radiography, ultrasonic, and eddy current) regarding low cost, good penetration in nonmetallic materials, good resolution and requirement of only one face of material for testing. In this paper, microwave open-ended rectangular waveguide was used to measure the electromagnetic properties of Portland cement concrete (PCC) over a frequency range of 7.0 to 13.0 GHz. PCC specimens of six different water cement ratio (w/c) were prepared. PCC dielectric properties were evaluated at different moisture content ranges from saturated to oven dry. The results show reflection coefficients, dielectric constants and loss factors increase with increasing moisture content of PCC. At the same values of moisture content, the reflection coefficients, dielectric constants and loss factors of PCC increase with decreasing w/c ratio. The measured values of reflection coefficients, dielectric constants and loss factors can be used to determine the moisture content of PCC.

Methods available for measuring the water quality of rivers, lakes, reservoirs, etc. involve the collection of water samples for these water bodies and subsequent chemical laboratory analysis. These methods and technologies provide accurate measurements and evaluation of water quality for a point in time and space; they are time consuming, expensive and do not provide either the continuous, spatial or temporal view of water quality needed for monitoring, assessing, or managing water quality. In this paper, the measured complex reflection coefficients and complex permittivity (dielectric constant and loss factor) of water using a microwave open-ended rectangular waveguide system called microwave reflectometer system (MRS) is used to monitor the water quality. MRS uses the electromagnetic properties of water to indicate the quality parameters of waste. This system offers the potential of relatively inexpensive, frequent, continuous and synoptic measurements using sensors immersed in the water bodies (reservoirs, rivers, lakes, treatment plant). Dielectric properties of water of different salinity are measured and evaluated.

Microwave nondestructive testing methods are fast, contactless, accurate and continuous techniques for the evaluation of moisture content, slope-of-grain, density of knots and specific gravity of timber. Dielectric properties of timber are determined by these factors. We describe how the dielectric properties were deduced from reflection and transmission coefficient measurements of Malaysian timber specimens using a free-space measurement system in the frequency range 8-12.5 GHz. Dielectric properties were evaluated over different angles between the electric field and the direction of grain. Relationships between density, modulus of elasticity, strength, grain angle (angle between the direction of grain and electric field) and dielectric properties of Malaysian timber were established.