Electrical Conductivity Of Concrete Research Articles

Impact of different water-reducing agents on the properties of limonite self-compacting conductive concrete

The application environment for concrete is becoming increasingly complex, accompanied by an intensification of its functional requirements. This paper presents a method for developing self-compacting concrete with conductive properties using limonite and graphite as the concrete conductive phases. In the process of concrete preparation, the limonite is initially treated by a pre-wetting method to prevent the surface depression caused by the addition of limonite during the concrete curing process. The second stage of the process involved optimising different proportions of limonite and graphite and different dosages of water-reducing agent, defoamer and dispersant to prepare concrete. The influence of different dosages of limonite and graphite and different dosages of water-reducing agent on the mechanics and electrical conductivity of concrete was studied in order to obtain self-compacting conductive concrete with performance indicators meeting the requirements of self-compacting and electrical conductivity. The results demonstrate that the mechanical and electrical properties of self-compacting conductive concrete prepared with polycarboxylic acid superplasticizer and retarding superplasticizer combined with superplasticizer are satisfactory, and the composite superplasticizer can function in conjunction with dispersant. The self-compaction index, slump expansion, expansion time T50 and J-ring expansion of fluid concrete meet the requisite standards. Once the concrete has reached the designated curing age, its compressive strength and flexural strength align with the anticipated design expectations, while its resistivity meets the stipulated conductivity index requirements.

Study on the mechanical and electrical conductivity properties of waste short carbon fibers concrete and the establishment of conductivity models

The properties of waste short carbon fibers (WSCFs) were firstly characterized in this paper, and the effects of WSCFs with different lengths and contents on the mechanical properties and electrical conductivity of concrete were mainly investigated. Conductive model for WSCFs concrete was established based on the core-shell structure. The results revealed that, in comparison to virgin carbon fibers, WSCFs contained a small amount of resin, and the microscopic surface of WSCFs was smoother, but the content of C elements was low, the wettability and graphitization were poorer. The compressive strength of concrete did not significantly change after being mixed with WSCFs. Compared with the control group (0 %), only when the WSCFs content was 1 %, the compressive strength was slightly improved. The splitting tensile strength decreased as the length of WSCFs increased at the same content. When the length of WSCFs was 10 mm or 20 mm, the resistivity of concrete decreased by 86.0 % and 90.3 %, respectively, at 0.5 % content (28 d). As curing age increased, the free water inside the concrete decreased, and fibers were wrapped by hydration products, resulting in an increase of resistivity. Increasing the length of WSCFs from 10 mm to 20 mm effectively increased the probability of fiber overlap, constructing a more connected conductive network and reducing the conductive threshold of concrete from 0.5 % to 0.4 %. The established conductivity model for WSCFs concrete exhibited high calculation accuracy. The calculation results showed that for WSCFs with a length ranging from 10 mm to 50 mm, the concrete resistivity was very close and fluctuated less for the WSCFs content greater than 0.5 %.

Non-destructive test system to monitor hydration and strength development of low CO2 concrete

Application of supplementary cementitious materials for production of low CO2 concrete affects the reaction kinetics, which alters the setting time and strength development. The different early-age behavior is of concern for quality control of concrete. Non-destructive test is very useful for monitoring the quality of low CO2 binder systems. This paper presents a new technique to monitor the electrical conductivity and temperature at different depths of hydrating concrete. Indices from monitoring system (conductivity, maturity and formation factor) are compared with data from widely-used methods (ultrasonic pulse velocity, penetration resistance and isothermal calorimetry). Results show that indices from the system can replicate the hydration evolution, setting time and compressive strength of low CO2 concrete. Electrical conductivity of concrete is very sensitive to mineral reactions and it reflects the hydration kinetic consistent with evolution of heat release. Linear correlations are found for penetration resistance in relation to ultrasonic pulse velocity, formation factor and maturity, respectively. The effects of binder type and water-to-binder ratio on hardening are strongly dependent on temperature. The proposed approach enables to include all these factors in characterizing the hardening process of concrete onsite. It is shown that formation factor performs better than ultrasonic pulse velocity on indicating the setting process. Formation factor is also a good parameter for quantitative description of compressive strength development, which is independent of the binder types, mixture proportions and curing ages.

Effect of Nanographite Conductive Concrete Mixed with Magnetite Sand Excited by Different Alkali Activators and Their Combinations on the Properties of Conductive Concrete

In order to obtain conductive concrete with good electrical conductivity and good mechanical properties, nanographite and magnetite sand excited by different activators and their combinations are added to ordinary concrete to obtain high quality and efficient conductive concrete. The optimal mixture ratio of alkali-excited conductive concrete and the effects of different activators and their combinations on the mechanics and electrical conductivity of concrete were studied. The microstructure of alkali-excited conductive concrete was analyzed by scanning electron microscope (SEM) to study its conductive mechanism. Results show that the conductive concrete obtained by compounding sodium hydroxide, sodium sulfate and calcium hydroxide has optimal mechanical and electrical properties when the graphite is 6% cement, and magnetite sand is 40% fine aggregate. The conductive concrete sample prepared by this method has a flexural strength of 6.84 MPa, a compressive strength of 47.79 MPa and a resistivity of 4805 Ω·cm (28 days). Compared with ordinary concrete (no nanographite and no magnetite sand), the compressive strength of conductive concrete is increased by 122.3%, the bending strength is increased by 116.5%, and the resistivity is reduced by 99.1%. SEM shows that the distribution of conductive materials in concrete is more uniform due to alkali excitation and calcium silicate hydrate (CSH) gel can be formed, which leads to better performance. The research in this paper is only a preliminary exploration of the characteristics of green conductive concrete, and the conductive heating characteristics and electromagnetic wave absorption properties of concrete, along with strength characteristics after adding conductive fillers, need to be further studied. It is suggested that further research should be carried out on the deicing characteristics of conductive concrete and the electromagnetic wave absorption properties used in stealth military engineering.

Electrical resistivity measurements to determine the steel fiber content of concrete

AbstractAlthough steel fiber reinforced concrete is becoming increasingly popular in the construction industry, its application is currently limited to certain areas. One reason is the lack of an economical non‐destructive testing method to determine the content, distribution, and orientation of steel fibers in fresh and hardened concrete. However, these parameters are decisive for the assessment of the static performance of a building component. In this article a new test method is proposed, which is based on the electrical conductivity of concrete. Using a two‐electrode experimental set‐up, measurements of the electrical conductivity were done on hardened concrete cubes with defined fiber content and a correlation between electrical conductivity and fiber content could be identified. Within the scope of extensive test series, the fiber content and the age of specimens were varied, and several identical series were produced and observed to ensure statistically verified results. At this stage of research the test method based on electrical conductivity measurement provides reliable results on the fiber content of preconditioned concrete cubes. Based on the results a new model was developed to quantify the fiber content of the examined cubes. This model is based on the estimation of the relative conductivity, the so‐called increase of conductivity. Undesired influences caused by aging, respectively hydration in the young concrete age were eliminated, by relating the conductivity of fiber reinforced concrete to an unreinforced concrete. Further investigations with focus on the influence of concrete composition and other specimen sizes are going to be conducted as next steps for the development of an in situ test setup for the diagnosis of concrete structures.

Possibilities of Utilization of Waste Materials in Production of Electrically Conductive Composites on Silicate Basis

The electrical conductivity of concrete can be achieved by adding steel wires or functional fillers. Commonly used fillers are nanotubes, carbon black, nickel powder and so on. These fillers are expensive, but there is a possibility to use waste materials. This is the subject of this experiment. The conductive properties of conductive sand, sludge from the wire drawing process, iron grinding dust waste and waste carbon were verified. From these fillers, waste carbon showed the best electrical properties (impedance). The impedance of the waste carbon was 0.31 Ω and the impedance of the cement composite containing 70% of the weight of waste carbon was less than 670 Ω.

Experimental study on the electrical conductivity of SSG composite concrete

to study the influence of steel slag, slag and graphite content and age on the electrical conductivity of concrete, the electrical resistivity of concrete specimens with specifications of A(100mm×100mm×100mm) and B(100mm×100mm×400mm) was tested. The results show that: With the increase of curing age and the increase of cement substitution by steel slag: slag, the concrete resistivity continues to increase, and the electrical conductivity continues to decrease; and the optimal blending ratio of steel slag: slag is 1:2, the influence of graphite content on concrete conductivity Larger; as the size of the test piece increases, the electrical resistivity of the concrete decreases.

Study on the Effects of Carbon Fibers and Carbon nanofibers on Electrical Conductivity of Concrete

In order to study the effects of carbon fibers and carbon nanofibers on the electrical conductivity of concrete, we adopt the four-electrode method to measure the resistivity of concrete with different test voltages, different ages and different fiber content. The test results show that both carbon fibers and carbon nanofibers can significantly reduce the electrical resistivity of concrete. When carbon fiber content and carbon nanofiber content are same, the resistivity of carbon fiber reinforced concrete (CFRC) is lower than that of carbon nanofiber reinforced concrete (CNFRC). The resistivity of CFRC and CNFRC can decrease with the increase of the test voltage, increase with the development of the concrete, and decrease with the increase of the fiber content. For concrete with an age of 28 days, CFRC has the largest decrease in resistivity when the carbon fiber content is between 0.2% and 0.3%, and the resistivity of CNFRC drops biggest when the carbon nanofiber content is between 0.1% and 0.3%.

Influence of Fineness of Fly Ash on the Carbonation and Electrical Conductivity of Concrete

The paper presents an investigation on the influence of the fineness of fly ash on the carbonation and electrical conductivity of concrete. Fly ash collected from three thermal power stations in India (with a Blaine’s fineness of 200, 255, and 305 m2/kg, respectively) were used for this study. The study also involved three replacement levels (15, 25, and 35% of cementitious materials) for each fly ash sample. Accelerated carbonation studies were performed on specimens cured for 3, 7, and 28 days. The electrical conductivity of concrete was evaluated by measuring the charge passed in coulomb (per ASTM C1202) on 28-day-cured specimens. The test results indicated that the carbonation depth of concrete increased as fly ash replacement increased. However, the carbonation resistances of concrete increased with increased fly ash fineness. Furthermore, the carbonation resistance of concrete increased significantly with a prolonged curing time. The coulomb charge passed through the concrete at an age of 28 days w...

Effects of Temperature, Chemical, and Mineral Admixtures on the Electrical Conductivity of Concrete

Abstract ASTM C1202 has become a very common test method for prequalification purposes and for performance-based specifications in North America. Although the test neither directly determines the permeability or chloride resistance, it has often been shown to have good correlation to those properties since electrical conductivity is also related to the porosity and connectivity of the pore structure. The prevalence of the test is largely based on its ease of execution and its wide acceptance and use by many state and provincial DOTs. More recently, ASTM subcommittee C09.66 has discussed replacing the above test method with a more rapid method measuring conductivity. Several factors affect the conductivity of concrete, mixture design, inclusion of chemical and mineral admixtures, the temperature during testing and the age or maturity at test time. Research was carried out to investigate the magnitude of these variables on measured conductivity. Conductivity was measured using the same equipment as the ASTM C1202 method with changes in the magnitude and duration of the applied voltage as well as the solutions used in the test cell chamber. Conductivity was measured every three hours starting at one day after casting until seven days and weekly until 28 days. Conductivity was found to decrease with hydration as expected. It was determined that mixture design and temperature have significant effects on measured conductivity while chemical admixtures have less influence with the exception of corrosion inhibitors. The developed test method presents potential as a tool for prequalification and quality control that can be directly related to maturity and durability.

Electrical conductivity of concrete containing silica fume

The influence of silica fume on concrete properties represents an important technical research. In general, silica fume tends to improve both mechanical characteristics and durability of concrete. Thus the electrical properties of concrete containing silica fume can be studied to clarify its physical performance during hydration. The electrical conductivity of neat cement, mortar and concrete pastes was measured during setting and hardening. The ordinary Portland cement was partially replaced by different amounts of silica fume by weight. The changes in the electrical conductivity were reported during setting and hardening after gauging with water. The results of this study showed that the electrical conductivity can be used as an indication for the setting characteristics as well as the structural changes of the hardened pastes made with and without silica fume.