Water Content Of Concrete Research Articles

Current Progress in Standardization of Shielding Concrete Composition for Japanese Facility Design

The working group on shielding materials under the Standards Committee of the Atomic Energy Society of Japan has been studying the standard composition of shielding concrete that has a clear basis for use in the design of Japanese facilities. The policy for determining the composition, the procedure of study, the results obtained to date, and future tasks are described. Concrete is broadly classified into silicon type and calcium type depending on the aggregate. The reference mix design and composition were selected from the Japanese recommendation, and minor elements in the composition were replaced with silicon and calcium while preserving their weight in order to reduce regional differences. However, the penetration dose calculation for 235U thermal fission neutrons indicated that iron and carbon should be retained. The penetration dose calculations for photons from 235U prompt fission and radioisotopes showed that the attenuation ratios of silicon-type and calcium-type concretes differ in the energy region where electron pair production becomes dominant. The water content of concrete was found to vary with thickness as a result of moisture migration analysis over time. Finally, a draft composition of silicon-type concrete by thickness was determined using the residual water content at 60 years after placement. A method for correcting the elemental content under different mix conditions was also proposed.

Machine Learning Modelling for Compressive Strength Prediction of Superplasticizer-Based Concrete

Superplasticizers (SPs), also known as naturally high-water reducers, are substances used to create high-strength concrete. Due to the system’s complexity, predicting concrete’s compressive strength can be difficult. In this study, a prediction model for the compressive strength with SP was developed to handle the high-dimensional complex non-linear relationship between the mixing design of SP and the compressive strength of concrete. After performing a statistical analysis of the dataset, a correlation analysis was performed and then 16 supervised machine learning regression techniques were used. Finally, by using the Extra Trees method and creating the SP variable values, it was shown that the compressive strength values of concrete increased with the addition of SP in the optimal dose. The results indicate that superplasticizers can often reduce the water content of concrete by 25 to 35 per cent and consequently resistivity increased by 50 to 75 per cent and the optimum amount of superplasticizers was up to 12 kg per cubic meter as well. From one point, the increase in superplasticizers does not lead to a rise in the concrete compressive strength, and it remains constant. According to the findings, SP additive has the most impact on concrete’s compressive strength after cement. Given the scant information now available on concrete-including superplasticizer, it is prudent to design a concrete mixing plan for future studies. It is also conceivable to investigate how concrete’s compressive strength is impacted by water reduction.

A deep learning approach to concrete water-cement ratio prediction

Concrete is a versatile construction material, but the water content can greatly influence its quality. However, using the trials and error method to determine the optimum water for the concrete mix results in poor quality concrete structures, which often end up in landfills as construction wastes, thus threatening environmental safety. This paper develops deep neural networks to predict the required water for a normal concrete mix. Standard data samples obtained from certified/leading laboratories were fed into a deep learning model (multilayers feedforward neural network) to automate the calibration of mixing power of the concrete water content for improved water control accuracy. We randomly split the data into 70%, 15% and 15%, respectively, to train, validate and test the model. The developed DNN model was subjected to relevant statistical metrics and benchmarked against the random forest, gradient boosting machines, and support vector machines. The performance indices obtained by the DNN model have the highest reliability compared to other models for concrete water prediction.

The Properties of Lightweight Aggregates Pre-Coated with Cement Pastes and Their Suitability for Concrete.

One of the biggest technological problems connected with the production of lightweight concretes made of porous aggregates is their much higher water absorption, which may cause on the one hand workability loss, and on the other hand excess water content in concrete. The aim of this research was to assess the effect of impregnation of lightweight aggregates (LWAs) with cement paste on their properties and to verify its effectiveness in concretes. Three types of lightweight aggregates differing in porosity and pore structure (sintered fly ash Lytag, expanded clay: Leca and Liapor) were selected for the tests. The following parameters were taken into consideration in the research program: LWA type and size, LWA initial moisture content, strength, and rheology of cement pastes. The tests of 22 different aggregates, plain and coated with cement paste, included density, crushing strength, and development of water absorption in time. The research program proved that porous aggregates, due to their impregnation with cement pastes, may be effectively sealed and strengthened. All tested LWAs showed a considerable decrease in water absorption by up to 71%. However, only Lytag aggregate showed a visibly enhanced crushing strength. Verification of effectiveness of aggregate sealing on the enhancement of concrete properties showed both a considerable reduction in water absorption of composites (by up to 52%) and a very high increase in their strength (by up to 107%).

APPLICABILITY OF VECTOR AUTOREGRESSIVE MODEL TO ESTIMATION OF INTERNAL MOISTURE CONDITION OF CONCRETE EXPOSED TO ORDINARY NATURAL ENVIRONMENT

To investigate the applicability of VAR-X model to estimating moisture condition of concrete exposed to ordinary natural environment, concrete internal humidity data reported previously were analyzed with weather data from Japan Meteorological Agency. The first 90 days were used for parameter estimation and the second 60 days were used to validate the model and predicted values. The results are summarized below. (1) Within the scope of this study, VAR-X model was applicable to the humidity data in the non-rainfall environment. VAR-X model was also able to predict the internal humidity for 60 days based on the estimated parameters and weather data (temperature and humidity), and the RMSE ranged from 0.87 to 2.04%. (2) It was judged that the VAR-X model was not appropriate to be applied to the humidity data of rainfall environment. The main reason for this is that the impact of rainfall was underestimated by assuming constant coefficients in the model. (3) The mechanisms of humidity fluctuation in concrete are discussed, which include the absorption and release of water and the temperature dependence of concrete water content. Based on the mechanism, difference between rainfall and non-rainfall environment was pointed out and the conditions under which the VAR-X model can be applied are discussed. (4) Methods of utilization and improvement of VAR-X model were discussed for cases where the moisture transfer characteristics of concrete changed and where the data increased or decreased in high humidity region. The advantages of time series analysis, including VAR-X model, were also pointed out in comparison with conventional physical models. VAR-X model can predict humidity fluctuations in concrete using weather data when certain conditions are met. In the future study, the model will be modified and its application to the durability evaluation of various materials will be investigated.

Quantification of the effect of temperature difference between concrete and indoor air, and water content in concrete on radon exhalation

Effects of temperature difference between indoor air and concrete, and water content in concrete, on Rn-222 exhalation were investigated. In concrete with 0% water content, the heat generated due to temperature difference between concrete and indoor air could raise Rn-222 exhalation rate by 2.6 times. The Rn-222 exhalation rate rose initially, then declined as water content in concrete was increased. The maximum Rn-222 exhalation rate was 4.4 mBq m−1 s−1 in concrete with 10% water content. A grey prediction model was established for predicting Rn-222 exhalation rates and exposure doses of residents due to different indoor temperature differences with concrete.

Calculation of Thermal Fields of Cracked Concrete at Elevated Temperatures

This paper analyzes the effects of cracking on the thermal field of concrete at elevated temperatures. In four concrete specimens with pre-made cracks, fire tests were performed. Then finite element analysis and theoretical analysis were conducted, which have indicated that heat conduction was the primary source of heat transfer in cracked concrete. At last mathematical software MATLAB was used to calculate the temperatures distributions of a simplified model based on theoretical analysis, which were compared with the test results. The results show that as the thermal diffusion of air is far greater than that of concrete, there is an increase in the thermal propagation through the cracked regions in comparison with undamaged regions, and the temperatures increase with the increase of cracks widths. The temperature of concrete farther away from a crack was less affected because concrete has a lower thermal diffusion coefficient. The water content of concrete has an impact on the temperature distributions, which should be considered at the early stage of fire when determining the concrete temperature distributions.

Determinant factor for dynamic equilibrium of transformation between vapor in atmosphere and water in concrete

Under certain conditions, liquid water in concrete pores can evaporate, forming vapor to the surrounding atmosphere; vapor in the surrounding atmosphere can condense, forming liquid water in concrete pores. Therefore, there exists a water-to-vapor transformation causing change of liquid water content in concrete. This study is aimed at analyzing the determinant factor for the water-to-vapor transformation based on the responses of relative humidity in concrete to different relative humidity and temperature of the surrounding atmosphere. Relative humidity in concrete was measured with two temperature and humidity (T&RH) probes (One was embedded into concrete and the other was placed in the cavity formed by embedding a PVC pipe) under two conditions: (1) constant temperature and variable relative humidity of the surrounding atmosphere (2) constant relative humidity and variable temperature of the surrounding atmosphere. Moreover, a specially designed device was adopted to verify the determinant factor for the water-to-vapor transformation. The results showed that relative humidity recorded by the embedded T&RH probe was always 100%, while that recorded by the placed T&RH probe had responses to the surrounding atmosphere under conditions (1) and (2). According to the results, the determinant factor for the water-to-vapor transformation is vapor partial pressure, namely absolute humidity, of the surrounding atmosphere. Furthermore, as long as there is liquid water in concrete, vapor in concrete pores is in saturation state, indicating the internal relative humidity of concrete should be a constant of 100%. Consequently, relative humidity in the cavity is inaccurate to represent moist condition of concrete.

Electrochemical methods for on‐site corrosion detection

AbstractThe corrosion mechanism is of electrochemical nature and then, electrochemical techniques are the most adequate to measure the process and quantify it. In present paper are briefly described the most applied on site: corrosion potential, resistivity, galvanic current, and polarization resistance. In general, due to the difficulty to measure quasi‐infinite in size reinforcement, the measurements are made on probes embedded in the cover attached to the bars. From the techniques used, only linear polarization is quantitative. Corrosion potential provides information about the corrosion risk, and resistivity is directly related with the concrete water content. The galvanic current is misleading if real size of anode and cathode are unknown. Although, frequently mistaken, galvanic current is not equal to corrosion rate and reference to areas involved is needed. Two examples are described on the monitoring of these methods.

EXPERIMENTAL STUDY ON THE COMPRESSIVE STRENGTH OF CONCRETE OF DIFFERENT STRENGTH GRADES EXPERIENCING ULTRALOW TEMPERATURE FREEZE-THAW CYCLE ACTION

Through experiments of concrete of different strength grades such as C40, C50 and C60 that experiences 0, 16 and 30 cycles of ultralow temperature freeze-thaw cycle action from 15℃ to -120℃ and -190℃, the effects of the strength grades on the concrete compressive strength are discussed. The test results show that the failure modes of the specimens with different concrete strength grades are similar and generally cone-shaped regardless of the loading at the lower or upper limit temperature, but the failure surface characteristics and so on are different. After experiencing ultralow temperature freeze-thaw cycle action, the relative concrete compressive strengths at the lower and upper limit temperatures decrease with the increase in the concrete water content. With an increase in the concrete strength grade, the relative concrete compressive strengths increase at the upper limit temperature, while the relative concrete compressive strength of every strength grade decreases with the increase in the number of freeze-thaw cycles. Although the relative concrete compressive strength in different ultralow temperature ranges increases at the lower limit temperature, there is obvious difference in the reasons for its increase. The variation trend of the relative concrete compressive strength with the increase in the number of freeze-thaw cycles is similar in a given ultralow temperature range regardless of the concrete strength grade, but there exists a difference between different ultralow temperature ranges. The influence of ultralow temperature freeze-thaw action on the concrete mechanical performance is different from that of natural ambient temperature freeze-thaw action, from which the degradation of the concrete compressive strength is much more serious. In practical engineering, the results from natural ambient temperature freeze-thaw action should not be directly applied to the design of concrete structures that undergo ultralow temperature freeze-thaw action.

Effective medium theories in electromagnetism for the prediction of water content in cement pastes

Permittivity is a widespread property used to estimate the water content in concrete. To improve the reverse conversion from permittivity measurements to moisture content, we suggest the building of an electromagnetic model of concrete. In this paper, such a model is developed for the case of cement pastes. It relies on electromagnetic homogenization schemes which require an information about the permittivity of the predominant species in the material. Estimating those properties over the frequency range [200 MHz; 1 GHz] was achieved by synthesizing model cementitious binders (C-S-H and portlandite mixtures), by characterizing their macroscopic permittivity with an open-ended coaxial probe and by identifying their intrinsic permittivity with a specific homogenization procedure combining effective medium equations. The identified values are used as inputs for a homogenization procedure estimating the water content in cement pastes. For a wide range of water content, the simulated and measured real parts of permittivity show a good agreement.

Influence of organic components and inorganic components of reed as a concrete admixture

Vegetation in closed water area improves the natural environment by providing a habitat for juvenile shellfish and fish and by facilitating the intake of nutrients by plants. For these aquatic fauna, nutrient discharge occurs as mature individuals are harvested as fishery resources. However, aquatic plants are not typically harvested, so nutrients taken up by the plants as they grow return to the water in dead vegetation. These plants will not make a sustained contribution to the purification of the overall aquatic environment unless a system is developed to harvest them. In this research, we examine how reeds can be recycled. A potential application for the reeds is in mineral/chemical concrete admixtures. Reeds are rich in inorganic silica and organic lignin, both of which are effective as concrete admixtures. Silica is typically amorphous and is used as a pozzolanic admixture to impart long-term strength to concrete. Lignin is used as a water reducer admixture, which reduces concrete water content or slows the setting rate. The silica and lignin contained in the reed were examined from the viewpoint of strength development and flow of concrete. From the viewpoint of strength development, it was confirmed that long-term strength can be expected by replacing ashes of reeds with 5% of cement. Then, to improve mortar flow, reed powder was added to mortar as a water reducer at a weight fraction of 1% and was suitable in terms of phenol concentration. The results indicate that reed can be used as a chemical and physical concrete admixture.

Non-Contact Terahertz Inspection of Water Content in Concrete of Infrastructure Buildings

Concrete is the most widely used for construction materials in the world. Water content of concrete is an important parameter in terms durability of concrete structures. Terahertz (THz) waves, for which concrete is a porous and absorbable material, have been studied in order to establish a new non-contact inspection technology for maintenance of concrete structures. In this study, THz transmittance and reflectance of concrete in drying process were measured with a 60 GHz GUNN diode and absorption coefficient is analyzed for concrete with various water contents. It is shown that quantitative detection below 10% is possible for the water content at surface area of concrete.

Determination of concrete water content by coupling electromagnetic methods: Coaxial/cylindrical transition line with capacitive probes

This paper deals with the development and the validation of an innovative, easy-to-use and on site technique for determination of concrete water content. The on-site technique is the capacitive probe, able to characterize in situ dielectric media in the 30–35MHz frequency band (around 33MHz). For the evaluation of water content in various civil engineering structures, a calibration methodology has to be developed and is presented herein. It is based on the complex permittivity estimation of various dispersive concretes, which is carried out by a cylindrical coaxial electromagnetic (EM) transition line allowing the characterization in laboratory of material samples in a large GPR frequency bandwidth [50–600MHz]. This methodology consists then on a coupling between the results of both the capacitive probes and the coaxial EM cell extrapolated at low frequency (33MHz). The extrapolation procedure used to link physically the results of the two techniques is provided by the 4parameter-variant of Jonscher's model which is parameterized to obtain dispersion curves of the complex permittivity for very wide frequency bands. The methodology is checked by a parametric study that associates the 4p-variant of Jonscher's model with the physical and hydric characteristics of the six concrete mix designs representing high performance and ordinary concretes at various hydric states. The surface testing results measured by capacitive probes on slabs are successfully compared to the extrapolated results obtained on cores.

新設コンクリート部材における水分特性と表層透気性に関する研究

Surface-layer air permeability depends strongly on the water content of concrete. Therefore, newly built structures, which contain a large amount of water, require water content evaluation during inspections. The relationships among the material age, surface-layer air permeability, relative humidity, and air permeability coefficient of newly cast concrete have been reported, but there have been few studies on the relationship between the water content and air permeability of young concrete. In this study, the effects of the water content of young concrete on surface-layer air permeability were investigated to propose a method for evaluating the durability of newly built concrete structures. To study the relationship between water behavior and air permeability in concrete in indoor and outdoor environments, specimens and actual-size walls containing embedded ceramic sensors were produced from ordinary Portland cement, Portland blast furnace cement type B, and fly ash cement. The relationships among the water content of concrete, Wenner method resistivity, and air permeability were determined. In addition, pore structure was analyzed by the mercury intrusion technique and discussed. The effects of the relationship between pore structure and water content on air permeability varied according to material age for different kinds of cement in an indoor environment. The results indicated that it is possible to evaluate the durability of concrete aged 28 days or older, for which the effects of structural changes can be removed.

Effect of water pressure on mechanical behavior of concrete under dynamic compression state

This paper reports the experimental study of water pressure environment effects on the mechanical behavior of concrete under a dynamic compression state with strain rates ranging from 10−5/s to 10−2/s. The water content of concrete under different water pressure (0, 2, 5, and 10MPa) was obtained, and the failure modes and the strength of concrete were proposed. Results show that strength and failure modes are remarkably affected by water content and strain rate. Under water pressure, the strength of concrete increases nonlinearly as strain rate rises, and the strain rate sensitivity of concrete increases with increasing water content. When the water content of concrete is higher than 1.27 times of wsac, (wsac is water content of concrete which becomes a fully saturated state in atmospheric condition), and concrete under the fast loading results in cone-type failure (CTF). Moreover, the area of crack surface and the volume of debris shedding also decrease as both water content and strain rate increases; however, when the water content of concrete is lower than wsac or the concrete under slow loading, slant shear failure (SSF) occurs. As explained through a basic poromechanics analysis, this dissimilarity is mainly attributed to the excess pore water pressure and the viscous stress inside the saturated concrete during fast (quasi-static or dynamic) experiments.

Thermal conductivity of structural lightweight aggregate concrete

This paper characterises the thermal conductivity of structural lightweight aggregate concrete with strength classes ranging from LC12/13 to LC55/60 and density classes from D1·6 to D2·0. The thermal conductivity of concrete is assessed by a transient test method, taking into account different types of lightweight aggregate and binder, as well as different water/binder ratios. The influence of the concrete constituents on its thermal conductivity is analysed and relations between this thermal property and both the density and water content of concrete are established. It is shown that the thermal conductivity of structural lightweight aggregate concrete can be half that of normal weight concrete of similar composition. A high exponential correlation between thermal conductivity and density of concrete is achieved. On average, thermal conductivity decreases about 0·6% per each 1% increment in aggregate porosity, 8·3% per each 50 l/m3 increment in coarse aggregate volume and 3–9% per each reduction of 1% by weight in water content.

Advanced online water content measurement for self-compacting concrete production in ready-mixed concrete plants

In ready-mixed concrete plants, the water content of self-compacting concrete (SCC) is generally controlled during the mixing process based on the stabilisation of mixer power consumption. This measurement system is however rarely calibrated, even though its signal is sensitive to the wear of mixers and the temperature of engines.The aim of this paper is to propose a calibration of mixing power as a measurement of the concrete water content that enables improving water control accuracy. A new approach based on the mixing power evolution is devised for a better determination of the signal stabilisation. The stabilisation time is then defined and considered as the necessary mixing time of each concrete batch. Experimental results obtained from 40 batches of different SCC compositions produced in a full-scale concrete plant have shown that, with the developed calibration method, the stabilisation of power consumption can be considered as a reliable indication of water content with a precision of ±3.8l/m3. It is also observed that the water-to-powder ratio (W/P) and the use of viscosity agent have significant effects on the power consumption evolution during mixing.

中性子によるコンクリート中の水分の可視化

中性子によるコンクリート中の水分の可視化

Digital fast neutron radiography of steel reinforcing bar in concrete

Neutron imaging has previously been used in order to test for cracks, degradation and water content in concrete. However, these techniques often fall short of alternative non-destructive testing methods, such as γ-ray and X-ray imaging, particularly in terms of resolution. Further,thermal neutron techniques can be compromised by the significant expense associated with thermal neutron sources of sufficient intensity to yield satisfactory results that can often precipitate the need for a reactor. Such embodiments are clearly not portable in the context of the needs of field applications. This paper summarises the results of a study to investigate the potential for transmission radiography based on fast neutrons. The objective of this study was to determine whether the presence of heterogeneities in concrete, such as reinforcement structures, could be identified on the basis of variation in transmitted fast-neutron flux. Monte-Carlo simulations have been performed and the results from these are compared to those arising from practical tests using a 252Cf source. The experimental data have been acquired using a digital pulse-shape discrimination system that enables fast neutron transmission to be studied across an array of liquid scintillators placed in close proximity to samples under test, and read out in real time. Whilst this study does not yield sufficient spatial resolution, a comparison of overall flux ratios does provide a basis for the discrimination between samples with contrasting rebar content. This approach offers the potential for non-destructive testing that gives less dose, better transportability and better accessibility than competing approaches. It is also suitable for thick samples where γ-ray and X-ray methods can be limited.