Concrete Moisture Research Articles

Analysis of Cracks on the Containment of Loop Nuclear Power Stations for 60 Days

The relation of tensile strength ＆ temperature stress and concrete fissure was researched firstly , then it showed the causes of late cracks on concrete by theoretical calculation, the result provided a simple theoretical calculation method to avoid concrete fissure. The construction methods to control the fissure was proposed: early strengthening cooling, managing maximum temperature of concrete through lately heat preservation, and overtime to preserving concrete moisture for controlling the late strain on mass concrete. This research has a great significance for controlling the fissure.

Evaluating laboratory-induced asphalt concrete moisture damage using surface waves

The feasibility of multichannel analysis of surface wave testing was considered against dynamic modulus, indirect tensile strength and visual rating as a potential indicator of asphalt concrete moisture damage. Three replicates of field-produced asphalt concrete plate specimens were each tested at four levels of air-void content and moisture conditioning using a similar method as used in AASHTO T283-02. The effect of the various conditioning levels was examined on each of the different test results. The indirect tensile strength correlated best with the number of conditioning cycles, followed by surface wave testing, while dynamic modulus was found to be least sensitive. Minimum retained parameter thresholds were developed for each method, according to a visual stripping rating of the broken tensile specimens. Given the reasonable performance, compared to the reference test results, multichannel surface wave testing was considered feasible for evaluating moisture damage effects in the laboratory-conditioned specimens.

Chloride Ion Ingress in Concrete Exposed to a Cyclic Wetting and Drying Environment

Concrete agricultural buildings are subjected to severe corrosion of their reinforcing steel by moisture and aggressive ions. Several accidents have indicated that corrosion is more severe in areas subjected to cyclic exposure to corrosive fluids than those submerged in the fluids. Laboratory experiments were conducted to study the effect of cyclic wetting-drying on the ingress of moisture and chloride ions in concrete. Expedited experiments were conducted using 10% NaCl solution and infrared lights for drying. The wetting and drying durations were 1 h and 7 h, respectively. Results show that chloride concentrations in the surface layers (0 to 5 mm) of the concrete samples that were subjected to cyclic wetting and drying were much higher than those in the saturated samples; the differences became greater as the experimental time continued from 14 to 45 to 90 days. In addition, the difference in Cl concentration decreased with the depth in the concrete samples. Overall, the rate of chloride transport in concrete under cyclic wetting and drying was quicker than that in immersed concrete. This indicates a potential for faster damage to concrete structures under cyclic wetting and drying conditions.

Simultaneous heat and moisture transfer in concrete with time-dependent boundary conditions

Temperature and moisture are responsible for the deterioration processes of concrete structures and the extensive failures in concrete elements often result from both thermal and moisture loads. Heat and moisture transfer in concrete with time-dependent boundary conditions was investigated by numerical simulation using the Coupling Temperature and Moisture Simulation System for Concrete (CTMSoft). The temperature and moisture distribution in concrete were numerically simulated through solving the coupling transfer equations based on heat and moisture transfer in porous media by analytical method inolving Laplace transformation and transfer function. The hygro-thermal induced by the moisture and temperature changes in concrete are analysed using CTMSoft. The comparison between the numerical and experimental (or Fiber Bragg Grating monitoring data) suggests that the numerical model can be used accurately to predict the deformation resulting from the simultaneous heat and moisture transfer.

Development of a moisture-modified maturity model for portland cement concrete pavements

In order to represent the concrete maturity and strength relationship, different mathematical models have been developed. In practice, there can be implementation of the logarithmic maturity and double logarithmic strength linear relationship for in-place strength gain and time of opening monitoring under variable temperature conditions. Concrete moisture was considered in the existing maturity concept context as a means for concrete strength predictability improvement. There was modification of a moisture modification factor Bazant developed on the basis of Powers' work, and the factor was included in an existing maturity model based on temperature. By using the corrected moisture modification factor, an improved relative strength and maturity relationship was established.

Use of capacitive and GPR techniques for the non-destructive evaluation of cover concrete

Two non-destructive techniques, namely ground penetrating radar (GPR) and a more original approach based on capacitive measurement, have been considered in this research project that focuses on the evaluation of cover concrete moisture content. Following a numerical modeling step for the capacitive technique, the two methods were successfully compared during an experimental campaign conducted in the laboratory against several control test slabs.

Using radar direct wave for concrete condition assessment: Correlation with electrical resistivity

This paper demonstrates that the direct wave of a radar ground-coupled antenna may be used for the nondestructive assessment of the physical condition of concrete, which directly influences the corrosion of the reinforcing bars in the structure. The validity of this method was evaluated by a comparison with the electrical resistivity method, which is frequently used for the evaluation of corrosion probability. Both methods were implemented in the laboratory on 72 concrete samples (25 × 25 × 8 cm 3) with various degrees of saturation and chloride contamination levels. On-site investigations were also carried out on the concrete slab (1080 m 2) of a car-park. The results of the laboratory tests show that the radar direct signal is strongly affected by variations in concrete moisture and chloride contamination level. The tests performed in real conditions confirm the good correlation between radar direct wave attenuation and electrical resistivity and, thus, the aptitude of the radar direct wave to detect concrete conditions leading to reinforcement corrosion.

Optical fiber sensors for monitoring ingress of moisture in structural concrete

Fiber optic-based humidity sensors, fabricated using fiber Bragg gratings coated with moisture sensitive polymer, are employed in detecting and monitoring the movement of moisture through standardized cubes made from samples of different types of structural concrete. Data obtained can give information on the properties of different types of concrete and thus on the migration of dissolved salts, e.g., sodium chloride, which is important in view of their deleterious effects on reinforcement bars within concrete. To undertake the research, two such optical fiber sensors were placed at varying distances from the edge of the cube face to the inner part of the concrete sample and subjected to a constant head of water at a constant temperature. The optical fiber sensors reacted to the ingress of water by detecting the moisture migrating through the sample, indicated by a shift in the Bragg wavelength of the sensor.

Effect of Concrete Moisture on Radar Signal Amplitude

The moisture content of concrete is a critical parameter for most of the physicochemical pathologies, such as steel reinforcement corrosion, alkali-aggregate reaction, and freezing-and-thawing cycles. Therefore, the detection of moisture is important for the diagnosis of concrete structures at early stages of deterioration. The present study was undertaken to assess the effect of the degree of saturation, water-cement ratio (w/c), and volumetric water content on the amplitude variation of direct and reflected radar waves. Four concretes with w/c of 0.5, 0.6, 0.7, and 0.78 were evaluated. Radar measurements were carried out on 72 samples saturated at 0, 20, 40, 60, 80, and 100%. Test results show that an increase in the degree of saturation leads to significant decrease in the amplitude of both direct and reflected waves. This is mainly attributed to the increase in complex permittivity related to the polarization and conduction mechanisms occurring in concrete. Generally, the radar measurements showed good repeatability, which was evaluated using the coefficient of variation, and the statistical dispersion of the direct wave amplitude was lower than that of the reflected wave. For dry and wet concrete, w/c did not appear as an influent parameter regarding the experimental results. A good correlation was found between the amplitude of direct and reflected waves for each degree of saturation. This suggests that the direct and reflected wave amplitudes provide similar information regarding the concrete moisture. Irrespectively of w/c and the depth of reflector, an empirical relationship between signal amplitude of direct wave and volumetric water content was established that can be used to estimate concrete moisture.

Effect of Moisture on the Spatial Uniformity of Cathodic Protection of Steel in Reinforced Concrete

Abstract A numerical model for the cathodic protection (CP) of steel in reinforced concrete was developed. Parameters were set to represent a three-dimensional section of a bridge beam exposed to the atmosphere and coated with a thermally sprayed zinc anode. Both the diffusion of oxygen and the conduction of charge within the concrete were considered explicitly through a two-dimensional finite element model. The diffusivity and conductivity were represented as functions of concrete moisture content. Electrochemical reactions considered at the rebar-concrete interface included the reduction of oxygen, the oxidation of iron, and the evolution of hydrogen in a constant-potential CP circuit. Reaction-kinetic parameters for actively corroding steel (not passivated steel) were used. Reactions at the zinc-concrete interface were not considered explicitly. The effectiveness of protection was found to vary significantly with both concrete moisture content and position on the rebar. For spatially uniform pore satur...

Non-destructive evaluation of concrete moisture by GPR: experimental study and direct modeling

Non-destructive evaluation of concrete moisture by GPR: experimental study and direct modeling

Non-destructive evaluation of concrete moisture by GPR: Experimental study and direct modeling

This paper reports research into the application of Ground Penetrating Radar (GPR) technology to the physical characterization of concrete and gives the details and results of an experimental study on the effect of concrete moisture on radar waves propagating through concrete laboratory slabs. Radar measurements were performed using a commercial radar system with 1.5 GHz ground-coupled antennas. The concrete slabs were conditioned so as to possess different degrees of saturation and a homogeneous moisture distribution. Electrical resistivity measurements were also carried out on each concrete sample to provide complementary information regarding the moisture content of the concrete. Interesting results were found concerning the ability of the radar technique to characterize the moisture state of concrete. Attention was especially focused on the amplitude, velocity and frequency spectrum of the waveforms recorded. In particular, the behavior of the transmitter-receiver direct wave was found to be greatly influenced by the moisture in the concrete. Finally, some experimental results were simulated using a simple dielectric model of heterogeneous mixtures.

Evaluation of Slab Shape Under Controlled Environmental Conditions

During the curing of Portland cement concrete (PCC) pavements, temperature and moisture gradients in the concrete cause pavement slabs to deform from their initial as-placed shape. Daily and seasonal environmental cycling can then cause the slabs to expand and contract horizontally with changes in average temperature and moisture conditions, and curl and warp vertically as temperature and moisture gradients change through the slab depth. This article reports on a study that evaluated slab shape under controlled environmental conditions. In the study, two 3.66 m (12 ft) wide, by 13.72 m (45 ft) long, by 254 mm (10 in) thick concrete pavements were constructed in the Ohio Accelerated Pavement Loading Facility (APLF). Transverse contraction joints were placed at 4.57 m (15 ft) intervals to create three contiguous 4.57 m (15 ft) long slabs in each pavement. Dowel bars were added to the joints in one pavement, and the other pavement was left undoweled. Results demonstrated large upward vertical deformations along the slab edges early in the curing cycle, and these deformations continued to increase throughout the duration of the tests. The slightly smaller vertical movements observed in the doweled pavement were attributed to the presence of the dowel bars. The authors conclude that by restraining joint movement, dowel bars transferred load to adjacent slabs and reduced slab deformation. They note that forces in the dowel bars were smaller than expected from reports on previous investigations, particularly during the curing process. When modeling PCC pavements, loss of support from the base should be considered as dead and live load stresses are generated in cantilevered slabs.

Development of a microwave frequency sensor for the long-term localised moisture monitoring of concrete

Monitoring the moisture levels in concrete over long periods of time is important, as moisture plays a pivotal role in the corrosion process of embedded reinforcement steel in concrete. It is also key in a number of other deterioration processes, and can be used as an indication of changes in the conditions, thus providing a useful early warning system for potential chemical attack. Maintenance needs are thus flagged up before damage is caused. Following an overview of these deterioration processes in concrete, this paper outlines the development of a microwave frequency sensor operating at around 1 GHz and utilising a transmission line either embedded into the concrete at the time of production or encapsulated in a porous medium and inserted into the concrete. It has been amply demonstrated that the method is capable of measuring the moisture content over a wide dynamic range, up to saturation. Trials showed that the encapsulating medium has necessarily to have a microstructure similar to the concrete to be monitored to ensure effective tracking of the concrete moisture content. The sensor appears to fulfil the various stringent conditions necessary for long-term condition monitoring of concrete structures.

Development of a microwave frequency sensor for the long-term localised moisture monitoring of concrete

Monitoring the moisture levels in concrete over long periods of time is important, as moisture plays a pivotal role in the corrosion process of embedded reinforcement steel in concrete. It is also key in a number of other deterioration processes, and can be used as an indication of changes in the conditions, thus providing a useful early warning system for potential chemical attack. Maintenance needs are thus flagged up before damage is caused. Following an overview of these deterioration processes in concrete, this paper outlines the development of a microwave frequency sensor operating at around 1 GHz and utilising a transmission line either embedded into the concrete at the time of production or encapsulated in a porous medium and inserted into the concrete. It has been amply demonstrated that the method is capable of measuring the moisture content over a wide dynamic range, up to saturation. Trials showed that the encapsulating medium has necessarily to have a microstructure similar to the concrete to be monitored to ensure effective tracking of the concrete moisture content. The sensor appears to fulfil the various stringent conditions necessary for long-term condition monitoring of concrete structures.

Influence of concrete relative humidity on the amplitude of Ground-Penetrating radar (GPR) signal

In order to improve radar technique efficiency and to offer innovative applications as non-destructive evaluation tools for civil engineering structures, the authors studied the influence of concrete moisture on GPR sounding. The presence of water in concrete leads to modifications of its electromagnetic properties and thus to specific effects upon waveform characteristics. In particular, the paper focuses on amplitude variations during processes which consume free water (hydration, drying). Radar measurements were carried out on laboratory samples using a commercial ground-coupled antenna of 1.5 GHz central frequency, while relative humidity profiles of the concrete were provided by specific sensors placed at various heights through the concrete samples. An increase in the amplitude of signals propagating through the samples was observed during hydration and drying. Moreover, radargrams recorded during the test also show that the direct wave propagating at the surface of the samples, is ereatly influenced by the evolution of concrete moisture. Concrete hygrometric measurements performed at the same time provide quantitative information on the effect of moisture reduction on radar signals.

ポリプロピレン繊維補強コンクリートの耐火性能

The delaminating and peeling concrete accidents for the tunnels or the bridges are the social problem in Japan. It is desirable to develop the concrete structures with high durability and high serviceability. The polypropylene fiber is believed to be one among the synthetic fiber to prevent the spalling of concrete fragment. As polypropylene fiber is elastic and flexible, it does not pierce the hands or the feet of the workers. It is easy to treat. The wide use of the polypropylene fiber is expected. However, the melting point of the polypropylene fiber is very low. It's about 160-170°C. The resistance to the fire accident of concrete with polypropylene fiber is very important for the safety of the public. In this study, the effect of temperature on the concrete strength and vapor explosion was examined. The air space by the vapored polypropylene fiber sets free vapor pressure of moisture in concrete. It is shown that the low melting point of the polypropylene fiber is not disadvantage at the fire accident on concrete structures.

The utility of a bimolecular expression to describe the heat generation and temperatures in curing Class HP concrete

For several days after concrete is poured, atmospheric conditions influence the hydration reactions of concrete's binder components and so may influence its long-term durability. Accurate concrete temperature and moisture forecasts would help engineers determine an optimal pour time. Some existing curing concrete models include complicated chemistry and/or microstructure development parameterizations or do not allow for mix design changes. A bimolecular heat generation expression that is simple but sufficiently detailed to account for mix design changes was improved for Class HP concrete. Analysis of published calorimetry data and those determined in this study indicated that a second-order formulation adequately describes the heat generation. Class HP binder has an activation energy of ∼35 kJ mol−1. After 72 h, Class HP pastes evolved 250–280 kJ kg−1. A method to account for the effect of retarders on Stage II length and Stage III hydration rates was developed. A curing concrete bridge model with the bimolecular expression predicted concrete temperatures to within 2 °C of observed temperatures and reasonable 72-h hydration fractions (∼0.6).

Energy Balances of Curing Concrete Bridge Decks

Atmospheric conditions for several days after concrete is poured influence the exothermic, temperaturedependent, hydration reactions of concrete’s cementitious (binding) components. Because excessively high concrete temperatures or lack of water eventually can lead to cracking, the initial days are critical to determining the concrete’s long-term durability. Accurate model forecasts of concrete temperatures and moisture would help engineers to determine an optimal time to pour. Such forecasts require adequate environmental predictions. Existing models of curing concrete bridge decks employed by engineers lack realistic boundary conditions and so cannot handle many atmospheric conditions. Atmospheric energy exchange parameterizations typically are intended for use over areas much larger than bridges and so may not be useful as boundary conditions in curingconcrete models. To determine proper boundary conditions for the curing-concrete model discussed here, energy balances of four curing concrete bridge decks were estimated from observations made in the atmosphere as well as inside the concrete. Common meteorological techniques to estimate energy balance terms were used to bound the estimates. Most (70%‐85%) of the concrete heat transfer occurred at the bridge’s top. Sensible, latent, net radiative, and runoff water (sprayed on the top surface) heat fluxes, respectively, contributed 6%‐24%, 15%‐ 58%, 10%‐34%, and 0%‐73% of the top surface heat transfer. Bottom heat transfer was less than 30% of the top surface transfer. Laboratory calorimetry and the energy balance results agree to within 20% that the hydration reactions evolved about 190 kJ kg21 by 24 h after mixing. This agreement validates the exchange coefficients proposed for the heat and moisture balances of these small areas both during periods when the concrete generated heat and later when the concrete was more passive in its environment.

Microwave Sensing of Moisture Content in Concrete Using Open-Ended Rectangular Waveguide

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.