Concrete Moisture Research Articles

The Comparison of One-Variable and Two-Variable Polynomial Regression Models to Measure the Cellular Concrete Moisture Using the Time Domain Reflectometry Method

The Comparison of One-Variable and Two-Variable Polynomial Regression Models to Measure the Cellular Concrete Moisture Using the Time Domain Reflectometry Method

Moisture Impact on Static and Dynamic Modulus of Elasticity in Structural Normal-Weight Concretes.

In the case of concrete built into a structure, the static secant modulus of elasticity (Ec,s) is often estimated based on its dynamic value (Ed) measured by the ultrasonic pulse velocity method instead of direct tests carried out on drilled cores. Meanwhile, the prevailing equations applied to estimate Ec,s often overlook the impact of concrete moisture. This study aimed to elucidate the moisture impact across two normal-weight structural concretes differing in compressive strength (51.6 and 71.4 MPa). The impact of moisture content was notably more evident only for the weaker concrete, according to dynamic modulus measurements. In other cases, contrary to the literature reports and expectations, this effect turned out to be insignificant. These observations may be explained by two factors: the relatively dense and homogeneous structure of tested concretes and reduced sensitivity of Ec,s measurements to concrete moisture condition compared to Ed measurements obtained using the ultrasonic method. Additionally, established formulas to estimate Ec,s were verified. The obtained modulus results tested under different moisture conditions of normal-weight concretes were also compared with those of lightweight aggregate concretes of identical volume compositions previously obtained in a separate study.

Discussion of “Nondestructive measurement of the capillary water absorption coefficient and water transport behaviors of porous building materials by using single-sided NMR”

In February 2024, Construction and Building Materials published the paper “Nondestructive measurement of the capillary water absorption coefficient and water transport behaviors of porous building materials by using single-sided NMR”, which claims to measure the capillary absorption of moisture in brick, sandstone, mortar and concrete by means of moisture content profiling with the ‘NMR mouse’, a low-field, single-sided, open-magnet NMR instrument. This critique formulates several serious concerns on the study’s outcomes and conclusions. The excessively large similarity of the capillary absorption behaviour of the four materials is peculiar, since it disregards the differences in their open porosities and pore sizes. The overly large capillary moisture contents are equally abnormal, as they exceed the moisture storage limit of the material’s pore structure. There appears to be an inconsistency between the moisture content profiles and the overall moisture masses. Finally, it is shown that the lengthy time interval necessary for a single NMR pass limits the applicability of the NMR mouse for capillary absorption coefficients of porous building materials.

Methodology for Determining the Correct Ultrasonic Pulse Velocity in Concrete

Quite often, concrete strength parameters must be determined in the shortest possible time. Due to the strong correlation between concrete’s mechanical and acoustic properties, ultrasonic devices can be used for this purpose. However, the ultrasonic pulse velocity (UPV) is influenced by a variety of factors, including the curing and exploitation conditions of the concrete, the presence of reinforcement, and other various physical factors. Ignoring these factors may contribute to the misinterpretation of the measurement data when determining the strength of the concrete. Typically, all these factors are analyzed independently. This publication consolidates the findings obtained from our research efforts and field expertise over the past two decades. It outlines the elaborated UPV measurement methodology based on the integration of a four-argument function: the hydration process phase of the hardened cement paste (or concrete aged three days and older), hardening (curing) condition, concrete moisture level, and ambient temperature. To understand the interactions of the key factors, different ultrasonic devices were used to measure the velocities of longitudinal and surface waves in concrete by applying direct and indirect transmission methods when concrete specimens were tested under different moisture and temperature conditions.

Meso-scale simulation of moisture transport in concrete during wet-dry cycles using 3D RBSM conduit model with variable diffusion model

This paper introduces the 3D RBSM Conduit model, an improved simulation program based on the Rigid Body Spring Model (RBSM), designed to accurately depict the intricate phenomenon of moisture transfer within concrete. This is achieved by incorporating an expanded diffusion model into the simulation framework. The diffusion coefficient is dynamically adjusted at each location and at each time step to accurately represent the precise moisture transfer processes occurring in the concrete. This dynamic adjustment allows the program to efficiently simulate the rate of moisture transport in concrete based on the moisture degree and the dry or wet state of the material. By adapting the diffusion coefficient to the changing conditions in this way, the program achieves simulated moisture transfer rates that align closely with the real-world behavior of moisture in concrete. It offers a dynamic model of the changes in concrete transmission during the switch from drying and wetting conditions. Further, the program exhibits inherent advantages in addressing water transfer problems involving nonlinear boundary conditions and transfer equations. In this study, the program is used to simulate various processes including drying, wetting, local wetting, and combined wet-dry cycles. The results reveal the lag in wet-dry transitions between the interior and exposed surface during the wet-dry conversion process due to retained interior moisture. The simulation captures the moisture variation in the transitional zone.

Experimental study on compressive strength of in situ concrete tested with arc pressure method

The innovative arc pressure testing method (APTM) is adopted in this study to obtain the strength of in situ concrete and reduce damage to the concrete structure. This method is related to the double shear plane of the concrete core. A specific APTM apparatus is used to apply loads in order to obtain the approximate pure shear stress and shear strength of the concrete core. Factors affecting the strength of concrete, such as aggregate type and concrete moisture, were found not to have an impact of the applicability of APTM. The compressive strength range of the tested cube concrete samples is 20–60 MPa. The reliability and repeatability of APTM are superior to in situ testing techniques such as Schmidt hammer (SRH) and pull-off testing methods. The experimental results indicate that APTM is suitable for in situ testing of concrete compressive strength of prefabricated buildings and beam–column joints in dense steel structures. Compared with other testing methods, its accuracy is much higher and the damage to the structure is minimised.

Fire resistance of axially loaded semi-precast composite columns

Recently, semi-precast composite (SPC) columns have been newly developed using steel angles and internal molds. Although the manufacturability, constructability, and seismic performance of SPC columns have been proven to meet design requirements, their structural responses under fire conditions (or fire resistance) have not yet been reasonably examined. Thus, in the present study, an experimental study was conducted for five full-scale SPC columns under standard fire conditions. The test parameters included the joint detail, axial load ratio, thickness of the precast section, and slenderness ratio. The test results show that the fire resistance rating was relatively low due to the high moisture contents and relatively high axial load ratio, and concrete spalling controlled the fire resistance of the columns. The concrete spalling was affected by the concrete moisture contents and permeability, the consequent moisture clog phenomenon, the relatively high axial load ratio, and the longitudinal weak planes between the concrete cover and confined concrete created by longitudinal and transverse bars. Addressing these effects, a finite element analysis (FEA) model was developed for SPC columns using ABAQUS. Although there were some discrepancies between the test and analysis results, the FEA model gave a conservative prediction, which is reasonable for design purpose considering the complexity of nonlinear thermal-stress analysis.

Measurement and modelling of the moisture distribution in early-age concrete in the joint of composite beam and hollow core slab

The building moisture in concrete can damage the surface material if applied too early before the excess moisture has dried out. The composite beam forms an abnormal structure at the joint of the hollow-core slab, in which the thickness of the structural concrete is almost the thickness of the entire slab. For this reason, the joint of the beam and hollow core slab must be taken into account when assessing the adequate drying of concrete structures. The considered composite beams are steel casing beams, which are casted full of concrete. To achieve a composite structure, there are holes in the sides of the casing, through which moisture from the concrete transfers to the surrounding structure. However, the drying of the concrete inside the beam is significantly limited. The level of relative humidity of the concrete inside the beam remains moderately high for a long time, depending on the quality of the concrete and, consequently, the self-desiccation of the concrete. When using concrete with a low water binder ratio, drying occurs at a level of about 85%RH as a result of self-desiccation. In the study, relative humidity in the joint was measured continuously and with instantaneous measurements. The relative humidity in the joint concrete was also monitored after the surface structure layers were installed. In addition, humidity was measured from below the surface material and continued until equilibrium was reached. The structure was simulated as a 3D model and studied using a concrete material model which takes into account the self-desiccation and the thermal dependence of the sorption. A good agreement was found to describe the effect of temperature changes on the relative humidity of concrete that can be observed in continuous measurement. In addition, a suitable prediction of relative humidity below the surface material can be achieved based on modelled relative humidity distribution before the installation of the surface structure.

A Numerical Study of Moisture and Ionic Transport in Unsaturated Concrete by Considering Multi-ions Coupling Effect

A Numerical Study of Moisture and Ionic Transport in Unsaturated Concrete by Considering Multi-ions Coupling Effect

Multi-scale modeling and simulation of bidirectional coupled moisture and heat transfer in concrete

The change of humidity and temperature field of concrete is closely related to its long-term time-varying performance of shrinkage and creep. Therefore, accurate prediction of temperature and humidity in concrete plays an important role in studying the service performance of concrete structures. In the study, the mechanism of coupled moisture and heat (M&H) transfer in concrete is systematically analyzed from three scales: micro-nano scale, mesoscale, and macroscale; meanwhile, a multi-scale theoretical model of coupled M&H transfer in concrete is established. In addition, a novel simulation method of bidirectional coupled of M&H is proposed and the corresponding ABAQUS subroutine is compiled. Based on the existing experiments, the concrete temperature and humidity data for 180 days were further monitored, which verified the feasibility of the proposed method. Finally, the prediction results of M&H transfer are analyzed and compared in three cases: uncoupling, unidirectional coupling, and bidirectional coupling. For the temperature prediction, the early hydration temperature rise is underestimated under the uncoupled model and the unidirectional coupled model that only considering the influence of temperature on humidity, and the prediction error of unidirectional coupled model that only considering the influence of humidity on temperature is relatively small. For the humidity prediction, both uncoupled and unidirectional coupled models underestimate the water consumption, and the closer to the surface of the concrete, the greater the error. Through experiments and numerical simulation analysis, it is suggested that the bidirectional coupled effect should be considered in the analysis of wet-heat field of concrete. This study provides a new way for the modeling and simulation of coupled M&H of concrete, and lays the foundation for the long-term performance research of infrastructure.

Effect of Moisture Condition of Structural Lightweight Concretes on Specified Values of Static and Dynamic Modulus of Elasticity.

The dynamic modulus of elasticity (Ed), specified by ultrasonic pulse velocity measurements, is often used, especially for concrete built into construction, to estimate the static modulus of elasticity (Ec,s). However, the most commonly used Equations for such estimations do not take into account the influence of concrete moisture. The aim of this paper was to establish this influence for two series of structural lightweight aggregate concrete (LWAC) varying in their strength (40.2 and 54.3 MPa) and density (1690 and 1780 kg/m3). The effect of LWAC moisture content turned out to be much more pronounced in the case of dynamic modulus measurements than for static ones. The achieved results indicate that the moisture content of the concrete should be taken into consideration in modulus measurements as well as in Equations estimating Ec,s on the basis of Ed specified by the ultrasonic pulse velocity method. The static modulus of LWACs was lower on average by 11 and 24% in relation to dynamic modulus, respectively when measured in air-dried and water-saturated conditions. The influence of LWAC moisture content on the relationship between specified static and dynamic moduli was not affected by the type of tested lightweight concrete.

Transport properties of moisture and ionic chelators in concrete

The transport properties of moisture and ionic chelators in the concrete affect not only the durability of the concrete, but also the effectiveness of the repair material in repairing cracks in the concrete. The transport of water and ionic chelators in the concrete was investigated by capillary absorption tests and ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometer). It was found that the smaller the radius of the capillary pore within the concrete, the longer it takes to saturate it with water.The different pore sizes of capillaries take different times to reach saturation, which is one of the reasons for the “square root shift phenomenon” of capillary water absorption in concrete. The higher the initial concentration, the easier it is for the ion chelators to be transported inside the concrete within a certain transport depth range. However, after a certain range of transport depth, the initial concentration does not have a significant effect on the transport of the ion chelators. This is not the same as the transport pattern of nonchelated ions. Comparing the transport processes of chelated and non-chelated ions within the concrete, it was found that chelated ions form aggregation zones when transported within the concrete. The analysis suggests that the repair of pores and cracks within the concrete by the chelating agent promotes the creation of aggregation zones. Other factors such as the presence of chelated ions, the transport medium, changes in porosity, and wet and dry cycles can all influence the formation of chelated ion aggregates.

Influence of Moisture in Concrete on the Photothermal Response—A New Approach for a Measurement Method?

Recently, the photothermal determination of the thermophysical properties of concrete under lab conditions was reported. Their values are mainly needed to look at the energy consumption of buildings. Additionally, changes in their values in relation to the initial state might also be a good indicator for material quality or for moisture. The present contribution explains the photothermal method in a more general way to indicate the potential for on-site application. Secondly, a special application case is regarded: the detection of moisture in concrete. Two concrete samples were soaked with water, followed by a drying period, to obtain different levels of water penetration. The water contents were determined by weighing, and the photothermal response was measured. The results show a large influence on the measured temperature transients, which is larger than expected from the original simple model. They clearly provide two points: the photothermal method is suited to detect moisture in concrete, but the magnitude of the actual measurement effect is not yet understood.

Research on behavior mechanism and performance of concrete shrinkage reducing agent

The research on the function and mechanism of shrinkage reducing agent shows that shrinkage reducing agents can greatly reduce the shrinkage rate of concrete without adversely affecting the mechanical properties of concrete. The mechanism of the shrinkage-reducing agent was tested and analyzed from the water evaporation rate of the solution and the surface tension of the solution. The results showed that the addition of the shrinkage reducing agent could significantly reduce the surface tension of the aqueous solution, and had little effect on the evaporation rate of the water on the surface of the aqueous solution; the surface tension test shows that the mechanism of shrinkage reducing agent reducing drying shrinkage is mainly to reduce the surface tension of pore solution; the analysis from the water evaporation rate test shows that shrinkage reducing agent has no significant effect on water evaporation inhibition, and inhibiting concrete moisture evaporation is not the most commonly used shrinkage reducing agent reduction mechanism.

Estimations of the elastic moduli of concrete at different temperatures and humidities by mesomechanics methods

Changes of environmental temperature and humidity affect the elastic modulus of concrete, which makes the vibration-based bridge health monitoring method unreliable. This research studied the effects of environmental temperature and moisture content on the effective elastic modulus of concrete by the mesomechanics methods. In meso level, for the two components of concrete, pores and micro cracks, effects of water in them on the effective elastic modulus at different temperatures were studied separately. Then estimations of the effective elastic moduli at different temperatures and moisture contents were proposed. To verify this, the calculated effective elastic moduli were compared with the experimental values. Finally, the mechanism of the variations of the effective elastic moduli with temperature was revealed. The proposed estimations of the effective elastic modulus can offer a simple and reliable approach to obtain the accurate elastic modulus of concrete based on the environmental temperature and concrete moisture content, which can eliminate their effects in bridge health monitoring.

ON THE USE OF POLARIZATION CAMERAS FOR THE DETERMINATION OF CONCRETE MOISTURE

Abstract. 3D concrete printing (3DCP) promises progress in the automation of the construction industry. The complexity and high quality requirements of 3DCP require automatic and digital control processes and systems that can continuously assess quality at any time and any place. In this paper, the relationship between the surface moisture of concrete and the degree of linear polarization (DolP) of light reflected from the concrete surface is investigated, which could serve as a basis for a camera-based control system. To proof this correlation, extensive practical investigations were carried out in which a mold-cast concrete specimen was illuminated with a white LED spotlight. The reflected light was recorded with a polarization camera, and the weight of the specimen served as a reference for the surface moisture. 14 experimental tests showed a high correlation between mass loss and DolP with a mean correlation coefficient of 0.994 in the last 60 minutes of the 180-minute observation period. The time series show an increasing DolP at the beginning of the observation period, which is probably due to the concrete bleeding and does not correlate with the mass loss. Further investigation into the factors influencing the DolP in the first part of the observation period needs to be carried out, either by testing influencing factors such as concrete bleeding or by finding a reliable method to measure surface moisture to correlate it with the DolP over the entire observation period. Nevertheless, the concept and methodology of data processing has been developed and prototyped, and a correlation has been demonstrated, that can provide a basis for the development of an operational camera-based concrete moisture monitoring system.

Parametric analysis related to dimensioning of tubular steel columns filled with concrete in a fire situation

ABSTRACT For the dimensioning of structural elements in fire situation, simplified equations and parameters are commonly used in analytical equations or numerical models. More complex equations or simplified values can be chosen by the designer for determine materials properties in high temperature in numerical models, however, numerical modeling can be quite sensitive to the variation of some of the physical and mechanical properties. In this paper, the sensitivity of the numerical model in relation to the values according to the level of simplification chosen was evaluated, presenting an analysis in relation to the results found to contribute to the choice of these parameters and presenting the indications found in the literature. In this sense, this work presents a study of sensitivity to the variation of the values of steel and concrete properties, presented in the Eurocode and Brazilian standards, in addition to the moisture content and emissivity of the surface exposed to fire, for the dimensioning, in a fire situation, of steel tube columns, of circular and square section, filled with concrete. The studies were carried out via numerical modeling developed in the software ABAQUS. It was verified that the resulting emissivity values equal to 0.7 or 0.8, recommended in the literature, are conservative, and the choice of either does not bring significant changes in the temperature field obtained for the structural elements under analysis. It was also verified that the concrete moisture content is a relevant aspect for the formation of its temperature field, also affecting, but to a lesser extent, the steel temperature. Regarding the physical and mechanical properties of the materials, this sensitivity study suggests the adoption of the values from the equations presented in Eurocodes, without simplifications, and with the specific heat and thermal conductivity of the concrete, adopted in accordance with the Eurocode 4.

Physical Measurement Analysis in Pre-Utility Covid-19 Isolation Room: A Case Study Universitas Mataram Teaching Hospital

Background: Negative pressure room is recommended for the treatment of COVID-19 patients. Aim this study to describe physical measurement analysis of isolation room Universitas Mataram Teaching Hospital. Methods: Newly developed negative pressure isolation room was physical measure using following instruments: anemometer, moisture meter, hygrometer and pressure gauge. Results: This study showed physical measurement as follow: 1) ACH (air change per hour) 23.3 / hour [minimum: 12+ ACH]; 2) the difference in pressure gradient between the inpatient room and anteroom -30 Pa [minimum -15 Pa]; 3) the mean of air temperature 24.8°C [21-24]; 4) air humidity 58% [maximum 65%] and 5) concrete moisture 22.45%. Conclusion: The COVID-19 isolation room at the Universitas Mataram Teaching Hospital meets the standard criteria.

Fire-Induced Failure of Long-Term Service and Fresh Concrete Beams Subjected to Fire

In engineering, reinforced concrete beams are subjected to natural erosion and the working stress state. However, previous studies regarding structural fire have focused on new concrete beams, and most results are obtained from no-stress-state tests. Hence, research that considers the natural erosion and working stress states of beam members in fire is lacking. In this study, fire experiments were performed to investigate the differences between long-term service concrete beams and new elements under loads. A technique using ARAMIS three-dimensional (3D) optical strain measurement was adopted; it provides increased sample throughput and 3D measurements that indicate the change in strain more intuitively. Results show that the moisture content of concrete determines the spalling degree of concrete under the influence of working stress. With the increase of concrete moisture content, the range of temperature of heated and backfire surface increases and the spalling phenomenon is more obvious, especially when the moisture content exceeds 2.5%. In addition, the long-term service specimens are affected by fire more easily, thereby accelerating the destruction process owing to the degree of carbonation.

Humidity and specimen preparation procedure: influence on compressive strength of concrete blocks

abstract: It is extremely important that the quality control of the concrete block used in structural masonry is conducted based on standard procedures that allow reliable estimation of the properties of these components. This work aims to analyze and evaluate the influence of the concrete block moisture on the result of the compression test. Hollow concrete blocks were prepared and subsequently maintained in different environments for various periods of time and under different conditions of temperature and humidity to determine the influence of the type of drying on the relative humidity of the block at the time of testing and consequently on its compressive strength. As a conclusion, it can be stated that, because it is necessary to use water in the process, the grinding rectification of the faces of the blocks led them to have high humidity, above 70%. If tested in this condition, the results of the compressive strength tests will be lower than that of blocks under usual environmental conditions. No differences were found in the average block strength when they were kept dry in the controlled environment of the laboratory during periods of 24 or 48 h. After grinding, it is not necessary to dry the blocks inside an oven at 40ºC before the tests; simply leaving them at a usual room temperature of 23ºC and humidity of 40 ± 5% for 24h is sufficient. The attempt to accelerate drying in an oven at 100ºC is not adequate because this leads to an increase in the compressive strength. From the results, it was possible to determine expressions to correlate the compressive strength as a function of the moisture of the block at the time of the test. The best-fit expressions are distinct for each block type, but the formulations are consistent in indicating a considerable difference in resistance as a function of moisture.