Superabsorbent polymers are cross-linked hydrogel networks possessing a large fluid uptake capaci... more Superabsorbent polymers are cross-linked hydrogel networks possessing a large fluid uptake capacity. When added to a cementitious mix they absorb part of the mixing water. During cement hydration, they provide this absorbed water as internal curing water to the cementitious matrix, which allows to maintain the internal relative humidity. In the ideal case, this permits to compensate for self-desiccation and to mitigate autogenous shrinkage. The kinetics of water release are hereby of utmost importance, and are studied by Nuclear Magnetic Resonance (NMR). Free water and SAP-entrained water could be clearly distinguished in the T2 relaxation spectra. The measured free and entrained water in function of the degree of hydration corresponded well to the Powers and Brownyard model, showing, however, a more S-shaped curve. Through NMR measurements a distinction could be made between SAPs that gradually released their stored water, maintaining effectively the internal relative humidity, and...
Journal of Thermal Envelope and Building Science, 2004
The precision of methods used for the determination of hygric properties of porous building mater... more The precision of methods used for the determination of hygric properties of porous building materials was investigated. The study was performed in the framework of the EU-initiated HAMSTAD-project. Six laboratories measured the selected hygric properties of three porous building materials. While the most measured properties show acceptable agreement, yet, it was found that some of the existing standards or commonly accepted measurement methods need improvement. Most striking were large variations in the results of the vapour transmission tests performed in accordance to the existing European Standard.
Journal of Thermal Envelope and Building Science, 2004
Several advanced non-destructive techniques are available to measure the evolution of content pro... more Several advanced non-destructive techniques are available to measure the evolution of content profiles with time, allowing the analysis of unsaturated flow and the determination of the moisture diffusivity of porous building materials. The reliability of six different techniques is investigated: the NMR-technique, the MRItechnique, the γ-ray attenuation technique, the capacitance method, the X-ray projection method and the TDR-technique. All of them were applied to measure the moisture content evolution during free uptake experiments on two building materials. Considering the limitations of some of the techniques, a good overall agreement is obtained. The work presented is an outcome of the EU-initiated HAMSTAD-project.
Salts are widely recognized as a major cause of the loss of many historical objects, such as maso... more Salts are widely recognized as a major cause of the loss of many historical objects, such as masonry, statues, and other artwork. To obtain information about the mechanisms underlying these damage processes we have studied the moisture and ion transport within two types of fired-clay brick: a modern type produced in the Netherlands and an old fired-clay brick from the city of Venice in Italy The time evolution of NaCl saturated samples of fired-clay brick during drying was measured using Nuclear Magnetic Resonance. The moisture content and amount of dissolved Na ions were measured quantitatively as a function of position. The NaCl concentration profiles obtained from these data reflect the competition between advection to the surface and redistribution by diffusion. For both types of brick, the fast drying Dutch fired-clay brick and the slow drying Venice fired-clay brick, an accumulation of NaCl at the drying surface is observed in the experiments.
Journal of Thermal Envelope and Building Science, 2004
Several advanced non-destructive techniques are available to measure the evolution of content pro... more Several advanced non-destructive techniques are available to measure the evolution of content profiles with time, allowing the analysis of unsaturated flow and the determination of the moisture diffusivity of porous building materials. The reliability of six different techniques is investigated: the NMR-technique, the MRItechnique, the γ-ray attenuation technique, the capacitance method, the X-ray projection method and the TDR-technique. All of them were applied to measure the moisture content evolution during free uptake experiments on two building materials. Considering the limitations of some of the techniques, a good overall agreement is obtained. The work presented is an outcome of the EU-initiated HAMSTAD-project.
Journal of Thermal Envelope and Building Science, 2004
The Boltzmann transformation method is used to determine the liquid water diffusivity from moistu... more The Boltzmann transformation method is used to determine the liquid water diffusivity from moisture content profiles as measured in a capillary water absorption experiment. An inter-laboratory comparison for analyzing the reliability of the determination method showed that the inaccuracy in the liquid water diffusivity is caused by scatter in the transformed data and by uncertainty in the boundary conditions at the intake surface and ahead of the steep moisture front. A methodology is proposed based on (1) the evaluation of the validity of the diffusion approach, (2) a simplified handling of the boundary conditions, (3) smoothing of the scattered data and (4) the evaluation of the quality of the determined liquid water diffusivity. For HAM (Heat-Air-Moisture transport) calculations values of the liquid water diffusivity for moisture contents higher than the capillary moisture content are disregarded. The liquid water diffusivity can be described by an exponential function limited at...
A recent advance in construction technology is the use of self-healing cementitious materials con... more A recent advance in construction technology is the use of self-healing cementitious materials containing synthetic microfibers and superabsorbent polymers. By stimulating autogenous healing by means of superabsorbent polymers, cracks are closed and this will cause an increase in durability and service life. However, this improved healing capacity has not been quantified yet in terms of increased further hydration and volume of healing products. This is needed to model the material and to stimulate the practical application in constructions. This paper provides quantitative data, obtained by an NMR study. Addition of 1 m% of selected superabsorbent polymer versus cement to a cementitious material, stimulated further hydration with nearly 40% in comparison with a traditional cementitious material, if 1 h water contact per day was allowed. At 90% relative humidity, no healing was observed in reference samples. While the further hydration around a crack in specimens with superabsorbent ...
The mathematical formulation of mass transfer in drying processes is often based on the diffusion... more The mathematical formulation of mass transfer in drying processes is often based on the diffusion equation. In principle the diffusion coefficient as a function of moisture content has to be determined experimentally. The most direct approach is to derive the diffusion coefficient from experimental moisture concentration profiles in the material during drying. In this work, the diffusion coefficient determined in
Superabsorbent polymers are cross-linked hydrogel networks possessing a large fluid uptake capaci... more Superabsorbent polymers are cross-linked hydrogel networks possessing a large fluid uptake capacity. When added to a cementitious mix they absorb part of the mixing water. During cement hydration, they provide this absorbed water as internal curing water to the cementitious matrix, which allows to maintain the internal relative humidity. In the ideal case, this permits to compensate for self-desiccation and to mitigate autogenous shrinkage. The kinetics of water release are hereby of utmost importance, and are studied by Nuclear Magnetic Resonance (NMR). Free water and SAP-entrained water could be clearly distinguished in the T2 relaxation spectra. The measured free and entrained water in function of the degree of hydration corresponded well to the Powers and Brownyard model, showing, however, a more S-shaped curve. Through NMR measurements a distinction could be made between SAPs that gradually released their stored water, maintaining effectively the internal relative humidity, and...
Journal of Thermal Envelope and Building Science, 2004
The precision of methods used for the determination of hygric properties of porous building mater... more The precision of methods used for the determination of hygric properties of porous building materials was investigated. The study was performed in the framework of the EU-initiated HAMSTAD-project. Six laboratories measured the selected hygric properties of three porous building materials. While the most measured properties show acceptable agreement, yet, it was found that some of the existing standards or commonly accepted measurement methods need improvement. Most striking were large variations in the results of the vapour transmission tests performed in accordance to the existing European Standard.
Journal of Thermal Envelope and Building Science, 2004
Several advanced non-destructive techniques are available to measure the evolution of content pro... more Several advanced non-destructive techniques are available to measure the evolution of content profiles with time, allowing the analysis of unsaturated flow and the determination of the moisture diffusivity of porous building materials. The reliability of six different techniques is investigated: the NMR-technique, the MRItechnique, the γ-ray attenuation technique, the capacitance method, the X-ray projection method and the TDR-technique. All of them were applied to measure the moisture content evolution during free uptake experiments on two building materials. Considering the limitations of some of the techniques, a good overall agreement is obtained. The work presented is an outcome of the EU-initiated HAMSTAD-project.
Salts are widely recognized as a major cause of the loss of many historical objects, such as maso... more Salts are widely recognized as a major cause of the loss of many historical objects, such as masonry, statues, and other artwork. To obtain information about the mechanisms underlying these damage processes we have studied the moisture and ion transport within two types of fired-clay brick: a modern type produced in the Netherlands and an old fired-clay brick from the city of Venice in Italy The time evolution of NaCl saturated samples of fired-clay brick during drying was measured using Nuclear Magnetic Resonance. The moisture content and amount of dissolved Na ions were measured quantitatively as a function of position. The NaCl concentration profiles obtained from these data reflect the competition between advection to the surface and redistribution by diffusion. For both types of brick, the fast drying Dutch fired-clay brick and the slow drying Venice fired-clay brick, an accumulation of NaCl at the drying surface is observed in the experiments.
Journal of Thermal Envelope and Building Science, 2004
Several advanced non-destructive techniques are available to measure the evolution of content pro... more Several advanced non-destructive techniques are available to measure the evolution of content profiles with time, allowing the analysis of unsaturated flow and the determination of the moisture diffusivity of porous building materials. The reliability of six different techniques is investigated: the NMR-technique, the MRItechnique, the γ-ray attenuation technique, the capacitance method, the X-ray projection method and the TDR-technique. All of them were applied to measure the moisture content evolution during free uptake experiments on two building materials. Considering the limitations of some of the techniques, a good overall agreement is obtained. The work presented is an outcome of the EU-initiated HAMSTAD-project.
Journal of Thermal Envelope and Building Science, 2004
The Boltzmann transformation method is used to determine the liquid water diffusivity from moistu... more The Boltzmann transformation method is used to determine the liquid water diffusivity from moisture content profiles as measured in a capillary water absorption experiment. An inter-laboratory comparison for analyzing the reliability of the determination method showed that the inaccuracy in the liquid water diffusivity is caused by scatter in the transformed data and by uncertainty in the boundary conditions at the intake surface and ahead of the steep moisture front. A methodology is proposed based on (1) the evaluation of the validity of the diffusion approach, (2) a simplified handling of the boundary conditions, (3) smoothing of the scattered data and (4) the evaluation of the quality of the determined liquid water diffusivity. For HAM (Heat-Air-Moisture transport) calculations values of the liquid water diffusivity for moisture contents higher than the capillary moisture content are disregarded. The liquid water diffusivity can be described by an exponential function limited at...
A recent advance in construction technology is the use of self-healing cementitious materials con... more A recent advance in construction technology is the use of self-healing cementitious materials containing synthetic microfibers and superabsorbent polymers. By stimulating autogenous healing by means of superabsorbent polymers, cracks are closed and this will cause an increase in durability and service life. However, this improved healing capacity has not been quantified yet in terms of increased further hydration and volume of healing products. This is needed to model the material and to stimulate the practical application in constructions. This paper provides quantitative data, obtained by an NMR study. Addition of 1 m% of selected superabsorbent polymer versus cement to a cementitious material, stimulated further hydration with nearly 40% in comparison with a traditional cementitious material, if 1 h water contact per day was allowed. At 90% relative humidity, no healing was observed in reference samples. While the further hydration around a crack in specimens with superabsorbent ...
The mathematical formulation of mass transfer in drying processes is often based on the diffusion... more The mathematical formulation of mass transfer in drying processes is often based on the diffusion equation. In principle the diffusion coefficient as a function of moisture content has to be determined experimentally. The most direct approach is to derive the diffusion coefficient from experimental moisture concentration profiles in the material during drying. In this work, the diffusion coefficient determined in
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