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Chapter 22. Coring, drilling and sampling techniques
No full textAn obvious method to determine the distribution of moisture in a material or structure is to take a sample from the intended position and then determine the moisture content or state of moisture on that sample.
Most of the measuring principles described in PART A are useful for measuring moisture on a sample but the result depends very much on the sampling technique that was used. Here the possibilities, limitations, errors and uncertainties with different sampling techniques are described.
The techniques used to take a number of samples from a series of depths in a structure or a specimen are several. The key issues are three:
a) taking the samples from the intended depths and documenting the actual depths,
b) taking representative samples, if required,
c) avoiding disturbing (drying) the samples as much as possible until the measurement.
The main principles of taking a series of samples are
1. drilling a (cylindrical) core, taking a larger piece of the material or taking a whole specimen and split it into smaller samples from different depths,
2. drilling holes and take the drill dust as samples,
3. using hammer and chisel to take samples from a specific depth
Chapter 26. Monitoring, remote measurement
No full textA special group of applications is “monitoring” where a series of moisture measurements are to be done in the same position at a number of occasions. This kind of application requires certain measures to overcome some special challenges when measurements are done during a longer period of time. Examples of such challenges are
- robustness of equipment for in-situ measurements (against weather exposure, construction work, etc.),
- climatic variations during measurements,
- long-term usage of a delicate measurement setup,
- less possibilities for repeated calibration,
- time lag between moisture variations and measurements,
- equipment/probes disturbing the moisture distribution to be measured,
- remote collection of data from the measurements,
- etc.
In this chapter a number of application examples are described where one or more of these challenges are handled in various ways
Development of interior relative humidity due to self-desiccation in blended cementitious system
No full textIn engineering practise, interior relative humidity (RH) of concrete significantly affects the transport properties and thus the service life of concrete structures. In this paper, the development of RH due to self-desiccation in blended cement pastes was studied from 1 day to 1.5 years. The pore structure and non-evaporable water content at same ages were determined by mercury intrusion porosimetry and thermogravimetric analysis, respectively. The results revealed that interior RH was significantly reduced at the first 105 days’ curing and falls off slightly afterwards, regardless of water to binder ratios and type of blends. Compared to ordinary Portland cement (OPC) paste, the OPC paste blended with slag shows much lower interior RH, whereas the addition of fly ash slightly increases the interior RH. Minor amount of limestone addition i.e., 5% wt. greatly increases the RH in ternary system consisting of OPC, slag and limestone, whilst slightly decreases the RH in OPC paste blended with fly ash. In the presence of blends, high total porosity corresponds to low interior RH. In case of self-desiccation, it is concluded that interior RH is mainly controlled by average pore size in the cement-based materials.Materials and Environmen
Mixture theory applied to chemical reactions and diffusion of different mediums in mature concrete: A hypothetical model, part I and part II
No full textEffect of moisture on tuff stone degradation
No full textTuff stone elements with a large length/width ratio often suffer damage in the form of cracks parallel to the surface and spalling of the outer layer. The response of tuff to moisture might be a reason for this behaviour. This research aimed at verifying if differential dilation between parts with different moisture content (as outer and inner part of partially encased mullion) can lead to damage. The effect of moisture on the degradation of Ettringen and Weibern tuff from the Eifel, Germany, has been investigated. A purpose-made weathering test was carried out to simulate the wetting-drying process. Despite no cracks developed during the test, existing cracks widened up and the flexural tensile strength of both materials decreased. The moisture transport properties their porosity and pore size of the stones were determined. Ettringen tuff has a considerable amount of very fine porosity, resulting in slow moisture transport and significant hygroscopic adsorption. Both tuff stones have an extreme hydric dilation. Environmental X-ray diffraction analyses showed that Ettringen tuff undergoes (reversible) mineralogic changes when subjected to RH cycles, whereas this does not occur for Weibern. The results support the hypothesis that moisture gradients in tuff elements may enhance decay in this stone
Chapter 8. Electrical resistance
No full textThe chapter deals with the methods and devices for the measurement of moisture in different building materials, such as concrete, brick, stone and wood
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