Measurement of moisture in concrete and masonry with special reference to neutron scattering techniques

E.H. Waters
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引用次数: 13

Abstract

Failures of surfacing materials on concrete floors (likewise on concrete or masonry walls) are usually due to dampness. A rapid and reliable method of determining the dryness of such structures could prevent this type of failure.

Present methods depend on conditions in the atmosphere adjacent to the floor etc. (indirect methods) or on changes in the properties of the concrete (direct methods). Indirect methods can be satisfactory if their criteria of dryness are soundly based. A well based procedure is the quasi-equilibrium method of British Standard C.P. 203, which has a long history of successful field use. Recently methods using the rate of emission of moisture have appeared. These may also be satisfactory but the bases of their criteria are not known.

Gravimetric methods are unsatisfactory because of the difficulty of obtaining a representative sample. Electrical conductivity has been used but is sensitive to factors other than moisture content. Dielectric properties vary with moisture content and have given reasonable results under laboratory conditions. Further work is needed to apply this method to field conditions. Micro-wave absorption has been used to determine moisture in walls but at present cannot be used for floor slabs on grade. The results vary with the nature of the material.

Neutron scattering has been widely used to determine moisture in soils and has been advocated for other materials including concrete. The method is direct and non-destructive and requires access to only one side of the speciment. Results have been claimed to depend solely on the water content, i.e., to be independent of the nature and density of the material. Experiments with concrete and timber have shown that this is not correct. Instrument response rises with density to such an extent that the same instrument response was obtained on a foamed concrete and a dense concrete with water contents in the ratio of 2:1. The composition of the sample also affects the response. This method therefore cannot safely be used with a common calibration curve for all substances.

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混凝土和砌体含水率的测量,特别参考中子散射技术
混凝土地板(混凝土或砖石墙也一样)表面材料的失效通常是由于受潮造成的。一种快速可靠的方法来确定这种结构的干燥程度,可以防止这种类型的故障。目前的方法取决于地面附近的大气条件等(间接方法)或混凝土性质的变化(直接方法)。如果间接方法的干燥标准有充分的依据,则间接方法可以令人满意。一种基于井的方法是英国标准cp . 203的准平衡法,该方法在现场应用中具有悠久的成功历史。最近出现了利用水分释放率的方法。这些也可能令人满意,但其标准的依据尚不清楚。重量法不能令人满意,因为难以获得有代表性的样品。电导率已被使用,但对水分含量以外的因素很敏感。介电性能随含水率的变化而变化,并在实验室条件下给出了合理的结果。将这种方法应用于现场条件还需要进一步的工作。微波吸收已被用于测定墙体的湿度,但目前还不能用于测定等级的楼板。结果因材料的性质而异。中子散射已被广泛用于测定土壤中的水分,并已被提倡用于包括混凝土在内的其他材料。该方法是直接和非破坏性的,只需要访问一侧的标本。结果被声称仅仅依赖于水的含量,也就是说,独立于材料的性质和密度。混凝土和木材的实验表明,这是不正确的。仪器响应随着密度的增加而增加,以至于在泡沫混凝土和含水量为2:1的致密混凝土上获得相同的仪器响应。样品的组成也会影响响应。因此,该方法不能安全地与所有物质的通用校准曲线一起使用。
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Author index Subject index Measurement of moisture in concrete and masonry with special reference to neutron scattering techniques Containment and siting of high power reactors Die friedliche anwendung von nuklearen explosionen: by Dr. Theo Ginsburg. Thiemig Taschenbuch Band 21. Verlag Karl Thiemig KG, München (1965), 240 pages. Price: DM 14.80
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