{"id":10039,"date":"2020-07-30T14:57:04","date_gmt":"2020-07-30T12:57:04","guid":{"rendered":"https:\/\/www.radtke-messtechnik.com\/?page_id=10039"},"modified":"2020-07-30T14:57:04","modified_gmt":"2020-07-30T12:57:04","slug":"kiln-method","status":"publish","type":"page","link":"https:\/\/www.radtke-messtechnik.com\/en\/methods-moisture-measurements\/kiln-method\/","title":{"rendered":"Kiln-Method"},"content":{"rendered":"
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What is Kiln Drying?<\/b><\/p>\n

When using the \u201cKiln Drying\u201d method, a sample is dried down to a constant weight by storing it in a warm, more dry environment. The term \u201cKiln Drying\u201d has its origin, in a wider sense, in the drying (curing, preserving) of consumables. Aside from \u201cKiln Drying\u201d there are other terms associated with this method such as \u201coven drying\u201d or \u201coven drying method\u201d. <\/span><\/p>\n

The higher temperature ensures that the (free) water in said sample becomes more mobile (volatile). However, too high temperatures can also lead to unwanted thermal reactions\/changes of the sampled material. the relative humidity inside the oven determines the equilibrium state the sample aspires to reach. The state of equilibrium is regarded as having been reached when over 24 hours of measurement, the weight loss is at less than 1<\/span>\u2030.<\/span><\/p>\n

 <\/p>\n

Dry Screed Samples<\/b><\/p>\n

Graphic 1 <\/b>shows the weight loss of three screed samples, which in turn have been dried at different temperatures.  The samples were first dried at 40<\/span>\u00b0C down to their constant weight, then at 50\u00b0C and so on until a temperature 105\u00b0C was reached. The blue bars represent a cement screed, the red bars an ettringite generating quick-drying screed and the green bars are for a calcium sulphate screed. The weight losses are lower at the lower temperatures up to 50\u00b0C. While the cement screed is not marked by an incredibly special weight loss, both the quick drying screed at 60\u00b0C and the calcium sulphate screed at 70\u00b0C exhibit a rather high weight loss.<\/span><\/p>\n

The weight loss of the quick drying screed can be ascribed to the partial decomposition of the ettringite. The weight loss of the calcium sulphate screed at 70\u00b0C can be ascribed to the first step in the decomposition of plaster into its hemihydrate. The second step of the decomposition of plaster occurs at a higher temperature (between 90 and 105\u00b0C). It is easily recognisable that quick-drying screeds also have a higher weight loss at around 70 to 105\u00b0C than a common cement screed. What the ettringite breaks down to has, thus far, not been determined. However, it is assumed, that  it breaks down into something called \u201c<\/span>Meta-Ettringite<\/b>\u201d, of which a third of the water content of an ettringite crystal is preserved. Therefore the weight loss at 60\u00b0C allows for the calculation of the ettringite in a sample. About 50% of the mass of ettringite is found in its crystalline water. <\/span><\/p>\n

If, like in the graph, around 2 wt-% of weight get lost at 60\u00b0C , it can be assumed, that the sample originally had formed around 6 wt-% ettringite. <\/span><\/p>\n

 <\/p>\n

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Bild 1: Three dry screed samples were dried at different temperatures until reaching their constant weight. Blue: a cement screed, Red: a quick-drying screed with ettringite and Green: a calcium sulphate screed. <\/span><\/figcaption><\/figure>\n

 <\/p>\n

Moist Screed Samples<\/b><\/p>\n

In contrast to the dried samples in Graph 1, moist screed samples were used for the following series of test. These samples are in fact of two cement screeds (blue and red) and one calcium sulphate screed (green). Unlike the dry samples, what stands out is that a considerable weight loss can be identified at the low temperature of 40\u00b0C. At 50\u00b0C only a small amount of weight gets lost. What is striking however, is the weight loss of the calcium sulphate screed sample at 70\u00b0C as well as at 105\u00b0C. <\/span><\/p>\n

 <\/p>\n

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Bild 2: Three moist screed samples were dried at different temperatures until reaching their constant weight. Blue and Red: two cement screeds and green a calcium sulphate screed. <\/span><\/figcaption><\/figure>\n

 <\/p>\n

Changes in the Drying Condition<\/b><\/p>\n

Due to the rising temperatures in an oven, the relative air humidity sinks. Simultaneously, the thermal strain on the samples rises due to the temperature rising (ettringit and calcium sulphate\/plaster break down). Graph 3 shows, how the relative air humidity changes in an oven, when the temperature is continuously raised. The oven represents an open system, which siphons air from the outside, heats it up and then transfers this into the oven. Therefore, the relative air humidity (and also the conditions for the aspired state of equilibrium) is strongly dependant on the ambient conditions outside of the oven. <\/span><\/p>\n

 <\/p>\n

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Bild 3: Changes of the drying conditions depending on the Oven temperature in an open (system) kiln drying oven. <\/figcaption><\/figure>\n<\/div>\n<\/div><\/div><\/div><\/div><\/div>","protected":false},"excerpt":{"rendered":"

What is Kiln Drying? When using the \u201cKiln Drying\u201d method, a sample is dried down to a constant weight by storing it in a warm, more dry environment. The term \u201cKiln Drying\u201d has its origin, in a wider sense, in the drying (curing, preserving) of consumables. Aside from \u201cKiln Drying\u201d there are other terms associated …<\/p>\n","protected":false},"author":319,"featured_media":0,"parent":7760,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"ngg_post_thumbnail":0,"footnotes":""},"class_list":["post-10039","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.radtke-messtechnik.com\/en\/wp-json\/wp\/v2\/pages\/10039","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.radtke-messtechnik.com\/en\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.radtke-messtechnik.com\/en\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.radtke-messtechnik.com\/en\/wp-json\/wp\/v2\/users\/319"}],"replies":[{"embeddable":true,"href":"https:\/\/www.radtke-messtechnik.com\/en\/wp-json\/wp\/v2\/comments?post=10039"}],"version-history":[{"count":2,"href":"https:\/\/www.radtke-messtechnik.com\/en\/wp-json\/wp\/v2\/pages\/10039\/revisions"}],"predecessor-version":[{"id":10041,"href":"https:\/\/www.radtke-messtechnik.com\/en\/wp-json\/wp\/v2\/pages\/10039\/revisions\/10041"}],"up":[{"embeddable":true,"href":"https:\/\/www.radtke-messtechnik.com\/en\/wp-json\/wp\/v2\/pages\/7760"}],"wp:attachment":[{"href":"https:\/\/www.radtke-messtechnik.com\/en\/wp-json\/wp\/v2\/media?parent=10039"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}