What do you mean by "hygroscopic water content"?

What do you mean by "hygroscopic water content"?

By reference to scientific paper Paresh H. Shah1 and DN Singh, Member ASTM Antrentunali, Journal of ASTM International, February 2006, Vol. 3, No. A. You can find the solution and the answer to your question, here's a summary of his research   

 ((ABSTRACT: Hygroscopic moisture content of the soil is usually determined by an air-drying method and has been related with the surface area and cation exchange capacity of the soil, by many researchers. However, as relative humidity influences the overall soil-water interaction, quantification of its impact on hygroscopic moisture content of the soil becomes mandatory. Incidentally, it has been noted that no standard methodology, which specifies determination of the soil hygroscopic moisture content exists in the literature. With this in view, laboratory investigations were carried out on soils, with entirely different properties, and by exposing them to different relative humidity and storage time. Based on the results, “optimal hygroscopic moisture content” of the soil has been defined and the methodology for its measurement has been proposed. Further, attempts were made to correlate hygroscopic moisture content of the soil with its surface area, cation exchange capacity, liquid limit, swelling potential, and electrical properties conductivity and dielectric constant. Such correlations will be of the utmost help in predicting these properties of the soil by knowing its hygroscopic moisture content. KEYWORDS: soils, hygroscopic moisture content, relative humidity, laboratory investigations, correlations ))   

*Attachment

A full scientific paper  

Article Methodology for Determination of Hygroscopic Moisture Content of Soils

Dear Saad Alasfoor, thank you for the answer and the paper. However, it still remains unclear for me – what was the reason of choosing 105°C temperature for drying soil samples. Moreover, I do not understand why ISO gives to options – 105°C and 50°C.  

It is good to stick with saturated-unsaturated water flow theory and moisture characteristic curves. therefore, soil water potential theory help better understand volumetric and /or gravimetric water content of a soil at a specific soil matric potential level. For example, soil moistur content at 31 bar negative pressure is known as the beginning of the range of soil hydgroscobic water content, which is never a piece of plant available water, but a molecular level water bouned strongly by soil particles. Further, most probably after 31 bar negative pressure, one will not have a chance to get a positive slope of specific water content (delTHETA/delMATRIC POTENTİAL) for any specific soil type. Hoever, heat and water content relations of a soil vary depending on the duration and level of heating, as a result of which soil water holding capacity characteristics change. Finally, hygroscobic water content should be less than residual water content for a soil.

The previous responders ignore my earlier question. The reason I asked it is that the concept of "hygroscopic water content" is not commonly used in the literature on soils. A few authors, like David Robinson, used it in some of their papers, but otherwise, the term is rarely used by soil physicists. It seems to me that unless you define precisely what is meant by the term, little progress can be made in its measurement. If you define "hygroscopic water content" as the water content of an air-dried soil, than you also have a possible protocole for measuring it. The question than becomes whether you can speed up the process of reaching an equilibrium with a given atmosphere (at a certain relative humidity) by first drying the soil in an oven at a set temperature. This would have to be tested. To my knowledge, the test has yet to be carried out.

Гигроскопическая влажность – влажность почвы, достаточно долго выдержанной в атмосфере лаборатории. В диапазоне влажностей воздуха от 20 до 60-80 % влажность почвы слабо зависит от этой влажности, поэтому в российском почвоведении гигроскопическую влажность считают почвенно-гидрологической константой (Шеин Е.В. Курс физики почв. МГУ, 2005. 432 с.).

Более точной константой является максимальная гигроскопическая влажность – влажность почвы после долгого ее выдерживания в атмосфере с влажностью 98 %. Необходимое время выдержки определяют путем периодического взвешивания образца до тех пор, пока масса не перестанет возрастать.

Затем влажность определяют, выдерживая образец 6 часов при температуре 105 С. Температура выбирается выше 100 С, чтобы процесс испарения проходил быстрее. Более высокая температура может приводить к разложению органического вещества почвы и искажать результаты измерения.

Hi

The answer is in the question. This is of the thermostat-weight method . The temperature only of 105 is used . From 110 occurs irreversible dehydration of secondary minerals.

Sorry into English, may be on Russian answer question?

Best regards.

Amount of moisture in soil (weight) = Weight of fresh soil sample - Weight of dry soil sample (dry at full sun light for 12 hours or at 100 °C for 1 hour)

Dear  Prof. Baveye,

Excuse me please for the late reply. In this question by the term “soil hygroscopic water” I meant the water adsorbed on the soil particles. Quantitatively – content of hygroscopic water equals air-dry-mass minus oven-dried mass. The point, which is unclear for me is the temperature… In most of the standards – such as ISO 11465:1993 ( Soil quality — Determination of dry matter and water content on a mass basis — Gravimetric method)  there are almost the same recommendations – to dry the soil sample at 105°C, BUT FOR SOIL SAMPLES WITH A HIGH ORGANIC MATTER CONTENT > 10%, for example peaty soils, the method of drying should be adapted. In this case, the sample should be dried to constant mass at 50 °C. What is the reason of such a huge decrease of drying temperature? Is the quality of the soil samples oven-dried at 50 °C and 105°C the same? Are the results comparable?

Best regards,

Tymur

Dear  Prof. Bobrov, Dr. Moiseev, Dr. Akis and Dr. Khan,

Thank you for your useful comments and suggestions! However, there are still some issues. I tried to highlight them in my previous answer.

Best regards,

Tymur

Hi!

This is of the thermostat-weight method . The temperature only of 105 is used.

Don't mix different methods. The normative documents look (in the past "ГОСТ-...").

Bye.

Tymur, can you at least give some characteristics of the soils you are talking about - and as Baveye mentioned, your definition of hygroscopic water is still vague. For most soils, 105 is the standard used. The standards you mentioned clearly stated that if you have highly organic soils, then 50 degrees may be used (presumably because of irreversible changes that may occur in the organic component. Thus, if you have a normal soil with organic matter less than 10%, then 105 degrees should be appropriate. Hope this helps

Dear Tymur Bedernichek, following link may be quite useful to you. Thanks

https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=10&cad=rja&uact=8&ved=0CFQQFjAJahUKEwiNzMjYlaPHAhWOxY4KHXNIAYo&url=http%3A%2F%2Fscialert.net%2Ffulltext%2F%3Fdoi%3Djas.2008.1732.1737%26org%3D11&ei=lgnLVY2pNI6LuwTzkIXQCA&usg=AFQjCNHE-AVWsXMsaLe8rIZepz3kvU2yEg&sig2=wUAcwwxmiNw48Itai3EhtA&bvm=bv.99804247,d.c2E