Gypsum phase analysis

Geoenviron mental Eng ineering GSP 241 © ASCE ASCE 2014 2014

. d e v r e s e r s t h g i r l l a ; y l n o e s u l a n o s r e p r o F . E C S A t h g i r y p o C . 7 1 / 2 1 / 9 0 n o t s a o C e n i h s n u S f o y t i s r e v i n U y b g r o . y r a r b i l e c s a m o r f d e d a o l n w o D

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Availability of Density Measuring Methods Estimating Gypsum Hemihydrate Content in Reclaimed Gypsums 1

2

3

4

Shinya Inazumi , Hiroaki Sano , Mikio Yamada and Hsin Ming Shang 1

Akashi National College of Technology, 679-3, Nishioka, Uozumi, Akashi, Hyogo 6748501, Japan; [email protected] 2 Oita National College of Technology, 1666, Maki, Oita, Oita 8700152, Japan; [email protected] 3 Fukui National College of Technology, Geshi, Sabae, Fukui 9168507, Japan; [email protected] 4 Jines Construction Co. Ltd., No.67, Lane 11, Kwang-Fu N.Road, Taipei City, Taiwan; [email protected] ABSTRACT: In order to utilize reclaimed gypsums (gypsum board waste) derived from waste plasterboards as geo-materials, thermal behaviors of the reclaimed gypsums and reagent gypsum are investigated in this paper. As the results, it was found that the dihydrate gypsum is changed into the hemihydrate gypsum under thermal condition of 90°C and the hemihydrate gypsum is changed into anhydrite under that of 120°C with heating of 24 hours. The followings were clarified in this paper. The cement density measuring method was available in order to measure the density of reclaimed gypsums; that density was depended on the drying conditions of the reclaimed gypsums; and the density measuring method was appropriate to estimate the gypsum hemihydrate content on reclaimed gypsums. INTRODUCTION

As more gypsum boards are produced, gypsum board waste from construction sites, and so on, is also increasing every year. According to the Gypsum Board Association of Japan, it is estimated that the total annual waste volume of gypsum boards may reach 2,969,000 tons in 2038 (Gypsum Board Association of Japan 2012): 159,000 tons from new construction sites and 2,810,000 tons from sites being demolished. Under such circumstances, development of new treatment methods not to dispose gypsum board waste (gypsum dihydrate) has become imperative in Japan. As one of such methods, many researchers have studied the applicability of gypsum board waste as foundation material in the civil engineering sector that consumes a high volume of gypsum in each construction project (Kamei and Shuku 2007a and 2007b; Horai et al. 2008; Kamei et al. 2009). The authors have also studied the application of gypsum

Geoenviron mental Eng ineering GSP 241 © ASCE 2014


dihydrate, hemihydrate and anhydrate obtained by crushing, fracturing, separating and burning the gypsum board waste as ground improvement materials. These studies were to actively leverage the water absorption and solidification properties achieved during the transformation of gypsum dihydrate from gypsum hemihydrate: when gypsum dihydrate is burned, it transforms to gypsum hemihydrate, and further transforms to gypsum dihydrate when it comes into contact with water (The Society of Inorganic Materials, Japan 1996). According to past studies, it has been reported, in relation to the application of gypsum board waste as ground improvement material, cement partially replaced with gypsum hemihydrate is likely to be more effective in engineering and economical aspects than the single use of cement. When the application as geo-material as well as ground improvement material is discussed, gypsum hemihydrate is mainly used. Therefore, the gypsum board waste has to be crushed, fractured and separated before the gypsum powder (gypsum dihydrate) is heated to be transformed into gypsum hemihydrate. Existing rotary kilns, newly developed furnaces, and so on, are used as the heating devices for this purpose. While the engineering effectiveness of gypsum recycled from the gypsum board waste has been reported, if such poor-quality “half-burned gypsum” manufactured by some companies with poor technical ability is distributed in the market, it is predicted that the reliability of the studies regarding the effective use of the gypsum recycled from gypsum board waste would be undermined, and it may become a considerable obstacle in the utilization of gypsum recycled from the gypsum board waste, while increasing in volume of the gypsum board waste, and reduction of the available free space in the management-oriented final disposal sites are anticipated. To avoid this situation, development of not only effective use but also quality control technology of the recycled gypsum should be actively developed. This study reviews in detail the thermal behavior of recycled and reagent gypsum from the viewpoint of recycled gypsum utilization as geo-material, and at the same time, discusses the methods to determine the content of the gypsum hemihydrate from the viewpoint of density as a simple quality judgment method of the recycled gypsum. Here, the gypsum gained by crushing, fracturing and separating the gypsum board waste shall be called “gypsum derived from the gypsum boards (recycled gypsum dihydrate)”. BASIC PROPERTIES OF RECYCLED GYPSUM AND REAGENT GYPSUM Thermal behavior of the recycled gypsum and reagent gypsum

A lot of literature describes gypsum dihydrate transforming to gypsum hemihydrate at 130-150°C, and to gypsum anhydrate at 200°C. However, the authors undertook burning for 24 hours at certain temperatures and found the gyp sum formation changes at a much lower temperature than the temperature described in the literature, and reported the formation change cannot be confirmed only by the temperatures.

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This indicates that the recycled gypsum dihydrate needs to be burned at a certain temperature and for a certain length of time so that the recycled gypsum hemihydrate can be used as a main ground improvement material, although different cases apply to the recycled gypsum dihydrate. Also, various burning treatments are required to test the application of the recycled gypsum as a geo-material. Particularly, “Test method for water content of soils (JIS A 1203: 2009)” (Japanese Geotechnical Society 2009a) and “Test method for density of soil particles (JIS A 1202: 2009)” (Japanese Geotechnical Society 2009b) are commonly implemented in all the geo-material tests and these tests require ovendrying at (110±5)°C to gain samples with a specified mass, and it usually takes about 18-24 hours. As mentioned above, the formation of gypsum is significantly influenced by heating temperature and time. Therefore, to use the recycled gypsum as a geo-material, the behavior under heating at 110°C should be identified. Therefore, to review the thermal behavior of gypsum in detail, changes in mass of different masses of gypsum during oven-drying, i.e., changes in the water content, were measured, and the formation change of gypsum was discussed based on the masses calculated considering the chemical Equations of the gypsum. In order to implement the tests, the gypsum board waste was transported to the intermediate treatment site for industrial waste in Oita City and a pile of the boards in a warehouse were crushed, fractured and separated from the original board paper using a crushing machine to obtain recycled gypsum dihydrate. Because there was no facility to thermally dehydrate gypsum dihydrate in such intermediate treatment site in Oita City, the heating unit installed in Isahaya City, Nagasaki Prefecture, was used to obtain gypsum hemihydrate from the above-mentioned recycled gypsum dihydrate. The gypsum sampled in April 2008 and July 2011 was used for this test. Because the recycled gypsum dihydrate forms particles of up to 2.5mm due to the performance of the crusher of the intermediate treatment site, the original particles were sieved and sorted by 2000μm, 850μm and 425μm sizes to use for the test to study the influence of the difference in particle diameter. The method for the heating test was as follows: samples were accurately weighed to 10g each at room temperature, and put into stainless containers of diameter 6 cm and height 3 cm. At that time, the surface of the samples were flattened as much as possible to help with the drying. Here, with 10g of sample, the thickness was about 3 6mm and the bulk density was 0.59g/cm . Next, the containers were placed in a constant-temperature drying oven (DX601 manufactured by Yamato Scientific Co., Ltd., interior capacity: 153L, temperature control range: +5 to 280°C, temperature control accuracy: ±1°C, temperature distribution accuracy: ±10°C (setting temperature at 280°C, exhaust vent 1/3 open)), which controlled the temperature by units of 10°C between 40-160°C, and was heated for 24 hours at specified temperatures. Further, a condition with a temperature setting of 45°C was added as prescribed in the method for quantifying the water content of gypsum included in “Methods for chemical analysis of gypsum” (JIS R 9101:1995)” (Japanese Sandards Association 1995). After heating, the samples were cooled down in a desiccator for 30 minutes until the temperature became room temperature and then the mass was measured. The heating

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tests were implemented on 6 samples at different temperatures and the average value was used, considering variations in the data. This time, because of the performance of the constant-temperature drying oven (temperature distribution accuracy: ±10°C), the influence of the temperature difference due to location in the oven was unavoidable. Taking this into consideration, 6 samples were prepared and placed in the same place in the drying oven, and measured and the temperature in the drying oven was adjusted as needed. The authors believe the reliability of the results was secured in this way. Here, when gypsum dihydrate and gypsum hemihydrate were heated, it is believed that a formation change occurs in a certain temperature range as shown as the chemical equations below (The Society of Inorganic Materials, Japan 1996). (1) From gypsum dihydrate to gypsum hemihydrate 1 3 CaSO4  2 H 2O  CaSO4  H 2O  H 2O 2 2

(1)

(2) From gypsum dihydrate to gypsum anhydrate CaSO4  2 H 2O  CaSO4  2 H 2O

(2)

(3) From gypsum hemihydrate to gypsum anhydrate 1 1 CaSO4  H 2 O  CaSO4  H 2O 2 2

(3)

Based on the molecular masses of above (1)-(3) chemical equations, the mass of gypsum hemihydrate generated from 10g of gypsum dihydrate is calculated as 8.43g. In similar ways, 7.91g of gypsum anhydrate is generated, and 9.38g of gypsum anhydrate is generated from 10g of gypsum hemihydrate. The mass of the recycled gypsum hemihydrate (▲) decreases at 110°C, but does not decrease along with a temperature rise at 120°C and higher. When the above phenomena are reviewed with the formation change of the gypsum related to the masses calculated from the Equations (1)-(3), it is implied that “the recycled gypsum dihydrate transforms to the recycled gypsum hemihydrate through thermal dehydration for 24 hours at 90°C” and “the recycled gypsum hemihydrate transforms to the recycled gypsum anhydrate through the thermal dehydration for 24 hours at 120°C”. The reagents were calcium sulfate dihydrate (reagent manufactured by Kanto Chemical Co., Ltd., Cica 1 Class, content: 98.0% or more) and calcined gypsum (reagent manufactured by Kanto Chemical Co., Ltd., Cica 1 Class, content: 99.0% or more). Hereafter, “calcium sulfate dihydrate” shall be called “reagent gypsum dihydrate” and “calcined gypsum” shall be called “reagent gypsum hemihydrate” corresponding to the representation of the recycled gypsum. For the masses of the samples in the test, by referring to the description in “Test method for water content of soils (JIS A 1203: 2009)” (Japanese Geotechnical Society 2009a), “If the maximum particle diameter of the sample is 2mm, the minimum mass required to measure is 10-30g”, the masses of the samples were



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varied in 4 categories within the range of 5-30g to review the influence of the sample volume on the mass change at heating. The heating test was implemented using 6 samples at each temperature and the average value was used, considering dispersion of the data, which was the same as when the recycled gypsum was tested. Figure 1 shows the relationship between heating temperature and mass of the reagent gypsum dihydrate and gypsum hemihydrate when the masses at the beginning of the test were 5g, 10g, 20g and 30g. Also, the masses calculated from above Equations (1)-(3) are shown as one chain line in the figure. When 5g, 20g and 30g of samples were used, the results were converted to 10g for indication purposes. The figure shows that although the reduction trend of the gypsum mass at heating, i.e., the thermal dehydration trend, depends on the gypsum mass at the beginning of the test, the mass of the reagent gypsum dihydrate (marked as ○△□▽ ) starts sharply decreasing at 80°C (First Phase) when heated, there is no major change at 90100°C, it decreases further at 110°C (Second Phase), and there is no major change at 120°C and more. Here, when inferred from the chemical Equations (1)-(3), the First Phase corresponds to the process in which 10g of gypsum dihydrate produces 8.43g of gypsum hemihydrate and the Second Phase corresponds to the process in which 10g of gypsum dihydrate produces 7.91g of gypsum anhydrate. These results imply the reagent gypsum dihydrate transforms to “gypsum hemihydrate through thermal dehydration for 24 hours at 90°C” and “gypsum anhydrate through thermal dehydration for 24 hours at 120°C”. Then, the mass of the reagent gypsum hemihydrate ( ● ▲ ■ ▼ ) decreases by heating at 40°C. Further, the mass starts decreasing at 110°C, there is no major mass 11 ○△□▽： Reagent dihydrate ●▲■▼： Reagent hemihydrate

）ｇ（

10

m

Weight of gypsum ○● 5ｇ △▲ 10ｇ □■ 20ｇ ▽▼ 30ｇ

9.38g m u s Gypsum hemihydrate →Gypsum anhydrate p 9 y g f Gypsum dihydrate 8.43g o t →Gypsum hemihydrate h 7.91g g 8 i e Gypsum dihydrate→Gypsum anhydrate W 45 ℃:by JIS R 9101

7 20

40

60

(Room temperature)

110 ℃:by JIS A 1203

80 100 120 140 160 180 200 220

Heating temperature T （ ℃）

Fig. 1 Relationship between heating temperature and mass of reagent gypsum dihydrate



change at 120°C and a mass change along with a temperature rise does not occur. The stage at 120°C corresponds to the process in which 10g of gypsum hemihydrate transforms to 9.38g of gypsum anhydrate. Also, this temperature corresponds to the temperature at which gypsum hemihydrate transforms to gypsum anhydrate after reagent gypsum dihydrate transforms to the gypsum hemihydrate, which was shown above. When judged comprehensively from the result of the heating tests of “the recycled gypsum” and “the reagent gypsum” above, it was empirically proved that “gypsum dihydrate transforms to gypsum hemihydrate through thermal dehydration for 24 hours at 90°C” and “gypsum hemihydrate transforms to gypsum anhydrate through thermal dehydration for 24 hours at 120°C.” Density of recycled gypsum and reagent gypsum

The analysis method of gypsum is prescribed in “Methods for chemical analysis of gypsum (JIS R 9101:1995)” (Japanese Sandards Association 1995) and it is different from the method for soil analysis. The reasons are that the state of gypsum varies depending on the volume of the contained bound water, that the properties vary depending on heating temperatures, and that gypsum hemihydrate transforms to gypsum dihydrate to be solidified when water is added, and so on. To understand the basic properties of gypsum as a geo-material, both of “Methods for chemical analysis of gypsum (JIS R 9101:1995)” (Japanese Sandards Association 1995) and “Geo-material test” should be considered. Especially, the items to be focused on are “water”, “pH” and “density”. The “density” is discussed below. When the density of soil particles for geo-material is measured, a pycnometer is typically used as a testing instrument, complying with the “Test method for density of soil particles (JIS A 1202: 2009)” (Japanese Geotechnical Society 2009b). However, this method cannot be applied to gypsum hemihydrate, because this method requires the immersion of the samples in distilled water to determine the volume of the soil particles, but the gypsum hemihydrate is solidified after reacting to water. Therefore, the test was implemented complying with the “density test” prescribed in “Physical testing method for cement (JIS R 5201: 1997) (Japanese Sandards Association 1997)”, in which mineral oil is used instead of water to determine the volume. Under the density test of soil particles, oven drying is implemented at 110°C to determine the mass of the soil particle. However, as mentioned in the gypsum heating test section, because the specified drying temperature for determining the gypsum water content in this method was 45°C, the test was implemented under the following 3 conditions: “natural state”, “dried at 45°C” and “dried at 110°C”. The test procedures were as follows: filled Le Chatelier flasks with mineral oil and placed them in a constant temperature room at a room temperature of 20°C until the temperature of the mineral oil become stable. Then, 3 types of recycled gypsums in 3 conditions were loaded into the Le Chatelier flasks and the air was removed. However, because it was difficult to remove air from gypsum, the test took a long time and it was inefficient to repeat the steps to remove the air and then place the flasks in the water tank until the surface of the mineral oil become flat. Therefore, the authors decided to implement the following procedure: after removing the air, the

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flasks were placed and left in the water tank, the scale of the mineral oil surface was read one day after that, then the flasks were shaken again to remove the air for another day. This procedure was repeated until the mineral oil surface became stable and then the values read at that time were taken as the measured values. A standing still period of 3-4 days was required. Also, although the specified cement volume for the test is 100g (Japanese Sandards Association 1997) under the method complying with the cement density test, the sample volume was adjusted to 85-90g, because the gypsum densities (reagent 3 3 gypsum dihydrate: 2.326g/cm , reagent gypsum hemihydrate: 2.681g/cm ) are 3 generally smaller than that of Portland Cement (3.15g/cm ). ESTIMATION ON CONTENT OF GYPSUM HEMIHYDRATE USING THE DENSITY METHOD

First, the density of gypsum dihydrate is referred to as ρGD (GD: abbreviation of Gypsum Dihydrate), and the density of gypsum hemihydrate is referred to as ρGH (GH: abbreviation of Gypsum Hemihydrate). Assuming that mass (mGD+mGH) and volume (VGD+VGH) of gypsum dihydrate and gypsum hemihydrate are mixed in recycled gypsum derived from a wasted gypsum board, the density of the sample ρ(GD+GH) can be calculated by the following Eq. (4):  GD  GH 



m GD



m GH

V GD



V GH

(4)

Where, m represents mass of gypsum and V represents volume of gypsum and the subscripts represent forms of gypsum. Then, the density of gypsum dihydrate ρGD and the density of gypsum hemihydrate ρGH can be represented as the following Eq. (5) by its definitional equations: V GD

m GD



 GD

, V GH



m GH

(5)

 GH

From Eq. (5) 

 GD

m GD V GD

,  GH



m GH

(6)

V GH

By substituting Eq. (6) for Eq. (4) m GD  GD  GH 



m GD m GD





 GD

m GH m GH  GH



m GH 1 m GD  GD m GH



1



1

(7)

 GH

On the other hand, the content gypsum hemihydrate in the recycled gypsum CGH (abbreviation of Gypsum Hemihydrate Content) can be defined as the following Eq. (8): C GH



m GH m GD



m GH



100

(8)


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The following Eq. (9) can be obtained by transforming Eq. (8): mGD



100

mGH



C GH

(9)

C GH

Finally, Eq. (10), which the authors propose, can be obtained by substituting Eq. (9) for Eq. (7): . d e v r e s e r s t h g i r l l a ; y l n o e s u l a n o s r e p r o F . E C S A t h g i r y p o C . 7 1 / 2 1 / 9 0 n o t s a o C e n i h s n u S f o y t i s r e v i n U y b g r o . y r a r b i l e c s a m o r f d e d a o l n w o D

 GD  GH 



100 100  C GH  GD



C GH

(10)

 GH

In this calculation, first calculate the density of gypsum dihydrate ρGD (reagent 3 gypsum dihydrate: 2.326g/cm ) and the density of gypsum hemihydrate ρGH (reagent 3 gypsum hemihydrate: 2.681g/cm ), next, calculate the density of the recycled gypsum ρ(GD+GH) in which gypsum hemihydrate content CGH is unknown, and then Eq. (10) can be used to calculate the gypsum hemihydrate content CGH and the gypsum dihydrate content (100-CGH). This way, the volumes of gypsum hemihydrate and gypsum dihydrate in the recycled gypsum can be estimated with the simple quality. Although the equations were established assuming the recycled gypsum contains only gypsum dihydrate and gypsum hemihydrate, there might be gypsum anhydrate depending on the heating temperature. However, as mentioned above, type 3 gypsum anhydrate is prone to return to gypsum hemihydrate by absorbing water and very easily and instantly transforms to gypsum hemihydrate on making contact with water or moisture in the atmosphere (The Society of Inorganic Materials, Japan 1996). Therefore, the authors didn't consider gypsum anhydrate to establish the above equations. As the next step, the authors empirically validated the above proposed Eq. (10) with the reagent gypsum. Specifically, to adjust gypsum so that the gypsum hemihydrate content was between 0 and 100%, gypsum dihydrate and gypsum hemihydrate with natural water content were weighed so that the mixture ratio of reagent gypsum dihydrate and hemihydrate became between 10:0 and 0:10, put them into a 500mℓ polyethylene container with a lid, and shook the container for 2 minutes so the content mixed evenly. After shaking, the content of the container (sample) was taken out, accurately weighed to a specified amount from 3 points, and a cement density test was performed. The sample amount was adjusted to 85-90g. Considering dispersion of the data, 3 samples were used for the test. Figure 2 shows the relationship between the set gypsum hemihydrate content and the density. The result (solid line) calculated by the proposed Eq. (10) is also shown in the figure. The figure shows the density values (marked with ○ ) determined by the experiment are nearly equation to the density values calculated using the proposed equations. Therefore, it is believed that estimation of the gypsum hemihydrate content CGH is possible by using the above-proposed Eq. (10). When an approximate expression (broken line in Fig. 1) was calculated using the minimum square method, the following Eq. (11) was obtained:


 

230

2.323  0.003591C GH r  0.999

2.8

3

＊Reagent gypsum hemihydrate ρ =2.681g/cm ＋

2.7

Experimental Eq.: ρ =2.323+0.003591C GH（ r=0.999）

）

3


m c 2.6 / g

（

ρ

2.5

y t i s 2.4 n e D

Proposed Eq. 3

＊Reagent gypsum dihydrate ρ =2.326g/cm ＋

2.3

○

Experimental value

2.2 0

20

40

60

80

100

Set gypsum hemihydrate content C GH=mGH/(mGD+mGH)× 100（ %） Fig. 2 Relationship between set gypsum hemihydrate content and density

(11) As the correlation of the empirical Eq. (11) was very high, again the validity of Eq. (10) was confirmed. The result of the density test of the recycled gypsum made in Oita Prefecture was shown in Chapter 2. To validate the quality of the recycled gypsum as well as the validity of the proposed Eq. (10) and the empirical Eq. (11), the density values determined from the experiment were substituted for Eqs. (10) and (11) to calculate the gypsum hemihydrate content CGH and the gypsum dihydrate content (100-CGH). CONCLUSIONS

The main findings from this study are as follows: (1) If heated for 24 hours, gypsum dihydrate transforms to gypsum hemihydrate at 90°C and to gypsum anhydrate at 120°C. (2) To determine the density of gypsum, the cement density test is effective, and the result depends on how much the sample is dried. (3) The validity of the estimation method of gypsum hemihydrate content using the density was empirically confirmed. Moreover, by calculating the gypsum hemihydrate content from the measurement result of the recycled gypsum density, the effectiveness of the quality control method based on the density was proven.


REFERENCES


Gypsum Board Association of Japan (2012). “Gypsum board handbook .” Horai, H., Kamei, T., Ogawa, Y. and Shibi, T. (2008). “Development of bassanite production system and its geotechnical engineering significance: Recycling of waste plasterboard.” Journal of Japanese Geotechnical Society, 3(2), 133-142. Japanese Geotechnical Society (2009a). “ Japanese Standards and Explanations of Laboratory Tests of Geomaterials.” 1/2, 104-114. Japanese Geotechnical Society (2009b). “ Japanese Standards and Explanations of Laboratory Tests of Geomaterials.” 1/2, 97-103. Japanese Sandards Association (1995). “ Methods for Chemical Analysis of Gypsum.” JIS R 9101:1995, 1-38. Japanese Sandards Association (1997). “ Methods for Chemical Analysis of Gypsum.” JIS R 5201:1997, 1-38. Kamei, T. and Shuku, T. (2007a). “Unconfined compressive strength of cementstabilized soils containing bassanite produced from waste plasterboard.” Journal of Japanese Geotechnical Society, 2(3), 237-244. Kamei, T., Kato, T. and Shuku, T. (2007b). “Effective use for bassanite as soil Improvement materials: Recycling of waste plasterboard.” Journal of Japanese Geotechnical Society, 2(3), 245-252. Kamei, T., Ogawa, Y. and Shibi, T. (2009). “Effect of curing periods on unconfined compressive characteristics of cement-stabilized soils utilizing bassanite: Beneficial use of waste plasterboard.” Journal of Geotechnical Engineering Society, 4(1), 99-105. The Society of Inorganic Materials, Japan (1996). “Semento-Sekkou-Sekkai Handbook .” Gihodo Shuppan.

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