The influence of hydration and swelling properties of gypsum on the preparation of lightweight brick using water supply reservoir sediment

Construction and Building Materials 94 (2015) 691–700

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The influence of hydration and swelling properties of gypsum on the preparation of lightweight brick using water supply reservoir sediment Han-Hsi Liang ⇑, Jie-Long Li Department of Architecture, National United University, No. 1, Lien-Da, Miaoli 36003, Taiwan

h i g h l i g h t s  The material properties of reservoir sediment were analyzed.  A procedure to produce lightweight brick made of reservoir sediment was proposed.  Gypsum content shows a dominating effect on density and compressive strength.  Parameters analysis and material performances of the sintering brick are considered.  The influence of adding gypsum on light weighting is feasible for application.

a r t i c l e

i n f o

Article history: Received 12 February 2015 Received in revised form 17 June 2015 Accepted 14 July 2015 Available online 18 July 2015 Keywords: Reservoir sediment Gypsum Sintering Lightweight brick Partition wall

a b s t r a c t The sediment of the Taiwan Shihmen Reservoir was used as the main material for sintering specimen. This study developed sintering bricks by adding various amounts of gypsum (10–30%), as well as changing the sintering temperature, sintering time, and water content. The Taguchi Orthogonal Array was used for experimental design and the density, shrinkage variation, and the mechanical performance were analyzed, in order to apply lightweight bricks to partition walls. The results showed that the gypsum hydration and swelling properties reduced the dry shrinkage and overall shrinkage of sintered material. The sintered brick had lower density than the control groups (the sintered materials without gypsum content) and red bricks on the market. In application, an appropriate material proportion (20% gypsum) was sintered into bricks, and the brick pier was used for compression test. The test results showed that the sintered bricks could be applied to lightweight partition walls. With a view to reducing the utilization of natural resources, using waste, and reducing cost, it is feasible to sinter reservoir sediment into lightweight brick. Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction The green building material labeling system of Taiwan emphasizes the recycling of green building materials, in an attempt to promote the reuse of recycled materials and reduce waste. Among the approved cases of green building materials from 2005 to 2012, there were 34 recycling green building material labels (8%), 57 high performance green building material labels (13.4%), and 329 healthful and ecological green building material labels (78.6%). It is obvious that recycled building materials should be highly valued. In addition, if the building materials have good performance and can overcome the defects in the performance of traditional building materials, thus improving the superiority of products, the requirement for high performance green building ⇑ Corresponding author. E-mail address: [email protected] (H.-H. Liang). http://dx.doi.org/10.1016/j.conbuildmat.2015.07.111 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.

materials can be satisfied. According to the definition of good materials by Spillman [1], the technology and development of building materials should include: (1) the reutilization of waste and the application of industry residual products; (2) the environmental load of building material production and product performance evaluation. This concept meets the basic characteristics of Taiwan’s green building materials: the content of natural resources as raw material for construction should be reduced as much possible, and the design of products should aim at improving application requirement and sustainable design [2]. Moreover, the products should be recyclable and bring less environmental pollution and waste [3]. The present construction industry’s concepts and technology in response to environmental and ecological variation are in urgent need. The severity of the problem of reservoir sediment in Taiwan is similar to that in California and Japan. Since the Taiwan Shihmen Reservoir began to store water in May 1963, typhoons, rainstorms,

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and other natural and man-made disasters have reduced the 290 mm3 water storage volume by 40% [4], severely impacting the reservoir’s storage function and normal operation. Typhoon Aere and Typhoon Mindulle in 2004 resulted in 27.8 mm3 of sediment deposition according to a survey of the Taiwan Water Resources Office, Ministry of Economic Affairs. The goal is to remove 250 km3 sediment per year, so as to reduce the deposition in the reservoir. However, it is difficult to dispose of such a large amount of sediment. Reusing reservoir sediment can provide an alternative solution, and further utilize Taiwan’s resources. Lightweight aggregate sintering technology has improved gradually, and related studies have developed lightweight aggregate on sediment, fly ash, combustion ash and fresh water sludge [5–8]. The materials have been tested for performance and have also been widely applied. Tang [9] sintered TFT–LCD glass powder and reservoir sediment to obtain a lightweight aggregate meeting the performance requirements. Bhatty and Redit [10] indicated that their specimen powder provided better workability and specimen compactness, because the pore size distribution in the specimen was consistent, and the foaming was uniform. The glassy layer generated from the formed specimen caused high viscosity, so that the specimen foaming was concentrated, and the specimen was lightened. Wei and Lin [5] studied reservoir sediment, of which the main constituent was SiO2 (64.55%), with an Al2O3 content of 16.06%, and a fluxing agent of about 19.39% (fluxing agent: Fe2O3 + K2O + Na2O + CaO), and found that the constituents could be sintered into lightweight aggregate. Chiang [11] sintered a mixture of clay and reservoir sediment, and changed the sintering temperature. The findings showed that the heavy metal leaching from the sintered body was much lower than Taiwan’s standard. The compressive strength was at its maximum when the sintering temperature was 1100 °C. Rahman [12] added rice husk ash to clay and sand to make light bricks. The results of this study showed that the addition of rice husk ash had no effect on the quality of bricks, and the compressive strength of the bricks increased with the addition of more rice husk ash, meeting the test criteria for bricks. Baspinar et al. [13] indicated that in the sintering process of waste containing CaSO4 in large particle sizes and clay in small particle sizes, the fine particles could fill up the gaps, which was favorable for stacking sintered particles. In other words, part of the constituents of the product of gypsum board powder was decomposed at 950–1050 °C. The gypsum content caused swelling in the material research and development [14]. Diatomaceous earth, lime, and gypsum have been mixed to develop lightweight bricks. The findings showed that different gypsum contents changed the strength and density of bricks [15]. In addition, a series of investigations have been carried out using gypsum in preparing the building material of non-fired bricks [16–18]. The physical and mechanical properties were investigated using borogypsum and semi-hydrated borogypsum as cement additives in prepared cements [19]. In recent years, Emrullahoglu Abi [20] has presented a study of the effects of using the borogypsum (CaSO42H2O) of boric acid production waste on brick properties. The brick clay and borogypsum (10 wt%) mixtures obtained a better compressive strength and decreased the bulk density of bricks. Vasconcelos et al. [21] have investigated the design process of the block in order to obtain an innovative solution for partition walls from flue-gas desulfurization gypsum (FGD gypsum), with the aim of reducing construction waste and energy consumption during building’ life-cycle. They concluded that the material and construction technology could provide good mechanical and thermal properties, and fulfill the stability and other requirements for partition walls. The composition of FGD gypsum is similar to natural gypsum and it is easy to obtain high purity. A hydration – re-crystallization process for preparing non-fired bricks involves hot-drying at 180 °C to dehydrate

gypsum into semi-hydrated gypsum (CaSO41/2 H2O) [22]. The industrial application of this method could help to significantly reduce environmental waste and enhance mechanical strength. The bi-hydrated gypsum (CaSO42H2O) could be modified to semi-hydrated gypsum (CaSO41/2H2O) through calcinations process. The water-immersed semi-hydrated gypsum will re-crystallize and turn into new gypsum (CaSO42H2O) crystals with irregular and porous microstructures. Muñoz Velasco et al. [23] have provided a review of research concerning the addition of different types of wastes into fired clay bricks. Four groups, organic, sludge, ashes, and inorganic additives in brick production were discussed along with procedures for making bricks and testing methods. In order to summarize the effects of the addition of certain wastes, they analyzed the material properties of water absorption, compressive strength, and bulk density as well as application characterization. In this research, sintered bricks were evaluated to determine their usefulness with b semi-hydrated gypsum added to reservoir sediment to improve its lightweight property and compare the sintered brick with those bricks with inorganic additives [23]. In view of above, this study applied the hydration and swelling properties of gypsum to the sintering of reservoir sediment, to explore the performance of lightweight bricks in building partition walls. The Taguchi method was used to design the experimental parameters, so as to discuss the volumetric shrinkage, density, water absorption, bending strength, and compressive strength under different parameters, to analyze the performance differences under different parameters. 2. Experimental materials and method This study combined the sediment from Taiwan Shihmen Reservoir with b-gypsum (CaSO41/2H2O), and changed the sintering temperature, sintering time, and water content, to discuss the practicality of its application to partition walls according to its basic and mechanical properties. 2.1. Specimen preparation and sintering procedure The reservoir sediment was collected from the settling tank of Shihmen Reservoir. The sediment was dried under the sun and thoroughly ground, and then dried at 100 °C for 24 h in a dry-oven before making the specimen to minimize the water content in the sediment. Due to the swelling effect of gypsum as it absorbs water and hardens [24,25], the b semi-hydrated gypsum was used in this study. Since the standard mix water content in b semi-hydrated gypsum was about 70%, the solidifying time was 25–35 min, and the water ratio for sediment molding was about 20%. Thus, the water content in the sintering process in this study is 35–45%. The test specimens were prepared by mixing the dried reservoir sediment and b semi-hydrated gypsum of 10%, 20%, and 30% (% by weight). Different proportions of water (35%, 40%, and 45%) were added slowly to the dry powder and mixed it by a mechanical mixer, then poured completely in the mold and pressed with a pressure of 5 MPa. A hydraulic press was used to make bricks with 220 mm (L)  110 mm (W)  55 mm (H) in size. The shaped bricks were removed from the molds after approximately 24 h and were dried in an electrical furnace maintained at 100 °C for 48 h before sintering. In terms of sintering temperature and time, the sintering temperature was increased from room temperature to 105 °C for 30 min to evaporate moisture, and then gradually increased to the sintering temperature at 5 °C/min. The sintering temperature variation range was 900– 1100 °C, the sintering time was 30 min, 1 h, and 2 h, respectively. 2.2. Material characteristics Shihmen Reservoir sediment is classified as fine sands (ML) and silty clay (CL) based on the Unified Soil Classification System. According to the X-ray diffraction (XRD) analysis of the reservoir sediment through #200 sieve (Fig. 1), the sediment contains five crystalline phases: Quartz, Ferrosilite, Illite, Clinochlore and Orthoclase. According to the aforementioned crystalline phases, the reservoir sediment consists of SiO2, Al2O3 and other fluxes (CaO, MgO, Fe2O3, K2O, Na2O). This study uses Inductively Coupled Plasma Atomic Emission Spectrometry (ICP–AES) to analyze the chemical composition of reservoir sediment and gypsum. The sediment contains 58.15% SiO2, 19.69% Al2O3, and 7.47% Fe2O3. Shihmen Reservoir sediment composition and the Toxicity Characteristic Leaching Procedure (TCLP) are shown in Table 1, which shows the composition ratio of sediment in different studies [5,9,11,26]. As seen, the composition of Shihmen Reservoir sediment is

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Fig. 2. Composition diagram of reservoir sediment and Riley’s bloating area. Fig. 1. XRD data from reservoir sediment dried at 105 °C.

Table 2 Experiment parameters and factor levels.

compared with the aggregate bloating area proposed by Riley [27]. The SiO2, Al2O3, and fluxes (CaO, MgO, Fe2O3, K2O, Na2O) content in the sediment are in the mix proportion range of a ceramic material with a good bloating property of Riley. Fig. 2 shows the chemical composition ratios of the reservoir sediment for the study, according to which, the sediment specimen generates a thermoplastic glass-phase at high temperature, namely, the sediment melts at high temperature and has considerable viscosity.

Experiment parameters (Control factor)

A, Gypsum content (%) B, Water content (%) C, Sintering temperature (°C) D, Sintering time (min)

Levels of parameter 1

2

3

10 35 900 30

20 40 1000 60

30 45 1100 120

2.3. Experimental method

Dry shrinkageð% by volumeÞ ¼ ½1  ð1  Sd =100Þ3   100

The performance analysis is aimed at the basic and mechanical properties of the sintering specimen, including volume shrinkage (dry shrinkage and sintering shrinkage), bulk density, water absorption, compressive strength, bending strength, and micro-structural analysis. The better lightweight brick was selected to carry out the brick prism compression test based on the basic and mechanical property analysis. The same five specimens of each sintering material were used for the basic and mechanical property tests. The bulk density and water absorption of the sintered specimens were measured by the Archimedes method according to ASTM C20 (2010) [28]. The mechanical properties of test specimens such as compressive and bending strengths were determined according to ASTM C67 (2009) [29]. The dry shrinkage and overall shrinkage characteristics of each sintering material were analyzed using the Chinese National Standard 2887 (CNS 2887) [30]. For the manufacture of bricks for shrinkage percentage test, a specific dimension of mold (115  25  25 mm3) was utilized. Before sintering the test specimen, the test specimen was removed from the mold and air dried under room temperature for 24 h before being placed in a 100 °C dry-oven for 24 h. The resultant size was then compared with the original size of the test specimen, and the amount of shrinkage is the dry shrinkage percentage. The values for the overall shrinkage percentage include the amount of shrinkage for the test specimen before and after the sintering process. After the sintering process, the test specimen was placed at room temperature for 24 h, and then measurements were performed against the size of the original test specimen, in order to obtain the amount of shrinkage generated. By comparing the data for dry shrinkage and overall shrinkage, we can clearly understand the dry molding properties of the sintered material, as well as changes in volumes generated during the sintering process. The shrinkage change in specimen volume during testing was determined using:

Overall shrinkageð% by volumeÞ ¼ ½1  ð1  Sf =100Þ3   100 In addition, the compression test of the brick prisms was examined using ASTM C1314 (2014) [31]. These testing results were used to evaluate the application characteristics of the lightweight partition walls. This study used the Taguchi method for experimental design [32–34], and used an orthogonal array to divide the samples into 9 groups. The parameters and levels are shown in Table 2. The additional properties were tested for the practical application values of the material. The signal to noise ratio (S/N) was used as index directly. The combination of control factors with the most robust quality under the effect of different parameters and levels was determined, and compared with the control group to look for the best material proportion. The interaction between process parameters is neglected in this study.

3. Results and discussion 3.1. Properties of reservoir sediment and gypsum The particle size of the reservoir sediment and gypsum was analyzed with a laser diffraction particle size analyzer. The results are shown in Fig. 3. As seen, the particle size of the sediment specimens was between 0.3 and 10 lm, and the mean was about 2.5 lm. The particle size of gypsum was 0.2–20 lm and the mean was 4 lm. It is obvious that the gypsum has coarse particles. Fig. 4 shows the differential thermal analysis (DTA) and thermal gravitation analysis (TG) of sediment and gypsum. As seen, the DTA curve of sediment has an obvious endothermic peak at about 102 °C, because the absorbed water on the sediment surface is removed when being heated. The TG curve shows the maximum TG loss ratio in this stage. This phenomenon indicates that the sample

Sd ¼ ðL  Ld Þ=Ld  100 where Sd is linear dry shrinkage; L is the initial length of specimen; Ld is the length of dried specimen

Sf ¼ ðL  Lf Þ=Lf  100 where Sf is linear overall shrinkage; L is the initial length of specimen; Lf is the length of sintered specimen

Table 1 Composition ratio of reservoir sediment in different studies. Content (%)

This study

[5]

[9]

[11]

[26]

TCLP concentration (mg/l)

[11]

SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O

58.15 19.69 7.47 0.72 2.58 1.54 4.09

64.55 16.06 4.95 0.33 0.086 6.85 1.99

53.4 23.8 10.9 1.8 2.5 1.5 5.1

70.14 15.45 5.37 0.64 1.64 1.02 5.24

59.31 19.97 6.53 1.41 2.02 0.01 0.08

Pb Cd Cr Cu Zn

0.07 ± 0.02 <0.008 <0.006 0.03 ± 0.03 1.15 ± 0.25

H.-H. Liang, J.-L. Li / Construction and Building Materials 94 (2015) 691–700

Cumulative percentage (%)

Reservoir sediment cumulative percentage Reservoir sediment volume frequency

Gypsum cumulative percentage Gypsum volume frequency

100

10

90

9

80

8

70

7

60

6

50

5

40

4

30

3

20

2

10

1

0

Volume frequency (%)

694

0

Particle Size (µm) Fig. 3. The particle size distribution of reservoir sediment and gypsum obtained from laser diffraction particle size analyzer.

should be preheated to this temperature in the sintering process to avoid cracking of the sintered material. When the temperature rises to 650 °C, the TG curve show weight loss, the silt soil interlayer water is heated and removed gradually in this process. There is an obvious endothermic reaction according to the DTA curve. The TG and DTA curves have similar performances at about 550 °C in the differential thermal analysis of gypsum. When the gypsum is heated to 950 °C, the curve has obvious differential thermal performance. This endothermic reaction is considered to result from the decomposition of calcium sulfate [13], providing a reasonable explanation for the lightweight effect of sintering bricks. 3.2. Experimental parameter analysis The experimental parameter analysis discussed the basic performance and mechanical performance of sintering brick, including compressive strength, bending strength, water absorption, bulk density, and shrinkage. The preparation of specimens and test procedures are described in the Section 2.1 and 2.3. The experimental mean values are shown in Table 3. The Taguchi method was used for analysis and the factor response graph determined the optimal and objective material proportion. According to the S/N response graph of selected factors in Fig. 5(a), the compressive and bending strength decreases as the gypsum content increases. Medium water content, high sintering temperature (1100 °C), and sintering time (2 h) are advantageous to the strength test for sintered material. The compressive and bending strength are the-larger-the-better quality characteristics in this study. From Fig. 5(b), the lightweight performance is better and the overall shrinkage is lower when the gypsum content is high. The overall shrinkage increases with a higher sintering temperature and longer sintering time. The water absorption increases with a higher gypsum content, and decreases as the sintering temperature and sintering time increase. The maximum bearable load decreases as the gypsum content increases. During the absorption process, the hardening of the b semi-hydrated gypsum fixed the shape of the plastic body of the reservoir sediment, and thereby reduced the shrinkage ratio of the test specimen. Also, due to the fact that calcium sulfate (CaSO4) went through pyrolysis and thus an increase in porosity [20], the ability of the specimen to absorb water also increased, thereby reducing the density and compressive strength.

In addition, adding an excessive amount of gypsum may cause the composition of the original reservoir sediment to fail to satisfy the bloating area for Riley [27], thereby affect the sintering properties of the material. In terms of the experimental parameters, the water content of the specimen greatly affects the difference of the mechanical performance in test results. The level of water content affects the formation of the plastic body for the test specimen. The adequate water content allows the hydration of the b semi-hydrated gypsum, which produces the hardening and shaping of the bi-hydrated gypsum (CaSO42H2O). In the case of an excessive amount of water, due to water loss during the heating process, bricks with lower density and poor mechanical properties are produced. In the event of the sintering temperature is higher, or the sintering time is longer, a greater effect can also be seen in terms of vitrification. The porosity of the material is then reduced. The same phenomenon can also be obtained by increasing the shrinkage rate, or reducing the water absorption rate [35]. The optimal combination of parameters and levels for achieving maximum compressive strength is A1B2C3D3, the optimal combination for minimum bulk density, overall shrinkage and water absorption are A3B3C1D1, A2B3C1D1, and A1B3C3D3, respectively. The S/N ratio analysis of compressive strength, density, water absorption, and overall shrinkage showed that, the optimal material proportion combinations are different. However, considering the overall performance, when the gypsum content is 10%, the experimental results of compressive strength and water absorption are the best, but the overall shrinkage is worse. Therefore, as the strength of a specimen is maintained at a certain demand, the 10% level of gypsum is appropriate. The compressive strength is better when the water content is at the level of 40%, and the compressive strength decreases obviously at the 45% level. The developed material in this study can be applied as a partition material and for strengthening lightweight compartment, while low density of test sample is preferred. However, the strength (=3.92 MPa according to CNS13481 [36]) should be considered, and the sintering time should be short, so as to meet the energy conservation and carbon reduction requirements. Therefore, the S6 material proportion meeting ASTM C330 [37] lightweight aggregate bulk density 50.88 g/cm3 is selected in this study, only the sintering temperature is changed to 1000 °C to discuss the future application. The result will be discussed later.

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H.-H. Liang, J.-L. Li / Construction and Building Materials 94 (2015) 691–700 Reservoir sediment DTA curve Reservoir sediment TG curve

Gypsum DTA curve Gypsum TG curve 100

60

99 50 98

97 40

30

95

TG (%)

DTA ( V)

96

94 20 93

92 10 91

0

90

Fig. 4. DTA and TG curves of reservoir sediment and gypsum.

Table 3 L9 orthogonal array and experimental results. Experiment number

Parameter (Level) A

B

C

D

S1 S2 S3 S4 S5 S6 S7 S8 S9 S50 S80 MS6

10(1) 10(1) 10(1) 20(2) 20(2) 20(2) 30(3) 30(3) 30(3) – – 20(2)

35(1) 40(2) 45(3) 35(1) 40(2) 45(3) 35(1) 40(2) 45(3) 40(2) 40(2) 45(3)

900(1) 1000(2) 1100(3) 1100(3) 1000(2) 900(1) 900(1) 1100(3) 1000(2) 1000(2) 1100(3) 1000(2)

30(1) 60(2) 120(3) 60(2) 120(3) 30(1) 120(3) 30(1) 60(2) 120(3) 30(1) 30(1)

Compressive strength (MPa)

Bending strength (MPa)

Bulk density (g/ cm3)

Overall shrinkage (%)

Water absorption (%)

5 17.39 24.53 13.12 8.21 2.67 3.71 5.77 1.66 26.69 32.4 7.13

3.2 9.52 11.36 8.01 3.57 2.02 2.87 2.57 1.14 13.19 15.29 3.48

1.31 1.35 1.39 1.19 1.01 0.82 1.05 0.99 0.87 1.71 2.44 0.87

31.52 39.81 50.89 26.41 16.78 9.19 15.24 19.62 12.87 52.44 64.58 11.95

20.62 17.21 9.83 14.38 29.41 38.99 21.36 21.19 38.92 5.85 2.32 35.45

S50 , S80 : control groups; MS6: sample of application analysis.

Fig. 6(a) and (b) show the typical scanning electron microscope (SEM), micrographs of the experimental S2 and S3 combination with 10% gypsum by changing the water content, sintering temperature, and sintering time. As seen, fine pores formed inside the samples after sintering. These fine pores are the dominant factor influencing the mechanical strength of samples. According to literature [8], the fire resistance of the clay for bricks is low, and the vitrification phenomenon occurs at about 1100 °C, thus the strength and hardness increase. The SEM micrograph of S3 shows a well-formed and dense matrix material than S2 at a lower sintering temperature. Fig. 6(c) and (d) show the micrographs of S6 and MS6 (sintering temperature increased to 1000 °C) with 20% gypsum. The vitrification and strength of MS6 are better than S6, and MS6 still has lightweight properties of low density and low shrinkage. As a result, it can be concluded that the experimental combination MS6 is suitable to be used as a partition material. 3.3. Sintering brick performance analysis According to the experimental results in Table 3, when the experimental parameter is S3, the gypsum content is 10%, sintering

temperature is 1100 °C, and sintering time is 2 h, the water absorption and compressive strength meet the first quality brick specified in CNS 382 [38]. S2 and S4 water absorption and compressive strength meet the specification of the second quality brick. The density of red bricks on the market of Taiwan is 2.4–2.6 g/cm3. According to this experiment, the density of the test specimen sintered at high temperature (1100 °C) is 0.99–1.39 g/cm3, the density of the test specimen sintered at temperature (1000 °C) is 0.87– 1.35 g/cm3, and the density of the test specimen sintered at low temperature (900 °C) is 0.82–1.31 g/cm3. Table 3 shows the density in this study is 0.82–1.39 g/cm3, and the lightweight effect (based on commercially available red brick density) is apparently increased. In this study provided nine sets of test materials for testing (S10 –S90 : the amount of gypsum is 0%), each experimental parameter corresponds to S1–S9 listed in Table 3. The measured density, dry shrinkage, and overall shrinkage were compared with the original S1–S9 and the results are shown in Fig. 7. Comparison results in Fig. 7 clearly indicate that, adding the b semi-hydrated gypsum reduced the density of the sintering material, dry shrinkage, and overall shrinkage. This phenomenon is obviously favorable to achieve the lightweight effect of sintered material. Results also show that when the gypsum content is =20%, the

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(a)

(b)

Fig. 5. S/N response graphs for the basic and mechanical performances.

(a) S2

(c) S6

(b) S3

(d) MS6

Fig. 6. Scanning electron micrograph images of reservoir sediment bricks with various experiment number: (a) S2; (b) S3; (c) S6; (d) MS6: S6 sintered at 1000 °C.

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H.-H. Liang, J.-L. Li / Construction and Building Materials 94 (2015) 691–700 Dry shrinkage percentage

Overall shrinkage percentage

Density

70

3 S1' ~S9' (control groups): Each experimental parameter corresponds to S1~S9 listed in Table 3 except for gypsum 0%.

2.5

50 2 40 1.5 30

Density (g/cm3)

Shrinkage percentage (%)

60

1 20 0.5

10

0

0 S1'

S1

S2'

S2

S3'

S3

S4'

S4

S5'

S5

S6'

S6

S7'

S7

S8'

S8

S9'

S9

Samples Fig. 7. Changes in dry shrinkage percentage, overall shrinkage percentage, and density for sintered samples.

(a)

(b)

Fig. 8. The property of (a) bulk density and (b) compressive strength in comparison with previous test bricks [23].

overall shrinkage is reduced significantly. The density and overall shrinkage are lower than S50 and S80 of the control group (as shown in Table 3). Fig. 7 also shows the dry shrinkage percentage (%) of test specimens before sintering. It is observed that when gypsum content =20% (S4–S9), the drying shrinkage is reduced obviously,

the overall shrinking percentage (%) before and after sintering has the same result. Compared with control groups (S10 –S90 ), the shrinkage of the 9 test specimens (S1–S9) with gypsum is reduced. It is obvious that the addition of an appropriate amount of gypsum can reduce the volumetric shrinkage of the molding for its

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Table 4 Test data for the five-layer and seven-layer prisms of the MS6 brick, red brick, and ALC block. Materials

Test No.

Length (mm)

Width (mm)

Height (mm)

hp/tp

Correction factor

Compressive strength (MPa)

Corrected strength (MPa)

Average strength (MPa)

MS6 (five-layer) 1 2 3

220 219 219

110 111 110

309 308 310

2.81 2.77 2.82

1.059 1.056 1.059

2.74 2.13 2.58

2.90 2.25 2.73

2.63

MS6 (seven-layer) 1 2 3

223 222 222

221 220 221

435 434 434

1.97 1.97 1.96

0.992 0.992 0.989

1.53 1.66 1.97

1.52 1.65 1.95

1.71

Red brick (five-layer) Red brick (seven-layer) ALC (five-layer) ALC (seven-layer)

6.97 5.23 0.58 0.51

hp/tp: ratio of prism height to least lateral dimension of prism [31].

hydration and hardening process. From Table 3, the compressive and bending strength of test specimens. S2, S3, and S4 have better compressive and bending strength. Considering the compressive and bending strength of material, excess gypsum content (20%) may reduce the strength of material. The compared results of the bulk density and compressive strength related to average value in all test specimens at different experimental parameters were determined in Fig. 8. Based on previous review [23], the test data from the papers is shown in the Fig. 8. Data has been classified two groups (900–950 °C and 1000–1100 °C) according to the sintered temperature of specimens. Similar to most previous researches, the tendencies by linear regression show a decreasing in the bulk density and compressive strength with increasing additive percentage. As can be seen in Fig. 8, the material density of this study is relatively lower compared with those bricks with inorganic additives. This means that a specimen with lower density and an appropriate compressive strength will provide a better lightweight partition material. However, if this material is applied to the compartment material of the lower strength requirement and to strengthening lightweight partition, the sintered material with gypsum is promising.

240 220 200 180

3.4. Sintering brick application analysis Load (kN)

160

The main purpose of this study is to obtain the appropriate sintering parameters, so the sintered bricks can be applied in lightweight partition walls. Based on brick vitrification and the lightweight characteristics, the MS6 brick significantly improves strength while also having properties such as low shrinkage and low density, and also reduces the load when it is applied during the building of the walls. Considering the future applications of lightweight bricks, MS6 are sintered into a unit brick of 220 mm  110 mm  55 mm. Using cement mortar, a five-layer and seven-layer brick prisms were built and kept under room temperature for 28 days. Based on ASTM C1314 [31], compression experiments were performed on the brick prisms. Before the experiment, the brick prisms were maintained at 24 ± 8 °C with a relative humidity of less than 80% for at least 2 days. In order to analyze and compare the mechanical behavior of the lightweight MS6 sintering brick with the red brick and autoclaved lightweight concrete (ALC) block on the market, three sets of brick prism tests were performed on the MS6 brick, red brick, and ALC block when they were all maintained under the same curing conditions for the same time. Table 4 shows the test data for the five-layer and seven-layer MS6 brick prism, including brick prism size, compressive strength, correction factor, corrected strength, and the average value of the compressive strength of the three types of brick prisms

140 120 100 80 60 40 20 0 0

5

10

15

20

25

30

35

Displacement (mm) Fig. 9. The load–displacement curves for various testing brick piers.

after correction according to ASTM C1314. Fig. 9 shows the test data for test groups from the MS6 brick, red brick, and ALC block with the closest average values. Compression tests were performed to the brick prism and the resultant load–displacement diagram are shown in Fig. 9. From Table 4 and the load–displacement diagram, it is observed that the compressive strength of the sintered brick is lower than the red brick, but it still has more strength than the ALC block. Moreover, its failure displacement is not lower than the red brick, meaning that it is applicable to lightweight partition walls. Fig. 10 compares the weights of commercially available red

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density. In the sintering process, specimens will generate pores because the combustion loss of gypsum content and organic substance in the sediment, so that the water absorption is high. The water absorption of S2 and S4 meets the second quality brick of CNS specifications. The water absorption of S3 (9.83%) meets the first quality brick of CNS specifications. When the sintering temperature is 900 °C, the water absorption value is relatively high. When the sintering temperature increases to 1100 °C, the water absorption decreases obviously, meaning that the vitrification of sintered material is affected by the sintering temperature, so that the water absorption is reduced. (4) According to the factor response analysis, as the compressive strength is important, the most significant experimental parameter is gypsum content, followed by water content, sintering temperature, and sintering time. Acknowledgements

Fig. 10. Photographs and weight difference for red brick and various sintered bricks.

The authors are grateful for the support to this research by the Ministry of Science and Technology, Taiwan under Project MOST102-2221-E-239-027. References

brick, 1000 °C sediment brick (MS6), 900 °C sediment brick (S6) and hollow brick (S6). The weight of the lightweight brick is reduced by 50% in this study. Photographs of the bricks after sintering are shown in Fig. 10. When the 900 °C sediment sintering brick (S6) is sintered into hollow brick, the lightweight performance is better. However, the results also indicated that other properties of the material with excellent lightweight effect, such as compressive strength and water absorption, are relatively worse. These properties are not very important in performance for application in partition walls [39]. However, if they are strengthened in future development, the lightweight brick could be more applicable. 4. Conclusion The following conclusions may be drawn from this study: (1) The basic performance of data analysis, material properties tests, and micro-structure in this study shows that if the gypsum is added to the reservoir sediment for sintering, the hydration and swelling of gypsum can reduce the dry shrinkage and overall shrinkage of sintered material. The sintered brick has lower density than the control groups of sintered material without gypsum content and commercially available red brick. The lightweight effect is obvious. The amount of gypsum content affects the characteristics of the sintered material. (2) At a high sintering temperature, the compressive strength of specimen material is also high. This phenomenon is the same as for the sintered material without gypsum. The addition of an appropriate amount of gypsum helps to reduce the shrinkage and obtain lightweight sintered material. The addition of gypsum has a negative impact on the strength and water absorption of sintered material. This study applied lightweight sintered material to partition walls, and proved the proposed method to be feasible for application. (3) When the sintering temperature is the same, the water absorption increases with the gypsum content, meaning the gypsum swelling property reduces the specimen bulk

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