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Mechanical properties of incineration bottom ash: the influence of composite species

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(1)Mechanical properties of incineration bottom ash: the influence of composite species Meng-Chia Wenga; Chiou-Liang Lina,*; Chun-I Hoa a. Department of Civil and Environmental Engineering, National University of Kaohsiung, Kaohsiung, 811, Taiwan, ROC. *. Corresponding author: Tel: +886-7-5919722; Fax: +886-7-5919376 E-mail address: cllin0407@nuk.edu.tw (C. L. Lin). ABSTRACT The mechanical properties, including strength, deformational behavior, and wetting softening phenomena of municipal solid waste incinerator (MSWI) bottom ash are one of the major concerns for reuse applications. However, owing to the complex constituents of municipal solid waste, the properties of MSWI bottom ash are often highly variable. A series of artificial specimens with controlled chemical components were tested in this study. The test results show that the artificial bottom ash possesses the following mechanical characteristics: (1) For the strength, the frictional angles of the bottom ash under dry and saturated conditions vary from 34.8o to 51.1o and 26.0o to 37.2o, respectively; (2) For the deformation, the shear stiffness increases with the normal stress arises and degrades upon increased shearing; (3) Significant wetting degradation of the strength and stiffness were observed. The multi-variable regression analysis was conducted to evaluate the associated influence of the chemical components on the strength. Among the evaluated components, Fe2O3 and Al2O3 are key factors; an increase in either results in higher strength at both dry and saturated conditions. The results were used to propose empirical relationships for dry and sat, expressed in terms of Fe2O3 and Al2O3. 26.

(2) Accordingly, a strength classification chart is proposed for engineering purposes. Keywords: MSWI bottom ash; Composition; Friction angle; Reuse 1. Introduction In Taiwan, incineration is a major method used to treat municipal waste. The Taiwanese government currently oversees nearly 25 municipal solid waste incinerators (MSWI). Although incineration decreases the volume of waste, the process generates bottom ash and fly ash. A yearly average of 5 million tons of waste is treated by incineration. This results in about 0.82 million tons of bottom ash and 0.16 million tons of fly ash produced annually. The total amounts of bottom and fly ash produced from 2001 to 2007 are shown in Table 1. However, fly ash and bottom ash often contain concentrations of heavy metals, and those ash must be tested the leaching concentrations of heavy metals by the toxicity characteristic leaching procedure (TCLP). The allowable level was made by Taiwan EPA and included many hazardous heavy metals, such as Hg, Pb, Cd, Cr and so on. The concentrations of heavy metal in fly ash usually exceed the allowable levels. Conversely, the leaching concentrations of heavy metals in bottom ash seldom exceed the allowable level. Most heavy metals with higher boiling points are found in the bottom ash. For bottom ash, the major components are SiO2, CaO, Fe2O3 and Al2O3. These four components constitute a major portion of various materials and products. Table 2 shows the components of bottom ash in different countries. The composition similarities to natural aggregates and cement allow bottom ash to be reused as a construction material in civil engineering, such as concrete (Pan et al., 2008; Pecqueur et al., 2001), lightweight aggregates (Qiao et al., 2008), and landfill and road base materials (Izquierdo et al., 2008). Therefore, the physical and mechanical properties of bottom ash have been one of the major concerns in engineering design. 27.

(3) According to previous studies (Izquierdo et al., 2008; Forteza et al., 2004; Kim and Prezzi, 2008; Li et al., 1995; Lee et al., 2004; Kamon et al., 2000; Vegas et al., 2008), bottom ash is characterized by high porosity, low specific gravity (1.9-2.3 g/cm3) and high moisture absorption (7.7-12.8 %).. Based on the unified soil. classification system (USCS), it is usually classified as SW or GW-GM, which mean well-graded sand or gravel, respectively. The compaction characteristics show that the maximum compacted dry unit weights of bottom ash vary from 14.6 to 17.5 kN/m3, and the corresponding optimum water contents are 14.8 % to 24.0 %. For the shear strength, the friction angles of bottom ash range from 24o-50o, and the cohesion measured from consolidated-drained triaxial tests ranges between 13.8-34.5 kPa (Li et al., 1995; Lee et al., 2004, Pandeline et al., 1997; Muhunthan et al., 2004). Overall, bottom ash exhibits high strength and well-graded size distribution, which make it feasible for use in embankments, landfills and road bases. However, the heterogeneous composition and different operation environments make the properties of bottom ash highly variable. For instance, the friction angles of bottom ash may vary widely (24o-50o), and are influenced by factors like the chemical composition, the operation conditions of the incinerator plant, the size distribution, the water content, the packing, etc. Hence, it is difficult for civil engineers to evaluate the mechanical properties for design purposes. In order to understand more about the mechanical properties of this material, this research aims to explore the influence of the chemical composition on the mechanical properties of bottom ash. To reduce the uncertainties and to control the designated composition, specimens of artificial bottom ash were used instead of those from incineration plants. A series of mechanical tests with controlled chemical components were conducted, and the strength and deformational characteristics, such as friction angle and stiffness, were explored. Afterward, the test results were used in a 28.

(4) multi-variable regression analysis to evaluate which components are the key factors influencing the strength of the bottom ash. 2. Experimental 2.1. Specimen preparation In order to systematically explore the mechanical behaviors of bottom ash, a series of artificial specimens with chemical compositions based on actual conditions were prepared. Considering the complex constituents of bottom ash, only four major components (usually present at more than 10 %), SiO2, CaO, Fe2O3 and Al2O3, were selected to simplify the synthesis. The pure chemicals were employed. The purity of four components is SiO2: 97.8%, CaO: 99%, Fe2O3: 99% and Al2O3: 99%, respectively. Figure 1 illustrates the actual proportions of the four major components of the bottom ash. To account for the possible distribution range of the components, four extreme conditions of chemical compositions were considered in this work. In order to ensure the various artificial MSWI bottom ash have the same characteristics, the standard operation process was established. Four major components (SiO2, CaO, Fe2O3 and Al2O3) were added into glass in sequence and stirred 5 minutes by glass bat. During experiment, one experiential operator prepared all artificial MSWI bottom ash alone to maintain the characteristic unity of bottom ash. The chemical compositions in weight of the artificial specimens in this study are summarized in Table 3. Moreover, to differentiate the influence of Fe2O3 and Al2O3, two proportions of the components, 1:1 and 3:1, respectively, were used, and the specimens are referred as Group A and Group B herein. For each set in Table 3, four specimens, weighing 200 g each, were prepared for successive direct shear tests. A total of 64 specimens were tested in this research. In addition to the chemical components, the grain size distribution curve of the specimen was specified to coincide with the municipal samples, as shown in Fig. 2. For the preparation of 29.

(5) specimens, the aggregates were ground from larger blocks or particles, and the shape of aggregates is angular or sub-angular. Owing to the sizes that testing equipment can accommodate, only the particles passing the No. 4 sieve (4.75 mm) were adopted in this study. Therefore, this study focuses on the mechanical properties of sand-sized bottom ash, which contains 90 % sand-sized material and approximately 10.0 % fine contents. Furthermore, the specimens were heated to 900oC for 90 minutes to simulate the forming process of bottom ash used in Taiwan. Afterward, half of the specimens were stored under dry conditions (water saturation S = 0 %) and the rest in wet conditions (water saturation S = 100 %). Wet specimens were soaked in water for at least 24 hours. The testing conditions of the specimens are summarized in Table 3. 2.2 Testing procedures The Atterberg limit tests (ASTM D4318-05) were firstly performed to determine the liquid limit (LL) and the plastic limit (PL) of the artificial bottom ash. The adopted instruments included the sieve shaker, the liquid limit test device, and the oven. The results allow the ash to be classified according to the USCS classification. Next, the mechanical characteristics of the artificial bottom ash were explored using direct shear tests. Every sample for direct shear test was prepared in a fixed weight (200 g) in dry condition, and then it is placed in the direct shear box in a loose state. The size of each specimen is 6.3 cm in diameter and about 3.5 cm in height. During the test, the normal stresses chosen were 0.31, 0.62, 1.24 and 1.87 kg/cm2 and the drained condition was allowed. The specimen was then sheared at a rate of 0.95 mm/min, which was determined according to ASTM D3080-90 code. Dial gages were used to measure the horizontal and vertical deformation of the specimens with a precision of 0.01 mm. The shear load was measured with a proving ring attached to the loading frame with 30.

(6) an accuracy of 0.003 kg/cm2. 3. Results and Discussion 3.1. Basic characteristics of artificial bottom ash The results of the Atterberg limit test indicate that the artificial samples exhibit no plasticity (NP). The grain size distribution curves of all specimens were specified to coincide with that of the municipal samples, as shown in Fig. 2. It gives the results for the uniformity coefficient (Cu) of the samples of 6.76, and the coefficient of gradation (Cz) of 1.09. This means that both Group A and Group B are classified as SW-SM based on USCS. For the soil classification AASHTO, the samples belong to A-1-b. The details of sample properties are given in Table 4. 3.2. Mechanical properties 3.2.1. Behavior during direct shear tests Taking set B1-D and B1-S (dry and saturated conditions) as examples, Figure 3 depicts the typical variations of shear displacement induced by shearing under direct shear tests. The saturated specimens (hollow symbol) exhibit lower strength than those of the dry specimens (solid symbol) under various normal stresses. Moreover, the stiffness (the slope of the curve) of the saturated specimens is also smaller than that of the dry specimens, indicating that the soaking of the specimen may induce deterioration in both stiffness and strength. However, the curves follow similar trends for both dry and saturated conditions. At the earlier stage, the initial stiffness increases with increasing normal stress applied. As the stress approaches the failure state, the peak strength is not significant, similar to that of loose sand, and all samples exhibit a fairly ductile behavior. The aforementioned behaviors are also observed in other sets of specimens. 3.2.2. Strength The failure envelopes of the artificial bottom ash tend to be linear when 31.

(7) expressed in the normal and shear stress plane, as illustrated in Fig. 4. As such, the linear relationship, known as the Mohr-Coulomb criteria (Eqn.1) shown in Fig. 4, is adopted:.  f   tan   c. (1). where fandare the shear strength and normal stress, respectively, and the parameters and c are the frictional angle and the cohesive intercept of the failure envelope, respectively. Taking set B1-D and B1-S as examples again, the results show the frictional angles are 51.1o for dry samples and 37.2o for saturated samples. There is no cohesive interception c of the two sets because of the cohesionless property. The values of the frictional angle for all specimens are summarized in Table 5. Table 5 shows that a fairly wide spectrum of frictional angles was obtained, in which the frictional angles under dry and saturated conditions vary from 34.8o to 51.1o and 26.0o to 37.2o, respectively. The sets A1 and B1 exhibit the highest dry friction angles in Groups A and B. By contrast, the lowest friction angles occur in sets A2 and B2. In addition, significant wetting degradation can be observed, and the decrease in frictional angle ranges from 19 % (B2) to as high as 38 % (A2). Furthermore, compared with the authentic bottom ash reported by Pandeline et al. (1997), it also exhibits a wide range of frictional angle for artificial bottom ash. However, the influence factors of strength, including the gradation, fine contents, porosity and water content of the specimen, are specified in this research, indicating that the chemical composition may play an important role on the bottom ash strength. Figure 5 further illustrates the relationship between the single chemical component and friction angles. In Fig. 5a, it can be seen that the content of Fe2O3 is a significant factor influencing friction angle under both dry and saturated conditions, and the. 32.

(8) friction angle increases linearly with the content of Fe2O3. Figure 5b shows that a nonlinear relationship may exist between the friction angle and the Al2O3 content. However, the content of SiO2, seems to only slightly influence the friction angle, shown in Fig. 5c. This is also the case for CaO, shown in Fig. 5d. Though the content of Fe2O3 appears to be a major influencing factor on the strength, the other results are vague. It indicates that the strength may be affected by more than one chemical component. Therefore, a multi-variable regression analysis is conducted in following section to distinguish the major or the minor parameters influencing the strength. 3.2.3. Shear stiffness Furthermore, deduced from the shear stress – displacement curves, the variations of shear stiffness of specimens (set B1-D and B1-S) under various normal stresses are plotted in Fig. 6. The stiffness used here is the secant stiffness at 50 % of peak strength. Figure 6 reveals that the stiffness is lower during the low stress stage and increases as the normal stress increases. Similar to results for the friction angle, the stiffness at the dry condition is higher than that for the saturated condition. The values of the stiffness for all specimens at the normal stress of 0.62 kg/cm2 are summarized in Table 5. A wide range of stiffness is given, and the magnitudes of stiffness under the dry and saturated conditions vary from 3.94 to 8.36 kg/cm2 and 2.17 to 4.84 kg/cm2, respectively. The set A4 shows the highest stiffness under dry conditions, and the lowest stiffness occurs in the set A1. At saturated conditions, the set A3 exhibits the highest stiffness, and the lowest stiffness occurs in the set B4. The relationship between the chemical components and stiffness are further explored. However, compared with the friction angle, the influence of the components on the stiffness is insignificant. 3.3. Regression analysis It is of interest to evaluate the associated influence of the components on the 33.

(9) strength. Since the strength is affected by more than one component, a multi-variable regression analysis proposed by Jeng et al. (2004) was used in this research. The process is briefly described as follows: When a material response (e.g., friction angle) was inter-affected by several factors (e.g, x1, x2, …, xn) such that a function F(= friction angle, ) exists, it could be expressed as: F  f ( x1 , x2 , ..., xn ). (2). The function form of F was unknown; however, it was assumed that F has the following form for the sake of simplicity:. F  f1 ( x1 ) f 2 ( x2 ) ... f n ( xn ). (3). Each function on the right hand side of Eqn. 3 represents the magnitude of the influence of each factor. Empirical functions of f(xi) could possibly be determined one by one using a single-variable regressive analysis of experimental data. The degree of influence varies from one factor to another. The goal was to find the most influential function, followed by the second-most influential function, and so on. The determination of the influential functions continued until the remaining factors have no meaningful influence, which meant that the increase of r2 < 0.05 when more factors are considered. Then the function forms of f(x1), f(x2), …, f(xn) needed to be further modified by the iteration process until the coefficient of correlation stops increasing. Using the aforementioned regressive process, the dry friction angle appeared to be strongly affected by two components, Fe2O3 and Al2O3, among all factors. Accordingly, the contents of Fe2O3 and Al2O3 were identified as the major factors influencing friction angle. Therefore, it was assumed the dry friction angle, (dry), could be approximately expressed as: 34.

(10) dry  f (Fe2 O3 , Al2 O3 , SiO 2 , CaO)  f1 (Fe 2 O3 ) f 2 (Al2 O3 ). (4). The functions f1 (Fe 2 O3 ) and f 2 (Al2 O3 ) could be determined by iterations of the regression analysis and are found to be: f1 (Fe 2 O3 )  10.0 ln(Fe2 O3 )  15.413. (5). f 2 (Al2 O3 )  1.034 (1  e 0.909(Al2O3 ) )28.494. (6). Substituting Eqns. 5 and 6 into Eqn. 4, the dry friction angle could be expressed in terms of Fe2O3 and Al2O3 as: dry  f1 (Fe 2 O3 ) f 2 (Al2 O3 )  10.34 *[ln(Fe 2 O3 )  1.541]* [(1  e 0.909(Al2O3 ) ) 28.494 ]. (7) where the units for dry, Fe2O3 and Al2O3 are degree, % and %, respectively. If the dry friction angle expressed by Eqn. 7 was defined as empirical dry, it could be compared to the actual dry, as shown in Fig. 7a. In general, the actual dry and the empirical dry were closely related, with a correlation coefficient square (r2) of 0.939.. As a result, Eqn. 7 provided a practical relationship for the prediction of the. dry strength of bottom ash based on the compositions. Moreover, Fig. 7b illustrates the variation of dry with two components for all specimens compared in this work. In Fig. 7b, the contour lines indicate the empirical dry and numbers near each symbol mark the actual dry. The specimens, despite different compositions, tend to have a greater dry for larger contents of Fe2O3 or Al2O3. Following a similar regressive process described in the abovementioned section, the empirical function for the saturated friction angle sat could be obtained. The contents of Fe2O3 and Al2O3 were also the major factors influencing saturated friction angle. As for the case of dry, sat is also affected by Fe2O3 and Al2O3, and the regressive functions g1 (Fe 2 O3 ) and g 2 (Al2 O3 ) were g1 (Fe2 O3 )  0.421(Fe2 O3 )  22.912. (8) 35.

(11) g 2 (Al2 O3 )  [1  0.0645*(Al2 O3 ) 1.022  0.0659*(Al2 O3 )]. (9). Then, the saturated friction angle could be expressed in terms of Fe2O3 and Al2O3 as:. sat  g1 (Fe2 O3 ) g 2 (Al2 O3 )  [0.421(Fe2 O3 )  22.912]* [. 1  0.0645* (Al2 O3 ) ] 1.022  0.0659 *(Al2 O3 ). (10) The actual sat and the empirical sat are compared and shown in Fig. 8a, which indicates a reasonably good agreement between the two magnitudes, with a correlation coefficient square (r2) of 0.853. Furthermore, the variations of sat with two components are presented in Fig. 8b. Figures 7b and 8b show that the content of Fe2O3 is the major influencing factor for both the dry friction angles and the saturated friction angles. As shown in Fig. 7b, the friction angle arises from 35o to 50o as the content of Fe2O3 increases under a fixed content of Al2O3. Compared with Fe2O3, the content of Al2O3 is a minor factor impacting the strength. The angle only increases about 5o as the content of Al2O3 increases under a fixed content of Fe2O3. Furthermore, the saturated friction angles, the influence of Al2O3 is insignificant. Although artificial specimens are much simpler than the bottom ash from MSW incineration, Figures. 7 and 8 provide an approximate strength classification according to the chemical components. In this case more Fe2O3 and Al2O3 result in greater friction angles. Though there may be few exceptions existed, the statement provides the major tendency. Last but not least, the limitation of Fig. 7 and 8 is notified that the classification only focuses on the instantaneous mechanical properties of bottom ash, and the durability or time-dependent problems are not considered here. In future experiments, more other components will be added to the artificial bottom ash, and more operational factors will be considered. 4. Conclusions. 36.

(12) The mechanical behavior of artificial bottom ash was systematically explored in this research. The experimental results show that the bottom ash possesses the following characteristics: (1) For the strength, the frictional angles of the bottom ash under dry and saturated conditions vary from 34.8o to 51.1o and 26.0o to 37.2o, respectively. (2) For the deformation, the shear stiffness increases as normal stress arises and degrades upon increasing shearing. As the stress approaches the failure state, the bottom ash exhibits fairly ductile behavior. (3) Significant wetting degradation of the strength and stiffness were observed, and the decrease in the frictional angle ranges from 19 % to 38 %. To evaluate the associated influence of chemical components on the strength, i.e. friction angle, a multi-variable regression analysis was conducted. Among the studied components, the contents of Fe2O3 and Al2O3 are found to be the major factors influencing the friction angles, and more Fe2O3 and more Al2O3 result in higher friction angles at both dry and saturated conditions. The analysis was used to determine and propose empirical functions dry and sat, express in terms of Fe2O3 and Al2O3. Since the mechanical behavior of bottom ash is influenced by lots of factors, it is an open question whether the empirical functions of strength, or the proposed classification method, can be applied to the MSWI bottom ash. Modification of the proposed empirical functions for more heterogeneous bottom ash may be necessary. However, this research did find the close links between the mechanical behavior and the composition, and these relationships are quantitatively analyzed and presented.. 37.

(13) Reference Forteza, R., Far, M., Segui, C., Cerda, V., 2004. Characterization of bottom ash in municipal solid waste incinerators for its use in road base. Waste Management 24, 899-909. Izquierdo, M., Querol, X., Josa, A., Vazquez, E., López-Soler, A., 2008. Comparison between laboratory and field leachability of MSWI bottom ash as a road material. Science of The Total Environment 389, 10-19. Jeng, F.S., Weng, M.C., Lin, M.L., Huang, T.H., 2004. Influence of petrographic parameters on geotechnical properties of Tertiary sandstones from Taiwan. Engineering Geology 73, 71-91. Kamon, M., Katsumi, T., Sano, Y., 2000. MSW fly ash stabilized with coal ash for geotechnical application. Journal of Hazardous Materials 76, 265-283. Kim, B., Prezzi, M., 2008. Compaction characteristics and corrosivity of Indiana class-F fly and bottom ash mixtures. Construction and Building Materials 22, 694-672. Lee, W.F., Chen, Y.S., Chen, Y.Y., Hu, T.C., Yao, D.C., 2004. The application of combustion bottom ash in geotechnical construction. Sino-Geotechnics 102, 69-78. Li, J.C., Lee, C., Ho, C.H., Jeng, C.J., 1995. Geotechnical Properties of Incinerator Residue in Taipei, in: Proceeding of the 10-th Asian Regional Conference on Soil Mechanics and Foundation Engineering, 477-480. Muhunthan, B., Taha, R., Said, J., 2004. Geotechnical Engineering Properties of Incinerator Ash Mixes. Journal of the Air and Waste Management Association 54, 985-991. Pan, J.R., Huang, C., Kuo, J.J., Lin, S.H., 2008. Recycling MSWI bottom and fly ash as raw materials for Portland cement. Waste Management 28, 1113-1118. 38.

(14) Pandeline, D.A., Cosentino, P.J., Kalajian, E.H., Chavez, M.F., 1997. Shear and Deformation Characteristics of Municipal Waste Combustor Bottom Ash for Highway Applications, Transportation Research Record No. 1577, TRB, National Research Council, Washington D.C., 101-108. Pecqueur, G., Crignon, C., Quenee, B., 2001. Behaviour of cement-treated MSWI bottom ash. Waste Management 21, 229-233. Pera, J., Coutaz, L., Ambroise, J., Chababbet, M., 1997. Use of incinerator bottom ash in concrete. Cement and Research 27, 1-5. Qiao, X.C., Ng, B.R., Tyrer, M., Poon, C.S., Cheeseman, C.R., 2008. Production of lightweight concrete using incinerator bottom ash. Construction and Building Materials 22, 473-480. Vegas, I., Ibañez, J.A., San José, J.T., Urzelai, A., 2008. Construction demolition wastes, waelz slag and MSWI bottom ash:A comparative technical analysis as material for road construction. Waste Management 28, 565-574.. 39.

(15) Table 1 MSWI bottom ash and fly ash product of incinerators of Taiwan from 2001 to 2007.. Year. Waste treatment by incineration (tonnes/year). Bottom ash (tonnes/year). Fly ash (tonnes/year). 2001. 3,922,387.0. 682,532.1. 116,144.8. 2002. 5,311,000.0. 920,047.8. 187,229.2. 2003. 5,470,736.0. 861,990.1. 189,612.2. 2004. 5,611,504.8. 855,923.2. 168,284.8. 2005. 5,614,930.1. 861,094.3. 158,838.9. 2006. 5,683,032.8. 858,289.7. 168,169.9. 2007. 4,994,230.3. 727,031.9. 150,987.8. Total. 3,660,7821.0. 5,766,909.1. 1,139,267.5. Average. 5,229,688.7. 823,844.2. 162,752.5. Source: collected from Taiwan EPA.. 40.

(16) Table 2 Chemical compositions of MSWI bottom ash from different countries. Country. Chemical composition. Taiwana. Japanb. Singaporeb. USAb. SiO2 (%). 43.1-56.5. 34.7-39.9. 26. 39.2-44.7. CaO (%). 11.8-21.6. 11.1-18.2. 16.8. 10.5-14.8. Fe2O3 (%). 5.6-19.1. 7.1-8.6. 13.1. 9.2-10.4. Al2O3 (%). 6.98-14.4. 12.3-16.5. 12.3-25.5. 17.0-17.4. Na2O (%). 5.79. 1.8-2.6. 1.9-2.5. 6.46-8.1. MgO (%). 1.35-1.8. 2.2-4.5. 1.0-2.0. 1.5-3. Source: a: Taiwan EPA. b : Pera et al. (1997). 41.

(17) Table 3 List of chemical compositions of artificial bottom ash and testing conditions in this research. SiO2 (%). CaO (%). Fe2O3 (%). Al2O3 (%). Condition. A1-D. 43. 12. 22.5. 22.5. Dry. A2-D. 57. 22. 10.5. 10.5. Dry. A3-D. 43. 22. 17.5. 17.5. Dry. A4-D. 57. 12. 15.5. 15.5. Dry. A1-S. 43. 12. 22.5. 22.5. Saturated. A2-S. 57. 22. 10.5. 10.5. Saturated. A3-S. 43. 22. 17.5. 17.5. Saturated. A4-S. 57. 12. 15.5. 15.5. Saturated. B1-D. 43. 12. 33.75. 11.25. Dry. B2-D. 57. 22. 15.75. 5.25. Dry. B3-D. 43. 22. 26.25. 8.75. Dry. B4-D. 57. 12. 23.25. 7.75. Dry. B1-S. 43. 12. 33.75. 11.25. Saturated. B2-S. 57. 22. 15.75. 5.25. Saturated. B3-S. 43. 22. 26.25. 8.75. Saturated. B4-S. 57. 12. 23.25. 7.75. Saturated. Set of specimens. Group A. Group B. 42.

(18) Table 4 Summary of grain size characteristics of artificial bottom ash. Specimen. D10 (mm). D30 (mm). D60 (mm). Cu a. Cz b. PI. Soil Type c. Group A & B. 0.075. 0.204. 0.507. 6.76. 1.094. NP. SW-SM. a: the uniformity coefficient Cu  D10 D60 b: the coefficient of gradation Cz  ( D10  D60 ) D302 c: the types of soil are defined by Unified Soil Classification System, USCS. Table 5 Mechanical properties of artificial bottom ash.. Set of specimens. Friction angle (Degree). Shear stiffness (kg/cm2). dry. sat. (ks)dry. (ks)sat. A1. 46.3°. 31.0°. 3.938. 2.621. A2. 41.8°. 26.0°. 5.323. 4.788. A3. 44.5°. 32.1°. 7.251. 4.842. A4. 46.2°. 37.0°. 8.357. 3.650. B1. 51.1°. 37.2°. 6.410. 4.437. B2. 34.8°. 28.3°. 6.574. 2.533. B3. 48.7°. 31.7°. 5.421. 2.242. B4. 48.0°. 31.5°. 7.994. 2.168. 43.

(19) SiO2 (%) 0. 100. 10. 90. 20. 80. 30. 70. 40. 4. 60. 2. 50 60. 50. 3. 1. 40. 70. 30. 80. This research Japan U.S.A Taiwan. 90. 20 10. 100 0. 0 10. 20. 30. 40. 50. 60. 70. 80. 90. 100. CaO (%). Fe2O3 + Al2O3 (%). Fig. 1. Major chemical compositions of MSWI bottom ash. The major components include SiO2, CaO, Fe2O3 and Al2O3. Four extreme compositions of the studied bottom ash were considered, and information of actual bottom ash is also included for comparative purposes. 100 This research Shinchu city. Percent passing (%). 90 80 70. Taipei city Taipei county - 1 Taipei county - 2. 60. Tainan county. 50 40 30 20 10 0 10. 1. 0.1. 0.01. Grain size (mm) Fig. 2. Grain size distribution curves of bottom ash from different municipal solid waste incinerators in Taiwan and the specimen. 44.

(20) 3.0. P=0.31 ksc - dry P=0.62 ksc - dry P=1.24 ksc - dry P=1.87 ksc - dry P=0.31 ksc - sat P=0.62 ksc - sat P=1.24 ksc - sat P=1.87 ksc - sat. 2. Shear stress (kg/cm ). 2.5 2.0 1.5 1.0 0.5 0.0 0. 5. 10. 15. 20. Shear displacement (%) Fig. 3. Variations of shear displacement induced by shearing under direct shear tests (Set B1-D and B1-S).. 3.0. 2. Shear stress (kg/cm ). 3.5. 2.5 2.0 1.5 1.0 0.5 0.0 0.0. 0.5. 1.0. 1.5. 2.0 2. Normal stress (kg/cm ) Fig. 4. Failure envelopes of the studied bottom ash.. 45. 2.5.

(21) 60. 60 ψ (dry). ψ (sat). 50. Friction angle (degree). Friction angle (degree). ψ (dry). 40. 30. 20 5. 10. 15. 20. 25. 30. ψ (sat). 50. 40. 30. 20. 35. 0. 5. Fe2O3 (%). 15. 20. 25. 20. 25. Al2O3 (%). (a) Fe2O3. (b) Al2O3 60. 60. ψ (dry). Friction angle (degree). ψ (dry). Friction angle (degree). 10. ψ (sat). 50. 40. 30. 20. ψ (sat). 50. 40. 30. 20 35. 40. 45. 50. 55. 60. 0. SiO2 (%). 5. 10. 15. CaO (%). (c) SiO2. (d) CaO. Fig. 5. The relations between the chemical components and friction angles.. 46.

(22) Dry condition Saturated condition. 2. Shear stiffness (kg/cm ). 25. 20. 15. 10. 5. 0 0.0. 0.5. 1.0. 1.5. 2.0. 2. Normal stress (kg/cm ) Fig. 6. The variation of shear stiffness corresponding to increases of normal stress.. 47.

(23) Predicted friciton angle. 60. 50 2. R = 0.9394 40. 30. 20 20. 30. 40. 50. 60. Actual friciton angle (a) Comparison of actual and empirical dry 25 ψ=35°. ψ=45°. ψ=40°. ψ=50° ψ=46.3°. Al2O3 (%). 20 ψ=44.5° ψ=46.2°. 15 ψ=51.1° ψ=41.8°. 10. ψ=48.7° ψ=48° ψ=34.8°. ψ=30°. 5 5. 10. 15. 20. 25. 30. 35. Fe2O3 (%) (b) Variation of dry with Fe2O3 and Al2O3 Fig. 7. Comparison of actual dry with empirical dry and variation of dry with Fe2O3 and Al2O3. The contour curves in (b) represent the empirical function of dry defined by Eqn. 7, and the actual value of dry is marked near each symbol.. 48.

(24) Predicted friciton angle. 40. 35. R2 = 0.8527. 30. 25. 20 20. 25. 30. 35. 40. Actual friciton angle (a) Comparison of actual and empirical sat 25 ψ=25°. ψ=30°. ψ=35°. ψ=31.0°. Al2O3 (%). 20. ψ=32.1°. 15. ψ=37.0° ψ=37.2° ψ=31.7°. 10. ψ=26.0°. ψ=31.5° ψ=28.3°. 5 5. 10. 15. 20. 25. 30. 35. Fe2O3 (%) (b) Variation of sat with Fe2O3 and Al2O3 Fig. 8. Comparison of actual sat with empirical sat and variation of sat with Fe2O3 and Al2O3. The contour curves in (b) represent the empirical function of sat defined by Eqn. 10.. 49.

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