Compaction and Consolidation Characteristics for Waste Materials (Sludge, Crushed Concrete and Incineration Ash)

K. Hashimoto1, M.R. Iqbal1, K. Kawamoto1, 2, T. Saito1, and S. Tachibana1, 2

1Graduate School of Science and Engineering Saitama University, JAPAN

2International Institute for Resilient Society Saitama University, JAPAN

E-mail: k.hashimoto.soillab@gmail.com Abstract: An effective use of limited space in existing waste disposal sites is essential due to the difficulty in constructing new facilities in Japan. The control of geotechnical properties for waste materials such as compaction and consolidation are key factors for reducing disposal space. In this study, compaction and consolidation characteristics for waste materials of sludge (D < 2.0 mm), crushed concrete (2.0 mm < D < 9.5 mm), and incineration ash (D < 2.0mm) were investigated with their different mixing proportions. Two mixed waste samples of sludge and crushed concrete or incineration ash were mainly used. For the compaction characteristics of two mixed samples, relationship between maximum dry density and mixing proportion of crushed concrete or incineration ash showed strong positive linear relation. Also, optimum moisture content of two mixed samples linearly decreased with increasing the mixing proportion of crushed concrete or incineration. Crushed concrete and incineration ash have completely different particle size distribution, however, two mixed samples of sludge and crushed concrete or incineration ash showed almost same compaction characteristics. Coefficients of compression for the mixed sample of sludge and incineration ash gradually decreased with increasing the mixing proportion of incineration ash, while for the mixed sample of sludge and crushed concrete, they decreased rapidly with increasing the mixing proportion of crushed concrete. Therefore, two mixed samples of sludge and crushed concrete or incineration ash showed different consolidation characteristics. Keywords: Compaction, Consolidation, Sludge, Crushed concrete, Incineration ash, Mixed waste materials

1. INTRODUCTION

Waste disposal sites are essential infrastructure facilities for human and industrial activities. Due to the lack of land and the difficulty in constructing new disposal facilities in Japan, it is needed to have an effective use of limited space in existing waste disposal sites. The control of geotechnical properties for waste materials such as compaction and consolidation are important to reduce disposal space. Therefore, the objectives of this study are to investigate compaction and consolidation characteristics for waste materials of sludge, crushed concrete, and incineration ash with their different mixing proportions.

2. MATERIALS AND METHODS

In this study, experiments were carried out based on Japanese Industrial Standards (JIS) or Japanese Geotechnical Society (JGS) Standards. Some test methods were partly modified as shown below.

2.1. Testing Materials

Figure 1 illustrates waste materials of sludge (D < 2.0 mm), crushed concrete (2.0 mm < D < 9.5 mm), and incineration ash (D < 2.0 mm) used in this study. Sludge was taken from Chiba prefecture, Japan and crushed concrete and incineration ash were collected from Saitama prefecture, Japan. The waste

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materials were mixed with various proportions based on mass ratio. In the following experiments, two mixed samples of sludge and crushed concrete or incineration ash were mainly used.

Figure 1 Waste materials used in this study, (a) sludge, (b) crushed concrete, and (c) incineration ash

2.2. Methodology

Basic physical and chemical properties test For each waste material, basic physical properties (specific gravity: Gs, moisture content, particle size distribution, and Atterberg limits) and chemical properties (pH, electric conductivity: EC, and loss on ignition: LOI) were determined. These tests were carried out by following JIS (JIS A 1202, JIS A 1203, JIS A 1204, and JIS A 1205) and JGS standards (JGS 0211-2009, JGS 0212-2009, and JGS 0221-2009). Standard proctor compaction test Standard proctor compaction test was carried out according to JIS A 1210. The test apparatus is shown in Figure 2 (a). For the mixed waste samples containing crushed concrete, the volume was measured without reshaping the samples after the compaction. Consolidation test Figure 2 (b) presents consolidation test apparatus. The test was carried out by using the mixed waste samples (D < 2.0 mm) based on JIS A 1217. Because the samples containing crushed concrete are heterogeneous, large consolidation apparatus was used. The waste samples were prepared by the standard proctor compaction with having degree of compaction, more than 90%.

Figure 2 Experimental apparatuses of (a) compaction test and (b) consolidation test

3. RESULTS AND DISCUSSION

3.1. Basic physical and chemical properties of waste materials

Table 1 shows basic physical and chemical properties of each waste sample. For both crushed concrete and incineration ash, liquid limit (𝑤𝑤𝐿𝐿 ) and plastic limit (𝑤𝑤𝑃𝑃 ) were not determined due to cohesionless materials. Specific gravity of incineration ash was larger than other two waste samples.

(a) (b) (c)

(a) (b)

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Figure 3 illustrates particle size distribution curve of mixed waste materials with various mixing proportions. Sludge consisted mainly of fine grain, while for crushed concrete and incineration ash, they were composed of coarser grain. Particle size distribution gradually became close to the distribution in sludge with increasing the mixing proportion of sludge.

Table 1 Basic physical and chemical properties of each waste sample

Figure 3 Particle size distribution curve of mixed waste materials with various mixing proportions

3.2. Compaction test characteristics of waste materials

Figure 4 presents compaction curve of mixed waste materials with various mixing proportions. Maximum dry density of sludge,crushed concrete, and incineration ash were 0.76 (g/m3), 1.45 (g/m3), and 1.51 (g/m3), respectively. Also, maximum dry density clearly increased with decreasing the mixing proportion of sludge. Figure 5 shows relationships between maximum dry density or optimum moisture content and mixing proportions of waste samples. For two mixed samples of sludge and crushed concrete or incineration ash, relationship between maximum dry density and mixing proportion of crushed concrete or incineration ash showed strong positive linear relation (r2 = 0.93). Also, optimum moisture content of two mixed samples linearly decreased with increasing the mixing proportion of crushed concrete or incineration. As shown in Figure 3, crushed concrete and incineration ash have completely different particle size distribution, however, two mixed samples of sludge and crushed concrete or incineration ash showed almost same compaction characteristics.

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Figure 4 Compaction curve of mixed waste materials with various mixing proportions

Figure 5 Relationshipsbetween (a) maximum dry density and mixing proportions of waste samples and (b) optimum water content and mixing proportions of waste samples

3.3. Consolidation test characteristics of waste materials

Figure 6 illustrates compression curve of mixed waste materials with various mixing proportions. Initial void ratio clearly decreased with decreasing the mixing proportion of sludge. Coefficient of compression for sludge, crushed concrete, and incineration ash were 0.25, 0.03, and 0.04, respectively. Figure 7 shows relationships between coefficient of compression and mixing proportions of waste samples or initial void ratio. Coefficient of compression for the mixed sample of sludge and incineration ash gradually decreased with increasing the mixing proportion of incineration ash, while for the mixed sample of sludge and crushed concrete, they drastically decreased with increasing the mixing proportion of crushed concrete. Therefore, two mixed samples of sludge and crushed concrete or incineration ash showed different consolidation characteristics.

(a) (b)

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Figure 6 Compression curve of mixed waste materials with various mixing proportions

Figure 7 Relationships between (a) coefficient of compression and mixing proportions of waste

samples and (b) coefficient of compression and initial void ratio. The regression lines have been determined without data for “sludge + concrete”.

4. CONCLUSION

In this study, compaction and consolidation characteristics for waste materials of sludge, crushed concrete, and incineration ash were investigated with their different mixing proportions. Two mixed waste samples of sludge and crushed concrete or incineration ash were mainly used. For the compaction characteristics of two mixed samples, relationship between maximum dry density and mixing proportion of crushed concrete or incineration ash showed strong positive linear relation. Also, optimum moisture content of two mixed samples linearly decreased with increasing the mixing proportion of crushed concrete or incineration. Crushed concrete and incineration ash have completely different particle size distribution, however, two mixed samples of sludge and crushed concrete or incineration ash showed almost same compaction characteristics. Coefficients of compression for the mixed sample of sludge and incineration ash gradually decreased with increasing the mixing proportion of incineration ash, while for the mixed sample of sludge and crushed concrete, they decreased rapidly with increasing the mixing proportion of crushed concrete. Therefore, two mixed samples of sludge and crushed concrete or incineration ash showed different consolidation characteristics.

(a) (b)

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ACKNOWLEDGEMENT

This study was supported from Science and Technology Research Partnership for Sustainable Development (SATREPS) by Japan Science and Technology Agency (JST) and Japan International Cooperation Agency (JICA). The authors deeply appreciate Mr. Kouhei Shinmura, Saitama University, for his support to laboratory tests.

REFERENCES

Japanese Industrial Standards (JIS). 2009. Test method for density of soil particles. JIS A 1202: 2009. Japanese Industrial Standards (JIS). 2009. Test method for water content of soils. JIS A 1203: 2009. Japanese Industrial Standards (JIS). 2009. Test method for particle size distribution of soils. JIS A 1204: 2009. Japanese Industrial Standards (JIS). 2009. Test method for liquid limit and plastic limit of soils. JIS A 1205: 2009. Japanese Industrial Standards (JIS). 2009. Test method for soil compaction using a rammer. JIS A 1210: 2009. Japanese Industrial Standards (JIS). 2009. Test method for one-dimensional consolidation properties of soils using incremental loading. JIS A 1217: 2009. Japan Geotechnical Society (JGS). 2009. Test method for pH of suspended soils. JGS 0211-2009. Japan Geotechnical Society (JGS). 2009. Test method for electric conductivity of suspended soils. JGS 0212-2009. Japan Geotechnical Society (JGS). 2009. Test method for ignition loss of soils. JGS 0221-2009.

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