Introduction Of Recycle Glass Cullet Engineering Essay

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In 2005, Australia is currently recovering 35 % which mean 278,000 tonnes of used glass containers. It is estimated base on national sales, that Australia generates consume around 900,000 tonnes per year of container glass in 2006. It currently recovering for recycling around 350,000 tonnes or 37 %recycle rate. (Warwick Hassan, Manager Product Stewardship Program, Sept. 2006)

On the other side, there is 6.2 % of glass cullet waste is discarded every year, which is generally approximate 12.8 million of glass cullet waste according to United States Environmental Protection Agency (USEPA). There is about 31 % is reused for re-melt applications and 7% is reused for host of secondary market, and the rest 62% are disposed in landfills. The portion that deserves attention is the large quantity, 62 % of waste glass that takes up space in landfills throughout the country. Therefore recycle the 62% of waste glass can saving landfill space. When the materials that you recycle are used to make new products, they don't go into landfills, so landfill space is conserved (Environmental systems of America). Recently, due to the over quantity of mixed-colour glass, it bring the container industry price paid for glass cullet have decreased.

Therefore, in Australia, engineer find a valuable uses for the waste glass that take up precious space. Australia has develop an alternative markets for waste glass in construction site, such as water filtration, road base, drainage backfill and foamed glass building blocks. It been estimated around 200,000 tonnes to 500,000 tonnes of waste glass will use in construction site. This following research basically presents the engineering properties of glass cullet and research of using glass cullet as backfill material for retaining wall structure (Warwick Hassan, Manager Product Stewardship Program, Sept, 2006).

Recycle glass cullet processing method can be varying, depending on the use. Rock crushing industry has derived several type of class crushing equipment which can produce glass cullet that used as construction aggregate. Rock crushers are slightly bigger than glass crusher that can produce capcity of 1 to 20 tons per hours. The typical glass crushing system consists of a crushing mechanism, feed hopper and a discharge chute. In feed and outlet conveyors and a screening mechanism can be optional components. The types of crushing mechanisms are:

Hammermill, rotating disk and breaker bar;

Rotating drum and breaker plate;

Rotating breaker bar, impactor, and helical fluted roller.

Normally, glass bottles are loaded into feed hopper, after that conveyed to the crusher, processed and screened to remove the oversize particles or debris, and then conveyed to a bin/floor. According to Dames & Moore's observation (Dames & Moore Inc, June, 1993), there are few factors need to be considered such as:

Cullet is more abrasive than natural aggregate which will result in greater wearing of surfaces and subsequently more frequent maintenance.

Cullet is also less dense than natural aggregate which may cause difficulties in existing crushed rock gravity feed systems.

Glass cullet may be handled, spread and compacted with conventional construction equipment. To make glass into small particles like sand, can use pulverizing. Civil engineering applications and products of pulverized glass can include glassphalt, concrete additive, building materials, filter media, drainage and erosion control, and reclamation of beaches.

Engineering physical properties of recycle glass cullet

This section present an overview of engineering physical properties of recycle glass cullet, and compare it with other typical granular material such as sand. The purpose is to demonstrating the equivalency use of recycle glass cullet performance to the conventional aggregate component in construction site. Classify recycle glass cullet properties can help identify the glass material and engineering properties for those used in different engineering design. The method to test glass cullet properties is Existing American Society for Testing and Materials (ASTM) test methods which is same as testing in soil and aggregates. (Dames & Moore Inc, March, 1993)

Appearance

The size of glass cullet analyzed considered for civil engineering applications are around 0.5 to 20 mm (Dames & Moore Inc, June, 1993) .The general particle shape of glass cullet is angular with small percentage flat or platy shape. The angular shape indicates a potential for glass cullet to cut or puncture a synthetic linear (geomembrane) or wedge into moving parts of construction equipment as investigated by the ASTM D2488 procedure. The level of debris is up to 5 to maximum 10 % which can affect it engineering properties. Debris may consist of paper, foil and plastic labels, plastic and metal caps, cork, paper bags, wood debris, food residue, grass and soil, depends on the collection of the glass and sorting procedures.

Specific Gravity

Specific gravity is defined as a measure of material's density which determines the amount of void in aggregate. According to test method (ASTM D 854, 1999) the specific gravity value for natural aggregate such as sand are around 2.6 to 2.8. However, the specific gravity value for coarse and fine glass cullet range is around 1.96 to 2.41 and 2.49 to 2.52 respectively.

Unit weight

Unit weight can define as relative density which is the ration of difference between the void ratio of a cohensionless soil in the losest state and any given void ratio. According to test method (ASTM D 4254, 1999) data, the unit weight for natural aggregate such as sand is around 12.5 kg/m3 to 20.4 kg/m3. However, for 100 percent glass cullet is around 12 kg/m3 to 17kg/m3. If glass cullet and aggregate blended together, the unit weight will increase when decreasing cullet content. Unit weight also directly affects compaction and shear strength. The unit weight of glass cullet is relatively insensitive to moisture a level which is an advantage in wet weather applications.

Gradation

Gradation can define as grain-size distribution program as the proportions by mass of a soil or fragmented rock distributed in specified particle- size ranges. Gradation of glass cullet can directly affect the engineering properties such as compaction, permeability, filtration, hydrostatic and trixial shear. Figure is the result after using sieve analysis method (ASTM D 653, 1993) According to figure, the gradation of glass cullet is very similar to natural aggregate crushed rock or gravelly sand.

Figure show the grain size distribution of glass cullet and gravelly sand used for mechanical testing by (Dames & Moore, 1993)

Durability and Workability

Durability is concern about hardness and toughness of the material. The test is using standard method (ASTM C 131, 1993 by Dames & Moore from the L.A abrasion tests). Durability can defined as the material classification property that affects its suitability for roadway base course and fill under fluctuating loads. Natural aggregate's resistance to abrasion is slightly higher than glass cullet. According to the L.A abrasion test result, glass cullet durability is still close to the normal limiting values of 30 % greater for 6.35 mm and 42 % greater for 19.05 mm than that of roadway aggregate. Debris levels will minimal influence the durability. Workability is about how much the material can handle the compaction. Compare with crush rock (subangular and gravelly sand(subround), glass cullet is generally angular shape which have better potential in workability as it can work well in different construction equipment.

Shear strength

Shear strength is defined as the maximum resistance of a soil or rock to shearing stresses. It can be effect bearing capacity and expressed by the angle of internal friction, Ф which measure in degree. According to (ASTM D 3080, 1999), the internal friction angle, Ф of typical granular soils for loose, silty sand and for dense, medium size gravel is 27 and 55 degree respectively. But, internal friction angle, Ф of glass cullet is around 49 to 53 degree which is slightly higher than normal natural aggregate. Debris level in glass cullet will not affect on shear strength. From table, Test results indicate that the strength of cullet is about the same as natural aggregate.

Table show the result of shear strength test of class cullet and conventional aggregate. (ASTM D 3080, 1999)

Compaction

Compaction which is design consideration that effect density control, can define as the densification of a soil by means of mechanical manipulation by used (ASTM D 698, 1999) method. Due to compactness of the bulk material, high shear strength of the individual particles and high inter-particle frictional resistance, it bring glass cullet compacted to a dense state is rigid and strong. However, heavy field compaction equipment can significantly affect density values for 100 percent cullet fills because of the gradation change. Glass cullet can placed or compacted in wet weather because of it not sensitive to moisture content.

Permeability

Permeability is defined as hydraulic conductivity which can test by method (ASTM D 2434, 1999). The permeability value of typical granular soils is around 0.01 to 0.001 cm/sec. But, result data show 100 percent glass cullet for fine cullet and coarse cullet have permeability value around 0.04 to 0.06 cm/sec and 0.18 to 0.26 cm/sec respectively. Nevertheless, cullet-aggregate blended together have permeability value between 100 percent cullet and granular soil. In general, when increasing cullet content, cullet size and debris level will also increase permeability value, but permeability value will decrease when increasing compaction.

Thermal Conductivity and chemical resistance

Thermal conductivity can define as the ability of the material to conduct or resist heat flow and it is a design consideration that affects bedding and backfill for conduct or other heat sources. According to result from (ASTM C 518, 1999) method, the thermal conductivity of glass cullet is around 0.26 to 0.64 W/mK, which is lower than sand that are 2.9 to 7.7 W/mK, which mean glass cullet conduct hear slower and still feasible for utility trench backfill. Base on data from (ASTM D 3042, 1999) even under highly acidic condition, glass cullet still possesses better chemical resistance, 99.8 % if compare with sand which is only 70.1 %.

Property

Test method

Recycle glass cullet

Natural aggregate: Sand

Specific Gravity

ASTM D 854

1.96 to 2.52

2.6 to 2.8.

Unit weight (kg/m3)

ASTM D 4254

12 to 17

12.5 to 20.4

Durability

ASTM C 131

30 to 42

NA

Shear strength:

Friction angle, Ф

ASTM D 3080

49 to 53

27 to 55

Compaction:

Optimum moist content (%)

Max dry density( kg/m3)

ASTM D 698

5

8 to 10

16.4 to 19.5

18.2 to 20.9

Permeability (cm/sec)

ASTM D 2434

0.04 to 0.26

0.01 to 0.001

Thermal Conductivity(W/mK)

ASTM C 518

0.26 to 0.64

2.9 to 7.7

Chemical resistance (%)

ASTM D 3042

99.8

70.1

Table show comparison of engineering physical properties of glass cullet and sand

Designing the retaining wall

The application for glass cullet in construction site can be general construction backfill, roadway construction, utility construction drainage, landfill construction and etc. Since different application, the glass cullet content and debris level may vary. The table below shows the positive result in using glass cullet in each application.

Table show the use of percentage of glass cullet in each application.

For the purpose of this research paper, it is focus in building a retaining wall with recycle glass cullet as backfill material, which mean it use 100 % recycle glass cullet as backfill material. Research paper also include the design and calculation of conventional retaining wall and retaining wall with recycle glass cullet as non- structure backfill material. This was done by comparing both of them and testifies the result of using glass cullet as non-structure backfill can support as conventional backfill. To make a thorough comparison, the retaining wall are designed for three different height: 4m, 6m, and 8 m. This research project has made few assumptions before measure and designs the retaining wall:

. no surcharge loading exists behind the wall,

Soil behind and below the wall assume to be silty clay which unit weight is 17.2 kg/m3, friction angle, Ф are 20 degree, cohesion,c is 30KN/m3

Using recycle cullet as backfill material which unit weight is 14.6 kg/m3, friction angle, Ф are 51 degree, cohesion, c is 0 KN/m3 and wall friction =3/4 friction angle =34 degree.

Assume geotextile fabric allowable strength, σG= 15 KN/m

Factor safety of rupture of reinforcement, FS(B)=1.5

Factor safety of pullout, FS(P)=1.5

Using above assumptions, the geotechnical design of retaining wall was performed to ensure safety against overturning, sliding, and bearing capacity (Coduto, 1994).

Result and analysis

From figure show the geotechnical design for 8m high retaining wall with glass cullet as backfill material has smaller dimensions compare with the retaining wall with sand as backfill material, which can lead cheaper design.

Backfill material of retaining wall

Overturning factor

Sliding factor

Bearing capacity factor

Recycle glass cullet

3.36

4.03

4.47

Sand

3.82

1.59

4.64

Table show the factor result of recycles glass cullet and sand in 4m height.

Backfill material of retaining wall

Overturning factor

Sliding factor

Bearing capacity factor

Recycle glass cullet

3.2

3.94

3.04

Sand

4.3

1.7

3.6

Table show the factor result of recycles glass cullet and sand in 6m height.

Backfill material of retaining wall

Overturning factor

Sliding factor

Bearing capacity factor

Recycle glass cullet

5.98

5.38

3.02

Sand

5.48

1.91

3.38

Table show the factor result of recycles glass cullet and sand in 8m height.

From those tables above, for sand, overturning factor and bearing capacity factor are slightly higher than recycled glass cullet for 4m and 6m height expect 8m height, but both value are close. But sliding factor of recycled glass cullet for 4m, 6m, and 8m height is much higher than sand's sliding factor.

Dames & Moore Inc., Glass Feedstock Evaluation Project, Task 1 - Testing Program Design, Clean Washington Center, March 1993.

Dames & Moore Inc., Glass Feedstock Evaluation Project, Task 2 - Environmental Suitability Evaluation, Clean Washington Center, June 1993.

Dames & Moore Inc., Glass Feedstock Evaluation Project, Task 3 - Equipment Evaluation, Clean Washington Center, June 1993.

Dames & Moore Inc., Glass Feedstock Evaluation Project, Task 4 - Engineering Suitability Evaluation, Clean Washington Center, June 1993.

Dames & Moore Inc., Glass Feedstock Evaluation Project, Task 5 - Evaluation of Cullet as a Construction Aggregate, Clean Washington Center, June 1993.

Karan S. Henry, Associate Member, ASCE, and Susan Hunnewell Morin, Frost Susceptibility of Crushed Glass Used, December 1997

Warwick Hassan, Manager Product Stewardship Program, September 2006.

Coduto, D.P. Foundation Design. Englewood Cliffs: Prentice, 1992.

Shin, C. J. an Sonntag, V. Using Recovered Glass as Construction Aggregate Feedstock. Transportation Research Record 1437,1994

King Country Department of Transportation - Road Services Division. Glass Cullet Backfill Demonstration Project, March, 1996.

Glass Packing Institute. Glass Recycling Percentage of Glass Containers Recycled in the U.S. Indianapolis, IN, February,1998

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