Determination of camptothecins in DMSO extracts of Nothapodytes foetida by direct injection capillary electrophoresis

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Artiﬁcial stone slab production using waste glass, stone fragments and vacuum

vibratory compaction

Ming-Yu Lee

a

, Chun-Han Ko

b

, Fang-Chih Chang

c,*

, Shang-Lien Lo

d

, Jyh-Dong Lin

a

, Ming-Yang Shan

e

,

Jeng-Ching Lee

a

Department of Civil Engineering, National Central University, 300 Jhongda Road, Jhongli City, Taoyuan County 32001, Taiwan, ROC b

School of Forestry and Resource Conservation, National Taiwan University, No 1, Section 4, Roosevelt Road, Taipei 106, Taiwan, ROC c

The Instrument Center of National Cheng Kung University, National Cheng Kung University, No. 1, University Road, Tainan City 701, Taiwan, ROC d

Research Center for Environmental Pollution Prevention and Control Technology, Graduate Institute of Environmental Engineering, National Taiwan University, 71 Chou-Shan Road, Taipei 106, Taiwan, ROC

e_{Department of Civil Engineering, Cheng Shiu University, 840 Chengching Road, Niaosong Township, Kaohsiung County 833, Taiwan, ROC}

a r t i c l e

i n f o

Article history: Received 27 June 2006

Received in revised form 27 March 2008 Accepted 27 March 2008

Available online 6 April 2008 Keywords:

Artiﬁcial stone slabs Waste glass Stone fragments Recycling

Compressive strength

a b s t r a c t

In this research, waste glass and stone fragments from stone slab processing are recycled as raw materials for making artificial stone slabs using vibratory compaction in a vacuum environment. Waste glass pow-der (40%) and fine granite aggregates (60%) are mixed with unsaturated polymer resins (8%) as binpow-der. Under compaction pressure of 14.7 MPa, vibration frequency of 33.3 Hz and vacuum condition at 50 mm Hg, artificial stone slabs with high compressive strength of 148.8 MPa, water absorption below 0.02%, density of 2.445, and flexural strength of 51.1 MPa are obtained after 2 min compaction. The arti-ficial stone slabs fabricated in this study prove to be superior to natural construction slabs in terms of strength and water absorption.

1. Introduction

During stone processing, a great amount of stone fragments are left as waste[1], while waste glass accounts for a major proportion of recycled materials collected [2,3]. Previous studies have re-ported the use of these waste materials for fabricating asphalt con-crete pavement and sidewalk slabs[4], aggregates for mixing with cement concrete[5–9]and its durability[10], low strength materi-als[11], lightweight aggregates [12], and construction materials such as red bricks with resins added. However, the wide difference in types and colors of these waste materials undermines the proﬁts of commercialized recycling [2,3]. Currently, most glass-making companies use merely 30–40% of waste glass in their production. Moreover, Waste glass can also be used to replace 10–15% of the sandstone used in asphalt pavement[4]. To date, there is no study on the fabrication of high-value construction slabs using recycled waste materials. Like real marble, high-value construction slabs have complex twists and veins that go deep into the stone. High-value construction slabs, therefore, provide a durable surface which is far more permanent and realistic in appearance than faux surfaces, usually wood, which are painted to resemble marble.

Natural stone slabs are quarried and processed in large amounts as construction materials because they are hard, durable, ﬁre-resis-tant, and have a glossy surface. The amount of slabs used world-wide in 2006 is estimated at 878.3 million square meter, demanding a total of 80.47 million tons of mined stone[13].

The amount of stone waste produced yearly in Taiwan reaches 500 thousand tons. Stone fragments, after being crushed, serves mainly as mixing aggregates, which are worth less than US$20 per ton[14]. Stone sludge has been employed to fabricate products such as calcium silicate boards, ceramic handicrafts, chemical materials and fertilizers using cementation, sintering and extrac-tion processes[1,14]; however, the high production cost and low market demand pose constraints in its recycling as raw material.

In spite of the large quantity used and high unit price, artificial stone slabs are more cost-efficient compared with high-class cera-mic slab because of their excellent flexural strength and surface gloss. For scagliola (scales or chips of marble) slabs to be suitable for paving floors, they must be durable with Mohs hardness above 6 and non-porous with water absorption below 0.02%.

This research aims to study the effect of the three processing con-ditions, namely compaction pressure, vacuum condition, and vibra-tion frequency, on the physical properties of artificial stone slabs fabricated at different glass/fine aggregate ratios. Artificial stone slabs obtained through vacuum vibratory compaction undergo

* Corresponding author. Tel.: +886 2 2362 5373; fax: +886 2 2392 8830. E-mail address:d90541003@ntu.edu.tw(F.-C. Chang).

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Cement & Concrete Composites

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traditional processing steps of grinding, cutting and polishing. Being non-porous and of low water absorption, artificial stone slabs are superior to natural ones, whose drawbacks include low flexural strength, high water absorption, and high porosity, thus making them ideal construction materials for covering walls or paving floors. In view of the depleting supply of natural resources, the recy-cling of stone leftover fragments and waste glass into construction materials not only creates brand-new products for use, but also offer an ecological and economic alternative to waste treatment. 2. Materials and methods

2.1. Waste glass powder

Of the recycled glass in Taiwan, container glass and window glass account for the greatest proportions. Table 1 shows the chemical composition of different types of waste glass. As can be seen, the recycled container glass used in this study is comprised of mainly SiO2, Na2O, CaO, and a small proportion of Al2O3 and MgO. Recycled glass collected was crushed, washed and dried. With impurities removed, the dried glass aggregates were ground into powder and sieved through Mesh No. 200.

2.2. Stone leftover fragments

Marble and granite are the main construction slabs used in Tai-wan. Marble leftover is not used for recycling because of its low Mohs hardness degree of 4, high porosity, and high water absorp-tion of 0.5%. In contrast, granite leftover is comprised of mainly SiO2, as shown inTable 1, and has Mohs hardness degree above 6 and water absorption below 0.06%. Granite leftover used in this research is taken from a slab processing factory in Hualien, Taiwan. The stone leftover fragments are crushed and graded into three categories: (1) 4 mm in diameter through Mesh No. 5, (2) 2 mm in diameter through Mesh No. 10, and (3) 0.6 mm in diameter through Mesh No. 30. After being washed and heated at 105 °C till constant weight is reached, the granite fragments can serve as aggregates for recycling.

2.3. Binder

The binder used in this research is unsaturated polymer resins (ETERSET 2238P, Chang Chun Company, Taiwan), with characteris-tics of intermediate viscosity and low exothermic temperature. It contains 32–37% styrene and its viscosity ranges between 450 and 550 cps when spindled at 60 rpm at 25 °C. Added with 0.5% of the hardener, which is comprised of 6% cobalt (Co), the binder becomes gelated within 19–33 min at 25 °C. The shortest harden-ing time ranges between 9 and 13 min while the highest sinterharden-ing temperature is 130–155 °C. The compressive strength of the binder tested using ASTM D 790 is found to be 102.0 MPa.

2.4. Sample preparation

Fig. 1summarizes the manufacturing process of artiﬁcial stone

slabs in this study. First, crushed and washed granite fragments are

categorized into three sizes. According to the densified mixture, the waste glass powder and fine aggregates are mixed at different mix proportions with unsaturated polymer resins added as the bin-der using the planetary gear mixer and put in a 120 mm 120 mm molding machine. The thickness of the original paste is 20 mm. With the vibration frequency and vacuum condition set, the sam-ple is compacted under compression using the vacuum vibratory compactor depicted inFig. 2. The molded samples are cured for 90 min in a drying oven at constant temperature of 95 °C and fur-ther cured at room temperature for 7 days. Finally, the samples are cut, grinded and polished into artificial stone slabs of 12 mm thick-ness with sharp edges removed.

The density and water absorption of the artificial stone slabs were analyzed according to ASTM C97. ASTM C880 and ASTM C170 were adopted to determine the flexural strength and com-pressive strength, respectively. Artificial stone slabs fabricated in this research are intensively compacted without air or pores; thus it was difficult to examine the pores between aggregates using the BET surface area analyzer. Instead, POM (Polarized optical micro-scope) observations were made to analyze the existence of pores and the structure of aggregates in the artificial stone slabs. 3. Results and discussion

3.1. Effects of compaction pressure

Fig. 3shows the compressive strength of artiﬁcial stone slabs

mixed at different glass/fine aggregate ratios and compacted under different compaction pressures. As can be seen, higher compressive strength can be obtained at glass/fine aggregate ratios between 45:55 and 50:50 and under compaction pressure exceeding 14.7 MPa. From the perspective of particle packing, the 45:55 and 50:50 mixing ratios appear to be most effective. That is, waste glass powder takes a role in filling the gaps between stone leftover fragments. When the waste glass powder is insufficient, the gaps cannot be entirely filled, which lowers the compressive strength. On the other hand, if the amount of waste glass powder is exces-sive, the compacted packing bursts as the waste glass powder, rather then the stone leftover fragments, directly receives the pres-sure with compacted packing, which lowers the level of compres-sive strength.

Table 2also shows the compressive strength of artiﬁcial stone

slabs prepared under different compaction pressures. As can be seen, under the highest vibration frequency of 50.0 Hz and vacuum condition at 50 mm Hg, compressive strength increases with increasing compaction pressure. For example, the sample reaches the highest compressive strength at 151.3 MPa under compaction pressure of 14.7 MPa. However, compaction pressure exceeding 19.6 MPa reduces compressive strength. This is because too high pressure crushes the edges of the stone fragment into pieces, as ob-served in the POM image shown inFig. 4(a). On the other hand, too low pressure cannot compact the aggregates, making the structure less densiﬁed as seen inFig. 4(b). For example, under compaction pressure of 4.9 MPa, the compressive strength reaches only 83.7 MPa, indicating that the lower the compaction pressure, the lower the compressive strength achieved.

Table 1

Chemical composition of waste glass and granite fragments

Element (%) SiO2 Al2O3 MgO CaO Na2O Fe2O3 Others

Waste glass Container 72.2 1.9 1.5 9.6 14.6 – 0.2

Window 72.0 1.3 3.5 8.2 14.3 – 0.7

Lamp 71.5 2.0 2.8 6.6 15.5 – 1.6

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3.2. Effects of vacuum

Fig. 5shows the changes in compressive strength of artiﬁcial

stone slabs mixed at different glass/ﬁne aggregate ratios and pacted under different vacuum levels. As can be seen, higher com-pressive strength can be obtained at glass/ﬁne aggregate ratios between 45:55 and 50:50 and under vacuum below 50 mm Hg. Moreover, as shown inTable 3, at vibration frequency of 50.0 Hz and compaction pressure of 14.7 MPa, compressive strength de-creases with vacuum conditions above 50 mm Hg.

As mentioned above, the binder used in this study is unsaturated polymer resins, which is viscous in nature. Once the structure is compacted, the air trapped between aggregates during mixing can-not be easily removed. Air can only be eliminated when compaction is conducted in a vacuum. Removing the air serves to prevent forma-tion of pores between aggregates, which will increase water absorp-tion and undermine the compacted structure, thus lowering compressive strength. Hence, it is important to reduce the air content in the molding machine during compaction. As seen in

Fig. 6(a), no pores are discernable in the densiﬁed structure formed

under vacuum at 50 mm Hg with compressive strength reaching 151.3 MPa. Under vacuum condition above 50 mm Hg, the air con-tent increases relatively, forming pores and undermining the com-pressive strength. As seen inFig. 6(b), a great number of pores are found in the sample prepared under vacuum at 200 mm Hg.

Surface treatment Mixing Gas storage tank Fuel supply system Stone fragments Pre-mixing Breaking/ meshing Vacuum vibratory Compaction Sintering cultivation Product packing Chemical treatment Cutting Pigment Binder Hardener Grinding Burnishing Glass Breaking/ meshing Air pollution prevention system Air

Fig. 1. Manufacturing procedure of artiﬁcial stone slabs.

Hydraulic

machine

Vacuum

pump

Mold

Vibration

motor

Power

cylinder

Base plate

Fig. 2. Vacuum vibrating compactor.

100 110 120 130 140 150 160 35:65 40:60 45:55 50:50 55:45 60:40 Compressive strength (MPa) 4.9MPa 14.7MPa 24.5MPa 34.3MPa Glass : Stone

Fig. 3. Effect of compaction pressure and glass/ﬁne aggregate ratio on compressive strength.

Table 2

Physical properties obtained under different compaction pressures

Compaction pressure (MPa) 4.9 9.8 14.7 19.6

Density 2.030 2.114 2.446 2.410

Water absorption (%) 0.221 0.203 0.011 0.015 Flexural strength (MPa) 27.9 46.3 52.7 44.6 Compressive strength (MPa) 83.7 119.2 151.3 128.4 Conditions: vibration frequency (50.0 Hz), vacuum (50 mm Hg).

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3.3. Effects of vibration frequency

Fig. 7shows the changes in compressive strength of artiﬁcial

stone slabs mixed at different glass/ﬁne aggregate ratios and

com-pacted under different vibration frequencies. As can be seen, higher compressive strength can be obtained at glass/fine aggregate ratio of 50:50 and vibration frequency of 50.0 Hz. Vibration serves to ad-just the orientation of the aggregates in order to pack them into a more compact structure. As seen inFig. 8(a), the microstructure of the artificial slab prepared under high vibration frequency is den-sified and closely compacted (the surface of fine stone fragments is covered by waste glass powder and unsaturated polymer resins), while a loosely compacted structure is seen inFig. 8(b) for artificial stone slabs prepared under low vibration frequency.

Table 4shows the physical properties of artiﬁcial stone slabs

pre-pared under different vibration frequencies. As can be seen, under

Fig. 4. POM image of sample prepared under (a) high pressure (14.7 MPa) and (b) low pressure (4.9 MPa).

100 110 120 130 140 150 160 35:65 40:60 45:55 50:50 55:45 60:40 Glass :Stone Compressive strength (MPa) 50mmHg 100mmHg 150mmHg 200mmHg

Fig. 5. Effect of vacuum and glass/ﬁne aggregate ratio on compressive strength.

Table 3

Physical properties obtained under different vacuum levels

Vacuum (mm Hg) 50 100 150 200

Density 2.444 2.303 2.248 2.048

Water absorption (%) 0.011 0.125 0.202 0.211 Flexural strength (MPa) 52.1 47.9 40.7 32.0 Compressive strength (MPa) 151.3 106.0 94.6 78.7 Conditions: vibration frequency (50.0 Hz), compaction pressure (14.7 MPa).

Fig. 6. POM image of sample prepared under vacuum condition (a) 50 mm Hg and (b) 100 mm Hg. 80 90 100 110 120 130 140 150 160 170 35:65 40:60 45:55 50:50 55:45 60:40 Glass : Stone Compressive strength (MPa) 8.3 Hz 16.7 Hz 33.3 Hz 50.0 Hz

Fig. 7. Effect of vibration frequency and glass/ﬁne aggregate ratio on compressive strength.

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compaction pressure of 14.7 MPa and vacuum at 50 mm Hg, better physical properties can be obtained at higher vibration frequencies. For example, at 50.0 Hz, the density is 2.448, the water absorption drops to 0.011%, ﬂexural strength reach 51.9 MPa, and compression strength rises to 151.3 MPa. It can be inferred from the results that within the short 2 min duration, vibration at too low frequency fails to compact the aggregates into a densiﬁed structure.

4. Conclusions

(1) This study has successfully manufactured artificial construc-tion slabs from stone leftover fragments crushed into fine aggregates and waste glass ground into powder. Under com-paction pressure of 14.7 MPa, vibration frequency of 33.3 Hz and vacuum condition at 50 mm Hg, we obtained artificial stone slabs of densified structure with compressive strength exceeding 148.8 MPa and water absorption below 0.02%. Moreover, both density and flexural strength of these mate-rials increase with increasing compressive strength. Hence, waste glass and stone fragments can be recycled into quality products of high unit price.

(2) Experimental results reveal that using high compaction pressure alone will not yield densiﬁed structure. Vibration is also needed to adjust the orientation of aggregates to become more closely compacted. In addition, excessive pres-sure crushes aggregates, producing cracks and thus decreas-ing the compressive strength. In this research, the optimal compaction pressure obtained is 14.7 MPa.

(3) Among the three processing conditions, compaction pres-sure is the chief determinant of compressive strength, while vibration frequency and vacuum condition inﬂuence com-pact density, which in turn affects compressive strength. To produce high-quality artiﬁcial stone slabs with no pores, the air trapped between aggregates during the mixing pro-cess must be eliminated using a vacuum pump. Only at vac-uum condition below 50 mm Hg can the formation of pores be prevented.

(4) The success of recycling techniques is dependent on the commercial proﬁts they can bring. Hence, the development of recycling techniques has to take into consideration mar-ket demand and unit price of the recycled products. This research has successfully led to three patents in Taiwan

[15–17]; and the market price of artiﬁcial stone slabs has

increased to US$4160 per cubic meter. In sum, the manufac-turing of artiﬁcial stone slabs from recycled waste products not only offers an ecological alternative to natural construc-tion stones, its producconstruc-tion and applicaconstruc-tions also generate great economic beneﬁts.

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Fig. 8. POM image of sample prepared under (a) high vibration frequency (50.0 Hz); (b) low vibration frequency (16.7 Hz).

Table 4

Physical properties obtained under different vibration frequencies

Vibration frequency (Hz) 8.3 16.7 33.3 50.0

Density 2.134 2.216 2.445 2.448

Water absorption (%) 0.210 0.205 0.012 0.011 Flexural strength (MPa) 29.6 38.2 51.1 51.9 Compressive strength (MPa) 109.5 123.3 148.8 151.3 Conditions: compaction pressure (14.7 MPa), vacuum (50 mm Hg).