الفهرس 
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Abstract
The continuous development of ornamental stones industry in Egypt due to the increasingly great demand of the Egyptian stones whether on the local or the international scale, led to a continuous and increasing accumulation of huge quantities of wastes in different forms which may reach about 55 – 85 % during all manufacturing stages. In the area of Shaq El – Thoaban only, about 70 % of these wastes is generating, which can be estimated as 800,000 tons of waste per year. These wastes have become of a hazardous effect on the surrounding communities due to the poverty of the wise management in recycling or even getting rid of these wastes in a safe mode.
The present study aims at characterization and evaluation of some ornamental stones – processing wastes at Shaq El-Thoaban area (Southern Cairo) and their suitability for some industrial applications.
This study throws light on the following items:
1. Industry of ornamental stones.
2. Characterization of ornamental stones wastes:
2.1. Physical properties.
2.2. Mineralogical composition.
2.3. Chemical analysis.
3. Preparation of cement composites using marble, granite and mixture of marble and granite wastes (on lab scale):
3.1. Mineralogical composition.
3.2. Physical properties.
3.3. Mechanical properties.
4. Industrial applications of marble wastes:
4.1. Manufacturing of concrete paving blocks:
4.1.1. Physical properties.
4.1.2. Mechanical properties.
4.2. Manufacturing of quicklime:
4.2.1. Available lime index.
4.2.2. Lime reactivity.
The main findings of the present study are given in the followings:
1. Industry of Ornamental Stones:
It passes through two stages:
1.1. Quarrying stage: This operation involves various stages: (i) Overburden Removal Stage; (ii) Extraction Stage. During each of these stages, huge amounts of stone fragments and powdered wastes are left around the quarry site depending on the technology owned by the quarrymen.
1.2. Processing stage: This operation takes place in the marble and granite processing plants in some industrial zones such as “Shaq El- Thoaban area” in Egypt, which involve slabs, tiles production with various dimensions through several stages which are: (i) Block Dressing Stage; (ii) Block Sawing Stage; (iii) Polishing and Slab Cutting Stage.
2. characterization of Marble and Granite Wastes:
Thirty five (35) samples of processing – ornamental stones wastes divided into: (25) marble samples and (10) granite samples were selected and characterized physically, mineralogical and chemically as follow:
2.1. Physical properties:
2.1.1. Particle size distribution:
About 90% of the particles are of grain size 27.3μm for marble sludge samples, while for granite samples are of grain size 50.03μm.
2.1.2. Specific Surface area:
The average surface area of marble sludge samples is about 0.6695 m2/g, while for granite sludge samples is about 0.4493 m2/g.
2.1.3. Specific gravity:
It ranges from 2.66 to 2.74 with an average of 2.69 for marble sludge samples, while for granite sludge samples generated from block cutter discs it ranges from 2.58 to 2.64 with an average of 2.61, while that generated from gang saws it ranges from 2.77 to 2.78.
2.1.4. Water content (as received from factory):
It ranges from 23.71 to 43.21 % with an average of 29.83 % for marble sludge samples, while for granite sludge samples it ranges from 29.38 - 48.05 % with an average of 38.64 %.
2.1.5. Whiteness index for marble samples: It ranges from (64.44 to 83.83 %) with an average of (76.89 %).
2.2. Mineralogical properties:
The XRD patterns revealed that all marble sludge samples are mainly composed of calcite mineral, while that of granite sludge samples, whether by gang saw or by block cutter machines, are mainly composed of quartz and feldspars (Microcline and Albite) with traces of calcite.
2.3. Chemical properties:
2.3.1. Marble samples: the chemical analysis revealed that all marble wastes are characterized by high CaO % content with an average of 55.15 %, very low MgO % content with an average of 0.21 %. These sludge wastes are also characterized by high loss on ignition with an average of 43.56 %, low content of Acid-Insoluble Residue with an average of 2.79 %, consequently, very low contents of SiO2 %, Al2O3 %. Concerning trace elements, (Sr) is the most abundant with an average of 375 ppm.
2.3.2. Granite samples: the chemical analysis revealed that the granite wastes, generated from cutting operation using block – cutter machine, consist mainly of SiO2 % with an average of 68.35 %, Al2O3 % with an average of 14.44 %, K2O % with an average of 5.38 %, Na2O % with an average of 4.67 %, Fe2O3 % with an average of 2.69 %, CaO % with an average of 1.62 %. Concerning trace elements, the most abundant elements are Sr with an average 222 ppm, Ba with an average 694 ppm, Ti with an average 1933 ppm and Zr with an average 324 ppm.
On the other hand, the granite wastes, generated from cutting operation using gang saw machine, consist mainly of SiO2 % with an average of 57.18 %, Al2O3 % with an average of 11.76 %, K2O % with an average of 4.61 %, Na2O % with an average of 4.76 %, Fe2O3 % with an average of 12.82 %, CaO % with an average 4.48 %. Concerning trace elements, the most abundant elements are Sr with an average of 211 ppm, Ba with an average of 537 ppm, Ti with an average of 1439 ppm and Zr with an average of 324 ppm.
3. Preparation of cement composites (on lab scale):
Three types of cement composites were prepared using different percentages of wastes: i) marble / cement composites (M10, M20, M30 and M40), ii) granite / cement composites (G10, G20, G30 and G40) and iii) marble + granite / cement composites (M20/G10, M20/G20, M30/G10 and M30/G20) as cement replacement, in addition to preparation of control cement paste (M 0) by using the standard water required for normal consistency. All these mixtures were cured using tap water for different curing times and tested mineralogically, physically and mechanically at every curing time as follow:
3.1. Physical properties:
3.1.1. Fresh cement composites:
3.1.1.1. Normal consistency, initial and final setting times:
The normal consistency of control and the other cement composites ranges from 24.5 to 29%.
The initial setting times of both control and the other cement composites ranges from 90 to 120 min.
The final setting times of both control and the other cement composites ranges from 175 to 220 min.
3.1.2. Hardened cement composites:
3.1.2.1. Water absorption, apparent porosity bulk density:
The water absorption of control and the other cement composites at 28 days curing ranges from 2.35 to 5.99 %.
The apparent porosity of control and the other cement composites at 28 days curing ranges from 5.25 to 11.95 %.
The bulk density of control and the other cement composites at 28 days curing ranges from 2.00 to 2.23 Kg/cm3 for dry density, while it ranges from 2.08 to 2.29 Kg/cm3 for saturated surface dry density.
3.2. Mechanical properties:
3.2.1. Compressive strength:
The compressive strength of control and the other cement composites at 28 days curing ranges from 49.95 to 80.02 MPa (509 to 816 Kg/cm2).
4. Manufacturing of concrete paving blocks:
Four types of concrete mixes were prepared using four percentages of marble wastes (M10, M20, M30 and M40) as cement replacement, in addition to preparation of control concrete mix (M 0). All the concrete mixes were air cured for different curing times and measured physically and mechanically.
4.1. Physical properties:
4.1.1. Water absorption, voids ratio and bulk density:
The water absorption of hardened control and marble concrete mixtures at 28 days curing ranges from 7.76 to 9.93 %.
The permeable pore space (voids) of hardened control and marble concrete mixtures at 28 days curing ranges from 16.75 to 20.53 %.
The bulk density of hardened control and marble concrete mixtures at 28 days curing ranges from 2.08 to 2.17 Kg/cm3 for dry density.
4.1.2. Rate of absorption (Sorptivity coefficient):
The initial rate of absorption (sorptivity coefficient) of hardened control and marble concrete mixtures at 28 days curing ranges from 3.6 × 10-2 and 7.9 × 10-2 mm/√s.
The secondary rate of absorption (sorptivity coefficient) of hardened control and marble concrete mixtures at 28 days curing ranges from 7.7 × 10-4 and 9.4 × 10-4 mm/√s.
4.1.3. Freeze –thaw durability:
The resistance to freeze-thaw (weight loss) of hardened control and marble concrete mixtures at 28 days curing after 49 cycles ranges from 0.26 to 2.69 Kg/m2.
4.2. Mechanical properties:
4.2.1. Compressive strength:
The compressive strength of hardened control and marble concrete mixtures at 28 days curing ranges from 26.42 to 36.60 MPa (269 to 373 Kg/cm2).
4.2.2. Flexural strength:
The flexural strength of hardened control and marble concrete mixtures at 28 days curing ranges from 2.41 to 4.38 MPa (24.60 to 44.64 Kg/cm2).
4.2.3. Abrasion resistance:
The resistance of hardened control and marble concrete mixtures to abrasion according to volume loss by (Böhme Method) ranges from 0.14 to 0.09 cm3/cm2, while according to groove width (Wide Wheel Method) ranges from 22.43 to 27.32 mm, and the abrasion index ranges from 0.10 to 0.25.
5. Manufacturing of Quicklime:
Six marble wastes samples were fired at 1000 °C for three soaking times.
5.1. Available lime content:
At soaking time (15 min.) the available lime content ranges from 88.40 to 96.87 % with an average 94.32 %
At soaking time (30 min.) the available lime content ranges from 92.44 to 97.83 % with an average 95.16 %.
At soaking time (120 min.) the available lime content ranges from 90.22 to 97.45 % with an average 94.31 %.
5.2. Lime reactivity: The average reactivity value (RDIN) of the quicklime fired at 1000 ºC for 30 min. soaking time is about 175 which exceed the limit of high reactive (RDIN value ˃ 30) as reported in [Potgieter et al., 2002].
CONCLUSIONS:
The above mentioned results indicate that:
I. All marble sludge wastes are composed mainly of calcium carbonate represented by calcite mineral of more than 97 %, while granite sludge wastes are composed mainly of silicon, aluminum, sodium and potassium oxides represented mainly by quartz and feldspars minerals.
II. The specific gravity of granite sludge is higher than that of marble sludge, while the grain size of marble sludge is finer than that of granite sludge wastes.
III. The addition of marble and/or granite wastes as a cement replacement in cement composites led to:
An insignificant slight increase in water absorption, apparent porosity up to 20 % marble or granite sludge waste additions which becomes observable at higher additions compared to the control.
An insignificant slight decrease in bulk density and compressive strength up to 20% waste addition which becomes observable at higher additions compared to control cement.
from the previous findings, it can be concluded that the optimum percentage of marble and granite powder wastes to be used as cement replacement in cement composites production with better physical and mechanical performance ranges from 10 – 20 % (MCC - 10, 20 and GCC -10, 20) of separate marble or granite wastes, and 30 – 40% of marble + granite wastes (MGCC 20/10, MGCC 30/10) can be used respectively.
IV. The addition of marble wastes as a cement replacement in concrete paving block - manufacturing led to:
An enhancement in apparent porosity (voids) consequently water absorption and bulk density (up to 20 % additions) compared to control mix and satisfy the standard specifications according to (ASTM C 902, 2009), (ASTM C 55, 2003), (ASTM C 90, 2011) and (ASTM C 129, 2003).
An improvement in initial and secondary absorption (up to 20 % additions) than other additions compared to control mix.
An improvement in freeze-thaw resistance (up to 20 % addition) than other additions compared to control mix and satisfy the standard specification according to (BS EN 1338, 2003) and (ASTM C 902, 2009).
An improvement in compressive and flexural strengths (up to 20 % additions) than other additions compared to control mix and satisfy the standard specification according to (ASTM C 902, 2009), (ASTM C 55, 2003), (ASTM C 90, 2011), (ASTM C 129, 2003) and (BS 6073, 1981).
An improvement in abrasion resistance (up to 20 % addition) than other additions compared to control mix and satisfy standard specification according to (BS EN 1338, 2003) and (ASTM C 902, 2009).
from the previous findings, it can be concluded that the optimum percentage of marble powder wastes to be used as cement replacement in manufacturing of concrete paving blocks with better physical and mechanical performance is 20% (MC-20)of marble wastes. The present study suggests a concrete mix comprising: marble powder waste (70 Kg/m3), Ordinary Portland cement (280 Kg/m3), coarse aggregate (1163 Kg/m3), fine aggregate (682 Kg/m3) and water (178 Kg/m3).
V.The calcinations of marble sludge wastes by firing at 1000 °C for 30 min. soaking time is considered the optimum condition for quicklime production of higher available lime content more than other soaking times with consequently higher lime reactivity.