ITS PRODUCTION METHOD THEREOF

Field of Invention

This present invention relates to a construction material and its production method thereof. In more particular, the present invention relates to a construction material incorporated with recycled waste materials which can provide adequate mechanical properties.

Background of The Invention

The consuming need for construction materials such as building blocks or bricks is growing at an alarming rate in order to meet the increasing demand of land exploitation for new buildings.

Manufacturing of the construction materials usually requires bulk quantities of cement, steel, aggregates and others. Hence, this would exert great pressure on discovering new natural resources in search of more raw materials and higher energy requirements. The use of alternative raw materials such as coal ash is encouraged to relieve the demanding pressure and to preserve the natural fertility of the top soil as well as minimize the accumulation of ash waste.

Fly ash is a burnt residue generated in combustion of pulverized coal whereas bottom ash refers to part of the non-combustible residues being resided at the bottom of the combustion furnace. Both of the fly ash and bottom ash are siliceous in nature and due to their geo-technical pozzolanic and physio-chemical properties, they are suitably useful in the fields of building products manufacturing and civil works. There are some prior arts relating to building blocks or the similar which are made of siliceous fly ash and several methods of producing the building blocks.

A United States Patent No. 4780144 discloses a method of producing a building element from a mixture of fly ash, slaked lime, water and coarse particles. The hardening of the building element is performed at elevated temperature of maximum 100°C and at atmospheric pressure in a water vapor containing atmosphere. Optionally, the hard-enable mixture may be partially granulated before use.

A method of producing or manufacturing durable such as freeze or thaw resistance, non-fired masonry units made of fly ash is described in another United States Patent No. 20070000412. The process comprising the steps of determining and adjusting the amount of calcium oxide and loss of ignition in the fly ash, determining the water content required for making the fly ash units, selecting and mixing an air-entrainment agent with water and fly ash, placing or injecting the fly ash mixture into molds, compacting the fly ash mixture in the molds, dislodging or releasing the compacted units from molds and curing the units in a wet environment.

An European Patent No. 751868 discloses steam hardened concrete including lightweight concrete and its manufacture thereof. The steam hardened concrete is manufactured from an aqueous mix containing at least one calciferous material of the group consisting of unslaked lime, slaked lime, cement, blast furnace slag and siliceous material. The siliceous material contains at least a portion of which is a finegrained siliceous material of fly ashes. A United States Patent No. 6068803 claims a method of making a building block from waste particulate siliceous materials such as fly ash, bottom ash and rock mineral fines includes employing a major amount of such waste particulate materials in combination with a calciferous additive and water to cure and shape the same under the influence of controlled pressure and temperature for a predetermined time. Hydrothermal curing of the compacted shape is preferably achieved in a saturated steam atmosphere using an autoclave or similar apparatus.

A process for the manufacture of lightweight, cellular building materials is described in an European Patent No. 1438062. The process comprising the steps of reacting a siliceous material which is pulverized fuel ash with a binder of quicklime and an adequate dispersion of calcium hydroxide, expanding the reaction mixture and subsequently hardening it at an elevated temperature.

The fly ash and bottom ash contain trace concentrations of toxic heavy metals including arsenic, beryllium, cadmium, barium, chromium, copper, lead, mercury, molybdenum, nickel, radium, selenium, thorium, uranium, vanadium and zinc. Incineration does not destroy these metals, but simply disperses them via the incinerator stack or concentrates them into bottom and fly ash residues. The hazardous nature of the fly ash and bottom ash would cause detrimental health effects and impart long term-risks and contaminants to the environment resulting from leaching or run-off into soil or groundwater.

Nonetheless, the prior arts do not acknowledged the treatment on fly ash or bottom ash to prevent heavy metals thereof from leaching or deposition before incorporating the ash residues to form the building blocks. The prior arts also do not disclose treatment of the fly ash and bottom ash by a wet slurry method.

Hence, it is desirable to invent a method of producing a construction material incorporated with fly ash and bottom ash which are treated to prevent heavy metals from deposition thereof. It is also desirable to invent a construction material incorporated with fly ash and bottom ash having adequate mechanical properties, light-weight and good fire retardant. Summary of The Invention The main object of the present invention is to invent a method of producing a construction material incorporated with fly ash and bottom ash which are treated to prevent heavy metals from deposition thereof.

Another object of the present invention is to invent a construction material incorporated with fly ash and bottom ash having adequate mechanical properties, light-weight and good fire retardant. Still, one object of the present invention is to invent a construction material which can serve as an alternative in replacement of conventional masonry materials such as ordinary clay bricks and cement bricks.

At least one of the preceding objects is met, in whole or in part, by the present invention, in which the embodiment of the present invention describes a method of producing a construction material comprising the steps of treating an aqueous slurry of bottom ash and fly ash chemically to prevent heavy metals thereof from deposition, settling the treated slurry to allow the bottom ash and fly ash to sediment and discarding the top aqueous layer of the settled slurry and incorporating the sediment to a mixture of hydrated lime, oil palm ash, mineral particles, a binder and a plasticizer thereby forming the construction material.

In the present invention, the method of producing the construction material is a wet slurry method by chemically treating the ash residues to prevent heavy metals from deposition thereof. The treated fly ash and bottom ash are recovered as sediment of the slurry in which the heavy metals present in the ash residues are converted to insoluble forms and being encapsulated from leaching.

Detailed Description of The Invention One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objects and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiment described herein is not intended as limitations on the scope of the invention.

The present invention discloses a method of producing a construction material comprising the steps of treating an aqueous slurry of bottom ash and fly ash chemically to prevent heavy metals thereof from deposition, settling the treated slurry to allow the bottom ash and fly ash to sediment and discarding the top aqueous layer of the settled slurry and incorporating the sediment to a mixture of hydrated lime, oil palm ash, mineral particles, a binder and a plasticizer thereby forming the construction material.

As disclosed in the present invention, the method of producing a construction material comprising the treating step on an aqueous slurry of bottom ash and fly ash chemically to prevent heavy metals thereof from deposition. The chemicals used is preferably calcium hydroxide and calcium sulphate.

The treating step involves the addition of calcium hydroxide to adjust the pH of the aqueous slurry to convert the soluble heavy metals ions into insoluble metal hydroxides, whereas calcium sulphate is to cause hardening and solidification of the ash residues to trap the heavy metals from leaching or deposition. Basically, the heavy metals are soluble at pH ranging from 5-7, therefore it is important for calcium hydroxide to adjust the pH to prevent the soluble metals from becoming mobile that will cause leaching.

In a preferred embodiment, the aqueous slurry is formed by stir mixing about 5-10wt % calcium hydroxide, 3-5wt% calcium sulphate and 20-50wt% water to 100% total weight of fly ash and bottom ash for about 1-2 hours. The pH of the slurry is regulated to a range of about 9.5-10.5 using calcium hydroxide thereby converting the soluble heavy metals to their insoluble forms. On the hands, the calcium sulphate is used to trap those insoluble heavy metals from deposition or leaching. The pH-regulated slurry would then be allowed to settle forming into a bottom sediment and a top aqueous layer.

Hereinafter, the present invention describes a method of producing the construction material comprising the step of settling the treated slurry to allow the bottom ash and fly ash to sediment and discarding the top aqueous layer of the settled slurry. In the preferred embodiment, the treated slurry is preferably settled for about 5-6 hours to allow the fly ash and bottom ash to sediment whereas the top aqueous layer is to be discarded and could be transported to a filtration tank for treatment.

Also disclosed in the present invention, the method of producing the construction material shall involve grinding of the fly ash and bottom ash to reduce the particle size so that higher surface area is provided for the chemically treating step and more homogeneous binding with other raw ingredients. The ground fly ash and bottom ash are preferably in the form of powder with particle size ranges from 50μιη to ΙΟΟμπι.

As further claimed in the present invention, a method of producing the construction material comprising the step of incorporating the sediment to a mixture of hydrated lime, oil palm ash, mineral particles, a binder and a plasticizer thereby forming the construction material.

In the present invention, due to the geo-technical pozzolanic of fly ash and bottom ash, the hydrated lime which reacts with the sediment of treated ash residues would cause cementitious characteristic to the building material. The oil palm ash preferably known as palm oil fuel ash (POFA) in pulverized form is also pozzolanic and could serve as a soundproof material and a thermal insulator. The mineral particles include gypsum and silica sand, wherein gypsum is acting similarly as calcium sulphate to trap the heavy metals in the ash residues from leaching or deposition whereas the silica sand such as mine sand can be used as a filler. Furthermore, the present invention discloses the use of a binder which is cement or Portland cement in particular to bind and solidify the raw ingredients together, trapping the heavy metals to be in stabilized condition within the construction material from leaching or deposition. The plasticizer is preferably sulfonated polymer for increasing fluidity and plasticity of the construction material to ease the mixing process.

One preferred embodiment of the present invention indicates the incorporation of the sediment to the mixture of raw ingredients in a dry mixing plant, whereby the mixture preferably contains 5-8wt% hydrated lime, 20-25wt% oil palm ash, 3-5wt% gypsum, 6-10wt% Portland cement, 8-10wt% nano silica sand and 3-5wt% superplasticizer is measured with desired proportions of the raw ingredients, would then be conveyed and fed into a pan mixer to which about 10-l5wt water is added.

The machinery used for measuring and processing of the construction material is closed to dust free and controlled by a central computer system for calculating of batch materials in high accuracy.

The method of producing the construction material further comprising a step of hardening the incorporated mixture by pressing and curing. A preferred embodiment discloses pressing of the construction material in a mold using hydraulic or mechanical press at a pressure ranges from 3000-5000psi and curing the molded product in open air for about 7-14 days or with steam heated to 70°C in 3 hours and cooled to 20°C in 6 hours. Apart from the wet slurry method as described above, an alternative method of producing the construction material is a dry mix treating method. In the dry mix method, pulverized ash residues of fly ash and bottom ash is mixed with hydrated lime and gypsum. The mixture is then moistened allowing the hydrated lime to adjust pH to a range of 9.5-10.5 and convert soluble heavy metals present in the ash residues to insoluble forms, whereas the gypsum shall trap the insoluble heavy metals to prevent them from deposition or leaching by solidification of the ash residues. In addition, the mixture could be further added with oil palm ash, cement, silica sand and superplasticizer prior to moistening. The present invention further claims a construction material comprising bottom ash, fly ash and a mixture of hydrated lime, oil palm ash, mineral particles, a binder and a plasticizer; wherein the bottom ash and the fly ash are acquired from the sediment of a settled aqueous slurry of bottom ash and fly ash in which the slurry is treated chemically to prevent heavy metals thereof from deposition followed by settlement to from the settled slurry. Another preferred embodiment of the present invention discloses a construction material comprising 30-35wt% bottom ash, 25-30wt% fly ash, 5-8wt% hydrated lime, 20-25wt% oil palm ash, 3-5wt gypsum, 6-10wt% Portland cement, 8-10wt% nano silica sand and 3-5wt superplasticizer.

The aqueous slurry of fly ash and bottom ash present with 20-50wt% water is treated chemically with the addition of about 5-10wt calcium hydroxide and 3-5 wt% calcium sulphate by 100% total weight of fly ash and bottom ash. The chemical treatment is followed by settlement of the slurry to allow the bottom ash and fly ash to sediment. A top aqueous layer from the settled slurry is discarded or transported for further treatment.

As claimed in the present invention, the construction material is used as a building block, building panel or road pavement. In specific, the construction material can be formed into housing bricks, building boards, roof tiles, asphalt concrete, paver block, road curb and others. Hardening of the construction material is performed by pressing and curing, preferably using hydraulic or mechanical press at a pressure ranges from 3000-5000psi and curing in open air for about 7-14 days or with steam heated to 70°C in 3 hours and cooled to 20°C in 6 hours.

The use of fly ash in replacement of Portland cement during manufacturing of construction material such as bricks or panels can improve the product by having increased strength, durability and resistance to chemical attacks.

High compressive strength eliminates product breakages as wastage during transport and handling, thus the cracking of plaster is reduced due to lower thickness or fluidity of mortar joint, plaster and basic material of the product. In the present invention, the compressive strength for a brick formed of the construction material is 9.00n/mm ² in average.

The bricks and panels shall be having adequate crushing strength in load bearing whereas lighter in weight than ordinary clay bricks hence they do not add extra load to the structure design. Moreover, the bricks and panels can give maximum light reflection without glare as they do not absorb heat but reflect heat. Due to the presence of oil palm ash or POFA, soundproof and thermal insulation properties are imparted to the construction material or product.

In the present invention, bricks formed of the construction material have water absorption of 6-12% against 20-25% for handmade clay bricks, thermal conductivity ranging from 0.90-1.05W/m ^2o C which is 20-30% lesser than those of concrete bricks, maximum average drying test shrinkage of 0.035-0.04%, coefficient of expansion ranging from 10 ^"14 xlO ^"6 and density ranging from 1800-1850kg/m. The low water absorption property of the bricks or panels reduces wall dampness and results in only sprinkling of water instead of soaking in water during application of plaster for masonry jointing. After proper brick pointing of joints, the bricks can be directly painted in dry distemper or cement paints and even directly applied with plaster of Paris or gypsum plaster without the backing coat of plaster such as cement mortar comparing to conventional methods.

Examples

Example 1

The analysis of hazardous heavy metals present in the bottom ash is shown in Table 1.

Table 1

No. Hazardous Organics Concentration (mg/kg)

Ash *TTLC

1 Silver (Ag) <0.2 500

2 Arsenic (As) 19 500

3 Barium (Ba) 189 10000

4 Beryllium (Be) <0.3 75

5 Cadmium (Cd) 4 100

6 Cobalt (Co) 36 8000

7 Chromium (Cr) 96 2500

8 Chromium Hexavalent (Cr ⁶ *) <0.1 500

9 Copper (Cu) 47 2500

10 Molybdenum (Mo) <0.5 3500

11 Nickel (Ni) 76 2000

12 Antimony (Sb) <14 500

13 Selenium (Se) <4.5 100

14 Thallium (TI) <57 700

15 Vanadium (V) 136 2400

16 Zinc (Zn) 20 5000

17 Mercury (Hg) 0.005 20 18 Lead (Pb) 41 1000

*TTLC = Total Threshold Limit Concentration

A sample brick comprising the bottom ash is submerged in water for 48 days to obtain a leaching solution. The analysis of hazardous heavy metals determined on the brick leaching solution is shown in Table 2.

*TCLP = Toxic Characteristic Leaching Procedure

From the table, the method of ICP stands for Inductively Coupled Plasma whereas AAS represents Atomic Absorption Spectrometry. In comparison, the leaching solution contains reduced amount of hazardous heavy metals than the ash itself because the heavy metals are trapped from deposition in the brick.

For treating the fly ash and bottom ash, calcium hydroxide or hydrated lime is used in adjusting pH suitable for reaction and converting soluble heavy metals in the ash residues to insoluble forms. Besides, calcium sulphate or gypsum is used to solidify the ash residues thereby trapping heavy metals within the brick from deposition or leaching.

Example 2

Sample brick containing bottom ash treated by calcium hydroxide and calcium sulphate is washed with water. Table 3 indicates a reverse mutation assay to determine the adverse mutagenic effects of the washed water from the sample brick using Salmonella typhimurium bacterial strains as the target cells.

The bacterial cultures used in the experimental testing includes Salmonella typhimurium strains TA98, TA100 and TA102. The test is carried out on varied concentrations of washed brick solution or extract using the method described by Maron and Ames (1983).

Fresh cultures of bacterial strains are grown in nutrient broth overnight at 37°C. The bacterial cultures and washed brick solutions are prepared in 0.9% NaCl solution shall be added into 2ml molten top agar. The contents are mixed and poured on glucose minimal agar plates. Incubation is conducted for 48 hours at 37°C and the revertant colonies would then be counted.

Table 3a, 3b and 3c indicates the revertant colonies produced by S. typhinurium strains TA98, TAIOO and TA102 in the presence of metabolic activation system (S9 mix) respectively.

Table 3a

Treatment Concentration Mean revertant colony

^g/plate) TA98 Reference limit Washed brick solution 1 313 24+5 sample 2 625 22+5 <36 (less than

2x of the

3 1250 18+1

colonies in

4 2500 21+3 negative control

5 5000 24+3

Negative control (0.9% - - 18+9 - NaCl)

Positive control (2AA) 1 0.5 275+93 >36

2 1.0 ND -

3 5.0 ND -

Table 3b

Treatment Concentration Mean revertant colony

^g/plate) TA100 Reference limit

Washed brick solution 1 313 108+10

sample 2 625 84+12 <202 (less than

2x of the

3 1250 104+18

colonies in

4 2500 97+5 negative control

5 5000 108+3

Negative control (0.9% - - 101+17 - NaCl)

Positive control (2AA) 1 0.5 ND -

2 1.0 1064+381 >202

3 5.0 ND -

Table 3c

Treatment Concentration Mean revertant colony

^g/plate)

TA201 Reference limit

Washed brick solution 1 313 87+16 <156 (less than sample 2 625 97+1 2x of the colonies in

3 1250 86+8 negative control

4 2500 101+8 5 5000 102+13

Negative control (0.9% - - 78+2 - NaCl)

Positive control (2AA) 1 0.5 ND -

2 1.0 ND -

3 5.0 158+12 >156

2AA = 2-aminoanthracene

ND = not done

From the results, the number of revertants from all bacterial test strains treated with the washed brick solution samples or extracts does not exceeded twice than those in the negative control, but a significant number of revertants is produced in the positive controls. Hence, the washed brick solution samples have not demonstrated a mutagenic effect under the condition of the test with Salmonella typhimurium and is not considered to be a mutagen.

Example 3

An alkaline comet assay is performed to assess the potential of DNA strand breaks or damage of a single mammalian cell in contact with the test material of washed brick solution.

The assay is carried out using a net concentration at 200mg/ml of the washed brick solution. Cell culture used which is American Type Culture Collection V79 Chinese hamster lung cells (CCL-93™) with passage number 7 is embedded on an agarose film on a microscope slide and lysed to remove cellular contents. The DNA helix is subsequently unwound under alkaline condition prior to electrophoresis and staining with ethidium bromine (EtBr) fluorescent dye.

During electrophoresis, broken DNA fragments shall migrate away from the nucleus and the fragments would be appeared as images of comets. The extend of DNA liberated from the head of the comet is directly proportional to the DNA strand breaks.

Table 4 shows that tail movement values for the test materials of washed brick solution, negative control and positive control.

The average scores in DNA damage for the washed brick solution is represented by the Tail moment value of 0.481 at the neat concentration of 200mg/ml. The result shows that the washed brick solution does not caused significant DNA damage in V79 cells and is considered non-genotoxic under the test condition.

Example 4

The number of V79 cells showing micro-nucleus formation following treatment with test materials of washed brick solution, negative control (Dulbecco's Modified Eagle's Medium) and positive control (Mitomycin C) is tabulated as below,

Table 5

Treatment Micronuclei Micronuclei Remark

formation (cells) frequency ( )

Washed brick solution

18+6 1.8 Negligible (lOOmg/ml) Washed brick solution

17+2 1.7 Negligible (200mg/ml)

Negative control

11+2 1.1 Negligible (growth medium)

Positive control

126+17 12.6 Positive (0^g/ml Mitomycin C)

Based on the results, the number of micro-nucleus formed in cells treated with washed brick solution is corresponded to that of negative control, both to be negligible. The positive control has produced high number of micro-nucleus as anticipated.

The washed brick solution does not induced significant micro-nucleus formation in V79 cells as compared to the positive control. Therefore, the washed brick solution is considered not clastogenic and non-genotoxic under the test condition. Example 5

Table 6 indicates the analysis of three samples comprising POFA Grey, OPC (ordinary Portland cement) and fly ash as below. The POFA is shown to be the best flame retardant among the others.

Table 6

Parameter Unit Results

POFA Grey OPC Fly Ash

Lost of Ignition % w/w

23.7 1.3 2.6 (as per sample)

Silicon (Si02) % w/w

46.6 43.1 82.9 (on dried basis)

Aluminum (A1203) % w/w

3.7 5.0 4.6 (on dried basis)

Iron (Fe203) % w/w

3.0 2.6 3.0 (on dried basis)

Calcium (CaO) % w/w 7.9 46.0 4.9 (on dried basis)

Magnesium (MgO) % w/w

4.1

(on dried basis) 1-1 1.1

Sodium (Na20) % w/w

0.1 0.2 0.2 (on dried basis)

Potassium (K20) % w/w

6.3 0.5 0.3 (on dried basis)

Phosphoras (P205) % w/w

4.6 0.2 0.4 (on dried basis)