This invention relates to non asbestos sandwich prefabricated panels with improved wet strength and sound insulation and manufacturing process thereof.

BACKGROUND OF THE INVENTION:

In the known art, the prefabricated panels has a core of lightweight aerated concrete sandwiched between fiber cement facing sheets on either side thereof. The fiber cement sheets are either asbestos based or non- asbestos based. The panels made with asbestos facing sheets are having superior wet strength than that of non-asbestos facing sheets and these panels can be used for interior and exterior applications whereas non asbestos based panels are used for only interior applications. Asbestos is a naturally occurring mining product. But day by day the availability of quality fibers is reduced tremendously. Hence it is essential to develop fiber cement sheets with alternative fibers to improve the wet strength and subsequently use these facing sheets for panels for external and internal applications. In order to enhance the wet strength of non-asbestos panels, in this invention non asbestos facing sheets with improved wet strength is developed and core is modified with reinforcing fibers.

WO2015050502 A1 teaches us the wall panels using first layer ECC (engineered cementicious composite) and second layer autoclaved aerated concrete. First and second layer joined by rib (traverses from first to second layer) Third layer is optional.

US2012103580(A1 ) relates to the top layer, radiant pipes are integrated to flow heat-carrying fluid.

US3590540 relates to thermosetting resin re-inforced with fibers are used. US3336713 teaches us two facings are filled with light weight polyurethane foam.

Conventionally the non-asbestos fiber cement facing sheets are produced by using 30 to 40% of cement, 40 to 60% siliceous material (silica/fly ash/micro silica), 6 to 10% of cellulose fibers (bleached/ unbleached soft wood pulp) and 0 to 5% of additives. Whereas asbestos fiber cement sheets are produced by using asbestos fibers instead of cellulosed fibers and other materials remaining same.

An attempt has been made for replacing lignocellulosic pulp such as wood pulp with jeans cotton rag either part quantity or full in facing sheets. Replacing lignocellulosic wood pulp with jeans cotton rag will help in de forestation and utilization waste raw materials and also helps in reducing the product cost. Replacing lignocellulosic wood pulp with jeans cotton rag also reduces the carbon foot print as the manufacturing of lignocellulosic pulp from biomass is an intensive process.

An attempt has been made to improve the wet strength of facing by introducing modified Poly ethylene terephthalate (PET) fibers compatible with cement slurry and wollastonite modified/ un modified having aspect ratio from 5 to 40. The wollastonite is modified with amino silane for bridging inorganic and organic materials. Modification of wollastonite helps in the better bonding of organic-cellulose pulp, synthetic fibers and inorganic binders.

An attempt has been made to improve the core properties of sandwich prefabricated panels, introduced high modulus reinforcing fibers such as poly ethylene terephthalate (PET). Poly vinyl alcohol, Poly propylene, nylon, carbon fibers, ceramic fiber, alkali resistant glass fiber and modified or un modified wollastonite etc. The above fibers are used either alone or in combination to improve the core properties and without affecting the aeration. OBJECTS OF THE INVENTION:

An object of the present invention is to manufacture of non-asbestos sandwich prefabricated panels with improved wet strength.

Another object of the present invention is to propose a process for preparing non asbestos sandwich prefabricated panels with improved wet strength.

Yet another object of the present invention is to propose to use environmentally friendly jeans pulp in the facing sheet by replacing wood pulp either part or full quantity.

Further object of the present invention is to introduce poly ethylene terephthalate (PET) fibers and modified/ unmodified wollastonite having aspect ratio of 5 to 40 to improve the wet strength of facing sheet.

Still further object of the present invention is to introduce high modulus reinforcing fibers such as poly ethylene terephthalate (PET), Poly vinyl alcohol, Poly propylene, nylon, carbon fibers, ceramic fiber, alkali resistant glass fiber and modified or unmodified wollastonite etc either alone or in combination in the core.

Still another object of the present invention is to eliminate use of asbestos fibers in the facing sheets as well as in core of sandwich panels.

BRIEF DESCRIPTION OF THE INVENTION:

Non-asbestos based sandwich prefabricated panels a pair of facings with a light weight concrete core sandwiched between the facing sheets wherein the light weight concrete core is made up of water 30 to 60% of total weight of the mix(w/w), 0.05-0.5% of an aerating agent such as aluminum powder, 0 to 20% of low density aggregate exfoliated vermiculite and/or perlite, 0 to 70% of pozzolonic material such as pulverized fly ash, , 0.1 -4% cellulose fibers (jeans/cotton), 0.1 -2% high modulus reinforcing fibers such as PET, PP, PVA, carbon fibers etc and remaining is Portland cement.

Manufacturing of non-asbestos facings consists of preparing a slurry; subjecting the said slurry on a screen and subsequently vacuum-filtered through a screen and or felt the step of forming thin films, applying the said thin films on accumulator rolls, before autoclaving the arranged product. The above prepared facing sheets are used for making sandwich prefabricated panels comprising, using facing sheets on both sides, keeping the facing sheets in extruder and pouring light weight cementicious slurry, reinforcing fibers along with aerating agent in between the facing sheets, allowing the aeration process and set the core to bond between core and facing sheets. These panels are cured by humid cure conditions to obtain the required strength.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to non-asbestos cement based sandwich prefabricated panels which have high wet strength and superior sound and thermal insulating properties.

Manufacturing of said panels involves two steps, in the first step non- asbestos facings with improved wet strength are manufactured and in the second step sandwich prefabricated panels are manufactured using the above facing sheets. Now the two steps are explained in greater details to explain this invention.

Manufacturing non-asbestos facing sheets

Non-asbestos Fiber cement facing sheets are produced by using combination of Cellulose, unmodified/modified wollastonite, cement and siliceous material such as fly ash and GGBS so as to permit satisfactory production thereof on a machine in which a slurry is formed on a screen and subsequently vacuum-filtered through a screen and or felt.

In the following paragraphs, wherein the fly ash is referred, it mean the fly ash, (it is a burnt and powdery derivative of inorganic mineral matter) that generates during the combustion of pulverized coal in the thermal power plant. Similarly wherein the term cellulose pulp is referred, it the cellulose pulp, which is obtained by mechanical pulping of jeans/cotton in loose or cloth form. Wollastonite is natural occurring mineral fiber having very good aspect ratio to attain strength and durability and also to reduce drying shrinkage. Wollastonite having aspect ratio 5 to 40 with/without chemical modification is used.

The process of the invention and its advantage will now be explained in greater detail with reference to the known method of manufacture of such sandwich wall panels for clear and better understanding of the invention.

STEP 1 - PREPARING THE SLURRY According to the present invention, manufacture of non-Asbestos fiber Cement based sandwich prefabricated panels comprising of the processing of fiber cement facing sheet is provided.

The said reinforcing fibers essentially included Cellulose Pulp (jeans/cotton/wood pulp) having fiber opening Deg.SR of 12 - 50 used in an amount of 5-20%, wollastonite (with/without chemical modification) in an amount of 0.5 to 8%, synthetic fiber such as PET in an amount of 0.2-2%, Portland cement in an amount of 20 to 55%, Siliceous material in the binder essentially pulverized fly ash having surface area of 2000-8000 cm ² /gm used in an amount of 15 - 50%, Ground granulated blast furnace slag having surface area greater than 2500 cm2/gm in an amount of 0 to 20% and fillers and additives in an amount of 0.05 to 5% by weight of the total mixing comprising or the reinforcing fibers, cement, fillers and additives. The mixing the above mentioned fibers with water to form a fiber slurry, adding binders comprising basically Ordinary Portland Cement, GGBS and siliceous materials such as herein described optionally with fillers and additives such as herein described to said fiber slurry followed by feeding the mixture thus formed to sheet forming machine such as herein described, demoulding and subsequently autoclaving and curing. While making slurry, care was taken to ensure there was homogeneous mixing of siliceous material, additives, GGBS and cement with reinforcing fibers.

Mixing/holding system ensured that solids are not separated from the aqueous solution, i.e. solids do not settle so that the lamination having uniform distribution of the binder and the reinforcing fibers is obtained in the process.

STEP 2: APPLICATION OF SLURRY

The recipe thus obtained in respect of the above formulations were independently run on pilot plant as well as in plant sheet forming machine such as HATSCHECK MACHINE where thin films are picked up and superimposed on accumulator roll. The composite is cut upon after building up to desired thickness and laid flat.

STEP 3: AUTOCLAVING

Flat sheets produced for desired thickness was conveyed to the autoclave where the sheets are heated at 160-190°C at 90 to 130 psi steam pressure for 10-15 hours. After autoclaving sheets were stacked before conditioning. Over a period of time, the sheets make it strong and acquire enough strength for using as facing sheets for panel production.

EXAMPLES:

Conventional verses invented facing sheets

Conventional facing Facing sheets of s. sheets present invention

Raw -

N

Material non-

0 asbestos

asbestos Example 1 Example 2 sheets

sheets

Ordinary

1 Portland 30-40 30-40 20-55 20-55

cement

Siliceous

materials

2 (Pulverized fly 40-60 40-60 15-50 15-50

ash/silica/micr

osilica)

3 GGBS 0-20 0-20 0-20 0-20

Asbestos

4 5-10 - - - fibers

Soft wood pulp

5 (bleached/unbl - 6-10 - 3-5

eached)

Cellulose pulp

6 0.5 - 5 - 5-20 5-10

(jeans/cotton)

Wollastonite

7 (modified/unm 0-8 - 0.5-8 0.5-8

odified)

Synthetic

8 0-2 - 0.2-2 0.2-2

fibers (PET)

9 Additives 0-5 0-5 0.05-5 0.05-5

Total 100 100 100 100 Properties

The wet and dry strength of Example 1 & 2 are improved than conventional non asbestos facing sheet. In addition to strength invented facing sheets are having low density than conventional asbestos and non-asbestos facing sheets.

Manufacturing non-asbestos sandwich prefabricated panels

Non-asbestos sandwich prefabricated panels are produced by using facing sheets on both sides and adding cementicious slurry containing cement, siliceous material such as fly ash and GGBS, core granules, synthetic fibers/mineral fibers, Cellulose pulp, wollastonite and aerating agents so as to permit satisfactory production thereof. In the following paragraphs, wherein the fly ash is referred, it mean the fly ash, (it is a burnt and powdery derivative of inorganic mineral matter) that generates during the combustion of pulverized coal in the thermal power plant. Similarly wherein the term cellulose pulp is referred, it the cellulose pulp, which is obtained by mechanical pulping of jeans/cotton in loose or cloth form. Wollastonite is natural occurring mineral fiber having very good aspect ratio to attain strength and durability and also to reduce drying shrinkage. Wollastonite with aspect ratio of 5 - 40 with/without chemical modification is used. High modulus fiber reinforcements such as polyethylene, polypropylene, PVA, carbon fibers, alkali resistant glass fibers are also used in staple form. Aerating agent is selected from aluminum powder or paste which reacts and liberates hydrogen gas. Core granules used are prepared by pulverizing waste core generated form rejected panels.

The process of the invention and its advantage will now be explained in greater detail with reference to the known method of manufacture of such sandwich prefabricated panels for clear and better understanding of the invention. STEP 4: NON ASBESTOS SAND WICH PREFABRICATED PANEL PREPARATION

The pair of facing which are obtained in step 3 of the present invention of fiber cement sheets of 4 - 6mm thickness. The said facing sheets are separated and supported by using conventional jigs and fixtures. The distance between the facing was kept to be 38-42 mm to achieve 50 mm thickness panel. Thickness and size of the panel is not limited to the mentioned thickness. Thereafter, the core mix slurry was introduced there between the facings and allowed to aerate and harden for a period of 12 to 24 hours. The slurry mixture contains ordinary Portland cement as main binder mixed with water and fly ash, cellulose pulp, reinforcement fibers, additives and aerating agent such as aluminum are poured in to the space between the two facing sheets.

After the core has hardened, the panels were separated from the jigs and thereafter the panels were subjected to humid curing by conventional technique to obtain panel having the following characteristic features:

The invented non-asbestos sandwich prefabricated panels are having very good wet strength and good sound and thermal insulating properties as described in the present claim of invention. EXAMPLES:

Conventional verses invented panels

Conventional panels Invented panels s. Raw - Material

No

Asbestos Non-asbestos Example 3 Example 4

Non-asbestos as prepared in

Facing sheets Asbestos Non-asbestos

example 1 in step 1

Core composition

Ordinary Portland

1 30-60 30-60 35-60 35-60 cement

Siliceous materials

2 (Pulverized fly 20-45 20-45 20-45 20-45 ash/silica/micro silica)

3 GGBS - - 0-20 0-20

4 Anhydrous Gypsum 0-15 0-15 0-15 0-15

5 Hydrated lime 0-15 0-15 0-15 0-15

Exfoliated

6 0-20 0-20 0-20 0-20 Vermiculite/perlite

7 Core granules - - 0-15 0-15

8 Aerating agent 0-0.5 0-0.5 0-0.5 0-0.5

Cellulose pulp

9 0-5 0-5 0.1-5 0.1-5

(jeans/cotton)

Wollastonite

10 - - 0.0-4 0.0-4 (modified/unmodified)

Reinforcement fibers

1 1 (ΡΕΤ,ΡΡ, PVA, Carbon, - - - 0.2-2 nylon, mineral fibers)

12 Additives 0-5 0-5 0.05-5 0.05-5

Total 100 100 100 100 Properties

Panel size : 3000 mm ^* 600 mm ^* 50 mm

The invented panels are having better uniformly distributed load and axial load at wet condition compared to conventional non asbestos panels. Whereas uniformly distributed load and axial load at wet condition of the invented panels are on par with conventional asbestos based panels. This data clearly indicating that the invented panels can be used for external and internal application like conventional asbestos based panels.

In addition to this the invented panels are having superior sound insulation properties than conventional asbestos and non-asbestos panels.

Panel size: 3000 mm ^* 600 mm ^* 75 mm

Present

Conventional

s. invention

Properties

No Properties of Standard

Asbestos non-asbestos panels as per

Example 4

1 Weight (kg/M ² ) 54 54 58

Uniformly distributed load (4 point UDL) In 2.9 spam (kg/M ² )

ASTM E-

2 dry 250 150 275

72 wet 175 102- 200

Axial load (KN/M)

ASTM E-

3 dry 312 275 318

72 wet 226 190 245

Flexural strength IS 2380

4 48 42 55

(kg/cm ² ) Part 4

Fire rating (minuets) BS 476

5 as per BS 476 Part 120 120 120 Part 20 &

20&22 22 Sound transmission

6 37 39 45 IS 9901

co-efficient (db)

Thermal conductivity

7 0.21 0.17 0.17 BS 4370

(W/m.°K)

Small Hard body

8 - Impact Passed Passed Severe BS 5234

Large soft body Severe duty duty Part 2

9 - impact

It is evident from the examples and the invented non-asbestos sandwich prefabricated panels has superior wet strength and sound & thermal insulation than conventional asbestos and non-asbestos panels.