|Title of Invention||
"AN APPARATUS AND A PROCESS FOR PRODUCTION OF SYNTHETIC LIGHTWEIGHT AGGREGATE"
|Abstract||An apparatus and a process for production of synthetic lightweight aggregate in controlled sizes and in wide range of densities from fine grained waste products like fly ash, crusher dust etc. Predetermined quantities of cement, sand, fly ash and/or stone dust, additive and water for the desired density of aggregate are mixed into a homogeneous consistency. Then appropriate quantity of preformed stable foam prepared from diluted foaming agent and coamrpessed air is added into the mixer and further mixed into homogeneous slurry. This mixed slurry is then poured, made to flow and cast into multiple spheroid shaped cells of specially designed battery moulds for predetermined size, where they are allowed to set into aggregate of target density. Opening-up of the batteries enables release and fall of aggregate into separate collection pits for each size of aggregate. The collected aggregate is further cured like any other concrete product with mist/water spray under ambient conditions till maturity and then dispatched to project sites.|
|Full Text||FIELD OF THE INVENTION
This invention relates to an apparatus and method for production of synthetic lightweight aggregates. BACKGROUND OF THE INVENTION
Aggregate is an essential ingredient of concrete, which in its different forms, is extensively used for all types of building and infrastructure. Referring specifically to infrastructures, it is generally known that most of the pavements and roadwork use aggregate even in the sub-base as also in the topping layer even if done with bitumen. It is used as ballast under railway tracks. It is also used for consolidation of weak soils, formation of filter beds, etc. Lightweight aggregate also finds application in insulation, non-structural fills, horticulture, etc. Aggregate is a broad term, which includes aggregate obtained from (a) natural sources, (b) aggregate produced from natural materials, and (c) synthetic materials. The natural aggregate type (a) in the form of sand and gravel may be obtained from river-beds or from pits in ground or obtained bt crushing of large blocks of tone collected from natural stone quarries. The aggregate type (b) is obtained by processing of naturally occurring materials like clay, shale, slate, etc. The third synthetic aggregate of (c) in its inorganic form include foamed slag, sintered pulverised fuel ash, aardelite, limenite, etc.
It is but evident that various types of aggregate meet the needs of different kinds of field application. The low density aggregate normally exhibit better thermal performance, while the heavier density version is more suited for structural applications. The aggregate from natural sources accounts for the bulk of the normal consumption. The aggregates obtained by processing of natural materials primarily caters to the special requirements of lightweight aggregate. The synthetic aggregate is a new trend in industry, primarily aimed at conserving the environment and making productive use of industrial waste bye products. This invention relates to synthetic or man-made aggregates and attempts to contribute towards die objectives mentioned above, by reducing degradation of natural resources through provision of substitute aggregate produced from environment polluting industrial waste products like pulverised fuel ash and/or stone dust left stockpiled at stone crushers after sale of regular sized aggregate. Most of the available patents facilitate production of synthetic aggregate in a limited range of densities and sizes. Examples of synthetic aggregate using prior art are LYTAG and AARDELITE. LYTAG is a lightweight aggregate, produced
by palletizing pulverised feel ash (PFA), which is then heated on a sinter strand at around 1250°C. The aggregate formed varies in size from 14mm down and the bulk dry density is typically in the range of 750-850 kg/m3 AARDELITE is another lightweight aggregate produced by pelletizing a mix of flyash, lime, water and gypsum and then cured in autoclaves.
Styron's US Patent 4624711 discloses a process for manufacture of lightweight aggregate from flyash, surfactant foam, accelerator and some additives warrants use of agglomeration process for forming of palletized aggregate, to be subsequently fired at 1800°F or alternatively at 300°F. Styron's other low energy input process as per US Patent 4741782 uses flyash, cement, some filler, water and chemical accelerator, but still involves processing of ingredients through a pelletizing device and subsequent curing of aggregate pellets in oxygen containing gas at temperature of 300°F.
Another US Patent 4377414 by Buschmann et al using flyash as an input material relates to production of definite shaped articles like pellets, bricks, blocks, tiles and the like by a closely controlled compaction process directly from flyash containing powder produced in a time based scrubbing process for removal of flyash and SO2 from the flue gases. Moreover, the patent does not relate to production of aggregate.
Walker's US Patent 4770831 for manufacture of lightweight aggregate uses flyash with 1-5% lime milk as a binder and pelletizes the same at a temperature of 45-100°C and subsequently cures the granules between 50-85°C. Weber's US patent 5484479 propagates a process of making synthetic aggregate by mixing class-C flyash with controlled feed of water spray and sugar based admixtures, consolidating the mixed soil like mass into a flat slab, allowed to set, which is subsequently broken and crushed into aggregate. Similarly, Ivokovich's US Patent 5704972 proposes use of C or F flyash, hydrated lime 2-10% and 3-12% alkali hydroxide, making slurry with 10-25% water, compacting slurry, introducing it into a rotary kiln for 2-30 mins, where it is heated to 150-1000°F. The pellets formed are removed to be thereafter crushed into aggregate of required size. In another version, the slurry is allowed to fell on a flat surface, roller compacted, cured and thus hydrolyzed product allowed to stay till it reaches predetermined compression level, where after it is excavated, crushed and screened to make desired sizes of aggregate. The preferred mix of this patent has
also been advocated in Gerbus's US Patent 6126738, but Gerbus has proposed dropping the wet mixture into conical piles using a radial stacker. US Patent 5762864 by Park deals with making lightweight aggregate from waste products like stone aggregate sludge, stone fragments and sewage plant sludge in 50:50 ratio, making sludge spheroids in rotary plate device, applying paper sludge onto the surface of these spheroids and then burning them at a temperature between 1000-1200°C in a furnace and then cooling them.
OBJECTS OF THE INVENTION
An object of this invention is to propose a process and apparatus for producing lightweight aggregate having predetermined densities.
Another object of this invention is to propose a process and apparatus for producing lightweight aggregate and wherein casting is carried out in one single operation.
Still another object of this invention is to propose a process and apparatus for producing lightweight aggregate and wherein the process is carried out at ambient temperature.
Yet another object of this invention is to propose a process and apparatus for producing lightweight aggregate which provides bulk densities of aggregate from 250kg/m3 to l800 kg/m3.
According to this invention there is provided a process for producing man made aggregate comprising preparing a slurry mix of cement, fine materials, additives, water and preformed foam to produce a slurry mix having uniform foam bubbles such that the ball bearing effect of the minute foam bubbles enables a smooth flow of the slurry mix, feeding the said slurry mix from the top to a battery mould of interconnected cells imparting an "external vibration to the moulds if required, filling the cells so as to drive entrapped air out of the cells; the filled material being allowed to set under ambient conditions to form cast aggregates, the batteries being opened upon hardening of the cast aggregate allowing said aggregates to drop into collection pits, and subjecting the aggregates to the step of further curing.
Further according to this invention there is provided an apparatus in the form of a battery mould for simultaneous casting of large quantity of specific sized artificial or man made aggregate comprising an assembly of a plurality of intermediate and end plates, each face of the intermediate plates and the inner face of the end plates having depressions of a shape and size depending on the size of aggregate to be produced, the depressions allowing information of small chambers for inflow of mix slurry, said depressions being inter-connected through channels, the face of one plate being joined with the face of an adjoining plate having matching mirror image depressions and channels on it's surfaces so as to form interconnected cells of desired aggregate size along the junction of these plates so that every addition of a matching plate surface adds an equal number of interconnected cells, the assembly of such plates forming a battery mould.
DESCRIPTION OF DRAWINGS AND INVENTION
Fig.l shows the assembly details of a typical battery mould having multiple
interconnected cells for simultaneous casting of a large number of specific sized
Fig. la shows elevation of the mould. Fig. 1b shows a plan view of the mould.
Fig. 1c shows a section elevation A-A of fig. Ic at a typical junction of plates; and Fig. 1d shows a sectional view B-B through middle of set of 5 internal plates Pi to P5 and 2 end plates E1, E2 of a battery mould.
Fig. 2 shows various stages in the production process. The selection of the input raw materials is from amongst cement (A), flyash (B), stone dust (c), sand (D), additive (E), water (F) and appropriate quantity of performed foam (K), stable under ambient conditions for a duration much beyond the final setting time of portland cement. The input raw materials are stored in appropriate silos/bins/tanks. The performed foam (K) of requisite quality may be freshly generated and supplied when required, by a foam generator (J), from a mixture of selected grade of foaming agent (G), water (E) and compressed air (H).
The process begins with feeding into the mixer (M) of properly batched quantities of specific raw materials from amongst (A), (B), (C), (D), (E) & (F) required for a particular type and density of aggregate being produced. Once the slurry in the mixer becomes homogenous, required quantity of pre-formed stable foam (K) is then fed into the mixer and mixing continued to ensure thorough mixing of foam with the mortar mix.
The mixed slurry is then fed onto top of different assemblies of multiple cell battery moulds (N-l), (N-2), (N-3), (N-4), (N-5), etc. for casting different sized aggregate of desired density. The details of battery moulds have been shown in fig. 1. The innumerable minute air bubbles in the fluid slurry of fine materials act as ball bearings and enable it to flow down due to gravity into the inter-connected spheroidal shaped multiple cells of different sized aggregate and fill them up. Subjecting the battery moulds to minor external vibration would hasten the flow and filing time gets substantially reduced. The filled slurry mix in the cells of the batteries is allowed to set for some time under ambient conditions, where after when the battery plates are opened, the hardened granules of different sized aggregate fall down into collection pits L1, L2 through Ln etc. from where these are removed for further maturity before dispatch.
Reference is now made to fig.l, a set of pre-molded or duly fabricated plates of hard durable material is assembled for each size of aggregate to be produced. The internal plates have on their two surfaces, mirror imaged pre-molded or drilled out semi-spherical depressions, to a depth slightly less than the radius of target spherical size of aggregate. These molded depressions are created in a staggered zigzag pattern, as shown in Section-AA fig.lc and are inter-connected with minor channels R along the surface and small holes across two faces near the bottom of depressions. These depressions fall short of the two sides and the bottom of the
plates to ensure leak-proof-ness. The two end plates of slightly smaller thickness have the matching molded depressions and minor channel depressions on the internal surfaces only as shown in plan of fig.lc. An assembly of a number of intermediate plates and two end plates duly bolted by belts S together constitutes one battery mould for casting one specific sized aggregate. The upper sides of the plates in the assembled battery are so cut as to expose almost half the depth of the cup-shaped depressions. The multiple rows of circular holes so created on the top surface of the assembled batteries serve as inlets for the flow of mixed slurry into multiple cells interconnected to the top holes inside different battery forms.
The batteries could alternatively also be so designed that instead of mixed slurry being fed from the holes formed on top surface created with the assembly of multiple plates held vertically, it could be organized from the top surfaced of a set of duly prepared and assembled battery of plates held horizontally. The length and depth/breadth of plates and their numbers in one battery depends on the scale of production and the available handling facilities. Likewise, the number of batteries for each size of aggregate to be produced would depend on the cycle time of operations and required quantum of daily output of that size.
Such sets of battery moulds of different depths of molded depressions are prepared for required size range of aggregates and their target daily output. Each battery mould is either provided with an in-built or has a provision for affixing a vibration mechanism when required or the battery could be transferred to a vibrating table during the filling operation. PREPARATION OF BATTERIES FOR CASTING
The molded/fabricated plate surfaces of each set of battery moulds are pre-coated with any known demolding agent and then assembled into a battery in readiness for the actual casting/filling/molding operation. PREPARATION OF FLUID SLURRY MIX FOR CASTING
Various stages in the production process have been depicted in fig.2. The primary input raw materials are cement (A), flyash (B), stone dust (C), sand (D), additive (E), such as accelerating agent for accelerating the hardening process if required, water (F) and preformed foam (K), stable under ambient conditions. This foam (K) maybe freshly generated and supplied as and when required through a foam generator (H) from a mixture of selected grade of foaming agent (G) such as NEOPOR-600 or equivalent, water (E) and air (H) duly compressed and used by the foaming generator (J). The raw materials are stored in appropriate silos/bins/tanks. Cement should preferably be high-grade portland variety. Flyash to preferably be of Grade I as per IS 3812 to economise on cost of production, though Grade II may also be used. The pre-formed foam has to be stable for duration much beyond the final setting time of portland cement, so that the structure of the aggregate being cast in the forms using this foam does not collapse during the hardening stage.
The process begins with feeding into the mixer (M) of property batched quantities of specific raw materials from amongst (A), (B), (C), (D), (E) & (F) required for a particular type and density of aggregate being produced. The lower target density output would primarily involve development of cement, flyash, water, hardening agent and higher proportion of foam. The higher density outputs would apart from cement + flyash as binders also involve higher input of stone dust/sand, but much lower input of foam. Once the slurry in the mixer becomes homogeneous, required quantity of pre-formed stable foam (K) is then fed into the mixer and mixing continued for a little while to ensure thorough mixing of foam with the mortar mix Feeding of batteries and maturing
The mixed slurry is then fed onto top of different assemblies of multiple cell battery moulds (N-l, (N-2), (N-3), (N-i), (N-n), etc. for casting different sized aggregate of desired density. The details of battery moulds have been shown in Fig.1. The innumerable minute air bubbles in the fluid slurry of fine materials act as ball bearings and enable it to flow down due to gravity into the inter-connected flattended sphere shaped multiple cells for different sized aggregate. Subjecting the battery moulds to minor external vibration would accelerate the flow of slurry into various empty cells upto the bottom of forms, filling these up and thereby pushing out entrapped air from these cells.
The filled material is allowed to mature till final setting time of the cement binder and consequent hardening of the filling under ambient conditions. This maturity period may be shortened through addition of approved early hardening admixture or adoption of any of the well-known accelerated curing techniques.
Opening of batteries and collection, of Hardened granules and some flnes
The battery moulds are ready to be opened-up the moment filled slurry has achieved adequate hardening. The individual plates of the battery are separated one after another enabling the hardened globules of filled material to fell on to bins on the floor. These collection bins can be made to slope away from the production area The batteries of different sized aggregates are emptied into
A little quantity of small sized grains is also produced along-with the specific sized aggregate . This is the bye product from the small sized inter-connecting channels between the cut-outs/depressions for the aggregate nodules. This small sized material is segregated from the aggregate and collected separately to serve as low-density sand for superior insulation plasters.
The aggregate so produced and collected from the ground bins is subjected to further mist/water spray curing and maturing., like any other concrete product, before delivery to the clients for use in their works.
Cleaning and Re-assembly of Battery Moulds
The opened-up plates of each battery are cleaned of any sticking slurry. The plate surfaces are once again film coated with appropriate de-moulding agent and reassembled into batteries ready to go through the cycle of operations once again.
Repetitive Uses of Battery Moulds feasible each day
It is easily feasible to have multiple uses of each battery moulds, in a 24-hour cycle of day, depending on the selection of the initial hardening process.
Shape of output Aggregate
The primary output of the process is aggregate of specific size and density with somewhat flattened spherical shape i.e. spheroidal. The cross section of the aggregate is circular in the plane of casting plates, while it is elliptical in the other two planes at right angle to the surface of these casting plates.
The process is more economical for production of larger sized aggregate, which is difficult to produce as per currently available other technologies. Therefore another way of obtaining a range of smaller sized lightweight aggregate in crushed form is to subject the larger sized granules as obtained above, to subsequent process of crushing and segregation through sieving into different size range.
1. A process for producing synthetic lightweight aggregate characterized by the steps of preparing a slurry mix of 400-150 kg of cement, fine materials such as stone dust/sand, water according to the consistency required, 800-100 litres of preformed foam in quantities such as herein described, 150-1000 kg of flyash and optionally additives such as accelerating agent to produce a slurry mix having uniform foam bubbles, feeding said slurry mix from the top to an apparatus in the form of a battery mould of interconnected cells imparting an external vibration to the molds if required, filling the cells so as to drive entrapped air out of the cells; allowing the filled material to set under ambient conditions so as to form cast aggregates, opening of the batteries upon hardening of the cast aggregate allowing said aggregates to drop into collection pits, and subjecting the aggregates to the step of curing.
2. The process as claimed in claim 1, wherein the plurality of said battery moulds are arranged in separate production lines as per size of aggregate being produced.
3. An apparatus in the form of a battery mould as claimed in claim 1 for simultaneous casting of large quantity of specific sized artificial or man made aggregate characterized in that an assembly of a plurality of intermediate and end plates, each face of the intermediate plates and the inner face of the end plates having depressions of a shape and size depending on the size of aggregate to the produced, said depressions being inter-connected through channels, the face of one plate being joined with the face of an adjoining plate having matching mirror image depressions and channels on it's surfaces so as to form interconnected cells of desired aggregate size along with junction of these plates.
4. An apparatus as claimed in claim 3 wherein said depressions are provided in an staggered relationship.
5. An apparatus as claimed in claim 3 wherein the depressions terminate in the proximity of the plate edges on the sides and the bottom.
6. The apparatus as claimed in claim 3 wherein the depressions are partially sheared off in the proximity of the top.
7. An apparatus and a process for production of synthetic lightweight aggregate substantially as herein described and illustrated in the accompanying drawings.
|Indian Patent Application Number||1160/DEL/2003|
|PG Journal Number||08/2009|
|Date of Filing||17-Sep-2003|
|Name of Patentee||GUR BAKSH SINGH|
|Applicant Address||C-102 KAVERI APARTMENTS, ALAKNANDA, NEW DELHI-110 019, INDIA.|
|PCT International Classification Number||C04B 18/04|
|PCT International Application Number||N/A|
|PCT International Filing date|