BHANUMATHIDAS, Nateri (32-10-55, Shri Venkateswara ColonySheela Nagar, Visakhapatnam 2, 530 01, IN)
BHANUMATHIDAS, Nateri (32-10-55, Shri Venkateswara ColonySheela Nagar, Visakhapatnam 2, 530 01, IN)
We Claim,
1) A process for the preparation of bricks and more particularly fly ash based bricks with cement and/or slag and/or lime and most preferably FaL-G based bricks and aerated concrete characterized in that the said products are not subjected to autoclaving but cured by hot water vapors in an Accelerated Curing Tunnel [ACT][I], for the gain in early strength through harmonized mineralogy formation.
2) A process as claimed in claim 1 wherein the said process comprising the steps of; a. optionally demineralizing water from a water source; heating the water to the maximum temperature of 90 degree Celsius by known methods, preferably from solar energy; b. storing the hot water in storage tanks; c. manufacturing the precast elements; d. loading the precast elements on a rail car; e. placing the plurality of rail cars inside the Accelerated Curing Tunnel [ACT][I]; f. allowing the hot water to be sprinkled on the hood (7); g. allowing the precast elements to be cured, inside ACT, for a sufficient period, say for example from a period ranging from 12 hours to a maximum period of 30 hours, preferably from 12 to 24 hours for curing; h. collecting the warm water into troughs for recirculation through a filter; i. cutting off the supply of hot water so as to cool the cured products; and j. removing the cured products from rail car for final use.
3) A process as claimed in claims 1 and 2 wherein the early strength achievable in 12 to 24 hours is more or less equivalent to the strength achievable from 14 to 28 days from the conventional methods.
4) A heat insulated apparatus or heat insulated equipment comprising; i. Accelerated Curing Tunnel [ACT][I] for curing the precast elements; ii. A plurality of rail cars for holding and movement of the precast elements; iii. A plurality of hot water pipelines capable for sprinkling the hot water over the hood; iv. A hood with a curvature placed beneath the roof of ACT so as to direct the hot water to pass or slide through the sidewalls of ACT; v. A plurality of troughs to collect warm water from the side walls vi. A means for the recirculation of warm water through due filtration.
5) A heat insulated apparatus or heat insulated equipment as claimed in claim 4 wherein the inside walls of ACT is covered by a sheet having low water absorption and high heat dissipation wherein the said sheet is either a metal sheet or a polymer sheet or a weather resistant masonry. 6) A heat insulated apparatus or heat insulated equipment as claimed in the claims 4 and 5 wherein the said heat insulated apparatus or heat insulated equipment is further connected to a plurality of insulated warm and hot water storage tanks.
7) A heat insulated apparatus or heat insulated equipment as claimed in claim 6 wherein heat sensors are provided to sense the drop in temperature either of stored water or running water.
8) A heat insulated apparatus or heat insulated equipment as claimed in claim 7 wherein the heat sensors send signals to heat sources such that heat sources start functioning automatically to maintain the desired temperature level.
9) A heat insulated apparatus or heat insulated equipment and the process as claimed in any of the previous claims is process specific but not product specific.
10) A heat insulated apparatus or heat insulated equipment and the process is substantially as herein described and exemplified. |
PATENT SPECIFICATION ON
ACCELERATED CURING SYSTEM AND PROCESS THERE OF
The present invention relates to a novel process to obtain rapid strength gain at elevated temperatures preferably within about 24 hours rather than about 14 to about 28 days of cementitious materials. The present invention also relates to the equipment for the manufacture thereof the cementitious products based on OPC, slag and fly ash, in order to expedite the strength gain. Such process and equipment give greater flexibility of recipe and utility specifications to rope in wide range of raw materials in natural and byproduct forms.
The present invention in particular relates to the preparation of bricks and more particularly fly ash based bricks with cement and/or slag and/or lime and most preferably FaL-G based bricks. The present invention also aims at cost-effective and highly reliable process for the preparation of cementitious precast elements as disclosed herein but without compromising on the international or national strength standards as stipulated. Such process is disclosed herein wherein the strength of the cementitious materials which is normally achievable either within 14 days or 28 days, say depending on the type of mix, is achievable within a maximum period of 30 hours, preferably by 24 hours, but this time is exclusive of cooling time required to overcome thermal stresses.
The present invention also relates to the equipment used to prepare the cementitious products, as described herein. The said equipment is designed such that heat loss is highly minimized at all strategic locations and most importantly aimed at reutilization of unutilized or untransferred heat energy.
PRIOR ART:
Accelerating strength of cementitious material at elevated temperatures is a known art.
In 1914 the Swedes discovered a mixture of cement, lime, water and sand that expands by added with aluminium powder, resulting in a material like wood but without the disadvantages of combustibility, decay and termite damage. However, this material could not develop strength at ambience, which was overcome by using autoclaves having steam temperature of 150-180 0 C at 8 to 12 bar pressure. This is further optimised as autoclaved aerated concrete (AAC), which is, otherwise, called as autoclaved cellular concrete.
The prestressed concrete elements along with moulds are subjected for accelerated curing at elevated temperatures of around 70-80 0 C so that the product attains rapid strength and able to take the stresses of prestressed wires when cut from the mould.
US 4613472 claims a process to achieve the short stiffening time by way of using an extremely high reactive binder. The claim talks of a method wherein the maximum temperature achieved by the mixture ranges between about 65 0 C and 75 0 C.
US 4655979 envisages autoclave curing at 150-190 0 C and also foamed slurry for the production of aerated concrete.
US 4214911 talks about hot water mixing at a temperature of 50 0 C, in order to accelerate the hydration chemistry, without defining the curing approach.
US 4683003 talks about high temperature and high pressure hydrothermal curing route, where the latter is not defined with regard to operational parameters.
The first batch of aerated concretes such as 'aerocrete' in UK were made with OPC, sand and aluminium powder. They were allowed to harden at ordinary temperatures and, although of reasonable strength, suffered from excessively high drying shrinkage. The Swedish Siporex and Ytong, and Danish Durox are some of the successive developments in autoclave route to answer the drying shrinkage.
IS:2185 (Part 3) - 1984, Specification for concrete masonry units - autoclaved cellular (aerated) concrete blocks, vide clause A-2 says,
"Suitable steam-curing is practically unavoidable in making the product with cement as binder and the same is absolutely essential when lime is used. Generally autoclaving is done for about 14 to 18 hours at about 700 kPa and about 185 0 C".
Thereby the ultimate cost of the finished product goes up, making the technology unviable in third world countries.
Operation of autoclave is a cost-intensive process step; one on account of high capital cost of the equipment and the other owing to dependence on energy-intensive input like steam. Hence it is desirable to dispense away this process step.
With regard to practice of FaL-G technology (covered by Patent No. 198639/1996), it is customary to cure bricks/blocks by spraying water at ambience, twice or thrice in a day, for over 14 to 28 days. By virtue of FaL-G invention, solid bricks and blocks attain strength, dispensing away the dependence on elevated temperatures, by maneuvering the chemistry of calcium alumino sulphate hydrate phases to higher levels, which the erstwhile technologies have controlled all along. This means, the weak strength development of fly ash-lime mixes is augmented in the presence of threshold levels of gypsum to achieve high early and ultimate strengths, dispensing away the need for autoclave curing. However it is observed that the same mix of specific fly ash and recipe attains 21-day strength in 24-36 hours at 60-80 0 C.
OBJECTS OF THE INVENTION
The first and foremost object of the invention is to manufacture the cementitious materials, rendering maximum strength within shorter period compared or in contrast with the state of art time limits to gain such desired strengths.
The next object of the present invention is to produce a very large number of cementitious elements in the shortest possible time so as to meet the voluminous demand of the market.
The next object of the present invention is to manufacture cost-effective (low cost) cementitious bricks without compromising on the quality of the final product.
The next object of the present invention is to prepare cementitious bricks and blocks, preferably fly ash based cementitious bricks; most preferably FaL-G based bricks and blocks.
The next object of the present invention is to invent an apparatus or equipment suitable to achieve the previous objects of the invention.
The next object of the invention is to invent an apparatus or equipment wherein the heat losses are highly minimized.
The next object of the invention is to invent an apparatus or equipment wherein the cementitious elements to be processed are subjected to or exposed to hot water vapor than the steam.
The next object of the invention is to invent an apparatus or equipment such that the untransferred heat energy is reutilized by recirculation of the medium.
The next object of the invention is to invent an apparatus or equipment capable of producing the final product in large quantities to suit the demand.
BRIEF DESCRIPTION OF THE PfVENTION
As known from the art, the cement bricks/blocks of the required size are prepared and then placed in a rail car that is moved into an Accelerated Curing Tunnel (ACT) and subjected for a maximum period of 24 to 30 hours. The said bricks are exposed to hot vapors during the said period and finally cooled by switching off the hot water vapor circuit. Then the cooled bricks are released out of the heat insulated ACT for final use.
An apparatus or equipment is designed to suit the purpose of the invention. In a most preferred embodiment the entire equipment along with the external support is made heat insulated. The said equipment comprises of an Accelerated Curing Tunnel of suitable length [ACT], the walls including roof of which are heat insulated, a bottom portion comprising the rails and rail cars to place and carry the bricks, a plurality of rail cars that travel through the length of the rails, a plurality of hot water inlet pipes to carry and sprinkle the hot water on a dome, a dome to receive the sprinkled water so as to allow the hot water to slide and pass along the side walls of ACT, a plurality of water collecting trough , preferably two troughs on either side of the entire length of ACT placed all along the side walls to collect the sliding water and a means to recirculate thus collected water.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS / FIGURES
Figure 1 is the cross sectional view of the ACT Figure 2 is the elevation of the ACT
The numeral as depicted in the figures defines as following; please note that the same numeral is mentioned for same part in both the figures.
Number 1 : Accelerated Curing Tunnel
Number 2 : Heat Insulated wall [all the sides including roof]
Number 3 : Rail car
Number 4 : Rails
Number 5 : Warm water collecting trough(s)
Number 6 : Hot water carrying pipe with nozzles
Number 7 : Hood
Number 8 : A bundle of precast elements placed on a rail car
DETAILED DESCRIPTION OF INVENTION:
The object of this invention is to accelerate strength gain at elevated temperatures, but without resorting to cost-intensive equipment such as autoclave, as well as the cost-involving utilities such as steam. For this purpose this invention developed a process and system to tap energy from any fuel including biomass, but preferably solar energy in order to make the approach sustainable in practice and affordable in long term perspective.
Though the process described herein is about FaL-G based cement brick manufacturing, the described process is to be understood that the said process is not restricted to this specific process alone but applicable to any process wherein the aim of process is to gain early strength of binding materials, and cementitious materials are not outside the scope of the present invention. The disclosure is made with respect to FaI-G cement bricks because these products are in great demand as on the date of filing this application. One of the embodiments of the present invention is to replace the bricks of clay with FaL-G cement bricks in the construction industry. This need is actual inspiration to work out and develop the present invention.
The apparatus or equipment of the present invention is process specific but not product specific. In other words the said equipment is capable of providing the hot water vapor required to cure the bricks and capable of collecting the warm water, the temperature of which is less than the hot water and to recirculate the warm water as hot water.
In a similar way it is to be understood that the variations that can be construed by the person skilled in the art are included in the present disclosure even such variations are not mentioned throughout of this specification.
Also the present disclosure does not depend on the type of mix used to manufacture the bricks. It is evident from the table as shown before the claim portion.
The apparatus or equipment of the present invention may be used to dry and to achieve the early strengths for any other similar products as the apparatus is process specific but not product specific. To achieve the desired results of other products the process parameters may vary but not the concept of the present disclosure. Therefore it is to be understood that the apparatus or equipment as disclosed herein is unique with respect to its operation and capable of extended use other than what is described and exemplified as herein.
The invention has concentrated on the following main features of practicing technologies:
■ Long periods of curing, running to couple of weeks in small-scale FaL-G units do not suit to high capacity plants because the investment cost on inventory, adding to the end product price.
■ Pozzolanic reactions are relatively slower than OPC and dependent on ambient temperature. Thus the finished product strengths do vary in accordance to climate, bringing variation in the finished product, depending on the season. FaL-G is no exception to this phenomenon. Induced curing at elevated temperatures imparts uniform strength regardless of seasonal variations.
■ FaL-G being a CDM project, use of renewable energy such as bio-mass or solar only can protect its sanctity in earning carbon credits.
For this purpose the inventors have taken advantage of the principles of cement chemistry, which develops rapid strengths at elevated temperatures. FaL-G being another hydraulic cement binder, the principles of accelerated curing would equally apply for FaL-G too.
FaL-G is a blend of fly ash-lime-gypsum, wherein the addition of gypsum at threshold levels achieves the optimum formation of mineralogical phases called 'calcium alumino sulphate hydrates (CASH)'. This mineralogy is considered as poison for structural concrete or mortar, during post hydration stage, which cracks the cast element through its profuse expansiveness by about 2.3 times as explained in the formula below:
3CaO + 3CaSO 4 + Al 2 O 3 + H 2 O - 3CaO.Al 2 O 3 .3CaSO 4 .32H 2 O
This mineralogy, which is otherwise called ettringite attains such profuse expansion because of its formation by taking 32 molecules of water. In order to contain this phenomenon, certain autoclaved processes, which invariably need CASH phase, control the input of gypsum to the order of 0.5 to 2.0%.
It may be mentioned that the same mineralogy dissociates into various formations through ageing out of which tricalcium alumino mono sulphate is the predominant and stable ultimate mineralogical formation.
The inventors have identified that the formation of ettringite during hydration and hardening stage is contributory whereas the same formation at post-hardened stage, once the product attains intra-matrix stability, is detrimental.
Hence, FaL-G process is synthesised to add optimum gypsum, commensurate to the reactive aluminate phases, for the optimum formation of calcium alumino sulphate phases as ettringite at the initial hydration and hardening stage. By this approach, the weak and delayed formation of calcium silicate hydrates (C-S-H) in fly ash-lime chemistry could be overcome to attain high early strengths to facilitate handling of the product at early age (12-24 hours).
To embody the whole process in a nutshell, the inventors have postulated a theory to identify the cement system in FaL-G which says:
"a weak mineralogical formation (C-S-H of fly ash-lime system) of a cementitous system can be made good of its strengths by initiating cement chemistry through formation of another conducive mineralogical phase (ettringite)'.
By this phenomenon, this invention has dispensed away the need of heavy-duty press as well as autoclave, which are mostly normal in the production of fly ash bricks with erstwhile technologies. Thereby this process has come 'down to the earth' to facilitate its adoption in cottage and tiny sector industries.
But, in such case, the ettringite formation should be progressive and conducive to the hydration and hardening phenomena of cement-system, which cannot be maintained in aggressive curing approach such as autoclaving. So, in a way, FaL-G process desists to use autoclave as an intrinsic obligation of the process, which, ultimately, is a blessing in disguise in economy point of view both on plant costs and utility costs.
FaL-G made its success to develop high density bricks or low density aerated concrete, devoid of autoclave, and still not yielding to shrinkage. When FaL-G is attempted towards production of aerated concrete the situation faced certain contradictory issues viz., without accelerated curing such as autoclaving the aerated FaL-G does not attain strength; with autoclaving the ettringite formation is profuse, leading to internal expansive stresses, cracking the cast products.
The innovative aspect of this patent is to attain the semblance of the process needs, in manufacturing High density FaL-G or aerated FaL-G at such elevated curing temperatures where the threshold input of sulphate compounds allows the 'ettringite formation progressively conducive to the hardening process' of the product. Such elevated curing temperatures do not envisage elevated pressures of steam and hence the object of not to use autoclave is vindicated.
According to the present invention and an exemplary the FaL-G based cement bricks (8) of any type of mix is precasted and placed on a rail car (3) and allowed to move on the fixed rails (4) throughout the length of Accelerated Curing Tunnel [ACT](I). The walls of ACT (2), including roof is insulated and made heat resistant by known means. A hood (7) is placed beneath the roof (2) of ACT (1) such that the curved ends meet the top portion of the inner face of the sidewalls (2). Or preferably the inner surface of the sidewalk (2) and the hood are made by the same material, preferably low water absorbing and high heat dissipating material. The inside walls of ACT are covered by a sheet having low water absorption and high heat dissipation wherein the said sheet is either a metal sheet or a polymer sheet or a weather resistant masonry. The most preferred metal is copper but due to high cost aluminum is preferred. A hot water inlet pipe or a plurality of such pipes (6) is placed above the hood (7) and beneath the roof of ACT (1), which has a means for sprinkling of hot water, supplied from hot water storage tankers. The sprinkled hot water slides down the hood (7) and slides through the sidewalls (2) and finally reaches warm water collecting trough (5) on either side. In one of the embodiments of the present invention the surface of the sidewalls are oriented to render more residential time for the hot water to shed its heat. Similarly the shape, size and length of ACT (1) are such that the retention time of hot water is enhanced to the desired level. For simplicity sake such variations are not described throughout the specification. The rail cars (3) are filled with precasted cement bricks and allowed to stay in the total length of ACT (1) for a period of 12 to 30 hours, preferably 12 hours, preferably 24 hours for curing and gain in desired strength. The retention time of bricks varies with the nature and type of mix of the ingredients. Once the desired strength is achieved then the supply of hot water is cut off and the bricks are allowed to cool down inside of ACT. After a prefixed time of cooling, then the rail cars are moved along with the extended length of rails for final packing and storing or packing and dispatching to the destination. The warm water collected in troughs (5) is recirculated via a strainer to hot water generators or hot water storage tankers, which are not shown in the drawings. Depending upon the process parameters the difference in temperature between hot water and warm water may vary in between 5 degree Celsius to 40 degree Celsius. The inlet hot water is generally in between 90 and 60-degree Celsius, preferably in between 85 to 75 degree Celsius most preferably around 80 degree Celsius.
To heat water various known embodiments are possible. The inventors mainly depended on solar heating system because this is sustainable, eco-friendly and cost effective in term perspective. Other fuels such as bio-mass or fossil fuels are not excluded but solar heating is preferred. To make the entire process more effective the hot water storage tankers, the warm water storage tankers and the possible pipelines connecting all these are insulated. In other words the heat loss is minimized throughout the process and wherever it is possible. Still the disclosed process is found to be very cost-effective. All these details are not shown in the accompanying figures.
The water source required to practice the present invention is any natural source. Care is being taken not to use salt water and or hard water. In one of the preferred embodiments, in case the water used is capable of forming scales on the walls of the containers then the said water is primarily subjected to demineralization to avoid the maintenance cost and to enhance the longevity of the equipment. Though the demineralization of water before the step of heating is not essential to practice the present invention but is still preferred to increase the life of equipment.
As disclosed herein before, as an exemplary, the heat source is solar source. The treated water is heated up normally to around 80-90 degree Celsius by using solar energy in a known manner. In other words there are a plurality of solar panels, which receives the solar energy and transmits the heat to water so as to achieve hot water for the purpose of the present invention. The hot water thus produced may be utilized immediately or may be stored for longer periods for subsequent use or when it is required. The provision of storing is preferred in this instant case where especially when a uniform intensity of light from sun is not possible. Therefore the idea of insulating the storage tanks and pipelines etc., In fact insulation of the entire equipment is mainly to serve two purposes. One is that heat loses are minimized and a continuous production is made possible without getting affected from non-availability of heat from sun. Other advantages like recirculation, reheating of water etc., are minimised but the inventors do not like to go into minor details as such advantages are obvious to the person skilled in the art. A plurality of hot water storage tanks are strategically placed such that they are connected to insulated warm water storage tanks on one side and on the other side to a means for providing hot water to ACT. In one of the embodiments of the present invention optionally there are additional heat sources that get activated through sensors to supply the heat energy either to maintain or to bring back the desired temperature of the hot water during storage or at the mixing point of hot and warm waters.
Accordingly the present invention relates to a process for the preparation of bricks and more particularly fly ash based bricks with cement and/or slag and/or lime and most preferably FaL-G based bricks and aerated concrete characterized in that the said products are not subjected to autoclaving but cured by hot water vapors in an Accelerated Curing Tunnel [ACT][I], for the gain in early strength through harmonized mineralogy formation.
In the cementitious mineralogy, predominantly the calcium sulpho-aluminates get profuse expansion at elevated temperatures such as in autoclaves. This is being regulated or harmonized in the present inventive process so that the formation of mineralogy is allowed without getting subjected to harmful effects.
Accordingly the present invention relates to a process wherein the said process comprising the steps of; a) Optionally demineralizing the water from a water source; b) Heating the water to the maximum temperature of 90 degree Celsius by known methods, preferably from solar energy; c) Storing the hot water in storage tankers; d) Manufacturing the precast elements; e) Loading the to be cured precast elements on a rail car; f) Placing the plurality of rail cars inside the Accelerated Curing tunnel [ACT][I]; g) Allowing the hot water to be sprinkled or sprayed on the hood (7);
h) Allowing the precast elements to be cured, inside ACT, for a sufficient period, say for example from a period ranging from 12 hours to a maximum period of 30 hours, preferably from 12 to 24 hours for curing; i) Collecting the warm water into troughs for recirculation through a filter; j) Cutting off the supply of hot water so as to cool the cured products; and k) Removing the cured products from rail car for final use.
Accordingly the present invention also relates to a heat insulated apparatus or heat insulated equipment comprising; i. Accelerated Curing Tunnel [ACT][I] for curing the bricks; ii. A plurality of rail cars for holding and movement of the bricks; iii. A plurality of hot water pipelines capable for sprinkling the hot water over the hood; iv. A hood with a curvature placed beneath the roof of ACT so as to direct the hot water to pass or slide through the sidewalls of ACT; v. A plurality of troughs to collect warm water from the side walls vi. A means for the recirculation of warm water through due filtration.
Autoclave curing specifies the pressure, temperature and duration for every recipe, which are normally frozen. In the present Solar curing system the curing parameters and recipe composition are flexible and changeable on each count depending on climatic and site conditions. This flexibility facilitates to tap waste heat in the form of steam, hot water or hot air at its available temperature to accomplish the curing, in view of the dependence on low temperature zones compared to autoclaving.
The Solar curing System :
Hot water is generated in solar panels to a temperature of 50 - 80 0 C and transferred to Hot Water Tank (HWT).
Hot water tank is followed with another Buffer Make-up Tank (BMT), associated with conventional heating systems using fuels such as bio mass, fuel oils, gas or any other heating media, wherein the heat is made up, depending on the process need and during the contingencies of cloudy and monsoon days.
The hot water is pumped to 'Accelerated Curing Tunnels (ACT)' and sprayed over a hood plate. The water tickles along the insulated sidewalls, in the course of which the temperature is dissipated into the tunnel.
After shedding its temperature in the tunnel, the tickled warm water containing elevated temperature than ambience, is collected into a channel, filtered through a strainer and recirculated to solar panels or BMT.
In the ACT a temperature difference around 10 0 C between top to bottom is observed which is harmonized by operating air circulatory fans within ACT.
The cured product is taken out of the ACT at specified time, allowed for conditioning to a specified duration before packed and despatched to the storage yard or the market.
The product attains three to five times of strength, over normal curing, within 24-36 hours depending on the temperature and recipe. In lime-route the role of this system is predominant where the strength gain is phenomenal.
Various mix designs were practiced vide above process in a pilot plant in order to understand the impact of accelerated curing with constituent-percentage. The following mix designs and strengths derived thereof indicate the potential of this invention:
Strength (kg/cm 2 )
Constituent %:Fly ash OPC/ Gypsum Filler Density With ace. W/o ace. Lime (kg/m 3 ) curing curing
Sample I 76 20 04 -- 1820 560 176
Sample II 38 04 01 57 1880 127 25
Sample DI 57 04 01 38 1800 78 16
Sample IV 19 04 01 76 2055 75 15
Sample V 60 30 10 - 1680 450 negligible
Sample VI 12 06 02 80 2320 220 negligible
Sample VII 76 18 06 — 1680 420 40
Sample VITI 35 04 01 60 2080 136 negligible
Samples I to IV are in OPC-route; V & VI are in Lime-route and VII & VIII are in OPC+Lime blend.
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