DESC:FIELD OF INVENTION
The present invention relates to the field of concrete for construction industries. The invention particularly relates to the creating an eco-friendly, durable cement-less substitute for concrete material by utilizing waste materials. The plaster composition of the invention has lower environmental impact, enhanced and tunable tensile strength. The invention also relates to methods of producing the plaster composite.
BACKGROUND OF THE INVENTION
Concrete is a chemically combined mass having filler and binder. Generally, inert materials such as rivers and, crush sand, brick chips, stone chips, gravel, etc. are used as fillers and binding materials such as cement and lime are used as binders. Traditionally, concrete is preferred as construction material due to its durability, cost-effectiveness and hence is being used worldwide for roadbeds, commercial and residential projects.
The concrete used widely has low tensile strength, further, the process of manufacturing concrete is not environment friendly as it uses a lot of energy and emits greater volumes of carbon dioxide. Additionally and presently, the Indian construction and civil infrastructure sector is facing severe shortage on availability of sand for plaster due to ban on rivers and mining and illegal crush sand mining. There is, thus, a long felt need for a concrete composition or a plaster composition that is sustainable and environment friendly. Further, the applications of plaster are not limited to construction applications. Plasters are used in other industries and arenas as well for aesthetic purposes. The applications of plasters are varied i.e. ranging from use in plaster mortar (plastering walls) to use in street murals or art installations, to use in non-structural elements such as interior furniture. It is important to note that the inherent properties and characteristics required of the plaster for different use may be varied. For example, plaster to be used for plastering walls shall require higher tensile strength as opposed to that required in the making of non-structural elements such as interior furniture or for making wall murals or garden aesthetic elements. The present inventor reports that to the best of his knowledge, there is not reported in literature any plaster material created out of resin sand waste with tunability in tensile strength to be used in various applications. In other words, there is not reported any plaster material obtained from resin sand waste with variation in tensile strength.
An environmental problem of the foundry activities is the management of industrial waste generated in different processes. Enormous amount of resin coated shell sand is procured annually for die casting processes. This resin sand can be neither being recycled fully nor can be disposed off. Despite being subjected to processes; the sand continues to contain residual resin content which is harmful. Further, due to its high abrasion properties, storage of this sand inside premises is not a feasible option.
Creating plaster from foundry waste has been previously disclosed in the prior art. Mavroulidou and Lawrence (Mavroulidou and Lawrence, Journal of Material Cycles and Waste Management, 2019, 21, 594–605) cite routing of foundry waste to use in concrete. IN201941012323 and IN201911036565 disclose use of foundry waste and recycled components to make cured eco-friendly cement.
Wherein the present inventors use resin sand from die casting foundry, binder, and other additives to enhance the property of concrete and to produce the eco-friendly cement-less plaster. The present invention offers a sustainable transformation of waste into an energy efficient product and method thereof, where waste of one industry is converted into a resource for another industry. A complete recycling of waste is the need of the hour. Thus, the present invention intends to provide the method and the plaster thereof for enhancing and extending the functionality of those described in the prior art. More particularly, to provide the method and the plaster thereof with variation in its tensile strength. In addition to incorporating this plaster as a structural element in construction for its durability for e.g., in sewer lines, marine structures, sewage treatment plant structures, etc., it also presents opportunity to be used as an aesthetic plaster in for e.g., street murals, aesthetic structures, home interior decorative items, etc.
Accordingly, the object of the invention is to provide an eco-friendly, durable cement-less substitute for concrete material with tunable tensile strength by utilizing waste materials from die casting foundry. Said plaster composition has lower environmental impact and exhibits enhanced and/or varied tensile strength. Another object of the invention is to provide a method of producing said plaster composite.

SUMMARY OF THE INVENTION
In view of the foregoing, for overcoming the disadvantages of the prior art, the primary object of the invention is to provide an eco-friendly, durable cement-less substitute for concrete material with tunable tensile strength by utilizing waste materials from die casting foundry. Another object of the present invention is to provide a process for manufacturing plaster composition using said resin sand waste materials and recycled components to enhance its performance. Disclosed herein are aspects, features, elements, implementations, and implementations for generation of solutions associated with the plaster and the process of manufacturing said plaster with tunable tensile strength.
According to one embodiment of the invention, is provided a plaster or a mortar prepared from used or discarded resin sand from die casting foundry. According to a preferred embodiment of the invention, is provided a plaster or a mortar with tunable tensile strength.
According to one embodiment of the invention, is provided used or discarded resin sand from die casting foundry.
According to one embodiment of the invention, is provided a method for preparing plaster and/or mortar from used or discarded resin sand from die casting foundry.
According to one embodiment of the invention, is provided a chemical solution that acts as a binding agent.
According to one embodiment of the invention, is provided an additive solution. According to a preferred embodiment, the additive is an alkali-activated additive solution. According to a more preferred embodiment, the alkali-activated additive is chosen from sodium hydroxide, sodium silicate, aluminum silicate, and/or magnesium silicate, and combinations thereof.
According to one embodiment of the invention, a mortar mixer shall be utilized to mix sand along with chemical additive to develop plaster mix. In an alternate embodiment, said mortar mix can be utilized for precast as well as in-situ applications.
According to one embodiment of the invention, colour pigments shall be added to make the mortar mix.
According to one embodiment of the invention, the silicon oxide-to-aluminum oxide ratio by mass of the source material shall be in the range of about 2.0 to about 3.5.
According to one embodiment of the invention, the alkali activated additive-to-resin sand ratio by mass shall in the range of about 0.25 to about 0.50.
According to one embodiment of the invention, concentration of sodium hydroxide shall be in the range of about 8 M to about 20 M. In a preferred embodiment, the concentration of sodium hydroxide shall be in the range of about 10 M to about 15 M. In a more preferred embodiment, the concentration of sodium hydroxide shall be 13 M.
According to one embodiment of the invention, the sodium silicate-to- sodium hydroxide liquid ratio by mass shall be in the range of about 0.40 to about 2.5.
According to one embodiment of the invention, the sodium hydroxide-to-sodium silicate ratio shall be critically maintained. In a preferred embodiment, said ratio shall be 1:1. According to an alternate embodiment of the invention, the sodium hydroxide-to-sodium silicate-to-magnesium silicate ratio shall be critically maintained to 1:1:0.5.
According to one embodiment of the invention, concentration sodium silicate solution shall comprise of solid content of about 50% and water content of about 50%.
According to one embodiment of the invention, concentration of aluminum silicate shall be 13.00 M.
According to one embodiment of the invention, the plaster shall be cured for about 1 -3 days with open air.
According to one embodiment of the invention, the plaster shall be evaluated for tensile strength parameters. According to a preferred embodiment of the invention, the tensile strength of the plaster shall range from 1 MPa to 5 MPa.
According to another and alternate embodiment of the invention, the final application using the plaster shall be achieved using methods such as 3D printing.

DETAILED DESCRIPTION OF THE INVENTION
The embodiments of the invention will now be described herein, with reference to the accompanying examples. It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.
The primary object of the invention is to provide an eco-friendly, durable cement-less substitute for concrete material with tunable tensile strength by utilizing waste materials from die casting foundry. Another object of the present invention is to provide a process for manufacturing plaster composition using said foundry waste materials and recycled components to enhance its performance. The sand used in gravity die casting is a quartz silica sand coated with resin material (that acts as a binder for shape formation). After the gravity die casting, the sand carries solidified aluminum metal compounds, which cannot be recovered and get mixed with sand. By virtue of this process the aluminum gets heterogeneously mixed with sand after gravity die casting aluminum liquid metal pouring. The traces of the aluminum compounds are found in the used resin sand. This sand can be effectively used in two ways: Firstly, partial replacement of regular quartz sand for creating high performance plaster and mortar along with cement. This is achieved by a direct partial replacement of regular quartz silica sand with 20% to 50% of used gravity die casting resin sand. The replacement percentage is co-related with the mix design, desired product performance, exposure and product category. And secondly, complete replacement for regular quartz sand for creating high performance plaster and mortar with geopolymer compounds. This is achieved by the process and embodiments described below. The present inventors report a novel plaster material and method to that achieve the aforementioned objective.
Also central to the invention is creating said plaster or mortar material with varied tensile strength. It should be noted that the plaster or mortar of the said invention shall be used in various applications, for example, the plaster can be used for applications in walls requiring high tensile strength; or in street murals or idols requiring moderate tensile strength; or for aesthetic purpose in non-structural elements such as interior furniture requiring low tensile strength. With this in mind, it is imperative that there be in place a process renders the plaster or mortar product the ability to create a material with tunable tensile strength.
To clarify the above and other purposes, features, and advantages of this invention, specific embodiment of this invention is especially listed and described in detail with the attached figures as follows. The principal and mode of operation of this invention have been described and illustrated in its embodiment. At the outset, a person skilled in the art will appreciate that this invention may be practiced otherwise, with modifications and variations, than is specifically described and illustrated. The invention should not be limited by the above-described embodiment, method, and examples, but by all embodiments and methods within the scope and spirit of the invention. In the following description of the invention, certain terminology will be used for the purpose of reference only, and is not intended to be limiting.
For the purpose of clarity, the expression “tunable tensile strength” shall not be construed as a material having the ability to possess varied tensile strength concurrently. The said expression shall be construed as the ability to create a plaster or mortar material with desired and varied tensile strength at a given point of time and in relevance to the end application.
Critical to the invention are sand and additive mix, characterized by ease to mix, apply and provide a better surface compared to that obtained by conventional cement. A person skilled in the art shall appreciate that the versatility of said plaster is in its attributes that it can be customized with different colour pigments to suit the end user/consumer needs. A person skilled in the art shall also appreciate that the product can be used as plaster or mortar. Accordingly, in one embodiment of the invention is provided a plaster and/or mortar prepared from used or discarded resin sand from die casting industry.
Central to the invention is used and discarded resin sand from die casting foundry. Thus, in one embodiment of the invention, resin sand from die casting foundry is used. Said resins and samples are tested for the particle shape, size and structure with Scanning Electron Microscopy, X-Ray Diffusion, Thermogravimetric Analysis and/or EDX. The inventors report that this is a very critical evaluation as it creates the baseline for designing the process for making the said plaster or mortar material. The present inventors report that the particle shape is the most critical aspect. Rounded sand particles, as seen in the Scanning Electron Micrographs, give lesser voids and render maximum workability to the plaster. As opposed to this, the non-rounded particles create bigger voids and render less workability. This has direct implications on the tensile strength of the material because the aggregate with rounded particles give minimum ratio of surface area to the volume thus requiring minimum material to create cement paste. Another critical aspect of the core source material is the inconsistency in composition. The used of discarded resin sand does not exhibit consistency in properties or composition between batches. This means that there is no direct co-relation between source material and the additives (type and amounts) to be used for making the plaster; in other words, a new mix design is required for each instance. A person skilled in the art will appreciate that the claimed plaster or mortar material is a result of intricate and considerable amount of experiment of parameters of source material and additives. This creates a distinction from the prior art materials and processes pertaining to cementless concrete materials created from waste.
Also central to the invention is a chemical solution that serves as a binding agent. In another embodiment, is a chemical solution that acts as a binding agent. Accordingly, a chemical solution is iterated and developed. Solutions shall be tested on a pre-decided range of samples in order to calibrate the precise proportion for additive development. It should be noted that the chemical additive solution acts as a binding agent by activating the cementitious properties in the used resin sand which are in basic form.
In another embodiment of the invention is provided an additive solution. Said additive solution can comprise of polymer alkali adhesive. Alkali activators shall be chosen from, but not limited to, such as sodium hydroxide, sodium silicate, magnesium silicate, aluminum silicate, pigments. Particularly, alkali activators shall be chosen from, but not limited to, sodium-based solutions such as sodium silicate, sodium hydroxide solution, potassium-based solutions, etc. In a preferred embodiment, additive solution shall comprise of sodium-based solutions. In another embodiment of the invention, combination of alkali activators shall be chosen.
In another embodiment, a mortar mixer shall be utilized to mix sand along with chemical additive to develop plaster mix. It should be noted that this plaster mix shall be applied later on concrete surface. In an alternate embodiment, sand mortar can be modified to be used as plaster for use as resilient protective cover for wall surfaces exposed to high chemical attacks. In another embodiment of the invention, colour pigments shall be added to make the mortar mix. This renders to the plaster mix aesthetic attributes. It should be noted that the plaster mix of the present invention is not only designed to have durability but also aesthetic functionality in order to extend the possible applications of the material. This makes it possible to use the plaster mix for casting murals, parts of furniture, creating outdoor and garden aesthetic elements. In an important embodiment, there is a direct co-relation between the tensile strength of the material and its end application. For example, plaster mix used for walls require 5 MPa tensile strength; 3 MPa for murals, garden aesthetic elements, and idols; 1 MPa for non-structural elements such as interior furniture. Thus, according to a preferred embodiment of the invention, the tensile strength of the plaster shall range from 1 MPa to 5 MPa. The addition of colour pigments enhances the mortar attributes to be used to cast murals, decorative interior items.
In an alternate embodiment, said mortar mix can be utilized for precast as well as in-situ applications. It should be noted that this makes it possible to use the mortar for applications ranging from non-structural elements to finishing &aesthetic products.
In one embodiment of the invention, the silicon oxide-to-aluminum oxide ratio by mass of the source material shall be critically maintained to achieve the desired homogenous mix for plastering. In a preferred embodiment, said ration shall be in the range of about 2.0 to about 3.5.
In one embodiment of the invention, the activator liquids-to-source material ratio by mass shall be critically maintained. In a preferred embodiment, said ratio shall be in the range of about 0.25 to about 0.50.
In one embodiment of the invention, concentration of sodium hydroxide shall be in the range of about 8 M to about 20 M. In a preferred embodiment, the concentration of sodium hydroxide shall be in the range of about 10 M to about 15 M. In a more preferred embodiment, the concentration of sodium hydroxide shall be 13 M.
In one embodiment of the invention, the sodium silicate-to- sodium hydroxide liquid ratio by mass shall be critically maintained. In a preferred embodiment, said ratio shall be in the range of about 0.40 to about 2.5.
In one embodiment of the invention, the sodium hydroxide-to-sodium silicate ratio shall be critically maintained. In a preferred embodiment, said ratio shall be 1:1. According to an alternate embodiment of the invention, the sodium hydroxide-to-sodium silicate-to-magnesium silicate ratio shall be critically maintained to 1:1:0.5.
In one embodiment of the invention, concentration sodium silicate solution shall comprise of solid content of about 50% and water content of about 50%.
In one embodiment of the invention, concentration of aluminum silicate shall be 13.00 M.
In one embodiment of the invention, the plaster shall be cured for about1-3 days with open air. In a preferred embodiment of the invention, the plaster shall be cured for about 1 day with open air. It should be noted that the said process eliminates any necessity of curing with water.
In an embodiment, a de-bonding test shall be conducted after 3 days. The plaster shall be evaluated for durability, tensile strength and/or thermal insulation parameters.
In an important embodiment of the invention, the final application using the plaster shall be achieved using methods such as 3D printing. While the claimed plaster can be used with traditional techniques, to overcome the drawbacks of these techniques – time consuming process and inevitable artificial errors, 3D printing can produce complex 3D structures in less amount of time. The 3D printing techniques offers an advantage of use of the claimed plaster in outputting desired external features combined with intricate internal characteristics and defects. Another advantage of the plaster claimed in the invention is the flexibility in workability of the plaster while 3D printing. Traditionally, plaster material is created and then used for printing. This creates an issue since the workability window of the plaster is very less, as less as 30 mins. The plaster of the present invention allows for simultaneous processes of creating plaster material and 3D printing. This allows presents the opportunity to create more critical shapes, detailing, and dimension. This feature is particularly useful in applications such as murals. The present inventions report that to the best of their knowledge there is no report of such use of geopolymer and flyash for 3D printing. It should be noted that while 3D printing, the proportion of the additives of the plaster are required to be further adjusted in order to achieve workability in application. This shall also construe a part of parameters considered for computing the mix design.
Example 1 –Mix design for plaster from discarded resin sand
Discarded resin sand was procured and analyzed for structure using Scanning Electron Microscopy and found to be rounded. Mix design represented in the following table was designed to maintain the additives ratio as NaOH:Na2SiO3:MgSiO3 (1:1:0.5). The resultant tensile strength for this mix design was evaluated and reported to be 3 MPa.

Item Amount
Discarded resin sand 1000 g
Discarded aluminum 200 g
Sodium hydroxide 100 g
Sodium silicate 100 g
Magnesium silicate 50 g
,CLAIMS:WE CLAIM:
1. A cementless plaster comprising discarded resin sand, discarded aluminum dust, and additives; mixed such that the plaster exhibits tensile strength from 1 MPa to 5 MPa.
2. A cementless plaster comprising discarded resin sand, discarded aluminum dust, and alkali-activated additives; mixed such that the plaster exhibits tensile strength from 1 MPa to 5 MPa.
3. The cementless plaster of Claim 2 wherein the alkali-activated additive is chosen from sodium hydroxide, sodium silicate, aluminum silicate, magnesium silicate, and combinations thereof.
4. The cementless plaster of Claim 2 wherein the alkali activated additive-to-resin sand ratio by mass shall in the range of about 0.25 to about 0.50
5. The cementless plaster of Claim 2 wherein the silicon oxide-to-aluminum oxide ratio by mass of the source material shall be in the range of about 2.0 to about 3.5.
6. The cementless plaster of Claim 2 wherein the sodium silicate-to- sodium hydroxide liquid ratio by mass shall be in the range of about 0.40 to about 2.5.
7. The cementless plaster of Claim 2 wherein the sodium hydroxide-to-sodium silicate ratio shall be 1:1
8. The cementless plaster of Claim 2 wherein the sodium hydroxide-to-sodium silicate-to-magnesium silicate ratio shall be 1:1:0.5.
9. A method of manufacturing cementless plaster comprising the steps: a) discarded resin sand and aluminum dust are mixed separately, b) alkali-activated additive solution in water is added, c) mortar mixer is used to mix resin sand, aluminum dust and alkali-activated additive solutions, and d) mix is cured in open air for 1-3 days.