Patent Publication Number: US-2023159399-A1

Title: Preparation of graphene nanosheets-based concrete additive

Description:
BACKGROUND 
     Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to being prior art by inclusion in this section. 
     FIELD OF THE INVENTION 
     The subject matter in general relates to a concrete additive. More particularly, but not exclusively, the subject matter relates a method for preparation of graphene nanosheets based concrete additive. 
     DISCUSSION OF THE RELATED ART 
     Concrete refers to cement as a cementing material, and sand and stone as aggregate. In the present days most of the construction is made of concrete. Concretes are often subjected to harsh environmental conditions such as wind, sunlight, high temperature, low temperature and the like, hence the performance of the concrete under extreme environments needs to be protected or improved. 
     Conventionally, additives are used protect the concrete from harsh environmental conditions. Although the existing concrete additives are various in types, certain problems are associated with the existing additives such as lower compressive strength and has single function due to which various additives needs to be used to achieve different effects. 
     In view of the forgoing discussion, there is need of an improved concrete additive which has various functions such as improving the compressive strength and the flexural strength of the concrete among others. 
     SUMMARY 
     In an embodiment, a method for preparing a graphene-nanosheets based concrete additive is disclosed. The method comprises mixing Polycarboxylate ether -A (PCE-A) to a retarder - based salt solution to obtain a retarder-based Polycarboxylate ether-A (PCE-A) solution. In the next step, a retarder based PCE solution is obtained by adding Polycarboxylate ether -B (PCE-B) to the retarder based Polycarboxylate ether - A (PCE-A) solution to which graphene nanosheets are added. Further, an air entrainment agent is added to graphene nanosheets based PCE solution to obtain the graphene nanosheets based concrete additive. 
     In an embodiment an additive for concrete is disclosed. The additive for concrete comprises graphene nanosheets, Polycarboxylate ether-A (PCE-A), Polycarboxylate ether - B (PCE-B) and at least one retarder. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       This disclosure is illustrated by way of example and not limitation in the accompanying figures. Elements illustrated in the figures are not necessarily drawn to scale, in which like references indicate similar elements and in which: 
         FIG.  1    illustrates a method flowchart  100  to prepare a graphene nanosheets based concrete additive, in accordance with an embodiment; 
         FIG.  2 A  is a SEM image of a cement concrete (control sample), in accordance with an embodiment; and 
         FIG.  2 B  is a SEM image of a cement concrete comprising graphene nanosheets based concrete additive (test sample), in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description includes references to the accompanying drawings, which form part of the detailed description. The drawings show illustrations in accordance with example embodiments. These example embodiments are described in enough detail to enable those skilled in the art to practice the present subject matter. However, it may be apparent to one with ordinary skill in the art that the present invention may be practised without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to unnecessarily obscure aspects of the embodiments. The embodiments can be combined, other embodiments can be utilized, or structural and logical changes can be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense. 
     In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one. In this document, the term “or” is used to refer to a non-exclusive “or”, such that “A or B” includes “A but not B”, “B but not A”, and “A and B”, unless otherwise indicated. 
     Referring to  FIG.  1   , a method  100  for preparing graphene nanosheets based concrete additive is provided, in accordance with an embodiment. The concrete additive or chemical admixture of the present invention involves incorporation of the graphene nanosheets to a polymer mainly polycarboxylate ether (PCE). 
     In an embodiment, at step  102 , at least one retarder is mixed with water to form a retarder salt solution. Further, more than one retarder may also be mixed with water. The retarders that may be used in the present invention are organic retarders or inorganic retarders. The retarders added may be for example but not limited to sugar, sodium thiosulfate and sodium gluconate, among others which may effect the hardening of concrete. It shall be noted that any other retarders may also be used that serves the purpose of the present invention. 
     In an embodiment, the retarder is mixed with the water at a speed chosen between 600 rpm and 800 rpm (rotation per minute) for a time period chosen between 10 minutes and 15 minutes. The mixing is carried out in a mechanical stirrer or any mixing means that serves the purpose of the present invention. 
     In an embodiment, the weight percentage of the retarder is chosen between 3% and 5% of the total amount of water. 
     In an embodiment, one or more different types of superplasticizers may be added to the retarder-based salt solution. At step  104 , a Polycarboxylate ether- A (PCE-A) is added to the retarder salt solution obtained at step  102  to form a retarder based Polycarboxylate ether -A (PCE-A) solution. It shall be noted that the PCE-A is not added immediately (added after some time) to the retarder-based salt solution formed by mixing the retarder with water. Upon addition of the PCE-A, the polymer chains react with water resulting in hydrolysis reaction. 
     In an embodiment, the retarder-based salt solution and the PCE-A are mixed at a speed chosen between 1200 rpm and 1500 rpm (rotation per minute) for a time period chosen between 10 minutes and 15 minutes. The mixing is carried out in a mechanical stirrer or any mixing means that serves the purpose of the present invention. 
     In an embodiment, the weight percentage of the PCE -A is chosen between 20% and 25% of the retarder-based salt solution. 
     At step  106 , Polycarboxylate ether- B (PCE-B) is added to the retarder based PCE-A solution obtained at step  104 . The retarder based PCE-A solution obtained at step  104  comprises water, at least one retarders and PCE-A. 
     In an embodiment, the Polycarboxylate ether- B (PCE-B) and the retarder based PCE-A solution are mixed to form a retarder based Polycarboxylate ether (PCE) solution. The mixing of the Polycarboxylate ether (PCE) - B and the retarder based PCE-A solution is carried out at a speed chosen between 1700 rpm and 2000 rpm (rotation per minute) for a time period chosen between 10 minutes and 15 minutes. The mixing is carried out in a stirrer for example a mechanical stirrer or any mixing means that serves the purpose of the present invention. Due to this mixing, polymerization takes place due to which smaller molecules (monomers or building blocks) are chemically combined to form larger molecules (polymer chains). 
     In an embodiment, the weight percentage of the PCE -B is chosen between 30% and 40% of the retarder based PCE-A solution. 
     At step  108 , graphene nanosheets (GNS) and the retarder based PCE solution obtained at step  106  are mixed to form graphene nanosheets based PCE solution. The graphene nanosheets and the retarder based PCE solution are mixed in a shear mixture. It shall be noted that the P H  of the retarder based PCE solution is checked prior to addition of the graphene nanosheets such that the P H  is maintained between 6 and 7. 
     In an embodiment, the shear mixing is carried out at a speed chosen between 2500 rpm and 3000 rpm for a time period chosen between 30 minutes and 45 minutes. 
     In an embodiment, the weight percentage of the graphene nanosheets is chosen between 0.5% and 5% of the retarder based PCE solution. 
     In an embodiment, the surface area of the graphene nanosheets is chosen between 320 m 2 /g and 550 m 2 /g. 
     The nanosized GNS are uniformly distributed throughout the polymer chain obtained in step  106 . That is to say, the pores in the polymer chain are completely filled with GNS. 
     In an embodiment, the graphene nanosheets used in the present invention is prepared by the method disclosed hereafter. 
     The graphene nanosheets is prepared by an aqueous-based exfoliation process from the raw materials such as exfoliated graphite (EG) or graphite. 
     In an embodiment, sodium cholate is dissolved in distilled water under stirring condition. In the next step, exfoliated graphene worms are shear mixed with sodium cholate solution at a speed chosen between 5000 rpm and 6000 rpm for one hour to four hours. 
     In the next step, a suspension obtained in the above step is kept at room temperature overnight. An upper solution from the suspension is collected and centrifuged at a speed chosen between 1000 rpm and 4000 rpm for 10 minutes to 40 minutes. The supernatant obtained by centrifugation is filtered and further dried to obtain the graphene nanosheets. 
     At step  110 , at least one air entrainment agent is added to the graphene nanosheets based PCE solution. The air entrainment agent is not added immediately to the graphene based PCE solution but added after 45 minutes. 
     In embodiment, the weight percentage of the air entrainment agent is chosen between 0.5% and 1% of the graphene nanosheets based PCE solution. 
     In an embodiment, the air entrainment agent and the graphene nanosheets based PCE solution are mixed at a speed chosen between 2000 rpm-2300 rpm (rotation per minute) for a time-period chosen between 5 minutes and 10 minutes. 
     In an embodiment, the air entrainment agents may be for example but not limited to vinsol resin, rosin resin and alkyl sulfonate among others. It shall be noted that any other entrainment agents may also be used that serves the purpose of the present invention. 
     At step  112 , the graphene nanosheets based concrete additive is obtained. The graphene nanosheets based concrete additive obtained is a black color solution. 
     Table 1 represents the chemical parameters of the graphene nanosheets based additive according to IS 9103 (1999). 
     
       
         
           
               
               
               
             
               
                 S. No. 
                 Parameter 
                 Specification 
               
             
            
               
                 1 
                 Appearance 
                 Greyish Black 
               
               
                 2 
                 pH 
                 7±1 
               
               
                 3 
                 Specific gravity 
                 1.1 -1.2 
               
               
                 4 
                 Solid content (%) 
                 35-45 
               
               
                 5 
                 Viscosity (cP) 
                 500-700 
               
            
           
         
       
     
     In an embodiment, the environment-friendly concrete additive disclosed in the embodiments of the present invention is more effective in improving the flexural strength and compressive strength of the concrete compared to the control sample as shown table 2. The control sample disclosed in table 2 comprises cement, water, coarse aggregate, fine aggregate, Vinsol Resin. The control sample does not comprise graphene nanosheets based concrete additive of the present invention, whereas the sample A or the test sample comprises the graphene nanosheets based concrete additive of the present invention in addition to the ingredients disclosed in the control sample.  
     
       
         
          TABLE 2
           
               
               
               
             
               
                 Properties of hardened concrete 
               
               
                 Test Performed 
                 Control sample 
                 Test sample comprising Graphene nanosheets based concrete additive (SAMPLE A) 
               
               
                 Compressive strength (psi) 
               
             
            
               
                 1 day 
                 1560 
                 2340 
               
               
                 3 days 
                 2370 
                 3400 
               
               
                 7 days 
                 3040 
                 4130 
               
               
                 28 days 
                 4220 
                 5040 
               
               
                 Flexural Strength (psi) 
               
               
                 3 days 
                 400 
                 495 
               
               
                 7 days 
                 525 
                 605 
               
               
                 28 days 
                 640 
                 715 
               
            
           
         
       
     
     In an embodiment, thermogravimetric analysis (TGA) study revealed that major degradation starts at 169° C. in polycarboxylate ether (PCE), whereas in Graphene nanosheets-PCE, the major degradation occurred at 195° C. This data indicates that thermal strength (aprox. 26° C.) increased in Graphene nanosheets -PCE when compared to PCE at the initial stage. In graphene nanosheets - PCE 15% of thermal strength was increased than PCE. Further, the PCE degraded to 50% at 335° C. whereas Graphene nanosheets-PCE degraded to only 20% at 335° C. This lower degradation is due to strong interaction between PCE and Graphene nanosheets which may prevent polymer chains from debundling and degradation, and significantly improving thermal stability. From this data it can be interpreted that that addition of Graphene nanosheets as a nanofiller increases the thermal strength stability of PCE. 
     Referring to  FIGS.  2 A- 2 B , illustrates SEM (scanning electron microscope) image of the control sample and the test sample. In control sample, concrete particles are mainly rods-like structures (50-150 nm width &amp; 200 to 800 nm length in size), irregularly shaped particles (30-100 nm in size) and nanoplates (500 to 1 micron in size) like structures. Whereas, the SEM image of the test sample depict that the structures of the concrete particles are mainly nanowires structures (20-60 nm in width, 500 nm to 1.5 microns in length) and some spherical particles (50 to 100 nm in size) along with some irregular shapes. The SEM image of the test sample also shows more interconnected wire structures, which is due presence of the PCE-Graphene nanosheets. These kinds of interconnected nanostructures give more strength to the concrete which could be the reason for the high strength of PCE-Graphene concrete than only cement concrete. 
     The graphene nanosheets based concrete additive of the present invention has certain advantages. The graphene nanosheet material uniformly spread along with polycarboxylate ether. Such incorporation reduces porosity and improve mechanical strength. Further, it also blocks the hollow space within the concrete and reduces water absorption and water permeability. Depending on the percentage of graphene nanosheets being used, the setting time and curing time of the concrete will be reduced and even the durability of the concrete structure will also be increased. The usage of graphene nanosheets based concrete additive also reduces the corrosion effect on the concrete. 
     Further, the additive of the present invention acts a shielding against an electromagnetic interference and gamma radiation. 
     The processes described above are described as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, or some steps may be performed simultaneously. 
     Although embodiments have been described with reference to specific example embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the system and method described herein. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. 
     Many alterations and modifications of the present invention will no doubt become apparent to a person of ordinary skill in the art after having read the foregoing description. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. It is to be understood that the description above contains many specifications, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the personally preferred embodiments of this invention.