Concrete and method relating thereto

Abstract

Concrete and Method Relating Thereto Concrete including cement, graphene, and a superplasticiser having an air entrainment agent. The amount of air-entrainment-agent is no more than 2% by weight of the superplasticiser.

Description

[0001] Concrete and Method Relating Thereto

[0002] The present invention relates to a concrete, and particularly to a graphene concrete. The invention further relates to a cementitious composition, and in particular to a graphene cementitious composition. The invention further relates to a method of forming a concrete or a cementitious composition.

[0003] Concrete is used in a variety of structural engineering applications, in general due to its good compressive strength, and ease and cost-effectiveness of production and laying.

[0004] When concrete is used in applications with repeated and variable high loading scenarios, pavement quality concrete (PQC) may be used. This is due to PQC’s higher tensile and flexural strength and improved durability over other concrete types. PQC may be used, for example, for highways, or airport runways or taxiways. PQC may have a tightly controlled quality of aggregate material compared to ordinary concretes.

[0005] However, it can still be necessary to reinforce the PQC with reinforcing bars (rebar) to further improve mechanical properties, such as tensile strength. The use of rebar increases the time, material requirement and environmental impact of the installation of the PQC.

[0006] It would therefore be desirable to provide a concrete which has improved mechanical properties, in particular a higher flexural and tensile strength, whilst reducing the time, material requirement and environmental impact of installation.

[0007] The present invention seeks to provide a solution to these problems.

[0008] According to a first aspect of the present invention, there is provided a concrete comprising: cement; graphene, wherein an amount of graphene is no more than 0.12% or no more than substantially 0.12% by weight of cement; and a superplasticiser including an air entrainment agent, wherein an amount of the air-entrainment-agent is no more than 2% by weight of an amount of the superplasticiser amount.

[0009] A superplasticiser improves the fluidity of fresh concrete and so allows for reduced levels of water, thus permitting for a stronger concrete to be made.

[0010] An air entrainment agent, also known as an air entraining agent or air entraining admixture, typically generates uniform and stable air bubbles in the concrete which, when set, form hollow voids. This is generally considered to improve the durability of concrete, due to providing greater resistance to damage due to a freeze-thaw cycle.

[0011] The composition for a graphene concrete according to the first aspect has been determined to provide particularly good compressive strength and flexural strength, compared to compositions which include higher amounts of air entrainment agent or no air entrainment agent. On the one hand, it is theorised that using an amount of air entrainment agent higher than 2% by weight of the superplasticiser reduces compressive and flexural strength, due to an interaction with the graphene. On the other hand, a concrete without any air-entrainment agent may provide a graphene concrete with insufficient durability and freeze-thaw resistance to be used as a PQC.

[0012] Therefore, a concrete which combines graphene and a superplasticiser with a small amount of air entrainment agent provides an improved concrete for use as PQC.

[0013] Such a concrete could have sufficient flexural and compressive strength so that rebar is not required, whilst being sufficiently durable for use as a PQC. This provides environmental benefits, due to a lower material requirement, along with allowing faster and more cost-effective installation.

[0014] The air entrainment agent already being pre-distributed in the superplasticiser may assist with distribution in the concrete.

[0015] Beneficially, the superplasticiser amount may be no more than 0.75% or substantially 0.75% by weight of cement.

[0016] Optionally, the air-entrainment-agent amount may be no more than 1 % or no more than substantially 1 % by weight of the superplasticiser amount.

[0017] In a preferable embodiment, the air-entrainment-agent amount may be 1 % or substantially 1 % by weight of the superplasticiser amount.

[0018] Preferably, the superplasticiser may comprise carboxylated polymers.

[0019] Additionally, the superplasticiser may be ADVA (RTM) 650 or CX SUPERCONCRETE P+ 650.

[0020] Advantageously, the graphene may be a constituent of the cement. As such, the graphene is pre-mixed into the cement, rather than being added during the mixing of the concrete. This allows for improved distribution of the graphene within the concrete, improving mechanical properties. In addition, such an arrangement can allow for easier mixing of concrete, in comparison to incorporating the graphene as a separate ingredient when mixing the concrete.

[0021] Advantageously, the graphene amount may be less than 0.008% or less than substantially 0.008% by weight of cement. It has been determined that lower amounts of graphene provide improved mechanical properties compared to higher amounts.

[0022] Preferably, the amount of graphene is at least 0.007% or substantially at least 0.007% by weight of cement.

[0023] Alternatively, the graphene amount may be at least 0.0075% or at least substantially 0.0075%.

[0024] Preferably, the graphene amount is 0.0075% or substantially 0.0075% by weight of cement.

[0025] In a preferable embodiment, the graphene may be nanoplatelets.

[0026] Beneficially, the nanoplatelets may have a thickness of between or substantially between 2 and 10 nm and / or a diameter of between or substantially between 2 and 7 pm.

[0027] Preferably, there is no further air entrainment agent than the air entrainment agent of the superplasticiser.

[0028] Additionally, the concrete may further comprise fly ash, aggregates and sand.

[0029] According to a second aspect of the invention, there is provided a runway, taxiway or highway comprising the concrete according to a first aspect of the invention. The concrete may be a PQC, and so may be suitable for use as part of a runway, taxiway or highway.

[0030] According to a third aspect of the invention, there is provided a method of forming a concrete according to a first aspect of the invention, comprising a step of: a powder of the cement being mixed with the graphene without or substantially without the presence of water and via resonant acoustic mixing. Mixing the cement powder with the graphene in a dry state ensures improved distribution of graphene, and therefore improved mechanical properties of the concrete.

[0031] It has been determined that resonant acoustic mixing ensures good distribution of the graphene in the cement, when mixing in a dry state. Having mixed the cement and graphene together in the absence of water, the graphenecement mix, or cementitious composition, may be mixed with water, admixtures and aggregates in an Eirich high shear mixer.

[0032] According to a fourth aspect of the invention, there is provided a cementitious composition comprising graphene, wherein an amount of graphene is less than 0.008% or less than substantially 0.008% of graphene by weight.

[0033] It has been determined that lower amounts of graphene provide improved mechanical properties compared to higher amounts.

[0034] Preferably, the cement comprises between 0.007% and 0.008% of graphene by weight.

[0035] Advantageously, the cement is a cement powder.

[0036] According to a fifth aspect of the invention, there is provided a method of forming a cement powder according to the fourth aspect of the invention, wherein the graphene is incorporated without or substantially without the presence of water.

[0037] Preferably, the graphene is incorporated via resonant acoustic mixing.

[0038] The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

[0039] Figure 1 shows a chart of compressive strength test results at different ages of five concrete samples in accordance with a first aspect of the present invention, M1 to M5, and three concrete samples, M6 to M8, not in accordance with the invention;

[0040] Figure 2 shows a chart of flexural strength test results at different ages of five concrete samples in accordance with the first aspect of the present invention, M1 to M5, and three concrete samples, M6 to M8, not in accordance with the invention;

[0041] Figure 3 shows a graph of freeze-thaw test results after different cycle numbers of a concrete sample in accordance with the first aspect of the invention, M5, and two concrete samples not in accordance with the invention, M6 and M7;

[0042] Figure 4 shows a chart of compressive strength test results of 11 concrete samples, P1 to P11 , at 7 days and 28 days after casting;

[0043] Figure 5 shows a chart of compressive strength test results of 3 concrete samples, P11 to P14, at 7 days and 28 days after casting; and Figure 6 shows a chart of flexural strength test results of 3 concrete samples, P11 to P14, at 7 days and 28 days after casting.

[0044] Preferred Examples

[0045] Composition and Methodology

[0046] Five samples of concrete, M1 to M5, were prepared using a graphene cement powder. Each sample M1 to M5 was made with a cement powder with a different amount of graphene, by weight of the cement powder, mixed with the cement powder.

[0047] The amounts of graphene and cement of each cement powder are as indicated in Table 1.

[0048] Table 1

[0049] The cement and graphene of each cement sample C1 to C5 were mixed together using resonant acoustic mixing to ensure a good distribution which is free of agglomerates. The cement samples were mixed without or substantially without the presence or addition of water. Suitable machines for such resonant acoustic mixing include the RAM5 and the RAM55 which can be obtained from Resodyn of 130 N Main St Suite 630, Butte, MT 59701 , USA.

[0050] The cement powder was ordinary Portland cement (OPC) of grading CEM 1 and can be obtained from CEMEX (RTM) of CEMEX House, Binley Business Park, Harry Weston Road, Coventry, West Midlands, CV3 2TY, United Kingdom, according to product name EN197-1 CEM1 52.5N.

[0051] The graphene was provided in the form of graphene nanoplatelets each having a thickness of between 2 nm and 10 nm and a diameter of between 2 pm and 7 pm. Such graphene, may be formed by an Interlayer Cleavage Method to exfoliate graphite into graphene nanoplatelets, and can be obtained from ACS Materia (RTM)I, LLC, 959 E Walnut Street #100, Pasadena, CA 91106, USA.. The concrete samples M1 to M5 were then prepared using cement samples C1 to C5 respectively. Three reference concrete samples M6 to M8 were prepared with cement powder without graphene; OPC grading CEM 1. The amount of cement used was identical across concrete samples M6 to M8.

[0052] In addition to the cement, concrete samples M1 to M8 were each prepared using other PQC components. This included water, sand, fly ash, and aggregates. The amounts and grades of the water, sand, fly ash and aggregates were identical across samples M1 to M8.

[0053] One or more admixtures were also used for samples M1 to M8. The admixture for samples M1 to M6 was only superplasticiser ADVA (RTM) 650. The amount of superplasticiser ADVA (RTM) 650 was equivalent to 0.75% by weight of cement of each sample, and 0.08% by weight of the total composition of each sample.

[0054] Samples M7 to M8 did not include superplasticiser ADVA (RTM) 650. Sample M7 included a plasticiser and an air entrainment agent, and M8 included a plasticiser only.

[0055] The superplasticiser ADVA (RTM) 650 can be obtained from GCP Applied Technologies (RTM) Inc. of 2325 Lakeview Pkwy Suite 450, Alpharetta, GA 30009, United States. ADVA (RTM) 650 is a modified synthetic carboxylated polymer superplasticiser and contains 1% of air entrainment agent. ADVA (RTM) also has a specific gravity (20°C) of 1.06, an alkali content (eq.Na20) of 1.00%, no chloride content, a freezing point of 0°C, and an amber / straw liquid appearance.

[0056] An alternative to ADVA (RTM) 650 could feasibly be considered such as CX SUPERCONCRETE P+ 650 which can be obtained from CHEMAX CONSTRUCTION CHEMICAL PVT. LTD. of 124. Avalon Business Hub, Katargam Surat-3945004, Gujarat, India. CX SUPERCONCRETE P+ 650 is a blend of organic polymers, having a light yellow-brown liquid appearance, a specific gravity of approximately 1.08 kg / L at 26°C, nil chloride content, and approximately 1 .5% air entrainment.

[0057] Since samples M1 to M6 do not include a further air entrainment agent, the air entrainment agent content of samples M1 to M6 is no more than 2% by weight of the superplasticiser ADVA (RTM) 650. Here, the content is 1% by weight of the superplasticiser ADVA (RTM) 650, since ADVA (RTM) 650 contains 1 % by weight of air entrainment agent. However, it will be appreciated that a further air entrainment agent may be added to the samples of M1 to M5, up to the value of a further 1% by weight of the superplasticiser, or up to 2% of the superplasticiser could be used.

[0058] The fly ash was PFA CEMEX (RTM) 450-N which can be obtained from CEMEX (RTM).

[0059] Each sample was mixed in a planetary concrete mixer with a capacity of 100 litres. The mixing procedure includes 60 seconds of dry mixing of the aggregates, sand, cement and fly ash followed by the addition of the water and plasticiser and / or air entrainment agent and a further 180 seconds of mixing.

[0060] The slump of each sample was then measured, the results of which are described hereinbelow, before the concrete samples were cast.

[0061] Twelve cubes, each having a side length of 100 mm, and twelve prisms, each having a dimension of 100 x 100 x 450 mm, were cast into moulds from each concrete mix. The moulds were filled in three lifts with a 20 second vibration after each lift.

[0062] The specimens were demoulded after 24 hours and stored under water at (20 ± 2) °C until the day of testing in accordance with EN 12390-2:2019.

[0063] Slump and Strength Testing

[0064] To test slump, within 5 minutes of finishing the mixing process, the slump of the concrete is measured in accordance with ‘BS EN 12350-2:2019 - Testing fresh concrete - Slump test. The results of slump as per Table 2 below

[0065] Table 2

[0066] To test compressive strength, tests were performed on each sample according to BS EN 12390-3:2019 and in a temperature-controlled room at (20 ± 2) °C. A test was performed on a casting from each concrete sample at the point of 3 days, 7 days, 14 days, and 28 days after casting. The results of the tests are provided in Table 3 and are represented in Figure 1 with error bars indicating the highest and lowest compressive strength measured at the given day for the given sample.

[0067]

[0068] Table 3

[0069] The compressive test results show that, at each age, each concrete sample of M1 to M5, containing graphene, provided improved compressive strength over each of reference concrete samples M6 to M8, which did not include graphene. Furthermore, at the 28 day test, the samples cast from M5, having the lowest amount of graphene, corresponding to 0.0075% by weight of cement, proved the strongest in compression.

[0070] A particularly striking comparison can be made at 28 days between M5, having the lowest amount of graphene corresponding to 0.0075% by weight of cement, and M7, with M5 providing on average 48% higher compressive strengths.

[0071] Flexural strength tests were performed in a temperature-controlled room at (20 ± 2) °C.

[0072] The samples were measured via 4-point bending, according to BS EN 12390-5:2019.

[0073] The specimens had a span of 420mm and distance of 140mm between the line loads. A test was performed on a casting from each concrete sample at the point of 3 days, 7 days, 14 days, and 28 days after casting. The results of the tests are provided in Table

[0074] 4 and are represented in Figure 2 with error bars indicating the highest and lowest flexural strength measured at the given day for the given sample.

[0075] Table 4

[0076] The flexural test results show that, by 14 days after casting, each concrete sample of M1 to M5, containing graphene, provided improved flexural strength over each of reference concrete samples M6 to M8, which did not include graphene. A striking comparison can be made at 28 days between M5, having the lowest amount of graphene corresponding to 0.0075% by weight of cement, and M7 with the M5 samples showing on average 13% higher flexural strengths.

[0077] Freeze-Thaw and Water Absorption Testing

[0078] Following the strength and slump testing, concrete composition M5 was identified as being particularly effective and was selected for freeze-thaw and water absorption testing. Testing was conducted according to ‘PD CEN / TS 12390-9:2016 Testing hardened concrete, part 9: Freeze-thaw resistance with de-icing salts - scaling’ and ‘BS 1881-122:2011 Testing concrete. Method for determination of water absorption’.

[0079] Concrete samples were prepared according to compositions M5, M6, and M7, with M6 and M7 acting as reference samples.

[0080] Each sample was mixed in a planetary concrete mixer with a capacity of 100 litres. The mixing procedure included 60 seconds of dry mixing of the aggregates, sand, cement and fly ash followed by the addition of the water and admixtures and a further 180 seconds of mixing. The samples were stored in a controlled environment at a temperature of 20 ± 2 °C and relative humidity of 65 ± 5% until the day of testing, which was 21 ± 1 day.

[0081] Four specimens were sawn from a cube of each sample by a water-cooled diamond cutting saw, each specimen being 50 ± 2 mm thick. The samples were lined with a 3 mm sheet on day 25 ± 1. At 28 days, the specimens were re-saturated using deionised water.

[0082] At 31 days, the specimens were placed in an environmental chamber and exposed to 56 cycles of freeze-thaw with de-icing salts. As such, a freezing medium was composed of 97% by mass of distilled water and 3% by mass of sodium chloride.

[0083] The amount of material scaled from the samples was measured after 7, 14, 28, 42 and 56 days, or cycles since each cycle took place over a day. The obtained measurements of the amount of scaled material in g / m2for each specimen is given in Tables 5, 6 and 7 and plotted in Figure 3 with error bars indicating the highest and lowest measurements for the given sample after the given cycle.

[0084] Table 5

[0085] Table 6

[0086] Table 7

[0087] During and after the tests, there was no visual cracking observed on any of the specimens.

[0088] To test water absorption, three cuboidal specimens of side length 100 mm were cast of each sample M5, M6, and M7. The specimens were stored at a temperature of 20 ± 2 °C and relative humidity of 95 ± 5% until the start of testing.

[0089] 24 days after casting, oven drying of the specimens was initiated. Three days later the samples were cooled, and the following day the water absorption test was undertaken. The measured water absorption of each specimen of each sample M5, M6, and M7 are provided in Tables 8, 9 and 10 below.

[0090] Table 8

[0091]

[0092] Table 9

[0093]

[0094] Table 10

[0095] From the freeze-thaw and water absorption testing, sample M5 scaled the least material and absorbed the least water. This evidences the excellent freeze-thaw resistance of sample M5, despite including significantly lower levels of air entrainment agent than sample M7.

[0096] Preliminary Research

[0097] Composition and Method - Part 1

[0098] To assist with determining the composition and method of manufacture of the preferred examples above, preliminary research was initially carried out.

[0099] Concrete samples P1 to P11 were prepared using Portland cement, sand, aggregate, and graphene, the graphene being used in varying amounts. Suitable graphene for use is as per the preferred examples described previously. A total amount of concrete was prepared using 563 kg of cement, 225 kg of water, 615 kg of fine aggregate, and 922 kg of coarse aggregate. Different add mixtures were added to separate samples of each concrete, and in different manners, as set out in Table 11 :

[0100] Table 11 The three-roll mill dispersion was carried out using an Exakt (RTM) 3-Roll Mill available from Exakt Tools Ltd., 56 Tannoch Drive, Cumbernauld, Glasgow, G67 2XX, United Kingdom. The three-roll mill dispersion was done with a 3:1 superplasticizer to graphene ratio, or a 1 :1 . ADVA (RTM) 650 to graphene ratio.

[0101] The further superplasticiser was a polycarboxylate superplasticizer.

[0102] For the resonant acoustic mixing, this was carried out without the presence of water and using a Resodyn LabRAM.

[0103] For P7, when dispersing graphene in water via high shear mixing without surfactant, the amount of graphene was 3.21 g and the amount of water was 4.3 kg. A suitable high shear mixer is the Silverson (RTM) LC5 obtainable from Silverson (RTM) Machines Ltd. Waterside, Chesham, Bucks, HP5 1 PQ, UK.

[0104] The concrete samples were cast and cured according to BS EN 12390-2:2009.

[0105] Testing - Part 1

[0106] Slump of each of the samples was measured prior to curing according to BS EN 12350- 2:2009. The results of this are given in Table 12.

[0107] Table 12

[0108] Compressive strength of test pieces made from each sample was measured according to BS EN 12390-3:2009 at 7 days after casting, and 28 days after casting.

[0109] Results are given in Table 13 below, and are visually indicated in Figure 4.

[0110] Table 13

[0111] Comparison of the results of sample P5 with the reference sample P1, each having 0.03% of graphene by weight of cement, at 28 days shows an improvement of approximately 4%. As such, these results indicate that dispersing graphene in cement dry via resonant acoustic mixing was a promising approach to pursue. An 11% improvement can be observed by comparing the results of sample P6 with P1 .

[0112] Composition and Method - Part 2

[0113] Three samples of concrete P12 to P14 were prepared using cement, water, fly ash, sand, aggregates and admixtures of an air entrainment agent and a plasticiser. No graphene was included in P12. In samples P13 and P14 the amount of graphene used was equivalent to 0.015%, and 0.03% by weight of cement respectively.

[0114] The cement was ordinary Portland cement, a suitable supplier of which is described above.

[0115] The graphene was dispersed within the air entrainment agent or plasticiser for inclusion in the concrete.

[0116] The concrete samples were cast and cured according to BS EN 12390-2:2009.

[0117] Testing - Part 2

[0118] Slump was measured prior to casting, according to BS EN 12350-2:2009, the results of which are provided in Table 14 below.

[0119] Table 14 The compressive strength of test pieces made from each sample was measured according to BS EN 12390-3:2009 at 7 days after casting, and 28 days after casting.

[0120] Results of the testing are given in Table 9 below, and are visually indicated in Figure 15.

[0121] Table 15

[0122] The flexural strength of test pieces made from each sample was measured according to BS EN 12390-5:2009 at 7 days after casting, and 28 days after casting.

[0123] Results are given in Table 10 below, and are visually indicated in Figure 16.

[0124] Table 16

[0125] The results indicate that the samples containing graphene had reduced compressive and flexural strength. This is thought to be due to an interaction between the graphene and air entrainment agent. As such, reducing the amount of air entrainment agent was identified as an important focus for further development.

[0126] It is therefore possible to provide a graphene concrete which has improved compressive and flexural strength. By utilising a superplasticiser and relatively low amounts of air entrainment agent, a superior concrete can be provided, which still provides necessary durability for use as a PQC.

[0127] The words ‘comprises / comprising’ and the words ‘having / including’ when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0128] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

[0129] The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention as defined herein.

Claims

Claims1 . A concrete comprising: cement; graphene, wherein an amount of graphene is no more than 0.12% or no more than substantially 0.12% by weight of cement; and a superplasticiser including an air entrainment agent, wherein an amount of the air-entrainment-agent is no more than 2% by weight of an amount of the superplasticiser.

2. A concrete as claimed in claim 1 , wherein the amount of superplasticiser is no more than 0.75% or substantially 0.75% by weight of cement.

3. A concrete as claimed in any one of the preceding claims, wherein the amount of air-entrainment-agent is no more than 1 % or no more than substantially 1% by weight of the amount of superplasticiser.

4. A concrete as claimed in claim 3, wherein the amount of air-entrainment-agent is 1 % or substantially 1 % by weight of the amount of superplasticiser.

5. A concrete as claimed in any one of the preceding claims, wherein the superplasticiser comprises carboxylated polymers.

6. A concrete as claimed in any one of the preceding claims, wherein the superplasticiser is ADVA (RTM) 650 or CX SUPERCONCRETE P+ 650.

7. A concrete as claimed in any one of the preceding claims, wherein the amount of graphene is less than 0.008% or less than substantially 0.008% by weight of cement.

8. A concrete as claimed in claim 7, wherein the amount of graphene is at least 0.007% or substantially at least 0.007% by weight of cement.

9. A concrete as claimed in any one of the preceding claims, wherein the amount of graphene is at least 0.0075% or substantially 0.0075% by weight of cement.

10. A concrete as claimed in any one of the preceding claims, wherein the amount of graphene is 0.0075% or substantially 0.0075% by weight of cement.11 . A concrete as claimed in any one of the preceding claims, wherein the graphene is nanoplatelets.

12. A concrete as claimed in claim 11 , wherein the nanoplatelets have a thickness of between or substantially between 2 and 10 nm and / or a diameter of between or substantially between 2 and 7 pm.

13. A concrete as claimed in any one of the preceding claims, wherein there is no further air entrainment agent than the air entrainment agent of the superplasticiser.

14. A concrete as claimed in any one of the preceding claims, wherein the concrete further comprises fly ash, aggregates and sand.

15. A runway, taxiway or highway comprising the concrete as claimed in any one of the preceding claims.

16. A method of forming a concrete as claimed in any one of claims 1 to 14, comprising a step of: a powder of the cement being mixed with the graphene without or substantially without the presence of water and via resonant acoustic mixing.

Images