AU2022361938A1

AU2022361938A1 - Low carbon alternative binders

Info

Publication number: AU2022361938A1
Application number: AU2022361938A
Authority: AU
Inventors: Ali Bagheri; David FARAH
Original assignee: Adelaide Brighton Cement Ltd
Current assignee: Adelaide Brighton Cement Ltd
Priority date: 2021-10-14
Filing date: 2022-10-07
Publication date: 2023-10-05
Also published as: WO2023060296A1

Abstract

The invention is a binder which is an alternative to traditional cementitious binders. An example of the binder uses ground granulated blast furnace slag, hydrated lime and cement kiln dust.

Description

LOW CARBON ALTERNATIVE BINDERS

FIELD OF INVENTION

[001] The invention is an alternative binder to traditional cementitious binders.

BACKGROUND TO THE INVENTION

[002] Traditional cementitious binders often are based on Ordinary Portland Cement (OPC). The process for producing OPC from limestone, and other natural sources of calcium, is an energy intensive process and results in the release of a large amount of greenhouse gases. The production of cement also requires the use of virgin limestone deposits, which are a limited resource.

[003] There are a number of waste materials from industrial processes which have been shown to have pozzolanic properties which make them useful as supplementary cementitious materials, such as blast furnace slag and fly ash. These “waste” products have long been used to supplement or replace a portion of the OPC in many of the traditional applications of OPC. However, as the world moves away from coal fired power plants, and also recycles more and more steel, these “waste” products are harder to obtain, and their use needs to be optimized.

[004] There have also been alkali-activated replacement binders, geopolymers, calcium sulphoaluminate cements and other hybrids, all trying to at least partially replace OPC in the final cementitious building and construction materials, and thereby reduce the embodied carbon in those materials.

[005] Some of the prior art alkali activators are very caustic or require large amounts of heat or energy for the activation reaction to occur. This may be impractical in certain circumstance or add to the existing safety issues in the handling of cementitious materials. They may also be complicated to transport, use or mix with the other materials, as they are supplied as liquids or require additional ingredients to activate them.

[006] There is still room for improvement in alternative binders generally, and for different binders that are fit for purpose in specific applications. SUMMARY OF INVENTION

[007] It is an object of this invention to provide an alternative binder which: a. exhibits a lower carbon footprint than the prior art alternative binders; b. does not pose any health and safety risks above those involved in the use of OPC; c. is able to be supplied as a single powder; and d. is able to be activated by the addition of water.

[008] The applicants have found that a combination of ground granulated blast furnace slag (GGBFS), a reactive source of calcium oxide or calcium hydroxide other than OPC, and cement kiln dust provides an alternative binder to ordinary cementitious binders. The binder created by the mixture of the 3 ingredients provides the desired properties of strength and durability.

[009] In a first aspect of the invention is an alternative binder which comprises a mixture of an aluminosilicate precursor, a reactive source of calcium oxide or calcium hydroxide other than OPC and cement kiln dust.

[010] In a second aspect of the invention the alternative binder comprises: a. 40-98 % aluminosilicate precursor selected from ground granulated blast furnace slag, fly ash, and kaolin, or a mixture thereof; b. 1-30% cement kiln dust; and c. 1-30 % lime, selected from hydrated lime and quicklime.

[011] In a third aspect of the invention the alternative binder comprises: a. 40-98 % ground granulated blast furnace slag; b. 1-30 % cement kiln dust; and c. 1-30 % hydrated lime.

[012] In a fourth aspect of the invention the alternative binder comprises: a. 40-98 % ground granulated blast furnace slag; b. 1-30 % cement kiln dust; and c. 1-30 % quicklime. [013] In a fifth aspect of the invention the alternative binder comprises: a. 60-92 % ground granulated blast furnace slag; b. 5-20% cement kiln dust; and c. 3-20 % lime.

[014] In a sixth aspect of the invention is the use of the binder for geotechnical engineering purposes. A mixture of the binder of the invention mixed with appropriate substrates may be useful in the stabilization of loose materials to provide slope stabilisation, land stabilisation, road works, infrastructure works, or mine backfilling.

[015] In a seventh aspect of the invention is a method of backfilling a mine using a backfill material comprising mine tailings and an alternative binder which comprises: a. 75 % ground granulated blast furnace slag/ neat mill slag; b. 15% cement kiln dust; and c. 10 % lime.

BRIEF DESCRIPTION OF THE DRAWINGS

[016] Figure 1 is a table showing a number of examples of the alternative binder of the invention and their characteristics in a number of ways which are important when selected a binder for different situations.

[017] Figure 2 is a graph showing the strength of concrete at 28 days post installation where the concrete is made with a binder within the scope of the invention, compared to a prior art mix and mine tailings.

[018] Figure 3 is a graph showing the strength of concrete at 7-, 14-, and 28-days post installation where the concrete is made with a binder within the scope of the invention, compared to a prior art mix and a second source of mine tailings.

DETAILED DESCRIPTION OF THE INVENTION

[019] The following detailed description of the invention refers to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings and the following description to refer to the same and like parts. Dimensions of certain parts shown in the drawings may have been modified and/or exaggerated for the purposes of clarity or illustration.

[020] Further advantages and improvements may very well be made to the present invention without deviating from its scope. Although the invention has been shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope and spirit of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices and apparatus. Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in this field.

[021] In the present specification and claims (if any), the word "comprising" and its derivatives including "comprises" and "comprise" include each of the stated integers but does not exclude the inclusion of one or more further integers.

[022] A reactive source of calcium oxide or calcium hydroxide has been used to encompass the use of slaked lime, lime water, lime, quick lime and any other source of calcium oxide or calcium hydroxide except for Ordinary Portland Cement.

[023] Lime has been used in this specification to encompass both hydrated lime and quicklime. Each has the properties required to activate the aluminosilicate precursors, although they have different safety and handling issues, as well as different energy inputs and environmental impacts. There are times when the lime is specified as either hydrated lime or quicklime.

[024] Ground granulated blast furnace slag is a by-product of the steel making process. The exact composition of the GGBFS will depend on its source as some steel manufactures add other ingredients to the steel making process. The term Neat Mill Slag (NMS) may also be used for GGBFS.

[025] Cement Kiln Dust (CKD) is inorganic mineral material derived from the clinker production process. Cement kiln dust has a high content of reactive lime and alkali materials as well as many mineral salts. It is the waste product of the production of cement from clinker in a rotary kiln. For each tonne of cement produced, between 60 and 70kgs of cement kiln dust is produced. However, in the past the cement kiln dust has been considered only as a waste material. It has been used as a minor additional constituent as filler within the manufacture of OPC-containing cement blends. This use was a way to minimise waste material that needed to be dumped.

[026] The inventors have now recognised the usefulness of CKD in creating cementitious blends that do not contain OPC.

[027] This new use will help minimize one of the biggest wastes in the cement production process.

[028] The inventors have found that when combined with lime and GGBFS, the CKD plays a role as an auxiliary activator in making a cementitious binder. The lime activates the GGBFS, with the CKD participating in the hydration reaction as an auxiliary activator to produce the cementitious binder.

[029] Both the quick lime and hydrated lime act as activators. There is no need to combine the two activators, but the different activators will be more useful in different situations in which binders are used. For example, a binder containing quicklime will produce higher heat than a binder containing hydrated lime, which may not be desirable. Quicklime is a more potent activator of the binder of the invention.

[030] Both quick lime and hydrated lime produce binders of comparable strength at 7 and 28 days as can be seen in Figure 1 .

[031 ] The alternative binder of the invention comprises: a. 40-98 % aluminosilicate precursor selected from ground granulated blast furnace slag, fly ash, and kaolin, or a mixture thereof; b. 1-30% cement kiln dust; and c. 1-30 % lime, selected from hydrated lime and quicklime.

[032] Ground granulated blast furnace slag is the preferred aluminosilicate precursor for use in the invention. It is a well-known and tested component of cementitious binders and materials and is readily available. It is a waste product as compared to kaolin which is a mineral, is required to be mined and is a finite resource. Fly ash is also a waste product produced by burning coal to produce electricity and so is more preferred than kaolin. But as the world moves away from using coal fired power stations, the availability of fly ash is getting scarcer. [033] In a more preferred aspect of the invention the alternative binder comprises: a. 60-90 % ground granulated blast furnace slag; b. 5-20% cement kiln dust; and c. 5-20 % lime.

[034] As discussed above, both quicklime and hydrated lime have their pros and cons. In the initial experiments, the inventors found that quicklime provided a slightly stronger, but still comparable product, than the binder with hydrated lime.

[035] There are two most preferred versions of the alternative binder of the invention. The first comprises: a. 40-98 % ground granulated blast furnace slag; b. 1-30 % cement kiln dust; and c. 1-30 % quicklime.

[036] The second most preferred alternative binder of the invention comprises: a. 40-98 % ground granulated blast furnace slag; b. 1-30 % cement kiln dust; and c. 1-30 % hydrated lime.

[037] Cementitious binders are used in a wide range of applications, requiring a wide range of strengths and durability. The uses go from applications like ground stabilization, which may require only a quite low strength, through mine stabilisation using backfill, to binding materials to make masonry products, to premix cement molded to produce larger scale building articles through to the wide range of strengths required by premix concrete in all the varied uses to which it can be put.

[038] The present invention was initially tested as a binder to be used in mine backfilling operations. In this instance, the binder is mixed with mine tailings and pumped back into the mined-out tunnels to fill them up and stabilise the mine. Mining of a new tunnel close by will be occurring simultaneously, or soon after, the backfilling of the exhausted tunnel. As a result, early strength is required, but not as high strength is required as is required in concrete being used in building high rise buildings.

[039] The proven use as in mine backfilling suggests that the binder of the invention would have uses in other geotechnical engineering purposes. A mixture of the binder of the invention mixed with appropriate substrates may be useful in the stabilization of loose materials to provide slope stabilisation, or land stabilisation.

[040] Further testing is underway for the use of the binder of the invention to be used in the production of masonry products. There will always be limitations on the use of any binder, but it is thought that the binder of the invention will have industrial applicability in many applications where traditional cementitious binders have been previously used. The dosing rates of the binder in the concrete mix will need to be varied depending on the end use and there will also be a need to vary the ratio of the ingredients used within the binder composition itself.

[041] A final aspect of the invention is a method of backfilling a mine using a backfill material comprising mine tailings and an alternative binder which comprises: a. 75 % ground granulated blast furnace slag/ neat mill slag; b. 15% cement kiln dust; c. and10 % lime.

DETAILED DESCRIPTION OF THE DRAWINGS

[042] Figure 1 shows the mortar test strengths of the examples of the invention.

[043] In both Figures 2 and 3 the Test 2 binder formulation was 80% ground granulated blast furnace slag 5% quicklime and 15% cement kiln dust. In Figure 3, Test 1 binder formulation was 75% ground granulated blast furnace slag 10% hydrated lime and 15% cement kiln dust.

[044] Figure 2 shows the results of using binders of the invention combined with mine tailings and compares the results at 28 days post installation. The figure also shows the difference between two dose strengths of the binder. In the group on the left 4.5% of the concrete made was a binder of the invention. As can be seen strength was greatly improved over the prior art at this level of inclusion.

[045] The tests were for using the binder to produce concrete being used in mine backfilling. The aggregate used was tailings from the mine being stabilized.

[046] Also the strength required for mine backfilling is lower than many other uses of concrete, so whilst the increase in strength was a welcome result, it was more than required for the circumstances. A lower level of binder (4% of the total mix rather than 4.5% which was the first dosage rate) was then tested as can be seen on the right hand side of the graph, and whilst the strength was still greater than the prior art, it was at more appropriate levels.

[047] The strength of the binder of invention, greater than a commercially available prior art binder at the same dosage rate, means that the customer can achieve the same result using a lower level of binder, thereby reducing costs, as well as lowering the carbon footprint of the backfill.

[048] Figure 3 shows the results of using binders of the invention combined with mine tailings and compares the results at 7, 14, and 28 days post installation. This concrete was made with mine tailing from a different mine than that shown in Figure 2. It can be seen from the table that again the binder of the invention outperforms the prior art binders in strength at 14 and 28 days. These results indicate that a reduction in the amount of the binder of invention may be able to be reduced, but tests at a lower dosage rate have not been conducted. In this instance, the prior art binder 1 did not provide any meaningful strength at all.

[049] The composition of mine tailings varies greatly from mine to mine and so there will be a need to work within the ranges of the amounts of the ingredients that comprise the binder, as well as altering the amount of binder used.

EXAMPLES

[050] Example 1

[051] 77 %wt. of ground granulated blast furnace slag with an average Blaine fineness of approximately 470 m²/kg was used. 9 %wt. of quicklime, as a source of calcium oxide, was employed to provide the required alkalinity for the activation of the GGBFS. 14 %wt. Cement kiln dust (CKD), was used as an auxiliary activation agent. The quicklime and CKD were used without any additional grinding or treatment and were utilized as received. The ingredients were blended together to form a single binder, which was used to prepare mortars with a binder : sand ratio of 1 :3 and water : binder ratio of 0.5. No additional chemical admixtures were used in the mortars.

[052] Prisms with dimensions of 40mm x 40mm x 160mm were produced. After an initial 24 hours of curing of the samples in a humidity cabinet, they were demoulded and stored in a lime saturated water bath until their nominated test date. Compressive strength measurements were conducted on three prisms for each binder at nominated ages and average values were reported at 7 and 28 days of curing. The mixing, sample preparation, storage and testing procedures were performed in accordance with the relevant requirements of AS 2350. The achieved results are depicted by Figure 1 .

[053] Example 2

[054] 86 %wt. of ground granulated blast furnace slag with an average Blaine fineness of approximately 470 m²/kg was used in this example. 5 %wt. of quicklime, as a source of calcium oxide, was employed to provide the required alkalinity for the activation of the GGBFS. 9 %wt. Cement kiln dust (CKD), , was used as an auxiliary activation agent. The quicklime and CKD were used without any additional grinding or treatment and were utilized as received. The ingredients were blended together to form a single binder which was used to prepare mortars with a binder : sand ratio of 1 :3 and water to binder ratio of 0.5. No additional chemical admixtures were used in the mortars.

[055] Prisms with dimensions of 40mm x 40mm x 160mm were produced. After an initial 24 hours of curing of the samples in a humidity cabinet, they were demoulded and stored in a lime saturated water bath until their nominated test date. Compressive strength measurements were conducted on three prisms for each binder at nominated ages and average values were reported at 7 and 28 days of curing. The mixing, sample preparation, storage and testing procedures were performed in accordance with the relevant requirements of AS 2350. The achieved results are depicted by Figure 1 . [056] Example 3

[057] 77 %wt. of ground granulated blast furnace slag with an average Blaine fineness of approximately 470 m²/kg was used in this example. 9 %wt. of hydrated lime, as a source of calcium oxide, was employed to provide the required alkalinity for the activation of the GGBFS. 14 %wt. Cement kiln dust (CKD), was used as an auxiliary activation agent. The quicklime and CKD were used without any additional grinding or treatment and were utilized as received. The ingredients were blended together to form a single binder which was used to prepare mortars with a binder : sand ratio of 1 :3 and water to binder ratio of 0.5. No additional chemical admixtures were used in the mortars.

[058] Prisms with dimensions of 40mm x 40mm x 160mm were produced. After an initial 24 hours of curing of the samples in a humidity cabinet, they were demoulded and stored in a lime saturated water bath until their nominated test date. Compressive strength measurements were conducted on three prisms for each binder at nominated ages and average values were reported at 7 and 28 days of curing. The mixing, sample preparation, storage and testing procedures were performed in accordance with the relevant requirements of AS 2350. The achieved results are depicted by Figure 1 .

[059] Example 4

[060] 73% wt. of ground granulated blast furnace slag with an average Blaine fineness of approximately 470 m²/kg was used in this example. 9 %wt. of hydrated lime, as a source of calcium oxide, was employed to provide the required alkalinity for the activation of the GGBFS. 18% wt. Cement kiln dust (CKD) was used as an auxiliary activation agent. The quicklime and CKD were used without any additional grinding or treatment and were utilized as received. The ingredients were blended together to form a single binder which was used to prepare mortars with a binder: sand ratio of 1 :3 and water to binder ratio of 0.5. No additional chemical admixtures were used in the mortars.

[061] Prisms with dimensions of 40mm x 40mm x 160mm were produced. After an initial 24 hours of curing of the samples in a humidity cabinet, they were demoulded and stored in a lime saturated water bath until their nominated test date. Compressive strength measurements were conducted on three prisms for each binder at nominated ages and average values were reported at 7 and 28 days of curing. The mixing, sample preparation, storage and testing procedures were performed in accordance with the relevant requirements of AS 2350. The achieved results are depicted by Figure 1 .

Claims

1 . A binder compromising a mixture of an aluminosilicate precursor, a source of calcium oxide or calcium hydroxide other than Ordinary Portland Cement and cement kiln dust.

2. A binder compromising a mixture of an aluminosilicate precursor, lime and cement kiln dust

3. A binder of claim 1 or 2 comprising: a. 60-98 % aluminosilicate precursor selected from ground granulated blast furnace slag, fly ash, and kaolin, or a mixture thereof; b. 1-20% cement kiln dust; and c. 1-20 % lime, selected from hydrated lime and quicklime.

4. A binder of claim 1 or 2 comprising: a. 60-98 % ground granulated blast furnace slag; b. 1-20 % cement kiln dust; and c. 1-20 % hydrated lime.

5. A binder of claim 1 or 2 comprising: a. 60-98 % ground granulated blast furnace slag; b. 1-20 % cement kiln dust; c. and 1-20 % quicklime.

6. A binder of claim 1 or 2 or 2 comprising: a. 70-90 % ground granulated blast furnace slag; b. 5-20% cement kiln dust; c. and5-10 % lime.

7. A method of backfilling a mine using a backfill material comprising mine tailings and a binder compromising a. 75 % ground granulated blast furnace slag/ neat mill slag; b. 15% cement kiln dust/ lime kiln dust; and c. 10 % lime.