GB2615847A

GB2615847A - Concrete composition and mineral additive therefor

Info

Publication number: GB2615847A
Application number: GB2211978.8A
Authority: GB
Inventors: McCann Mark; Service Jonathan
Original assignee: Fp Mccann Ltd
Current assignee: Fp Mccann Ltd
Priority date: 2022-08-17
Filing date: 2022-08-17
Publication date: 2023-08-23
Also published as: GB202211978D0

Abstract

A mineral concrete additive for the manufacture of precast concrete structure or elements, comprising quarry fines having a particle size distribution with d90 of 40-90 µm, d50 of 10-30 micrometres and d10 of 1-5 microns. The quarry fines may comprise: 50-80% by weight of processed basalt stone and 20-50 wt% of one or more of limestone, granite or greywacke; 70-90 wt% of processed basalt and 10-30 wt% processed recycled concrete; or 50-90 wt% processed basalt and 10-50 wt% milled soda-lime glass powder. A concrete composition may comprise a binder fraction including the additive, an aggregate fraction and water. The binder fraction may comprise Portland cement or alkali activated binder. The concrete composition may comprise either 0.04-1.5 wt% mineral additive and 3.8-29.7 wt% binder or 0.2-7.5 wt% mineral additive and 3.0%-28.5 wt% binder; the composition may also comprise 60-92 wt% combined aggregate, 4-12 wt% water, and 0-3 wt% chemical admixture.

Description

Concrete Composition and Mineral Additive therefor

FIELD OF THE INVENTON

This invention relates to a concrete composition and to a mineral additive for a concrete composition for use in the manufacture of precast concrete elements and structures.

BACKGROUND OF THE INVENTION

Quarry fines (also called quarry dust) are created during many quarrying operations and are regarded as waste material with limited industrial uses. There have been prior art attempts to utilise quarry fines as an aggregate filler for concrete, typically as a partial replacement for sand. However, partial or full replacement of natural sand with quarry fines (having a typical size range of between 0.1mm and 4mm) is known to result in decreased workability of the concrete mix (mixes are referred to as "harsh"). This is caused by higher water demand of the concrete mix with unprocessed quarry fines. Typically particles of the quarry fines have angular shape and the quarry fines contain higher percentage of a filler material (i.e. particles below 63pm) than sand.

It is also normally expected that the use of an aggregate filler (most particles passing 63 pm) as a substitution of a part of the aggregate fraction in the concrete mix composition would have a detrimental effect on the workability and strength of concrete. It is also well established that comparing similar concrete mixes, the mix having lower cement (or binder) content would yield lower compressive strength.

In precast concrete structures and elements, the demoulding strength of the cast structure or element is of particular concern, where the structure or element is removed from a mould before full strength has been reached (typically to provide a 24 hour mould turnover period required for production efficiency). Therefore any reduction in the proportion of Portland cement as a binder in the concrete composition would be considered to significantly and undesirably reduce the demoulding strength of the material and render the concrete composition unsuitable for use in the manufacture of precast concrete structures or elements.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a mineral concrete additive for the manufacture of precast concrete structures or elements, said additive comprising quarry fines having a particle size distribution with d90 of 40-90 pm, d50 of 10-30 pm and d10 of 1-5 pm.

Preferably said quarry fines have a particle size distribution with d90 less than 65pm. Said quarry fines may have a particle size distribution with d90 of between 50pm and 65pm.

In one embodiment said quarry fines comprise 50% to 80% by weight of processed basalt stone and 20% to 50% by weight of one or more of limestone, granite or greywacke.

In an alternative embodiment said quarry fines comprise 70% to 90% processed 20 basalt stone and 10% to 30% by weight processed recycled concrete.

In an alternative embodiment said quarry fines comprise 50% to 90% by weight processed basalt stone and 10% to 50% by weight milled soda-lime glass powder.

According to a further aspect of the present invention there is provided a concrete composition for the manufacture of precast concrete structures or elements comprising: a binder fraction including a mineral additive in accordance with the first aspect of the invention; an aggregate fraction; and water.

The binder fraction may be between 1% and 5% by weight of said mineral additive. In one embodiment said binder fraction may comprise 5% by weight of said mineral additive.

In an alternative embodiment said binder fraction may comprise between 5% and 25% by weight of said mineral additive. In such embodiment the water content may be adjusted accordingly. The binder fraction may comprise between 10% and 20% by weight of said mineral additive.

In one embodiment said binder fraction may comprise Portland cement and said mineral additive.

Said binder fraction may comprise a blend of Portland cement and one or more of fly ash, ground granulated blast-furnace slag (GGBS), silica fume and metakaolin, 15 and said mineral additive.

In an alternative embodiment said binder fraction may comprise an alkali activated binder.

The concrete composition may further comprise one or more chemical admixtures, for example adapted to improve workability of the concrete, reduce shrinkage and/or reduce water demand, regulate setting of concrete and/or increasing the freeze-thaw resistance of concrete, such as plasticisers, superplasticisers, retarders, accelerators, air-entraining admixtures, etc. In accordance with a further aspect of the present invention there is provided a concrete composition for the manufacture of precast concrete structures or elements comprising: 0.04% to 1.5% by weight of a mineral additive in accordance with the first aspect of the present invention; 3.8% to 29.7% by weight of a binder; 60% to 92% by weight of a combined aggregate fraction; 4% to 12% by weight of water; and 0% to 3% by weight of one or more chemical admixtures.

According to a further aspect of the present invention there is provided a concrete composition comprising for the manufacture of precast concrete structures or elements comprising: 0.2% to 7.5% by weight of a mineral additive in accordance with the first aspect of the present invention; 3.0% to 28.5% by weight of a binder 60% to 92% by weight of a combined aggregate fraction; 4% to 12% by weight of water fip 0% to 3% by weight of one or more chemical admixtures Said binder may comprise or include Portland cement.

DETAILED DESCRIPTION OF THE INVENTION

A mineral additive for precast concrete application in accordance with an embodiment of the present invention comprises quarry fines, preferably from quarried processed basalt stone, having a particle size distribution with d90 of 40-90 pm, d50 of 10-30 pm and dl 0 of 1-5 pm.

The quarry fines are processed (i.e. reduced in size by a suitable grinding process and/or graded by size via a suitable grading process) in order to provide the required particle size distribution. Preferably the quarry fines are processed to have a particle size of less than 65pm for at least 90% of the material (d90). The quarry fines may have a particle size distribution with d90 of between 50pm and 65pm.

At least a portion of the basalt fines in the mineral additive may be substituted with one or more of: fines from processing other types of quarried stone (preferably 20% to 50% by weight), such as limestone, granite or greywacke; fines from processing recycled concrete into secondary aggregate (preferably 10% to 30% by weight); a finely milled soda-lime glass powder (preferably 10% to 50% by weight).

The inventors have discovered that such mineral additives, based on the appropriately processed basalt stone fines, processed to have similar or greater fineness than cement binder with which they are mixed, provides surprising benefits when used to replace a portion of the binder in a concrete composition, in particular for the manufacture of precast concrete structures or elements.

It has been observed that, at a lower replacement of the binder (1% to 5% by weight) with the mineral additive, there is no change to workability of the concrete nor, to its compressive strength (including the demoulding and lifting strengths) 112 when compared to a control mix and therefore no requirement to change the water content of the composition. Since no changes to water content or admixture dosage were made, the effect of the mineral additive is unexpected. The mineral additive is an inert material, hence leading to cement (or binder) dilution. Further, as the water content is not adjusted, the resulting water to binder content is higher than in a control mix. Considering this, it would be expected to see a decrease in compressive strength -in contrast to maintained compressive strength, which was observed.

This positive influence of the partial replacement of the cement/binder with the mineral additive is believed to be caused by the fine nature of the mineral additive. Fine particles of the mineral additive act like micro-aggregates, physically densifying the hardened paste and providing nucleation sites for the initial growth of the hydrates, leading to improved early age compressive strength.

Larger binder replacements (5% to 25% by weight) result in some reduction of both workability and strength, hence both water and admixture adjustment are required to achieve the desired properties.

The mineral additive can also be used to replace partially or fully (from 10% to 30 100% by weight) a filler material (such as limestone powder, fly ash or GGBS) used in proportioning self-compacting concrete (SCC) mixes.

Due to its fine nature, the mineral additive improves viscosity of the mix and has a beneficial effect on water bleeding and segregation of concrete. Partial substitution of the binder, or partial or full substitution of the filler in SCC, leads to reduced shrinkage of concrete. This is because replacing part of the binder or filler with an inert non-shrinking fine material, acting as a micro-aggregate, results in a physical restraint of shrinkage forces.

Valorisation of waste quarry fines to form a mineral additive, with controlled particle size distribution and composition, for precast applications, has the following benefits: - technical (concrete) -securing the required early age demoulding and lifting 113 strength of precast concrete products made with reduced binder content, - sustainability (concrete) -carbon reduction of concrete mixes via partial substitution of a carbon intensive binder (e.g. based on Portland cement), - economical (concrete) -savings related to a partial substitution of expensive binder materials (e.g. Portland cement, fly ash, GGBS, silica fume), with a cheap 15 valorised waste material, - economical (waste quarry fines) -turning waste into value added product, - environmental (waste quarry fines) -reduction in stockpiles of waste quarry dust.

Concrete compositions for precast applications containing the mineral additive as 20 described above have been found to secure appropriate demoulding and lifting strength of concrete products for efficient mould turnover and reduction in concrete binder content.

Where the mineral additive replaces 1% to 5% by weight of a binder (i.e. Portland 25 cement or Portland cement-based binder with the addition of fly ash, GGBS, silica fume and/or metakaolin) it is not required to change the water content of the concrete mix composition.

In a preferred embodiment, where no added water is required, there is provided a 30 concrete composition for the manufacture of precast concrete structures or elements comprising the mineral additive at 1% to 5% replacement of the binder and having the following composition: 0.04% to 1.5% by weight of the mineral additive; 3.8% to 29.7% by weight of a binder; 60% to 92% by weight of a combined aggregate fraction; 4% to 12% by weight of water; and 0% to 3% by weight of one or more chemical admixtures.

Alternatively, there is provided a concrete composition for the manufacture of precast concrete structures or elements comprising the mineral additive at 5% to 25% by weight replacement of the binder and having the following composition: 0.2% to 7.5% by weight of the mineral additive; 3.0% to 28.5% by weight of a binder 60% to 92% by weight of a combined aggregate fraction; 4% to 12% by weight of water; and 0% to 3% by weight of one or more chemical admixtures.

By processing the quarry fines to a particle size comparable to that of the binder, partial replacement of the binder with the quarry fines does not cause the expected large loss in performance of the concrete composition, especially when used for the manufacture of precast concrete structures and elements, while providing numerous advantages, as discussed above.

zo The invention is not limited to the embodiments described herein but can be amended or modified without departing from the scope of the present invention as defined by the claims.

Claims

CLAIMS1. A mineral concrete additive for the manufacture of precast concrete structures or elements, said additive comprising quarry fines having a particle size distribution 5 with d90 of 40-90 pm, d50 of 10-30 pm and d10 of 1-5 pm.
2. A mineral concrete additive as claimed in claim 1, wherein said quarry fines have a particle size distribution with d90 less than 65pm.
113 3. A mineral concrete additive as claimed in claim 1 or claim 2, wherein said quarry fines comprise 50% to 80% by weight of processed basalt stone and 20% to 50% by weight of one or more of limestone, granite or greywacke.
4. A mineral concrete additive as claimed in claim 1 or claim 2, wherein said quarry 15 fines comprise 70% to 90% processed basalt stone and 10% to 30% by weight processed recycled concrete.
5. A mineral concrete additive as claimed in claim 1 or claim 2, wherein said quarry fines comprise 50% to 90% by weight processed basalt stone and 10% to 50% by 20 weight milled soda-lime glass powder.
6. A concrete composition for the manufacture of precast concrete structures or elements comprising: a binder fraction including a mineral additive as claimed in any of claims 1 to 5; an aggregate fraction; and water.
7. A concrete composition as claimed in claim 6, wherein said binder fraction comprises between 1% and 5% by weight of said mineral additive.
8. A concrete composition as claimed in claim 6, wherein said binder fraction comprises between 5% and 25% by weight of said mineral additive.
9. A concrete composition as claimed in any of claims 6 to 8, wherein said binder fraction comprises Portland cement and said mineral additive.
10. A concrete composition as claimed in any of claims 6 to 8, wherein said binder 5 fraction comprises a blend of Portland cement and one or more of fly ash, ground granulated blast-furnace slag (GGBS), silica fume and metakaolin, and said mineral additive.
11. A concrete composition as claimed in any of claims 6 to 8, wherein said binder 10 fraction comprises an alkali activated binder.
12. A concrete composition as claimed in any of claims 6 to 11, further comprising a chemical admixture for improving workability.
13. A concrete composition for the manufacture of precast concrete structures or elements comprising: 0.04% to 1.5% by weight of a mineral additive as claimed in any of claims 1 to 5; 3.8% to 29.7% by weight of a binder; 60% to 92% by weight of a combined aggregate fraction; 4% to 12% by weight of water; and 0% to 3% by weight of one or more chemical admixtures.
14. A concrete composition for the manufacture of precast concrete structures or elements comprising: 0.2% to 7.5% by weight of a mineral additive as claimed in any of claims 1 to 5; 3.0% to 28.5% by weight of a binder; 60% to 92% by weight of a combined aggregate fraction; 4% to 12% by weight of water; 0% to 3% by weight of one or more chemical admixtures.
15. A concrete composition as claimed in claim 13 or claim 14, wherein said binder comprises or includes Portland cement.