NL2021223B1

NL2021223B1 - Method for producing concrete based on vegetal aggregate

Info

Publication number: NL2021223B1
Application number: NL2021223A
Authority: NL
Inventors: Gerhard Nicolaas Schotanus Jacobus
Original assignee: Gerhard Nicolaas Schotanus Jacobus; Johannes Cornelis Willemsen
Priority date: 2018-07-02
Filing date: 2018-07-02
Publication date: 2020-01-07

Abstract

The application describes a method for producing concrete products based on vegetal aggregate, a binding agent, sand, gravel and water. The method comprises: mixing sand, gravel, binding agent, vegetal aggregate and water to obtain a first concrete composite; pouring and curing the first concrete composite to obtain an intermediate bio-based concrete product; crushing the first intermediate concrete product to obtain a bio-based concrete granulate; mixing a concrete mixture and the bio-based concrete granulate to obtain a second concrete composite; and further processing the second concrete composite to obtain the concrete products. The method enables to produce compacted concrete with fibrous vegetal particles in it.

Description

TECHNICAL FIELD

The subject disclosure relates to a method for producing a concrete based on vegetal materials. More particular, the subject disclosure relates to a method for producing concrete based on vegetal aggregate.

BACKGROUND ART

The production of concrete and mortar based on an exclusively vegetal aggregate such as, for example, wood, hemp or reed fibers, is already known. In a first operational step during the production of such mortar, the shredded vegetal raw material is pre-mineralized. During this pre-mineralization, the vegetal particles are placed in a mineralization bath, or are wetted or sprayed with a mineralization liquid, wherein aluminium sulphate or cement is usually used as mineralizator. The vegetal particles are then dewatered and dried. At the work site, the dried, pre-mineralized particles can then be mixed with the mixing water and cement as aggregate to form a mortar. Pre-mineralization of the vegetal aggregate ensures that a solid bond is formed between the vegetal aggregate and the hardened cement paste, so that the concrete possesses the desired bending tensile strength and resistance to pressure. In this respect, it should be noted that the known pre-mineralization of the vegetal aggregate is costly and is, in addition, potentially harmful to the environment.

WO0212145A2 discloses a method for producing cement or mortar based on exclusively vegetal aggregate, a mineral binding agent, and mixing water. Instead of pre-mineralizing the vegetal aggregate in a separate operational step, when mixing the concrete or mortar, 4 -14 kg non hydratable mineralizator is added per cubic meter vegetal aggregate. A preferred mineralizator is raw calcium carbonate. The mineralizator is deposited only on the surface of the vegetal aggregate particles and thus does not affect the cellular structure of the particles of the vegetal aggregate.

SUMMARY OF INVENTION

It is an object of the present technology to provide an alternative method to produce concrete products based on a vegetal aggregate in a simple and economical manner; the hardened concrete having a relatively low specific volumetric mass density and good properties with respect to bending tensile strength, compressive strength and storage of carbon dioxide in the form of vegetal particles.

According to a first aspect of the subject technology, this object is achieved by the method for producing concrete products having the features of claim 1. Advantageous embodiments and further ways of carrying out the present technology may be attained by the measures mentioned in the dependent claims.

The method for producing concrete products comprising vegetal particles according to the subject technology is characterized by mixing sand, gravel, binding agent, vegetal aggregate and water to obtain a first bio-based concrete composite. Pouring and curing the first bio-based concrete composite to obtain an intermediate bio-based concrete product. Crushing the first intermediate concrete product to obtain a bio-based concrete granulate. Mixing a concrete mixture and the bio-based concrete granulate to obtain a second bio-based concrete composite; and further processing the second bio-based concrete composite to obtain the concrete products.

It has been found that when compacting technics are used to produce concrete with one mixing step concrete products with vegetal aggregate, mechanical tension is build up in the vegetal particle. When the mould or form work is removed before the concrete is completely hardened, the compressive stress in the vegetal particles is released by expansion of the particles and as a result the concrete product will expand. By this expansion of the unhardened concrete, the tensile strength of the final hardened concrete product is reduced significantly. According to the subject technology, the vegetal particles or pieces are first immobilized in concrete. This concrete with vegetal particles is subsequently crushed to aggregate with form-retaining parts with a desired grain size. The hardened composite of gravel, sand and binding agent around the vegetal particles in a form-retaining part, protects the vegetal particles against forces acting on the outside of the form-retaining part. When this aggregate with form retaining parts is used as a substitute of at least a part of gravel and optionally cement of a mixture to produce concrete, compacting of the concrete will not result is compressive stress in the vegetal particles. Consequently, removing the mould or form work from the concrete product will not result in expansion of the product and reduction of the tensile strength of the product.

In an embodiment, the further processing action comprises pouring and compacting the second concrete composite in a mould to obtain concrete products and before hardening removing the concrete products from the mould.

In an embodiment, the vegetal aggregate comprises fibrous particles with lengths up to 10cm, in particular with length ranging from 1-5 mm, more in particular with length ranging from 1-3 mm. Preferably, the length of the fibrous particles should be smaller than the maximal grain size of the bio-based concrete aggregate.

In an embodiment, the binding agent is at least one taken from a group comprising: cement, polymers, geopolymers, lignin, alkali-activated aluminosilicates, and sodium metasilicate.

In an embodiment, the intermediate bio-based concrete product has a strength according to concrete strength class C20/25, C25/30 or C28/35.

In an embodiment, the bio-based concrete aggregate has a grain size in the range of 0 - 16mm. This feature has the advantage that the bio-based concrete aggregate comprises both large particles and very small particles. The distribution of the particle size (grading) will determine the amount of gravel and cement of a concrete mixture that could be replaced by the bio-based concrete aggregate.

In an embodiment, the first concrete composite is obtained by mixing sand, gravel, binding agent, and water to obtain a first concrete mixture, adding vegetal aggregate to the first concrete mixture to obtain a second concrete mixture and mixing the second concrete mixture to obtain the first concrete composite. This feature has the advantage that by adding the vegetal aggregate as latest component to a homogeneous concrete mixture, clumping of the vegetal particles in the concrete mixture is significantly reduced. As a result the mixing time can be reduced to obtain a concrete mixture wherein the vegetal particles are homogenous distributed.

In an embodiment, the first concrete composite comprises per cubic meter 0,01 - 60kg vegetal aggregate. An additional advantage of the subject disclosure is that the mixing process of the final concrete mixture is almost not dependent on the amount of vegetal aggregate in the concrete as the vegetal aggregate is already encapsulated by a concrete composite comprising sand, gravel and binding agent.

In an embodiment, the vegetal aggregate is chopped Miscanthus, more particular Miscanthus 'Giganteus'. Miscanthus uses a lot of carbon dioxide to grow and to make its organic fibers. In this way, more carbon dioxide can be stored in the concrete product.

DESCRIPTION OF EMBODIMENTS

In an embodiment of the method for producing a concrete product which concrete comprises vegetal aggregate, first a homogenous mixture is made by mixing per cubic meter: 400kg Portlandcement CEM I 52,5 N as binding agent, 655kg wet concrete sand, 205kg wet gravel with a grain size in the range 2-8mm and approximately 101 water. The mixing is done in a conventionally known way,

e.g. by using a pan mixer. As soon as the mixture is homogenous, 14kg Miscanthus Giganteus is added as vegetal aggregate to the mixture. The mixture is poured in a form of a product that can easily be broken in to parts which can be crushed by a crushing machine. A suitable form is a concrete slab with a thickness of 10 - 20 cm.

After pouring and curing the mixture, the thus obtained intermediate bio-based concrete product is crushed to obtain a granulate that can be used as bio-based concrete aggregate to produce concrete products wherein the biobased concrete aggregate replaces a part of the gravel and cement that is normally used to produce concrete. Bio-based in the context of the present disclosure means that the aggregate comprises organic substances derived from living (or once-living) organisms. The bio-based concrete aggregate has physical characteristics that look like the physical characteristics of standard concrete. That’s why the bio-based concrete aggregate can be used to replace a part of the gravel and cement of a concrete mixture without changing the recipe significantly. The part of the gravel and cement/binding agent that will be replaced by bio-based concrete aggregate depends on the grain size distribution of the bio-based concrete aggregate. The more dust-like particles, i.e. particles with a grain size corresponding to the binding agent, the bio-based concrete aggregate has, the more binding agent can be replaced by the bio-based concrete aggregate. Preferably, the bio-based concrete aggregate has a maximum grain size which corresponds to the grain size of the gravel used to produce the concrete.

In the concrete parts of the bio-based concrete aggregate, the vegetal aggregate, i.e. the vegetal fibrous particles, is now immobilized in the parts of the bio-base concrete granulate. Pressure forces acting on the exterior of a part will minimally be transferred to the vegetal particles or fibers encapsulated in the part. This makes it possible to use the bio-based concrete aggregate as aggregate to produce compacted concrete. The forces applied during compacting will not result in compression stress in the vegetal fibrous particles, and the concrete product will not expand when the product is removed from its mould or formwork. This applies to all known concrete compacting processes such as but not limited to internal vibration, external vibration, pressing, tamping and shocking.

In an embodiment of the final concrete product, a concrete mixture is made wherein per cubic meter 200 litre gravel is replace by 200 litre bio-based concrete granulate as described above. Assuming that the weight of gravel is 2200kg/m³ and the weight of bio-based concrete granulate is 1200kg/m³, this results in a weight reduction of 200kg/m³.

It should be noted that 1 cubic meter Miscanthus Giganteus has a weight of approximately 120kg. Depending on the application of the concrete and the required specifications, to produce a cubic meter an amount of Miscanthus Giganteus could be added in the range of 0 - 0,5m³

The sequence in which the additives are introduced is unimportant. In order to prevent the vegetal aggregate sticking together and forming lumps in the mixer, it is, however advantageous to mix the sand, gravel, binding agent to a obtain a homogenous mixture before the vegetal aggregate is added.

In the embodiment given of the method to produce the bio-based concrete aggregate, Portlandcement CEM I 52,5 N is used as binding agent. Instead of Portlandcement, any other suitable binding agent or combination of binding agents might be used such as, but not limited to: cement, polymers, geopolymers, lignin, alkali-activated aluminosilicates and sodium metasilicate.

It might be clear, from the description above, that there is no expensive premineralization of the vegetal aggregate.

The vegetal aggregate to be used is not limited to Miscanthus Giganteus. It is preferred that the vegetal aggregate be produced from fibrous, rapidly growing plants, for example, by shredding or chopping. The following, amongst others, can be used as vegetal aggregate: the wood of coniferous trees, hemp, and reeds. The wood from deciduous trees is not suitable because of its high sugar content. Above all, it is all the plants of the 04 group, which are characterized by a high level of photosynthesis performance, that are preferred. The rapidly growing plants of the Miscanthus family are particularly useful. A preferred type of Miscanthus is Miscanthus Giganteus, which has a very high silicon content. To generate the high silicon content, the plant extracts carbon dioxide from the air. In this way one can say that carbon dioxide is indirectly stored in the vegetal aggregate and by using the aggregated to produce concrete, carbon dioxide is indirectly stored in the concrete.

The size of the fibrous particles in the vegetal aggregate can be in a range of 1- 3 mm width and 3-60 mm length but is not limited to these ranges and might be larger or smaller.

It should further be noted that mixtures of different plants can be used as raw materials for vegetal aggregate.

Depending of the application of the concrete the bio-based concrete product has a strength according to concrete strength class C20/25, C25/30 or C28/35. However, it might in future be possible to produce concrete products with the bio-based concrete aggregate with a strength of a higher concrete strength class.

The bio-based concrete aggregate can be produced with any possible grain size. For example, bio-based concrete aggregate with a grain size of 0-32mm, 2 - 5mm, 4-16mm and 16-32mm. By sieving the parts of the granulate obtained by crushing the slab obtained by mixing, pouring and hardening a mixture of a binding agent, sand, gravel, water and vegetal aggregate, a bio-based concrete aggregate can be obtained with a predefined grain size distribution. This makes it possible to replace with equal amounts gravel and/or binding agent having the same grain size distribution by the bio-base concrete aggregate without changing the recipe to obtain a concrete product with approximately the same characteristics.

The ingredients sand, gravel and minerals for binding agent may be obtained by mining or extraction directly from nature as raw materials and primary building materials. However, said ingredients may also be obtained by recycling concrete. By crushing the concrete waste, sewing the crushed concrete and mixing the particles, secondary building materials are obtained which can be used to replace at least partially primary building materials in a mixture for concrete. The method according to the subject disclosure is suitable to be used in the circular economy to produce bio-based concrete granulate from recycled sand, gravel and minerals. It might be clear that when vegetal based concrete is recycled, the obtained secondary building materials also comprises a fraction of vegetal material that might be reused.

The concrete products that can be made by the subject disclosure are not limited to concrete pavement tiles, curb stones, concrete stones, concrete bicycle pathways, entrance blocks, bends, corner pieces, walling stones, street furniture, concrete pipes and all other repetitive or semi-repetitive produced concrete elements.

The subject disclosure may also be used to produce concrete parts that are used in composite products, such as street furniture comprising concrete and wooden or plastic parts.

While the invention has been described in terms of several embodiments, it is contemplated that alternatives, modifications, permutations and equivalents thereof will become apparent to those skilled in the art upon reading the specification.

Claims

CONCLUSIONS:

A method for producing concrete products based on vegetable aggregate material, a binder, sand, gravel and water, the method comprising:

mixing sand, gravel, binder, vegetable aggregate, and water to obtain a first concrete composition;

and, casting and curing the first concrete composition to obtain a bio-based concrete intermediate;

characterized in that, the method further comprises:

breaking the first bio-based concrete intermediate to obtain a bio-based concrete granulate;

mixing a concrete mixture and the bio-based concrete granulate to obtain a second concrete composition; and further processing the second concrete composition to obtain the concrete products.

The method of claim 1, wherein the further processing comprises:

pouring and compacting the second concrete composition in a mold to obtain concrete products;

before curing, removing the concrete products from the mold.

The method according to any of claims 1-2, wherein the vegetable aggregate material comprises fibrous particles with lengths up to 10 cm, in particular with a length in the range of 1-5 mm, more in particular with a length in the range of 1-3 mm.

The method of any one of claims 1 to 3, wherein the binder is at least one from a group comprising: cement, polymers, geopolymers, lignin, alkali-activated aluminosilicates, and water glass.

The method according to any one of claims 1 to 4, wherein the bio-based concrete intermediate has a strength according to the concrete strength class C20 / 25, C25 / 30 or C28 / 35.

The method of any one of claims 1 to 5, wherein the bio-based concrete aggregate has a grain size in the range of 0-16 mm.

The method of any one of claims 1 to 6, wherein the first concrete composition is obtained by:

mixing sand, gravel, binder and water to obtain a first concrete mixture;

adding vegetable aggregate material to the first concrete mix to obtain a second concrete mix;

mixing the second concrete mixture to obtain the first concrete composition.

The method according to any of claims 1 to 7, wherein the first concrete composition comprises 0.01 - 60 kg of vegetable aggregate per cubic meter.

The method of any one of claims 1 to 8, wherein the vegetable aggregate material is minced Miscanthus, more particularly Miscanthus 'Giganteus'.

The method of any one of claims 1 to 9, wherein the first concrete composition per cubic meter: 400 kg Portland cement CEM I 52.5 N, 655 kg wet concrete sand, 205 kg wet gravel 2-8 mm, 14 kg Miscanthus and approximately 10 l of water.

The method of any one of claims 1-10, wherein the concrete products are at least one from a group comprising: concrete pavement tiles, curb stones, concrete stones, concrete cycle paths, entry blocks, bends, corner pieces, wall bricks, street furniture and all other repetitive or semi-repetitively produced concrete elements.

A product comprising at least one concrete component made by a method according to any of claims 1-11.