Concrete composition

Abstract

A concrete composition based on binder, sand, gravel, water, and an elongated plant aggregate is described, where the binder comprises cement and the concrete composition, based on parts by weight per part cement, comprises 0.2 – 0.7 parts water, 1.8 - 3.0 parts sand, and 2.5 – 5.0 parts gravel and / or aggregate, and the elongated plant aggregate is selected from cut stem sections of grasses, hemp, Jerusalem artichoke, or flax or palm plumes and mixtures thereof, and where the elongated plant aggregate is formed by plant stem sections with a length of 10 – 80 mm which naturally comprise a hard, substantially dimensionally stable bark and a compressible pith, of which the natural volume of the pith is greater than the natural volume of the bark, from which pith has been removed, where the volume of the pith after removal is less than the volume of bark.

Description

Plant material is treated with a mineralizer before being added to a concrete composition. For example, EP 1307411 describes adding finely ground stone flour as a mineralizer to a concrete composition with plant aggregates. EP 2069255 describes a method for preparing a concrete composition in which the composition contains lye such as calcium hydroxide. EP 2069255 discloses cut stem sections of grasses, hemp, Jerusalem artichoke, flax, or palm fronds and mixtures thereof as plant aggregates. In addition to bonding problems, swelling of the plant material also occurs due to the water present in the concrete composition, resulting in a weakened product. NL2021223 describes a method in which plant filler material without mineralizer is added to a concrete composition, after which the concrete is allowed to harden and then processed into granulate. This granulate is then used as a component in a subsequent concrete composition.This would reduce both the bonding and swelling problems. However, this method is less attractive because preparing a concrete composition effectively requires preparing it twice. It has been shown that the bonding and swelling problems can be significantly reduced or even solved by removing a substantial portion of the pith from the aforementioned stem parts before incorporating them into the concrete composition as aggregate. This eliminates the undesirable dynamic character of the stem material and produces an aggregate with the desired static character.The invention therefore relates to a concrete composition of the aforementioned type, and is characterized in that the elongated plant aggregate is formed by plant stems with a length of 10–80 mm, which naturally comprise a hard, essentially rigid bark and a compressible pith, the natural volume of which is greater than the natural volume of the bark from which the pith has been removed, and the volume of the pith after removal is less than the volume of the bark. By removing the bark, a firm and more adhering plant filler material with the desired static properties is obtained. The volume of the pith of the plant stem parts after removal of the pith is less than two times, preferably three times less, and more preferably four times less than the volume of the bark. The bulk density increases preferably by at least 20%, more preferably by 20–40%, after removal of the pith.The bulk density of the plant stem parts is preferably 20–40% higher after removal of the pith than the bulk density before removal of the pith.35 The natural volume of the pith and bark can be easily determined from the bulk density by weighing and measuring the volume of the starting material of stem parts with a stable bark and compressible pith, on the one hand, and the stem parts from which the pith has been removed, on the other. For this purpose, the material is spread from a height of 2–5 cm into a 1-litre measuring cup with a diameter of 12 cm, without compaction, after which the volume of 1 litre is weighed. In an advantageous embodiment, the plant stem parts are selected from cut stem parts of grasses, hemp, Jerusalem artichoke, flax or palm plumes and mixtures thereof, in particular of grasses, such as cereals, reeds, more particularly of the Miscanthus family, especially Miscanthus gigantheus, also known as elephant grass.Elephant grass stem material has proven to be an excellent aggregate for concrete building elements, especially when most of the pith has been removed. Furthermore, elephant grass assimilates a large amount of carbon dioxide, allowing it to be stored in the concrete. The plant-based stems typically have a length of 10–80 mm, preferably 10–40 mm. In wet (wetcast) concrete, a fiber length of 10–40 mm is preferred. For damp concrete, a length of 10–25 mm is preferred. Plant stem sections, particularly those of elephant grass, preferably have an average diameter of 5–7 mm before pith removal, and an average diameter of 2–3 mm after removal. This diameter was determined by measuring 200 individual stem sections separately. It was found that the variation in length and the average did not change significantly when measuring more than 200 stem sections.The plant stem parts preferably have an average length of 20–30 mm before removal of the pith, and an average length of 10–20 mm after removal, with the length after removal being 50–75% of the length before removal. The length was also determined by measuring 200 individual stem parts separately. It was also found that the variation in diameter and the average when measuring more than 200 stem parts did not change significantly when determining the length. The content of fine material with a size of 125 μm or lower is preferably less than 3%. The diameter of the vegetable stem parts is preferably 5 mm or less. The moisture content is preferably 15% or less, preferably between 6 and 14%, more preferably between 8 and 12%, and most preferably not more than 11%. The specific gravity of the 30 vegetable stem parts is preferably between 80 and 160 kg / m3.In order to remove the pith from the stem parts, the vegetable stem parts are, in a special embodiment of the invention, subjected to a pith removal treatment, which pith removal treatment comprises the steps of: a. providing stem parts with a length of 10–80 mm; b. providing a steam mill, comprising a cutting chamber in which knives are accommodated rotating in a vertical plane and a feed tube extending laterally from an inlet opening to an outlet opening, which outlet opening is connected to the cutting chamber, and an elongated loading element extending from outside the feed tube through the inlet opening at a distance from at least the bottom of the feed tube to the feed tube, c. applying an air flow in the feed tube of the steam mill, which the inlet opening is directed towards the cutting chamber, whereby a first air flow is formed at the inlet opening through the channel-shaped loading elements and a second air flow is formed below the channel-shaped loading elements; d.inserting the stem sections into the feed tube via the loading element, whereby the first air stream moves the stem sections into the cutting chamber and the second air stream prevents the stem sections from contacting at least the underside of the feed tube; e. exposing the stem sections to rotating knives in the cutting chamber, whereby the stem sections are cleaved and the pith is released from the bark; f. removing the cleaved, de-pitted stem sections from the cutting chamber and separating the released pith; and g. taking the resulting cleaved, de-pitted stem sections as the elongated vegetable aggregate for the concrete composition. In the first step, stem sections of the desired length can be obtained by harvesting suitable crops, that is, crops whose stems have a substantially dimensionally stable bark surrounding a compressible pith, and cutting the stems to the desired length.This can be done mechanically, for example, with a maize harvester, where stem sections of the desired length can be automatically provided. The length of the stem sections can often be adjusted in the harvester. The stem length is preferably 10–80 mm, more preferably 10–40 mm. This stem length can be obtained by setting the stem length to 20 mm in the harvester. After harvest, the stem sections contain quite a bit of pith, which in volume makes up significantly more than half of the total stem material, the remainder being made up of the bark. In Miscanthus, the bark content is approximately 70% vol. It has been found that the majority of the pith can be removed from the stem material using a specially adapted steam mill, also known as a chopper. Straw mills are known in the industry, for example from the company Himelor Agerskov.Such steam mills have a cutting chamber in which rotating blades are housed in a vertical plane and a feed pipe that extends laterally from an inlet opening to an outlet opening, which is connected to the cutting chamber. By applying an air stream moving substantially transversely to the direction of rotation of the rotating blades, the chopped material is conveyed from the inlet opening through the feed pipe into the cutting chamber. The air stream is usually generated by a fan positioned on the side of the cutting chamber opposite the side to which the feed pipe is connected. The fan draws the chopped material into the cutting chamber and then blows it out through an outlet. In order to separate the pith from the bark of the stem parts, it has now been discovered that the 5 stem parts must be brought into the cutting room in a free flow.This means that the stem parts are free from contact with the feed tube before entering the cutting chamber, as a result of which the stem parts move through the air flow essentially parallel to the direction of the air flow. It has been found that when the stem parts are in this orientation, i.e., oriented essentially perpendicular to the rotating blades, they are struck by the blades in such a way that a significant portion of the pith is knocked loose from the bark. To achieve such a free air flow, contact of the stem parts in the feed tube, at least near the feed opening in the cutting chamber, must be prevented so that the stem parts can orient themselves parallel to the air flow direction. To achieve the desired orientation of the stem parts, the flow mill comprises an elongated loading element that extends from outside the feed tube through the inlet opening on distance from at least the bottom of the supply pipe to the supply pipe.The loading element can be designed as a plate, with the plate extending into the feed tube at a distance from at least the bottom of the feed tube. This loading element divides the inlet opening into at least a first air inlet opening bounded by the top of the loading element and the top of the feed tube, and a second air inlet opening bounded by the bottom of the loading element and the bottom of the feed tube. At the inlet opening, the air flow is divided into a first air flow located above the loading element and a second air flow located below the loading element. The part of the loading element located outside the feed tube serves to load the stem parts to be treated and then move them into the cutting chamber via the feed tube. The loading element does not extend beyond the entire length of the supply pipe, that is to say up to the outlet opening, but over only a part of it.Preferably the loading element extends up to a maximum of one half of the supply tube therein, more preferably up to a quarter or less. By inserting the stem sections into the feed tube via the loading element, the stem sections are moved into the cutting chamber by the first air stream, while the second air stream, which flows from the feed tube's inlet opening beneath the loading element, enters the feed tube. Because the stem sections are moved towards the cutting chamber by the first air stream in the feed tube, the underlying second air stream prevents the stem sections from contacting the underside of the feed tube. It is also possible for the second air stream to be applied to one or both sides of the feed tube, or 5 BE2025 / 5341 around the first air stream. For this purpose, the loading element can be designed, for example, as a trough, with a width less than the width of the feed tube, so that the second air inlet opening is also formed on one or both sides next to the loading element.The loading element at the inlet opening of the feed tube can also be tubular and smaller than the feed tube at the inlet opening. This allows a second airflow opening to be created around the first airflow opening, allowing the stem sections, which are moved through the feed tube by the first airflow, to be surrounded by the second airflow, which promotes the alignment of the stem sections parallel to the direction of the airflow. By applying the airflow and feeding the stem sections into the feed tube via the loading element, the stem sections are moved into the intended orientation parallel to the direction of the airflow through the feed tube and enter the cutting chamber in this orientation when the blades strike the stem, cleaving the stem lengthwise and releasing a significant portion of the stem pith.15 The airflow moves the discharged pith and the de-marrowed bark out of the cutting chamber, allowing the pith to be separated from the bark. Because the pith is largely pulverized by the cutting chamber, while the bark material is essentially only cut into smaller pieces by the splitting process, it can be easily separated based on, for example, a difference in size or specific gravity, by sieving or using a downdraft purification method known in the art. The powder can be collected for use as a filler in various applications, including, for example, sawdust. In an attractive embodiment, the de-marrowed stem fragments are sieved on a shaking sieve with sieve openings of 2–4 mm, thus removing the powdery pith and the very small stem fragments.In a typical application of a steam mill, the feed tube is often angled upward from the work floor on which the steam mill is located. The material to be cut is sucked from the work floor into the cutting chamber through the feed tube against gravity. A significant portion of the material to be cut comes into contact with the underside of the feed tube. To implement the method according to the invention, in which the stem pieces must be brought into the cutting chamber in a free flow, it is advantageous if the feed tube of the steam mill is angled downward from the inlet opening to the outlet opening, and the stem pieces enter the cutting chamber, partly under the influence of gravity. In this arrangement, the stem material is moved downward into the cutting chamber by both the air flow and the influence of gravity.It has been found that in this arrangement, the stem sections hardly or never come into contact with the underside of the feed tube due to the presence of the underlying second air stream, while the flow rate of the stem sections is considerably higher than when the feed tube extends from the ground to the cutting chamber. In another advantageous embodiment, the feed tube is rectangular at the location of the inlet opening, and the loading element is designed as a rectangular chute, with the width of the chute corresponding to the width of the inlet opening. Thus, a second air flow opening is formed under the loading element across the entire width of the feed tube, so that the second air flow is located under the first air flow across the entire width of the feed tube. Preferably, the loading element can be tilted relative to the feed tube near the inlet opening.Tilting the loading element changes its angle relative to the feed tube, allowing the stem material loaded onto the loading element to be fed into the feed tube at the desired speed. If the loading element includes a flat base plate that extends beyond the feed opening in the feed tube, tilting also allows the height of the secondary air stream to be adjusted. Tilting downwards will bring the flat base plate closer to the bottom of the feed tube, resulting in a narrower passage for the secondary air stream. When the loading element is tilted upwards, the passage will actually increase. This embodiment is particularly advantageous when the loading element has a flat base plate, which preferably has a width corresponding to the width of the supply pipe, which in that case is preferably rectangular. In this embodiment, too, the loading element is preferably designed as a tiltable chute.In a subsequent advantageous embodiment, the plane in which the blades rotate in the steam mill has a diameter of 0.8–1.2 m, and the rotational speed in step e. is preferably 1200–1800 revolutions per minute (rpm).25 The plant stem parts as provided in step e. preferably have a bulk density of 100–140 kg / m3. The bulk density is determined by pouring the dried material from a height of 2-5 cm into a 1-liter measuring cup with a 12 cm diameter, without compacting, and weighing the 1-liter volume. 30 The vegetable stem pieces are preferably moved into the cutting chamber at a flow rate of 10-20 m³ / h. This flow rate can be easily adjusted by the professional based on the angle of the feed pipe relative to the working floor, the strength of the air flow, the position of the loading element, the loading speed of the stem material, and the choice of stem material. 35 Vegetable stem pieces, after conventional harvesting and cutting to the desired length of 10-80 mm, usually contain 60-80 vol.% marl and correspondingly 20-40 vol.% bark.The method described herein makes it possible to remove up to 90% of the pith from the stem material. This means that with an original pith:bark volume ratio of 70:30, the ratio can be reduced to 7:30 after treatment according to the method described herein, resulting in a pith volume of more than four times less than the bark volume. The invention therefore also relates to stem parts with a length of 10–80 mm that naturally comprise a hard, essentially dimensionally stable bark and a compressible pith, 5 of which the natural pith volume is greater than the natural bark volume from which the pith has been removed, whereby the pith volume after removal is less than the bark volume, preferably two times less, more preferably three times less, and even more preferably four times less than the bark volume. The pith removal takes place preferably by applying the method described herein.10 The concrete composition preferably comprises 10–50 kg of the plant stem parts per 1 m3, more preferably 15–40 kg / m3, even more preferably 20–30 kg / m3.Although various suitable binders are known for concrete compositions, such as (geo)polymers, lignin, alkali-activated aluminum silicates, and sodium metasilicate, cement is preferred as a binder, especially blast furnace cement (CEMIII) and Portland 15 cement (CEMI). With a view to raw material circularity, blast furnace cement is most preferred, with blast furnace slag also being reused as a raw material. Blast furnace cement (CEMIII / B; NEN 3550:HS) is particularly preferred in this regard. Although various concrete compositions are known to those skilled in the art, the concrete composition, based on weight per part cement, preferably comprises 0.2–0.7 parts water, 1.8–3.0 parts sand, and 2.5–5.0 parts gravel and / or granulate. The gravel / granulate can various components of varying particle sizes, such as chippings and recycled concrete aggregate. In particular, the concrete composition is an earth-moist composition, as defined by NEN standard EN 12350-4. The concrete composition is preferably free of mineralizers.Mineralizers are known in the art and act as binders between the plant material and the cement composition. For example, as described in EP 1307411, various mineralizers are described as a ground mineral material that forms hydrates in reaction with the water added to the composition. For example, EP 2069255 describes slaked lime and aluminum sulfate as a mineralizer. In a subsequent embodiment, the invention relates to a concrete product comprising the concrete composition according to any of the preceding claims in a hardened form, that is, a concrete product manufactured with the concrete composition as described above. In particular, it concerns products manufactured from earth-moist concrete. Attractive examples are concrete edging (NEN-EN 1340), pavement tiles (NEN-EN 35 1339), concrete paving stones (NEN-EN1338) and grass concrete tiles (BRLK1101), road surface slabs and prefabricated building elements such as wall elements.8 BE2025 / 5341 In another embodiment, the invention relates to the use of plant stem parts that naturally comprise a hard, essentially rigid bark and a compressible pith, the natural volume of the pith of which is greater than the natural volume of the bark from which the pith has been removed, the volume of the pith after removal being less than the volume of the bark as a filler or reinforcing agent in a concrete composition. These plant stem parts are preferably subjected to a pith removal treatment as described above before being incorporated into the concrete composition, and are advantageously selected from cut stem parts of grasses, hemp, Jerusalem artichoke, or flax, or palm plumes, and mixtures thereof, as a filler or reinforcing agent in a concrete composition, as described above. The length, average length, diameter, average diameter, and bulk density are preferably as described above. The invention will be further explained below with the aid of the following figures and examples.Figure 1 is a view of a device according to the invention, and Figure 2 is a cross-section of the device of Figure 1 through line L. Figure 3 is a photograph of harvested, dried elephant grass stem material with an average length of 25 mm, with the length of most of the stem sections ranging from 10 to 80 mm. The average diameter of the stem sections is 6 mm. Figure 4 is a photograph of the stem material of Figure 3, treated according to the pitting procedure described herein, with the average length reduced to 16 mm and the average diameter of the stem sections to 2.5 mm. Reference numerals: 1: power mill25 2: cutting chamber 3: blades 4: feed pipe with top4A, bottom4B side4C 5: inlet opening 6: outlet opening30 7: loading element 8: fan 9: exhaust 10: hinge 11: first air flow opening35 12: second air flow opening S1: first air flow S2: second air flow 9 BE2025 / 5341 Figures 1 and 2 show a power mill1 with a circular cutting chamber2 containing rotating blades3 during operation.An inlet tube 4 extends laterally from the cutting chamber 2, slightly upwards. The inlet tube 4 has a rectangular inlet opening 5 and tapers to a round outlet opening 6 that connects to the cutting chamber 2 with 5 axis A as its center. The inlet opening 5 is limited in height by the top 4A and bottom 4B of the feed tube 4 and in width by its sides 4C. The feed channel 4 can also be round starting from the inlet opening 5, tapering or not towards the outlet opening 6. An elongated loading element7 extends from outside the supply pipe4 through the inlet opening5 at a distance from at least the bottom4B of the supply pipe4 to the supply pipe4. At the location of the inlet opening5, the loading element7 divides the inlet opening5 into a first air inlet opening11 located above and a second air inlet opening12 located below. In the case shown, the loading element is gutter-shaped with a substantially flat base plate7A and side walls7B. The loading element extends with its base plate7A to the supply pipe4.In the case shown, the width of the loading element 7 corresponds to the width of the inlet opening 5, defined by the two side walls 4C of the feed tube 4. At point 12, the loading element can be tilted vertically relative to the feed tube 4. The feed element can also extend into the feed tube 5 as a closed 20 cylindrical tube at the location of the inlet opening 5, which design is particularly suitable when the inlet opening 5 of the feed tube 4 is round. The loading element then has a smaller diameter than the feed openings and extends preferably concentrically. In such an arrangement, a concentric second air inlet opening is formed around a first air inlet opening. A flexible tube with a suction nozzle, through which the stem parts can be fed into the steam mill, can then be connected to the loading element 25.Behind the cutting chamber, that is, on the side opposite the attachment of the supply tube, a fan is placed that can generate an air stream that runs through the cutting chamber via the inlet opening 5, the supply tube 4, and the air stream is blown out of the cutting chamber 2 through a tangentially arranged exhaust duct 30. Due to the presence of the loading element 7 in the inlet opening 5 of the supply duct 4, the air stream is divided into a first air stream S1 and a second air stream S2, which, in the case shown, flow through the first air inlet opening 11 and the second air inlet opening 12, respectively. Air inlet opening 11 is bounded by the top 4A and sides 4C of the supply tube 4 and by the base plate 7A of the loading element 7. The lower air inlet opening 12 is bounded by the bottom 4B and sides 4C of the supply tube 4 and by the base plate 7A of the loading element 7.10 BE2025 / 5341 After applying the air stream, the stem sections are placed on the section of the loading element 7 located outside the supply tube 4, after which the stem sections are sucked into the cutting chamber 2 by the first air stream S1. The underlying second air stream S2 prevents the stem sections from colliding with the underside 4A of the supply tube 4, causing them to lose speed and no longer be aligned parallel 5 to the air stream, which is necessary for splitting the stem sections lengthwise and releasing the pith from the bark. The height of the second air stream can be varied by tilting the loading element at the point of tilting 12 relative to the supply tube 4. When tilted upwards, the inlet angle for the The stem material becomes sharper and the flow rate increases, while the second air stream is narrowed10, because the end of the loading element7 located in the feed tube4 is moved towards the bottom4 of it, thus reducing the distance between them.The second air stream becomes narrower, but also flows faster. Because the stem sections in the first air stream are directed parallel to the air stream, they are split lengthwise in the cutting chamber by the rotating blades, and most of the pith is released from the bark. The split bark and pith are then blown out of the cutting chamber through the exhaust, where they can then be separated. Figure 3 shows elephant grass stem material before the lengthwise splitting process described above, where the stem sections are either still intact around the stem or have already split, but in that case the pith is still bark. Figure 4 shows the stem material after the lengthwise splitting process, where it is clearly visible that most of the pith has disappeared. Example 1 Removal of marrow from 25 Miscanthus grass, harvested with a harvesting machine (New Holland, USA) with a stem length setting of 20 mm, was dried to a bulk density of 120 kg / m3.The bulk density was determined by pouring the dried material from a height of 2-5 cm into a 1-liter measuring cup with a 12 cm diameter, without compacting, and weighing the 1-liter volume. The stem pieces had an average length of 25 mm and an average diameter of 6 mm and are shown in Figure 3. This material was fed into a straw mill (Himel, Germany), in which the feed pipe, oriented towards the working floor, was reversed so that it faced upwards. A funnel-shaped chute, 100 cm long, was placed in the rectangular feed opening, 10 cm of which extended into the feed pipe. The section of the chute outside the feed pipe tapered from a width of 80 cm to 40 cm. The section inside the feed pipe was 40 cm wide. The chute was inclined at an angle of 15° to the feed channel. 11 BE2025 / 5341 The steam mill was operated at 1800 rpm and the elephant grass flow rate was 15 m³ / hour. The material collected from the steam mill's outlet was sieved through a vibrating sieve with a mesh size of 3 mm.The obtained material had an average length of 16mm and an average diameter of 2.5mm, which was given.