Cementitious paste and concrete with bottom ash and natural fibers

Abstract

The present invention relates to a cementitious paste, comprising i) bottom ash in an amount of between 1 and 40 wt.% % of the combined weight of bottom ash and cement, wherein the bottom ash has a particle size as determined by sieve analysis according to standard ASTM C136-06 (2015) such that at least 90 % of the particles pass a sieve having a size of 1 mm; ii) cement in an amount of between 60 - 99 % of the combined weight of bottom ash and cement; wherein the combined weight of cement and bottom ash is between 90 and 99.9 wt. % based on the dry weight of the cementitious paste; iii) natural fibers in an amount of 0.1 to 10 wt.% based on the dry weight of the cementitious paste; and iv) water in a weight ratio to the dry weight of the cementitious paste of between 0.4 : 1 to 0.8 : 1. The present invention moreover relates to a concrete composition comprising the cementitious paste and aggregate material. In addition, the invention relates to the use of bottom ash, the use of the cementitious paste and concrete compositions as well as to building products.

Description

[0001] Cementitious paste and concrete with bottom ash and natural fibers

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a cementitious paste and to a concrete composition comprising said cementitious paste. Moreover, the invention relates to the use of said cementitious paste, and to the use of bottom ash and natural fibers in concrete compositions. In addition, the invention relates to building products.

[0004] Background

[0005] The present invention is related to cementitious pastes, concretes and building materials. Currently, all of these require large amounts of cement. The increasing demand worldwide for buildings, leads to an increasing demand for cement, which in turn leads to increased harvesting of raw materials for cement manufacturing. This causes a reduction in the quantity of non-renewable resources such as limestone. In addition, the harvesting of resources from natural surroundings damages the green landscape which is the habitat of flora and fauna exposing it to the risk of ecological imbalance. The present invention is related to a cementitious paste wherein bottom ash is used.

[0006] Bottom ash (BA) is part of the non-combustible residue of combustion in for example power plants or incinerators. The portion of the ash that escapes up the chimney or stack is, referred to as fly ash and the portion of ash that falls to the bottom (e.g. into the bottom hopper of a coal-burning furnace) is referred to as bottom ash. Bottom ash (BA) is the main residue from municipal solid waste incineration (MSWI), which accounts for around 80% of the total mass of solid residues. Europe’s total annual production of MSWI-bottom ash is about 20 million tons and an enormous amount thereof ends up in landfills, resulting in high fees, occupied lands, and environmental pollution. There is hence a strong motivation to find uses for said bottom ash instead of it being landfilled.

[0007] Currently, bottom ash is used for example as lightweight aggregates in road pavement but there are issues with contaminant leaching, as will be discussed below. The publication by Akinyemi et al. "Development of banana fibers and wood bottom ash modified cement mortars." In Construction and Building Materials 241 (2020):118041 discloses on the use of wood bottom ash to replace part of the lightweight aggregates.

[0008] Bottom ash has similar chemical components as other prior art supplementary cementitious materials, such as fly ash from a coal-burning furnace (see Table 1).

[0009] Table 1. Chemical components of the coal-burning furnace fly ash and MSWI-bottom ash.

[0010] In addition, bottom ash can provide pozzolanic reactions. However, when bottom ash is used as a cement replacement, there are two main technical obstacles to overcome. Firstly, a low compressive strength is observed for cementitious pastes and concretes comprising bottom ash, most likely due to a high amount of pores (high porous formation). Secondly, bottom ash comprises significant amounts of contamination, such as heavy metal ions, chloride, and sulfate anions, that leach from the bottom ash when present in cementitious pastes and concretes. Both of these (low strength and leaching) are highly undesirable.

[0011] There is therefore a need for a way to be able to use bottom ash as a cement replacement without the above disadvantages. There is a need for upgrading bottom ash to a cementitious material to provide bottom ash-based building products, thereby achieving the practical application of bottom ash in such bottom ash-based building products and at the same time reducing the consumption of cementitious raw material thereby reducing the depletion of natural resources as well as reducing the damage to the landscape afflicted during harvesting of these natural resources. The present invention addresses all of the above problems of depletion of natural cement resources, the damage to the landscape, the use of bottom ash in cementitious pastes without the negative issues of low strength and leaching.

[0012] STATEMENT OF THE INVENTION

[0013] In one aspect, the invention relates to a cementitious paste, comprising:

[0014] * bottom ash in an amount of between 1 and 40 wt.% % of the combined weight of bottom ash and cement, wherein the bottom ash has a particle size as determined by sieve analysis according to standard ASTM C136-06 (2015) such that at least 90 % of the particles pass a sieve having a size of 1 mm;

[0015] * cement in an amount of between 60 - 99 % of the combined weight of bottom ash and cement; wherein the combined weight of cement and bottom ash is between 90 and 99.9 wt. % based on the dry weight of the cementitious paste;

[0016] * natural fibers in an amount of 0.1 to 10 wt.% based on the dry weight of the cementitious paste; and

[0017] * water in a weight ratio to the dry weight of the cementitious paste of between 0.4 : 1 to 0.8 : 1.

[0018] In another aspect, the invention relates to a concrete composition comprising the cementitious paste according to the invention and aggregate material.

[0019] In another aspect, the invention relates to the use of bottom ash having a particle size as determined by sieve analysis according to standard ASTM C136-06 (2015) such that at least 90 % of the particles pass a sieve having a size of 1 mm as a substitute for cement together with natural fibers in a concrete composition.

[0020] In another aspect, the invention relates to the use of the cementitious paste or the concrete composition according to the invention for outdoor building products or indoor building products.

[0021] In another aspect, the invention relates to a building product comprising of the cementitious paste or the concrete composition according to the invention. Below several preferred features are disclosed. These features are applicable to the cementitious paste, the concrete compositions, the uses as well as the building products unless specified otherwise.

[0022] DETAILED DESCRIPTION

[0023] The present invention is elucidated below with a detailed description. When used in these specifications and claims, the terms “comprises” and “comprising” and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

[0024] Brief description of drawings

[0025] The present invention is described hereinafter with reference to the accompanying drawings in which embodiments of the present invention are shown.

[0026] Figures 1a and 1 b are schematic drawings of a concrete composition according to the prior art (fig. 1 a) and according to the invention (fig. 1 b) with the effect of the invention on the pore size;

[0027] Figure 2 is a schematic drawing of a concrete composition according to the invention with the effect of the invention on capillary absorption;

[0028] Figure 3a and 3b are flow chart for the preparation of the cementitious paste and concrete composition according to the invention, respectively;

[0029] Figure 4 is a graph showing curves for the particle size of milled bottom ash (grey curves) invention as well as Portland cement (black curves) in volume percentage (solid curves) as well as cumulative volume percentage (dashed curves);

[0030] Figure 5 shows a picture and enlargement thereof of a sisal fiber used in the present invention;

[0031] Figure 6 shows a bar diagram of the compressive strength for examples according to the invention (E1 and E2) as well as comparative examples (CE1 and CE2);

[0032] Figure 7 shows photographs showing the pore distribution for examples according to the invention (E1 and E2) as well as comparative examples (CE1 and CE2) (left photographs) as well as the extracted pore distribution using imaging software (right pictures); Figure 8 shows graphs depicting the distribution of fine pores (the diameter below 2 mm) for examples according to the invention (E1 and E2) as well as comparative examples (CE1 and CE2) obtained from micro-computed tomography (micro-CT).

[0033] Detailed description of the invention and its embodiments

[0034] The invention provides a solution to the current issues with cement, since it finds an effective solution to the encountered issues associated with the use of bottom ash as a cementitious material, namely low compressive strength and leaching. The present inventors have found that by the combination of using bottom ash with a specific particle size and the use of natural fibers, one or more of the objects are achieved.

[0035] The present inventors have observed that with bottom ash used as is (without previously reducing the particle size thereof), it does not provide the required pozzolanic properties that are required to use bottom ash successfully as a cement replacement. In particular, a low compressive strength was observed. The present inventors have carried out some analyses and found out that the pozzolanic properties can be increased by reduction of the particle size of the bottom ash.

[0036] However, when the particle size of the bottom ash was reduced in order to achieve the claimed particle size, the problems of leaching that were already present when using bottom ashes as a fine aggregate where even increased. Without wishing to be bound by a particular theory, the present inventors believe that this is caused by the increased surface area that is obtained by reducing the size of the bottom ash particles, leading to increased leaching.

[0037] The present inventors have first tested cementitious paste in which part of the cement is replaced by bottom ash with a specific particle size. The inventors found that the use of bottom ash with a specific particle size as a replacement of part of the cement did provide sufficient pozzolanic properties. However, the inventors observed that this cementitious paste has a low compressive strength. Without wishing to be bound to a particular theory, the present inventors believe that this is due to metallic aluminium that is present in bottom ash. This metallic aluminium was found to generate hydrogen gas under the alkaline environment that is present in these cementitious pastes, leading to a porous structure of the hardened matrix as clearly visible in Figure 1a, which leads to reduced compressive strength property. In addition, the leaching of contaminants was observed.

[0038] Without wishing to be bound to a particular theory, the present inventors have observed that the use of natural fibers in the cementitious paste and concrete composition according to the present inventors has surprising effects. The natural fibers were found to have a high stiffness and fine diameter, and the use thereof in combination with the cementitious paste with bottom ash was shown to improve the compressive strength compared to a paste without natural fibers. Without wishing to be bound to a particular theory, the present inventors believe that the large number of pores and larger pores that were observed in cementitious pastes in which part of the cement was replaced by bottom ash, are filled by these natural fibers, leading to the improved compressive strength, as illustrated in Figure 1b.

[0039] In addition, the natural fibers used were observed to significantly reduce the leaching of contaminants from the resulting pastes and concrete compositions. Natural fibers were observed to have a hollow lumen structure. Without wishing to be bound to a particular theory, the present inventors believe that in view of said hollow lumen, these natural fibers can absorb contaminating ions (for example heavy-metal ions, chloride ions, and sulfate ions) through capillary suction, consequently limiting the leaching of through capillary suction by immobilizing these ions within the fibers and hence within the paste / composition.

[0040] The present inventors have thus inventively found that the incorporation of bottom ash with a specific particle size as well as the incorporation of natural fibers provides a cost-effective and green solution to the above encountered barriers of bottom ash utilization.

[0041] In a first aspect, the present invention relates to a cementitious paste. A possible process for preparing such a cementitious paste is illustrated in the flow chart of Figure 3a. A bottom ash with the specifications according to claim 1 , in this particular process a milled bottom ash, is mixed with cement after which natural fibers and water are added in an amount complying with the ranges of claim 1. A cementitious paste is herewith obtained.

[0042] In a second aspect, the present invention relates to a concrete composition. A possible process for preparing such a concrete composition is illustrated in the flow chart of Figure 3b. A bottom ash with the specifications according to claim 1 , in this particular process a milled bottom ash, is mixed with cement, after which natural fibers, aggregates and water are added in an amount complying with the ranges of claim 1. A concrete composition is herewith obtained.

[0043] Bottom ash

[0044] The bottom ash is present in the cementitious paste in an amount of between 1 and 40 wt.% based on the combined weight of bottom ash and cement. In other words, between 1 and 40 wt.% of cement is replaced by bottom ash. The combined weight of cement and bottom ash is between 90 and 99.9 wt. % based on the dry weight of the cementitious paste. This means that between 0.1 and 10 wt.% of other dry materials may be present, including the natural fiber discussed in more detail below. With “dry materials” in the context of the present invention is meant all materials that are not liquid. This includes the inorganic solids (as discussed above) as well as the natural fiber according to the invention.

[0045] In an embodiment, bottom ash is present in the cementitious paste in an amount of at least 5 wt.%, preferably at least 10 wt.%, more preferably at least 15 wt.%, or even 20 wt.%, 25 wt.% or 30 wt.% based on the combined weight of bottom ash and cement. If less than 1 wt.% of cement is replaced by bottom ash, the positive effect on the reduced use of cement is not sufficiently present. It is preferred to replace as much cement as possible, but the strength needs to be kept as the desired predetermined value and the leaching has to be kept below desired predetermined values.

[0046] The bottom ash used in the present aspects has a specific particle size that may be obtained by crushing or milling bottom ash that is obtained to a proper grain / particle size. This will have the effect of exposing more pozzolanic reactions. According to the invention, at least 90 % of the bottom ash particles pass a sieve having a size of 1 mm, meaning that at least 90% of all particles of the milled bottom ash have a size of less than 1 mm. The sieving analysis is carried out according to standard ASTM C136-06 (2015). At least 90 % of all particles will pass through a 1 mm sieve (a No. 18 US mesh sieve). Preferably, at least 95 wt.%, at least 98 wt.%, at least 99 wt.%, at least 99.5 wt.%, at least 99.9 wt.% or 100 wt.% of all particles will pass through a 1 mm sieve (a No. 18 US mesh sieve). The ASTM C136-06 test method is the standard test method for sieve analysis of fine and coarse aggregates.

[0047] In an embodiment, the bottom ash has a particle size as determined by sieve analysis according to standard ASTM C136-06 (2015) such that at least 90 % of the particles pass a sieve having a size of 500 micrometer. At least 90 % of all particles will pass through a 500 micrometers sieve (a No. 35 US mesh sieve).

[0048] In an embodiment, at least 90 % of the bottom ash particles pass a sieve having a size of 105 micrometers, meaning that at least 90% of all particles of the milled bottom ash have a size of less than 105 micrometers. At least 90 % of all particles will pass through a 105 micrometers sieve (a No. 140 US mesh sieve).

[0049] In an embodiment, at least 90 % of the bottom ash particles pass a sieve having a size of 32 micrometer, meaning that at least 90% of all particles of the milled bottom ash have a size of less than 32 micrometer. At least 90 % of all particles will pass through a 32 micrometer sieve (a No. 450 US mesh sieve).

[0050] The bottom ash used in the present invention may have a particle size as determined by sieve analysis according to standards ASTM C136-06 (2015) in the range of 0.0001 mm - 1 mm (viz. 0.1 - 1000 micrometer), preferably of 0.0005 mm - 0.1 mm (viz. 0.5 - 100 micrometer).

[0051] In an embodiment, as bottom ash, municipal solid waste incineration (MSWI) - bottom ash is used. MSWI-bottom ash comprises as the main component silicon dioxide. Bottom ash generally comprises between 21 and 60 wt. % of silicon dioxide (SiC>2), between 10 and 37 wt.% of aluminium oxide (AI2O3) between 0 and 22 wt.% of calcium oxide (CaO), between 0 and 4 wt.% of magnesium oxide (MgO), and between 5 and 37 wt.% of ferric oxide (Fe2Os) . The composition of the MSWI bottom ash used for the present examples is disclosed below in Table 2.

[0052] Cement

[0053] The cement is present in the cementitious paste in an amount of between 60 - 99 % of the combined weight of bottom ash and cement. The combined weight of cement and bottom ash is between 90 and 99.9 wt. % based on the dry weight of the cementitious paste. This means that between 0.1 and 10 wt.% of other dry materials may be present, including the natural fiber discussed in more detail below.

[0054] In an embodiment, as cement Portland cement is used, preferably ordinary Portland cement or OPC or ordinary cement. This refers to a mixture of e.g. Portland cement clinker and gypsum. OPC is the most common type of cement in general use around the world. It is usually made from limestone and produced by heating limestone and clay minerals to provide a clinker that, after grinding thereof, is mixed with a few percentages of gypsum.

[0055] Cement (e.g. OPC) generally comprises between 61 and 67 wt.% of calcium oxide (CaO), between 19 and 23 wt. % of silicon dioxide (SiO2), between 2.5 and 6 wt.% of aluminium oxide (AI2O3), between 1.5 and 4.5 wt.% of sulphur oxide (SO3), and between 0 and 6 wt.% of ferric oxide (Fe2Os).

[0056] According to the invention, at least 90 % of the cement particles pass a sieve having a size of 1 mm, meaning that at least 90% of all particles of the milled bottom ash have a size of less than 1 mm. The sieving analysis is carried out according to standard ASTM C136-06 (2015). At least 90 % of all particles will pass through a 1 mm sieve (a No. 18 US mesh sieve). Preferably, at least 95 wt.%, at least 98 wt.%, at least 99 wt.%, at least 99.5 wt.%, at least 99.9 wt.% or 100 wt.% of all particles will pass through a 1 mm sieve (a No. 18 US mesh sieve). The ASTM C136-06 test method is the standard test method for sieve analysis of fine and coarse aggregates. In an embodiment, the bottom ash has a particle size as determined by sieve analysis according to standard ASTM C136-06 (2015) such that at least 90 % of the particles pass a sieve having a size of 500 micrometer. At least 90 % of all particles will pass through a 105 micrometers sieve (a No. 35 US mesh sieve).

[0057] In an embodiment, at least 90 % of cement particles pass a sieve having a size of 105 micrometers, meaning that at least 90% of all particles of the milled bottom ash have a size of less than 105 micrometers. At least 90 % of all particles will pass through a 105 micrometers sieve (a No. 140 US mesh sieve).

[0058] The cement (e.g. OPC) used in the present invention may a particle size as determined by sieve analysis according to standards ASTM C136-06 (2015) in the range of 0.0001 mm - 1 mm (viz. 0.1 - 1000 micrometer), preferably of 0.0005 mm - 0.1 mm (viz. 0.5 - 100 micrometer).

[0059] Natural fibers

[0060] The present cementitious paste comprises natural fibers in an amount of 0.1 to 10 wt.% based on the dry weight of the cementitious paste (this is the combined weight of all dry components, including bottom ash, cement and natural fibers). In a preferred embodiment, the natural fibers are added in an amount of between 0.5 and 5 wt.%, such as between 1 and 3 wt.%.

[0061] With natural fibers is meant a fiber that is obtained from a natural source, such as directly from plants or artificially made fibers that are from vegetable origin.

[0062] In an embodiment, the natural fibers are plant fibers, or artificial fibers derived from vegetable origin. In an embodiment, the plant fibers are selected from the group consisting of sugarcane bagasse fiber, banana fiber, sisal fiber, ramie fiber, bamboo fiber, linen fiber, jute fiber, hemp fiber, flax fiber, abaca fiber, cotton fiber, and wood fiber, for example sisal fiber. In an embodiment, the artificial fibers derived from vegetable origin are selected from the group consisting of regenerated cellulose fiber. In an embodiment, the natural fibers have a diameter of between 50 and 1000 micrometers, such as between 150 and 320 micrometers. The diameter of the natural fiber is for example at least 100 micrometers or at least 200 micrometers or most 900 micrometers, 800 micrometers, 700 micrometers, or 600 micrometers. In an embodiment, the natural fibers have a diameter of between 100 and 500 micrometers For sisal fiber the diameter is preferably between 100 and 500 micrometers, such as between 150 and 320 micrometers.

[0063] Water

[0064] The amount of water that is added is expressed based on the solids. With solids in the context of the amount of water inorganic solid powders in the form of cement and bottom ash are meant. Natural fibers or aggregates are in the context of the present invention not including in the solids for determining the water content. For regular cement-based compositions this is called the water-cement ratio (w / c ratio, or water- to-cement ratio, sometimes also called the Water-Cement Factor, f). This is the ratio of the mass of water (w) to the mass of cement (c) used in a cementitious mix. In the present invention, this is expressed as the water-to-solid ratio (w / s ratio), being the ratio of the mass of water (w) to the mass of inorganic solids(s) used in a cementitious mix. In an embodiment, the water-to-solid ratio (w / s ratio) is the ratio of the mass of water (w) to the combined weight of cement and bottom ash used in a cementitious mix. This w / s ratio is from 0.4: 1 to 0.8: 1 (also depicted as 0.4-0.8) to ensure the workability of the cementitious paste or concrete composition during preparation thereof.

[0065] As water any type of water may be used, based on the requirements to be determined by a skilled person. Usually city (tap) water is used as mixing water. Tests should be performed, however, to determine if desired properties can be achieved. Acceptance criteria for mixing water are for example given in ASTM C94 (2023) being the standard specification for ready-mixed concrete.

[0066] Cementitious pastes

[0067] A cementitious paste according to the invention may comprise or may consist of bottom ash, cement, natural fibers and water. In an embodiment, one or more additives may be present in addition to the bottom ash, cement, natural fibers and water, such as a (super) plasticizer additives to increase the workability. Preferably, the cementitious paste according to the present invention comprises between 0 and 5 wt.% of one or more additives. Preferably, the cementitious paste according to the present invention comprises at least 95 wt.%, preferably at least 98 wt.%, at least 99 wt.% or even 100 wt.% of bottom ash, cement, natural fibers and water.

[0068] It is preferred to replace as much cement as possible, but the strength needs to be kept as the desired predetermined value and the leaching has to be kept below desired predetermined values. When more bottom ash is present the type and amount of fibers can be tuned to achieve the desired characteristics of the invention.

[0069] The cementitious paste can be prepared by mixing the components in any desirable order that is known to a person skilled in the art. Common mixing devices may be used.

[0070] In an embodiment, the cementitious paste of the invention has a compressive strength measured according to EN 12390-3:(2019) after 3 days of curing at least 7 MPa. In an embodiment, the cementitious paste of the invention has a compressive strength measured according to EN 12390-3:(2019) after 28 days of curing at least 10 MPa. In an embodiment, the cementitious paste of the invention has a compressive strength measured according to EN 12390-3:(2019) after 3 days of curing at least 7 MPa and after 28 days of curing at least 10 MPa.

[0071] In an embodiment, the cementitious paste of the invention has a leaching of nickel (Ni) ions that is equal to or less than 0.1 mg / kg of dry matter measured according to EN 12457-4 (2002) after 28 days of curing.

[0072] In an embodiment, the cementitious paste of the invention has a leaching of zinc (Zn) ions that is equal to or less than 0.4 mg / kg of dry matter measured according to EN 12457-4 (2002) after 28 days of curing. In an embodiment, the cementitious paste of the invention has a leaching of nickel (Ni) ions that is equal to or less than 0.1 mg / kg of dry matter measured according to EN 12457-4 (2002) after 28 days of curing.

[0073] In an embodiment, the cementitious paste of the invention has a leaching of zinc (Zn) ions that is equal to or less than 0.4 mg / kg of dry matter measured according to EN 12457-4 (2002) after 28 days of curing.

[0074] In an embodiment, the cementitious paste of the invention has a leaching of molybdenum (Mo) ions that is equal to or less than 0.2 mg / kg of dry matter measured according to EN 12457-4 (2002) after 28 days of curing.

[0075] In an embodiment, the cementitious paste of the invention has a leaching of lead (Pb) ions that is equal to or less than 0.8 mg / kg of dry matter measured according to EN 12457-4 (2002) after 28 days of curing.

[0076] In an embodiment, the cementitious paste of the invention has a leaching of metal ions measured according to EN 12457-4 (2002) after 28 days of curing as follows:

[0077] * for nickel (Ni) equal to or less than 0.1 mg / kg of dry matter and / or

[0078] * for zinc (Zn) equal to or less than 0.4 mg / kg of dry matter and / or

[0079] * for molybdenum (Mo) equal to or less than 0.2 mg / kg of dry matter and / or

[0080] * for lead (Pb) equal to or less than 0.8 mg / kg of dry matter and / or

[0081] The cementitious paste may be used in a concrete composition according to the invention. In an embodiment, the cementitious paste is present in an amount of between 20 and 40 wt.% based on the weight of the concrete composition.

[0082] In a specific embodiment, the cementitious paste comprises

[0083] * MSWI-bottom ash in an amount of between 15 and 30 wt.% of the combined weight of bottom ash and cement;

[0084] * Portland cement in an amount of between 70 - 85 wt. % of the combined weight of bottom ash and cement; wherein the combined weight of cement and bottom ash is between 95 and 99 wt. % based on the dry weight of the cementitious paste;

[0085] * natural fibers, preferably sisal fibers, in an amount of 1 to 5 wt.% based on the dry weight of the cementitious paste; and

[0086] * water in a weight ratio to the dry weight of the cementitious paste of between 0.4 : 1 to 0.5 : 1.

[0087] The present inventors have observed that with this specific embodiment, excellent results are obtained in terms of compression string as well as leaching behavior.

[0088] Aggregates

[0089] Aggregates are typical components of concrete compositions. Aggregates are inert granular materials, for example, sand, gravel, crushed stone. In addition to water and cement, these are the basic ingredients of any concrete composition. Typically, aggregates account for 60 to 75 vol.% of the total volume of concrete. Generally, aggregates are divided into two distinct categories, namely fine aggregates and coarse aggregates. Fine aggregates generally consist of natural sand, crushed stone, burnt clays, cinders, fly ash. They normally have a size between 0.074 and 4.76 mm (e.g. they pass through a 4.76 mm sieve (No. 4 US mesh) and retained on a 0.074 mm sieve (No. 200 US mesh). Coarse aggregates, for example, gravel or crushed stone (e.g. rock, boulders, cobbles, pre-used concrete etc.), are the particles that retain on a 4.76 mm sieve.

[0090] In an embodiment, the aggregate material is in an amount of between 60 and 80 wt.% based on the weight of the concrete composition. In an embodiment, a mixture of fine and coarse aggregate is used, depending on the application and local requirements.

[0091] Concrete composition

[0092] In an aspect, the present invention relates to a concrete composition comprising the cementitious paste according to the invention and aggregate material. In an embodiment, the cementitious paste is present in an amount of between 20 and 40 wt.% based on the weight of the concrete composition and wherein the aggregate material is in an amount of between 60 and 80 wt.% based on the weight of the concrete composition.

[0093] The concrete composition can be prepared by mixing the components in any desirable order that is known to a person skilled in the art. Commonly used mixing devices may be used.

[0094] Use of bottom ash

[0095] In an aspect, the invention relates to the use of bottom ash having a particle size as determined by sieve analysis according to standard ASTM C136-06 (2015) such that at least 90 % of the particles pass a sieve having a size of 1 mm as a substitute for cement together with natural fibers in a concrete composition.

[0096] In an embodiment, the bottom ash has a particle size as determined by sieve analysis according to standard ASTM C136-06 (2015) such that at least 90 % of the particles pass a sieve having a size of 500 micrometer. At least 90 % of all particles will pass through a 500-micrometer sieve (a No. 35 US mesh sieve).

[0097] In an embodiment, at least 90 % of the bottom ash particles pass a sieve having a size of 105 micrometers, meaning that at least 90% of all particles of the milled bottom ash have a size of less than 105 micrometers. At least 90 % of all particles will pass through a 105-micrometer sieve (a No. 140 US mesh sieve).

[0098] Use of cementitious paste

[0099] In an aspect, the invention relates to the use of the inventive cementitious paste for outdoor building products, preferably road pavement blocks, or indoor building products, preferably hollow blocks for an insulation wall layer. In this embodiment, the cementitious paste is used as the final product. Adding aggregate to arrive at the inventive concrete compositions is optional. Aggregate conventionally have a lower price that the cementitious paste and hence in view of cost reduction reasons, it can be advantageous to use the inventive concrete composition instead of the invention cementitious paste. In an aspect, the invention relates to the use of the inventive concrete composition for outdoor building products, preferably road pavement blocks, road pavement layer, and floor pavement for parking or indoor building products, preferably hollow blocks for an insulation wall layer and cement-based composite plates.

[0100] Building product

[0101] In an aspect, the invention relates to a building product comprising the concrete composition or the cementitious paste according to the invention. In an embodiment, the building product is an outdoor building product, preferably a road pavement block, road pavement layer, and floor pavement for parking or an indoor building product, preferably a hollow block for an insulation wall layer and cement-based composite plates.

[0102] Effects of the invention

[0103] The present invention was found to achieve one or more of the objects disclosed above. The present invention has several effects and advantages. The invention allows the practical use of bottom ash thereby saving municipal waste incineration plants significant costs compared to landfilling. In addition, it provides environmental benefits since there is landfill, and in addition, since the leaching of contaminants that would take place in a landfill is reduced / eliminated. Moreover, there is a significant reduction in the use of natural cement resources leading to slower depletion of natural resources and less harm to landscaping during the harvesting thereof. In addition, concrete producers have significant increases in profits by using solid waste instead of costly natural resources. When waste fibers are used, the costs are further reduced. This invention does not require any special investments or equipment, the inventive paste and composition can be produced using conventional concrete manufacturing plants.

[0104] The present invention thus allows the use of bottom ash as a replacement for cementitious materials, thereby producing high-strength cementitious pastes and concrete compositions leading to building materials with reduced pollution. Although certain aspects of the invention have been described, the scope of the appended claims is not intended to be limited solely to these specific aspects. The claims are to be construed literally, purposively, and / or to encompass equivalents. The scope of the present invention is defined by the appended claims. One or more of the objects of the invention are achieved by the appended claims.

[0105] EXAMPLES

[0106] The present invention is further elucidated based on the Examples below which are illustrative only and not considered limiting to the present invention.

[0107] Materials and methods

[0108] MSWI- bottom ash is obtained from Heros, the Netherlands.

[0109] Portland cement (also called ordinary Portland cement (OPC)) is obtained from ENCI, the Netherlands and is classified as PC 52.5. “PC” being the symbol for Portland cement while the number 52.5 indicates the minimum desired strength value achieved within 28 days.

[0110] Sisal fibers are obtained from Wageningen University with an average fiber diameter of sisal fibers is between 150 and 320 micrometers.

[0111] Preparation of bottom ash with correct particle size

[0112] MSWI-bottom ash is milled using a vibratory disc mill (e.g. RS300 by Retsch). The milled bottom ash is subjected to a sieving analysis according to standard ASTM C136-06 (2015) such that at least 90 % of the particles pass a sieve having a size of 105 micrometer. During the sieving analysis the material to be analyzed is vibrated through a series of sequentially decreasing sieves (sieves with different mesh sizes), the coarser particles being retained by each sieve and the finer particles passing through.

[0113] Particle size and chemical composition of milled bottom ash and Portland cement

[0114] The full particle size distribution of OPC and milled bottom ash was measured by laser diffraction technique (using a Mastersizer 2000, Malvern) and the data is presented in Figure 4. From this drawing, it is clear that at least 90% of all particles of the milled bottom ash have a size of less than 105 micrometers (in other words at least 90 % of the particles pass a sieve having a size of 105 micrometers). The elemental chemical composition of the milled bottom ash and OPC are disclosed below in Table 2 and was determined by the X-ray fluorescence (XRF) using the fused beads method. The Loss on Ignition (LOI) is 8.2 for milled bottom ash and 1.4 for OPC and was evaluated by oven drying at 105 °C to a constant mass before calcining at 1000 °C for 1 h, cooling, and re-weighing.

[0115] Table 2. Exact chemical composition of milled bottom ash and OPC

[0116] Natural fibers

[0117] Sisal fiber is used for the examples according to the invention. These fibers have a chemical composition comprising cellulose (67.0 - 78.0 wt.%), hemicellulose (10.0 - 14.2 wt.%), and lignin (8.0 - 11.0 wt.%). The average fiber diameter of sisal fibers is between 150 and 320 micrometers. According to the invention either 15 wt.% or 30 wt.% of OPC is replaced by sisal fibers.

[0118] The appearance of the fracture surfaces of sisal fibers was investigated using scanning electron microscopy (SEM). The cross-section analyses are performed on specimens covered with Au by using a Thermo Fisher Phenom Pro-X microscope under an accelerating voltage of 15 kV. Figure 5 shows a picture and enlargement thereof of a sisal fiber used in the present invention and clearly shows a hollow structure in the interior of the fiber.

[0119] Examples

[0120] Several different cementitious pastes were prepared having the composition as shown in Table 3 below. A first comparative (CEO) was prepared without natural fibers or bottom ash present. A second comparative (CE1) was prepared without natural fibers but in which 15 wt.% of the OPC has been replaced by bottom ash. E1 is an example according to the invention comprising 2 wt.% of fibers and in which 15 wt.% of the OPC has been replaced by bottom ash. E1 can be compared to CE1 to see the effect of the addition of fibers. A third comparative (CE2) was prepared without natural fibers but in which 30 wt.% of the OPC has been replaced by bottom ash. E2 is an example according to the invention comprising 2 wt.% of fibers and in which 30 wt.% of the OPC has been replaced by bottom ash. E2 can be compared to CE2 to see the effect of the addition of fibers.

[0121] Table 3. Cementitious paste - composition milled bottom ash and OPC

[0122] &amount in wt.% based on the combined weight of the solid materials in the cementitious paste, being sisal fibers, milled bottom ash and OPC

[0123] Preparation of cementitious pastes

[0124] The pastes were all prepared with a water-to-powder (also called water-to-solid) ratio of 0.45. Firstly, the solid materials (OPC and / or milled BA and / or sisal fibers) were homogeneously mixed in a kitchen mixer for a period of 3 minutes. Subsequently, water was added to the mixture and the pastes was continued to be mixed for 3 minutes (2 minutes with a low speed and then 1 minute with a high speed). Finally, the pastes obtained were cast into a plastic mould for cubic samples (40 mm x 40 mm x 40 mm size) and covered with a damp polyethylene film to avoid water evaporation. Testing of cementitious pastes

[0125] The cementitious pastes (CE1 , E1 , CE2, and E2) were tested for compressive strength.

[0126] One day after casting, the samples were demoulded and cured in a climatic chamber (20 °C, RH>95%) for either 3 or 28 days. The sample CEO was cured in the mould for 3 days to ensure sufficient hardening for the sample demoulding. All samples were submitted to compressive strength testing according to the standard EN 12390-3 (2019) and EN 196-1 for the 28-day samples, all in triplicate. The significance of the difference between the experimental samples and reference samples was statistically analysed by one-way ANOVA, and P -value<0.05 was considered statistically significant.

[0127] Figure 6 shows two bar diagrams showing the compressive strength in MPa measured after 3 days of hardening or 28 days of hardening. The results in Figure 6 show that for a cementitious paste in which 15 wt.% of the OPC was replaced by milled bottom ash the addition of natural fibers increased the compressive strength from 7.30 MPa to 11.35 MPa after 3 days of hardening and from 10.49 MPa to 14.22 Mpa after 28 days of hardening.

[0128] The results in Figure 6 show that for a cementitious paste in which even 30 wt.% of the OPC was replaced by milled bottom ash the addition of natural fibers increased the compressive strength from 4.62 MPa to 7.01 MPa after 3 days of hardening and from 5.37 MPa to 9.96 MPa after 28 days of hardening. This clearly shows that adding natural fiber has a positive effect on the compressive strength of the cementitious paste after 3 days and 28 days.

[0129] The cementitious pastes (CE1 , E1 , CE2, and E2) were tested for pore size after 28 days of hardening. Figure 7 shows pictures (left) side which can be used to visually observe the effect of the addition of natural fibers. Both for the pastes is in which 15 wt.% and the pastes in which 30 wt.% of the OPC was replaced by milled bottom ash, a reduction in pores is observable. The same is observed from the extracted pore-size images on the right. For Micro-CT (Scanco Medical AG, Switzerland) measurement, after 28 days of hydration, the samples were cut into small cuboids (15 x 15 x 10 mm3), and dried for 24 hours.

[0130] The cementitious pastes (CEO, CE1 , E1 , CE2, and E2) were tested for leaching behaviour. The leaching test, according to EN 12457-4 (2002) was performed on the paste samples cured at 28 days. The leaching level of heavy metal ions, chloride, and sulfate anions was evaluated.

[0131] Table 1 Leaching test legislation limit

[0132] # units for concentrations given as mg per kg of dry matter

[0133] This clearly showed that by adding natural fibers to the cementitious paste the leaching can be reduced for all contaminants.

[0134] The greenhouse gasses (GHG) emissions (in kilogram of CO2 equivalent per ton of material were determined for the cementitious pastes (CE1 , E1 , CE2, and E2). The greenhouse gas (GHG) emissions of paste preparation were estimated by the method of the life cycle assessment (LCA). The LCA modeling was performed using SimaPro software. Table 4 below shows the results. From this, it is clear that by replacing 15 wt.% of the OPC with milled bottom ash (CEO vs CE1) a reduction of almost 20 % in emission can be obtained and by replacing 30 wt.% of the OPC by milled bottom ash (CEO vs CE2) a reduction of almost 25 % on emission can be obtained. This can be further reduced by the addition of the natural fibers to a total reduction of 30 and 32 wt.% respectively. Without wishing to be bound by a particular theory, the present inventors believe that when incorporating natural fibers, these natural fiber occupy a certain volume percentage of the volume of the final product. Hence the natural fiber incorporation reduces the cement usage to avoid the CO2 emission from cement manufacturing. In addition, when the plants grow which produce the natural fibers, the growth process can absorb a large amount of CO2 from air.

[0135] Table 4. GHG emissions n.a. = not applicable since not present

[0136] The present inventors have also tested oil palm fibers and have found similar results, regarding the characteristics of compressive strength (improvement) and leaching immobilizing (contaminant ion reduction).

Claims

CLAIMS1. Cementitious paste, comprising:* bottom ash in an amount of between 1 and 40 wt.% % of the combined weight of bottom ash and cement, wherein the bottom ash has a particle size as determined by sieve analysis according to standard ASTM C136-06 (2015) such that at least 90 % of the particles pass a sieve having a size of 1 mm;* cement in an amount of between 60 - 99 % of the combined weight of bottom ash and cement; wherein the combined weight of cement and bottom ash is between 90 and 99.9 wt. % based on the dry weight of the cementitious paste;* natural fibers in an amount of 0.1 to 10 wt.% based on the dry weight of the cementitious paste; and* water in a weight ratio to the dry weight of the cementitious paste of between 0.4 : 1 to 0.8 : 1.

2. Cementitious paste according to claim 1 , wherein the bottom ash has a particle size as determined by sieve analysis according to standard ASTM C136-06 (2015) such that at least 90 % of the particles pass a sieve having a size of 500 micrometer, preferably of 105 micrometer.

3. Cementitious paste according to claim 1 or 2, wherein the natural fibers are plant fibers, or artificial fibers derived from vegetable origin.

4. Cementitious paste according to claim 3, wherein the plant fibers are selected from the group consisting of sugarcane bagasse fiber, banana fiber, sisal fiber, ramie fiber, bamboo fiber, linen fiber, jute fiber, hemp fiber, flax fiber, abaca fiber, cotton fiber, and wood fiber.

5. Cementitious paste according to claim 3, wherein the artificial fibers derived from vegetable origin are selected from the group consisting of regenerated cellulose fiber.

6. Cementitious paste according to any one of the preceding claims, wherein the natural fibers have a diameter of between 50 and 1000 micrometer.

7. Cementitious paste according to any one of the preceding claims, wherein as cement Portland cement is used.

8. Cementitious paste according to any one of the preceding claims, wherein as bottom ash, municipal solid waste incineration (MSWI) - bottom ash is used.

9. Cementitious paste according to any one of the preceding claims, comprising:* MSWI -bottom ash in an amount of between 15 and 30 wt.% of the combined weight of bottom ash and cement;* Portland cement in an amount of between 70 - 85 wt. % of the combined weight of bottom ash and cement; wherein the combined weight of cement and bottom ash is between 95 and 99 wt. % based on the dry weight of the cementitious paste;* sugarcane bagasse fibers in an amount of 1 to 5 wt.% based on the dry weight of the cementitious paste; and* water in a weight ratio to the dry weight of the cementitious paste of between 0.4 : 1 to 0.5 : 1.

10. Cementitious paste according to any one of the preceding claims, wherein the compressive strength measured according to EN 12390-3:(2019) is as follows:* after 3 days of curing at least 7 MPa and / or* after 28 days of curing at least 10 MPa.

11. Cementitious paste according to any one of the preceding claims, wherein the leaching of metal ions measured according to EN 12457-4 (2002) after 28 days of curing is as follows:* for nickel (Ni) equal to or less than 0.1 mg / kg of dry matter and / or* for zinc (Zn) equal to or less than 0.4 mg / kg of dry matter and / or* for molybdenum (Mo) equal to or less than 0.2 mg / kg of dry matter and / or* for lead (Pb) equal to or less than 0.8 mg / kg of dry matter and / or12. Concrete composition comprising the cementitious paste according claims 1- 11 and aggregate material.

13. Concrete composition according to claim 12, wherein the cementitious paste is present in an amount of between 20 and 40 wt.% based on the weight of the concrete composition and wherein the aggregate material is in an amount of between 60 and 80 wt.% based on the weight of the concrete composition.

14. Use of bottom ash having a particle size as determined by sieve analysis according to standard ASTM C136-06 (2015) such that at least 90 % of the particles pass a sieve having a size of 1 mm as a substitute for cement together with natural fibers in a concrete composition.

15. Use of the cementitious paste according claims 1-11 or the concrete composition according to claims 12 or 13 for outdoor building products, preferably road pavement blocks, road pavement layer, or floor pavement for parking or indoor building products, preferably hollow blocks for an insulation wall layer or cement-based composite plates.

16. Building product comprising the concrete composition according to claims 12 or 13 or the cementitious paste according claims 1-11.

17. Building product according to claim 17, wherein the building product is an outdoor building product, preferably a road pavement block, road pavement layer, or floor pavement for parking or an indoor building product, preferably a hollow block for an insulation wall layer or and cement-based composite plates.