Patent Application
20230047807
The disclosure relates to hemp-based geopolymers, including construction compositions containing alkali-activated hemp products.
Construction materials have experienced rapid development throughout the past decades. These developments mainly aim to improve mechanical properties, increase durability, and improve the sustainability of construction materials. Sustainable concrete production requires efforts to replace conventional cement partially or fully, which is responsible for about 5-7% of the global total carbon dioxide (CO2) emissions. Concrete is a construction material containing an aggregate and a binder. Aggregates are usually sand and gravel or crushed stone, while binders are usually cement and water. Mortar is composed of binder, fine sands, and lime and is used as a binding material when building with brick, block, and stone. Alkali-activated binders have been represented as an alternative to cement-based binders. These binders are commonly composed of aluminosilicate precursors, alkali solutions, and aggregates. Alkali-activated binders have shown acceptable mechanical and durability properties, and they can incorporate waste materials in their production. Nevertheless, alkali-activated binders have problems that limit their application, such as significant drying shrinkage, high efflorescence, low strength, and long or short setting time.
Provided here are compositions and methods to address these shortcomings of the art and provide other additional or alternative advantages. The disclosure herein provides one or more embodiments of hemp-based compositions and methods of making and using them. One such composition includes an aluminosilicate-based binder containing a first hemp derivative and an aggregate containing a second hemp derivative. The first and second derivatives are derived from a woody core of a hemp plant. The first hemp derivative can be substantially hemp hurd powder. The second hemp derivative can be substantially coarse hemp hurd. The aluminosilicate-based binder can be one or more of ordinary Portland cement (OPC), lime, zeolite, magnesium oxide cement, magnesium phosphate cement, and ground granulated blast furnace slag.
Embodiments of hemp-based compositions include hemp-based concrete compositions. One such comprising an aluminosilicate-based binder containing hemp hurd powder, a mineral aggregate, and an alkali activator. In certain embodiments, the hemp-based concrete compositions contain coarse hemp hurd. The mineral aggregate can contain river sand, fly ash, or a combination thereof. The alkali activator can contain one or more of a silicate, a metal aluminate, an alkali-metal hydroxide, ammonium hydroxide, and an alkaline earth metal hydroxide. The alkali activator contains sodium silicate and sodium hydroxide. The hemp-based concrete compositions can contain the hemp hurd powder in the admixture at an amount ranging from about 1 wt. % to about 20 wt. %. The hemp-based concrete compositions can contain the hemp hurd powder in the admixture at an amount ranging greater than about 1 wt. %. The hemp-based concrete compositions can contain the hemp hurd powder in the admixture at an amount ranging greater than about 5 wt. %.
Embodiments include methods of production of hemp-based concrete compositions with a binder containing a first hemp derivative and an aggregate containing a second hemp derivative. The first and second derivatives are derived from a woody core of a hemp plant. The first hemp derivative can be substantially hemp hurd powder. The second hemp derivative can be substantially coarse hemp hurd. One such method includes the following steps: combining a first hemp derivative and a binder component to form an admixture, combining an aqueous solution of an alkali activator with the admixture to form a slurry, and supplying a second hemp derivative to the slurry to form a hemp-based concrete composition.
Embodiments herein include methods for producing a hemp-based construction composition. One such method combining hemp hurd powder and a binder component to form an admixture; supplying an aqueous solution of an alkali activator to the admixture to form a binder slurry; combining hemp hurd with the binder slurry to form a hemp-based concrete slurry; supplying the hemp-based concrete slurry to a plurality of molds; and allowing the hemp-based concrete slurry to harden in the plurality of molds, thereby producing the hemp-based construction composition. In certain embodiments, the aqueous solution of the alkali activator contains one or more of a silicate, a metal aluminate, an alkali-metal hydroxide, ammonium hydroxide, and an alkaline earth metal hydroxide. The hemp-based concrete compositions can contain the hemp hurd powder in the admixture at an amount ranging from about 1 wt. % to about 20 wt. %. The hemp-based concrete compositions can contain the hemp hurd powder in the admixture at an amount ranging greater than about 1 wt. %. The hemp-based concrete compositions can contain the hemp hurd powder in the admixture at an amount ranging greater than about 5 wt. %. The binder component can be one or more of ordinary Portland cement (OPC), lime, zeolite, magnesium oxide cement, magnesium phosphate cement, and ground granulated blast furnace slag. In certain embodiments, the binder component is ground granulated blast furnace slag. The alkali activator can contain one or more of a silicate, a metal aluminate, an alkali-metal hydroxide, ammonium hydroxide, and an alkaline earth metal hydroxide. The alkali activator contains sodium silicate and sodium hydroxide. In certain embodiments, the alkali activator contains sodium silicate and sodium hydroxide at a ratio of 2.5:1 and at a molality of 10 M.
Certain embodiments of the hemp-based construction compositions have a density of less than about 1.5 g/cm3. Certain embodiments of the hemp-based construction compositions have a compressive strength greater than 4 MPa. Certain embodiments of the hemp-based construction compositions have a global warming potential ranging from about 300 kgCO2eq/m3 to about 700 kgCO2eq/m3. Certain embodiments of the hemp-based construction compositions have a CO2 sequestration ranging from about 90 kgCO2eq/m3 to 180 kgCO2eq/m3.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
Embodiments will be readily understood by the following detailed description in conjunction with the accompanying drawings. Embodiments are illustrated by way of example and not by way of limitation in the accompanying drawings.
The present disclosure describes various embodiments related to cement compositions containing hemp-based polymers, methods of making these compositions, and methods of use thereof. Further embodiments may be described and disclosed.
In the following description, numerous details are set forth in order to provide a thorough understanding of the various embodiments. In other instances, well-known processes, devices, and systems may not been described in particular detail in order not to unnecessarily obscure the various embodiments. Additionally, illustrations of the various embodiments may omit certain features or details in order to not obscure the various embodiments.
In the following detailed description, reference is made to the accompanying drawings that form a part of this disclosure. Like numerals may designate like parts throughout the drawings. The drawings may provide an illustration of some of the various embodiments in which the subject matter of the present disclosure may be practiced. Other embodiments may be utilized, and logical changes may be made without departing from the scope of this disclosure.
The description may use the phrases “in some embodiments,” “in various embodiments,” “in an embodiment,” or “in embodiments,” which may each refer to one or more of the same or different embodiments. Furthermore, the terms “comprising,” “including,” “having,” and the like, as used with respect to embodiments of the present disclosure, are synonymous.
As previously discussed, alkali-activated binders have problems that limit their application, such as significant drying shrinkage, high efflorescence, low strength, and long or short setting time. Disclosed here are embodiments to address these drawbacks. These embodiments were developed by selecting the suitable precursor type and content, the alkali activation properties and content, and the curing method. Supplementary cementitious materials (SCM), such as fly ash, are used as a potential aluminosilicate precursor in producing alkali-activated binders. The aggregates used in producing alkali-activated binders can either be natural or recycled. As an aggregate is an essential component in concrete, utilizing recycled aggregate can reduce the global demand on natural aggregate and have significant impact on the weight, cost, and properties of alkali-activated concrete. Plant-based aggregate is a sustainable option in producing mixtures with alkali-activated binders. Utilizing this type of renewable aggregate creates links between the construction and agricultural industries and help reduce the construction sector's ecological impact.
Embodiments include construction materials containing hemp derivatives. Hemp derivatives as used herein refer to any substance or product derived or collected or extracted from a hemp plant, including but not limited to products from a woody core of a hemp plant. Hemp hurd is the woody core (xylem and pith) of the hemp plant and a by-product of the hemp industry. Hemp hurd characterized by its lightweight and good acoustic properties due to its porous structure, good thermal insulation properties, rapid growth rate, and high ability of carbon dioxide sequestration. Hemp hurd powder has a particle size ranging from about 1 micrometer (μm) to about 100 μm or less. In certain embodiments, the particle size can range from about 1 μm to about 75 μm. In certain embodiments, the particle size can range from about 10 μm to about 70 μm. The coarse hemp hurd has particle dimensions ranging from about 0.1 mm to about 40 mm, or from about 1 mm to about 30 mm, or from about 1 mm to about 20 mm, or from about 1 mm to about 10 mm, or from about 1 mm to about 7 mm. In certain embodiments, the coarse hemp hurd has average particle dimensions of about 10 mm. In certain embodiments, the coarse hemp hurd has average particle dimensions of about 5 mm. In certain embodiments, the coarse hurd can be separated from bast fibers by hammer milling hemp stalks and passing the materials through a screen, whose pore sizing can be varied to vary the size of the hemp hurd. Hemp hurd powder can be produced by milling the hemp hurd down to the desired particle sizes for a powder.
Embodiments include hemp-based concrete compositions with a binder containing a first hemp derivative and an aggregate containing a second hemp derivative. In certain embodiments, the first hemp derivative contains substantially hemp hurd powder. In certain embodiments, the second hemp derivative contains substantially coarse hemp hurd. Embodiments include a hemp-based concrete composition containing an aluminosilicate binder with hemp hurd powder and an alkali activator, and coarse hemp hurd as a component of the aggregate. As used herein, “substantially contains(ing)” means that the composition or component may include other ingredients, so long as the other ingredients do not constitute more than 20% by mass or more relative to the whole composition. Embodiments include hemp-based concrete compositions with a binder containing a first hemp derivative and a rock or a mineral aggregate. Mineral aggregates include one or more of silica, silicates, carbonates, sulfates, iron sulfides, and iron oxides. Rock aggregates include one or more of igneous rocks (such as granite, syenite, diorite, gabbro, peridotite, volcanic glass, felsite, and basalt), sedimentary rocks (such as conglomerate, sandstone, claystone, shale, limestone, dolomite, chalk, and chert), and metamorphic rocks (such as marble, slate, phyllite, schist, amphibolite, hornfels, and gneiss).
Embodiments include hemp-based binder compositions containing a hemp derivative and an aluminosilicate-based binder. The hemp derivative can be combined with a mineral admixture, which is suitable for alkali-activated cementitious composites to produce an aluminosilicate-based binder. Embodiments include an alkali-activated binder containing hemp hurd powder, river sand, fly ash, and an alkali activator. The hemp-based binders can be used as a mortar, plaster/render, crack filler and as a plaster repair material.
The alkali activator can contain one or more of a silicate, a metal aluminate, an alkali-metal hydroxide, ammonium hydroxide, and an alkaline earth metal hydroxide. In certain embodiments, the alkali activator contains one or more of sodium silicate and sodium hydroxide. The alkali activator can be an aqueous mixture of sodium silicate and sodium hydroxide. The amount of sodium silicate and sodium hydroxide in a particular mixture can range from a ratio of 3:1 to 1:1. In certain embodiments, the alkali activator can be an aqueous mixture of sodium silicate and sodium hydroxide at a ratio of 2.5:1 and at a molality of 10 M.
In certain embodiments, the hemp-based concrete contains different binders in addition to a hemp derivative. These binders include but are not limited to ordinary Portland cement (OPC), lime, a combination of lime and cement, binders containing zeolite, magnesium oxide cement, magnesium phosphate cement, ground granulated blast furnace slag, and binders comprised of supplementary cementitious materials. Hemp derivatives include coarse hemp hurd, hemp hurd powder, hemp fibers, or a combination thereof.
Embodiments include an alkali-activated hemp-based composition containing coarse hemp hurd as a natural aggregate and hemp hurd powder as a part of the binder. Embodiments include this composition being suitable for building products, such as lightweight masonry units using alkali-activated hemp-based materials. In certain embodiments, the binder contains alkali-activated ground granulated blast furnace slag (GGBFS) and coarse hemp hurd powder. Coarse hemp hurd is used to replace mineral aggregate in the mixture compositions. Various embodiments disclosed and described may relate to high-strength lightweight alkali-activated bricks containing hemp hurd powder and coarse hemp hurd.
Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simplify subsequent reference to such steps. It is to be appreciated that certain features are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination. Further, reference to values stated in ranges include each and every value within that range.
In certain embodiments, the hemp-based concrete compositions have a density ranging from about 0.8 g/cm3 to about 1.5 g/cm3, or from about 0.9 g/cm3 to about 1.5 g/cm3, or from about 1 g/cm3 to about 1.4 g/cm3, or from about 1.1 g/cm3 to about 1.4 g/cm3, or from about 1.15 g/cm3 to about 1.3 g/cm3. In certain embodiments, the alkali-activated hemp-based concrete compositions have a density of about 0.8 g/cm3. In certain embodiments, the alkali-activated hemp-based concrete compositions have a density of about 0.9 g/cm3. In certain embodiments, the alkali-activated hemp-based concrete compositions have a density of about 1 g/cm3. In certain embodiments, the alkali-activated hemp-based concrete compositions have a density of about 1.2 g/cm3 or lower. In certain embodiments, the alkali-activated hemp-based concrete compositions have a density of about 1.3 g/cm3 or lower.
In certain embodiments, the alkali-activated hemp-based concrete compositions have a compressive strength ranging from about 4 MPa to about 25 MPa, or from about 5 MPa to about 20 MPa, or from about 10 MPa to about 25 MPa, or from about 10 MPa to about 20 MPa, or from about 15 MPa to about 25 MPa, or from about 15 MPa to about 20 MPa. In certain embodiments, the alkali-activated hemp-based concrete compositions have a compressive strength of about 4 MPa or greater. In certain embodiments, the alkali-activated hemp-based concrete compositions have a compressive strength of about 6 MPa or greater. In certain embodiments, the alkali-activated hemp-based concrete compositions have a compressive strength of about 10 MPa or greater. In certain embodiments, the alkali-activated hemp-based concrete compositions have a compressive strength of about 15 MPa or greater.
In certain embodiments, the alkali-activated hemp-based concrete compositions have a water absorption by immersion ranging from about 25% to about 50%, or from about 30% to about 50%, or from about 35% to about 50%, or from about 25% to about 45%, or from about 30% to about 45%, or from about 35% to about 45%, or from about 35% to about 45%.
In certain embodiments, the alkali-activated hemp-based concrete compositions have a capillary coefficient ranging from about 0.01 kg/m2 min0.5 to about 0.2 kg/m2 min0.5, or from about 0.015 kg/m2 min0.5 to about 0.15 kg/m2 min0.5, or from about 0.015 kg/m2 min0.5 to about 0.14 kg/m2 min0.5, or from about 0.02 kg/m2 min0.5 to about 0.14 kg/m2 min0.5, or from about 0.02 kg/m2 min0.5 to about 0.135 kg/m2 min0.5, or from about 0.025 kg/m2 min0.5 to about 0.135 kg/m2 min0.5, or from about 0.0267 kg/m2 min0.5 to about 0.133 kg/m2min0.5.
In certain embodiments, the alkali-activated hemp-based concrete compositions have a global warming potential ranging from about 250 kgCO2eq/m3 to about 750 kgCO2eq/m3, or from about 260 kgCO2eq/m3 to about 740 kgCO2eq/m3, or from about 270 kgCO2eq/m3 to about 730 kgCO2eq/m3, or from about 280 kgCO2eq/m3 to about 720 kgCO2eq/m3, or from about 280 kgCO2eq/m3 to about 700 kgCO2eq/m3, or from about 280 kgCO2eq/m3 to about 690 kgCO2eq/m3, or from about 300 kgCO2eq/m3 to about 650 kgCO2eq/m3. In certain embodiments, the alkali-activated hemp-based concrete compositions have a global warming potential greater than about 400 kgCO2eq/m3. In certain embodiments, the alkali-activated hemp-based concrete compositions have a global warming potential greater than about 500 kgCO2eq/m3. In certain embodiments, the alkali-activated hemp-based concrete compositions have a global warming potential greater than about 600 kgCO2eq/m3.
In certain embodiments, the alkali-activated hemp-based concrete compositions have a CO2 sequestration ranging from about 80 kgCO2eq/m3 to about 200 kgCO2eq/m3, or from about 90 kgCO2eq/m3 to about 200 kgCO2eq/m3, or from about 100 kgCO2eq/m3 to about 180 kgCO2eq/m3, or from about 100 kgCO2eq/m3 to about 175 kgCO2eq/m3, or from about 120 kgCO2eq/m3 to about 180 kgCO2eq/m3. In certain embodiments, the alkali-activated hemp-based concrete compositions have a CO2 sequestration greater than 90 kgCO2eq/m3. In certain embodiments, the alkali-activated hemp-based concrete compositions have a CO2 sequestration greater than 100 kgCO2eq/m3. In certain embodiments, the alkali-activated hemp-based concrete compositions have a CO2 sequestration greater than 120 kgCO2eq/m3.
Embodiments include methods of production of hemp-based concrete or mortar compositions. Embodiments include methods of production of hemp-based concrete compositions with a binder containing a first hemp derivative and an aggregate containing a second hemp derivative. One such method includes the following steps: combining a first hemp derivative and a binder component to form an admixture, combining an aqueous solution of an alkali activator with the admixture to form a slurry, and supplying a second hemp derivative to the slurry to form a hemp-based concrete composition. In certain embodiments, each of the hemp derivatives can be soaked in the activator to affect certain properties, such as the unhardened workability. The binder component can be one or more of ordinary Portland cement (OPC), lime, a combination of lime and cement, zeolite, magnesium oxide cement, magnesium phosphate cement, ground granulated blast furnace slag, and other supplementary cementitious materials. The binder component can be an aluminosilicate-based binder or any mineral admixture, which is suitable for alkali-activated cementitious composites to produce an aluminosilicate-based binder. In certain embodiments, the first hemp derivative contains substantially hemp hurd powder. The hemp hurd powder can be present in the admixture at an amount ranging from about 1 wt. % to about 20 wt. %, or from about 1 wt. % to about 10 wt. %, or about 1 wt. % to about 5 wt. %. In certain embodiments, the second hemp derivative contains substantially coarse hemp hurd. The alkali activator can contain one or more of a silicate, a metal aluminate, an alkali-metal hydroxide, ammonium hydroxide, and an alkaline earth metal hydroxide. In certain embodiments, the alkali activator contains one or more of sodium silicate and sodium hydroxide. The alkali activator can be an aqueous mixture of sodium silicate and sodium hydroxide. The amount of sodium silicate and sodium hydroxide in a particular mixture can range from a ratio of 3:1 to 1:1. In certain embodiments, the alkali activator can be an aqueous mixture of sodium silicate and sodium hydroxide at a ratio of 2.5:1 and at a molality of 10 M.
Embodiments include methods of production of hemp-based construction compositions with a binder containing a first hemp derivative and an aggregate containing a second hemp derivative. One such method includes the following steps: combining a first hemp derivative and a binder component to form an admixture, combining an aqueous solution of an alkali activator with the admixture to form a slurry, supplying a second hemp derivative to the slurry to form a hemp-based concrete composition, supplying the hemp-based concrete composition to a plurality of molds; and allowing the hemp-based concrete composition to harden in the plurality of molds, thereby producing the hemp-based construction compositions. The construction compositions can be bricks, tiles, roofing materials, wall materials, or flooring materials. The binder component can be one or more of ordinary Portland cement (OPC), lime, a combination of lime and cement, zeolite, magnesium oxide cement, magnesium phosphate cement, ground granulated blast furnace slag, and other supplementary cementitious materials. The binder component can be an aluminosilicate-based binder or any mineral admixture, which is suitable for alkali-activated cementitious composites to produce an aluminosilicate-based binder. In certain embodiments, the first hemp derivative contains substantially hemp hurd powder. The hemp hurd powder can be present in the admixture at an amount ranging from about 1 wt. % to about 20 wt. %, or from about 1 wt. % to about 10 wt. %, or about 1 wt. % to about 5 wt. %. In certain embodiments, the second hemp derivative contains substantially coarse hemp hurd. The alkali activator can contain one or more of a silicate, a metal aluminate, an alkali-metal hydroxide, ammonium hydroxide, and an alkaline earth metal hydroxide. In certain embodiments, the alkali activator contains one or more of sodium silicate and sodium hydroxide. The alkali activator can be an aqueous mixture of sodium silicate and sodium hydroxide. The amount of sodium silicate and sodium hydroxide in a particular mixture can range from a ratio of 3:1 to 1:1. In certain embodiments, the alkali activator can be an aqueous mixture of sodium silicate and sodium hydroxide at a ratio of 2.5:1 and at a molality of 10 M.
Embodiments of the hemp-based cement compositions contain different alkali activators and hemp hurd powder. The percentage content of the alkali activators and hemp derivatives affect the compressive strength, density, water absorption by immersion and capillarity action, fire resistance, efflorescence, and carbonation resistance.
Various embodiments disclosed and described may relate to high-strength lightweight alkali-activated construction materials, such as bricks, tiles, roofing materials, flooring materials, drywall, particle boards, or fiber boards, containing hemp powder and coarse hemp hurd. Embodiments include bricks containing hemp powder and coarse hemp hurd with an alkali activator. In certain embodiments, these bricks have a density less than about 1.3 g/cm3 and a compressive strength greater than 4 MPa. In addition, reducing the alkali activator content increases the carbon dioxide sequestration capacity up to 180 kgCO2 eq/m3 for the developed alkali-activated hemp-based materials.
Various examples are provided to illustrate selected aspects of the hemp-based compositions.
Certain compositions contain the following components: the hemp powder, GGBFS, the coarse hemp hurd, and an alkali-activator. To prepare the alkali-activator, sodium hydroxide (NaOH) and sodium silicate (Na2SO3) were mixed at a ratio of 2.5. Solid NaOH flakes were mixed with distilled water to have liquid sodium hydroxide with a molarity of 10 mol/L. The mixing process was performed twenty-four hours prior to mixing the materials. This molarity has significant effect on gaining the mechanical strength of alkali-activated materials (AAM).
As shown in
The chemical composition of grade 100 GGBFS used in this study is listed in Table 1. It indicates that the GGBFS is rich in calcium oxide (CaO) and silicon oxide (SiO2), and it is used as a precursor in the produced alkali-activated hemp mortar. The relative density of GGBFS typically ranges from 1050 to 1375 kg/m3.
Seven mixes were prepared during a two-phase experimental program which is listed in Table 2. In the first phase, the contents of the hemp hurd powder (20% by volume), GGBFS (80% by Vol.), and the hemp-hurd-to-binder ratio of 45 were all kept constant. However, varying amounts of sodium silicate and sodium hydroxide were used in each mixture to investigate the effects of the alkali-activation process on the matrix properties of the developed hemp hurd-based alkali-activated material. In the second phase, all mixture contents were kept constant except for the amounts of the hemp hurd, which were gradually increased. The increase in hemp hurd was performed to study the influence of its content on the ability to produce lightweight materials.
Various tests were performed to measure the properties of the compositions. The number and dimensions of each specimen and the testing standards used are mentioned.
Density: For each mixture, three cubic specimens with an edge of 50 mm were prepared. The weight and dimensions of each cubic specimen were measured. A digital caliper was used to measure the dimensions of each cube. The dry density was then calculated by dividing the mass of each specimen by the apparent volume. The reported density is the average of three measured samples for each mixture composition.
Compressive strength: Cubic specimens with 50 mm nominal edge lengths were used for the compression testing in accordance with ASTM C109/C109M. A displacement rate of 1.8 mm/min and a load cell with a capacity of 100 KN were used. The results were averaged from three tested samples at 14 days for each mixture. The effect of using different proportions of the alkali activator and coarse hemp hurd on the compressive strength is shown in
Water absorption by immersion: Based on ASTM C1585-04, three 50-mm cubes from each mixture at the age of 28 days were initially dried at 100° C. for 48 hours. Then, the samples were submerged in water for 48 hours. Afterward, the samples were removed from the water, and the saturated weight of each sample was measured. The results were obtained by averaging three tested samples for each mixture. Water absorption (Wm) is computed using the Equation 1:
W
m=(Ms−Md)/Md×100 (1)
Where Ms stands for saturated mass, and Md is dry mass.
In addition, three 50-mm cubic specimens were immersed in water, and then buoyancy mass (Mb) was measured using a fixed steel basket to scale. The apparent porosity of specimens was calculated by Equation 2:
Apparent porosity=(Ms−Md)/(Ms−Mb)×100 (2)
The effect of using different proportions of the alkali activator and coarse hemp hurd on the degree of water absorption and the apparent porosity is shown in
The relationship between water absorption and the dried density is shown in
Water absorption by capillarity: The water absorption coefficient by capillary action was measured based on BS EN1015-18:2002. The lateral surfaces of three 50-mm cubic specimens of 28 days' age were covered by paraffin. The capillary water absorption coefficient was calculated using Equation 3. Aw is the capillary water absorption coefficient, A is the surface area, ΔB is the absorbed mass, and √t is the time (min 0.5).
A
w
=ΔB/(A√t) (3)
The degree of water absorption by capillarity indicates the degree of porosity of the mix. The rate of capillary suction depends on the network of porosity and tortuosity, the tensile strength of water, and the pore size of a water meniscus.
The capillary coefficient is highly correlated with the apparent porosity as shown in
High temperature resistance: Two cubes were subjected to high temperatures to assess the post-heating residual-strength when subjected to elevated temperatures.
High temperature exposure has a significant impact on the mass and compressive strength of the produced alkali-activated hemp mixtures, as shown in
Carbonation resistance: Cubes (50 mm nominal) from each mixture at 28 days were used to determine the carbonation resistance. The specimens were placed in a carbonation chamber for two days. CO2 gas was circulated with a concentration of 5%, 50% relative humidity (RH), pressure of 40 psi, and a temperature of 23° C. The influence of carbonation was then investigated by assessing the density and compressive strength before and after CO2 exposure. To assess the degree of CO2 sequestration, three carbonated specimens of each mixture were placed in the oven at 105° C. for 24 hours to evaporate the absorbed water.
Efflorescence: Cubes with 50 mm edges were used to evaluate efflorescence. The cubes were kept in a tray half-filled with distilled water at room temperature and were inspected visually at 24, 48, 72, and 503 hours. The influence of efflorescence on the compressive strength was then evaluated. Efflorescence is one of the problems associated with alkali-activated binders exposed to water or a high humidity environment. It is responsible for forming a chemical reaction product on the external surface of alkali-activated materials. The durability and long-term performance may be affected due to cracks associated with high amounts of efflorescence. Therefore, this evaluation is necessary to assess the feasibility of alkali-activated hemp hurd mixture as a construction building material.
Increasing the hemp content on the other hand will further reduce the rate of efflorescence as can be seen for mixture 6 and mixture 7 in
Global warming potential (GWP) and carbon footprint: Table 3 presents the global warming potential (GWP) for each component of the produced hemp hurd-based alkali-activated material. The assessment of GWP of each component has been performed using the EcoInvent database except for the negative GWP of the hemp, which was obtained from reference. The negative GWP of the hemp has been explained because of the biogenic CO2 uptake during hemp production.
The influence of using different contents of the alkali activator and the hemp hurd on the GWP and the carbon footprint is presented in
An increase in the degree of CO2 sequestration can be seen in
The degree of greenhouse gases (GHG) emission, sequestration, and the carbon footprint corresponding to each mixture is presented in
Reduction in the carbon footprint is more significant when decreasing the alkali activator. However, the lowest carbon footprint is associated with mixture 6 having the least amount of alkali activator content and an increased coarse hemp hurd content. Further increase in the coarse hemp hurd content will increase the overall carbon footprint as can be see for mixture 7. According to
The disclosed data indicate the mechanical and durability properties of hemp-based alkali-activated materials to be used as sustainable construction bricks. In certain embodiments, gradually reducing the alkali activator content increases the density and compressive strength up to 1.2 g/cm3 and 17 MPa, respectively. The compressive strength is highly correlated with the dry density of developed hemp-based alkali-activated material. The alkali activator content has more influence on increasing the compressive strength rate than the coarse hemp hurd content. Reducing the alkali activator content reduces the rate of water absorption by immersion down to 25% and increasing the coarse hemp hurd content increases it up to 40%. The alkali activator content indicated higher impact on the apparent porosity and the degree of water absorption by immersion than the coarse hemp hurd content. Reducing the alkali activator content will decrease the capillary coefficient to 0.027 kg/m2 min0.5 due to the reduced porosity. In contrast, increasing the coarse hemp hurd content will increase porosity and the capillary coefficient up to 38% and 0.127 kg/m2 min0.5, respectively. Exposing mixtures to CO2 gas flow increases the density and compressive strength by 2-12% and 9-100%, respectively. The rate of efflorescence is reduced when the alkali activator content is decreased, or the coarse hemp hurd content is increased. After efflorescence, samples with the least alkali activator content (mixtures 4 and 5) have witnessed a 17% and 11% increase in the compressive strength. In contrast, the compressive strength has decreased by an average of 44% for samples with an increased coarse hemp hurd content. Reducing the alkali activator content increases CO2 sequestration up to 180 kgCO2eq/m3, while increasing the coarse hemp hurd content reduces it to 88 kgCO2eq/m3.
To assess the effect of the hemp-hurd powder on the alkali-activated ground granulated blast furnace slag (GGBFS, Grade 100) binder, three mixtures were prepared. A neat alkali-activated GGBFS paste was prepared, and two others had 1.78% and 3% Ground hemp hurd (100-micron max) GGBFS replacement by weight. Each mixture was placed into 50 mm cube molds and exposed to 60 degrees C. for 24 hours. Following heat curing, the samples were weighed and tested with an average of three cube results as shown in
The embodiments have been described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the embodiments. For all ranges disclosed herein, such ranges are intended to include any combination of the stated upper and lower limits, even if specific combinations are not specifically described. It should be understood that although the disclosure contains certain aspects, embodiments, and optional features, modification, improvement and variation of such aspects, embodiments, and optional features can be resorted to by those skilled in the art, and that such modifications, improvements, and variations are considered to be within the scope of this disclosure.
This application claims the benefit of and priority to U.S. Provisional Application No. 63/226,897, filed Jul. 29, 2021, which is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63226897 | Jul 2021 | US |
