Patent Grant
11104611
The presently disclosed subject matter generally relates to use of swine waste biochar as a replacement of cement pastes in the manufacture of concrete.
The hydration and setting behavior of fresh cement pastes, particularly cement pastes modified with partial cement replacement materials (PCRM), are critical in the development of sustainable structural concrete. The hydration of cement is a complex phenomenon that occurs when water is added to cement. Through dispersion, dissolution, agglomeration, and chemical reactions, the cement pastes transition from a fluid state to a solid state. During early-age hydration of Ordinary Portland Cement (OPC), its four major phases (Tricalcium Silicate, Dicalcium Silicates, Tricalcium Aluminates, and Tetracalcium Aluminoferrites) move and react with water to form cement paste. Cement paste is a multi-phase product of cement and water. The chemical changes that take place during cement paste hydration often affect the progressive setting of the paste, wherein there is a change from an initial semifluid mixture to a solid composite. With the pursuit of more sustainable PCRM, the setting and hydration behavior of PCRM modified cement paste system are of interest.
Biochar is a carbon-rich substance typically produced via pyrolysis, a thermochemical process used at elevated temperatures in the absence of oxygen. Swine waste biochar (SB) is isolated after thermochemical liquefaction of swine waste as disclosed herein. Swine waste biochar is a black solid residue comprising a porous network of carbonates and/or aromatic carbon, as well as minerals, including calcium and silica.
Water absorption is increasingly used to quantify the durability of cementitious systems. Concrete is only partly saturated and so the initial absorption of water and salts is at least in part by capillary action and is heavily influenced by concrete pore volumes and pore connectivity. Concrete with high water absorption is susceptible to freezing and thawing, as water enters in the cement paste, and even in the aggregates. High water absorption also facilitates the ingress of contaminative substances, which can lead to concrete deterioration.
The presently disclosed subject matter provides, in one aspect, a cementitious composition comprising swine waste biochar and cement. The presently disclosed subject matter provides, in another aspect, a composition comprising about 1 part by weight cementitious materials, about 1 to about 3 parts by weight fine aggregate, about 1 to about 5 parts by weight coarse aggregate, and about 0.2 to about 0.6 parts by weight water, wherein the cementitious materials comprise from about 0.25% to about 30% by weight swine waste biochar and about 99.75% to about 70% by weight cement.
The presently disclosed subject matter provides, in another aspect, a method of accelerating the setting of a cement paste comprising combining cement with swine waste biochar to obtain a blended mix before the addition of water. The presently disclosed subject matter provides, in another aspect, a reducing the water absorption of a cement paste comprising combining cement with swine waste biochar to obtain a blended mix before the addition of water.
Accordingly, it is an object of the presently disclosed subject matter to provide a cementitious composition comprising swine waste biochar and cement.
An object of the presently disclosed subject matter having been stated hereinabove, and which is achieved in whole or in part by the presently disclosed subject matter, other objects will become evident as the description proceeds when taken in connection with the accompanying drawings as best described hereinbelow.
It will be understood that the drawings are for the purpose of describing embodiments of the inventions and are not intended to limit the inventions thereto.
This description is not intended to be a detailed catalogue of all the ways in which the present invention may be implemented or of all the features that may be added to the present invention. For example, features illustrated with respect to one embodiment may be incorporated into other embodiments, and features illustrated with respect to a particular embodiment may be deleted from that embodiment. Thus, one or more of the method steps included in a particular method described herein may, in other embodiments, be omitted and/or performed independently. In addition, numerous variations and additions to the embodiments suggested herein, which do not depart from the instant invention, will be apparent to those skilled in the art in light of the instant disclosure. Hence, the following description is intended to illustrate some particular embodiments of the invention, and not to exhaustively specify all permutations, combinations and variations thereof. It should therefore be appreciated that the present invention is not limited to the particular embodiments set forth herein. Rather, these particular embodiments are provided so that this disclosure will more clearly convey the full scope of the invention to those skilled in the art.
The terminology used herein is for the purpose of describing particular embodiments of the present invention only and is not intended to limit the present invention. Although the following terms are believed to be well understood by one of skill in the art, the following definitions are set forth to facilitate understanding of the presently disclosed subject matter.
All references listed herein, including but not limited to all patents, patent applications and publications thereof, and scientific journal articles, are incorporated herein by reference in their entireties to the extent that they supplement, explain, provide a background for, or teach methodology, techniques, and/or compositions employed herein.
I. Definitions
While the following terms are believed to be well understood by one of ordinary skill in the art, the following definitions are set forth to facilitate explanation of the presently disclosed subject matter.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the presently disclosed subject matter belongs.
Following long-standing patent law convention, the terms “a”, “an”, and “the” refer to “one or more” when used in this application, including the claims.
The term “and/or” when used in describing two or more items or conditions, refers to situations where all named items or conditions are present or applicable, or to situations wherein only one (or less than all) of the items or conditions is present or applicable.
The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and/or.”
As used herein “another” can mean at least a second or more.
The term “comprising”, which is synonymous with “including,” “containing,” or “characterized by” is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. “Comprising” is a term of art used in claim language which means that the named elements are essential, but other elements can be added and still form a construct within the scope of the claim.
As used herein, the phrase “consisting of” excludes any element, step, or ingredient not specified in the claim. When the phrase “consists of” appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole.
As used herein, the phrase “consisting essentially of” limits the scope of a claim to the specified materials or steps, plus those that do not materially affect the basic and novel characteristic(s) of the claimed subject matter.
With respect to the terms “comprising”, “consisting of”, and “consisting essentially of”, where one of these three terms is used in the specification, the presently disclosed subject matter can include the use of either of the other two terms.
Unless otherwise indicated, all numbers expressing quantities of size, capacity, percentage (%), and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the presently disclosed subject matter.
As used herein, the term “about”, when referring to a value is meant to encompass variations of in one example ±20% or ±10%, in another example ±5%, in another example ±1%, and in still another example ±0.1% from the specified amount, as such variations are appropriate to perform the disclosed methods.
As used herein, “swine waste biochar” (‘SB’) refers to the biochar obtained from a thermochemical processing of swine waste as disclosed herein.
In one embodiment, SB is mechanically milled before incorporation into cement and/or cement paste. In another embodiment, SB particles undergo alkali treatment using sodium hydroxide, potassium hydroxide, and/or ammonia solutions.
As used herein, “cement” refers to Portland cement, which is typically prepared by sintering a mixture of components including calcium carbonate (as limestone), aluminum silicate (as clay or shale), silicon dioxide (as sand), and miscellaneous iron oxides. The term “Portland cement” includes all cementitious compositions which meet the requirements of the ASTM (as designated by ASTM Specification C150), including but not limited to Type I, type IA, type II, type IIA, type III, type IIIA, type IV, and type V. Portland cement can include mixtures of such Types as well.
As used herein, “cementitious materials” refers to the portion of a hardenable mixture that provides for binding or uniting the other materials present in the mixture, and thus includes cement, optionally in combination with swine waste biochar or other additives. In some embodiments, swine waste biochar comprises from about 0.25% to about 70% by weight of the cementitious materials, or about 0.5% to about 60% by weight. In some embodiments, swine waste biochar comprises from about 0.5% to about 50% by weight of the cementitious materials, or about 1% to about 40% by weight. In some embodiments, swine waste biochar comprises from about 1.25% to about 30% by weight of the cementitious materials. In some embodiments, swine waste biochar comprises from about 2.5% to about 15% by weight; in some embodiments, swine waste biochar comprises from about 5% to about 12.5% of the cementitious materials; in other embodiments, from about 7.5% to about 10% of the cementitious materials. In one embodiment, the balance of cementitious materials is cement, such as, for example, Portland cement, or Type I/Type IA. In another embodiment, the balance of cementitious materials is cement and another additive, such as for example, fly ash, plant-based biochar, or other additives known to those of skill in the art.
In one embodiment, swine waste biochar comprises no more than about 70% by weight of the cementitious materials, no more than about 60% by weight, no more than about 50% by weight, or no more than about 40% by weight. In another embodiment, swine waste biochar comprises no more than about 30% by weight of the cementitious materials. In one embodiment, swine waste biochar comprises no more than about 20% by weight of the cementitious materials, or no more than about 10%, or no more than about 5%. In one embodiment, the balance of cementitious materials is cement, such as, for example, Portland cement. In another embodiment, the balance of cementitious materials is cement and another additive.
In one embodiment, swine waste biochar comprises about 1.25% by weight of the cementitious materials and cement comprises the balance. In another embodiment, swine waste biochar comprises about 2.5% by weight of the cementitious materials, about 5%, about 7.5%, about 10%, about 12.5%, about 15%, about 20%, about 30%, about 40%, about 50%, about 60%, or about 70%. In one embodiment, the balance of cementitious materials is cement, such as, for example, Portland cement. In another embodiment, the balance of cementitious materials is cement and another additive.
As used herein “cement paste” refers to a composition comprising cement and water. Cement paste is a multi-phase product of cement and water, having a complex structure, composition, and morphology, each of which varies with time. Cement pastes typically comprise calcium hydroxide crystals, aluminates, and unreacted cement particles which are all embedded in a matrix of amorphous nanostructured hydration product referred to as calcium-silicate-hydrate (C-S-H) gel.
When the cementitious materials comprise both cement and swine waste biochar, the paste is designated herein as: SBx, CP-SBx, CPx, or CPx-Y where x is the weight percent of SB present in the mix and Y is the treatment temperature of SB, where applicable.
As used herein “concrete” refers to a hardenable mixture comprising cementitious materials; a fine aggregate, such as sand: a coarse aggregate, such as but not limited to crushed basalt coarse aggregate; and water.
The presently disclosed subject matter provides, in one aspect, a cementitious composition comprising swine waste biochar and cement. In one embodiment, swine waste biochar comprises between about 0.25% and about 30% by weight of the composition. In another embodiment, the swine waste biochar comprises between about 1% and about 15% by weight of the composition. In yet another embodiment, the swine waste biochar comprises about 40%-60% carbon, about 25%-45% oxygen, about 2%-11% phosphorus and about 2%-10% calcium. In yet another embodiment, the swine waste biochar comprises about 50-60% carbon and about 25%-35% oxygen, or the swine waste biochar comprises about 55% carbon, about 30% oxygen, about 5% phosphorus and about 5% calcium.
The presently disclosed subject matter provides, in another aspect, a composition comprising about 1 part by weight cementitious materials, about 1 to about 3 parts by weight fine aggregate, about 1 to about 5 parts by weight coarse aggregate, and about 0.2 to about 0.6 parts by weight water, wherein the cementitious materials comprise about 0.25% to about 40% by weight swine waste biochar and about 99.75% to about 60% by weight cement. In another embodiment, the cementitious materials comprise about 0.25% to about 30% by weight swine waste biochar and about 99.75% to about 70% by weight cement or the cementitious materials comprise about 1% to about 30% by weight swine waste biochar and about 99% to about 70% by weight cement. In one embodiment, the swine waste biochar comprises about 40%-60% carbon, about 25%-45% oxygen, about 2%-11% phosphorus and about 2%-10% calcium. In another embodiment, the swine waste biochar comprises about 50-60% carbon and about 25%-35% oxygen, or the swine waste biochar comprises about 55% carbon, about 30% oxygen, about 5% phosphorus and about 5% calcium. In one variation of any aspect or embodiment, the fine aggregate is sand and the coarse aggregate is stone.
In another embodiment, the cementitious materials comprise about 1% to about 15% by weight swine waste biochar and about 99% to about 85% by weight cement. In yet another embodiment, the swine waste biochar comprises about 40%-60% carbon, about 25%-45% oxygen, about 2%-11% phosphorus and about 2%-10% calcium. In another embodiment, the swine waste biochar comprises about 50-60% carbon and about 25%-35% oxygen, or the swine waste biochar comprises about 55% carbon, about 30% oxygen, about 5% phosphorus and about 5% calcium. In one variation of any aspect or embodiment, the fine aggregate is sand and the coarse aggregate is stone.
The presently disclosed subject matter provides, in another aspect, a method of accelerating the setting of a cement paste comprising combining cement with swine waste biochar to obtain a blended mix before the addition of water. In one embodiment, the cement paste containing swine waste biochar has a shorter initial time of setting and/or a shorter final time of setting compared to cement paste that does not contain swine waste biochar.
The presently disclosed subject matter provides, in another aspect, a reducing the water absorption of a cement paste comprising combining cement with swine waste biochar to obtain a blended mix before the addition of water. In one embodiment, the water absorption is reduced by at least about 60% compared to water absorption of cement paste that does not contain swine waste biochar. In another embodiment, water absorption is reduced by at least about 70%, or at least about 80% compared to cement paste that does not contain swine waste biochar.
As shown herein, swine-waste biochar (‘SB’) has a direct effect on the hydration and setting behavior of cement pastes. SB is not an inert material in cement pastes, but instead accelerates polymerization as a result of hydration reactions. As shown herein, when mixing water was added to the dry cement/SB binder mix, chemical reactions occurred between the calcium silicates of ordinary Portland cement and the carboxylic surface functional groups of SB; calcium-silicate-hydrate, calcium-aluminate-sulfate-hydrate, calcium hydroxide, as well as calcium-carboxylate-salts (C-C-S) were observed in SB modified pastes before C-S-H in the FTIR spectra. In particular, the porous and negatively-charged carbonaceous surfaces of SB resulted in its adsorption of capillary water and reduced the flow of the swine-waste biochar modified cement pastes. With the addition of water to the dry swine-waste biochar/cement binder mix, chemical reactions between carboxylate anions from swine-waste biochar and calcium cations from Portland cement resulted in the development of Calcium-Polycarboxylate-Salts, which reduced the initial setting times of cement pastes modified with swine-waste biochar. Based on the dilution effect of the partial replacement of Portland cement with SB, the flow and setting of cement pastes are improved.
As early as 15 minutes after water was added to the dry binder mix of ordinary Portland cement with a 20% SB replacement by mass, C-C-S was observed and appears to accelerate setting of the cement pastes-chemical reactions between the calcium cations from Portland cement and carboxylate anions from SB can lead to the development of C-C-S, which can provide additional nucleation sites, accelerating the development of commonly observed calcium-silicate-hydrates (C-S-H). The spectroscopic shift for polymerizing silica for C-S-H was observed 270 minutes after the addition of water to the dry cement/SB binder mix for cement pastes with 20% SB;
The shorter initial and final times of setting obtained for SB modified cement pastes correlated with the early observation of C-C-S in the FTIR spectra, suggesting that C-C-S accelerated the setting and development of cement pastes modified with SB. Furthermore, SB in cement pastes contributed seeding sites to support the growth of hydrated products. In one embodiment, an SB replacement percentage of 15% at a 0.28 water/binder ratio showed a good setting time.
As shown herein, SB can be used as a partial cement replacement material. Without being bound by theory, carboxylate anions in SB react with calcium cations from Portland cement to form Calcium-Polycarboxylate-Salts (C-P-S), alongside the typical Calcium-Silicate-Hydrate (C-S-H) and Calcium Hydroxide (CH) from Portland cement hydration. These concurrent reactions accelerate the setting of SB modified cement paste and improve water penetration resistance.
In some embodiments the SB-modified cement has a reduced surface hardness.
The following Examples have been included to provide guidance to one of ordinary skill in the art for practicing representative embodiments of the presently disclosed subject matter. In light of the present disclosure and the general level of skill in the art, those of skill can appreciate that the following Examples are intended to be exemplary only and that numerous changes, modifications, and alterations can be employed without departing from the scope of the presently disclosed subject matter.
Experimental Materials and Methods
Type 1/1A normal Portland cement (specific gravity of 3.15 and a pH between 12 and 13) as specified by the American Society for Testing Materials (ASTM C-150) was purchased from Home Depot (Cobb County, Ga., U.S.). Potable water was obtained from a faucet in the Soils Laboratory at North Carolina Agricultural & Technical State University.
Swine-waste biochar (SB), a black carbon-rich powdery substance, was obtained from a thermochemical process as disclosed in Fini, E. H., Kalberer, E. W., Shahbazi, A., Basti, M., You, Z., Ozer, H., and Aurangzeb, A. “Chemical characterization of biobinder from swine manure: sustainable modifier for asphalt binder.” Journal of Materials in Civil Engineering, 23(11), 2011, 1506-1513.
In particular, about 1 gallon of swine manure slurry (typically about 80%-95% liquid by weight), was charged in a 1.5 gallon autoclave. Nitrogen gas was used to purge the reactor three times. The purged reactor was then heated over the course of ˜2.5 hours to a setting temperature of 340° C., and the pressure of raised to a reaction pressure of 10.3 MPa. The reaction was completed in about 15 minutes. The reactor was then cooled to room temperature using a recycled ice-water cooling coil over the course of at least about 2 hours. After cooling, the by-product gas was released from the autoclave, returning the reactor to atmospheric pressure.
The reaction mixture, including bio-oil, solid and aqueous phases, was vacuum filtered. The filtrate, typically referred to as black water, was isolated. The sticky residue was then rinsed once with 10-50% solvent (either acetone or a 30:70 acetone/toluene mixture) and vacuum filtered. The fine solid residue in the filter was isolated as bio-char
Table 1 shows the mix design for the cement pastes used in this Example.
Following the mix design for the different specimen listed in Table 1, the components (SB, cement, and water) were weighed. SB was manually dry mixed with cement until a uniform binder mix was obtained. Mixing overcame the cohesive interparticle van der Waals' forces present in SB clusters. Electrostatic interactions between SB and cement enhanced SB adsorption to the particle surfaces of cement, thereby creating a more uniform mix. The dry mixing process reduced the agglomeration of SB, enhanced its dispersion in cement powders, and improved the uniformity of the dry binder mix. After the dry binder mixing, the ASTM wet mechanical mixing process (ASTM C305-14) for cement pastes was followed (ASTM C305-14, Standard Practice for Mechanical Mixing of Hydraulic Cement Pastes and Mortars of Plastic Consistency. ASTM International, West Conshohocken, Pa. 2015, found at www.astm.org.)
The ASTM C1437 standard test for the flow of hydraulic cements assessed the impact of SB on the flow of cement pastes (ASTM C1437-15, Standard Test Method for Flow of Hydraulic Cement Mortar. ASTM International, West Conshohocken, Pa. 2015, found at www.astm.org.). After placing the specimens on the flow table, the flow table was dropped 25 times. Four different base diameter (d) readings of the spread cement paste specimen were taken at the four lines scribed on the flow table top. The average base diameter (da) was the sum of the four base diameters (d) divided by 4. The Flow Percent (F) is the resulting increase in the average base diameter (da) of the tamped specimen, expressed as a percentage of the original inside base diameter (D) of the mold (Equation 1).
F=(da˜D)/D×100 Equation 1
The ASTM C191 standard test was used to determine the time for setting of the cement paste specimens using the Vicat Needle Method as described in American Standards for Testing Materials (2013a). (ASTM C191-13, Standard Test Methods for Time of Setting of Hydraulic Cement by Vicat Needle, ASTM International, West Conshohocken, Pa., 2013, found at www.astm.org.) The initial setting time was recorded when a 25 mm needle penetration was obtained.
Fourier Transform Infrared (FTIR) spectroscopy at room temperature was used to characterize each of the cement, swine-waste biochar, and cement pastes, using a Varian 670 FTIR Spectrometer (4000 cm−1 to 500 cm−1). Scanning Electron Microscopy (SEM) was used to examine the microstructure of specimens using a Carl Zeiss Auriga SEM-FIB Crossbeam Workstation. The specimens were placed on carbon conductive tabs on stub mounts, and then positioned in the SEM equipment for imaging. Energy Dispersive Spectroscopy (EDS) analysis was used to provide elemental analysis of the specimens.
Results and Discussion
SEM and EDS of SB
The SEM images of SB clusters show rough exterior surfaces (
FTIR Spectra of SB and Cement
FTIR spectra (
Strong FTIR signals (
Flow of SB Modified Cement Pastes
The presence of SB reduced the flow of cement pastes. In particular, SB10.00 had the least flow percent (47%), while SB0.00 had the highest flow percent (77%),
Without being bound by theory the reduction in the flow of cement pastes supplemented with SB may be attributed to SB's carboxyl functional groups resulting in negative charges on the porous surfaces of SB. Upon addition of water the cement/SB binder dry mix, a portion of the water was adsorbed into the pores on the surface of carbonaceous SB. Due to its high surface areas and its high porosity, water was pulled into SB pores through capillary forces. The retention of some of the mixing water in the SB pores reduced the available mixing water. Higher replacement percentages of SB resulted in further reductions in capillary water, yielding closer packing of binder particles. Reductions in inter-particle distances were observed; as was increased viscosity and reduced flow of the SB-substituted cement pastes.
At a constant water/binder ratio, as the replacement percentage of SB was increased and that of cement was decreased, the flow of cement paste was reduced. Cement pastes with higher percentages of SB require higher water/binder ratios increasing the availability of mixing water, which improve flow and workability. The flow-reducing characteristic of cement pastes modified with SB provides for the development of flow-reducing binders.
Setting of SB-Modified Cement Pastes
The presence of SB reduced the initial setting times of cement pastes; however, the setting times for all the SB-substituted cement pastes were within the acceptable limits prescribed by ASTM.
Without being bound by theory, the difference between the initial setting times of cement pastes with SB and the control cement pastes may be attributed to the development of Calcium Polycarboxylate Salts (C-P-S), initiated when water was added to the dry cement and SB binder mix.
Together with the EDS results, these FTIR results demonstrate the development of C-P-S reduced the setting times of SB modified cement pastes. The presence of C-P-S resulted in the creation of additional nucleation or seeding sites that enhanced the precipitation of more hydrates in the pore space. As shown herein, the use of SB as a cement paste replacement has rapid-setting concrete applications.
Experimental Materials and Methods
Type 1/1A normal Portland cement (specific gravity of 3.15 and a pH between 12 and 13) as specified by the American Society for Testing Materials (ASTM C-150) was purchased from Home Depot. Potable water was obtained from a faucet in the Soils Laboratory at North Carolina Agricultural & Technical State University.
Swine-waste biochar (SB), a black carbon-rich powdery substance, was obtained from a thermochemical process as generally disclosed in Fini, E. H., Kalberer, E. W., Shahbazi, A., Basti, M., You, Z., Ozer, H., and Aurangzeb, A. “Chemical characterization of biobinder from swine manure: sustainable modifier for asphalt binder.” Journal of Materials in Civil Engineering, 23(11), 2011, 1506-1513.
In particular, about 1 gallon of swine manure slurry (typically about 80%-95% liquid by weight), was charged in a 1.5 gallon autoclave. Nitrogen gas was used to purge the reactor three times. The purged reactor was then heated over the course of ˜2.5 hours to a setting temperature of 340° C., and the pressure of raised to a reaction pressure of 10.3 MPa. The reaction was completed in about 15 minutes. The reactor was then cooled to room temperature using a recycled ice-water cooling coil over the course of at least about 2 hours. After cooling, the by-product gas was released from the autoclave, returning the reactor to atmospheric pressure.
The reaction mixture, including bio-oil, solid and aqueous phases, was vacuum filtered. The filtrate, typically referred to as black water, was isolated. The sticky residue was then rinsed once with 10-50% solvent (either acetone or a 30:70 acetone/toluene mixture) and vacuum filtered. The fine solid residue in the filter was isolated as bio-char
The elemental composition of SB was obtained using the scanning electron microscopy-energy dispersive spectra (Table 2).
Using a Zetasizer Nano-S (Malvern instrument) Dynamic Light Scattering (DLS) the mean particle size of SB was 509.6 nm and the SB surfaces were negatively charged.
Following the mix proportions for the SB-modified cement pastes listed in Table 3, cement and SB were manually dry mixed for about 5 minutes to obtain a uniform binder mix. Potable water was placed in the mixing bowl of a 4.73 liter ELE mechanical mortar mixer (ASTM C305 compliant). The dry cement/SB binder mix was then added and allowed to sit for 30 seconds for water absorption. The mechanical mixer was started at a slow speed (139 revolutions per minute) and then mixed for 30 seconds. The mixer was then stopped for 15 seconds and the sides of the mixing bowl were scrapped. The mixer was re-started and the paste was mixed at medium speed (285 revolutions per minute) for 60 seconds. The specimens were then immediately extracted for the Vicat setting tests.
For the FTIR and Raman spectroscopic analysis, cement and SB were manually dry mixed in a small plastic dish using the mix proportions listed in Table 3. Mixing water was then added to the dry ordinary Portland cement/SB binder mix and made to soak for 30 seconds for water absorption and then manually mixed for about 60 seconds. The specimens were extracted for FTIR and Raman tests. Shifts in characteristic peaks in the FTIR and Raman spectra were used to investigate hydration reactions during the setting of the modified cement pastes.
Fourier Transform Infrared Spectroscopy (FTIR) was used to obtain useful information regarding the development of key hydration products in SB modified cement pastes. FTIR analysis was conducted with a Varian 670 FTIR Spectrometer using a Pike “miracle” Attenuated Total Reflectance (ATR) accessory for Attenuated total internal reflection FTIR. In an ambient atmosphere, the background spectrum was collected before sample analysis. Sixteen scans were recorded over the measurement range between 400 and 4000 cm−1, with a spectral resolution of 4 cm−1. The obtained spectra were corrected with a linear baseline.
Raman Spectroscopy (Horiba XploRA One Raman Confocal Microscope System) was used to evaluate cement, SB, and all cement pastes. During each test, scanning was carried out from 150 cm−1 to 3500 cm−1. Samples were illuminated with a 532 nm laser. The exposure time for each scan was 10 seconds and about 1 minute was used to acquire each spectrum. The spectra were corrected using a linear baseline.
American Society for Testing and Materials (ASTM C191) for the time of setting of hydraulic cement by the Vicat Needle was followed to determine the initial setting times, as well as the final setting times of all cement pastes. The initial time of setting was recorded when a needle penetration of 25 mm was attained. Final setting was achieved when there was no complete circular penetration on the cement paste.
Results and Discussion
Early Hydration Products Detected by FTIR-ATR
FTIR (
Capillary Water:
While the dry cement and SB had limited water bands at 3360 cm−1, the 15-minute spectra in
Calcium-Aluminate-Sulfate-Hydrate:
Prior to the addition of water, the bend at 1124 cm−1 in the spectra for dry cement was assigned to S—O stretching for sulfates in cement. The 15-minute spectra (
Calcium-Carboxylate-Salts (C-C-S):
The earliest appearance of C-C-S was observed as weak bends on the FTIR spectra (1459 cm−1 and 1538 cm−1) as early as 15 minutes after water was added to CP-SB20. The weak bends become more distinct and strengthen with time as hydration progresses. More developed bends, as shown in the 60-minute spectra for CP-SB20, correlate to the salts of carboxylic acids. The weak peaks observed at 1538 cm−1 and 1575 cm−1 in the 60-minute spectra were assigned to carboxylate groups at multi-layer coverage in precipitated C-C-S. As shown in
Calcium-Silicate-Hydrate:
A key hydrate associated with strength development, C-S-H, was not detected early but emerged later in the 270-minute spectra for CP-SB20 (
The Si—O asymmetric stretching vibration of undissolved calcium silicates (910 cm−1) in Portland cement were still present in CP-SB00 and CP-SB10. Clinker (undissolved calcium silicates in cement) dissolution is typically correlated with C-S-H formation. Notably, the clinker bands almost completely disappeared in the 270-minute spectra for CP-SB15 and CP-SB20, suggesting that clinker consumption progressed at a much higher rate in SB modified cement pastes. Without being bound by theory, SB may have also created additional nucleation sites for the development of C-S-H, thus accelerating the polymerization of C-S-H in SB modified cement pastes. C-S-H developed on the calcium silicate particles, while calcium hydroxide crystals grow in the pore space.
Calcium Hydroxide:
FTIR stretches for calcium hydroxide (CH) were not observed in any of the 270-minute spectra. However, CH was observed at 3637 cm−1 in all the 7-day pastes (
Early Hydration Products Detected by Raman
In agreement with FTIR results, Raman spectra showed the presence of C—C (955 cm−1, 770 cm−1), C—COO (1574 cm−1, 875 cm−1), and C—H (1474 cm−1, 1353 cm−1) surface functional groups. Peaks for aluminates (761 cm−1, 525 cm−1), calcium silicates (849 cm−1), gypsum (1016 cm−1), and carbonates (1098 cm−1) were observed in the Raman spectra for Portland Cement. These data confirmed that SB is not inert, and that chemical reactions occurred when water was added to SB modified cement. Consistent with the data, four key hydration products were formed with the addition of water: calcium-carboxylate salts, calcium-silicate-hydrate, calcium-aluminate-sulfate-hydrate, and calcium hydroxide.
Calcium-Carboxylate-Salts (C-C-S):
After 60 minutes, the most dominant peaks during the setting of cement pastes modified with SB were for C—H (1469 cm−1, 1357 cm−1 and 1089 cm−1) and COO— (1598 cm−1 and 880 cm−1) in C-C-S in CP-SB15 and CP-SB20). An increase in the intensities of the CP-SB20 peaks (1338 cm−1, 1455 cm−1, and 1582 cm−1) corresponding to progressive increments in C-C-S was noted when the 90 minute spectrum for CP-SB20 was compared its 270 minute spectra. In the 270-minute spectra, a peak emerged at 1629 cm−1, which is attributed to aluminum-carboxylate-salts (A-C-S), formed from reaction of aluminum cations from the dissolution of tricalcium aluminates in cement with the carboxylate anions from SB.
Calcium-Silicate-Hydrate (C-S-H):
The peaks observed at 460 cm−1 and 625 cm−1 in CP-SB00 were assigned to polymerized C-S-H from the hydration of calcium silicates in cement; while in CP-SB15 and CP-SB20, the peaks at 430 cm−1 and 600 cm−1 were assigned to polymerized C-S-H. This shift to a lower Raman frequency for C-S-H was consistently observed in all the other SB modified cement pastes. Without being bound by theory, the lower C-S-H peaks in the SB modified pastes may be attributed to changes in the bond length and strength of C-S-H, as a result of the earlier development of C-C-S in the SB modified cement pastes. These findings provided strong evidence that C-C-S from SB had intruded in the growth and maturation of C-S-H, and perhaps weakened the linkages and microstructural development of C-S-H in the cement pastes modified with SB. The C-S-H peaks in the SB modified pastes appeared to be more intensive, suggesting that C-S-H had developed much faster in the SB modified pastes, as compared to the control paste. Without being bound by theory, this may be explained by the additional nucleation sites created by SC that allowed C-S-H to develop much faster in the SB modified cement pastes.
Calcium-Aluminate-Sulfate-Hydrate:
The peaks at 987 cm−1 in SB modified pastes and 995 cm−1 in CP-SB00 are assigned to ettringite. The lower Raman shifts for the hydrates in the SB modified cement pastes was attributed to the interference from C-C-S. Unhydrated calcium silicates were also observed at 519 cm−1 and 854 cm−1 in both pastes.
Calcium Hydroxide:
Two peaks (1483 cm−1 and 1613 cm−1) were assigned to calcium hydroxide in the control pastes These Raman peaks are masked by the C-C-S peaks in the cement pastes modified with SB.
Setting Times of Cement Pastes Vicat Needle Test
Results from the Vicat Needle Time of Setting Test (
Compared to CP-SB00, an 80% reduction in the final time of setting was observed when 20% of ordinary Portland cement was replaced with SB (CP-SB20). (
During the typical inactive induction period of the control cement pastes (CP-SB00), as shown herein C-C-S in cement pastes modified with SB continued to develop and mature. The presence of SB in pastes provided additional nucleation sites in the pore spaces and advanced the accelerated development and setting of the hydration products. These additional nucleation sites resulted in faster interactions and linkages among the different hydrated products, thus accelerating the setting of SB modified cement pastes. SB first disperses non-uniformly in the cement paste. After that, reactive carboxylic acid surface functional groups present in SB react with calcium ions from cement to form C-C-S. As hydration proceeded and the capillary water was consumed, C-C-S and other key Portland cement hydrated products coalesce to form a solid paste.
Experimental Materials and Methods
Type 1/1A Portland cement met the standard composition requirements specified by the American Society for Testing Materials (ASTM). Cement has a specific gravity of 3.15, and the bulk density of bagged cement is approximately 1000-1300 kg/m3. Mixing water was obtained from the Soils Laboratory at NC A&T State University.
SB340 is the black carbon that was obtained swine-manure as disclosed in Examples 1 and 2. After the initial isolation from a reaction at 340° C. (yielding ‘SB340’), SB340 underwent additional treatments at 400° C., 600° C., and 800° C. for 2 hours in a laboratory furnace in the presence of nitrogen gas, yielding specimens SB400, SB600, and SB800, respectively.
The elemental composition of each sample was obtained using the scanning electron microscopy-energy dispersive spectra. The samples were prepared by adhering the powder to an aluminum stub using carbon tape. An environmental SEM (Zeiss Evo LS-10) was used at 50 Pa operating pressure (N2 gas) and 20 kV gun voltage. The Zetasizer Nano-S (Malvern instrument) Dynamic Light Scattering instrument was used for particle size analysis.
The textural properties of samples were determined using the Micromeritics ASAP 2020 instrument. The dry samples (0.08 g-0.2 g) were degassed in a N2 atmosphere at a temperature of 120° C. for 4 h. The degassed sample was then subjected to physisorption analysis with N2 as the adsorbate gas in a liquid nitrogen bath at 77 K. The multilayer adsorption model by Brunauer-Emmett-Teller was used to calculate the surface area, while the pore volume was evaluated using the Barrett-Joyner-Halenda model.
FTIR analysis for surface functional groups of the samples was conducted using a Varian 670 FTIR Spectrometer with a Pike “miracle” attenuated total reflectance accessory for attenuated total internal reflection FTIR. In an ambient atmosphere, the background spectrum was collected before analyzing the samples. In total, 16 scans were recorded over the measurement range between 400 and 4000 cm−1, with a spectral resolution of 4 cm−1. The obtained spectra were corrected with a linear baseline.
Following the single-step method described in ASTM D7348-13, the loss of ignition (LOI) was used to estimate the volatile and organic matter in SB samples (American Society for Testing and Materials, 2013). Approximately, 1 g of SB was placed in a crucible and weighed (W1) before combustion in a furnace. The furnace was heated at 10° C./min to gradually raise its temperature to 500° C. at the end of 1 h. Heating was continued at a ramp rate of 8° C./min until temperature rose from 500° C. to 950° C. The combustion temperature was maintained at 950° C. for an additional 2 hours and then allowed to cool to room temperature. The crucible with SB ash was weighed (W2). The following equation was used to calculate LOI for each sample:
The dry bulk density (DBD) of the dry SB (10 g) samples was obtained by dividing the mass (M) of each sample by its corresponding volume (V) in a volumetric cylinder. The following equation was used to calculate the LBD of each sample:
The DBD of the dry cement/SB binder mix was obtained after manually mixing 8.5 g of cement with 1.5 g of SB for about 5 minutes to obtain a uniform dry cement/SB binder mix. The volume of the mix was measured using a volumetric cylinder. Using Equation (2), the DBD of the 10 g blended dry cement/SB binder were also determined. Table 4 shows the mix proportions for all the different dry cement/SB binder blends utilized in this example.
Following the mix design in Table 4, the dry cement/SB binders were manually mixed for about 5 minutes until a homogenous mix was obtained. After that, the ASTM wet mechanical mixing process (ASTM C305-14) was followed and the wet cement pastes were placed in 50 mm×50 mm×50 mm cube molds and sprinkle cured for seven days at room temperature (˜23° C.). After initial weights of 7-day and 28-day old cement paste samples were taken, they were oven dried and weighed every 24 hours until a consistent oven dry mass (M0) was obtained. Using the volume of each cube (Vc), the oven dry densities (ODD) of each oven dry cube sample was obtained using the following equation:
The samples were then fully immersed in water. The mass of each sample (Mt) was taken at specific times (t) after initial immersion (t=0). During the initial water absorption period, the mass (Mt) of each specimen at the following times (t) after initial water immersion: 1, 5, 10, 20, 30, 40, 50, and 60 minutes. The following equation was used to calculate the water absorption percentage (WAPt) for each sample at the specified time (t):
Results and Discussion
Physical characteristics of SBs
Table 5 shows that with increments in SB treatment temperatures, mean particle size reduced from 822 nm for SB340 to 405 nm for SB800. Particle size reductions were attributed to the fact that with increasing treatment temperatures, the more labile organic matter and volatile substances present on SB surfaces evaporated. SB surface areas increased from 9.3 m2/g for SB340 to 50.9 m2/g for SB600. This correlated well with pore volumes which also increased from 0.041 cm3/g in SB340 to 0.105 cm3/g in SB600. Lower surface areas and larger particle sizes observed in low treatment temperatures (LTT)-SBs (SB340,
SB400). At high treatment temperatures (HTTs) (600° C., 800° C.), the aromatization, dehydrogenation and dehydration of amorphous carbon chains to more crystalline carbons increased the total porosity. This implied that the release of the volatile components in SB resulted in the generation of more micropores in SB thereby reducing the particle sizes, while increasing the surface areas and pore volumes in HTT-SBs.
The surface area of SB800 was ˜50% less than that of SB600. This is indicative of the fact that the formation of the high ash content (at 800° C.) resulted in the collapse of the pore structure, thereby decreasing the average pore volume and surface area, but increasing the pore diameter. The lower LOIs obtained for HTT-SBs confirmed their higher ash content and lower volatile matter when compared to the LTT-SBs. The loss of volatile matter is mostly attributed to reactions associated with organic carbon burning. All the SBs had LOI values that were lower than the allowable maximum LOI limits specified for fly ash in ASTM C618-17 (American Society for Testing and Materials, 2017). Considering that unburned carbon in cement replacement materials such as fly ash significantly affects the color and water requirement for normal consistency in concrete mixtures, SBs with LOIs lower than specified ASTM limits are most beneficial for concrete performance. The dry bulk densities of LTT-SBs were slightly higher than those of HTT-SBs as a result of the more dominant presence of volatile matter in LTT-SBs. However, all SB samples had bulk densities that were <50% of the bulk density of cement (1.00 g/cm3). Compared to SBs, Portland cement had lower surface area (2.3 m2), pore diameter (9.4 nm), and pore volume (0.004 cm3/g).
SEM images revealed the porous and amorphous surfaces of clusters of SB340, SB600, and SB800. In agreement with the pore diameter results, SB600 appeared to have the most uniform surfaces with smaller SB clusters and pore sizes. Significant textural differences were not observed in the bio-chars because they were of the same feedstock.
Surface Elemental Composition
Table 6 shows that carbon and oxygen were the dominant elements in SB. Carbon content reduced from SB340 (46.9 percent) to SB600 (28.75 percent), after which it increased in SB800 (53.76 percent). This was because as treatment temperature increased from 340° C. to 600° C., decarbonation of the amorphous/labile carbon portions of the organic matter (celluloses, lignin, sugars,
hydrocelluloses, aminoglycans) also increased. Although the amorphous carbon content decreased with increasing temperature, the more crystalline Sp2 hybridized (aromatic and olefins) recalcitrant carbon fractions of the SB (which are more resistant to thermal degradation) increased as temperature was increased to 800° C. The decarbonation of amorphous carbon was accompanied by increases in the percentage of minerals. The composition of minerals increased from 14.48% in SB340 to 26.98% in SB600. The reduction of minerals components from 26.98% in SB600 to 11.77 percent in SB800 was attributed to the melting and vaporization of minerals such as phosphorus at 800° C.
The O/C ratio was highest in SB600 (1.54) and lowest in SB800 (0.64). At 600° C., there was significant decomposition of the mineral oxides and oxygenated salts resulting in the increase in oxygen. In contrast the very low O/C ratio at 800° C. indicated that most minerals had been converted to ashes with minimal oxygen content at that temperature. Concurrently, minerals such as phosphorus were reduced as well in SB800, when compared to the lower temperature SBs. Phosphorus was the most dominant element in SB800.
Surface Functional Groups by FTIR
Compared to SB340, aromatic C═O and C═C in esters and carboxyl groups in SB600 decreased with temperature increases as indicated by the reduction in intensity peaks at 1,745-1,508 cm−1. Notably, the stretches from 1,000 to 1,300 cm−1 for C—O in esters and carboxyl groups were dominant in both SB340 and SB600.
Effect of SB Percentage on Water Absorption
Reduction in WAPs of SB modified cement pastes is mostly attributed to the presence of hydrophobic aliphatic C—H surface functional groups in residual bio-oils and tars that were unable to escape at 340° C. (
Despite the fact that cement had lower surface areas (2.3 m2) and smaller pore volumes (0.004 cm3/g) when compared to SB340, the control cement pastes (CP0.00) still absorbed more water. This confirmed that SB surface functional groups, and not textural properties, greatly influenced the water absorption differences observed between the control cement paste (CP0.00) and the SB modified cement pastes. As shown in
Effect of Water/Binder Ratio on Water Absorption
As a greater volume of the pastes were occupied by water, a less dense paste with a weaker microstructure resulted. Upon the evaporation of excess water during oven heating, the escaped water left greater voids in the 0.4 pastes. This led to an overall increase in the capillary porosity of the 0.4 water/binder pastes, and consequently, a more positive water sucking pressure that imbibed more water to fill the empty capillary pores within the pastes.
Effect of SB Treatment Temperatures on the Water Absorption
Among all the seven-day old samples,
Results shown in
Contrary to LTT-SB cement pastes, HTT-SB pastes (CP15-600, CP15-800) had WAPs similar to the control paste. Notably, no statistically significant differences (p<0.05) existed among control pastes (CP0.00-NO SB), CP15-600, and CP15-800. From
CP15-600 had the highest WAPs because coupled with the lack of hydrophobic alkyl groups, CP15-600 was modified with SB600, which had the highest surface areas and pore volumes (Table 5). However, compared to CP15-600, CP15-800 had a slightly lower WAP because it had slightly lower surface areas and pore volumes (Table 5). Considering its low LOI and high mineral content, this was attributed to the high ash content in SB800 which had degraded the pores and as such resulted in a slight reduction of its surface areas and pore volumes.
Table 7 shows that the control cement and pastes had higher DBDs and ODDs when compared to SB modified binders and their respective pastes. The lower bulk densities of SB modified powders and their associated pastes were as a result of the lower dry densities of the SBs (Table 5) that were used to partially replace cement in the SB modified pastes.
Despite the higher densities associated with control pastes, they had higher WAPs. This provided a strong indication that the lower WAPs observed in LTT-SB modified cement pastes were not associated with their lower oven dry densities, but rather mostly resulted from the hydrophobic behavior of the surface functional groups of LTT-SBs.
Effect of Aging on Water Absorption
In summary, SB treatment temperatures modified SB chemical composition and textural properties. Notably, LTT increased hydrophobicity of SB, while higher temperature treatments increased hydrophilicity. Consequently, the changes in the physical and chemical properties of SB exhibited a profound effect on the WAPs of SB modified cement pastes. By homogeneously mixing water with the dry cement/SB binder, SB was dispersed within the cement paste matrix. As hydration progressed and capillary water was consumed, key hydration products grew into the pore space that was originally occupied by water. The cement paste then set and developed strength; however, with capillary porosity within the cement paste matrix. The presence of hydrophobic alkyl functional groups from LTT-SB altered surface chemistry of the capillary pores within the hardened LTT-SB modified cement paste. Considering that these pores provided the primary transport routes in and out of the cement paste, changes in the surface chemistry of the pores reduced capillary water absorption; improving the durability of the cement pastes disclosed herein.
It will be understood that various details of the presently disclosed subject matter may be changed without departing from the scope of the presently disclosed subject matter. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation.
The presently disclosed subject matter claims the benefit of U.S. Provisional Patent Application Ser. No. 62/670,381 filed May 11, 2018; the disclosure of which is incorporated herein by reference in its entirety.
This invention was made with government support under Grant Number 1546921 awarded by the National Science Foundation. The government has certain rights in the invention.
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| Number | Date | Country | |
|---|---|---|---|
| 20190345061 A1 | Nov 2019 | US |
| Number | Date | Country | |
|---|---|---|---|
| 62670381 | May 2018 | US |
