UTILIZATION OF HEAVY OIL ASH TO PRODUCE HIGH QUALITY CONCRETE

Inventors: Mohammed Al-Mehthel

Mohammed Maslehuddin

Abdulaziz S. Al-Utaibi

Mohammed Rizwan Ali

Assignees: Saudi Arabian Oil Company and

King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia

BACKGROUND OF THE INVENTION

Field of _, the Invention

[0001] The present invention relates to a method and apparatus for producing high quality concrete utilizing heavy oil ash. More specifically, the invention relates to using heavy oil ash instead of, or in addition to, cement to produce high quality heavy oil ash Portland cement concrete.

Description of the Related Art

[0002] Conventional concrete can typically have Portland cement and water, plus any of a variety of aggregates, such as sand or gravel. Upon mixing, a "hydraulic reaction" occurs between the water and the cement, and. the result is a cement paste that binds the aggregates together. High quality concrete can be produced by adding silica fume or fly ash as a partial replacement or as an addition to the Portland cement. The silica fume and fly ash can react with calcium hydroxide from the cement (pozzolanic reaction). The pozzolanic reaction can increase the strength and denseness of concrete after it cures. Unfortunately, these pozzolans are relatively expensive and, thus, increase the cost of the concrete.

SUMMARY OF THE INVENTION

[0003] In view of the foregoing, concrete mixtures that include heavy oil ash, and methods of preparing the heavy oil ash cement concrete mixtures, are provided as embodiments of the present invention. Oil Ash (OA) is a black powder type of waste material that results from burning oil in power generation plants.

[0004] In embodiments, OA is used as a partial replacement of. or as an addition to. the cement to produce high quality OA-Portland cement concrete. The properties of OA cement concrete are better than those of ordinary Portland cement concrete. In embodiments, up to 5% OA can be used as a replacement of cement resulting in an increase to the 28-day compressive strength of concrete by 28% compared to concrete made with 100% ordinary Portland, cement (OPC): up to 5% OA can be used as a replacement of cement resulting in a decrease of the 28-day concrete permeability to chloride by more than 50% compared to concrete made with 100% OPC; up to 10% OA can be used as an addition to concrete resulting in an increase to the 28-day compressive strength of concrete by approximately 25% and decrease to the 28-day concrete permeability to chloride by more than 50%, compared to concrete made with 100% OPC.

[0005] A significant quantity of OA is produced due to burning of heavy or cracked fuel oil in power generation plants. This quantity is expected to increase with further increases in the use of heavy or cracked oil. Therefore, it is desirable to use this byproduct as a useful material. The utilization of OA in construction materials would also find an outlet for this byproduct material, protect the environment and eliminate the need for building special areas to dispose of OA.

[0006] Presently, high quality concrete is produced with the use of silica fume or fly ash as pozzolanic materials. Both fly ash and silica fume are expensive. This invention will eliminate the need for using fly ash and silica fume to produce high quality concrete. Embodiments can reduce the required quantity of cement, thus decreasing the cost of resulting concrete, while also reducing the carbon foot print. Embodiments include a method of disposing of OA by using the OA to produce high quality concrete. Embodiments can reduce or eliminate the requirements for special disposal facilities for OA. Furthermore, the concrete produced with OA can have better quality than concrete produced using only- ordinary Portland concrete ('OPC").

[0007] In embodiments, a heavy oil ash cement concrete can include aggregates, heavy oil ash fines, which can be made up of at least 90% carbon and at least 80% of the heavy oil ash fines can be finer than 45 micrometer (#325 sieve), wherein the heavy oil ash fines do not have cementitious properties, and do not react with lime. Embodiments can also include water and. cement, the heavy oil ash cement concrete being the result of mixing of the water and cement in the presence of the heavy oil ash fines and aggregate. The heavy oil ash cement can have a cement matrix, that defines a plurality of pores, with the heavy oil ash fines filling at least a portion of the plurality of pores.

[0008] in embodiments of the heavy oil ash cement concrete, the cement can be Portland cement, and the proportion of water, Portland cement, heavy oil ash fines, and aggregates can be approximately 8 parts water, 19 parts cement, 1 part heavy oil ash fines, and preferably 99 parts aggregate. In embodiments, the cement can be Portland cement and the water to Portland, cement ratio can be approximately 0.4 to 0.44 and. the weight of the heavy oil ash fines can equal approximately 5% to 10% of the w eight of the Portiand cement.

[0009] in embodiments, the cement can be Portiand cement, and the proportion of water, Portland cement, heavy oil ash fines, and aggregates can be approximately 8 parts water, 20 parts cement, 1 part heavy oil ash fines, and preferably 99 parts aggregate. The heavy oil ash concrete can be free of fly ash and silica fume. The weight of the heavy oil ash fines can be about 5% to about 10% of the weight of the cement. In embodiments, the weight of the heavy oil ash fines can be at least about 5% of the weight of the cement. The compressive strength of the heavy oil ash cement concrete, after 28 days of curing, can be at least 68 MPa. In embodiments, at least 28 days after curing, a chloride permeability of the heavy oil ash cement concrete can be less than 2,000 Coulombs.

[0010] Embodiments of the invention can include a method of disposing of heavy oil ash. The method can include the steps of providing a predetermined, quantity of a cement; providing a predetermined quantity of water, with the predetermined, quantity of water being between about 35% and. 50% the predetermined, quantity of the cement. The method can also include the steps of preparing a predetermined quantity of heavy oil ash fines, the predetermined quantity of heavy oil ash fines having a weight up to about 10% by weight of a weight of the predetermined quantity of the binder, and the heavy oil ash fines having a carbon content greater than about 90%. The method can also include the steps of preparing a predetermined quantity of aggregate, and combining the cement, water, aggregate, and heavy oil ash such that the cement and water react to create the heavy oil ash cement concrete, the heavy oil ash cement having a cement matrix, the cement matrix defining a plurality of pores, and the heavy oil ash filling at least a portion of the plurality of pores.

[0011] in Embodiments, the cement can include Portiand cement. In embodiments, the step of providing heavy oil ash fines can include burning a heavy fuel oil to produce the heavy oil ash fines. The ratio of water, cement, heavy oil ash fines, and aggregates can be approximately 8 parts w ^r ater, 19 parts cement. I part heavy oil ash. and preferably 99 parts aggregates. In embodiments, the heavy oil ash fines do not react with lime. The heavy oil ash fines can include, by weight, about 5% to about 10% of the heavy oil ash cement concrete.

[0012] in embodiments of the heavy oil ash cement concrete, the heavy oil ash cement concrete can include water; Portland cement; aggregate; and heavy oil ash fines which can include heavy oil ash and be substantially free of fly ash and silica fume. The heavy oil ash can include at least 90% carbon and at least 80% of the heavy oil ash can be finer than 45 micrometer (#325 sieve). In embodiments, the heavy oil ash does not have cementitious properties and is not reactive with lime. In embodiments, the heavy oil ash cement concrete is the result of mixing the water and Portland cement in the presence of the heavy oil ash fines and aggregate. The heavy oil ash cement can have a cement matrix, which can define a plurality of pores and the heaw oil ash fines can fill at least a portion of the plurality of pores.

[0013] In embodiments, the weight of the heavy oil ash fines can equal at least 5% of the weight of the Portland cement. The water to Portland cement ratio can be approximately 0.4 and the weight of the heavy oil ash fines can equal approximately 5% to 10% of the weight of the Portland cement. The ratio of water, Portland cement, heavy oil ash, and aggregates can be approximately 8 parts water, 20 parts cement, 1 part heavy oil ash fines, and preferably 99 parts aggregate. In one embodiment, at least 28 days after curing, a chloride permeability of the oil ash concrete is less than 2000 coulombs.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] So that the manner in which the above-recited features, aspects and advantages of the invention, as well as others that will become apparent, are attained and can be understood in detail, more particular description of the invention briefly summarized above can be had by reference to the embodiments thereof that are illustrated in the drawings that form a part of this specification. It is to be noted, however, that the appended drawings illustrate some embodiments of the invention and are, therefore, not to be considered limiting of the invention's scope, for the invention can admit to other equally effective embodiments.

[0015] FIG. 1 is a graph showing the compressive strength development in various embodiments of heavy oil ash concrete having heavy oil ash ("HOA") used, as a replacement of a portion of cement.

[0016] FIG. 2 is a graph showing chloride permeability in various embodiments of heavy oil ash concrete having HOA used as a replacement of a portion of cement.

[0017] FIG. 3 is a graph showing corrosion potentials in various embodiments of heavy oil ash concrete having HOA used as a replacement of a portion of cement.

[0018] FIG. 4 is a graph showing corrosion current density on steel in various embodiments of heavy oil ash concrete having HOA used, as a replacement of a portion of cement. [0019] FIG. 5 is a graph showing compressive strength development in various embodiments of heavy oil ash concrete having HOA used as an addition to the concrete.

[0020] FIG. 6 is a graph showing chloride permeability in various embodiments of heavy oil ash concrete having HOA used, as an addition to the concrete.

[0021] FIG. 7 is a graph showing corrosion potentials in various embodiments of heavy oil ash concrete having HOA used as an addition to the concrete.

[0022] FIG. 8 is a graph showing corrosion current density on steel in various embodiments of heavy oil ash concrete having HOA used as an addition to the concrete.

DETAILED DESCRIPTION OF THE INVENTION

[0023] Heavy oil ash is a residue resulting from the combustion of heavy oil or cracked oil. Heavy oil is generally defined as fuel oil having relatively long hydrocarbon chains such as, for example, carbon lengths of between about 12-70 carbon atoms or between about 20-70 carbon atoms. Heavy fuel oil can be classified as "No. 5 fuel oil" or "No. 6 fuel oil" as classified by the American Society for Testing and Materials (ASTM). Due to its high viscosity, heavy fuel oil is sometimes preheated before combustion in, for example, a power generation plant.

[0024] Cracking, in the oil refining industry, generally refers to breaking down complex organic molecules into simpler molecules by breaking the long-chain hydrocarbons into shorter hydrocarbon chains. Various processes can be used to crack oil including, for example, catalytic processes. After the cracking process, the resultant hydrocarbons can be separated into various types of fuel, including, for example, fuel gas, liquefied petroleum gas ("LPG"), gasoline, light cycle oils, and heavy fuel oil. The heavy fuel oil produced by the cracking process can be referred to as "cracked fuel oil." For purposes of this application, cracked fuel oil and heavy fuel oil are both referred to as heavy fuel oil, unless othenvise specified. Electricity production plants can use heavy fuel oil and are expected to use increasing quantities of heavy fuel oil in the future. Combustion of heavy fuel oil produces residue, including ash. As one of ordinary skill will appreciate, the heavy oil ash can, and to some extent must, due to environmental restrictions, be captured rather than being released into the atmosphere.

[0025] Heavy oil ash ("HOA") is a black powder type of waste material that results from burning of heavy oil. Heavy oil ash has unique characteristics compared to other types of ash. Typically, heavy oil ash includes more than about 90% by weight carbon. The remaining less than about 10% by weight of the heavy oil ash can frequently include sulfur, magnesium, and vanadium. Heavy oil ash can include various particle sizes. In one embodiment, about 16% by weight of the heavy oil ash is retained on a #325 sieve, while about 84% by weight of the material passes through the #325 sieve. This indicates that about 84% by weight of the ash can be finer than about 45 micrometers. As used herein, the term "about" is understood to include values thai are within 5% of the stated value.

[0026] Heavy oil ash can contain various elements. For example, Table 1 presents a typical chemical analysis of HOA. The amounts of each element can vary depending upon the source of the heavy oil fly ash. The HOA used in embodiments of the present invention can contain more than about 90 wt. % carbon because it is formed by burning heavy oils.

[0027] As can be seen in Table 1 , the elemental composition of the HOA used in embodiments of the present invention is substantially different from that of traditional fly ash thai has been previously used in concrete.

[0028] Unlike HOA, traditional fly ash is generally produced by burning coal. The main chemical components of the traditional fly ash are silicon dioxide (Si0 ₂ ), aluminum oxide (AI ₂ O ₃ ), and iron oxide (Ρε ₂ 0 ₃ ) and it is in accordance with ASTM C618. Fly ash is generally categorized depending on the type of coal burned. For example, class F fly ash is produced by burning anthracite and bituminous coal, while Class C fly ash is produced by burning lignite or sub-bituminous coal.

[0029] Concrete is a composition made from cement, water, and aggregate or aggregates. While "aggregate" can be plural, the term "aggregates" generally refers to more than one type or more than one size of aggregate. Cement is a binder that can bind the aggregates together. Ordinary Portland cement ("OPC") is one such binder that can bind to other materials, such as fine and coarse aggregates, thereby holding them together. A material that is a paste that can harden to bind materials together, in the manner of cement, is said to be a cementitious material or to have cementitious properties. One of skill in the art will appreciate that water can be added to dry cement to make cement paste. The water-cement ratio ("w/c ratio") of OPC is typically between about 0.25 and 0.5. By way of explanation, a w/c ratio of 0.25 indicates that there is one part water to four parts Portland, cement (1/4=0.25). A w/c ratio of 0.5 indicates one part water to two parts cement.

[0030] As one of ordinary skill will appreciate, various types of conventional aggregates can be used as a filler in the concrete. As one of skill in the art will appreciate, the term "aggregates" can refer to aggregate of multiple types or sizes. Aggregate can include, for example, sand, gravel, crashed rock, slag, or any other type of aggregate. When aggregate is used in concrete, the cement generally coats the aggregates and then binds them together in a matrix. When aggregates of various sizes are used, the smaller aggregate materials can fill voids between the larger aggregate materials, thus creating a more dense matrix. The aggregates used in concrete can be defined in terms of coarse aggregate and fine aggregate. Fine aggregates, also referred to as "fines," can include natural sand, crushed stone, or other suitable fine particles, with most particles smaller than 5 mm. Coarse aggregates generally include gravel or crashed stone with particles predominantly larger than 5 mm and typically between 9.5 mm and 37.5 mm.

[0031] A pozzolan is a finely divided siliceous or siliceous and aluminous material that reacts chemically with slaked lime (calcium hydroxide) at ordinary temperature and in the presence of moisture to form a calcium silicate hydrate or other cementitious compounds. A material that has such pozzolanic properties is considered a pozzolan. Fly ash is a pozzolan. When fly ash is used in concrete, in conjunction with Portland cement, it can contribute to the properties of the hardened concrete through hydraulic or pozzolanic activity, or both. Therefore, fly ash can be used in concrete as an additive or partial replacement of cement.

[0032] When cement is mixed with water, chemical reactions cause the cement to crystallize and the crystals interlock the aggregates thereby giving strength to concrete. During this reaction, lime (calcium hydroxide} can become available within the concrete. It is this lime thai can react with fly ash to give concrete increased strength. Over time, lime in the cement reacts with fly ash to fill the pores in the concrete and to further bind the concrete. The strength of concrete is often measured at 28 days because of the additional strength developed over the first 28 days as the fly ash reacts with the lime.

[0033] The standards controlling fly ash for use as a pozzolanic material are defined by ASTM C618. In particular, the carbon content, measured by the loss on ignition ("LOI") should be less than 6% or 4%, depending on the governing body. Because of the pozzolanic properties, it is common to make concrete wherein 30% or more of the Portland cement is replaced with fly ash. Similarly, silica fume, also having pozzolanic properties, can be used as a cement binder in concrete.

[0034] In contrast to the foregoing uses of fly ash in concrete, concrete mixtures that include heavy oil ash are provided as embodiments of the present invention. In embodiments of the present invention, the heavy oil ash contains more than about 90 wt. % carbon. In an aspect, the heavy oil ash does not have cementitious or pozzolanic properties. Indeed, the HOA generally does not react with calcium hydroxide, or lime. In embodiments, the LOI of HOA is greater than 60%. In embodiments, the LOI of HOA is greater than 75%. In embodiments, the LOI of HOA is greater than 85%. In some embodiments, no processing of the HOA is required prior to using it in the HOA cement concrete. In some embodiments, no processing to reduce the carbon content is required or used.

[0035] In various embodiments, the concrete of the present invention can include cement, water, heavy oil ash, and aggregates to create "heavy oil ash cement concrete" or HOA cement concrete. In one embodiment, voids, gaps, or pores (collectively referred to as "pores") can exist within the concrete matrix, and. substantially all or at least a portion of the pores can be filled with HOA fines. In some embodiments, fly ash or silica fume is not used in the HOA cement concrete. In other embodiments, the HOA cement concrete is substantially free of fly ash and silica fame.

[0036] In one embodiment, up to 10% by weight of the Portland cement can be replaced with heavy oil ash. The compressive strength of the HOA cement concrete can be greater than the compressive strength of OPC concrete. Up to 10% HOA can be used as replacement of cement. In some embodiments, for example, about 7% of the cement is replaced with HOA. In one embodiment wherein 5% of the Portland cement is replaced by HOA, the compressive strength of the HO A cement concrete is about 30% greater than the compressive strength of OPC concrete. In one embodiment wherein 5% of the Portland cement was replaced with HOA, the compressive strength of the HOA concrete was at least 68 MPa. Furthermore, in this embodiment, the 28 day concrete permeability to chloride is decreased by more than 50%. Indeed, in one embodiment, the chloride permeability of the HOA concrete, 28 days after curing, can be less than 2000 coulombs.

[0037] One embodiment is based on concrete having 2 parts water and 5 parts cement, thus having a w/c ratio of 0.4. In this embodiment, however, approximately 5% of the cement is replaced with HOA. Due to the replacement, the composition of the mixture is approximately 8 parts water, 19 parts cement, and 1 part HOA. The w/c of this embodiment is, thus, 0.421. Similarly, in some embodiments, the w/c ratio is approximately 0.42 to 0,44. In some embodiments, the w/c ratio can be approximately 0.4 to 0.44. In some embodiments, the amount of water in the mixture can be between about 35% and 50% of the amount of cement. In some embodiments, the weight of the HOA can equal approximately 5-10% of the weight of the Portland cement. Embodiments can have about 1 to about 99 parts aggregates. A preferred embodiment can have about 99 parts aggregates.

[0038] In one embodiment, heavy oil ash can be added to Portland cement concrete mixture, wherein the amount of HOA is equal to or up to 10% of the weight of the Portland cement. In this embodiment, wherein HOA equal to 10% of the weight of the Portland cement, is added to the concrete mixture, the compressive strength of the HOA concrete, after it cures, is about 25% greater than the compressive strength of OPC concrete. Furthermore, in this embodiment, the 28 day concrete permeability to chloride is decreased by more than 50%>.

[0039] In an alternate embodiment, a concrete mixture having a composition that includes approximately 8 parts water, 20 parts cement, and 1 part HOA is provided, thus having a w/c ratio of about 0.4. The composition can include HOA that has been added, in an amount up to about 10% by weight of the cement, for example OPC, or in certain embodiments between about 5% and 10% by weight of the cement. Embodiments can have about 1 to about 99 parts aggregates. A preferred embodiment can have about 99 parts aggregates.

EXAMPLES

[0040] Table 2 shows the cement, water, and heavy oil ash mixtures of various exemplary embodiments. In embodiments defined as "Replacement," the defined percentage of HOA is used to replace the same amount, by weight, of Portland cement. Because that percentage of Portland cement has been removed, the w/c ratio is increased. In embodiments defined as "Addition," the HOA is added to the mixture and, thus, the w/c ratio is not changed.

[0041 ] The compressive strength development in the HOA cement concrete specimens prepared with varying proportions of HO A, as a replacement of cement, is depicted in Figure 1. The compressive strength increased with age in all the specimens. In some embodiments, maximum compressive strength was noted in the concrete specimens prepared with 5% HOA, as a replacement of cement, while the minimum compressive strength was noted in the concrete specimens prepared with 10% HOA. The compressive strength of 0% HOA and 7% HOA was almost similar. The compressive strength of 0, 5, 7, and 10% HOA cement concrete specimens, after 90 days of curing, was 54, 68, 56, and 50 MPa, respectively .

[0042] The chloride permeability in the HOA cement concrete specimens prepared with varying percentages of HOA. as a replacement of Portland cement, is shown in Figure 2. Maximum chloride permeability, both at 28 and 90 days, was noted in the concrete specimen prepared without any HOA while minimum chloride permeability was noted in the concrete specimens with 5% HOA,

[0043] The corrosion potentials on steel in the concrete specimens prepared with varying percentages of HOA, as a replacement of cement, are shown in Figure 3. The corrosion potential increased (i.e., became more negative) with age in all the concrete specimens. After about 250 days, the maximum potentials (the most negative values) were noted, in the concrete specimens prepared without any HOA while the minimum potentials (most positive) were noted in the concrete specimens with 5% HOA. The horizontal line 300 represents the ASTM C876 threshold value, which is -270 mV SCE. [0044] Figure 4 depicts the corrosion current density on steel in the HOA cement concrete specimens prepared with various percentages of HOA as a replacement of cement. The corrosion current density was the minimum in the concrete specimens prepared with 5% HOA.

[0045] The data in Figures 1 through 4 indicate that the compressive strength and durability characteristics of 5% HOA, used as a replacement of cement, were better than those of control and other concrete specimens.

Evaluation of HOA as an addition to Concrete

[0046] The compressive strength development in HOA cement concrete specimens prepared with various percentages of additional HOA, added as an addition to concrete, is plotted in Figure 5. The compressive strength increased, with age in all the concrete specimens. Further, the compressive strength increased with an increase in the HOA content in the concrete. After 90 days of curing, the compressive strength of concrete specimens with 0, 5, 7, and 10% HOA was 54, 56, 60, and 65 MPa, respectively. The increased compressive strength of concrete specimens prepared with HOA can be attributed to the filler effect of this material

[0047] The chloride permeability in the HOA cement concrete specimens prepared with varying additional quantities of HOA, as an addition to concrete, is shown in Figure 6. Maximum chloride permeability was noted, in the concrete specimens prepared without any FIOA. The chloride permeability generally decreased with increasing quantity of HOA. A more or less similar pattern was noted in the concrete specimens cured for 90 days.

[0048] The corrosion potentials on steel in the HOA cement concrete specimens prepared with varying additional quantities of HOA, as an addition to concrete, are depicted in Figure 7. The potentials generally tended to increase (became more negative) with time and decreased (became less negative) with increasing quantity of HOA, The horizontal line 700 represents the ASTM C876 threshold, value, which is -270 mV SCE.

[0049] The corrosion current density on steel in the FIOA cement concrete specimens prepared with varying additional quantity of FIOA, as an addition to concrete, is plotted in Figure 8. The corrosion current density on steel in 10% HOA cement concrete was very low compared to that in the other cement concrete specimens.

[0050] As shown in Table 3, the results in Figures 5 through 8 indicate that the mechanical properties and durability characteristics of concrete specimens prepared with HOA as an addition were better than the control mixes. Further, both the strength and durability increased with increasing quantity of HOA.

Table 3: Comparison between concrete made with HOA, and OPC

[0051] The concentration of heavy metals leached from the HOA cement concrete are shown in Table 4. All the heavy metals are within the allowable limits.

Table 4: Concentration of metals in HOA cement concrete

[0052] The above results indicate that 5% replacement of cement with HO A or up to 10% addition of HOA to concrete is helpful in producing high quality concrete.

[0053] Although the present invention has been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereupon without departing from the principle and. scope of the invention. Accordingly, the scope of the present invention should be determined by the following claims and their appropriate legal equivalents. [0054] The singular forms "a", "an" and "the" include plural referents, unless the context clearly dictates otherwise.

[0055] Optional or optionally means thai the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0056] Ranges may be expressed herein as from about one particular value, and'or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particuiar value and ^' or to the other particuiar value, along with all combinations within the said range.

[0057] Throughout this application, where patents or publications are referenced, the disclosures of these references in their entireties are intended to be incorporated, by reference into this application, in order to more fully describe the state of the art to which the invention pertains, except when these reference contradict the statements made herein.