Method and apparatus for the curing of composite material by control over rate limiting steps in water removal

Abstract

The invention encompasses equipment used to condition a recirculating gas stream in order to cure a CO.sub.2 Composite Material (CCM) and processes that use such equipment to cure the CCM. The gas conditioning equipment allows for a process that controls, reduces or eliminates the rate-limiting steps associated with water removal during the curing of a composite material. The equipment may include, but will not be limited to, control over the temperature, relative humidity, flow rate, pressure, and carbon dioxide concentration within the system; which includes the conditioning equipment, any vessel containing the CCM, and the material itself. Flow rate control can be used as a means to achieve uniformity in both gas velocity and composition.

Claims

1. A controller, comprising: a microprocessor configured to operate under control of a set of instructions recorded on a first machine-readable medium, said microprocessor when operating under said set of instructions performing: controlling operation of at least one of a source of carbon dioxide, a gas flow subsystem, a temperature control subsystem, and a humidity control subsystem; flowing a process gas containing carbon dioxide so as to contact a material to be cured by reaction with said carbon dioxide in said process gas, and curing the material by the reaction with carbon dioxide; monitoring at least one parameter selected from a group of monitored parameters consisting of an elapsed time from said instituting of said flow, a carbon dioxide concentration, a relative humidity, a flow rate, a temperature, and a pressure of said process gas as said process gas is being provided; and performing at least one of: recording said at least one parameter, transmitting said at least one parameter to a data handling system, or to displaying said at least one parameter to a user.

2. The controller of claim 1, wherein said microprocessor when operating under said set of instructions receives a start command from an external source.

3. The controller of claim 1, wherein said microprocessor when operating under said set of instructions determines a state of cure of said material to be cured by reaction with said carbon dioxide.

4. The controller of claim 1, wherein said microprocessor when operating under said set of instructions monitors at least one parameter selected from the group of parameters consisting of a carbon dioxide concentration, a relative humidity, a flow rate, a temperature, a pressure, and a flow duration of said process gas as said process gas is removed from contact with said material to be cured by reaction with said carbon dioxide.

5. The controller of claim 1, wherein said microprocessor when operating under said set of instructions monitors at least one parameter selected from the group of parameters consisting of a carbon dioxide concentration, a relative humidity, a flow rate, a temperature, and a pressure at one or more locations within a curing chamber.

6. The controller of claim 1, wherein said gas flow subsystem comprises: at least one of a valve, a flow regulator, a mass flow controller, a blower, and a gas delivery structure; said gas flow subsystem configured to provide a process gas comprising carbon dioxide as a reagent in fluid contact with a material to be cured by reaction with said carbon dioxide.

7. The controller of claim 1, wherein said gas flow subsystem is compatible with water vapor in addition to said process gas comprising carbon dioxide as a reagent.

8. The controller of claim 1, wherein said gas delivery structure is a gas permeable layer placed adjacent the material to be cured by reaction with said carbon dioxide.

9. The controller of claim 1, wherein said temperature control subsystem comprises: at least a selected one of a heater and a cooler, said temperature control subsystem configured to control a temperature of a process gas containing carbon dioxide so as to cause said process gas to attain a desired temperature prior to coming into contact with a material to be cured by reaction with said carbon dioxide in said process gas.

10. The controller of claim 1, wherein said humidity control subsystem comprises: at least a selected one of a water vapor source and a water vapor removal apparatus, said humidity control subsystem configured to control a humidity of a process gas containing carbon dioxide so as to cause said process gas to attain a desired humidity prior to coming into contact with a material to be cured by reaction with said carbon dioxide in said process gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The objects and features of the invention can be better understood with reference to the drawings described below, and the claims. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the drawings, like numerals are used to indicate like parts throughout the various views.

(2) FIG. 1 is a schematic diagram of an embodiment of a curing system for use with CO.sub.2 Composite Material.

(3) FIG. 2 is a schematic diagram of an embodiment of an alternate curing system for use with CO.sub.2 Composite Material.

(4) FIG. 3 is a perspective view of a curing chamber suitable for curing elongate specimens of CO.sub.2 Composite Material.

(5) FIG. 4 is a view of the curing chamber of FIG. 3 containing an elongate specimen of CO.sub.2 Composite Material to be cured.

(6) FIG. 5 is a view of the curing chamber of FIG. 3 when closed to allow curing to be performed.

(7) FIG. 6 is an image of a plenum used to deliver a curing atmosphere to a sample of CO.sub.2 Composite Material having an interior circular channel.

(8) FIG. 7 is an image of a sample of CO.sub.2 Composite Material that was cured using flow in an interior circular channel.

(9) FIG. 8 is an image that illustrates the difference in reaction depth as a function of flow rate.

(10) FIG. 9 is a graph that illustrates the differences in reaction depth, gas flow in cubic feet per minute and amount of water removed from specimens of CO.sub.2 Composite Material cured in systems using 1 fan and 3 fans.

(11) FIG. 10 is a graph showing data for water removal rate as a function of flow rate for gases having different relative humidity.

(12) FIG. 11 is a process flow chart illustrating the steps in a process of placing and curing a composite material in an outdoor location.

(13) FIG. 12 is an image that illustrates a perforated PVC grid used for gas delivery to a cast-in-place section of pervious CO.sub.2 Composite Material.

(14) FIG. 13 is an image that illustrates pervious CO.sub.2 Composite Material being poured over the gas delivery system of FIG. 12.

(15) FIG. 14 is an image that illustrates a section of pervious CO.sub.2 Composite Material that is covered with plastic sheeting and that has a CO.sub.2 inlet connected thereto.

(16) FIG. 15 is an image that shows gas flow regulators and a flow meter used to control the CO.sub.2 supply to the pervious CO.sub.2 Composite Material section of FIG. 14.

(17) FIG. 16 is an image that shows a cured section of pervious CO.sub.2 Composite Material after 22 hours using the embedded CO.sub.2 delivery system of FIG. 12.

(18) FIG. 17 is a process flow chart illustrating the steps of placing and curing CO.sub.2 Composite Material using the cast-in-place process.

(19) FIG. 18 is an image showing a mold that allows CO.sub.2 delivery to and through Enkavent material.

(20) FIG. 19 is an image showing uncured CO.sub.2 Composite Material mix for use in a cast-in-place process.

(21) FIG. 20 is an image showing a mold 1800 after casting a CO.sub.2 Composite Material and connection of the process gas line for curing the CO.sub.2 Composite Material with CO.sub.2.

(22) FIG. 21 is an image showing a section cut from a slab of CO.sub.2 Composite Material after carbonation curing.

(23) FIG. 22 is a view of a curing chamber made of flexible material.

(24) FIG. 23 is a view of the flexible material being installed to form the curing chamber of FIG. 22.

(25) FIG. 24 is a view of a clamping method for holding the flexible material of the curing chamber of FIG. 22 to a rigid support.

(26) FIG. 25 is a view of another embodiment of a curing chamber having some flexible walls and some relatively rigid walls.

(27) FIG. 26 is a view of a modular gas handling system that can be used with various curing chambers.

(28) FIG. 27 is a schematic diagram showing a gas handling system that has multiple gas delivery ports and multiple gas recovery ports.

(29) FIG. 28 is a screenshot of a computer based control system for a curing chamber showing a schematic of the system to be controlled.

(30) FIG. 29 is a screenshot of a computer based control system for a curing chamber showing a number of components that can be controlled and showing how parameter values that are measured can be displayed.

(31) FIG. 30 is a screenshot of a computer based control system for a curing chamber showing a recipe screen in which parameters for various periods or steps in a curing process can be entered by a user or displayed to a user.

(32) FIG. 31 is a screenshot image of an historical trend report for a curing operation, showing a graph 3100 in which curve 3110 represents total CO.sub.2 consumed, curve 3120 represents relative humidity, and curve 3130 represents temperature.

DETAILED DESCRIPTION

(33) The invention relates to methods of processing or curing composite materials by means of controlling the atmospheric conditions in and around the material in a precise manner; as well as the equipment involved in doing so.

INCORPORATION BY REFERENCE

(34) Any patent, patent application, patent application publication, journal article, book, published paper, or other publicly available material identified in the specification is hereby incorporated by reference herein in its entirety. Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material explicitly set forth herein is only incorporated to the extent that no conflict arises between that incorporated material and the present disclosure material. In the event of a conflict, the conflict is to be resolved in favor of the present disclosure as the preferred disclosure.

(35) CO.sub.2 Composite Material

(36) The present invention relies in part on the use of materials that undergo curing in the presence of carbon dioxide (CO.sub.2) that can be supplied in gaseous form and that is believed to be active in hydrated form (e.g., as a water soluble carbonate derived from H.sub.2CO.sub.3). The cured materials that result from such processes will be referred to collectively herein as CO.sub.2 Composite Material (CCM) or CO.sub.2 Composite Materials (CCMs). The chemistry and preparation of various kinds of CO.sub.2 Composite Material has been described in various patent documents, including U.S. Patent Application Publication No. 20140127450 A1, published May 8, 2014 and U.S. Patent Application Publication No. 20140127458 A1, published May 8, 2014.

(37) The CO.sub.2 Composite Materials may exhibit aesthetic visual patterns as well as display compressive strength, flexural strength and water absorption similar to that of the corresponding natural materials. The CO.sub.2 Composite Materials can be produced using the efficient gas-assisted hydrothermal liquid phase sintering (HLPS) process at low cost and with much improved energy consumption and carbon footprint. In fact, in preferred embodiments of the process, CO.sub.2 is consumed as a reactive species resulting in net sequestration of CO.sub.2.

(38) The CO.sub.2 Composite Materials can be made to display various patterns, textures and other characteristics, such as visual patterns of various colors. In addition, the CO.sub.2 Composite Materials exhibit compressive strength, flexural strength and water absorption properties similar to conventional concrete. The CO.sub.2 Composite Materials can be cured to a point where they are ready for use in time intervals (such as hours) that are often considerably reduced from the times required to cure conventional concrete (such as days to weeks). Furthermore, the CO.sub.2 Composite Materials can be produced using the energy-efficient HLPS process and can be manufactured at low cost and with favorable environmental impact. For example in preferred embodiments of the invention, CO.sub.2 is used as a reactive species resulting in sequestration of CO.sub.2 in the produced CO.sub.2 Composite Materials with in a carbon footprint unmatched by any existing production technology. The HLPS process is thermodynamically driven by the free energy of the chemical reaction(s) and reduction of surface energy (area) caused by crystal growth. The kinetics of the HLPS process proceed at a reasonable rate at low temperature because a solution (aqueous or nonaqueous) is used to transport reactive species instead of using a high melting point fluid or high temperature solid-state medium.

(39) Discussions of various aspects of HLPS can be found in U.S. Pat. No. 8,114,367, U.S. Pub. No. US 2009/0143211 (Applications. Ser. No. 12/271,566), U.S. Pub. No. US 2011/0104469 (Applications. Ser. No. 12/984,299), U.S. Pub. No. 20090142578 (Applications. Ser. No. 12/271,513), WO 2009/102360 (PCT/US2008/083606), WO 2011/053598 (PCT/US2010/054146), WO 2011/090967 (PCT/US2011/021623), U.S. application Ser. No. 13/411,218 filed Mar. 2, 2012 (Riman et al.), U.S. application Ser. No. 13/491,098 filed Jun. 7, 2012 (Riman et al), U.S. Provisional Patent Application No. 61/708,423 filed Oct. 1, 2012, and U.S. Provisional Patent Application Nos. 61/709,435, 61/709,453, 61/709,461, and 61/709,476, all filed Oct. 4, 2012, each of which is expressly incorporated herein by reference in its entirety for all purposes.

(40) The terms rate-limiting step or rate limiting steps refer to one or more steps that are restricting or controlling the time a carbonation reaction takes.

(41) Flow is the movement of gas described as a velocity and/or volume, using velocity in fps (feet per second) or volumetrically as cfm (cubic feet per minute).

(42) The term temperature or temperature range represents one or more of the overall internal system temperature, a gas temperature, and a sample temperature.

(43) The term relative humidity represents the ratio of the partial pressure of water vapor in a gas in the system to the saturated vapor pressure of water in that gas at a certain temperature, which may vary throughout the system.

(44) The term CO.sub.2 concentration represents the amount of CO.sub.2 in a system divided by the total volume of gas in that system, expressed as a percentage.

(45) The invention contemplates a process that maximizes the carbonation rate of a composite material by controlling the drying rate of that material. The process can include a carbonation duration is between 0 and 1,000 hours. The process can include a CO.sub.2 Composite Material that has a permeability in the range of 0% and 100%. The process can include a CO.sub.2 Composite Material that has a carbonation depth of the CCM in the range of 0 and 36 inches. The process can include a CO.sub.2 Composite Material wherein the amount of water removed from the CCM is equal to between 0% and 99% of the CCM mass.

(46) The invention encompasses the equipment used to condition a recirculating gas stream in order to cure a CCM and processes that use such equipment to cure the CCM. The gas conditioning equipment allows for a process that controls, reduces or eliminates the rate-limiting steps associated with water removal during the curing of a composite material. The equipment may include, but will not be limited to, control over the temperature, relative humidity, flow rate, pressure, and carbon dioxide concentration within the system; which includes the conditioning equipment, any vessel containing the CCM, and the material itself. Flow rate control can be used as a means to achieve uniformity in both gas velocity and composition.

(47) The equipment can comprise various subsystems. The subsystems can include a curing chamber, a source of carbon dioxide, a gas flow subsystem, a temperature control subsystem, a humidity control subsystem, and a controller in communication with at least one of the source of carbon dioxide, the gas flow subsystem, the temperature control subsystem, and the humidity control subsystem; and at least one controller configured to control independently during a time period when the material that consumes CO.sub.2 as a reactant is being cured at least a respective one of the flow rate of the gaseous carbon dioxide, the circulation of the gas through the curing chamber, the temperature of the gas, and the humidity in the gas.

(48) Curing Chambers

(49) Various types of curing chambers and apparatus can be employed for curing CCMs. Some curing chambers and apparatus may be provided in permanent or semi-permanent facilities, while others may be used for a time (e.g., temporary installation) and some may be used once (e.g., curing a CCM in place, for example at some out-of-doors location, such as curing a CCM for form a slab for a walkway, a driveway, a road, a landing strip, or a support slab for a structure). FIG. 1 and FIG. 2 are schematic diagrams of embodiments of a curing system for use with CO.sub.2 Composite Material.

(50) In some embodiments, the chamber or enclosure itself may be designed for one or a few repetitions of a curing process, or may be designed to last for an indefinitely long number of repetitions of a curing process. In some embodiments, the relative cost of the chamber as compared to the value of the product being cured will serve as a guide as to the materials and methods of construction of the chamber or enclosure.

(51) Source of Carbon Dioxide

(52) Carbon dioxide may be provided from any convenient source that can supply sufficient gas quantities at high enough purity. In some embodiments, the source of carbon dioxide is gas generated from liquid carbon dioxide. In some embodiments, the source of carbon dioxide is gas provided in the form of gas in a high pressure cylinder. In some embodiments, the source of carbon dioxide is effluent from a combustion system that is processed to provide a supply of purified carbon dioxide.

(53) Gas Flow Subsystem

(54) In some embodiments there is provided a gas flow subsystem for providing the necessary gases (e.g., CO.sub.2, water vapor, air, and possibly other gases) that are useful for curing a CCM. The gas flow system includes as components one or more of valves, flow regulators, mass flow controllers, and blowers that are suitable for causing gas flows at desired flow rates (e.g., suitable mass per unit of time), desired pressures, and desired compositions (e.g., ratios or proportions of carbon dioxide to water to air and possibly other gases). The curing chamber can further include structures that control the flow rates and flow directions in the curing chamber, as well as the physical locations of gas inlets and outlets.

(55) Temperature Control Subsystem

(56) In some embodiments there is provided a temperature control subsystem that allows the provision of gas having desired gas temperature. The temperature control subsystem can be useful to control reaction rates as a function of temperature, as well as operational parameters such as relative humidity that have a temperature dependence. The temperature control system can comprise one or more heaters, one or more coolers, one or more sensors configured to measure a gas temperature at a location, and a communication port configured to communicate with a controller. In some embodiments, the communication is unidirectional, for example communication in which the controller sends a control signal to control the temperature control subsystem by causing at least one of the heater and the cooler to operate. In other embodiments, the communication is unidirectional, in which the temperature control system sends signals representing parameters such temperature and relative humidity to a controller. In some embodiments, signals can be communicated in both directions.

(57) Humidity Control Subsystem

(58) In some embodiments there is provided a humidity control subsystem that allows the control of the relative humidity in the process gas used in the system. The humidity control subsystem can be used to add water vapor to the process gas that is supplied to the curing chamber if the relative humidity is too low or if one wishes to add water to a CCM during the curing process, and it can be used to remove water vapor from process gas that exits or is exhausted from the curing chamber if the relative humidity is too high or if one wishes to extract water from a CCM during the curing process. For example, the apparatus to add water vapor can be a source of water, a valve, and a spray head or spray nozzle. In another embodiment, the apparatus to add water vapor can be a steam generator. The steam generator can include a submersible heater. In other embodiments, water vapor can be added by bubbling a gas through a water bubbler. The apparatus to remove water can be a chiller, a condenser or a heat exchanger. The humidity control subsystem includes humidity sensors that can measure the reactive humidity of the process gas at various locations in the gas flow systems, such as at the location where process gas enters or exits the curing chamber, and as appropriate, at other locations in the curing chamber or in the gas flow subsystem.

(59) Subsystem for Controlling the Curing Process Parameters

(60) In some embodiments, a subsystem for controlling the curing process parameters (e.g., a controller) is provided to control operational parameters for curing a CCM including controlling process step sequences, durations and timing, and for logging data measured during curing operations. In various embodiments, the controller is in communication with at least one of the source of carbon dioxide, the gas flow subsystem, the temperature control subsystem, and the humidity control subsystem. In some embodiments, the controller is in communication with sensors that provide data about the process, such as temperature, humidity, flow rates, gas pressures, gas compositions and the like. The controller is configured to control independently at least a respective one of the flow rate of the gaseous carbon dioxide, the circulation of the gas through the curing chamber, the temperature of the gas, and the humidity in the gas during a time period when the material that consumes CO.sub.2 as a reactant is being cured.

(61) In general, each subsystem can be provided as a reusable module that can be operationally connected to the other subsystems, for example using conventional off-the-shelf mechanical and electrical connectors. In some embodiments, a complete control and operations system can then be provided by assembling one or more modules of each type of subsystem as may be required for a given curing operation. For curing procedures that are expected to be carried out repeatedly, a complete control and operations system can be provided as a unit. In the event that some portion of the control and operations system malfunctions, a relatively expeditious repair can be made by substituting an entire subsystem for the malfunctioning component, and repair of that component can be conducted off-line, e.g., without significantly affecting the curing process for a given curing operation, so that the curing process can be accomplished with only a minor deviation from the expected process duration. In particular, CCMs lend themselves to such correction of temporary malfunctions, because the CCM simply stops curing when the concentration of CO.sub.2 is reduced sufficiently (e.g., when CO.sub.2 is lacking in the curing gas). This is different from the curing of conventional concrete, which is initiated by the presence of water (H.sub.2O), and which in general cannot be interrupted once the conventional concrete mixture becomes wet.

(62) Turning now to FIG. 1, there is shown a schematic diagram of an embodiment of a curing system for use with CO.sub.2 Composite Material. In FIG. 1 there is a gas conditioning system 102 and a curing chamber 120 which are connected together by a gas delivery tube 140 and a gas recovery tube 142. The gas conditioning system 102 includes elements of each of a source of carbon dioxide, a gas flow subsystem, a temperature control subsystem, a humidity control subsystem and a subsystem for controlling the curing process parameters. In the embodiment of FIG. 1, the gas delivery tube 140 and the gas recovery tube 142 can be any convenient size tabulation, for example a 6 inch diameter metal pipe. A gas source such as a CO.sub.2 supply 130, and, as needed, sources of other gases such as air and/or water vapor are provided. The gas delivery and conditioning system can include a controller 116, such as a programmable logic controller (PLC) or another microprocessor-based controller, such as a general purpose programmable computer that can operate using a set of instructions recorded on a machine-readable medium. As illustrated in FIG. 1 a typical curing chamber 120 can include a plenum 122 that is configured to provide a gas atmosphere by way of one or more locations at which gas can be injected into the curing chamber to create a gas flow 124 having desired properties such as flow velocity or flow patterns in various portions of the curing chamber 120. The curing chamber in some embodiments will be as simple as an enclosure that can contain a CCM to be processed and process gas with an inlet and an outlet to allow the gas to be introduced and as needed removed. Additional details of such systems will be provided hereinafter.

(63) FIG. 2 is a schematic diagram of an embodiment of an alternate curing system for use with CO.sub.2 Composite Material. Many of the components illustrated in FIG. 2 can be the same as those shown in FIG. 1, but there can be additional, or different, components. For example, both the embodiments of FIG. 1 and FIG. 2 use a number of thermocouples or other temperature sensors (104, 104, 104, 104, 104, collectively temperature sensors 104) and a plurality of relative humidity sensors (106, 106, collectively relative humidity sensors 106), which can be for example dry-bulb wet-bulb sensors that utilize the psychrometric ratios for carbon dioxide and water vapor or dipole polarization water vapor measurement instruments or chilled mirror hygrometers or capacitive humidity sensors.

(64) As illustrated in FIG. 2, the CO.sub.2 supply 130 can be connected to the CO.sub.2 inlet by way of different flow control pathways, such as valves 210, 212, and 214 which may be used to provide a high flow rate, for example during a purging cycle, or by way of valves 220, 222, flow controller 224, and valve 226 which may be used to provide a more precisely controlled flow rate (typically having a slower flow rate than that used in a purge cycle). In the embodiment shown in FIG. 2, the piping used to connect the gas conditioning system 102 can be larger than that used in the system illustrated in FIG. 1. For example, the piping can be 8 inch pipe. Another difference is the size of heaters used to heat the gas provided to the curing chamber, which in FIG. 1 is illustrated as six 1.3 kW heaters (114), while the heating system in FIG. 2 includes eighteen 1.8 kW heaters (214). As will be understood, in any particular system the precise capacities of the various components will be sized in relation to the intended amount of material to be cured in the curing chamber 120.

(65) The controller 116 can receive data from the temperature sensors 104 and the relative humidity sensors 106, and can communicate bi-directionally (e.g., take data from and send commands to) the valves, the chiller (or cooler) 110, the chiller (or cooler) heat exchanger 112, the blower 108, the heaters (114, 214) and the CO.sub.2 supply 130 so as to be able to log data as a function of time, make determinations regarding the state of curing of a load in the curing chamber 120, and take corrective or predetermined actions so as to control the curing process. The controller 116 can also receive commands from a user, display information to the user, and record data and the commands that may be issued from time to time so that a record of the curing process may be produced in machine-readable form for later use.

(66) Gas Flow in the Curing Chamber

(67) The gas flow in the curing chamber in various embodiments can include gas flows external to the body, gas flows internal to the body, gas flows through a porous or pervious body, or combinations of such gas flows. The gas delivery system includes the gas delivery tube 140, the gas recovery tube 142, and the plenum 122, which can have many forms. In some embodiments, the plenum 122 directs gases to the outside of green bodies of CO.sub.2 Composite Material. In other embodiments, the plenum 122 directs gases to internal passages or openings in green bodies of CO.sub.2 Composite Material. In still other embodiments, the plenum 122 directs gases both to the outside of and to internal passages or openings in green bodies of CO.sub.2 Composite Material.

(68) Internal Gas Delivery System

(69) This type of gas delivery system is comprised of linked, gridded piping having a specific spacing and size, which delivers gas, or fluid through a series of holes distributed throughout the piping system, to a surrounding CO.sub.2 Composite Material body. The supply of gas (including carbon dioxide) is then regulated to match or come close to matching the sequestration rate of CO.sub.2 in the CO.sub.2 Composite Material. This is one method to rapidly cure a section of CO.sub.2 Composite Material. In the typical internal gas delivery system, the piping system is left imbedded in the CO.sub.2 Composite Material sample after it is cured. The piping system can act additionally as a means of reinforcement, and can provide the ability to perform cleaning or maintenance of CO.sub.2 Composite Material via a compressed air or water backwashing technique.

(70) Some of the benefits of this approach include but are not limited to a reduction in cure time, reduction of carbon footprint associated with a cast-in-place CO.sub.2 Composite Material application, improved life of pervious CO.sub.2 Composite Material sections due to the ability to backwash debris out of pervious CO.sub.2 Composite Material and the presence of a reinforcing grid. Standard practice for the placing of pervious concrete with Portland cement based systems calls for a 7-28 day curing period before the area can be used. With the gas delivery system, final strength of a CO.sub.2 Composite Material can be achieved in as little as 1 day. In the trial outlined below a supply of CO.sub.2 is regulated at 1.7 kg per hour. The result after 22 hours was a carbonation extent of 40% in relation to the potential of the CO.sub.2 Composite Material to carbonate. This correlates to 43% CO.sub.2 efficiency. Based on this data, we can control the gas supply rate to match the sequestration rate of the CO.sub.2 Composite Material thereby improving the efficiency of CO.sub.2 usage and optimizing the time needed to effect the curing process.

(71) An embodiment of an internal gas delivery system for curing elongate specimens such as railroad ties is now described.

(72) FIG. 3 is a perspective view of a curing chamber suitable for curing elongate specimens of CO.sub.2 Composite Material. The curing chamber in FIG. 3 has a flexible wall 310 that is supported by frame members 320. The closure of flexible wall 310 may be accomplished by the use of weights, or by the use of magnetic stripping and magnetic frame members. Other flexible wall systems are described in more detail hereinafter.

(73) FIG. 4 is a view of the curing chamber of FIG. 3 containing an elongate specimen 410 (a railroad tie) of CO.sub.2 Composite Material to be cured.

(74) FIG. 5 is a view of the curing chamber of FIG. 3 when closed to allow curing to be performed. The flexible wall 310 is fully deployed in this view.

(75) In using a system as shown in FIG. 3 through FIG. 5, the process gas is supplied to at least one internal aperture that traverses the length of the CCM to be cured. The curing can then proceed from the inside of the green body toward the outside. Data has been obtained for such curing processes.

(76) FIG. 6 is an image of a plenum used to deliver a curing atmosphere to a sample of CO.sub.2 Composite Material having an interior circular channel. As may be seen in FIG. 6, the plenum 610 is a pipe having a circular cross section that can be placed in fluid communication with a circular channel in a sample of CO.sub.2 Composite Material to be cured.

(77) FIG. 7 is an image of a sample 700 of CO.sub.2 Composite Material that was cured using flow in an interior circular channel 710 and gas flow on the exterior of the sample. As shown in FIG. 7, the sample 700 has a circular region 720 that has been cured, a rectangular peripheral region 730 that has been cured, and an uncured region 740 between the cured regions 720 and 730. This demonstrates the ability to cure the CCM from the inside using internal process gas flow and from the outside using gas flow exterior to the sample.

(78) FIG. 8 is an image that illustrates the difference in reaction depth as a function of flow rate. In FIG. 8 it is apparent that for the geometry examined, a higher flow rate led to a greater depth of cure in the same time interval.

(79) FIG. 9 is a graph that illustrates the differences in reaction depth, gas flow in cubic feet per minute and amount of water removed from specimens of CO.sub.2 Composite Material cured in systems using 1 fan and 3 fans. It is apparent that reaction depth, gas flow in cubic feet per minute and amount of water removed from specimens of CO.sub.2 Composite Material all increase when more capacity to move the reactive gas is provided.

(80) FIG. 10 is a graph showing data for water removal rate as a function of flow rate for gases having different relative humidity. As is seen in FIG. 10, using a higher flow rate and a lower relative humidity tends to increase the rate at which water is removed from the sample. It is believed that the reaction of CCM with CO.sub.2 occurs preferentially at the interface where water-saturated CCM is in contact with gaseous CO.sub.2, so more rapid removal of water correlates with faster rates of cure.

ExampleCure Pervious Co.SUB.2 .Composite Material in Place

(81) The process of curing pervious CO.sub.2 Composite Material in place is shown in FIG. 11 through FIG. 16. This is an installation that was made on the ground to one side of a building. It is an example of a true outdoor cast in place application in use.

(82) FIG. 11 is a process flow chart illustrating the steps in a process of placing and curing a composite material in an outdoor location. The process can be divided into steps. In step 1110, one prepares the area where the CO.sub.2 Composite Material is to be installed and cured. This can include digging, grading, setting out forms, and the like. In step 1120, one pours or otherwise installs a first layer of pervious CO.sub.2 Composite Material. The activity of installing the CO.sub.2 Composite Material includes forming the body to be cured using any one or more of casting, pouring, vibrating, pressing, and the like, depending on the CO.sub.2 Composite Material formulation or mix workability.

(83) In step 1130, one places or installs a gas delivery structure, which in some embodiments can be a tube or pipe with holes defined in a wall thereof. FIG. 12 is an image that illustrates a perforated PVC grid 1210 used for gas delivery to a cast-in-place section of pervious CO.sub.2 Composite Material. The first layer 1220 of material to be cured is also seen, as can a gas connection point 1230.

(84) In step 1140, one pours or installs a second (final) layer of pervious CO.sub.2 Composite Material over the gas delivery structure. FIG. 13 is an image that illustrates pervious CO.sub.2 Composite Material 1310 being poured over the gas delivery system 1210 of FIG. 12. However, it should be understood that the installation of the gas delivery structure and the material to be cured at the desired location can be performed in any order, including placing the gas delivery structure in place first, and then placing the material to be cured thereafter, or first placing the material to be cured and then installing the gas delivery structure.

(85) In step 1150, one covers the installed material, for example with a tarpaulin (a tarp) and one hooks up the gas line. FIG. 14 is an image that illustrates a section of pervious CO.sub.2 Composite Material that is covered with plastic sheeting 1410 and that has a CO.sub.2 inlet 1420 connected to gas connection point 1230.

(86) Before the installed mixture is cured it may be necessary to dry or remove excess water from the uncured CO.sub.2 Composite Material using one or more of air drying, draining, or gas recirculation conditioning to get the material to the proper conditions to begin the curing process. In some embodiments, it may be necessary to add water to a dry mixture of uncured CO.sub.2 Composite Material.

(87) In step 1160, one supplies gas to cure the CO.sub.2 Composite Material. FIG. 15 is an image that shows gas flow regulators and a flow meter used to control the CO.sub.2 supply to the pervious CO.sub.2 Composite Material section of FIG. 14. In FIG. 15, there are seen a high pressure regulator 1510, low pressure regulator 1520, gas delivery piping 1530, a CO.sub.2 mass flow meter 1540, and a CO.sub.2 mass flow meter readout 1550.

(88) FIG. 16 is an image that shows a cured section of pervious CO.sub.2 Composite Material after 22 hours using the embedded CO.sub.2 delivery system of FIG. 12.

(89) In some embodiments, sensors can be positioned within the volume of the CO.sub.2 Composite Material to be cured so that operational parameters during the curing process may be monitored. Such sensors are in general sacrificial or one time use sensors in that they are generally not removed and recovered after the CO.sub.2 Composite Material has been cured, but rather are permanently fixed in the CO.sub.2 Composite Material.

Example: Cast-in-Place Curing System

(90) A cast-in-place curing system involves systems and methods for carbonating a CO.sub.2 Composite Material in the absence of any sealed vessel. This cast-in-place curing technique involves the use of a gas permeable barrier being used as a layer to allow CO.sub.2 to diffuse through a cast section of CO.sub.2 Composite Material. This is a procedure for rapid strength generation and the permanent sequestration of carbon dioxide gas, leading to a reduction in the carbon footprint associated with cast-in-place concrete applications. This process is less energy intensive than all previous carbonation curing techniques as no temperature-controlled or sealed vessel is needed. It has been demonstrated for the first time that a significant level of strength (+2,000 psi) can be achieved using the described cast-in-place techniques with a dense CO.sub.2 Composite Material.

(91) CO.sub.2 Composite Material has been carbonated via bottom-up carbonation curing process. This trial involved successful carbonation without the use of a sealed vessel to produce a CO.sub.2 Composite Material slab having compressive strengths in excess of 2,000 psi.

(92) We have used of Enkavent material to create a gas permeable layer for providing a larger CO.sub.2 delivery surface to allow for carbonation in a cast-in-place system.

(93) FIG. 17 is a process flow chart illustrating the steps of placing and curing CO.sub.2 Composite Material using the cast-in-place process. In step 1710 one prepares an Enkavent layer with permeable coating by positioning the material in the location where the CO.sub.2 Composite Material is to be cast and cured. In step 1720 one pours (or otherwise places) the CO.sub.2 Composite Material to be cast-in-place. In step 1730 one connects a curing system gas line in fluid communication with the Enkavent layer. In step 1740 one starts the flow of gas into the Enkavent layer. In step 1750 one supplies CO.sub.2 gas to cure CO.sub.2 Composite Material for a time period long enough to effect the cure desired.

(94) FIG. 18 is an image showing a mold 1800 that allows CO.sub.2 delivery to and through Enkavent material, in which the frame 1810 is arranged to contain the CO.sub.2 Composite Material in a desired size and shape. As seen in FIG. 18, the mold 1800 has a gas delivery line 1840 that introduces process gas below a porous screen 1830 that supports a layer of Enkavent material 1820. Enkavent material is available from available commercially from Enka Geomatrix Systems, a Division of BASF Corporation of Enka, N.C., and its successor, Colbond, Inc. Enkavent material is described in more detail in U.S. Pat. Nos. 4,212,692, 5,960,595 and 6,487,826. The CO.sub.2 Composite Material is positioned adjacent the Enkavent material.

(95) FIG. 19 is an image showing uncured CO.sub.2 Composite Material mix for use in a cast-in-place process.

(96) FIG. 20 is an image showing a mold 1800 after casting a CO.sub.2 Composite Material and connection of the process gas line for curing the CO.sub.2 Composite Material with CO.sub.2.

(97) FIG. 21 is an image showing a section 2110 cut from a slab of CO.sub.2 Composite Material after carbonation curing.

(98) Flexible-Wall Curing Chamber

(99) Another type of curing chamber that can be employed to cure specimens of CO.sub.2 Composite Material is illustrated in FIG. 22 through FIG. 24. This is a chamber made from a flexible material, such as plastic sheet material, to form a chamber having flexible walls. In a preferred embodiment the flexible material may be coated with a reflective layer, such as aluminum, so as to be reflective of infrared radiation. Similar material is commonly used in blankets or ponchos used in human rescue operations, or given to marathon runners at the end of a race so that the person's body heat can be more easily retained. In the embodiments described next, the wall is provided to contain a gas used in curing specimens of CO.sub.2 Composite Material placed within the chamber so that the properties of the gas, such as composition, temperature, relative humidity and flow rate, can be controlled. In some embodiments, sensors may be situated within the chamber to provide data about the properties of the gas and the conditions within the chamber during a curing operation.

(100) FIG. 22 is a view of a curing chamber 2200 made of flexible material 2210 that is attached to a rigid base 2220 by a clamping system. In one embodiment, the flexible material is metalized plastic sheet. Other materials that can be used as the flexible material are Mylar and latex.

(101) FIG. 23 is a view of the flexible material being installed to form the curing chamber of FIG. 22.

(102) FIG. 24 is a view of a clamping method for holding the flexible material of the curing chamber of FIG. 22 to a rigid support. As illustrated in FIG. 24, a rigid base 2410 and a flexible sheet 2420 are connected by the use of rigid rods 2430 and clamps 2440. In the embodiment shown the rigid rods 2430 have square or rectangular cross sections. In some embodiments a deformable gasket 2450 may be placed between the mating surfaces of the rigid base 2410 and the flexible sheet 2420 so as to provide a more hermetic seal. The gasket 2450 can be any material that is chemically compatible with the curing gas and that is sufficiently soft so that it forms a substantially hermetic seal when compressed between the mating surfaces of the rigid base 2410 and the flexible sheet 2420. Examples of such materials that can be used as gaskets are closed cell plastic foam sheet and viscous liquids such as petroleum based gels. In other embodiments, a channel filled with a liquid that is compatible with the curing atmosphere, such as water, can be provided at the location in which the mating surfaces of the rigid base 2410 and the flexible sheet 2420 are situated.

(103) FIG. 25 is a view of another embodiment of a curing chamber 2500 having some flexible walls 2510 and some relatively rigid walls 2520. In the embodiment shown in FIG. 25, the aperture 2530 may be covered with a material that is transparent in a spectral region of interest, such as the visible or the infrared, so that visual observations or instrument-based electromagnetic radiation observations, such as optical pyrometry or gas flow or gas composition measurements may be made. 2540 is a fitting used to make a connection to a gas conditioning system 102 as previously described (e.g., 2540 is used as the connection to one of a gas delivery tube 140 and a gas recovery tube 142).

(104) Modular Gas Handling System

(105) FIG. 26 is a view of a modular gas handling system that can be used with various curing chambers.

(106) FIG. 27 is a schematic diagram showing a gas handling system 2710 that has multiple gas delivery ports 2730, 2730, 2730 and multiple gas recovery ports 2740, 2740, 2740 by way of which it in fluid communication with a curing chamber 2720. The modular gas handling system of FIG. 27 can be viewed as a multiple number of modular gas handling systems of FIG. 26 that operate in parallel under the control of a controller. The gas handling system of FIG. 27 can be used to provide gas flows having individually controlled flow rates, gas compositions and gas temperatures so that gas glows that are tailored to specific regions of a single curing chamber can be provided and controlled. As needed, multiple sets of sensors can be provided so that each gas flow stream can be individually monitored and controlled.

(107) Computer-Based Control System

(108) In order to control the operation of the curing system in a more convenient manner, there is provided at least one controller in communication with at least one of the source of carbon dioxide, the gas flow subsystem, the temperature control subsystem, and the humidity control subsystem. The at least one controller is configured to control independently during a time period when the material that consumes CO.sub.2 as a reactant is being cured at least a respective one of the composition of the gas provided for the curing process, the flow rate of carbon dioxide, the rate or velocity of circulation of the gas through the curing chamber or through the CCM being cured, the direction of circulation of the gas through the curing chamber, the temperature of the gas, and the humidity in the gas.

(109) In a preferred embodiment, the controller is a general purpose computer that is operated under a set of instructions recorded on a machine-readable medium, or a similar electronic device as described in more detail hereafter. In some embodiments, an operator can control some (or all) of the operations in a curing process by overriding the controller, or by providing specific instructions to the controller that are performed as the operator directs. For example, some of the steps in a curing process having to do with setting up the curing chamber, loading CCM material to be cured, unloading the cured material at the end of a curing cycle, and the like, may be more conveniently performed under the control of a human operator. In many instances a human operator can take into consideration variations in the CCM materials themselves and how they are mechanically handled more easily than can a preprogrammed controller. After the preliminary steps are completed, the human operator can turn over control of the process to a controller, which can control the process for the duration of the curing time. Another benefit of using a controller is that the controller can record and generate a log of the operational parameters that are set as targets, and can record the corresponding actual parameters that are measured during the curing process, so that the precision of the curing process can be increased over time by reprogramming the instructions that control a specific process to cause the actual measured operational parameters to adhere more closely to the values that are set as targets. A well-known example of such improvement in control is the used of proportional-integral-derivative (P-I-D) control when one is trying to set a change in a parameter that finally attains a steady state after a time interval, while attempting to minimize undershoot (too low a value) and overshoot (too high a value) as the desired steady state value is approached.

(110) FIG. 28 is a screenshot of a computer based control system for a curing chamber showing a schematic of the system to be controlled. In FIG. 28 there is shown a schematic of the curing chamber 2810, components of the gas handling system 2820, a plurality of data windows 2830 for the display of process parameters such gas compositions, temperature, pressure, relative humidity, blower speed or flow rates in real time, (e.g., in substantially the then current time as the process proceeds), a schematic of the CO.sub.2 source 2840 and associated valves, and a schematic of a source of water/water vapor 2850.

(111) FIG. 29 is a screenshot of a computer based control system for a curing chamber showing a number of components that can be controlled and showing how parameter values that are measured can be displayed. The screenshot that is illustrated is a diagnostic panel in which are displayed the states 2910 of various components such as blowers, heaters, valves and the like, the desired or programmed values 2920 of various operating parameters, such as temperature, relative humidity, percentage CO.sub.2 and the like. The current measured values 2930 provided by various sensors, and a display 2940 of the step that is monitored (here purge) and some of the parameters that are being controlled. The diagnostic information that is displayed may be different for different steps in the process.

(112) FIG. 30 is a screenshot of a computer based control system for a curing chamber showing a recipe screen in which parameters for various periods or steps in a curing process can be entered by a user or displayed to a user. As may be seen, the recipe screen can be used to enter individual steps 3010 with their desired operating parameters. A set of buttons 3020 is provided to allow a user to conveniently select different parts of a curing operation, such as control of gas compositions (e.g., a button labeled CO.sub.2 control), relative humidity conditions (e.g., a button labeled RH control), operation of the controller itself (e.g., a button labeled PID control) and many other parameters. There are also provided buttons to save a recipe to a machine-readable medium or memory, or to recall a previously saved recipe from memory. In some embodiments, the screen itself is a touchscreen. In some embodiments, a pointing device such as a mouse may be used. In some embodiments, a keyboard, a numeric pad, and/or an on screen keyboard may be used in enter data or commands.

(113) FIG. 31 is a screenshot image of an historical trend report for a curing operation, showing a graph 3100 in which curve 3110 represents total CO.sub.2 consumed, curve 3120 represents relative humidity, and curve 3130 represents temperature.

DEFINITIONS

(114) Unless otherwise explicitly recited herein, any reference to an electronic signal or an electromagnetic signal (or their equivalents) is to be understood as referring to a non-volatile electronic signal or a non-volatile electromagnetic signal.

(115) Recording the results from an operation or data acquisition, such as for example, recording results at a particular frequency or wavelength, is understood to mean and is defined herein as writing output data in a non-transitory manner to a storage element, to a machine-readable storage medium, or to a storage device. Non-transitory machine-readable storage media that can be used in the invention include electronic, magnetic and/or optical storage media, such as magnetic floppy disks and hard disks; a DVD drive, a CD drive that in some embodiments can employ DVD disks, any of CD-ROM disks (i.e., read-only optical storage disks), CD-R disks (i.e., write-once, read-many optical storage disks), and CD-RW disks (i.e., rewriteable optical storage disks); and electronic storage media, such as RAM, ROM, EPROM, Compact Flash cards, PCMCIA cards, or alternatively SD or SDIO memory; and the electronic components (e.g., floppy disk drive, DVD drive, CD/CD-R/CD-RW drive, or Compact Flash/PCMCIA/SD adapter) that accommodate and read from and/or write to the storage media. Unless otherwise explicitly recited, any reference herein to record or recording is understood to refer to a non-transitory record or a non-transitory recording.

(116) As is known to those of skill in the machine-readable storage media arts, new media and formats for data storage are continually being devised, and any convenient, commercially available storage medium and corresponding read/write device that may become available in the future is likely to be appropriate for use, especially if it provides any of a greater storage capacity, a higher access speed, a smaller size, and a lower cost per bit of stored information. Well known older machine-readable media are also available for use under certain conditions, such as punched paper tape or cards, magnetic recording on tape or wire, optical or magnetic reading of printed characters (e.g., OCR and magnetically encoded symbols) and machine-readable symbols such as one and two dimensional bar codes. Recording image data for later use (e.g., writing an image to memory or to digital memory) can be performed to enable the use of the recorded information as output, as data for display to a user, or as data to be made available for later use. Such digital memory elements or chips can be standalone memory devices, or can be incorporated within a device of interest. Writing output data or writing an image to memory is defined herein as including writing transformed data to registers within a microcomputer.

(117) Microcomputer is defined herein as synonymous with microprocessor, microcontroller, and digital signal processor (DSP). It is understood that memory used by the microcomputer, including for example instructions for data processing coded as firmware can reside in memory physically inside of a microcomputer chip or in memory external to the microcomputer or in a combination of internal and external memory. Similarly, analog signals can be digitized by a standalone analog to digital converter (ADC) or one or more ADCs or multiplexed ADC channels can reside within a microcomputer package. It is also understood that field programmable array (FPGA) chips or application specific integrated circuits (ASIC) chips can perform microcomputer functions, either in hardware logic, software emulation of a microcomputer, or by a combination of the two. Apparatus having any of the inventive features described herein can operate entirely on one microcomputer or can include more than one microcomputer.

(118) General purpose programmable computers useful for controlling instrumentation, recording signals and analyzing signals or data according to the present description can be any of a personal computer (PC), a microprocessor based computer, a portable computer, or other type of processing device. The general purpose programmable computer typically comprises a central processing unit, a storage or memory unit that can record and read information and programs using machine-readable storage media, a communication terminal such as a wired communication device or a wireless communication device, an output device such as a display terminal, and an input device such as a keyboard. The display terminal can be a touch screen display, in which case it can function as both a display device and an input device. Different and/or additional input devices can be present such as a pointing device, such as a mouse or a joystick, and different or additional output devices can be present such as an enunciator, for example a speaker, a second display, or a printer. The computer can run any one of a variety of operating systems, such as for example, any one of several versions of Windows, or of MacOS, or of UNIX, or of Linux. Computational results obtained in the operation of the general purpose computer can be stored for later use, and/or can be displayed to a user. At the very least, each microprocessor-based general purpose computer has registers that store the results of each computational step within the microprocessor, which results are then commonly stored in cache memory for later use, so that the result can be displayed, recorded to a non-volatile memory, or used in further data processing or analysis.

(119) Theoretical Discussion

(120) Although the theoretical description given herein is thought to be correct, the operation of the devices described and claimed herein does not depend upon the accuracy or validity of the theoretical description. That is, later theoretical developments that may explain the observed results on a basis different from the theory presented herein will not detract from the inventions described herein.

(121) While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be affected therein without departing from the spirit and scope of the invention as defined by the claims.