Patent Publication Number: US-2022234247-A1

Title: Systems and methods for curing a precast concrete product

Description:
CROSS-REFERENCE 
     This application is a continuation of U.S. patent application No. 17/116,350 filed on Dec. 9, 2020, which claims priority on U.S. Patent Application No. 62/945,936 filed Dec. 10, 2019, the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The application relates generally to precast concrete products, and more particularly to systems and methods for curing such precast concrete products. 
     BACKGROUND 
     Concrete products are ubiquitous in building structures in many parts of the world. Hence, improvements in systems and methods for curing precast concrete products are always desirable, and even small improvements in systems and methods for curing precast concrete products may provide extensive advantages to today&#39;s construction industries. 
     SUMMARY 
     Precast concrete products, e.g. pipes, manholes, culverts, are conventionally cured with heat and steam or with carbon dioxide where they are placed in sealed enclosed chambers, spaces, rooms or vessels. Calcium-rich materials, e.g. hydraulic cement, slag, non-hydraulic cement, containing calcium silicate phases react with carbon dioxide in the presence of water and are converted to strength-contributing phases including calcium carbonates. 
     The present description relates to a method of producing a precast concrete product where the fresh concrete is cured with carbon dioxide to gain its strength. The walls of the demoulded and optionally preconditioned concrete product acts as vessels to hold the pressure. In certain embodiments, neither an external pressurized vessel nor curing chamber are utilized to activate concrete. Instead, the internal or external space of hollow concrete products is used as a chamber and carbon dioxide unidirectionally penetrates the concrete walls. No external air tight enclosure is required. This innovation relates to production of precast concrete products, such as hollow precast concrete products, including but not limited to concrete pipes, culvert boxes, manholes, box girders and hollow core slabs. 
     In one aspect, there is accordingly provided a method of curing a concrete product having a cavity within the concrete product and an opening into the cavity, the method comprising: positioning the concrete product on a base, sealing the opening using a cover plate, introducing carbon dioxide (CO2) into the cavity to execute carbonation of the concrete product, and in response to the concrete product attaining a target strength (and/or other targeted specification(s)), unsealing the opening. 
     The method as described above and herein may further include, in whole or in part, and in any combination, one or more of the following additional features and/or steps. 
     In some embodiments, introducing the CO2 into the cavity includes pressurizing the cavity to a first pressure for a first period of time, followed by increasing the pressure in the cavity to a second pressure for a second period of time. 
     In some embodiments, introducing the CO2 is done through the cover plate and/or the concrete product. 
     In some embodiments, the opening is one of an open top end of the concrete product and an open bottom end of the concrete product, and the positioning includes placing the other one of the open top end and the open bottom end onto the base so as to seal the other one of the open top end and the open bottom end. 
     In some embodiments, the method comprises balancing the first and second pressures with the cover plate such that the cover plate continues sealing the opening during presence of the first and second pressures. 
     In some embodiments, the method comprises casting and demoulding the concrete product prior to positioning the concrete product, and wherein the steps of positioning the concrete product and introducing the CO2 are executed after and proximate in time to the step of demoulding. 
     In some embodiments, the steps of positioning the concrete product and introducing the CO2 are executed immediately after the step of demoulding. 
     In some embodiments, the method comprises executing at least one of setting, hydration, and pre-conditioning steps with respect to the concrete product prior to the step of introducing the CO2. 
     In some embodiments, the method comprises hydrating the concrete product after completion of the step of introducing the CO2. 
     In some embodiments, the method comprises pressurizing the cavity to a pre-determined pressure of the CO2. 
     In some embodiments, the method comprises varying the pre-determined pressure of the CO2. 
     In some embodiments, the pre-determined pressure is at least atmospheric pressure. 
     In some embodiments, the sealing the opening is such that at least some CO2 is allowed to escape from the cavity during the carbonation of the concrete product. 
     In some embodiments, the casting is executed using one or a combination of zero-slump concrete, wet concrete, and self-compacting concrete. 
     In some embodiments, fresh concrete is made using one or a combination of hydraulic cement, non-hydraulic cement, slag, pozzolanic materials, fly ash, silica fume and calcium hydroxide as binder. 
     In some embodiments, the casting is executed as one of dry casting and wet casting. 
     In some embodiments, the introducing the CO2 is executed by introducing a gas containing CO2 at a concentration of between 5% and 99.5% CO2 by mass. 
     In another aspect, there is provided a system for curing a precast concrete product having a cavity therein, the cavity having an open bottom end and an open top end, comprising: a base sized to receive the precast concrete product thereon and to cover the bottom end of the cavity, a cover plate sized to be received on top of the precast concrete product and to cover the top end of the cavity, a source of carbon dioxide gas (CO2), and a CO2 conduit fluidly connected to the source of CO2 and being configured to fluidly connect to the cavity. 
     The system as described above and herein may further include, in whole or in part, and in any combination, one or more of the following additional features and/or steps. 
     In some embodiments, the system comprises a height control system connected between the base and the cover plate and being operable to move the cover plate between a closed position in which the cover plate covers the top end of the cavity, and an open position. 
     In some embodiments, the system comprises a frame connected between the base and the cover plate, the cover plate being hinged to the frame to move between a closed position in which the cover plate covers the top end of the cavity, and an open position. 
     In some embodiments, the CO2 conduit fluidly connects to the cavity via one or more of the cover plate, a wall of the precast concrete product, and the base; and the source of CO2 is configured to pressurize the cavity to at least two different pressures that are at or above atmospheric pressure. 
     In some embodiments, a flow control valve is disposed in fluid flow communication with the source of CO2, the flow control valve configured to control a rate and/or a pressure of the CO2 gas supplied into the cavity. 
     In another aspect, there is provided a method of curing a concrete product having a cavity therein, the method comprising: sealing the cavity; executing carbonation of the concrete product by introducing carbon dioxide (CO2) gas into the cavity, and in response to the concrete product attaining a target specification (such as strength and/or other targeted specification(s)), unsealing the cavity. 
     The method as described above and herein may further include, in whole or in part, and in any combination, one or more of the following additional features and/or steps. 
     In some embodiments, the method includes disposing at least one container into the cavity prior to sealing the cavity, the at least one container containing the CO2 gas pressurized therein, and wherein introducing the CO2 gas into the cavity includes releasing the CO2 gas into the cavity from the at least one container. 
     In some embodiments, introducing the CO2 into the cavity includes pressurizing the cavity to a first pressure for a first period of time, followed by increasing the pressure in the cavity to a second pressure for a second period of time. 
     In some embodiments, the at least one container includes at least one of a tire tube and a tire. 
     In some embodiments, introducing the CO2 into the cavity includes operating at least one valve fluidly connected to the at least one of the tire tube and the tire. 
     In some embodiments, sealing the cavity is executed using a cover plate and further comprising balancing the first and second pressures with the cover plate such that the cover plate continues sealing the opening during presence of the first and second pressures. 
     In some embodiments, the method includes casting and demoulding the concrete product prior to the sealing the cavity, and wherein the step of introducing the CO2 is executed after and proximate in time to the step of demoulding. 
     In some embodiments, the step of introducing the CO2 is executed immediately after the step of demoulding. 
     In some embodiments, the method includes executing at least one of setting, hydration, and pre-conditioning steps with respect to the concrete product prior to the step of introducing the CO2. 
     In some embodiments, the method includes hydrating the concrete product after completion of the step of introducing the CO2. 
     In some embodiments, the method includes pressurizing the cavity to a pre-determined pressure of the CO2. 
     In some embodiments, the method includes varying the pre-determined pressure of the CO2. 
     In some embodiments, the pre-determined pressure is at least atmospheric pressure. 
     In some embodiments, the method includes sizing the at least one container to occupy between 10% and 98% of a volume of the cavity. 
     In some embodiments, at least one of the tire tube and the tire is used. 
     In some embodiments, the casting is executed as one of dry casting and wet casting. 
     In some embodiments, introducing the CO2 is executed by introducing a gas containing CO2 at a concentration of between 5% and 99.5% CO2 by mass. 
     In another aspect, there is provided a method of curing a concrete product, the method comprising: enclosing an outer surface of the concrete product in a sleeve having a shape conforming at least in part to the outer surface of the concrete product, such that the sleeve is disposed proximate but spaced apart from the outer surface to define a space between the outer surface and the sleeve; sealing the space between the outer surface and the sleeve; introducing carbon dioxide (CO2) gas into the space between the outer surface and the sleeve to execute carbonation of the concrete product, wherein at least some of the CO2 gas passes through the outer surface of the product in an inward direction; and in response to the concrete product attaining a target specification (such as strength and/or other targeted specification(s)), unsealing the space between the outer surface and the sleeve. 
     The method as described above and herein may further include, in whole or in part, and in any combination, one or more of the following additional features and/or steps. 
     In some embodiments, the concrete product includes a cavity therein and an opening into the cavity, and enclosing the outer surface of the concrete product excludes sealing the opening. 
     In some embodiments, enclosing the outer surface of the concrete product leaves the opening open. 
     In some embodiments, introducing the CO2 gas into the space is executed through the sleeve. 
     In some embodiments, sealing the space between the outer surface of the concrete product and the sleeve includes disposing a cover plate over the concrete product, the cover plate being operatively connected to the sleeve at least during the step of introducing the CO2 gas by being one or more of: weighted to balance a pressure of the CO2; hinged to the sleeve; and guided relative to the sleeve. 
     In some embodiments, the cover plate includes an opening therein, the opening aligning at least in part with the opening into the cavity of the concrete product when the cover plate is disposed over the concrete product. 
     In another aspect, there is provided a system for curing a precast concrete product having a cavity therein, the cavity having an open bottom end and an open top end, comprising: a base sized to receive the precast concrete product thereon and to thereby cover the bottom end of the cavity, a sleeve sized to encompass the concrete product therein, the sleeve having a bottom end that is disposed on and sealed with respect to the base, a cover plate sized to be received on top of the precast concrete product and to thereby cover the top end of the cavity, the cover plate being operatively connected to the sleeve to seal a space between the sleeve and an outer surface of the concrete product when the cover plate and to thereby seal the space, and a source of carbon dioxide gas (CO2) configured to be fluidly connected to the space. 
     The system as described above and herein may further include, in whole or in part, and in any combination, one or more of the following additional features and/or steps. 
     In some embodiments, the source of CO2 fluidly connects to the space via at least one of the sleeve and the cover plate. 
     In some embodiments, the cover plate is hinged to the sleeve to be pivotable between an open position in which the concrete product is movable into and out of the sleeve and a closed position in which the cover plate seals the space between the concrete product and the sleeve. 
     In some embodiments, the source of CO2 is configured to pressurize the cavity to at least two different pressures that are at or above atmospheric pressure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference is now made to the accompanying figures in which: 
         FIG. 1  is a schematic of a system for curing a concrete product; 
         FIG. 2A  is a schematic of a system for curing a concrete product, according to another embodiment; 
         FIG. 2B  is a schematic of a sealing mechanism for one or more concrete products, according to another embodiment; 
         FIG. 3  is a schematic of a system for curing a concrete product, according to another embodiment; 
         FIG. 4  is a schematic cross section of a part of the system of  FIG. 3 ; 
         FIG. 5  is a schematic of non-limiting embodiments of examples of alternative of a cover plate, and a schematic of a base, of the system of  FIG. 1 ; 
         FIG. 6  is a schematic of a system for curing a concrete product, according to another embodiment; 
         FIG. 7  is a schematic of a system for curing a concrete product, according to another embodiment; 
         FIG. 8  is a schematic of a system for curing a concrete product, according to another embodiment; 
         FIG. 9  is a schematic of a system for curing a concrete product, according to another embodiment; 
         FIG. 10  is a schematic of a system for curing a concrete product, according to another embodiment; 
         FIG. 11  is a schematic of a system for curing a concrete product, according to another embodiment; 
         FIG. 12  is a schematic of various sealing portions of the systems according to some embodiments described herein; 
         FIG. 13  shows a method of curing a concrete product; 
         FIG. 14  shows another method of curing a concrete product; and 
         FIG. 15  shows another method of curing a concrete product. 
     
    
    
     DETAILED DESCRIPTION 
     Precast concrete products, e.g. pipes, manholes, culverts, are conventionally cured with heat and steam. Precast concrete products can also be cured with carbon dioxide, where they are placed in sealed enclosed chambers, spaces, rooms or vessels. Calcium-rich materials, e.g. hydraulic cement, slag, non-hydraulic cement, containing calcium silicate phases react with carbon dioxide in the presence of water and are converted to strength-contributing phases including calcium carbonates. 
     The present description relates to systems and methods of producing a precast concrete product (P) where the fresh concrete is cured with carbon dioxide (CO2) to gain its strength. In some embodiments, the walls of the demoulded and in some embodiments preconditioned concrete product (P) act to contain and hold the CO2 pressure, and thereby help reduce curing times and cost. With the present technology, at least some aspects of the production of hollow concrete products (P), such as precast concrete products including concrete pipes, culvert boxes, manholes, box girders and hollow core slabs may be improved. 
     With the above in mind, the present description first describes non-limiting embodiments of a system for curing a precast concrete product (P), then describes non-limiting examples of various possible materials and casting methods that may be associated with the system, and then describes non-limiting examples of various possible methods of curing concrete which may for example be executed using one or more of the illustrated embodiments of the system. 
     System  100   
     Referring to  FIG. 1 , there is shown a system  100  for curing a precast concrete product (P). The system  100  includes a base  102 , such as a floor for example, a lower seal  104  disposed on the base  102 , and an upper seal  106  engaged with a cover plate  108 . The seals  104 ,  106  may be rubber gaskets, sealers, epoxy,  0 -rings or any other suitable seals. The seals  104 ,  106  may encompass the concrete product (P) like a sleeve, such as shown with numeral  306 ′ in  FIG. 5  for example. Such sleeve-like concrete product (P) may cover up to about 20% of a height of the concrete product (P) in some embodiments. Although such configurations may provide sealing advantages, other height percentages are also contemplated. In some embodiments, the lower seal  104  and/or the upper seal  106  may be omitted. 
     In this embodiment, the seals  104 ,  106  and the cover plate  108  are annular to match and seal corresponding part(s) of the concrete product (P), although other shapes and seals may be used such as for example when the concrete product (P) is of a different shape. In some embodiments the cover plate  108  is dimensioned and/or its material is selected so as to provide a weight of the cover plate that balances the gas pressures that may be present within the concrete product (P) as described in this document. As will be described and shown below in more detail, in its various embodiments and applications/systems, the cover plate  108  may be weighted (e.g. to hold the concrete product (P) sealed as described without requiring any additional mechanical forces to be applied to the cover plate  108 ), and/or may be hinged and/or may be guided on one or more rods/supports, and/or may be translatable automatically (e.g. via a suitable conventional powered actuation mechanism). The base  102 , the seals  104 ,  106  and the cover plate  108  are sized to cover a cavity (C) in an precast concrete product (P) of at least one size. In some embodiments, the seals  104 ,  106  and the cover plate  108  are made sufficiently large to be able to enclose and cure, as described in detail below, any one of a number of different sizes of precast concrete products (P) and/or cavities (C). 
     The system  100  further includes a carbon dioxide (CO2) source  110  operable to supply CO2 into the cavity (C) in the precast concrete product (P), and a pressure gauge  112  mounted through the cover plate  108  for monitoring gas pressure in the cavity (C). As shown, in some embodiments, one or more suitable CO2 conduits  110 P, such as pipes or ducts for example, fluidly connect to the carbon dioxide (CO2) source  110  to receive CO2 therefrom. The CO2 conduits  110 P pass through the cover plate  108 , for supplying the CO2 into the cavity (C) in the precast concrete product (P) for curing the precast concrete product (P). In other embodiments, the concrete product (P) may have a different shape. 
     In some embodiments, the interface(s) between the CO2 conduits  110 P and the cover plate  108  may be sealed so as to be at least substantially impermeable to gas. In some embodiments, to facilitate movement of the cover plate  108  on an off each given concrete product (P), the CO2 conduit(s)  110 P may in part or in whole be made flexible. In other embodiments, the CO2 conduits  110 P may be rigid and/or removable from the cover plate  108 , such as via clip-on connectors, to provide for the movement of the cover plate  108  on an off each given concrete product (P). 
     The carbon dioxide (CO2) source  110  may be any suitable carbon dioxide (CO2) source, such as a conventional carbon dioxide (CO2) source, and is therefore not described herein in detail. In some embodiments, the carbon dioxide (CO2) source  110  is configured to control the rate and pressure of the CO2 supplied into the cavity (C) in the precast concrete product (P). To this end, and as shown in  FIG. 1 , the carbon dioxide (CO2) source  110  and/or one or more of the CO2 conduits  110 P may include manual and/or actively controlled flow control valves  114 . The flow control valves  114 , and their associated controls, may be conventional and are therefore not described herein in detail. 
     The cover plate  108  in this embodiment is made from a suitable metal, and is dimensioned to have a weight sufficient to maintain the cavity (C) in the precast concrete product (P) at least substantially sealed during the curing process. It will be understood that the cover plate  108  may be made to have different weights, depending on the pressure(s) to which the carbon dioxide (CO2) source  110  may be configured to pressurize the cavity (C) in the precast concrete product (P) with CO2. That is, the weight of the cover plate  108  may be selected to sufficiently compress the seals  104 ,  108  to maintain the cavity (C) in the precast concrete product (P) at least substantially sealed during the curing process. In other embodiments, the seals  104 ,  108  and the cover plate  108  may have a different shape, depending on the shape of the cavity (C) and the shape of the precast concrete product (P) to be sealed and cured. 
     System  200   
     Now referring to  FIG. 2A , there is shown a system  200  for curing a precast concrete product (P). The system  200  is similar to the system  100 , and therefore the corresponding parts of the system  200  are labeled with the same reference numerals as used with respect to system  100 . 
     A difference between the system  100  and the system  200  is that the system  200  includes a cover plate  108  that is mounted to a height control system  204 . In this embodiment, the height control system  204  includes a vertically oriented support member  206 , such as a steel rod for example. The support member  206  is at its lower end  206 A connected to the base  102  via a suitable connection, such as a sealed connection to prevent escape of CO2 from the cavity (C) through an interface between the support member  206  and the base  102 . At its upper end  206 B, once the cover plate  108  reaches to the proper position, the support member  206  connects to a center of the cover plate  108  via a translating assembly  208  received over the upper end  206 B of the support member  206 . In other embodiments, such as for example when the concrete product is shaped to be positionable around the support member  206  by horizontally moving the product proximate to and in some embodiments over the support member  206 , the cover plate  108  may remain connected to the translating assembly  208  while the concrete product (P) is being placed into position. In other embodiments, different configurations of the sealing mechanism may be used. For example, as shown in  FIG. 2B , the sealing mechanism may have a support member such as a frame that includes one or more rods  206 ′ disposed at one or more distances from each other that are selected to allow one or more concrete products (P) to be moved under the cover plate  108 ′ while the cover plate  108 ′ is movably/translationally connected to the one or more rods  206 ′. Once in position, the translating assembly  208 ′, whether manual and/or automatic, may be operated to move the cover plate  108 ′ into position to seal the inside(s) of the concrete product(s) (P). To this end, and as shown with a double-ended arrow in  FIG. 2B , the translating assembly  208 ′ may be configured to be movable/translatable up and down. In an embodiment, once the cover plate  108 ′ seals the concrete product(s) (P) it may be fixed in place via one or more suitable mechanisms, which may be automatic or manual (e.g. bolts/nuts).  FIG. 2B  thus shows a different embodiment of a sealing mechanism, which may be connected to a CO2 source, such as the CO2 source of  FIG. 2A , and may thus be a part of the system  200 . Any number of sealing mechanisms may be used to cure multiple concrete products (P) in parallel. Any number of CO2 sources may be used for each concrete product (P) and/or sealing mechanism. 
     The translating assembly  208  may be threaded onto a corresponding thread on the upper end  206 B of the support member  206  and may be manually operable by rotation thereof about the support member  206  in one of two directions to translate the cover plate  108  up or down relative to the support member  206 . It is contemplated that any other suitable construction of the translating assembly  208  may be used, including but not limited to an actively actuated translating assembly  208  that may be controlled via one or more suitable actuators, such as electric motors, that may be operatively connected to a suitable controller, such as a computer for example. Since these details may be conventional, they are not described herein in detail. In other embodiments, the translating assembly  208  may be a different type of translating assembly, such as a hydraulic and/or an electric translating assembly operable to provide for the functionality of the system  200  as described herein. 
     System  300   
     Now referring to  FIGS. 3 and 4 , there is shown a system  300  for curing a precast concrete product (P). The system  300  is similar to the system  100 , and therefore the corresponding parts of the system  300  are labeled with the same reference numerals as used with respect to system  100 . 
     A difference between the system  100  and the system  300  is that the system  300  includes one or more frame members  302  forming a frame that supports the cover plate  306 . The one or more frame members  302  may be disposed vertically and may be optionally connected to the base  102 . In another example, the frame can be attached to the floor or placed on the floor. In some embodiments, a single frame member  302  may form the frame  302 F. The frame  302 F in this embodiment is open on opposed lateral sides of the precast concrete product (P), as shown in  FIG. 4 , and is thus does not form a chamber over the precast concrete product (P). In other embodiments, the frame  302 F may be different. The frame/support  302 F may be larger in size than concrete product (P) in order to encompass the concrete product (P). The frame/support  302 F may be made of steel, iron, stainless steel, FRP, plastic or aluminum, although these are non-limiting examples. The frame/support  302 F may not need to be covered and/or may be made using one or more meshes. 
     Another difference between the system  100  and the system  300  is that in the system  300 , the cover plate  306  is hinged, via one or more hinges  304  for example, to a top portion of the frame  302 F so as to be movable between a closed position  306 C and an open position  3060  (shown in dashed line in  FIG. 3 ). In this embodiment, and although need not be the case in other embodiments, the cover plate  306  is pivotable about the one or more hinges  304  between the closed position  306 C and the open position  3060 . 
     In the closed position  306 C, the cover plate  306  encloses the cavity (C) in the precast concrete product (P), to enable a CO2 curing process to take place as described herein below. In the open position  3060 , the cover plate  306  does not obstruct the top portion of the frame  302 F sufficiently to enable the precast concrete product (P) to be inserted into the frame  302 F for curing, and to enable the precast concrete product (P) to be removed from the frame  302 F after curing. It is contemplated that any other movable connection, such as a translational joint, may be used instead of or in addition to the hinge  304 . 
     As shown in  FIG. 3 , in this embodiment, one of the frame members  302  is threaded at a top end thereof and passes through a slot or aperture in the cover plate  306  when the cover plate  306  is in the closed position  306 C. A bolt and/or nut, and/or other securement locks the cover plate  306  in the closed position  306 C by being attached to the top end of that frame member  302  and/or may be tightened to increase compression of the upper seal(s)  106  by the cover plate  306 . It is contemplated that any suitable securement may be used. In some embodiments, the securement may be omitted. 
     Now referring to  FIG. 4 , as shown in this embodiment the upper seal  106  is annular and thinner than a wall of the precast concrete product (P). In at least some embodiments and applications, this helps improve the enclosure of the cavity (C) and placement of the precast concrete product (P) into the system  300 . In some embodiments, the upper seal  106  may have a different thickness and/or shape. Now referring to  FIG. 5 , in some embodiments, the cover plate  306  may have a different shape. 
     One alternative example of the cover plate  306  is shown in the center drawing of  FIG. 5  and labeled as  306 ′. Still referring to  FIG. 5 , in some embodiments, the base  102  may be separate from the floor on which at least part of the system  300  may be positioned, and may have different suitable shapes. One alternative example of the base  102  is shown in the right drawing of  FIG. 5  and labeled as  102 ′. In some embodiments, such as in the non-limiting alternative embodiment  102 ′ for example, the lower seal(s)  104  may be part of the base  102 ′ and/or may be omitted. 
     System  400   
     Now referring to  FIG. 6 , there is shown a system  400  for curing a precast concrete product (P). The system  400  is similar to the system  100 , and therefore the corresponding parts of the system  300  are labeled with the same reference numerals as used with respect to system  100 . 
     A difference between the system  100  and the system  400  is that the system  400  has a base  402  that includes a base portion  402 B, which may be for example cast from concrete or otherwise made part of a floor for example (or as another example may be separate from the floor), and a base plate  402 P disposed on the base portion  402 B. In some embodiments, the base plate  402 P may be an integral part of the base portion  402 B and/or may be omitted. As shown, in this embodiments, the lower seal  104  is an integral part of the base plate  402 P, although this may not be the case in other embodiments. 
     As shown, the CO2 conduits  110 P from the CO2 source  110  pass through the base portion  402 B of the base  402  and are positioned to open into the cavity (C) of the precast concrete product (P) when the precast concrete product (P) is positioned in the system  400 , over the outlets of the CO2 conduits  110 P. In some embodiments, the system  400  may be configured to cure precast concrete products (P) that may have more than one cavity (C). In some such embodiments, the system  400  may have one or more CO2 conduits  110 P per each cavity (C) of the precast concrete products (P), such as for example more than two CO2 conduits  110 P in total. 
     Description of Cover plate: it can be weight, hinged or guided on rod (similar top cover systems as  100 ,  200  and  300 ). 
     System  500   
     Now referring to  FIG. 7 , there is shown a system  500  for curing a precast concrete product (P). The system  500  is similar to the system  100 , and therefore the corresponding parts of the system  500  are labeled with the same reference numerals as used with respect to system  100 . 
     A difference between the system  100  and the system  500  is that the system  500  has one or more CO2 conduits  110 P that traverse a wall of the precast concrete products (P) as shown. While in this embodiment, the system  500  has two CO2 conduits  110 P, in other embodiments, the system  500  may have one, or more than two, CO2 conduits  110 P with corresponding CO2 conduit(s)  110 P traversing the wall(s) of the precast concrete products (P) to inject CO2 into the cavity (C) thereof during a curing process. 
     In some embodiments, the system  500  may include an injection assembly  502  for each of the one or more CO2 conduits  110 P, which may help limit or preclude CO2 leakage out of the cavity (C) during a curing process. Now referring to  FIG. 7 , there are shown three non-limiting examples of the injection assembly  502  are shown, and labeled  502 A,  502 B,  502 C, respectively. The injection assembly  502 A may include an epoxy or other suitable sealer  504  in the interface between the CO2 conduit  110 P and the aperture defined through the wall of the precast concrete product (P) that receives the CO2 conduit  110 P therein. In some embodiments, the epoxy and/or other suitable sealer  504  that may be injected into the interface for example, although other installation methods may also be used. 
     The injection assembly  502 B may include a rubber stopper  506  with suitable one or more apertures defined therethrough, which may be attached to or inserted into the outer end of the CO2 conduit  110 P and/or into the interface between the CO2 conduit  110 P and the aperture defined through the wall of the precast concrete product (P) that receives the CO2 conduit  110 P therein, as shown. The rubber stopper  506  is one example of a sealing member  506  that may be used. Other sealing member(s) are also contemplated. 
     For example, the injection assembly  502 C may include an expanding plug  508  with suitable one or more apertures defined therethrough, which may be attached to or inserted into the outer end of the CO2 conduit  110 P and/or into the interface between the CO2 conduit  110 P and the aperture defined through the wall of the precast concrete product (P) that receives the CO2 conduit  110 P therein, as shown. The expanding plug  506  is another example of the sealing member  506  that may be used. Other sealing member(s) are also contemplated. 
     System  600   
     Now referring to  FIG. 8 , there is shown a system  600  for curing a precast concrete product (P). The system  600  may use a base  102  and one or more seals  104  as described above. However, in this embodiment the system  600  may have a cover plate  602  that is dimensioned and/or be made from material(s) selected so as to provide a weight of the cover plate  602  that balances the  002 -containing gas pressures that may be present within the concrete product (P). In other embodiments of the system  600 , the cover plate  602  may be for example hinged or guided on rod(s) similar to the other embodiments described herein (e.g. similar to top cover systems of  100 ,  200 , and/or  300 ). The  002 -containing gas in this embodiment may be provided by one or more containers  604  containing pressurized  002 -containing gas(s). In some embodiments, the container(s)  604  may be vehicle tires and/or tire tubes as shown schematically in  FIG. 8 . In some embodiments, to reduce waste, the container(s)  604  may be used vehicle tires and/or tubes. The container(s)  604  may retrofitted with one or more valve(s)  606 , such as conventional valves which may be passive or powered, configured to release the gas to provide for pressurization of the concrete product (P) as described in this document. In some embodiments, one or more of the containers may be interconnected via one or more conduits  608  so as to reduce a number of valves  606  to less than one-per-container  608 . In some embodiments, and although this may be different in other embodiments, the valve(s)  606  may be configured to provide an overall flow rate of the gas that is less than  30  standard cubic feet per minute. This may allow to have a single valve  606  per multiple containers  604 . In some embodiments, the  002 -containing gas in the container(s)  604  may have a CO2 concentration between 5% and 99.5% by mass. 
     In some embodiment&#39;s, the container(s)  604  may be sized to occupy between 10% and 98% of the volume of the cavity (C) and may be positioned therein to be out of contact with the inner wall(s) of the concrete product (P) that define the cavity (C). In an aspect, this may lower CO2 volume/content needed to fill the cavity (C) and may allow the cavity (C) to be filled by CO2 more quickly, as smaller free volume of the cavity (C) would be available. In addition, at the end of the carbonation process, a smaller amount of CO 2  remains inside the cavity (C). This makes the exhaustion process faster and the uses less CO2 for the carbonation process. The built-up pressure between the concrete walls of the product (P) and the container(s)  604  allows the gas/CO2 to penetrate the concrete walls and allows CO2 to react with binder in the concrete walls in the presence of water, thereby carbonating/increasing strength of the product (P). In some applications and depending on use for example, the object(s)  604  may be re-filled and re-used for each new concrete product (P) to be carbonated using the system  600 , or may be sized and/or pressurized to carbonate two or more concrete products (P) before needing a re-fill. 
     System  700   
     Referring now to  FIG. 9 , yet another embodiment of a system  700  is shown. Similar to the system  600 , the system  700  includes the step of reducing the  002 -finable volume of the cavity (C) with one or more objects  702 . As shown, in some embodiments, the object(s)  702  may be a balloon containing a gas, i.e. inflatable bag, inflatable plastic or inflatable rubber is placed inside the cavity (C) and may be inflated to occupy between 10% and 98% of the volume of the cavity (C), with goals and outcomes similar to those described with respect to the system  600  above. 
     The filling gas can be air, nitrogen, carbon dioxide, oxygen or any other gas. 
     The object  702  holding the gas can be made of flexible materials such as plastic. The gas pressure inside the object  702  may be higher than the pressure of CO 2  introduced into the cavity (C). Furthermore, the object  702  may be made of steel, iron, aluminum or FRP. The object  702  may be re-used for each new product (P) to be carbonated using the system  700 . 
     System  800   
     Referring now to  FIG. 10 , yet another embodiment of a system  800  is shown. Similar to the system  700 , the system  800  includes the step of reducing the  002 -finable volume of the cavity (C) with one or more objects  802 . As shown, in some embodiments, the object(s)  802  may be a hollow manifold, bladder, tube, and the like. 
     System  900   
     Referring now to  FIG. 11 , yet another embodiment of a system  900  is shown. The system  900  includes an external sleeve  902  disposed proximate the outer walls of the concrete product (P) and receiving CO2 from one or more CO2 sources  110 . The sleeve  902  should be made of steel, iron, aluminum, FRP, plastic or any other suitable material. The sleeve  902  may be made of impermeable materials preventing the gas from escaping. Accordingly, when introduced into the sleeve  902 , the CO2 pressurizes at the outer surfaces of the walls of the product (P) and therefore penetrates the walls inwardly into the cavity (C) as shown with arrows in  FIG. 11 . The sleeve  902  may in shape correspond to the shape of the product (P) and may at one end (e.g. bottom) be enclosed by the base  102  and seal(s)  104 , and at the top end may be enclosed/sealed by a cover plate  904  which may be implemented similar to any one of the embodiments described above, except that the cover plate  904  may include an opening  906  positioned to be in fluid communication with the cavity (C). The opening  906  may allow the CO2 to escape the cavity (C) after having passed thru the walls of the product (P). In some embodiments, the opening  906  may be used to de-pressurize the cavity (C) so as to create a larger pressure differential across the walls of the product (P) and thereby increase CO2 infiltration through the walls. In some cases this may help speed up the carbonation process. To de-pressurize the cavity (C) any suitable means may be used, such as one or more conventional fans, pumps, vacuums and the like. 
     As an example, the system  900  may be used to execute a carbonation process whereby after an optional pre-conditioning of the product (P) as described herein, the product (P) is encompassed by the sleeve  902 . The gap between the product and the sleeve  902  may be more than  1  mm from all sides/edges. Carbon dioxide gas is introduced into the space between the product (P) and sleeve  902 . The concentration of injected carbon dioxide may be higher than 5%. The gas penetration into the concrete walls is thereby executed uni-directionally inward into the cavity (C). The gas may be either injected at the constant flow rate during the carbonation process or variable flow rate. In the case of variable injection flow rate, the flow rate may be lower than  30  standard cubic feet per minute, at the beginning and may be gradually increased over time. The initial low-flow rate approach may help reduce the porosity of concrete product (P) without causing significant leakage. When calcium carbonates and other carbonation reaction products are generated and partially fill the pores in the concrete product (P), a higher carbon dioxide flow rate may be applied. This approach may help develop a rapid early strength and may reduce significant leakage. 
     The rate of CO2 pressure built-up pressure may depend on the rate of gas injection, volume of space between the sleeve  902  and product, concrete mixture proportion, permeability of concrete, porosity, concrete type and product geometry. The carbonation reaction may be an exothermic reaction. No additional and external heat/temperature may be required for the carbonation curing process. The activation process may be executed at the ambient temperature and ambient humidity. The built-up pressure between the concrete walls and external sleeve  902  may allow the gas to penetrate the concrete walls and allow carbon dioxide to react with the binder in the presence of water. In this configuration, the reaction starts from the outer surface of the product (P). In some embodiments, the gas injection and carbonation curing process may be continued for at least  5  minutes. 
     A portion of the gas inside the space between the product (P) and sleeve  902  may travel through the concrete wall and exit from the inner layer of the product (P). At the end of the carbonation curing process, if some carbon dioxide remains inside the space, it may be released before the product (P) is released from the system  900 . In another configuration, the sleeve  902  may be sized to be positioned inside the cavity (C) to encompass the inner concrete walls of the product (P) and the CO 2  gas may thus penetrate from the inner layer to the outer layer of the product (P). 
     Materials 
     The concrete products (P) referred to in the description of the various embodiments of the systems  100 - 900  above may be made from prior art concrete with any known conventional method in prior art. In some embodiments, concrete may include Portland cement or other hydraulic cements as the main cementing material. Fresh concrete may be zero-slump concrete, wet concrete or self-compacting concrete (SCC) for example. Concrete products may be either dry cast or wet cast. 
     In some embodiments, concrete may be produced with slag-based binder. The main binder in the production of slag-based concrete may be slag from steel and stainless steel factories. Other by-products materials such as zinc, iron, copper and sludge may be also utilized as the binder. Various steel slags may be collected from steel factories that practice different methods of steel production. Among the types of slag that may be incorporated as the main binder in production of slag-based concrete may be: stainless steel slag, reducing steel slag, oxidizing steel slag, converter steel slag, electrical arc furnace slag (EAF slag), basic oxygen furnace slag (BOF slag), ladle slag, fast-cooled steel slag and slow-cooled steel slag. 
     The calcium oxide content of slag may be more that 10%, more than 15%, and in some embodiments more than 20%. The silica oxide content may be more than 6%, more than 8%, and in some embodiments more than 12%. The total iron oxide content of slag may be less than 40%, and in some embodiments less than 30%. Steel slag may have a cumulative calcium silicate content of at least 20% and a free lime concentration of less than 10%. All of the above values are based on the mass/weight of slag. In some embodiments, the bulk density of the slag may fall within a range of 1.0 to 2.0 g/cm3 and its apparent density may vary from 2.0 to 6.0 g/cm3. 
     Slags may be ground to a smaller size in some embodiments before being incorporated into the mix to produce concrete. Grinding of slag may be performed with any mechanical machine such as a ball mill, rod mill, autogenous mill, SAG mill, pebble mill, high pressure grinding rolls, VSI or tower mill. The grinding process may be executed either wet or dry. If a wet process is chosen for grinding the slag, the ground slag may be either dried completely or semi-dried at the end of the grinding. Passing slags through sieves is an alternative option to obtain slag with a smaller grain size. Slags passed through mesh#  10  (2000 microns), mesh#  50  (297 microns), mesh#  200  ( 74  microns), mesh#  400  ( 37  microns) may be used as binder. Sieves may be utilized to screen slags either after or before grinding. Thus, one of, or combination of, grinding and screening methods may be executed in order to obtain slag with a proper particle size. 
     In some embodiments, the slag may be pulverized and/or screened to a Blaine fineness of at least 150 m2/kg, and at least 200 m2/kg. In some embodiments, for using slag in slag-based concrete, fifty percent of slag may be smaller than 200 microns (D50=200), smaller than 150 microns (D50=150), smaller than 100 microns (D50=100), smaller than 50 microns (D50=50), smaller than 25 microns (D50=25), and in some embodiments smaller than 10 microns (D50=10). In some embodiments, the free lime content of the slag may be reduced with any standard known method in the prior art before it is incorporated into the mix. In other embodiments, the slag may first be aged to reduce its calcium hydroxide content and then incorporated into the mix. Slag content may be no less than 5% of the weight of concrete, and in some embodiments no less than 20% of the weight of concrete. 
     Various types of aggregate, including natural or artificial normal weight and lightweight aggregates, may be incorporated into the concrete as filler in the production of slag-based concrete. Examples of potential lightweight aggregates includes natural lightweight aggregate (e.g. pumice), expanded clay aggregate, expanded shale aggregate, recycled plastic aggregates and expanded iron slag aggregate. Other usable aggregates include: crushed stone, manufactured sand, gravel, sand, recycled aggregate, granite, limestone, quartz, chalk powder, marble powder, quartz sand and artificial aggregate. These aggregates may be incorporated into the mix as fine and/or coarse aggregates. Aggregate content may be as high as  90 % of the weight of concrete. 
     Mineral and chemical admixtures may be introduced into the mix in some embodiments. Mineral admixtures may include fillers, supplementary cementitious materials, and pozzolanic materials. Possible mineral admixtures include one or a combination of: fly ash, calcinated shale, silica fume, zeolite, GGBF, limestone powder, hydraulic cement and non-hydraulic cement. Chemical admixtures meanwhile may be introduced into the mix to satisfy specific properties. Possible chemical admixtures include but are not limited to: accelerators, retarders, viscosity modifying agents, air entertainers, foaming agents, ASR inhibitors, anti-wash-out, corrosion inhibitors, shrinkage reducers, crack reducers, plasticizers, super plasticizers, water reducers, water repellants, efflorescence controls and workability retainers. Fibers may be added in some embodiments to the slag-based concrete. One or combination of cellulous fiber, glass fiber, micro synthetic fibers, micro synthetic fibers, natural fibers, PP fibers, PVA fibers and steel fibers may be incorporated into the mix. 
     Slag-based concrete products may be either dry cast or wet cast concrete. The fresh slag-based concrete may be made as zero-slump concrete, wet concrete or self-compacting concrete (SCC). For example, in some embodiments, a water to slag ratio, by mass, of self-compacting concrete (SCC) may be more than 0.2. In some embodiments, the water to slag ratio, by mass, of wet cast concrete may be higher than 0.1. In some embodiments, the water to slag ratio, by mass, of dry cast concrete may be less than 0.5. 
     Mixing and Production 
     The concrete products (P) referred to in the description of the various embodiments of the systems 100-900 above may be made using prior art mixing methods. In some embodiments, the concrete products (P) may be made by uniformly mixing all batch ingredients which may include: binders, aggregates, chemical admixtures, mineral admixtures, fibers and water. For example, in one approach, dry ingredients are mixed for at least 1 minute, then water and other liquid ingredients are added after the mixing. In another approach, water may be gradually added during the mixing of dry ingredients. The water content of wet-cast concrete and self-compacting concrete may be higher than that of dry-cast or zero-slump concrete, if no water-reducing admixture is incorporated. Any existing method, technique and equipment used in the prior art to produce the concrete products (P) may be implemented for the production of zero-slump concrete, wet concrete and self-compacting/consolidating conventional concrete and slag-based concrete. 
     Reinforcement 
     As shown in  FIG. 2A  for example, the concrete products (P) referred to in the description of the various embodiments of the systems  100 - 900  above may have a wall thickness of between about 1 mm and 350 mm for example (although any other thicknesses may likewise be used), and may be optionally reinforced with reinforcing material (PR) such as carbon steel, stainless steel, and/or FRP reinforcement bars. In one embodiment, before casting a concrete product (P), the mould is prepared and reinforcing material, in some embodiments, are placed inside the mould before casting. In some embodiments, the diameter of the bars (PR) may vary from 1 mm to 100 mm, with a yield strength between 100 MPa and 2100 MPa for example. In some embodiments, the reinforcements (PR) of a precast concrete product (P) may be designed in accordance with codes and standards that may apply to a jurisdiction for which the precast concrete product (P) may be designed. These particular measurements and characteristics are non-limiting examples only. 
     Casting and placement 
     Fresh concrete may be cast into a suitable conventional mould with any known method in the prior arts. The fresh concrete can be zero-slump concrete (dry concrete), wet concrete or self-compacting concrete. The mould, made of steel, iron, aluminum, plastic or FRP, should be lubricated prior to casting to ease the demoulding process. Wet-cast concrete may be vibrated inside the mould by internal or external vibrators, in some embodiments and applications for no more than 120 seconds. The dry-cast concrete may be formed with a combination of pressing/compacting and vibration. No internal or external vibration may be required for self-compacting concrete. The formed concrete product can be either dry cast or wet cast concrete. Steel, FRP or other types of concrete reinforcement may be installed inside the mould prior to casting, to reinforce concrete for example. 
     Preconditioning 
     Prior to a given carbonation activation process, a concrete product (P) may be subjected to preconditioning. Preconditioning is optional and depends on the type of concrete (conventional or slag-based), type of concrete product (dry-cast or wet-cast) and mixture proportions. Under certain conditions, preconditioning is not necessary. The process of preconditioning reduces the water content of the concrete to a second water-to-binder ratio by weight prior to CO2 curing. In some embodiments, the preconditioning step may be executed either prior to or following demoulding. 
     In preconditioning of some demoulded concrete products (P) (out of mould), and depending on the methods and/or materials used to produce a given concrete product (P): after demoulding, the concrete product (P) product may begin to reduce its water content to generate extra voids inside the concrete. The rate of evaporation of the demoulded concrete depends on the temperature, relative humidity, initial water content, surface area of the product and air flow if the mould is exposed to wind. In addition to natural evaporation, in a preferred embodiment, one or a combination of the following evaporation and/or heating equipment may be used to accelerate the evaporation rate: heating elements, drum heaters, floor heating mats, fans, heaters, blowers or fan heaters. 
     The heating appliances (e.g. elements/wires or floor heating mats or drum heaters) may be installed so as to cover the exterior or interiors surfaces of the demoulded concrete product (P). The elements heat the demoulded concrete walls and may accelerate the evaporation process to reduce the moisture content of the concrete. Fans, heaters, fan heaters and blowers may be placed inside the hollow demoulded concrete product (P) (to reduce the moisture content from inside) or may be placed in front of the exterior surfaces (to reduce the moisture content from outside). 
     These preconditioning steps may continue until the initial water-to-binder content, based on mass, is reduced by up to 95%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10% or 1%. The increase of porosity defined in terms of volume created within the demoulded concrete by either of the above preconditioning methods in concrete is 90%, 60%, 50%, 40%, 30%, 20%, 10%, 5% or 0.1% of the concrete volume. The water-to-binder ratio of the preconditioned concrete may be less than the first water-to-binder ratio by weight. 
     Preconditioning of concrete inside the mould may occur before a given concrete product (P) is demoulded. In this case, the concrete product (P) may be preconditioned and/or set inside the mould before it is demoulded. For example, for wet-cast concrete and self-compacting concrete, it may be preferred that the concrete is preconditioned and/or set inside the mould, if preconditioning is required. 
     The mould may be kept at ambient temperature and humidity, allowing free water to gradually evaporate. This may allow the partial or full hydration and setting of the binder. The hydration and setting rate may depend on the type of binder, its chemical compositions and the concrete mixing proportions. Fans, heaters, fan heaters, blowers, heating elements/wires, floor heating mats or drum heaters may be utilized to accelerate the preconditioning and setting of concrete while concrete remains inside the mould. In another example, the concrete product (P) may remain inside the mould to fully or partially set without implementing any of the above-mentioned preconditioning method. In another example, a portion of the preconditioning step may occur inside the mould and the remaining portion may occur out of the mould. 
     Demoulding 
     The concrete products (P) may be demoulded immediately after casting or may be set/preconditioned/hydrated inside the mould for example for up to 7 days before demoulding. In another example, the concrete can be immediately demoulded and subjected to the carbonation curing right after casting. Demoulding may be undertaken in a given embodiment where the compressive strength of the concrete is at least 0.01 MPa. These particular measurements and characteristics are non-limiting examples only. 
     Methods of Curing/Carbonation 
     With the systems  100 - 900  described in this document in mind, methods of curing concrete products (P) are described next. A non-limiting example of the methods of the present technology, method  1000 , is shown in  FIG. 13 . 
     In one particular embodiment of a method of curing a precast concrete product (P) demoulded concrete product is sealed from the bottom and top, or sides, such as using the base(s)  102 , the cover plate(s)  108 , the seal(s)  104 ,  106  and/or the injection assembly(ies)  502  described above. As described above, in some embodiments, sealing may be done by rubber gasket  106 , sealers  504 , epoxy  504 , O-ring  106  or any other known sealing method in the prior art. This may limit or at least substantially prevent CO2 from leaking out of the cavity (C) of the concrete product (P). In another example, the bottom sealer/seal  104  may be placed inside the mould before casting the concrete product (P) and the concrete product (P) may be cured according to one or more methods described herein while being at least partially in the mold. In examples where only the weight of the cover plate  108  is used to seal the top of the concrete product (P), the cover plate  108  may apply pressure to the upper seal(s)  106  to ensure minimum CO2 leakage from the upper end of the concrete product (P). 
     The weight of cover plate(s)  108  may be selected so as to not crack or damage the concrete product (P). The weight and thickness of the cover plate(s)  108  may be chosen to be more than the applied force to keep the cover plate(s)  108  in place. In some embodiments, the thickness of the cover plate(s)  108  may be more than 1 mm. In some embodiments, the cover plate(s)  108  may be made of steel, iron, stainless steel, FRP, plastic or aluminum. Depending on which of the systems  100 - 900  described above are used, the cover plate(s)  108  may or may not be connected anywhere to the base  102 , and may thus simply rest on top of the concrete product (P) to cover the cavity (C). As seen above, in some such embodiments, the cover plate(s)  108  include at least one aperture that is connected to one or more CO2 sources  110  via one or more CO2 conduits  110 P. In some embodiments, the diameter of each such aperture may be between about 1 mm and 500 mm. These particular measurements and characteristics are non-limiting examples only. 
     The CO2 may be introduced in pure form, or as part of a suitable gas, such as an inert gas, through the aperture(s) in the cover plate(s)  108  and/or via the CO2 conduit(s)  110 P. One non-limiting example is a gas containing CO2 that may be introduced into the cavity (C) to cure the optionally preconditioned concrete product (P) may be introduced at ambient temperature at a concentration of, for example, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 99.5% CO2 by mass. 
     The CO 2  may be injected to fill the cavity (C) inside the concrete product (P). In some such embodiments, the CO 2  may be injected to fill the cavity (C) to atmospheric pressure or one or more pressures above atmospheric pressure. In some embodiments, the internal pressure may monitored with the pressure gauge  112  installed in the cover plate(s)  108 . As described above, in some embodiments, the internal pressure may monitored and controlled via a controller and flow control valve(s)  114 , using the pressure sensor(s)  112  installed in the cover plate(s)  108 . 
     In some embodiments, the concrete product (P) may be carbonated under CO2 gas for a time of between 5 minutes and 15 minutes for example depending on the concentration of the CO2 for example. In some embodiments, the CO2 curing process may continue for up to 72 hours. These particular measurements and characteristics are non-limiting examples only. 
     In some embodiments of the concrete product (P), no external energy or heat may be required during the carbonation curing process. The CO2 activation process may be an exothermic reaction that increases the temperature of the concrete product (P). 
     In some embodiments, the carbonation curing process may be executed at atmospheric pressure, or under a constant carbon dioxide pressure, above atmospheric pressure or under various gas pressures during the activation process. In some embodiments, the carbonation curing process may be executed either variable CO2 pressure. For example, in some embodiments, an initial pressure of the CO2 in the cavity (C) may be brought to between 0 and 10 psig for between, for example, 5 minutes and 15 minutes, depending on the particular composition of the concrete product (P). 
     The pressure of the CO2 in the cavity (C) may then be increased gradually over time to one or more higher pressures. Such initial low-pressure approaches may help reduce the porosity of concrete without causing significant leakage. In some cases, when calcium carbonates and other carbonation reaction products are generated and they partially fill the pores in concrete, a higher carbon dioxide pressure may be applied. Such an approach may help in developing a rapid early strength of the concrete product (P) and may help reduce leakage. 
     In some embodiments, at each pressure increment, the carbonation curing may continue for at least 5 minutes. This interval approach may help prevent carbon dioxide from escaping through the outer layer of product and may also help protect the integrity of the concrete product (P) at early ages. In some embodiments, the pressure of the CO2/gas in the cavity (C) may be brought down at the end of the carbonation activation process to minimize the amount of carbon dioxide remaining inside the cavity (C) before the cavity (C) is unsealed. In some embodiments, the remaining gas may be vented out into the atmosphere or recycled at the end of the curing process. In some embodiments, the recycling step(s) may be executed without bringing down the gas pressure. This recycled gas may be used for the next batch production. 
     The applied pressure of the gas in the cavity (C) may vary from atmospheric pressure to for example 100 psig, depending on the thickness of the walls, porosity, maturity of concrete, concrete mixture proportion, shape, and concrete ingredients of the concrete product (P), and/or on the sealing methods used to seal the cavity (C). In some embodiments, the cavity (C) may not be fully air tight. Part of the injected gas may be allowed to leak from the ends of the product or may fully penetrate through the wall&#39;s thickness and eventually be released from the outer layer of the concrete product (P). 
     In some embodiments, once a target strength (and/or other target specification(s), such as for example specified in The cured concrete product (P) should satisfy the minimum standard requirement described in ASTM/ACl/CSA/NBC, as may be applicable for one or more intended uses) of the concrete product (P) is achieved, the CO2 gas supply may be shut off to the cavity (C) such as via the flow control valve(s)  114  described above, the remaining gas in the cavity (C) may be recycled or simply vented to atmosphere, the cavity (C) may be opened such as by moving the cover plate(s)  108  to the open position  3060  as described above, the CO2 conduit(s)  110 P may be removed from the walls of the concrete product (P) (if any were inserted thereinto as described above), and the cured concrete product (P) may then be taken out of whichever system  100 ,  200 ,  300 ,  400 ,  500  was used. 
     In some embodiments in which a system is used with a hinged and/or secured covering plate  108 , the hinging and/or securement may help reduce an effort required to operate the system and/or may help reduce a weight of the covering plate  108  that is required, respectively. In embodiments where no automated jack/movement/lifting system is used to move the cover plate(s)  108  between the closed and open positions  306 C,  3060 , such as described above with respect to system  200 , the cover plate(s)  108  may be lifted or otherwise moved between the closed and open positions  306 C,  3060  by a crane, forklift or other suitable equipment. The same or similar suitable equipment may be used to take the cured concrete product (P) out of the system  100 ,  200 ,  300 ,  400 ,  500 . 
     After the cured concrete product (P) is taken out, the system  100 ,  200 ,  300 ,  400 ,  500  may then be ready to receive a new precast concrete product (P) therein for curing using one or more of the methods described above. In methods in which one or more CO2 conduit(s)  110 P are inserted through the wall(s) of the precast concrete product (P), after the precast concrete product (P) is cured/carbonated and the CO2 conduit(s)  110 P are removed from the walls, the aperture(s) remaining in the concrete product (P) after curing may be filled with a suitable material, such as filled with cement paste, grout, concrete, mortar, polymer or epoxy. 
     Now referring to  FIG. 14 , there is shown yet another method  1100  for curing a concrete product (P) having a cavity (C) therein. The method  1100  may include disposing at least one container (e.g.  604 ) containing pressurized carbon dioxide (CO2) gas into the cavity (C), sealing the cavity (C); introducing the CO2 into the cavity (C) from the at least one container to execute carbonation of the concrete product, and in response to the concrete product attaining a target strength (and/or other target specification(s)), unsealing the cavity (C). 
     In some embodiments of the method  1100 , the step of introducing the CO2 into the cavity (C) may include pressurizing the cavity (C) to a first pressure for a first period of time, followed by increasing the pressure in the cavity (C) to a second pressure for a second period of time. In some embodiments of the method  1100 , the at least one container may include at least one of a tire tube and a tire. In some embodiments of the method  1100 , the introducing the CO2 into the cavity (C) may include operating at least one valve fluidly connected to the at least one of the tire tube and the tire. In some embodiments of the method  1100 , the sealing the cavity may be executed using a cover plate, such as a suitable one of the cover plates described above, and may further comprise balancing the first and second pressures with the cover plate such that the cover plate continues sealing the opening during presence of the first and second pressures. In some embodiments of the method  1100 , the method  1100  may include casting and demoulding the concrete product prior to the sealing the cavity, and the step of introducing the CO2 may be executed after and proximate in time to the step of demoulding. In some embodiments of the method  1100 , the step of introducing the CO2 may be executed immediately after the step of demoulding. 
     In some embodiments of the method  1100 , the method  1100  may also comprise executing at least one of setting, hydration, and pre-conditioning steps with respect to the concrete product prior to the step of introducing the CO2. In some embodiments of the method  1100 , the method  1100  may also comprise hydrating the concrete product after completion of the step of introducing the CO2. In some embodiments of the method  1100 , the method  1100  may also comprise pressurizing the cavity to a pre-determined pressure of the CO2. In some embodiments of the method  1100 , the method  1100  may also comprise varying the pre-determined pressure of the CO2. In some embodiments of the method  1100 , the pre-determined pressure may be at least atmospheric pressure. In some embodiments of the method  1100 , the method  1100  may also comprise sizing the at least one container to occupy between 10% and 98% of a volume of the cavity. In some embodiments of the method  1100 , the at least one of the tire tube and the tire may be used (i.e. previously used products, thereby allowing reducing a footprint of the method  1100  on the environment). In some embodiments of the method  1100 , casting of the product (P) may be executed as one of dry casting and wet casting. In some embodiments of the method  1100 , the introducing the CO2 may be executed by introducing a gas containing CO2 at a concentration of between 5% and 99.5% CO2 by mass. 
     Referring to  FIG. 11 , there is also provided a method  1200  of curing a concrete product (P), which may include enclosing an outer surface (OS) of the concrete product (P) in a sleeve  902  having a shape conforming at least in part, as shown in  FIG. 11  for example, to the outer surface (OS) of the concrete product (P), such that the sleeve  902  is disposed proximate, also as shown in  FIG. 11 , the outer surface (OS) to define a space  908  between the outer surface (OS) and the sleeve  902 , sealing the space  908  between the outer surface (OS) and the sleeve  902 , and introducing CO2 into the space  908  between the outer surface (OS) and the sleeve  902  to execute carbonation of the concrete product (P). As shown, in some embodiments, the step of introducing the CO2 may include at least some of the CO2 passing through the outer surface (OS) of the product toward in an inward direction (i.e. in a direction from the sleeve  902  into the concrete product (P)). In some embodiments of the method  1200 , the method may also include, in response to the concrete product (P) attaining a target strength (and/or other target specification(s)), unsealing the space  908  between the outer surface (OS) and the sleeve  902 , and for example taking the sleeve  902  off the concrete product (P) or taking the concrete product (P) out of the sleeve  902 , depending on the particular embodiment of the system  900  used to execute the method  1200 . 
     As seen in  FIG. 11 , in some such embodiments the concrete product (P) includes a cavity (C) therein and an opening into the cavity (C), and the enclosing the outer surface (OS) of the concrete product (P) excludes sealing the opening (O) into the cavity (C). Further as seen in  FIG. 11 , in some such embodiments, the enclosing the outer surface (OS) of the concrete product (P) may leave the opening (O) open, for example to facilitate passing of CO2 through the walls of the concrete product (P). Yet further in some such embodiments, the introducing CO2 into the space may be executed through the sleeve  902 . Further as seen in  FIG. 11 , in some such embodiments, the sealing the space  908  between the outer surface (OS) and the sleeve  902  includes disposing a cover plate  904  over the concrete product (P), the cover plate  904  being operatively connected to the sleeve  902  at least during the step of introducing the CO2, such as by being pivotably connected thereto for example or as described in any of the embodiments above as another example. As seen in  FIG. 11 , in some such embodiments the cover plate  904  may include an opening  904 ′ therein, and the opening  904 ′ may align at least in part with the opening (O) into the cavity (C) of the concrete product (P) when the cover plate  904  is disposed over the concrete product (P). 
     The systems and methods described herein may be used to produce concrete products (P) that may at least satisfy minimum standard requirement(s) described in ASTM/ACl/CSA/NBC. The systems and methods described herein may be used to produce concrete products (P) which may be made using one or a combination of hydraulic cement, non-hydraulic cement, slag, pozzolanic materials, fly ash, silica fume and calcium hydroxide as binder. The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the present technology. For example, a given system for curing a precast concrete product (P) may have a combination of at least some of the features from one or more of the abovementioned embodiments. Still other modifications which fall within the scope of the present technology will be apparent to those skilled in the art, in light of a review of this disclosure.