阅读说明：本技术 置换空气碳化(dac)工艺和系统 (Replacement air carbonization (DAC) processes and systems ) 是由 扎伊德·艾尔·古尔雷 保罗·韦恩·哈格斯特 于 2018-09-26 设计创作，主要内容包括：本发明涉及二氧化碳气体通过施加压力差来固化混凝土介质的用途,该压力差通过用纯CO<Sub>2</Sub>气体部分置换固化箱中存在的原始环境体积的空气而产生。(The invention relates to the use of carbon dioxide gas for curing concrete media by applying a pressure difference by using pure CO 2 The gas partially displaces the original ambient volume of air present in the curing oven.)

1. Use of carbon dioxide gas for curing concrete media by applying a pressure difference by using pure CO₂The gas partially displaces the original ambient volume of air present in the curing oven.

2. Use according to claim 1, comprising an air displacement step prior to carbonization for generating suction and achieving a negative pressure of 0 to-5 psig within the curing oven.

3. Use according to claim 1, comprising a purging step prior to carbonization, wherein CO₂The gas continuously flows into the curing oven, displacing a portion of the volume of ambient air through the open outlet, while removing CO from the air₂When the concentration of (D) exceeds 10,000ppm, the outlet is closed.

4. Use according to claim 3, wherein, after the purging step, the CO inside the curing oven₂The concentration reaches 20 to 50 percent.

5. Use according to claims 2 to 4, further comprising the steps of: controlled CO injection₂Until the internal pressure reaches 0psig to +2psig and remains constant during the carbonation process, the resulting pressure differential creates sufficient head pressure to better diffuse the gas in the concrete material and improve the carbonation reaction.

6. Use according to claims 1 to 5, wherein the demand for pressure during carbonization is marginalized.

7. Use according to claim 1 for the preparation of precast or dry cast reinforced concrete products and non-reinforced concrete products.

8. Use according to claim 7, wherein the precast or dry cast concrete product is selected from: blocks, pavers, synthetic stones, bricks, hollow boards, pipes, wall boards, fiber cement boards, and retaining walls.

9. Use according to claims 1 to 8, wherein the concrete curing box is selected from: kilns, chambers, autoclaves, vessels, tents, said tanks being designed or modified to be airtight and capable of withstanding marginal deviations in pressures below and above ambient conditions.

10. A replacement air carbonation system for curing concrete media using carbon dioxide gas, the system comprising:

an air-tight and pressurizable chamber with a composite lining of spray-coated polyurethane/polyurea, with flexible or rigid door assembly, wherein,by using pure CO₂The gas partially displaces the original ambient volume of air present in the curing oven to apply and create the pressure differential.

11. The displaced air carbonization system of claim 10, wherein the door assembly is comprised of any one or combination of the following materials: polymer, plastic, aluminum, and/or steel.

12. A displaced air carbonation system according to claim 10 or claim 11 wherein the composite liner is comprised of a first Sprayed Polyurethane Foam (SPF) layer having a thickness of 25mm to 50mm and a second polyurea layer having a thickness of 2mm to 10mm, the composite liner being used to relieve internal stresses caused by pressure differences imposed by the system.

13. A kit for converting a chamber system into an airtight and pressurizable tank, the kit comprising:

spray-coated polyurethane/polyurea composite liners;

polymer sheet door assembly.

14. The kit of claim 13, wherein the composite liner is comprised of a first Spray Polyurethane Foam (SPF) layer having a thickness of 25mm to 50mm and a second polyurea layer having a thickness of 2mm to 10 mm.

Technical Field

The disclosed subject matter relates generally to the use of carbon dioxide gas to cure concrete media by applying a pressure differential by using pure CO₂The gas partially displaces the original ambient volume of air present in the curing oven (curing enclosure).

Background

The carbonation process involves the calcium silicate component of portland cement, namely tricalcium silicate (3 CaO. SiO)₂；C₃S-alite) and dicalcium silicate (2 CaO. SiO)₂；C₂S-belite) which accounts for the majority of the cement. CO 2₂The gas reacts with these calcium silicates in the presence of water to form C-S-H and CaCO₃(according to the following reaction formulas 1 and 2).

2C₃S+3CO₂+3H₂O→C-S-H+3CaCO₃(1)

(also: 2(3 CaO. SiO)₂)+3CO₂+3H₂O→3CaO·2SiO₂·3H₂O+3CaCO₃)

2C₂S+CO₂+3H₂O→C-S-H+CaCO₃(2)

(also: 2(2 CaO. SiO. cndot.)₂)+CO₂+3H₂O→3CaO·2SiO₂·3H₂O+CaCO₃)

In general, C-S-H is considered to be a phase that contributes to the binding of concrete and is one of the products (and much lower amounts of calcium hydroxide) that are typically produced by hydration reactions between cement and water. In the presence of sufficient CO₂In the presence of CO, the rate of phase formation is significantly increased₂But also acts as a reagent to accelerate the reaction that precipitates calcium carbonate (rather than calcium hydroxide). Thus, carbonation is sometimes considered an accelerator for cement hydration. Young et al [1]And Bukowski et al [2]Showed pure CO in a short time₂Upon exposure, the calcium silicate powder rapidly solidifies. This physical development is associated with the equally rapid formation of C-S-H according to equations 1 and 2. It was found that CaCO is produced simultaneously in the reaction₃The crystals are intimately mixed with C-S-H at the nanoscale. These nano CaCO₃The precipitate strengthens the C-S-H matrix, resulting in a resilient composite adhesive matrix.

It would be highly desirable to have a readily adaptable industrial process which actually utilizes carbonization as a means to actively act on portland cement during the normal production cycle to obtain a highly elastic concrete preform characterized by an instantaneous high C-S-H content, higher than commercial standardsMuch stronger and physically reinforced CaCO₃The crystalline precipitated form beneficially sequesters the ability of carbon dioxide.

Disclosure of Invention

The present invention proposes an alternative process configuration to that covered by U.S. provisional patent application No. 62/217,239-PCT/CA2016/051076, which was developed to facilitateThe technology is widely used in existing and new precast concrete plants. The present invention introduces a new curing system that can be integrated rather easily as a design modification to a new curing apparatus or as a physical retrofit to an already running curing process. For the production ofConcrete product (CO)₂Used as a curing agent) that marginalizes the pressure dependence of carbonization. The new system configuration relies on applying a pressure differential sufficient to effect the reaction, rather than promoting CO by increasing the pressure₂Diffusion and carbonization. By first evacuating the ambient air by suction/vacuum and then injecting CO₂Gas to achieve (pressure) difference. Suction may result in a slight negative pressure, which is only temporarily maintained to technically purge as much air volume as possible by the arrangement. The residual volume of ambient air in the curing chamber is minimized, but in practice it is unavoidable. After the partial purge (semi-purge), CO is started₂Injection and conditioning are carried out so that carbonization occurs at any pressure between 0psig and 2psig slightly above gauge pressure. Such operating conditions allow for the carbonisation curing to be carried out in a slightly modified conventional steam curing chamber (the industry benchmark process). The proposed system and related process are assigned the acronym DAC, which is an acronym for displaced air carbonization (displaced air carbonization).

According to the invention, the use of carbon dioxide gas for curing concrete media by applying a pressure difference by using pure CO is provided₂Partial replacement of the original ambient volume present in the curing oven by gasIs generated.

The use of the present invention may also include an air displacement step prior to carbonization for creating suction and achieving a negative pressure of 0psig to-5 psig within the curing oven.

The use of the invention may also include a purge step prior to carbonization, wherein CO is₂The gas continuously flows into the curing oven, displacing a portion of the volume of ambient air through the open outlet, while removing CO from the air₂When the concentration of (D) exceeds 10,000ppm, the outlet is closed.

Solidifying the CO inside the tank after the purging step₂The concentration can reach 20 to 50 percent.

The use of the invention may further comprise the steps of: controlled CO injection₂Until the internal pressure reaches 0psig to +2psig and remains constant during the carbonation process, the resulting pressure differential creates sufficient head pressure to better diffuse the gas in the concrete material and improve the carbonation reaction.

The pressure requirements during carbonization can be marginalized.

The use of the invention can be used for the preparation of pre-cast or dry-cast reinforced concrete products and non-reinforced concrete products.

The precast or dry cast concrete product may be selected from: blocks (masonry units), pavers, synthetic stones, bricks, hollow boards, pipes, wall panels, fiber cement boards, and retaining walls.

The concrete curing box may be selected from: kilns, chambers, autoclaves, vessels, tents (tents), wherein the box (enclosure) is designed or modified to be airtight and capable of withstanding marginal deviations (margin) of pressures below and above ambient conditions.

According to the present invention there is provided a replacement air carbonation system for curing concrete media using carbon dioxide gas, the system comprising:

an air-tight and pressurizable chamber with a composite lining of sprayed polyurethane/polyurea, with flexible or rigid door assembly, by using pure CO₂Partially displacing gas present in curing chambersThe original ambient volume of air exerts and creates a pressure differential.

The door assembly may be constructed of any one or combination of the following materials: polymer, plastic, aluminum, and/or steel.

The composite liner may be comprised of a first Spray Polyurethane Foam (SPF) layer having a thickness of 25mm to 50mm and a second polyurea layer having a thickness of 2mm to 10mm, wherein the composite liner is used to relieve internal stresses caused by pressure differences applied by the system.

According to the present invention, there is provided a kit for converting a chamber system into an airtight and pressurizable tank, the kit comprising:

spray-coated polyurethane/polyurea composite liners;

polymer sheet door assembly.

The composite liner may be comprised of a first spray coated polyurethane foam (SPF) layer having a thickness of 25mm to 50mm and a second polyurea layer having a thickness of 2mm to 10 mm.

The features and advantages of the present subject matter will become more apparent in light of the following detailed description of selected embodiments thereof, as illustrated in the accompanying drawings. It will be appreciated that modifications can be made to various aspects of the disclosed and claimed subject matter, all without departing from the scope of the claims. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive, and the full scope of the subject matter is set forth in the claims.

Drawings

Other features and advantages of the present disclosure will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a process flow diagram of the DAC process for producing a standard 20cm concrete block (CMU);

FIG. 2 shows a schematic of a typical full-scale curing chamber converted to a DAC curing system;

FIG. 3 shows a cross-section of a composite inner wall liner of a DAC system;

FIG. 4 shows the DAC curing system before and after the onset of carbonation curing;

FIG. 5 shows a prototype DAC system;

FIG. 6 shows a prototype air displacement exhaust system;

FIG. 7 shows (a) a housing with a standard 20cm CMU block; (b) a 5mm neoprene polymer sheet that is securely fixed to make the box airtight; and

fig. 8 shows the DAC box system when deflated by suction and then inflated to a constant pressure of 0.5psig during carbonization.

It should be noted that throughout the drawings, like features are identified by like reference numerals.

Detailed Description

DAC process

The DAC process proposes a method for curing concrete products using carbon dioxide instead of steam (conventional curing route). The generation of steam consumes water and natural gas, both of which can be avoided by the DAC process. Reducing cement (the most expensive raw material) can provide further cost savings without sacrificing building codes.The concrete product is superior to the commercial standard in environmental protection performance and durability performance, and is also obviously improved in chemical resilience and physical resilience. The DAC process is applicable to precast concrete products (both reinforced and non-reinforced), including but not limited to: concrete blocks, pavers, pipes, fiber cement slabs and hollow slabs. The process can be adapted to existing vapor curing systems, modified by physical modification, without incurring significant irrecoverable capital costs. Figure 1 is a process flow diagram detailing the steps of the DAC process to produce a20 cm CMU (concrete block).

The various steps in figure 1 are described in more detail below,

i. block molding: this step follows the conventional block forming process with the only difference that the cement content can be reduced. By passing through CO₂The high strength obtained with the treated blocks allows to partially offset the cement content (up to 25%) by directly reducing the cement content and/or replacing it with cement fillers.

Preset (pre)-setting): presetting is an important preparatory step requiring close monitoring and control of the water loss experienced by the mass prior to carbonization. The loss of moisture creates space within the paste composition of the wet mass, thereby promoting CO₂Diffuse and reach the optimal carbonization degree. According to a number of previous parametric studies, mass losses of 30% to 50% of the total water in the mass produce selective results in terms of reaction. The residual moisture content in the cake is to some extent a key parameter-too much, blocking of CO due to clogging₂Diffusing; if the amount is too small, the cement particles will not participate in the reaction due to insufficient water. In the presence of CO₂Previously, it was necessary to maintain an optimum moisture content. In fact, water has two important roles: the water being CO₂A gaseous solvate and calcium silicate dissolving medium; water is a reactant for the subsequent multi-step carbonization reaction that produces C-S-H (calcium silicate hydrate) and CaCO₃The composite adhesive matrix of (1).

C₃S：2(3CaO.SiO₂)+3CO₂+3H₂O→3CaO.2SiO₂.3H₂O+3CaCO₃(1)[1]

C₂S：2(2CaO.SiO₂)+CO₂+3H₂O→3CaO.2SiO₂.3H₂O+CaCO₃(2)[2]

The reaction formulas (1) and (2) show tricalcium silicate (C), which is the main component of cement during carbonization, respectively₃S) and dicalcium silicate (C)₂S) is generally stoichiometric. CO 2₂Final conversion of gas to stabilized CaCO₃. C-S-H and CaCO₃All nucleated in the pores of the wet paste previously occupied by water. It is generally known that C-S-H hydrate affects the adhesive strength of hardened concrete. When calcium silicate is CO₂Upon activation, the rate of formation of this phase is significantly accelerated. Young et al [1]And Bukowski et al [2]Showed pure CO in a short time₂Upon exposure, the calcium silicate powder will rapidly consolidate, which is associated with the same rapid formation of C-S-H.

Drying was quantified by monitoring the weight change experienced by a representative block. Based on the formula of equation 3, the sought dryness is reduced to an absolute final drynessThe formula also takes into account the absorption characteristics of the aggregate (aggregate) for the target weight. This formula calculates the weight reduction that a single block needs to undergo, in this case taking into account a target loss rate of 35% of the total moisture content. The achievement of a weight reduction marks the end of the preset step. For example, WL of NW blocks with initial weight of 16.8kg and aggregate uptake of 3%_35％It was 0.349 kg.

WL_35％＝[(M_{Aggregate material}×A_{Aggregate material})+(M_{Block body}× moisture%)]×35％ (3)

WL_35％: target moisture loss rate of 35% by mass

M_{Aggregate material}: mass of aggregate in block

A_{Aggregate material}: absorption rate of aggregate

M_{Block body}: mass of block

Carbonization: this step is carried out after the appropriately prepared (primed) concrete product has been placed in a curing box and sealed. After ensuring the air-tightness, the tank is sucked (by using pumps, venturis, compressors, etc.) to partially replace the ambient volume of air originally present in the tank. This may result in a partial vacuum condition and a negative pressure of 0.00psig to-5.00 psig may be recorded in the tank. This state is maintained only briefly until CO is injected₂The gas, pressure was returned to atmospheric (0psig) up to 2.00 psig. The primary purpose of the-ve/+ ve pressure difference is to create sufficient head to allow better diffusion of the gas through the concrete material, thereby improving the carbonization reaction.

During carbonization, CO is carefully controlled₂Gas injection to ensure that the concrete medium absorbs its target CO within a given range of curing conditions and time₂Capacity. This "self-cleaning" function was developed to ensure that the injected gas was completely consumed by the concrete, avoiding the release of gas into the atmosphere at the end of the carbonation cycle. A regulator is used to ensure that the carbonization pressure (0psig to 2psig) in the tank is accurately maintained. When the concrete absorbs CO₂The pressure drops, thereby causing the regulator to fight by replenishing the tank with more gas. Flow meters for measuringChemically injected CO₂Total amount of the components. Once the target gas capacity that can be absorbed by the concrete charge is reached, the gas supply is stopped.

For quantifying the CO absorbed by the concrete charge₂Equation 4 may be used. This allows for precise adjustment of the gas injection during carbonization.

Q_CO2＝N×M_{Block material}× (Binder%) × U_CO2(4)

Wherein the content of the first and second substances,

Q_CO2: CO injected per load₂Total amount of gas, Kg

N: number of concrete units (e.g. blocks, pavers, pipes) of the curing charge

M_{Block material}: average mass of the individual blocks, Kg

Adhesive%: the percentage of binder (i.e. cement) in the concrete mix design%

U_CO2: target CO₂Absorption, expressed as mass% of binder (usually 15% to 25%),%)

Equation 4 applies generally to precast concrete. According to a large number of previous experiments, under defined processing conditions, it was conservatively assumed that the concrete unit might trap CO₂Quantity (U)_CO2) Equal to 20% of the initial mass of cement. For example, assuming 10 standard normal weight 20cm concrete blocks (CMUs), an average weight of 17kg per block, and a cement content of 9.7%, the charge may absorb CO₂The amount was 3.3 kg (Q)_CO2＝10×17kg×9.7％×20％)。

DAC system

This section details the components of the DAC curing system, which embodiments are applicable to both new and existing vapor curing apparatuses. The flexibility generally converts any curing system (kiln, vessel, chamber, etc.) into a gas tight box capable of withstanding pressure differences of-5 psig during pumping to up to 2psig during carbonization. Figure 2 shows a typical full-scale DAC curing system, representing a modified version of the most commonly used steam curing chamber. The inset of this figure is a close-up lens of a cross-section of a wall showing a composite liner composed of two successive sprayed layers. The cross-section of the wall shows a polyurethane/polyurea composite liner. The first layer is a Spray Polyurethane Foam (SPF) material of 25mm to 50mm thickness, typically used for insulation purposes of the structure. The second layer is a flexible "polyurea" material having a thickness of 2mm to 10 mm. Both materials exhibit a high elastic deformation tolerance.

The composite liner relieves stresses on the interior walls of the tank caused by the applied pressure differential. It creates a bladder-like compartment, significantly eliminating the dimensional changes imposed during the procedure. An air displacement step is performed prior to carbonization to generate suction and achieve any negative pressure of 0psig to-5 psig. However, the vacuum effect is kept small to avoid delamination of the liner. During carbonation, when the concrete-carrying tank is inflated, the build-up of internal pressure is contained by the lining mainly by the tension and deformation of the material. Figure 3 shows the internal load dissipation during inflation. The polyurea layer undergoes a slight volume expansion, which translates into a tension in the material. The swelling also causes a dimensional deformation () of the SPF layer which in turn absorbs some of the load generated by the internal pressure. The dual relief effect of the composite liner minimizes direct pressure on the actual chamber walls. In this manner, a non-compressible chamber can be converted into an airtight, compressible curing device without any significant structural modification to the chamber.

Many types of spray and non-spray polyurethane foam and polyurea coatings can be used, which vary widely in composition, density and mechanical properties. The present invention is not limited to the use of a particular product or brand, but rather, generally, material qualification standards are set forth to ensure that the liner assembly is properly applied. The first foam (SPF or other spray foam) layer needs to be viscous, porous and slightly malleable so as to be resiliently compressible under load on the liner. The SPF layer is preferably a medium density closed-cell spray foam (ccSPF). Light density open-cell spray foams (ocSPF) may also be used. The second polyurea layer (or other equivalent spray-on polymer or elastomeric material) needs to be seamless, highly viscous and have excellent tensile strength (>20MPa) and be able to achieve > 200% elongation. Self-healing elastomeric polyureas can also be used. Generally, any liner system that is composed of more than one component, meets the above-described attributes, and functions as intended may be interchanged with a given implementation.

Another important feature of the DAC system is the door assembly, where a flexible polymer sheet is used and secured at the open end of the cabinet. After the concrete material is filled, the polymer door is firmly fixed/clamped, so that the box body is completely airtight. The thickness of the door can be based on the desired tensile properties (>20MPa) was adjusted. Before carbonization, a suction pump is used to partially displace the ambient volume of air present in the tank. The flexible polymer door provides a visual indication of this step, where the sheet material will contract internally. By injecting CO once a sufficient amount of air has been discharged₂The gas begins to carbonize until the tank expands and the internal pressure is maintained at 0psig to 2psig throughout the carbonization process. Also, as shown in fig. 4, the polymer sheet protrudes outward during carbonization. The carbonization is continued until the target amount of CO₂(Q_CO2) And (4) completely injecting.

Proof of concept

Scaled-down conceptual validation of DAC systems and processes was performed in the field of a concrete block (CMU) plant. The locally produced CMU block is DAC processed using the prototype shown in fig. 5. For the box, a wooden box was used, inside which a 50mm thick SPF layer was first sprayed (Bayseal 2.7 indulthane from Elastochem) and then a 2mm polyurea layer (9511 HT from Elastochem). Using high purity liquefied CO₂Gas, injection is controlled by a trim valve and regulator. Figure 6 shows a gas displacement exhaust system. A venturi pump is used to generate the suction required to partially displace the ambient volume of air prior to carbonization.

After the prepared concrete block was placed in the box (fig. 7(a)), a 5mm neoprene polymer sheet was firmly fixed using screws and high pressure sealant (X-Trasil HT) as shown in fig. 7 (b). The air in the tank was then evacuated using a venturi pump, and after 5 to 10 minutes the pressure gauge read a negative pressure of-3 psig. As shown in fig. 8, the resulting suction force results in concave deformation of the polymer sheet. Shortly after CO injection began₂Gas until a positive pressure of 0.5psig is reached and maintained throughout the carbonization period (which lasts about 10 hours). Fig. 8 also shows the expansion state of the tank during carbonization. The carbonization is continued until a target CO is provided which can be absorbed by the mass₂Quantity (using equation 4, Q)_CO2＝1.33kg CO₂)。

The final mass achieved an average of 310g of CO₂Absorption and average 1 day compressive strength of 38 MPa.

While the foregoing description has described and shown in the drawings preferred embodiments, it will be apparent to those skilled in the art that modifications may be made without departing from the disclosure. Such modifications are to be considered as possible variations included within the scope of the present disclosure.

Reference to the literature

Young,J.F.；Berger,R.L.；Breese,J.1974.Accelerated Curing of CompactedCalcium silicate Mortars on Exposure to CO2.Journal of the American CeramicSociety 57(9),394-397.

Bukowski,J.M.；Berger,R.L.1979.Reactivity and Strength Development ofCO₂Activated Non-Hydraulic Calcium Silicates.Cement and Concrete Research 9(1),57-68.