Alkali-free planted concrete

Abstract

This invention relates to an alkali-free vegetated concrete, comprising the following components: a special cementitious material for non-fired alkali-free vegetated concrete, non-fired silt ceramsite, a water-reducing agent, tap water, and liquid CO2. The special cementitious material for non-fired alkali-free vegetated concrete comprises the following components: S95 mineral powder, steel slag powder, desulfurized gypsum powder, polyferric sulfate, and potassium alum. The non-fired silt ceramsite comprises the following components: the special cementitious material for non-fired alkali-free vegetated concrete and river / lake silt. The alkali-free vegetated concrete of this invention can utilize large quantities of steel slag, desulfurized gypsum, and river / lake silt, is non-sintering, has low cost, extremely low carbon emissions, and ultra-low alkali content. Rapid carbonation using liquid CO2 eliminates the need for long-term carbonization curing and large-scale investment in carbonization curing equipment. The resulting product exhibits superior physical and mechanical properties and durability compared to ordinary vegetated concrete, and is alkali-free. It effectively solves the common problem of high alkali content after hydration in ordinary vegetated concrete, promoting plant growth.

Description

Technical Field

[0001] This invention relates to a type of concrete, and more particularly to a high-strength, low-carbon, and durable alkali-free plantable concrete that can make extensive use of river and lake silt and industrial solid waste. Background Technology

[0002] Vegetated concrete, also known as green concrete, is widely used in water conservancy, highways, railways, waterways, environmental protection, and ecology. Ecological concrete technology is now widely applied in my country, offering advantages such as high strength, durability, erosion resistance, freeze-thaw resistance, and ecological sustainability in vegetated concrete slope protection. It is extensively used in ecological concrete slope protection for rivers, lakes, waterfronts, and highway wetland parks. This technology integrates fundamental knowledge from engineering mechanics, soil science, ecology, and botany to support slopes or sides, forming a comprehensive slope protection system composed of engineering and vegetation. It has become the preferred technology in many river and lake shoreline ecological restoration projects.

[0003] Currently, conventional methods for reducing alkali content in vegetation concrete mainly include incorporating mineral admixtures and acidic additives into the concrete, selecting neutral cementitious materials, surface treatment, and carbonation. However, existing alkali reduction technologies often adversely affect the strength and durability of the concrete, thereby reducing the service life of the vegetation.

[0004] Reference: Liao Wenyu, Shi Xian, Huang Zefeng, Cui Zhihong. Study on alkalinity reduction technology and planting effect of vegetation concrete [J]. Concrete, 2013(7). It is proposed to reduce alkalinity by using accelerated carbonation of vegetation concrete, and the surface pH of the resulting vegetation concrete is <8.2, and the strength is comparable to that of uncarbonated vegetation concrete. However, the carbonation alkalinity reduction method proposed in this paper uses ordinary Portland cement, which has a limited degree of carbonation reaction and requires long-term accelerated carbonation (≥30d) to neutralize the alkaline hydration product Ca(OH)2, which increases the construction difficulty and curing cost. In addition, the carbonation curing of ordinary Portland cement can only reduce the pH of the concrete surface, and CO2 is difficult to penetrate into the concrete interior, resulting in a still high alkalinity inside the concrete. Furthermore, the continued hydration of cement in the later stage will still lead to an increase in alkalinity.

[0005] Chinese patent application number 2022109358435 discloses a low-carbon vegetated concrete and its preparation method. This low-carbon vegetated concrete effectively balances properties such as low alkalinity, high strength, and good durability. However, because it uses low-calcium carbonized cement as the main binder, its hydration activity is extremely low. Therefore, it requires two compaction processes in the mold during molding, and carbonization requires in-mold carbonization. This leads to a complex and costly production process. The two compaction processes are much more time-consuming than pouring, and in-mold carbonization requires a large number of steel molds. Furthermore, the carbonization process is corrosive, requiring corrosion-resistant steel or anti-corrosion coatings for the steel molds, further increasing costs. Furthermore, its binder is low-calcium carbonized cement, made from high-purity limestone (CaCO3 content ≥95wt%) and quartz powder (SiO2 content ≥95wt%). The product is prepared by mixing, homogenizing, pressing, calcining (temperature 1280–1400℃, time 3–6h), and grinding according to the designed Ca / Si ratio. The specific surface area is controlled at 520 kg / cm². The limestone powder used has a CaCO3 content of 70wt% and a specific surface area of ​​350 kg / cm². The coarse aggregate is basalt crushed stone with a particle size of 10–25 mm; all are high-carbon emission materials. Carbonation curing is performed in two steps: the mold curing regime is as follows: carbonation time 1–6h, carbonation temperature 20–30℃, CO2 concentration 20–30 vol%, and pressure at atmospheric pressure. The carbonization reaction regime after demolding is as follows: carbonization time 6–18 h, carbonization temperature 50–80 °C, CO2 concentration 50–100 vol%, and pressure 0.5–1.5 MPa. Not only are the carbonization steps complicated, but large-scale pressurized carbonization kettles are also required, resulting in huge investments.

[0006] River and lake silt is unconsolidated, soft, fine-grained or extremely fine-grained soil formed by physicochemical and biochemical processes in still or slow-moving water environments. It contains pollutants such as heavy metals and organic matter, and its indiscriminate dumping will produce foul odors, inevitably causing secondary pollution to the surrounding environment. It is also an endogenous source of pollution for polluted water bodies such as black and odorous water bodies.

[0007] None of the aforementioned patent documents mention the large-scale use of river and lake silt to prepare vegetated concrete. The carbonization methods used have drawbacks such as long carbonization time, large investment in carbonization equipment, non-low-carbon raw materials, and cumbersome production, making it difficult to promote on a large scale. Summary of the Invention

[0008] The technical problem to be solved by this invention is: to overcome the shortcomings of the existing technology, to provide a high-strength, low-carbon, and durable alkali-free vegetation concrete that can make large-scale use of river and lake silt and industrial solid waste. This involves introducing steel slag, slag desulfurization gypsum, and polyferric sulfate to prepare a special cementitious material for non-fired alkali-free vegetation concrete. This special cementitious material is then mixed with river and lake silt to prepare non-fired silt ceramsite, and this special cementitious material is used to bind the lightweight non-fired silt ceramsite. Liquid CO2 is introduced and stirred to prepare the alkali-free vegetation concrete, achieving the goals of carbonization curing enhancement, low cost, CO2 sequestration, and alkali-free properties.

[0009] The technical solution adopted in this invention is: an alkali-free vegetation concrete, comprising the following components by weight percentage:

[0010] Special cementitious material for non-fired, alkali-free, plant-grown concrete: 38.44%–40.08%

[0011] Non-fired silt ceramsite 45.46%

[0012] Water-reducing agent 0.40%

[0013] Tap water 13.18%

[0014] Liquid CO2 content: 0.88–2.52%.

[0015] Furthermore, the special cementitious material for non-fired, alkali-free, plant-grown concrete comprises the following components by weight percentage:

[0016] S95 mineral powder 38.5%

[0017] Steel slag powder 40.0%

[0018] Desulfurized gypsum powder 20.0%

[0019] Polyferric sulfate 1.0%

[0020] Potassium alum 0.5%.

[0021] Furthermore, the non-fired sludge ceramsite comprises the following components by weight percentage:

[0022] Special cementitious material for non-fired, alkali-free, plant-grown concrete (20.0%)

[0023] 80.0% of the river and lake sediment.

[0024] Furthermore, the water content of the river and lake silt is 65-75%. Due to the high water content of the river and lake silt, no water needs to be added. The non-fired silt ceramsite can be prepared by directly mixing the non-fired alkali-free vegetation concrete special cementitious material and the river and lake silt.

[0025] Furthermore, the water-reducing agent is a liquid polycarboxylic acid with a solid content of 11%.

[0026] Furthermore, the liquid CO2 has a purity of 95%, which can rapidly carbonize calcium-containing materials, such as plant-based concrete.

[0027] The CO2 used is high-purity liquid CO2 with a purity of 95%, which can rapidly carbonize vegetated concrete. The production process is simple and efficient, making it neutral and alkali-free, with multiple benefits: First, the CO2 introduced forms carbonation products, which are permanently sealed once the vegetated concrete has hardened. Second, the carbonation products fill the micropores of the concrete, improving its pore structure and making it stronger. Third, this environmentally friendly vegetated concrete has both economic and environmental benefits and can generate additional carbon tax value in the future. Fourth, the carbonation reaction also makes the vegetated concrete neutral and alkali-free, suitable for plant growth.

[0028] Furthermore, the specific surface area of ​​the S95 mineral powder, steel slag powder, polyferric sulfate, and potassium alum is 600 m². 2 / g.

[0029] Specifically, S95 mineral powder is a conventional material, ground to a specific surface area of ​​600 m². 2 It exhibits high activity after / g.

[0030] Steel slag powder is a conventional material, ground to a specific surface area of ​​600 m². 2 It exhibits high activity after / g.

[0031] Polyferric sulfate is a conventional material, ground to a specific surface area of ​​600 m². 2 After being diluted to a concentration of 10 g, it exhibits high activity and a strong activity-activating effect. It also becomes acidic when dissolved in water, reacting with alum, calcium ions, and sulfate ions to form potassium ferrous sulfate, KFe3(OH)6(SO4)2, with a solubility of 10. -93.21 It can increase the strength of cementitious materials and make them neutral and alkali-free.

[0032] Polyferric sulfate, as a novel, high-quality, and highly efficient inorganic polymeric flocculant based on iron salts, is non-toxic, harmless, safe, and reliable. It exhibits significant effects in removing turbidity, color, oil, water, bacteria, odor, algae, and COD, BOD, and heavy metal ions from water. It is ground to a specific surface area of ​​600 m². 2 The activity is very high after / g, and it is very easy to grind to a specific surface area of ​​600m². 2The S95 ore powder, steel slag powder, desulfurized gypsum powder, potassium alum, etc. after / g form a synergistic activating effect. After hydration, they generate complex salt minerals such as ettringite Aft--3CaO·Al2O3·3CaSO4·32H2O, CSH (calcium silicate) gel--xCaO·SiO2·yH2O, and jaundice iron alum--KFe3(OH)6(SO4)2. They also form silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra. Calcium hydroxide is not generated, making the entire system stable, high-strength, and dense, and ensuring that the cementing material is neutral and alkali-free.

[0033] Potassium alum is a common material, ground to a specific surface area of ​​600 m². 2 After being diluted to a concentration of 10 g, it exhibits high activity and a strong activity-activating effect. It also forms a weakly acidic solution in water, reacting with polyferric sulfate, calcium ions, and sulfate ions to form potassium ferric sulfate, KFe3(OH)6(SO4)2, with a solubility of 10. -93.21 It can increase the strength of cementitious materials and make them neutral and alkali-free.

[0034] Polyferric sulfate and potassium alum are acidic and weakly acidic substances, respectively. Compared with conventional acidic additives such as calcium dihydrogen phosphate and ferrous sulfate used in current vegetation concrete, these substances promote the formation of calcite, calcium silicate gel, and potassium ferric alum in the system and avoid the formation of calcium hydroxide. This greatly enhances the strength, toughness, flexural strength, density, and durability of hardened alkali-free vegetation concrete and achieves alkali-free neutrality. In addition, since these two substances are water-soluble and acidic, they can also greatly promote the dissolution of liquid CO2 and accelerate the carbonation reaction.

[0035] Clearly, based on the complex salt effect and silicon tetracoordination isomorphism effect of the solid waste-based cementitious system, by grinding to a specific surface area of ​​600 m², 2 The synergistic effect of the five components—steel slag powder, desulfurized gypsum powder, potassium alum, polyferric sulfate, and S95 mineral powder—along with the acidity of potassium alum and polyferric sulfate reducing alkalinity and accelerating CO2 dissolution, and the rapid carbonation effect of liquid CO2, results in a composite strengthening effect of 1+1+1+1>4 in terms of reinforcement, toughening, durability, carbon emission reduction, and alkalinity reduction.

[0036] By employing a non-sintering process and adding polyferric sulfate and alum, ultra-low alkali cement with excellent physical and mechanical properties can be prepared through only one grinding process. Its carbon emissions and alkalinity are far lower than those of ordinary cement that undergoes a two-grinding-one-calcination process.

[0037] The present invention has the following advantages over the prior art:

[0038] 1. It can make extensive use of steel slag, desulfurized gypsum and river and lake silt, without sintering, with low cost, extremely low carbon emissions and ultra-low alkali content;

[0039] 2. Rapid carbonation using liquid CO2 eliminates the need for long-term carbonation curing and large-scale investment in carbonation curing equipment. The resulting product exhibits superior physical and mechanical properties and durability compared to ordinary planted concrete, and is alkali-free.

[0040] 3. It can effectively solve the common problem of high alkali content after ordinary vegetated concrete hydration and promote plant growth. Detailed Implementation

[0041] The embodiments of the present invention are described in detail below. The embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0042] Example 1

[0043] Step 1: Preparation of special cementitious material for non-fired, alkali-free, plant-based concrete:

[0044] Mix the following components by weight percentage: S95 mineral powder 38.5%, steel slag powder 40.0%, desulfurized gypsum powder 20.0%, polyferric sulfate 1.0%, and potassium alum 0.5%, thoroughly, and grind them into a fine powder with a specific surface area of ​​600 μL using a tube mill. 2 / g, to obtain a special cementitious material for non-fired alkali-free plant-based concrete;

[0045] Step 2: Preparation of non-fired sludge ceramsite:

[0046] Mix the following components by weight percentage: 20.0% of the special cementitious material for non-fired alkali-free vegetation concrete (obtained in step one) and 80.0% of river and lake silt, and obtain non-fired silt ceramsite.

[0047] Step 3: Preparation of alkali-free vegetation concrete:

[0048] The following components by weight percentage are mixed evenly in a closed mixer and allowed to stand for 15 minutes to obtain the alkali-free vegetation concrete of the present invention: 40.08% cementitious material for non-fired alkali-free vegetation concrete (obtained in step one), 45.46% non-fired silt ceramsite (obtained in step two), 0.40% water-reducing agent, 0.88% liquid CO2, and 13.18% tap water.

[0049] The physical and mechanical properties of the alkali-free vegetation concrete were tested according to the method in JC / T 2557-2020 "Vegetated Concrete".

[0050] Example 2

[0051] The difference from Example 1 is as follows:

[0052] Step 3: Preparation of alkali-free vegetation concrete:

[0053] The following components by weight percentage are mixed evenly in a closed mixer and allowed to stand for 15 minutes to obtain the alkali-free vegetation concrete of this invention.

[0054] Example 3

[0055] The difference from Example 1 is as follows:

[0056] Step 3: Preparation of alkali-free vegetation concrete:

[0057] The following components by weight percentage are mixed evenly in a closed mixer and allowed to stand for 15 minutes to obtain the alkali-free vegetation concrete of this invention.

[0058] Example 4

[0059] The difference from Example 1 is as follows:

[0060] Step 3: Preparation of alkali-free vegetation concrete:

[0061] The following components by weight percentage are mixed evenly in a closed mixer and allowed to stand for 15 minutes to obtain the alkali-free vegetation concrete of this invention.

[0062] Comparative Example 1

[0063] This comparative example is commercially available planted concrete, which includes the following components by weight percentage: 525 cement 26.05%, fly ash 10.63%, crushed stone 48.43%, gypsum 1.75%, water-reducing agent 0.38%, and tap water 12.76%.

[0064] Comparative Example 2

[0065] Based on Example 1, the amount of liquid CO2 was reduced, the amount of special cementitious material for non-fired alkali-free plant-grown concrete was increased, and the rest remained unchanged.

[0066] The following components by weight percentage were mixed evenly in a closed mixer and allowed to stand for 15 minutes to obtain the vegetation concrete of Comparative Example 2 of this invention.

[0067] Comparative Example 3

[0068] Based on Example 4, the amount of liquid CO2 was increased, the amount of special cementitious material for non-fired alkali-free plant-grown concrete was reduced, and the rest remained unchanged.

[0069] The following components by weight percentage were mixed evenly in a closed mixer and allowed to stand for 15 minutes to obtain the vegetation concrete of Comparative Example 3 of this invention.

[0070] Table 1. Performance of alkali-free vegetation concrete prepared in Examples 1-4 and comparative examples 1-3 of this invention.

[0071]

[0072] As can be seen from the performance data of Examples 1 to 4 in the table, when the dosage of the special cementitious material for non-fired alkali-free planted concrete is 38.44% to 40.08%, the compressive strength increases and the pH value decreases as the dosage decreases until it becomes neutral and alkali-free. When the dosage of liquid CO2 is 0.88% to 2.52%, the compressive strength continues to increase and the pH value decreases as the dosage increases until it becomes neutral and alkali-free. Therefore, it is evident that liquid CO2 has a significant effect on improving the compressive strength of planted concrete and reducing alkalinity.

[0073] Compared to Comparative Example 1, the 28-day compressive strength of the alkali-free planted concrete obtained in this example can be increased by up to 112.4%, and the pH value can be as low as 7.00. Both physical and mechanical properties are superior to conventional products on the market. Comparative Example 2, which reduced the amount of liquid CO2 and increased the amount of special cementitious material for non-fired alkali-free planted concrete based on Example 1, had an insufficient amount of CO2, resulting in a pH value of 8.02, which is weakly alkaline and does not reach alkali-free neutrality. Its mechanical properties also decreased, even worse than Example 1. Comparative Example 3, which increased the amount of liquid CO2 and reduced the amount of special cementitious material for non-fired alkali-free planted concrete based on Example 4, achieved a pH value of 7.00, which is neutral and alkali-free. However, due to the excessive reduction in cementitious material, its strength was even lower than Comparative Example 2, which is also undesirable.

[0074] The alkali-free vegetation concrete prepared by this invention has a much lower carbon emission than ordinary vegetation concrete because most of the raw materials are solid waste and high-temperature sintering is not used. It has significant economic and social benefits.

Claims

1. An alkali-free plantable concrete, characterized in that, The product comprises the following components by weight percentage: 38.44–40.08% special cementitious material for non-fired, alkali-free, plant-grown concrete. Non-fired silt ceramsite 45.46% Water-reducing agent 0.40% Tap water 13.18% Liquid CO2 content: 0.88–2.52%; The aforementioned non-fired, alkali-free, vegetation-grown concrete special cementitious material comprises the following components by weight percentage: S95 mineral powder 38.5%. Steel slag powder 40.0% Desulfurized gypsum powder 20.0% Polyferric sulfate 1.0% Potassium alum 0.5%; The non-fired sludge ceramsite comprises the following components by weight percentage: Special cementitious material for non-fired, alkali-free, plant-grown concrete (20.0%) River and lake silt content: 80.0%; The water-reducing agent is a liquid polycarboxylic acid with a solid content of 11%. The purity of the liquid CO2 is 95%; The specific surface area of ​​the S95 ore powder, steel slag powder, polyferric sulfate, and potassium alum is 600 m². 2 / g; the water content of the river and lake silt is 65-75%.

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