Gray commercial concrete using red mud-fly ash for synergic color mixing and preparation method thereof

Abstract

The invention discloses gray commercial concrete for synergistically toning by using red mud and fly ash and a preparation method of the gray commercial concrete. The gray commercial concrete is prepared from the following components in parts by mass: 100 parts of cement, 15 to 25 parts of red mud, 20 to 30 parts of fly ash, 0 to 10 parts of mineral powder, 0.1 to 0.3 part of carbon black or iron black, 1.0 to 1.5 parts of nano CaCO3, 1.0 to 1.2 parts of polycarboxylate superplasticizer, 280 to 380 parts of aggregate and 40 to 55 parts of water. The sand ratio is 35-45%, and the water-binder ratio is 0.38-0.45; the color difference delta E between the concrete and a reference sample is less than or equal to 1.5, the 28-day compressive strength is greater than or equal to 30 MPa, and the chloride ion diffusion coefficient is less than or equal to 1000 * 10 <-12 > m < 2 According to the invention, the color of the red mud and fly ash is consistent with that of a reference sample prepared from ordinary Portland cement (delta E is less than or equal to 1.5) on the premise of not adding pigments and not carrying out decolorization treatment by regulating and controlling the co-doping ratio of the red mud and the fly ash, and the red mud and fly ash composite material is suitable for coating-free engineering scenes such as municipal prefabricated parts, landscape concrete and pavement bricks.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a gray commercial concrete with synergistic color adjustment using red mud and fly ash, and its preparation method. Background Technology

[0002] Red mud is a highly alkaline industrial solid waste generated during the extraction of alumina from bauxite. It is reddish-brown in color and, due to the presence of coloring components such as Fe2O3, is traditionally considered to affect the appearance of concrete, thus limiting its high-value utilization in commercial concrete. Current engineering practices commonly employ decolorization treatment or reduce the dosage of red mud, resulting in low utilization rates and high treatment costs.

[0003] Fly ash, as a byproduct of thermal power plants, is mostly light to dark gray in color and has certain potential for color adjustment. However, current technology lacks research on the synergistic use of red mud and fly ash for color adjustment rather than "decolorization," and no related patents have been published. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a gray commercial concrete with synergistic color adjustment using red mud and fly ash, and its preparation method. By adjusting the ratio of red mud to fly ash and combining it with trace amounts of color-adjusting additives, the color of the reference sample prepared with ordinary silicate cement (ΔE≤1.5) can be achieved without adding pigments or performing decolorization treatment. This method is suitable for painting-free engineering scenarios such as municipal precast components, landscape concrete, and paving bricks.

[0005] To achieve this technical objective, the present invention adopts the following solution:

[0006] In a first aspect, the present invention provides a gray commercial concrete using red mud and fly ash synergistic color adjustment, comprising the following components by mass parts: 100 parts cement, 15-25 parts red mud, 20-30 parts fly ash, 0-10 parts mineral powder, 0.1-0.3 parts carbon black or iron black, 1.0-1.5 parts nano-CaCO3, 1.0-1.2 parts polycarboxylate superplasticizer, 280-380 parts aggregate, and 40-55 parts water; sand ratio 35-45%, water-cement ratio 0.38-0.45; color difference ΔE between the concrete and the reference sample ≤1.5, 28-day compressive strength ≥30 MPa, and chloride ion diffusion coefficient ≤1000×10⁻⁶. -12 m 2 / s.

[0007] Furthermore, the reference specimens were reference concrete specimens without red mud, fly ash, colorant and nano CaCO3 under the same water-cement ratio, the same batch of cement and the same curing conditions; the 28-day CIELAB color space parameters of the reference specimens were: L*∈[60.0,64.0], a*∈[+0.7,+1.7], b*∈[+3.7,+5.3].

[0008] Furthermore, the cement is P·O 42.5 ordinary Portland cement; the aggregate is medium sand with a fineness modulus of 2.6 to 3.0 and 5 to 20 mm continuously graded crushed stone.

[0009] Furthermore, the specific preparation method of the reference specimens is as follows: 100 parts of P·O 42.5 cement, 350 parts of standard aggregate (medium sand + 5-20mm crushed stone), 45 parts of water, and 1.0 part of polycarboxylate superplasticizer from the same batch were mixed and molded according to JGJ 55 "Specification for Mix Proportion Design of Ordinary Concrete". The specimens were cured for 28 days at (20±2)℃ and RH≥95%. The CIELAB color space parameters were measured using a spectrophotometer under a D65 light source as the reference value for calculating ΔE.

[0010] Furthermore, the red mud is Bayer process red mud, with an Fe2O3 content of ≥30%, a particle size of ≤80μm, and a reddish-brown color.

[0011] Furthermore, the fly ash is Class II fly ash, gray in color, with a loss on ignition ≤5% and a particle size ≤45μm.

[0012] Furthermore, the particle size of carbon black or iron black is ≤1μm, the dosage is ≤0.3%, and it is pre-dispersed ultrasonically in 20% mixing water before mixing.

[0013] Furthermore, the mass ratio of red mud to fly ash is 1:1 to 1:1.5.

[0014] Secondly, the present invention provides a method for preparing gray commercial concrete using the aforementioned synergistic color adjustment of red mud and fly ash, comprising the following steps: (a) Ultrasonic dispersion: Add carbon black or iron black to the mixing water accounting for 20% of the total water volume, and ultrasonically disperse for 5 min at 40 kHz and 300 W to form a stable suspension. (b) Solid waste premixing: Red mud, fly ash, mineral powder, and nano-CaCO3 are dry-mixed in a mixer for 60 seconds, with a mixing uniformity of ≥95%; (c) Mixing cement and aggregate: Add cement and aggregate, continue dry mixing for 30 seconds, so that the solid waste mixture coats the surface of the aggregate; (d) Wet mixing: Add the remaining 80% water, polycarboxylate superplasticizer and the suspension from step (a), wet mix for 120s, and control the discharge temperature to ≤35℃ to obtain gray commercial concrete.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a type of commercial concrete with "controllable color + high red mud content". Red mud provides a reddish-brown base color, fly ash provides a gray neutral color, trace amounts of carbon black / iron black are used for fine-tuning, and mineral powder enhances the later strength, achieving color consistency of ΔE≤1.5, ensuring that the red mud content is ≥15%, the 28-day strength is ≥ ordinary C30 concrete, and the durability meets the GB / T14902 standard, achieving the synergistic effect of no painting, no decolorization, low cost, and high content. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0017] Example 1

[0018] With 1m 3 Based on C30 concrete, the dosage of each component is as follows: 1.0 kg of carbon black (tinting strength ≥95%, particle size ≤1 μm) was added to 34 kg of mixing water (accounting for 20% of the total water volume) and pre-dispersed by ultrasonication for 5 min at 40 kHz and 300 W to obtain a stable suspension. Premix 60kg of red mud (Bayer process, Fe2O3≥30%), 80kg of fly ash (Grade II, gray), 30kg of mineral powder (S95), and 5kg of nano CaCO3, and dry mix for 60s; Add 350kg of cement (P·O 42.5) and 1100kg of aggregate (440kg of medium sand, fineness modulus 2.6-3.0; 660kg of crushed stone, 5-20mm continuous gradation, sand ratio 40%), and continue dry mixing for 30s; Add 136 kg of remaining water, 4 kg of polycarboxylate superplasticizer (20% solid content), and the above carbon black suspension, wet mix for 120 seconds, and discharge to obtain gray commercial concrete.

[0019] The concrete performance was tested using the following methods, and the results are shown in Table 1: Red mud content: The proportion of red mud added to the amount of cement; 3d, 7d, and 28d compressive strength: all were tested according to GB / T 50081 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", and cured to the corresponding age according to standard. Chloride ion diffusion coefficient: based on NT BUILD 492 (or GB / T 50082); Mass loss after 300 freeze-thaw cycles: based on GB / T 50082 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete"; Reinforcing bar potential: According to ASTM C876, "Standard Test Method for Half-Cell Potential of Reinforcing Bars in Concrete"; Color difference ΔE: Measured using a spectrophotometer (D65 light source, 10° field of view, 8mm measuring aperture). The CIELAB color space model is calculated using the formula: ΔE=√[(ΔL*)²+(Δa*)²+(Δb*)²].

[0020] The reference sample was ordinary silicate cement concrete (P·O 42.5, water-cement ratio 0.45, cured for 28 days) without red mud, fly ash, colorant and nano CaCO3. The specific preparation method is described in Comparative Example 1. The actual measurements by spectrophotometer were: L*=62.3, a*=+1.2, b*=+4.5.

[0021] In Example 1, the measured values ​​of the concrete were: L*=61.8, a*=+1.5, b*=+4.7. The calculated ΔE=0.6≤1.5, and the color was neutral gray (b* value+4.7).

[0022] Example 2

[0023] The 1.0 kg carbon black in Example 1 was replaced with 1.2 kg iron black (Fe3O4 ≥ 98%, particle size ≤ 1 μm, bluish-black color), and ultrasonically dispersed in 34 kg of mixing water (parameters same as in Example 1). Because the density of iron black is 5.18 g / cm³... 3 () greater than carbon black (1.8 g / cm³) 3 (The ultrasonic time needs to be extended to 8 minutes to prevent sedimentation.) The remaining components and steps are the same as in Example 1.

[0024] Tests showed that the concrete in Example 2 had L*=61.8, a*=+1.0, b*=+3.2, and ΔE=1.4. The color was bluish-gray (b* value +3.2, leaning towards blue).

[0025] As can be seen from Examples 1 and 2, when the reference cement is reddish (b*>+5.0), iron black is preferred to neutralize the red color; when the reference cement is yellowish, carbon black is preferred.

[0026] Comparative Example 1

[0027] Prepare 1m 3Ordinary C30 concrete: 350 kg of cement (P·O42.5, clinker content 16% C4AF, C3A content 7%) and 1100 kg of aggregate (440 kg of medium sand + 660 kg of crushed stone) were added to a forced mixer and dry-mixed for 60 seconds until uniform; 190 kg of water and 5 kg of polycarboxylate superplasticizer were added and wet-mixed for 180 seconds, then discharged. The concrete was mixed and molded according to JGJ 55 "Specification for Mix Proportion Design of Ordinary Concrete". Specimens were cured for 28 days at (20±2)℃ and RH≥95%. The CIELAB color space parameters were measured using a spectrophotometer under a D65 light source as the reference value for calculating ΔE. The measured CIELAB parameters after 28 days were: L*=62.3, a*=+1.2, b*=+4.5. The concrete performance was tested, and the results are shown in Table 1.

[0028] Table 1. Concrete performance test results

[0029]

[0030] Comparative Example 2

[0031] 3.0 kg of iron oxide black pigment was directly mixed with 5 kg of water by hand to form a slurry (without ultrasonic dispersion); 350 kg of cement (P·O 42.5), 1100 kg of aggregate (440 kg of medium sand + 660 kg of crushed stone), and 60 kg of fly ash (Grade II, used only as an admixture, not for color matching) were added to a mixer and dry-mixed for 60 seconds; the above pigment slurry, the remaining 165 kg of water, and 5 kg of polycarboxylate superplasticizer were added, and wet-mixed for 180 seconds (3 minutes), then discharged. The concrete performance test results are shown in Table 1.

[0032] Comparative Example 2 uses a traditional iron oxide pigment tinting scheme. Although the initial color difference ΔE=1.2 meets the requirements, it has the following drawbacks: (1) Poor color stability: After 1000h of UV aging, ΔE increased to 3.5, and obvious fading occurred; (2) High cost: The unit price of pigment is 6 yuan / kg, and the usage is 3kg / m³. 3 Cost: 18 yuan / m 3 This invention costs only 4 yuan / m 3 ; (3) Durability deterioration: The chloride ion diffusion coefficient is higher than the benchmark, and the steel bar potential is close to the corrosion threshold; (4) Poor workability: pigments are prone to agglomeration, requiring increased water-reducing agent dosage and easily clogging pumps.

[0033] In contrast, Example 1 utilizes red mud and fly ash for synergistic color adjustment, eliminating the need for pigments. Its color stability (ΔE change < 0.5), cost, and durability are significantly better than the traditional scheme in Comparative Example 2. For a detailed comparison between the two, please refer to Table 2.

[0034] Table 2 Comparison of traditional color matching methods with Example 1

[0035]

[0036] Performance and mechanism analysis of concrete prepared in Example 1

[0037] (I) Upper limit of admixture and compatibility analysis

[0038] Table 3

[0039]

[0040] Total adhesive material = cement + red mud + fly ash + mineral powder = 350 + 60 + 80 + 30 = 520 kg / m³ 3

[0041] The actual proportion of admixtures is 10 / 520 = 1.92%. All admixtures are within the safety window, are fully compatible with the cementitious system, and can be directly used in reinforced concrete structures.

[0042] (II) Verification of coexistence with Class II fly ash

[0043] Comparison benchmark: The benchmark specimen without carbon black and nano CaCO3 (the composition of the adhesive is the same as in Example 1, except that the colorant and nucleating agent are missing).

[0044] Strength comparison: +1.2% (28d, from 33.8MPa to 34.2MPa)

[0045] Chloride ion diffusion coefficient: -15% (from 1000×10) -12 m 2 / s decreased to 850×10 -12 m 2 / s)

[0046] Conclusion: No strength shrinkage, no adverse reactions, and refined pore structure.

[0047] (III) Validation of coexistence with calcium nitrite / calcium formate (optional early-strength adjuvant)

[0048] Table 4

[0049]

[0050] (iv) Mechanism Analysis

[0051] This invention achieves its technical effect through synergistic color adjustment of red mud and fly ash combined with enhancement by nano-CaCO3 crystal nuclei. The key mechanism is verified as follows: 1. Verification of color adjustment mechanism Method: CIELAB parameters were measured using a spectrophotometer (D65 light source); Conclusion: When the mass ratio of red mud (reddish-brown) to fly ash (gray) is 1:1 to 1:1.5, they complement each other and neutralize to form neutral ash. After slight adjustment with trace amounts of carbon black (0.19% binder), ΔE ≤ 1.5.

[0052] 2. Strengthen mechanism verification Methods: SEM observation + mercury intrusion porosimetry (MIP) measurement of borehole structure; Conclusion: Nano-CaCO3 provides nucleation sites, and the total porosity decreased by 29% (0.058→0.041mL / g) after 28 days, with the critical pore size decreasing to 78nm.

[0053] 3. Interface Adhesion Verification Methods: Splitting tensile strength test + microhardness test; Conclusion: Reducing the ITZ thickness from 35 μm to 22 μm resulted in an 18% increase in interfacial bond strength.

[0054] (v) Verification methods and results of key performance indicators

[0055] Table 5

[0056]

[0057] Key conclusions: Workability: Slump 180±20mm, good compatibility with polycarboxylate system, no pump blockage. Volumetric stability: 90-day carbonization depth 4.2mm (reference 5.5mm), adiabatic temperature rise 28.5℃, comparable to the reference. Durability: The chloride ion diffusion coefficient meets Q-IV environmental requirements (≤1000×10). -12 m 2 / s).

[0058] (vi) Safety verification of reinforcing steel bars

[0059] Table 6. Verification of Reinforcing Steel Passivation and Corrosion Resistance

[0060]

[0061] Safety conclusion: Fe2O3 in red mud exists in a solid state, and the Fe concentration in the pore solution is <0.5 mg / L (below the detection limit), thus not initiating corrosion. Carbon black / iron black contains no Cl - SO4 2- The electrical conductivity is consistent with that of the reference slurry (0.18 S / m). The total amount of admixtures is 1.92% of the adhesive material, which is far below the standard limit (≤40%), and there is no risk of alkali-aggregate reaction.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; if these modifications and variations fall within the scope of the claims of the present invention and their equivalents, they should all be considered to be within the protection scope of the present invention.

Claims

1. A gray commercial concrete using red mud and fly ash for synergistic color adjustment, characterized in that, The following components, by weight, are included: 100 parts cement, 15-25 parts red mud, 20-30 parts fly ash, 0-10 parts mineral powder, 0.1-0.3 parts carbon black or iron black, 1.0-1.5 parts nano-CaCO3, 1.0-1.2 parts polycarboxylate superplasticizer, 280-380 parts aggregate, and 40-55 parts water; sand ratio 35-45%, water-cement ratio 0.38-0.45; color difference ΔE between concrete and reference sample ≤1.5, 28-day compressive strength ≥30MPa, and chloride ion diffusion coefficient ≤1000×10⁻⁶. -12 m 2 / s.

2. The gray commercial concrete using red mud and fly ash synergistic color adjustment according to claim 1, characterized in that, The reference specimens were concrete specimens without red mud, fly ash, colorant and nano CaCO3, with the same water-cement ratio, the same batch of cement and the same curing conditions; the 28-day CIELAB color space parameters of the reference specimens were: L*∈[60.0,64.0], a*∈[+0.7,+1.7], b*∈[+3.7,+5.3].

3. The gray commercial concrete using red mud and fly ash synergistic color adjustment according to claim 1, characterized in that, The cement is P·O 42.5 ordinary Portland cement; the aggregate is medium sand with a fineness modulus of 2.6 to 3.0 and 5 to 20 mm continuously graded crushed stone.

4. The gray commercial concrete using red mud and fly ash synergistic color adjustment according to claim 1, characterized in that, The red mud is Bayer process red mud, with Fe2O3 content ≥30%, particle size ≤80μm, and color reddish-brown.

5. The gray commercial concrete using red mud and fly ash synergistic color adjustment according to claim 1, characterized in that, The fly ash is Class II fly ash, gray in color, with a loss on ignition ≤5% and a particle size ≤45μm.

6. The gray commercial concrete using red mud and fly ash synergistic color adjustment according to claim 1, characterized in that, The particle size of carbon black or iron black is ≤1μm, the dosage is ≤0.3%, and it is pre-dispersed in 20% mixing water by ultrasonication before mixing.

7. The gray commercial concrete using red mud and fly ash synergistic color adjustment according to claim 1, characterized in that, The mass ratio of red mud to fly ash is 1:1 to 1:1.

5.

8. A method for preparing gray commercial concrete using red mud and fly ash synergistic color adjustment as described in any one of claims 1-7, characterized in that, Includes the following steps: (a) Ultrasonic dispersion: Add carbon black or iron black to the mixing water accounting for 20% of the total water volume, and ultrasonically disperse for 5 min at 40 kHz and 300 W to form a stable suspension. (b) Solid waste premixing: Red mud, fly ash, mineral powder, and nano-CaCO3 are dry-mixed in a mixer for 60 seconds, with a mixing uniformity of ≥95%; (c) Mixing cement and aggregate: Add cement and aggregate, continue dry mixing for 30 seconds, so that the solid waste mixture coats the surface of the aggregate; (d) Wet mixing: Add the remaining 80% water, polycarboxylate superplasticizer and the suspension from step (a), wet mix for 120s, and control the discharge temperature to ≤35℃ to obtain gray commercial concrete.

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