Method for designing mix proportion of thin-wall special-shaped bare concrete

Abstract

The invention discloses a thin-wall special-shaped fair-faced concrete mix proportion design method which comprises the following steps: determining main parameter indexes of thin-wall special-shaped fair-faced concrete according to specifications in combination with working conditions of thin-wall special-shaped fair-faced concrete; selecting materials according to the parameter indexes, carrying out preliminary design on a mix proportion, and preparing trial concrete in a laboratory; recording preliminary parameters of trial concrete, including the slump, the expansion and the concrete volume weight under the working conditions of simulating concrete leaving and pump entering, and checking whether the obtained parameters of the slump, the expansion and the concrete volume weight meet the parameter indexes or not; if not, the mix proportion is adjusted in a targeted mode according to the index difference; the working condition during construction is simulated, the trial concrete is poured into the special test mold, and whether the strength and the impression meet the parameter indexes or not after 28 days is detected; if not, the mix proportion is adjusted in a targeted mode according to the index difference; and determining the optimal proportion and the material dosage range of the thin-wall special-shaped bare concrete through mathematical statistics and an interpolation method.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, and specifically relates to a concrete mix design method. Background Technology

[0002] Fair-faced concrete, named for its highly decorative effect, directly utilizes the finished surface of concrete, eliminating the need for traditional exterior decoration processes. Unlike ordinary concrete, fair-faced concrete demands high surface quality, requiring a smooth, even surface with uniform color, sharp edges, and freedom from damage and contamination. Thin-walled, irregularly shaped fair-faced concrete, building upon conventional fair-faced concrete, leverages its unique structural expressiveness, spatial shaping capabilities, and artistic appeal to be widely used in high-quality public buildings emphasizing iconic status, cultural significance, and spatial experience.

[0003] Thin-walled, irregularly shaped fair-faced concrete is prone to drying shrinkage and plastic shrinkage cracks due to its thin walls, complex shapes, dense reinforcement, large surface area to volume ratio, and rapid water loss. It must possess the ability to flow uniformly and fill every corner of the formwork without relying on strong vibration, thus avoiding internal voids and surface defects. Simultaneously, due to rapid water loss, it is essential to reduce early hydration heat, autogenous shrinkage, and drying shrinkage.

[0004] Compared to ordinary concrete and fair-faced concrete, thin-walled irregular-shaped fair-faced concrete has higher requirements for high fluidity, self-compacting properties, and crack resistance. Summary of the Invention

[0005] In view of the technical defects of existing thin-walled irregular-shaped fair-faced concrete, the present invention provides a design method for mix proportion of thin-walled irregular-shaped fair-faced concrete.

[0006] To achieve the above objectives, the following technical solution is adopted: A method for mix design of thin-walled, irregularly shaped fair-faced concrete includes the following steps: S1: Determine the main parameter indicators of thin-walled irregular fair-faced concrete according to the specifications and the working conditions of thin-walled irregular fair-faced concrete. S2: Select materials based on the aforementioned parameters, conduct preliminary mix design, and prepare trial concrete in the laboratory; S3: Record the preliminary parameters of the trial concrete mix, including the slump, spread, and unit weight of the concrete under simulated conditions before the concrete leaves the factory and enters the pump. Verify whether the obtained slump, spread, and unit weight parameters meet the specified parameters. If not, adjust the mix proportions accordingly based on the differences in the parameters. S4: Simulate the working conditions during construction by pouring the trial concrete into a specially made test mold and testing whether the strength and appearance meet the parameters after 28 days; if not, adjust the mix proportions accordingly based on the differences in the parameters. S5: When all the above parameters are met, the variables are carefully controlled to conduct multiple trial mixes, and the mix ratio is iteratively optimized. The optimal mix ratio and material dosage range of thin-walled irregular fair-faced concrete are determined by mathematical statistics and interpolation methods.

[0007] According to the above scheme, the specifications mentioned in step S1 include the "Specification for Mix Proportion Design of Ordinary Concrete" JGJ 55-2011 and the "Technical Specification for Application of Fair-faced Concrete" JGJ 169-2009.

[0008] According to the above scheme, the parameters mentioned in step S1 include the slump and spread of the fair-faced concrete mixture upon entering the pump, concrete strength, concrete unit weight, and concrete surface color. Because thin-walled, irregularly shaped fair-faced concrete has thin walls, complex shapes, and dense reinforcement, it requires higher fluidity and self-compacting properties compared to ordinary fair-faced concrete. Therefore, when designing thin-walled, irregularly shaped fair-faced concrete, the slump upon entering the pump should be 220±20mm, and the spread upon entering the pump should be 450±50mm.

[0009] According to the above scheme, the materials mentioned in step S2 include C (cement), K (mineral powder), F (fly ash), W (water), S (sand), G (crushed stone) and admixtures.

[0010] In the optimized scheme, the cement (C) is ordinary Portland cement with a strength of not less than 42.5 grade. The mineral powder (K) is required to be ≥S95 grade. The fly ash (F) is required to be Class F (calcined anthracite / bituminous coal) Grade I ash (fineness: 45μm square hole sieve residue ≤12.0%; loss on ignition ≤5.0%), with a fineness of ≤8.0% being preferred. The water source (W) is unconditionally tap water. The sand (S) is preferably manufactured sand (controllable gradation, mud content close to 0, and particle angularity to improve pumpability), requiring the parent rock strength of manufactured sand to be ≥100MPa (granite / basalt is best), and the stone powder content ≤5%; secondly, natural river sand (smooth particle shape, low water requirement). When using natural river sand, chloride ion testing is required to ensure no sea sand is mixed in, and the mining depth is >2m below the riverbed surface (to reduce mud and shells). Sea sand (even if purified), mountain sand (high mud content), and recycled sand (complex composition, risk of color difference) are prohibited. The particle size distribution should be in the middle to coarser section of Zone II, with a fineness modulus strictly controlled between 2.6 and 2.9, mud content preferably ≤1.0%, and mud lump content preferably ≤0.3%. Granite is the preferred parent material for the crushed stone (G), followed by basalt; limestone, sandstone, and marble are prohibited. Particle shape should be spherical or cubic, with needle-like and flaky particle content ≤5% and dust adhesion ≤0.02%. The admixtures are mainly water-reducing agents and concrete synergists.

[0011] In a further optimized scheme, the sand (S) and crushed stone (G) should preferably be materials from the same source, mined from the same layer, and from the same batch (or with no color difference between batches), and mixing materials from different sources is strictly prohibited; sufficient space should be reserved at the mixing plant to store raw materials, and the sand and gravel required for construction should be delivered in one go. The storage site should not be located in open areas such as docks to avoid problems with moisture content. Polypropylene fibers can also be added to inhibit plastic shrinkage cracks. The fiber length should preferably be 16-19 mm, and the dosage should preferably be 0.6-1.2 kg / m³. 3 It effectively improves the crack resistance of concrete without affecting its workability.

[0012] According to the above scheme, in the preliminary design of the mix proportion of thin-walled irregular fair-faced concrete in step S2, the relevant design parameters should be within the following range: ① Water-cement ratio (W / B) should be 0.35~0.45 (preferably lower); ② Total amount of cementitious materials (B) should be 450~550kg / m³. 3 (Moderate); ③ Cement (C) should account for 50% to 70% of the total adhesive material; ④ Fly ash (F) should account for 15% to 30% of the total adhesive material; ⑤ Mineral powder (K) should account for 15% to 35% of the total adhesive material; ⑥ Water consumption per unit (W) should be 150 to 170 kg / m³ (as low as possible); ⑦ Sand ratio (SP) should be 38% to 45%.

[0013] According to the above scheme, when preparing the test concrete in the laboratory in step S2, the sand (S) and crushed stone (G) should be air-dried and sun-dried 12 hours before mixing to control the moisture content of the aggregate and ensure the accuracy of the experimental data. The particle size distribution of crushed stone (G) should be 5-16mm continuous gradation (or 5-10mm single-size coarse aggregate), with 9.5-16mm particles accounting for 60%-85% and 4.75-9.5mm particles accounting for 15%-40%. The gradation ratio should be determined by crushed stone stacking test with the principle of minimizing porosity.

[0014] According to the above scheme, in step S3, the time when the laboratory mixing is completed is used as the simulated working condition when the concrete leaves the batching plant. The slump, spread, and concrete density at this time are detected and recorded as the basis for testing the concrete leaving the batching plant during formal construction. After that, the concrete is mixed to simulate the working condition before the concrete is pumped into the pump. After the time required for transportation to the site is reached, the slump, spread, and concrete density at this time are detected and recorded.

[0015] According to the above scheme, in step S4, the rationality of the crushed stone (G) particle size distribution is determined by the concrete strength and appearance (whether the aggregate is concentrated in the lower part). The concrete density index is taken from GB / T 50080 based on the concrete strength, and is generally around 2400 kg / m³.

[0016] According to the above scheme, if the color of the concrete does not meet the requirements in step S4, the color can be darkened by increasing the amount of fly ash, or the color can be brightened by adding lime powder.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By proposing a complete and targeted mix design method for thin-walled irregular-shaped fair-faced concrete, the problem of high performance requirements and non-standard and inaccurate mix design schemes for thin-walled irregular-shaped fair-faced concrete is solved. It is highly operable and achieves the effect of providing general guidance for the mix design of thin-walled irregular-shaped fair-faced concrete.

[0018] 2. By clarifying the design performance reference indicators for thin-walled irregular-shaped fair-faced concrete and the specific parameter requirements and allowable deviation requirements for the dosage of each major material, this study, based on practical experience, sets higher requirements than the standard specifications and provides strong guidance. It solves the risk that unclear material standards during the trial mixing of thin-walled irregular-shaped fair-faced concrete can lead to distorted experimental data and uncontrollable quality and common defects in the on-site thin-walled irregular-shaped fair-faced concrete due to mix proportion issues. At the same time, it promotes the strengthening of the control of raw materials for thin-walled irregular-shaped fair-faced concrete.

[0019] 3. By clarifying the adjustment methods for the deviation of relevant parameters from the target value during the concrete trial mixing process, the problem of lack of guidance for deviations during the trial mixing process is solved, further improving the operability of the mix design method for thin-walled irregular fair-faced concrete, and making it suitable for the entire process of mix design for thin-walled irregular fair-faced concrete. Detailed Implementation

[0020] The following embodiments further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0021] Case Background: The foundation of a landmark library building in a coastal educational complex is constructed using exposed concrete. It features an irregular shape, high strength (C50), exceptional height and length (13 meters high, 200 meters in circumference), thin-walled cavities (150mm-400mm thick), and serves as a load-bearing supporting structure. The design strength of the foundation concrete is C50. To convey a sense of solemnity, the construction unit requested that the surface color of the finished concrete be a darker shade than the original concrete color. The concrete mixing plant is located close to the project site, with a transportation time of 20 minutes. The pumping time is considered to be 30 minutes (considering special circumstances, slump and spread data should also be tested at 60 minutes).

[0022] S1: Analysis and mix design for this working condition: Based on the "Specification for Mix Design of Ordinary Concrete" and the "Technical Specification for Application of Fair-faced Concrete," and considering the thin-walled, irregularly shaped fair-faced concrete working condition of the project, the main parameters and indicators of the thin-walled, irregularly shaped fair-faced concrete are determined. The concrete design strength is C50, requiring a darker color. Considering the thin walls, complex shape, and dense reinforcement of the fair-faced concrete in this project, higher requirements are placed on the high fluidity and self-compacting properties of the concrete. The preliminary design of relevant indicators is as follows (subsequent adjustments will be made based on materials and trial mix results): ① Water-cement ratio (W / B) should be 0.35–0.45 (preferably low); ② Total amount of cementitious materials (B) should be 450–550 kg / m³ (moderate); ③ Cement (C) should account for 50%–70% of the total cementitious materials; ④ Fly ash (F) should account for 15%–30% of the total cementitious materials; ⑤ Mineral powder (K): accounting for 15%–35% of the total cementitious materials; ⑥ Unit water consumption (W) should be 150–170. kg / m³ (as low as possible); ⑦ Sand ratio (SP) should be 38%~45%; ⑧ Pump slump index is 220±20mm, expansion index is 450±50mm.

[0023] S2: Materials are configured according to the working conditions and main parameter indicators. Due to the high requirements for the appearance quality of thin-walled irregular fair-faced concrete, high-quality raw materials are required. The selection is as follows: ①C (cement) is Conch brand P.O42.5 ordinary Portland cement; ②K (mineral powder) is S95 grade; ③F (fly ash) is Class I ash of F type; ④W (water) is tap water; ⑤S (sand) is medium-coarse granite parent rock manufactured sand (fineness modulus 2.6~2.9); ⑥G (crushed stone) parent material is granite, cubic particles, needle-like and flaky particle content ≤5%, two specifications of 5~10mm and 10~16mm are selected; ⑦Admixtures are Yongju concrete liquid water-reducing agent (polycarboxylate-based high-performance water-reducing agent) and inorganic concrete synergist.

[0024] Based on material specifications, standard requirements, and on-site conditions, a preliminary mix design was conducted. The mix was then prepared in the laboratory using forced mixing equipment based on the trial mix design. With a slump of 220 and a preference for a darker color, a commonly used concrete mix design was developed as a benchmark, based on materials frequently used by the production unit. The proportions of each material are as follows: C (cement) 330 kg / m³ 3 K (mineral powder) 80kg / m 3 F (coal ash) 90kg / m 3 W (water) 155kg / m 3 S (sand) 645kg / m 3 G1 (10-16mm crushed stone) 870kg / m 3 G2 (5-10mm crushed stone) 160kg / m 3 Water-reducing agent 6.75 kg / m³ 3 Synergist 3.5kg / m3 .

[0025] The amount of thin-walled irregular-shaped fair-faced concrete used is approximately 2000m³. 3 The sand (S) and crushed stone (G), which have the greatest impact on concrete quality, are all sourced from the same origin and from the same batch. Sufficient space is reserved at the mixing plant to store the raw materials, ensuring that the sand and gravel required for construction are delivered in one go. After determining the preliminary mix proportions and before laboratory preparation, the sand (S) and crushed stone (G) are air-dried for 12 hours before mixing to control the moisture content of the aggregates and ensure the accuracy of experimental data.

[0026] S3: Record preliminary parameters of the trial concrete mix, including slump and spread under simulated concrete conditions before and after pumping, as well as concrete unit weight. Measured data are as follows: Slump at discharge 215, spread 460 / 395; Slump and spread at pumping (half an hour) 150, 280 / 290, unit weight 2432 kg / m³. 3 .

[0027] The slump and spread of the simulated concrete before pumping were verified, as well as the unit weight of the trial concrete mix. The conclusions are as follows: the unit weight meets the requirements, but the slump and spread losses are too large, failing to meet the on-site requirements for thin-walled, irregularly shaped fair-faced concrete construction. Data analysis indicates a need to improve the water retention performance of the concrete. The solutions are to increase the water content, increase the water-reducing agent, and increase the sand ratio. After multiple tests and adjustments, the optimal final mix proportion is as follows: C (cement) 330 kg / m³. 3 K (mineral powder) 80kg / m 3 F (coal ash) 90kg / m 3 W (water) 160kg / m 3 S (sand) 645kg / m 3 G1 (10-16mm crushed stone) 870kg / m 3 G2 (5-10mm crushed stone) 160kg / m 3 Water-reducing agent 7.75 kg / m³ 3 Synergist 3.5kg / m 3 The measured data are as follows: Slump and spread at the pump outlet: 230, 500 / 460; Slump and spread at the pump inlet (half an hour): 220, 450 / 470; Bulk density: 2423 kg / m³ 3 .

[0028] S4: Simulate construction conditions by pouring trial concrete into specially designed molds (3 molds per set). The molds are made of plastic-coated templates specifically designed for fair-faced concrete, measuring 200mm × 500mm × 500mm. A 50cm vibrator is used in conjunction with a rubber mallet for compaction. Standard curing is applied. Check the concrete strength at 3 days and 28 days, and the visual quality at 100% strength (primarily observing whether the color meets requirements and whether there are quality defects such as air bubbles, cracks, and aggregate buildup). Specifically, if cracks are prevalent, polypropylene fibers can be added to inhibit plastic shrinkage cracks. The fiber length should be 16–19mm, and the dosage should be 0.6–1.2 kg / m³. 3 It can effectively improve the crack resistance of concrete without affecting its workability; the measured strength of the test blocks all meet the requirements; the experimental data of the defect-free test blocks are extracted separately, and the causes of defects are analyzed to avoid them in a targeted manner.

[0029] S5: Based on the mix proportions used for the concrete surface color confirmed by the construction unit, multiple trial mixes were conducted with precise control of variables. The mix proportions were iteratively optimized, and the optimal mix proportions and material dosage ranges for thin-walled irregular-shaped fair-faced concrete were determined through mathematical statistics and interpolation methods. The allowable deviations for the actual material dosages in the final mix proportions are as follows: cementitious materials ±1.0%, coarse aggregate ±2%, fine aggregate ±2%, mixing water ±0.3%, and admixtures ±0.5%.

[0030] The mix design method for thin-walled irregular-shaped fair-faced concrete of the present invention has been applied in the first phase of the Yangtze River Delta Integration Yueqing Industry-University-Research Base Project, with significant results and has been fully affirmed by all parties. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0031] It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The above embodiments are for illustrative purposes only and are not intended to limit the invention. Those skilled in the art can make various modifications or variations without departing from the spirit and scope of the invention. Therefore, all equivalent technical solutions should also fall within the scope of this invention and should be defined by the claims.

Claims

1. A method for mix design of thin-walled, irregularly shaped fair-faced concrete, characterized in that... Includes the following steps: S1: Determine the main parameter indicators of thin-walled irregular fair-faced concrete according to the specifications and the working conditions of thin-walled irregular fair-faced concrete. S2: Select materials based on the aforementioned parameters, conduct preliminary mix design, and prepare trial concrete in the laboratory; S3: Record the preliminary parameters of the trial concrete mix, including the slump, spread, and unit weight of the concrete under simulated conditions before the concrete leaves the factory and enters the pump. Verify whether the obtained slump, spread, and unit weight parameters meet the specified parameters. If not, adjust the mix proportions accordingly based on the differences in the parameters. S4: Simulate the working conditions during construction by pouring the trial concrete into a specially made test mold and testing whether the strength and appearance meet the parameters after 28 days; if not, adjust the mix proportions accordingly based on the differences in the parameters. S5: When all the above parameters are met, the variables are carefully controlled to conduct multiple trial mixes, and the mix ratio is iteratively optimized. The optimal mix ratio and material dosage range of thin-walled irregular fair-faced concrete are determined by mathematical statistics and interpolation methods.

2. The mix design method for thin-walled irregular-shaped fair-faced concrete as described in claim 1, characterized in that... The specifications mentioned in step S1 include the "Specification for Mix Proportion Design of Ordinary Concrete" JGJ 55-2011 and the "Technical Specification for Application of Fair-faced Concrete" JGJ169-2009.

3. The mix design method for thin-walled irregular-shaped fair-faced concrete as described in claim 1, characterized in that... The parameters mentioned in step S1 include the slump and spread of the fair-faced concrete mixture upon entering the pump, concrete strength, concrete density, and concrete surface color.

4. The mix design method for thin-walled irregular-shaped fair-faced concrete as described in claim 1, characterized in that... The materials mentioned in step S2 include cement, mineral powder, fly ash, water, sand, crushed stone and admixtures.

5. The mix design method for thin-walled irregular-shaped fair-faced concrete as described in claim 4, characterized in that... The material also includes polypropylene fibers with a length of 16–19 mm and a dosage of 0.6–1.2 kg / m³. 3 .

6. The mix design method for thin-walled irregular-shaped fair-faced concrete as described in claim 1, characterized in that... In step S2, the preliminary design of the mix proportion for thin-walled irregular-shaped fair-faced concrete is a water-cement ratio of 0.35–0.45; the total amount of cementitious materials is 450–550 kg / m³. 3 Cement accounts for 50%–70% of the total adhesive material; fly ash accounts for 15%–30% of the total adhesive material; mineral powder accounts for 15%–35% of the total adhesive material; the unit water consumption is 150–170 kg / m³; and the sand ratio is 38%–45%.

7. The mix design method for thin-walled irregular-shaped fair-faced concrete as described in claim 1, characterized in that... In step S2, when preparing the test concrete in the laboratory, the crushed stone particle gradation adopts a 5-16mm continuous gradation or a 5-10mm single-size coarse aggregate; when using continuous gradation, the proportion of 9.5-16mm particles is 60%-85%, and the proportion of 4.75-9.5mm particles is 15%-40%.

8. The mix design method for thin-walled irregular-shaped fair-faced concrete as described in claim 1, characterized in that... In step S3, the time when the laboratory mixing is completed is used as the simulated working condition when the concrete leaves the batching plant. The slump, spread, and concrete density at this time are detected and recorded as the basis for testing the concrete leaving the batching plant during formal construction. After that, the concrete is mixed to simulate the working condition before the concrete is pumped into the pump. After the time required for transportation to the site is reached, the slump, spread, and concrete density at this time are detected and recorded.

9. The mix design method for thin-walled irregular-shaped fair-faced concrete as described in claim 1, characterized in that... In step S4, the rationality of the aggregate particle size distribution is judged by the concrete strength and appearance.

10. The mix design method for thin-walled irregular-shaped fair-faced concrete as described in claim 1, characterized in that... If the color of the concrete does not meet the requirements in step S4, the color can be darkened by increasing the amount of fly ash or brightened by adding lime powder.