Ggbs-based low carbon concrete for pile foundation construction

Abstract

This invention discloses a low-carbon self-compacting concrete, particularly suitable for pile foundation construction. This concrete utilizes a high proportion of granulated blast furnace slag (GGBS), incorporates a viscosity modifier consisting of a polycarboxylate superplasticizer and a hydrophilic viscosity modifier, nano-modified silica fume, and a specially designed aggregate gradation. This carefully selected mix proportion ensures high workability, segregation resistance, and strength while significantly replacing ordinary Portland cement with granulated blast furnace slag, thereby reducing the implicit carbon content. This invention also provides C45 and C60 grade self-compacting concrete formulations with improved workability, including slump flow, L-box test values, V-funnel test time, J-ring height difference, and segregation resistance.

Description

This invention relates to the field of slag-based low-carbon concrete for pile foundation construction. Specifically, the self-compacting concrete provided by this invention can improve the workability of concrete while incorporating a high amount of granulated blast furnace slag. Background Art

[0002] Concrete is the most widely used building material in structural foundations, but traditional concrete often suffers from poor workability. In deep foundation construction such as pile foundations, concrete must be poured into areas with dense reinforcement and deep sections, where sufficient vibration and compaction are difficult. Insufficient compaction of traditional concrete can lead to problems such as voids, honeycomb structures, reduced durability, and poor structural performance.

[0003] Traditionally, duct-cast concrete is evaluated by slump tests upon arrival at the construction site to infer its workability; however, these tests do not fully reflect key properties such as the fluidity and pumpability of concrete during actual pouring. Therefore, concrete that initially appears acceptable may exhibit defects such as voids, cracks, and discontinuities during pouring. These defects are identified through subsequent ultrasonic testing and core sampling, and often result in excessively high porosity and compressive strength below design requirements in the concrete. These hidden defects can lead to drilled pile failure and require costly remedial measures, resulting in significant project delays.

[0004] Therefore, self-compacting concrete has been developed in the industry to overcome these limitations. According to the ENFARC guidelines, self-compacting concrete is defined as a highly fluid, non-segregating concrete that can completely fill the formwork and encase the reinforcing steel under gravity alone, without any external mechanical vibration or intervention, while maintaining homogeneity and exhibiting good anti-segregation and anti-bleeding properties.

[0005] However, traditional self-compacting concrete formulations typically rely on large amounts of ordinary Portland cement and chemical additives, which increases costs and environmental impact, and may even raise compliance issues.

[0006] Granulated blast furnace slag is an increasingly noteworthy auxiliary cementitious material that can replace ordinary Portland cement, with a significantly lower carbon footprint compared to ordinary Portland cement. However, due to the irregular morphology and glassy appearance of granulated blast furnace slag particles, if a large amount of granulated blast furnace slag is added to the mixture, the finished product often has problems such as high viscosity, short slump retention period, and increased risk of segregation and bleeding.

[0007] Therefore, it is necessary to develop a self-compacting concrete formula that can incorporate high amounts of slag to reduce the carbon footprint while maintaining good workability and other properties that are crucial for deep foundation applications such as pile foundation construction. This invention meets this need. 1 HK 30135232 A Specification Summary of the Invention

[0008] This document provides a low-carbon self-compacting concrete for pile foundation construction.Specifically, this concrete comprises: a cementitious material composed of ordinary Portland cement, granulated blast furnace slag, and silica fume; an aggregate composition composed of 10 mm coarse aggregate, 20 mm coarse aggregate, and crushed stone fines; water; and a viscosity-modifying admixture comprising a polycarboxylate superplasticizer and a hydrophilic viscosity modifier. In particular, in some embodiments, the average particle size of the granulated blast furnace slag may be less than 10 micrometers.

[0009] Furthermore, the dosage ranges of each component are as follows: Ordinary Portland cement: 81-270 kg / m³; Granulated blast furnace slag: 270-405 kg / m³; Silica fume: 0-60 kg / m³; Crushed stone: 850-1000 kg / m³; 10 mm coarse aggregate: 300-500 kg / m³; 20 mm coarse aggregate: 150-330 kg / m³; Water: 170-220 liters / m³; Viscosity adjusting admixture: 5.5-11 liters / m³.

[0010] In one embodiment, the weight ratio of ordinary Portland cement: granulated blast furnace slag: silica fume in the cementitious material is 0.15-0.50:0.50-0.75:0-0.10.

[0011] According to one embodiment, the hydrophilic viscosity modifier has a pH of 7.0 to 9.5 in a 1% w / w deionized aqueous solution and a viscosity of 3100 to 3800 mPa·s in a 1.5% w / w deionized aqueous solution.

[0012] According to yet another embodiment, the polycarboxylate superplasticizer has a pH of 6 to 9 and a viscosity of 50 to 100 mPa·s.

[0013] According to yet another embodiment, the hydrophilic viscosity modifier content is 2.0-2.5% by weight of the total viscosity modifier additive. More specifically, the hydrophilic viscosity modifier is selected from carboxymethyl cellulose, hydroxypropyl cellulose, or combinations thereof.

[0014] According to yet another embodiment, the total amount of gelling material is 480 to 540 kg / m³.

[0015] According to another embodiment, the granulated blast furnace slag has a Blaine surface area greater than 0.4 m² / g, a glass content greater than 67%, and a 28-day activity index greater than 84%; in addition, the silica fume has a silica content of at least 85%, a specific surface area of ​​at least 15 m² / g, and a pozzolanic activity index of at least 105%.

[0016] According to another embodiment, the weight ratio of the 20 mm coarse aggregate to the cementitious material is 0.31–1.57, the weight ratio of the 10 mm coarse aggregate to the cementitious material is 0.31–1.26, the weight ratio of the crushed stone fines to the cementitious material is 0.94–1.88, and the weight ratio of water to the cementitious material is 0.32–0.40.

[0017] According to another aspect of the present invention, C45 grade self-compacting concrete is prepared using the above-mentioned concrete, wherein the ratio of ordinary 2 HK 30135232 A silicate cement: granulated blast furnace slag: silica fume is 0.38-0.42: 0.48-0.52: 0.08-0.12, the weight ratio of water to cementitious materials is 0.37-0.39, the weight ratio of 20 mm coarse aggregate to cementitious materials is 0.58-0.62, the weight ratio of 10 mm coarse aggregate to cementitious materials is 0.58-0.62, the weight ratio of crushed stone to cementitious materials is 1.75-1.81, and the weight ratio of viscosity adjusting admixture to cementitious materials is 0.015-0.019.

[0018] According to one embodiment, the slump spread of the above-mentioned C45 grade self-compacting concrete is 670-690 mm, the L-shaped box test value is not less than 0.75, the V-shaped funnel test time is 23-27 seconds, the J-shaped ring height difference is 8-12 mm, and the sieve separation rate is 7.5-10%.

[0019] According to another embodiment, C60 grade self-compacting concrete is prepared using the above-mentioned concrete, wherein the ratio of ordinary Portland cement: granulated blast furnace slag: silica fume is 0.20-0.28: 0.65-0.71: 0.08-0.12, the ratio of water to cementitious material is 0.34-0.36, the weight ratio of 20 mm coarse aggregate to cementitious material is 0.33-0.37, the weight ratio of 10 mm coarse aggregate to cementitious material is 0.83-0.86, the weight ratio of crushed stone to cementitious material is 1.78-1.82, and the weight ratio of viscosity adjusting admixture to cementitious material is 0.023-0.027.

[0020] According to another embodiment, the slump of the above-mentioned C60 grade self-compacting concrete is 660-740 mm, the L-shaped box test value is not less than 0.75, the V-shaped funnel time is 20-26 seconds, the J-shaped ring height difference is 8-14 mm, and the sieve separation rate is 8-13%. Brief Description of the Drawings

[0021] Embodiments of the invention are described in more detail below with reference to the accompanying drawings, in which:

[0022] Figures 1A to 1D provide microscopic images of key components of the concrete of the present invention for material characterization. Figure 1A shows a scanning electron microscope (SEM) image of granulated blast furnace slag, Figure 1B shows a SEM image of silica fume (SF), Figure 1C shows a SEM image of ultrafine granulated blast furnace slag, and Figure 1D shows a SEM image of cement.

[0023] Figures 2A and 2B compare the particle size of the cementitious materials in commercially available concrete formulations and exemplary embodiments of the concrete formulation of the present invention. Figure 2A shows a comparison of the cementitious material particle size distribution between a commercially available C45 grade concrete formulation and an exemplary embodiment of the C45 grade concrete formulation of the present invention.Figure 2B shows a comparison of the particle size distribution of cementitious materials in a commercially available C60 grade concrete formulation and an exemplary embodiment of the C60 grade concrete formulation of the present invention.

[0024] Figures 3A and 3B compare the aggregate gradation of commercially available concrete formulations and exemplary embodiments of the concrete formulation of the present invention. Figure 3A shows a comparison of the aggregate gradation of commercially available C45 concrete formulations and exemplary embodiments of the C45 grade concrete formulation of the present invention. Figure 3B shows a comparison of the aggregate gradation of commercially available C60 concrete formulations and exemplary embodiments of the C60 grade concrete formulation of the present invention.

[0025] Figure 4 lists the chemical composition of each component of the cementitious material used in the concrete formulation of the present invention.

[0026] Figure 5 lists the glass content and physical properties of four different types of granulated blast furnace slag used in the present invention.

[0027] Figure 6 lists the apparent particle density and water absorption of different types of aggregates.

[0028] Figure 7 lists the solid content, density, and water reduction rate of different polycarboxylate superplasticizers used in the present invention. 3 HK 30135232 A Specification

[0029] Figures 8A to 8D show different proportions of the C45 concrete formulation of the present invention. Specifically, Figure 8A shows the proportion with 50% granulated blast furnace slag and a cementitious material content of 520 kg / m³; Figure 8B shows the proportion with polycarboxylate superplasticizer containing viscosity modifier added based on Figure 8A; Figure 8C shows the proportion with different contents of silica fume added based on Figure 8B; Figure 8D shows the proportions of C45 concrete formulations with different aggregate gradations.

[0030] Figure 9 shows the workability of the slag-based concrete proportion shown in Figure 8D, which was evaluated by slump spread test, L-shaped box test, V-shaped funnel test, J-shaped ring test and sieve separation test.

[0031] Figures 10A and 10B illustrate an exemplary embodiment of the C45 concrete formulation of the present invention, which comprises 50% granulated blast furnace slag and 540 kg / m³ of cementitious materials. Figure 10A lists the mix proportions of the C45 concrete formulation; Figure 10B lists the workability of the C45 concrete formulation.

[0032] Figures 11A and 11B illustrate an exemplary embodiment of the C60 concrete formulation of the present invention, which comprises 65% granulated blast furnace slag and 540 kg / m³ of cementitious materials. Figure 11A lists the mix proportions of the C60 concrete formulation; Figure 11B lists the workability of the C60 concrete formulation.

[0033] Figures 12A to 12C illustrate the setup of the test apparatus for evaluating the workability of the concrete formulation of the present invention.Figure 12A shows a schematic diagram of the overall assembly of the L-shaped box; Figure 12B shows a schematic diagram of the overall assembly of the V-shaped funnel; Figure 12C shows a schematic diagram of the overall assembly of the J-shaped ring.

[0034] Figure 13 compares the particle size distribution of three types of granulated blast furnace slag used in the exemplary concrete formulation of the present invention.

[0035] Figures 14A to 14C show the particle size distribution of different types of aggregates used in the concrete formulation of the present invention. Figure 14A shows the particle size distribution of 20 mm coarse aggregate; Figure 14B shows the particle size distribution of 10 mm coarse aggregate; Figure 14C shows the particle size distribution of crushed stone fine aggregate.

[0036] Figure 15 shows the 28-day compressive strength of slag-based concrete under different cementitious material dosages of the present invention.

[0037] Figure 16 shows the workability test results and physical illustration of an exemplary concrete formulation of the present invention. Detailed Description

[0038] According to various embodiments, the present invention provides a low-carbon self-compacting concrete for pile foundation construction. Specifically, low carbon emissions are achieved by incorporating a higher proportion of granulated blast furnace slag into concrete.

[0039] As mentioned above, granulated blast furnace slag, as an auxiliary cementitious material, is a low-carbon alternative to ordinary Portland cement, especially considering that the supply of another auxiliary cementitious material, fly ash, is decreasing due to the phase-out of coal-fired power plants. Typically, the carbon footprint of granulated blast furnace slag is less than 10% of that of ordinary Portland cement, and at the same high substitution rate, slag-based concrete has higher strength than fly ash-based concrete.

[0040] However, granulated blast furnace slag has a glassy morphology in the form of flakes or strips, which leads to workability defects due to its tendency to agglomerate and high interparticle friction, thus seriously affecting the quality of the tremie concrete in cast-in-place piles. 4 HK 30135232 A Specification

[0041] In view of the above challenges, the present invention provides a formulation that employs specially designed additives and material preparation methods to improve the above-mentioned workability problems.

[0042] Hydrophilic viscosity modifier

[0043] Hydrophilic viscosity modifiers are usually water-soluble polymers that can adsorb a large amount of water through hydrogen bonding or electrostatic interactions, forming a hydration layer or a three-dimensional network structure, thereby increasing the viscosity and cohesion of the slurry.

[0044] Hydrophilic viscosity modifiers can rheologically modify granulated blast furnace slag, thereby improving the rheological properties and durability of high-content granulated blast furnace slag self-compacting concrete. This is achieved by the hydrophilic viscosity modifier combining with the slag particles in the concrete. This combination forms a network that can stabilize the mixture and introduce free water into the mixture, thereby reducing the overall viscosity of the mixture, thus maintaining more stable fluidity and preventing segregation.

[0045] Polycarboxylate ether (PCE) superplasticizer

[0046] The polymer chains of PCE adsorb onto the surface of cement and granulated blast furnace slag particles, forming steric hindrance that separates the particles from each other. This helps to form a well-dispersed system, reducing the amount of water required to achieve the desired fluidity, and ultimately helping to reduce the water-cement ratio. The water-cement ratio is a key factor in improving the durability and strength of concrete, especially in high-dosage granulated blast furnace slag self-compacting concrete.

[0047] However, in high-dosage granulated blast furnace slag concrete, the workability usually decreases rapidly because the polycarboxylate ether superplasticizer adsorbs prematurely onto the surface of highly active cementitious materials. Therefore, a slow-release polycarboxylate ether superplasticizer can be used, in which the polycarboxylate ether superplasticizer is preloaded in a porous carrier material and released slowly over time. This method can maintain a stable concentration of free polycarboxylate ether superplasticizer throughout the construction window, thereby extending the duration of the self-compacting properties of the concrete mixture.

[0048] This microencapsulation adsorption slow-release strategy is based on a two-step mechanism. In the first adsorption stage, porous materials with high specific surface area and abundant pore structure, such as mesoporous silica, zeolite, or activated carbon, adsorb polycarboxylate ether molecules in their surface and internal pores. Adsorption is mainly promoted by van der Waals forces, electrostatic interactions, or capillary effects. The effectiveness of this stage is affected by pore size and pore distribution, with mesoporous materials being particularly suitable for accommodating relatively large polycarboxylate ether polymer molecules.

[0049] The second stage is controlled release, controlled by diffusion kinetics. As mixing and hydration reactions proceed, PCE molecules gradually diffuse from the pores into the surrounding slurry. Smaller pore sizes and more tortuous channels help to slow this release and prolong the duration of effective dispersion. This slow-release property prevents cement particles from rapidly becoming saturated with adsorption and helps to delay slump loss, thereby ensuring the stability of rheological properties during construction.

[0050] Nano-modified silica fume

[0051] Silica fume is a finely dispersed mineral admixture, typically determined by X-ray fluorescence spectroscopy (XRF) to have a silica content exceeding 85%. These ultrafine particles fill the voids between cement, granulated blast furnace slag, and aggregates, significantly increasing the overall bulk density, refining the microstructure, reducing porosity, and limiting water migration within the cement paste. Due to their nanometer-scale size, silica fume efficiently fills micropores, enhancing inter-particle interlocking, minimizing bleeding and segregation, and stabilizing fresh concrete to prevent defects such as aggregate settling or water separation. For example, see Figures 2A and 2B, which show a comparison of the cementitious material particle size distribution between commercially available formulations and this formulation.

[0052] Another characteristic of silica fume is its high specific surface area, which increases the viscosity and cohesion of the paste, further preventing component segregation.Although it increases the water consumption of the mixture, this effect can be offset by precisely adjusting the amount of superplasticizer, thereby maintaining fluidity without increasing the water:cement ratio, and thus maintaining a low free water content, thereby achieving true self-compacting performance.

[0053] Optimization of aggregate gradation and incorporation of ultrafine granulated blast furnace slag

[0054] Optimizing the particle size distribution of aggregates and cementitious materials is the basis for achieving true self-compacting performance of high-volume granulated blast furnace slag self-compacting concrete. By precisely screening and adjusting the aggregate composition gradation (10 mm and 20 mm coarse aggregates and crushed stone fines), the aggregates of each particle size smoothly transition to the next particle size, minimizing interparticle friction and eliminating large voids. This gradation maximizes the bulk density, thereby reducing the amount of slurry used, improving fluidity, and preventing blockage during the casting process.

[0055] At the same time, the present invention replaces the standard S95 granulated blast furnace slag with ultrafine granulated blast furnace slag with a significantly smaller particle size. This ultrafine particle size can fill the micropores between larger particles, thereby improving anti-segregation performance and throughput in L-shaped box, V-shaped funnel and J-shaped ring tests. By finely adjusting the amount of superplasticizer to match the increased surface area, an optimal balance between viscosity and yield stress can be achieved, ensuring that the mixture has good cohesion while maintaining fluidity. Figures 3A and 3B compare the aggregate gradation of commercially available formulations and the formulation of the present invention in C45 and C60 grade concrete, respectively.

[0056] Examples

[0057] Based on the formulation of the present invention, the following exemplary self-compacting concretes were prepared and subjected to various tests to evaluate their workability. This document provides relevant material selection, preparation, mixture composition, preparation process, test methods and results for these exemplary embodiments.

[0058] Material Characterization

[0059] Cementitious Materials

[0060] Cement, granulated blast furnace slag and silica fume were used as cementitious materials in slag-based low-carbon concrete. Granulated blast furnace slag from three different companies (labeled GGBS-1, GGBS-2, and GGBS-3, respectively) were used to evaluate the quality control of granulated blast furnace slag production in Hong Kong, China. The chemical composition and glass content of the cementitious materials are shown in Figures 4 and 5, respectively. In addition, the particle size distribution of the granulated blast furnace slag is shown in Figure 13. The results show that the physical and chemical properties of the granulated blast furnace slag are quite similar.

[0061] In addition, silica fume was used as an additional nano-cementing material to avoid potential bleeding and segregation problems. Generally, the stronger the fluidity of the mixture, the stronger the tendency to bleed, which in turn leads to segregation in the plastic state, where the released water migrates upwards, causing heavier particles (usually aggregates) to settle downwards.Due to the ball bearing effect, silica fume can fill the voids between cement, granulated blast furnace slag, and aggregates, reducing the space for water to form bleeding channels.

[0062] Aggregates

[0063] This study used three different types of aggregates, including 20 mm coarse aggregate, 10 mm coarse aggregate, and crushed stone fine aggregate. Figures 14A to 14C show their particle size distribution, and Figure 6 lists their apparent particle density and water absorption rate.

[0064] Polycarboxylate superplasticizers and viscosity modifiers

[0065] To improve mixing efficiency, this study used three different brands of polycarboxylate superplasticizers (labeled A, B, and C, respectively) to adjust the fresh mix performance of slag concrete. Figure 7 shows the solid content, density, and water reduction rate of the polycarboxylate superplasticizers. These admixtures are characterized by a comb-like structure, consisting of a polycarboxylate ester backbone containing carboxylate (-COO⁻) functional groups and long polyether side chains (usually polyoxyethylene or polyoxypropylene). This molecular structure imparts excellent dispersion properties through induced electrostatic repulsion and steric hindrance, thereby enhancing water-reducing effect and workability.

[0066] For each brand, different types of polycarboxylate superplasticizers are used, including slow-release type (labeled as Type 1) and water-reducing type (labeled as Type 2 or Type 3) to ensure good workability and maintainability. When selecting polycarboxylate superplasticizers, different ratios of slow-release to water-reducing types (40%:60%; 50%:50%; 60%:40%) are used, with a total polycarboxylate superplasticizer content of 2.1%. The results show that PCE superplasticizers of Brand 1 and Brand 3 are prone to bleeding and segregation, indicating that their water-reducing efficiency is relatively low. In addition, compared with PCE superplasticizer of Brand 2, concrete mixed with these two PCE superplasticizers requires a longer mixing time, resulting in lower mixing efficiency. Therefore, PCE superplasticizer of Brand 2 is selected as the superplasticizer.

[0067] In addition, to adjust the rheological properties and stability of slag-based low-carbon concrete, a viscosity modifier is considered for addition to the concrete. The combination of polymer and particles leads to an increase in particle size and resistance; furthermore, an increase in polymer concentration leads to bridging of particles, forming a more rigid network. Particle bridging leads to the formation of large flocs that can trap free water. Carboxymethyl cellulose and hydroxypropyl cellulose are selected as viscosity modifiers.

[0068] Material Preparation and Optimization

[0069] Sieving and Particle Size Control

[0070] By carefully sieving and controlling the particle size distribution of the aggregate composition, the mixture can achieve a uniform gradation. This increases the bulk density, reduces voids, and forms a denser microstructure. A well-graded aggregate system can improve the workability of concrete, reduce segregation, and help improve the strength and durability of concrete.

[0071] Aggregate Moisture Content Control

[0072] Maintaining the uniformity of aggregate moisture content is one of the keys to the overall performance of concrete. Variations in moisture content can lead to instability in the water-cement ratio, which can adversely affect the workability and hydration kinetics of the mixture. Therefore, maintaining a constant amount of effective water available for hydration can stabilize the workability of concrete and reduce the risk of slump loss or bleeding. 7 HK 30135232 A Specification

[0073] Reactivity Index and Vitreous Content of Granulated Blast Furnace Slag

[0074] The performance of concrete with high granulation blast furnace slag content is highly dependent on the reactivity of the granulated blast furnace slag. A high vitreous content (typically >80%) indicates that the granulated blast furnace slag has higher reactivity, enabling it to effectively participate in the pozzolanic reaction. This reactivity generates more hydrated calcium silicate (CSH) gel, thereby enhancing the strength and durability of the concrete. Monitoring the reactivity index ensures that the slag used meets the necessary conditions for optimal performance.

[0075] Specific Surface Area and Pozzolanic Activity of Silica Fume

[0076] The quality and reactivity of silica fume are crucial for improving the long-term durability of concrete. Silica fume with a specific surface area greater than 15,000 m² / kg ensures sufficient reactive surface area for pozzolanic reaction and effective particle packing. Its 7-day pozzolanic activity index must exceed 105% to make a significant contribution to early strength development. By selecting high-performance silica fume that meets these criteria, the microstructure of concrete can be densified, permeability reduced, and resistance to corrosive ions such as chlorides and sulfates enhanced.

[0077] Mixing Steps

[0078] 1. Weigh each material (cement, granulated blast furnace slag, silica fume, aggregate, water, additives) according to the mix design.

[0079] 2. Add cement, granulated blast furnace slag, silica fume, crushed stone, and aggregate to a concrete mixer and dry mix for 1-2 minutes.

[0080] 3. Add water and liquid phase additive to the dry mix, and wet mix for 4-6 minutes until a uniform mixture with the required consistency is obtained.

[0081] 4. Unload the fresh concrete from the mixer into a transport vehicle or formwork for fresh mix performance testing.

[0082] 5. Perform slump flow, L-shaped box test, V-shaped funnel test, J-shaped ring test and sieve separation test on the fresh concrete.

[0083] Workability evaluation and evaluation method

[0084] To test the workability of self-compacting concrete, the slump flow test (EN 12350-8), L-shaped box test (EN 12350-10), V-shaped funnel test (EN 12350-9), J-shaped ring test (EN 12350-12) and sieve separation test (EN 12350-11) are used.

[0085] Specifically, the slump spread test is used to evaluate the flowability of self-compacting concrete.The L-shaped box test is used to evaluate the fluidity and flowability of concrete. The V-shaped funnel test is used to test the flowability and consistency of fresh concrete. The shorter the flow time, the higher the fluidity of the concrete and the lower the flow resistance. The J-shaped ring test is used to test the flowability of concrete. The sieve segregation test is used to evaluate the segregation resistance of concrete.

[0086] The specific steps of each test are as follows:

[0087] Slump flow test

[0088] 1. Use a standard cone and place it on a flat plate. 8 HK 30135232 A Instruction manual

[0089] 2. Fill the cone with concrete continuously in one go without compaction.

[0090] 3. Lift the cone vertically at a uniform speed.

[0091] 4. Measure the maximum diameter of the concrete spread and the diameter perpendicular to the maximum diameter direction.

[0092] 5. Calculate the average of these two diameters and obtain the slump flow.

[0093] L-shaped box test

[0094] 1. The L-shaped box consists of a vertical section and a horizontal section. Figure 12A shows a typical setup of the L-shaped box. Three steel bars are installed at the beginning of the horizontal section to simulate steel bars.

[0095] 2. Ensure the L-shaped box is clean and level. Close the gate to separate the vertical and horizontal sections.

[0096] 3. Pour concrete into the vertical section of the L-shaped box and let it stand for 60±10 seconds.

[0097] 4. Smoothly lift the gate to allow the concrete to flow into the horizontal section. Observe the concrete flowing through the steel bars.

[0098] 5. Measure the height of the concrete at the end of the horizontal section as H2 and the height of the concrete at the end of the vertical section as H1.

[0099] 6. Calculate the ratio of H2 to H1.

[0100] V-shaped funnel test

[0101] 1. Referring to the V-shaped funnel test apparatus shown in Figure 12B, place fresh concrete into the slump cone section. 1. Open the outlet to allow concrete to flow through the narrow V-shaped outlet.

[0102] 2. Measure the time required for all concrete to flow through the outlet, which is the V-shaped funnel flow time.

[0103] J-ring test

[0104] 1. Place the J-ring (a circular steel frame with reinforcing bars at the opening) on ​​top of the slump cone device (see Figure 12C for a typical device).

[0105] 2. Place fresh concrete into the cone, allowing it to flow laterally across the tightly packed reinforcing bars on the J-ring.

[0106] 3. Measure the difference in slump between the center of the J-ring and the area around the ring.

[0107] Sieve separation test

[0108] 1. Prepare a square perforated plate sieve with a 5 mm aperture, a sieve frame diameter greater than 300 mm, and a height of 30 mm.

[0109] 2. Pour 10 ± 0.5 liters of concrete into the sample container and tighten the container lid to prevent moisture evaporation.1. Place the concrete horizontally for about 15 ± 0.5 minutes without stirring. After standing for a period of time, observe whether there is any bleeding and record it.

[0110] 3. Place the container on a balance, weigh the empty container and record its mass (mp) in grams. Then, place the dry sieve on the receiver and record the mass again or zero the balance.

[0111] 4. After standing for 15 ± 0.5 minutes, open the sample container lid and record whether there is any bleeding on the concrete surface.

[0112] 5. With the sieve and receiver still on the balance and the top of the sample container 500 ± 50 mm away from the top of the sieve, carefully and steadily pour 4.8 ± 0.2 kg of concrete (including bleeding) into the center of the sieve in one go. 9 HK 30135232 A Instruction Manual

[0113] 6. Record the actual mass mc (in grams) of the concrete on the sieve.

[0114] 7. Let the concrete stand in the sieve for 120±5 seconds, then remove the sieve vertically without stirring.

[0115] 8. Record the mass (in grams) of the receiver (including the material passing through the sieve).

[0116] The segregation rate SR was calculated according to the following formula, with the result accurate to 1%: = !" −! × 100 #

[0117] Example 1 - C45 grade concrete

[0118] 1.1. Cementitious material dosage of C45 grade concrete

[0119] The dosage of cementitious material has a key influence on the performance of concrete. Increasing the dosage of cementitious material can improve the compressive strength of concrete and improve its workability. In addition, it should be noted that, according to local regulations and guidelines, the total dosage of cementitious material in concrete should not exceed 550 kg / m³. Therefore, this study selected four different cementitious material dosages, namely 480, 500, 520 and 540 kg / m³, to study the effect of cementitious material dosage on the performance of slag-based low-carbon concrete, and first adopted 50% granulated blast furnace slag admixture. Figure 15 shows the 28 28-day compressive strength. Increasing the amount of cementitious material from 480 kg / m³ to 540 kg / m³ increased the 28-day compressive strength from 52.7 MPa to 71.8 MPa. The results show that a higher amount of cementitious material can improve the hydration degree of concrete, while using 50% granulated blast furnace slag can reduce the carbon emissions of concrete without affecting its compressive strength. Furthermore, considering that the slag-based low-carbon concrete described in this invention should reach a C45 strength grade for use in bored pile foundations in Hong Kong, this means that its compressive strength should exceed the grade strength by at least 12 MPa (i.e., 57 MPa) to ensure compliance with the standard (General Specifications for Civil Engineering, 2006 edition).Therefore, the use of 480 kg / m³ and 500 kg / m³ of cementitious material cannot meet the compressive strength requirements. Therefore, a cementitious material dosage of 520 kg / m³ (as shown in Figure 8A) was used to further study slag-based low-carbon concrete.

[0120] 1.2 C45 Additive Dosage

[0121] As mentioned above, this study used polycarboxylate superplasticizer and viscosity modifier of brand No. 2 to prepare slag-based low-carbon concrete. Therefore, this invention specifically formulated and used a viscosity-reducing polycarboxylate superplasticizer and viscosity modifier combination (denoted as PCE w / VMA). Accordingly, four different PCE w / VMA dosages (the ratio of PCE w / VMA to cementitious material, from 1.9% to 2.2%) were used to evaluate the effect of different dosages on the workability of slag-based low-carbon concrete. The results showed that when 1.9% and 2.0% PCE w / VMA were used, the slump spread of the slag-based low-carbon concrete was 480 mm and 530 mm, respectively, neither of which reached the target slump spread of 660 mm. In contrast, when 2.1% and 2.2% PCE w / VMA were added, the slump spread reached 680 mm and 720 mm, respectively. At the same time, the slag-based low-carbon concrete with 2.2% PCE w / VMA added showed bleeding and segregation. Therefore, 2.1% PCE w / VMA was finally selected as the chemical admixture for the slag-based low-carbon concrete, and its detailed mix design is shown in Figure 8B.

[0122] 1.3 C45 silica fume content

[0123] According to the standard, the silica fume content shall not exceed 10% of the total amount of cementitious materials. Therefore, 0%, 5% and 10% silica fume were added to the cementitious materials, and the updated mix design is shown in Figure 8C. The results indirectly show that the addition of silica fume significantly improves the workability of concrete. Without the addition of silica fume, the fresh concrete could not reach the end of the L-shaped box. When the amount of silica fume increased to 5% and 10%, the PL value increased to 0.2 and 0.4, respectively. This shows that adding silica fume is an effective method to improve the workability of slag-based low-carbon concrete, and 10% silica fume was used as an auxiliary cementitious material here.

[0124] 1.4 C45 aggregate gradation

[0125] Figure 8D shows the concrete mix proportions with different aggregate gradations. All proposed workability tests were carried out in accordance with the above-described steps, and the corresponding results are listed in Figure 9. Through comprehensive comparison of multiple test data, the conclusion is that mix proportion No. 9 has the best performance, with a slump spread of 660 mm and an L value of 0.82.

[0126] To further optimize the workability of slag-based low-carbon concrete, the total amount of cementitious material was slightly increased from 520 kg / m³ to 540 kg / m³ (marked as No. 11 in Figure 10A) based on mix proportion 9. Its workability performance is shown in Figure 10B. The results show that increasing the amount of cementitious material to 540 kg / m³ effectively improves the workability of slag-based low-carbon concrete. The V-funnel test time was 25 seconds, and the J-ring test value was also significantly improved to 10 mm. Therefore, mix proportion 11 represents the final realization of C45 grade slag-based low-carbon concrete, with optimized workability and a 28-day compressive strength of 63 MPa.

[0127] Example 2 - C60 Grade Concrete

[0128] Based on the analysis similar to that above, C60 grade slag-based low-carbon concrete was also formulated and prepared according to the present invention, marked as No. 12 in Figures 11A and 11B. Figures 11A and 11B respectively show the mix proportions and workability of C60 grade granulated blast furnace slag-based low-carbon concrete. Therefore, the No. 12 mix proportion is the final determined C60 grade slag-based low-carbon concrete with optimized workability, and its 28-day compressive strength reaches 80 MPa.

[0129] Several embodiments and detailed features of the present disclosure have been briefly described above. The embodiments described in the present disclosure can be readily used as the basis for designing or modifying other processes and structures to achieve the same or similar purposes and / or obtain the same or similar advantages as those described in the embodiments of the present disclosure. Such equivalent constructions do not depart from the spirit and scope of the present disclosure, and various changes, substitutions and modifications can be made without departing from the spirit and scope of the present disclosure.

[0130] As used herein, terms such as “approximately,” “substantially,” “essentially,” and “about” are used to describe and explain minute variations. When used in conjunction with an event or situation, the term can refer to a situation where the event or situation occurs precisely, or an situation where the event or situation occurs approximately. As used herein with respect to a given value or range, the term “about” generally means within ±10%, ±5%, ±1%, or ±0.5% of a given value or range. A range can be expressed herein as from one endpoint to another or between two endpoints. Unless otherwise stated, all ranges disclosed in this disclosure include endpoints. The term “substantially coplanar” in the specification 11 HK 30135232 A can refer to two surfaces located within a few micrometers (μm) along the same plane, such as within 10 μm, 5 μm, 1 μm, or 0.5 μm along the same plane. When referring to “substantially” identical values ​​or characteristics, the term can refer to values ​​within ±10%, ±5%, ±1%, or ±0.5% of the average value.12 HK 30135232 A Claim 1. A low-carbon self-compacting concrete, characterized in that it comprises: a cementitious material composed of ordinary Portland cement, granulated blast furnace slag, and silica fume; an aggregate composition composed of 10 mm coarse aggregate, 20 mm coarse aggregate, and crushed stone fines; water; and a viscosity-modifying admixture composed of a polycarboxylate superplasticizer and a hydrophilic viscosity modifier; wherein the amount of ordinary Portland cement is 135-270 kg / m³; wherein the amount of granulated blast furnace slag is 270-405 kg / m³; wherein the amount of silica fume is 25-60 kg / m³; wherein the amount of crushed stone fines is 850-1000 kg / m³; wherein the amount of 10 mm coarse aggregate is 300-500 kg / m³; wherein the 20 mm coarse aggregate is 135-270 kg / m³; wherein the amount of granulated blast furnace slag is 270-405 kg / m³; wherein the amount of 20 mm coarse aggregate ... The amount of coarse aggregate is 150-330 kg / m³; the amount of water is 170-220 liters / m³; the amount of viscosity modifier is liters / m³; and the Blaine surface area of ​​the slag powder is greater than 0.4 m² / g. 2. The concrete according to claim 1, characterized in that the weight ratio of ordinary Portland cement: granulated blast furnace slag: silica fume in the cementitious material is 0.15-0.50:0.50-0.75:0-0.10. 3. The concrete according to claim 1, characterized in that the hydrophilic viscosity modifier has a pH value of 7.0 to 9.5 in a 1% w / w deionized aqueous solution and a viscosity of 3100 to 3800 mPa·s in a 1.5% w / w deionized aqueous solution. 4. The concrete according to claim 1, characterized in that the polycarboxylate superplasticizer has a pH value of 6 to 9 and a viscosity of 50 to 100 mPa·s. 5. The concrete according to claim 1, characterized in that the content of the hydrophilic viscosity modifier is 2.0-2.5% by weight of the total viscosity modifier admixture. 6. The concrete according to claim 1, characterized in that the hydrophilic viscosity modifier is selected from carboxymethyl cellulose, hydroxypropyl cellulose, or a combination thereof. 7. The concrete according to claim 1, characterized in that the total amount of the cementitious material mixture is 480 to 540 kg / m³. 8. The concrete according to claim 1, characterized in that the granulated blast furnace slag has a Blaine surface area greater than 0.4 m² / g, a vitreous content greater than 67%, and a 28-day activity index greater than 84%.9. The concrete according to claim 1, wherein the silica fume has a silica content of at least 85%, a specific surface area of ​​at least 15 m² / g, and a pozzolanic activity index of at least 105%. 10. The concrete according to claim 1, wherein the weight ratio of the 20 mm coarse aggregate to the cementitious material is 0.31 to 1.57. 11. The concrete according to claim 1, wherein the weight ratio of the 10 mm coarse aggregate to the cementitious material is 0.31 to 1.26. 12. The concrete according to claim 1, wherein the weight ratio of the crushed stone to the cementitious material is 0.94 to 1.88. 13. The concrete according to claim 1, wherein the weight ratio of the water to the cementitious material is 0.32 to 0.40. 14. The concrete according to claim 1, wherein the weight ratio of the viscosity-adjusting admixture to the cementitious material is 0.015 to 0.030. 15. A C45 grade self-compacting concrete, characterized in that it comprises the concrete as described in claim 1, wherein: the ratio of ordinary Portland cement: granulated blast furnace slag: silica fume is 0.38-0.42: 0.48-0.52: 0.08-0.12; the ratio of water to cementitious material is 0.37-0.39; the mass ratio of 20 mm coarse aggregate to cementitious material is 0.58-0.62; the mass ratio of 10 mm coarse aggregate to cementitious material is 0.58-0.62; the weight ratio of crushed stone to cementitious material is 1.75-1.81; and the weight ratio of viscosity adjusting admixture to cementitious material is 0.015-0.019. 16. The C45 grade self-compacting concrete according to claim 15, characterized in that the concrete has: a slump spread of 670-690 mm; an L-shaped box test value of not less than 0.75; a V-shaped funnel test time of 23-27 seconds; a J-shaped ring height difference of 8-12 mm; and a sieve separation rate of 7.5-10%. 17. A C60 grade self-compacting concrete, characterized in that it comprises the concrete according to claim 1, wherein: the ratio of the ordinary Portland cement: the granulated blast furnace slag: the silica fume is 0.20-0.28:0.64-0.71:0.08-0.12; the ratio of water to the cementitious material is 0.34-0.36; the mass ratio of 20 mm coarse aggregate to the cementitious material is 0.33-0.37; and the mass ratio of 10 mm coarse aggregate to the cementitious material is 0.83-0.86.The weight ratio of the crushed stone to the cementitious material is 1.78-1.82; the weight ratio of the viscosity adjusting admixture to the cementitious material is 0.023-0.027. 2 HK 30135232 A Claim 18. The C60 grade self-compacting concrete according to claim 17, characterized in that the concrete has: a slump spread of 660-740 mm; an L-shaped box test value of not less than 0.75; a V-shaped funnel test time of 20-26 seconds; a J-shaped ring height difference of 8-14 mm; and a sieve separation rate of 8-13%. 3 HK 30135232 A Figure 1A 1 HK 30135232 A Figure 1B 2 HK 30135232 A Figure 1C 3 HK 30135232 A Figure 1D 4 HK 30135232 A Figure 2A 5 HK 30135232 A Figure 2B 6 HK 30135232 A Figure 3A 7 HK 30135232 A Figure 3B 8 HK 30135232 A Figure 4 Figure 5 9 HK 30135232 A Figure 6 Figure 7 Figure 8A 10 HK 30135232 A Figure 8B Figure 8C Figure 8D 11 HK 30135232 A Figure 9 Figure 10A Figure 10B Figure 11A 12 HK 30135232 A Figure 11B Figure 12A 13 HK 30135232 A Figure 12B 14 HK 30135232 A Figure 12C 15 HK 30135232 A Figure 13 16 HK 30135232 A Figure 14A 17 HK 30135232 A Figure 14B 18 HK 30135232 A Figure 14C 19 HK 30135232 A Figure 15 Figure 16 20 HK 30135232 A.

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