Ultra-high performance concrete prepared from waste slurry of concrete mixing plant and design method of mix proportion of ultra-high performance concrete

Abstract

The invention discloses ultra-high performance concrete prepared from waste slurry of a concrete mixing plant. The ultra-high performance concrete is mainly prepared from the following raw materials in parts by mass: 380-460 parts of waste slurry, 580-650 parts of cement, 80-155 parts of silica fume, 80-275 parts of fly ash, 550-750 parts of fine quartz sand, 250-430 parts of coarse quartz sand, 30-50 parts of a liquid additive, 50-60 parts of tap water and 140-160 parts of steel fibers. The invention further discloses a design method of the mix proportion of the ultra-high performance concrete. The invention provides a new way for recycling the waste slurry of the concrete mixing plant, not only reduces the emission of engineering wastes, but also reduces the comprehensive cost of concrete production, realizes the recycling of resources, conforms to the standard and requirement of green production, and achieves the purpose of protecting the environment. The method has good economic and environment-friendly benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and particularly relates to a super high performance concrete using waste slurry from a concrete mixing plant as a raw material and a design method for its mix proportion. Background Art

[0002] During the production of concrete in a concrete mixing plant, a large amount of waste slurry is generated. Its direct discharge not only has a serious impact on the ecological environment but also is a waste of resources. Super high performance concrete (UHPC) has broad application prospects due to its excellent properties such as ultra-high strength, high durability, and environmental friendliness. However, the raw material cost of traditional UHPC is high. If waste slurry can be used as one of the raw materials for preparing super high performance concrete, it can achieve the dual benefits of recycling waste and reducing the cost of UHPC, meeting the requirements of green production. However, the waste slurry has a high impurity content, complex composition, and a highly alkaline liquid environment. How to design the UHPC mix proportion using waste slurry so that the formed components can meet the performance requirements of UHPC is a key problem. Summary of the Invention

[0003] The object of the present invention is to provide a super high performance concrete prepared using waste slurry from a concrete mixing plant.

[0004] The object of the present invention is also to provide a design method for the mix proportion of the above-mentioned super high performance concrete prepared using waste slurry from a concrete mixing plant.

[0005] The last object of the present invention is to provide a preparation method for the above-mentioned super high performance concrete.

[0006] The present invention reasonably utilizes the waste slurry generated during the concrete production process and converts it into one of the raw materials of UHPC, ensuring that the super high performance concrete prepared using waste slurry meets or approaches the traditional UHPC standards in terms of key properties such as strength, durability, and workability. At the same time, it significantly reduces the discharge of engineering waste, realizes the recyclability of resources, reduces the comprehensive cost of super high performance concrete production, and achieves the goals of green, low-carbon, and environmental protection.

[0007] The above first object of the present invention can be achieved by the following technical solution: A super high performance concrete prepared using waste slurry from a concrete mixing plant, which is mainly made of the following raw materials in parts by mass: 380 - 460 of waste slurry, 580 - 650 of cement, 80 - 155 of silica fume, 80 - 275 of fly ash, 550 - 750 of fine quartz sand, 250 - 430 of coarse quartz sand, 30 - 50 of liquid admixture, 50 - 60 of tap water, and 140 - 160 of steel fiber, wherein the solid content of the waste slurry is 60% - 70%.

[0008] Preferably, the solid components of the waste slurry mainly include hydrated and unhydrated cement, silica fume, fly ash, and fine sand, and the mass ratio of the cement, silica fume, fly ash, and fine sand is 5-6:1-2:1-2:4-5; the liquid component of the waste slurry is mainly wastewater, and the pH value of the wastewater is 8-10.

[0009] The solid content of the slurry is the mass percentage of the dry basis in the slurry.

[0010] Preferably, the waste slurry of the present invention is prepared by the following method:

[0011] (1) Drainage ditches and sumps are set in the concrete mixing and forming area, and the collected concrete is stirred, produced, washed, and the site is rinsed to obtain preliminary waste slurry.

[0012] (2) Stones and coarse sand particles in the preliminary waste slurry are removed by a grille, and then further filtered through a filter screen and a filter to remove fine suspended matters, obtaining the waste slurry after impurity removal.

[0013] (3) The waste slurry after impurity removal is diluted with tap water and acid reagents are added for preparation to obtain the waste slurry.

[0014] In the present invention, the cement is selected as ordinary Portland cement, preferably ordinary Portland cement with a strength grade of 52.5, which can reduce the heat released by the hydration reaction.

[0015] By mass, the ultra-high performance concrete prepared from the waste slurry of the concrete mixing plant provided by the present invention includes 380-460 parts of waste slurry, preferably 400-460 parts. The present invention selects waste slurry as one of the raw material components of ultra-high performance concrete, utilizes the filling effect and packing effect of fine particles in the waste slurry to optimize the microstructure pores of UHPC, improve the density and workability; utilizes the alkaline environment in the waste slurry to accelerate the hydration rate of the UHPC cementitious material; utilizes the nucleation effect and induction effect generated by ions in the waste slurry to improve the hydration degree of the UHPC cementitious material. To a certain extent, the recycling of water, cementitious material, and sand particles is realized, the production cost of ultra-high performance concrete is reduced, green production is achieved, and the purpose of low-carbon environmental protection is achieved.

[0016] Based on 380-460 parts by weight of the waste slurry, the ultra-high performance concrete provided by the present invention includes 580-650 parts of cement, preferably 600-630 parts, and more preferably 610-620 parts. Due to the addition of waste slurry in the present invention, the amount of cement used can be reduced, thereby reducing the production cost and being more environmentally friendly.

[0017] In the present invention, the cement is selected as ordinary Portland cement, preferably ordinary Portland cement with a strength grade of 52.5, which can reduce the heat released by the hydration reaction.

[0018] Based on 380 - 460 parts by mass of waste slurry, the ultra - high performance concrete provided by the present invention includes 80 - 155 parts of silica fume, preferably 100 - 125 parts, and more preferably 110 - 115 parts. In the present invention, the silica fume can undergo a secondary hydration reaction with the calcium hydroxide produced by cement hydration to generate more gel bodies, fill the pores, and improve the density of UHPC. At the same time, it improves the internal structure of UHPC, enables better bonding between the matrix and the fibers, enhances the constraint of the fibers on the matrix, and improves the toughness of the material.

[0019] In the present invention, the particle size of the silica fume is 0.15 - 0.25 μm. By adding silica fume with an extremely fine particle size, the pores between UHPC particles are filled, making the paste more uniform, improving fluidity, and facilitating molding.

[0020] Based on 380 - 460 parts by weight of waste slurry, the ultra - high performance concrete provided by the present invention includes 80 - 275 parts of fly ash, preferably 110 - 240 parts, and more preferably 150 - 205 parts. In the present invention, the fly ash is preferably class I fly ash, and the particle size of the silica fume is 0.15 - 0.25 μm. The class I fly ash particles added in the present invention are spherical and have a smooth surface, playing a "ball - rolling" role in the UHPC mixture, which can reduce the friction between particles, significantly improve the fluidity of the mixture, and facilitate pouring and molding. At the same time, fly ash can reduce the alkali content in the concrete, reduce the possibility of reaction between alkali and reactive aggregates, reduce the risk of damage to UHPC formed components caused by alkali - aggregate reaction, and extend the service life of the components.

[0021] Based on 380 - 460 parts by weight of waste slurry, the ultra - high performance concrete provided by the present invention includes 550 - 750 parts of fine quartz sand, preferably 600 - 700 parts; and 250 - 430 parts of coarse quartz sand, preferably 300 - 400 parts. The particle size of the fine quartz sand is 0.2 - 0.6 mm; the particle size of the coarse quartz sand is 0.6 - 1.2 mm. In the present invention, the aggregates are selected as fine quartz sand and coarse quartz sand, and the usage ratio of the two is 1:0.45 - 0.57. In the present invention, by using a mixture of fine quartz sand and coarse quartz sand, the particle gradation is more reasonable. The coarse sand forms a skeleton, and the quartz sand fills the pores, reducing the friction and cohesion between particles, improving the fluidity of the mixture, facilitating better filling of the mold during the molding process of UHPC. At the same time, the multi - level particle structure formed by the mixture of fine and coarse quartz sand can make the cohesion of the mixture more suitable.

[0022] Based on 380 - 460 parts by weight of waste slurry, the ultra - high performance concrete provided by the present invention includes 30 - 50 parts, preferably 35 - 45 parts, more preferably 38 - 42 parts of liquid admixture. In the present invention, the liquid admixture is a polycarboxylate water - reducing agent with a solid content of 30% - 40%. The polycarboxylate water - reducing agent added in the present invention has a high water - reducing rate, can greatly reduce the water demand of the UHPC mixture, and still enable the mixture to have good fluidity under a low water - binder ratio.

[0023] Based on 380 - 460 parts by weight of waste slurry, the ultra - high performance concrete provided by the present invention includes 140 - 160 parts, preferably 145 - 155 parts of steel fiber. The steel fiber is a copper - plated straight - type steel fiber with a diameter of 0.18 - 0.22 mm, a length of 6 - 19 mm, and a tensile strength of 1800 - 2200 MPa. The steel fiber added in the present invention can be closely combined with the cement paste in UHPC, etc., enhance the cohesiveness of the mixture, prevent the mixture from segregation and bleeding during transportation and pouring, and ensure the uniformity of the mixture. At the same time, it improves the ability of the formed component to resist bending deformation, making the formed component have better impact and vibration resistance.

[0024] Based on 380 - 460 parts by weight of waste slurry, the ultra - high performance concrete provided by the present invention includes 50 - 60 parts of tap water.

[0025] The above - mentioned second object of the present invention can be achieved by the following technical solutions: The method for designing the mix proportion of the ultra - high performance concrete prepared by using the waste slurry of a concrete mixing plant includes the following steps:

[0026] (1) Select the raw materials for preparing ultra - high performance concrete, including waste slurry, cement, silica fume, fly ash, fine quartz sand, coarse quartz sand, liquid admixture, tap water, and steel fiber;

[0027] (2) Design the mix proportion of each raw material in the ultra - high performance concrete, including:

[0028] (2.1) Determine the proportion of cement, silica fume, and fly ash in the ultra - high performance concrete, and calculate the material relationship among cement, silica fume, and fly ash;

[0029] (2.2) Determine the proportion of fine quartz sand and coarse quartz sand in the ultra - high performance concrete;

[0030] (2.3) Determine the mortar - to - aggregate ratio of the ultra - high performance concrete, so as to obtain the proportion of cement, silica fume, fly ash, fine quartz sand, and coarse quartz sand. The binder in the mortar - to - aggregate ratio is the cementitious material, and the cementitious material includes cement, silica fume, and fly ash. The aggregate in the mortar - to - aggregate ratio is fine quartz sand and coarse quartz sand;

[0031] (2.4) Determine the water-binder ratio of ultra-high performance concrete, as well as the dosages of waste slurry, liquid admixture, and steel fiber.

[0032] (2.5) Determine the amount of cement used, and calculate the amounts of waste slurry, silica fume, fly ash, fine quartz sand, coarse quartz sand, liquid admixture, tap water, and steel fiber.

[0033] Preferably, in step (2.1), the mass ratio of the cement to silica fume and fly ash is 1: 0.14 - 0.24: 0.14 - 0.4.

[0034] Preferably, in step (2.2), the mass ratio of the fine quartz sand to the coarse quartz sand is 1: 0.45 - 0.57.

[0035] Preferably, in step (2.3), the mortar-binder ratio is 0.9 - 1: 1.

[0036] Preferably, in step (2.4), the water-binder ratio is 0.05 - 0.07: 1.

[0037] Preferably, in step (2.4), the dosage of the waste slurry is 40% - 50% of the total mass of the cement, silica fume, and fly ash as the binder materials.

[0038] Preferably, in step (2.4), the dosage of the liquid admixture is 4% - 4.8% of the total mass of the cement, silica fume, and fly ash as the binder materials.

[0039] Preferably, in step (2.4), the dosage of the steel fiber is 14% - 18% of the total mass of the cement, silica fume, and fly ash as the binder materials.

[0040] The present invention provides a mix proportion design method for ultra-high performance concrete prepared using waste slurry from a concrete mixing plant, which can rationally utilize the waste slurry generated during the concrete production process and convert it into one of the raw materials for ultra-high performance concrete. At the same time, it determines the appropriate proportions of waste slurry, binder materials, sand materials, and steel fiber; utilizes the filling effect and packing effect of fine particles in the waste slurry to optimize the microstructure of UHPC pores and improve the density; utilizes the nucleation effect generated by the alkaline environment and ions in the waste slurry to accelerate the hydration rate of UHPC binder materials and improve the hydration degree of UHPC binder materials, so that the mechanical properties of ultra-high performance concrete prepared using waste slurry far exceed those of traditional concrete materials. It designs a universal process that can adapt to waste slurry from different sources and properties, is not limited to a specific production line, is easy to promote in various concrete production scenarios, and accelerates the green transformation of the industry. It reduces the comprehensive cost of concrete production.

[0041] The above last object of the present invention can be achieved by the following technical solution: The above method for preparing ultra-high performance concrete includes the following steps:

[0042] (1) Prepare waste slurry;

[0043] (2) Mix cement, silica fume, fly ash, fine quartz sand, coarse quartz sand and steel fibers to obtain a dry mixture;

[0044] (3) Mix water, waste slurry and liquid admixture to obtain a wet mixture;

[0045] (4) Mix and stir the dry mixture and the wet mixture to obtain ultra-high performance concrete prepared by using the waste slurry from a concrete mixing plant.

[0046] In step (2) of the present invention, cement, silica fume, fly ash, quartz sand and steel fibers are mixed to obtain a dry mixture. In the present invention, the mixing is preferably preceded by a pre-stirring treatment; the time of the pre-stirring is preferably 180 s. Through the pre-stirring in the present invention, the particles of each solid raw material are fully mixed with the steel fibers.

[0047] In step (3) of the present invention, water, waste slurry and liquid admixture are mixed to obtain a wet mixture. In the present invention, the mixing is preferably carried out under stirring conditions.

[0048] After obtaining the dry mixture and the wet mixture, in the present invention, the dry mixture and the wet mixture are mixed to obtain ultra-high performance concrete prepared by using the waste slurry from a concrete mixing plant. In the present invention, the mixing is preferably carried out under stirring conditions; the time of the stirring is preferably 480 s. Through the stirring in the present invention, the dry mixture and the wet mixture are uniformly mixed and fully reacted.

[0049] The present invention has the following advantages: The ultra-high performance concrete provided by the present invention innovatively and reasonably utilizes the waste slurry generated in the concrete production process and converts it into one of the raw materials of UHPC, which not only reduces the discharge of engineering waste, but also realizes the recyclability of resources, reduces the comprehensive cost of ultra-high performance concrete production, achieves the purpose of green, low-carbon and environmental protection, and has good application prospects. Specific Embodiments

[0050] The present invention will be further described below in conjunction with specific embodiments. The following embodiments are only for illustrative purposes and should not be construed as limitations on the present invention. Unless otherwise specified, the raw materials and equipment used in the following embodiments are obtained through conventional commercial channels.

[0051] The solid content of the waste slurry of the present invention is 60%-70%, and the solid components of the waste slurry are mainly hydrated and unhydrated cement, silica fume, fly ash and fine sand, and the mass ratio of the cement, silica fume, fly ash and fine sand is 5-6:1-2:1-2:4-5; the liquid component of the waste slurry is mainly waste water, and the pH value of the waste water is 8-10.

[0052] The methods for obtaining waste slurry in the present invention include but are not limited to the following:

[0053] Set up dedicated drainage ditches and sumps in the concrete mixing and forming area of the concrete mixing plant to collect waste slurry generated from concrete production, cleaning, site flushing, etc.;

[0054] Remove larger particles such as stones and sand grains in the wastewater with a grille, and further filter out fine suspended solids through a filter screen;

[0055] Dilute the waste slurry with urban tap water to make the water content reach 30%-40%, that is, the solid content is 60-70%, and add acidic agents such as sulfuric acid and hydrochloric acid to make the pH value reach 8-10.

[0056] The method for mix proportion design of ultra-high performance concrete prepared by using waste slurry from a concrete mixing plant provided by the present invention includes the following steps:

[0057] (1) Select raw materials for preparing ultra-high performance concrete, including waste slurry, cement, silica fume, fly ash, fine quartz sand, coarse quartz sand, liquid admixture, tap water and steel fiber;

[0058] (2) Design the mix proportion of each raw material in the ultra-high performance concrete, including:

[0059] (2.1) Based on the simple particle close packing formula, determine the material ratio among cement, silica fume and fly ash in the ultra-high performance concrete, and calculate the material relationship among cement, silica fume and fly ash;

[0060]

[0061] In the formula: G(R) is the proportion of particles with the maximum particle size of R in the total volume (%); R max is half of the maximum particle size D max of each raw material particle (m); n is the number of each raw material particle (pieces); m is the usage amount of the solid particles of the raw material (parts); ρ is the density of the solid particles of each raw material (parts / m 3 ).

[0062] The mass ratio of cement, silica fume and fly ash is 1:(0.14-0.24):(0.14-0.4).

[0063] (2.2) Determine the material ratio between fine quartz sand and coarse quartz sand in the ultra-high performance concrete;

[0064] The mass ratio of fine quartz sand to coarse quartz sand is 1:(0.45-0.57).

[0065] (2.3) Determine the cement-sand ratio of ultra-high performance concrete to obtain the material usage ratios among cement, silica fume, fly ash, fine quartz sand, and coarse quartz sand. The binder in the cement-sand ratio refers to the binder materials, which include cement, silica fume, and fly ash. The sand in the cement-sand ratio refers to fine quartz sand and coarse quartz sand;

[0066]

[0067] In the formula: B / A is the cement-sand ratio, and the value range is (0.9 - 1):1; m B is the usage amount (parts) of the binder materials; m A is the usage amount (parts) of quartz sand.

[0068] (2.4) Determine the water-binder ratio of ultra-high performance concrete and the dosages of waste slurry, liquid admixture, and steel fiber;

[0069]

[0070] In the formula: W / B is the water-binder ratio, and the value range is (0.05 - 0.07):1; m B is the usage amount (parts) of the binder materials; m w is the usage amount (parts) of water.

[0071] The dosage of the liquid admixture is 4% - 4.8% of the total mass of the binder materials.

[0072] Prepare UHPC mortar based on waste slurry, cement, silica fume, fly ash, fine quartz sand, coarse quartz sand, water, and liquid admixture. Conduct fluidity and slump tests by controlling different dosages of waste slurry. When the fluidity of UHPC mortar is 200 - 220 mm and the slump is 220 - 260 mm, the dosage of waste slurry is 40% - 50% of the total mass of the binder materials.

[0073] The dosage of steel fiber is (14% - 18%) of the total mass of the binder materials.

[0074] (2.5) Determine the amount of cement used and calculate the amounts of waste slurry, silica fume, fly ash, fine quartz sand, coarse quartz sand, liquid admixture, tap water, and steel fiber.

[0075] The mix proportion design method for preparing ultra-high performance concrete using waste slurry from a concrete mixing plant provided by the present invention determines the material usage relationship between cementitious materials according to the theoretical formula of particle close packing, and further determines the dosages of waste slurry, sand, water, liquid admixture, and steel fiber based on the mortar ratio, water-cement ratio, and mortar test. The ultra-high performance concrete prepared based on this method can efficiently solve the problem of recycling waste slurry, achieving the purpose of making full use of the filling effect and packing effect of fine particles in the waste slurry, optimizing the micro-pore structure of UHPC, and improving the density. It not only saves the use of raw materials and reduces production costs, but also enhances the mechanical properties and durability of ultra-high performance concrete. At the same time, it is beneficial to environmental protection and meets the requirements of green production. Given its excellent performance and environmental protection advantages, this method can be widely promoted in various engineering production scenarios, helping to accelerate the green transformation process of related industries.

[0076] Furthermore, the formula of the ultra-high performance concrete prepared using waste slurry from a concrete mixing plant in the present invention is obtained, which is mainly made of the following raw materials in parts by mass: 380 - 460 of waste slurry, 580 - 650 of cement, 80 - 155 of silica fume, 80 - 275 of fly ash, 550 - 750 of fine quartz sand, 250 - 430 of coarse quartz sand, 30 - 50 of liquid admixture, 50 - 60 of tap water, and 140 - 160 of steel fiber.

[0077] The ultra-high performance concrete in the present invention can be prepared by the following method:

[0078] (1) Prepare waste slurry: Pretreat the waste slurry generated in concrete production to obtain the pretreated waste slurry;

[0079] (2) Mix cement, silica fume, fly ash, quartz sand, and steel fiber to obtain a mixed dry material;

[0080] (3) Mix water, the pretreated waste slurry, and the liquid admixture to obtain a mixed wet material;

[0081] (4) Mix and stir the mixed dry material and the mixed wet material to obtain the ultra-high performance concrete prepared using waste slurry from a concrete mixing plant.

[0082] The present invention can improve the mixing uniformity in a shorter mixing time by adopting the above preparation sequence.

[0083] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts shall fall within the protection scope of the present invention.

[0084] Example 1

[0085] The ultra-high performance concrete prepared from the waste slurry of a concrete mixing plant in this example is made from the following raw materials in parts by mass: 390 of pretreated waste slurry, 600 of ordinary Portland cement with a strength grade of 52.5, 100 of silica fume with a particle size of 0.2 μm, 200 of Class I fly ash, 600 of quartz sand with a particle size of 0.2 - 0.6 mm, 300 of quartz sand with a particle size of 0.6 - 1.2 mm, 40 of polycarboxylate water reducer with a solid content of 30% - 40%, 60 of tap water, and 150 of copper-plated straight steel fibers with a length of 15 mm, a diameter of 0.2 mm, and a tensile strength of 2000 MPa.

[0086] Preparation method:

[0087] Add the cement, silica fume, fly ash, fine quartz sand, coarse quartz sand, and steel fibers into a drum mixer and dry mix for 180 s to obtain a mixed dry material;

[0088] Add the waste slurry, water, and polycarboxylate water reducer into a mixing bucket and stir with a stirring rod for 180 s to obtain a mixed wet material;

[0089] Slowly add the mixed wet material to the above-mentioned mixed dry material and stir for 480 s to obtain the ultra-high performance concrete prepared from the waste slurry of a concrete mixing plant.

[0090] Example 2

[0091] The ultra-high performance concrete prepared from the waste slurry of a concrete mixing plant in this example is made from the following raw materials in parts by mass: 420 parts of pretreated waste slurry, 600 parts of ordinary Portland cement with a strength grade of 52.5, 100 parts of silica fume with a particle size of 0.2 μm, 200 parts of Class I fly ash, 600 parts of quartz sand with a particle size of 0.2 - 0.6 mm, 300 parts of quartz sand with a particle size of 0.6 - 1.2 mm, 55 parts of tap water, 40 parts of polycarboxylate water reducer with a solid content of 30% - 40%, and 150 parts of copper-plated straight steel fibers with a length of 15 mm and a diameter of 0.2 mm.

[0092] Preparation method:

[0093] Add the cement, silica fume, fly ash, fine quartz sand, coarse quartz sand, and steel fibers into a drum mixer and dry mix for 180 s to obtain a mixed dry material;

[0094] Add the waste slurry, water, and polycarboxylate water reducer into a mixing bucket and stir with a stirring rod for 180 s to obtain a mixed wet material;

[0095] Slowly add the mixed wet material to the above-mentioned mixed dry material and stir for 480 s to obtain the ultra-high performance concrete prepared from the waste slurry of a concrete mixing plant.

[0096] Example 3

[0097] The ultra-high performance concrete prepared using waste slurry from a concrete mixing station in this embodiment is made from the following raw materials in parts by weight: 450 parts of pretreated waste slurry, 600 parts of ordinary Portland cement with a strength grade of 52.5, 100 parts of silica fume with a particle size of 0.2 μm, 200 parts of Class I fly ash, 600 parts of quartz sand with a particle size of 0.2-0.6 mm, 300 parts of quartz sand with a particle size of 0.6-1.2 mm, 50 parts of tap water, 40 parts of a polycarboxylate water reducer with a solid content of 30%-40%, and 150 parts of copper-plated straight steel fibers with a length of 15 mm and a diameter of 0.2 mm.

[0098] Preparation method:

[0099] Cement, silica fume, fly ash, fine quartz sand, coarse quartz sand and steel fiber were added into a drum mixer and dry-mixed for 180 seconds to obtain a mixed dry material;

[0100] Add waste slurry, water and polycarboxylate water reducer into a mixing bucket and stir with a stirring rod for 180 seconds to obtain a mixed wet material;

[0101] The mixed wet material was slowly added to the mixed dry material and stirred for 480 seconds to obtain ultra-high performance concrete prepared using waste slurry from a concrete mixing station.

[0102] Comparative Example 1

[0103] The ordinary ultra-high performance concrete of this comparative example is made of the following raw materials in parts by mass: 800 parts of ordinary Portland cement with a strength grade of 52.5, 200 parts of silica fume with a particle size of 0.2 μm, 200 parts of Class I fly ash, 700 parts of quartz sand with a particle size of 0.2-0.6 mm, 400 parts of quartz sand with a particle size of 0.6-1.2 mm, 240 parts of tap water, 40 parts of a polycarboxylate water reducer with a solid content of 30%-40%, and 180 parts of copper-plated straight steel fibers with a length of 15 mm and a diameter of 0.2 mm.

[0104] Preparation method:

[0105] Cement, silica fume, fly ash, fine quartz sand, coarse quartz sand and steel fiber were added into a drum mixer and dry-mixed for 180 seconds to obtain a mixed dry material;

[0106] Add water and polycarboxylate water reducer into a mixing bucket and stir with a stirring rod for 180 seconds to obtain a mixed wet material;

[0107] The mixed wet material was slowly added to the mixed dry material and stirred for 480 seconds to obtain ultra-high performance concrete prepared using waste slurry from a concrete mixing station.

[0108] The performance test results of the ultra-high performance concrete prepared in Examples 1-3 and Comparative Example 1 at 28 days are shown in Table 1. The test standard is the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T 50081-2019).

[0109] Table 1 28-day performance of ultra-high performance concrete prepared in Examples 1-3

[0110] Number Compressive strength / MPa Flexural strength / MPa Tensile strength / MPa Example 1 124.76 27.67 7.43 Example 2 131.44 28.12 9.01 Example 3 121.97 25.74 6.92 Comparative Example 1 128.44 28.24 8.54

[0111] As can be seen from the results in Table 1, the compressive strength, flexural strength, and tensile strength of the specimens in Examples 1, 2, 3, and Comparative Example 1 all meet the requirements for ultra-high performance concrete in the "Technical Specification for Reactive Powder Concrete Structures" (JGJ / T 413-2019). Through the horizontal comparison of Examples 1, 2, and 3, it can be seen that the incorporation of an appropriate amount of waste slurry improves the mechanical strength of UHPC formed using waste slurry.

[0112] The carbon emissions generated during the production of concrete in Examples 1-3 and Comparative Example 1 are shown in Table 3, and the calculation standard is the "Standard for Calculation of Building Carbon Emissions" (GB / T 51366-2019).

[0113] Table 2 Carbon emissions generated during the production of UHPC in Examples 1-3 and Comparative Example 1

[0114] Number <![CDATA[Carbon emissions (k, gCO2)]]> Example 1 1030 Example 2 1030 Example 3 1030 Comparative Example 1 1340

[0115] As can be seen from the results in Tables 1 and 2, on the premise of the same level of mechanical strength, the carbon emissions generated during the production of UHPC formed using waste slurry (such as Examples 1, 2, and 3) are significantly reduced compared to the production of ordinary UHPC (Comparative Example 1), with a reduction of approximately 300 kg CO2. This shows that the incorporation of waste slurry can greatly reduce the carbon emissions generated during the production process, and the UHPC formed using the waste slurry from the concrete mixing plant in this invention meets the requirements of green and low-carbon concrete.

[0116] Example 4

[0117] Different from Example 1, the ultra-high performance concrete prepared using the waste slurry from the concrete mixing plant provided in this example is made from the following raw materials in parts by mass: 455 parts of waste slurry, 650 parts of ordinary Portland cement, 130 parts of silica fume, 130 parts of fly ash, 666 parts of fine quartz sand, 333 parts of coarse quartz sand, 50 parts of tap water, 40 parts of polycarboxylate water reducer, and 130 parts of steel fiber.

[0118] Example 5

[0119] Different from Example 1, the ultra-high performance concrete prepared from the waste slurry of a concrete mixing plant provided in this example is made of raw materials with the following mass ratio: 410 parts of waste slurry, 620 parts of ordinary Portland cement, 140 parts of silica fume, 140 parts of fly ash, 680 parts of fine quartz sand, 320 parts of coarse quartz sand, 60 parts of tap water, 43 parts of polycarboxylate water reducer, and 147 parts of steel fiber.

[0120] Example 6

[0121] Different from Example 1, the ultra-high performance concrete prepared from the waste slurry of a concrete mixing plant provided in this example is made of raw materials with the following mass ratio: 400 parts of waste slurry, 590 parts of ordinary Portland cement, 90 parts of silica fume, 220 parts of fly ash, 690 parts of fine quartz sand, 310 parts of coarse quartz sand, 55 parts of tap water, 42 parts of polycarboxylate water reducer, and 160 parts of steel fiber.

[0122] The ultra-high performance concrete prepared from the waste slurry of a concrete mixing plant in the present invention utilizes the waste slurry in the concrete production process, designs the mix proportion according to the dense packing theory formula, and is prepared according to the given preparation method. The mechanical properties of the obtained ultra-high performance concrete meet the current specifications and reach the strength requirements of ultra-high performance concrete. Through a scientific and reliable mix proportion design method, the present invention reasonably utilizes the waste slurry generated in the concrete production process and converts it into one of the raw materials of ultra-high performance concrete, so that the ultra-high performance concrete prepared from the waste slurry reaches or approaches the traditional UHPC standard in terms of key properties such as strength, durability, and workability. It provides a new way for the recycling of the waste slurry of a concrete mixing plant, reduces the discharge of engineering waste, realizes the recycling of resources, achieves the purpose of environmental protection, green and low-carbon environmental protection, and at the same time reduces the comprehensive production cost of ultra-high performance concrete. It has good economic, environmental and social benefits.

[0123] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. Ultra-high performance concrete prepared from waste slurry of a concrete mixing plant, characterized in that, It is mainly made of the following raw materials in parts by mass: 380 - 460 of waste slurry, 580 - 650 of cement, 80 - 155 of silica fume, 80 - 275 of fly ash, 550 - 750 of fine quartz sand, 250 - 430 of coarse quartz sand, 30 - 50 of liquid admixture, 50 - 60 of tap water, and 140 - 160 of steel fiber.

2. The ultra-high performance concrete prepared by using the waste slurry of a concrete mixing plant according to claim 1, characterized in that, The solid content of the waste slurry is 60% - 70%. The solid components of the waste slurry are mainly hydrated and unhydrated cement, silica fume, fly ash, and fine sand. The mass ratio of the cement, silica fume, fly ash, and fine sand is 5 - 6:1 - 2:1 - 2:4 - 5. The liquid component of the waste slurry is mainly waste water, and the pH value of the waste water is 8 - 10.

3. The ultra-high performance concrete prepared by using the waste slurry of a concrete mixing plant according to claim 2, characterized in that, The waste slurry is obtained by the following method: (1) Set a drainage ditch and a sump in the concrete mixing and forming area, and the collected concrete is stirred, produced, washed, and the site is rinsed to obtain preliminary waste slurry. (2) Remove stones and coarse sand particles in the preliminary waste slurry with a grille, and then further filter out fine suspended matter through a filter screen and a filter to obtain the waste slurry after impurity removal. (3) Dilute the waste slurry after impurity removal with tap water and add an acidic agent for preparation to obtain the waste slurry.

4. The ultra-high performance concrete prepared by using the waste slurry of a concrete mixing plant according to claim 1, wherein, The cement is ordinary Portland cement with a strength grade of 52.

5. The particle size of the silica fume is 0.15 - 0.25 μm. The fly ash is Class I fly ash. The particle size of the fine quartz sand is 0.2 - 0.6 mm. The particle size of the coarse quartz sand is 0.6 - 1.2 mm. The steel fiber is copper-plated straight steel fiber. The diameter of the steel fiber is 0.18 - 0.22 mm, the length is 6 - 19 mm, and the tensile strength is 1800 - 2200 MPa. The liquid admixture is polycarboxylate water reducer.

5. The method for mix proportion design of ultra-high performance concrete prepared by using waste slurry from a concrete mixing plant according to any one of claims 1 to 4, characterized in that, It includes the following steps: (1) Select the raw materials for preparing ultra-high performance concrete, including waste slurry, cement, silica fume, fly ash, fine quartz sand, coarse quartz sand, liquid admixture, tap water, and steel fiber. (2) Design the mix ratio of each raw material in the ultra-high performance concrete, including: (2.1) Determine the material ratio among cement, silica fume, and fly ash in the ultra-high performance concrete, and calculate the material relationship among cement, silica fume, and fly ash. (2.2) Determine the material ratio between fine quartz sand and coarse quartz sand in the ultra-high performance concrete. (2.3) Determine the mortar-cement ratio of the ultra-high performance concrete, so as to obtain the material ratio among cement, silica fume, fly ash, fine quartz sand, and coarse quartz sand. The binder in the mortar-cement ratio is the cementitious material, and the cementitious material includes cement, silica fume, and fly ash. The sand in the mortar-cement ratio is fine quartz sand and coarse quartz sand. (2.4) Determine the water-binder ratio of the ultra-high performance concrete and the dosages of waste slurry, liquid admixture, and steel fiber. (2.5) Determine the dosage of cement, and calculate the dosages of waste slurry, silica fume, fly ash, fine quartz sand, coarse quartz sand, liquid admixture, tap water, and steel fiber.

6. The method according to claim 5, characterized in that, In step (2.1), the mass ratio of cement, silica fume, and fly ash is 1: 0.14 - 0.24: 0.14 - 0.4; in step (2.2), the mass ratio of fine quartz sand to coarse quartz sand is 1: 0.45 - 0.57; in step (2.3), the mortar-to-cement ratio is 0.9 - 1:

1.

7. The method according to claim 5, wherein In step (2.4), the water-to-binder ratio is 0.05 - 0.07:

1.

8. The method according to claim 5, wherein In step (2.4), the dosage of waste slurry is 40% - 50% of the total mass of the cementitious materials, namely cement, silica fume, and fly ash.

9. The method according to claim 5, characterized in that, In step (2.4), the dosage of liquid admixture is 4% - 4.8% of the total mass of the cementitious materials, namely cement, silica fume, and fly ash; the dosage of steel fiber is 14% - 18% of the total mass of the cementitious materials, namely cement, silica fume, and fly ash.

10. The preparation method of the ultra-high performance concrete according to any one of claims 1 to 4, characterized in that, It includes the following steps: (1) Prepare waste slurry; (2) Mix cement, silica fume, fly ash, fine quartz sand, coarse quartz sand, and steel fiber to obtain a mixed dry material; (3) Mix water, waste slurry, and liquid admixture to obtain a mixed wet material; (4) Mix and stir the mixed dry material and the mixed wet material to obtain ultra-high performance concrete prepared by using the waste slurry from a concrete mixing plant.

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