Low-bleeding concrete and preparation process thereof

Abstract

The invention belongs to the technical field of building material preparation, and particularly relates to low-bleeding concrete and a preparation process thereof. Comprising the following components in parts by weight: 100-120 parts of cement, 260-300 parts of river sand, 360-400 parts of pebbles, 35-55 parts of mineral powder, 30-50 parts of silica fume, 60-90 parts of water and 2.2-5 parts of a composite additive, the composite additive is a binding body composed of a nano inorganic filler, a water reducing agent and a water-retaining agent, and the particle size of the binding body is 1-10 microns. The bonding body is slowly dissolved in water of concrete to release the water reducing agent, the water retaining agent and the nano inorganic filler, so that the concrete can be prevented from being too sticky, water molecule migration can be effectively reduced, the bleeding rate is remarkably reduced by coupling an organic-inorganic synergistic effect mechanism, and meanwhile, the compressive strength is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of building material preparation, and particularly relates to low-bleeding concrete and a preparation process thereof. Background Art

[0002] In construction projects, concrete bleeding refers to the phenomenon in which water in the mixture floats to the surface due to gravity, which directly leads to three major technical defects: deterioration of structural performance: after the formation of bleeding channels, the imbalance of the water-cement ratio in the surface layer causes sand and cracks (the loss of compressive strength in 28 days can reach 15% to 30%); decreased durability: the pores left after water evaporation accelerate the penetration of chloride ions (the measured diffusion coefficient increases by 2 to 3 times), significantly shortening the service life; uncontrolled construction quality: the bleeding layer interferes with the interfacial adhesion between the finishing and the secondary pouring (the bonding strength is reduced by more than 40%).

[0003] Current methods for controlling bleeding include: mineral admixtures: adding silica fume (5%–10%) or nanosilica to reduce bleeding through a micro-filling effect (bleeding rates can be reduced to 1.2%), but this is costly and increases viscosity; thickeners: using hydroxypropyl methylcellulose (HPMC) to extend the migration path of water molecules, but at dosages exceeding 0.1%, this significantly delays setting time (initial setting delay ≥3 hours); and optimized grading: adjusting the sand ratio (38%–42%) and fineness modulus (2.3–2.8), but this is sensitive to raw material fluctuations and suffers from poor stability. Furthermore, concrete strength is a key performance indicator, and improving it while reducing bleeding is a pressing issue. Therefore, a composite modification technology is urgently needed to address these issues. Summary of the Invention

[0004] The present invention aims to provide a low-bleeding concrete and its preparation process. By forming a micron-sized bonded body with nano-inorganic fillers, a water-reducing agent, and a water-retaining agent, the bonded body slowly dissolves and releases the active ingredients. While ensuring fluidity, the water bleeding rate is controlled within 0.5%, while significantly improving the concrete's strength.

[0005] To achieve the above object, the present invention provides a low bleeding concrete comprising: 100-120 parts of cement, 260-300 parts of river sand, 360-400 parts of pebbles, 35-55 parts of mineral powder, 30-50 parts of silica fume, 60-90 parts of water, and 2.2-5 parts of composite admixture; The composite admixture is a bonded body composed of nano inorganic filler, water reducing agent and water retaining agent, and the particle size of the bonded body is 1-10 microns.

[0006] Furthermore, the particle size of the nano inorganic filler is 100-300 nm; the nano inorganic filler is at least one of silica fume or fly ash.

[0007] Furthermore, the water reducer is a polycarboxylate water reducer; and the water retaining agent includes one or more of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl methyl cellulose, and polyacrylamide.

[0008] Furthermore, the content of each component in the composite admixture is calculated as 100%, including 10%-25% of nano inorganic filler, 35%-50% of water reducer, and the rest is the water retaining agent.

[0009] Furthermore, the content of each component in the composite admixture is calculated as 100%, including 15%-25% of nano inorganic filler, 35%-45% of water reducer, and the rest is the water retaining agent.

[0010] Furthermore, the preparation method of the composite admixture includes: dispersing the nano inorganic filler, water reducing agent and water retaining agent in water, drying and bonding them, and then crushing them to obtain a bonded body with a particle size of 1-10 microns.

[0011] Furthermore, the ratio of the amount of water added to the sum of the mass of the nano-inorganic filler, the water reducing agent and the water retaining agent is (2-10):1.

[0012] Furthermore, the particle size of the pebbles is 5-20 mm.

[0013] The present invention also provides a preparation process of low bleeding concrete, comprising the following steps: S1. Mix part of the water with river sand and pebbles, then add cement, mineral powder and silica fume and mix evenly; S2, adding the composite admixture and the remaining water and mixing evenly; S3. After pouring and forming, curing is carried out to obtain low water bleeding concrete.

[0014] Furthermore, in step S1, the partial water is 65%-75% of the total water.

[0015] Compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects: 1. The low-bleeding concrete provided by the present invention prepares nano-inorganic fillers, water-reducing agents, and water-retaining agents into a micron-sized bond. The bond dissolves in the concrete, continuously releasing part of the water-reducing agent, water-retaining agent, and nano-inorganic fillers. At the same time, the remaining insoluble three-dimensional network structure with reduced particle size effectively locks in water through the synergistic effect of the released multiple components, significantly reducing the bleeding rate while ensuring the slump. It is suitable for use in self-compacting concrete.

[0016] 2. The present invention reasonably controls the content of nano-inorganic fillers, water-reducing agents and water-retaining agents, thereby forming a composite bond and partially dissolving and releasing the composite effective components, thereby reducing the water bleeding rate and improving the strength.

[0017] 3. The preparation method of the composite admixture of the present invention is simple, the raw materials are easily available, and it is convenient for practical application. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the dissolution and sustained-release principle of the composite admixture of the present invention. DETAILED DESCRIPTION

[0019] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0020] The invention provides low-bleeding concrete, comprising: 100-120 parts of cement, 260-300 parts of river sand, 360-400 parts of pebbles, 35-55 parts of mineral powder, 30-50 parts of silica fume, 60-90 parts of water, and 2.2-5 parts of a composite admixture; the composite admixture is a binder composed of a nano-inorganic filler, a water-reducing agent, and a water-retaining agent, and the particle size of the binder is 1-10 microns.

[0021] Do this, such as Figure 1 The micron-sized binder slowly dissolves in the concrete, releasing part of the water-reducing agent, water-retaining agent and nano-inorganic filler. The remaining part is a three-dimensional network structure formed by the water-reducing agent, water-retaining agent and nano-inorganic filler. Due to its small particle size, it can also play a nano-filling role, thereby synergistically playing a water-locking role, significantly reducing the water bleeding rate, and preventing the problem of low fluidity due to excessive initial water-retaining agent.

[0022] Furthermore, the nano-inorganic filler has a particle size of 100-300 nm and is at least one of silica fume or fly ash. Smaller particle sizes of nano-inorganic fillers facilitate bonding with the water-reducing agent and water-retaining agent to form a cohesive mass. They also facilitate breakage, preventing overly large particles from becoming difficult to dissolve. The released small particles of silica fume or fly ash can also reduce water seepage by filling pores.

[0023] Furthermore, the water-reducing agent is a polycarboxylate water-reducing agent; and the water-retaining agent includes one or more of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl methylcellulose, and polyacrylamide. Water-reducing agent molecules adsorb on the surface of cement particles to form a double layer. This disrupts the cement flocculation structure through electrostatic repulsion or steric hindrance, releasing trapped free water. This allows the concrete to achieve equivalent fluidity at a lower water-cement ratio and reduces the amount of free water that can be exuded. The long hydrophilic chains of the water-retaining agent form hydrogen bonds with water molecules, increasing the viscosity of the slurry and hindering water migration and upwelling. Polyacrylamide polymer chains can form a three-dimensional network structure to bind free water.

[0024] Furthermore, the composite admixture comprises, calculated based on 100% by mass, 10%-25% of the nano-inorganic filler, 35%-50% of the water-reducing agent, and the remainder of the water-retaining agent. The amount of nano-inorganic filler should not be too large, as this may result in a bond that is too strong, difficult to break, and difficult to dissolve and release the active ingredient. If the amount of nano-inorganic filler is too low, it may be difficult to form a micron-sized bond.

[0025] Furthermore, the content of each component in the composite admixture is calculated as 100%, including 15%-25% of nano inorganic filler, 35%-45% of water reducer, and the rest is the water retaining agent.

[0026] Furthermore, the preparation method of the composite admixture includes: uniformly dispersing the nano-inorganic filler, water-reducing agent, and water-retaining agent in water, drying and bonding the mixture, and then crushing the mixture to obtain a bonded body with a particle size of 1-10 microns, preferably 1-5 microns. The ratio of the amount of water added to the sum of the mass of the nano-inorganic filler, water-reducing agent, and water-retaining agent is (2-10):1, preferably (5-8):1.

[0027] Furthermore, the particle size of the pebbles is 5-20 mm.

[0028] The present invention also provides a preparation process of low bleeding concrete, comprising the following steps: S1. Mix part of the water with river sand and pebbles, then add cement, mineral powder and silica fume and mix evenly; S2, adding the composite admixture and the remaining water and mixing evenly; S3. After pouring and forming, curing is carried out to obtain low water bleeding concrete.

[0029] Furthermore, in step S1, the partial water is 65%-75% of the total water.

[0030] Example 1 A low-bleeding concrete comprises: 100 parts of cement, 280 parts of river sand, 380 parts of pebbles, 45 parts of mineral powder, 50 parts of silica fume, 80 parts of water, and 3.5 parts of a composite admixture; the composite admixture is a binder consisting of silica fume (average particle size 200 nm), a polycarboxylate water-reducing agent, and a carboxymethyl cellulose water-retaining agent, and the binder has an average particle size of 3 microns.

[0031] The preparation method of the composite admixture comprises: uniformly dispersing 20 wt % of silica fume, 40 wt % of a water reducing agent and 40 wt % of a water retaining agent in water (the water is 6 times the total mass of the composite admixture), drying, bonding and then crushing to obtain the composite admixture.

[0032] The preparation process of low bleeding concrete includes the following steps: S1. Mix 70% water with river sand and pebbles, then add cement, mineral powder and silica fume and mix evenly; S2, adding the composite admixture and the remaining water and mixing evenly; S3. After pouring and forming, the concrete is cured for 28 days to obtain low water bleeding concrete.

[0033] Example 2 The difference from Example 1 is that the average particle size of the bonded body is 1 micron.

[0034] Example 3 The difference from Example 1 is that the average particle size of the bonded body is 5 microns.

[0035] Example 4 The difference from Example 1 is that 20 wt % of the silica fume, 45 wt % of the water reducing agent and 35 wt % of the water retaining agent are evenly dispersed in water (the water is 6 times the total mass of the composite admixture), dried and bonded, and then crushed to obtain a composite admixture.

[0036] Example 5 The difference from Example 1 is that the preparation method of the composite admixture includes: evenly dispersing 10% silica fume, 45% water reducer and 45% water retaining agent in water (the water is 6 times the total mass of the composite admixture), drying and bonding, and then crushing to obtain the composite admixture.

[0037] Example 6 The difference from Example 1 is that the amount of the composite admixture is 2.2 parts.

[0038] Example 7 The difference from Example 1 is that the water-retaining agent is polyvinyl alcohol.

[0039] Comparative Example 1 The difference from Example 1 is that the preparation method of the composite admixture includes: uniformly dispersing 30% silica fume, 40% water reducer and 30% water retaining agent in water (the water is 6 times the total mass of the composite admixture), drying and bonding, and then crushing to obtain the composite admixture.

[0040] Comparative Example 2 The preparation method of the composite admixture includes: uniformly dispersing silica fume and a water reducer in water (the water is 6 times the total mass of the composite admixture) at a mass ratio of 1:2, so as to prevent adhesion, and thus centrifugally separating to obtain the composite admixture. The water reducer has a low coverage rate and a high loss.

[0041] Comparative Example 3 The difference from Example 1 is that the preparation method of the composite admixture includes: uniformly dispersing 20% ​​silica fume, 40% water reducer and 40% water retaining agent in water (the water is 20 times the total mass of the composite admixture), and then centrifuging to obtain the composite admixture.

[0042] Comparative Example 4 The difference from Example 1 is that a low water bleeding concrete includes: 100 parts of cement, 280 parts of river sand, 380 parts of pebbles, 45 parts of mineral powder, 50.7 parts of silica fume, 80 parts of water, 1.4 parts of polycarboxylate water reducer, and 1.4 parts of carboxymethyl cellulose water retaining agent.

[0043] According to JGJ / T 283-2012 "Technical Specification for Application of Self-compacting Concrete", the pressure water bleeding rate B of the concrete slurry of the embodiment and the comparative example was tested. p and slump.

[0044] The compressive strength of the concrete of the embodiment and the comparative example after curing for 28 days was tested according to JGJ / T 283-2012 "Technical Specification for Application of Self-compacting Concrete".

[0045] Table 1 Test results of examples and comparative examples As can be seen from Table 1, the composite admixture of the present invention is slow-released, and the water-reducing agent releases faster and more, which can improve the slump in 1h, the pressure bleeding rate is low, and has a higher compressive strength. The slump of Comparative Example 4, which directly adds the three components of the composite admixture in equal amounts, is significantly reduced, the pressure bleeding rate is significantly increased, and the compressive strength is reduced, indicating that the component released by the composite admixture of the present invention can also improve the compressive strength. When the silica fume dosage of Comparative Example 1 is too much, it is not easy to dissolve and release, resulting in an increase in the pressure bleeding rate, and the composite admixture that is not fully dissolved and released is also limited to the degree of strength improvement. When no water-retaining agent is added, it is impossible to bond, so only part of the water-reducing agent is coated on the silica fume, and its pressure bleeding rate increases, and the strength is also not good. When the water dosage of Comparative Example 3 is too much, a dispersed suspension is formed. After centrifugation, the resulting product is released quickly because it does not form a bonded body, and the small-particle three-dimensional network structure composed of the water-reducing agent, water-retaining agent and nano-inorganic filler of the present invention cannot be formed, so that its strength is not significantly improved.

[0046] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A low bleeding concrete, characterized in that: include: 100-120 parts of cement, 260-300 parts of river sand, 360-400 parts of pebbles, 35-55 parts of mineral powder, 30-50 parts of silica fume, 60-90 parts of water, 2.2-5 parts of composite admixture; The composite admixture is a bonded body composed of nano inorganic filler, water reducing agent and water retaining agent, and the particle size of the bonded body is 1-10 microns.

2. The low bleeding concrete according to claim 1, characterized in that The particle size of the nano inorganic filler is 100-300 nm; the nano inorganic filler is at least one of silica fume or fly ash.

3. The low bleeding concrete according to claim 1, characterized in that The water reducing agent is a polycarboxylic acid water reducing agent; the water retaining agent includes one or more of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl methyl cellulose, and polyacrylamide.

4. The low bleeding concrete according to claim 1, characterized in that The components in the composite admixture include 10%-25% of nano inorganic filler, 35%-50% of water reducing agent, and the rest of the water retaining agent, calculated based on 100% by mass.

5. The low bleeding concrete according to claim 1, characterized in that The components in the composite admixture include 15%-25% of nano inorganic filler, 35%-45% of water reducing agent, and the rest of the water retaining agent, calculated based on 100% by mass.

6. The low bleeding concrete according to claim 1, characterized in that The preparation method of the composite admixture comprises: dispersing the nano inorganic filler, water reducing agent and water retaining agent in water, drying and bonding them, and then crushing them to obtain a bonded body with a particle size of 1-10 microns.

7. The low bleeding concrete according to claim 6, characterized in that The ratio of the amount of water added to the sum of the mass of the nano-inorganic filler, the water reducing agent and the water retaining agent is (2-10):

1.

8. The low bleeding concrete according to claim 1, characterized in that: The particle size of the pebbles is 5-20 mm.

9. A process for preparing the low bleeding concrete according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. Mix part of the water with river sand and pebbles, then add cement, mineral powder and silica fume and mix evenly; S2, adding the composite admixture and the remaining water and mixing evenly; S3. After pouring and forming, curing is carried out to obtain low water bleeding concrete.

10. The process for preparing low bleeding concrete according to claim 9, characterized in that: In step S1, the partial water is 65%-75% of the total water.

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