CN113979688B - Recycled concrete capable of being repeatedly utilized in cold regions and preparation method - Google Patents

Abstract

The invention belongs to the technical field of building materials, and in particular relates to a recycled concrete that can be used multiple times in cold regions and a preparation method. The recycled concrete comprises the following components by weight: 860-912 parts of recycled coarse aggregate, 692-692 parts of river sand 736 parts, Portland cement 286~312 parts, silica fume 22~24 parts, fly ash 88~96 parts, slag 44~48 parts, water reducing agent 2.2~2.4 parts, air entraining agent 0.26~0.29 parts and water 169~182 copies. The recycled concrete provided by the invention, which can be used for many times in cold regions, has the advantages of high strength and good frost resistance. The physical properties of aggregates are required, and they can be applied to structural concrete again. The second-generation recycled concrete prepared by using it also has excellent mechanical and anti-freezing properties, which enables the recycled concrete to be reused many times, and solves the problem of environmental pollution by waste recycled concrete in cold areas. The problem.

Description

A kind of recycled concrete that can be used repeatedly in cold regions and its preparation method

technical field

The invention belongs to the technical field of building materials, and in particular relates to a recycled concrete which can be used repeatedly in cold regions and a preparation method thereof.

Background technique

With the continuous improvement of the country's requirements for the sustainable development of the construction industry, the popularity of recycled concrete has become inevitable. For cold regions, a large number of recycled concrete structures are exposed to freeze-thaw environments. Due to natural disasters or reaching the design service life, these recycled concrete structures are dismantled and become waste recycled concrete. They are likely to be scrapped due to the failure of frost resistance durability and cannot be recycled. , become useless waste. These waste recycled concrete not only need a lot of manpower and material resources to dispose of, but also occupy a lot of land resources and pollute the environment.

However, under the condition of full replacement, the mechanical properties and frost resistance of recycled concrete are generally poor, and the safety reserve is small. When the loss of frost resistance durability occurs, it is often accompanied by serious damage to the internal structure, which will lead to the second generation of recycled coarse aggregate. The physical properties are reduced, so waste recycled concrete in cold regions is often not recommended to be reapplied in structural concrete as coarse aggregate.

In the prior art, there is no recycled concrete with good mechanical properties, strong anti-freeze performance and reusable performance that can solve the problem that concrete cannot be reusable in cold regions.

Contents of the invention

In order to solve the deficiencies of the prior art, the object of the present invention is to provide a recycled concrete that can be used repeatedly in cold regions. The recycled concrete has high strength and good frost resistance, and after 300 times of freezing and thawing, the recycled concrete is broken to obtain The second-generation recycled coarse aggregate can be applied to structural concrete again, which solves the problem that waste recycled concrete cannot be reused many times in cold regions.

Another object of the present invention is to provide a method for preparing recycled concrete that can be used repeatedly in cold regions, which is beneficial to the industrial production of concrete and its products.

In order to solve the deficiencies in the prior art, the technical solution provided by the invention is:

A recycled concrete that can be used repeatedly in cold regions, including the following components by weight: 860-912 parts of recycled coarse aggregate, 692-736 parts of river sand, 286-312 parts of Portland cement, 22-22 parts of silica fume 24 parts, 88-96 parts of fly ash, 44-48 parts of slag, 2.2-2.4 parts of water reducing agent, 0.26-0.29 parts of air-entraining agent and 169-182 parts of water.

Preferably, the recycled coarse aggregate is Class I recycled coarse aggregate or Class II recycled coarse aggregate specified in GB/T25177-2010, with a particle size of 5-25mm.

Preferably, the strength grade of the Portland cement is not lower than 42.5.

Preferably, the weight ratio of Portland cement, silica fume, fly ash and slag is 13:1:4:2.

Preferably, the ratio of the weight of the water to the total weight of the Portland cement, silica fume, fly ash and slag is 0.35-0.41.

Preferably, the river sand is medium sand with a fineness modulus of 2.5-2.6.

Preferably, the water-reducing agent is a polycarboxylate-based water-reducer, a naphthalene-based water-reducer or a sulfamic acid-based water-reducer, and the water-reducing efficiency is not less than 25%.

Preferably, the air-entraining agent is rosin air-entraining agent, saponin air-entraining agent or fatty alcohol air-entraining agent.

A method for preparing recycled concrete that can be reused in cold regions, comprising,

S1: Weigh each component according to the weight part of the aforementioned recycled concrete that can be used repeatedly in cold regions;

S2: Add the recycled coarse aggregate and river sand into the mixing vessel and stir evenly;

S3: Add 45% to 55% of water into the stirring container and stir evenly;

S4: Add portland cement, silica fume, fly ash and slag into the mixing container and stir evenly;

S5: Put the water reducing agent, the air-entraining agent and the remaining water into the mixing container and stir evenly to obtain the aforementioned recycled concrete that can be used many times in cold regions.

Preferably, in the step S2, the stirring time is 60-100s;

In the step S3, the stirring time is 60-100s;

In the step S4, the stirring time is 30-50s;

In the step S5, the stirring time is 120-150s.

Beneficial effects of the present invention:

1) The mixing ratio of the present invention is reasonable, and the prepared recycled concrete that can be used repeatedly in cold regions has a slump greater than 160mm, a compressive strength greater than 35MPa, a flexural strength greater than 4MPa, and the mass loss after freezing and thawing for 300 times The ratio is less than 3%, the relative dynamic elastic modulus is greater than 70%, and the performance is good.

2) The second-generation recycled coarse aggregate obtained after 300 times of freeze-thaw crushing of recycled concrete provided by the present invention, which can be used repeatedly in cold regions, has an apparent density greater than 2290kg/m ³ , a water absorption rate of less than 7%, and a crush value of less than 25%, firmness (mass loss) is less than 12%, fine powder content is less than 2.5%, mud content is less than 1%, needle flake particle content is less than 8%, physical properties meet the requirements for the use of Class III recycled coarse aggregate, and can be used in Structural concrete, the second-generation recycled concrete prepared by using it, the compressive strength is greater than 35MPa, the flexural strength is greater than 3.5MPa, the mass loss rate after freezing and thawing for 300 times is less than 4%, and the relative dynamic elastic modulus is greater than 65%, Various performances are good, realizing multiple utilization of discarded recycled concrete in cold regions.

Detailed ways

The present invention will be further described below in combination with embodiments. The following embodiments are only used to illustrate the technical solutions of the present invention more clearly, but not to limit the protection scope of the present invention.

The embodiment of the present invention provides a recycled concrete that can be used multiple times in cold regions, including the following components by weight: 860-912 parts of recycled coarse aggregate, 692-736 parts of river sand, and 286-312 parts of Portland cement , 22-24 parts of silica fume, 88-96 parts of fly ash, 44-48 parts of slag, 2.2-2.4 parts of water reducing agent, 0.26-0.29 parts of air-entraining agent and 169-182 parts of water. Portland cement, silica fume, fly ash and slag are used as cementitious materials.

Regenerated coarse aggregate and sand play the role of the skeleton. After mixing various cementitious materials with water, the aggregate is wrapped to make the recycled concrete have a certain degree of workability. Among them, silica fume, fly ash and slag are due to their activity and The difference in density can play a morphological effect, activity effect and micro-aggregate filling effect in recycled concrete, forming a super-superposition effect, which in turn compacts the internal pores and interface transition zone of recycled concrete, and improves the mechanical and frost resistance of recycled concrete. Therefore, the ability to resist freeze-thaw damage is stronger. At the same time, due to the secondary hydration of the mortar, part of the damage is compensated, ensuring that the physical and mechanical properties of the second-generation recycled coarse aggregate are relatively good.

In an optional embodiment of the present invention, the recycled coarse aggregate is commercially available Type I recycled coarse aggregate or Type II recycled coarse aggregate specified in GB/T25177-2010, with an apparent density greater than 2350kg/m ³ and water absorption The rate is less than 5%, the crushing value is less than 20%, the firmness (mass loss) is less than 10%, the content of fine powder is less than 2%, the content of mud is less than 0.7%, the content of needle-shaped particles is less than 10%, and the particle size is 5-25mm .

In an optional embodiment of the present invention, the strength grade of Portland cement is not lower than 42.5.

In an optional embodiment of the present invention, the weight ratio of Portland cement, silica fume, fly ash and slag is 13:1:4:2.

In an optional embodiment of the present invention, the ratio of the weight of water to the total weight of cementitious materials (Portland cement, silica fume, fly ash and slag) is 0.35-0.41.

In an optional embodiment of the present invention, the river sand is medium sand with a fineness modulus of 2.5-2.6.

In an optional embodiment of the present invention, the water reducer is polycarboxylate water reducer, naphthalene type water reducer or sulfamic acid water reducer, and the water reducing efficiency is not less than 25%. Among them, the polycarboxylic acid-based water reducer is a preferable water reducer.

In an optional embodiment of the present invention, the air-entraining agent is a rosin-type air-entraining agent, a saponin-type air-entraining agent or a fatty alcohol-type air-entraining agent. Among them, the fatty alcohol air-entraining agent is the preferred air-entraining agent.

Embodiments of the present invention also provide a method for preparing recycled concrete that can be used repeatedly in cold regions, comprising the following steps:

S1: Weigh each component according to the weight part of the aforementioned recycled concrete that can be used repeatedly in cold regions;

S2: Add recycled coarse aggregate and river sand into the mixing container, and dry stir for 60-100 seconds;

S3: add 45%-55% water into the stirring container and stir for 60-100s;

S4: Add Portland cement, silica fume, fly ash and slag into the mixing container and stir for 30-50 seconds;

S5: Add the water reducing agent, the air-entraining agent and the remaining water into the mixing container and stir for 120-150 seconds, and mix evenly to obtain the aforementioned recycled concrete that can be used many times in cold regions.

In an optional embodiment of the present invention, the stirring container is a stirrer.

The present invention measures the slump of recycled concrete according to GB/T50080-2016 "Standards for Test Methods of Performance of Ordinary Concrete Mixtures", and measures the 28d compressive strength, 28d flexural strength, and according to GB/T50082-2009 "General Concrete Long-term Performance and Durability Test Method Standard", the mass loss rate after 300 rapid freeze-thaw tests and relative dynamic modulus of elasticity are used to characterize the prepared concrete. Performance of recycled concrete that has been used many times in cold regions.

In addition, according to GB/T25177-2010 "Recycled Coarse Aggregate for Concrete", the present invention measures the prepared recycled concrete that can be used multiple times in cold regions. Physical properties of recycled coarse aggregate, and used it to prepare the second generation recycled concrete, measured the 28d compressive strength, 28d flexural strength of the second generation recycled concrete, and the mass loss rate after 300 rapid freeze-thaw tests, The relative dynamic elastic modulus is used to characterize the performance of the second generation recycled concrete.

In the following examples, the air-entraining agent is a fatty alcohol air-entraining agent purchased from Jiangsu Subote New Material Co., Ltd., the model is GYQ-E100, and the main component is fatty alcohol polyoxyethylene ether. The water reducer is a polycarboxylate water reducer purchased from Jiangsu Subote New Materials Co., Ltd., the model is PCA-I, and the main component is butenedioic acid-acrylic acid-allyl polyethylene glycol copolymer.

Embodiment one

1) Preparation of recycled concrete:

Step 1: Prepare 883 parts of recycled coarse aggregate, 736 parts of river sand, 286 parts of ordinary portland cement, 22 parts of silica fume, 88 parts of fly ash, 44 parts of slag, 182 parts of water, polycarboxylate 2.2 parts of water agent, 0.26 parts of GYQ-E100 air-entraining agent. Among them, the apparent density of recycled coarse aggregate is 2442kg/m ³ , the water absorption rate is 3.8%, the crushing value is 15.6%, the firmness (mass loss) is 9.2%, the fine powder content is 0.8%, and the mud content is 0.3%. , the content of needle flake particles is 6.7%, and the particle size is 5-25mm. The river sand is medium sand with a fineness modulus of 2.6. The strength grade of ordinary Portland cement is 42.5, the mass ratio of ordinary Portland cement, silica fume, fly ash and slag to the total cementitious material is 13:1:4:2, and the water-binder ratio is 0.41. The water reducing efficiency of polycarboxylate water reducer is 25%.

Step 2: Add the recycled coarse aggregate and river sand into the mixer and dry mix for 60s.

Step 3: Add 91 parts of water into the mixer and stir for 60 seconds.

Step 4: Add Portland cement, silica fume, fly ash and slag into the mixer and stir for 30 seconds.

Step 5: Add polycarboxylate superplasticizer, GYQ-E100 air-entraining agent and the remaining 91 parts of water into the mixer and stir for 120 seconds, and mix well to obtain recycled concrete.

2) Preparation of the second generation recycled concrete:

After freezing and thawing the recycled concrete prepared in Step 5 for 300 times, waste recycled concrete was obtained, and then the waste recycled concrete was crushed to obtain second-generation recycled coarse aggregate with a particle size greater than 4.75mm; the second-generation recycled coarse aggregate was replaced in step 1 The recycled coarse aggregate used in the method, other components remain unchanged, and the second-generation recycled concrete is prepared according to the content of each component in step 1 and steps 2 to 5.

Embodiment two

1) Preparation of recycled concrete:

Step 1: Prepare 897 parts of recycled coarse aggregate, 718 parts of river sand, 299 parts of ordinary portland cement, 23 parts of silica fume, 92 parts of fly ash, 46 parts of slag, 175 parts of water, polycarboxylate 2.3 parts of water agent, 0.28 parts of GYQ-E100 air-entraining agent. Among them, the apparent density of recycled coarse aggregate is 2442kg/m ³ , the water absorption rate is 3.8%, the crushing value is 15.6%, the firmness (mass loss) is 9.2%, the fine powder content is 0.8%, and the mud content is 0.3%. , the content of needle flake particles is 6.7%, and the particle size is 5-25mm. The river sand is medium sand with a fineness modulus of 2.6. The strength grade of ordinary Portland cement is 42.5, the mass ratio of ordinary Portland cement, silica fume, fly ash and slag to the total cementitious material is 13:1:4:2, and the water-binder ratio is 0.38. The water reducing efficiency of polycarboxylate water reducer is 25%.

Step 2: Add the recycled coarse aggregate and river sand into the mixer and dry mix for 70s;

Step 3: Add 87.5 parts of water into the mixer and stir for 70 seconds;

Step 4: Add Portland cement, silica fume, fly ash and slag into the mixer and stir for 40 seconds;

Step 5: Add polycarboxylate superplasticizer, GYQ-E100 air-entraining agent and the remaining 87.5 parts of water into the mixer and stir for 130 seconds, and mix evenly to obtain recycled concrete.

2) Preparation of the second generation recycled concrete:

After freezing and thawing the recycled concrete prepared in Step 5 for 300 times, waste recycled concrete was obtained, and then the waste recycled concrete was crushed to obtain second-generation recycled coarse aggregate with a particle size greater than 4.75mm; the second-generation recycled coarse aggregate was replaced in step 1 The recycled coarse aggregate used in the method, other components remain unchanged, and the second-generation recycled concrete is prepared according to the content of each component in step 1 and steps 2 to 5.

Embodiment three

1) Preparation of recycled concrete:

Step 1: Prepare 912 parts of recycled coarse aggregate, 692 parts of river sand, 312 parts of ordinary portland cement, 24 parts of silica fume, 96 parts of fly ash, 48 parts of slag, 169 parts of water, polycarboxylate 2.4 parts of water agent, 0.29 parts of GYQ-E100 air-entraining agent. Among them, the apparent density of recycled coarse aggregate is 2442kg/m ³ , the water absorption rate is 3.8%, the crushing value is 15.6%, the firmness (mass loss) is 9.2%, the fine powder content is 0.8%, and the mud content is 0.3%. , the content of needle flake particles is 6.7%, and the particle size is 5-25mm. The river sand is medium sand with a fineness modulus of 2.6. The strength grade of ordinary Portland cement is 42.5, the mass ratio of ordinary Portland cement, silica fume, fly ash and slag to the total cementitious material is 13:1:4:2, and the water-binder ratio is 0.35. The water reducing efficiency of polycarboxylate water reducer is 25%.

Step 2: Add the recycled coarse aggregate and river sand into the mixer and dry mix for 90s;

Step 3: Add 84.5 parts of water into the mixer and stir for 90 seconds;

Step 4: Add Portland cement, silica fume, fly ash and slag into the mixer and stir for 50s;

Step 5: Add polycarboxylate superplasticizer, GYQ-E100 air-entraining agent and the remaining 84.5 parts of water into the mixer and stir for 150 seconds, and mix evenly to obtain recycled concrete.

2) Preparation of the second generation recycled concrete:

After freezing and thawing the recycled concrete prepared in Step 5 for 300 times, waste recycled concrete was obtained, and then the waste recycled concrete was crushed to obtain second-generation recycled coarse aggregate with a particle size greater than 4.75mm; the second-generation recycled coarse aggregate was replaced in step 1 The recycled coarse aggregate used in the method, other components remain unchanged, and the second-generation recycled concrete is prepared according to the content of each component in step 1 and steps 2 to 5.

comparative example

1) Preparation of recycled concrete:

Step 1: Prepare 883 parts of recycled coarse aggregate, 736 parts of river sand, 440 parts of ordinary Portland cement, 182 parts of water, 1 part of polycarboxylate superplasticizer, and 0.2 part of GYQ-E100 air-entraining agent in parts by weight. Among them, the apparent density of recycled coarse aggregate is 2442kg/m ³ , the water absorption rate is 3.8%, the crushing value is 15.6%, the firmness (mass loss) is 9.2%, the fine powder content is 0.8%, and the mud content is 0.3%. , the content of needle flake particles is 6.7%, and the particle size is 5-25mm. The river sand is medium sand with a fineness modulus of 2.6. Ordinary Portland cement has a strength grade of 42.5 and a water-binder ratio of 0.41. The water reducing efficiency of polycarboxylate water reducer is 25%.

Step 2: Add the recycled coarse aggregate and river sand into the mixer and dry mix for 60 seconds;

Step 3: Add 91 parts of water into the mixer and stir for 60 seconds;

Step 4: Add Portland cement to the mixer and stir for 30s;

Step 5: Add polycarboxylate superplasticizer, GYQ-E100 air-entraining agent and the remaining 91 parts of water into the mixer and stir for 120 seconds, and mix well to obtain recycled concrete.

2) Preparation of the second generation recycled concrete

Step 6: Freezing and thawing the prepared recycled concrete 300 times to obtain waste recycled concrete, and then crushing the waste recycled concrete to obtain the second-generation recycled coarse aggregate with a particle size greater than 4.75mm; replace the second-generation recycled coarse aggregate with the step The recycled coarse aggregate used in step 1, other components remain unchanged, and the second-generation recycled concrete is prepared according to the content of each component in step 1 and steps 2-5.

Table 1 Mechanics and frost resistance performance data of recycled concrete

Table 2 Performance data of the second generation recycled coarse aggregate

Table 3 Mechanics and frost resistance performance data of the second generation recycled concrete

As can be seen from Table 1, the slump of recycled concrete prepared in the present invention that can be used repeatedly in cold regions is greater than 160mm, the compressive strength is greater than 35MPa, the flexural strength is greater than 4MPa, and the quality after freezing and thawing for many times 300 times The loss rate is less than 3%, the relative dynamic elastic modulus is greater than 70%, and the performance is good. In the comparative example, only a small amount of water reducing agent and air-entraining agent was added, which was not enough to make the recycled concrete have better working performance. At the same time, the cementitious material was only cement, which could not play a role in mineral admixtures (silica fume, fly ash and slag). ) resulting in a poorer pore structure of the recycled concrete, and therefore poorer performance.

It can be seen from Table 2 that the physical and mechanical properties of the second-generation recycled coarse aggregate obtained by crushing the waste recycled concrete after 300 times of freezing and thawing meet the requirements of Class III recycling of GB/T25177-2010 "Recycled Coarse Aggregate for Concrete" Coarse aggregate performance requirements can again be applied to structural concrete. Because the recycled concrete in the embodiment has added mineral admixtures (silica fume, fly ash and slag), the secondary hydration of the mortar has occurred in the quick freezing test, which has made up for part of the freeze-thaw damage, so the first in the embodiment The physical properties of the second-generation recycled coarse aggregate are better than those of the comparative example.

It can be seen from Table 3 that the compressive strength of the second-generation recycled concrete is greater than 35MPa, the flexural strength is greater than 3.5MPa, the mass loss rate after freezing and thawing for 300 times is less than 4%, and the relative dynamic elastic modulus is greater than 65%. This item has good performance and meets the performance requirements of structural concrete in cold regions. This shows that the second-generation recycled coarse aggregate can be used in cold regions, realizes the multiple utilization of waste recycled concrete in cold regions, and solves the problem of waste recycled concrete polluting the environment. .

The above is only a preferred embodiment of the present invention, and it should be pointed out that for those of ordinary skill in the art, without departing from the technical principle of the present invention, some improvements and modifications can also be made. It should also be regarded as the protection scope of the present invention.

Claims (9)

1. A recycled concrete that can be used repeatedly in cold regions is characterized in that it consists of the following components by weight: 860-912 parts of recycled coarse aggregate, 692-736 parts of river sand, 286-736 parts of Portland cement 312 parts, 22~24 parts of silica fume, 88~96 parts of fly ash, 44~48 parts of slag, 2.2~2.4 parts of water reducing agent, 0.26~0.29 parts of air-entraining agent and 169~182 parts of water; The aggregate is Class I recycled coarse aggregate or Class II recycled coarse aggregate specified in GB/T25177-2010, with a particle size of 5-25 mm. 2. A kind of recycled concrete that can be used repeatedly in cold regions according to claim 1, characterized in that the strength grade of the Portland cement is not less than 42.5. 3. A recycled concrete that can be used repeatedly in cold regions according to claim 1, characterized in that the weight ratio of Portland cement, silica fume, fly ash and slag is 13:1:4 :2. 4. A kind of recycled concrete that can be used repeatedly in cold regions according to claim 1 is characterized in that, the weight of the water and the total weight of the Portland cement, silica fume, fly ash and slag The ratio is 0.35~0.41. 5. A recycled concrete that can be used multiple times in cold regions according to claim 1, wherein the river sand is medium sand with a fineness modulus of 2.5-2.6. 6. A recycled concrete that can be used multiple times in cold regions according to claim 1, wherein the water reducer is polycarboxylate water reducer, naphthalene water reducer or sulfamic acid water reducer Water agent, the water reducing efficiency is not less than 25%. 7. A kind of recycled concrete that can be used repeatedly in cold regions according to claim 1, characterized in that, the air-entraining agent is rosin air-entraining agent, saponin air-entraining agent or fatty alcohol air-entraining agent . 8. A method for preparing recycled concrete that can be used repeatedly in cold regions, characterized in that it comprises, S1: Weigh each component according to the weight of the recycled concrete that can be used multiple times in cold regions according to any one of claims 1 to 7; S2: Add the recycled coarse aggregate and river sand into the mixing vessel and stir evenly; S3: add 45%~55% water into the mixing container and stir evenly; S4: Add portland cement, silica fume, fly ash and slag into the mixing container and stir evenly; S5: Add the water reducing agent, the air-entraining agent and the remaining water into the mixing container and stir evenly to obtain the recycled concrete that can be used multiple times in cold regions according to any one of claims 1 to 7. 9. A kind of preparation method of recycled concrete that can be used repeatedly in cold regions according to claim 8, is characterized in that, In the step S2, the stirring time is 60 ~ 100 s; In the step S3, the stirring time is 60 ~ 100 s; In the step S4, the stirring time is 30 ~ 50 s; In the step S5, the stirring time is 120-150 s.