CN115043620A

CN115043620A - Method for preparing early-strength precast concrete by taking sand as grinding medium

Info

Publication number: CN115043620A
Application number: CN202210221776.0A
Authority: CN
Inventors: 苏英; 史虎雄; 曾昊清; 郑正旗; 贺行洋; 杨进; 王迎斌; 马庆红; 赵浩祥; 李韦龙; 吴磊; 李承昊
Original assignee: Hubei University of Technology
Current assignee: Hubei University of Technology
Priority date: 2022-03-09
Filing date: 2022-03-09
Publication date: 2022-09-13
Anticipated expiration: 2042-03-09
Also published as: CN115043620B

Abstract

The invention provides a method for preparing early strength precast concrete by taking sand as a grinding medium, which comprises the following steps: firstly, preparing the following raw materials in a certain proportion: sand, admixture, cement, water, coarse aggregate and additive; the particle size of the sand is 2.0-3.5 mm; secondly, taking part of the sand, part of the admixture, part of the cement and part of the water, putting the mixture into grinding equipment according to a certain proportion under the condition of not additionally adding a grinding medium, and carrying out wet grinding treatment to obtain cement-based slurry; and finally, mixing the cement-based slurry with the rest of the raw materials to prepare the early-strength precast concrete. According to the invention, the fine aggregate sand with a specific particle size is adopted to replace grinding balls, the cement and the admixture are subjected to wet grinding and activating treatment, the activated cement-based slurry and the rest raw materials are used for producing the member concrete, the preparation process is simple and efficient, the prepared concrete has high early strength, and the application requirement in the field of manufacturing of assembled members can be met.

Description

Method for preparing early-strength precast concrete by taking sand as grinding medium

Technical Field

The invention belongs to the technical field of building concrete materials, and particularly relates to a method for preparing early-strength precast concrete by taking sand as a grinding medium.

Background

The assembly type construction mode is the development trend of future building engineering, and the prefabricated member concrete is the foundation stone of the assembly type construction. Different from the construction mode of cast-in-place construction, the fabricated construction is to manufacture the concrete prefabricated part in a flow line production mode in a factory, so that the early strength of the concrete used by the prefabricated part is required to be high enough to meet the working procedure requirements of demoulding, hoisting and the like.

Factories generally use large amounts of cement (more than 85%) and smaller amounts of admixtures (less than 15%) to achieve the goal of early high strength of concrete, which results in high costs for the production of prefabricated parts and high carbon emissions. Because the price of the cement is 500-700 yuan/ton, and the admixture is 180-210 yuan/ton; carbon dioxide emissions per ton of cement produced are about 0.7 tons, while carbon dioxide emissions from admixtures are close to zero. The use of some activating means to increase the activity of the admixture and increase its mixing amount in concrete is one of the effective methods to solve the above problems.

In the field of building materials, wet grinding is a commonly used technical means for enhancing the activity of an admixture, and is particularly suitable for ultra-fine treatment of the admixture, and the admixture after the wet grinding treatment can be mixed into concrete with higher mixing amount without causing reduction of mechanical properties; the curing temperature can be reduced under the condition of the same mixing amount, and even steam curing is avoided. In the wet milling process, in order to ensure a sufficiently high number of mechanical forces (known academically as "stress frequency"), milling balls of particularly small particle size are usually used as milling media.

However, in the wet milling process, the viscosity of the slurry is increased sharply along with the sharp reduction of the particle size of the particle group, so that the separation of the grinding balls and the slurry is difficult, and the situation of blocking the discharge port of the mill often occurs. In addition, the hydration activity of the cement can be rapidly improved after the cement is subjected to wet grinding, so that the hydration reaction of the cement can be vigorously carried out. Since the cement hydration speed is not easy to control, the cement is easy to harden and block pipelines in the mill cylinder by using the traditional wet grinding and stirring method, and even if the wet grinding treatment process of the cement is smoothly completed and removed, the cement remained in the mill can be hardened by hydration, which can seriously affect the safety of equipment. Although the problems can be solved by timely cleaning the interior of the mill and removing the blockage of the discharge port, the construction time is increased, the smooth processing is affected, the water consumption is high, and the problems cause no small obstruction to the popularization and application of the wet grinding process.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides the method for preparing the early-strength precast concrete by taking sand as the grinding medium, which avoids the use of the grinding medium (grinding balls and the like), can properly reduce the hydration activity of cement in the wet grinding process, avoids the risk of material blockage, reduces unnecessary construction time and improves the construction efficiency.

The invention provides a method for preparing early strength precast concrete by taking sand as a grinding medium, which comprises the following steps:

s1, preparing the following raw materials according to a certain proportion: sand, admixture, cement, water, coarse aggregate and additive; the particle size of the sand is 2.0-3.5 mm;

s2, taking part of the sand, part of the admixture, part of the cement and part of the water, putting the mixture, the cement and the water into a grinding device according to a certain proportion, and carrying out wet grinding treatment to obtain cement-based slurry;

and S3, mixing the cement-based slurry with the rest of the raw materials to prepare the early-strength precast member concrete.

The general idea of the invention is as follows: from the raw material for the preparation of the precast concrete, a part of fine aggregate (sand) having a specific particle size is taken out in place of a conventional grinding medium (such as grinding balls or the like), and a part of the admixture and a part of the cement in the raw material are subjected to a treatment wet-grinding treatment. Specifically, the sand with the particle size of 2.0-3.5 mm is used as the raw material, so that the wet grinding treatment can be performed on other raw materials instead of grinding balls; can be used as fine aggregate and discharged together with cement-based slurry after wet grinding. The conventional grinding medium is grinding balls made of materials with higher hardness, such as stainless steel, alumina, zirconia, agate and the like.

By adopting the preparation method provided by the invention, on one hand, the sand is used for replacing grinding balls to grind materials, the fine aggregate is gradually ground, the particle size of the particles is reduced, the surface tends to be flat and round, the shape of the fine aggregate is very close to that of the grinding balls, the wet grinding function of other raw materials can be realized by replacing the grinding balls, the grinding media in the slurry are not required to be separated after the wet grinding treatment, the operation flow is simplified, and the construction time is greatly saved; on the other hand, the hardness of the fine aggregate sand is lower than that of the conventional grinding ball, a more slight grinding mode is provided, the fine aggregate sand is ground in cooperation with cement and the admixture without severe grinding, and meanwhile, the alkaline liquid phase environment generated by the cement can reduce the mechanical activation energy required by the activation of the admixture, so that the wet grinding strength is further reduced, and the conditions of severe reaction, even hardening and material blocking caused by overhigh hydration activity are effectively avoided.

Preferably, in the invention, the sand with the particle size of 2.0-3.5 mm can be obtained by screening the fine aggregate.

In the present invention, in the step S2, the weight ratio of the sand, the admixture, the cement, and the water in the grinding apparatus is 200: (20-70): (20-70): (40-140). Under the condition of the proportion, the matching degree of the materials is better, and better wet grinding effect can be obtained.

Further, in the step S2, the wet grinding device includes a vertical stirring mill, the rotation speed of the wet grinding process is 1000 to 3000r/min, and the time of the wet grinding process is 10 to 20 min. Preferably, the rotation speed of the wet grinding process is 3000r/min, and the time of the wet grinding process is 20 min. Under the condition, the admixture has higher levigating activity and can improve the strength of concrete.

Further, in the step S2, the particle size of the sand in the cement-based slurry is 1.0 to 2.0 mm. In the invention, after the step of wet grinding treatment, the sand used as a grinding medium is ground to have a particle size of 1.0-2.0 mm, and then the ground sand is discharged along with the cement-based slurry and is mixed with the sand with a particle size of 2.0-3.5 mm in the rest raw materials, so as to realize the preparation of the precast concrete. In the invention, two fine aggregates with different particle sizes are mixed with each other, so that the fine aggregate gradation required by the mixing ratio can be provided for the concrete, the gaps among the coarse aggregates are filled, and the strength of the concrete is increased.

On the basis of the technical scheme, the sand is selected from natural sand or machine-made sand, preferably the machine-made sand and obtained by screening, and the Mohs hardness of the sand is more than or equal to 6.5; the cement is selected from 42.5 grade or above silicate cement; the coarse aggregate comprises crushed stone and/or fine stone.

On the basis of the technical scheme, the admixture comprises an admixture with volcanic ash activity and/or an admixture with self-hydration activity. Preferably, the admixture comprises one or more of mineral powder, fly ash and steel slag powder.

On the basis of the technical scheme, the additive is selected from a polycarboxylic acid water reducing agent or a naphthalene water reducing agent.

In some preferred embodiments, in the step S2, the weight of the part of the sand accounts for 20-30% of the total weight of the sand in the step S1. Preferably, the weight of the part of the sand accounts for 24-26% of the total weight of the sand in the step S1.

In some preferred embodiments, in step S1, the amount of each raw material includes, by weight: 750-820 parts of sand, 40-80 parts of admixture, 280-340 parts of cement, 140-180 parts of water, 1000-1150 parts of coarse aggregate and 8-12 parts of additive.

Compared with the prior art, the invention has the beneficial effects that:

(1) the method for preparing the early-strength precast concrete provided by the invention takes part of sand with specific particle size in the raw materials as a grinding medium to prepare cement-based slurry through wet grinding treatment, and then the cement-based slurry is mixed with the rest raw materials to prepare the early-strength precast concrete. According to the method, a conventional grinding medium is not required to be additionally added, so that the grinding medium and the grinding material are not required to be separated, the cement-based slurry subjected to wet grinding treatment and the fine aggregate are discharged from a wet grinder together, the construction steps are saved, the construction time is shortened, and the hardening accident of the grinding equipment is avoided.

(2) According to the method for preparing the early-strength precast concrete, sand with a specific particle size is used as a grinding medium, and compared with a conventional grinding medium (such as grinding balls made of materials with higher hardness, such as stainless steel, alumina, zirconia or agate), the early-strength precast concrete has lower hardness and can be wet-ground together with an admixture and cement only by slight wet grinding; in addition, the alkaline liquid phase environment generated by the cement can reduce the mechanical activation energy required by the activation of the admixture, can reduce the wet grinding strength, and avoids the occurrence of severe reaction, even hardening and material blocking caused by overhigh hydration activity.

(3) The cement-based slurry prepared by the method can directly replace part of raw materials to prepare early-strength precast concrete, compared with the conventional method for wet grinding by adopting grinding media such as zirconia and the like, the preparation method provided by the invention has the advantages that the process is simpler, the operation time is saved, the construction cost is obviously reduced, the early strength of the prepared concrete is high, the strength can reach 17.3MPa within 22h of room-temperature curing, and the method is suitable for manufacturing assembled members.

Drawings

Fig. 1 is a schematic flow chart of a method for preparing early strength precast concrete by using sand as a grinding medium according to the present invention.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.

For the convenience and simplicity of describing the present invention, the most common concrete grade of C30 is used in the examples of the present invention, but this is not to be construed as limiting the present invention to the concrete grade of C30, and other concrete grades can be implemented by referring to the preparation method provided by the present invention.

The present invention will be further described with reference to specific examples, but is not limited thereto, which are exemplified by C30 grade concrete used in Wuhan's precast concrete plant. The formulation of the raw materials in the C30 grade concrete is as follows:

TABLE 1

The grain size of the machine-made sand in the above table is 2.0-3.5 mm.

In examples 1-3, the following Table 2 shows the raw materials and their amounts used to make a cement-based slurry:

TABLE 2

Note: production of 1m for each example ³ Concrete of

Example 1

Step 1: preparing raw materials according to the raw material mixing ratio shown in table 1;

and 2, step: weighing the machine-made sand, the fly ash, the cement and the water according to the dosage shown in the table 2, and placing the materials in a vertical stirring mill for mixing; starting the vertical stirring mill, and operating at the rotating speed of 3000R/min for 10min to prepare 280kg of cement-based slurry;

and step 3: and (3) mixing the cement-based slurry prepared in the step (2) with the rest raw materials (specifically, 300kg of ordinary portland cement, 25kg of fly ash, 969kg of broken stone, 126kg of fine stone, 590kg of machine-made sand, 120kg of water and 9.5kg of additives) to prepare the early-strength precast concrete.

Example 2

and 2, step: weighing machine-made sand, fly ash, cement and water according to the dosage shown in Table 2, and placing the materials in a vertical stirring mill for mixing; starting the vertical stirring mill, and operating at the rotating speed of 1000R/min for 20min to prepare 360kg of cement-based slurry;

and 3, step 3: and (3) mixing the cement-based slurry prepared in the step (2) with the rest raw materials (specifically, 250kg of ordinary portland cement, 25kg of fly ash, 969kg of broken stone, 126kg of fine stone, 590kg of machine-made sand, 90kg of water and 9.5kg of additives) to prepare the early-strength precast concrete.

Example 3

and 2, step: weighing the machine-made sand, the fly ash, the cement and the water according to the dosage shown in the table 2, and placing the materials in a vertical stirring mill for mixing; starting the vertical stirring mill, and operating at the rotating speed of 1500R/min for 15min to prepare 335kg of cement-based slurry in total;

and step 3: and (3) mixing the cement-based slurry prepared in the step (2) with the rest raw materials (specifically, 300kg of ordinary portland cement, 969kg of broken stone, 126kg of fine stone, 590kg of machine-made sand, 90kg of water and 9.5kg of admixture) to prepare the early-strength precast concrete.

Examples 4 and 5 the formulations of the raw materials involved in the preparation of the concrete are given in table 3 below:

TABLE 3

The grain size of the machine-made sand in the above table is 2.0-3.5 mm.

In examples 4 and 5, the following table 4 is set forth for the raw materials and amounts thereof involved in preparing cement-based slurries:

table 4:

note: production of 1m for each example ³ Concrete of

Example 4

Step 1: preparing raw materials according to the raw material mixing ratio shown in table 3;

step 2: weighing machine-made sand, fly ash, cement and water according to the dosage shown in Table 4, and placing the materials in a vertical stirring mill for mixing; starting a vertical stirring mill, and running for 20min at the rotating speed of 1000R/min to prepare 430kg of cement-based slurry in total;

and 3, step 3: and (3) mixing the cement-based slurry prepared in the step (2) with the rest raw materials (specifically, 275kg of ordinary portland cement, 969kg of broken stone, 126kg of fine stone, 590kg of machine-made sand, 20kg of water and 9.5kg of admixture) to prepare the early-strength precast concrete.

Example 5

and 2, step: weighing the machine-made sand, the fly ash, the cement and the water according to the dosage shown in the table 4, and placing the materials in a vertical stirring mill for mixing; starting the vertical stirring mill, and operating at the rotating speed of 2000R/min for 10min to obtain 480kg of cement-based slurry in total;

and 3, step 3: and (3) mixing the cement-based slurry prepared in the step (2) with the rest raw materials (specifically, 225kg of ordinary portland cement, 969kg of broken stone, 126kg of fine stone, 590kg of machine-made sand, 90kg of water and 9.0kg of admixture) to prepare the early-strength precast concrete.

Comparative example 1

The preparation method of the early-strength precast concrete comprises the following steps:

step 1: preparing raw materials according to the raw material mixing ratio shown in Table 1, and preparing 200kg of zirconia with the particle size range of 1.0-2.0 mm;

step 2: 20kg of admixture (fly ash), 20kg of cement, 40kg of water and 200kg of zirconia in the raw materials are mixed in a special vertical stirring mill; starting the vertical stirring mill, and running for 10min at the rotating speed of 3000R/min to obtain 280kg of mixed material in total;

and 3, step 3: separating the mixture and zirconia by using a sieve with the particle size smaller than 1.0-2.0 mm to obtain 80kg of cement-based slurry;

and 4, step 4: and (3) mixing 80kg of the cement-based slurry obtained after separation in the step (3) with the rest raw materials (300 kg of cement, 25kg of fly ash, 969kg of broken stone, 126kg of fine stone, 790kg of machine-made sand, 9kg of additive and 120kg of water) to prepare the early-strength precast concrete.

Application example

The early strength precast concrete prepared in examples 1 to 5 and comparative examples 1 and 2 was used to prepare a cured cubic test piece having a side length of 150mm according to a standard method, and a cubic compressive strength test was performed. Wherein the standard curing conditions are specifically as follows: the temperature is 20 +/-2 ℃, and the relative humidity is more than 95%. The results of the relevant tests are shown in table 5 below:

TABLE 5

As can be seen from the above table,

comparative example 1 is the early strength precast concrete prepared by the conventional method, and example 1 is the early strength precast concrete prepared by the method provided by the invention. By comparison, the early strength of the concrete prepared in example 1 was significantly improved relative to that of comparative example 1 when the admixture was used in an amount of 12.3 wt% based on the total weight of cement and admixture under the same curing conditions. The compressive strength of the concrete under the standard curing condition for 22 hours is 16.2MPa, which is improved by 44 percent compared with the comparative example 1; on the premise that the concrete of the comparative example 1 is subjected to standard curing after being steamed for 7 hours, the strength of the concrete can be kept equal to that of the concrete of the example 1. The method provided by the invention can be used for preparing the precast concrete with good early strength without steam curing, and can effectively save energy consumption required by the steam curing process.

Example 2 more cement raw material is wet ground compared with example 1, the compressive strength of 22h under standard curing conditions is further improved (53% compared with comparative example 1); more admixture is ground in the example 3, and the 22h compressive strength is higher than that of the comparative example 1 under the condition of shortening the steam curing time (from 7h to 5 h).

Further, in examples 4 and 5, the amount of the admixture in the raw materials is increased by 9.5 wt%, and the compressive strength result of 22h under the standard curing condition is increased by 38% and 42% respectively compared with that of comparative example 1; meanwhile, under the condition of standard curing after steaming for 6 hours, the mechanical strength which is not lower than that of the comparative example 1 is obtained. The method provided by the invention can shorten the steam curing time, save energy consumption, replace part of cement in the raw materials by more admixtures, save construction cost and have good economic benefit.

The method provided by the embodiment of the invention can prepare the concrete with excellent performance, and effectively meets the application requirement in the field of manufacturing of early-strength prefabricated parts. Furthermore, the preparation method using the sand as the grinding medium provided by the invention can simplify a wet grinding process, facilitate the production of concrete, save the construction time and obviously improve the construction efficiency. Compared with the traditional preparation method, the preparation method provided by the invention can save the sieving time of zirconia for 2 hours in each batch of embodiment, and save the using amount of 200kg of zirconia. In addition, the preparation method provided by the invention can avoid abrasion caused by using the zirconium oxide as a grinding medium, and the average service life of each device can be prolonged by at least 2-3 years.

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.

Claims

1. A method for preparing early strength precast concrete by taking sand as a grinding medium comprises the following steps:

s2, taking part of the sand, part of the admixture, part of the cement and part of the water under the condition of not additionally adding a grinding medium, putting the mixture into a grinding device according to a certain proportion, and carrying out wet grinding treatment to obtain cement-based slurry;

and S3, mixing the cement-based slurry with the rest raw materials to prepare the early-strength precast concrete.

2. The method according to claim 1, wherein in step S2, the weight ratio of sand, admixture, cement and water in the grinding device is 200: (20-70): (20-70): (40-140).

3. The method according to claim 1, wherein in the step S2, the equipment for wet grinding treatment comprises a vertical stirring mill, the rotation speed of the wet grinding treatment is 1000-3000 r/min, and the time of the wet grinding treatment is 10-20 min.

4. The method according to claim 1, wherein in the step S2, the particle size of the sand in the cement-based slurry is 1.0-2.0 mm.

5. The method as claimed in claim 1, wherein the sand is obtained by screening machine-made sand, and the Mohs hardness of the sand is more than or equal to 6.5; the cement is selected from 42.5 grade or above silicate cement; the coarse aggregate comprises crushed stone and/or fine stone.

6. The method of claim 1, wherein the admixture comprises an admixture having pozzolanic activity and/or an admixture having self-hydrating activity.

7. The method of claim 6, wherein the admixture is selected from the group consisting of one or more of mineral fines, fly ash, and steel slag fines.

8. The method of claim 1, wherein the admixture is selected from one of a polycarboxylic acid water reducer or a naphthalene based water reducer.

9. The method of claim 1, wherein in step S2, the portion of the sand is 20-30% by weight of the total weight of the sand in step S1.

10. The method according to any one of claims 1 to 9, wherein in the step S1, the raw materials are used in an amount by weight, which includes: 750-820 parts of sand, 40-80 parts of admixture, 280-340 parts of cement, 140-180 parts of water, 1000-1150 parts of coarse aggregate and 8-12 parts of additive.