CN107417207B - Preparation method of expansive concrete for restraining concrete composite structure - Google Patents

Abstract

The invention belongs to the technical field of building materials, and discloses a preparation method of expanded concrete for restraining a concrete composite structure, which comprises the following steps: (1) firstly, calculating the weight ratio of the required cement, the expanding agent, the sand, the pebbles and the water according to the volume and the mixing ratio for preparing the expansive concrete, then sequentially adding the sand, the cement and the expanding agent into a stirrer according to the weight ratio, and mixing and stirring for 115-125s, (2) adding the required water according to the weight ratio into the stirrer, and mixing and stirring for 55-65s, and (3) adding the required pebbles according to the weight ratio into the stirrer, and mixing and stirring for 115-125s to prepare the target material expansive concrete. The expanded concrete provided by the invention not only becomes more compact in a constrained state, improves the compressive strength in the constrained state, but also can generate larger self-stress in the concrete and the constrained member, improves the bonding property of the concrete and the constrained member, and effectively avoids the hysteresis of the constrained action.

Description

Preparation method of expansive concrete for restraining concrete composite structure

Technical Field

The invention relates to a preparation method of expansive concrete for a confined concrete composite structure, and belongs to the technical field of building materials.

Background

The confined concrete composite structure comprises steel pipe confined concrete, Fiber Reinforced Plastic (FRP) pipe confined concrete and the like, and the external confined material can effectively constrain the lateral deformation of the concrete, so that the concrete is in a three-dimensional compressed state, and the strength and the ductility of the concrete are effectively improved. However, the constraint can only be exerted under the condition that the concrete is compressed and further generates certain lateral deformation, so that the constraint has certain hysteresis, which undoubtedly limits the exertion of the function of the constraint material. Research has shown that, for FRP constraint concrete columns, when the constraint effect of FRP is fully exerted, the concrete is destroyed. In addition, the hysteresis of this restraint is further exacerbated by the self-shrinkage of the concrete during curing. If adopt an inflation concrete, during the maintenance, the inflation not only can make the more closely knit of concrete owing to receive the restraint, improves the intensity of concrete, but also can produce certain self stress, improves the cohesiveness of concrete and restraint component, avoids restraint function's hysteresis quality.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention provides a preparation method of expanded concrete for restraining a concrete composite structure. The expansive concrete prepared by the method has the advantages that the expansion is restrained during maintenance, so that the concrete is more compact, the strength of the concrete is improved, larger self-stress can be generated, the bonding performance of the concrete and a restraining member is improved, and the hysteresis of the restraining action is avoided.

In order to achieve the purpose of the invention and solve the problems existing in the prior art, the invention adopts the technical scheme that: a method of preparing expansive concrete for constraining concrete composite structures, comprising the steps of:

step 1, firstly, preparing the volume of the expansive concrete and the kg/m of cement, namely, the expansive agent, sand, pebble and water, 445-455:45-54:582-591:990-1000:215-225³The mixing proportion is calculated, the weight proportion of the required cement, the expanding agent, the sand, the pebble and the water is calculated, then the sand, the cement and the expanding agent are added into a stirrer according to the weight proportion, the mixture is stirred for 115-125s, the rotating speed of the stirrer is controlled to be 40-50 r/min, the sand is selected from river sand with medium sand in the particle grade, the cement is selected from ordinary portland cement with the reference number of 42.5, and the expanding agent is selected from calcium oxide expanding agent;

step 2, adding the water required in the step 1 into a stirrer according to the weight ratio, and mixing and stirring for 55-65s, wherein the rotating speed of the stirrer is controlled at 40-50 revolutions per minute;

and 3, adding the stone required in the step 1 into a stirrer according to the weight ratio, controlling the rotating speed of the stirrer to be 40-50 revolutions per minute, mixing and stirring for 115-125 seconds, and discharging to obtain the target material expanded concrete, wherein the stone is selected from crushed stone with the particle size of 5-15 mm.

The invention has the beneficial effects that: a method of preparing expansive concrete for constraining concrete composite structures, comprising the steps of: (1) firstly, calculating the weight ratio of the required cement, the expanding agent, the sand, the pebbles and the water according to the volume and the mixing ratio of the prepared expanded concrete, then adding the sand, the cement and the expanding agent into a stirrer according to the weight ratio, mixing and stirring for 115-125s, and controlling the rotating speed of the stirrer to be 40-50 r/min. (2) And (3) adding the water required by the calculation in the step (1) into a stirrer, and mixing and stirring for 55-65s, wherein the rotating speed of the stirrer is controlled at 40-50 revolutions per minute. (3) And (3) adding the stone required by calculation in the step (1) into a stirrer, controlling the rotating speed of the stirrer to be 40-50 rpm, mixing and stirring for 115-125s, and discharging to obtain the target material expansive concrete. Compared with the prior art, the expansive concrete is used for restraining a concrete structure, and because the expansion of the concrete is restrained during curing, the expansion reaction develops towards the inner hole and the interface of the concrete on one hand, so that the concrete is more compact, and the strength of the concrete is improved; on the other hand, the constraint is stretched outwards, so that self-stress is generated in the constraint material and the concrete, the bonding performance of the concrete and the constraint member is improved, and the constraint hysteresis is effectively avoided.

Drawings

FIG. 1 is a graph showing the expansion of the expansive concrete prepared in example 2 as a function of time.

FIG. 2 is a graph of mid-pipe hoop strain versus time for the CFRP pipe of example 3.

Detailed Description

The present invention will be further described with reference to the following examples.

Example 1

The preparation volume is 0.04m³The expansive concrete of (1), 23.64kg of river sand with the particle grade of medium sand, 18.00kg of ordinary portland cement with the label of 42.5 and 1.80kg of calcium oxide are sequentially added into a mixer, mixed and stirred for 120s, and the rotating speed of the mixer is controlled at 45 revolutions per minute; adding 8.80kg of water into the stirrer, and mixing and stirring for 60s, wherein the rotating speed of the stirrer is controlled at 45 revolutions per minute; finally, 39.80kg of crushed stone with the particle size of 10mm is added into a stirrer, the rotating speed of the stirrer is controlled at 45 revolutions per minute, and after 120 seconds of mixing and stirring, the target material expansive concrete is obtained after discharging.

Dividing the prepared expansive concrete into three groups, respectively filling the three groups of expansive concrete into cubic molds with the side length of 150mm, placing the cubic molds on a vibrating table for vibrating for 30s, then scraping the concrete on the tops of the molds, covering a preservative film, placing the molds at room temperature for 24 hours, removing the molds of the two groups of cubic molds, respectively adopting standard curing and room-temperature sealing curing for 28 days, and adopting constraint sealing curing for 28 days without removing the molds of the other group of cubic molds. The concrete mechanical property test result is as follows: the cubic compressive strength of the expanded concrete in standard curing is 29.04Mpa, the cubic compressive strength of the expanded concrete in room-temperature sealing curing is 37.21Mpa, and the cubic compressive strength of the expanded concrete in restrained sealing curing is 41.20 Mpa. The expanded concrete prepared by the method has the advantages that under the condition of confined sealing maintenance, the interior of the concrete is more compact due to the expansion of the concrete, and the cubic compressive strength of the concrete is obviously improved, so that the expanded concrete can be widely used for confined concrete composite structures.

Example 2

Preparation volume was 0.02m³The expansive concrete of (1), 11.80kg of river sand with the particle grade of medium sand, 9.00kg of ordinary portland cement with the label of 42.5 and 0.90kg of calcium oxide are sequentially added into a mixer, mixed and stirred for 120s, and the rotating speed of the mixer is controlled at 45 revolutions per minute; adding 4.40kg of water into the stirrer, and mixing and stirring for 60s, wherein the rotating speed of the stirrer is controlled at 45 revolutions per minute; and finally, adding 19.90kg of crushed stone with the particle size of 10mm into a stirrer, controlling the rotating speed of the stirrer at 45 revolutions per minute, mixing and stirring for 120 seconds, and discharging to obtain the target material expansive concrete.

Filling the prepared expansive concrete into a 400X 100mm prism mould, placing the mould on a vibrating table, vibrating for 30s, scraping the concrete on the top of the mould, covering a preservative film, placing the mould for 6 hours at room temperature, then removing the mould, and sealing and curing the prism expansive concrete at room temperature for 28 days, wherein the free expansion performance of the prism expansive concrete is shown in figure 1. As can be seen from FIG. 1, the expanded concrete prepared by the method has large free expansion, the free expansion reaches 1.02% in 28 days, the expansion reaction is concentrated in the first day, and then the expansion reaction is kept stable.

Example 3

Preparation of 0.02m³The expansive concrete is prepared from 11.80kg of river sand with medium sand as granule grade, 9.00kg of common sand with 42.5Sequentially adding the silicate cement and 0.90kg of calcium oxide into a stirrer, and mixing and stirring for 120s, wherein the rotating speed of the stirrer is controlled at 45 revolutions per minute; adding 4.40kg of water into the stirrer, and mixing and stirring for 60s, wherein the rotating speed of the stirrer is controlled at 45 revolutions per minute; and finally, adding 19.90kg of crushed stone with the particle size of 10mm into a stirrer, controlling the rotating speed of the stirrer at 45 revolutions per minute, mixing and stirring for 120 seconds, and discharging to obtain the target material expansive concrete.

The prepared expansive concrete is filled into a CFRP pipe with the diameter of 150mm and the height of 300mm, the CFRP pipe is placed in a vibrating table for vibrating for 30s, then the concrete at the top of the CFRP pipe is strickled off, a preservative film is covered, the room temperature curing is carried out for 28 days, the circumferential strain in the middle of the CFRP pipe during the curing is monitored by a strain gage, and the curve of the change of the strain along with time is shown in figure 2. As can be seen from FIG. 2, the expansive concrete prepared by the method can generate about 1400 micro-strain in the middle of the CFRP pipe, which is 12% of the limit strain of the CFRP pipe. The calculated self-stress of 2.12MPa is formed in the concrete column and is 7.3 percent of the compressive strength of the concrete. Because the self-stress effect is obvious, the bonding performance of the concrete and the constraint member can be obviously improved, and the stress lag is effectively avoided.

Claims (1)

1. A preparation method of expansive concrete for restraining a concrete composite structure is characterized by comprising the following steps:

step 1, firstly, preparing the volume of the expansive concrete and the kg/m of cement, namely, the expansive agent, sand, pebble and water, 445-455:45-54:582-591:990-1000:215-225³The mixing proportion is calculated, the weight proportion of the required cement, the expanding agent, the sand, the pebble and the water is calculated, then the sand, the cement and the expanding agent are added into a stirrer according to the weight proportion, the mixture is stirred for 115-125s, the rotating speed of the stirrer is controlled to be 40-50 r/min, the sand is selected from river sand with medium sand in the particle grade, the cement is selected from ordinary portland cement with the reference number of 42.5, and the expanding agent is selected from calcium oxide expanding agent;

step 2, adding the water required in the step 1 into a stirrer according to the weight ratio, and mixing and stirring for 55-65s, wherein the rotating speed of the stirrer is controlled at 40-50 revolutions per minute;

and 3, adding the stone required in the step 1 into a stirrer according to the weight ratio, controlling the rotating speed of the stirrer to be 40-50 revolutions per minute, mixing and stirring for 115-125 seconds, and discharging to obtain the target material expanded concrete, wherein the stone is selected from crushed stone with the particle size of 5-15 mm.

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