CN110272221B

CN110272221B - Preparation method of modified coral sand concrete

Info

Publication number: CN110272221B
Application number: CN201910447528.6A
Authority: CN
Inventors: 王耀城; 闵冲; 江雪雷; 李周义; 杨文根; 邢锋; 李龙元; 白云
Original assignee: Shenzhen University
Current assignee: Shenzhen University
Priority date: 2019-05-27
Filing date: 2019-05-27
Publication date: 2022-05-17
Anticipated expiration: 2039-05-27
Also published as: CN110272221A

Abstract

The invention discloses a preparation method of modified coral sand concrete, which comprises the following steps: selecting a predetermined amount of coral sand and crushing; preparing cement paste and wrapping the crushed coral sand to form wrapped sand; maintaining the wrapped sand; and (5) taking the cured coating sand as an aggregate, and pouring to form coral sand concrete. The coral sand concrete prepared by the invention not only can enhance the compression resistance and the folding resistance of the coral sand aggregate concrete, but also can effectively delay and even restrict the outward seepage of chloride ions in the coral sand, thereby effectively protecting the reinforcing steel bars in the concrete and improving the service life of the concrete structure.

Description

Preparation method of modified coral sand concrete

Technical Field

The invention relates to the technical field of durability of concrete materials, in particular to a preparation method of modified coral sand concrete.

Background

With the development of social economy, the method combines the practical situation of China to see that: land resources on land are not enough to meet the current development requirements, so the development of islands and the enlargement of the construction of islands have important strategic significance on the development of socioeconomic performance in China. However, since the reefs are distributed near the coastal areas and far away from the inland, traffic is inconvenient and resources on the islands are limited, if a building on the island is built, a series of problems such as building cost, building material sources, construction period and the like are necessarily considered, and certain difficulties are brought to development and construction.

In island engineering, coral sand or sea sand has been used as a fine aggregate in countries such as japan, uk, and denmark, and concrete mixed with seawater has been used as a building material.

However, although the coral sand aggregate can be used for replacing the common aggregate to prepare the concrete, the strength of the coral sand concrete can well meet the actual engineering construction requirements of the island, but the porosity of the coral sand concrete is high, external harmful substances are easy to permeate into the concrete, and the coral sand concrete also contains some chloride ions and other ions, so that the durability problem that the chloride ions cause the corrosion of reinforcing steel bars in the concrete is solved; the coral sand has the characteristics of light weight, high angle, multiple pores (including internal pores), irregular shape and the like. Nevertheless, sea sand is still used in large quantities and coral sand is also slowly used in order to better solve the problems of shortage of inland river sand resources, transport costs and construction periods of coastal and offshore islands and to accelerate national economic construction. However, sea sand and coral sand have a common disadvantage that the content of chloride ions is too high, so that the corrosion of steel bars in concrete is accelerated, and the structural durability is reduced.

Meanwhile, due to the nature of the coral aggregates, the coral aggregates are used as building materials, and the performance of the prepared coral concrete is greatly different from that of common concrete and is also different from that of common lightweight aggregate concrete. Therefore, in the use of the coral aggregate concrete, on the premise of ensuring sufficient working strength and good working performance stability, a manufacturing method with better economic benefit than common concrete is sought, which is an important direction in the research of the coral aggregate concrete. Therefore, the method for improving the performance of the coral concrete by finding an economical and efficient method has important significance, and also has important significance for the research on the performance of the improved coral sand aggregate.

At present, the research at home and abroad mainly focuses on the aspects of durability, reinforcing rib materials, modification technology and the like. The main focus is: (1) the study on the corrosion of steel bars, such as stainless steel bars, composite bars and other special steel bars; (2) polypropylene fiber, glass fiber, carbon fiber, sisal fiber and the like are doped in the coral sand concrete; (3) the coral coarse aggregate is subjected to unsaturated pre-wetting treatment, and is doped with metakaolin and fly ash, so that the pore state of the coral sand concrete is improved, and 5% of metakaolin, 15% of mineral powder and 15% of fly ash are respectively added into the coral sand concrete in a single-doping and complex-doping manner to be modified; (4) a method for carrying out strengthening modification treatment on coral sand aggregates by adopting a polyvinyl alcohol solution is also provided; (5) and microbial induced calcium carbonate precipitation (MICP) techniques, among others. However, these modification operations have problems of relatively complicated steps and high cost.

Thus, the prior art has yet to be improved and enhanced.

Disclosure of Invention

In view of the defects of the prior art, the invention aims to provide the preparation method of the modified coral sand concrete, which can effectively delay and even restrain the outward permeation of chloride ions in the coral sand, thereby effectively protecting the steel bars in the concrete and prolonging the service life of the concrete structure.

In order to achieve the purpose, the invention adopts the following technical scheme:

a preparation method of modified coral sand concrete comprises the following steps:

selecting a predetermined amount of coral sand and crushing;

preparing cement paste and wrapping the crushed coral sand to form wrapped sand;

maintaining the wrapped sand;

and (5) taking the cured coating sand as an aggregate, and pouring to form coral sand concrete.

Further, in the preparation method of the modified coral sand concrete, the step of preparing cement paste and wrapping the crushed coral sand to form the wrapped sand specifically comprises:

pouring water into the first portion of cement and stirring to form cement paste;

after the cement paste is completely stirred, pouring the crushed coral sand into the cement paste and stirring the mixture until the mixture is uniform;

and pouring the second part of cement into the uniformly stirred coral sand and stirring until the second part of cement is uniform to form the coated sand.

Further, in the preparation method of the modified coral sand concrete, after the step of selecting the predetermined amount of coral sand and crushing, the method further comprises the following steps:

and screening the crushed coral sand.

and drying the crushed coral sand.

Further, in the preparation method of the modified coral sand concrete, before the step of maintaining the coated sand, the method further comprises the following steps:

and covering a waterproof film on the surface of the wrapped sand.

Furthermore, in the preparation method of the modified coral sand concrete, the mass of the first part of cement is equal to that of the second part of cement.

Further, in the preparation method of the modified coral sand concrete, the cement is sulphoaluminate cement, high-alumina cement or alkali-activated material.

Further, in the preparation method of the modified coral sand concrete, the water is deionized water.

Furthermore, in the preparation method of the modified coral sand concrete, the water cement ratio of the cement paste is 0.38-0.42.

Furthermore, in the preparation method of the modified coral sand concrete, the water cement ratio of the cement paste is 0.40.

Compared with the prior art, the preparation method of the modified coral sand concrete provided by the invention comprises the following steps: selecting a predetermined amount of coral sand and crushing; preparing cement paste and wrapping the crushed coral sand to form wrapped sand; maintaining the wrapped sand; and (5) taking the cured coating sand as an aggregate, and pouring to form coral sand concrete. The coral sand concrete prepared by the invention not only can enhance the compression resistance and the folding resistance of the coral sand aggregate concrete, but also can effectively delay and even restrict the outward seepage of chloride ions in the coral sand, thereby effectively protecting the reinforcing steel bars in the concrete and improving the service life of the concrete structure.

Drawings

FIG. 1 is a flow chart of a preparation method of modified coral sand concrete provided by the invention;

FIG. 2 is a flow chart of step S200 in the preparation method of the modified coral sand concrete provided by the invention;

FIG. 3 is a schematic structural diagram of a coral sand not coated with cement paste after the coral sand is crushed in the preparation method of the modified coral sand concrete provided by the invention;

FIG. 4 is a schematic structural diagram of the coral sand after being crushed and wrapped with cement paste in the preparation method of the modified coral sand concrete provided by the invention.

Detailed Description

The invention provides a preparation method of modified coral sand concrete, which can effectively delay and even restrain the outward seepage of chloride ions in coral sand, thereby effectively protecting reinforcing steel bars in concrete and prolonging the service life of a concrete structure. Meanwhile, in order to make the objects, technical solutions and effects of the present invention clearer and clearer, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

At present, in practical engineering structures for concrete applications, cracks and pores are inevitable, and the occurrence of cracks and pores can be reduced or delayed as far as possible. Although the available potential of the coral sand is quite huge, the coral sand has the defects of high porosity, light weight, high edge angle, high content of ions harmful to reinforced concrete and the like. Therefore, a new coral sand concrete modification method is needed to overcome the disadvantages and solve some problems in practical engineering.

Referring to fig. 1, a flow chart of a preparation method of modified coral sand concrete provided by the invention is shown, wherein the preparation method comprises the following steps:

s100, selecting a predetermined amount of coral sand and crushing;

s200, preparing cement paste and wrapping the crushed coral sand to form wrapped sand;

s300, maintaining the wrapped sand (natural maintenance, wherein the maintenance time depends on the cement paste product)

Seed);

and S400, pouring the cured coated sand serving as an aggregate to form coral sand concrete.

In order to better perform the wrapping treatment on the crushed coral sand to obtain a proper wrapped sand sample, the method further comprises the following steps between the steps S100 and S200: and screening the crushed coral sand. The step enables the tester to obtain the coral sand with proper grain diameter according to the actual requirement.

And comprising the steps of: and drying the crushed coral sand. The step can remove the water in the coral sand and prevent the effect of wrapping the cement paste.

Before step S300, the method further includes the steps of: and covering a waterproof film on the surface of the wrapped sand. The waterproof film can be a common preservative film, because the coral sand is extremely strong in water absorption, once the coral sand is placed under the condition that the air humidity is 0.95, a sample can absorb a large amount of water, the sample is quickly hydrated, the test detection is influenced, and the structure is favorable in practical engineering.

Through the steps, firstly, the cement paste is used for wrapping the coral sand crushed particles to form new mixed modified coral aggregate particles, so that the working strength and other properties of the coral sand concrete are improved simply and efficiently; and secondly, the cement slurry wraps the coral sand broken particles to effectively delay and even restrict the seepage of chloride ions in the coral sand, so that the reinforcing steel bars in the concrete are effectively protected, and the service life of the concrete structure is prolonged.

Specifically, the step S100 includes: taking a certain amount of raw coral sand as required, pouring the raw coral sand into a jaw crusher, adjusting the crushing particle size of the jaw crusher (automatically setting as required), and then crushing.

Referring to fig. 2, the step S200 includes:

s210, pouring water into the first cement and stirring to form cement paste;

s220, after the cement paste is completely stirred, pouring the crushed coral sand into the cement paste and stirring the mixture uniformly;

and S230, pouring the second part of cement into the uniformly stirred coral sand, and stirring until the second part of cement is uniform to form the coated sand.

Wherein the water is preferably deionized water; the cement is preferably high-alumina phase-containing rapid hardening and early strength cement, and can specifically comprise sulphoaluminate cement, high-alumina cement or an alkali-activated material system; the mass of the first part of cement is equal to that of the second part of cement; the cement paste preferably has a water cement ratio of 0.38 to 0.42.

The specific implementation of steps S210 to S230 is as follows:

1) preparing a test, namely taking a plurality of grams of dried crushed aggregates, placing the dried crushed aggregates into a container, taking a certain amount of deionized water into the container, and weighing one electronic scale and a plurality of containers.

2) Taking a certain amount of aggregate, placing the aggregate in a container, taking deionized water Xg with a certain water-cement ratio and high-alumina phase cement as two parts: respectively 0.5Yg, the cement paste amount Zg, high-alumina phase salt cement Hg, and the water-cement ratio is 0.38-0.42.

3) And pouring weighed deionized water into one part of high-alumina phase cement quickly, pouring weighed aggregate into cement paste quickly after complete stirring, starting stirring and uniformly stirring, then pouring the other part of cement into the uniformly stirred aggregate, stirring until the mixture is completely uniform, and then starting curing.

With reference to fig. 3 and 4, through the above steps, the cement paste can fill the pores in the coral sand, effectively reduce the porosity of the coral sand aggregate, thereby improving the compactness of the coral sand concrete, reducing the permeability coefficient of chloride ions, enhancing the durability of the interface transition region such as strength, and the like, and simultaneously, the sea island resources can be fully utilized, so that the cost of the concrete is reduced.

In addition, in order to explore the most suitable water cement ratio of the cement paste and the mass ratio of the coral sand to the cement paste, the invention provides the following embodiment:

the steps are repeated to carry out coral sand wrapping test exploration, the obtained exploration results are shown in table 1, and the following are preliminarily obtained: a certain amount of coral sand corresponds to a proper water-cement ratio range and mortar amount, and the difference between primary coating and secondary coating. Tables 2 and 3 simply define the evaluation criteria of the coating thickness of the cement paste on the coral sand and the amount of residual cement paste, respectively. The titration results of Cl- (chloride ion) deposition are shown in tables 4 and 5. Therefore, through a series of researches of the first embodiment, the invention finally selects the cement paste with the water cement ratio of 0.4 and the mixing ratio standard of coral sand to cement paste of 4:3 (coral sand 100g, cement paste amount 75g) to test and prepare the modified coral sand concrete.

TABLE 1 coral Sand coating test exploration

Wherein, 25+25 represents that the cement is equally divided into two parts, one part of the cement and deionized water are firstly used for preparing slurry to wrap the aggregate, and after the slurry is vibrated to wrap for a period of time, the rest part of the cement is added to the wrapped aggregate to be stirred.

TABLE 2 Cement paste wrap thickness criteria

Is excellent in	3
		Good effect	2
Medium and high grade	1
		Not good	0

TABLE 3 residual Cement Mass evaluation criteria

Superior food	0
		Good wine	1
Difference (D)	2

Cl^-The precipitation titration is illustrated: selecting 4 groups of coated mortar and raw sand, respectively adding the coated mortar and raw sand into deionized water for 1, 3 and 5 days, and titrating Cl in supernatant^-Concentration (3 of each group were used in parallel).

TABLE 4-Cl^-Titration results

TABLE 5 data results (mg/L) for chloride titration

Meanwhile, in order to test the performance of the concrete test block obtained by the steps, the invention provides the following embodiment two:

1. according to the test proportion of the first example (100 g of coral sand, 75g of cement paste, 0.4 of water cement ratio, and the cement is divided into two equal parts), a certain amount of broken coral aggregates, deionized water, fast-hardening early-strength high-alumina phase cement (divided into 2 parts equally) and standard sand are taken;

2. mixing half of the cement with deionized water to prepare slurry, and uniformly stirring;

3. pouring the aggregate into the slurry for stirring, pouring the other half of the cement into a stirrer for stirring after a period of time, and maintaining after the cement is uniformly stirred;

4. test block pouring is carried out by using the wrapped aggregate, each group of three samples has the size of 40X40X160mm, and the obtained comparative test data are shown in Table 6.

TABLE 6 test block comparative test data

After the test block is made, the test block is maintained, and the flexural strength and compressive strength comparison data of 1d, 3d and 7d are carried out, and the results are shown in tables 7 and 8.

TABLE 7 test piece flexural Strength/Mpa

Age of maintenance	1d	3d	7d
				Non-wrapped coral sand	5.83	7.73	8.12
Wrapped coral sand	6.13	7.97	9.12
				Standard sand	5.42	6.27	6.54

TABLE 8 test piece compressive Strength/Mpa

Age of maintenance	1d	3d	7d
				Non-wrapped coral sand	13.26	19.01	24.26
Wrapped coral sand	13.65	20.9	25.4
				Standard sand	12.93	14.63	22.35

And (3) analyzing test results: from the analysis in tables 5, 6, 7 and 8, it can be known that the coral aggregates coated with reasonable cement paste can enhance the compressive and flexural properties of the coral sand aggregate concrete and inhibit the precipitation of chloride ions. And it is reasonable to believe that: the inhibition of the precipitation of chloride ions should also be better studied; and the strength after wrapping can achieve the desired results and trends, which of course requires further research and optimization.

Therefore, the modified coral sand concrete prepared by the preparation method provided by the invention can effectively delay the seepage of chloride ions in coral sand in marine environment and coastal environment, simultaneously can reduce the porosity of the coral sand concrete, improve the thickness and strength of an interface transition area, and improve the strength of aggregates, thereby enhancing the compressive strength of the coral concrete and the overall durability of the coral sand concrete such as resistance to chloride ion corrosion, and fully utilize coral resources and effectively solve the resource problem of river sand shortage; and the method can also reduce the random exploitation of river sand and protect the environment.

In conclusion, the invention provides a preparation method of modified coral sand concrete, which comprises the following steps: selecting a predetermined amount of coral sand and crushing; preparing cement paste and wrapping the crushed coral sand to form wrapped sand; maintaining the wrapped sand; and (5) taking the cured coating sand as an aggregate, and pouring to form coral sand concrete. The coral sand concrete prepared by the invention not only can enhance the compression resistance and the folding resistance of the coral sand aggregate concrete, but also can effectively delay and even restrict the outward seepage of chloride ions in the coral sand, thereby effectively protecting the reinforcing steel bars in the concrete and improving the service life of the concrete structure.

It should be understood that equivalents and modifications of the technical solution and inventive concept thereof may occur to those skilled in the art, and all such modifications and alterations should fall within the scope of the appended claims.

Claims

1. The preparation method of the modified coral sand concrete is characterized by comprising the following steps of:

selecting a predetermined amount of coral sand, crushing, and screening and drying the crushed coral sand;

maintaining the wrapped sand;

taking the cured coating sand as an aggregate, and pouring to form coral sand concrete;

the step of preparing cement paste and wrapping the broken coral sand to form the wrapped sand specifically comprises the following steps:

pouring water into the first portion of cement and stirring to form cement paste, wherein the water cement ratio of the cement paste is 0.38-0.42;

and pouring the second part of cement into the uniformly stirred coral sand and stirring until the second part of cement is uniform to form wrapped sand, and covering a waterproof film on the surface of the wrapped sand, wherein the waterproof film is a preservative film.

2. The method for preparing modified coral sand concrete according to claim 1, wherein the mass of the first portion of cement is equal to the mass of the second portion of cement.

3. The method for preparing modified coral sand concrete according to claim 1, wherein said cement is a sulphoaluminate cement, a high alumina cement or an alkali activated material.

4. The method for preparing modified coral sand concrete according to claim 1, wherein said water is deionized water.

5. The method for preparing modified coral sand concrete according to claim 1, wherein the cement paste has a water cement ratio of 0.40.