阅读说明：本技术 一种利用甘蔗渣灰制备低缩型混凝土的方法 (Method for preparing low-shrinkage concrete by using bagasse ash ) 是由 王德辉 罗素蓉 王雪芳 吴文达 于 2021-07-19 设计创作，主要内容包括：本发明属于混凝土制备技术领域,具体涉及一种利用甘蔗渣灰制备低缩型混凝土的方法。其是对回收的甘蔗渣灰进行煅烧粉磨,并将煅烧粉磨后的甘蔗渣灰进行化学成分分析和性能表征。将甘蔗渣灰按照一定比例取代水泥,并与水泥、水、天然细骨料和天然粗骨料按照一定的比例拌合,制备出性能满足要求的低缩型混凝土。本发明甘蔗渣在一定温度下煅烧时,甘蔗渣灰含有大量的无定形氧化物,且内部多孔,可作为辅助性胶凝材料取代水泥,制备绿色高性能混凝土,并降低混凝土的自收缩。因此,本发明方法不仅可降低混凝土的自收缩,还可减少二氧化碳排放,节约土地,保护环境。(The invention belongs to the technical field of concrete preparation, and particularly relates to a method for preparing low-shrinkage concrete by utilizing bagasse ash. The method comprises the steps of calcining and grinding the recovered bagasse ash, and carrying out chemical component analysis and performance characterization on the bagasse ash after calcining and grinding. The bagasse ash replaces cement according to a certain proportion, and is mixed with the cement, water, natural fine aggregate and natural coarse aggregate according to a certain proportion to prepare the low-shrinkage concrete with the performance meeting the requirement. When the bagasse is calcined at a certain temperature, the bagasse ash contains a large amount of amorphous oxides, is porous inside, can be used as an auxiliary cementing material to replace cement, prepare green high-performance concrete, and reduce the self-shrinkage of the concrete. Therefore, the method of the invention not only can reduce the self-shrinkage of the concrete, but also can reduce the emission of carbon dioxide, save land and protect environment.)

1. A method for preparing low-shrinkage concrete by using bagasse ash is characterized by comprising the following steps: the method comprises the following steps:

(1) recycling bagasse;

(2) calcining and grinding the recycled bagasse;

(3) carrying out chemical component analysis and performance characterization on the bagasse ash after calcination and grinding;

(4) substituting bagasse ash for cement according to a certain proportion, and mixing the bagasse ash with cement, water, natural fine aggregate and natural coarse aggregate at normal temperature;

(5) and (4) preparing the mixture obtained in the step (4) to obtain the low-shrinkage concrete.

2. A process for the preparation of low-shrinkage concrete from bagasse ash according to claim 1, characterized in that: the calcining temperature in the step (2) is 600-700 ℃, and the grinding time is 1.5-2.5 hours.

3. A process for the preparation of low-shrinkage concrete from bagasse ash, according to claim 2, characterized by: the calcining temperature in the step (2) is 700 ℃, and the grinding time is 2 hours.

4. A process for the preparation of low-shrinkage concrete from bagasse ash according to claim 1, characterized in that: the grain size of the bagasse ash in the step (3) is less than 100 mu m; wherein SiO is₂The content is less than 70 wt%.

5. A process for the preparation of low-shrinkage concrete from bagasse ash according to claim 1, characterized in that: and (4) the cement substitution rate of the bagasse ash in the step (4) is 10-30 wt%.

6. A process for the preparation of low-shrinkage concrete from bagasse ash according to claim 5, characterized in that: the cement substitution rate of the bagasse ash in the step (4) is 20 wt%.

7. A process for the preparation of low-shrinkage concrete from bagasse ash according to claim 1, characterized in that: in the step (4), 210-270 parts by weight of cement, 30-90 parts by weight of bagasse ash, 90-150 parts by weight of water, 700-800 parts by weight of natural fine aggregate and 1200-1300 parts by weight of natural coarse aggregate are mixed according to parts by weight of raw materials.

8. A process for the preparation of low-shrinkage concrete from bagasse ash according to claim 1, characterized in that: and (4) the cement in the step (4) is ordinary portland cement, and the strength grade is P.O 42.5.

9. A process for the preparation of low-shrinkage concrete from bagasse ash according to claim 1, characterized in that: the natural fine aggregate in the step (4) is river sand, and the apparent density is 2640kg/m³And the particle size is 0-4.75 mm.

10. The use according to claim 1The method for preparing the low-shrinkage concrete from the bagasse ash is characterized by comprising the following steps: the natural coarse aggregate in the step (4) is macadam with apparent density of 2670kg/m³And the particle size is 4.75-20 mm.

Technical Field

The invention belongs to the technical field of concrete preparation, and particularly relates to a method for preparing low-shrinkage concrete by utilizing bagasse ash.

Background

The annual output of cement in China is about 23 hundred million tons, and about 0.866 ton of carbon dioxide emission is generated per one ton of cement clinker production, and the carbon emission amount accounts for about 9 percent of the total national emission amount. In order to achieve the aim of 'carbon dioxide emission strives to reach a peak value before 2030 years and strives to achieve carbon neutralization before 2060 years', the carbon emission can be reduced by adding auxiliary cementing materials to replace cement. Meanwhile, China is a big agricultural country, generates a large amount of agricultural solid waste every year, wherein the annual output of the bagasse is about 20 ten thousand tons, and the bagasse is usually treated by adopting an incineration or landfill mode. The bagasse is treated by adopting an incineration or landfill mode, so that a large amount of land is consumed, and a large amount of pollution is easily generated.

Early-age concrete undergoes hydration of the cementitious material and evaporation to lose water (under dry conditions), with concomitant chemical shrinkage and a decrease in the relative humidity inside the concrete, so early shrinkage of the concrete is almost unavoidable. The problems of structural cracking and engineering loss caused by early shrinkage of concrete are increasingly prominent, so researchers provide various methods for regulating and controlling the shrinkage of concrete; by using the admixture, the early chemical shrinkage-reducing development process of the concrete is adjusted, and the purpose of adjusting and controlling the early shrinkage of the concrete can be achieved. There are studies that show that: the fly ash can effectively regulate and control the early self-shrinkage of the concrete. However, no report is found at present for regulating and controlling the self-shrinkage of concrete by adopting agricultural solid wastes as an auxiliary cementing material to be doped into the concrete.

The rice hull ash has the characteristics of porosity and large specific surface area, has small particle size, can be doped into concrete to fill the pores among cement particles, improves the strength and durability of the concrete, can promote the setting and hardening of the composite cementing material, greatly shortens the setting time and improves the early strength. Moreover, the main component of the rice hull ash is silicon dioxide, and the silicon dioxide can react with a hydration product calcium hydroxide of cement to generate secondary hydrated calcium silicate, so that the strength and the durability of the concrete are further improved. However, the small particle size of the rice husk ash optimizes the pore size of the concrete and also increases the self-shrinkage of the concrete, which leads to early cracking of the concrete.

Aiming at the problems, the application recycles the bagasse to replace a part of cement, and the utilization of the characteristics of the bagasse ash can be expected to solve the problems. When the bagasse is calcined at a certain temperature, the bagasse ash contains a large amount of amorphous oxides, is porous inside, can be used as an auxiliary cementing material to replace cement, prepare green high-performance concrete, and reduce the self-shrinkage of the concrete. Therefore, the bagasse ash is used in the concrete, so that the self-shrinkage of the concrete can be reduced, the carbon dioxide emission can be reduced, the land is saved, and the environment is protected.

Disclosure of Invention

The invention aims to provide a method for preparing low-shrinkage concrete by utilizing bagasse ash, which can consume a large amount of bagasse and increase the recovery rate of the bagasse, thereby effectively improving the current situation that the recovery rate of the bagasse is not high at present.

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

a method for preparing green concrete by using bagasse ash comprises the following steps:

(1) recycling bagasse;

(2) calcining and grinding the recycled bagasse;

(3) carrying out chemical component analysis and performance characterization on the bagasse ash after calcination and grinding;

(4) substituting bagasse ash for cement according to a certain proportion, and mixing the bagasse ash with cement, water, natural fine aggregate and natural coarse aggregate according to a certain proportion at normal temperature;

(5) and (4) preparing the mixture obtained in the step (4) to obtain the low-shrinkage concrete.

Further, the calcining temperature in the step (2) is 600-700 ℃, preferably 700 ℃, and the grinding time is 1.5-2.5 hours, preferably 2 hours.

Further, the particle size of the bagasse ash in the step (3) is less than 100 μm; wherein SiO is₂The content is less than 70 wt%.

Further, in the step (4), the cement substitution rate of the bagasse ash is 10-30 wt%, and preferably 20 wt%.

Further, in the step (4), 210-270 parts by weight of cement, 30-90 parts by weight of bagasse ash, 90-150 parts by weight of water, 700-800 parts by weight of natural fine aggregate and 1200-1300 parts by weight of natural coarse aggregate are mixed according to parts by weight of raw materials.

Further, the cement in the step (4) is ordinary portland cement, and the strength grade is P.O 42.5.

Further, the natural fine aggregate in the step (4) is river sand, and the apparent density of the natural fine aggregate is 2640kg/m³And the particle size is 0-4.75 mm.

Further, the natural coarse aggregate in the step (4) is macadam with apparent density of 2670kg/m³And the particle size is 4.75-20 mm.

The self-shrinkage of concrete is the shrinkage caused by the fact that the internal moisture is consumed by hydration of the cementing material and the internal humidity is reduced in the process of setting and hardening, and the concrete can crack early and is not favorable for the durability of a concrete structure. This application promotes the self-constriction that reduces the concrete through adding the bagasse ash, prevents the early fracture of concrete.

The invention has the following remarkable advantages:

(1) the method takes the bagasse ash as an auxiliary cementing material to prepare the green concrete, can realize the resource utilization of the bagasse, can reduce the self-shrinkage of the concrete, reduce the emission of carbon dioxide, save land and protect environment. By controlling the calcining process and the grinding system, the green concrete prepared from the bagasse ash has stable performance.

(2) The invention controls the calcining process and the grinding system of the bagasse ash, prepares the green concrete by the bagasse ash through scientifically designing the mixing proportion, and leads the performance of the green concrete to meet the performance requirement.

Drawings

FIG. 1 is a scanning electron micrograph of cement, bagasse ash and rice husk ash: (a) cement; (b) bagasse ash; (c) rice husk ash.

Detailed Description

In order to make the present invention more comprehensible, the technical solutions of the present invention are further described below with reference to specific embodiments, but the present invention is not limited thereto.

Examples

(1) Recycling bagasse and rice husks;

(2) calcining and grinding the recycled bagasse and rice hulls at 600 ℃, 650 ℃ and 700 ℃ for 1.5, 2 and 2.5 hours;

(3) the chemical compositions and physical properties of the bagasse ash and rice husk ash were measured, and the results are shown in tables 1 and 2, and the scanning electron micrograph of the cement, bagasse ash and rice husk ash is shown in FIG. 1;

TABLE 1 chemical composition of bagasse ash and Rice Hull Ash (%)

TABLE 2 physical Properties of bagasse Ash and Rice husk Ash

(4) Replacing 20wt% of cement with bagasse ash having calcination temperatures of 600, 650, and 700 ℃ and grinding times of 1.5, 2, and 2.5 hours, respectively, and mixing 240 parts by weight of cement, 60 parts by weight of bagasse ash and rice hull ash, 150 parts by weight of water, 780 parts by weight of sand, and 1170 parts by weight of stone, as shown in table 3;

TABLE 3 concrete mixing proportion of the doped bagasse ash under different calcination temperatures and grinding times

(5) And (3) carrying out stirring, vibration forming, demolding and curing processes on the mixture obtained in the step (4), and testing the particle size, the specific surface area, the strength and the content of calcium hydroxide of the concrete doped with bagasse ash under different conditions of examples 1-6, wherein the test results are shown in Table 4.

TABLE 4 Performance of concrete doped with bagasse ash at different calcination temperatures and grinding times

As can be seen from Table 4, as the calcination temperature is increased, the difference between the 45 μm sieve residue and the specific surface area of the bagasse ash is small, and the activity index is increased, the content of calcium hydroxide is reduced, which indicates that the increase of the calcination temperature has little influence on the particle size of the bagasse ash, but increases the reactivity thereof. Along with the increase of the grinding time, the 45 mu m sieve residue of the bagasse ash is reduced, the specific surface area is increased, but the activity index and the content of calcium hydroxide are not changed greatly, which shows that the grinding time influences the particle size distribution of the bagasse ash, but has small influence on the reaction activity of the bagasse ash. Comprehensively considering the energy consumption ratio, and finally determining the optimal calcining temperature and the optimal powder time of the bagasse ash to be 700 ℃ and 2 hours;

(6) replacing cement with the bagasse ash and the rice husk ash at the calcination temperature and the powder time of 700 ℃ for 2 hours according to 10 wt%, 20wt% and 30 wt%, and mixing 210-270 parts by weight of cement, 30-90 parts by weight of bagasse ash and rice husk ash, 150 parts by weight of water, 780 parts by weight of sand and 1170 parts by weight of stone, as shown in Table 5;

TABLE 5 Green concrete mixing ratio

(7) And (3) carrying out stirring, vibration molding, demolding and curing on the mixture obtained in the step (6), and testing the 28-day compressive strength, the elastic modulus, the 3-day self-shrinkage and the chloride ion permeability of the green concrete under different mixing ratios, wherein the test results are shown in Table 6.

TABLE 6 Properties of Green concretes at different mix ratios

As can be seen from Table 6, as the bagasse ash substitution rate increased, the 28-day compressive strength, elastic modulus and 3-day self-shrinkage of the green concrete decreased, and the chloride ion permeability decreased first and then increased. With the increase of the rice husk ash substitution rate, the 3-day self-shrinkage of the concrete is increased continuously, the 28-day compressive strength and elastic modulus are increased and then decreased, and the chloride ion permeability is decreased and then increased. Compared with bagasse ash, the strength of the concrete doped with rice hull ash is higher, but the self-shrinkage is also larger, mainly because of the significant difference in physicochemical properties between the two. The main component of the rice hull ash is silicon dioxide, and the rice hull ash reacts with calcium hydroxide which is a cement hydration product to form hydrated calcium silicate, so that the strength of concrete is facilitated; the main components of the bagasse ash are silicon oxide, aluminum oxide and iron oxide, and the main components react with calcium hydroxide which is a cement hydration product to form calcium silicate hydrate, calcium aluminate hydrate and calcium ferrite hydrate, and the strength of the concrete is also facilitated, such as reaction equations (1) - (3). However, since the content of silica in rice hull ash is as high as 91.87%, and the content of silica, alumina, and iron oxide in rice hull ash is only 75.71%, the amount of reactable oxides is less than that of rice hull ash, and thus the strength improvement effect is inferior to that of rice hull ash. On the other hand, the grain diameter of the rice husk ash is smaller, the pore diameter is optimized by the filling effect, the pressure of the capillary pore is increased, and the self-contraction of concrete is not facilitated. The bagasse ash has relatively large particle size, and during the calcination process of the bagasse ash, a large amount of plant fibers inside are burnt to form carbon dioxide, so that a large amount of holes are left, and during the stirring process, the holes absorb water and release water when concrete is coagulated and hardened, thereby being beneficial to improving the self-shrinkage of the concrete.

SiO₂+Ca(OH)₂→CaSiO₃+H₂O

(1)

Al₂O₃+3Ca(OH)₂→3CaO·Al₂O₃·6H₂O

(2)

Fe₂O₃+Ca(OH)₂→CaO·Fe₂O₃·H₂O

(3)

As can be seen from Table 6, the overall performance of the concrete is optimal when the bagasse ash is substituted by 20%. Comprehensively considering the influence of the bagasse ash on the performance of the concrete, the substitution rate of the bagasse ash is recommended to be 20%.

The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.