CN112551958A

CN112551958A - Seawater and coral sand mixed red mud-coal gangue based polymer concrete and preparation method thereof

Info

Publication number: CN112551958A
Application number: CN202011518748.2A
Authority: CN
Inventors: 龙志林; 匡凤兰
Original assignee: Xiangtan University
Current assignee: Xiangtan University
Priority date: 2020-12-21
Filing date: 2020-12-21
Publication date: 2021-03-26

Abstract

The invention discloses seawater and coral sand mixed red mud-coal gangue base polymer concrete which comprises red mud, coal gangue, coral sand, broken stone, a sodium hydroxide solution, a water glass solution, artificial seawater and a water reducing agent. The preparation method comprises the following steps: preparing artificial seawater; screening out fine sand by using coral sand; the big coal gangue is smashed after being knocked into small pieces; air-drying or drying the red mud slurry until the moisture content is lower than 3%, measuring the pH value of the red mud slurry, and then crushing the red mud slurry; preparing a red mud-coal gangue mixed raw material; preparing a sodium hydroxide solution; lowering the water glass into a mold through a sodium hydroxide solution; mixing a sodium hydroxide solution with the water glass solution after the mold is lowered to form an alkaline activator; designing the total proportion of materials; all prepared raw materials are prepared into finished products. The concrete prepared by the invention has high compressive strength and slump, low cost and wide application range, not only solves the recycling of two large solid wastes, but also provides a new building material source for island construction.

Description

Seawater and coral sand mixed red mud-coal gangue based polymer concrete and preparation method thereof

Technical Field

The invention belongs to the field of comprehensive utilization of bulk wastes and green building materials, and particularly relates to seawater and coral sand mixed red mud-coal gangue based polymer concrete and a preparation method thereof.

Background

With the development of the aluminum industry, the amount of red mud is increasing day by day. The accumulated red mud not only occupies a large amount of farmlands, but also seriously pollutes the surrounding environment. Coal gangue is a waste rock separated in coal mining and washing processes. With the advent of geopolymer cements, there has been great progress with respect to the comprehensive utilization of industrial waste.

The cement hydration product of the existing cement-based coral concrete is prepared from C-S-H gel, Ca (OH)₂And AFt, while south China sea is in a tropical climate zone, the marine environment is complex, the chemical compositions, the pH value, the salinity, the ocean current, the tidal range and the like of seawater in different sea areas are different, the stability and the corrosion resistance of cement hydration products in a severe marine environment are poor, the service environment can seriously affect the durability of the cement-based coral concrete, and the cement-based coral concrete cannot be mutually coordinated with the stability in the severe environment.

The coral sand is light and porous, has rough surface and is easy to break, high-strength coral concrete cannot be prepared by using the traditional cement-based material, and the friction of slurry can be increased when the content of shells in the coral sand is higher, so that the slump of the concrete is reduced. High levels of chloride salts in seawater accelerate cement hydration and set up at an increased rate, leading to premature setting. The content of the chlorine salt mixed in the seawater and the sea sand is higher, and the reduction of the working performance of the cement-based concrete is aggravated.

Furthermore, it is well known that island construction has become an important task in ocean development. However, many islands are far from the continent, and if all raw materials are supplied from the continent by shipping, construction costs are high and construction periods are long. Therefore, the use of seawater and sea sand is of great significance for island construction. The geopolymer cementing material has the characteristics of high temperature resistance, corrosion resistance, high strength and the like, but the related research of applying the geopolymer cementing material to the preparation of coral concrete is limited at present.

Disclosure of Invention

The embodiment of the invention aims to provide seawater and coral sand mixed red mud-coal gangue based polymer concrete and a preparation method thereof, which solve the problem of recycling two large solid wastes, prepare a geopolymer under the condition of not adding other high-activity activators, and provide a new green environment-friendly material for island and reef construction by using coral sand as a fine aggregate.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

the seawater and coral sand mixed red mud-coal gangue based polymer concrete comprises, by mass, 6.5% -15% of red mud, 6.5% -15% of coal gangue, 21% -28% of coral sand, 33% -42% of broken stone, 0.65% -1.7% of a sodium hydroxide solution, 3.4% -4.8% of a water glass solution, 3.8% -9.2% of artificial seawater, and 1.2% -1.4% of a water reducing agent.

Furthermore, the crushed stone is coarse aggregate, the crushed stone is screened graded crushed stone, the crushed stone with the particle size of 5-10mm accounts for 30% of the total mass of the crushed stone, and the crushed stone with the particle size of 10-20mm accounts for 70% of the total mass of the crushed stone;

the coral sand is fine aggregate, and the coral sand is screened fine sand with the particle size of 0.25-0.35 mm.

Further, the concrete further comprises 3-8% of MgO by mass percent.

Further, the concrete also comprises 2-4% of LDHs (layered double hydroxides) by mass percent.

Further, the concrete also comprises nano particles SiO according to the mass percentage₂ 0.5％-10％。

The invention adopts another technical scheme that:

a preparation method of seawater and coral sand mixed red mud-coal gangue based polymer concrete comprises the following steps:

step 1: preparing artificial seawater;

step 2: sieving fine sand with coral sand of 0.25-0.35 mm; the crushed stone is graded crushed stone, the crushed stone with the grain diameter of 5-10mm accounts for 30% of the total mass of the crushed stone, and the crushed stone with the grain diameter of 10-20mm accounts for 70% of the total mass of the crushed stone;

and step 3: breaking large coal gangue into small stone blocks with the particle size of 2-4mm, and then crushing the small stone blocks;

and 4, step 4: air drying or oven drying at 90-100 deg.C until the water content is less than 3%, measuring pH, and pulverizing;

and 5: preparing a red mud-coal gangue mixed raw material;

step 6: mixing solid sodium hydroxide with common water to prepare a sodium hydroxide solution;

and 7: the modulus of the water glass is adjusted to 1.6-2.2 by sodium hydroxide solution;

and 8: mixing sodium hydroxide solution with the water glass solution after the mold is reduced to form an alkaline activator,

and step 9: mixing all prepared raw materials, stirring, injection molding, curing, demolding, naturally placing, and finally forming a finished product.

Further, the artificial seawater in the step 1 comprises the following components in percentage by mass:

NaCl:Na₂SO₄:MgCl₆H₂O:KCl:CaCl₂＝24.5:4.1:11.1:0.7:1.2；

the pH value of the red mud obtained in the step 4 is 9-11.

Further, the step 5 is specifically to mix the red mud and the coal gangue according to a certain proportion, the mass ratio of the red mud to the coal gangue is 1:2.3-2.3:1, 20% -30% of deionized water is added, the mixture is kneaded into a round ball with the diameter of 2-3cm, the round ball is placed into an oven to be dried at 90-100 ℃ to remove free water, the round ball is placed into a muffle furnace to be calcined for 2 hours at 600-750 ℃, finally the round ball is taken out to be cooled, the round ball is placed into a grinder to be ground for 30 minutes, and finally the ground mixture is sieved by a sieve with the aperture of 0.08mm to obtain the red mud-coal gangue mixed raw material.

Further, the sodium hydroxide solution in the step 6 is 5-8 mol/l;

the mass ratio of the water glass solution to the sodium hydroxide solution in the alkaline activator solution in the step 8 is (2-7.38): 1.

further, the total mixture ratio of the raw materials in the step 9 is specifically as follows: 6.5 to 15 percent of red mud, 6.5 to 15 percent of coal gangue, 21 to 28 percent of coral sand, 33 to 42 percent of broken stone, 0.65 to 1.7 percent of sodium hydroxide solution, 3.4 to 4.8 percent of water glass solution, 3.8 to 9.2 percent of artificial seawater and 1.2 to 1.4 percent of water reducing agent;

the step 9 specifically comprises the following steps: firstly, adding a red mud-coal gangue mixture after calcination and grinding into a stirrer, adding coral sand and broken stone, uniformly stirring, and after stirring for one minute, sequentially adding a sodium hydroxide solution, a water glass solution, artificial seawater and a water reducing agent into the stirrer, quickly stirring for 2 minutes, and then slowly stirring for 5 minutes to fully react; and finally, grouting and molding the mixture, pouring for two times, vibrating and compacting on a vibrating table, wrapping a plastic film on each group of three test blocks, curing and curing for 24 hours in a standard curing chamber, demolding, and then transferring back to the curing chamber for natural placement until curing reaches a set age to obtain a red mud-coal gangue mixture coral concrete finished product.

The invention has the beneficial effects that: the invention synthesizes the two bulk wastes of the red mud and the coal gangue to prepare the composite geopolymer, utilizes the rich aluminosilicate components of the red mud and the coal gangue, and utilizes the calcium oxide in the red mud as a calcium source to improve the activity of the coal gangue, obviously improves the cementation behavior of the red mud-coal stone mixture, can improve the strength by adding the coal gangue, has complementary action of the two, and does not add other active agents. In addition, seawater and coral sand are used for replacing common water and common river sand, and the problem of scarcity of island construction materials is solved. The concrete prepared by the invention has excellent performance, is a novel green environment-friendly material, and has the characteristics of high strength in early stage, high temperature resistance, corrosion resistance, good durability and the like; compared with the traditional cement-based coral concrete, the compressive strength and the slump of the concrete are obviously improved. The invention has the advantages of wide material source, simple manufacture, low cost and wide application range. Not only solves the recycling of two large solid wastes, but also provides a new building material source for the construction of the island.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a flow chart of the preparation;

FIG. 2 is a graph showing the change of compressive strength of polymer coral concrete with age in different mass ratios of red mud and coal gangue.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious 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.

The invention utilizes the composite activation of the red mud and the coal gangue to obtain a geopolymer raw material with higher activity, and then sodium hydroxide solution and water glass solution are mixed to be used as alkaline activating agents to prepare the geopolymer, and the geopolymer can be used as a material for replacing cement. And then coral sand is used as fine aggregate, broken stone is used as coarse aggregate, a certain amount of water reducing agent is added, and artificial seawater is used for preparing the concrete.

The concrete comprises the following materials in percentage by mass: 6.5-15% of red mud, 6.5-15% of coal gangue, 21-28% of coral sand, 33-42% of broken stone, 0.65-1.7% of sodium hydroxide solution, 3.4-4.8% of water glass solution, 3.8-9.2% of artificial seawater and 1.2-1.4% of water reducing agent (or other modified materials are additionally added).

Wherein the red mud is from environmental protection science and technology limited of Qingfengda of Tianjin, is waste left by alumina preparation by Bayer process, is alkaline, and has SiO as main component₂、Al₂O₃、CaO、Fe₂O₃Etc.; the coal gangue is solid waste discharged in coal mining process and coal washing process of Hunan Tan mine, and the main component of the coal gangue is Al₂O₃、SiO₂The components of the red mud and the coal gangue are shown in table 1; coral sand is mined from an island in south China sea, the particle size range is 0.075mm-2mm, and the particle size distribution of broken stone is 5-12 mm; sodium hydroxide is an industrial-grade white flaky solid and is easily soluble in water; initial water glass modulus 3.3, Na₂The O content is 8.3 percent, and the Baume degree is 40; the water reducing agent is a PCA-I polycarboxylic acid high-performance water reducing agent produced by a certain company in Jiangsu province.

TABLE 1 chemical composition of red mud and coal gangue

The preparation steps of the concrete are as follows:

step 1: the artificial seawater is prepared according to the standard of ASTMD1141-2003,

the artificial seawater comprises the following components in percentage by mass:

NaCl:Na₂SO₄:MgCl₆H₂O:KCl:CaCl₂＝24.5:4.1:11.1:0.7:1.2。

step 2: sieving fine sand with coral sand of 0.25-0.35 mm; the crushed stone is graded crushed stone, and 30 percent of the mass of all crushed stones is between 5 and 10mm, and 70 percent of the mass of all crushed stones is between 10 and 20 mm.

And step 3: breaking the large coal gangue into small stone blocks with the grain diameter of 2-4mm, and then crushing the small stone blocks.

And 4, step 4: air drying or oven drying at 90-100 deg.C until the water content is less than 3%, measuring pH, and pulverizing. The pH value is measured mainly for discussing the influence of the alkalinity of the red mud on the reaction and the product of the whole geopolymer; generally, the alkalinity of red mud is in the range of 10 ± 1.

And 5: mixing red mud and coal gangue according to a certain ratio, wherein the mass ratio of the red mud to the coal gangue is (1:2.3-2.3:1), adding 20-30% of deionized water, kneading into round balls with the diameter of 2-3cm, putting the round balls into an oven, drying at 90-100 ℃ to remove free water, putting the round balls into a muffle furnace, calcining at 600-750 ℃ for 2h, taking out the round balls, cooling, grinding in a grinder for 30min, and sieving the ground mixture by using a sieve with the aperture of 0.08mm to obtain a red mud-coal gangue mixed raw material;

the unburned coal gangue has extremely low gelling activity, and at a proper temperature, clay components in the coal gangue can be dehydrated and decomposed into amorphous silica and alumina with hydraulic gelling activity. However, because the content of calcium oxide in the coal gangue is very low, the degree of improving the activity of the coal gangue by calcining is limited, and the gelling activity of the coal gangue can be effectively improved by adding a proper amount of calcium oxide in the calcining process. The red mud has high calcium oxide content, and if the red mud is combined with coal gangue, the calcium content of the coal gangue can be supplemented to a certain extent. In addition, the red mud also has the characteristic of high alkalinity, alkaline materials such as water glass, caustic soda, lime and the like can be used for exciting the activity of mineral components in the red mud, and zeolite structural materials with high strength, corrosion resistance and stable chemical properties can be formed after the coarse and fine aggregates are matched. In turn, because the addition of the coal gangue can change the Si/Al ratio of the whole mixture, the cement material with higher strength can be generated more easily. The special composite activation process of the invention also enables the activation performance of the two materials to reach the highest. Therefore, the combination of the two materials of the red mud and the coal gangue can make up the defects of a single raw material in terms of chemical components and chemical activity, and can be beneficial to changing the ratio of Si/Al to Na/Al in a geopolymer system. The composite activation mode can fully combine the two materials and promote the activation of the two materials.

Step 6: the sodium hydroxide is prepared into a solution with the concentration of 5-8 mol/l. The sodium hydroxide solution is prepared by mixing solid sodium hydroxide with common water.

High alkali concentrations may promote the formation of geopolymers, but too high a concentration may reduce the strength of the geopolymer. The type of alkali is another factor influencing the excitation effect, and OH-ions in an alkaline medium can break Al-O, Si-O and Al-O-Si bonds in the coal gangue to ensure that (SiO)₄)^4-The polymerization degree of tetrahedron is reduced, and the tetrahedron is easy to react with Ca²⁺Calcium aluminate and calcium silicate are formed by reaction, so that the reaction speed and the gel strength are improved;

and 7: the modulus of the water glass is adjusted to 1.6-2.2 by sodium hydroxide solution, namely SiO₂/Na₂Water glass solution with O weight ratio in the range of 1.6 to 2.2.

In the alkaline activator, the appropriate water glass modulus can improve the gelling property of the red mud and the coal gangue. In the polymerization process, after silicon and aluminum are separated out, the silicon and aluminum are immediately mixed with sodium silicate or potassium silicate to form a high-concentration prepolymer in a short time, the concentration of the prepolymer is increased, the polymerization speed is accelerated, and a favorable reaction environment is created for the formation of a gel.

And 8: mixing a sodium hydroxide solution with the sodium silicate solution after the mold is reduced to form an alkaline activator, wherein the mass ratio of the sodium silicate solution to the sodium hydroxide solution in the alkaline activator solution is (2-7.38): 1.

the performance of geopolymers can be influenced by the mixing amount of alkaline activators, and various alkaline activators can excite the activity of gelled materials such as red mud, coal gangue and the like to different degrees, but NaOH and Na₂O·nSiO₂The exciting effect of the mixture is best because the compressive strength of the geopolymer is reduced along with the increase of the doping amount and the Na is singly doped for the NaOH solution₂O·nSiO₂The compressive strength of the solution is increased along with the increase of the mixing amount, but the excessive mixing amount can shorten the setting time and reduce the compressive strength, and the water glass solution is expensive, so that the two solutions are added simultaneously, thereby being economical and beneficial to activity excitation.

And step 9: an orthogonal test is designed, and four level value variables are set for five factors, namely, the mass ratio (0.5-2) of the red mud to the coal gangue, the concentration (5-8mol/L) of the sodium hydroxide solution, the modulus of the water glass (1.6-2.2), the mass ratio (2.5-6) of the water glass solution to the sodium hydroxide solution and the water-gel ratio (0.2-0.4) to perform the orthogonal test, wherein NS/NH refers to the mass ratio of the water glass solution to the sodium hydroxide solution as shown in Table 2.

TABLE 2 design values of orthogonal design test variables

Step 10: according to the specification of the technical specification of lightweight aggregate concrete (JGJ51-1990), the total mixing proportion of the materials is designed as follows: 6.5 to 15 percent of red mud, 6.5 to 15 percent of coal gangue, 21 to 28 percent of coral sand, 33 to 42 percent of broken stone, 0.65 to 1.7 percent of sodium hydroxide solution, 3.4 to 4.8 percent of water glass solution, 3.8 to 9.2 percent of artificial seawater, 1.2 to 1.4 percent of water reducing agent, or other modified materials are additionally added.

Wherein the water reducing agent is one of the modified additives, and can be not added if the experimental mixing degree meets the requirement; other modifying additives are various in types, different in performance and different in dosage and are added according to the actual experimental conditions.

Step 11: the detailed mixing process is shown in fig. 1: firstly, adding a red mud and gangue mixture which is calcined and ground into a stirrer, then adding coral sand and broken stones, uniformly stirring, mixing for one minute, then sequentially adding a sodium hydroxide solution, a water glass solution, artificial seawater and a water reducing agent into the stirrer at the same time, and quickly mixing for 2 minutes and then slowly mixing for 5 minutes to fully react. And finally, grouting and molding the mixture (the length is multiplied by the width is multiplied by 100mm and multiplied by 100mm) for molding, pouring twice, vibrating and compacting on a vibrating table, wrapping a plastic film on each group of three test blocks, curing and curing for 24 hours in a standard curing chamber (T20 +/-2 ℃, RH is more than or equal to 90 percent, wherein RH represents relative humidity, and the relative humidity is the ratio of the actual water content of air to the theoretical maximum water content), demolding, and then transferring the mixture back to the curing chamber for natural placement until the mixture is cured to a set age, thereby obtaining the red mud-gangue mixture coral concrete finished product.

The coarse and fine aggregates and the red mud-coal gangue mixture are firstly stirred uniformly, so that the reaction contact area can be enlarged, and the reaction is promoted to be fully carried out. The reason why the sodium hydroxide solution is added first and then the water glass solution is added is that the sodium hydroxide and OH are added first, and Ca in the raw materials is firstly added⁺、Si⁴⁺、Al³⁺Is rapidly dissolved out and Na⁺Is favorable for dispersing particles and plays a role in wetting, and when the water glass is added, the activity of the raw materials is fully excited to generate more gelled products. The water glass plays a role in cementing and promotes the further formation of products. Mg in seawater²⁺Ion exchange reaction with silicate radical in alkali solution to produce MSH gel and SiO₂Gelling, resulting in a decrease in soluble silica content in the PH and alkaline solutions. Finally, the seawater is added, so that the interaction between the alkaline solution and the seawater can be avoided, and the concrete strength reduction caused by the activation of the alkali can be inhibited to a certain extent. With the addition of seawater, the content of soluble chlorides increases significantly, thus leading to a decrease in the pH value in seawater-mixed geopolymer concrete and a rapid development of early strength, especially in the case of the simultaneous introduction of seawater and sea sand. Both seawater and sea sand generally contain a large amount of Cl^-，Cl^-In the mixing ofThe process may be carried out with some cations, e.g. Na⁺，Ca²⁺And the combination of the components accelerates the hydration reaction, and is equivalent to an early strength agent of concrete, so that the early mechanical property of the concrete is developed more quickly. When sea water or sea sand is used in geopolymer concrete, the drying shrinkage rate may be slightly increased because the reason is explained as follows, firstly, sea sand has a slightly larger void ratio than river sand, which may result in a larger void size between particles in sea sand, and more slurry will be filled between the voids of sea sand than river sand, resulting in an increase in drying shrinkage rate of geopolymer concrete itself due to higher shrinkage rate of paste inside a skeleton formed by aggregated particles. Secondly, because the density values of the seawater and the sea sand are both larger than the density value of the fresh water river sand, when the fresh water or the river sand is completely replaced by the seawater or the sea sand according to the weight and the mass ratio of the components is not changed, the volume content of the slurry in each cubic volume is increased, and the shrinkage is more remarkable. The seawater sand is introduced to improve the capability of resisting chloride ion permeation, because gaps in the seawater sand are large, slurry can completely enter the seawater sand, the formed structure is very compact, chloride ions are difficult to enter the seawater sand, and secondly, because in the concrete using the seawater, more cementing materials are used, the binding capability of chloride is stronger, and the chloride ion permeability is weakened. The geopolymer concrete prepared by using the seawater coral sand can achieve good practical effect.

For the industrial application of the floor polymer, which is restricted by the poor carbonization resistance and the reduction of chloride ion penetration resistance caused by the microcrack caused by drying shrinkage, the volume stability and durability of the floor polymer can be modified by utilizing the modification materials such as MgO, Layered Double Hydroxides (LDHs) and nano particles.

The reactive MgO may react with water to form Mg (OH)₂，Mg(OH)₂In CO₂Under the gas environment, water can be continuously absorbed to generate expansive trihydrates magnesite and flaky brucite/sphenesite, and carbides have obvious cementing and filling effects and can improve the anti-carbonization performance of the cementing material. In addition, Mg (OH)₂The crystals may fill the pores, with some Mg (OH)₂Can also continuously participate in the polymerization reaction to generate the expanding product silicic acidMagnesium hydrate (M-S-H) or hydrotalcite-like compound phase, wherein the hydrotalcite-like compound has stronger capability of absorbing chloride ions, and has obvious shrinkage compensation effect and chloride ion permeation resistance effect on geopolymers. The hydrotalcite-like phase can also adsorb CO₂Produce a brucite phase and reduce CO in pores₂Concentration and reduced formation of bicarbonate phase. Unreacted MgO particles can be directly carbonized to generate magnesium carbonate and hydrated magnesium carbonate, and the carbonization resistance of the geopolymer is improved. After MgO is mixed, amorphous magnesium-containing hydrate gel is generated, and the gel consumes unbound water in pores to densify the structure and reduce CO₂The compressive strength of the geopolymer is improved at the same time through the diffusivity of the pore structure. The mixing amount of MgO is 3% -8%.

Layered Double Hydroxides (LDHs) are a general term for natural hydrotalcite and synthetic hydrotalcite-like compounds, and are intercalation materials with anion exchange capacity. The anion exchange and structure reconstruction characteristics of the LDHs can be utilized to improve the chloride ion permeation resistance of the geopolymer. The layered metal hydroxide after calcination treatment can realize layered structure restoration by adsorbing Cl < - > ions in a NaCl solution, and the calcined layered metal hydroxide can reduce the chloride ion permeation amount and is beneficial to forming a dense slurry structure by geopolymers. The doping amount of the LDHs ranges from 2% to 4%.

The proper amount of nano particles mixed into cement-based material can accelerate volcanic ash reaction, reduce material porosity, improve interface transition zone and fill pores as non-reactive particles, such as nano SiO₂Nano Al₂O₃And nano TiO₂And the like are widely applied to cement-based materials to improve the mechanical property and the durability of the cement-based materials. Such as nano SiO₂Can participate in polymerization reaction, promote the decomposition of amorphous phase and the formation of aluminosilicate gel, and reduce the porosity of geopolymer. Partially unreacted SiO₂Can fill pores, improve the pore structure and contribute to structure densification, thereby reducing the damage of exchange among substances and erosion media to the structure and improving the carbonization resistance and the chloride ion permeation resistance of the geopolymer gelled material. However, the nanoparticles have a large specific surface area and are mixedMore water is needed in the process, the mixing is not uniform easily, or more pores are generated after the curing, the residual unreacted nano particles are filled in the pores and are easy to aggregate, and regional defects are generated to reduce the mechanical property and the durability of the polymer gel material. In addition, in practical application, the parameters such as the type of the silicon-aluminum raw material, the mass ratio of Si and Al substances and the like need to be paid attention, so that the doping amount of the nano particles cannot be too much and is different from 0.5 to 10 percent according to the type. In the actual engineering, a proper amount of water reducing agent can be added to solve the problem of uneven mixing.

The invention utilizes the characteristic that the red mud and the coal gangue are rich in aluminosilicate components, and the calcium oxide in the red mud is taken as a calcium source to improve the activity of the coal gangue and obviously improve the cementation behavior of the red mud-coal stone mixture, and the addition of the coal gangue can improve the strength and has complementary action. The invention prepares the red mud-coal gangue based polymer without adding other active agents, and provides a basis for the popularization and the application of the two wastes. In addition, seawater is used for replacing common water, and coral sand is used for replacing common river sand, so that a new idea is provided for the development of island construction building materials.

Examples 1 to 4:

step 1: preparing artificial seawater according to the mass ratio:

NaCl:Na₂SO₄:MgCl₆H₂O:KCl:CaCl₂＝24.5:4.1:11.1:0.7:1.2；

step 2: sieving fine sand with coral sand of 0.25-0.35 mm; the crushed stone is graded crushed stone, and 30 percent of the mass of all crushed stones is between 5 and 10mm, and 70 percent of the mass of all crushed stones is between 10 and 20 mm;

and 4, step 4: air drying or oven drying at 90-100 deg.C until the water content is less than 3%, measuring pH to 9-11, and pulverizing;

and 5: preparing a red mud-coal gangue mixed raw material; the mass ratio of the red mud to the coal gangue is 1:2.3-2.3:1, 20% -30% of deionized water is added, the mixture is kneaded into round balls with the diameter of 2-3cm, the round balls are placed into an oven to be dried at 90-100 ℃ to remove free water, the round balls are placed into a muffle furnace to be calcined for 2 hours at 600-750 ℃, finally the round balls are taken out to be cooled, the mixture is placed into a grinder to be ground for 30 minutes, and finally the ground mixture is sieved by a sieve with the aperture of 0.08mm to obtain the red mud-coal gangue mixed raw material.

Step 6: mixing solid sodium hydroxide with common water to prepare 5-8mol/l sodium hydroxide solution;

and step 9: mixing all prepared raw materials, stirring, injection molding, curing, demolding, naturally placing, and finally forming a finished product. The total proportion of the raw materials is as follows: 6.5 to 15 percent of red mud, 6.5 to 15 percent of coal gangue, 21 to 28 percent of coral sand, 33 to 42 percent of broken stone, 0.65 to 1.7 percent of sodium hydroxide solution, 3.4 to 4.8 percent of water glass solution, 3.8 to 9.2 percent of artificial seawater and 1.2 to 1.4 percent of water reducing agent;

the method specifically comprises the following steps: firstly, adding a red mud-coal gangue mixture after calcination and grinding into a stirrer, adding coral sand and broken stone, uniformly stirring, and after stirring for one minute, sequentially adding a sodium hydroxide solution, a water glass solution, artificial seawater and a water reducing agent into the stirrer, quickly stirring for 2 minutes, and then slowly stirring for 5 minutes to fully react; and finally, grouting and molding the mixture, pouring for two times, vibrating and compacting on a vibrating table, wrapping a plastic film on each group of three test blocks, curing and curing for 24 hours in a standard curing chamber, demolding, and then transferring back to the curing chamber for natural placement until curing reaches a set age to obtain a red mud-coal gangue mixture coral concrete finished product.

Comparative example:

stirring cement and sand for 2min, adding seawater and water reducing agent, stirring for 3min, adding coral, and stirring for 3min until all materials are mixed uniformly.

As shown in table 3, a 28-day compressive strength comparison and slump comparison of conventional cement-based coral concrete versus the geopolymer coral concrete of the present application is shown.

Table 3: comparison result of compression strength and slump of cement-based coral concrete and geopolymer coral concrete

Wherein: example 1, step 5, putting into oven, drying at 95 deg.C to remove free water, putting into muffle furnace, calcining at 750 deg.C for 2 h; step 6, mixing solid sodium hydroxide with common water to prepare 6.5mol/l sodium hydroxide solution; and step 7, the modulus of the water glass is adjusted to 2.1 by a sodium hydroxide solution.

Example 2, step 5, placing in an oven, drying at 90 ℃ to remove free water, and then placing in a muffle furnace, calcining at 600 ℃ for 2 h; step 6, mixing solid sodium hydroxide with common water to prepare 5mol/l sodium hydroxide solution; and step 7, the modulus of the water glass is adjusted to 1.6 by a sodium hydroxide solution.

Example 3: step 5, putting the mixture into an oven, drying the mixture at 90 ℃ to remove free water, and then putting the mixture into a muffle furnace to calcine the mixture for 2 hours at 600 ℃; step 6, mixing solid sodium hydroxide with common water to prepare 5mol/l sodium hydroxide solution; and step 7, the modulus of the water glass is adjusted to 1.6 by a sodium hydroxide solution.

Example 4: step 5, putting the mixture into an oven, drying the mixture at 100 ℃ to remove free water, and then putting the mixture into a muffle furnace to calcine the mixture for 2 hours at 750 ℃; step 6, mixing solid sodium hydroxide with common water to prepare 8mol/l sodium hydroxide solution; and step 7, the modulus of the water glass is adjusted to be 2.2 by a sodium hydroxide solution.

The prepared concrete material is tested by adopting a method of a flow consistency test bed in ASTM C230 in a fluidity test; the setting time is measured by adopting the international examination method for water consumption, setting time and stability of the standard consistency of cement; the unconfined compressive strength test is referred to geotechnical test method standard (GB/T50123-1999), and an electronic universal tester is adopted for testing, wherein the loading mode is displacement loading, and the loading rate is 0.5 mm/min.

As can be seen from table 3: the compressive strength and the collapse degree of the geopolymer coral concrete are obviously superior to those of cement-based coral concrete.

FIG. 2 is a graph showing the change of compressive strength of polymer coral concrete with age in different mass ratios of red mud and coal gangue: the horizontal coordinate is 0.5-2 for the mass ratio of the red mud to the coal gangue, and the vertical coordinate for the compressive strength. FIG. 2 mainly shows the compressive strength changes of geopolymer coral concrete prepared from 0.5-2 mass ratios of four red mud coal gangues in ages of 3 d, 7 d and 28d respectively, and it can be seen that the compressive strength of the geopolymer coral concrete prepared from the four mass ratios is increased rapidly in the early stage and is highest in 28d compressive strength, wherein the compressive strength of the three ages is higher than that of the other three masses when the mass ratio of the red mud coal gangues is 1.5, and the 28d compressive strength reaches 41.9MPa, so that the effect is considerable.

The slump range of the design test is between 90 and 160mm, and the slump has good fluidity; the initial setting time is 60-120 min, the final setting time is 220-600min, the early strength and quick hardening characteristics are achieved, and the requirements of national standard GB175-1999 on ordinary portland cement are met; the 28-day compressive strength is 30-45MPa, reaches the C35 concrete strength standard, has the characteristics of early strength and quick hardening, and has wide application space in the aspect of highway subgrade emergency repair.

The coral aggregates are coarse, have large gaps, have strong water absorption capacity, and have large friction force and occlusal force with cement paste, so the cement-based coral concrete has small slump and weak working performance. Geopolymers, unlike cement, have unique chemical properties and reaction mechanisms. The red mud and the coal gangue generate zeolite substances in a strong alkali environment, and the substances have chain structures similar to organic polymers and can be matched with [ SiO ] on the surfaces of mineral particles₄]^4-And [ AlO ]₄]^4-The tetrahedron forms chemical bonds through dehydroxylation, so that the concrete obtains high strength and has excellent physicochemical properties. Therefore, the geopolymer coral concrete has better working performance and compressive strength than cement-based coral concrete.

Compared with cement-based materials, the reaction product of the geopolymer is stable, the impermeability is strong, and the geopolymer has strong erosion resistance to aggressive ions such as chloride, sulfate and the like in the environment, so that the geopolymer is feasible and excellent in preparation of the geopolymer coral concrete by replacing the cement-based materials and combining coral sand with the geopolymer.

All the embodiments in the present specification are described in a related manner, and the same and similar parts among the embodiments may be referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, for the system embodiment, since it is substantially similar to the method embodiment, the description is simple, and for the relevant points, reference may be made to the partial description of the method embodiment.

The above description is only for the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.

Claims

1. The seawater and coral sand mixed red mud-coal gangue based polymer concrete is characterized by comprising, by mass, 6.5% -15% of red mud, 6.5% -15% of coal gangue, 21% -28% of coral sand, 33% -42% of broken stone, 0.65% -1.7% of a sodium hydroxide solution, 3.4% -4.8% of a water glass solution, 3.8% -9.2% of artificial seawater and 1.2% -1.4% of a water reducing agent.

2. The seawater and coral sand mixed red mud-coal gangue based polymer concrete as claimed in claim 1, wherein the crushed stones are coarse aggregates, the crushed stones are screened graded crushed stones, crushed stones with a particle size of 5-10mm account for 30% of the total mass of the crushed stones, and crushed stones with a particle size of 10-20mm account for 70% of the total mass of the crushed stones;

3. The seawater and coral sand mixed red mud-coal gangue based polymer concrete as claimed in claim 2, further comprising MgO 3-8% by mass.

4. The seawater and coral sand mixed red mud-coal gangue based polymer concrete as claimed in claim 3, further comprising 2-4% of LDHs by mass.

5. The seawater and coral sand mixed red mud-coal gangue based polymer concrete as claimed in claim 4, wherein the concrete further comprises nano particles SiO in percentage by mass₂ 0.5％-10％。

6. A preparation method of seawater and coral sand mixed red mud-coal gangue based polymer concrete is characterized by comprising the following steps:

step 1: preparing artificial seawater;

and 5: preparing a red mud-coal gangue mixed raw material;

7. The preparation method of the seawater and coral sand mixed red mud-coal gangue based polymer concrete as claimed in claim 6, wherein the artificial seawater of step 1 comprises the following components in parts by mass:

NaCl:Na₂SO₄:MgCl₆H₂O:KCl:CaCl₂＝24.5:4.1:11.1:0.7:1.2；

the pH value of the red mud obtained in the step 4 is 9-11.

8. The preparation method of the seawater and coral sand mixed red mud-coal gangue based polymer concrete as claimed in claim 6, wherein the step 5 is specifically mixing the red mud and the coal gangue according to a certain ratio, the mass ratio of the two is 1:2.3-2.3:1, adding 20% -30% of deionized water, kneading into round balls with the diameter of 2-3cm, putting the round balls into an oven to be dried at 90-100 ℃ to remove free water, then putting the round balls into a muffle furnace to be calcined at 600-750 ℃ for 2h, finally taking out and cooling, putting the round balls into a grinder to be ground for 30min, and finally sieving the ground mixture by a sieve with the aperture of 0.08mm to obtain the red mud-coal gangue mixed raw material.

9. The preparation method of the seawater and coral sand mixed red mud-coal gangue based geopolymer concrete as recited in claim 6, wherein the sodium hydroxide solution of step 6 is 5-8 mol/l;

10. the preparation method of the seawater and coral sand mixed red mud-coal gangue based polymer concrete as claimed in claim 6, wherein the total ratio of the raw materials in the step 9 is specifically as follows: 6.5 to 15 percent of red mud, 6.5 to 15 percent of coal gangue, 21 to 28 percent of coral sand, 33 to 42 percent of broken stone, 0.65 to 1.7 percent of sodium hydroxide solution, 3.4 to 4.8 percent of water glass solution, 3.8 to 9.2 percent of artificial seawater and 1.2 to 1.4 percent of water reducing agent;