CN111320446B - High-strength self-waterproof phosphogypsum roadbed material and preparation method thereof - Google Patents
High-strength self-waterproof phosphogypsum roadbed material and preparation method thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
- C04B28/14—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing calcium sulfate cements
- C04B28/145—Calcium sulfate hemi-hydrate with a specific crystal form
- C04B28/147—Calcium sulfate hemi-hydrate with a specific crystal form beta-hemihydrate
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- C04B11/00—Calcium sulfate cements
- C04B11/02—Methods and apparatus for dehydrating gypsum
- C04B11/028—Devices therefor characterised by the type of calcining devices used therefor or by the type of hemihydrate obtained
- C04B11/036—Devices therefor characterised by the type of calcining devices used therefor or by the type of hemihydrate obtained for the dry process, e.g. dehydrating in a fluidised bed or in a rotary kiln, i.e. to obtain beta-hemihydrate
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- C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
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Abstract
The invention discloses a high-strength self-waterproof phosphogypsum roadbed material, which is prepared by calcining a phosphogypsum raw material to obtain modified phosphogypsum powder for preparing the phosphogypsum roadbed material, and further effectively promoting the generation of alpha-hemihydrate gypsum by regulating and controlling the water content and the input amount of the phosphogypsum raw material in a closed calcination environment in the process of converting calcium sulfate dihydrate into hemihydrate gypsum in the first time so as to remarkably improve the mechanical property and the waterproof property of the obtained phosphogypsum roadbed material. The modification method provided by the invention is extremely simple and convenient to operate, can realize 100% recycling of the phosphogypsum waste, has important economic and environmental benefits, and is suitable for popularization and application.
Description
Technical Field
The invention belongs to the technical field of building materials, and particularly relates to a high-strength self-waterproof phosphogypsum roadbed material and a preparation method thereof.
Background
Phosphogypsum is a phosphorus-containing and calcium sulfate dihydrate (CaSO) 4 ·2H 2 O) mainly II type industrial solid wastes. According to the statistics of national development and improvement committee, the national yield of phosphogypsum reaches 6000 million tons, but the comprehensive utilization rate is less than 20 percent. On the other hand, the total mileage of roads in China breaks through 450 kilometers, and the development of the transportation industry is not only dedicated to the improvement of the pavement performance, but also faces multiple stresses of the loss of high-quality aggregates, the development of green economy and the like. The phosphogypsum has certain hydration hardening strength, if the phosphogypsum is used for road construction, a large amount of phosphogypsum can be consumed, the construction cost of a road can be greatly reduced, and the phosphogypsum has remarkable social benefit and economic benefit.
Chinese patent CN 104909698A "a modified phosphogypsum highway subgrade filler and a preparation method thereof" is to mix calcined phosphogypsum with raw material phosphogypsum according to a certain proportion to improve the gelling property thereof and obtain a pavement base filler with a certain strength, but the phosphogypsum subgrade filler obtained by the method has a compressive strength of less than 1.5MPa and cannot meet the strength requirement of a high-grade pavement on the base layer material. Chinese patent CN 108275931A 'phosphogypsum modified material and application thereof in a road base' discloses a road base and a water-stable layer material formed by mixing modified phosphogypsum with 10 raw materials such as fly ash, cement, surfactant and the like, wherein the compressive strength of the material reaches 5-6MPa, but the composition of the material is extremely complex, and the cost and the control of a construction process are still required to be further improved. Chinese patent CN 108409276A modified phosphogypsum roadbed material is prepared by mixing phosphogypsum with sand, carbide slag and other raw materials according to a certain proportion and then adding a curing agent, and the CBR value of the material meets the specification requirements through tests. Chinese patent CN 109626925A "preparation method of phosphogypsum roadbed material based on high-temperature activation and hydraulicity improvement" proposes a method for preparing roadbed material by mixing phosphogypsum with waterproofing agent and portland cement after high-temperature calcination.
Disclosure of Invention
The invention mainly aims to provide a high-strength self-waterproof phosphogypsum roadbed material and a preparation method thereof, the method relates to a simple process, not only realizes high-efficiency recycling of industrial solid waste phosphogypsum, but also ensures that the strength of the roadbed material meets the performance requirements of heavy traffic and above pavements, has good water damage resistance, and is suitable for popularization and application.
In order to achieve the purpose, the invention adopts the technical scheme that:
a preparation method of a high-strength self-waterproof phosphogypsum roadbed material comprises the following steps:
1) Providing a phosphogypsum raw material with a certain water content;
2) In a closed sintering device, heating the phosphogypsum raw material obtained in the step 1) to 150-170 ℃ for calcination treatment, and then cooling and crushing to obtain modified phosphogypsum powder with the crystal water content of 1-4%;
3) And adding a proper amount of retarder into the obtained modified phosphogypsum powder, uniformly stirring, adding a proper amount of water, stirring, stewing and forming to obtain the phosphogypsum roadbed material.
In the scheme, the water content of the phosphogypsum raw material is 20-30wt%.
In the scheme, the phosphogypsum raw material is a phosphogypsum solid waste provided by a phosphate fertilizer or phosphoric acid production plant; wherein the content of the calcium sulfate dihydrate accounts for 70-95% of the total mass of the phosphogypsum.
In the scheme, the calcining treatment time is 8-16h.
In the scheme, the ratio of the mass of the phosphogypsum raw materials in the closed sintering equipment to the volume of the closed sintering equipment is (200-300) to 1g L; in a closed sintering device, the internal pressure of the device is about 1.2-1.5 atmospheric pressures and the environment is damp and hot by regulating and controlling the water content, the using amount and the sintering temperature of the phosphogypsum raw material in unit sintering volume, thereby providing environmental conditions for converting the dihydrate gypsum into the alpha-hemihydrate gypsum.
In the scheme, the crushing step adopts a high-speed rotary crusher, the rotating speed is 20000-25000r/min, and the crushing time is 5-8s.
In the scheme, the retarder is a protein retarder, and the doping amount of the protein retarder is 0.3-0.7% of the mass of the modified phosphogypsum powder.
In the scheme, the mixing amount of the water in the step 3) is 23-27% of the mass of the modified phosphogypsum powder.
In the scheme, the material stewing time is 3-5h, and the mixed modified phosphogypsum roadbed material is placed in a closed unheated container for standing in the material stewing process, so that the uniform moisture of the roadbed material is ensured.
The phosphogypsum roadbed material prepared according to the scheme can effectively give consideration to high strength (the seven-day unconfined compressive strength is 7-10 MPa) and self-waterproof performance (the dynamic stability of the soaked water residue is more than 80%), can realize 100% recycling of phosphogypsum waste, and has important environmental and application significance.
The principle of the invention is as follows:
1) The main component of the phosphogypsum is calcium sulfate dihydrate, the heating temperature is controlled to be 150-170 ℃, the calcium sulfate dihydrate is quickly dehydrated and converted into the semi-hydrated gypsum, when the semi-hydrated gypsum is mixed with water, the original calcium sulfate dihydrate particles in the raw materials serve as crystal nuclei, the semi-hydrated gypsum quickly absorbs water and is converted into calcium sulfate dihydrate crystals, the crystals are mutually crossed and grown to form a compact network structure, and the high crystallization strength is shown; the alpha-type hemihydrate gypsum is in a short column shape and has relatively large crystal grains after being dissolved and recrystallized, calcium sulfate dihydrate crystal grains generated by the reaction with water are regular and are completely arranged, and compared with the needle-shaped beta-hemihydrate gypsum, the alpha-type hemihydrate gypsum has relatively good integrity and relatively low porosity, and the obtained hydration product has relatively high beard strength and water resistance; the invention firstly provides that the calcining air pressure is higher than the atmospheric pressure and the environment is damp and hot by regulating and controlling the water content and the input amount of the phosphogypsum raw material in the closed calcining environment, provides environmental conditions for converting the dihydrate gypsum part into the alpha-hemihydrate gypsum, and ensures that the obtained hydration product shows excellent mechanical property and waterproof property.
2) The modified phosphogypsum powder (the main component is the mixture of alpha-semi-hydrated gypsum and beta-semi-hydrated gypsum) is further added with the protein retarder, the protein is adsorbed on the surface of calcium sulfate dihydrate particles, the formation of germs is delayed, the crystallization speed of the modified powder is delayed, the on-site construction requirement is met, and the service performance of the obtained phosphogypsum roadbed material is further ensured.
Compared with the prior art, the invention has the beneficial effects that:
1) The invention realizes 100 percent recycling of the phosphogypsum waste based on the physical and chemical changes of the main components of the phosphogypsum, and produces the pavement base material which has high strength and good water damage resistance and meets the construction requirements by adding the retarder; from the aspect of economic benefit, the cost of the pavement can be reduced by about 20 percent, and the construction period can be shortened by more than 20 percent; has important practical significance on the reasonable resource utilization of wastes and the sustainability of social development.
2) The invention firstly proposes that in the process of converting calcium sulfate dihydrate into semi-hydrated gypsum through dehydration, the calcination pressure is higher than atmospheric pressure and the environment is damp and hot through regulating and controlling the water content and the input amount of the phosphogypsum raw material in a closed calcination environment, the generation of alpha-semi-hydrated gypsum is effectively promoted, and the mechanical property and the waterproof property of the obtained phosphogypsum roadbed material are obviously improved; and the related modification method is extremely simple, convenient to operate and suitable for popularization and application.
3) The invention can effectively meet the performance requirements of heavy traffic and the road surface on the road base material while realizing the high-efficiency recycling of the industrial solid waste phosphogypsum, reduces the requirement of road construction on high-quality base materials and has important economic and environmental benefits.
Drawings
FIG. 1 is a schematic view of the hardening principle of calcium sulfate alpha-hemihydrate;
FIG. 2 is a schematic view of the hardening principle of beta-calcium sulfate hemihydrate.
Wherein 1 is alpha-sulfuric acid hemihydrate, 2 is beta-calcium sulfate hemihydrate, and 3 is calcium sulfate dihydrate colloidal particles; 4 are calcium sulfate dihydrate crystals, 5 are staggered crystals.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In the following examples, a rut test piece is formed by referring to a T0703 wheel rolling method in road engineering asphalt and mixture test procedures thereof JTG E20-2011; and (4) carrying out a water immersion rut dynamic stability test by referring to T0719, and testing the water damage resistance of the water immersion rut dynamic stability test.
In the following examples, the phosphogypsum raw material is taken from solid waste produced by phosphate fertilizer or phosphoric acid production plants, wherein the content of calcium sulfate dihydrate is 85wt%; and the natural water content is measured according to road geotechnical test regulation JTG E40-2007.
In the following examples, the protein retarder used was a plant protein gypsum retarder provided by new building materials ltd.
Examples 1 to 2
A high-strength self-waterproof phosphogypsum roadbed material and a preparation method thereof are disclosed, which are used for exploring the influence of crystal water modified phosphogypsum powder with different contents on the performance of the roadbed material, and specifically comprise the following steps:
1) Determining the natural water content of the phosphogypsum raw material to be 25.8% according to JTG E40-2007 Specification for Highway soil engineering test;
2) Adding the phosphogypsum raw material into a closed sintering device, and controlling the mass (g) of the phosphogypsum in the closed sintering device to be 240-volume ratio (L) of the phosphogypsum to the device; and the phosphogypsum in the closed sintering equipment needs to be layered and placed in a separate tray, and is not stacked in a centralized way; then calcining for 6, 7, 8, 9 and 10 hours respectively at the temperature of 160 ℃ (wherein the calcining time is 7 hours and 8 hours, corresponding to examples 1 and 2, and the calcining time is 6 hours, 9 hours and 10 hours, corresponding to comparative examples 1, 2 and 3), cooling, crushing by a high-speed rotary crusher (the rotating speed is 20000-25000r/min, the crushing time is 5-8 s), and obtaining modified phosphogypsum powder with the crystal water content of 0.3%, 1.4%, 2.9%, 4.2% and 5.3% (the crystal water content is determined by a rapid moisture tester);
3) Adding a protein retarder accounting for 0.7 percent of the mass of the modified phosphogypsum powder into the modified phosphogypsum powder, adding water accounting for 25 percent of the mass of the modified phosphogypsum powder, uniformly mixing, performing compaction test, stewing for 5 hours, and measuring the dry density and the water content of the material; and a cylindrical test piece with the height-diameter ratio of phi 50mm being 1 is adopted, and the unconfined compressive strength of the test piece for seven days is tested.
The change conditions of the dry density and the compressive strength of compacted test pieces obtained by modifying the phosphogypsum powder with different crystal water contents are shown in table 1, and the table shows that the compressive strength of the test pieces is increased along with the increase of the original crystal water content, but the dry density of the test pieces is reduced when the crystal water content is higher, because the calcium sulfate dihydrate is formed at a higher speed when the content of the hemihydrate is higher, the construction is not facilitated; the higher the original crystal water content is, the higher the material strength is, but the relative workability is deteriorated, so the original crystal water content of the high-strength phosphogypsum roadbed material is controlled to be between 1 and 4 percent.
TABLE 1 Performance test results of roadbed materials obtained by modifying phosphogypsum powder with different crystal water contents
Examples 3 to 4
A high-strength self-waterproof phosphogypsum roadbed material and a preparation method thereof are disclosed, which explore the influence of different retarder doping amounts on the performance of the roadbed material, and specifically comprise the following steps:
1) Determining the natural water content of the phosphogypsum raw material to be 26.5% according to 'Highway geotechnical test regulation' JTG E40-2007;
2) Adding the phosphogypsum raw material into a closed sintering device, and controlling the mass (g) of the phosphogypsum in the closed sintering device to be 260 to the volume ratio (L) of the phosphogypsum in the closed sintering device; and the phosphogypsum in the closed sintering equipment needs to be layered and placed in a separate tray, and is not stacked in a centralized way; then calcining for 8h at 160 ℃, cooling, and crushing by adopting a high-speed rotary crusher (the rotating speed is 20000-25000r/min, the crushing time is 5-8 s) to obtain modified phosphogypsum powder with the crystal water content of 2.8% (the crystal water content is determined by adopting a rapid moisture tester);
3) Adding protein retarders accounting for 0.1%, 0.3%, 0.5%, 0.7% and 0.9% of the modified phosphogypsum powder respectively (wherein the addition amount is 0.5% and 0.7%, corresponding to examples 3 and 4, the addition amounts are 0.1%, 0.3% and 0.9%, corresponding to comparative examples 4, 5 and 6 respectively), adding water accounting for 25% of the modified phosphogypsum powder, uniformly mixing, performing compaction test, stewing for 5 hours, and measuring the dry density and the water content; and a cylindrical test piece with the height-diameter ratio of phi 50mm being 1 is adopted to test the seven-day unconfined compressive strength of the test piece.
The change conditions of the dry density and the compressive strength of a compacted test piece made of the phosphogypsum roadbed material obtained under different mixing amounts of the retarder are shown in a table 2, and it can be seen from the table that under the condition of stewing for 5 hours, the dry density of the test piece is gradually increased along with the increase of the mixing amount of the retarder, the compressive strength is firstly increased and then tends to be stable, because the retarder delays the conversion of calcium sulfate hemihydrate into calcium sulfate dihydrate, the raw material is softer in the forming process, so the forming density is high, after 7 days of maintenance, most of the calcium sulfate hemihydrate in the test piece is converted into calcium sulfate dihydrate crystals, and the more dense the test piece is, the higher the crystallization strength is. In addition, after 0.1% of retarder braising material is only added for 5 hours, a large amount of hard particles appear in the material, the forming is difficult, and the construction is not facilitated; meanwhile, the retarder is used for delaying the hardening speed, and the excessive addition has little influence on the compression strength of the test piece, so that the consumption of the retarder is 0.5-0.7 percent of the quality of the modified phosphogypsum powder.
TABLE 2 Performance test results of roadbed materials obtained under different retarder doping amounts
Examples 5 to 6
A high-strength self-waterproof phosphogypsum roadbed material and a preparation method thereof are disclosed, and the method is used for exploring the influence of different durations of different braising materials on the performance of the roadbed material and specifically comprises the following steps:
1) Determining the natural water content of the phosphogypsum raw material to be 24.6 percent according to the highway geotechnical test regulation JTG E40-2007;
2) Adding the phosphogypsum raw material into a closed sintering device, and controlling the mass (g) of the phosphogypsum in the closed sintering device to be 200 to the volume ratio (L) of the phosphogypsum in the closed sintering device; and the phosphogypsum in the closed sintering equipment needs to be layered and placed in a separate tray, and is not stacked in a centralized way; then calcining for 8h at 160 ℃, cooling, and crushing by adopting a high-speed rotary crusher (the rotating speed is 20000-25000r/min, the crushing time is 5-8 s) to obtain modified phosphogypsum powder with the crystal water content of 2.8% (the crystal water content is determined by adopting a rapid moisture tester);
3) Adding a protein retarder accounting for 0.7% of the modified phosphogypsum powder into the modified phosphogypsum powder, adding water accounting for 25% of the modified phosphogypsum powder, uniformly mixing, performing compaction test, and measuring the dry density and the water content, wherein the material stewing time is respectively 1h, 3h, 5h and 7h (the material stewing time is respectively 3h and 5h, which correspond to examples 5 and 6, and the material stewing time is respectively 1h and 7h, which correspond to comparative examples 7 and 8); and a cylindrical test piece with the height-diameter ratio of phi 50mm being 1 is adopted, and the unconfined compressive strength of the test piece for seven days is tested.
The change conditions of the dry density and the compressive strength of the obtained modified phosphogypsum compaction test piece are shown in the table 3, and the longer the material stewing time is, the more unfavorable the test piece is for forming, and meanwhile, when the mixing amount of the retarder is 0.7%, the material strength is obviously reduced after the material stewing time exceeds 5h.
Table 3 performance test results of roadbed materials under different stewing time lengths
Examples 7 to 9
A high-strength self-waterproof phosphogypsum roadbed material and a preparation method thereof are disclosed, which explore the influence of different water addition amounts on the performance of the roadbed material, and specifically comprise the following steps:
1) Determining the natural water content of the phosphogypsum raw material to be 28.6 percent according to JTG E40-2007 Specification for Highway soil engineering test;
2) Adding the phosphogypsum raw material into a closed sintering device, and controlling the ratio (L) of the mass (g) of the phosphogypsum in the closed sintering device to the volume (L) of the device to be 240; and the phosphogypsum in the closed sintering equipment needs to be layered and placed in a separate tray, and is not stacked in a centralized way; then calcining for 8h at the temperature of 160 ℃, cooling, and crushing by adopting a high-speed rotary crusher (the rotating speed is 20000-25000r/min, the crushing time is 5-8 s) to obtain modified phosphogypsum powder with the crystal water content of 3.1% (the crystal water content is determined by adopting a rapid moisture tester);
3) Adding a protein retarder accounting for 0.7 percent of the modified phosphogypsum powder, then respectively adding water accounting for 21 percent, 23 percent, 25 percent, 27 percent and 29 percent of the modified phosphogypsum powder (wherein the water addition amount is 23 percent, 25 percent and 27 percent respectively correspond to examples 7, 8 and 9, and the water addition amount is 21 percent and 29 percent respectively correspond to comparative examples 9 and 10), uniformly mixing, performing compaction test, and measuring the dry density and the water content of the modified phosphogypsum powder, wherein the stewing time is 4 hours; and a cylindrical test piece with the height-diameter ratio of phi 50mm being 1 is adopted to test the seven-day unconfined compressive strength of the test piece.
The change conditions of the dry density and the compressive strength of the modified phosphogypsum compaction test piece obtained under different water addition amounts are shown in a table 4, and it can be seen from the table that when the water addition amount is too small, the conversion of the calcium sulfate hemihydrate is incomplete and the strength is lower; when the water addition amount is too large, the dry density of the test piece is reduced, and the strength is reduced to a certain degree; the high-strength phosphogypsum roadbed material has the water addition amount of 23-27%.
TABLE 4 detection results of properties of roadbed materials with different water adding amounts
Example 10
A high-strength self-waterproof phosphogypsum roadbed material is explored, and the water stability of the phosphogypsum roadbed material produced by the method is explored, and the method specifically comprises the following steps:
1) Determining the natural water content of the phosphogypsum raw material to be 26.9% according to 'Highway geotechnical test regulation' JTG E40-2007;
2) The phosphogypsum raw materials are adopted to manufacture two groups of rutting test pieces, the manufacturing method refers to a T0703 wheel rolling method in road engineering asphalt and mixture test procedure JTG E20-2011, the phosphogypsum raw materials are uniformly mixed, 0.7% of retarder is added, the materials are sealed for 4 hours, a proper amount of raw materials are filled into 300 x 50mm standard rutting test pieces, a rutting forming instrument is not heated and is rolled and formed, and the two groups of test pieces are numbered 10-1 and 10-2.
3) Adding the phosphogypsum raw material into a closed sintering device, and controlling the mass (g) of the phosphogypsum in the closed sintering device to be 240-volume ratio (L) of the phosphogypsum to the device; and the phosphogypsum in the closed sintering equipment needs to be layered and placed in a separate tray, and is not stacked in a centralized way; then calcining for 8h at the temperature of 160 ℃, cooling, and crushing by adopting a high-speed rotary crusher (the rotating speed is 20000-25000r/min, the crushing time is 5-8 s) to obtain modified phosphogypsum powder with the crystal water content of 3.0% (the crystal water content is determined by adopting a rapid moisture tester);
4) Adding a protein retarder accounting for 0.7 percent of the modified phosphogypsum powder into the modified phosphogypsum powder, respectively adding water accounting for 25 percent of the modified phosphogypsum powder, uniformly mixing, then carrying out blank sealing for 4 hours, and forming two groups of test pieces by adopting a wheel rolling method, wherein the test pieces are numbered 10-3 and 10-4.
5) And (5) carrying out a water-soaking rutting dynamic stability test piece by referring to T0719, and testing the water damage resistance of the rutting test piece. The specific results are shown in Table 5.
Preparing four groups of rut test pieces by referring to a T0703 wheel milling method in road engineering asphalt and mixture test procedure JTG E20-2011, wherein a test piece I and a test piece II are formed by adopting phosphogypsum raw materials (natural water content is 26.9%), and a rut forming instrument is not heated; the third and fourth test pieces adopt phosphogypsum as modified materials of the phosphogypsum treated by the method, wherein the doping amount of the retarder is 7 per mill, the material sealing is performed for 4 hours, and the water addition amount is 25 percent; a dynamic stability test of the submerged track is carried out by referring to T0719, the water damage resistance of the submerged track is tested, and specific results are shown in a table 5.
TABLE 5 dynamic stability test results for different phosphogypsum materials
As can be seen from Table 5, the dynamic stability of the phosphogypsum rut test piece which is not treated by the method is 1129 times/mm, the dynamic stability under the soaking condition is 456 times/mm, and the residual dynamic stability of the soaking is 40.3%, which indicates that the water damage resistance is poor; the dynamic stability of the phosphogypsum modified rut test piece treated by the method is 6032 times/mm, the dynamic stability of the phosphogypsum modified rut test piece is 5891 times/mm under the soaking condition, the residual dynamic stability of the soaking is 97.7 percent, and the phosphogypsum modified rut test piece can show excellent water damage resistance.
Example 11
The method for exploring the influence of the natural water content of the phosphogypsum raw material and the calcining air pressure control on the performance of the obtained roadbed material specifically comprises the following steps:
1) Three groups of tests are respectively taken for processing; the first group of samples (comparative example 11) are air-dried and aired, and the actual measurement result shows that the natural water content is 15.8%; the natural water content of the second group of samples (6-2) is controlled between 20 and 30 percent as described in the patent, and 25.4 percent is actually measured (example 11); the third group of samples (comparative example 12) are mixed with water on the basis of the original phosphogypsum, and the actual measurement moisture content is 42.1%;
2) The technological parameters of the phosphogypsum heat treatment are as follows: controlling the heating temperature to be 160 ℃, the ratio (L) of the mass (g) of the phosphogypsum in the closed sintering equipment to the volume of the equipment to be 250, controlling the content of crystal water of the phosphogypsum material after heat treatment to be about 3% through the calcination time length, and calcining for 6 hours, 8 hours and 12 hours respectively in three groups of tests;
3) Respectively grinding the materials after heat treatment, adding 0.7% of retarder, adding 25% of water, mixing, sealing the materials for 4 hours, and then performing compaction and seven-day unconfined compressive strength tests according to JTG E51 of Highway engineering inorganic binder stable material test regulations; evaluating the water stability performance of the phosphogypsum roadbed material by different natural water contents and calcining air pressures by adopting the method for testing the stability of the soaking residual in water in the embodiment 10; the test results are shown in Table 6.
TABLE 6 Performance test results of phosphogypsum road base materials with different natural water contents
As can be seen from table 6, when the content of the natural crystal water in the modified phosphogypsum roadbed material is constant, the natural water content has a great influence on the compressive strength and the water damage resistance of the roadbed material, which is specifically shown that when the natural water content is low, the compressive strength and the water damage resistance are obviously reduced; when the natural water content is higher, the strength and the water damage resistance of the natural water are reduced to a certain degree. When the natural water content is low, the air pressure in the closed sintering equipment cannot meet the air pressure requirement required by the patent in the heat treatment process, so that the prepared phosphogypsum roadbed material cannot generate alpha-hemihydrate gypsum which greatly contributes to the strength; when the natural water content is too high, part of dihydrate gypsum in the original phosphogypsum cannot be dehydrated to produce the hemihydrate gypsum, and when the content of the dihydrate gypsum in the modified phosphogypsum roadbed material is too high, the dihydrate gypsum does not participate in the reaction in the hydration and crystallization process, so that the formed uniform and compact crystallization product is adversely affected, and the strength of the prepared phosphogypsum roadbed material is reduced to a certain extent.
Comparative example 13
The road performance of the phosphogypsum road bed material is compared with the road performance of the phosphogypsum road bed material obtained by using original-state phosphogypsum (phosphogypsum raw material) and further adding silicate cement accounting for 3 percent of the mass of the phosphogypsum, wherein the natural water content of the original-state phosphogypsum is 26.9 percent, compaction and seven-day unconfined compressive strength tests are directly carried out without any treatment, and a sample is numbered (1); taking a sample (1), preparing the phosphogypsum roadbed material according to the method of the patent example 8, compacting and carrying out a seven-day unconfined compressive strength test, wherein the sample is numbered (2); adding 3% of Portland cement into the formula of the modified phosphogypsum roadbed material according to the embodiment 8, adding water, mixing, compacting, performing seven-day unconfined compressive strength test, and numbering the sample (3); the specific test results are shown in Table 7.
TABLE 7 road performance of different components phosphogypsum roadbed material
As can be seen from table 7, the compressive strength of the undisturbed phosphogypsum is only 0.95MPa, because the dihydrate gypsum in the undisturbed phosphogypsum does not have hydraulicity and only depends on intermolecular attraction formed in the forming static pressure process to provide strength, which indicates that the undisturbed phosphogypsum can not be used for paving the base course of the pavement; the maximum dry density of the phosphogypsum modified roadbed material added with the cement is greater than that of a sample without the cement, but the compressive strength of the phosphogypsum modified roadbed material is far lower than that of the roadbed material without the cement; the invention utilizes the hydration characteristic of the dihydrate gypsum, provides the roadbed strength by means of the mutual crosslinking of dihydrate gypsum crystals, and after the silicate cement is added, on one hand, the cement hydration process can seize water molecules with the hemihydrate gypsum, so that the hemihydrate gypsum can not be hydrated; on the other hand, the generated ettringite crystals have larger molecular weight and can directly block the growth path of dihydrate gypsum crystals, so that the overall strength of the prepared roadbed material is reduced. Macroscopically, the roadbed material added with cement contains hard particles with higher strength, so that the phosphogypsum cannot form a compact roadbed material after being formed, and is easy to loosen and fall off after external force is applied.
The above results show that: the phosphogypsum roadbed material disclosed by the patent controls the components of a final calcined product to a great extent by regulating and controlling the preparation process; the prepared roadbed material fully utilizes the hydration characteristic of the alpha-semi-hydrated gypsum to realize the high strength and self-waterproof characteristic of the roadbed material. In addition, it needs to be further pointed out that in the use process of the phosphogypsum roadbed material, any cementing material is not needed to be added, 100% recycling of the solid waste phosphogypsum is realized, and the phosphogypsum roadbed material has important social, environmental and economic benefits.
The above embodiments are merely examples for clearly illustrating the present invention and do not limit the present invention. Other variants and modifications of the invention, which are obvious to those skilled in the art and can be made on the basis of the above description, are not necessary or exhaustive for all embodiments, and are therefore within the scope of the invention.
Claims (5)
1. A preparation method of a high-strength self-waterproof phosphogypsum roadbed material is characterized by comprising the following steps:
1) Providing a phosphogypsum raw material with a certain water content;
2) In a closed sintering device, heating the phosphogypsum raw material obtained in the step 1) to 150-170 ℃ for calcining, and then cooling and crushing to obtain modified phosphogypsum powder with the crystal water content of 1-4%;
3) Adding a proper amount of retarder into the obtained modified phosphogypsum powder, uniformly stirring, adding a proper amount of water, stirring, stewing and forming to obtain the phosphogypsum roadbed material;
the water content of the phosphogypsum raw material is 20-30wt%; the calcination treatment time is 8-16h;
the ratio of the mass of the phosphogypsum raw material in the closed sintering equipment to the volume of the closed sintering equipment is (200-300) g:1L;
the mixing amount of the water in the step 3) is 23-27% of the mass of the modified phosphogypsum powder;
the stewing time is 3-5h.
2. The preparation method according to claim 1, wherein the phosphogypsum raw material is a phosphogypsum solid waste provided by a phosphate fertilizer or phosphoric acid production plant; wherein the content of the calcium sulfate dihydrate accounts for 70-95% of the total mass of the phosphogypsum.
3. The method as claimed in claim 1, wherein the pulverizing step is carried out by using a high-speed rotary pulverizer at 20000-25000r/min for 5-8s.
4. The preparation method of claim 1, wherein the retarder is a protein retarder, and the mixing amount of the protein retarder is 0.3-0.7% of the mass of the modified phosphogypsum powder.
5. The high-strength self-waterproof phosphogypsum roadbed material prepared by the preparation method of any one of the claims 1-4.
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