CN118026560A - Basic magnesium sulfate cement and preparation method thereof - Google Patents
Basic magnesium sulfate cement and preparation method thereof Download PDFInfo
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- CN118026560A CN118026560A CN202311759176.0A CN202311759176A CN118026560A CN 118026560 A CN118026560 A CN 118026560A CN 202311759176 A CN202311759176 A CN 202311759176A CN 118026560 A CN118026560 A CN 118026560A
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- magnesium sulfate
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- sulfate cement
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- CSNNHWWHGAXBCP-UHFFFAOYSA-L Magnesium sulfate Chemical compound [Mg+2].[O-][S+2]([O-])([O-])[O-] CSNNHWWHGAXBCP-UHFFFAOYSA-L 0.000 title claims abstract description 112
- 239000004568 cement Substances 0.000 title claims abstract description 63
- 229910052943 magnesium sulfate Inorganic materials 0.000 title claims abstract description 56
- 235000019341 magnesium sulphate Nutrition 0.000 title claims abstract description 51
- 238000002360 preparation method Methods 0.000 title claims abstract description 21
- 238000012360 testing method Methods 0.000 claims abstract description 79
- 238000011282 treatment Methods 0.000 claims abstract description 48
- 239000000395 magnesium oxide Substances 0.000 claims abstract description 33
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 33
- 235000019796 monopotassium phosphate Nutrition 0.000 claims abstract description 27
- 229910000402 monopotassium phosphate Inorganic materials 0.000 claims abstract description 25
- 238000000034 method Methods 0.000 claims abstract description 23
- 238000007598 dipping method Methods 0.000 claims abstract description 22
- 239000000126 substance Substances 0.000 claims abstract description 22
- 238000005507 spraying Methods 0.000 claims abstract description 21
- 239000000654 additive Substances 0.000 claims abstract description 17
- 239000013078 crystal Substances 0.000 claims abstract description 14
- 238000003756 stirring Methods 0.000 claims abstract description 14
- GNSKLFRGEWLPPA-UHFFFAOYSA-M potassium dihydrogen phosphate Chemical compound [K+].OP(O)([O-])=O GNSKLFRGEWLPPA-UHFFFAOYSA-M 0.000 claims abstract description 10
- 238000001816 cooling Methods 0.000 claims abstract description 8
- 239000010881 fly ash Substances 0.000 claims abstract description 8
- LWIHDJKSTIGBAC-UHFFFAOYSA-K potassium phosphate Substances [K+].[K+].[K+].[O-]P([O-])([O-])=O LWIHDJKSTIGBAC-UHFFFAOYSA-K 0.000 claims abstract description 8
- 238000002156 mixing Methods 0.000 claims abstract description 4
- 238000002791 soaking Methods 0.000 claims description 32
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 claims description 21
- PJNZPQUBCPKICU-UHFFFAOYSA-N phosphoric acid;potassium Chemical compound [K].OP(O)(O)=O PJNZPQUBCPKICU-UHFFFAOYSA-N 0.000 claims description 17
- 230000000996 additive effect Effects 0.000 claims description 11
- 238000012423 maintenance Methods 0.000 claims description 11
- 230000008569 process Effects 0.000 claims description 9
- 238000011418 maintenance treatment Methods 0.000 claims description 7
- 239000001509 sodium citrate Substances 0.000 claims description 7
- NLJMYIDDQXHKNR-UHFFFAOYSA-K sodium citrate Chemical compound O.O.[Na+].[Na+].[Na+].[O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O NLJMYIDDQXHKNR-UHFFFAOYSA-K 0.000 claims description 7
- 239000000203 mixture Substances 0.000 claims description 4
- CPLXHLVBOLITMK-UHFFFAOYSA-N Magnesium oxide Chemical compound [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 52
- 238000006703 hydration reaction Methods 0.000 description 16
- 230000036571 hydration Effects 0.000 description 15
- 239000007921 spray Substances 0.000 description 14
- 238000007654 immersion Methods 0.000 description 12
- 229920006395 saturated elastomer Polymers 0.000 description 10
- 230000008859 change Effects 0.000 description 8
- 239000011777 magnesium Substances 0.000 description 8
- 239000000463 material Substances 0.000 description 8
- 230000000052 comparative effect Effects 0.000 description 5
- 239000011159 matrix material Substances 0.000 description 5
- 230000004048 modification Effects 0.000 description 5
- 238000012986 modification Methods 0.000 description 5
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 description 3
- 229910019142 PO4 Inorganic materials 0.000 description 3
- 150000001447 alkali salts Chemical group 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 230000003247 decreasing effect Effects 0.000 description 3
- 238000011161 development Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 description 3
- 238000005457 optimization Methods 0.000 description 3
- 239000011148 porous material Substances 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 230000009467 reduction Effects 0.000 description 3
- 238000011160 research Methods 0.000 description 3
- 238000001228 spectrum Methods 0.000 description 3
- 230000002195 synergetic effect Effects 0.000 description 3
- 230000009466 transformation Effects 0.000 description 3
- 238000002425 crystallisation Methods 0.000 description 2
- 230000008025 crystallization Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 229910052500 inorganic mineral Inorganic materials 0.000 description 2
- 235000010755 mineral Nutrition 0.000 description 2
- 239000011707 mineral Substances 0.000 description 2
- 229940111688 monobasic potassium phosphate Drugs 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 206010058314 Dysplasia Diseases 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000004566 building material Substances 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000012669 compression test Methods 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-M dihydrogenphosphate Chemical compound OP(O)([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-M 0.000 description 1
- 238000004134 energy conservation Methods 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000011049 filling Methods 0.000 description 1
- 238000005470 impregnation Methods 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 238000011068 loading method Methods 0.000 description 1
- GVALZJMUIHGIMD-UHFFFAOYSA-H magnesium phosphate Chemical compound [Mg+2].[Mg+2].[Mg+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O GVALZJMUIHGIMD-UHFFFAOYSA-H 0.000 description 1
- 239000004137 magnesium phosphate Substances 0.000 description 1
- 229960002261 magnesium phosphate Drugs 0.000 description 1
- 229910000157 magnesium phosphate Inorganic materials 0.000 description 1
- 235000010994 magnesium phosphates Nutrition 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000005192 partition Methods 0.000 description 1
- 230000035515 penetration Effects 0.000 description 1
- 239000010452 phosphate Substances 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 1
- 230000008092 positive effect Effects 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000004445 quantitative analysis Methods 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 239000002910 solid waste Substances 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- OLZDXDPSDUSGIS-UHFFFAOYSA-N sulfinylmagnesium Chemical compound [Mg].S=O OLZDXDPSDUSGIS-UHFFFAOYSA-N 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
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- Curing Cements, Concrete, And Artificial Stone (AREA)
Abstract
The invention provides basic magnesium sulfate cement and a preparation method thereof, wherein the method comprises the following steps: s1: basic magnesium sulfate cement preparation: preparing MgSO 4·7H2 O, adding water and stirring until crystals are completely dissolved to obtain MgSO 4·7H2 O solution, cooling, and further adding MgO, fly ash and chemical additives for mixing and stirring to obtain basic magnesium sulfate cement paste; pouring the basic magnesium sulfate cement paste prepared in the step S1 into a mould to form a basic magnesium sulfate cement sample; s2: curing: and then carrying out primary air curing on the sample before demolding, further placing the sample into a curing box for secondary air curing, then adopting monopotassium phosphate solution to carry out spraying and/or dipping curing treatment on the sample, placing the test block back into the curing box for curing after the treatment is finished, and carrying out dipping treatment on the test block after the curing is finished to obtain the basic magnesium sulfate cement. The basic magnesium sulfate cement prepared by the method has good water resistance and high strength, and has higher commercial value and popularization value.
Description
Technical Field
The invention relates to the field of preparation of basic magnesium sulfate cement, in particular to basic magnesium sulfate cement and a preparation method thereof.
Background
Basic Magnesium Sulfate Cement (BMSC) is a novel magnesia cementing material obtained by modifying traditional Magnesium Oxysulfide (MOS) cement by chemical additives, and is prepared by light burned magnesia powder (MgO), magnesium sulfate (MgSO 4·7H2 O), water and a small amount of chemical additives according to a certain proportion, and is solidified and hardened in air, wherein the main strength hydration product is basic salt hydrate 5Mg (OH) 2·MgSO4·7H2 O phase (5.1.7 phase). BMSC has the excellent performances of light weight, low alkali, quick setting, early strength, high strength, fire resistance, rib protection and the like, and is commonly used for producing building materials such as light partition boards, fire-proof door core boards, decorative hanging boards and the like. The raw materials are rich in mineral resources, the production energy consumption is low, the utilization rate of solid waste is high, and the method has the advantages of energy conservation, material conservation, land conservation, low carbon emission and the like, is environment-friendly, is hopeful to become the core of ecological cement products in the future, and promotes the sustainable development of the building industry.
Magnesia cements are typical air-hardening cements, and the water stability of the hydration products is a major reason limiting their wide application. However, compared with the traditional MOS cement, the BMSC modified by the chemical additive has very low solubility of the hydration product 5.1.7 phase (good crystallinity), can exist stably in water for a long time without decomposition, so that the BMSC performance is changed in quality, and the compressive strength and the water resistance are remarkably improved. However, the expansion stress and volume deformation caused by the transformation of residual MgO of hydration product into Mg (OH) 2 after soaking still result in the reduction of BMSC compressive strength, and in addition, the dysplastic 5.1.7 phase may also encounter water to reduce BMSC cohesive strength.
Therefore, the BMSC after modification by the chemical additive still has the water resistance problem caused by the dysplasia of the 5.1.7 phase of the hydration product and the volume stability, and the problem that the current research needs to be focused on and solved. The further improvement of BMSC water resistance through micro-structure optimization and hydration product residual MgO conversion on the basis of chemical additive modification is a very urgent and important research subject in the development and application of magnesia cementing materials, and has important theoretical significance and practical significance for enriching the subject basis of magnesia cementing materials, perfecting the subject durability theoretical system of BMSC and promoting the development and application of BMSC in constructional engineering.
Disclosure of Invention
The invention aims to provide a preparation method of basic magnesium sulfate cement, which aims to solve the problems of general strength and poor water resistance of basic magnesium sulfate cement prepared by a conventional preparation method.
In order to solve the problems, the invention provides a preparation method of basic magnesium sulfate cement, which comprises the following steps:
S1: basic magnesium sulfate cement preparation: preparing MgSO 4·7H2 O, adding water and stirring until crystals are completely dissolved to obtain MgSO 4·7H2 O solution, cooling, and further adding MgO, fly ash and chemical additives for mixing and stirring to obtain basic magnesium sulfate cement paste; pouring the basic magnesium sulfate cement paste prepared in the step S1 into a mould to form a basic magnesium sulfate cement sample;
S2: curing: and then carrying out primary air curing on the sample before demolding, after the primary curing is finished, further placing the sample into a curing box for secondary air curing, then adopting a monopotassium phosphate solution with the concentration of more than or equal to 80% to carry out spraying and/or dipping curing treatment on the sample, placing the test block back into the curing box for curing after the treatment is finished, and then carrying out soaking treatment on the test block for 11-13 hours to obtain the basic magnesium sulfate cement.
In a preferred scheme, in the step S1, the molar ratio of MgO, mgSO 4·7H2 O and water is 8:1:10, and the addition amount of the fly ash is 30% of the mass of MgO.
As a preferable scheme, the chemical additive is a mixture of citric acid and sodium citrate, and the mass ratio of the citric acid to the sodium citrate is 1:3, and the addition amount of the chemical additive is 0.2% of the magnesium oxide based on the amount of the substance.
In the step S1, the temperature of the added water is 90-100 ℃ in the stirring process, and the water is continuously heated in the stirring process; the cooling conditions are as follows: cooled to room temperature.
As a preferable solution, in the step S2, the conditions of the first air curing are: curing for 24 hours at 20+/-2 ℃ and 60+/-5% relative humidity in standard air.
As a preferable solution, in the step S2, the conditions of the second air curing are: curing under standard air conditions to day 7.
Preferably, in the step S2, the concentration of the potassium dihydrogen phosphate solution is 90% -100%, and the spraying and/or soaking maintenance treatment time is 8-16 hours.
Preferably, the spraying and/or dipping treatment is carried out for 12 hours.
Preferably, the soaking (immersing) time is 12 hours, and the time for returning to the curing box is 3 days, namely, the curing is continued for 3 days under the standard air condition (20+/-2 ℃ C., 60+/-5%).
The invention aims to solve the other technical problem of providing basic magnesium sulfate cement to solve the problems of more cracks, general strength and poor stability of conventional basic magnesium sulfate cement.
The invention also provides basic magnesium sulfate cement, which is prepared by the preparation method.
The invention starts from the reduction cause of the compressive strength of the BMSC after soaking, the composition and the crystallization degree of the BMSC are regulated and controlled through the mole ratio of raw materials, the pH value of a mineral admixture and a chemical admixture, the stability of a hydration product 5.1.7 phase (5 Mg (OH) 2·MgSO4·7H2 O) is increased, the crystallization degree of the 5.1.7 phase is further regulated and controlled through the compounded chemical admixture comprising citric acid and sodium citrate with a specific ratio, the 5.1.7 phase generates thicker crystals, the microstructure optimization of the BMSC is realized, and according to the reaction principle of magnesium phosphate cement, the residual MgO of the hydration product is converted by adopting KH 2PO4 or NH 4H2PO4 solution impregnation treatment, and the volume stability and the pore filling rate of the BMSC after soaking are increased. Finally, the improvement of BMSC mechanical strength and water resistance is realized based on the optimization of micro-structure and the transformation of residual MgO.
The basic magnesium sulfate cement prepared by the preparation method of the basic magnesium sulfate cement has high mechanical strength, compact 5Mg (OH) 2·MgSO4·7H2 O crystal, high stability and reliability, good compactness of the product and high water resistance.
Drawings
FIG. 1 is a schematic illustration of sample flooding in an embodiment;
FIG. 2 is a schematic diagram of a block compression test in an embodiment;
FIG. 3 is a graph showing the change in strength of each group of test pieces after spray curing for different periods of time using different concentrations of potassium dihydrogen phosphate solution;
in FIG. 3, the columns with immersion time 0 are control groups cured with standard air only, and other immersion times are grouped with saturated, 90%, 80%, 0% strength monobasic potassium phosphate solutions in that order;
FIG. 4 is a graph showing the strength change of each group of test blocks after soaking after spray curing;
In FIG. 4, the columns with immersion time 0 are control groups maintained only with standard air, and other immersion times are grouped with saturated, 90%, 80%, 0% strength monobasic potassium phosphate solutions in that order;
FIG. 5 is a graph showing the rate of change of the volume of a test block at different stages;
wherein a, b, c, d respectively corresponds to groups of saturated, 90%, 80% and 0% concentration potassium dihydrogen phosphate solutions;
in the graph a, when the abscissa is 2-3, the broken lines from top to bottom sequentially correspond to groups of saturation 12h, saturation 16h and saturation 24 h;
in the graph b, when the abscissa is 2-3, the broken lines from top to bottom correspond to groups of 90%12h, 90%16h and 90%24h in sequence;
In the graph c, when the abscissa is 2-3, the broken lines from top to bottom correspond to groups of 80%12h, 80%16h and 80%24h in sequence;
in the graph d, when the abscissa is 2-3, the broken lines from top to bottom sequentially correspond to groups of 0 16h, 0 12h and 024 h;
FIG. 6 is a microstructure of a test block treated with solutions of different concentrations;
Wherein, the left graph is a microstructure of the test block after being sprayed and cured by the saturated concentration solution, and the right graph is a microstructure of the test block after being sprayed and cured by the 90% concentration solution;
FIG. 7 is a microstructure of a test block after immersion in solutions of different concentrations;
Wherein, the left graph is a microstructure of the immersed test block treated by the saturated concentration solution, and the right graph is a microstructure of the immersed test block treated by the 90% concentration solution;
FIG. 8 is an XRD spectrum of a test block under different treatments;
wherein J and BJ respectively represent the water immersion after spray curing and the primary spray curing treatment, and B (saturated) and 90 (90%) respectively represent the concentration of the spray curing solution.
Detailed Description
The following description of the present invention will be made clearly and fully, and it is apparent that the embodiments described are some, but not all, of the embodiments of the present invention. All embodiments obtained by a person of ordinary skill in the art without making any inventive effort based on the embodiments of the present invention are within the scope of the present invention.
The invention provides basic magnesium sulfate cement and a preparation method thereof, wherein the basic magnesium sulfate cement comprises the following steps:
S1: basic magnesium sulfate cement preparation: preparing MgSO 4·7H2 O, adding water and stirring until crystals are completely dissolved to obtain MgSO 4·7H2 O solution, cooling, and further adding MgO, fly ash and chemical additives for mixing and stirring to obtain basic magnesium sulfate cement paste; pouring the basic magnesium sulfate cement paste prepared in the step S1 into a mould to form a basic magnesium sulfate cement sample;
S2: curing: then carrying out primary air curing on the sample before demolding, after the primary curing is finished, further placing the sample into a curing box for secondary air curing, then adopting a monopotassium phosphate solution with the concentration of more than or equal to 80% to carry out spraying and/or dipping curing treatment on the sample, placing the test block into the curing box for curing after the treatment is finished, and then carrying out soaking treatment on the test block for 11-13 hours to obtain basic magnesium sulfate cement; said method.
In a preferred scheme, in the step S1, the molar ratio of MgO, mgSO 4·7H2 O and water is 8:1:10, and the addition amount of the fly ash is 30% of the mass of MgO.
As a preferable scheme, the chemical additive is a mixture of citric acid and sodium citrate, and the mass ratio of the citric acid to the sodium citrate is 1:3, and the addition amount of the chemical additive is 0.2% of the magnesium oxide based on the amount of the substance.
In the step S1, the temperature of the added water is 90-100 ℃ in the stirring process, and the water is continuously heated in the stirring process; the cooling conditions are as follows: cooled to room temperature.
As a preferable solution, in the step S2, the conditions of the first air curing are: curing for 24 hours at 20+/-2 ℃ and 60+/-5% relative humidity in standard air.
As a preferable solution, in the step S2, the conditions of the second air curing are: curing in an air curing box for 7 days.
Preferably, in the step S2, the concentration of the potassium dihydrogen phosphate solution is 90% -100%, and the spraying and/or soaking maintenance treatment time is 8-16 hours.
Preferably, the spraying and/or dipping maintenance treatment is carried out for 12 hours.
Preferably, the time of the soaking treatment is 12 hours, and the time of the soaking treatment is 3 days.
The invention also provides basic magnesium sulfate cement, which is prepared by the preparation method.
The following provides specific examples to develop and explain the above technical solutions of the present invention:
Example 1:
S1: basic magnesium sulfate cement preparation: the molar ratio of the raw materials of alpha-MgO (active magnesium oxide) and MgSO 4·7H2O、H2 O required for preparing BMSC cement is 8:1:10. During preparation, mgSO 4·7H2 O is dissolved by hot water at 90-100 ℃, and is continuously heated and stirred until crystals are completely dissolved to obtain MgSO 4·7H2 O solution, after cooling to room temperature, the MgSO 4·7H2 O solution is mixed with MgO, fly ash and a chemical additive, and stirred for 4 minutes to obtain uniform BMSC cement paste, wherein the addition amount of the chemical additive is 0.2 percent of the molar amount of MgO, and the BMSC cement paste is molded under a steel mold with the molar amount of 40X 40mm 3 and the molar amount of 40X 160mm 3 and is respectively used for measuring the strength and the volume deformation of a test block;
S2: curing: before the sample is demolded, the sample is subjected to primary standard air curing for 24 hours at the temperature of 20+/-2 ℃ and the relative humidity of 60+/-5%, then is placed in a curing box for secondary standard air curing for seven days, then the test block is subjected to spray curing treatment (8-16 hours) by using a saturated concentration potassium dihydrogen phosphate solution according to time groups, the test block is placed back into the curing box for curing for three days after the treatment is finished, as shown in fig. 1, and then is subjected to water soaking treatment, wherein the water soaking time is 12 hours, and volume measurement is carried out in the curing process.
Example 2:
Example 2 is similar to example 1, except that: in the step S2, the concentration of the potassium dihydrogen phosphate solution is 90%;
example 3:
example 3 is similar to example 1, except that: in the step S2, the concentration of the potassium dihydrogen phosphate solution is 80%;
example 4:
example 4 is similar to example 1, except that: in the step S2, the spraying maintenance time is 10 hours;
example 5:
example 5 is similar to example 1, except that: in the step S2, the spraying maintenance time is 16 hours;
Example 6:
example 6 is similar to example 1, except that: in the step S2, the soaking time is 11 hours;
example 7:
Example 7 is similar to example 1 except that: in the step S2, the soaking time is 13 hours;
example 8:
example 8 is similar to example 1, except that: in the step S2, soaking maintenance treatment is adopted, namely, a sample is put into a monopotassium phosphate solution with the same concentration for soaking treatment;
Comparative example:
The present invention sets up a number of control experiments, providing a number of comparative examples for comparison, as shown in the contents of fig. 3-8, and fig. 3-8 provide performance data for a number of comparative examples, as well as the relevant stages and final products of the embodiments of the present invention:
The method specifically comprises the following steps:
in the step S2, a potassium dihydrogen phosphate solution with the concentration of 0, namely water, is adopted as a comparison condition; in the step S2, the spraying time is 1/3/5/8/16/24 hours in sequence as a comparison condition; in the step S2, soaking time is 0/24 hour in sequence as a comparison condition; and standard air curing was used as a control condition.
The above examples and comparative examples were subjected to test comparison of correlation properties, and the test methods and results are as follows:
the testing method comprises the following steps:
the clamp was held against the block as shown in FIG. 2, and the compressive strength was measured at a loading rate of 2400N/s. The mean value of the three samples was taken with a deviation of + -10% as the compressive strength of the BMSC samples.
After the test block was demolded, the volume was measured once each before and after the spray treatment with a monopotassium phosphate solution and with a vernier caliper (precision 0.01), thereby obtaining the volume deformation during maintenance.
The sample was dried under vacuum for at least 72 hours prior to sample preparation, the sample for XRD quantitative analysis was ground to a powder (about 70 μm), and XRD data was collected under CuK alpha radiation in the 2 theta range of 5-70 deg., at a scan rate of 2 deg./min. BMSC cement samples for microscopic testing were sectioned at the desired age by a precision cutter and soaked in isopropyl alcohol to terminate the hydration reaction. Cutting a sample for microscopic morphology test into slices, spraying metal, and observing fracture morphology by using a scanning electron microscope.
Experimental data and analysis
Compressive strength test:
FIG. 3 shows the strength change of the test block after the dipping treatment with potassium dihydrogen phosphate solutions of different concentrations for different times, the treatment process is called dipping maintenance, and the same manner can be adopted, namely the dipping treatment manner is adopted in the following description of the invention, and the result is similar.
By observing the results of spray curing of the monopotassium phosphate solutions of all concentrations, it was found that the compressive strength of BMSC cements as a whole tended to rise first and then fall with increasing spray time, and peaked at 12 hours, i.e., the treatment conditions of inventive example 1. Under standard air curing, the main hydration products of the test block include basic salt hydrate 5Mg (OH) 2·MgSO4·7H2 O (abbreviated as 5.1.7 phases, hereinafter the same), mg (OH) 2 and unhydrated MgO. After the treatment of the potassium dihydrogen phosphate solution, the rest MgO is converted into Mg (OH) 2, and the 5.1.7 phase crystals become stronger, so that the test block is strengthened, and the compressive strength of the test block is improved.
It is noted that the strength of the test block is significantly improved after time-limited dip curing under the conditions of the present invention (8-16 hours, and the corresponding time after different spray times at specific concentrations is greater than standard air curing as shown in fig. 1), which is more pronounced with saturated and 90% strength solutions than standard air curing, blank and dip groups. This shows that the spraying treatment or the dipping treatment of the potassium dihydrogen phosphate solution plays a positive role in improving the performance of BMSC cement. This enhancement is mainly reflected in the modification of the crystal structure and in the conversion of unhydrated material. Through the test, the performance of BMSC cement under different conditions can be more fully known, and powerful support is provided for the research and application of the invention.
As shown in fig. 4, fig. 4 is a graph showing the strength change of the immersed and maintained test block after immersion, and the strength of the test block is reduced and then slightly increased with the increase of the spraying time after the treatment of the saturated concentration solution; for the test block treated by the 90% concentration solution, the strength is slightly reduced; the strength of the test block treated with the 80% concentration solution is obviously reduced, and on the contrary, the strength of the test block which is always immersed in water is improved after immersion. By the rising trend of the strength of the dipping curing group of the monopotassium phosphate solution, we can know that the unhydrated residual MgO exists in the test block which is not treated by the solution, and the residual MgO is gradually converted into Mg (OH) 2 along with the increase of the first spraying time, so that the strength is increased, therefore, the dipping time is required to be controlled within the limit range of the invention, and the performance of the product can be further improved.
The invention also uses the above-mentioned multiple standard air curing, spraying/dipping curing and soaking curing by specific concentration potassium dihydrogen phosphate solution, and multiple synergistic action, finally raising the performance of test block.
Furthermore, by the results of the immersed solution group, it was observed that the immersed group as a whole was significantly reduced in strength as compared with the blank group and the three solution-treated groups. In contrast, the strength of the block treated with the potassium dihydrogen phosphate solution was enhanced, and especially the block subjected to the water-immersed maintenance for 12 hours had the highest strength, indicating that the saturation and 90% concentration treatment effects were good, i.e., the treatment conditions of example 1/2 of the present invention.
Volumetric deformation test:
as shown in fig. 5, fig. 5 shows the change in volume deformation of the test block during the dipping curing for different times using different concentrations of potassium dihydrogen phosphate. By observing the pictures, the volume deformation rate of the test block is positive under the treatment of solutions with different concentrations for the first time, namely, the test block is expanded. The volume deformation rate gradually decreases with the extension of the spray curing time. In connection with the intensity data in fig. 3/4 of the present invention, it can be concluded that: with the increase of the dipping curing time, the strength of the test block is in a decreasing trend, and for the test block with longer spraying curing time, the change of the volume deformation rate is more severe, and the conditions of expanding first and then contracting second and the like possibly occur, so that the strength is decreased.
Under the action of the soaking treatment, the relation between the volume deformation rate and the strength of the test block is similar to that of the soaking maintenance treatment. After soaking, the test block swells again, but the volume deformation rate is smaller than that of soaking maintenance. In addition, after the immersion treatment, the strength of the test piece was decreased with the increase of the shower maintenance time. This result shows that the re-dipping and curing treatment has an effect on the volume deformation and strength of the test block, and also shows that the dipping and curing time has a critical effect on the performance of the test block.
Scanning by using an electron microscope:
As shown in FIG. 6 and FIG. 7, FIG. 6/7 is a microstructure characteristic diagram of a test block under the treatment of saturated and 90% concentration solution spray curing. Since the BMSC test block hydration product contains not only the basic salt hydrate 5Mg (OH) 2·MgSO4·7H2 O (5·1·7 phases), mg (OH) 2, which provides strength, but also the remaining MgO that is not hydrated, this may cause the material to assume a loose state. However, after spray curing, a large amount of Mg (OH) 2 in the shape of a sheet or flower is remarkably present in the matrix of the test block material, and meanwhile, the 5.1.7 phase crystals in the shape of a needle exhibit a very thick form, which provides strength to the material. In addition, the generated Mg (OH) 2 and 5.1.7 phase crystals are embedded into the matrix, so that not only is the compactness of the matrix improved, but also pores can be filled, water penetration is reduced, and the process is beneficial to improving the overall performance of the test block and improving the strength, water resistance and durability of the test block.
After the test block is subjected to phosphate soaking maintenance and then soaking treatment, the substrate becomes denser obviously from the microstructure. In addition, mg (OH) 2 embedded on the matrix is reduced (form transformation occurs) and instead is a more abundant 5.1.7 phase crystal. By combining the strength test data of the invention, the strength of the test block which is soaked after solution treatment and is soaked after being soaked and maintained by the dihydrogen phosphate is obviously higher than that of the test block which is soaked all the time.
It is worth noting that the volume deformation of the test block after the dipping treatment is increased, the trend of slight expansion is presented, the early timely release of expansion stress is realized, the later-stage volume stability of BMSC is facilitated, the durability is improved, and the phenomenon is also reflected in the microstructure. This shows that the solution treatment has a positive effect on the overall strength of the test block, and at the same time, the structure of the test block is adjusted on a microscopic level so that the test block is more compact and ordered, which further shows that the quality inspection of the whole and each step of the invention has a synergistic effect.
XRD spectrum:
FIG. 8 is an XRD spectrum of a test block under different treatments, J and BJ respectively show the immersion treatment after immersion curing and the primary immersion curing treatment, and B and 90 respectively show the solution concentration of spray curing: XRD results show that the hydration products of the test block are the same in type after solution treatment, and the peaks of the main hydration products 5.1.7 and Mg (OH) 2 are not obviously changed before and after dip curing, so that the 5.1.7 phase has better stability, mg (OH) 2 generated in dip curing fills inter-crystal pores of the 5.1.7 phase, the compactness of the matrix is improved, and the compactness is also shown by data of strength and volume deformation rate, and under dip curing, the synergistic effect of residual MgO reduction and compact microstructure enables the test block to have higher compressive strength and water resistance.
By the above examples and tests on examples and comparative examples, it is further illustrated that:
(1) In the test block with the curing time of 12 hours by dipping (or spraying) the potassium dihydrogen phosphate solution, the strength of the test block is high whether the test block is dipped once or dipped again after dipping. After being subjected to soaking (or spraying) maintenance treatment by a scanning electron microscope, the hydration product in the test block is successfully converted into Mg (OH) 2, and the 5.1.7 phase crystals have a coarser structure, so that in the invention, 12 hours is the optimal soaking maintenance time, and the performance of the test block is better when the concentration of the potassium dihydrogen phosphate solution is controlled to be more than 80%, preferably more than 90%; the test block has better performance when the soaking time is controlled to be 11-13 hours, preferably 12 hours.
(2) With the increase of the dipping curing time, the volume deformation rate is gradually reduced, and the volume deformation is changed greatly. At the same time, the strength increases with increasing rate of volume deformation, which further supports the above-mentioned view of the best performance of the 12-hour spray-cured test block.
(3) After the test block is immersed and cured, the volume deformation is increased, and the test block is slightly expanded. By comparing the intensity with the rate of deformation of the volume, it can be seen that, substantially with increasing volume, the intensity increases accordingly. Thus, increasing the compactness of the test block and early release of the expansion stress also promotes strength enhancement of the test block.
(4) The hydration products of the 5.1.7 phases do not show obvious change after soaking, which shows that the 5.1.7 phases have better stability. This observation further underscores the reliability and stability of the hydration product in an aqueous environment.
Although the present disclosure is described above, the scope of protection of the present disclosure is not limited thereto. Various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the disclosure, and these changes and modifications will fall within the scope of the invention.
Claims (10)
1.A preparation method of basic magnesium sulfate cement is characterized in that: the method comprises the following steps:
S1: basic magnesium sulfate cement preparation: preparing MgSO 4·7H2 O, adding water and stirring until crystals are completely dissolved to obtain MgSO 4·7H2 O solution, cooling, and further adding MgO, fly ash and chemical additives for mixing and stirring to obtain basic magnesium sulfate cement paste; pouring the basic magnesium sulfate cement paste prepared in the step S1 into a mould to form a basic magnesium sulfate cement sample;
S2: curing: and then carrying out primary air curing on the sample before demolding, after the primary curing is finished, further placing the sample into a curing box for secondary air curing, then adopting a monopotassium phosphate solution with the concentration of more than or equal to 80% to carry out spraying and/or dipping curing treatment on the sample, placing the test block back into the curing box for continuous curing after the treatment is finished, and then carrying out soaking treatment on the test block for 11-13 hours to obtain the basic magnesium sulfate cement.
2. The method for preparing basic magnesium sulfate cement according to claim 1, wherein: in the step S1, the molar ratio of MgO, mgSO 4·7H2 O and water is 8:1:10; the addition amount of the fly ash is 30% of the mass of MgO.
3. The method for preparing basic magnesium sulfate cement according to claim 1, wherein: the chemical additive is a mixture of citric acid and sodium citrate, and the mass ratio of the citric acid to the sodium citrate is 1:3, and the addition amount of the chemical additive is 0.2% of the MgO in terms of the amount of the substance.
4. The method for preparing basic magnesium sulfate cement according to claim 1, wherein: in the step S1, the temperature of the added water is 90-100 ℃ in the stirring process, and the water is continuously heated in the stirring process; the cooling conditions are as follows: cooled to room temperature.
5. The method for preparing basic magnesium sulfate cement according to claim 1, wherein: in the step S2, the conditions of the first air curing are as follows: curing for 24 hours at 20+/-2 ℃ and 60+/-5% relative humidity in standard air.
6. The method for preparing basic magnesium sulfate cement according to claim 1, wherein: in the step S2, the conditions of the secondary air curing are as follows: curing under standard air conditions to day 7.
7. The method for preparing basic magnesium sulfate cement according to claim 1, wherein: in the step S2, the concentration of the potassium dihydrogen phosphate solution is 90% -100%, and the spraying and/or soaking maintenance treatment time is 8-16 hours.
8. The method for preparing basic magnesium sulfate cement according to claim 7, wherein: in the step S2, the spraying and/or impregnating curing treatment time is 12 hours.
9. The method for preparing basic magnesium sulfate cement according to claim 1, wherein: in the step S2, the time of the soaking treatment is 12 hours, and the time of the continuous maintenance in the replacement maintenance box is 3 days.
10. Basic magnesium sulfate cement, characterized in that: the basic magnesium sulfate cement is prepared by the preparation method of any one of claims 1 to 9.
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