Composite delayed coagulation type magnesium phosphate cement and preparation method thereof

Abstract

The invention discloses composite delayed coagulation type magnesium phosphate cement and a preparation method thereof, and relates to the technical field of building materials, the composite delayed coagulation type magnesium phosphate cement comprises a dead burned magnesium oxide and mineral admixture mixture, phosphate, a composite retarder and glue-containing water, in the dead burned magnesium oxide and the mineral admixture, the mass ratio of dead burned magnesium oxide to the mineral admixture is 3: 2, and the mass ratio of phosphate to the composite retarder to the glue-containing water is 1: 1. The mass ratio of the dead burned magnesium oxide and mineral admixture mixture to the phosphate is 3: 1, the mass of the composite retarder is 7-24% of the mass of the dead burned magnesium oxide and mineral admixture mixture, and the water-binder ratio in the glue is 0.18-0.20. The preparation method comprises the steps of high-temperature pretreatment of the mineral admixture, metering and dry mixing of all the components and cement mixing. The attapulgite and the kaolin which are treated at high temperature are mixed with dead burned magnesium oxide, so that the heat release rate at the initial stage of a hydration reaction is reduced, the cement setting time is prolonged, meanwhile, micro holes and cracks in a cement matrix can be filled, the compactness of a magnesium phosphate matrix is improved, and finally the strengths at different ages are improved.

Description

Technical Field

[0001] The invention relates to the technical field of building materials, and in particular to a composite slow-setting magnesium phosphate cement and a preparation method thereof. Background Art

[0002] Magnesium phosphate cement is an inorganic cementitious material that is made of high-temperature calcined magnesium oxide, soluble acid phosphate, and mineral admixtures as raw materials, mixed in a certain proportion, and quickly solidifies and hardens to produce a certain strength after adding water. Compared with traditional silicate cement, magnesium phosphate cement has the advantages of short setting time, high early strength, stable volume, good wear resistance and frost resistance, and can be stably bonded with used old concrete. Therefore, it can be used to quickly repair local damage or structural failure of buildings. It has great advantages and development prospects in the field of rapid repair in civil engineering. However, during the hydration process of magnesium phosphate cement, the strong acid-base reaction releases a large amount of heat, which increases the temperature in the system, and the early hydration reaction is violent, resulting in an extremely fast setting speed, which generally does not exceed 6 minutes without adding a retarder. The time left for construction personnel to operate is extremely short, which greatly limits the application of magnesium phosphate cement.

[0003] Studies have shown that the addition of retarders can have a certain effect on the heat release rate of the magnesium phosphate cement system in the early stage, reduce the hydration heat release during the cement hardening process, prolong the time required to reach the peak hydration temperature, and prolong its setting and hardening time, thereby meeting the construction operability requirements. Currently, borax is mainly used as a retarder for magnesium phosphate cement, but under the action of traditional retarders such as borax, the setting time of magnesium phosphate cement generally does not exceed 30 minutes, and with the increase in the amount of retarders such as borax, the strength of magnesium phosphate cement will decrease.

[0004] Therefore, it is urgent to study a new type of slow-setting magnesium phosphate cement. Summary of the invention

[0005] In order to solve the above technical problems, the present invention discloses a composite retarded magnesium phosphate cement and a preparation method thereof. The magnesium phosphate cement prepared by the method has the advantages of adjustable setting time and reliable strength development at various ages. While using a composite retarder to extend the setting time of the magnesium phosphate cement, adding attapulgite and kaolin treated at a high temperature of 550°C can take into account both the early strength and the late strength of the magnesium phosphate cement matrix.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The first aspect of the present invention proposes a composite retarded magnesium phosphate cement, comprising a mixture of dead-burned magnesium oxide and mineral admixtures, phosphate, a composite retarder, and glue-containing water, wherein the mass ratio of the dead-burned magnesium oxide and the mineral admixture is 3:2, the mass ratio of the mixture of the dead-burned magnesium oxide and the mineral admixture to the phosphate is 3:1, the mass of the composite retarder is 7% to 24% of the mass of the mixture of the dead-burned magnesium oxide and the mineral admixture, and the water-binder ratio in the glue-containing water is 0.18 to 0.20.

[0008] Optionally, the dead-burned magnesium oxide is prepared by calcining magnesite at a temperature of 1000-1500° C., with a mass fraction of >95%.

[0009] Optionally, the phosphate has a specific surface area of ​​not less than 260 m 2 / kg of potassium dihydrogen phosphate.

[0010] Optionally, the mineral admixture is at least one of attapulgite and kaolin treated at high temperature, the attapulgite content is 0% to 40%, and the kaolin content is 0% to 40%.

[0011] Optionally, the composite retarder is composed of borax, glucose, ethylenediaminetetraacetate and chitosan, accounting for 2.5%, 2% to 8%, 2% to 8%, and 1% to 4% of the mass of the mixture of dead-burned magnesium oxide and mineral admixtures, respectively.

[0012] Optionally, the ethylenediaminetetraacetate salt is one or two of disodium ethylenediaminetetraacetate, dipotassium ethylenediaminetetraacetate, and ferric ethylenediaminetetraacetate.

[0013] The second aspect of the present invention provides a method for preparing the above-mentioned composite slow-setting magnesium phosphate cement, comprising the following steps:

[0014] (1) High-temperature pretreatment of mineral admixtures: The weighed mineral admixtures are subjected to high-temperature treatment and ground in a ball mill to a specific surface area of ​​400 m 2 / kg;

[0015] (2) Measuring and dry mixing of each component: first, adding the mineral admixture after high temperature pretreatment to the dead-burned magnesium oxide powder in proportion and stirring evenly to obtain a mixture of the dead-burned magnesium oxide and the mineral admixture; adding chitosan to the phosphate and stirring evenly; then mixing the mixture of the dead-burned magnesium oxide and the mineral admixture with the phosphate added with chitosan to obtain an intermediate material; weighing borax, glucose and ethylenediaminetetraacetate according to the proportion, mixing them thoroughly to obtain a composite retarder;

[0016] (3) Cement mixing: first, add the composite retarder into the glue-containing water and stir until fully dissolved. Then, add the composite retarder solution into the intermediate material obtained in step (2) and stir fully to obtain composite retarded magnesium phosphate cement.

[0017] Optionally, in step (1), the high temperature treatment is heating in a high temperature furnace at a temperature of 550° C. for 60 minutes.

[0018] Optionally, in step (2), the phosphate has a specific surface area of ​​not less than 260 m 2 / kg of potassium dihydrogen phosphate.

[0019] Optionally, in step (2), the ethylenediaminetetraacetic acid salt is one or two of disodium ethylenediaminetetraacetate, dipotassium ethylenediaminetetraacetate, and ferric ethylenediaminetetraacetate.

[0020] In step (2), the reason why phosphate is first mixed with chitosan is that chitosan is slightly soluble in water and soluble in acid solution. Mixing it with phosphate in advance can make it adhere to the phosphate better and dissolve better in the subsequent mixing process of adding water, thereby effectively inhibiting the early hydration rate of cement.

[0021] The beneficial effect of the present invention is that the present invention mixes high-temperature treated attapulgite and / or kaolin with dead-burned magnesium oxide, which reduces the heat release rate in the initial stage of the hydration reaction to a certain extent, prolongs the setting time of magnesium phosphate cement, and can also fill tiny holes and cracks in the cement matrix, thereby improving the density of the magnesium phosphate matrix, and ultimately improving the strength at different ages. The synergistic effect of mineral admixtures and composite retarders greatly prolongs the setting time of magnesium phosphate cement, which largely alleviates the problem of a significant decrease in the strength of magnesium phosphate cement caused by existing retarders.

[0022] The addition of composite retarder makes the setting time adjustable. The components in the composite retarder regulate the setting time of magnesium phosphate cement through staged synergistic action. First, the dissolution of borax absorbs heat, the system temperature decreases, and the hydration reaction is initially slowed down. At the same time, the dissolved glucose and borax will be adsorbed on the surface of dead-burned magnesium oxide particles to form a protective film to prevent it from contacting the outside, further slowing down the initial hydration rate. As the reaction proceeds, the pH and temperature of the solution gradually increase, the protective film on the surface of the dead-burned magnesium oxide particles is gradually destroyed, the dead-burned magnesium oxide contacts and reacts with the solution, and the Mg in the solution 2+ Increase, at this time EDTA and chitosan to Mg in solution 2+ Finally, as the pH and temperature of the solution further increase, the early synergistic mechanism gradually fails, and Mg 2+After being released, the reaction continues. The composite retarder can gradually release the heat of the matrix in the initial hydration stage, avoiding the problem of intense hydration reaction caused by heat concentration in the initial stage of hydration. At the same time, the gradual progress of the hydration reaction also ensures that the final product of the hydration reaction does not decrease, so the strength at each age does not drop significantly, achieving a balance between extending the setting time and developing the cement strength. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention is clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

[0024] A composite slow-setting magnesium phosphate cement comprises a mixture of dead-burned magnesium oxide and mineral admixtures, phosphate, a composite retarder and glue-containing water, wherein the mass ratio of the dead-burned magnesium oxide and the mineral admixture is 3:2, the mass ratio of the mixture of the dead-burned magnesium oxide and the mineral admixture to the phosphate is 3:1, the mass of the composite retarder is 7% to 24% of the mass of the mixture of the dead-burned magnesium oxide and the mineral admixture, and the water-binder ratio in the glue-containing water is 0.18 to 0.20.

[0025] Optionally, the dead-burned magnesium oxide is prepared by calcining magnesite at a temperature of 1000-1500° C., with a mass fraction of >95%.

[0026] Optionally, the phosphate has a specific surface area of ​​not less than 260 m 2 / kg of potassium dihydrogen phosphate.

[0027] Optionally, the mineral admixture is at least one of attapulgite and kaolin treated at high temperature, the attapulgite content is 0% to 40%, and the kaolin content is 0% to 40%. The sum of the dead-burned magnesium oxide and the mineral admixture is 100%.

[0028] Optionally, the composite retarder is composed of borax, glucose, ethylenediaminetetraacetate and chitosan, accounting for 2.5%, 2% to 8%, 2% to 8%, and 1% to 4% of the mass of the mixture of dead-burned magnesium oxide and mineral admixtures, respectively.

[0029] Optionally, the ethylenediaminetetraacetate salt is one or two of disodium ethylenediaminetetraacetate, dipotassium ethylenediaminetetraacetate, and ferric ethylenediaminetetraacetate.

[0030] The preparation method of the composite slow-setting magnesium phosphate cement comprises the following steps:

[0031] (1) High-temperature pretreatment of mineral admixtures: The weighed mineral admixtures were subjected to high-temperature treatment by heating them in a high-temperature furnace at 550°C for 60 min and then grinding them in a ball mill to a specific surface area of ​​400 m 2 / kg;

[0032] (2) Measuring and dry mixing of each component: first, adding the mineral admixture after high temperature pretreatment to the dead-burned magnesium oxide powder in proportion and stirring evenly to obtain a mixture of the dead-burned magnesium oxide and the mineral admixture; adding chitosan to potassium dihydrogen phosphate and stirring evenly; then mixing the mixture of the dead-burned magnesium oxide and the mineral admixture with the potassium dihydrogen phosphate added with chitosan to obtain an intermediate material; weighing borax, glucose and ethylenediaminetetraacetate according to the proportion, mixing them thoroughly to obtain a composite retarder;

[0033] (3) Cement mixing: first, add the composite retarder into the glue-containing water and stir until fully dissolved. Then, add the composite retarder solution into the intermediate material obtained in step (2) and stir fully to obtain composite retarded magnesium phosphate cement.

[0034] Embodiment 1:

[0035] Each raw material is weighed according to the mass percentage, specifically: in the mixture of dead-burned magnesium oxide and mineral admixtures, the dead-burned magnesium oxide is 60%, the attapulgite is 15%, and the kaolin is 25%; the mass ratio of the total mass of the mixture of dead-burned magnesium oxide and mineral admixtures to potassium dihydrogen phosphate is 3:1; the mass of the composite retarder is 7.5% of the total mass of the mixture of dead-burned magnesium oxide and mineral admixtures, of which borax is 2.5%, glucose is 2%, dipotassium ethylenediaminetetraacetate is 2%, and chitosan is 1%.

[0036] Accurately weigh the masses of heavy burned magnesium oxide, attapulgite and kaolin, add the three into the instrument and stir evenly for 5 minutes to make the three evenly mixed, then add chitosan into potassium dihydrogen phosphate and stir for 4 minutes to make the mixture evenly mixed; mix the mixture of heavy burned magnesium oxide and mineral admixture with potassium dihydrogen phosphate added with chitosan to obtain an intermediate material; then add borax, glucose and dipotassium ethylenediaminetetraacetate into the instrument in turn and stir to make the components of the composite retarder fully mixed, then add the composite retarder into water with a water-binder ratio of 0.19 and stir for 5 minutes to make it fully dissolved; finally, add the composite retarder solution into the intermediate material and stir sufficiently to obtain retarded magnesium phosphate cement.

[0037] Embodiment 2:

[0038] Each raw material is weighed according to the mass percentage, specifically: in the mixture of dead-burned magnesium oxide and mineral admixtures, the dead-burned magnesium oxide is 60%, the attapulgite is 25%, and the kaolin is 15%; the mass ratio of the total mass of the mixture of dead-burned magnesium oxide and mineral admixtures to potassium dihydrogen phosphate is 3:1; the mass of the composite retarder is 12.5% ​​of the total mass of the mixture of dead-burned magnesium oxide and mineral admixtures, of which borax is 2.5%, glucose is 4%, dipotassium ethylenediaminetetraacetate is 4%, and chitosan is 2%.

[0039] Accurately weigh the masses of heavy burned magnesium oxide, attapulgite and kaolin, add the three into the instrument and stir evenly for 5 minutes to make the three evenly mixed, then add chitosan into potassium dihydrogen phosphate and stir for 4 minutes to make the mixture evenly mixed; mix the mixture of heavy burned magnesium oxide and mineral admixture with potassium dihydrogen phosphate added with chitosan to obtain an intermediate material; then add borax, glucose and dipotassium ethylenediaminetetraacetate into the instrument in turn and stir to make the components of the composite retarder fully mixed, then add the composite retarder into water with a water-binder ratio of 0.19 and stir for 5 minutes to make it fully dissolved; finally, add the composite retarder solution into the intermediate material and stir sufficiently to obtain retarded magnesium phosphate cement.

[0040] Example 3

[0041] Each raw material is weighed according to the mass percentage, specifically: in the mixture of dead-burned magnesium oxide and mineral admixtures, the dead-burned magnesium oxide is 60%, the attapulgite is 20%, and the kaolin is 20%; the mass ratio of the total mass of the mixture of dead-burned magnesium oxide and mineral admixtures to potassium dihydrogen phosphate is 3:1; the mass of the composite retarder is 17.5% of the total mass of the mixture of dead-burned magnesium oxide and mineral admixtures, of which borax is 2.5%, glucose is 6%, dipotassium ethylenediaminetetraacetate is 6%, and chitosan is 3%.

[0042] Accurately weigh the masses of heavy burned magnesium oxide, attapulgite and kaolin, add the three into the instrument and stir evenly for 5 minutes to make the three evenly mixed, then add chitosan into potassium dihydrogen phosphate and stir for 4 minutes to make the mixture evenly mixed; mix the mixture of heavy burned magnesium oxide and mineral admixture with potassium dihydrogen phosphate added with chitosan to obtain an intermediate material; then add borax, glucose and dipotassium ethylenediaminetetraacetate into the instrument in turn and stir to make the components of the composite retarder fully mixed, then add the composite retarder into water with a water-binder ratio of 0.19 and stir for 5 minutes to make it fully dissolved; finally, add the composite retarder solution into the intermediate material and stir sufficiently to obtain retarded magnesium phosphate cement.

[0043] Example 4

[0044] Each raw material is weighed according to the mass percentage, specifically: in the mixture of dead-burned magnesium oxide and mineral admixtures, the dead-burned magnesium oxide is 60%, the attapulgite is 30%, and the kaolin is 10%; the mass ratio of the total mass of the mixture of dead-burned magnesium oxide and mineral admixtures to potassium dihydrogen phosphate is 3:1; the mass of the composite retarder is 22.5% of the total mass of the mixture of dead-burned magnesium oxide and mineral admixtures, of which borax is 2.5%, glucose is 8%, dipotassium ethylenediaminetetraacetate is 8%, and chitosan is 4%.

[0045] Accurately weigh the masses of heavy burned magnesium oxide, attapulgite and kaolin, add the three into the instrument and stir evenly for 5 minutes to make the three evenly mixed, then add chitosan into potassium dihydrogen phosphate and stir for 4 minutes to make the mixture evenly mixed; mix the mixture of heavy burned magnesium oxide and mineral admixture with potassium dihydrogen phosphate added with chitosan to obtain an intermediate material; then add borax, glucose and dipotassium ethylenediaminetetraacetate into the instrument in turn and stir to make the components of the composite retarder fully mixed, then add the composite retarder into water with a water-binder ratio of 0.19 and stir for 5 minutes to make it fully dissolved; finally, add the composite retarder solution into the intermediate material and stir sufficiently to obtain retarded magnesium phosphate cement.

[0046] Example 5

[0047] In this comparative example, the mass proportion of dead-burned magnesium oxide is 80%, the mass proportion of attapulgite is 20%, and the rest is the same as in Example 3.

[0048] Example 6

[0049] In this comparative example, the mass proportion of dead-burned magnesium oxide is 80%, the mass proportion of kaolin is 20%, and the rest is the same as in Example 3.

[0050] Comparative Example 1

[0051] In this comparative example, no glucose was added, and the rest was the same as in Example 1.

[0052] Comparative Example 2

[0053] In this comparative example, dipotassium ethylenediaminetetraacetate was not added, and the rest was the same as in Example 2.

[0054] Comparative Example 3

[0055] In this comparative example, chitosan was not added, and the rest was the same as in Example 3.

[0056] Comparative Example 4

[0057] In this comparative example, no glucose, dipotassium ethylenediaminetetraacetate and chitosan were added, and the rest were the same as in Example 4.

[0058] The setting time of each embodiment and comparative example was determined according to the test method of "setting time" in GB / T 1346-2011 "Test method for water consumption, setting time and stability of cement standard consistency" and JC / T2537-2019 "Magnesium phosphate repair mortar"; the compressive strength of each embodiment and comparative example at 3 hours, 1 day and 28 days was determined with reference to "Determination of compressive strength" in GB / T 17671-2021 "Test method for strength of cement mortar", and the results are shown in Table 1.

[0059] Table 1

[0060]

[0061] From the results in Table 1, it can be seen from the changing characteristics of Examples 1-4 that the addition of the composite retarder can significantly extend the setting time of magnesium phosphate cement, and as the amount of the composite added increases, the setting time of cement is significantly extended. At the same time, it can be seen from the strength data of Examples 1-4 that the addition of the composite retarder has a relatively small effect on the long-term performance of cement.

[0062] A pairwise comparative analysis of Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, Example 3 and Comparative Example 3, and Example 4 and Comparative Example 4 shows that the addition of a single retarder has limited effect on regulating the setting time of cement, while the composite retarder can significantly prolong the setting time of magnesium phosphate cement and delay the early hydration process of cement. At the same time, the composite retarder has relatively little effect on the later strength of cement.

[0063] By comparing Examples 5 and 6 with Example 3, it can be seen that after the high-temperature treated attapulgite and kaolin are added to magnesium phosphate cement, not only the initial hydration rate of cement can be delayed and the setting time can be prolonged, but also the later strength of cement can be improved to a certain extent. The effect of kaolin is slightly lower than that of attapulgite.

[0064] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A composite slow-setting magnesium phosphate cement, characterized in that: The invention comprises a mixture of dead-burned magnesium oxide and mineral admixtures, phosphate, a composite retarder and glue-containing water, wherein the mass ratio of the dead-burned magnesium oxide and the mineral admixtures is 3:2, the mass ratio of the mixture of the dead-burned magnesium oxide and the mineral admixtures to the phosphate is 3:1, the mass of the composite retarder is 7% to 24% of the mass of the mixture of the dead-burned magnesium oxide and the mineral admixtures, and the water-binder ratio in the glue-containing water is 0.18 to 0.

20.

2. A composite slow-setting magnesium phosphate cement as claimed in claim 1, characterized in that: The dead-burned magnesium oxide is prepared by calcining magnesite at a temperature of 1000-1500° C., with a mass fraction of more than 95%.

3. A composite slow-setting magnesium phosphate cement as claimed in claim 1, characterized in that: The phosphate has a specific surface area of ​​not less than 260 m 2 / kg of potassium dihydrogen phosphate.

4. A composite slow-setting magnesium phosphate cement as claimed in claim 1, characterized in that: The mineral admixture is at least one of attapulgite and kaolin treated at high temperature, the attapulgite content is 0% to 40%, and the kaolin content is 0% to 40%.

5. A composite slow-setting magnesium phosphate cement as claimed in claim 1, characterized in that: The composite retarder consists of borax, glucose, ethylenediaminetetraacetate and chitosan, which account for 2.5%, 2%-8%, 2%-8% and 1%-4% of the mass of the mixture of dead-burned magnesium oxide and mineral admixtures respectively.

6. A composite slow-setting magnesium phosphate cement as claimed in claim 5, characterized in that: The ethylenediaminetetraacetate salt is one or two of disodium ethylenediaminetetraacetate, dipotassium ethylenediaminetetraacetate, and ferric ethylenediaminetetraacetate.

7. A method for preparing the composite slow-setting magnesium phosphate cement according to any one of claims 1 to 6, characterized in that: The steps include: (1) High-temperature pretreatment of mineral admixtures: The weighed mineral admixtures are subjected to high-temperature treatment and ground in a ball mill to a specific surface area of ​​400 m 2 / kg; (2) Measuring and dry mixing of each component: first, adding the mineral admixture after high temperature pretreatment to the dead-burned magnesium oxide powder in proportion and stirring evenly to obtain a mixture of the dead-burned magnesium oxide and the mineral admixture; adding chitosan to the phosphate and stirring evenly; then mixing the mixture of the dead-burned magnesium oxide and the mineral admixture with the phosphate added with chitosan to obtain an intermediate material; weighing borax, glucose and ethylenediaminetetraacetate according to the proportion, mixing them thoroughly to obtain a composite retarder; (3) Cement mixing: first, add the composite retarder into the glue-containing water and stir until fully dissolved. Then, add the composite retarder solution into the intermediate material obtained in step (2) and stir fully to obtain composite retarded magnesium phosphate cement.

8. The method for preparing a composite slow-setting magnesium phosphate cement according to claim 7, characterized in that: In step (1), the high temperature treatment is to place the product in a high temperature furnace at a temperature of 550° C. and heat it for 60 minutes.

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