CN109867456B

CN109867456B - Application of magnesium sulfate, portland cement containing magnesium sulfate, preparation method and application thereof

Info

Publication number: CN109867456B
Application number: CN201711254448.6A
Authority: CN
Inventors: 刘赞群; 邓德华
Original assignee: Central South University
Current assignee: Central South University
Priority date: 2017-12-01
Filing date: 2017-12-01
Publication date: 2021-08-31
Anticipated expiration: 2037-12-01
Also published as: CN109867456A

Abstract

The invention relates to an application method of magnesium sulfate and a novel portland cement system: magnesium sulfate is added into the Portland cement semi-finished product (cement clinker grinding fine powder or cement clinker and mixed material grinding fine powder) to form a new Portland cement system. In the novel portland cement system, the content of magnesium sulfate is greater than or equal to 3 wt%, and is less than or equal to the saturated concentration of a magnesium sulfate aqueous solution; the invention also provides a preparation method and application of the portland cement system. The invention adopts magnesium sulfate to replace gypsum in the existing portland cement system, and the formed new cement has longer setting time, better water retention and cohesiveness and higher compressive strength, can obviously reduce the cement grinding amount, reduce the cement production energy consumption, consume industrial waste, and is a green and environment-friendly cement product.

Description

Application of magnesium sulfate, portland cement containing magnesium sulfate, preparation method and application thereof

Technical Field

The invention relates to a cement material, in particular to a Portland cement material added with magnesium sulfate.

Background

The concrete is the civil engineering material with the largest usage in the world, and the main component raw material of the concrete is portland cement which is the cement variety with the largest usage in the world, statistics show that the cement capacity of countries and regions in the world in 2015 is 60 hundred million tons, the cement yield (demand) is 41 hundred million tons, and the cement is basically portland cement. However, with the change of concrete production and construction modes and the attention of the whole society to environmental protection, some problems in the existing silicate cement are urgently needed to be improved so as to be more suitable for the requirements of construction of constructional engineering. The main problems are shown in the following aspects:

(1) the general portland cement (GB175) is the most common cementing material for producing concrete, and comprises three parts of clinker, admixture and gypsum, wherein the mineral composition of the cement clinker is tricalcium silicate C₃S, dicalcium silicate C₂S, tricalcium aluminate C₃A and tetracalcium aluminoferrite C₄And (5) AF. When cement is added with water and stirred, C in cement clinker₃The reaction of a with water rapidly produces hydrated dicalcium aluminate and hydrated tetracalcium aluminate, two metastable hydrates, which convert to stable hydrated tricalcium aluminate. Due to the rapid progress of the process, the consistency of the cement paste is suddenly and rapidly increased instantly and loses the fluidity, so that the phenomenon of flash set or false set occurs, and the engineering application value of the Portland cement is lost. Therefore, the Portland cement clinker is just a Portland cement semi-finished product and has no application value. When the portland cement contains gypsum CaSO₄·2H₂O, C in cement paste at the initial stage of hydration reaction₃A is first reacted with CaSO₄·2H₂SO in O₄ ^2-The reaction to form high-sulfur hydrated calcium sulphoaluminate (ettringite) with fast reaction speed, but the ettringite with low solubility is quickly separated out as colloidal particles and deposited on the surface of cement particles to form a gel film layer, thereby delaying the further hydration of cement clinker minerals and avoiding flash coagulation or pseudo coagulation. Therefore, the cement obtained by grinding the cement clinker and the gypsum together in the process of producing the portland cement is a product with real engineering application value.

However, since gypsum is a slightly soluble substance, for example, the content of gypsum is too much, gypsum which is not completely dissolved in the hydration reaction of cement can continuously generate ettringite in the hardened cement slurry, and volume expansion is generated, so that the volume stability of portland cement is caused. Therefore, in the portland cement system, the amount of gypsum must be controlled within a certain range, thereby limiting the effect of gypsum on regulating the setting and hardening time of cement. With the popularization of commercial concrete in construction engineering, long-distance and long-time concrete transportation and construction become a normal state, the concrete is required to have longer working time, and the slump of the concrete can still meet the design requirement when the concrete is transported to a construction site. In order to ensure the working time of concrete, the setting and hardening time of cement is generally prolonged by adding a retarder. However, incompatibility is easy to occur between the retarder and the chemical components of the cement, or due to improper mixing amount of the retarder, the phenomenon that the cement is abnormally coagulated and hardened is often caused, the normal construction of the concrete is influenced, the strength of the concrete is reduced, and the durability of the concrete is influenced. Therefore, it would be advantageous to develop a new Portland cement system having a longer setting time than the existing Portland cement without affecting the mechanical properties and durability of the cement, and which would be more useful in ensuring the construction of concrete in construction works.

In fact, the setting and hardening of the existing portland cement are difficult to adjust, and the requirements of various working conditions are not easy to meet. If a new Portland cement system can be invented, the Portland cement system has the function of adjusting the setting time, is more convenient to use, and is suitable for the requirements of different environments and different construction conditions, such as the temperature of the Portland cement system can be increased during winter construction, the temperature of the Portland cement system can be reduced during summer construction, and the like.

(2) The concrete has the advantages that the concrete is not only required to have longer setting and hardening time, but also has the additional characteristic that the slump of the fresh concrete is generally larger so as to meet the requirement of pumping construction, and simultaneously, the slump loss of the concrete can be buffered. Due to the use of the water reducing agent, the fresh concrete is particularly sensitive to the water consumption, and the phenomena of segregation, layering, bleeding and the like are very easy to occur when the fluidity is higher, so that the normal pumping construction of the concrete is influenced, and the construction quality problems of uneven distribution of the cross section of the hardened concrete, cracking and the like are caused. In order to prevent the problems of segregation, delamination, bleeding and the like of fresh concrete, a thickening agent can be added to improve the viscosity of the fresh concrete, but physical thickening or chemical thickening can bring other negative effects to cement slurry, such as cracking caused by increase of cement shrinkage deformation, strength reduction caused by increase of gas content and the like. Therefore, if a new portland cement system can be invented, which is characterized by higher viscosity, it will help to reduce or avoid the quality problems of segregation, delamination and bleeding of the fresh cement paste and the fresh concrete.

(3) The production process of the portland cement is 'two-grinding and one-burning': firstly, grinding limestone, clay and the like for producing cement, and then calcining at 1450 ℃ to form clinker; after the clinker is cooled, the clinker, the mixed material and the gypsum are ground again to finally become a cement finished product. Obviously, the production process of portland cement needs to consume a large amount of energy, and the development of more environment-friendly and more green inorganic cementing materials is always the most concerned problem in the research community, and the most successful measure at present is to replace a part of clinker by mixed materials, for example, the common portland cement contains 15% of the mixed materials, so that the clinker consumption is reduced, and the whole calcination energy consumption is reduced. However, the cement grinding is the last process of cement manufacture, and is also the process with the most power consumption, and 70% of the electric energy in the whole production process needs to be consumed, so if a new portland cement system can be invented, the whole cement grinding amount can be directly reduced, and the energy consumption in the whole cement production can be directly and obviously reduced.

Disclosure of Invention

In order to solve the technical problem, the invention provides application of magnesium sulfate, and aims to replace gypsum with magnesium sulfate and obtain a completely novel portland cement system with excellent performance by adding magnesium sulfate to a portland cement (also referred to as cement for short) semi-finished product (ground fine powder of cement clinker or ground fine powder of cement clinker and mixed material).

The second purpose of the invention is to provide a novel Portland cement and to provide a novel Portland cement system.

The third object of the present invention is to provide the method for producing cement, which is intended to reduce the energy consumption for producing cement by grinding only cement clinker or cement clinker and admixture.

The fourth purpose of the invention is to provide an application method of the Portland cement.

The application of magnesium sulfate is characterized by that the magnesium sulfate is added into the semi-finished product of silicate cement (cement clinker fine-ground powder or cement clinker and mixed material fine-ground powder; said invention also is called cement semi-finished product) so as to obtain the silicate cement; in the portland cement, the content of magnesium sulfate is more than or equal to 3 wt%.

In the invention, magnesium sulfate is directly doped into the cement semi-finished product to form a new Portland cement system. Researches show that the addition of the magnesium sulfate with the content can comprehensively improve the performance of the obtained cement, for example, obviously prolong the retardation time of the cement, improve the viscosity of the cement paste and improve the compressive strength of the hardened cement paste. According to the method, the magnesium sulfate is doped for the first time to modify the cement semi-finished product, so that the production energy consumption of the cement can be greatly reduced, and the multiple properties of the prepared cement can be unexpectedly improved.

In the application, the magnesium sulfate is provided with crystal water or is not provided with the crystal water.

The magnesium sulfate is anhydrous magnesium sulfate (MgSO)₄Magnesium sulfate monohydrate MgSO₄·H₂O, magnesium sulfate dihydrate MgSO₄·2H₂O, magnesium sulfate trihydrate MgSO₄·3H₂O, magnesium sulfate tetrahydrate MgSO₄·4H₂O, magnesium sulfate pentahydrate MgSO₄·5H₂O, magnesium sulfate hexahydrate MgSO₄·6H₂O, magnesium sulfate heptahydrate MgSO₄·7H₂Any one of O or a mixture of any two or more thereof.

The magnesium sulfate is preferably a magnesium sulfate industrial byproduct which is obtained by industrial production and industrial magnesium desulphurization and contains anhydrous water and crystallized water. For example, magnesium sulfate may be a by-product of magnesium desulfurization.

In the application, the effective content of magnesium sulfate accounts for 3-30 wt% of the prepared Portland cement; (ii) a Further preferably 5 to 20 wt%; more preferably 5 to 15 wt%.

The invention also provides Portland cement, which comprises a cement semi-finished product and magnesium sulfate; the semi-finished cement product is ground fine powder of cement clinker; or cement clinker and mixed material fine powder;

the effective content of magnesium sulfate in the portland cement is greater than or equal to 3 wt% and less than or equal to 30 wt%.

The inventor breaks away from the technical barrier of the prior art that the finished Portland cement product is generally modified, and firstly proposes the idea of improving various performances of cement by doping magnesium sulfate in the semi-finished Portland cement product. The Portland cement of the invention uses magnesium sulfate to replace the common gypsum in the existing cement system, and forms a completely new cement system with the cement semi-finished product.

The present inventors have also studied and found that the addition amount of magnesium sulfate in cement has a great influence on the performance of magnesium sulfate. Research shows that the addition amount of magnesium sulfate in the cement is more than or equal to 5 wt%, a good retarding effect can be achieved, and in addition, the viscosity of the gelled slurry can be unexpectedly improved, and the cohesiveness and the water retention of the cement slurry are improved.

Preferably, the content of magnesium sulfate in the cement is 5-20 wt%; more preferably 5 to 15 wt%.

The cement clinker is silicate cement clinker.

The mixed material is an active mixed material and an inactive mixed material.

The cement consists of a cement semi-finished product and magnesium sulfate; wherein the content of magnesium sulfate is 5-20 wt%; more preferably 5 to 15 wt%.

In the invention, the portland cement is a mixture of a cement semi-finished product and magnesium sulfate which are mixed with each other; or cement semi-finished products and A/B materials with independent magnesium sulfate.

The cement of the invention can have two existing forms according to the existing states of the components in the cement: 1. The cement is a mixture of a cement semi-finished product and magnesium sulfate; 2. in the cement, the cement semi-finished product and magnesium sulfate exist separately (are not mixed and contacted with each other before use; namely, the A/B material).

The invention is preferably cement, wherein the cement semi-finished product and the magnesium sulfate A/B material. Namely, before use, the cement semi-finished product is not contacted with magnesium sulfate, and in the use process, the cement semi-finished product and the magnesium sulfate are mixed and contacted; the mixing and contacting method can be that the cement semi-finished product and the magnesium sulfate are directly mixed and then added with water to be stirred for use; or dissolving magnesium sulfate in water, and stirring with the cement semi-finished product for use.

The invention also provides a preparation method of the Portland cement, which comprises the steps of grinding the cement clinker or grinding the cement clinker and the mixed material to obtain a cement semi-finished product;

adding magnesium sulfate into the cement semi-finished product, and uniformly mixing to obtain the cement in the form of a mixture:

or the obtained cement semi-finished product and magnesium sulfate are separately packaged to obtain the cement with mutually independent components.

The preparation method of the invention only needs to grind the cement clinker or the mixed material; compared with the existing cement grinding, the grinding amount of gypsum is eliminated, and the energy consumption can be obviously reduced; and gypsum thermal decomposition in the grinding process is not considered, so that the production cost of the ball mill is further reduced.

In the invention, the cement clinker and the magnesium sulfate do not need to be milled together by ball milling, compared with the existing cement milling, the energy consumption can be reduced, the hydration reaction between the water generated by the heated decomposition of the gypsum and the cement clinker in the ball milling process can be avoided, and the effective components of the cement finished product are reduced.

The invention also provides an application method of the Portland cement, which is to mix the cement with water and stir the mixture evenly.

The application method can be divided into two application modes according to the state of whether the components in the cement are mixed or not: application 1: when the components in the cement exist in the form of mixture, the mixture of the cement semi-finished product and the magnesium sulfate is mixed with water and used. Application 2: when the components in the cement exist in mutually independent forms, the magnesium sulfate is dissolved by water and then is mixed with the cement semi-finished product to prepare the gelled slurry when being applied.

The application 2 of the invention overturns the conventional cement application method, and magnesium sulfate is directly prepared into the aqueous solution, so that the hydration reaction between the magnesium sulfate and cement clinker particles is more favorably realized, the system is more uniform, and the obtained compressive strength is higher.

Advantageous effects

First, technical Effect

(1) Magnesium sulfate is an easily soluble substance, is dissolved in water to prepare a magnesium sulfate aqueous solution, and is stirred with a portland cement semi-finished product (ground powder of cement clinker or ground powder of cement clinker and mixed material).

(2) The magnesium sulfate is used for replacing gypsum and is dissolved in water for use, so that the adverse effect of reducing the effective components of the cement caused by chemical reaction between water vapor produced by decomposing the gypsum and the cement clinker due to overhigh temperature in the ball milling process of the conventional portland cement clinker and the gypsum is avoided.

(3) The solubility of magnesium sulfate is relatively high (e.g., MgSO. sub.20 ℃ C.)₄·7H₂Solubility of O is 35.5) in its solubility rangeThe prepared magnesium sulfate solution can be mixed with C in the cement hydration process₃The reaction A is complete, and the volume stability of the cement is not affected, so that the dosage of the magnesium sulfate in the novel portland cement can exceed the dosage of the gypsum in the conventional portland cement, and the setting and hardening of the portland cement are further regulated and controlled.

(4) The magnesium sulfate with different water of crystallization, when dissolved, is somewhat exothermic, e.g. MgSO₄And MgSO₄·H₂O; some will be endothermic, e.g. MgSO₄·7H₂And O, the temperature of the slurry can be adjusted by adopting magnesium sulfate of different crystal water, so that the hydration of the cement is delayed or intensified, and different working condition requirements (such as the requirement of cooling mass concrete construction and the requirement of heating concrete in winter construction) are met.

(5) Magnesium sulfate dissolved in water with Mg introduced²⁺When cement clinker is stirred with water, a large amount of OH is generated^-，Mg²⁺Under alkaline conditions, rapidly precipitate to form insoluble Mg (OH)₂The cement paste has higher viscosity, better water retention and cohesiveness than the existing portland cement, and improved homogeneity.

Second, economic and social effects

(1) The invention adopts magnesium sulfate to replace gypsum in general portland cement, only grinds or cement clinker (+ mixed material) into powder when producing cement, dissolves magnesium sulfate in water to prepare aqueous solution, and mixes the magnesium sulfate aqueous solution and the powder for use when using, can reduce the grinding amount of more than 5% of solid in cement production, further reduces the energy consumption of cement production, and is a more green and more environment-friendly invention product.

(2) The invention adopts magnesium sulfate to replace gypsum in the general portland cement, can not consider the cooling measure in the ball milling process of the existing portland cement clinker and gypsum, further reduces energy consumption, simplifies the cost of ball milling equipment, and has important influence on the ball milling process of the cement clinker.

(3) In recent years, the haze pollution in China has the characteristics of high occurrence frequency, wide influence range and high treatment difficulty. The study showed that the sulfate salt isAn important chemical component in the atmospheric fine particulate matter PM2.5 during heavy pollution is SO emitted by industry₂The gas is generated in the atmosphere through an oxidation process. To reduce haze formation, the industrial SO must be reduced from the source₂And (4) discharging. According to statistics, 2015 years of China's SO₂The emission is as high as 2043.9 ten thousand tons, and the emission is mainly concentrated in coal-fired industrial boilers for steel, thermal power, portland cement production, domestic heating and the like, and the SO in the air needs to be reduced₂And (4) performing desulfurization and denitrification treatment on the boiler exhaust gas. Because of the advantages of high desulfurization efficiency, stable operation, small floor area, low comprehensive cost and the like, more and more enterprises adopt the magnesium desulfurization to treat the exhaust gas, but how to reasonably consume the byproduct MgSO₄·7H₂O becomes a key for restricting the popularization and the application of magnesium desulphurization. The invention provides a scientific and large-dosage consumption MgSO (MgSO)₄·7H₂The O method shows that the national cumulative cement yield is 22 hundred million tons in 2016 (1-11 months) according to the data of the national Bureau of statistics, and MgSO 5 is calculated according to the mixing amount of 5% gypsum in the substituted general portland cement₄·7H₂The required amount of O can reach 1.1 hundred million tons. Therefore, the novel portland cement system can reduce the production energy consumption of cement, can also consume a large amount of byproducts formed by haze treatment, forms a novel industrial chain, and has important economic and social effects.

Drawings

FIG. 1 is a graph comparing the viscosity of cement paste with a water cement ratio (W/C) of 0.45 in example 3 and comparative example 3;

FIG. 2 is a graph comparing the viscosity of cement paste with a water cement ratio (W/C) of 0.50 in example 3 and comparative example 3;

FIG. 3 is a graph comparing the hydration heat release rates of cement slurries having a water-cement ratio (W/C) of 0.45 in example 4 and comparative example 4;

FIG. 4 is a graph comparing the hydration heat release rates of cement slurries having a water-cement ratio (W/C) of 0.50 in example 4 and comparative example 4;

FIG. 5 is a graph comparing the hydration exotherm rates of cement slurries incorporating a mineral admixture for example 5 and comparative example 5 at a water-to-cement (W/C) ratio of 0.45;

FIG. 6 is a graph showing a comparison of compressive strengths of cement slurries having a water cement ratio (W/C) of 0.50 in examples 5 and 6.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

The following examples and comparative examples show the amount of magnesium sulfate in the cement system, unless otherwise stated.

Comparative example 1:

the P.I portland cement is formed by 95% of portland cement clinker and 5% of gypsum, the water cement ratio is 0.4, and the powder and water are stirred according to the stirring and testing method in the specification GB/T to obtain cement paste. Dividing the slurry into two parts, wherein one part is used for testing the initial setting time and the final setting time of the cement slurry; the other part is poured into a cubic steel mould with the thickness of 20mm multiplied by 20mm, the cubic steel mould is immediately covered by a plastic film, the mould is removed after the maintenance is carried out for 1 day in the environment with the temperature of 20 +/-2 ℃, and the test piece is soaked in water with the temperature of 20 +/-1 ℃ to ensure that the interval between the test pieces and the depth of the upper surface of the test piece are not less than 5 mm. And after the cubic test piece is maintained for 7d, 14d, 28d and 60d, taking out the test piece from water, wiping the surface of the test piece with a wet cleaning cloth, drying for 2 hours in an environment with the temperature of 20 +/-2 ℃ and the relative humidity of 60 +/-5%, testing the compressive strength on a press machine in accordance with GB/T17671, and taking the arithmetic mean value of the test data of the six test pieces as a test result.

Comparative example 2

The P.I portland cement is formed by 95% of portland cement clinker and 5% of gypsum, the water cement ratio is 0.45 to 0.50, and the cement slurry obtained by stirring the powder and the water is poured into a cubic steel die with the thickness of 20mm multiplied by 20mm according to a clean slurry stirring method in GB/T standard and is immediately covered by a plastic film. And (3) maintaining the test piece in an environment of 20 +/-2 ℃ for 1 day, then removing the mold, and soaking the test piece in water of 20 +/-1 ℃ to ensure that the interval between the test pieces and the depth of the upper surface of the test piece are not less than 5 mm. And after the cubic test piece is maintained for 7d, 14d, 28d and 60d, taking out the test piece from water, wiping the surface of the test piece with a wet cleaning cloth, drying for 2 hours in an environment with the temperature of 20 +/-2 ℃ and the relative humidity of 60 +/-5%, testing the compressive strength on a press machine in accordance with GB/T17671, and taking the arithmetic mean value of the test data of the six test pieces as a test result.

Comparative example 3

The P.I portland cement is composed of 95% portland cement clinker and 5% gypsum, the water cement ratio is 0.45 to 0.50, the powder and water are stirred according to the clean slurry stirring method in the specification GB/T to obtain cement slurry, and the viscosity of the slurry is immediately tested by a Rheoplus QC type coaxial cylinder rheometer (shear strain rate control) produced by Anton Paar company in Germany. The sample cylinder of the rheometer has a volume of 163ml, a height of 118mm and an inner diameter of 42mm, is sleeved in a constant-temperature outer cylinder, and is connected with a temperature control device, the temperature is set to be 25 ℃, the temperature control precision is 0.1 ℃, and the model of a cross rotor is ST 22-4V-40. Before testing, the rheometer is calibrated, the rotor is detached during calibration and automatically calibrated according to the program carried by the rheometer, and the rotor, the sample cylinder and the outer cylinder are kept at the constant temperature of 25 ℃ for 30 min.

Comparative example 4

The PI portland cement is formed by 95% of portland cement clinker and 5% of gypsum, the water cement ratio is 0.45 and 0.50, an eight-channel cement hydration heat measuring instrument produced by American TA instruments company is adopted to test the heat release curve of the cement, and the test temperature is 20 +/-0.2 ℃.

Comparative example 5

The method is characterized in that 90% of portland cement clinker, 5% of II-grade fly ash and 5% of gypsum are adopted to form 1# ordinary portland cement, 85% of portland cement clinker, 10% of II-grade fly ash and 5% of gypsum are adopted to form 2# ordinary portland cement, the water cement ratio is 0.45, an eight-channel cement hydration heat measuring instrument produced by American TA instruments company is adopted to test the heat release curve of cement, and the test temperature is 20 +/-0.2 ℃.

Example 1

Using the same portland cement clinker as in comparative example 1, MgSO 5%, 6% and 7% was calculated as the amount of admixture₄·7H₂O (based on the weight of the cement system), water cement ratio of 0.4, MgSO4₄·7H₂Dissolving O in water to prepare a solution, and stirring cement clinker and magnesium sulfate solution according to a stirring and testing method in the specification GB/T to obtain cement paste. Dividing the slurry into two parts, wherein one part is used for testing the initial setting time and the final setting time of the cement slurry; in additionOne part of the test piece is poured into a cubic steel mould with the thickness of 20mm multiplied by 20mm, the test piece is immediately covered by a plastic film, the mould is removed after the maintenance is carried out for 1 day in the environment with the temperature of 20 +/-2 ℃, and the test piece is soaked in water with the temperature of 20 +/-1 ℃ so as to ensure that the interval between the test pieces and the depth of the upper surface of the test piece are not less than 5 mm. And after the cubic test piece is maintained for 7d, 14d, 28d and 60d, taking out the test piece from water, wiping the surface of the test piece with a wet cleaning cloth, drying for 2 hours in an environment with the temperature of 20 +/-2 ℃ and the relative humidity of 60 +/-5%, testing the compressive strength on a press machine in accordance with GB/T17671, and taking the arithmetic mean value of the test data of the six test pieces as a test result.

Example 2

Adopting 95% cement clinker and 5% MgSO₄·7H₂O cement system with water cement ratio of 0.45 to 0.50, MgSO₄·7H₂Dissolving O in water to prepare a solution, stirring cement clinker and magnesium sulfate solution according to a stirring method in the specification GB/T to obtain cement slurry, pouring the cement slurry into a cubic steel mould with the thickness of 20mm multiplied by 20mm, and immediately covering the cement slurry with a plastic film. And (3) maintaining the test piece in an environment of 20 +/-2 ℃ for 1 day, then removing the mold, and soaking the test piece in water of 20 +/-1 ℃ to ensure that the interval between the test pieces and the depth of the upper surface of the test piece are not less than 5 mm. And after the cubic test piece is maintained for 7d, 14d, 28d and 60d, taking out the test piece from water, wiping the surface of the test piece with a wet cleaning cloth, drying for 2 hours in an environment with the temperature of 20 +/-2 ℃ and the relative humidity of 60 +/-5%, testing the compressive strength on a press machine in accordance with GB/T17671, and taking the arithmetic mean value of the test data of the six test pieces as a test result.

Example 3

Adopting cement clinker plus 2%, 3%, 4%, 5%, 6%, 7% MgSO₄·7H₂The viscosity of the resulting cement slurry was immediately tested using a Rheoplus QC type coaxial cylindrical rheometer (shear strain rate controlled) manufactured by Anton Paar, Germany, according to the neat slurry mixing method of GB/T at a water-cement ratio of 0.45 or 0.50 in an O cement system (all based on the weight of the cement system). The sample cylinder of the rheometer has a volume of 163ml, a height of 118mm and an inner diameter of 42mm, is sleeved in a constant-temperature outer cylinder, and is connected with a temperature control device, the temperature is set to be 25 ℃, and the temperature is controlledThe precision is 0.1 ℃, and the model of the cross-shaped rotor is ST 22-4V-40. Before testing, the rheometer is calibrated, the rotor is detached during calibration and automatically calibrated according to the program carried by the rheometer, and the rotor, the sample cylinder and the outer cylinder are kept at the constant temperature of 25 ℃ for 30 min.

FIG. 1 shows the system of comparative example 3 (95% Portland cement clinker + 5% gypsum, water cement ratio 0.45; see CS5 in FIG. 1) and the system of example 3 (cement clinker + 2%, 3%, 4%, 5%, 6%, 7% MgSO 4) at a water-cement ratio of 0.45₄·7H₂O, the water-cement ratio is 0.45; comparison of the viscosities of MS 2%, MS 3%, MS 4%, MS 5%, MS 6%, MS 7% in fig. 1, respectively.

FIG. 2 shows the system of comparative example 3 (95% Portland cement clinker + 5% gypsum, water cement ratio 0.5; see CS5 in FIG. 2) and the system of example 3 (cement clinker + 2%, 3%, 4%, 5%, 6%, 7% MgSO 4) at a water-cement ratio of 0.5₄·7H₂O, the water-cement ratio is 0.5; comparison of viscosity for MS 2%, MS 3%, MS 4%, MS 5%, MS 6%, MS 7%, respectively, in fig. 2.

Example 4

Adopts cement clinker with 2%, 3%, 4%, 5%, 6%, 7% MgSO4 & 7H₂The water cement ratio of the O cement system (all based on the weight of the cement system) is 0.45 and 0.50, and an eight-channel cement hydration heat measuring instrument produced by American TA instruments company is adopted to test the heat release curve of the cement system, and the test temperature is 20 +/-0.2 ℃.

FIG. 3 shows the system of comparative example 4 (95% Portland cement clinker + 5% gypsum, water cement ratio 0.45; see CS5 in FIG. 3) and the system of example 4 (cement clinker + 2%, 3%, 4%, 5%, 6%, 7% MgSO 4) at a water-cement ratio of 0.45₄·7H₂O, the water-cement ratio is 0.45; respectively showing the cement paste hydration heat release curves of MS 2%, MS 3%, MS 4%, MS 5%, MS 6% and MS 7% in the figure 3.

FIG. 4 shows the system of comparative example 4 (95% Portland cement clinker + 5% gypsum, water cement ratio 0.5; see CS5 in FIG. 4) and the system of example 4 (cement clinker + 2%, 3%, 4%, 5%, 6%, 7% MgSO 4) at a water-cement ratio of 0.5₄·7H₂O, the water-cement ratio is 0.5; MS 2% in FIG. 4 respectively,MS 3%, MS 4%, MS 5%, MS 6%, MS 7%) hydration exotherm.

Example 5

90% of portland cement clinker, 5% of II-grade fly ash, 5% of MgSO4 & 7H2O form 1-1# portland cement, 85% of portland cement clinker, 10% of II-grade fly ash, MgSO4 & 7H2O form 2-1# portland cement, the water-cement ratio is 0.45, an eight-channel cement hydration heat measuring instrument produced by American TA instruments company is adopted to test the heat release curve of cement paste, and the test temperature is 20 +/-0.2 DEG C

Example 6

Adopts cement clinker with 5 percent, 6 percent and 7 percent of MgSO4 & 7H₂In the O-cement system (all based on the weight of the cement system), magnesium sulfate was dissolved in water at a water-cement ratio of 0.4. According to the stirring method in the specification GB/T, cement clinker and magnesium sulfate solution are stirred to obtain cement slurry, the cement slurry is poured into a cubic steel mould with the thickness of 20mm multiplied by 20mm, and the cubic steel mould is immediately covered by a plastic film. And (3) maintaining the test piece in an environment of 20 +/-2 ℃ for 1 day, then removing the mold, and soaking the test piece in water of 20 +/-1 ℃ to ensure that the interval between the test pieces and the depth of the upper surface of the test piece are not less than 5 mm. And after the cubic test piece is maintained for 7d, 28d and 60d, taking out the test piece from water, wiping the surface of the test piece with a wet cleaning cloth, drying for 2 hours in an environment with the temperature of 20 +/-2 ℃ and the relative humidity of 60 +/-5%, testing the compressive strength on a press machine conforming to GB/T17671, and taking the arithmetic mean value of the test data of six test pieces as a test result.

Example 7

Adopts cement clinker with 5 percent, 6 percent and 7 percent of MgSO4 & 7H₂And (3) mixing the cement clinker powder and the magnesium sulfate crystals to obtain the cement in an O cement system (both taking the weight of the O cement system and the weight of the cement system as a reference). According to the stirring method in the specification GB/T, cement and water are stirred according to the water cement ratio of 0.4 to obtain cement paste, the cement paste is poured into a cubic steel mould with the thickness of 20mm multiplied by 20mm, and the cubic steel mould is immediately covered by a plastic film. And (3) maintaining the test piece in an environment of 20 +/-2 ℃ for 1 day, then removing the mold, and soaking the test piece in water of 20 +/-1 ℃ to ensure that the interval between the test pieces and the depth of the upper surface of the test piece are not less than 5 mm. After the cube test piece is cured for 7d, 28d and 60d, the test piece is taken out of the water, the bright water on the surface of the test piece is wiped by a wet ragDrying for 2 hours in an environment with the temperature of 20 +/-2 ℃ and the relative humidity of 60 +/-5 percent, testing the compressive strength on a press machine which accords with GB/T17671, and taking the arithmetic mean value of test data of six test pieces as a test result.

Example 1 and comparative example 1 compare 95% cement clinker + 5% gypsum (P.I Portland cement), 95% cement clinker + 5% MgSO 5% at 0.4 water cement ratio₄·7H₂O, 94% cement clinker and 6% MgSO₄·7H₂O and 93% cement clinker + 7% MgSO₄·7H₂And O, initial setting and final setting time of four kinds of slurry, and compressive strength of 7d, 14d, 28d and 60d cement stones. The results are shown in Table 1.

TABLE 1 comparison of setting time and compression strength at different ages of cement slurries of comparative example 1 and example 1

As can be seen from Table 1, the novel portland cement system of the present invention has a longer initial setting specimen than general portland cement (P.I), but the final setting time is not increased much, which is beneficial to prolonging the initial setting working time of cement paste or concrete, but does not affect the final setting time to slow down the construction progress. As can also be seen from Table 1, the novel Portland cement of the invention is present over MgSO₄·7H₂When the content of O is 5%, the compressive strength of the set cement is greater than that of the general silicate set cement with the same content of 5% of gypsum; the new Portland cement of the invention is over MgSO₄·7H₂When the content of O is 6 percent and 7 percent, the compressive strength of the set cement is basically consistent with that of the general silicate set cement with the content of 5 percent gypsum.

Example 2 and comparative example 2 compare 95% cement clinker + 5% gypsum formed set cement with 95% cement clinker + 5% Mg8O at a water cement ratio of 0.45,0.50₄·7H₂O-formed set cements 7d, 14d, 28d and 60d compressive strength. The results are shown in Table 2.

TABLE 2 comparison of compressive strengths of cement slurries of different ages in comparative example 2 and example 2

As can be seen from Table 2, the novel Portland cement paste of the present invention has a compressive strength greater than that of the conventional Portland cement paste under the same conditions, when the water cement ratio is between 0.45 and 0.50.

Example 3 and comparative example 3 compare a cement slurry of 95% cement clinker + 5% gypsum with cement clinker + 2%, 3%, 4%, 5%, 6%, 7% MgSO at a water cement ratio of 0.45,0.50₄·7H₂Comparison of the viscosities of the cement slurries formed, the results of the tests are shown in fig. 1-2. As can be seen, when the amount of the magnesium sulfate is 4%, the viscosity of the slurry is not different from that of the slurry in the comparative example 3, and the slurry viscosity is obviously improved only when the yield of the magnesium sulfate is more than or equal to 5%.

Example 4 and comparative example 4 compare a cement slurry of 95% cement clinker + 5% gypsum with cement clinker + 2%, 3%, 4%, 5%, 6%, 7% MgSO at a water cement ratio of 0.45,0.5₄·7H₂And (4) comparing hydration heat release curves of cement paste formed by O, and the test results are shown in figures 3-4. As can be seen from the figure, when the magnesium sulfate is 2% and 3%, the exothermic peak is earlier than that in comparative example 4, which indicates that the effect of retarding is not exerted; when the amount of magnesium sulfate is 4%, although the exothermic peak appears after that of comparative example 4, the exothermic peak is narrow and high, which is not favorable for cement hydration and strength development.

Example 5 and comparative example 5 compare the exotherm for a gypsum portland cement slurry consisting of 5% and 10% grade II fly ash blended with a magnesium sulfate cement system cement slurry at a water cement ratio of 0.45 and the test results are shown in fig. 5. As can be seen from the figure, in the silicate cement doped with the mineral admixture (fly ash), the exothermic peak of a cement system consisting of magnesium sulfate, cement clinker and the mineral admixture is shifted backwards, and the effect of retarding coagulation is achieved.

Examples 6 and 7 compare the influence of two magnesium sulfate external mixing modes on the compressive strength of the hardened cement paste for 7 days, 28 days and 60 days under the water cement ratio of 0.40, and the test results are shown in a figure 6 (in the figure 6, 5-7% mixing refers to mixing the magnesium sulfate with cement clinker in advance and then adding water for hydration, and 5-7% dissolving refers to mixing the magnesium sulfate with the cement clinker for pulping). As can be seen, the compressive strength of the cement paste obtained in example 6 is higher than that of the cement paste obtained in example 7, which indicates that the external mixing mode of dissolving magnesium sulfate in water to form a solution and then stirring the solution with cement powder is more beneficial to the improvement effect of magnesium sulfate on the cement semi-finished product.

Claims

1. The application of the magnesium sulfate is characterized in that gypsum is replaced by magnesium sulfate crystals, and the magnesium sulfate crystals are mixed with a portland cement semi-finished product to prepare portland cement;

the semi-finished product of the portland cement is ground fine powder of cement clinker; or a grinding powder material of cement clinker and mixed materials;

in the portland cement, the content of magnesium sulfate is 5-20 wt%;

the mineral composition of the cement clinker is tricalcium silicate C₃S, dicalcium silicate C₂S, tricalcium aluminate C₃A and tetracalcium aluminoferrite C₄AF。

2. The Portland cement is characterized by consisting of a Portland cement semi-finished product and magnesium sulfate; the semi-finished product of the portland cement is ground fine powder of cement clinker or ground fine powder of cement clinker and a mixed material;

in the Portland cement, the content of magnesium sulfate is 5-20 wt%;

3. The portland cement of claim 2, wherein the magnesium sulfate is anhydrous magnesium sulfate (MgSO)₄Magnesium sulfate monohydrate MgSO₄·H₂O, magnesium sulfate dihydrate MgSO₄·2H₂O, magnesium sulfate trihydrate MgSO₄·3H₂O, magnesium sulfate tetrahydrate MgSO₄·4H₂O, magnesium sulfate pentahydrate MgSO₄·5H₂O, magnesium sulfate hexahydrate MgSO₄·6H₂O, magnesium sulfate heptahydrate MgSO₄·7H₂Any one of O or a mixture of any two or more thereof.

4. A Portland cement as claimed in any one of claims 2 to 3, wherein the cement is a mixture of a portland cement semi-finished product and magnesium sulfate; or a Portland cement semi-finished product and an A/B material with independent magnesium sulfate.

5. A method for preparing Portland cement according to any one of claims 2 to 4, characterized in that cement clinker is ground, or cement clinker and mixed material are ground together to obtain the semi-finished Portland cement;

adding magnesium sulfate into the portland cement semi-finished product, and uniformly mixing to obtain cement in a mixture form:

or the obtained portland cement semi-finished product and magnesium sulfate are separately packaged to obtain cement with mutually independent components.

6. A method for using the Portland cement according to any one of claims 2 to 4, wherein the Portland cement is mixed with water and stirred uniformly to prepare cement paste.

7. The method of using Portland cement according to claim 6, wherein the components of Portland cement are present in the form of a mixture of a semifinished Portland cement product and magnesium sulfate, and the Portland cement is directly mixed with water to prepare the cement slurry when it is used.

8. The method of using portland cement of claim 6, wherein the components of portland cement are present as a portland cement semi-finished product and magnesium sulfate independently; when the cement paste is applied, magnesium sulfate is firstly dissolved by water to prepare a magnesium sulfate aqueous solution, and then the magnesium sulfate aqueous solution is mixed with a portland cement semi-finished product to prepare the cement paste.