CN115403333B

CN115403333B - Durable cement mortar

Info

Publication number: CN115403333B
Application number: CN202211048045.7A
Authority: CN
Inventors: 陈芳山
Original assignee: Tangshan Fengluan New Materials Co ltd
Current assignee: Tangshan Fengluan New Materials Co ltd
Priority date: 2022-08-30
Filing date: 2022-08-30
Publication date: 2023-09-05
Anticipated expiration: 2042-08-30
Also published as: CN115403333A

Abstract

The invention discloses durable cement mortar which comprises the following raw materials in parts by weight: 20-50 parts of cement, 60-150 parts of sand, 1-3 parts of modifier and 8-20 parts of water. According to the invention, magnesium oxide and stearic acid are mixed, a nonionic surfactant is added, and a magnesium stearate emulsion is prepared by utilizing a simple chemical reaction, so that the magnesium stearate emulsion is used as a modifier of cement mortar, and the hydrophobic property of the inner surface and the outer surface of the mortar is obviously improved; the addition of the cobaltosic oxide further improves the hydrophobic property of the mortar, the mechanical strength, the water resistance and the chloride ion resistance of the mortar, and the shrinkage performance of the cement mortar.

Description

Durable cement mortar

Technical Field

The invention belongs to the technical field of building materials, and particularly relates to durable cement mortar.

Background

At present, the high content of carbon dioxide in the atmosphere has a certain influence on natural environment and human survival. Human activities such as combustion of fossil energy, production of cement, etc. are major sources of carbon dioxide emissions. Among them, cement production and manufacture is considered as one of the most industries that lead to an increase in carbon dioxide emissions. Cement mortar is mortar prepared from cement, fine aggregate, water and other additives according to construction requirements, and is widely applied to the fields of masonry, plastering, decoration engineering and the like. Cement is the most used gel material. Therefore, the functional substances are added into the cement mortar to modify the cement mortar, so that the durability of the cement mortar is improved, the utilization rate of resources is improved, and the environment is protected.

CN 113387667A discloses a impervious cement mortar, which consists of the following raw materials in parts by weight: 95-130 parts of quicklime, 50-82 parts of kaolin or modified kaolin, 260-295 parts of water, 3-6 parts of water reducer, 32-40 parts of aggregate and 10-23 parts of grinding aid, wherein the grinding aid consists of triisopropanolamine cyclic borate, coconut diethanolamide, borax, triethyl orthoacetate, modified acacia, magnesium stearate and water in a mass ratio of (34-40) to (10-16) to (17-22) to (3-5) to (10-14) to (0.7-1.5) to (48-53). The impervious cement mortar has excellent mechanical properties, high compressive and flexural strength, and good impervious performance and cracking resistance. However, the method has the defects of numerous formulation raw materials, complex preparation method and lack of evaluation on the durability and self-shrinkage performance of the cement mortar.

CN 111960760A discloses a high damping modified cement mortar and a preparation method thereof, comprising the following components in parts by weight: 50-60 parts of cement, 100-120 parts of sand, 25-30 parts of water, 4-6 parts of styrene-acrylic emulsion, 0.2-0.5 part of water reducer, 0.1-0.3 part of defoamer, 1-3 parts of internal damping additive and 3-7 parts of external damping additive, wherein the internal damping additive is stearic acid/butadiene rubber compound, and the external damping additive is erucamide/steel fiber/butadiene rubber compound. The high-damping modified cement mortar provided by the invention has the effect of improving the poor damping effect of the cement mortar. The invention adds a plurality of organic modifiers, the mechanical strength of the mortar is not high, and the compatibility of the mortar is worth considering.

Substances for promoting cement hydration are added into the cement mortar, so that the compactness of hydration products is enhanced, and the mechanical property and durability of the cement mortar are required to be improved.

Disclosure of Invention

In view of the defects of the prior art, the technical problem to be solved by the invention is to provide the durable cement mortar which has high mechanical strength, good dry shrinkage deformation performance and good durability.

Improving the water resistance and the impermeability of the cement mortar is an important way for improving the durability of the cement mortar. Currently, the most commonly used methods are classified into surface modification and additive modification. The surface hydrophobic modification method is to carry out hydrophobic modification on the surface after the concrete is solidified, so that a hydrophobic protective layer is formed on the surface of the concrete, and the surface hydrophobic modification method is generally realized through surface coating or dipping. The surface hydrophobically modified approach has a number of disadvantages. When the concrete is exposed to the external environment, the surface coating tends to age, the concrete is easy to crack, and the surface hydrophobic layer is cracked and peeled off, so that the water resistance and the impermeability of the concrete are rapidly reduced. The additive modification may be a more efficient way to modify the surface. The additive modification is to add a modifier in the concrete stirring process, so as to improve the waterproof and impervious performances of the surface and the inside of the concrete. Therefore, compared with the surface hydrophobic modification method, the concrete prepared by the hydrophobic additive method has better performance and longer service life. Currently used hydrophobing agents are mainly liquid silanes and siloxanes, silane emulsions, hydrophobic stearic acid. The inventor optimizes and adjusts the added hydrophobe based on the modification of the additive, and discovers that the introduction of silane or siloxane inhibits the hydration of cement to a certain extent. Probably because the hydrophobicity of the silane weakens the interaction forces between the aggregate and the hydration products at the interface to some extent. Stearic acid or its derivatives are difficult to disperse uniformly in cement mortar systems. Therefore, the modification of the existing hydrophobing agent reduces the influence of the hydrophobing agent on cement hydration, improves the dispersion of the hydrophobing agent in the mortar, and is an effective way for improving the overall performance of the durable cement mortar. The cost of stearic acid is lower and the preparation of the derivative is easier relative to silanes and siloxanes. The invention prepares the high-performance modifier by the combined action of stearic acid, magnesium oxide and surfactant, and adds the modifier into cement slurry.

However, the modifier is a nano magnesium stearate emulsion formed by heating and reacting stearic acid, magnesium oxide and a surfactant, and has good dispersion property and low surface tension when being added into cement slurry, and has a promotion effect on initially hydrated ettringite, so that the overall hydrophobicity and mechanical property of the cement slurry are improved. However, the hydration speed of the cement is increased and the release of hydration heat is increased after the modifier is added, so that the self-shrinkage performance of the cement mortar is improved. In order to solve the problem, a large number of experiments show that the addition of the structured cobaltosic oxide can be used as a template for forming early ettringite, delay the release of hydration heat, stabilize the structure of hydration products and reduce the influence of the modifier on the self-shrinkage of cement mortar.

In order to achieve the above purpose, the invention provides a durable cement mortar, which comprises the following raw materials: cement, sand, modifier and water.

Preferably, the durable cement mortar comprises the following raw materials in parts by weight: 20-50 parts of cement, 60-150 parts of sand, 1-3 parts of modifier and 8-20 parts of water.

Preferably, the cement is one of ordinary Portland cement, slag Portland cement and fly ash Portland cement.

The sand is common river sand with the grain diameter of 0.35-0.5 mm.

The preparation method of the modifier comprises the following steps:

(1) Dispersing magnesium oxide in water to form a suspension;

(2) Heating stearic acid to melt, adding nonionic surfactant and water, then adding ammonia water, and stirring to form a system I; and (3) dropwise adding the suspension in the step (1) into a continuously stirred system I, continuing to react after the dropwise adding is finished, and cooling and adjusting the solid content to obtain the modifier.

Further, the preparation method of the modifier comprises the following steps in parts by weight:

(1) Mixing 3-5 parts of magnesium oxide with 20-30 parts of water, treating for 20-60 min under the ultrasonic power of 50-100W, and then continuously stirring to form suspension;

(2) Heating and melting 20-50 parts of stearic acid at 70-90 ℃, adding 1-3 parts of nonionic surfactant and 100-150 parts of water, and stirring for 30-60 min; then adding 0.3-1 part of ammonia water, and continuing stirring and reacting for 30-60 min to form a system I; dropwise adding the suspension obtained in the step (1) into a continuously stirred system I, and continuously stirring for reaction for 30-60 min after complete dropwise adding; naturally cooling to 20-30 ℃, and regulating the solid content to 20-30% by using water to obtain the modifier.

More preferably, the preparation method of the modifier comprises the following steps:

(1) Mixing soluble metal cobalt salt with an organic solvent, stirring to form a solution, collecting insoluble matters after solvothermal reaction, washing, drying, calcining, crushing and sieving to obtain cobaltosic oxide;

(2) Dispersing magnesium oxide in water to form a suspension;

(3) Heating stearic acid to melt, adding nonionic surfactant and water, then adding ammonia water, and stirring to form a system I; and (3) dropwise adding the suspension in the step (2) into a continuously stirred system I, adding the cobaltosic oxide in the step (1) after dropwise adding, continuously reacting, and cooling and adjusting the solid content to obtain the modifier.

In some preferred embodiments, the preparation method of the modifier comprises the following steps in parts by weight:

(1) Mixing 0.5-1 part of cobalt nitrate hexahydrate, 20-30 parts of isopropyl alcohol and 5-10 parts of glycerol, and stirring for 30-60 min to form a solution; carrying out solvothermal reaction on the solution at 160-180 ℃ for 6-8 hours, naturally cooling, collecting insoluble matters, washing, drying, calcining, crushing and sieving to obtain cobaltosic oxide;

(2) Mixing 3-5 parts of magnesium oxide with 20-30 parts of water, treating for 20-60 min under the ultrasonic power of 50-100W, and then continuously stirring to form suspension;

(3) Heating and melting 20-50 parts of stearic acid at 70-90 ℃, adding 1-3 parts of nonionic surfactant and 100-150 parts of water, and stirring for 30-60 min; then adding 0.3-1 part of ammonia water, and continuing stirring and reacting for 30-60 min to form a system I; dropwise adding the suspension obtained in the step (2) into a continuously stirred system I, adding 1-5 parts of the cobaltosic oxide prepared in the step (1) after complete dropwise adding, and continuously stirring and reacting for 30-60 min; naturally cooling to 20-30 ℃, and regulating the solid content to 20-30% by using water to obtain the modifier.

Most preferably, the preparation method of the modifier comprises the following steps in parts by weight:

(1) Mixing 0.5-1 part of cobalt nitrate hexahydrate, 0.05-0.1 part of 2-mercapto-1-methylimidazole, 20-30 parts of isopropanol and 5-10 parts of glycerol, and stirring for 30-60 min to form a solution; carrying out solvothermal reaction on the solution at 160-180 ℃ for 6-8 hours, naturally cooling, collecting insoluble matters, washing, drying, calcining, crushing and sieving to obtain cobaltosic oxide;

Preferably, the nonionic surfactant in the step (3) is at least one of fatty alcohol polyoxyethylene ether O-20, fatty alcohol polyoxyethylene ether O-25 and fatty alcohol polyoxyethylene ether AEO-9.

The invention has the beneficial effects that:

mixing magnesium oxide and stearic acid, adding a nonionic surfactant, preparing magnesium stearate emulsion by utilizing a simple chemical reaction, and obviously improving the hydrophobic property of the inner surface and the outer surface of the mortar as a modifier of the cement mortar; the addition of the cobaltosic oxide further improves the hydrophobic property of the mortar, the mechanical strength, the water resistance and the chloride ion resistance of the mortar, and the shrinkage performance of the cement mortar.

Drawings

FIG. 1 is a scanning electron microscope image of tricobalt tetraoxide prepared according to the examples and comparative examples of the present invention;

fig. 1A is comparative example 2, fig. 1B is example 2, and fig. 1C is example 3.

Detailed Description

Introduction of partial materials in the embodiments of the present invention:

cement, portland cement PO 42.5, purchased from hubei new cement limited.

River sand, common river sand belongs to grade I sand and is purchased from Shijiuzhou forest mineral products limited company.

Fatty alcohol polyoxyethylene ether AEO-9, purchased from Shandong, sanchen New Material technology Co., ltd.

2-mercapto-1-methylimidazole, available from Shanghai Aba Ding Shenghua technologies Co.

The preparation method of the cement mortar test piece comprises the following steps: putting the cement mortar prepared by the method into a stirrer, stirring for 2min at a stirring speed of 80r/min, then filling the cement mortar into a mould, vibrating for 15s while filling the mortar, and scraping the surface of the mould by using a lime cutter after filling; and then placing the mould with the mortar in an environment with the relative humidity of 90% at 20 ℃ for curing, demoulding after 48 hours, and curing until the curing time is 28 days to obtain the cement mortar test piece.

The test pieces of 40mm multiplied by 160mm are used for strength test and self-shrinkage test of mortar; 70.7mm by 70.7mm test piece the water absorption test method is used for testing the water absorption of the mortar; a cylindrical sample with a diameter of 100mm and a height of 50mm was used for the chloride ion permeability test of the mortar.

Example 1

A durable cement mortar is composed of 20kg of cement, 60kg of river sand, 1kg of modifier and 8.2kg of water.

The preparation method of the modifier comprises the following steps:

(1) Mixing 3kg of magnesium oxide with 25kg of water, treating for 30min at an ultrasonic power of 50W and a frequency of 40kHz, and stirring for 30min at a stirring rate of 350r/min to form a suspension;

(2) Heating and melting 3.5kg of stearic acid at 80 ℃, adding 1kg of fatty alcohol polyoxyethylene ether AEO-9 and 100kg of water, and stirring for 30min at a stirring rate of 350 r/min; then adding 0.5kg of ammonia water, and continuing stirring to react for 3min to form a system I; dropwise adding the suspension obtained in the step (1) into a continuously stirred system I at a dropwise adding rate of 0.5kg/min, and continuously stirring for reaction for 30min after complete dropwise adding; naturally cooling to 25 ℃, and adjusting the solid content to 25% by using water to obtain the modifier.

Example 2

The preparation method of the modifier comprises the following steps:

(1) Mixing 0.8kg of cobalt nitrate hexahydrate, 25kg of isopropyl alcohol and 5kg of glycerin, and stirring at a stirring rate of 450r/min for 30min to form a solution; transferring the solution to a reaction kettle, carrying out solvothermal reaction for 8 hours at 180 ℃, naturally cooling to 25 ℃, collecting insoluble matters, washing three times with acetone and water respectively, drying for 6 hours in a constant-temperature oven at 80 ℃, transferring to a muffle furnace at 550 ℃ for calcining for 2 hours, naturally cooling to 25 ℃, crushing, and sieving with a 325-mesh screen to obtain cobaltosic oxide;

(2) Mixing 3kg of magnesium oxide with 25kg of water, treating for 30min at an ultrasonic power of 50W and a frequency of 40kHz, and stirring for 30min at a stirring rate of 350r/min to form a suspension;

(3) Heating and melting 3.5kg of stearic acid at 80 ℃, adding 1kg of fatty alcohol polyoxyethylene ether AEO-9 and 100kg of water, and stirring for 30min at a stirring rate of 350 r/min; then adding 0.5kg of ammonia water, and continuing stirring to react for 3min to form a system I; dropwise adding the suspension obtained in the step (2) into a continuously stirred system I at a dropwise adding rate of 0.5kg/min, adding 2kg of the cobaltosic oxide prepared in the step (1) after complete dropwise adding, and continuously stirring and reacting for 30min; naturally cooling to 25 ℃, and adjusting the solid content to 25% by using water to obtain the modifier.

Example 3

The preparation method of the modifier comprises the following steps:

(1) Mixing 0.8kg of cobalt nitrate hexahydrate, 0.05kg of 2-mercapto-1-methylimidazole, 25kg of isopropyl alcohol and 5kg of glycerin, and stirring at a stirring rate of 450r/min for 30min to form a solution; transferring the solution to a reaction kettle, carrying out solvothermal reaction for 8 hours at 180 ℃, naturally cooling to 25 ℃, collecting insoluble matters, washing three times with acetone and water respectively, drying for 6 hours in a constant-temperature oven at 80 ℃, transferring to a muffle furnace at 550 ℃ for calcining for 2 hours, naturally cooling to 25 ℃, crushing, and sieving with a 325-mesh screen to obtain cobaltosic oxide;

Comparative example 1

The modifier is 25wt.% magnesium stearate suspension.

Comparative example 2

A durable cement mortar is composed of 20kg of cement, 60kg of river sand, 1kg of modifier and 8.2kg of water

The modifier comprises the following steps:

(1) Mixing 0.8kg of cobalt nitrate hexahydrate, 0.2kg of urea and 30kg of water, and stirring at a stirring rate of 450r/min for 30min to form a solution; transferring the solution to a reaction kettle, carrying out solvothermal reaction for 8 hours at 180 ℃, naturally cooling to 25 ℃, collecting insoluble matters, washing three times with acetone and water respectively, drying for 6 hours in a constant-temperature oven at 80 ℃, transferring to a muffle furnace at 550 ℃ for calcining for 2 hours, naturally cooling to 25 ℃, crushing, and sieving with a 325-mesh screen to obtain cobaltosic oxide;

Test example 1

The compressive strength of 40 mm. Times.40 mm. Times.160 mm cement mortar test pieces was tested with reference to the standard GB/T17671-1999 cement mortar strength test method (ISO method), and the results are shown in Table 1. The composition of the conventional mortar in the table is substantially the same as in example 1, except that no modifier is added.

TABLE 1 Strength test results of Cement mortars

From the results of Table 1, it can be seen that the compressive strength of comparative example 1, in which a magnesium stearate suspension was added as an improver, was rather lowered relative to that of the conventional mortar. This is probably because magnesium stearate has a hydrophobic character, which reduces the interaction of the aggregate and the binder at the interface transition zone to some extent. The compressive strength of example 1, to which the magnesium stearate composite emulsion was added, was slightly higher than that of the conventional mortar, probably because the early magnesium stearate composite emulsion can promote the hydration reaction to proceed without consuming calcium hydroxide, thereby increasing cement hydration products and slightly improving the strength of the cement mortar. In comparative example 2, example 2 and example 3, cobaltosic oxide is added into the magnesium stearate composite emulsion, so that the compressive strength is further improved. This is probably because the tricobalt tetraoxide can be used as an initial template for ettringite formation, so that hydration products are promoted to form a more stable structure, and the tricobalt tetraoxide particles with high mechanical properties can bear part of stress, so that the strength of the mortar test piece is improved. As shown in fig. 1, it can be seen that there is a significant difference in the structures of the tricobalt tetraoxides of comparative example 2, and example 3. The hydrothermally prepared cobaltosic oxide (fig. 1A, example 1) is a lamellar agglomerate-like structure; the tricobalt tetraoxide of example 2 (fig. 1B) takes on a spherical shape; example 3 (fig. 1C) is a sheet with a multilayered structure. The cement mortar of example 3 has the best compressive strength, possibly affected by the tricobalt tetraoxide structure.

Test example 2

The water contact angle of the test piece may reflect the hydrophilicity of the test piece. And wetting water on the surface of the object to be measured, wherein the contact angle is more than 90 degrees and the object to be measured is hydrophobic. The 40mm×40mm×160mm cement mortar test pieces were cut, and the water contact angles of the inner and outer surfaces of the cement mortar were measured, and the results are shown in table 2.

TABLE 2 Water contact angles of inner and outer surfaces of test pieces

	Inner surface water contact angle (°)	External surface water contact angle (°)
			Common mortar	26	35
Example 1	83	119
			Example 2	93	128
Example 3	101	134
			Comparative example 1	61	113
Comparative example 2	88	123

As can be seen from the test results of Table 2, the cement mortar without the modifier has both inner and outer surfaces that are hydrophilic. The addition of magnesium stearate in comparative example 1 can improve the hydrophilicity of the mortar and reverse the wetting of the outer surface. Example 1 with magnesium stearate emulsion the hydrophilicity of the mortar test pieces was further improved, but the interior of the mortar was still hydrophilic. The same is true for comparative example 2. Both the inner and outer surfaces of the mortars of example 2 and example 3 were hydrophobic. This may be related to the structure of the tricobalt tetraoxide. The mortar of comparative example 3 has the best hydrophobicity, probably because the addition of 2-mercapto-1-methylimidazole not only improves the structure of tricobalt tetraoxide, but also enhances its dispersibility in emulsion systems, making the hydrophobic film easier to form.

The water absorption of a 70.7mm×70.7mm×70.7mm mortar sample was tested with reference to standard JC 474-2008 mortar, concrete waterproofing agent. Drying a standard mortar sample and a mortar sample to be tested to constant weight in a constant temperature oven at 80 ℃, and respectively weighing and recording the weight m at the moment _t1 And m ₁ The method comprises the steps of carrying out a first treatment on the surface of the Then placing the mixture into a tank with two steel bars at the bottom, immersing the standard mortar sample and the mortar sample to be tested into water with the height of 35mm, keeping the water surface constant, taking out the mixture after keeping the mixture in an environment with the temperature of 20 ℃ and the relative humidity of 90% for 48 hours, wiping the water on the surface of the test sample, and respectively weighing the recorded weights m of the standard mortar sample and the mortar sample to be tested _t1 And m ₂ The method comprises the steps of carrying out a first treatment on the surface of the Calculate the water absorption= (m ₂ -m ₁ )/(m _t2 -m _t1 ). The results are shown in Table 3.

Table 3 water absorption results of test pieces

	Water uptake (%)
		Common mortar	4.5
Example 1	2.6
		Example 2	2.1
Example 3	1.8
		Comparative example 1	4.3
Comparative example 2	2.4

As can be seen from the test results of the above table, the cement mortar test piece prepared in example 3 of the present invention has the lowest water absorption capacity because both the inside and the outside of the mortar are hydrophobic, water drops are repelled on the surface and are difficult to penetrate into pores, and the water absorption capacity is remarkably reduced; the cobaltosic oxide has a certain water-retaining effect, so that the free water content in the new mortar is reduced, micropores and capillary holes in the cement mortar hydration and maintenance processes are further reduced, and the passage way of water in the mortar is reduced.

Test example 3

And (3) testing the chloride ion permeation resistance of a cylindrical cement mortar test piece with the diameter of 100mm and the height of 50mm by adopting a rapid chloride ion migration coefficient method according to the standard GB/T50082-2009 common concrete long-term performance and durability test method standard. The results are shown in Table 4. Lower penetration depth, lower permeability coefficient, represents better resistance to chloride ions.

TABLE 4 results of resistance to penetration of chloride ions of cement mortar test pieces

From the results shown in Table 4, it can be seen that the mortar prepared in example 3 of the present invention has the best anti-permeability, probably because the mortar has a compact matrix structure and good strength, reduces chloride ion diffusion channels, and significantly reduces the permeability coefficient of chloride ions.

Test example 4

The self-shrinkage performance of the mortar test piece is tested by referring to the standard JGJ/T70-2009 building mortar basic performance test method standard. The results are shown in Table 5.

TABLE 5 self-shrinkage results of cement mortars

	Self-contraction (mu epsilon)
		Common mortar	-536
Example 1	-628
		Example 2	-486
Example 3	-432
		Comparative example 2	-601

From the test results of the above table, it can be seen that the self-shrinkage of the test piece prepared by adding the magnesium stearate emulsion of example 1 is increased, which is probably because the hydrophobicity of the mortar test piece is enhanced, the magnesium stearate promotes hydration reaction, and water is consumed, so that the self-drying effect inside the mortar is more obvious. Comparative example 2 was also added with hydrothermally prepared tricobalt tetroxide, which was probably because the tricobalt tetroxide as an ettringite template refined the pore structure. Example 3, with the addition of the 2-mercapto-1-methylimidazole modified cobaltosic oxide and magnesium stearate emulsion, has the best self-shrinkage performance, probably due to good dispersibility, overall hydrophobicity of the mortar, and a refined pore structure, enhancing capillary pressure and internal stress, thereby significantly improving the self-shrinkage performance of the mortar.

Claims

1. The durable cement mortar is characterized by comprising the following raw materials: 20-50 parts of cement, 60-150 parts of sand, 1-3 parts of modifier and 8-20 parts of water;

the preparation method of the modifier comprises the following steps in parts by weight:

2. The durable cement mortar of claim 1, wherein the cement is one of portland cement, slag portland cement, fly ash portland cement.

3. The durable cement mortar according to claim 1, wherein the sand is ordinary river sand having a particle size of 0.35 to 0.5mm.

4. The durable cement mortar of claim 1, wherein the preparation method of the modifier comprises the following steps in parts by weight:

5. The durable cement mortar according to claim 1 or 3, wherein the nonionic surfactant is at least one of fatty alcohol-polyoxyethylene ether O-20, fatty alcohol-polyoxyethylene ether O-25, and fatty alcohol-polyoxyethylene ether AEO-9.