A self-compacting concrete preparation method based on shear thinning and thickening effect and self-compacting concrete prepared thereby

Abstract

The application discloses a self-compacting concrete preparation method based on shear thinning and thickening effects and self-compacting concrete prepared by the method. The self-compacting concrete is prepared by stirring cement, fly ash, water, sand, gravel, a shear thinning agent, a shear thickening agent and a glass microsphere starch solution in a certain order, and the water, the cementing material and the shear thinning agent are added in batches. Firstly, the shear thinning effect is used to realize uniform mixing of wrapped neat paste and aggregates; secondly, the shear thickening effect is used to improve the wrapped thickness of the wrapped neat paste on the aggregates; then, the secondary neat paste is added to realize uniform mixing with the aggregates under the action of the shear thinning effect, and the self-compacting concrete is prepared by adjusting the rotating speed and mixing the glass microsphere starch suspension. The shear thinning and thickening effects of the concrete neat paste and the mixture are fully utilized, the self-compacting concrete production process is improved, and the performance of the self-compacting concrete is improved.

Description

Technical Field

[0001] This invention relates to the field of concrete production technology, specifically to a method for preparing self-compacting concrete based on shear thinning and thickening effects, and the resulting self-compacting concrete. Background Technology

[0002] Currently, concrete batching plants produce concrete by dumping all raw materials into the mixing device together, without paying attention to the order in which cementitious materials and aggregates are added. To improve production efficiency, enhance the performance of the mixture, and reduce energy consumption, adjusting the mixing sequence is a better production method. Currently, the main method for improving concrete performance by adjusting the mixing sequence is to add materials in stages. This involves ensuring the quality of raw materials such as sand, aggregate, and cementitious materials, and strictly adhering to the concrete mix proportions. First, sand and water are added and mixed, then cementitious materials are added and mixed to form mortar, and finally, aggregate is added so that the mortar coats the aggregate. There are currently two main production schemes for this method: The first is to feed sand and aggregate in stages, with the intermediate hopper opening twice. Specifically, during the first feeding, the intermediate hopper door is opened, and sand and cementitious materials are added to the main mixer. After mixing evenly, the intermediate hopper is opened again, and aggregate is added and mixed. However, this method, due to its use of a single hopper, requires strict control over the transportation and input time of raw materials. Often, the inability to precisely control the feeding and mixing times leads to a significant extension of the mixing time, resulting in low concrete production efficiency and failing to demonstrate the high efficiency and energy-saving advantages of this process. The second method involves modifying the equipment by establishing double intermediate hoppers, which can be parallel horizontally or stacked vertically. Specifically, sand and gravel are stored separately in the double intermediate hoppers, and then poured into the mixer sequentially. This method saves 15% of energy compared to the conventional process, but because this method requires the double intermediate hoppers to be positioned high, overflow or mixing problems frequently occur.

[0003] In general, the two technical means currently used in batching plants to produce concrete differ; the former is highly efficient and produces high-quality concrete, while the latter reduces energy consumption. In current production, methods to improve concrete performance by adjusting the mixing sequence are also frequently employed. However, no literature has yet proposed adjusting the shear rate to alter the consistency of the paste, thereby achieving better mixing of aggregates and paste, further improving the properties of the mixture, and ultimately enhancing the concrete's performance. Summary of the Invention

[0004] To further improve the performance of self-compacting concrete, this invention proposes a method for preparing self-compacting concrete based on shear thinning and thickening effects, utilizing existing step-by-step mixing production technology. By fully utilizing the shear thinning and thickening effects of concrete paste and mix, the production process of self-compacting concrete is improved, thereby enhancing its performance.

[0005] This invention provides a method for preparing self-compacting concrete based on shear thinning and thickening effects. The self-compacting concrete is obtained by mixing cement, fly ash, water, sand, gravel, shear thinner, shear thickener, and glass microsphere starch solution in a certain order. The specific steps are as follows:

[0006] (1) Mix the sand and gravel aggregates with the first batch of water and stir evenly to form pre-wet aggregates;

[0007] (2) Mix the first batch of cementitious materials (cement and fly ash) with the second batch of water and the first batch of shear thinner by controlling the mixing equipment to mix them evenly at high speed, so that the slurry is thinned to form a clean slurry.

[0008] (3) Pour the pre-wetted aggregate described in step (1) into the clean slurry wrapped in step (2), and add shear thickener and stir to form modified aggregate A;

[0009] In this step, the slurry thinned in step (2) is mixed with the pre-wetted aggregate. Its thinning properties are used to achieve rapid coating of the aggregate. A shear thickener is further added to reduce its thinning effect and increase its thickening effect, thereby increasing the coating thickness of the slurry on the surface of the aggregate and reducing the phenomenon of water bleeding and segregation.

[0010] (4) Mix the second batch of cementitious material and the third batch of water evenly, add the second batch of shear thinner and stir at high speed to form a secondary slurry; in this step, the remaining slurry is thinned by high-speed stirring and the action of shear thinner.

[0011] (5) Pour the secondary slurry obtained in step (4) into the modified aggregate A in step (3) and stir evenly to obtain a mixture;

[0012] In this step, the thinned slurry formed in step (4) is poured into the mixture in step (3) to coat the particles a second time, thereby increasing the degree of thinning of the surface-coated slurry and increasing the workability of the slurry.

[0013] (6) Slowly add glass microsphere starch solution to the mixture in step (5) above and stir evenly to obtain self-compacting concrete.

[0014] The water component is added in three batches in each step. In step (1), the first batch of water accounts for 5% to 10% of the total water mass, the second batch of water accounts for 20% to 30% of the total water mass, and the remainder is added in the third batch in step (4).

[0015] The cementitious material composed of cement and fly ash is added in two batches. In step (2), the mass of the first batch of cementitious material accounts for 20%-40% of the total mass of cementitious material, and the remainder is added in the second batch in step (4).

[0016] The shear thinner is added in two batches. The amount of shear thinner used in the first batch in step (2) accounts for 20% to 40% of the total mass of the shear thinner, and the remainder is added in the second batch in step (4).

[0017] The stirring speed in step (2) is 200-300 r / min, and the stirring time is 30 s.

[0018] The specific preparation of step (3) includes: pouring the pre-wetted aggregate from step (1) into the coated slurry, stirring evenly, reducing the rotation speed to 0.5-5 r / min and adding the shear thickener, maintaining the rotation speed at a low speed of 20-50 r / min for 30s until the mixture is evenly stirred, gradually increasing the rotation speed to 260-300 r / min, maintaining it for 30s, and stirring to form modified aggregate A.

[0019] In step (4), the stirring speed is increased to 200-300 r / min and maintained for 10-15 seconds to form a secondary slurry.

[0020] The stirring speed in step (5) is maintained at 260-300 r / min.

[0021] In step (6), glass microsphere starch solution is added and stirred evenly for 30 seconds. Then, the rotation speed is slowly reduced to 4-10 r / min to obtain self-compacting concrete.

[0022] In this invention, the glass microsphere starch solution has a thinning-thickening effect. Adding a thinning-thickening agent to the slurry in step (5) can increase the consistency of the slurry under high-speed conditions and increase the coating of the aggregate by the neat slurry in step (5). Since the concrete needs to maintain high fluidity at low speed during transportation after production, the glass microsphere starch solution is added. Through its reverse thinning-thickening effect, by adjusting its dosage and the proportion of each component, a higher degree of thinning can be achieved under low-speed rotation conditions during transportation, which is convenient for construction application.

[0023] Furthermore, the raw materials in the self-compacting concrete of the present invention are expressed in the following weight fractions:

[0024]

[0025]

[0026] Furthermore, the shear thinner of the present invention is obtained by ultrasonically dispersing nonionic cellulose ether and carbon microspheres at a mass ratio of 100:0.2-0.5;

[0027] The nonionic cellulose ether is preferably methyl cellulose ether or hydroxyethyl cellulose.

[0028] Furthermore, the shear thickener of the present invention is a mixed suspension formed by mixing nano-silica, glass fiber, polyacrylamide and polycarboxylate superplasticizer in a mass ratio of 1:1 to 2:0.5 to 1:5 to 10, adding 2 to 5 times the mass of water to the mixture, and ultrasonically dispersing it.

[0029] The molecular weight of the polyacrylamide is not less than 12 million.

[0030] Furthermore, the glass microsphere starch solution of the present invention is a mixed suspension obtained by adding 5-10 parts by weight of glass microspheres and 1-2 parts by weight of carbon microspheres to 100 parts by weight of starch aqueous solution and dispersing them evenly by ultrasonication; the mass fraction of the starch aqueous solution is 10-20%.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] (1) In order to achieve a good coating effect of cement on aggregate, a shear thinner is first used to thin the slurry. After the aggregate is added, it can adhere evenly on the surface of the aggregate. After the mixture is evenly coated, the rotation speed is reduced and the adhesion is improved by reverse thickening of the slurry. On this basis, a shear thickener is added first, and the rotation speed is increased to make the aggregate and slurry coating more compact. The use of a shear thickener based on polyacrylamide improves the adhesion and aggregation between aggregate and slurry and slurry particles, reduces the dispersibility of slurry and aggregate in liquid, and improves its compactness, so that the slurry added later cannot cause destructive disturbance to it, and reduces the occurrence of the phenomenon of slurry peeling off the coated aggregate.

[0033] (2) After achieving good coating of aggregates by the slurry, the remaining cementitious material is thinned into a slurry and poured into the modified aggregates. The mixture is then rotated at a relatively high speed and stirred until homogeneous. A glass microsphere starch solution is then added. The glass microsphere starch solution exhibits the characteristic of first thinning and then thickening with increasing rotation speed, and conversely, thinning and then thickening with decreasing rotation speed. Therefore, after adding the solution, maintaining or further increasing the rotation speed increases the viscosity of the outer slurry, allowing the slurry to adhere and coat the aggregates a second time. After forming a viscous slurry under high-speed stirring conditions, the rotation speed is slowly reduced to thin the surface slurry. Then, at a certain rotation speed, self-compacting is achieved.

[0034] (3) The method of the present invention first achieves uniform mixing of the coating paste and aggregate through the shear thinning effect, and further improves the coating thickness of the coating paste on the aggregate through the shear thickening effect, so as to achieve complete coating of the aggregate by the coating paste. The overall stability and non-dispersibility of the coating paste after coating the aggregate are achieved by adding different additives. Secondly, the uniform mixing between the secondary coating paste and the aggregate is achieved under the action of the shear thinning effect. By adjusting the rotation speed and adding glass microsphere starch suspension, the thickening-thinning effect of the mixture is achieved, and a high-performance self-compacting concrete is prepared. Detailed Implementation

[0035] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] The component parts in each embodiment and comparative example are expressed as parts by mass.

[0037] Example 1

[0038] The mix proportions for self-compacting concrete are as follows: 300 parts cement, 150 parts fly ash, 800 parts sand, 920 parts gravel, 190 parts water, 10 parts shear thinner, 2 parts shear thickener, and 0.5 parts glass microsphere starch solution.

[0039] A method for preparing self-compacting concrete based on shear thinning and thickening effects is as follows:

[0040] (1) Mix all the aggregates with 5% water (9.5 parts) and stir evenly to wet them, forming pre-wet aggregates;

[0041] (2) Mix 300 parts of cement and 150 parts of fly ash evenly, take 20% (90 parts) of the total amount, add 20% (38 parts) of water, stir evenly, add 40% (4 parts) of shear thinner, control the speed of the mixing equipment to 200 r / min, stir for 30s until evenly mixed, and form a coating paste.

[0042] (3) Pour the pre-wetted aggregate into the coated slurry, stir evenly, reduce the speed to 5r / min, add 2 parts of shear thickener, maintain the speed at 20r / min for 30s until the mixture is evenly stirred, gradually increase the speed to 300r / min, maintain for 30s, and form modified aggregate A.

[0043] (4) Mix the remaining cementitious material and water evenly, add the remaining shear thinner - 6 parts of shear thinner (60% of the total amount), increase the shear rate to 300 r / min, and maintain for 15 seconds to form a secondary neat slurry.

[0044] (5) Pour the secondary paste into the modified aggregate A at a speed maintained at 300 r / min and stir evenly.

[0045] (6) Slowly add 0.5 parts of glass microsphere starch solution to the above mixture. After the addition is complete, stir evenly and maintain for 30 seconds. Then slowly reduce the speed to 4 r / min to obtain self-compacting concrete.

[0046] The shear thinner is obtained by ultrasonically dispersing methyl cellulose ether and carbon microspheres at a mass ratio of 100:0.2.

[0047] The shear thickener is a mixed suspension formed by mixing nano-silica, glass fiber, polyacrylamide and polycarboxylate superplasticizer in a mass ratio of 1:1:0.5:5, adding 2 times the amount of water, and ultrasonically dispersing.

[0048] The polyacrylamide has a molecular weight of 12 million.

[0049] The glass microsphere starch solution is a mixed suspension obtained by adding 5 parts by mass of glass microspheres and 1 part by mass of carbon microspheres to 100 parts by mass of starch aqueous solution and then dispersing them evenly by ultrasonication; the mass fraction of the starch aqueous solution is 10%.

[0050] Example 2

[0051] The mix proportions for self-compacting concrete are as follows: 450 parts cement, 60 parts fly ash, 890 parts sand, 850 parts gravel, 230 parts water, 5 parts shear thinner, 5 parts shear thickener, and 2 parts glass microsphere starch solution.

[0052] A method for preparing self-compacting concrete based on shear thinning and thickening effects is as follows:

[0053] (1) Mix all the aggregates with 10% water (23 parts) and stir evenly to wet them, forming pre-wet aggregates.

[0054] (2) Mix 450 parts of cement and 60 parts of fly ash evenly, take 40% (204 parts) of the total amount, add 30% of the total water (69 parts), stir evenly, add 20% (1 part) of the total amount of shear thinner, control the speed of the mixing equipment to 300 r / min, stir for 30s until evenly mixed, and form a coating paste.

[0055] (3) Pour the pre-wetted aggregate into the coated slurry, stir evenly, reduce the speed to 0.5 r / min, add 5 parts of shear thickener, maintain the speed at 50 r / min for 30s until the mixture is evenly stirred, gradually increase the speed to 260 r / min, maintain for 30s, and form modified aggregate A.

[0056] (4) Mix the remaining cementitious material and water evenly, add 4 parts of the remaining shear thinner, increase the shear rate to 200 r / min, and maintain for 10 s to form a secondary neat slurry.

[0057] (5) Pour the secondary paste into the modified aggregate A at a rotation speed of 260 r / min and stir evenly.

[0058] (6) Slowly add 2 parts of glass microsphere starch solution to the above mixture. After the addition is complete, stir evenly and maintain for 30 seconds. Slowly reduce the rotation speed by 8 r / min to obtain self-compacting concrete.

[0059] The shear thinner is obtained by ultrasonically dispersing hydroxyethyl cellulose and carbon microspheres at a mass ratio of 100:0.5.

[0060] The shear thickener is a mixed suspension formed by mixing nano-silica, glass fiber, polyacrylamide and polycarboxylate superplasticizer in a mass ratio of 1:2:1:10, adding 5 times the amount of water, and ultrasonically dispersing.

[0061] The polyacrylamide has a molecular weight of 15 million.

[0062] The glass microsphere starch solution is a mixed suspension obtained by adding 10 parts by mass of glass microspheres and 2 parts by mass of carbon microspheres to 100 parts by mass of starch aqueous solution and then dispersing them evenly by ultrasonication; the mass fraction of the starch aqueous solution is 20%.

[0063] Example 3

[0064] The mix proportions for self-compacting concrete are as follows: 350 parts cement, 100 parts fly ash, 860 parts sand, 900 parts gravel, 220 parts water, 8 parts shear thinner, 5 parts shear thickener, and 1 part glass microsphere starch solution.

[0065] A method for preparing self-compacting concrete based on shear thinning and thickening effects is as follows:

[0066] (1) Mix all the aggregates with 7.5% water (16.5 parts) and stir evenly to wet them, forming pre-wet aggregates.

[0067] (2) Mix 350 parts of cement and 100 parts of fly ash evenly, take 30% (135 parts) of the total amount, add 25% (55 parts) of water, stir evenly, add 3 parts of shear thinner, control the speed of the mixing equipment to 250 r / min, stir for 30s until evenly mixed, and form a coating paste.

[0068] (3) Pour the pre-wetted aggregate into the coated clean slurry, stir evenly, reduce the speed to 3r / min, add 5 parts of shear thickener, maintain the speed at 30r / min for 30s until the mixture is evenly stirred, gradually increase the speed to 280r / min, maintain for 30s, and form modified aggregate A.

[0069] (4) Mix the remaining cementitious material and water evenly, add the remaining 5 parts of shear thinner, increase the shear rate to 250 r / min, and maintain for 12 s to form a secondary neat slurry.

[0070] (5) Pour the secondary paste into the modified aggregate A at a rotation speed of 280 r / min and stir evenly.

[0071] (6) Slowly add 1 part of glass microsphere starch solution to the above mixture. After the addition is complete, stir evenly and maintain for 30 seconds. Slowly reduce the rotation speed to 10 r / min to obtain self-compacting concrete.

[0072] The shear thinner is obtained by ultrasonically dispersing nonionic cellulose ether and carbon microspheres at a mass ratio of 100:0.4; the nonionic cellulose ether is preferably obtained by mixing methyl cellulose ether and hydroxyethyl cellulose at a mass ratio of 1:1.

[0073] The shear thickener is a mixed suspension formed by mixing nano-silica, glass fiber, polyacrylamide and polycarboxylate superplasticizer in a mass ratio of 1:1.5:0.8:7, adding 3 times the amount of water, and ultrasonically dispersing.

[0074] The polyacrylamide has a molecular weight of 14 million.

[0075] The glass microsphere starch solution is a mixed suspension obtained by adding 8 parts by mass of glass microspheres and 1.5 parts by mass of carbon microspheres to 100 parts by mass of starch aqueous solution and then dispersing them evenly by ultrasonication; the mass fraction of the starch aqueous solution is 15%.

[0076] Comparative Example 1

[0077] The proportions are the same as in Example 3, except that the preparation method is to directly mix the raw materials in Example 3 evenly to obtain self-compacting concrete.

[0078] Comparative Example 2

[0079] The proportions are the same as in Example 3, except that no shear thinner is added in step (2), no shear thickener is added in step (3), no shear thinner is added in step (4), and no glass microsphere starch solution is added in step (6).

[0080] Comparative Example 3

[0081] The ratio is the same as in Example 3, except that no shear thinner is added in step (2), and all the shear thinner is added to step (4).

[0082] Comparative Example 4

[0083] The proportions are the same as in Example 3, except that no shear thickener is added in step (3).

[0084] Comparative Example 5

[0085] The ratio is the same as in Example 3, except that no shear thinner is added in step (4), but is added entirely to step (2).

[0086] Comparative Example 6

[0087] The proportions are the same as in Example 3, except that glass microsphere starch solution is not added in step (6).

[0088] Comparative Example 7

[0089] The proportions are the same as in Example 3, except that shear thinner and shear thickener are not added in preparation steps (2), (3), and (4).

[0090] Comparative Example 8

[0091] The mixing ratio is the same as in Example 3, except that no speed adjustment is performed in any of the preparation steps. The mixing speed is maintained at 45 r / min, which is the same as that used in conventional concrete production.

[0092] Comparative Example 9

[0093] The proportions are the same as in Example 3, except that carbon nanospheres are not added to the shear thinner.

[0094] Comparative Example 10

[0095] The proportions are the same as in Example 3, except that carbon nanospheres are not added to the glass microsphere starch solution.

[0096] Comparative Example 11

[0097] The proportions are the same as in Example 3, except that glass fibers are not added to the shear thickener.

[0098] Comparative Example 12

[0099] The proportions are the same as in Example 3, except that polyacrylamide is not added to the shear thickener.

[0100] Comparative Example 13

[0101] The proportions are the same as in Example 3, except that no polycarboxylate superplasticizer is added to the shear thickener.

[0102] The performance tests of the concrete prepared in each embodiment and comparative example are shown in Table 1.

[0103] Table 1. Performance tests of concrete in each embodiment and comparative example.

[0104] Group Extension range (mm) 28-day compressive strength (MPa) Example 1 710×700 48.2 Example 2 720×710 47.8 Example 3 690×700 49.4 Comparative Example 1 450×460 37.5 Comparative Example 2 450×450 36.8 Comparative Example 3 660×680 42.9 Comparative Example 4 700×690 40.5 Comparative Example 5 480×500 41.5 Comparative Example 6 510×520 43.4 Comparative Example 7 490×510 37.8 Comparative Example 8 620×610 44.1 Comparative Example 9 640×650 43.1 Comparative Example 10 660×660 43.6 Comparative Example 11 690×700 44.8 Comparative Example 12 690×710 43.9 Comparative Example 13 660×650 36.8

[0105] As shown in Table 1, compared to the self-compacting concrete produced by the traditional mixing and stirring methods of the current concrete batching plant in Comparative Example 1, the self-compacting concrete produced using the present invention has a 230-270mm increased flowability at the mixer. This indicates that under the same mix proportions, the concrete fluidity and workability are significantly improved through shear thinning and thickening effects. Simultaneously, the 28-day compressive strength is increased by more than 9MPa, demonstrating that the present invention can significantly improve the mechanical properties of self-compacting concrete. This shows that shear thinners and shear thickeners cannot effectively improve the workability of concrete when the mixing method is not optimized. This is mainly because the shear thinning and shear thickening effects depend on changes in the shear rate. Without optimizing the shear rate, the performance of the concrete mixture cannot be optimized.

[0106] Compared to Comparative Example 2, it can be seen that without the use of shear thinners and shear thickeners, the slump and compressive strength of the concrete decreased significantly, similar to the data in Comparative Example 1. This indicates that when the mixing method is unreasonable, whether or not shear thinners and shear thickeners are added has little impact on the performance of the concrete.

[0107] Compared to Comparative Example 3, it can be seen that using a shear thickener first, followed by a single application of a shear thinner, fails to achieve a good concrete modification effect. This is mainly because the shear thickener increases the viscosity of the concrete mixture. If it is not thinned beforehand, the paste becomes viscous, resulting in poor adhesion to the aggregates, more pores, weak adhesion, and poor concrete performance.

[0108] Compared to Comparative Example 4, it can be seen that although the concrete mix volume did not decrease significantly without the use of a shear thickener, the concrete strength deteriorated. This is mainly because without the constraint of a shear thickener, using only a shear thinner easily leads to bleeding and segregation of the paste, resulting in the degradation of concrete performance.

[0109] As can be seen from Comparative Example 5, thinning followed by thickening does not significantly improve the workability of concrete. This is mainly because while thinning followed by thickening improves the coating of the paste on the aggregate, it also reduces the fluidity and self-compacting properties of the concrete mixture due to the thickening effect.

[0110] Compared to Comparative Example 6, it can be seen that without the use of glass microsphere starch solution, the thinning-thickening transition effect cannot eliminate the adverse effects on the concrete mixture caused by the secondary addition of thinner. This will cause the slurry to gradually thicken as the rotation speed decreases after thinning under high speed conditions, resulting in poor workability and decreased mechanical properties of the concrete.

[0111] Compared to Comparative Example 7, it can be seen that adding only glass microsphere starch solution causes the concrete to thicken under high-speed conditions, resulting in poorer workability. Even though it gradually thins as the rotation speed decreases, it still cannot eliminate the adverse effects of thickening the concrete mixture, thus making the final performance of the concrete worse.

[0112] Compared to Comparative Example 8, it can be seen that without adjusting the rotation speed, the thinning and thickening effects cannot be achieved, resulting in a lack of significant improvement in the fluidity and mechanical properties of the concrete mixture.

[0113] Compared to Comparative Example 9, it can be seen that carbon nanospheres can significantly promote the thinning effect of concrete. This is mainly due to the small particle size and good slip properties of carbon nanospheres, which can increase the fluidity of concrete and achieve effects that traditional cellulose ether thinners cannot. Furthermore, their addition reduces the difficulty of thinning, facilitating concrete mixing and production. Meanwhile, compared to Comparative Example 10, it can be seen that the thinning effect of carbon nanospheres in glass microsphere starch solution is still significant, effectively improving the workability of concrete and exhibiting good thinning effects at lower rotation speeds.

[0114] Compared to Comparative Examples 11 and 12, it can be seen that the absence of glass fiber or polyacrylamide in the shear thickener negatively impacts the thickening effect of concrete. Compared to Comparative Example 13, it can be observed that although the addition of polycarboxylate superplasticizer increases the fluidity of the concrete mixture (due to its thinning effect), the lack of polycarboxylate superplasticizer in the thickener leads to a decrease in concrete workability and mechanical properties. This indicates that the dispersing effect of polycarboxylate superplasticizer is essential during the thickening process of concrete, facilitating uniform dispersion of the paste and achieving aggregate coating, improving coating uniformity, and ultimately enhancing concrete performance.

Claims

1. A method for preparing self-compacting concrete based on shear thinning and thickening effects, characterized in that, The self-compacting concrete is obtained by mixing cement, fly ash, water, sand, gravel, shear thinner, shear thickener, and glass microsphere starch solution in a certain order. The specific steps are as follows: (1) Mix the sand and gravel aggregates with the first batch of water and stir evenly to form pre-wet aggregates; (2) The first batch of cementitious material, the second batch of water, and the first batch of shear thinner are mixed evenly by controlling the mixing equipment at high speed to thin the slurry and form a clean slurry. (3) Pour the pre-wetted aggregate from step (1) into the slurry from step (2), and add shear thickener and stir to form modified aggregate A; (4) Mix the second batch of cementitious material and the third batch of water evenly, add the second batch of shear thinner and stir at high speed to form a secondary clean slurry; (5) Pour the secondary slurry obtained in step (4) into the modified aggregate A in step (3) and stir evenly to obtain a mixture; (6) Slowly add glass microsphere starch solution to the mixture in step (5) above and stir evenly to obtain self-compacting concrete; The water component is added in three batches in each step, with the first batch accounting for 5% to 10% of the total water mass, the second batch accounting for 20% to 30% of the total water mass, and the remainder added in the third batch. The cementitious material composed of cement and fly ash is added in two batches, with the first batch accounting for 20%-40% of the total cementitious material mass and the remainder added in the second batch. The shear thinner is added in two batches, with the first batch accounting for 20% to 40% of the total mass of the shear thinner, and the remainder added in the second batch. The shear thinner is obtained by ultrasonically dispersing nonionic cellulose ether and carbon microspheres at a mass ratio of 100:0.2~0.

5. The shear thickener is a mixed suspension formed by mixing nano-silica, glass fiber, polyacrylamide and polycarboxylate superplasticizer in a mass ratio of 1:1~2:0.5~1:5~10, adding 2~5 times the mass of water to the mixture, and then ultrasonically dispersing it. The molecular weight of the polyacrylamide is not less than 12 million.

2. The method for preparing self-compacting concrete based on shear thinning and thickening effects according to claim 1, characterized in that, The stirring speed in step (2) is 200~300 r / min, and the stirring time is 30 s; The specific preparation of step (3) includes: pouring the pre-wetted aggregate from step (1) into the coated slurry, stirring evenly, reducing the rotation speed to 0.5~5 r / min and adding the shear thickener, maintaining the rotation speed at a low speed of 20~50 r / min for 30s until the mixture is evenly stirred, gradually increasing the rotation speed to 260~300 r / min, maintaining it for 30s, and stirring to form modified aggregate A; In step (4), the stirring speed is increased to 200-300 r / min and maintained for 10-15 seconds to form a secondary slurry; The stirring speed in step (5) is maintained at 260~300 r / min; In step (6), glass microsphere starch solution is added and stirred evenly for 30 seconds. Then, the rotation speed is slowly reduced to 4~10 r / min to obtain self-compacting concrete.

3. A method for preparing self-compacting concrete based on shear thinning and thickening effects according to claim 1 or 2, characterized in that, The raw materials in the self-compacting concrete are expressed in the following parts by weight: 300-450 parts cement 60-150 parts fly ash 800-890 parts of sand 850-920 portions of pebbles 190-230 parts water 5-10 parts shear thinner 2-5 parts shear thickener 0.5 to 2 parts of glass microsphere starch solution.

4. The method for preparing self-compacting concrete based on shear thinning and thickening effects according to claim 1, characterized in that, The nonionic cellulose ether is methylcellulose ether or hydroxyethylcellulose.

5. The method for preparing self-compacting concrete based on shear thinning and thickening effects according to claim 3, characterized in that, The glass microsphere starch solution is a mixed suspension obtained by adding 5-10 parts by weight of glass microspheres and 1-2 parts by weight of carbon microspheres to 100 parts by weight of starch aqueous solution and dispersing them evenly by ultrasonication; the mass fraction of the starch aqueous solution is 10-20%.

6. A self-compacting concrete prepared by the preparation method according to any one of claims 1 to 5.

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