High-performance underwater non-dispersible concrete

Abstract

The present application relates to a kind of high-performance underwater non-dispersible concrete, including 450-750 parts by mass of fine aggregate, 700-1050 parts by mass of coarse aggregate, 350-450 parts by mass of cement, 150-260 parts by mass of water, also including fly ash, mineral powder, silica fume, polycarboxylic acid water-reducing agent, underwater non-dispersible concrete polyacrylamide;Wherein, underwater non-dispersible concrete polyacrylamide is a terpolymer, including acrylamide structural unit, acrylic acid structural unit and allyl-A-D-galactopyranoside structural unit, the molar ratio of the three structural units is (50-70): (15-25): (15-25). By adding the polyacrylamide-based flocculant specially adapted for the concrete of underwater construction in concrete, concrete is made to have excellent anti-dispersion, fluidity, compressive strength and water-land strength ratio, so that concrete can meet the requirements of underwater construction and has excellent strength performance.

Description

Technical Field

[0001] The present application relates to the field of concrete, and in particular to high-performance underwater non-dispersible concrete. Background Art

[0002] Since the early 1970s, researchers around the world have been working to improve the properties of concrete. By adding special admixtures, such as flocculants, to ordinary concrete, they have achieved self-leveling during underwater pouring without causing cement and aggregate segregation and dispersion, thus meeting the technical requirements of underwater construction.

[0003] The construction of new, complex, long-span sea and river crossing bridges is placing higher demands on the performance of concrete used in underwater environments. Currently, the most commonly used flocculants in underwater concrete are cellulose and polyacrylamide. However, due to their different production applications and the increasing performance requirements for underwater concrete, these two flocculants no longer meet the requirements of structural engineering concrete.

[0004] Studies have shown that when cellulose is compounded with naphthalene-based water reducers in alkaline environments, the chemical reaction forms a gel, leading to poor compatibility. This incompatibility also occurs when compounded with polyalkyl sulfonate water reducers, resulting in an abnormal increase in viscosity. While the addition of cellulose anti-dispersion agents significantly improves the anti-dispersion properties of underwater non-dispersible concrete, it also increases the concrete's air content by 1-2.3%, which directly reduces compressive strength by 5-10%.

[0005] For polyacrylamide-based flocculants, as the amount of polyacrylamide increases, the PAM dispersed in the hydrated cement forms crosslinks between the solidified particles, resulting in an increase in the degree of product densification and a decrease in porosity. Anionic polyacrylamide (APAM) is most suitable for inducing cement flocculation to form flocs because it can react chemically with the Ca2+ produced by cement hydration to form ionic compounds and wrap around the surface of cement particles, forming an incomplete continuous network system, which is manifested in the improvement of the mechanical properties of concrete on a macro scale, but the construction performance is poor. Especially in underwater environments, the two main defects of concrete are easy dispersion, insufficient firmness and insufficient salt tolerance. At present, research on improving the dispersibility, firmness and salt tolerance of underwater concrete is relatively insufficient, especially research based on high-performance underwater non-dispersible concrete is particularly insufficient. Therefore, the present application aims to provide a high-performance underwater non-dispersible concrete that is particularly suitable for underwater construction. Summary of the Invention

[0006] In order to solve the above-mentioned defects existing in the existing underwater construction concrete, this application provides a polyacrylamide-based flocculant that is particularly suitable for underwater construction concrete through structural design of polyacrylamide. Then, based on the addition of this polyacrylamide-based flocculant, the components of the concrete are optimized and the corresponding performance is studied, and finally a high-performance underwater non-dispersible concrete is obtained.

[0007] A high-performance underwater non-dispersible concrete comprises 450-750 parts by mass of fine aggregate, 700-1050 parts by mass of coarse aggregate, 350-450 parts by mass of cement, 150-260 parts by mass of water, fly ash, mineral powder, silica fume, a polycarboxylate water reducer, and polyacrylamide for underwater non-dispersible concrete; wherein, with the total mass of the fine aggregate, coarse aggregate, cement, and water being denoted as M, the mass of the fly ash / M=0-5%, the mass of the mineral powder / M=0-5%, the mass of the silica fume / M=0-3%, the mass of the polycarboxylate water reducer / M=0.5-3%, and the mass of the polyacrylamide for underwater non-dispersible concrete / M=0.3-1%;

[0008] The polyacrylamide for underwater non-dispersible concrete is a ternary copolymer comprising an acrylamide structural unit, an acrylic acid structural unit and an allyl-A-D-galactopyranoside structural unit. The ternary copolymer has a structure shown in formula (I).

[0009]

[0010] Wherein, in formula (I), x:y:z=(50-70):(15-25):(15-25).

[0011] Furthermore, the average molecular weight of the polyacrylamide is 13 million to 17 million, and more preferably, the average molecular weight of the polyacrylamide is 14 million to 16 million.

[0012] Furthermore, the mass fraction / M of the fly ash is preferably 1-5%; more preferably, the mass fraction / M of the fly ash is 1-3%.

[0013] Furthermore, the mass fraction / M of the mineral powder is preferably 1-5%; more preferably, the mass fraction / M of the mineral powder is 2-4%.

[0014] Furthermore, the mass fraction / M of the silica fume is preferably 0.5-3%; more preferably, the mass fraction / M of the silica fume is 0.5-1%.

[0015] Furthermore, the mass fraction / M of the polyacrylamide for underwater non-dispersible concrete is preferably 0.4-0.8%.

[0016] Furthermore, after the concrete is formed in underwater construction, the harmless pore content in the obtained concrete structure is greater than 45%; more preferably, the harmless pore content in the obtained concrete structure is greater than 48%; most preferably, the harmless pore content in the obtained concrete structure is greater than 50%.

[0017] A method for preparing polyacrylamide for underwater non-dispersible concrete comprises the following steps:

[0018] 1) dissolving acrylamide, acrylic acid, and allyl-A-D-galactopyranoside in deionized water at a molar ratio of (50-70):(15-25):(15-25) to prepare an aqueous solution with a total mass concentration of 15-35%;

[0019] 2) adding urea, EDTA-2Na, and sodium formate to the aqueous solution in sequence, and stirring at room temperature to obtain a uniform solution;

[0020] 3) Adjust the pH to 7-8 with NaOH solution, and then introduce nitrogen to deoxygenate for 20-40 minutes;

[0021] 4) adding an azo initiator, wherein the mass ratio of the azo initiator to acrylamide is 0.2-0.8 wt.%; and sealing and heat-insulating the reaction at 10-25° C. for 3-5 hours;

[0022] 5) adding an oxidant, wherein the mass ratio of the oxidant to acrylamide is 0.2-0.8 wt.%; and sealing and heat-insulating the reaction at 25-45° C. for 3-5 hours;

[0023] 6) The obtained colloidal product is taken out, dried, and crushed to obtain a powdery polyacrylamide having the structure represented by formula (I).

[0024] In the preparation method of polyacrylamide for underwater non-dispersible concrete, the mass ratio of urea to acrylamide is 0.1wt.%-0.5wt.%; the mass ratio of EDTA-2Na to acrylamide is 0.1wt.%-0.3wt.%; the mass ratio of sodium formate to acrylamide is 0.1wt.%-0.5wt.%; the azo initiator is selected from one or more of azobisisobutylcyanide, azobiscyanovaleric acid, azobisisobutylamidine hydrochloride, azobisisobutylimidazoline hydrochloride, and azobisisopropylimidazoline; and the oxidant is selected from one or more of ammonium persulfate, sodium persulfate, and potassium persulfate.

[0025] In this application, by adding a polyacrylamide-based flocculant that is particularly suitable for underwater construction into concrete, the concrete has excellent anti-dispersion, fluidity, compressive strength and water-to-land strength ratio, so that the concrete can meet the requirements of underwater construction and have excellent strength performance.

[0026] Furthermore, this application conducted a comprehensive analysis of the compressive strength tests and mercury intrusion tests on concrete specimens with different polyacrylamide dosages for underwater non-dispersible concrete, and found that the improvement in concrete strength caused by polyacrylamide for underwater non-dispersible concrete is not only reflected in a decrease in porosity, but also in an increase in the content of harmless pores and a decrease in the content of harmful pores and multi-harmful pores. Furthermore, this application defines the polyacrylamide dosage for underwater non-dispersible concrete and the harmless pore content of the concrete structure, respectively, limiting the mass parts / M of polyacrylamide for underwater non-dispersible concrete to 0.3-1, preferably to 0.4-0.8, and limiting the harmless pore content in the concrete structure obtained after underwater construction and molding to greater than 45%, preferably greater than 48%, and most preferably greater than 50%. This effectively ensures a high-performance underwater non-dispersible concrete with a maximum 28-day underwater compressive strength of 48.6 MPa. DETAILED DESCRIPTION

[0027] The specific solutions of this application will be described in detail below.

[0028] Preparation Example 1

[0029] A method for preparing polyacrylamide for underwater non-dispersible concrete comprises the following steps:

[0030] 1) Weigh 42.65 g (about 0.6 mol) of acrylamide, 14.41 g (about 0.2 mol) of acrylic acid, and 44.04 g (about 0.2 mol) of allyl-A-D-galactopyranoside, and dissolve them in 404.4 g of deionized water to obtain an aqueous solution with a total mass concentration of 20 wt.%;

[0031] 2) adding 0.17 g of urea (approximately 0.4 wt.% of acrylamide), 0.085 g of EDTA-2Na (approximately 0.2 wt.% of acrylamide), and 0.17 g of sodium formate (approximately 0.4 wt.% of acrylamide) to the aqueous solution in sequence, and stirring uniformly at room temperature;

[0032] 3) Adjust the pH to 8 with NaOH solution, and then introduce nitrogen to deoxygenate for 28 minutes;

[0033] 4) Add 0.26 g of azobisisobutylimidazoline hydrochloride (approximately 0.6 wt.% of acrylamide) and seal the container and heat at 20° C. for 4 hours;

[0034] 5) Add 0.26 g of ammonium persulfate (approximately 0.6 wt.% of acrylamide) and seal the container and heat at 35° C. for 5 hours;

[0035] 6) The obtained colloidal product is taken out, dried and crushed to obtain powdered polyacrylamide, which is recorded as M1.

[0036] The product M1 of Example 1 was subjected to infrared spectroscopy (IR) and quantitative 13C spectrum determination.

[0037] In the IR spectrum, the stretching vibration peak of the carbonyl group (C=O) in the amide group appears at around 1656 cm-1, the stretching vibration peak of the primary amide (-NH2) in the amide group appears at 3348 cm-1; the stretching vibration peak of the secondary amide (-NH) is at 3178 cm-1; the stretching vibration peak of -CN is at 1119 cm-1; the absorption peaks at 1405 cm-1 and 1549 cm-1 are the symmetric and antisymmetric stretching vibration peaks of the carboxyl group (-COO-), respectively; the characteristic absorption peak of the methylene (-CH2) in the skeleton is at 2918 cm-1; the peak at 1316 cm-1 is caused by the stretching vibration of the methine (-CH).

[0038] Quantitative 13C spectrometry revealed characteristic peaks for the pyranose rings C1-C6 at 61.02-102.77 ppm. The integrated area of the characteristic peaks revealed an x:y:z ratio of approximately 3:1:1. Viscometry revealed a viscosity-average molecular weight (Mv) of 14.83 million, with a monomer conversion rate exceeding 99.9%. This confirms that the polyacrylamide prepared in this example has the structure shown in Formula (I).

[0039]

[0040] And the x:y:z is 3:1:1.

[0041] Concrete's anti-dispersion and fluidity are important performance indicators for underwater non-dispersible concrete. Since concrete's primary binder is cement paste, the viscosity of the cement paste fundamentally affects its performance. To more fundamentally test the effects of polyacrylamide on the optimization of concrete's anti-dispersion and fluidity in underwater concrete, a water-cement ratio of 0.45 was selected for the cement paste. 0.4 wt.% polyacrylamide was added to the cement paste. Test samples were then tested for anti-dispersion and fluidity. See Table 1 for cement composition:

[0042] Table 1

[0043] <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> CaO MgO <![CDATA[SO3]]> NaO <![CDATA[K2O]]> 21.436 5.08 2.934 62.74 2.46 3.84 0.85 0.66

[0044] In the anti-dispersion test, the turbidity of the supernatant after the cement passes through the water layer is used to evaluate the flocculation properties of polyacrylamide. The lower the turbidity, the better the cement's anti-dispersion properties, that is, the better the polyacrylamide's flocculation properties. The test was conducted strictly in accordance with the anti-dispersion requirements of DL / T 5117-2000 and KCI-AD102. In the fluidity test, the jump table test specified in GB / T 2419-2005 was used to determine the fluidity of the cement paste incorporating polyacrylamide. The specific test results are shown in Table 2.

[0045] Table 2

[0046] Turbidity (NTU) Expansion (mm) Example 1 10.5 16.3

[0047] From the turbidity and expansion test results in Table 2, it can be seen that the polyacrylamide for underwater non-dispersible concrete prepared in Preparation Example 1 has good anti-dispersion and fluidity when applied to cement paste. Therefore, it can be expected that the polyacrylamide also has good anti-dispersion and fluidity when applied to concrete for underwater construction.

[0048] Example

[0049] Furthermore, in order to clarify the role of the underwater non-dispersible concrete polyacrylamide prepared in Preparation Example 1 in concrete for underwater construction, the underwater non-dispersible concrete polyacrylamide prepared in Preparation Example 1 was added to the concrete in different amounts, and its expansion, turbidity, and strength were tested. The microstructure of the concrete was analyzed by mercury intrusion porosimetry, and the mechanism of action of the underwater non-dispersible concrete polyacrylamide in the concrete was summarized, so as to adjust the component ratio of the concrete and optimize the macroscopic properties of the concrete.

[0050] In this embodiment, cement is P.0425R; fine aggregate is river sand with a fineness modulus of 2.7; coarse aggregate is 5-20 mm continuously graded crushed stone; fly ash is Class F II fly ash; mineral powder is S95 grade slag powder; silica fume is SF-1102; polycarboxylate water-reducing agent is PCA III polycarboxylate water-reducing agent; and polyacrylamide for underwater non-dispersible concrete is the polyacrylamide prepared in Preparation Example 1.

[0051] Example 1

[0052] In this embodiment, a high-performance underwater non-dispersible concrete includes 600 parts by mass of fine aggregate, 800 parts by mass of coarse aggregate, 400 parts by mass of cement, and 200 parts by mass of water, where the total mass M of the fine aggregate, coarse aggregate, cement, and water is 2000 parts by mass; the concrete also includes 40 parts by mass of fly ash (40 / 2000=2%), 40 parts by mass of mineral powder (40 / 2000=2%), 20 parts by mass of silica fume (20 / 2000=2%), 40 parts by mass of polycarboxylate water reducer (40 / 2000=2%), and 2 parts of polyacrylamide for underwater non-dispersible concrete (2 / 2000=0.1%).

[0053] Example 2

[0054] In this embodiment, a high-performance underwater non-dispersible concrete includes 600 parts by mass of fine aggregate, 800 parts by mass of coarse aggregate, 400 parts by mass of cement, and 200 parts by mass of water, where the total mass M of the fine aggregate, coarse aggregate, cement, and water is 2000 parts by mass; the concrete also includes 40 parts by mass of fly ash (40 / 2000=2%), 40 parts by mass of mineral powder (40 / 2000=2%), 20 parts by mass of silica fume (20 / 2000=2%), 40 parts by mass of polycarboxylate water reducer (40 / 2000=2%), and 4 parts of polyacrylamide for underwater non-dispersible concrete (4 / 2000=0.2%).

[0055] Example 3

[0056] In this embodiment, a high-performance underwater non-dispersible concrete includes 600 parts by mass of fine aggregate, 800 parts by mass of coarse aggregate, 400 parts by mass of cement, and 200 parts by mass of water, where the total mass M of the fine aggregate, coarse aggregate, cement, and water is 2000 parts by mass; the concrete also includes 40 parts by mass of fly ash (40 / 2000=2%), 40 parts by mass of mineral powder (40 / 2000=2%), 20 parts by mass of silica fume (20 / 2000=2%), 40 parts by mass of polycarboxylate water reducer (40 / 2000=2%), and 6 parts of polyacrylamide for underwater non-dispersible concrete (6 / 2000=0.3%).

[0057] Example 4

[0058] In this embodiment, a high-performance underwater non-dispersible concrete includes 600 parts by mass of fine aggregate, 800 parts by mass of coarse aggregate, 400 parts by mass of cement, and 200 parts by mass of water, where the total mass M of the fine aggregate, coarse aggregate, cement, and water is 2000 parts by mass; the concrete also includes 40 parts by mass of fly ash (40 / 2000=2%), 40 parts by mass of mineral powder (40 / 2000=2%), 20 parts by mass of silica fume (20 / 2000=2%), 40 parts by mass of polycarboxylate water reducer (40 / 2000=2%), and 8 parts of polyacrylamide for underwater non-dispersible concrete (8 / 2000=0.4%).

[0059] Example 5

[0060] In this embodiment, a high-performance underwater non-dispersible concrete includes 600 parts by mass of fine aggregate, 800 parts by mass of coarse aggregate, 400 parts by mass of cement, and 200 parts by mass of water, where the total mass M of the fine aggregate, coarse aggregate, cement, and water is 2000 parts by mass; the concrete also includes 40 parts by mass of fly ash (40 / 2000=2%), 40 parts by mass of mineral powder (40 / 2000=2%), 20 parts by mass of silica fume (20 / 2000=2%), 40 parts by mass of polycarboxylate water reducer (40 / 2000=2%), and 10 parts by mass of polyacrylamide for underwater non-dispersible concrete (10 / 2000=0.5%).

[0061] Example 6

[0062] In this embodiment, a high-performance underwater non-dispersible concrete includes 600 parts by mass of fine aggregate, 800 parts by mass of coarse aggregate, 400 parts by mass of cement, and 200 parts by mass of water, where the total mass M of the fine aggregate, coarse aggregate, cement, and water is 2000 parts by mass; the concrete also includes 40 parts by mass of fly ash (40 / 2000=2%), 40 parts by mass of mineral powder (40 / 2000=2%), 20 parts by mass of silica fume (20 / 2000=2%), 40 parts by mass of polycarboxylate water reducer (40 / 2000=2%), and 12 parts by mass of polyacrylamide for underwater non-dispersible concrete (12 / 2000=0.6%).

[0063] Example 7

[0064] In this embodiment, a high-performance underwater non-dispersible concrete includes 600 parts by mass of fine aggregate, 800 parts by mass of coarse aggregate, 400 parts by mass of cement, and 200 parts by mass of water, where the total mass M of the fine aggregate, coarse aggregate, cement, and water is 2000 parts by mass; the concrete also includes 40 parts by mass of fly ash (40 / 2000=2%), 40 parts by mass of mineral powder (40 / 2000=2%), 20 parts by mass of silica fume (20 / 2000=2%), 40 parts by mass of polycarboxylate water reducer (40 / 2000=2%), and 14 parts of polyacrylamide for underwater non-dispersible concrete (14 / 2000=0.7%).

[0065] Example 8

[0066] In this embodiment, a high-performance underwater non-dispersible concrete includes 600 parts by mass of fine aggregate, 800 parts by mass of coarse aggregate, 400 parts by mass of cement, and 200 parts by mass of water, where the total mass M of the fine aggregate, coarse aggregate, cement, and water is 2000 parts by mass; the concrete also includes 40 parts by mass of fly ash (40 / 2000=2%), 40 parts by mass of mineral powder (40 / 2000=2%), 20 parts by mass of silica fume (20 / 2000=2%), 40 parts by mass of polycarboxylate water reducer (40 / 2000=2%), and 16 parts of polyacrylamide for underwater non-dispersible concrete (16 / 2000=0.8%).

[0067] Example 9

[0068] In this embodiment, a high-performance underwater non-dispersible concrete includes 600 parts by mass of fine aggregate, 800 parts by mass of coarse aggregate, 400 parts by mass of cement, and 200 parts by mass of water, where the total mass M of the fine aggregate, coarse aggregate, cement, and water is 2000 parts by mass; the concrete also includes 40 parts by mass of fly ash (40 / 2000=2%), 40 parts by mass of mineral powder (40 / 2000=2%), 20 parts by mass of silica fume (20 / 2000=2%), 40 parts by mass of polycarboxylate water reducer (40 / 2000=2%), and 18 parts of polyacrylamide for underwater non-dispersible concrete (18 / 2000=0.9%).

[0069] Example 10

[0070] In this embodiment, a high-performance underwater non-dispersible concrete includes 600 parts by mass of fine aggregate, 800 parts by mass of coarse aggregate, 400 parts by mass of cement, and 200 parts by mass of water, where the total mass M of the fine aggregate, coarse aggregate, cement, and water is 2000 parts by mass; the concrete also includes 40 parts by mass of fly ash (40 / 2000=2%), 40 parts by mass of mineral powder (40 / 2000=2%), 20 parts by mass of silica fume (20 / 2000=2%), 40 parts by mass of polycarboxylate water reducer (40 / 2000=2%), and 20 parts of polyacrylamide for underwater non-dispersible concrete (20 / 2000=1%).

[0071] Example 11

[0072] In this embodiment, a high-performance underwater non-dispersible concrete includes 600 parts by mass of fine aggregate, 800 parts by mass of coarse aggregate, 400 parts by mass of cement, and 200 parts by mass of water, where the total mass M of the fine aggregate, coarse aggregate, cement, and water is 2000 parts by mass; the concrete also includes 40 parts by mass of fly ash (40 / 2000=2%), 40 parts by mass of mineral powder (40 / 2000=2%), 20 parts by mass of silica fume (20 / 2000=2%), 40 parts by mass of polycarboxylate water reducer (40 / 2000=2%), and 24 parts of polyacrylamide for underwater non-dispersible concrete (24 / 2000=1.2%).

[0073] Performance testing:

[0074] 1. Anti-dispersion performance test

[0075] The turbidity test was performed using the turbidity method. A sample of the upper layer of water after the concrete slurry has passed through was placed in a sample bottle and shaken evenly. The bottle was then placed in the sample chamber of the turbidity meter. The "X" scale on the sample bottle was aligned with the baseline of the turbidity meter. The lid was closed and the key was pressed to read the value. The turbidity meter beeped three times and the reading was recorded. The average of the two measurements was taken as the turbidity value for the water sample. The results are shown in Table 3.

[0076] 2. Flowability test

[0077] The table jump test specified in GB / T 2419-2005 was used to determine the expansion. The results are shown in Table 3.

[0078] 3. Compressive strength test

[0079] The compressive strength of underwater and land-formed test blocks was determined according to the relevant provisions of DL / T 5117-2000. Any side other than the forming surface of the test block was selected as the compressive surface. The test block was uniformly loaded until it cracked. The press readings were recorded and the average value of the three test blocks was taken as the final strength.

[0080] The compressive strength is calculated according to formula (2):

[0081] (2),

[0082] Where P is the compressive strength of the specimen, in MPa; F is the force applied to the specimen, in Newton; and S is the compressive area of the specimen, in mm². The 7-day onshore compressive strength, 7-day underwater compressive strength, 28-day onshore compressive strength, and 28-day underwater compressive strength of the specimen were measured, and the corresponding land-water strength ratio was calculated. The results are shown in Table 4.

[0083] 4. Mercury intrusion test

[0084] The concrete of Examples 2, 3, 6, and 10 were formed underwater to obtain 100×100×100 mm underwater mortar specimens. These specimens were placed in a fully automatic mercury porosimeter and the pore structure distribution of the specimens was determined in strict accordance with the relevant provisions of the national standard GB / T21650.1-2008. The pressure range was 0 MPa-414 MPa, and the pore diameter range was 3.6 nm-400 μm. The porosity of each specimen was first measured, and then the pore size distribution was evaluated based on the cumulative mercury intrusion percentage within the pores. Pores with a diameter less than 20 nm were classified as harmless, those with a diameter of 20-50 nm were classified as slightly harmful, those with a diameter of 50-200 nm were classified as harmful, and those with a diameter greater than 200 nm were classified as highly harmful. The results are shown in Table 5.

[0085] Table 3

[0086] Turbidity (NTU) Expansion (mm) Example 1 243 121 Example 2 167 186 Example 3 128 212 Example 4 105 231 Example 5 103 236 Example 6 98 242 Example 7 99 246 Example 8 95 245 Example 9 98 237 Example 10 97 224 Example 11 96 193

[0087] The results in Table 3 indicate that the concrete of the present application exhibits excellent turbidity and expansion properties, making it suitable for underwater construction environments. Furthermore, as the amount of polyacrylamide used in the concrete slurry increases, the turbidity shows a decreasing trend. However, after the percentage of polyacrylamide used in underwater non-dispersible concrete reaches 0.4%, the turbidity tends to remain relatively stable even with further increases in the amount of polyacrylamide used in underwater non-dispersible concrete.

[0088] At low dosages, the expansion of concrete mortar increases with increasing polyacrylamide content. This is because cement particles have the same surface charge, leading to mutual repulsion. With the addition of less polyacrylamide, the repulsive energy between particles decreases due to the dual effects of double layer compression and charge neutralization. The interaction between particles becomes dominated by attractive energy, resulting in an attraction between cement particles. This macroscopically manifests as increased viscosity and reduced fluidity. As the polyacrylamide content continues to increase, the number of polyacrylamide chains in the system increases, tightly enveloping the cement particles. Steric hindrance and vacancies increase the repulsive force between cement particles, increasing the distance between particles. This macroscopically manifests as a decrease in viscosity and increased fluidity. After the polyacrylamide content reaches a certain value, a spatial network is formed due to the dual effects of polyacrylamide chain bridging and hydrogen bonding, causing cement particles to aggregate. This decreases the distance between particles, which macroscopically manifests as an increase in viscosity and a decrease in fluidity.

[0089] Table 4

[0090]

[0091]

[0092] Table 5

[0093]

[0094] The results in Table 4 demonstrate that the concrete of this application exhibits excellent strength, particularly underwater compressive strength and water-to-land strength ratio, meeting concrete standards exceeding C40. Furthermore, the results in Table 4 indicate that the strength of the concrete initially increases and then decreases with increasing percentages of polyacrylamide used in underwater non-dispersible concrete. To analyze the reasons for this finding, Table 5 presents the porosity and pore size distribution of test blocks obtained from underwater forming of the three concretes of Examples 2, 3, 6, and 10.

[0095] Judging from the porosity results in Table 5, as the percentage of polyacrylamide used in underwater non-dispersible concrete increases, the porosity of the concrete specimens gradually decreases. Theoretically, the strength of concrete should be negatively correlated with its porosity. However, the results in Tables 4 and 5 do contradict this. Furthermore, through analysis of the pore size distribution results of each specimen, it was found that as the percentage of polyacrylamide used in underwater non-dispersible concrete increases, the content of harmless pores in the pore size distribution of the specimens first increases and then decreases, while the content of harmful pores and multiple harmful pores first decreases and then increases. Due to the increase in the content of harmful pores and multiple harmful pores, even if the overall porosity decreases, the macroscopic strength performance of the entire concrete specimen also shows a downward trend.

[0096] The reason for this result may be that the underwater non-dispersible concrete polyacrylamide added during underwater mortar molding has a certain water absorption capacity. The more the amount added, the stronger the water absorption. When the amount added is too much, the more water is not discharged during molding. These waters evaporate during the hardening process of the mortar, causing certain micropores, which appear in the microscopic morphology as an increase in the content of harmful pores and multiple harmful pores, and then in the macroscopic morphology as a decrease in compressive strength.

Claims

1. A high-performance underwater non-dispersible concrete, comprising 450-750 parts by mass of fine aggregate, 700-1050 parts by mass of coarse aggregate, 350-450 parts by mass of cement, 150-260 parts by mass of water, fly ash, mineral powder, silica fume, polycarboxylic acid water reducer, and polyacrylamide for underwater non-dispersible concrete; wherein: The total mass of fine aggregate, coarse aggregate, cement and water is recorded as M, the mass of fly ash / M=0-5%, the mass of mineral powder / M=0-5%, the mass of silica fume / M=0-3%, the mass of polycarboxylate water reducer / M=0.5-3%, and the mass of polyacrylamide for underwater non-dispersible concrete / M=0.3-1%; The polyacrylamide for underwater non-dispersible concrete is a ternary copolymer comprising an acrylamide structural unit, an acrylic acid structural unit and an allyl-A-D-galactopyranoside structural unit. The ternary copolymer has a structure shown in formula (I). Wherein, in formula (I), x:y:z=(50-70):(15-25):(15-25).

2. The high performance underwater non-dispersible concrete according to claim 1, characterized in that: The average molecular weight of the polyacrylamide is 13 million to 17 million, and after the high-performance underwater non-dispersible concrete is formed through underwater construction, the content of harmless pores in the obtained concrete structure is greater than 45%.

3. The high performance underwater non-dispersible concrete according to claim 2, characterized in that: The average molecular weight of the polyacrylamide is 14 million to 16 million, and / or after the high-performance underwater non-dispersible concrete is formed in underwater construction, the harmless pore content in the obtained concrete structure is greater than 48%.

4. The high performance underwater non-dispersible concrete according to claim 1, characterized in that: The mass fraction / M of the fly ash is 1-5%, and / or the mass fraction / M of the mineral powder is 1-5%, and / or the mass fraction / M of the silica fume is 0.5-3%.

5. The high performance underwater non-dispersible concrete according to claim 4, characterized in that: The mass fraction / M of the fly ash is 1-3%, and / or the mass fraction / M of the mineral powder is 2-4%, and / or the mass fraction / M of the silica fume is 0.5-1%.

6. The high performance underwater non-dispersible concrete according to claim 1, characterized in that: After the high-performance underwater non-dispersible concrete is formed through underwater construction, the content of harmless pores in the obtained concrete structure is greater than 50%.

7. The high performance underwater non-dispersible concrete according to claim 1, characterized in that: The preparation method of the polyacrylamide for underwater non-dispersible concrete comprises the following steps: 1) dissolving acrylamide, acrylic acid, and allyl-A-D-galactopyranoside in deionized water at a molar ratio of (50-70):(15-25):(15-25) to prepare an aqueous solution with a total mass concentration of 15-35%; 2) adding urea, EDTA-2Na, and sodium formate to the aqueous solution in sequence, and stirring at room temperature to obtain a uniform solution; 3) Adjust the pH to 7-8 with NaOH solution, and then introduce nitrogen to deoxygenate for 20-40 minutes; 4) adding an azo initiator, wherein the mass ratio of the azo initiator to acrylamide is 0.2-0.8 wt.%; and sealing and heat-insulating the reaction at 10-25° C. for 3-5 hours; 5) adding an oxidant, wherein the mass ratio of the oxidant to acrylamide is 0.2-0.8 wt.%; and sealing and heat-insulating the reaction at 25-45° C. for 3-5 hours; 6) The obtained colloidal product is taken out, dried, and crushed to obtain a powdery polyacrylamide having the structure represented by formula (I).

8. The high performance underwater non-dispersible concrete according to claim 7, characterized in that: The mass ratio of the urea to the acrylamide is 0.1wt.%-0.5wt.%; and / or the mass ratio of the EDTA-2Na to the acrylamide is 0.1wt.%-0.3wt.%; and / or the mass ratio of the sodium formate to the acrylamide is 0.1wt.%-0.5wt.%; and / or the azo initiator is selected from one or more of azobisisobutylcyanide, azobiscyanovaleric acid, azobisisobutylamidine hydrochloride, azobisisobutylimidazoline hydrochloride, and azobisisopropylimidazoline; and / or the oxidant is selected from one or more of ammonium persulfate, sodium persulfate, and potassium persulfate.

Images