Phosphate-type polycarboxylate superplasticizer with slow-release function, preparation method thereof, concrete admixture composition and application thereof

Abstract

The application discloses a phosphate type polycarboxylic water reducing agent with slow-release function, a preparation method thereof, a concrete admixture composition and application thereof, and belongs to the technical field of phosphate type polycarboxylic water reducing agents, and comprises (a) a carboxylic monomer unit, accounting for 70-85% of the total mole ratio; (b) a vinyl phosphate monomer unit, accounting for 2-8% of the total mole ratio; and (c) a functional polyether macromonomer unit, accounting for 10-25% of the total mole ratio, and the structural general formula is as follows: CH2=C(R)-C(=O)-O-(CH2) n -C(=O)-O-(CH2CH2O) m -CH2CH2-O-P(=O)(OH)-OH; wherein R=H or CH3, n=1-3, and m=10-40. The application realizes slow release of the polycarboxylic water reducing agent, significantly improves the workability maintenance capability of the mud-containing concrete in high-temperature long-distance transportation while keeping high water-reducing rate.

Description

Technical Field

[0001] This invention belongs to the technical field of phosphate ester-type polycarboxylate superplasticizers, specifically relating to a phosphate ester-type polycarboxylate superplasticizer with slow-release function, a concrete admixture composition and its application, especially suitable for high-plasticity concrete projects in high-temperature and long-distance transportation scenarios. Background Technology

[0002] Polycarboxylate superplasticizers (PCEs) have become the mainstream admixtures for modern concrete due to their high water reduction rate, low dosage, and environmental friendliness. Currently, PCEs are widely produced industrially by copolymerizing methoxy polyethylene glycol monomethacrylate (HPEG) with acrylic acid (AA). However, the presence of ester bonds (-COO-) between the main chain and side chains of this type of PCE makes it prone to uncontrolled hydrolysis in the highly alkaline environment of cement paste (pH≈12.5-13.5) and under high temperature conditions. This leads to the complete detachment of the polyether side chains, loss of steric hindrance effect, and rapid loss of concrete slump, making it difficult to meet the requirements of long-distance transportation (>2 hours) or summer construction.

[0003] The typical time for concrete from mixing and transportation to pouring is 60-180 minutes. During this period, it is necessary to maintain fluidity (slump / spread). If PCE is released at full capacity from the beginning, the initial dispersion is too strong, the cement hydrates rapidly, and there is no "reserve power" to maintain fluidity later; especially at high temperatures, 50% of the slump may be lost within 30 minutes. If PCE is released too slowly (e.g., half-life > 3 hours), there is insufficient dispersion capacity in the initial stage, and the concrete is viscous when it leaves the mixer, making it impossible to pump. A hydrolysis half-life of 60-120 minutes allows PCE to continuously "supply energy" during the critical 1-2 hours, achieving an ideal slow-release curve of "not excessive in the early stage and not lagging behind in the later stage".

[0004] PCE disperses cement particles through a dual action of "electrostatic repulsion + steric hindrance," specifically: adsorption: main chain carboxyl groups (-COO) - ) and Ca on the surface of cement particles 2+ Formation of ionic or coordinate bonds; extension: hydrophilic polyether side chains extend into the water to form a hydration layer; repulsion: when two particles approach each other, the overlapping side chains generate entropic and osmotic repulsion, which prevent flocculation.

[0005] Therefore, there is an urgent need for a new type of PCE with controllable molecular structure, simple synthesis, and both anti-mud and intelligent slow-release functions. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, one of the objectives of this invention is to provide a phosphate ester type polycarboxylate superplasticizer with slow-release function, so as to achieve the slow release of polycarboxylate superplasticizer, and significantly improve the workability retention of mud-containing concrete during high-temperature and long-distance transportation while maintaining a high water reduction rate.

[0007] The second objective of this invention is to provide a method for preparing a phosphate ester-type polycarboxylate superplasticizer with a slow-release function, which is simple to prepare and convenient for on-site construction.

[0008] The third objective of this invention is to provide a concrete admixture composition.

[0009] One of the objectives of this invention is achieved through the following technical solution:

[0010] A phosphate ester type polycarboxylate superplasticizer with slow-release function, comprising

[0011] (a) Carboxylic acid monomer units, accounting for 70-85% of the total molar ratio;

[0012] (b) Vinyl phosphate monomer units, accounting for 2-8% of the total molar ratio;

[0013] (c) Functionalized polyether macromonomer units, accounting for 10-25% of the total molar ratio, have the following general structural formula:

[0014] CH2=C(R)-C(=O)-O-(CH2) n -C(=O)-O-(CH2CH2O) m -CH2CH2-OP(=O)(OH)-OH;

[0015] Where R = H or CH3, n = 1-3, m = 10-40;

[0016] The hydrolysis half-life of the -(CH2)nC(=O)-O- linker in the structure is 60-120 minutes at 25°C and pH=12.5.

[0017] Furthermore, the vinyl phosphate monomer is vinylphosphonic acid.

[0018] Furthermore, its weight-average molecular weight is 20,000-40,000 g / mol.

[0019] Furthermore, when applied to manufactured sand concrete with a mud content of ≥3%, the slump retention rate after 3 hours is ≥90%.

[0020] The second objective of this invention is achieved by the following technical solution:

[0021] A method for preparing a phosphate ester-type polycarboxylate superplasticizer with sustained-release function includes the following steps:

[0022] The reaction is carried out using a free radical copolymerization reaction at a temperature of 50-70℃ for 2-4 hours.

[0023] The third objective of this invention is achieved by the following technical solution:

[0024] A concrete admixture composition comprising the aforementioned phosphate ester-type polycarboxylate superplasticizer with slow-release function, wherein the dosage is 0.15-0.30% of the mass of the cementitious material.

[0025] Furthermore, the concrete transportation time is ≥2 hours and the ambient temperature is ≥30℃.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] This invention provides a phosphate ester-type polycarboxylate superplasticizer with slow-release function. Before hydrolysis, the polyether-phosphate ester side chains are "locked" by ester bonds, which may be coiled or shielded, resulting in weak steric hindrance. After hydrolysis, free HO-[polyether-phosphate ester] fragments are released. These fragments have hydrophilic polyether chains, providing steric hindrance, and the phosphate ester at the end can be adsorbed onto cement particles (especially C3A). The ester-linked polyether (slowly hydrolyzed) Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments. It should be noted that, without conflict, the embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0029] 1. Damage to the C3A surface passivation layer

[0030] Initial hydration of C3A produces a dense layer of hexagonal hydrated calcium aluminate (C4AH). 13 Phosphate esters, through strong coordination, locally dissolve or disturb the passivation layer, exposing the fresh C3A surface and accelerating hydration.

[0031] 2. Induced nucleation

[0032] The adsorbed phosphate groups can serve as heterogeneous nucleation sites, promoting the hydration of products (such as C4AH). 13 AFt) grows directionally around it; shortens the induction period and advances the hydration exothermic peak.

[0033] 3. Regulating the morphology of hydration products

[0034] Studies have shown (Zhang et al., Cem. Concr. Res. 2022) that phosphate-containing PCE can transform C3A hydration products from a plate-like to a fibrous or network-like structure, thereby improving the early structural compactness.

[0035] Example 1

[0036] This embodiment provides a phosphate ester-type polycarboxylate superplasticizer with sustained-release function, comprising:

[0037] (a) Carboxylic acid monomer units, accounting for 70-85% of the total molar ratio;

[0038] (b) Vinyl phosphate monomer units, accounting for 2-8% of the total molar ratio;

[0039] (c) Functionalized polyether macromonomer units, accounting for 10-25% of the total molar ratio, have the following general structural formula:

[0040] CH2=C(R)-C(=O)-O-(CH2) n -C(=O)-O-(CH2CH2O) m -CH2CH2-OP(=O)(OH)-OH;

[0041] Where R = H or CH3, n = 1-3, m = 10-40;

[0042] The hydrolysis half-life of the -(CH2)nC(=O)-O- linker in the structure is 60-120 minutes at 25°C and pH=12.5.

[0043] In practice,

[0044] HPEG-2400 (methyl allyl alcohol polyoxyethylene ether, Mn=2400) 100g;

[0045] Acrylic acid (AA) 25g;

[0046] Vinylphosphonic acid (VPA) 3.5g;

[0047] HPEG-2400 is first reacted with succinic anhydride to introduce -COOH, and then esterified with phosphate-containing polyethylene glycol to obtain a functionalized macromonomer (containing -COO-CH2-COO- linker).

[0048] Thioglycolic acid (chain transfer agent) 0.8g;

[0049] 150g of deionized water;

[0050] 1.2g of ammonium persulfate (initiator) is dissolved in 20g of water.

[0051] Functionalized polyether macromonomer units, acrylic acid, vinylphosphonic acid, and mercaptoacetic acid were dissolved in water, and N2 was bubbled through the solution for 30 min. The solution was heated to 60 °C, and ammonium persulfate solution was added dropwise (for 2 h). The mixture was kept at this temperature for 2 h. After cooling, the pH was adjusted to 6.5 with NaOH to obtain a pale yellow liquid with a solid content of 40%.

[0052] Comparative Example 1

[0053] Comparative Example 1 provides a phosphate ester type polycarboxylate superplasticizer with slow-release function: comprising 100g of HPEG-2400 (methyl allyl alcohol polyoxyethylene ether, Mn=2400);

[0054] Acrylic acid (AA) 25g;

[0055] Vinylphosphonic acid (VPA) 3.5g; without functionalized macromonomers (containing -COO-CH2-COO- linker), synthesized by conventional method (HPEG+AA), other conditions are the same.

[0056] Performance test (C40 concrete, manufactured sand with 4% mud content, ambient temperature 35℃)

[0057] II. Slump Test

[0058] Cement: P·O42.5, 320kg / m³;

[0059] Water-to-binder ratio: 0.38;

[0060] Sand ratio: 40%;

[0061] The dosage of the phosphate ester-type polycarboxylate superplasticizer with slow-release function provided in Example 1 is 0.25% of the mass of the cementitious material;

[0062] The slump was determined according to GB / T50080-2016, and the compressive strength was determined according to GB / T50081-2019.

[0063] Mixing: First, dry mix for 30 seconds, then add water and phosphate ester type polycarboxylate superplasticizer with slow-release function, and wet mix for 60 seconds;

[0064] Slump test: Use a standard slump cone (100mm inner diameter, 300mm height); fill in three layers, tamp each layer 25 times; after lifting the cone, measure the slump height (mm); record the initial slump (T=0min).

[0065] III. Slump Loss at 2h

[0066] Test standard: Section 4.1 of GB / T50080-2016

[0067] Test procedure: Pour the concrete mixture into a sealed container, cover it with a film to prevent moisture evaporation; let it stand at room temperature of 20℃±2℃ for 2 hours; measure the slump again;

[0068] Calculate the slump loss: Slump loss = Initial slump - 2h slump

[0069] IV. 1-day compressive strength

[0070] Test standard: GB / T50081-2019 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete"

[0071] Test steps:

[0072] Molding: Pour the concrete mixture into a 100×100×100mm mold and compact it;

[0073] Standard curing: 20℃±2℃, RH≥95%, curing for 1 day;

[0074] After demolding, the specimens were cured in water for one day.

[0075] The compressive strength was measured using a press, and the average value of three specimens was taken. The test results are shown in Table 1.

[0076] Table 1

[0077] sample Initial slump (mm) 1h slump retention rate 2h slump retention rate 1-day concrete strength (MPa) Example 1 220 95% 92% 28 Comparative Example 1 215 85% 62% 20

[0078] The results showed that, compared with Comparative Example 1, the phosphate ester polycarboxylate superplasticizer with slow-release function provided in Example 1 had a high slump retention rate of 60-120 minutes, indicating a long hydrolysis half-life. This suggests that the addition of functionalized polyether macromonomer units and the introduction of -(CH2)nC(=O)-O- linkages into the polyether side chain structure of PCE significantly improves long-term plasticity retention and early strength.

[0079] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A phosphate ester-type polycarboxylate superplasticizer with slow-release function, characterized in that, include (a) Carboxylic acid monomer units, accounting for 70-85% of the total molar ratio; (b) Vinyl phosphate monomer units, accounting for 2-8% of the total molar ratio; (c) Functionalized polyether macromonomer units, accounting for 10-25% of the total molar ratio; HPEG-2400 is first reacted with succinic anhydride to introduce -COOH, and then esterified with phosphate-containing polyethylene glycol to obtain the functionalized polyether macromonomer unit.

2. The phosphate ester type polycarboxylate superplasticizer with slow-release function according to claim 1, characterized in that, The vinyl phosphate monomer is vinylphosphonic acid.

3. The phosphate ester type polycarboxylate superplasticizer with slow-release function according to claim 1, characterized in that, Its weight-average molecular weight is 20,000-40,000 g / mol.

4. The phosphate ester type polycarboxylate superplasticizer with slow-release function according to claim 1, characterized in that, When applied to manufactured sand concrete with a mud content of ≥3%, the slump retention rate after 2 hours is ≥90%.

5. A concrete admixture composition, characterized in that, The product contains a phosphate ester-type polycarboxylate superplasticizer with slow-release function as described in any one of claims 1-4, with an admixture amount of 0.15-0.30% of the mass of the cementitious material.

6. The application of the concrete admixture composition according to claim 5 in high-temperature, long-distance concrete transportation, characterized in that, The concrete transportation time is ≥2 hours and the ambient temperature is ≥30℃.