CN111635497B - Underwater concrete anti-dispersant and preparation method thereof - Google Patents
Underwater concrete anti-dispersant and preparation method thereof Download PDFInfo
- Publication number
- CN111635497B CN111635497B CN202010457580.2A CN202010457580A CN111635497B CN 111635497 B CN111635497 B CN 111635497B CN 202010457580 A CN202010457580 A CN 202010457580A CN 111635497 B CN111635497 B CN 111635497B
- Authority
- CN
- China
- Prior art keywords
- dispersant
- initiator
- parts
- organic monomer
- sol
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F292/00—Macromolecular compounds obtained by polymerising monomers on to inorganic materials
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B24/00—Use of organic materials as active ingredients for mortars, concrete or artificial stone, e.g. plasticisers
- C04B24/24—Macromolecular compounds
- C04B24/26—Macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
- C04B24/2652—Nitrogen containing polymers, e.g. polyacrylamides, polyacrylonitriles
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2103/00—Function or property of ingredients for mortars, concrete or artificial stone
- C04B2103/40—Surface-active agents, dispersants
- C04B2103/408—Dispersants
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Organic Chemistry (AREA)
- Ceramic Engineering (AREA)
- Inorganic Chemistry (AREA)
- Health & Medical Sciences (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Structural Engineering (AREA)
- Curing Cements, Concrete, And Artificial Stone (AREA)
Abstract
The invention relates to an underwater concrete anti-dispersant and a preparation method thereof, wherein the underwater concrete anti-dispersant is prepared by taking an organic monomer and an inorganic sol as raw materials through chemical synthesis reaction, the organic monomer is selected from one or more of acrylamide, sodium acrylate, N-hydroxymethyl acrylamide, ethylene imine, acrylic acid and methacrylic acid, and the inorganic sol is selected from one or more of silicon oxide colloid, aluminum oxide colloid, iron oxide colloid, aluminum hydroxide colloid, iron hydroxide colloid, magnesium hydroxide colloid and aluminum silicate colloid. The underwater concrete anti-dispersant has the advantages that the 7d land-water compressive strength ratio is more than or equal to 72 percent, the 28d land-water compressive strength ratio is more than or equal to 87 percent, the content of suspended solids is less than or equal to 90mg/L, and the product performance is excellent. Meanwhile, the dosage of the anti-dispersing agent is small, and the anti-dispersing agent can achieve good anti-dispersing effect when the mixing amount is 0.25 percent, is far lower than that of the existing like products, and can reduce the production cost of underwater concrete.
Description
Technical Field
The invention relates to the technical field of concrete admixtures, in particular to an underwater concrete anti-dispersant and a preparation method thereof.
Background
The underwater concrete is influenced by factors such as water dilution, flowing water scouring and the like in the pouring operation process, the concrete entity quality is difficult to meet the engineering requirements, and unconventional measures such as cofferdam drainage, immersed tube and conduit construction and the like are additionally adopted, so that the construction difficulty is increased, and the engineering progress is delayed. The underwater concrete anti-dispersing agent is an additive special for underwater concrete pouring engineering, can realize underwater self-compaction of concrete, has good underwater anti-dispersion property, inhibits the separation phenomenon of cement and aggregate during underwater operation, does not influence the construction water quality, can greatly simplify the construction process, reduce the construction cost, reduce the construction risk and ensure the engineering quality.
Currently, underwater concrete dispersants on the market are more in variety, and the main technical routes are almost two. Firstly, by adding viscosity-increasing substances such as silica fume, cellulose and the like, the cohesiveness of concrete is increased, and the scouring and dilution of a water body are resisted, so that the dispersibility resistance of underwater concrete is met; on the premise of meeting the workability of the fresh concrete, the internal cohesion of the concrete is increased by adding chemical substances, and the whole hydrophobic outer surface of the concrete is realized, so that the immersion of a water body is avoided, the dilution and the scouring of the water body are resisted, and the dispersibility resistance of the underwater concrete is realized.
Patent CN108947313A discloses an anti-dispersant, which mainly comprises two components of a solid agent and a liquid agent, wherein the weight ratio of the solid agent is as follows: cellulose ether 4%, silica fume 93% and super absorbent resin 3%; the weight ratio of the liquid is as follows: 86% of polycarboxylic acid high-efficiency water reducing agent and 14% of tributyl ester; the dosage of the solid agent is 9.6 percent of the dosage of the cement, and the dosage of the liquid agent is 1.4 percent of the dosage of the cement. The patent CN108503260A discloses an underwater anti-dispersion concrete admixture for construction, which comprises, by weight, 1-2 parts of methylcellulose, 1-2 parts of hydroxypropyl methyl starch, 2-5 parts of zeolite powder, 10-15 parts of stearic acid, 10-12 parts of a naphthalene-series high-efficiency water reducing agent, 1-2 parts of sepiolite fibers, 3-5 parts of polyacrylamide, 1-3 parts of polyvinyl alcohol, 3-5 parts of sodium aluminate, 20-22 parts of a polycarboxylic acid water reducing agent, 63-73 parts of water and 10-12 parts of polyacrylamide. The amount of the anti-dispersant in the concrete is usually more than 5%. CN106977160A discloses an underwater undispersed concrete and a preparation method thereof, and the related anti-dispersant comprises a flocculating agent, silica fume and a tackifying auxiliary agent, wherein the flocculating agent is 2-5 parts, the silica fume is 10-15 parts, and the tackifying auxiliary agent is 2-5 parts. The amount of the anti-dispersant in the concrete is usually more than 5%.
The product comprises the products related to the patent and other underwater concrete anti-dispersant products on the market, the defects of low water/land compressive strength ratio, high content of suspended substances, large dosage of the anti-dispersant in concrete and the like exist in the actual use process, and meanwhile, the existing anti-dispersant preparation process mainly comprises compounding of a tackifier and a water reducer, so that the product performance is unstable.
Disclosure of Invention
Aiming at the defects and shortcomings in the prior art, the invention provides an underwater concrete anti-dispersant and a preparation method thereof.
One of the purposes of the invention is to provide an underwater concrete anti-dispersant, which is prepared by taking an organic monomer and an inorganic sol as raw materials through chemical synthesis reaction, wherein the organic monomer is selected from one or more of acrylamide, sodium acrylate, N-hydroxymethyl acrylamide, ethylene imine, acrylic acid and methacrylic acid, and the inorganic sol is selected from one or more of silicon oxide colloid, aluminum oxide colloid, iron oxide colloid, aluminum hydroxide colloid, iron hydroxide colloid, magnesium hydroxide colloid and aluminum silicate colloid.
According to some preferred embodiments of the invention, the organic monomer is acrylic acid and N-methylolacrylamide, acrylamide and ethyleneimine, or acrylamide.
According to some preferred embodiments of the present invention, the inorganic sol is an iron oxide sol, an aluminum hydroxide sol, an aluminum silicate sol, or a magnesium hydroxide sol.
According to some preferred embodiments of the present invention, the raw materials comprise, in parts by weight: 60-200 parts of organic monomer, 10-30 parts of inorganic colloid, 0-1 part of urea, 0-0.5 part of initiator A and 0-0.2 part of initiator B, preferably 100-180 parts of organic monomer, 12-22 parts of inorganic colloid, 0.01-0.5 part of urea, 0-0.5 part of initiator A and 0.01-0.5 part of initiator B.
According to some preferred embodiments of the present invention, the initiator a is selected from one or more of hydrogen peroxide, ammonium persulfate and potassium persulfate.
According to some preferred embodiments of the present invention, the initiator B is one or more of sodium bisulfite, sodium hypophosphite, and sodium dihydrogen hypophosphite.
Another object of the present invention is to provide a method for preparing the anti-dispersant, comprising the steps of:
step 1), dissolving the organic monomer into the inorganic sol under inert atmosphere, adding urea, and stirring to obtain premixed sol;
step 2), dropwise adding a mixed solution of an initiator A and an initiator B into the sol to initiate polymerization of the organic monomer to obtain a reaction solution;
step 3), sealing and standing the reaction solution to obtain polymer gel;
and 4), drying the polymer gel to constant weight, and grinding into powder to obtain the polymer gel.
According to some preferred embodiments of the present invention, in step 1), the inert atmosphere is selected from one or more of an argon atmosphere, a nitrogen atmosphere, and a helium atmosphere; adding urea at 50-90 ℃; the stirring time is 20-40 min.
According to some preferred embodiments of the present invention, in the step 2), the reaction time is 2-7 h; and/or in the step 3), the sealing and standing time is more than 4 hours, preferably 4-5 hours.
According to some preferred embodiments of the present invention, in the step 4), the temperature for drying is 40 to 60 ℃.
The invention has the beneficial effects that: the addition amount of the novel anti-dispersing agent is less than 0.5 percent of the total amount of the cementing material, and the addition amount is far lower than that of the existing anti-dispersing agent (generally more than 8 percent). The compression strength ratio of the formed concrete test piece in water body/air is more than 85 percent; the content of suspended substances is less than 100mg/L, and the index is greatly higher than the specified value of the relevant standard. The anti-dispersant adopting a specific formula and process conditions has good comprehensive performance; meanwhile, because the mixing amount is far lower than that of the existing product, the application of the product can reduce the production cost of the underwater concrete, and has good social and economic benefits.
Detailed Description
The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention. The examples do not show the specific techniques or conditions, according to the technical or conditions described in the literature in the field, or according to the product specifications.
In the present invention, the instruments and the like used are conventional products which are purchased from regular vendors, not indicated by manufacturers. The raw materials used in the invention can be conveniently bought in domestic product markets.
Example 1
A preparation method of an underwater concrete anti-dispersant (code number N1) comprises the following steps:
step 1: under argon atmosphere, 100 parts of acrylamide and 20 parts of ethylene imine organic monomer are dissolved into 12 parts of iron oxide sol, the organic-inorganic reaction system is kept at a constant temperature of 70 ℃, and 0.02 part of urea is added and stirred for 30 min.
Step 2: a mixed solution of 0.02 part of ammonium persulfate and 0.01 part of sodium hypophosphite was slowly dropped into the above sol to initiate polymerization of the organic monomer, and reacted for 4 hours.
And step 3: the reaction solution was sealed and allowed to stand for 5 hours to obtain a polymer gel.
And 4, step 4: and (3) placing the gel in a vacuum drying oven at 45 ℃ to be dried to constant weight, and grinding the gel into powder to obtain the underwater concrete anti-dispersant N1.
Example 2
A preparation method of an underwater concrete anti-dispersant (code number N2) comprises the following steps:
step 1: 160 parts of acrylamide and 10 parts of ethylene imine organic monomer are dissolved in 15 parts of aluminum hydroxide sol in nitrogen atmosphere, the organic-inorganic reaction system is kept at a constant temperature of 60 ℃, and 0.015 part of urea is added and stirred for mixing for 35 min.
Step 2: a mixed solution of 0.02 part of ammonium persulfate and 0.01 part of sodium hydrogen sulfite was slowly dropped into the above sol to initiate polymerization of the organic monomer, and reacted for 5 hours.
And step 3: the reaction solution was sealed and left to stand for 4.5 hours to obtain a polymer gel.
And 4, step 4: and (3) placing the gel in a vacuum drying oven at 55 ℃ for drying to constant weight, and grinding into powder to obtain the underwater concrete anti-dispersant N2.
Example 3
A preparation method of an underwater concrete anti-dispersant (code number N3) comprises the following steps:
step 1: under nitrogen atmosphere, 100 parts of acrylic acid and 60 parts of N-hydroxymethyl acrylamide organic monomer are dissolved into 20 parts of aluminosilicate sol, so that the organic-inorganic reaction system keeps a constant temperature of 80 ℃, and 0.02 part of urea is added and stirred for 40 min.
Step 2: a mixed solution of 0.01 part of ammonium persulfate, 0.01 part of potassium persulfate and 0.01 part of sodium hypophosphite is slowly dropped into the above sol to initiate polymerization of the organic monomer, and the reaction is carried out for 6 hours.
And step 3: the reaction solution was sealed and allowed to stand for 5 hours to obtain a polymer gel.
And 4, step 4: and (3) placing the gel in a vacuum drying oven at 55 ℃ for drying to constant weight, and grinding into powder to obtain the underwater concrete anti-dispersant N3.
Example 4
A preparation method of an underwater concrete anti-dispersant (code number N4) comprises the following steps:
step 1: under the atmosphere of helium, 160 parts of acrylamide organic monomer is dissolved into 15 parts of aluminum hydroxide and 5 parts of magnesium hydroxide sol, the organic-inorganic reaction system is kept at a constant temperature of 70 ℃, and 0.03 part of urea is added and stirred and mixed for 40 min.
Step 2: a mixed solution of 0.03 parts of ammonium persulfate and 0.01 parts of sodium hydrogen sulfite was slowly dropped into the above sol to initiate polymerization of the organic monomer, and reacted for 4 hours.
And step 3: the reaction solution was sealed and allowed to stand for 5 hours to obtain a polymer gel.
And 4, step 4: and (3) placing the gel in a vacuum drying oven at 50 ℃ to be dried to constant weight, and grinding the gel into powder to obtain the underwater concrete anti-dispersant N4.
Examples of the experiments
To further evaluate the dispersant effect of the underwater concrete described in the examples, comparative tests of the dispersant resistant concrete of the examples with reference concrete (no dispersant added) and using the existing dispersant resistant agent (UWB) were carried out and the dispersant effect test and analysis of the underwater concrete were carried out:
(1) concrete mixing proportion
The reference concrete, the UWB concrete and the concrete composition of the examples are shown in table 1 below.
TABLE 1 base concrete to example concrete mix ratio
(2) The anti-dispersion effects of the reference concrete and the N1-N4 of the embodiment of the invention are tested according to the technical specification of the hydraulic concrete admixture (DL/T5100-2014).
(3) Anti-dispersion effect
The anti-dispersion effect test values are shown in table 2 below:
TABLE 2 anti-Dispersion Effect test results
From the test effects of the embodiments 1 to 4 of the invention, the compressive strength ratio of the 7d land and the 28d land is not less than 72%, the compressive strength ratio of the 28d land and the 28d land is not less than 87%, the content of suspended solids is not more than 90mg/L, and is much higher than the index value of the technical specification of hydraulic concrete admixtures (DL/T5100-2014). Meanwhile, the dosage of the anti-dispersing agent is small, and the anti-dispersing agent can achieve good anti-dispersing effect when the dosage is 0.25 percent, which is far lower than that of the existing similar products (such as UWB 5 percent).
Although the invention has been described in detail hereinabove with respect to a general description and specific embodiments thereof, it will be apparent to those skilled in the art that modifications or improvements may be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.
Claims (9)
1. The underwater concrete anti-dispersant is characterized in that the underwater concrete anti-dispersant is prepared by taking an organic monomer and an inorganic sol as raw materials through chemical synthesis reaction, wherein the organic monomer is acrylamide and ethylene imine, and the inorganic sol is ferric oxide sol or aluminum hydroxide sol; the raw materials comprise the following components in parts by weight: 60-200 parts of organic monomer, 10-30 parts of inorganic colloid, 0.01-1 part of urea, 0.02-0.5 part of initiator A and 0.01-0.2 part of initiator B.
2. The dispersion inhibitor according to claim 1, wherein the dispersion inhibitor comprises 100 to 180 parts of an organic monomer, 12 to 22 parts of an inorganic colloid, 0.01 to 0.5 part of urea, 0.02 to 0.5 part of an initiator A, and 0.01 to 0.2 part of an initiator B.
3. The dispersion inhibitor of claim 1, wherein the initiator A is selected from one or more of hydrogen peroxide, ammonium persulfate and potassium persulfate.
4. The dispersion inhibitor according to claim 1, wherein the initiator B is one or more of vitamin C, sodium bisulfite, sodium hypophosphite, and sodium dihydrogen hypophosphite.
5. The method for preparing the dispersion inhibitor according to any one of claims 1 to 4, comprising the steps of:
step 1), dissolving the organic monomer into the inorganic sol under inert atmosphere, adding urea, and stirring to obtain premixed sol;
step 2), dropwise adding the mixed solution of the initiator A and the initiator B into the premixed sol obtained in the step 1) to initiate the polymerization of the organic monomer, so as to obtain a reaction solution;
step 3), sealing and standing the reaction solution to obtain polymer gel;
and 4), drying the polymer gel to constant weight, and grinding into powder to obtain the polymer gel.
6. The method according to claim 5, wherein in step 1), the inert atmosphere is selected from one or more of an argon atmosphere, a nitrogen atmosphere, and a helium atmosphere; adding urea at 50-90 ℃; the stirring time is 20-40 min.
7. The preparation method according to claim 5, wherein in the step 2), the polymerization time is 2-7 h; and/or in the step 3), the sealing and standing time is more than 4 h.
8. The preparation method of claim 7, wherein in the step 3), the sealing is stopped for 4-5 h.
9. The method according to any one of claims 5 to 8, wherein the drying temperature in step 4) is 40 to 60 ℃.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202010457580.2A CN111635497B (en) | 2020-05-26 | 2020-05-26 | Underwater concrete anti-dispersant and preparation method thereof |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202010457580.2A CN111635497B (en) | 2020-05-26 | 2020-05-26 | Underwater concrete anti-dispersant and preparation method thereof |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN111635497A CN111635497A (en) | 2020-09-08 |
| CN111635497B true CN111635497B (en) | 2021-07-20 |
Family
ID=72327064
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202010457580.2A Active CN111635497B (en) | 2020-05-26 | 2020-05-26 | Underwater concrete anti-dispersant and preparation method thereof |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN111635497B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113149710B (en) * | 2021-04-14 | 2022-04-01 | 石家庄市长安育才建材有限公司 | Concrete surface modifier and preparation method thereof |
| CN113336464B (en) * | 2021-07-28 | 2021-10-29 | 湖南大学 | Concrete thickener and preparation method thereof |
| CN114957559B (en) * | 2022-05-24 | 2023-09-15 | 佳化化学科技发展（上海）有限公司 | Amide water reducer and preparation method thereof |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105585272A (en) * | 2015-10-22 | 2016-05-18 | 湖州绿色建材开发有限公司 | Novel concrete reinforcing agent |
| CN108623741A (en) * | 2018-05-03 | 2018-10-09 | 北京工业大学 | A kind of organic low alkali accelerator of formation inierpeneirating network structure and preparation method thereof |
| CN110342859A (en) * | 2019-03-12 | 2019-10-18 | 北京市政建设集团有限责任公司 | A kind of silicon hybridization acrylates cement composite grouting material and preparation method thereof |
| CN110387222B (en) * | 2019-08-01 | 2021-12-10 | 西南石油大学 | Porous gel plugging agent, preparation method and application thereof |
| CN110304872B (en) * | 2019-08-16 | 2021-09-21 | 陈晓星 | Nano modified cement-based underwater non-dispersible material and preparation method thereof |
-
2020
- 2020-05-26 CN CN202010457580.2A patent/CN111635497B/en active Active
Also Published As
| Publication number | Publication date |
|---|---|
| CN111635497A (en) | 2020-09-08 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN111635497B (en) | Underwater concrete anti-dispersant and preparation method thereof | |
| CN104788629B (en) | A kind of polycarboxylate water-reducer and its normal temperature preparation method | |
| CN105367720B (en) | A kind of diminishing collapse protective poly-carboxylic acid water reducing agent and preparation method thereof | |
| CN109400821B (en) | Concrete bleeding-resistant inhibitor with water reducing function and preparation method thereof | |
| CN108948294B (en) | Anti-mud slow-release slump retaining agent containing cyclodextrin side groups and preparation method thereof | |
| CN105924592B (en) | Viscosity-reducing polycarboxylic acid water reducer and preparation method thereof | |
| CN109337024B (en) | Preparation method of retarding polycarboxylate superplasticizer | |
| CN113372549B (en) | Vinyl-terminated hyperbranched polymer, viscosity-reducing polycarboxylate superplasticizer with hyperbranched structure and preparation method of viscosity-reducing polycarboxylate superplasticizer | |
| CN111777722A (en) | Anti-mud slump-retaining polycarboxylate superplasticizer and preparation method thereof | |
| CN111100253A (en) | Concrete anti-sensitive polycarboxylate superplasticizer and preparation method thereof | |
| CN114213603B (en) | Mud-resistant slow-release polycarboxylate superplasticizer and preparation method and application thereof | |
| CN115974451B (en) | Efficient environment-friendly water reducer and preparation method thereof | |
| WO2020001008A1 (en) | Preparation method for micro-crosslinked powder polycarboxylate water reducing agent | |
| CN112390921A (en) | Synthetic viscosity-reducing polycarboxylate superplasticizer and preparation method thereof | |
| CN114315209B (en) | Preparation method of fluorocarbon-containing viscosity-reducing polycarboxylate superplasticizer | |
| CN112126022A (en) | Formula and preparation method of polycarboxylate superplasticizer | |
| CN110627972A (en) | Novel mud-resistant polyether polycarboxylic acid water reducer and normal-temperature synthesis process thereof | |
| CN113354765A (en) | Viscosity-reducing polycarboxylate superplasticizer and preparation method thereof | |
| CN111961148B (en) | Reaction air-entraining type polycarboxylate superplasticizer and preparation method thereof | |
| CN111808244B (en) | Polycarboxylate superplasticizer with high water reduction and high adaptability and preparation method thereof | |
| CN109626860B (en) | Preparation method of block viscosity-reducing concrete admixture | |
| CN109721271B (en) | Polycarboxylate water reducing agent composition for self-compacting high-workability concrete | |
| CN109665745B (en) | Multifunctional polycarboxylic acid water reducing agent and preparation method thereof | |
| CN108706899B (en) | Preparation method of modified cement dispersant | |
| CN108892755B (en) | Slow-release polycarboxylate superplasticizer and preparation method and application thereof |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant |