An active repairing agent for road network cracks, a preparation method and application thereof

Abstract

This invention proposes an active repair agent for road network cracks, its preparation method, and its application, belonging to the technical field of road materials. It addresses the technical problems of slow strength improvement and limited traffic access after road network crack repair. The active repair agent comprises component A and component B. Component A includes the following raw materials in parts by weight: 20-40 parts reactive diluent, 20-30 parts modified asphalt, 10-30 parts toughening agent, 4-8 parts silane coupling agent, and 100 parts filler; component B is a curing agent solution. This invention achieves rapid curing by complexing the reactive diluent with an inorganic calcium salt curing agent to form a spatial network structure. The active repair agent features strong penetration and rapid strength formation, allowing for immediate traffic access after network crack repair.

Description

Technical Field

[0001] This invention belongs to the technical field of road materials, and particularly relates to an active repair agent for road network cracking, its preparation method, and its application. Background Technology

[0002] Network cracking is a common defect in asphalt roads, characterized by high incidence, significant damage, and high repair difficulty. Its main manifestations include: interconnected or partially connected cracks appearing on the road surface, with crack widths less than 10mm, block sizes of approximately 20-50cm, generally exhibiting a tortoise-shell pattern, and rapid propagation. If network cracked pavements are not repaired and maintained in a timely manner, they will significantly affect driving comfort and reduce the road's service life.

[0003] Currently, non-grooving repair methods are mainly used to repair micro-cracks such as network cracks. Patent CN106830767A discloses a recycled seal material for treating network cracks in asphalt pavement and its preparation method. Its characteristic is that it is composed of an organic-inorganic composite emulsion and fine aggregates. This recycled seal material has strong permeability and provides excellent sealing and waterproofing within the cracks, significantly improving the regeneration and restoration effect of aged asphalt. Patent CN113956844A discloses a room-temperature repair material for network cracks, its preparation method, and its application. It utilizes diesel fuel combined with a spreader and warm mix agent to increase the water-soluble capacity of asphalt. Simultaneously, the dilution effect of diesel fuel and water on the asphalt gives it good flowability. This material can be used immediately at room temperature to directly repair network cracks in asphalt pavement.

[0004] The above-mentioned method uses repair materials with good fluidity and permeability, which can fill, waterproof and repair network cracks. However, due to the liquid nature of the repair materials, the strength increases slowly, and there are certain restrictions on opening the road after repair. Summary of the Invention

[0005] To address the technical problems of slow strength improvement and restrictions on traffic opening after road network crack repair, this invention proposes an active repair agent for road network cracks, its preparation method, and its application. The active diluent undergoes a complexation reaction with an inorganic calcium salt curing agent, intertwining to form a spatial network structure and rapidly building strength, thus solving the problem of traffic restrictions after repair.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] An active repair agent for road network cracking includes component A and component B. Component A comprises the following raw materials in parts by weight: 20-40 parts of active diluent, 20-30 parts of modified asphalt, 10-30 parts of toughening agent, 4-8 parts of silane coupling agent, and 100 parts of filler; component B is a curing agent solution.

[0008] The active diluent comprises the following parts by weight: 10-15 parts of a polyhydroxy compound, 5-8 parts of a saturated fatty acid, 20-30 parts of an organic acid anhydride, 6-10 parts of a phthalate ester, and 0.5-1 parts of a catalyst.

[0009] The polyhydroxy compound is one or more of sorbitol, xylitol, or glucose; the saturated fatty acid is lauric acid and / or myristic acid; the organic acid anhydride is nadic anhydride and / or alkenyl succinic anhydride; and the catalyst is p-toluenesulfonic acid and / or trifluoromethanesulfonic acid.

[0010] The active diluent is synthesized by mixing a polyhydroxy compound, an organic acid anhydride, and a phthalate ester to carry out a first reaction; then adding a mixture of a catalyst and a saturated fatty acid to carry out a second reaction; and finally obtaining the active diluent by vacuum distillation.

[0011] The first reaction temperature is 120-140℃ and the time is 0.5-1h; the second reaction temperature is 140-160℃ and the time is 2-4h; the vacuum distillation pressure is 10-20kPa.

[0012] The modified asphalt is polyethylene modified asphalt and / or EVA modified asphalt; the toughening agent is deketoxime type silicone sealant and / or deamide type silicone sealant.

[0013] The silane coupling agent is vinyltrimethoxysilane or / and aminosilane; the filler is corundum or / and quartz sand.

[0014] The curing agent solution is a suspension of calcium hydroxide and calcium silicate with a concentration of 10-30 wt% and a mass ratio of calcium hydroxide to calcium silicate of 1:(1-3).

[0015] A method for preparing an active repair agent for road network cracking, wherein the preparation of component A includes the following steps: heating modified asphalt to 110-130℃, adding toughening agent and active diluent in sequence, and shearing and mixing; then adding silane coupling agent and filler, and stirring and mixing.

[0016] A method for applying an active repair agent for road cracks involves blowing and sweeping the cracked pavement until the surface and cracks are dust-free, first spraying component B, then evenly spraying or scraping component A until the cracks are filled, and then spraying component B again; the dosage of component B is 0.2-0.3 kg / m². 2 The dosage of component A is 2-5 kg / m³. 2 .

[0017] The beneficial effects of this invention are:

[0018] (1) The reactive diluent of the present invention has ester groups, long aliphatic chains and terminal hydroxyl and terminal carboxyl functional groups distributed on its molecular chain, which has the dual functions of efficient viscosity reduction and reaction curing. Through the complexation reaction between the terminal functional groups of the reactive diluent and the inorganic calcium salt curing agent, a spatial network structure is formed and the diluent is cured quickly.

[0019] (2) The silicone toughening agent of the present invention can react slowly with water or moisture to form a cross-linked structure, and the silane coupling agent can form a bridging effect between inorganic fillers and organic polymers, thereby improving the later strength and durability of the repair agent.

[0020] (3) The active repair agent of the present invention has the characteristics of strong permeability and fast strength formation, and traffic can be opened after the network crack repair is completed. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1

[0023] An active repair agent for road network cracking, the preparation method includes the following steps:

[0024] 15 parts xylitol, 30 parts alkenyl succinic anhydride, and 10 parts phthalate were added to a glass reactor equipped with a stirrer, thermometer, and condenser for the first reaction at 140°C for 1 hour. Then, a mixture of 1 part trifluoromethanesulfonic acid catalyst and 8 parts myristic acid was added for the second reaction at 160°C for 4 hours. Finally, low molecular weight products and unreacted monomers were removed by vacuum distillation at 10 kPa to obtain the active diluent.

[0025] 30 parts of EVA-modified asphalt were heated to 130°C, and 30 parts of deamide-type silicone toughening agent and 20 parts of reactive diluent were added sequentially. The mixture was sheared and mixed at a shear rate of 4000 rpm for 50 min. Then, 8 parts of aminosilane and 100 parts of quartz sand were added and the mixture was stirred and mixed at a stirring rate of 1000 rpm for 60 min to obtain an active repair agent for road network cracking.

[0026] After sweeping the cracked pavement until the surface and cracks are free of dust, spray 0.1 kg / m² of water. 2 A suspension of calcium hydroxide and calcium silicate with a concentration of 10 wt% and a mass ratio of 1:2 was then uniformly coated at a depth of 5 kg / m². 2 Apply the active repair agent until it fills the crack, then spray 0.1 kg / m². 2Once the network crack repair is completed, a 10wt% suspension can be used to open the road to traffic.

[0027] Example 2

[0028] An active repair agent for road network cracking, the preparation method includes the following steps:

[0029] 13 parts xylitol, 27 parts alkenyl succinic anhydride, and 8 parts phthalate were added to a glass reactor equipped with a stirrer, thermometer, and condenser for the first reaction at 135°C for 50 min. Then, a mixture of 0.8 parts trifluoromethanesulfonic acid catalyst and 7 parts myristic acid was added for the second reaction at 155°C for 3.5 h. Finally, low molecular weight products and unreacted monomers were removed by vacuum distillation at 14 kPa to obtain the active diluent.

[0030] 27 parts of EVA-modified asphalt were heated to 125°C, and 25 parts of deamide-type silicone sealant and 25 parts of reactive diluent were added sequentially. The mixture was sheared and mixed at a shear rate of 3500 rpm for 40 min. Then, 7 parts of aminosilane and 100 parts of quartz sand were added and the mixture was stirred at a stirring rate of 800 rpm for 50 min to obtain an active repair agent for road network cracking.

[0031] After sweeping the cracked pavement until the surface and cracks are free of dust, spray 0.2 kg / m² of water. 2 A suspension of calcium hydroxide and calcium silicate with a concentration of 20 wt% and a mass ratio of 1:2 was then uniformly coated at a rate of 4 kg / m². 2 Apply the active repair agent until it fills the crack, then spray 0.1 kg / m². 2 Once the network crack repair is completed, a 20wt% suspension can be used to open the road to traffic.

[0032] Example 3

[0033] An active repair agent for road network cracking, the preparation method includes the following steps:

[0034] 12 parts glucose, 23 parts nadic anhydride, and 7 parts phthalate were added to a glass reactor equipped with a stirrer, thermometer, and condenser for the first reaction at 128°C for 40 min. Then, a mixture of 0.7 parts p-toluenesulfonic acid catalyst and 6 parts lauric acid was added for the second reaction at 148°C for 2.8 h. Finally, low molecular weight products and unreacted monomers were removed by vacuum distillation at 18 kPa to obtain the active diluent.

[0035] 25 parts of polyethylene modified asphalt were heated to 120°C, and 17 parts of deketoxime type silicone toughening agent and 35 parts of reactive diluent were added sequentially. The mixture was sheared and mixed at a shear rate of 3000 rpm for 30 min. Then, 6 parts of vinyltrimethoxysilane and 100 parts of carborundum were added and stirred and mixed at a stirring rate of 500 rpm for 40 min to obtain an active repair agent for road network cracking.

[0036] After sweeping the cracked pavement until the surface and cracks are free of dust, spray 0.1 kg / m² of water. 2 A suspension of calcium hydroxide and calcium silicate with a concentration of 30 wt% and a mass ratio of 1:2 was then uniformly sprayed at a concentration of 3 kg / m³. 2 Apply the active repair agent until it fills the crack, then spray 0.2 kg / m². 2 A suspension of calcium hydroxide and calcium silicate with a concentration of 30wt% can be opened to traffic after the network crack repair is completed.

[0037] Example 4

[0038] An active repair agent for road network cracking, the preparation method includes the following steps:

[0039] Ten parts of sorbitol, 20 parts of nadic anhydride, and 6 parts of phthalate were added to a glass reactor equipped with a stirrer, thermometer, and condenser for the first reaction at 120°C for 0.5 h. Then, a mixture of 0.5 parts of p-toluenesulfonic acid and 5 parts of lauric acid was added for the second reaction at 140°C for 2 h. Finally, low molecular weight products and unreacted monomers were removed by vacuum distillation at 20 kPa to obtain the active diluent.

[0040] 20 parts of polyethylene modified asphalt were heated to 110°C, and 10 parts of deketoxime silicone sealant and 40 parts of reactive diluent were added sequentially. The mixture was sheared and mixed at a shear rate of 2000 rpm for 20 min. Then, 4 parts of vinyltrimethoxysilane and 100 parts of carborundum were added and stirred at a stirring rate of 300 rpm for 30 min to obtain an active repair agent for road network cracking.

[0041] After sweeping the cracked pavement until the surface and cracks are free of dust, spray 0.1 kg / m² of water. 2 A suspension of calcium hydroxide and calcium silicate with a concentration of 20 wt% and a mass ratio of 1:2 was then uniformly sprayed at a rate of 2 kg / m³. 2 Apply the active repair agent until it fills the crack, then spray 0.1 kg / m². 2 Once the network crack repair is completed, a 20wt% suspension can be used to open the road to traffic.

[0042] Comparative Example 1

[0043] The suspension of calcium hydroxide and calcium silicate from Example 1 was not sprayed, while all other conditions remained unchanged.

[0044] Comparative Example 2

[0045] The reactive diluent in Example 1 was replaced with 180# solvent oil, and the suspension of calcium hydroxide and calcium silicate was not sprayed, while the other conditions remained unchanged.

[0046] Effect Comparison

[0047] Table 1 Comparison of performance indicators of road crack repair agents

[0048]

[0049] As shown in Table 1, the active repair agents prepared in Examples 1-4 have shorter final setting times and higher tensile strengths compared to Comparative Examples 1-2, and their water permeability and friction properties are also superior. The active repair agent of this invention features strong permeability and rapid strength formation, allowing traffic to resume immediately after the network crack repair is completed.

[0050] Example 5

[0051] An active repair agent for road network cracking, the preparation method includes the following steps:

[0052] Ten parts of glucose, three parts of xylitol, 20 parts of nadic anhydride, and six parts of phthalate were added to a glass reactor equipped with a stirrer, thermometer, and condenser for the first reaction at 130°C for 30 min. Then, 0.5 parts of p-toluenesulfonic acid catalyst, a mixture of 2 parts of myristic acid and 6 parts of lauric acid were added for the second reaction at 150°C for 4 h. Finally, low molecular weight products and unreacted monomers were removed by vacuum distillation at 20 kPa to obtain the active diluent.

[0053] 25 parts of polyethylene modified asphalt were heated to 120°C, and 15 parts of deketoxime type silicone toughening agent and 35 parts of reactive diluent were added sequentially. The mixture was sheared and mixed at a shear rate of 3000 rpm for 30 min. Then, 5 parts of vinyltrimethoxysilane and 100 parts of carborundum were added and stirred and mixed at a stirring rate of 500 rpm for 40 min to obtain an active repair agent for road network cracking.

[0054] After sweeping the cracked pavement until the surface and cracks are free of dust, spray 0.1 kg / m² of water. 2 A suspension of calcium hydroxide and calcium silicate with a concentration of 15 wt% and a mass ratio of 1:1 was then sprayed evenly at a rate of 3.5 kg / m³. 2 Apply the active repair agent until it fills the crack, then spray 0.2 kg / m². 2 Once the network crack repair is completed, a 15wt% suspension can be used to open the road to traffic.

[0055] Example 6

[0056] An active repair agent for road network cracking, the preparation method includes the following steps:

[0057] 15 parts of sorbitol, 25 parts of alkenyl succinic anhydride, and 10 parts of phthalate were added to a glass reactor equipped with a stirrer, thermometer, and condenser for the first reaction at 128°C for 40 min. Then, a mixture of 0.7 parts of p-toluenesulfonic acid catalyst and 6 parts of lauric acid was added for the second reaction at 148°C for 2.8 h. Finally, low molecular weight products and unreacted monomers were removed by vacuum distillation at 18 kPa to obtain the active diluent.

[0058] Ten parts of polyethylene modified asphalt and 15 parts of EVA modified asphalt were mixed and heated to 120°C. Then, 17 parts of deketoxime type silicone toughening agent and 35 parts of reactive diluent were added sequentially, and the mixture was sheared and mixed at a shear rate of 3000 rpm for 30 min. Then, 6 parts of vinyltrimethoxysilane and 100 parts of carborundum were added, and the mixture was stirred and mixed at a stirring rate of 500 rpm for 40 min to obtain an active repair agent for road network cracking.

[0059] After sweeping the cracked pavement until the surface and cracks are free of dust, spray 0.1 kg / m² of water. 2 A suspension of calcium hydroxide and calcium silicate with a concentration of 25 wt% and a mass ratio of 1:2 was then uniformly sprayed at a rate of 3 kg / m³. 2 Apply the active repair agent until it fills the crack, then spray 0.2 kg / m². 2 Once the network crack repair is completed, a 25wt% suspension can be used to open the road to traffic.

[0060] Example 7

[0061] An active repair agent for road network cracking, the preparation method includes the following steps:

[0062] 12 parts glucose, 20 parts nadic anhydride, 10 parts alkenyl succinic anhydride, and 7 parts phthalate were added to a glass reactor equipped with a stirrer, thermometer, and condenser for the first reaction at 120°C for 40 min. Then, a mixture of 0.7 parts p-toluenesulfonic acid catalyst and 6 parts lauric acid was added for the second reaction at 155°C for 3 h. Finally, low molecular weight products and unreacted monomers were removed by vacuum distillation at 18 kPa to obtain the active diluent.

[0063] 25 parts of polyethylene modified asphalt were heated to 130°C, and 10 parts of deketoxime type silicone toughening agent, 10 parts of deamide type silicone sealant and 35 parts of reactive diluent were added in sequence. The mixture was sheared and mixed at a shear rate of 3000 rpm for 30 min. Then, 6 parts of vinyltrimethoxysilane and 100 parts of carborundum were added and stirred at a stirring rate of 500 rpm for 40 min to obtain an active repair agent for road network cracking.

[0064] After sweeping the cracked pavement until the surface and cracks are free of dust, spray 0.1 kg / m² of water. 2 A suspension of calcium hydroxide and calcium silicate with a concentration of 10 wt% and a mass ratio of 1:3 was then uniformly sprayed at a concentration of 3 kg / m³. 2 Apply the active repair agent until it fills the crack, then spray 0.2 kg / m². 2 Once the network crack repair is completed, a 10wt% suspension can be used to open the road to traffic.

[0065] Example 8

[0066] An active repair agent for road network cracking, the preparation method includes the following steps:

[0067] Ten parts of glucose, 30 parts of nadic anhydride, and 10 parts of phthalate were added to a glass reactor equipped with a stirrer, thermometer, and condenser for the first reaction at 128°C for 40 min. Then, a mixture of 0.5 parts of p-toluenesulfonic acid catalyst and 5 parts of lauric acid was added for the second reaction at 148°C for 2.8 h. Finally, low molecular weight products and unreacted monomers were removed by vacuum distillation at 18 kPa to obtain the active diluent.

[0068] 22 parts of polyethylene modified asphalt were heated to 120°C, and 17 parts of deketoxime type silicone toughening agent and 35 parts of reactive diluent were added sequentially. The mixture was sheared and mixed at a shear rate of 3000 rpm for 30 min. Then, 6 parts of vinyltrimethoxysilane, 80 parts of corundum and 80 parts of 20% quartz sand were added and the mixture was stirred and mixed at a stirring rate of 500 rpm for 40 min to obtain an active repair agent for road network cracking.

[0069] After sweeping the cracked pavement until the surface and cracks are free of dust, spray 0.2 kg / m² of water. 2 A suspension of calcium hydroxide and calcium silicate with a concentration of 20 wt% and a mass ratio of 1:2 was then uniformly sprayed at a rate of 2.5 kg / m². 2 Apply the active repair agent until it fills the crack, then spray 0.05 kg / m². 2 Once the network crack repair is completed, a 20wt% suspension can be used to open the road to traffic.

[0070] Example 9

[0071] An active repair agent for road network cracking, the preparation method includes the following steps:

[0072] Ten parts of sorbitol, three parts of glucose, 20 parts of alkenyl succinic anhydride, and six parts of phthalate were added to a glass reactor equipped with a stirrer, thermometer, and condenser for the first reaction at 135°C for 1 hour. Then, a mixture of 0.8 parts of p-toluenesulfonic acid and 0.2 parts of trifluoromethanesulfonic acid catalyst with 6 parts of lauric acid was added for the second reaction at 148°C for 2.8 hours. Finally, low-molecular-weight products and unreacted monomers were removed by vacuum distillation at 18 kPa to obtain the active diluent.

[0073] 28 parts of polyethylene modified asphalt were heated to 120°C, and 17 parts of deketoxime type silicone toughening agent and 35 parts of reactive diluent were added sequentially. The mixture was sheared and mixed at a shear rate of 3000 rpm for 30 min. Then, 6 parts of vinyltrimethoxysilane and 100 parts of carborundum were added and stirred and mixed at a stirring rate of 500 rpm for 40 min to obtain an active repair agent for road network cracking.

[0074] After sweeping the cracked pavement until the surface and cracks are free of dust, spray 0.1 kg / m² of water. 2 A suspension of calcium hydroxide and calcium silicate with a concentration of 30 wt% and a mass ratio of 1:2 was then uniformly sprayed at a concentration of 3 kg / m³. 2 Apply the active repair agent until it fills the crack, then spray 0.2 kg / m². 2 Once the network crack repair is completed, a 30wt% suspension can be used to open the road to traffic.

[0075] Example 10

[0076] An active repair agent for road network cracking, the preparation method includes the following steps:

[0077] 15 parts glucose, 20 parts nadic anhydride, and 10 parts phthalate were added to a glass reactor equipped with a stirrer, thermometer, and condenser for the first reaction at 120°C for 40 min. Then, a mixture of 0.7 parts p-toluenesulfonic acid catalyst and 6 parts lauric acid was added for the second reaction at 140°C for 3 h. Finally, low molecular weight products and unreacted monomers were removed by vacuum distillation at 18 kPa to obtain the active diluent.

[0078] 25 parts of polyethylene modified asphalt were heated to 120°C, and 17 parts of deketoxime type silicone toughening agent and 35 parts of reactive diluent were added sequentially. The mixture was sheared and mixed at a shear rate of 3000 rpm for 30 min. Then, 6 parts of vinyltrimethoxysilane and 100 parts of carborundum were added and stirred and mixed at a stirring rate of 500 rpm for 40 min to obtain an active repair agent for road network cracking.

[0079] After sweeping the cracked pavement until the surface and cracks are free of dust, spray 0.1 kg / m² of water. 2 A suspension of calcium hydroxide and calcium silicate with a concentration of 20 wt% and a mass ratio of 1:2 was then uniformly sprayed at a rate of 3 kg / m³. 2 Apply the active repair agent until it fills the crack, then spray 0.2 kg / m². 2 Once the network crack repair is completed, a 20wt% suspension can be used to open the road to traffic.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An active repair agent for road network cracking, characterized in that, The product comprises component A and component B. Component A includes the following raw materials in parts by weight: 20-40 parts reactive diluent, 20-30 parts modified bitumen, 10-30 parts toughening agent, 4-8 parts silane coupling agent, and 100 parts filler. Component B is a curing agent solution. The reactive diluent includes the following raw materials in parts by weight: 10-15 parts polyhydroxy compound, 5-8 parts saturated fatty acid, 20-30 parts organic acid anhydride, 6-10 parts phthalate ester, and 0.5-1 part catalyst. The polyhydroxy compound... The compound is one or more of sorbitol, xylitol, or glucose; the saturated fatty acid is lauric acid and / or myristic acid; the organic acid anhydride is nadic anhydride and / or alkenyl succinic anhydride; the catalyst is p-toluenesulfonic acid and / or trifluoromethanesulfonic acid; the active diluent is synthesized by: mixing the polyhydroxy compound, organic acid anhydride, and phthalic acid ester to carry out a first reaction; then adding a mixture of catalyst and saturated fatty acid to carry out a second reaction; finally, obtaining the active diluent by vacuum distillation; The curing agent solution is a suspension of calcium hydroxide and calcium silicate, with a suspension concentration of 10-30 wt% and a mass ratio of calcium hydroxide to calcium silicate of 1:(1-3).

2. The active repair agent for road network cracking according to claim 1, characterized in that, The first reaction temperature is 120-140℃ and the time is 0.5-1h; the second reaction temperature is 140-160℃ and the time is 2-4h; the vacuum distillation pressure is 10-20kPa.

3. The active repair agent for road network cracking according to claim 1, characterized in that, The modified asphalt is polyethylene modified asphalt and / or EVA modified asphalt; the toughening agent is deketoxime type silicone sealant and / or deamide type silicone sealant.

4. The active repair agent for road network cracking according to claim 3, characterized in that, The silane coupling agent is vinyltrimethoxysilane or / and aminosilane; the filler is corundum or / and quartz sand.

5. The method for preparing the active repair agent for road network cracking according to any one of claims 1-4, characterized in that, The preparation of component A includes the following steps: heating the modified asphalt to 110-130℃, adding the toughening agent and reactive diluent in sequence, and shearing and mixing; then adding the silane coupling agent and filler, and stirring and mixing.

6. The method of applying the active repair agent for road network cracking according to any one of claims 1-4, characterized in that, After cleaning the cracked pavement surface and cracks, spray component B first, then evenly spray or scrape component A until the cracks are filled, and then spray component B again; the dosage of component B is 0.2-0.3 kg / m². 2 The dosage of component A is 2-5 kg / m³. 2 .

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