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MMA waterproof coatings applications and problems in bridges

Date:2014年8月18日 11:33

Abstract: With the deepening of China's high standards to promote large-scale infrastructure, bridges vulnerable to rain erosion problem is getting attention by professionals. MMA polymer waterproof coating waterproof protection as a high-end domestic construction material is currently being rolled out to use the bridge. MMA introduced in the domestic bridge waterproof waterproof coating application, and analyzes the application of the existing problems, proposed solutions to the problem and measures.

1 MMA waterproof coating profile

The full name of MMA (methyl methacrylate), generated by the action of acetone and hydrocyanic acid by-product of acrylonitrile production of acetone cyanohydrin, acetone cyanohydrin treatment production methylpropanamide sulphate with concentrated sulfuric acid, and then generate the direct esterification of methanol. MMA MMA waterproof coating is reactive to the major component of the liquid resin, with the initiator (a curing agent) benzoyl peroxide (BPO) reactions, radical polymerization, and the formation of methyl methacrylate having a molecular toughness cured waterproof coating. In foreign countries, MMA is widely used in municipal roads, concrete bridge deck, steel bridge decks, piers, pipes, industrial flooring, glass and steel products, such as Manhattan Bridge, the Turkish Bosporus suspension bridge, etc.; domestic MMA main the purpose is the production of polymer PMMA, the main consumption areas for advertising light boxes, signs, household items, furniture and other industries, basically belong to the low-end market, in recent years, increasingly large area in the high-speed railway bridges, highways and other projects in the steel girder. With lower production costs and raw material MMA, MMA waterproof coating will further develop in the high-end engineering market.

2 MMA waterproof coating applied waterproofing of bridge

Production Principle 2.1 MMA waterproof coating

The starting material of the hard monomer MMA (methyl methacrylate), soft monomer (acrylate prepolymers) and benzoyl peroxide according to a certain proportion of input temperature and a stirring device with a reactor, the reaction temperature must be time after adding a chain terminating agent, polymerization reaction was stopped and cooled to obtain a prepolymer. The prepolymer resin, a hard monomer and a crosslinking monomer (polyethylene glycol dimethacrylate, etc.) after dilution with soft monomer, then the proportion of added accelerator, sealing wax, leveling agents, antifoaming agents, etc. MMA waterproof coating additives production. MMA waterproof coating is carried out using a redox initiator system, room temperature curing, the coating provides a hard monomer is a rigid, soft monomer provides flexibility to the film, a crosslinking monomer containing a large amount of an ether bond due to effectively improve the flexibility of the film , strength and tear properties. MMA selected by testing waterproof coating formulation, including the realization of the tensile strength, tear strength, impact toughness, a balanced combination of various physical properties of hardness, low temperature resistance, and elongation at break including.

Construction Technology 2.2 MMA waterproof coating

MMA waterproof layer from the bottom to top followed by primer (primary treatment agent, including repair), the first layer of waterproof membrane, a second layer of waterproof membrane, the construction process is as follows:

2.2.1The concrete surface treatment

Automatic sandblasting machine with dust-free treatment of concrete surface, the concrete surface roughness between CSP3-CSP5, where blasting machine can not handle a manual grinding machine processing, and finally with a large hole for the local repair putty base surface, deep patching holes and other defects.

2.2.2Construction of the base surface treatment agent for concrete

Roll coating layer by way of MMA waterproof membrane supporting concrete surface treatment agent to the concrete surface, coating evenly, seamless coating, no obvious defects. When the base surface treatment agent in hard work and inspection before they were MMA waterproof layer construction.

2.2.3The first layer of waterproof membrane construction

Waterproof membrane construction should adopt special two-component airless spray equipment, prepare the appropriate quality in accordance with the requirements of Part A construction product instructions, B component and a curing agent, a curing agent is added to the first component B, stir then mixed with the A component metrics applicator, after mixing, ejected.

2.2.4The second layer of waterproof membrane construction

After the completion of construction of the first floor waterproof membrane, waterproof membrane to check the apparent circumstances of the local area for manual repair. After curing the repair area, directly in the underlying waterproofing membrane to separate the surface layer waterproof membrane coating, color and underlying waterproofing membrane area. After curing the surface layer of the water repellent film, the water repellent film appearance inspection, the repair manual for the local area, and detects the total thickness of the waterproof film and a waterproof layer and the adhesive strength of the concrete. Each layer dry film thickness of not less than 0.75 mm, the total thickness of not less than 1.5 mm, MMA waterproof material total amount of not less than 2.25 kg / m2.

3 MMA bridge waterproof waterproof coating applications in problem analysis

3.1 In the main bridge waterproofing applications problems and solutions

The main problem affecting the quality of the MMA, together with the bridge deck waterproofing system and the underlying cement mortar off together, because we have means of transportation on the bridge high above, shedding personal equipment would pose a security risk. Analysis: First, the following primary cement mortar during construction clean-up is not clean, resulting in cement mortar layer is not strong links with the grass roots, and gradually separated under rain erosion, while the role of means of transport by the wind and fall off; Second Construction when possible low temperatures and more rain and snow, the base surface moist; third is tight project schedule, construction management and supervision of staff did not meet the conditions under the waterproof membrane barbaric construction. Solution: First, strictly control the bridge deck and the underlying cement mortar quality, strict blasting treatment process to ensure that the main structure of the bridge and bridge engineering concrete strength; Second, strict construction process to ensure that the base surface moisture content of less than 10% before proceeding paint membrane construction; Third strict construction risk management requirements by law, when the project quality and progress clashed quality management put in the first place.

Performance Comparison 3.2 MMA waterproof coatings and other waterproof material

Currently deck waterproof coating using a wider range of polyurea SPUA, polyurethane waterproofing membrane, etc., MMA waterproof coating with them has obvious advantages, mainly for inter-layer adhesion excellent (no interfacial bond agent); concrete base surface high bonding strength; excellent resistance to aging and yellowing resistance, long life (20 a above); humidity and low temperature environment, construction can fast curing (except rainy days); dual group after the sub-cold spray airless spray equipment construction without preheating the material, construction speed, average daily construction 超过2000 m2, and construction 1 h can pass (without curing process). MMA waterproof coatings and polyurea SPUA is as follows:

Between (a) layer adhesion. MMA system compatibility is better, there is no inter-layer adhesion problems; SPUA exist between poor adhesion layer, peel strength is generally not high.

(2) facade construction. MMA in the steep face of the base construction is more difficult; SPUA a few seconds can be cured, there is no facade construction problems.

(3) take the seams. MMA system compatibility is good, there is no recoating issues, can be intermittent construction, no lap seam; SPUA not repeat interval construction, construction continues on the old polyurea need brushing special layer between the adhesive, otherwise take the seams easy to peel. When the actual construction, to ensure quality, MMA waterproof layer coating is interrupted, waterproofing system in every lap bit reserved about 50 mm wide.

(4) weathering resistance. MMA acrylic waterproof material has excellent weathering performance, no other material can be applied directly to the railroad protective surface layer; SPUA polyurea waterproofing materials are generally aromatic polyurea, limited weathering performance, easy-yellowing, can not be used for railroad surface layer, to be construction material weathering protection.

(5) low temperature construction. MMA waterproof coating can be carried out under conditions of -20 ℃curing; SPUA generally above 5 ℃for construction, lower temperature, the relevant supporting materials are difficult to cure properly, the impact of construction quality.

(6) re-painted and repaired. MMA material has good inter-layer adhesion, can be re-coated construction, easy repair and maintenance; inter-layer adhesion SPUA poor construction can not be re-painted in the seams need to take special inter-layer construction adhesive, easy to repair maintenance.

(7) Construction equipment. MMA relatively slow response of waterproof material, the use of pre-mixed approach, professional airless spray equipment are construction work, materials do not need to mix in the muzzle at, you can take the form of a single tube, relatively simple; SPUA proprietary polyurea waterproofing materials needed high-temperature high-pressure spray equipment, materials react faster mixed cured in an instant the gun, the operator need for professional training, but also to the construction of large equipment inconvenience.

Identification of 3.3 MMA waterproof coatings and other waterproof material

MMA due to higher raw material prices, often unscrupulous suppliers to win lucrative real ones, polyurethane, polyurethane urea (half polyurea), pure polyurea waterproof coating instead of MMA and other raw materials, leading to the bridge deck waterproofing ineffective. MMA waterproof coatings and other waterproof material identification methods are mainly three types:

3.3.1visual identification

A waterproof coating is a MMA resin component, B component and a curing agent (benzoyl peroxide, BPO) to the packaging of three components, wherein the components A, B are the liquid component, the curing agent is a powder, and since MMA contain a considerable amount of methyl methacrylate monomer, and therefore the waterproof resin coating MMA methyl methacrylate main odor peculiar pungent smell; polyurethane, polyurethane urea (half polyurea), pure polyurea coatings are waterproof is a two-component packaging, the powder does not contain a curing agent. Users only need to understand the product's packaging and smells can simply identify the MMA resin waterproof coating.

3.3.2Test Test

According to the waterproof membrane construction process, if A, B components are not mixed with hardener no any response, no film, no cure and hold heat, add the curing agent opposite effect, you can determine if the material is MMA waterproof coating; polyurethane, polyurethane urea (half polyurea), pure polyurea waterproof coatings by A, B component directly after mixing can be cured film, without adding any curing agent.

3.3.3Special Inspection

Physical and mechanical properties according to MMA waterproof coating indicators and test methods: a measuring dry time, MMA resin waterproof coating film of dry time is generally 10 ~ 30 min; polyurethane waterproof coating dry time is 2 ~ 4 h, polyurethane urea (semi-polyurea), pure polyurea waterproofing coating dry time is less than 2 min. Second test tensile strength, tensile strength ≥12 MMA resin waterproofing membrane MPa, or a knife cut under a 100 mm ×10 mm test pieces, hand difficult to pull off; polyurethane, polyurethane urea (half polyurea), pure polyurea waterproofing membrane tensile strength are ≤6 MPa, hand it is easy to pull off, and therefore polyurethane, polyurethane polyurea, pure polyurea waterproofing membrane is required 7 days curing to achieve the ultimate strength. Three dry hardness measured with a hardness tester waterproof film measured MMA resin hardness (Shore D) is generally ≥50; polyurethane, polyurethane urea (half polyurea), pure polyurea waterproof film hardness (Shore D) is generally ≤forty five.

3.4 MMA quality control measures waterproof coating

(A) for the production of waterproofing products and processes are identified, to prevent mix of different products in the production process to achieve traceability.

(2) strictly control the production feeding, and feeding amount of each ingredient, time control, control, recording conditions, the entire production process is closely monitored.

(3) prohibit the production process into the next one semi-failed process to avoid losses.

(4) concrete deck at least 7 days curing, surface strength meet the requirements, the base surface must be firm, smooth, dry, clean, no obvious uneven, holes, cracks, no laitance, release agents, grease and other contaminants .

(5) to deal with the concrete surface prior to primer construction treated to remove concrete base surface laitance, loose particles, grease and other contaminants, to keep the concrete surface is clean, dry, flatness and surface roughness should meet the requirements.

(6) Construction MMA waterproof layer waterproof spray paint to spray the main mechanization, corner site, supplemented by artificial brush. After opening the package lid-time run out, if the lid is not closed after running out of A materials, scrap materials added after B hardener.

(7) The total thickness of the waterproofing membrane with ultrasonic thickness testing, each interval of 10 m laid four measurement points, the middle of the track layout 2, around each laid a protective wall. Bond strength test binding site, with a vernier caliper measurement test pull spindle surface MMA resin waterproof layer thickness.

(8) waterproof layer construction process focused on controlling the moisture content of the base surface, grass quality, brushing treatment agent quality grass, MMA waterproof layer quality, supervision and tracking test. Waterproof layer construction is completed, after passing the self-test report to supervision departments to verify, before after acceptance.

Within 24 h after (9) does not allow completion of primary treatment agent brushing Exalted stampede or other operations, when necessary, to cover a whole, to avoid being contaminated water and dust affect MMA waterproof layer coating and adhesive force grassroots level.

4 MMA prospect waterproof coating

MMA waterproof coating has high strength, strong adhesion, super weather, easy construction, greater elongation, etc., and for the solvent-free room temperature fast curing, in line with requirements of environmental protection and sustainable development of the country. With Japan's Nippon, ICI and other multinational companies to enter the United Kingdom, high-grade paint, new paint formulations introduction of domestic production, the demand for MMA will increase dramatically. SPUA and other domestic use polyurea waterproof coatings for curing speed, resulting in poor adhesion between the layers off a large area after use, waterproof membrane layer is increased due to the need to protect the bridge carrying the load, the current need for a bridge waterproofing mature product substitution , MMA bridge waterproof coating fully meet the requirements. Not recommended for high elasticity exposed can continue to use polyurea SPUA, in addition, we should vigorously promote MMA paint.

TypeInfo: Industry News

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