Table 1 Requirements for bridges facing waterproof materials 1) Adaptability to bridge conditions (flatness, cleanliness, etc.) during service period during construction; 2) Good adaptability to changes in temperature and humidity; 3) Easy construction , Not limited by the geometric factors of the bridge deck; 4) The bridge surface has good adhesion, especially at the corners; 5) It can resist loose aggregates, fuel pollution, pedestrian traffic, falling objects before paving. Destruction; 7) It is not damaged by hot asphalt mixture at high temperature and has good adhesion to the surface layer 1) Good temperature adaptability; 2) It is impermeable, and has good adhesion to surface layer and bridge surface; 3) Not to be pierced by aggregates under heavy traffic; Turning) Shear stress; 5) Ability to resist cracks on bridge decks; 6) Not to be damaged by water and salts, including water pressure due to driving loads; When the surface layer is repaired, the waterproof layer is not damaged. Because the cross-sea bridge is in the harsh environment conditions of the sea, and the cross-sea project tends to have a higher requirement on the service life of the structure (usually more than a hundred years), the water resistance of the bridge structure is Infringement becomes the focus of most concern .
The general bridge waterproofing system consists of two parts, rigid waterproof (self-waterproofing of concrete itself) and deck waterproof layer. The imperfect bridge deck waterproofing system is an important cause of bridge damage. Therefore, a perfect waterproof system must be set up to separate the concrete from the water. In general, no matter how the concrete construction quality can not be fully guaranteed without cracking, therefore, the waterproof layer system is particularly important.
After many years of practice and exploration by experts at home and abroad, combined with the specific conditions of their respective countries and regions, the types of structures chosen for waterproofing concrete bridge deck decks are not the same.
Japan adopts the form of paving: asphalt layer + plate waterproof material + asphalt rubber binder + concrete; asphalt layer + 3-layer neoprene waterproof material + neoprene adhesive concrete; asphalt layer + emulsified asphalt (bonding ) + asphalt layer (waterproof) + asphalt rubber binder.
Denmark adopts the form of paving: applying epoxy resin as a base coat on the grit-blasted bridge deck, and laying a modified asphalt membrane fully bonded to the bridge surface with asphalt concrete on it.
France requires that all bridges be provided with a waterproof layer, and it is recommended that the waterproof material be preferentially coated with a film or coil made of a high molecular polymer. The primer layer is generally a modified synthetic rubber emulsion, and the surface layer thickness is generally 710cm. .
1 Waterproof layer function and technical requirements Waterproof adhesive material can completely seal the capillary pores and fine cracks of cast-in-situ concrete on the concrete box girder (permeation and consolidation) to block water from bottom to top from the cement concrete bridge deck into the bridge In surface pavement, it can also block water from top to bottom from the bridge deck into the cement concrete bridge. The material not only requires better adhesion to the pavement layer and cement concrete, but also requires better waterproof performance, and also has good penetration and consolidation of the cement concrete and bridge deck micro cracks (see Table 1). This is the key to achieving excellent durability of the bridge deck pavement.
Waterproof coatings for waterproof layers have been rapidly developed since they were applied in the 1970s. According to relevant information, the main products are classified into three categories: polymer waterproof coating, modified asphalt, and asphalt-based waterproof coating.
Polymer waterproof coatings currently include polyurethane, silicone rubber waterproof coatings, water-based EPDM rubber composite waterproof coatings, CB-type acrylic elastomer waterproof coatings, etc.; modified asphalt waterproof coatings are neoprene latex asphalt, SBS modified asphalt, SBR modified asphalt, PVC coal tar and other waterproof coatings; asphalt-based waterproof coating bentonite asphalt, water-based asbestos asphalt, lime asphalt, emulsified asphalt and other waterproof coatings.
SBS asphalt, JS elastic waterproof mortar, anti-carbonation coating, epoxy resin four kinds of waterproof materials were selected as the bridge deck waterproof layer, through the test to test the bond properties, corrosion resistance, shear resistance and so on.
2 Test materials The cement adopts Conch brand P*O42.5 ordinary portland cement. The chemical composition and properties are shown in Table 2 and Table 3; Sand is the standard sand.
Table 2 Chemical composition (mass)% of cement Table 3 Slippage and shedding due to detachment between basic properties of cement, the thinner the layer, the greater the problem. Therefore, the inter-layer bonding is very important. The bridge deck pavement is generally a reinforced concrete slab, but considering the difference between the surface performance of cement concrete and the surface properties of the cement mortar, the surface of the test uses a cement mortar surface instead of the cement concrete surface.
The test adopts the eight-character mould method and is maintained in four ways. The test results are shown in Table 5. The asphalt used in asphalt mixture is AH-70 domestic asphalt.
The aggregate used for the test was basaltic lithotripsy, finely divided limestone was used as the ore powder, and the test grade was AC-161. In this test, the waterproof layer material used was SBS asphalt, JS elastic waterproof mortar, anti-carbonation coating and epoxy resin.
3.1 All kinds of waterproof material ultimate tensile strength, elongation test A variety of waterproof materials were filmed on the polyester glass paper, the thickness of 1.54mm. After a week of conservation, according to room temperature, 180 °C bake 3h after the normal temperature 2h these two ways to test. The test results are shown in Table 4. Table 5 Hydration strength after curing for 28 days Maintenance mode Bond strength after 28 days/MPa Carbonated coating JS Elastic waterproof mortar SBS modified asphalt Epoxy standard maintenance 1.632.071.052.37 Seawater erosion 0.630. 800.451.733% Sodium sulfate solution 0.600.650.431.82 High temperature (80C) 1.882.28-3.53 Table 4 Ultimate tensile strength and elongation of various materials z Test The results of Table 4 show that the anti-carbonation coating and JS elastic waterproof The ultimate tensile strength and elongation of the mortar are ideal. Once the epoxy resin forms a dense and complete coating film, it will not be softened due to the influence of high temperature, that is, the softness of the asphalt mixture is poor, and convection is likely to occur during the construction process. Shedding, separation between layers, and because of its own extensibility and crack resistance is very poor, when the structure produces a large deformation is easy to crack, especially when the crack depth exceeds the thickness of the waterproof coating penetration layer, the waterproof function of the waterproof material is also It disappeared.
The pull test is used to determine the bond strength between the cement concrete layer and the waterproof layer. Asphalt pavement on the bridge deck is paved on a rigid base surface, and the modulus of elasticity of cement concrete and asphalt concrete is different by several hundred times, so the asphalt mixture surface layer is basically under pressure. The main reason for the damage of the bridge deck is not the tensile stress, but the combination of the upper and lower layers of the climatic conditions of the trans-ocean bridge, and in reference to foreign countries such as Japan, Germany and other related cement concrete deck pavement technical specifications based on the bond strength The indicators are: no less than 1.0 MPa at normal temperature, and not less than 0.8 MPa in seawater and sulfate environments. During the test, it was found that SBS asphalt was used as a test piece for the adhesive layer, which was easily deformed in the curing process and could not meet the resistance requirements. High temperature performance, while the remaining three materials can meet the technical requirements under normal temperature and high temperature curing conditions. In the aspect of corrosion resistance, the decay rate of various materials is relatively serious, and the corrosion resistance of the epoxy resin is better, followed by JS elastic mortar.
Impermeability Impermeability Test Method: Prepare impervious test standard block, curing for 28 days; flatten the upper and lower surfaces with a wire brush, and then apply various waterproof materials or combinations on the test block (reference 6 blocks, every other Type 3), curing 7d; mold, and side wax to prevent side leakage; starting from 0.1MPa, plus 0.1MPa every 8h, until 1MPa stabilized after 48h; demoulding, split open, measure the water seepage height.
Impermeability comparison is shown.
Table 6 Shear Strength of Waterproof Layer Coating Shear Strength/MPa Normal Temperature Artificial Seawater 3%. Sodium Sulphate Epoxy 0.360.160.15JS Elastic Waterproof Mortar 1.090.550.51SBS Modified Bitumen 0.130.050.14 Anti-Carbonizing Coating 1.440.550.51 3.4 Adhesion to the Overlaying Asphalt Pavement As the waterproof layer is topped with the asphalt mixture as the surface layer, the hot asphalt compounding method is used at home and abroad. This requires that the waterproof material must not be mixed with hot asphalt. The material is damaged at high temperatures and maintains good adhesion to the surface.
In the test, it was found that the adhesion between epoxy resin and asphalt was poor, and the fracture surface was an epoxy-asphalt surface. After the epoxy resin was applied on the bridge base layer, a dense film was formed and it could not adhere to the asphalt mixture pavement layer. Knot. The section of JS elastic waterproof mortar is the contact surface of paint and asphalt, and the section of anti-carbonation coating is the contact surface between coating and cement mortar, indicating that the adhesion of anti-carbonizing coating and asphalt is stronger than JS waterproof mortar.
3.5 Shear resistance test Cement concrete bridge deck and asphalt concrete pavement layer should form a whole force structure to resist the effect of vehicle dynamic load. These two levels are bonded together by bonding materials. Under the action of vehicle loads, these two levels are mainly affected by shear forces and pressure.
Destruction of shear will appear congested and oversaw. Common shear failure situation: As the modulus of the reinforced concrete on the bridge surface is much larger than the modulus of the asphalt concrete and the waterproof layer, and the thickness of the asphalt concrete is thin, the asphalt layer undergoes a large shear force and causes no definite damage surface shear. Deformation.
The shear failure occurred due to insufficient adhesion between the waterproof layer and the asphalt concrete and bridge deck.
The shear strength is an important guarantee for the quality of the bridge deck. Therefore, the direct jacking method was used to test the shear strength of the waterproof layer. The shear resistance test model is as shown.
Calculated according to the test data to obtain the shear strength of the waterproof layer is shown in Table 6. Test results It can be found that the flexible material occupies a large advantage, because the flexible waterproof material (JS elastic waterproof mortar, anti-carbonation coating) has a certain degree of extension deformation Performance, so its high shear strength.
In the actual environment, the deck receives the dynamic loading of traffic vehicles at high frequency, and the reinforced concrete structure is under frequent reciprocating force deformation. The waterproof layer needs to be able to withstand the deformation of the reciprocating structure of the deck, so the effect of anti-carbonizing coating and JS coating is better. ideal.
4 Conclusion For the technical requirements of the bridge deck waterproof bridge, the ultimate tensile strength of the waterproof material, elongation, and the upper and lower concrete adhesion, shear strength, impermeability, etc. shall be tested in order to waterproof Layer technology meets various requirements and extends the service life of the bridge.
When the epoxy resin is used as a waterproof layer of a sea-crossing bridge, it has good affinity with cement concrete, strong adhesion, and good corrosion resistance. However, the epoxy resin and the upper bituminous mixture are poor in softness, weak in adhesion, prone to flooding and falling of the asphalt concrete, and the cost is high.
JS elastic waterproof mortar has good ultimate tensile strength, elongation and high temperature resistance, and has strong adhesion to cement concrete. However, this system has poor corrosion resistance and is attenuated under seawater and sulphate curing conditions. The rate is large, and although this system has a certain high-temperature softening function, but the affinity with the asphalt mixture is weak, there will still be stratification.
The adhesion of the anti-carbonation material to the cement concrete and the asphalt mixture is strong. At the same time, this system has good ultimate tensile strength, elongation and high temperature resistance, and the impermeability is better and the cost is lower. This material has poor corrosion resistance and a large decay rate.
SBS asphalt and cement concrete and asphalt mixture bond strength is good, but poor high temperature performance is its main drawback, easy to cause waterproof layer flow, thickness is not the case, affecting the function of waterproof impermeability.
Comparison of the performance of various waterproof materials found that: The use of single or multiple waterproof materials alone as a waterproof layer has certain defects, and the combined use of two or more materials can achieve good results.
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