A salt-freezing resistance test device for highway concrete bridge maintenance materials

Abstract

The invention relates to a method for testing the salt-freezing resistance of a highway concrete bridge maintenance material. An antifreeze solution is contained in a high-low temperature alternating climate test box, and a stainless steel test mold is provided. Six cylindrical rubber molds are installed in the stainless steel test mold. A concrete or mortar test piece is installed in each rubber mold. A stainless steel clamp is provided at the upper end of the concrete or mortar test piece. A salt solution with a mass fraction of 3.5% is contained above the stainless steel clamp. The size of the concrete or mortar test piece is Φ100mm*50mm. The method has the advantage of being able to objectively evaluate the salt-freezing resistance of the highway concrete bridge maintenance material.

Description

Technical Field

[0001] The invention belongs to the technical field of performance testing of highway bridge maintenance materials (maintenance materials refer to concrete, mortar and coating materials used for repairing), and relates to a salt-freezing resistance performance testing device for highway concrete bridge maintenance materials. Background Art

[0002] The main causes of concrete damage today are steel corrosion, frost damage in cold climates, and physical and chemical effects in corrosive environments. Salt-freeze damage to concrete generally refers to concrete exfoliation damage caused by chloride salts under conditions of freeze-thaw cycles. According to the statistics of meteorological data in Liaoning Province, the number of harmful freeze-thaw cycles in cold areas can reach 85 to 103 times per year. The concrete components of highway bridges in this area that have been in service for more than 15 years have been damaged by salt-freeze to varying degrees, which can cause concrete expansion and cracking, and steel corrosion. According to the degree of damage caused by the durability disease of this type of bridge, repair concrete, mortar or coating materials are required for repair.

[0003] The root cause of salt freeze damage is the freezing pressure generated by the freeze-thaw cycle and the crystallization pressure generated by the dry-wet cycle, which ultimately leads to concrete damage. Existing test methods mostly test the freeze-thaw cycle, ignoring the dry-wet cycle. In addition, most mortar curing materials are evaluated for their salt freeze resistance by referring to the concrete inspection method, which fails to objectively evaluate the material's salt freeze resistance.

[0004] Currently, there is no suitable test method to evaluate the anti-salt-freeze performance of such maintenance materials. The present invention provides an anti-salt-freeze test device to test the anti-salt performance of highway bridge maintenance materials. Summary of the invention

[0005] In view of the deficiencies of the prior art, the present invention simulates the salt-freezing damage process of a concrete bridge in an actual environment under hot and humid conditions with alternating high and low temperatures.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a salt-freezing resistance test device for highway concrete bridge maintenance materials, including a high-low temperature alternating climate test chamber, and its technical points are: a stainless steel test mold is arranged in the high-low temperature alternating climate test chamber, and antifreeze is filled inside the stainless steel test mold. Six cylindrical rubber molds are installed inside the stainless steel test mold, and a concrete or mortar specimen is installed inside each rubber mold. A stainless steel clamp is arranged at the upper end of the concrete or mortar specimen, and a salt solution with a mass fraction of 3.5% is filled above the stainless steel clamp. The size of the concrete or mortar specimen is a cylinder of Φ100mm*50mm.

[0007] The beneficial effects of the present invention are as follows: the corrosion environment of highway concrete bridges is well simulated by the set freeze-thaw and wet-dry cycle mechanism and the deicing salt solution corrosive medium; the combined effects of salt freeze-thaw and wet-dry cycle on concrete or mortar specimens are realized by the high and low temperature alternating climate test chamber and the test device of the present invention; the salt freeze resistance of the highway concrete bridge maintenance material can be objectively evaluated by the three test results of specimen appearance, mass loss rate and freeze-thaw and wet-dry cycle number. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0009] The reference numerals are as follows:

[0010] 1. High and low temperature alternating climate test chamber 2. Stainless steel test mold 3. Antifreeze 4. 3.5% mass fraction salt solution 5. Concrete or mortar specimen 6. Stainless steel clamp 7. Rubber mold. DETAILED DESCRIPTION

[0011] like Figure 1 As shown, the present invention relates to a salt-freezing resistance test device for highway concrete bridge maintenance materials, comprising a high-low temperature alternating climate test box, wherein: the high-low temperature alternating climate test box 1 contains antifreeze 3 inside, and is provided with a stainless steel test mold 2, six cylindrical rubber molds 7 are installed inside the stainless steel test mold, a concrete or mortar test piece 5 is installed inside each rubber mold, a stainless steel clamp 6 is provided at the upper end of the concrete or mortar test piece, a salt solution 4 with a mass fraction of 3.5% is filled above the stainless steel clamp, and the size of the concrete or mortar test piece is a cylinder of Φ100mm*50mm.

[0012] Furthermore, the dimensions of the stainless steel test mold 2 specimen are 500mm*300mm*300mm in length, width and height respectively; the dimensions of the rubber mold 7 are Φ110mm*210mm; the dimensions of the stainless steel clamp 6 are Φ115mm*25mm; the dimensions of the concrete or mortar specimen 5 are cylinders of Φ100mm*50mm; the height of the antifreeze liquid 3 is 200mm; and the height of the salt solution with a mass fraction of 3.5% is 3mm.

[0013] Furthermore, the external test environment meets the following requirements: temperature (20±2)°C, relative humidity (65±5)%.

[0014] The freeze-thaw protection cycle system is: -25℃~+20℃, -25℃ for two hours, +20℃ for two hours, and one freeze-thaw cycle is completed within four hours. The dry-wet cycle system is 40℃, humidity 65%, and wind speed not less than 5m / s. Air dry for 2 hours, fill with 3mm high 3.5% deicing salt solution and soak for 2 hours. One dry-wet cycle is completed within four hours. The mechanism of a complete freeze-thaw and dry-wet cycle is 30 freeze-thaw cycles first, and then 10 dry-wet cycles. The test ends after five complete freeze-thaw and dry-wet cycles.

[0015] The salt solution has a mass fraction of 3.5% and is prepared using deicing salt.

[0016] Concrete and mortar specimens are immersed in water at the age of 21 days until the age of 28 days. Coating specimens need to be painted on the concrete base specimens at the age of 28 days, then immersed in water for 7 days and then subjected to salt frost resistance test.

[0017] The specific method is as follows:

[0018] Step 1) The tested concrete mix ratio is made according to the repair concrete mix ratio, the mortar mix ratio is made according to the repair mortar mix ratio, and the coating product is applied according to the recommended brushing amount of primer, topcoat and intermediate paint, with six specimens in each group.

[0019] Step 2) Before the test, heat the high and low temperature alternating climate test chamber 1 to +20℃ and keep it for 30 minutes; at the same time, put the stainless steel test mold 2 filled with antifreeze 3 into the high and low temperature alternating climate test chamber 1. The height of the antifreeze is 200mm. During the entire test process, it is necessary to ensure that the liquid level of the antifreeze is higher than the liquid level of the salt solution.

[0020] Step 3) Dry the specimen to constant weight before testing and record the initial value , then soak the specimen in water for 7 days and then take it out for testing.

[0021] Step 4) Place the concrete or mortar specimen 5 into the rubber mold 7, tighten the stainless steel clamp 6, and use clean water to test whether the concrete or mortar specimen 5 and the rubber mold 7 are clamped before placing the stainless steel test mold 2. After no leakage occurs, pour a 3.5% mass fraction salt solution 4 into the rubber mold 7, maintain a height of 3mm, and then cover it tightly.

[0022] Step 5) Start a complete freeze-thaw and dry-wet cycle: -25℃~+20℃, -25℃ for two hours, +20℃ for two hours, and one freeze-thaw cycle is completed within four hours. The dry-wet cycle system is: 40℃, humidity 65%, wind speed not less than 5m / s. Air dry for 2h, fill with 3mm high 3.5% deicing salt solution and soak for 2h; one dry-wet cycle is completed within four hours; the mechanism of a complete freeze-thaw and dry-wet cycle is 30 freeze-thaw cycles and 10 dry-wet cycles.

[0023] Step 6) After each freeze-thaw and dry-wet cycle test, wash the concrete or mortar specimen, dry it to constant weight, and test the specimen mass to an accuracy of 0.01g; after N freeze-thaw and dry-wet cycles, the mass loss rate of a single concrete or mortar specimen should be calculated according to the following formula (Formula 1):

[0024] (1)

[0025] Where:

[0026] ——After N freeze-thaw and dry-wet cycles The mass loss rate (%) of each concrete or mortar specimen, accurate to 0.01;

[0027] ——Freeze-thaw and dry-wet cycle Mass of concrete or mortar specimen (g)

[0028] ——After N freeze-thaw and dry-wet cycles, The mass of a concrete or mortar specimen (g).

[0029] The average mass loss rate of each group of concrete or mortar specimens should be the final measured value of the formula average of the mass loss rate test results of the six groups of specimens. When a test result is negative, it should be eliminated; if one of the six measured values ​​exceeds the average value, If the measured values ​​of three groups of specimens exceed the average value, 10%, the test results of this group will be invalid.

[0030] Step 7) The concrete test can be stopped if any of the following conditions occur:

[0031] 1. Complete the freeze-thaw and dry-wet cycles of 5 mechanisms;

[0032] 2. The mass loss rate of the specimen exceeds 3%.

[0033] Step 8) The mortar test can be stopped if one of the following conditions occurs:

[0034] 1. Complete freeze-thaw and dry-wet cycles of 3 mechanisms;

[0035] 2. The mass loss rate of the specimen exceeds 3%.

[0036] Step 9) During the coating test, the test can be stopped if any of the following conditions occur:

[0037] 1. If bubbles, cracks, peeling, or powdering occurs on the coating surface, the test may be stopped;

[0038] 2. Complete freeze-thaw and wet-dry cycles of 3 mechanisms.

[0039] Step 10) Evaluation of salt-freeze resistance of concrete or mortar:

[0040] 1. Surface appearance: slight spalling, moderate spalling (some aggregate exposed), severe spalling (through cracks, aggregate exposed);

[0041] 2. The number of completed freeze-thaw and wet-dry cycles;

[0042] 3 Mass loss rate of specimens after freeze-thaw cycles.

[0043] Step 11) Evaluation of coating anti-salt frost performance:

[0044] 1. Surface appearance: bubbles, cracks, peeling, and powdering;

[0045] 2 Ratio of mass loss rate of tested concrete to that of reference concrete. The mass loss rate is calculated according to formula (1), and the freeze-thaw mass loss ratio is calculated according to formula (2). The test results are accurate to 1%.

[0046] (2)

[0047] Where:

[0048] ——Mass loss ratio of the tested coating specimen to the reference concrete specimen, %.

[0049] ——Freeze-thaw cycle mass loss rate of the tested concrete, %.

[0050] Δm2——mass loss rate of freeze-thaw cycle of benchmark concrete, %.

Claims

1. A method for testing the salt-freezing resistance of highway concrete bridge maintenance materials, comprising the following steps: Step 1: The required concrete or mortar specimen (5) is manufactured according to the repair concrete or mortar mix ratio, and a rubber mold (7) is placed in the stainless steel test mold (2) used. One stainless steel test mold (2) in each high and low temperature alternating climate test chamber (1) constitutes a group, and each group has six rubber molds (7); Step 2: Before the test, the high and low temperature alternating climate test chamber (1) is heated to +20°C and maintained for 30 minutes. At the same time, a stainless steel test mold (2) filled with antifreeze (3) is placed in the high and low temperature alternating climate test chamber (1). The height of the antifreeze (3) is 200 mm. During the entire test process, the liquid level of the antifreeze (3) is always higher than the liquid level of the salt solution. Step 3: Before the test, the concrete or mortar specimen (5) is dried to a constant weight and the initial value is recorded. The specimen is then immersed in water for 7 days and then taken out for testing. Step 4: Place the concrete or mortar specimen (5) into the rubber mold (7), install a clamp on the top of the concrete or mortar specimen (5), tighten the stainless steel clamp (6), and use clean water to test whether the concrete or mortar specimen (5) and the rubber mold (7) are tightly clamped before placing it into the stainless steel test mold (2). After no leakage occurs, pour a salt solution with a mass fraction of 3.5% into the rubber mold (7), keep the height at 3 mm, and then cover it tightly; Step 5: Start a complete freeze-thaw and dry-wet cycle: the temperature range of the high and low temperature alternating climate test chamber (1) is set at -25°C to +20°C, the duration of -25°C is two hours, the duration of +20°C is two hours, and one freeze-thaw cycle is completed within four hours. The dry-wet cycle system is 40°C, humidity is 65%, wind speed is not less than 5m / s, air drying for 2 hours, filling with 3mm high 3.5% deicing salt solution and soaking for 2 hours, and one dry-wet cycle is completed within four hours. The mechanism of a complete freeze-thaw and dry-wet cycle is 30 freeze-thaw cycles and 10 dry-wet cycles. Step 6: After completing each freeze-thaw and wet-dry cycle test, wash the specimen, dry it to constant weight, and test the mass of the specimen with an accuracy of 0.01g; The salt-freezing resistance test device for highway concrete bridge maintenance materials comprises a high-low temperature alternating climate test chamber (1), which is characterized by: A stainless steel test mold (2) is arranged in the high and low temperature alternating climate test box (1), and an antifreeze liquid (3) is contained in the stainless steel test mold (2). Six cylindrical rubber molds (7) are installed in the stainless steel test mold (2), and a concrete or mortar test piece (5) is installed in each rubber mold (7). A stainless steel clamp (6) is arranged at the upper end of the concrete or mortar test piece (5), and a salt solution (4) with a mass fraction of 3.5% is contained above the stainless steel clamp (6). The size of the concrete or mortar test piece (5) is a cylinder with a size of Φ100mm*50mm; The dimensions of the stainless steel test mold (2) are 500 mm*300 mm*300 mm in length, width and height respectively, the dimensions of the rubber mold (7) are Φ110 mm*210 mm, the dimensions of the stainless steel clamp (6) are Φ115 mm*25 mm, the height of the antifreeze liquid (3) is 200 mm, and the height of the 3.5% by mass salt solution (4) is 3 mm; The external test environment requirements are: temperature (20±2)℃, relative humidity (65±5)%.

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