Method for evaluating early freezing performance of concrete

Abstract

The invention discloses a concrete early-stage freezing performance evaluation method, which comprises the following steps: firstly, establishing a relation curve of ventilation time and maturity under standard curing, then pre-burying a temperature sensor in a concrete project, and when concrete in the concrete project is cured to a test age, detecting the freezing damage degree and calculating the maturity at the same time, so as to evaluate the early-stage freezing performance of the concrete. The actual ventilation time is obtained by detecting the degree of frozen damage, the corresponding maturity of a concrete project in a test age is calculated according to temperature data provided by a temperature measuring instrument, the calculated maturity is compared with a relation curve of the concrete ventilation time and maturity under standard curing, the standard curing ventilation time corresponding to the maturity value is obtained, and the concrete ventilation time is calculated according to the standard curing ventilation time. And comparing the ventilation time for two times and then evaluating. The problem that most of existing concrete freezing evaluation methods can cause great damage to the concrete structure is solved.

Description

Technical Field

[0001] The invention relates to the technical field of building construction, and in particular to a method for evaluating the early freezing performance of concrete. Background Art

[0002] Concrete is the most common, largest and most widely used building material in civil engineering. It plays an important role in ensuring structural safety, reliability and durability. Therefore, the control of concrete quality is particularly important. my country's "Winter Construction Code for Construction Engineering" stipulates that when the average day and night temperature on the construction site is stable below 5℃ for 5 consecutive days, it is called winter construction of concrete. The average day and night temperature refers to the average of the highest and lowest temperatures or the average of the outdoor temperatures at 6:00, 14:00 and 21:00 local time. The temperature in the north is low in winter, and many building materials freeze due to water content, which brings many difficulties to construction. Concrete constructed in winter contains water inside, and low temperature will cause freezing, weakening the cement hydration and affecting its mechanical properties, resulting in the progress of winter construction being affected and the construction quality being difficult to control. If the strength development of on-site concrete cannot be fed back in a timely and accurate manner, the probability of hidden dangers in the quality of the project will be greatly increased. At present, there is a lack of freezing evaluation methods for early frozen concrete. Most of the existing evaluation methods will cause a large degree of damage to concrete projects, thereby affecting concrete projects. Summary of the invention

[0003] In order to overcome the defects of the prior art, a method for evaluating the early freezing performance of concrete is provided to solve the problem that most of the existing concrete freezing evaluation methods will cause a large degree of damage to the concrete structure.

[0004] To achieve the above object, a method for evaluating the early freezing performance of concrete is provided, comprising the following steps:

[0005] A relationship curve between the air permeability time and maturity of concrete components under standard curing conditions is constructed, and the relationship curve is:

[0006] M = ∑(T+15) × Δt,

[0007] Where M is the maturity of the concrete component, Δt is the ventilation time of the concrete component, and T is the average temperature of the concrete component within the time period Δt;

[0008] A temperature sensor is embedded in the concrete structure to be tested, and the temperature sensor collects the actual temperature value of the concrete structure to be tested;

[0009] When the concrete structure to be tested is cured to the test age, a plurality of test holes are opened on the surface of the concrete structure to be tested and the test holes are sealed, wherein the diameter of the test holes is 10 mm and the depth is 40 mm;

[0010] Vacuuming the test hole to make the air pressure in the test hole reach -55KPa and timing;

[0011] When the air pressure value in the test hole reaches -50 KPa, the actual air permeability time of the concrete structure to be tested is obtained;

[0012] Based on the relationship curve and the actual temperature value, a standard air permeability time of the concrete structure to be tested is calculated;

[0013] The degree of freezing damage of the concrete structure to be tested is evaluated based on the standard air permeability time and the actual air permeability time.

[0014] Furthermore, the concrete mix ratio of the concrete component is the same as that of the concrete structure to be tested.

[0015] Furthermore, the number of test points for the air permeability time of each concrete component is 3 to 10.

[0016] The beneficial effect of the present invention is that the method for evaluating the early freezing performance of concrete of the present invention establishes a relationship curve between the air permeability time and maturity of concrete test blocks under standard curing conditions, and combines the air permeability time test method to evaluate the freezing degree of early concrete and the early strength of concrete constructed in winter, thereby accurately and timely evaluating the freezing degree of concrete in winter construction.

[0017] The concrete early freezing performance evaluation method of the present invention only causes minor damage (20mm deep) to the evaluation object, ensuring the integrity of the evaluation object and ensuring that the subsequent performance of the evaluation object is not affected. The concrete early freezing performance evaluation method of the present invention can quickly and repeatedly detect the degree of concrete damage caused by freezing at negative temperatures in winter, scientifically determine the demoulding time and maintenance plan, and is an important detection technology to ensure the quality of concrete engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Other features, objects and advantages of the present application will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

[0019] Figure 1 Schematic diagram of air permeability time detection of a concrete structure to be tested according to an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The present application will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant inventions, rather than to limit the inventions. It should also be noted that, for ease of description, only the parts related to the invention are shown in the accompanying drawings.

[0021] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0022] The present invention provides a method for evaluating early freezing performance of concrete, comprising the following steps:

[0023] S1. Construct the relationship curve between the air permeability time and maturity of concrete components under standard curing conditions. The relationship curve is:

[0024] M = ∑(T+15) × Δt,

[0025] Wherein, M is the maturity of the concrete component, Δt is the ventilation time of the concrete component, and T is the average temperature of the concrete component within the time period Δt.

[0026] Specifically, the process of establishing the relationship curve between ventilation time and maturity:

[0027] Under standard curing conditions, multiple concrete test blocks (i.e., concrete components) having the same concrete mix ratio as the concrete structure to be tested are cured;

[0028] When the concrete component reaches the test age, the air permeability time test is carried out under standard curing conditions, and multiple measuring points are determined on each concrete test block to obtain representative values ​​of the air permeability time of the concrete component at different curing ages;

[0029] The maturity is calculated based on temperature and age, and a relationship curve between ventilation time and maturity is established.

[0030] The representative value of concrete air permeability time and the calculated maturity value are placed in a rectangular coordinate system to establish a relationship curve between concrete air permeability time and maturity.

[0031] As a preferred implementation, the number of test points for the air permeability time of each concrete component is 3 to 10.

[0032] In the air permeability time test conducted to establish the relationship curve between the air permeability time and maturity of concrete under standard curing conditions, the number of measuring points ranges from 3 to 10.

[0033] S2. A temperature sensor is embedded in the concrete structure to be tested, and the temperature sensor collects the actual temperature value of the concrete structure to be tested.

[0034] In this embodiment, the concrete mix ratio of the concrete component and the concrete structure to be tested is the same.

[0035] As a preferred implementation, the temperature sensor 7 is provided in conjunction with a temperature tester 8 , and the temperature sensor 7 is connected to the temperature tester 8 .

[0036] S3. When the concrete structure to be tested is cured to the test age, a plurality of test holes are opened on the surface of the concrete structure to be tested and the test holes are sealed. The diameter of the test holes is 10 mm and the depth is 40 mm.

[0037] S4. Evacuate the test hole to make the air pressure in the test hole reach -55KPa and start timing.

[0038] S5. When the air pressure in the test hole reaches -50 KPa, the actual air permeability time of the concrete structure to be tested is obtained.

[0039] In this embodiment, combined with Figure 1 As shown, the detection of the actual air permeability time of the concrete structure to be tested and the air permeability time of the concrete component includes the following steps:

[0040] The concrete member or concrete structure 5 is cured to a test age.

[0041] A series of test holes 6 (at least 3, preferably 6) with a diameter of 10 mm and a depth of 40 mm are drilled on the concrete surface of the concrete component or concrete structure 5.

[0042] Use an ear bulb to blow away the loose and fine dust in the test holes, insert a fixed-shape silicone resin plug into each test hole and make sure the end of the plug is flush with the concrete surface.

[0043] Use a steel wire to drill a hole in the plug and ensure that a test hole with a depth of 20 mm and a diameter of 10 mm is connected to the outside atmosphere through a needle.

[0044] An air filter is placed between the needle tube and the hose 3, and a handheld small vacuum pump 4 is connected to the upper interface of the instrument with the hose, and the vacuum pump knob is turned to the "on" position. The instrument is a concrete air permeability detector 1, and the power cord 2 of the concrete air permeability detector 1 is connected to the power supply through a plug 9.

[0045] Through stable vacuuming, the system reaches a vacuum greater than -55KPa. During this process, when the vacuum degree reaches -50KPa or -55KPa, the two diode indicator lights light up.

[0046] Close the vacuum pump valve and make sure the timer is not running and displays 00:00 (if not, reset it). At this time, the -50KPa and -55KPa two diode indicators are always on.

[0047] When the vacuum degree in the test hole reaches -55KPa, the diode indicator light on the left turns off and the timer starts running.

[0048] When the vacuum degree in the test cave reaches -50KPa, the diode indicator light on the right turns off and the timer stops running; record the time reading and convert it into seconds. This time (ventilation time) is the time it takes for the air pressure in the cave to drop from -55KPa to -50KPa.

[0049] Repeat the test until the error between the two time readings is within ±2%.

[0050] In this embodiment, the distance between the test holes and the edge of the concrete member or the concrete structure is at least 30 mm, and the distance between the test holes is at least 30 mm.

[0051] S6. Based on the relationship curve and the actual temperature value, the standard air permeability time of the concrete structure to be tested is calculated.

[0052] S7. Based on the standard air permeability time and the actual air permeability time, the degree of freezing damage to the concrete structure to be tested is evaluated.

[0053] The maturity of the concrete project calculated according to the temperature development during the test age is the maturity of the on-site concrete. The maturity value of the concrete project is found on the relationship curve between the concrete ventilation time and maturity under standard curing conditions. The ventilation time corresponding to this maturity is the standard curing ventilation time. Compare the standard curing ventilation time and the actual ventilation time. The greater the difference between the standard curing ventilation time and the actual ventilation time, the higher the degree of freezing of the concrete project. The smaller the difference between the standard curing ventilation time and the actual ventilation time, the lower the degree of freezing of the concrete project.

[0054] The concrete early freezing performance evaluation method of the present invention only causes minor damage (20mm deep) to the evaluation object, ensuring the integrity of the evaluation object and ensuring that the subsequent performance of the evaluation object is not affected. The concrete early freezing performance evaluation method of the present invention can quickly and repeatedly detect the degree of concrete damage caused by freezing at negative temperatures in winter, scientifically determine the demoulding time and maintenance plan, and is an important detection technology to ensure the quality of concrete engineering.

[0055] The concrete early freezing performance evaluation method of the present invention is easy to operate and has simple steps, and is time-saving and labor-saving compared to a compressive strength test method of pre-curing a large number of specimens under the same curing conditions.

[0056] The concrete early freezing performance evaluation method of the present invention is flexible in operation and has a wide range of applications. It can set measuring points at multiple locations in a concrete project to test the freezing state of different locations in the concrete project. The present invention is also applicable to freezing tests of concrete at various stages, especially at an early age.

[0057] The method for evaluating the early freezing performance of concrete of the present invention establishes a relationship curve between the air permeability time and maturity of concrete test blocks under standard curing conditions, and combines the air permeability time test method to evaluate the freezing degree of early concrete and the early strength of concrete constructed in winter, thereby accurately and timely evaluating the freezing degree of concrete in winter construction.

[0058] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solution formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the above features are replaced with the technical features with similar functions disclosed in this application (but not limited to) by each other.

Claims

1. A method for evaluating the early freezing performance of concrete, characterized in that: The following steps are involved: A relationship curve between the air permeability time and maturity of concrete components under standard curing conditions is constructed, and the relationship curve is: M = ∑(T+15) × Δt, Where M is the maturity of the concrete component, Δt is the ventilation time of the concrete component, and T is the average temperature of the concrete component within the time period Δt; A temperature sensor is embedded in the concrete structure to be tested, and the temperature sensor collects the actual temperature value of the concrete structure to be tested; When the concrete structure to be tested is cured to the test age, a plurality of test holes are opened on the surface of the concrete structure to be tested and the test holes are sealed, wherein the diameter of the test holes is 10 mm and the depth is 40 mm; Vacuuming the test hole to make the air pressure in the test hole reach -55KPa and timing; When the air pressure value in the test hole reaches -50 KPa, the actual air permeability time of the concrete structure to be tested is obtained; Based on the relationship curve and the actual temperature value, a standard air permeability time of the concrete structure to be tested is calculated; The degree of freezing damage of the concrete structure to be tested is evaluated based on the standard air permeability time and the actual air permeability time.

2. The method for evaluating early freezing performance of concrete according to claim 1, characterized in that: The concrete component has the same concrete mix ratio as the concrete structure to be tested.

3. The method for evaluating early freezing performance of concrete according to claim 1, characterized in that: The number of test points for the air permeability time of each concrete component is 3 to 10.

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