CN110568167B - Nondestructive testing method for prejudging long-term durability of concrete in natural environment - Google Patents
Nondestructive testing method for prejudging long-term durability of concrete in natural environment Download PDFInfo
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- CN110568167B CN110568167B CN201910853499.3A CN201910853499A CN110568167B CN 110568167 B CN110568167 B CN 110568167B CN 201910853499 A CN201910853499 A CN 201910853499A CN 110568167 B CN110568167 B CN 110568167B
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/38—Concrete; ceramics; glass; bricks
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Abstract
The invention provides a nondestructive testing method for prejudging long-term durability of concrete in a natural environment. The quality of long-term durability is represented by forming concrete samples under standard curing and natural curing conditions and detecting the change of relative dynamic elastic modulus of concrete under two curing conditions of different ages. The standard-maintained test piece is placed back to a maintenance room after being detected to the age, the long-age concrete test piece can be transferred along with the removal of the maintenance room according to the engineering site conditions, the long-age concrete test piece is continuously and periodically observed, and if the long-age concrete test piece tends to be stable under 5y or a certain age, the value can be used for replacing a test result of a longer age; and (4) continuously placing the naturally cured test piece in a natural environment after the test of the age. And (3) taking the dynamic elastic modulus of the test piece at each age under the standard curing condition as a reference, calculating the relative dynamic elastic modulus attenuation value of the test piece at each age under natural curing, and prejudging the long-term durability of the concrete.
Description
Technical Field
The invention relates to the field of application of new technologies of hydroelectric engineering, in particular to a nondestructive testing method for prejudging long-term durability of concrete in a natural environment.
Background
The long-term durability of the concrete is closely related to the service life, and the evaluation of the long-term durability of the concrete mainly starts from the aspects of concrete carbonization performance, frost resistance, impermeability and the like, but the problems of damage of test pieces exist in carbonization tests, frost resistance tests and impermeability tests.
At present, a large number of concrete test blocks which are cured to 3y, 5y and longer ages are required to be formed in long-term performance research of large-scale hydropower engineering concrete, the number of the concrete test blocks is large, the concrete test blocks are not suitable for storage, meanwhile, a test method adopted causes the damage of the test blocks, the sustainable observation cannot be carried out, and related research results of long-term durability are rarely reported at home and abroad. The nondestructive testing method for the long-term durability of the concrete in the natural environment is not disclosed.
Disclosure of Invention
The invention aims to make up for the defects in the prior art, and provides a method for quickly, nondestructively and economically prejudging the long-term durability of concrete.
In order to achieve the technical characteristics, the invention aims to realize that: a nondestructive testing method for prejudging long-term durability of concrete in a natural environment adopts concrete test blocks under different curing conditions, and prejudges whether the long-term durability of the concrete is good or bad according to dynamic elastic modulus attenuation under the natural curing condition and the relative standard curing condition respectively; the concrete test block is repeatedly detected according to age, and long-term durability observation can be performed according to engineering requirements.
The different curing conditions comprise standard curing conditions and natural curing conditions;
the standard curing condition meets the technical requirements of DL/T5150-;
the natural maintenance condition depends on the actual engineering and takes the outdoor climate condition near the engineering as the standard.
And measuring the measured values of the natural vibration frequency of the concrete test block under a plurality of groups of natural curing conditions and relative standard curing conditions by adopting a dynamic elastic modulus tester or other similar equipment, calculating the average value, and further calculating the relative dynamic elastic modulus according to DL/T5150-2017.
The relative dynamic elastic modulus is the ratio of the transverse dynamic elastic modulus of the concrete test block under natural curing conditions of different ages to the transverse dynamic elastic modulus of the concrete test block under standard curing conditions.
The concrete long-term durability pre-judging operation is that a curve is made according to the relation between the attenuation value or retention value of the relative dynamic elastic modulus and the age to perform trend pre-judging; referring to the criterion of the freeze-thaw damage in the concrete frost resistance test, the attenuation value of 40% or the retention value of 60% is taken as a boundary, and if the attenuation value is lower than 40% or the retention value is greater than 60%, the durability at the age is judged to be excellent.
The observation ages of the long-term durability performance observation are 5y, 10y and 20 y.
The DL/T5150-2017 is a hydraulic concrete test procedure.
The natural maintenance condition is consistent with the environment condition of the project entity, and the natural maintenance condition is placed in the outdoor environment near the project, and under the same condition, the natural maintenance condition is characterized by wind, rain, sunshine, snow-buried climate and temperature change.
The invention has the following beneficial effects:
1. short detection time
Conventional long-term durability of concrete is characterized by a freeze resistance test or a permeability resistance test. In the aspect of detection time, each freeze-thaw cycle in the anti-freezing test needs 4 hours, and 600 hours are estimated according to 150 times of freeze-thaw cycles; in the impermeability test, the water pressure of 0.1MPa is increased at intervals of 8h, and the estimated requirement is 64h according to the impermeability grade of 8. According to the method, according to the dynamic elastic modulus tester, a resonance point is found only through the gain of the vibration exciter and the vibration pickup, rough adjustment and fine adjustment, the self-vibration frequency is read out through the digital counter, the dynamic elastic modulus can be obtained through calculation, each test piece can be estimated for 5 minutes, a group of tests can be completed within 15 minutes, the test time is greatly saved, and the operation is convenient and fast.
2. Nondestructive and sustainable test piece
Based on long-term observation of the performance of large engineering concrete, the observation period can be as long as 10y, 20y or even longer, a concrete sample to be detected is precious enough, the conventional freeze resistance and impermeability tests or carbonization tests belong to damage tests, the concrete sample is damaged to different degrees, and the potential of long-term sustainable detection is absent. The method disclosed by the invention can be used for carrying out long-term repeated detection along with the increase of the age only by molding the test piece under two conditions of natural curing and standard curing, and has strong sustainability.
3. Good economical efficiency and can be popularized
The conventional long-term durability test of concrete has a small expense with the extension of an observation period, no matter the cost of raw materials, the power cost of equipment and the construction cost of on-site coring in the forming or detecting process. The method has the advantages of small forming amount, low equipment power consumption, sustainable observation, excellent economy and easy popularization and application.
Drawings
The invention is further illustrated by the following figures and examples.
FIG. 1 is a graph showing the relative dynamic elastic modulus decay of concrete test blocks under different curing conditions.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and the accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not used as limiting the present invention.
Example 1:
a nondestructive testing method for prejudging long-term durability of concrete in a natural environment adopts concrete test blocks under different curing conditions, and prejudges whether the long-term durability of the concrete is good or bad according to dynamic elastic modulus attenuation under the natural curing condition and the relative standard curing condition respectively; the concrete test block is repeatedly detected according to age, and long-term durability observation can be carried out according to engineering requirements.
Further, the different curing conditions comprise standard curing conditions and natural curing conditions;
further, the standard curing conditions meet the technical requirements of DL/T5150-;
furthermore, the natural maintenance condition depends on the actual engineering and is subject to the outdoor climate condition near the engineering.
Further, a dynamic elastic modulus tester or other similar equipment is adopted to measure the measured values of the natural vibration frequency of the concrete test block under multiple groups of natural curing conditions and relative standard curing conditions, and the average value is calculated, so that the relative dynamic elastic modulus is calculated according to DL/T5150 plus 2017.
Further, the relative dynamic elastic modulus is a ratio of the transverse dynamic elastic modulus of the concrete test block under natural curing conditions of different ages to the transverse dynamic elastic modulus of the concrete test block under standard curing conditions.
Further, the concrete operation of prejudging the long-term durability of the concrete is to make a curve according to the relation between the attenuation value or retention value of the relative dynamic elastic modulus and the age to carry out trend prejudgment; referring to the criterion of the freeze-thaw damage in the concrete frost resistance test, the attenuation value of 40% or the retention value of 60% is taken as a boundary, and if the attenuation value is lower than 40% or the retention value is greater than 60%, the durability at the age is judged to be excellent.
Further, the observation ages of the long-term durability performance observation are 5y, 10y and 20 y.
Further, the DL/T5150 and 2017 are the test procedures of hydraulic concrete.
Furthermore, the natural maintenance conditions are consistent with the environmental conditions of the engineering entity, and the natural maintenance conditions are placed in the outdoor environment near the engineering entity under the same conditions of wind blowing, rain, sun, snow-buried climate and temperature change.
Example 2:
two groups of concrete test blocks C are formed 90 25, 3 in each group, with dimensions 100mm x 400 mm. And the group of curing rooms are placed in the quasi curing condition that the temperature is controlled to be 20 +/-3 ℃ and the relative humidity is not less than 95 percent. The other group is placed on the roof of a test room 2km away from the supporting project and exposed to natural conditions.
And respectively curing the two groups of test pieces to different ages, and calculating to obtain a final measured value of the relative dynamic elastic modulus. As shown in table 1 below.
TABLE 1 relative dynamic elastic modulus of test pieces under different curing conditions
By comparing the values of the dynamic elastic modulus, the attenuation values are inversely calculated, and the trend prediction is performed according to the age curve, as shown in the following table 2 and fig. 1.
TABLE 2 attenuation of the relative dynamic elastic modulus of the test pieces under different curing conditions
| Age (d) | 28 | 90 | 180 | 365 | 1095 | 1825 | 3650 |
| Relative dynamic elastic modulus (%) | 97.62 | 97.72 | 94.97 | 92.06 | 91.03 | 90.02 | 91.12 |
| Relative dynamic modulus attenuation value (%) | 2.38 | 2.28 | 5.03 | 7.94 | 8.97 | 9.98 | 8.88 |
As can be seen from fig. 1, the values of the relative dynamic modulus attenuation for 10 years under the natural curing conditions of the concrete at this strength level are all much less than 40%, and it is predicted that the long-term durability is excellent.
Claims (3)
1. A nondestructive testing method for prejudging the long-term durability of concrete in a natural environment is characterized by comprising the following steps: adopting concrete test blocks under different curing conditions, and pre-judging whether the long-term durability of the concrete is good or bad according to the attenuation of relative dynamic elastic modulus under natural curing conditions and relative standard curing conditions; the concrete test block is repeatedly detected according to age, and long-term durability observation can be carried out according to engineering requirements;
the different curing conditions comprise standard curing conditions and natural curing conditions;
the standard curing condition meets the technical requirements of DL/T5150-;
the natural maintenance condition depends on the actual engineering and is based on the outdoor climate condition near the engineering;
measuring the measured values of the natural vibration frequency of a plurality of groups of concrete test blocks under natural curing conditions and relative standard curing conditions by adopting a dynamic elastic modulus tester or other similar equipment, calculating the average value, and further calculating the relative dynamic elastic modulus according to DL/T5150-containing materials 2017;
the observation age of the long-term durability observation is 5y, 10y and 20 y;
the relative dynamic elastic modulus is the ratio of the transverse dynamic elastic modulus of the concrete test block under natural curing conditions of different ages to the transverse dynamic elastic modulus of the concrete test block under standard curing conditions; the concrete long-term durability pre-judging operation is that a curve is made according to the relation between the attenuation value or retention value of the relative dynamic elastic modulus and the age to perform trend pre-judging; referring to the criterion of the freeze-thaw damage in the concrete frost resistance test, the attenuation value of 40% or the retention value of 60% is taken as a boundary, and if the attenuation value is lower than 40% or the retention value is greater than 60%, the durability at the age is judged to be excellent.
2. The nondestructive testing method for predicting the long-term durability of concrete in a natural environment according to claim 1, wherein the nondestructive testing method comprises the following steps: the DL/T5150-2017 is a hydraulic concrete test procedure.
3. The nondestructive testing method for predicting the long-term durability of concrete in a natural environment according to claim 1, wherein the nondestructive testing method comprises the following steps: the natural maintenance condition is consistent with the environment condition of the project entity, and the natural maintenance condition is placed in the outdoor environment near the project, and under the same condition, the natural maintenance condition is characterized by wind, rain, sunshine, snow-buried climate and temperature change.
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