At present, engineering testing, a lot of test method of concrete strength testing, such as drilling method, pulling method, indentation, shooting method, rebound method, ultrasonic method, ultrasonic rebound comprehensive method, ultrasonic attenuation method, ray method of falling ball method, the rebound method and ultrasonic rebound method is lossless the detection method
The use of bridge engineering with high strength digital resiliometer sonic rebound tester to test the strength of concrete is a kind of nondestructive testing of concrete compressive strength, extensive determination of compressive strength of concrete is a kind of effective method, simple equipment, convenient operation, rapid detection test, low cost, and does not damage the normal concrete using simple method. This paper mainly introduces the principle, characteristics and methods of rebound instrument to measure the strength of concrete, and the factors influencing the detection intensity value, for the majority of peer reference.
Rebound method, ultrasonic rebound method is widely used in nondestructive testing methods, test parameters and nondestructive testing of concrete compressive strength block (ultrasonic velocity value, rebound value, pull-out strength etc.) relationship between established called curve, it is the basis of nondestructive testing of concrete strength of presumption. The curve according to the material sources, divided into unified strength test curve, area curve and special (calibration curve) three.
1, the detection principle and characteristics
The 1.1 principle
Due to the existence of a relationship between the compressive strength of concrete and the surface hardness, resilience and instrument of elastic hammer is the stretch blow in the concrete surface, the rebound height (read by hammer rebound value) is proportional to the surface hardness and concrete. It reflects the concrete surface hardness to the rebound value, according to the hardness of the surface compressive strength of concrete can be calculated.
With the rebound method to test the compressive strength of concrete, while the detection accuracy is not high, but has the advantages of simple equipment, convenient operation, rapid test, and has low detection cost, and does not damage the normal use of concrete, so it is widely used in the field of direct determination. There are many factors affecting the accuracy of rebound method, such as operation method, instrument performance and climate conditions. To this end, we must master the correct method of operation, pay attention to the maintenance and calibration of resiliometer. "Technical specification for inspection of concrete strength by rebound method"
One simple digital resiliometer provisions: detection of concrete rebound method age ranged from 7d to 1000D, not suitable for the detection of surface and internal quality are made concrete and special molding defects or obvious difference inside the concrete, the detection range is greatly limited by the rebound method. In addition, due to the strength of high strength concrete base is large, even if the relative error is only 15%, the absolute error will be great and the detection result is meaningless, so the rebound method is not applicable to the detection of high strength concrete (>C60 concrete) compressive strength.
The use of high-strength digital resiliometer sonic rebound tester for Bridge Engineering
2, factors affecting detection performance.
Main factors influencing the detection performance of resiliometer:
(1) the assembly size of the main parts of resiliometer movement, including elastic length, elastic hammer hammer spring shock length and the elastic hammer off position.
(2) the quality of the main parts of the relevant parts including spring stiffness, the bomb hit the front end of the rod spherical radius, friction, impact pointer length and elastic hammer jump.
(3) assembly quality, such as the zero adjustment screw, fixed strike spring core and coaxial degree.
3, steel anvil calibration function
Methods of rebound instrument of our traditional rate is: in the steel anvil standard, the vertical downward rate instrument. According to the main factors influencing the detection performance of resiliometer, only steel anvil rate as qualified or not is often ill. Only in the premise of quality instrument 3 assembly and the main parts, steel anvil rate value it can be used as a standard to test whether or not qualified.
4, detection method
4.1 data acquisition
4.1.1 measured the rebound value
The selected test area by using the sampling method, uniform distribution in the range of 20cm * 20cm online. The selected test area is relatively smooth and clean, there is no cellular and rough surface, no cracks, cracks, spalling, spallation phenomenon. Nondestructive test specification using rebound tester in accordance with, according to the "rebound method to test the compressive strength of concrete technical specifications" (JG J/T23-2001) regulations, measured 16 rebound value in each test area. All readings are accurate to 1. Measurement distance not less than 20mm, the distance between the measured point component edge is not less than 30mm. When detecting the axis of resiliometer is always perpendicular to the detected point where the surface area.
The carbonation depth of 4.1.2
In the test area to carry on the carbonation depth determination. When the carbonation depth is more than 2mm, should be in each test area for carbonation depth determination.
4.2 strength calculation
4.2.1 rebound value calculation
From each test area received 16 rebound value, excluding the 3 large and 3 small value, the remaining 10 rebound value according to the following formula to calculate the average value: Rm= Ri/10
In the formula, Rm is the average rebound value, accurate to 0.1; Ri is the first I measuring point rebound value.
4.2.2 rebound correction
The resiliometer non horizontal direction detection of concrete pouring side, the rebound value of press correction. Alpha +Ra alpha Rm=Rm
In the formula, the average rebound Rma non horizontal direction detection area measured values, accurate to 0.1; the average rebound correction Ra alpha non horizontal direction detection test area value.
The resilience instrument detecting horizontal concrete surface when the value, or the equivalent of detecting horizontal concrete pouring surface rebound values, press type correction: Rm=Rmt+Rat, Rm=Rmb+Rab.
In the formula, Rmt, Rmb for the horizontal direction (or equivalent to the horizontal direction) detection of concrete pouring surface, the bottom surface, the average rebound value of the area, accurate to 0.1; Rat, the modified Rab pouring of concrete surface, the bottom surface of the springback value. If the test when the elastic instrument spring impact rod is neither horizontal and non concrete surface should rebound value first angle correction, and then pouring surface correction.
4.2.3 carbonation depth calculation
For the calculation of sampling of carbonation depth should be using the method of mathematical statistics, the average value as the measurement area of carbonation depth.
Dm= Sigma di/n, DM is the average carbonation depth measured area value calculation to 0.5mm, dm>6mm, Di in dm=6mm; the I measured carbonation depth value; n carbonation depth measurement times of survey area.
Determine the 4.2.4 test areaconcrete strength
According to each rebound test area average Rm and carbonation depth value DM, access to special area or curve, curve, or test areaconcrete strength conversion table, checking the strength of the measured value is the area of concrete strength. When the strength is higher than 50Mpa or lower than 10Mpa, not shown, available Neichafa calculation.
For a single structure or component determination, number of measured a component, structure or component test area strength value is the strength of the presumption of the structure or component value; for the structure or component sampling, the sampling survey area and the number of members in the group, the average strength of the structure or component meet the corresponding variance under the premise, take the average intensity value minus 1.645 times the standard deviation of strength for estimating the strength of the structure or component value.
Analysis of 4.3 abnormal data
The concrete strength is not constant, it follows normal distribution. Nondestructive test of concrete strength test belongs to multiple measurements, suspicious data may encounter individual error is not reasonable, should be removed. According to the statistics theory, the absolute value of error is large, the probability is small, when the designated probability or the guaranteed rate, the data corresponding to determine reasonable range. Therefore, you can choose a "value" to measure and compare data, beyond the decision value is that contains gross error and should be removed.