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Technical specification for testing compressive strength of concrete by shearing method
作者:管理員    發布于:2019-09-02 15:40:59    文字:【】【】【
1 general
In order to standardize the method of shearing and testing the compressive strength of ordinary concrete and ensure the detection accuracy, this procedure is formulated.
This procedure is applicable to the detection of structural concrete compressive strength (hereinafter referred to as concrete strength) with a right-angled section and a shear pressure. When there is a requirement for the strength of the concrete in the structure, it can be tested according to this regulation, and the concrete strength is estimated. The test results can be used as the basis for the treatment of concrete strength problems. This procedure does not apply to the detection of the strength of structural concrete with significant differences in surface and internal quality or internal defects.
Personnel using the shear tester for engineering testing should pass special technical training and should hold the corresponding qualification certificate.
The shear strength method is used to detect and estimate the concrete strength. In addition to the implementation of this regulation, it should also comply with the relevant national standards.
2 terms
  Shear pressing method: Using a special shearing instrument to apply a pressure perpendicular to the bearing surface at the right angle of the concrete member, causing local shear failure at the right angle of the member, and estimating the concrete strength according to the shearing pressure.
Shear pressure: The maximum value on the shear gauge load table when shear failure occurs at the test site.
  Positioning: The test site when the concrete strength is measured by the shearing method.
 Measured concrete strength conversion value
The compressive strength value of the concrete of the current age calculated by the shearing force of the measured position by the strength measurement formula, the value of which corresponds to the test part of the tested component under the condition and age, the side length of 150 mm cube test block The value of the compressive strength.
3 shear meter
3.1 Technical requirements
The shearing device shall consist of a base frame, a screw, a cylinder, a hand pump, a digital pressure gauge, etc. (Fig. 3.1.1)

  1-screw handle; 2-screw; 3-base frame; 4-indenter; 5-pressure cylinder; 6-hand pump; 7-digital pressure gauge; 8-hand pump handle; 9-press screw ;10-bearing plate
 The shearing instrument should have a product certificate
The shear should meet the following requirements:
1 The diameter of the pressure gauge head should be 20mm ± 0.2mm;
2 The pressure gauge should be equipped with a limit device. After the shearing device is in place, the cylindrical surface of the indenter is perpendicular to the bearing surface of the member.
The adjacent faces should be tangent;
3 The working stroke of the indenter should not be less than 15mm;
4 The maximum shear pressure should not be less than 70kN;
5 Under the maximum shear pressure, the lateral deformation of the pedestal should not be greater than 1/500 of the length of the pedestal;
6 The minimum index of the digital pressure gauge should be 0.1kN, and the relative error between the reading of the digital pressure gauge after 5kN increment and the standard pressure sensor or dynamometer should be within 2%;
7 Digital pressure gauges should have peak hold, time delay power off function and data storage function;
8 The size of the bearing plate should not be less than 40mm × 45mm, and the angle of any rotation should not be less than 2
9 The shearing device should be equipped with a safety device to prevent the instrument from falling.
3.1. 4
  The ambient temperature of the shearer should be -10 ° C ~ 40 ° C
3. 2 Calibration and maintenance of the shear
3.2.1 The shear should be calibrated if it has one of the following conditions:
  1 Before the new shear gauge is activated;
2 exceeds the calibration validity period;
 3 The cumulative number of shearing times exceeds 1000 times;
 4 Suffering from severe impact or other damage;
  5 Replace hydraulic oil and parts;
 6 after repair;
  7 When there is doubt about the test value.
The calibration period of the shearing instrument should be 1 year. The digital pressure gauge reading, the head diameter and the working stroke of the shearing instrument should be calibrated. The positioning screw size and the deformation of the base frame should be checked. The calibration result should be consistent with this. Requirements of Article 3.1.3 of the Regulations.
The shear should be maintained as follows:
1 The exposed parts of the instrument should be regularly scrubbed, and the dust on the positioning screw and the pressure screw should be scrubbed. The lubricant should be applied to the screw after scrubbing;
2 When the instrument is not used for a long time, the battery in the digital pressure gauge should be taken out.
  After the shearing instrument is used, the extrusion head should be returned to the cylinder body, so that the return spring is in a free state. The dirt and dust on the instrument should be removed, and the instrument should be placed in a dry and cool place.
4 Detection technology
 4.1 General provisions
  The concrete of the structure or component to be tested shall comply with the following requirements:
  1 Concrete for concrete shall comply with the current national standard "General Portland Cement" GB 175;
  2 Concrete sand and stone aggregates shall comply with the current industry standard “Standards for Sand and Stone Quality of Common Concrete and Standards for Inspection Methods” JGJ 52;
3 Concrete should be made by ordinary molding process;
4 Templates made of steel molds, wooden molds and other materials shall comply with the current national standard "Construction Quality Acceptance Specifications for Concrete Structure Engineering"
The provisions of GB 50204;
  5 age should not be less than 14d;
6 compressive strength should be in the range of l0MPa ~ 60MPa;
  7 The thickness of the structure or component should not be less than 80mm.
4.1.2 Before the concrete strength test of the structure or component, the inspector should understand the following conditions:
  1 Project name and name of the construction, design, construction, supervision (or supervision) unit;
 2 structure or component name, dimensions, quantity and concrete design strength rating;
  3 cement type, strength grade; sand, stone type and particle size; concrete mix ratio;
4 concrete production and transportation methods, formwork, pouring, curing conditions and molding date;
 5 necessary design drawings and construction records;
6 Detection of the cause.
The strength of the structure or component concrete can be measured by a single component or by inspection lot sampling. When sampling according to the inspection batch, the number of components shall not be less than 10% of the number of components in the same batch; when the appearance quality of the concrete in the same inspection batch is poor or the concrete strength difference is large, the number of components shall not be less than the same. 15% of the number of batch components.
  When the structure or component is to be inspected according to the inspection lot, the same unit (single) engineering component that meets the following conditions can be used as the same inspection lot:
   1 concrete strength grade is the same;
2 Concrete raw materials, mix ratio, molding process, curing conditions and age are basically the same;
   3 The same type of components;
   4 The environment is the same.
4.1.5 The number and arrangement of positioning should meet the following requirements:
   1 Three positions should be evenly arranged on the tested components. When the absolute value of the difference between the maximum and minimum values of the three shear pressures and the intermediate value exceeds the intermediate value of l5%, two additional positions should be measured. .
   2 The positioning position should be evenly arranged along the longitudinal direction of the component, and the adjacent two positioning positions should be arranged on different sides of the component. The distance between the two parts of the measuring position should not be less than 0.2m, and the distance between two adjacent measuring positions should not be less than 0.3m.
3 The concrete at the position should be flat and free of defects such as cracks, looseness, holes and honeycombs. The positioning position shall not be placed on the top surface of the concrete molding;
   4 The angle between adjacent faces at the positioning position should be 88-92. Between the time, when this requirement is not met, the grinding wheel can be slightly polished;
   5 Positioning should avoid embedded parts and steel bars.
4.1.6 The positioning of structures or components should be clearly marked.
4. 2 Shear pressure measurement
Before the test, the working condition of the barometer should be checked. The test can only be carried out after confirming that it is in good working order.
When testing, the shearing device should be installed in position. The axis of the circular indenter should be perpendicular to the bearing surface of the member. The adjacent surface perpendicular to the bearing surface of the indenter should be tangent (Fig. 4.2.2). ).

Figure 4.2.2
 Shearing device installation instructions
4.2.3 When testing the components, effective protective measures should be taken to prevent the shearing instrument and concrete from falling off and injuring people.
4.2.4 After turning on the digital pressure gauge, press the clear key and put the digital pressure gauge in the peak hold state.
4.2.5 Shake the handle of the hand pump, the shear pressure should be applied continuously and evenly. The speed of the force should be controlled within 1.0kN/s until the concrete in the shearing part is destroyed. Record the damage state and the shearing pressure at the time of destruction to the nearest 0.1kN.
4.2.6 When one of the following conditions occurs in the shear failure surface, the test is invalid and should be added at a distance of 0.3m to 0.5m from the measuring position.
1 with exposed steel bars;
  2 Exposed embedded parts;
3 There are inclusions;
 4 There is a hole;
5 Other abnormal conditions.
4.2.7 After the test, the concrete damage caused by the shear pressure test shall be repaired.
 Hangzhou Sansi Instrument Co., Ltd. Main Products:
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