JGJ/T70-2009 has a description of a group of mortar blocks changed from 6 blocks to 3 blocks

First, the standard maintenance requirements of the original specification is a cement mortar mixture temperature of 20 ± 3 °, relative humidity 60-80 °;

Second, the cement mortar and the micro-foam mortar should be at a temperature of 20±3° and a relative humidity of 90° or more;

Third, the specimens are not less than 10mm apart during maintenance. The new standard requires standard maintenance conditions: a cement mortar, mixed mortar uniform temperature specifications 20 ± 2 °, relative humidity 90 ° or more. And when maintenance is required, water cannot be dropped on the mixed mortar test block, and it should be covered with plastic paper.

Criteria for Testing Compressive Strength of Building Mortar Cubes in Test Methods for Building Mortar Basic Properties (JGJ/T 70-2009) 9.0.1 This method is applicable to the determination of the compressive strength of mortar cubes.

9.0.2 The equipment used in the compressive strength test shall meet the following requirements:

1 trial size is   With 70 .7 × 70.7 × 70.7mm end of the test mode, a predetermined reference material and section J G3019 4.2.1 4.1.3. Should have sufficient rigidity and easy disassembly. The inner surface of the test mold should be machined, and the unevenness should be no more than 0.05 mm per 100 mm. The non-perpendicularity of adjacent surfaces after assembly shall not exceed ±0.5°;

2 Steel boring bars: 10 mm in diameter, 350 mm in length, rounded at the end;

3   Pressure tester : the accuracy is 1%, and the failure load of the test piece should not be less than 20% of the press range and not more than 80% of the full range;

4 Cushion: The upper and lower platens of the tester and the test piece can be interposed with steel backing plates. The size of the backing plate should be larger than the pressure surface of the test piece, and the unevenness should be no more than 0.02mm per 100 mm.

5 Shaking table : The vertical amplitude of no-load mid-table shall be 0.5±0.05mm, the no-load frequency shall be (50±3) Hz, the amplitude uniformity of no-load table shall not be greater than 10%, and at least one test can be fixed (or use magnetic force). Suction cups) Three tryouts.

The preparation and maintenance of cube compressive strength specimens should be carried out in the following steps.

1 Use cubic specimens, 3 specimens each.

2 Apply an external sewing joint of the wiper and other sealing material to the oblique wiper test mold, apply a thin layer of engine oil or mold release agent to the test mold, and fill the prepared mortar with a mortar at one time. The molding method is determined according to the consistency. When the consistency is ≥50 mm, it is formed by artificial vibroflotation. When the consistency is less than 50 mm, vibrating table is used to form the vibrator. 1) Artificial vibration: Use a crowbar to evenly insert the cymbals 25 times in a spiral manner from the edge to the center. If the mortar sinks below the test dies during the boring process, mortar should be added at any time. The putty knife can be used for several times, and used. The test mold was raised 5 mm to 10 mm while shaking each time 5 times, so that the mortar was 6 mm to 8 mm above the top surface of the test mold. 2) Mechanical vibration: Fill the mortar once with the test mold and place it on the vibration table. The vibration of the test mold must not jump, vibrate for 5 to 10 seconds or until the surface discharges; no vibration is allowed.

3 After the surface water is slightly dry, the mortar above the test mold part is scraped off and smoothed along the top surface of the test mold.

4 After the test specimens are prepared, they shall be allowed to stand (24±2) h at room temperature of (20±5)°C. When the temperature is lower than the bottom, the time may be extended appropriately, but it shall not exceed two days and nights, and then the specimens shall be tested. Number, remove the mold. Immediately after removing the mold, the test piece shall be placed in a standard curing room with a temperature of °C or higher immediately after the test piece with the temperature of (20 ± 2) °C and a relative humidity of 90% or more is removed. During maintenance, the test pieces shall be separated from each other by no less than 10 mm. The top of the curing slurry in the standard sand curing room should be covered to prevent water droplets from falling on the test pieces.

The compressive strength test of 9.0.4 mortar cubes shall be carried out according to the following steps:

1 The test piece shall be tested in time after it is removed from the maintenance site. Before the test, wipe the surface of the test piece clean, measure the size, and check its appearance. Based on this, the pressure bearing area of ​​the test piece is calculated. If the difference between the measured size and the nominal size does not exceed 1 mm, the nominal size can be calculated;

2 Place the test piece on the lower plate (or lower plate) of the tester. The pressure surface of the test piece shall be perpendicular to the top surface of the test piece, and the center of the test piece shall be the center of the lower plate (or lower plate) of the tester. alignment. When the tester is started, when the upper platen is close to the test piece (or the upper plate), adjust the ball seat so that the contact surface is under pressure. The pressure test shall be carried out continuously and evenly. The loading speed shall be 0.2kN～1.5kN per second (When the mortar strength is not more than 5Mpa, the lower limit shall be taken, and when the mortar strength is greater than 5Mpa, the upper limit shall be taken). When the rapid deformation begins near the destruction, stop adjusting the throttle of the test machine until the test piece is broken, and then record the failure load.

9.0.5 The compressive strength of mortar cubes should be calculated as follows:

Fm, cu = Nu (9.0.5) A where fm, cu_____ mortar cube specimen compressive strength (Mpa);

NU_____ specimen damage load (N);

A_____ specimen bearing area (mm2) The compressive strength of the mortar cube specimen should be accurate to 0.1Mpa.

The arithmetic average of the three test specimens was 1.3 times (f2) as the average value of compressive strength of the mortar cube specimens of the set of specimens (accurate to 0.1 Mpa).

When the difference between the maximum and minimum values ​​of the three measured values ​​and the median value exceeds 15% of the median value,

Then, the maximum value and the minimum value are removed together, and the intermediate value is taken as the compressive strength value of the test piece; if there is a difference between the two measured values ​​and the median value exceeding 15% of the median value, the The test results of the group specimens are invalid.