Differences:
1. Different definitions:
①The standard cured test block is the test block cured in the standard curing room. The specification stipulates that the test piece is in (20 ±3)℃, the humidity must be above 90% in a standard curing room, and must be cured for 28 days.
② The same-cured test block refers to the test piece that is sampled and made at the concrete pouring site, and is cured according to the curing conditions of the on-site structural entity (that is, placed near the component for curing). The test block under such conditions resists The compressive strength value better reflects the concrete strength of the structural entity. The cumulative curing temperature is generally from the beginning of curing until the daily average outdoor temperature reaches 600 degrees/day before starting the pressure test. However, when the temperature in the construction area is special, it should also be ensured that the curing time cannot be less than 14 days and cannot be higher than 60 days.
2. Different objects:
① For concrete inspection batches, at least one group must be retained for each inspection batch;
② For strength levels, each strength The number of grade retentions is determined based on needs. Generally, it is best to have as many as standard maintenance retentions.
3. Different functions:
① It is used for acceptance. After the results of all test blocks come out, they must be evaluated. The evaluation results must be qualified, otherwise structural testing will be done;
② Sampling re-inspection is generally used for actual structural measurement. If the inspection is qualified, a few fewer points can be done during the structural inspection (that is, less rebound is done, or even no structural inspection is required).
4. Different sampling methods and proportions:
① Each inspection batch is generally required to be retained. Concrete mixed on site, with the same strength level, the same mix ratio, and the same production process will be mixed every time. One sampling unit (that is, one group should be kept when the following conditions are met) should comply with the following regulations:
a. 100 plates per mix, but no more than 100m3.
b. According to each workstation shift.
c. Each cast-in-place floor.
d. When the amount of continuous concrete pouring is greater than 1000m3, it shall be calculated as every 200m3. If commercial concrete is used: the concrete used for delivery inspection is calculated as 100m3, and the concrete mixed in one workbench shift is less than 100m3 as each workbench shift. When the continuous supply of concrete is greater than 1000m3, it is calculated as every 200m3.
② The number of specimens to be retained according to the same strength level and maintained under the same conditions with the same strength should be determined according to the quantity and importance of the concrete project. It should not be less than 10 groups, and should not be less than 3 groups. , important parts (beams, slabs and columns in the main body) can be left in the same manner as standard maintenance.
5. Maintenance is different:
① The curing environment of concrete standard curing test blocks is (20±3) ℃, and the humidity is more than 90%. Generally, standard curing is required at the construction site. room, or send it to the standard curing room of the laboratory for curing immediately after the mold is removed.
② Test blocks with the same conditions must be placed near the representative parts and protected.
6. The conditions for submission for inspection are different:
①The standard age of the test block is 28 days and cannot exceed the age.
② The age of test blocks in the same culture is generally 14-60d, that is, the equivalent curing age can be taken as the age corresponding to when the daily average temperature reaches 600°C.d day by day, 0°C and below Age is not included; the equivalent curing age should not be less than 14 days, nor should it be greater than 60 days.
Extended information:
1. The location and quantity of concrete test block samples
It is clearly stipulated in 7.4.1 of the specification that it is used to check the concrete of structural components. Strength test blocks should be randomly selected from the concrete pouring site. Sampling and retention of test blocks should comply with the following regulations: 1. No more than 100 cubic meters of concrete with the same mix ratio shall be sampled less than once; 2. Sampling shall not be taken when less than 100 trays of concrete with the same mix ratio are mixed per work shift. Less than once; 3. When a continuous pouring exceeds 1,000 cubic meters; every 200 cubic meters; sampling is done once; for each floor and the same mix proportion of concrete, sampling must be done not less than once; 4. At least one set of standard curing tests should be retained for each sampling. Blocks, the number of retention groups of test blocks maintained under the same conditions should be determined according to actual needs.
The so-called actual needs are explained in Appendix D of the specification: the structural members or structural parts corresponding to the test blocks maintained under the same conditions should be jointly decided by all parties including the supervision (construction) construction, etc. What is the basis for selection? The inspection of structural entities is limited to important parts of structural components such as columns, walls, and beams that involve structural safety.
Parts such as cushions that do not involve structural safety do not need to retain test blocks of the same condition. The number of retained test blocks of the same condition shall be in accordance with the provisions of the "Specifications": the number of retained test blocks of the same strength level and the same condition of maintenance shall be determined according to the quantity and importance of the concrete project, and should not be less than 10 groups (evaluated by statistical methods). And should not be less than 3 groups (evaluated by non-statistical methods).
When there are projects with anti-seepage requirements, concrete test blocks should be randomly sampled at the pouring site. For concrete with the same mix ratio in the same project, sampling should not be less than once. The number of retention groups can be determined according to actual needs.
2. Production and maintenance of concrete test blocks
The test blocks for concrete strength evaluation are divided into standard cured test blocks and co-cured test blocks. Standard cured test blocks refer to the standard cured test blocks. For test blocks cured in a laboratory, the standard stipulates that the standard cured test blocks must be maintained at a temperature of 20±2°C, a humidity greater than 95%, and cured for 28 days; the co-cured test blocks refer to test blocks made of concrete randomly selected at the pouring site. The blocks are randomly selected at the construction site and the daily average temperature accumulates to 600 degrees Celsius at the site according to on-site curing conditions. At the same time, the "Specifications" also stipulate that the equivalent maintenance cycle should not be less than 14 days. In the case of high-rise building construction, we usually also have to leave the demolition test blocks. In winter, the temperature is low and the strength of concrete develops slowly, which requires a longer period of demolition. In summer, the temperature is high and the concrete The strength of concrete develops rapidly. Generally, under 7 days of on-site curing conditions, the concrete strength can reach more than 90%, which can appropriately shorten the formwork removal period.
Baidu Encyclopedia-Concrete Test Block Strength Assessment