GB/T 50107-2010Standard for evaluation of concrete compressive strength (English PDF)

2.1 Terminology

2.1.1 Concrete

It is an engineering material made of cement, aggregate and water according to a certain ratio, and hardened by mixing, molding, curing and other processes.

2.1.2 Age of concrete

The time, in days or hours, that concrete has experienced since the addition of water and mixing.

2.1.3 Strength of concrete

The mechanical properties of concrete represent its ability to resist external forces. Concrete strength in this standard refers to the concrete cube compressive strength.

2.1.4 Conformity assessment evaluation of conformity

The determination of whether the concrete strength is qualified or not according to certain rules.

2.1.5 Inspection batch inspection batch

Concrete aggregate consisting of concrete meeting the specified conditions and used for conformity assessment.

2.1.6 Inspection period

Statistical period specified for determining the standard deviation of the strength of an inspection lot of concrete.

2.1.7 Sample size sample size

The number of groups of concrete specimens used for conformity assessment representing the inspection lot.

2.2 Symbols

mfcu——the average value of the compressive strength of concrete cubes in the same inspection batch;

fcu,k—standard value of concrete cube compressive strength;

fcu,min——the minimum value of the compressive strength of concrete cubes in the same inspection batch;

——Standard deviation of the compressive strength of concrete cubes of the same inspection batch in the evaluation method with unknown standard deviation;

sigma0——in the evaluation method with known standard deviation, the standard deviation of the compressive strength of concrete cubes in inspection batches;

lambda1, lambda2, lambda3, lambda4—conformity assessment coefficients;

fcu,i——the representative value of the cube compressive strength of the i-th group of concrete specimens;

n - sample size.

4.1 Sampling of concrete

4.1.1 For the sampling of concrete, it is advisable to formulate the division plan of the inspection lot and the corresponding sampling plan according to the requirements of the inspection and evaluation method specified in this standard.

4.1.2 Concrete strength samples should be randomly selected at the place where the concrete is poured.

4.1.3 The sampling frequency and quantity of test pieces shall meet the following requirements.

1 For every 100 trays, but no more than 100m3 of concrete with the same mix ratio, the sampling frequency should not be less than once;

2 When the concrete with the same mix ratio is mixed in each working shift, the sampling frequency should not be less than once when there are less than 100 trays and 100m3;

3 When the concrete with the same mix ratio for one continuous pouring exceeds 1000m3, sampling should not be less than once for every.200m3;

4 For building buildings, each floor and concrete with the same mix ratio shall be sampled no less than once.

4.1.4 The total number of test specimens that should be made for each batch of concrete samples, in addition to meeting the number of groups necessary for the concrete strength assessment specified in Chapter 5 of this standard, should also be reserved for the inspection of the concrete strength of the structure or component during the construction stage. of test pieces.

4.2 Fabrication and maintenance of concrete specimens

4.2.1 At least one set of standard curing test pieces shall be prepared for each sampling.

4.2.2 Each group of 3 test pieces shall be made by sampling the concrete from the same plate or the same vehicle.

4.2.3 The molding method and standard curing conditions of the concrete specimens used for testing and evaluating the strength of concrete shall comply with the current national standard GB/T 50081 "Standards for Test Methods of Mechanical Properties of Ordinary Concrete".

4.2.4 For components that are cured by steam, the test pieces should be cured under the same conditions as the components first, and then placed under standard curing conditions for further curing. The sum of the two curing periods should be the age specified in the design.

4.3 Tests on concrete specimens

4.3.1 The cubic compressive strength test of concrete specimens shall be carried out in accordance with the provisions of the current national standard "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" GB/T 50081.The determination of the strength representative value of each group of concrete specimens shall meet the following requirements.

1 Take the arithmetic mean value of the strength of three specimens as the strength representative value of each group of specimens;

2 When the difference between the maximum or minimum strength value of a group of test pieces and the middle value exceeds 15% of the middle value, take the middle value as the strength representative value of the group of test pieces;

3 When the difference between the maximum and minimum strength values of a group of test pieces and the middle value exceeds 15% of the middle value, the strength of this group of test pieces should not be used as the basis for evaluation.

Note. When evaluating the strength of concrete mixed with mineral admixtures, according to the design requirements, the concrete strength greater than 28d can be used.

4.3.2 When non-standard size test pieces are used, the compressive strength should be multiplied by the size conversion factor to convert the compressive strength of standard size test pieces with a side length of 150mm. The size conversion factor shall be adopted according to the following provisions.

1 When the concrete strength grade is lower than C60, take 0.95 for a cube specimen with a side length of 100mm, and take 1.05 for a cube specimen with a side length of.200mm;

2 When the concrete strength grade is not lower than C60, it is advisable to use standard size test pieces; when using non-standard size test pieces, the size conversion factor should be determined by the test, and the number of test pieces should not be less than 30 pairs.

5.1 Evaluation of statistical methods

5.1.1 When statistical methods are used for evaluation, the following provisions shall be followed.

1 When the continuous production of concrete, the production conditions remain consistent for a long period of time, and the strength variability of the same type of concrete with the same strength level remains stable, it should be evaluated according to the provisions of Article 5.1.2 of this standard.

2 Other situations should be evaluated according to the provisions of Article 5.1.3 of this standard.

5.1.2 The sample size of an inspection batch should be three consecutive groups of test pieces, and their strength should meet the following requirements at the same time.

The standard deviation of the compressive strength of concrete cubes in the test batch shall be calculated according to the following formula.

When the concrete strength grade is not higher than C20, the minimum value of its strength should still meet the requirements of the following formula.

When the concrete strength grade is higher than C20, the minimum value of its strength should meet the following requirements.

In the formula. mfcu—the average compressive strength of concrete cubes in the same inspection batch (N/mm2), accurate to 0.1 (N/mm2);

fcu,k—standard value of concrete cube compressive strength (N/mm2), accurate to 0.1 (N/mm2);

sigma0——the standard deviation of the compressive strength of concrete cubes in the test batch (N/mm2), accurate to 0.01 (N/mm2); mm2;

fcu,i——Cubic compressive strength representative value (N/mm2) of the i-th group of concrete specimens of the same type and the same strength grade in the previous inspection period, accurate to 0.1 (N/mm2); this inspection period should not less than 60d and not greater than 90d;

n - the sample size in the previous inspection period, the sample size in this period should not be less than 45;

fcu,min - the minimum compressive strength (N/mm2) of concrete cubes of the same inspection batch, accurate to 0.1 (N/mm2).

5.1.3 When the sample size is not less than 10 groups, its intensity should meet the following requirements at the same time.

The standard deviation of the compressive strength of concrete cubes in the same inspection batch should be calculated according to the following formula.

In the formula. - the standard deviation (N/mm2) of the concrete cube compressive strength of the same inspection batch, accurate to 0.01 (N/mm2); when the calculated value of the standard deviation of the concrete strength of the inspection batch is less than 2.5N/mm2, it should be 2.5 N/mm2;

lambda1, lambda2—conformity assessment coefficients, to be taken according to Table 5.1.3;

n—sample size in the inspection period.

Table 5.1.3 Conformity Assessment Factors for Concrete Strength

5.2 Evaluation by non-statistical methods

5.2.1 When the sample size used for evaluation is less than 10 groups, non-statistical methods shall be used to evaluate concrete strength.

5.2.2 When the strength of concrete is assessed by non-statistical methods, its strength shall meet the following requirements at the same time.

In the formula. lambda3, lambda4—conformity assessment coefficients, which should be taken according to Table 5.2.2.

Table 5.2.2 Non-statistical method conformity assessment coefficient of concrete strength

5.3 Qualification assessment of concrete strength

5.3.1 When the test results meet the requirements of Article 5.1.2 or Article 5.1.3 or Article 5.2.2, the strength of this batch of concrete shall be assessed as qualified; if the above requirements cannot be met, the strength of this batch of concrete shall be rated as unqualified.

5.3.2 As for the unqualified batch of concrete, it can be handled according to the relevant current national standards.