The method of sampling inspection of steel and cement and concrete test blocks is urgent

I don't know if you're talking about sampling or testing?

The sampling method is as follows:

1. Steel bar: each specification, each grade, and each production batch shall not exceed 60 tons as a group. Two unprocessed raw materials are randomly selected from the steel bar pile, and a section of about 45 cm long and a section of about 30 cm long steel bar (the specific length is determined according to the model of the experimental machine) from a distance of more than 1 meter from the end of the pile, and the other is cut by the same method, a total of four sections as a group.

2. Cement: each strength grade, each type, and each factory number shall not exceed 200 tons as a group. Randomly select 10 bags of cement, use a cement sampler to take about 1 kg from each bag, a total of 10 kg mix and stir evenly, pack it in an airtight plastic bag, and tie the bag tightly.

3. Concrete: each strength grade, each shift, every 100 trays (about 100 cubic meters), and each part is a group. Fill the concrete mixture from the outlet of the mixer to make one test block, and make two more pieces from different trays, a total of 3 pieces as a group.

Generally, a group of test blocks is required to make an additional group of test blocks for backup or maintenance under the same conditions. If there is a part with impermeability requirements, another group of impermeability test blocks (6) should be made, and if it is a pavement or site, a group of bending test blocks (3) should be made.

As for the inspection method, there is a lot of expertise involved, which cannot be explained here.

Different places have different sampling inspection methods, which will not differ too much in general, and can be sent for inspection according to the requirements of local testing stations. I have here the "Quality Requirements and Sampling Rules for Main Incoming Inspection Products" of Guangzhou City. If you want it, please leave your email address and I will send it to you.

Ask your local laboratory.

They have requirements!

Answer: 1. 4 pieces of raw materials for steel bars in 1 group (50 cm long), and it should be noted that 50 cm on the head of the steel bar cannot be asked when sampling.

2. The compressive strength of the concrete test block (standard maintenance, the same conditions, and the demoulding test block are all 1 group of 3) 100 square meters to take 1 group.

3. One group of impermeable test blocks is 6 500 square meters and 1 group.

4. 1 group of mortar test blocks is 6 250 square meters and 1 group.

The strength test of concrete test blocks is stipulated in the "Building Materials" (183 pages of test results): the arithmetic average of the measured values of the three specimens is used as the compressive strength value of the group of specimens. If the difference between one of the three measured values and the intermediate value exceeds 15% of the intermediate value, the maximum value and the minimum value are rounded together, and the intermediate value is taken as the compressive strength value of the group of specimens; If the difference between the two measured values and the median value is more than 15% of the median value, the test results of the test specimen in this group are invalid.

The strength of the test block exceeds the standard value by 200%, strictly speaking, the compressive strength value of this group of specimens is invalid, and our local requirement is that it must be measured with a rebound tester on site.

The test time exceeds the specified 28 days, which is the time delayed by national holidays in our local area (because it must reach 28 days, and no test will be carried out for less than 28 days), in addition, more than 7 days must be tested on site. Otherwise, an expert should be asked to extrapolate the compressive strength value for 28 days according to the compressive strength value of the overage period.

The strength of cement slurry is represented by the strength grade of cement, that is, the number of cement.

The cement product standard all refer to the GB T17671 1999 method as the strength test method of the standard, and the GB177 85 method is no longer used.

2.The cement label is changed to strength grade The six cement standards implement the strength grade expressed by MPA, such as etc., so that the value of the strength grade is the same as the minimum value of the cement 28-day compressive strength index. The new standard also uniformly plans the strength grade of cement in China, and Portland cement is divided into 3 strength grades and 6 types, namely.

The other five major cements are also divided into 3 grades and 6 types, namely.

3.Strength age and strength index setting of each age: The strength age specified in the new standards of the six general cement standards is 3 days and 28 days, and each age has flexural and compressive strength index requirements.

A batch of steel bars, the same plant, and the same kind of steel bars not exceeding 60 tons are sent for inspection and approval;

Each structure of concrete specimens is not less than one group of specimens, and the concrete produces more than 100 trays and a group of specimens per day;

Cement slurry is used to test molds to make test pieces.

Cement: powdered hydraulic inorganic cementitious material. After adding water and stirring into a slurry, it can be hardened in air or better hardened in water, and can firmly cement sand, stone and other materials together.

The word cement is derived from the Latin word caementum, which means crushed stone and flake. The mixture of early lime and volcanic ash is similar to modern lime pozzolana cement [1], and the concrete made from cemented crushed stone is not only strong when hardened, but also resistant to fresh or salt water. For a long time, as an important cementitious material, it has been widely used in civil construction, water conservancy, national defense and other projects.

GB T 12573-2008 Sampling method for cement.

GB Steel for reinforced concrete Part 2: Hot rolled ribbed steel bar Steel bar for concrete Part I.

Reinforcement reference standard "CCGF hot-rolled round steel bar for reinforced concrete" and "CCGF hot-rolled ribbed steel bar".

Cement refers to the standard "CCGF 303-2008 Cement".

The mortar test block refers to the standard "Ready-mixed mortar JGT 230-2007".

In order to determine whether a product is qualified, it must be inspected. The inspection method can be divided into two types: one-by-one inspection and sampling inspection. The concrete mixture is a plastic material, and the inspection of its properties can only be carried out by sampling.

The homogeneity of concrete is very poor, the system is complex, and it has the uncertainty of microstructure and the uncertainty of performance. Therefore, in order to bring the sample closer to the truth value, it is necessary to increase the number of samples, and the larger the number of samples, the better the representativeness. For a certain structural concrete, in order to make the sampling have a certain representativeness, the number of strength samples is generally not less than 10 groups.

If the quantity is too small, it is difficult to represent the overall strength of concrete, and the probability of misjudgment is quite large. But in actual operation, it is impossible to take a large number of samples, which is bound to affect the representativeness of the test results, and it is inevitable to cause fault error, especially when only 1 group of concrete specimens are formed in the same inspection batch, it is easier to cause the occurrence of "false" unqualified problem.

It should also be noted that when sampling and inspecting the production of specimens, it should be measured whether the trial mold meets the provisions of the technical requirements in the JG3019 standard of "Concrete Mold Trial". There are quality problems in the trial mold produced by some small manufacturing plants, which cannot meet the requirements of standard technical indicators at all, and the inspectors do not have the habit of measuring the size of the specimen before the test. Therefore, when the specimen fails, it cannot provide an analytical basis for traceability.