A kind of
Testing test
Project determination
There are many kinds of building materials used in the construction site, and the entry test and test materials projects shall be subject to the provisions of the state, industry and local construction authorities (or departments concerned). For example, the cement used for preparing concrete should be inspectted according to batch inspection for its stability, strength, setting time and fineness. Concrete coarse aggregate should be inspecting items according to routine gradation, density, mud content and mud content, and needle particle content. If the concrete used for concrete is greater than or equal to C35, it must be crushed index.
Ambient temperature and humidity
Temperature and humidity have great influence on the performance of some building materials. Therefore, environmental conditions are specified in the standard for material maintenance and testing. Such as elastomer modified asphalt waterproofing membrane (SBS) waterproof material, its performance is more sensitive to environmental temperature. The room temperature should be controlled at 23 C and + 2 C when tensile test is required. 9 groups of samples made from elastomer modified asphalt waterproofing membrane (SBS) from the same parent were used as tensile strength (longitudinal) tests. The 9 sets of samples were divided into 3 large groups, and then the tensile tests were carried out at 5 degrees centigrade as a temperature difference. 1 large samples were tested in the standard environment of 23 degrees Celsius. The other 2 large samples were subjected to tensile tests at 28 and 18 degrees respectively. After the test, the average tensile strength of the 3 samples in each group was calculated. It was found that the average tensile strength of the 3 samples tested at 28 degree temperature was 2.85% lower than that of the 3 samples tested at 23 temperature standard temperature, while the average tensile strength of 3 samples tested at 18 degree temperature was 3.55% higher than that of 3 samples tested at 23 temperature standard temperature. To some extent, the test can reflect the influence of environmental temperature and humidity on material testing. Therefore, it is necessary to control temperature and humidity within the prescribed limits when testing.
Sampling sample
The sampling should be representative. Generally, a number of samples are randomly drawn from different parts of a batch of materials (different batches of different materials). The number of samples is related to the accuracy of the test results. The small quantity, the location of the sample and the deviation of the method will make the test error increase, and even the opposite result will be obtained. However, in practice, the sampling is not representative, the sampling quantity is not enough, and the sampling method is incorrect. For example, bags of cement shall be taken from the batch of not less than 20 bags of cement, equivalent to 120 kg. However, in practice, the inspection personnel repeatedly seized half bags or whole bags of cement as samples. After testing, some indicators of cement did not meet the standard requirements. After sampling according to the standard requirements, the test results were completely consistent with the relevant national standards.
About data
Handle
Due to various reasons, the discreteness of test results is sometimes greater in the same set of samples. In order to ensure the accuracy and reliability of the test results, the test results of some materials are trade-off. For example, in the strength and flexural test of cement mortar, the data that exceed the mean value of 10% in 3 strength values should be removed and the average value of other data should be calculated. In addition, the average value of compressive strength of concrete and mortar is also calculated. The revision of calculation results is carried out according to GB/T8107 - 2012 "numerical revision rules". The mantissa is carried according to the "four house six into five single and two methods", and the effective digit is kept according to the standard. For example, according to the regulations of GB/T228.1 - 2010 "tensile test method for metallic materials at room temperature", the determination results of the performance of steel (including steel bars) should be revised according to the requirements of relevant product standards. When there is no specific requirement, when the strength value is less than 200N/m, the interval between revisions is 1N/m 1000N/m, when the strength value is 200 ~ 1000N/m, the interval between revisions is 5N/m, when the strength value is >1000N/m, the interval between revisions is 10N/m. In addition, we should follow the stipulations of no revision in the calculation process. For example, the apparent density test of sand, JGJ52 - 2006 "quality standard and testing method for ordinary concrete sand" stipulates that two tests should be done, but the apparent density value of each calculation should not be revised. Only the ending number of the two results should be revised to 0. Otherwise, the transmission of large errors will be added, which will affect the accuracy of the test results.
About error
problem
The test method should be carried out strictly according to the standards. However, due to the difference in proficiency of the operators and the homogenization of the materials, the equipment and the environmental conditions, the test results will be error. There are 3 kinds of test errors. One is the error between the same set of samples. If the error is within the prescribed range, it is permitted, but if it exceeds the permitted scope, it should be re tested. For example, in the determination of compressive strength or flexural strength of concrete samples, if the deviation between the two measured values and the intermediate values exceeds 15% of the intermediate value, the group test should be redone. Another kind of error is to divide the same sample into 2 or 3 samples, and the error between the results obtained by the same method on the same instrument is called parallel test error. For example, the sieve analysis of sand, the fineness modulus between the two tests should be >0.20, and the apparent density should be two times >20kg/m3. Another kind of error is the error of the same material and the same sample in different test equipment, which is called the reproducibility error or the contrast test error. The test is generally divided into two parts, such as cement, steel and other homogeneous materials. One is handed over to the geological inspection organization and the other is left in the unit. The results of the two test units are analyzed and compared. If the relative error is large, the causes should be identified and improved. This experiment can be carried out 1~2 times a year, in order to improve the testing quality of the unit.
Loading speed
The strength value will be higher than the intrinsic strength of the material. If the yield point of the reinforcement is measured, the loading rate will be faster and the yield point will be improved. The flexural, compressive and loading speed of cement, concrete, brick and other samples will affect the results. Therefore, loading speed should be operated strictly according to material standards and operating rules. The loading should be continuous and uniform. When the sample starts to deform rapidly and close to failure, stop adjusting the throttle of the test machine until the maximum load value of the sample is detected.
Sample process control
Material testing method and its malpractice are all methods of material inspection. It is originally a sample sent by the construction enterprise. After the implementation of the project supervision in early 90s, the engineer will sign the witness on the sheet, and then the construction technician will send the sample to the material inspection center (station). It should be admitted that most construction enterprises can sample the materials according to the regulations, but they can not deny that the construction personnel have not sampled according to the regulations, or simply sent fake samples, such as water bars, bricks, and concrete and mortar for composite materials. In this way, the sample can not represent the overall sample, even if the sample is qualified, it can not represent the qualified material. Some materials inspection departments seem to know this simple relationship. Therefore, in the test report, it states: "the conclusion of this test is only responsible for the incoming samples". Because the material samples are not necessarily true, the evaluation of the engineering quality is not entirely true. Therefore, according to the inspection report and other technical data, even if the project is evaluated as excellent, the engineering quality supervision station may not be able to achieve good standards in the end. If any other link is out of control again, it will be possible to have an engineering structural accident. From the above analysis, the samples of the material testing method of "send style" can not fully represent the authenticity of the engineering quality, and can not effectively control and prevent engineering structural accidents. To reform the current material testing methods, change the "inspection type of construction enterprises" to the "sampling inspection type of inspection departments", and cancel the material testing centers of enterprises and colleges and universities, and change them to the test results issued by the government departments for building materials testing centers, so as to ensure the authenticity and fairness of the test results. Its tasks and decisions determine that the building material inspection department must change the nature of the law that aims at making profit and turning it into management and supervision. In this way, the material inspection center (station) can be classified as a government department that is able to work with the engineering quality supervision station, or can be merged into the engineering quality supervision station, and the leaders of the local construction committee should be unified, so as to increase the detection and supervision ability of the engineering quality and change the detection mode.
Reference:
National Building Engineering Quality Supervision and inspection center, Shanghai Construction Engineering Inspection Industry Association "construction engineering testing technology and management." Beijing: Chemical Industry Press, 2006 edition.
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