Building materials paper 2000 words 1 analysis of related technologies of building materials testing
1, classification and inspection items of building materials
According to their position or performance in buildings, building materials can be roughly divided into three categories, namely, building structural materials (materials used for stress components and structures of buildings), wall materials (materials used for interior, exterior and partition walls of buildings) and building functional materials (non-load-bearing materials that undertake certain building functions). There are many kinds of building materials used in the construction site, and the entry inspection and test materials shall be subject to the provisions of the national, industrial and local construction authorities (or relevant departments) and the Measures for Compilation of Technical Archives for Completion of Provincial Construction Projects.
For example, the stability, strength, setting time and fineness of cement used in concrete preparation need to be tested in batches; The particle gradation, density, silt content, block content and needle-like particle content of concrete coarse aggregate should be tested. C35 concrete should be crushed, the newly adopted loose aggregate should also be tested for firmness, and the active aggregate should be tested for activity. For synthetic polymer waterproof materials, according to GB18173.1-2000, the physical properties, such as tensile strength at break, elongation at break, water impermeability and low-temperature bending, should be tested in batches. The determination of material testing items should be based on ensuring the quality of the project. It is not up to the requirements to only test the original certificate without sampling according to the regulations, or to sample and test the items incompletely.
2, the number and method of sampling
Sampling should be representative. Generally, a specified number of samples are randomly selected from different parts of a batch of materials (steel is intercepted from specified parts), that is, not only the sampling quantity should be correct, but also the sampling position and method should be carried out according to regulations. The number of samples is related to the accuracy of the test results. Too few samples and the deviation of sampling position and method will increase the test error and even get the opposite result. However, in actual detection, there are often some problems such as unrepresentative sampling, insufficient sampling quantity and incorrect sampling method. For example, no less than 20 bags of bagged cement should be randomly selected from this batch of cement, with a total mass of at least 12kg.
In practical work, many times, inspectors take half a bag or a whole bag of cement as samples at one time, and the strength value of cement after testing does not meet the standard requirements, and then take samples on the spot according to the standard requirements for re-testing, and the test results fully meet the national standards; Another example is that when the welded steel bar specimens are sent for inspection, some abandoned steel bar heads on the construction site are used as simulated specimens or the sampling method is incorrect; For another example, according to the standard, 6 pressure welded steel parts should be submitted for inspection, 3 tensile tests and 3 bending tests, while some only send 3 specimens for inspection, so even if all the tensile test results of 3 specimens are qualified, it is still impossible to judge whether the batch of specimens are qualified.
3. Analysis of the main points of common building materials detection technology
In the practice of quality control of building materials, we deeply understand that the quality control of engineering materials should be improved by combining self-inspection with parallel detection by the construction unit, tracking detection with witness sampling by the supervision unit, and testing with experiment. Enterprise self-inspection, social supervision and government supervision? Quality assurance system, firmly established? A century-old plan, quality first? Policy. This paper summarizes several testing and sampling methods of building materials.
3. 1 steel bar detection
When the reinforcement comes into the site, the mechanical properties of the specimen shall be tested according to the current national standard "Hot Rolled Ribbed Reinforcement for Reinforced Concrete" GB 1499, and its quality must meet relevant standards. 1) When sampling, 500 mm ~ 1000 mm rebar should be intercepted from any rebar end, and then sampling should be conducted. 2) Cold-drawn steel bars: acceptance shall be carried out in batches, and each batch of cold-drawn steel bars of the same grade and diameter with the weight not exceeding 20t shall be regarded as an inspection lot. 3) Steel bar welding. Welding of steel bars in building construction is generally divided into flash butt welding, resistance spot welding, arc welding, electroslag pressure welding, submerged arc welding of T-joint of embedded parts, and gas pressure welding of steel bars.
(1) flash butt welding: its mechanical properties test includes tensile test and bending test, and the tensile sample length is average? 500 mm (500 mm ~ 650 mm), and the length of cold-formed specimens is generally 250 mm (250 mm ~ 350 mm).
(2) Resistance spot welding: The shear test adopts hot-rolled steel bar spot welding, and the specimen length is average? 600mm In order to pull out the solder joint of low-carbon steel wire, in addition to shear test, tensile test should be done for smaller steel wire, and the length of the specimen is average. 500mm(500mm~650mm).
(3) Arc welding and electroslag pressure welding: The tensile test is carried out under the condition of site installation, and the length of the specimen is average? 500mm(500mm~650mm).
3.2 Detection of Cement and Sandstone
Sandstone, cement and admixture are the most basic and used building materials in building engineering. In the past, when testing these products in building engineering, only the strength of the products and some conventional technical indicators related to strength were tested. Nowadays, sand, stone, cement and even backfill should be tested for radioactivity.
Acceptance of cement entering the site: inspect the variety, grade, package or bulk warehouse number and factory date of the cement entering the site, and re-inspect its necessary performance indicators such as strength and stability. Its quality must conform to the current national standard "Portland Cement and Ordinary Portland Cement" GB 175. When there is doubt about the quality of cement in use or the cement factory date is more than 3 months (quick-hardening portland cement is more than 1 month), it should be reinspected and used according to the reinspection results. ?
Sampling method of sand and gravel: When sampling the water in the pile, the sampling parts should be evenly distributed. In the upper, middle and lower parts of the material pile, five different parts are evenly distributed to form a group of samples, and eight parts of sand in each part are roughly equal, and each part 15 parts of stone is roughly equal. Sand and cement are submitted for inspection at the same time, and the inspection of concrete mixture ratio and mortar mixture ratio is generally presented at the same time with the inspection report of sand and cement. When mixing concrete or masonry mortar for the first time, at least one set of standard curing specimens (standard curing condition: temperature 20? 30℃, 90% relative humidity and 10 mm ~ 20 mm) are used as the basis for verifying the mixture ratio. At the same time, according to the proportion of mortar, the particle size, cement dosage, mixing time and mortar workability of mixed sand for masonry mortar were tested.
3.3 concrete engineering
The strength grade of structural concrete must meet the design requirements. Specimens used to check the concrete strength of structural members should be randomly selected at the concrete pouring site, and the construction records and test reports of specimen strength should be checked in time. For concrete structures with impermeability requirements, concrete specimens should be randomly selected at the pouring site, and the impermeability test report should be checked at any time to ensure the construction quality.
The control of environmental temperature and humidity in the process of testing has a great influence on the performance of some building materials, so the environmental conditions in the process of material maintenance and testing are clearly stipulated in the standard and must be strictly observed. According to GB/T17671-1999 Cement Mortar Strength Test Method, the ambient temperature of the specimen during molding should be kept at 20℃? 2℃, relative humidity should be >; 50%; The curing temperature of the specimen before form removal is 20℃? 65438 0℃, relative humidity should be >; 90%; The curing temperature of the sample in water is controlled at 200℃? 10C. Another example is the waterproof material such as elastomer modified asphalt waterproofing membrane (SBS), whose performance is sensitive to the ambient temperature, and the room temperature is required to be controlled at 23℃ during the tensile test. 2℃。
4. Concluding remarks
With the rapid development of China's construction industry, people pay more and more attention to the quality of building materials. As the foundation of building engineering, the quality of building materials directly affects the safety of building engineering. Before construction, we must attach great importance to the testing of building materials, strictly implement quality standards, constantly sum up experiences and lessons, constantly improve the practical operation level, ensure the accuracy of testing results, and ensure the quality of building materials and the safety of engineering use.
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