Concrete additive news and tec > Concrete block additive > On the existing problems of concrete test block and its strength evaluation

On the existing problems of concrete test block and its strength evaluation

Concrete block additive 2021-07-22 07:30 146
On the existing problems of concrete test block and its strength evaluation? Abstract: This paper analyzes some common problems existing in concrete test and concrete strength evaluation by construction units, and points out concrete sample sampling according to relevant standards and specifications, Key words: concrete cube compressive strength, concrete qualification evaluation strength, scale curing, curing under the same conditions, Chinese Library Classification No.: tu755.6 document identification code: a concrete is a kind of construction engineering material with large consumption, long history and booming development, Concrete cube compressive strength is one of the main parameters used to judge the quality of concrete. The quantitative standard of concrete quality by concrete cube compressive strength is the average value and standard deviation or coefficient of variation of concrete strength. The quality of concrete is directly related to the safety and durability of building structure, The quality of concrete is determined by the quality of raw materials, the quality of concrete mix proportion, the accuracy of measurement, the quality of concrete mixing and forming, and the quality of curing. Therefore, in concrete construction, each factor affecting the quality of concrete should be inspected and controlled according to the requirements of relevant standards, However, the control effect is ultimately reflected in the compressive strength of concrete test blocks. Therefore, the compressive strength test of concrete test blocks is the most critical link in the control of concrete production. The relevant specifications of various countries clearly stipulate that a certain number of test blocks must be reserved for a certain batch of concrete, It is also required that the pressure test results of the test block at the specified age should be used as the basis for evaluating the concrete quality. However, through many years of test work, it is found that some concrete test blocks made on site can not truly and comprehensively reflect the strength of concrete and can not correctly participate in the strength evaluation of concrete, The following is to discuss the existing problems. 1.1 the concrete test mold is not standardized, the internal size and the flatness of perpendicularity are not standard, so that the size of the concrete test specimen does not meet the standard requirements, and even lacks edges and corners. According to Article 2.0.4 of gbj81-85 test method for mechanical properties of ordinary concrete, the test mold used to make the test specimen is made of cast iron or steel, It should have enough rigidity and easy disassembly. The inner surface of the test mold should be machined. The unevenness should not exceed 0.05itlln per 100itlln, and the non perpendicularity of each adjacent surface should not exceed 0.5 after assembly. The test mold should be cleaned and coated with a layer of mineral grease or other release agent on its inner wall before making the test specimen, However, some construction units do not have this kind of test mold, but only nail the wooden board into the general specification of the wooden mold, which makes the test pieces do not meet the specification requirements. Some test molds have been deformed and continue to be used, and the test blocks become parallelogram. Some do not wipe the release agent on the inner part of the test mold before making the test pieces, which makes it difficult to remove the mold and the size defect, Article 3.0.1 of GBJ107-87 standard for concrete strength inspection and evaluation stipulates that concrete specimens shall be randomly selected at the place of concrete pouring, and the sampling frequency shall meet the following requirements: 1) every 100 plates of concrete with the same mix proportion but not more than 100rn3, Sampling times shall not be less than once; 2) The sampling frequency of less than 100 plates of concrete with the same mix proportion mixed in each working shift shall not be less than once. The reason why the specification stipulates this is that the randomness of concrete sampling should be adhered to in the qualification assessment of concrete strength, which is an important condition to make the selected specimens representative, and the concrete mixture at the mixer mouth should be considered, When the concrete is transported to the pouring place, the uniformity of the concrete is related to the degree of segregation, so it is stipulated that the samples should be taken at the pouring place. When the statistical method is used to inspect and evaluate the concrete strength, the sampling frequency is an important factor to ensure the expected inspection efficiency, After the formwork is removed, it is not cured according to the regulations, and it is casually placed on the construction site. It is recalled that during the sample delivery test, some specimens are over 28d old, and the time is too long, and there are only two specimens left in one group. The internal temperature gradient of the concrete is too large, which will produce certain temperature cracks. Therefore, 3 conclusion by adding a certain amount of mineral admixtures (such as fly ash, silica fume, etc.) into the concrete, Mineral admixtures and fine particles can be more fully distributed among cement particles. The high specific surface area of active fine admixtures can reduce the porosity of cement paste, improve the compactness of cement paste, and increase the water resistance, The addition of mineral admixture is beneficial to the hydration reaction of concrete and the formation of CSH gel, which expands during the hydration process, blocks the internal pores of cement paste and the crevice between cement paste and aggregate, makes the structure more dense and improves the impermeability of concrete. 1) with the increase of fly ash content, slump and expansion of lightweight aggregate concrete first increase and then decrease. 2) with the increase of fly ash content, the compressive strength of lightweight aggregate concrete first increases and then decreases. 3) the addition of fly ash can improve the impermeability of lightweight aggregate concrete. When the content is less than 50%, the greater the content, the better the impermeability. 4) comprehensive analysis, The optimum content of fly ash in this test is 15%, strengthanddurabilityofhighper—