Concrete materials play an important role in construction projects. Concrete admixtures are an important component of concrete and affect the performance and quality of concrete to a great extent. Concrete admixtures have become one of the indispensable main materials of modern concrete, playing a great role in improving the performance and quality of concrete, and making a huge contribution to the quality of concrete projects. Therefore, it is very necessary to test the quality of admixtures. This paper explains the importance and necessity of concrete admixture testing by introducing the testing standards for concrete admixtures, cement issues in quality testing tests, and the main content of admixture quality testing.
1 Introduction
With the development of construction projects, the requirements for concrete quality have gradually increased. Since concrete admixtures can improve the properties of concrete to a certain extent, they are used in engineering projects. The status in construction is also constantly improving, so the quality inspection of concrete admixtures needs to be very cautious. These include issues such as testing standards, testing items, and test materials [1].
2 Necessity of quality inspection of concrete admixtures
Concrete admixtures are an important method and means of concrete modification, which in turn play a key role in the development of concrete and also contribute to the quality of concrete. A valid guarantee is provided. If the quality of the admixture does not meet the requirements, it will greatly affect the quality and performance of the concrete, thus affecting the construction of the entire project. The quality of the admixture meets the requirements and can promote project development in many aspects. In the application process of concrete, the quality of admixtures must be strictly controlled. Testing and testing are the most important means of quality control, so quality testing of concrete admixtures is very necessary [2].
3 Issues with testing standards for concrete admixtures
3.1 Different testing items for admixtures
At present, many departments in our country have promulgated relevant standards for concrete admixtures. Documents and standards, these standards stipulate the quality requirements and dosage of admixtures to a certain extent, thereby ensuring that they can meet the requirements of project development. The “Technical Specifications for the Application of Concrete Admixtures” (GB50119-2013) stipulates a number of strictly prohibited items, but there are no restrictions on them in the “Concrete Admixtures” (GB8076-2008); “Polycarboxylic acid-based high-performance admixtures” “Water Admixture” (JG/T223-2007) has the item “corrosion effect on steel bars” and specifies that the test should be carried out according to the method of “Concrete Admixture” (GB8076-2008), while “Concrete Admixture” (GB8076-2008) has There is no such provision. There are many differences between various standards, which leads to many inspection processes without knowing which standard should be used for inspection, leaving the construction unit at a loss when submitting inspections. Inconsistent testing standards for concrete admixtures will affect the judgment of quality testing results. In this way, concrete admixture manufacturers have an opportunity to take advantage of it, which affects the development of the admixture itself to a certain extent.
3.2 Testers do not pay enough attention to the differences in admixture testing indicators
The national mandatory indicators include high-performance water-reducing agents, high-efficiency water-reducing agents, ordinary water-reducing agents, and air entrainment The index requirements for various concrete admixtures such as water-reducing admixtures and pumping agents cover a wide range, and the quality requirements for admixtures are also relatively high. The industry standards and index requirements of the Ministry of Construction are different from those of the national standard. For example, for high-performance water-reducing admixtures, there is a big gap in the index requirements of the two standards, which is manifested in many aspects. Among them, for the compressive strength ratio, the construction standard’s requirement for water-reducing agent is not less than 140% for 7 days and not less than 130% for 28 days; the national standard’s requirement for water-reducing agent is not less than 125% for 7 days, and not less than 120% for 28 days. %. They are both high-performance water-reducing agents in concrete, but they have different index requirements, which greatly affects the conclusion of the test.
3.3 Different proportions and dosages of testing materials
During the testing process of concrete admixtures, there is a problem of different proportions and dosages of testing materials, which causes deviations in the testing results. This is also Problems that often occur during the testing of additives have always been the main factor affecting quality testing. In the process of testing admixtures, different tests must be done on the materials used for testing. The cement dosage and sand rate used when testing admixtures are important testing indicators in the process of testing admixtures. The control of these indicators must be very accurate and there must be no mistakes, otherwise the results of the quality testing will be affected. In the process of quality testing of concrete admixtures, it is necessary to control the testing materials to ensure that during each test, the proportion and dosage of the testing materials are consistent to improve the comparability and accuracy of the testing results [3 ].
4. Cement issues in quality inspection tests
4.1 The influence of concrete cement varieties
The benchmark cement used for testing must be carried out by manufacturers jointly certified by various relevant departments. Production can meet the requirements of quality inspection. For the testing unit, there are not many admixture samples for testing and the production time of the samples cannot be determined. At the same time, after the cement is produced and transported to the testing unit, whether its validity period can meet the requirements has also become a problem. This creates difficulties in benchmark cement detection. On the other hand, the pure Portland cement used for testing is nowIt is very difficult to find in the market, and even if you make it yourself in the laboratory, it is difficult to meet the requirements. If the cement produced on the market is used for testing, it will inevitably cause the test results to be incomparable due to the different reference materials used.
4.2 Compatibility issues between cement and admixtures
During the process of testing admixtures, mixing cement and admixtures together may cause compatibility issues. There are two main reasons for this situation:
(1) The influence of the composition of admixtures. In order to adapt to the needs of different engineering constructions, the composition of admixtures applied to concrete must be adjusted. Appropriate adjustments are made, which makes the compatibility between admixtures and cement more complicated, thus affecting the test results;
(2) The influence of cement, due to the various properties of cement and Changes in mineral composition, gypsum materials, alkali content and other factors will become the main factors affecting the compatibility of cement and admixtures. Therefore, if different manufacturers and different batches of cement are used to test admixtures, the test results will definitely have great deviations.
However, as far as the construction unit is concerned, it is hoped that the cement actually used on site will be used to test the admixtures. The conclusion drawn in this way is relatively more targeted and applicable, and it also solves the problem of compatibility between the two.
5 Main contents of admixture quality testing
The cement used for quality testing is the Portland benchmark cement stipulated by the state. Its safety strength level is 42.5, and its fineness and standard consistency are respectively are 1.5% and 26.5%, the initial setting time and final setting time are 3.42h and 4.37h respectively; the mix ratio is prepared in accordance with relevant requirements, and the testing method is carried out in accordance with the document requirements issued by relevant national departments. These include concrete admixtures, concrete admixture homogeneity test methods, concrete pumping agents and other document specifications that set requirements for the quality inspection process.
The standards for quality testing of concrete admixtures should be consistent. Testing of products of the same variety should be carried out under the same proportions, the same items, the same test methods and the same environmental conditions. The cement, sand, gravel and other materials used have a great impact on the quality testing results of concrete admixtures. At present, most ready-mixed concrete batching plants, admixture manufacturers, and even many third-party testing agencies do not use benchmark cement when testing the quality of concrete admixtures, but “use local materials.” Most of the stones used are 10 to 30 mm in size, or even larger, which causes a large deviation in the detection results. However, this kind of detection is more targeted and deserves to be promoted.
6 Conclusion
Today’s engineering construction and development have a wide range of applications for concrete, and concrete admixtures play a huge role in improving the performance of concrete. Therefore, scientific quality testing can promote the development of concrete engineering to a certain extent. This article analyzes common problems in the testing process of admixtures, hoping to play a certain role in their quality testing.
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