I. Background of standard revision
Sand aggregate is the most used material in infrastructure construction projects. China's annual production and sales volume is about 20 billion tons, accounting for half of the world's total. Sand and gravel aggregate is widely used in infrastructure construction such as buildings, roads, bridges, water conservancy, hydropower and so on, which is closely related to the survival and development of human beings, and has made positive contributions to benefiting the lives of urban and rural people and serving the needs of national economic construction. The quality of sand and gravel aggregate directly affects the quality of construction projects, which is related to the national economy and people's livelihood. 20 1 1 year, the national standards Committee issued building sand (GB/t14684-20165438) and building pebbles and gravels (GB/t14685-2065448).
With the strengthening of ecological environmental protection and the rapid development of construction projects, in recent years, there have been problems such as unbalanced supply and demand and high prices in the sand and gravel industry, which have attracted great attention from government departments and extensive attention from all walks of life. In order to solve the practical problem of natural sand and gravel resources depletion, vigorously developing machine-made sand and gravel has become the only way for the safe and high-quality development of sand and gravel industry under the new situation. However, problems such as inconsistent performance indicators and limited sources of machine-made sand and gravel hinder the transformation, upgrading and green development of the sand and gravel industry.
In view of the above situation, China Building Materials Federation takes the lead in organizing, and China Sandstone Association, Beijing Jianzhu University and other units are jointly responsible for revising the national standards for building sand, pebbles and gravel, further improving the quality and supply level of sand and gravel products, meeting the needs of infrastructure construction in China, and providing solid technical support for the healthy, orderly and high-quality development of the sand and gravel industry.
Second, the main revised contents of the standard
(1) GB/T 14684-2022 building sand
The new standard stipulates the classification and category, general principles, technical requirements, test methods, inspection rules, marks, storage and transportation of building sand, which is suitable for cement concrete and its products in building engineering and sand for ordinary mortar.
Combined with the demand of high performance concrete, the new standard puts forward higher requirements for Grade I sand, including the classification requirements of sieve residues, the index of flake particle content of machine-made sand and the corresponding testing methods.
Compared with version 20 1 1, the new version of the standard has been revised in terms of terms definition, general principles, technical requirements, test methods and inspection rules. The main contents are as follows:
1. Changed and added terms and definitions.
In the revision of the standard, in order to express completely, scientifically and easily understand related terms and definitions, the definitions of natural sand, machine-made sand and methylene blue (MB) values were changed, the definition and classification of mixed sand and the definition of flaky particles of machine-made sand were added.
2. The technical requirements have been revised.
In recent years, with the rapid development of sand and gravel industry and the increasingly complex sources of sand and gravel raw materials, relevant technical indicators need to be revised and adjusted in time to ensure the concrete quality of downstream products.
In the classification, the fineness modulus range of ultra-fine sand is increased, the grain grading requirements of first-class sand are changed, the technical indexes and fineness modulus requirements of sub-meter sieve residue are increased, and the technical requirements of powder content, mud content and harmful substances of machine-made sand and machine-made gravel are modified.
At the same time, in order to meet the application requirements of high performance concrete, optimize the particle shape of aggregate and improve the quality of Class I machine-made sand, the technical requirements of flake particle content are put forward. The test method is verified by the test, and the flaky particle content of Class I machine-made sand is determined to be ≤ 10% in coordination with relevant standards, and the flaky particle content of machine-made sand increases accordingly.
3. The test method of clay content is modified.
With the development and progress of concrete technology, the application of machine-made sand is more and more common. Because the silt content index of machine-made sand has been extended to the standard and detection method of natural sand, the inapplicability of this method is increasingly prominent. By improving the test method, the problem that stone powder in machine-made sand is misjudged as mud block is solved.
4. Inspection rules have been modified.
The ex-factory inspection items have been changed, the inspection items of chloride and shell content have been added for purified sea sand, and the inspection items of flake particle content have been added for Grade I machine-made sand.
In terms of batch rules, in order to adapt to the large-scale development of sand and gravel production enterprises, this revision is changed to "according to the same classification, category and daily output, the daily output does not exceed 4000t, every 2000t is a batch, and less than 2000t is also a batch; The daily output exceeds 4,000 t, and the output of continuous production is one batch every 8 hours, and that of less than 8 hours is also one batch. "
File content: GB/T14684-2011building sand.
(2) GB/T 14685-2022 "Pebbles and Gravels for Building"
The new standard stipulates the classification, general provisions, technical requirements, test methods, inspection rules, signs, storage and transportation of pebbles and gravels for construction, and is applicable to pebbles and gravels for cement concrete and its products in construction projects (except hydraulic structures). At the same time, the new standard takes into account the rational utilization of resources, and puts forward higher requirements for the particle shape of Class I coarse aggregate in combination with the demand of high performance concrete, and puts forward corresponding indicators and test methods.
Compared with the 20 1 1 version, the new version of the standard has been revised in terms of terminology definition, technical requirements and test methods. The main contents are as follows:
1. Changed and added terms and definitions.
In the revision of the standard, in order to express completely and scientifically, and to understand related terms and definitions easily, the definitions of pebbles, crushed stones and pebbles' mud content and firmness were revised, and the definitions of irregular particles and crushed stones' mud content were added.
2. The technical requirements have been revised.
In recent years, with the rapid development of sand and gravel industry and the increasingly complex sources of sand and gravel raw materials, relevant technical indicators need to be revised and adjusted in time to ensure the concrete quality of downstream products.
The standard revised the technical requirements such as particle gradation, content of crushed stone mud powder and mud, content of needle-like particles, compressive strength of rock, water absorption and alkali-aggregate reaction. The technical requirements of irregular particle content of first-class aggregate are put forward, which ensures the particle shape quality of first-class aggregate together with needle-like and flake-like particle content.
3. The test method has been modified.
In order to standardize the determination of irregular particle content, the standard adds the test method of irregular particle content. Through repeated screening of the same sample, comparative screening of different samples and screen screening of the same product from different manufacturers, the method is verified, which ensures the reliability, science and rationality of the test method.
The test method of "crushing index" is revised, and the step of "removing needle-like particles" is deleted, which reflects the real compressive capacity of crushed stone more intuitively, and the revised method is more scientific and easy to operate.
4. Inspection rules have been modified.
The provisions of ex-factory inspection items, type inspection and assembly rules were revised. Considering that the requirements for durability of concrete in engineering construction are getting higher and higher, and the sources of aggregate are becoming more and more diversified and complicated, more attention should be paid to the potential alkali-aggregate reaction, so the alkali-aggregate reaction should be changed from the original requirements to the required items for type inspection.
Third, the significance of the implementation of standards
GB/T 14684-2022 Building Sand and GB/T 14685-2022 Building Pebbles and Gravels are the key standards to guide and standardize the healthy and orderly development of China's gravel industry. The promulgation and implementation of this standard will be of great significance to the transformation and upgrading of the industry, the improvement of the quality of engineering construction and the integration with the international community.
In terms of industrial transformation and upgrading, GB/T 14684-2022 "Building Sand" increased the technical requirements and inspection methods of flake particle content of Grade I machine-made sand, optimized the particle morphology of aggregate and improved the quality of Grade I machine-made sand. In GB/T 14685-2022 "Pebbles and Crushed Stones for Building", the grain shape control index and test method are added to scientifically and accurately evaluate the product performance of concrete coarse aggregate, effectively meet the application requirements of high-performance concrete and support the high-quality development of the industry.
In terms of improving the construction quality of building engineering, GB/T 14684-2022 "Building Sand" deeply studies the influence mechanism of the potential activity of carbonate manufactured sand such as limestone and dolomite on the performance of concrete, and adds the alkali-carbonate reaction test method of manufactured sand. GB/T 14685-2022 "Pebbles and Crushed Stones for Building" moderately adjusted the technical requirements of Grade III pebbles and crushed stones, effectively ensured the stability and consistency of concrete product quality under the background of changeable lithology of coarse aggregate parent rock, and ensured the quality of construction projects.
The main technical indicators of the above two newly revised standards have been applied in many foreign engineering construction projects such as Karachi Nuclear Power Station, and have reached the international advanced level after expert review, which is of positive significance for speeding up the "going out" of China's sandstone products, technologies and equipment and building a China sandstone brand with international influence.