Product description

The laboratory of Hunan Renjian Concrete Co., Ltd. is configured as a first-class laboratory in the construction industry. According to national environmental protection requirements, it has the ability to produce various specifications of commercial concrete. It can produce C10-C80 according to the requirements of customers and the relevant national technical indicators. Various grades and special commercial concrete.

Since commercial concrete is mixed in a centralized manner, the quality and mixing ratio of raw materials can be strictly controlled online, which can ensure the quality requirements of concrete; the mixture is required to have good workability, that is, high fluidity, small slump loss, no bleeding and no bleeding. Good separation and pumpability; economy, low cost and high performance-price ratio.

The choice of raw materials and requirements, and the choice of cement: usually Portland cement, ordinary silica cement or slag cement is used. The basic requirement for cement is to choose cement with a large richness coefficient when the same label is used, because cement is to make concrete gain strength The "foundation"; when the strength is the same, choose cement with a small water requirement. The standard consistency of cement requires water from 21% to 27%. When preparing concrete, using cement with a small water demand can reduce the amount of cement; choose high C3 S, low C3A (<8%), and low alkali content (<1%). Cement with moderate specific surface (3400cm2/g3600cm2/g) and good particle size distribution; use cement with different marks reasonably. When preparing fluid concrete below C30, 32.5Mpa silica salt cement is recommended; when preparing high-performance concrete above C30-C40, 42.5Mpa ordinary silica cement is recommended. 

Choose the right type of cement for concrete for different purposes. For example, if early strength or winter construction is required, use R-type Portland cement as much as possible, and use slag cement or ordinary silica cement for mass concrete. Selection of fine mineral admixtures Commonly used fine mineral admixtures include fly ash, ground slag, zeolite powder, and silica fume. The basic requirement for mineral fine admixtures when preparing commercial concrete is to fully meet the requirements of various concretes such as houses, roads, bridges, subways, dams, airports, and ports. The price is low, it has a certain hydration activity, and it can replace part of the cement. Under the condition of ensuring the strength and other properties, more mineral admixtures should be added to reduce the cost of concrete; the water demand ratio is small (<100%), Reasonable particle grading can improve the fluidity of the mixture;  Rationally use different types of fine admixtures, use Class II fly ash when preparing fluid concrete below C60, and use Class I fly ash or ground slag for C60～C80. . The choice of aggregates, both coarse and fine aggregates, should meet the requirements of relevant standards. The correct choice of aggregate can ensure the workability, strength and economy of concrete. Fine aggregate: reasonable sand particle size distribution and low mud content are beneficial to the improvement of strength and workability. The high water demand of artificial sand and weathered mountain sand, and the unreasonable particle shape and gradation reduce the fluidity of the mixture. River sand is an ideal fine aggregate, and the fineness modulus should be selected correctly when using it. Coarse sand is used when preparing high-strength concrete, and medium sand is used for ordinary fluid concrete. The fineness modulus of sand affects the sand ratio and water consumption of concrete. High sand ratio requires more water and fast slump loss. Low sand rate is prone to bleeding and segregation. Coarse aggregate: The maximum particle size and gradation of stones affect the water consumption, sand rate and workability of concrete. High-strength crushed stone should be used when preparing high-strength concrete and high-performance concrete, and its maximum particle size should be 19mm or 25mm, because the strength of high-strength concrete is almost half the strength of stone. Ordinary fluid concrete uses crushed stones with a maximum particle size of 25mm or 31.5mm. When using the pumping process, the maximum particle size of the stones should be less than one-third of the pump outlet pipe diameter, otherwise the pump will block. At present, there are few crushed stones continuously graded in the market, and most of them are single-grain grades. In this case, two graded graded stones should be used. If single-grain stones are used, the sand rate should be increased. The sand ratio of concrete is related to the maximum particle size of the stones, the sand ratio of large stones is small, and the ratio of small stones is large. Among them is the question of reasonable cooperation. When preparing fluid concrete, if a larger particle size (such as 31.5mm) of crushed stone is used in combination with medium-fine sand (Mx=2.50), the sand rate and water consumption can be reduced, thereby reducing the cost of concrete. 

Selection of admixtures The admixtures used in commercial concrete should include: air-entraining water-reducing agent, high-efficiency retarding air-entraining water-reducing agent, retarding water-reducing agent, high-efficiency retarding water-reducing agent, pumping agent, high-efficiency pumping agent, etc. . Principles for selecting admixtures:  Choose the corresponding admixture varieties according to the type of concrete prepared;  Determine the water reduction rate and the requirements of the admixture according to the concrete raw materials, mixing ratio and label;  according to the type of project, climate conditions, and transportation Factors such as distance and pumping height determine the requirements for slump loss, setting time and early strength; other special requirements (such as impermeability, frost resistance, corrosion resistance, wear resistance, etc.). Finally, the admixture can only be applied after passing the concrete test and economic evaluation.

Based on the design concept of ultra-high performance concrete (UHPC), the company has developed UHPC suitable for spraying construction and smoothing after spraying construction in accordance with the characteristics of spraying construction and trenchless repair of underground sewage structures, realizing UHPC "spraying" Draw up three goals: "Hanging" and "Good performance". We optimized the wet spraying machine, and developed a small spray construction robot arm and surface smoothing device suitable for underground pipe culvert repair, which can realize mechanized construction. The weight of the robot arm is only 800Kg, and it is convenient to hoist in and out of the pipe culvert. Constructed a 20m box culvert and arch culvert with the same size model. After more than one year of UHPC spray construction method research, the optimized combination of UHPC material, wet spraying machine and spraying manipulator was summarized, which realized the unification of mechanical spraying and surface smoothing . UHPC spray construction is fast, flexible, and seamless. The water can be passed after the plastering is completed and quickly set. It is suitable for various cross-sectional structures in the Hongqi Canal. The construction period is tight and temporary drainage may be required, which is conducive to the later construction of the project. UHPC spray construction is not only suitable for the repair of Hongqi Canal, but also has good applicability for the repair of pipe culverts, tunnels, bridges and building structures. The national patent case has been filed, the national patent case number: 11569C19FP07443UHPC.

participated in the compilation of the Local Standards and Regulations DBCJ "Construction Waste Recycled Aggregate Concrete Application Technical Guidelines" issued by the Changsha Housing and Urban-Rural Construction Bureau on 2019-11-01 and implemented on 2020-01-01. It has been repeatedly awarded by the Municipal Bureau of Quality Supervision and Concrete Association and the title of "Promise-keeping Contract Unit".