The dosage of rust inhibitors varies depending on their type and rust inhibitor effect requirements. In engineering applications, it is generally determined through the manufacturer's recommended dosage and field tests. This article gives the dosage range of R I type rust inhibitor and calcium nitrite rust inhibitor with a concentration of 30%, so as to provide reference values for engineering and technical personnel who have not used rust inhibitors.
The dosage of R I type rust inhibitor depends on the amount of corrosive medium entering the cement concrete within the design life. When chlorine salt is the main component, from the research and test results, R I/C l- ≥ 018, has significant rust-inhibiting effect, R I/C l- ≥110, and can keep steel bars from rusting for a long time. For safer and more reliable calculations, use R I/C l- ≥ 112; for aqueous formulations, R I/C l- ≥ 310; when the amount of chlorine salt entering the cement concrete during the design basis period is unclear, Table 4 can be used Select the dosage of rust inhibitor. It should be noted: R I-1N type rust inhibitor contains Na+ and K+. Use with caution when containing (or containing) alkali aggregate. The recommended dosage of calcium nitrite rust inhibitor solution with a concentration of 30% can be selected according to Table 5.
Technical control indicators
Technical requirements for cement concrete quality
Cement concrete mixed with rust inhibitors generally requires an impermeability grade of not less than S 8; The 28 d shrinkage strain should not be greater than 1×10-4; for components located in the splash zone of bridges in southern seawater, due to the higher temperatures and longer duration in the south, the steel bars will corrode faster and more seriously, requiring chloride ions to be incorporated into the cement concrete of these components The permeability in the product should not be greater than 2 000 C.
Domestic and foreign research and engineering practice have shown that adding rust inhibitors and active ultra-fine mineral admixtures at the same time, such as fly ash, silica fume, ground slag, etc., can achieve better anti-rust effects. Obviously, the reason is that in addition to the certain rust-inhibiting effect of rust inhibitors, active mineral admixtures are beneficial to improving the compactness of concrete and can enhance the ability of concrete structures to resist erosion by external corrosive media. Please refer to Table 6 for the mixing method and appropriate dosage of admixtures. Among them, adding fly ash has the best effect on reducing deformation and improving crack resistance, while adding silica fume and finely ground slag can both increase dry shrinkage. Silica fume also increases its own volume shrinkage, so attention should be paid to strengthening maintenance during construction.
The frost resistance grade of prestressed concrete and reinforced concrete in seawater environment, the maximum water-cement ratio, the minimum cement dosage and the minimum strength grade, etc.
All affect the anti-corrosion durability of the structure. Important factors should be strictly controlled to meet the requirements of Table 7.
Adding rust inhibitors to concrete mixtures will affect the performance of the concrete.
The resistance to chloride ion permeability of cement concrete mixed with rust inhibitors is the most important indicator. It affects the migration speed of chloride ions in cement concrete, which in turn affects the time when steel bars begin to rust to a great extent. and rate. Compared with the reference sample without rust inhibitor, the reduction in compressive strength is allowed to be reduced by 10%, but this reduction must be supplemented by using high-efficiency water reducing agents to reduce water consumption; when rust inhibitors are used alone, cement concrete The compressive strength must be sufficient and must meet the requirements in Table 7 after hardening. The setting time of cement concrete mixed with rust inhibitors can be adjusted by adding a retarder or accelerator.
Technical requirements for cement concrete structure construction
The minimum protective layer thickness of prestressed concrete and reinforced concrete in seawater environment is an important indicator to ensure the anti-corrosion durability of the structure.
Other technical requirements
The construction joints of concrete mixed with rust inhibitors should not be located in the splash zone or water level change zone; cement concrete pouring should be continuous and uniformity and compactness should be ensured , there should be no exposed tendons, voids, cold joints, slag inclusions, loose roofs, etc.; Cement concrete maintenance should generally use fresh water, and prestressed structures should not use seawater for maintenance. When there is a lack of fresh water, they should be wrapped in plastic film or sprayed with health care agents for moisture maintenance. The time should not be less than 21 days; exposed reinforcement is the entry channel provided by the structure for chloride ions, which will accelerate corrosion. Therefore, the formwork of cement concrete structures in a corrosive environment should be externally fixed or suspended formwork erection, and shall not be removed from the structure. After the lead-out steel bars are erected and fixed, and after the formwork is removed, bolts, steel bars, tie rods, nails, and embedded parts shall not be exposed on the surface of the structure. </p
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