Abstract : The production of ultra-low prestressed concrete curved beam with 32m post-tensioned ultra-low prestressed concrete is the most difficult to manufacture. The C65 high-strength concrete has high modulus of elasticity and the concrete is cross-cast with steel fiber reinforced concrete. The 200m long distance pump give away. Key words : Jiaozhou-Xinyu railway; ultra-low height beam; high-strength concrete; steel fiber concrete; pumping concrete; construction technology Railway cross-line lots and plains river network area need low building height, simple construction, low cost and high cost of the beam, the beam can greatly reduce the embankment height, significant economic benefits. 32m ultra-low height curve beam, concrete design strength grade C65, the amount of cement, the initial setting time is short, requiring the construction schedule must be accelerated to shorten the construction cycle. By pumping fluid concrete, so that the steel-intensive, difficult to cut the problem has been well resolved. When the ultra-low height beam is tensioned, excessive tensile stress will be generated on the upper edge of the concrete to resist the pre-stress of the anchoring stage of the transmission force, and a small amount of steel fiber will be added to increase the cracking resistance of the concrete. High-strength concrete and steel fiber concrete cross construction, increasing the difficulty of pouring. The preparation of high-strength concrete, raw material selection is the most important, followed by mix design, construction control, the three interrelated, mutual constraints, only carefully designed, well-organized, in order to produce high quality beam. 2 raw material selection (1) cement selection The preparation of high-strength concrete, should use high-strength grade cement in order to control the amount of cement to avoid the drawbacks caused by excessive use of cement. After comparison, C65 concrete is prepared with 52.5 grade cement to fully meet the requirements of the specification. Specifically, the first two beams use Gezhouba Cement Plant's low heat 52.5-dam cement produced by the Three Gorges Project. The cement features: small heat of hydration, slow temperature rise, low early strength, high late strength and long stretch time. However, due to its long cementing distance and difficult supply, the strength development is too slow to affect pedestal turnover. After a variety of factors analysis, switch to Shandong Cement Factory production "Wuyue" 52.5 cement. The early strength of the cement, hydration heat larger, faster setting time, initial setting 1.5h. Therefore, pouring, should take measures to make concrete initial setting time in more than 3h. (2) admixture Because "Prefabricated post-tensioned prestressed concrete railway bridge simply supported beams" (GB7418-87) does not specify allowable admixture, and the relevant technical documents have not stated, due to than, in the selection of materials not be considered. (3) fine aggregate The preparation of high strength concrete sand, mainly to meet the following technical indicators: ①sand must be non-alkali active material; ② sand fineness modulus 310 ~ 312, the sand hardness is high, gradation curve is reasonable; ③ clay content of less than 1% Block; ④ sand sturdy meet the specifications. After testing Dagu River before Zhu sand, to meet the above critical requirements. (4) coarse aggregate In the 120km radius of Jiaozhou Liangchang area, there are 3 producing areas of gravel suitable for the preparation of high strength concrete. After investigation, 120m away from the Mianhu gravel, the parent rock is limestone, the compressive strength of 142MPa, and the concrete strength ratio More than 210 times, in line with regulatory requirements. The production process is hammer crushing, rolling sieve grading, 5 ~ 20mm grading is good, needle flake, crush index values ​​meet the specifications, preparation of C65 concrete gravel. Before preparation, all with a forced mixer stirring, rinse to completely remove the mud and stone powder. (5) water Mixing, curing water are used drinking water. (6) superplasticizer Preparation of high-strength concrete, superplasticizer selection is the key technology. After a number of well-known manufacturers screening, analysis, Zibo NOF-1A affordable, small bleeding, was selected as beam superplasticizer. 3 mix design (1) 32m ultra-low profile girder body concrete mix design Concrete strength grade C65, elastic modulus ≥ 3170 × 104MPa, slump requirements of about 160mm. The test strength of concrete shall be in accordance with Table 5.8.4 of "Code for Construction of Railway Concrete and Masonry" (TB10210-2001). Because of the new beam field, there is no statistical data. The standard deviation δ of concrete strength is 510MPa when the concrete strength level is greater than C40, and the calculated strength of concrete preparation is 73.2MPa. Cement activity guaranteed by the value of 52.5MPa calculated to ensure the guarantee rate. The water-cement ratio was calculated to be 0.322 using the linear relationship between water-cement ratio and strength. As the total amount of aggregate aggregate changes in a very small range, high-strength concrete, high elastic modulus concrete gravel dosage range is more limited, usually 1100 ~ 1180kg / m3, directly set the amount of coarse aggregate per m3 of concrete, and then adjust Sand rate. The proportion of the gravel to take 1140kg / m3. According to "Design Specification for Ordinary Concrete Mixing Proportion" (JJG55-2000), the maximum cement content of high-strength concrete should not exceed 550kg, and the maximum water consumption is calculated as 550 × 01322 = 177kg. The optimum dosage of admixture is 018% ~ 110%, the dosage of admixture is 019%, according to the assumed bulk density method, the initial compounding ratio is calculated. Assuming a bulk density of 2465kg / m3, the mixing ratio of C65 concrete per m3 is: Cement: Sand: Gravel: Water: admixture = 550:593:1140:177:4195. Test mix results: when the water consumption of 172kg, slump reached 175mm, according to the slump decreased 10mm, the amount of water increase or decrease 215kg calculation, the actual water consumption should be 169kg / m3, the amount of cement should be 169 ÷ 01322 = 525kg, Using a fixed water method. Respectively, select the amount of cement 520,530,540,550 corresponding water-cement ratio: 01325,01319,01313,01307, respectively, to calculate the mix ratio, and the trial mix adjustment, using the absolute volume method to calculate the amount of unilateral material, 7d and 28d intensity R) and elastic modulus (E) in Table 1. Table 1 concrete strength and elastic modulus (2) C65 bridge deck steel fiber concrete mix design The design strength of steel fiber reinforced concrete grade C65, the design modulus of elasticity 3170 × 104MPa, its main purpose is to resist tensile stress suffered by the bridge deck. The strength of steel fiber reinforced concrete is the same as that of concrete. Under the same condition of water-cement ratio, the compressive strength of steel fiber reinforced concrete is 10% higher than ordinary concrete, but 10% more for cement. Therefore, the amount of cement and beam concrete water-reducing admixture is still 0.9%. The content of steel fiber in concrete accounts for 1.3% ~ 2.0% of the volume of concrete, and the purpose of incorporation is to increase the crack resistance. To ensure the elastic modulus to meet the design requirements, it is necessary to reduce the sand rate, the sand rate decreases, the steel fiber dosage is small, combined with the actual mixing, the amount of cement per plate 200kg, steel fiber bag 20kg, when adding 40kg steel Fiber, the amount of steel fiber per cubic meter of concrete 108kg, exactly 2 bags per plate, easy construction, steel fiber volume ratio of 114%, within the specified range. Calculate the amount of steel fiber reinforced concrete with the amount of cement with the same amount of concrete beam, steel fiber reinforced concrete compressive strength at 10% higher than ordinary concrete, therefore, water-cement ratio allowed to increase 5%. Water consumption can be adjusted within 169 ~ 177kg (Table 2). Table 2 steel fiber concrete mix design according to sand rate decreasing hair test mix adjustment results 4 construction control (1) The construction of detailed rules to ensure the construction quality of beam concrete, with a reasonable theoretical mix is ​​the premise that qualified raw materials is the key to construction control is also crucial, which is even more important for high-strength concrete. In accordance with the method of total quality management, the reasons were analyzed, the countermeasures were taken, the procedures for strengthening the inspection of raw materials, concrete mixing, pouring, vibrating, curing and dismantling of molds were strictly regulated in accordance with the regulations and carried out before the construction Pre-job training. (2) Accurate measurement of concrete mixing is to ensure the quality of concrete mixing the fundamental, therefore, developed a strict quality management system. The first few dishes, check the measuring instruments show the value of disk, so that it remains accurate. Feeding all automation, accuracy control within the allowable range of the specification. (3) pouring and pouring Pumping construction, the first pouring finished beam body, and then pouring deck steel fiber concrete, pouring two concrete intervals of about 3.5h. First select the construction of low-temperature at night, followed by mixing amount of retarder, the initial setting time extended to 4h above. Feed slump 160mm, conveying 200m distance, storage slump of 130 ~ 140mm, pump pressure below 28MPa, pumpability is better. (4) steam curing requirements After pouring concrete, the static stop 6h, heating rate 5 ℃ / h, rose to 45 ℃ constant temperature, constant temperature 24h, pressure test, when the intensity of 53.5MPa, stop steam, cooling, cooling rate 5 ℃ / h, about 6h. (5) The initial tensile strength and ultimate tensile strength of concrete can reach 53.5MPa, and the initial tensioning can be carried out. The compressive strength and elastic modulus of concrete at 15 ~ 20d are tested. When the strength reaches 68.5 MPa or more and the elastic modulus reaches 3.70 × 104 MPa or more, the final pull is performed. 5 experience (1) In order to ensure that the compressive strength and elastic modulus of high strength concrete beam meet the design requirements, it is feasible to design the concrete mixture ratio method by using the maximum amount of stones. (2) Steel fiber reinforced concrete to meet the design requirements of strength and elastic modulus, breaking the conventional steel fiber reinforced concrete sand rate of 50% to 60% of the restrictions, the sand rate down to 46%, to ensure the strength and elasticity of steel fiber reinforced concrete Modulus, broaden the application of steel fiber concrete. (3) In the condition of low sand rate, the steel fiber reinforced concrete has been successfully pumped 200m long and has access to information without any precedent to achieve a technological breakthrough. references: [1] Zhu Qingjiang editor. High strength and high performance concrete research and application. Beijing: China Building Materials Industry Press, 1999.
For a mineral Beneficiation Plant, there are still some percentage which are not liberating the ore thoroughly, so it's necessary to separate them and send to Ball Mill for regrinding, both Spiral Classifier and hydro-cyclone are here to achieve the function of mineral classifying, spiral classifier is used to separate the ore and gangue with overflow method, the fine particles will overflow the spiral classifier meanwhile the gangue sets at the bottom of the spiral classifier, and will move upwards to the higher end, finally will be sent back to ball mill, and the hydro-cyclone is to separate the two parts by gravity difference.both of them are commonly used for mineral beneficiation plant, for example, gold ore processing plant, copper ore processing plant, zinc ore processing plant, lead ore processing plant, graphite processing plant, iron ore processing plant, and so on.
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1 Overview Serial number Cement / kg Sand / kg Stone / kg Water / kg Water reducer / kg Gray water ratio Water-cement ratio R7 / MPa E7 / MPa R28 / MPa E28 / MPa 1 520 640 1140 169 4.68 3.077 0.325 54.6 3.45x104 65.8 3.65x104 2 530 630 1140 169 4.77 3.136 0.319 56.4 3.50x104 68.7 3.74x104 3 540 621 1140 169 4.86 3.195 0.313 58.8 3.61x104 74.2 3.98x104 4 550 611 1140 169 4.95 3.254 0.307 59.6 3.60x104 74.8 3.91x104
Table 1 shows that when the amount of cement reached 550kg / m3, the strength and modulus of elasticity no longer proportional increase; No. 3 C65 beam concrete is reasonable and reasonable. Serial number Sand rate
/% cement
/ kg Sand / kg Stone / kg Water / kg Steel fiber / kg Admixture / kg Slump / mm Workability R28 / MPa E28 / MPa 1 36 540 621 1100 169 108 4.86 120 Bleeding 68.8 3.81x104 2 41 540 706 1015 172 108 4.86 140 Poor cohesion 76.3 3.86x104 3 46 540 792 929 172 108 4.86 160 Good cohesion 74.1 3.87x104 4 51 540 878 843 172 108 4.86 170 Good cohesion 69.5 3.67x104
After analysis and test results, using the 3rd mix, concrete strength, elastic modulus, slump meet the design requirements.
[2] Yong edited. Design and construction of special concrete. Beijing: China Building Industry Press, 1993.
/%cement
/ kg sand / kg stone / kg water / kg steel fiber / kg admixture / kg slump / mm workability R28 / MPaE28 / MPa.86120 bleeding 68.83.81x104.86140 poor cohesion 76.33.86x104 1084.86160 Good cohesion 74.1 3.87x104 4.86170 Good cohesion 69.5 3.67x104
