Tofu water source project is located in the southern oil transformation of Yumen River, is a city of water based water conservancy project. The drain sand sluice pier, floor adopting C 70 high strength and abrasion resistant concrete the about preparation of single doped with ordinary cement concrete strength up to a maximum of 350#. Provincial Hydropower Engineering Bureau of prepared C 70 high strength micro silica fume concrete, adopting the second feeding and superplasticizer compound process, the use of relatively low - grade, cement 525 # incorporation of micro silicon powder prepared ~ C70 C80. High strength concrete with anti abrasion and anti cavitation performance meets the requirements of engineering design and construction.
1 cement dosage of choice.
Through a large number of experiments, the strength of the cement is not significantly increased than m3 / 620kg. This is mainly because of the strength of concrete can not play together by cement mortar and thick bone filled, especially the effect of coarse aggregate. Cement consumption increases, which is equivalent to the increase of cement mortar, reduce the unit volume of aggregate, and the concrete strength is not high. From the destruction of concrete specimens, the full play of the concrete strength of the damage is the total shear failure, and stone damage.
Cement production of Qilian Mountains in Yongdeng cement factory 525# ordinary portland cement, the dosage of m3 / 600kg around, the most should not exceed 620kg / m3. In order to save cement to improve the concrete physical properties, the incorporation of about 15% of the micro silicon powder replacing part of the cement, ordinary portland cement dosage 5l0kg / m3.
2 water cement ratio
Preparation of C70 high strength micro silica fume concrete, water cement ratio is key parameter for concrete strength, water cement ratio is smaller with the concrete strength higher, but the construction more difficult, in order to reduce the dosage of cement and meet the construction workability requirements, usually by adding superplasticizer and micro silica powder way, both to prevent the use of superplasticizer and greatly reduce the water cement ratio, the concrete slump loss caused by large has construction of concrete with adverse and can increase the physical properties of concrete, concrete slump loss delay, water cement ratio fell to about 0.28. Here refers to the water cement ratio is a mixture of water and cement and micro silica fume quantity than actually complete hydration of cement required quantity is little. The amount of water cut is enough to meet the requirements of cement strength, and to reduce the water cement ratio of high strength concrete. Through the test and finally determine the C 70 silica fume concrete water cement ratio from 0.28 to 0.32.
3 admixture.
The principle of selecting admixture is to have a relatively high water reduction rate, the higher the degree of enhancement is not harmful elements. Through a lot of experiments, 3 kinds of high efficiency water reducer are selected from 17 kinds of water reducer. In order to ensure the quality, the UNF series of high efficiency water reducing agent is determined by the calibration test.
4 sand rate selection,
In order to reduce the impact of sand ratio on the strength of concrete, and to meet the performance of abrasive wear, the use of less sand ratio to reduce the amount of cement, to maximize the role of the coarse aggregate. The sand ratio is low, the coarse aggregate has a large area, and the concrete strength is low, and the impact resistance of the coarse aggregate is better than that of the coarse aggregate. The experimental determination, sand rate control in 28% ~ 3o% is appropriate.
Due to the coarse aggregate size to the maximum size of the different, wear rate is different, the observation of wear test after test pieces found d = 40mm under, the coarse aggregate is pulled out larger proportion, and between D=40mm of coarse aggregate by the mortar filled, taking into account the wear rate and the aggregate is pulled out of the hole size, the optimum coarse aggregate maximum particle diameter of about 25 mm). For gravel and pebbles, and the cement mortar of the bonded gravel is better than the gravel, and more suitable for the requirements of the concrete, and finally determine the use of 5 ~ 20mm limestone crushing stone as coarse aggregate, the main technical indicators see Table 1
Table 1.jpg
5 selection of feeding mode
High strength concrete cement dosage is large, the use of a feeding way prone to wet and sticky phenomenon. The two feeding method can not only solve the above problems, but also increase the strength of concrete. At present, the domestic use of the two feeding method has cement mortar, cement mortar method, etc.. Without changing the mix ratio, the order of the material is changed, and the compressive strength of the specimen can be increased by 20%. The comparison tests of mortar and net pulp method show that there are some limitations, especially in the case that the amount of cement is used more frequently. Therefore, the choice of mortar method as a way of feeding.
6 compressive strength and abrasion resistance
In order to improve the concrete impact abrasion resistance, must meet the following conditions: 1) to enhance the strength of concrete, the concrete surface evenly wear; 2) aggregate maximum particle size should be appropriate, to avoid being flow scour out the formation of large cavities; 3) mortar bond strength should be too; 4) will be greater than the area of strong wear resistance of mortar and coarse aggregate, is a reasonable choice of kinds of coarse aggregate and sand rate.
The higher the compressive strength, the lower the rate of the wear rate. General relative to the gravel concrete, the curve of the use of pebble concrete to the big side of the movement, which is due to the surface roughness, easy to wear. On the other hand, the bond between sand and gravel, the compressive strength of large, so the gravel surface is smooth and less easy to wear, but the bond strength of sand slurry and aggregate, low compressive strength, so the curve of the gravel concrete to the side of the high abrasion resistance. Adhesion of gravel and mortar is large, difficult to pull out but easy to be removed. Comprehensive consideration, even if the wear is slightly larger, compared with the gravel gravel is more suitable for high strength and wear resistant concrete. Regardless of mortar or coarse aggregate, to obtain uniform wear, the compressive strength of the C70 ~ C80MPa above
