Concrete is a kind of traditional building material with excellent comprehensive performance, especially its economy, plasticity and durability. With the development of the society, profound changes have taken place in the fields of raw materials, mix proportion, production and transportation, construction technology and quality control. Pumping concrete has gradually become a common type of concrete construction. It has the construction speed, good quality, save labor, construction convenience and so on. It is widely used in general industrial and civil construction concrete, bridges, road concrete, mass concrete, high-rise building structural concrete and other projects. It can be both horizontal and vertical delivery can also be directly cast fabric. It requires concrete not only to meet the design strength, durability, etc., but also to meet the requirements of the pipeline transportation of concrete mixes, that is required concrete mix has good pumpability. In this paper, a large residential area at the junction of Shenzhen City and Dongguan City as an example, preliminary technical discussion and economic analysis on the construction of ultra-long distance concrete pumping.
First, the project instance profile
The large residential area covers an area of ​​180,000 square meters, construction area of ​​29.65 square meters. The total volume of concrete reached 96,000 cubic meters. Residential area mountain water, elegant environment, away from the urban area, like a paradise. However, at the same time, it is also far away from the existing commercial concrete mixing plant. In addition, the traffic jam on the road is often serious, and the concrete can not meet the construction and schedule requirements. Under such circumstances, the construction side, after submitting the report to the administrative authority for approval, set up a modern concrete mixing plant in the construction area and adopted the 1m3 mandatory mixing machine from Shaoguan Construction Machinery Factory and the complete set of automatic computerized batching equipment of Zhongsheng Construction Machinery Company. And supporting the establishment of a three-tier laboratory, concrete mix design and routine quality inspection.
Due to the wide construction site, the side length of 397 × 453 meters, building up to 26 as many. It consists of multiple levels (6 levels), small high level (12 levels) and high level (18 levels). Therefore, a total of two sets of HBT6016110S (A) type and Shenglong Construction Machinery HBT60S16110 (A) type of high-pressure trailing concrete pump were used and were directly pumped to the pouring site in the mixing station. The average conversion level of 757 meters, the farthest conversion level of up to 1350 meters.
Second, the choice of materials
1, cement:
A, the amount of cement: In pumping concrete, cement mortar plays the role of lubricating pipe wall and the transfer of pressure, when the amount of cement is too small, easy to work and poor resistance, resistance, easy to plugging. Excessive amount of cement, cost increases, but also not conducive to mass concrete construction, prone to temperature cracks. At the same time, too much cement, concrete viscosity increases, pumping resistance increases. "Ordinary concrete mix design rules" (JGJ55-2000) provides: In pumping concrete, the total amount of cement and mineral admixtures should not be less than 300 kg / cubic meter.
B, cement varieties: concrete varieties have a certain impact on the pumpability. Due to the poor water retention of slag cement, bleeding, the project pumping distance, it is not used. It is proposed to use ordinary ordinary Portland cement. After the procurement department of the market price of the market survey, the final decision to use Hongshuihe 42.5R bulk cement.
2, Sand: It uses medium sand mined in the nearby riverway, the content of which is not more than 3%, the content of chloride ion is not more than 0.02%, and the sieve residue of 0.315% mm is not less than 16%.
3, gravel: the use of the adjacent urban construction group stone quarry mining nominal size of 16-31.5mm stones, clay content of not more than 1%.
4, fly ash: Huangpu Power Plant using wind election two fly ash, fineness (0.045mm square hole sieve more than) not more than 20%, loss on ignition less than 8%.
5, pumping agent: building treasure JZB-3-type superplasticizer. Solid content of 40%, Na2SO4 <3.0%, water reduction rate ≥ 18, and with Hongshuihe 42.5R cement has good compatibility.
6, water: using tap water.
Third, concrete mix design
1, concrete requirements: the strength of various labels, from C20-C40; durability, to ensure the life of the building more than 70 years; high mobility, you can adapt to ultra-long-distance pumping; high workability, that is, easy construction, easy Operation, after mechanical vibration to achieve a higher density.
2, with the design of concrete laboratory Concrete construction experience obtained from the past in the transport pipe when the slump loss according to the length of the pipe up to 10% -30%; based on the mix of concrete design principles and strength standards control value , The factory slump was initially set at 200-220mm, the slump of the delivery pipe outlet was initially set at 140-160mm, and the amount of concrete material used per cubic meter was as follows:
After pouring again test, the construction mix in the pipe outlet slump basically remained between 140-160mm, can better meet the construction requirements. Test specimens left on-site according to the provisions of pressure test, have reached the eligibility criteria.
Fourth, concrete pumping construction Concrete pumping construction, the unreasonable placement of concrete pumps, unscientific cloth pipe, and not strict construction operations, will result in a lot of waste and unnecessary losses. Therefore, reasonable and scientific on-site construction is very necessary.
1, reasonable placement of concrete pump. Under normal circumstances, if the site conditions permit, the concrete pump should be placed in the middle of the building or the surrounding location, so that during construction can reduce the pipe length, shorten the concrete pumping stroke, saving manpower and time. In addition, the larger concrete pump power, we must ensure adequate electricity, reliable grounding. Pump installed stable, solid ground smooth.
2, reasonable cloth tube. Correct cloth is to ensure the smooth operation of the necessary conditions for pumping, should pay attention to the following points in the layout:
a) Conduct plumbing design carefully before construction, draw sketch of piping, list specifications of various fittings, connectors and fittings, and put forward a list.
b) As far as possible to choose the shortest distance to arrange the pipeline, if necessary, can cross or pass the obstacle to overcome the obstacles to be raised when the pipeline should be set at the highest point of the release valve.
c) In the same pipe as much as possible to keep the concrete section unchanged, try not to use tapered pipe or elbow.
d) vertical upward piping, it is appropriate to use the ground horizontal pipe length of not less than 1/4 of the vertical length, generally not less than 15m, and should be set at the concrete pump outlet 3m-6m at the root of the pipeline to set the cut-off valve to prevent concrete mixing Compound flow backwards.
e) When the piping is inclined downwards, the air valve should be set on the upper end of the inclined tube, and the air valve can be put into the air if necessary to balance the pressure in the tube. The bottom of the down-inclined tube shall have horizontal piping of sufficient length to enhance the resistance to possible drop of concrete due to its own weight and avoid creating vacuum in the piping.
f) Piping should be placed in the beginning of the new pipe section, because the pressure is relatively high. After long-term use of the pump tube wear larger, do not configure this type of tube in the pump pressure larger range of unacceptable old tube can not be used.
g) Piping can not be affixed to the layout, it should be set up at both ends of the pipe branch å—– Publish media æ—¨ С С??? 白 白 白 白 白 è‹¡ è‹¡ 没 milk æ½ è‹¡ 凉?
h) The south is hot in summer. During construction, the pipe should also be covered with sacks or straw mats and wet with cold water to prevent the concrete slump loss under high temperature from causing blockage.
3, concrete pumping. Pumping process, the pipeline installation is completed check is correct, the pump check the power and the pump control section are in normal condition, before starting the air to run.
a) After the idling is normal, pump the appropriate amount of water, wet concrete hoppers, pistons, and the inner wall of the delivery pipe directly to the site of concrete contact.
b) After confirming that there is no foreign matter in the pipe by pump water, it should pump cement mortar with the same composition as mortar in concrete without too much mortar to lubricate the whole pipe.
c) After the mortar has been pumped, the concrete should be immediately pumped until it reaches the concrete end of the pipe.
d) When pumping, the concrete pump should be slow, uniform and ready to reflect the state of the pump. Pump speed should be slow first, and gradually accelerated. At the same time should observe the pressure of concrete pumps and the work of the system. After the system is running smoothly, it can pump at normal speed.
e) Concrete pumping should be carried out continuously.
f) In the pumping process, should keep the concrete pump hopper in the amount of concrete not less than the suction port, or may be caused by inhalation of air at the outlet caused by splashing concrete injury.
g) When the duct is clogged and can not be pumped, the following measures should be taken to eliminate:
a. Repeat the positive pump and the reverse pump, and gradually loosen the concrete in the plugged parts to achieve pumpability.
b. With a wooden hammer percussion, make it loose, and then positive and negative pump operation, remove the blockage. When the above two methods are invalid, should first anti-pressure pump twice, and then open the pipe, remove the clogging, tighten the joint before re-pumping.
h) After the pumping, the concrete pipe and hopper should be cleaned. Finally, the work of concrete pump should reach the stop position than that of longitudinal rod. Turn off the main power, and the pump can not leave until it is locked.
Fifth, quality assurance measures
(1) accurate measurement: In the process of quality control of concrete, accurate measurement is the most important. Especially the amount of water, we must deduct the sand, stone moisture content, water-cement ratio error is less than%.
(2) Clear beams, pillars, foundation and water in the pit: water is usually easy to be poured on the above parts after the work such as washing steel bar, wetting the template or after rain, and when the concrete flows to the place Due to the local water-cement ratio is too large and there is a sharp drop in intensity, not too deep is more likely to appear segregation washing phenomenon, which led to the sand layer, sandstone, so water must be cleaned.
(3) to prevent leakage of slurry: Due to the large flow of concrete, when the template has more than 2cm2 after the hole, can easily lead to leakage. Leakage will make the concrete honeycomb, Ma face, strict winners caused by local loose, resulting in loss of strength, must be destroyed and re-pouring.
(4) Preventing excessively thick slurry: The way and timing of mechanical vibration shall be carried out according to the specific provisions of the construction manual. When pillars, large-volume foundation and girders are to be cast, rubble (clean) shall be sprinkled at the end of construction Balanced orthopedic content. When the floating slurry of water, should also be appropriate to join the same amount with the same brand of cement to improve water-cement ratio. When the floating pulp is too thick, it should be removed before the next procedure.
(5) to strengthen conservation due to the incorporation of fly ash and plasticizers, it must strengthen conservation. In particular, pouring molding should be kept within 14 days after the wet state, so that fly ash and Ca (OH) 2 chemical reaction, the formation of gelling components, thereby enhancing the strength of concrete.
Six, economic analysis
Seven, conclusion
The quality of concrete is composed of many aspects, from the production, transportation, pouring, vibration, conservation, each process will have a direct impact on it. Therefore, we should strengthen control. However, improvements and innovations in conveying technology, such as ultra-long-distance concrete pumping construction technology, are technically feasible. Economically, energy consumption can be reduced and labor and machinery investment can be reduced, thereby saving costs and increasing power.
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