A residential building project in Songbei District, Harbin, with a construction area of 27,000 square meters, 25 floors and 2 underground floors. The circumference of concrete external wall is 312m, and the wall thickness is 0.35m.. The basement waterproofing design adopts structural self-waterproofing, and SBS modified drainage waterproofing membrane is attached. Because of the high groundwater level in Songbei area, there is a requirement for the impermeability of concrete. Therefore, every working procedure must be strictly controlled in the construction process to ensure the impermeability of concrete.
Measures to improve impermeability of 1 concrete.
Improve the impermeability of waterproof concrete. First of all, measures should be taken to control the technical parameters of concrete mixture ratio. By reasonably selecting and controlling water-cement ratio, cement dosage, sand ratio and lime-sand ratio, and adding appropriate additives, the structural properties of concrete are improved to improve its impermeability. Secondly, through reasonable construction technical measures, the compactness of concrete can be improved and the generation and development of concrete cracks can be controlled.
2. Key analysis of construction.
Because of the high groundwater level in Songbei area, the impermeability of concrete is strictly required. When the wall formwork is installed and reinforced, the key parts of concrete that are easy to leak are the treatment of pull bolts, the position of construction joints and the treatment of post-pouring belt. If these key nodes and other parts are not handled properly during construction, the impermeability of concrete may be poor and water seepage may occur. In severe cases, piping will occur, which will affect the normal use function. Must be strictly controlled to prevent water seepage quality problems.
3 Selection of materials and tools
① cement. P.P42.5R ordinary portland cement, it is forbidden to use expired, wet and deteriorated cement; ② Coarse aggregate. 5-3 1.5mm continuous graded gravel, the maximum particle size should not be greater than 40mm, the silt content should not be greater than 1%, and the water absorption should not be greater than1.5%; ③ Fine aggregate. Appropriate use of medium sand, silt content shall not be greater than 3%; (4) mixing water. Drinking water or natural clean water; ⑤ Fly ash. First-class fine fly ash; ⑥ additives. SDB- 1 pumping agent and UEA-S micro-expansive agent are used, and their performance should meet the relevant requirements of the industry standard "concrete expansive agent", and their mixing performance should meet the design requirements and relevant regulations. When mixed with SDB- 1 pumping agent, it should be used after trial mixing. SDB-20 antifreeze is used for post-cast strip. ⑦ Main machines and tools. Concrete pump, vibrator, chute, bucket string, iron plate, shovel, bucket, etc.
4 Mix proportion design
In the construction mixture ratio, the strength grade of impervious concrete for basement exterior wall is C50P8, and the post-pouring zone is C55P 10, both of which are ready-mixed pumping concrete with slump of180 30 mm. ..
The mixing ratio of C50P8 is: cement 400kg, sand 652kg, crushed stone114kg, fly ash 95kg, SDB 14.2kg, UEA-S33.4kg, water 160kg.
The mixing ratio of C55P 10 is 420kg cement, 692kg sand, 90kg crushed stone 1223kg fly ash, SDB 16.3kg UEA-53.4kg water, and the water-cement ratio is 0.27.
5 operating conditions
5. 1 steel bar and formwork construction is completed, and the concealed inspection and preview formalities shall be handled. Pay attention to check that when the iron wire and bolt fixing the formwork pass through the concrete wall, water stop measures should be taken. Especially whether the pipes or embedded parts have been waterproof. The wooden formwork should be watered and wetted in advance, and the sundries falling in the formwork should be cleaned up.
5.2 According to the construction plan, make technical disclosure.
5.3 The materials were tested, and the concrete mixture ratio was put forward by the laboratory test, and the impermeability grade of the test was increased by 0.2MPa according to the design requirements.
5.4 Due to the high underground water level, dewatering and drainage should be continued during the construction of underground waterproof project, so as not to affect the project quality.
6 operation flow
Process preparation → transportation → concrete pouring → maintenance.
7 Construction technical measures
7. 1 The longitudinal and transverse reinforcement of the slab wall shall be firmly bound at each point. And set up Rachel reinforcement to prevent the fastening buckle from loosening and the reinforcement from shifting when vibrating, which will cause the reinforcement to be exposed. When binding transverse steel bars, the ends of binding wires should be bent inward. It is forbidden to form concrete leakage channels between binding wires and wall Rachel corner formwork.
7.2 The formwork adopts large steel formwork, and the preset bolts pass through the wall. Weld the steel sleeve three times (once in the middle and once at the end of the road 3cm inward). Both sides of the joint are fully welded with steel plate water stop rings with a diameter of 90mm, and the weld is full. The flat-fell seam of the template is blocked with asbestos strips to prevent slurry leakage. Before installation, the formwork shall be coated with release agent and fully wetted. Formwork should be firmly supported. It is forbidden to use templates, so as not to affect the compactness of concrete. The formwork can only be removed when the strength of the mixed soil specimen under the same conditions reaches more than 75% of the design strength. When the formwork is dismantled, it shall be dismantled together with the stow-wood, and the opposite bolt shall be pulled out. After the casing is grooved and the stow-wood is watered, it shall be sealed and compacted with expansive cement mortar, smoothed, calendered and watered for maintenance.
Concrete pouring: it should be poured continuously, leaving no or less construction joints.
7.3 According to the design requirements, the bottom plate should not be left with construction joints or on the post-cast strip.
7.4 Concrete pouring and vibrating. Before pouring, the water, lead wire, sawdust and other sundries in the formwork should be removed. The external wall concrete is poured into the formwork by chute, and the concrete is gradually advanced from one side. The thickness of each pouring is about 0.4m, and it will be vibrated evenly on the concrete slope and poured to the top. The moving distance of concrete vibrating is not more than 1.5 times of the action radius of vibrating rod. When operating the vibrator, plug it in quickly and pull it out slowly. For reinforced areas, the maximum particle size of coarse aggregate should not exceed.
7.5 Treatment of construction joints. According to the design of this project, 800mm wide post-pouring belt is set in the middle of the building, and construction joints are set between the floor, roof and wall. The horizontal construction joint of the wall should be left on the wall not less than 200mm from the bottom. In the hole position of the wall, the construction joint should not be less than 300mm from the edge of the hole. Construction joints should adopt convex joints (wall thickness greater than 30cm) or stepped joints, straight joints and metal water stops (wall thickness less than 30cm). Tongue-and-groove joints are used for construction joints, and B.W waterstop is used for vertical construction joints, combined with post-pouring zone and deformation joints.
7.6 After the final set of concrete, it shall be cured with water for no less than 14d. After the final set of concrete, the horizontal plane should be cured with water immediately. Immediately after form removal, spray the curing mold for curing. When the average temperature of the day is below 5℃, don't water it. According to the construction progress, the construction time of basement exterior wall slab (except post-pouring belt) is autumn, the temperature is about 20℃, and the humidity is nearly 90%, which is equivalent to the standard maintenance condition, creating favorable conditions for reducing temperature cracks.
7.7 During the basement construction, it is necessary to continuously reduce the underground water level to a safe level to avoid quality accidents such as water leakage at the initial stage of concrete pouring due to excessive underground water pressure, thus affecting the whole project quality.
7.8 Protection of waterproof concrete. After spraying curing film on the concrete surface for 2 days, SBS waterproofing membrane shall be constructed, and the foundation pit shall be backfilled in time to prevent the strength, growth and quality of concrete from being affected by external temperature difference and foreign body collision.
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