The slump of underwater concrete is strictly controlled, mostly between 180 ~ 220 mm, and the concrete can't separate and bleed. Interchangeability is important. The dosage of cement is slightly higher than that of ordinary concrete. There is special underwater concrete. See the construction manual for construction specifications.
Ordinary concrete: cement concrete with dry density of 2000 ~ 2800kg/m3, generally using No.325 or No.425 cement, with strength grade of C 10~C60 ~ C60 and slump of 90 ~ 240 mm.. Widely used in civil engineering, municipal engineering, etc.
Construction technology of underwater concrete engineering
1. Construction preparation
1. 1 material
1. 1. 1 cement: 425# or 225# ordinary portland cement shall be used, with factory certificate and passed the test.
1. 1.2 sand: medium sand or coarse sand, with silt content not more than 3%.
1. 1.3 crushed stone: particle size 10 ~ 40mm, and silt content is not more than 2%.
1.2 condition
1.2. 1 Construction machinery and equipment must meet the following requirements:
There are at least two 1.2. 1. 1 concrete mixers.
1.2. 1.2 conduit matching shall not be less than the required number of cast-in-place piles.
1.2. 1.3 at least one 75W generator shall be configured according to the on-site electricity consumption for emergency power failure when pouring concrete.
1.2.2 The inventory of concrete materials on site must meet the construction needs. Underwater concrete shall not be poured under the condition of insufficient materials.
2. Operation process
2. 1 underwater concrete mixture shall meet the following requirements:
2. 1. 1 Small water pouring concrete must have good workability. The mixture ratio should be determined through experiments, the slump should be 160 ~ 220 mm, the cement dosage per cubic meter of concrete should be not less than 360kg, and the cement grade should be not less than 425#.
2. 1.2 In order to prevent the flange from hanging on the reinforcing cage when the conduit is hoisted, effective measures can be taken, such as setting a conical protective cover or welding triangular stiffening plates.
2.2.3 Before using the conduit, pressure test shall be conducted, with the pressure generally being 0.6 ~ 1 MPa, and whether the concrete waterproof ball plug can pass shall be tested.
2.2.4 The threaded conduit shall be used with care, and it shall not collide with the thread of the conduit interface or squeeze the nozzle during transportation and stacking. Clean the conduit immediately after each use of pouring concrete. Oil the threads of the conduit side interface in time to prevent rust.
2.3 pouring underwater concrete shall comply with the following provisions:
2.3. 1 When pouring begins, the hoisting position of precast concrete waterproof ball plug should be close to the water surface, and the distance from the bottom of the conduit to the bottom of the hole should be 0.5m. After the plug is drained, the catheter shall not be inserted back into the bottom of the hole.
2.3.2 Before pouring begins, there must be enough concrete storage in the storage hopper, so that the bottom of the conduit can be buried in underwater concrete at one time, and the depth is more than 0.8m.
2.3.3 With the rise of concrete, the conduit should be lifted and removed appropriately. Generally, the bottom of the conduit should be buried 2 ~ 4m below the concrete surface, not more than 6m and not less than1m.. It is forbidden to lift the bottom of the conduit out of the concrete surface.
2.3.4 In the process of underwater concrete pouring, there should be a special person to measure the buried depth of the conduit and fill in the underwater concrete pouring record.
2.3.5 When a complete set of retaining wall grab piles are used to pour concrete, not only the conduit but also the liners should be lifted and removed in time, and the bottom of the liners should be no more than 6m and less than 1m below the concrete surface.
2.3.6 Underwater concrete pouring shall be carried out continuously without interruption. Therefore, there should be strict construction organization design and auxiliary facilities before pouring. In case of machine failure, power failure, water cut-off, pipe blockage, water inflow and other accidents, effective measures should be taken immediately to deal with them, and records should be made at the same time.
2.3.7 When lifting the conduit, avoid touching the reinforcing cage. When the concrete surface is close to the bottom of the reinforced cage, the buried pipe of the conduit should be strictly controlled not to be too deep. When the concrete surface rises to the inside of the reinforcing cage for 3 ~ 4m, the conduit shall be lifted so that the bottom of the conduit is higher than the bottom of the reinforcing cage to prevent the reinforcing cage from floating. In addition, a cross-shaped steel bar should be welded on the stiffening hoop at the bottom of the full set of retaining wall grab pile reinforcement cage.
2.4 The pouring amount of concrete for the last time should be controlled so as not to make the pile top too high or too low. Generally, it should be controlled at about 0.8m above the designed pile top elevation.
2.5 When pouring concrete into the pile body, the test blocks retained by each pile shall depend on the concrete quantity of the pile body, but not less than one group.
3. Quality standards
3. 1 guaranteed project
3. 1. 1 cement, water, aggregate, additives, etc. When used in underwater concrete engineering, the compressive strength of concrete must meet the design requirements and construction specifications.
3. 1.2 The mixture ratio, raw material measurement and mixing of underwater concrete must comply with the provisions of construction specifications.
3. 1.3 After hole cleaning, the specific gravity of mud at the bottom of the hole and the thickness of sediment must comply with the provisions of construction specifications.
3.2 Inspection and evaluation criteria (allowable deviation)
In addition to the height of laitance specified in the design, the allowable deviation of grouting elevation is +200mm.
4. Construction considerations
4. 1 Avoid common faults in engineering quality
4. 1. 1 waterproof ball plugs shall be made in strict accordance with the specified dimensions. Every time the waterproof ball plug is placed, it is necessary to test whether it can pass through the catheter smoothly. Do not use unqualified waterproof ball plugs.
4. 1.2 The inner wall of the conduit dismantled during grouting shall be cleaned in time to prevent the cement mortar remaining on the inner wall of the civil pipeline from condensation and hinder the smooth passage of the waterproof ball plug.
4. 1.3 It is necessary to ensure that the bottom of the conduit is buried in the underwater concrete to a depth of more than 0.8m during the first pouring. The storage capacity of concrete in the storage hopper must be sufficient. How much concrete should be poured for the first time should be calculated carefully to avoid mistakes.
4. 1.4 Measure the rise of concrete at any time when pouring. Before removing the conduit, carefully measure the depth of the conduit buried in the concrete, carefully calculate how many conduits need to be removed, prevent the conduit from being removed too much, and lift the bottom of the conduit out of the concrete surface.
4. 1.5 After pouring a bucket of concrete, it is advisable to lift the conduit and dismantle it in time according to the regulations, so as to prevent the conduit from being buried in the concrete for too long, and the buried depth exceeds the regulations, resulting in pipe burying accidents.
4. 1.6 When the conduit is blocked and the concrete has not yet been initially set, it shall be handled in the following ways.
4. 1.6. 1 Use the lifting equipment of the drilling rig to lift a section of rail or other heavy objects to impact the conduit, so as to flush the blocked concrete, or quickly lift the conduit, flush the conduit with high-pressure water, and refill the waterproof ball plug.
4. 1.6.2 When pouring, when the waterproof ball plug rushes out of the conduit, the conduit should continue to descend until the conduit can no longer be inserted, then lift the conduit slightly and continue pouring concrete, so that the newly poured concrete can be well combined with the original poured concrete.
4.2 Main safety technologies
4.2. 1 crane drivers should pay attention to safety, obey orders and strictly abide by relevant operation procedures when lifting heavy objects such as concrete.
4.2.2 Workers working high above the ground should wear neat clothes and safety belts, and it is forbidden to wear shoes with nails that are easy to slip when working high above the ground.
4.2.3 There should be sufficient lighting for construction at night, and wires and cables on site should not be pulled randomly, and should be overhead for more than 2m.