Construction joint refers to the concrete pouring process, design or construction needs due to pouring the earlier section, after the pouring of concrete joints formed between.  Construction joint is not a real problem of "joint", it is only after the pouring of concrete for more than the initial setting time, and the first one between the pouring of concrete joint surface, called the combination of the surface of the construction joint.
       Concrete pouring for the formation of the joint surface successively prone to various hazards and quality problems, therefore, different structural works on the construction joint of the address have to be doubly cautious.
1, what is a construction joint?
Construction Joints: construction organization needs for construction of units in each district located between the left seam.  Construction joint is not a real problem of "joint", it is only after the pouring of concrete for more than the initial setting time, and the first one between the pouring of concrete joint surface, called the combination of the surface of the construction joint.
       2, construction joints and design method?
The location of construction joints in the structure should be set by the shear site of the smaller and easier construction, and should meet the following requirements: Column should remain level seam, beam, plate, wall should remain vertical joints.
  (1) construction joints should be retained in the base top, beam or crane beam bracket below the crane beam above, without beam column below the cap.
  (2) and the floor together into a whole big section beam, construction joints should be kept in the bottom panel the following 20mm ~ 30 mm Office.  When the plate under the beam when asked, kept in the lower part of beam prop.
  (3) one-way board, construction joints should be kept in parallel to the short side plate anywhere.
  (4) primary and secondary beams of the floor, should the direction of pouring down the secondary beams, construction joints should be kept in secondary beams span the middle 1 / 3 range.
  (5) wall construction joints should be kept in the door lintel across the hole in 1 / 3 range, can stay in the vertical and horizontal walls of the junction.
  (6) the construction of stairs, stepping board joints should remain in the 1 / 3.
  (7) Pool Wall's construction joints should remain in the floor above the surface of 200 mm ~ 500 mm of vertical walls.
  (8) two-way force floor, concrete, arch, shell, storage, equipment foundations, and other complex multi-storey frame structure, construction joint location of the design requirements should be set to stay.
  3 problems phenomenon often
Construction joints of concrete aggregate concentration, concrete crisp, new and old concrete Stem into clear water leakage along the crevice.
  4, put forward some concrete action.
  1, vertical joint surface chiseling method
After the final setting of concrete, baffle removed, or a steel bar with a hatchet to cut the surface of chiseling to remove loose stones, concrete strength is very low at this time, digging depth 20 ~ 30MM easier to be the second pouring concrete, the early use of water pressure to clean the joint surface, side pouring cement a side brush elements to enhance the bite force.
  2, increase the aggregate method
Beam, plate larger gap caused by retention of Heavy, coated the surface of floating, a corresponding layer thickness of bleeding, treatment of construction joints difficult; like to scrape the surface of the floating pulp or secondary vibration effects of poor Add coarse aggregate method can be used, will be thrown into the graded clean gravel floating in the cytoplasm, re-vibrated to prevent stones concentrated.  This makes joints pouring concrete in the larger Department, the aggregate thickness uniform slurry does not leak and intensity will not decrease, but also increase the interface bond strength and the old and new bite force.
  3, removal of floating pulp
When the concrete body was smaller, simpler way is to iron trowel to scrape off the surface of the floating layer of slurry, deep <25MM, and dug out the stripe pressure can increase the level of construction joints in the bonding quality of the combination of old and new concrete favorable.
  4, secondary development of vibration method
Master of time, after the initial setting in concrete and final setting before the second restore, it will sink in the stones and re-mixed combination of a floating Whey to make it more uniform compaction, joint practice of re-vibration that is effective One of the measures.
  5, continue pouring concrete construction joints, shall meet the following requirements:
  (1) has been pouring the concrete, the compressive strength of not less than 1.2 MPa.
  (2) has been hardened concrete surface, should clear the cement film and loose stones, and weak concrete floor, and be fully wet and clean, and not water.  That is to do: remove the breast skin, Wei Lu coarse sand, rough surface.
  (3) before pouring, horizontal construction joints are advised to covered 10 mm ~ 15 mm thick layer of cement mortar, the concrete mix and mortar within the same composition.
  (4) vibration compacting concrete should be careful to ensure the close integration of old and new concrete.
  (5) waterproof concrete structure design, its layout and wall thickness of steel should be considered to facilitate the construction, easy to ensure quality.
  (6) should be continuous waterproof concrete pouring, construction joints should be few and retention.  When construction joints be retained, they should observe the following: first, floor, roof construction joints should not be left, bottom arch, vault should not remain vertical construction joint.  Second, the wall should remain vertical construction joint.  Horizontal construction joints should not remain in the maximum shear and bending moment with the Department or the bottom side wall junction, should remain above the bottom surface of not less than 300 mm of the wall on.  When the wall has holes, the holes from the edge of construction joints should not be less than 300 mm.  Combined with the level of arch wall construction joints, should remain in the arch (board) wall joints below 150 mm ~ 300 mm Department, the first arch the back wall of the construction joints may stay in the line of bagging, but must pay attention to strengthening waterproofing.  Joints in welcoming the water stop to water laminates, coated waterproof outer coating and mortar approach.  Third, the role of the equipment to withstand power should not be retained based on construction joints.
  (7) is greater than 2 m high wall, it is appropriate vibrating string or tube sliding tube blanking.