(1) reinforcement control. The supervisor shall check whether the specification, shape, size, quantity, spacing, lap length and joint position of steel bars in the post-cast strip meet the design requirements and construction specifications, especially when the steel bars in the post-cast strip are disconnected, the area percentage of binding lap joints shall not exceed 25%, and the welded joints shall not exceed 50%. Because of the long exposure time, the corrosion of steel bars in post-pouring zone is inevitable, so before concrete pouring, the granular or flaky old rust on the surface of steel bars should be derusted. If the steel bar is bent or compressed, it should be corrected in time before concrete pouring.
(2) Control of formwork support system. The supervisor requires the formwork support frame to be installed and formed at one time, and it will be dismantled after the concrete pouring of the post-cast strip is completed, so as to ensure the flat bottom of the slab. Before the concrete pouring of the post-cast strip, the structures on both sides of the middle beam slab of the post-cast strip are in cantilever stress state for a long time. Therefore, the supervisor requires that the formwork and support within the span cannot be removed during construction, otherwise it may cause bearing capacity and stability problems of various parts of the structure. This part of formwork support system must be dismantled from top to bottom after the concrete strength of post-cast strip reaches the design strength.
(3) Control the connection of the seams on both sides. If steel wire mesh is used, the single-layer steel wire mesh must be tightened, and the steel wire mesh must be firmly bound with the steel support. The interface between steel wire mesh plate and steel wire mesh plate and the interface of 50mm protective layer under the mouth must be closed, and the bottom of 50mm protective layer can be cut open when it meets the longitudinal reinforcement of the bottom plate; In the process of pouring concrete, the vibrating rod should be controlled at a distance of about 300mm from the wire mesh to avoid strong vibration and welting vibration, and the spacing between vibrating points should be strictly controlled at about 400 mm. If the quick closing net is used, the concrete vibrating should be controlled at about 450mm away from the quick closing net, and the bleeding gathered on the concrete surface during vibrating should be eliminated as soon as possible. To ensure that there is no gap behind the fast-closing net and concrete slurry will not flow down the net; In the basement floor construction, the supervisor should require that the upper and lower boundaries of the fast and easy-to-collect net be 50mm away from the upper and lower surfaces of the floor, so as to avoid the formation of the fast and easy-to-collect net through the floor and provide a channel for water seepage.
(4) Concrete pouring control. The supervisor shall supervise the whole process of concrete pouring and make records. In the process of pouring concrete on both sides of post-cast strip, symmetrical pouring method should be adopted to ensure that the template of post-cast strip will not shift; Before pouring concrete in the post-cast strip, clean up the sundries in the post-cast strip, chisel off the loose stones of concrete on both sides, clean up the surface, keep it moist and brush the cement slurry; The concrete pouring temperature of the post-cast strip should be lower than the concrete pouring temperature on both sides as far as possible, and the construction should be carried out in the low temperature season; Post-cast strip should be constructed after the shrinkage and deformation of concrete on both sides are basically stable, generally after the concrete age on both sides reaches 42 days, but the post-cast strip of high-rise building should be constructed after the concrete pouring on the structural roof14 days; In order to prevent the loss of cement slurry in concrete, improve the compactness of concrete, and thus improve the crack resistance of concrete, the vibrating time should be appropriately extended, and then smoothed and calendered several times after 1 ~ 2 hours to reduce surface cracks.
(5) Anti-leakage measures. It is the key to do a good job of anti-leakage measures to adopt the joint form of post-pouring belt suitable for engineering characteristics and its waterproof practice with concrete joints on both sides. Usually, tongue-and-groove joints or step joints should be adopted, and a water stop or a combination of water stops should be set in the middle of the joints. If the steel plate waterstop is used for waterproofing, the seam of the steel plate waterstop must be lap welded, the lap length is more than or equal to ≥50mm, and it must be welded in four directions, and the welding must be full, without slag inclusion, meat biting and bubbles; Brush the joint between the inner wall and the ceiling post-pouring belt twice with flexible elastic putty to avoid tiny cracks in the process of settlement and expansion of the structure; When the post-cast strip needs to stop water in advance, the concrete in the post-cast strip should be thickened locally, and an external paste or embedded water stop should be added; Micro-expansive concrete with shrinkage compensation should be used in post-cast strip, and the strength grade should be improved by one grade.
(6) Protection measures for semi-finished products. In order to facilitate the cleaning of the post-cast strip in the basement floor before concrete pouring, the groove of the post-cast strip is irrigated to both sides, and a collecting well is built at the drainage end of the post-cast strip to clean up the garbage and water in the post-cast strip. The water collecting wells on both sides should be pumped in time to keep the post-cast strip in a state of no water accumulation and reduce the corrosion degree of steel bars; In order to facilitate the internal cleaning of the post-pouring belt of the basement floor and the installation of the water stop, it is necessary to cut off the upper reinforcement of the floor at the post-pouring belt at a proper position, leave a manhole, and weld and fill the cut reinforcement after the post-pouring belt is closed; Before the initial setting of concrete pouring on both sides is completed, the laitance in the post-pouring zone shall be cleaned with high-pressure water gun in time, and the laitance that cannot be cleaned with water gun shall be tamped with long brazing rod in time, so that even if there are some loose sediments, it is easier to clean them later; Before pouring concrete in the post-cast strip, brick retaining walls and wooden cover plates should be used for closed protection on both sides of the post-cast strip, so as to prevent caking pollution of concrete and mortar and massive accumulation of construction waste, prevent the damage of external water stop, prevent the steel bars from being polluted in engineering construction, and ensure that the steel bars are not trampled.
(7) finished product protection measures. Before the concrete strength reaches 1.2N/mm2, no trampling or construction operation is allowed; After the initial setting of concrete in post-cast strip, it shall be cured within 12h, and the concrete surface shall be kept moist during the curing period, and the curing time shall not be less than 28d. The curing measures can be sprayed with concrete curing agent, which can effectively keep the water in the concrete from evaporating, effectively cure the concrete, increase its strength and avoid surface cracks as much as possible without affecting the construction of subsequent processes.
2.3. Late control
After the construction of post-cast strip is completed, the supervisor shall conduct quality acceptance according to GB50208-2002 Code for Quality Acceptance of Underground Waterproofing Works, and collect and sort out the following documents and records in time: design change documents; Raw materials factory certificate, quality inspection report and approach sampling test report; Concrete mix ratio report; Construction records of concrete projects; Acceptance records of concealed works; Supervise inspections and on-site records; Supervision engineer's notice and reply; List of contact persons for supervision; Architectural audio-visual materials; Other necessary documents and records.
References:
[1] Gong Xiaonan, Yan Ping, Yu Jianlin. Proceedings of the 3rd Symposium on Geotechnical Mechanics and Engineering, China International Broadcasting Press, 1997.
[2] GB50 108-200 1 Technical Specification for Waterproofing of Underground Engineering [S].