I. Overview of the Project
There are 10#, 1 1# and 12# buildings in the second phase of a residential area. There are three floors above ground 18+09, and the basement is connected with the underground 1 floor, with frame-shear structure. The building area is about 36562m2, of which the basement area accounts for1131m2, with a length of 134.4m and a width of 84m. According to the location and function of the main building, the basement is divided into 10 area with post-pouring belt.
The basement floor, wallboard and roof run through the post-cast strip, with a width of 800mm and a total length of about 900m m. The post-cast strip is reinforced with steel bars.
Second, the raft post-cast strip construction control measures
Template design of "2. 1" post-pouring belt
According to the construction characteristics of this project, the raft post-cast strip structure is 600mm lower than the adjacent foundation, and the foundation on both sides adopts the form of foreign ports. The upper part of tongue-and-groove is 300mm, leaving 800mm wide for pouring post-cast strip, and the lower part of tongue-and-groove is 600mm along with the foundation raft construction. Before pouring concrete on both sides, the formwork shall be set up for reinforcement, and the formwork shall be reinforced in strict accordance with the requirements of the prior planning scheme.
"2.2" Concrete pouring of post-cast strip
The following points should be paid attention to in the process of concrete pouring of post-cast strip:
(1), strictly control the pouring thickness of concrete in post-cast strip and the working range of vibrating rod, so as to avoid excessive internal shrinkage stress during pouring and outward expansion of formwork caused by reducing the lateral pressure of rib-sparse formwork;
(2) The slump of concrete should be properly controlled. Excessive slump easily leads to concrete segregation; If the slump is too small, it will increase the pumping difficulty in construction;
(3) In order to prevent the size deviation of the steel wire mesh template during pouring, it can be tied to the raft steel mesh with Ф16 steel bars to resist the lateral pressure of concrete. On the steel wire mesh template, the edges of post-cast strip are ensured to be neat and smooth with wood square braces after pouring;
(4) In order to ensure the effective combination of micro-expansive concrete and old structure, a 50mm cement mortar bonding layer with the same proportion should be laid before pouring;
⑤ The strength grade of micro-concrete in the post-pouring zone is one grade higher than that of the raft on the same floor, and UEA mixed with 10%~ 12% is used to compensate the shrinkage concrete. After using shrinkage-compensating concrete, the post-cast strip can be continuously poured, which greatly shortens the pouring period of the post-cast strip.
Treatment of vertical construction joints before "2.3" concrete pouring
The treatment of vertical construction joints should do the following:
(1), when sparse wooden formwork is used as the vertical construction joint of shear wall, it should be removed as soon as possible and cut hair manually in time;
(2), if the scene with wire mesh external wood square as the main stare blankly template of vertical construction joints, should also be dismantled as soon as possible and timely removal of wire mesh. The exposure of steel wire mesh will form a leakage channel, which has great hidden danger to the waterproof quality of post-cast strip.
(3) For some concrete surfaces that need post-treatment and have been finally set, roughening treatment is needed. Effective stress mechanism of strengthening micro-expansive concrete on concrete on both sides.
"2.4" Protection Measures for Finished Products of Post-pouring Belt
In order to prevent the concrete falling from the upper structure from polluting the steel bars of the post-cast strip and preventing people from falling, before pouring, the top of the post-cast strip is closed with battens or the whole plate, and temporary railings are set around it, and no-pass signs are set.
"2.5" Measures to prevent water accumulation in post-pouring zone
In order to prevent water accumulation in post-cast strip, the following measures can be taken:
(1), when the post-cast strip is connected to the foundation pit of tower crane, a temporary brick wall with a height of 200mm can be built around the foundation pit. Cement mortar mixed with waterproof powder is plastered outside the water retaining sill to prevent water from infiltrating into the post-cast strip;
(2), in order to effectively block the construction water around the construction surface, cement mortar can be used on both sides of the post-cast strip to make 10cm water retaining strips.
Third, the construction measures of wallboard post-pouring belt
Construction measures of wallboard post-cast strip mainly include:
(1), basement wallboard post-cast strip. Construction joints are supported by wood formwork with sparse reinforcement, and 800mm wide post-cast strip is filled with foam board. Prevent the deformation caused by the inward extrusion of concrete on both sides of post-cast strip.
Considering the time requirement of waterproof treatment of basement exterior wall and pouring of post-cast strip, the formwork at the post-cast strip of wallboard can be made into concave-convex shape: the exterior wall protrudes 200mm wide, and the wallboard on both sides of post-cast strip can be continuously poured, and the concave post-cast strip part can be constructed after the completion of external wall backfilling.
(2) Before pouring concrete in the wallboard post-cast strip, the filling foam should be removed manually, and the block heads on both sides of the wall should be chiseled;
(3) After the scum and loose stones on the concrete surface are washed off with a high-pressure water gun, UEA is used to compensate shrinkage concrete pouring.
Fourth, the basement roof post-cast strip construction measures
Construction measures for post-cast strip of basement roof are as follows:
(1) The bottom formwork of roof post-cast strip adopts independent support system, and the support system of post-cast strip area and other parts is set according to the principle of "each system does not affect each other". The formwork system within the span of post-cast strip shall not be dismantled, and the formwork system of post-cast strip can only be dismantled after the main structure and basement garage are completed and the settlement is stable;
(2) Before pouring concrete, inspect the lower support, and handle the unreliable places in time, and don't underestimate the reliability of formwork support because of the small workload;
(3) Before pouring concrete, stick 10mm wide foam plastic strips on both sides of post-cast strip to ensure smooth joints and prevent slurry leakage and root rot.
Five, defects in the process of post-cast strip construction and treatment measures.
The main shortcomings in the construction process and the corresponding improvement measures are as follows:
(1), before pouring concrete, you must check the reinforcement and support of the template. If the support is not in place, the concrete cast will look and feel crooked or outward and inward.
(2) During the napping treatment of post-cast strip, special personnel should be assigned to master the initial setting and final setting time, and it is advisable to control it in 3 ~ 4 h generally. We must not neglect the napping treatment, which will cause the hidden danger of concrete leakage in the post-cast strip;
(3), if the local hair is not ideal, can use electric pickaxe to cut hair manually, but to grasp the final setting time of concrete, the earlier the hair treatment, the more labor costs;
④ Micro-expansive agent UEA should be used to compensate shrinkage concrete in post-cast strip to avoid cracking of new and old concrete due to shrinkage.