[Abstract] This paper discusses the advantages and possible problems of the construction technology of concrete inclined roof based on practical experience, aiming at communicating and discussing with colleagues, improving the construction quality of construction projects, and promoting the faster development of the construction industry.
[Key words] Construction industry; Construction technology; Concrete inclined roof pouring; Discussion; Development
The pouring of inclined concrete roof is one of the main construction techniques in construction. However, due to the complexity of inclined roof forms, the quality of construction is difficult to be guaranteed. The construction of waterproofing and defense is very difficult. Once leakage occurs, maintenance is also very difficult, which brings great trouble to users. Therefore, construction technology should be strictly controlled in the construction of inclined concrete roof pouring project. To reduce the appearance of cracks and hemp surfaces, so as to avoid possible problems in the use of houses.
Method of pouring inclined concrete roof
(1) One-sided template method
One-sided formwork method is the simplest and most common method in the concrete construction system in the construction industry, but there are many factors affecting the quality of pouring in the process of execution, such as the smoothness of the formwork itself, the inclination angle of the roof, the thickness and compactness of concrete and other factors will affect the construction process and construction quality. In order to minimize and avoid these problems, in actual construction, the collapse parameters of concrete itself can be controlled within the range of 30-50 mm, and the flow direction of concrete itself can be controlled by a fixed way, and the construction can be carried out in stages. The smoothness of inclined roof must be ensured to the maximum extent. It can be smoothed with 1:2.5 cement mortar and vibrated at the same time.
In the concrete operation of one-sided formwork method, in order to ensure that concrete does not slide, it mainly relies on the concrete's own condensation force, steel displacement band, formwork resistance and so on to avoid the surface movement of concrete. The excessive angle of formwork makes the resistance of formwork to concrete difficult to offset the sliding force of concrete itself. Slow and persistent displacement of concrete before initial solidification can easily lead to leakage due to insufficient concrete density. Therefore, when the inclination of roof is above 26 degrees, the construction method of single-sided formwork is not suitable.
(2) Double-sided splint method
When the East-West slope is greater than or equal to 75 degrees, the double-sided splint method must be used to ensure the construction quality. Short reinforcing bars are needed to support the construction process, and water stop sheets are added to achieve the purpose of water stop and seepage control. In addition, a 400 x 400 mm concrete pouring hole should be set in the middle of the outer side of the two formwork.
Double-sided formwork method can make concrete achieve the purpose of high internal density and smooth surface. But because the thickness of the template itself is small, and then remove the thickness of the steel bar and protective layer, the middle gap is generally not more than 50 mm. In this case, if there are some errors in the binding of the steel bar, it is difficult to insert the tamping bar, thus causing difficulties in the construction process. In construction, attention must be paid to preventing honeycombs caused by improper concrete pouring method and displacement of reinforcing bars. Workers can not observe how full the concrete is in the formwork during construction. They can take the way of tapping and listening to the sound and place the vibrator at the bottom of the formwork to make the concrete flow down and enrich. To strictly control the collapse of concrete, the general control is 50-70 mm, depending on the construction temperature. For sloping roofs with large slopes, in order to ensure waterproofing effect and structural safety of layers, double-sided splint method should be preferred.
2. Quality Problems and Improvement Methods Easily Occurring in the Casting Process of Concrete Inclined Roof
(1) Cause analysis of quality problems
In many cases, after removing the formwork, there are no obvious holes in the inclined roof, but honeycomb and hemp are all over the roof. If these honeycomb voids are connected with each other, the roof may leak, and the maintenance work is very difficult because there is no obvious leak point.
What are the factors affecting the process quality of inclined concrete roofing?
The degree of inclination of inclined roof itself, the strength of formwork and support system, the performance of concrete, the setting of steel bar and the concrete operation of workers will all have an impact on the quality of building. Concrete relies on its own sluggish force, the resistance of the formwork surface and the supporting force of steel bars to resist its own gravity so as not to slide up and down in the formwork. If the inclination of inclined roof is large, the vibration of concrete will be very difficult. As soon as the vibrator is pulled, the concrete will drop down, resulting in insufficient compactness of concrete. In addition, the roof is mostly made of double-layer steel bars with dense steel mesh, which leads to the phenomenon of honeycomb and hemp in inclined roof.
(2) Improvement methods
(1) To strictly control the roof slope, first of all, we should carefully lay the formwork. The formwork itself and the supporting system must achieve a certain stability, stiffness and strength, so as to withstand the weight of the newly poured concrete, lateral pressure and the load generated in the construction process. The setting of diagonal braces can not be ignored.
(2) Attention should be paid to the maintenance control of concrete, especially in the early stage. We should fully maintain the wet state of concrete surface and prohibit the operation or placing objects during the maintenance period.
(3) When pouring inclined roof, we should adopt the method of pouring from the foot of the slope up to the bottom up. Casting randomly will cause the closure of the front and back concrete between the initial setting. When vibrating with vibrating rod, attention should also be paid to fast insertion and slow pull-out, vibration point uniformity, avoid creating voids, and ensure the density of concrete. Strictly in accordance with the predetermined construction sequence, a section of one-time continuous casting completed. Reasonably arrange and plan the sequence and route of pouring, and keep and handle construction joints strictly in accordance with the requirements of design and construction specifications.
(4) The slope of inclined roof is large and the density of concrete is insufficient. It is easy for concrete to flow and segregate in the process of vibration, which results in large shrinkage of concrete and cracks on the surface of concrete. If the density of concrete is too large and too dry, it will be difficult to vibrate, so it is advisable to control the slump of concrete in the range of 60 - 90 mm. By mixing expansive agent in concrete, the expansive effect of expansive agent can effectively reduce the occurrence of concrete cracks, thus improving the waterproof performance of concrete.
(5) In order to resist the tension cracks caused by the self-weight problem before concrete solidification, the erecting bars can be set in the middle of the negative bending distance reinforcing bars at the two ends of slab removal on the inclined roof slab. During construction, steel bars should be tied to control the thickness of the protective layer of negative bars in the support of slabs. In the process of concrete pouring and tamping, the builders can adopt springboards to avoid trampling on negative bars and reduce the deformation of negative bars. It is strictly forbidden to walk up and down the negative tendons.
(6) In order to ensure the construction quality, it is necessary to strictly control the water-cement ratio of concrete. Adding polypropylene fibers to concrete can improve the crack resistance and impermeability of concrete, and effectively reduce the occurrence of cracks. In some Asian countries, increasing the research and development of building materials has become the mainstream. The foam concrete with excellent performance is more and more favored by the construction industry. Many residential buildings have begun to use foam concrete as building material, and its application in overseas construction projects is more extensive. The application of foam concrete to speed up the progress of construction projects, while improving the quality of building construction.
3. Safety technical measures in pouring and tamping of inclined concrete roof
(1) When workers enter the construction site, they must first take their own safety measures. Wear safety helmet, fasten seat belt, and prohibit wearing shoes with hard soles for work.
(2) When pouring concrete on inclined roofs, it is necessary to ensure that the construction workers have a firm foothold, depending on the specific circumstances, and when necessary, to install protective nets or other safety facilities to ensure the safety of workers.
(3) A concrete blanking platform shall be set up in pouring and tamping. The equipment used in construction must undergo strict inspection before construction to ensure the safety of the equipment before use.
(4) Concrete pouring and tamping should be carried out from bottom to top. When pouring Inclined Beams and roof slabs, working platforms must be set up. It is strictly forbidden to operate directly above the formwork or on the support.
(5) Before using the vibrator in operation, the first thing to do is to check the voltage of the power supply and whether to install the leakage switch, etc. to ensure the good condition of the line, and the power cord must not have joints.
Concluding remarks
From this article, we can see that at present, slope roof is widely used in the construction of construction projects. Its advantage is that it can play an excellent waterproof and drainage efficiency. The construction of concrete slant roof casting technology is difficult. During the construction period, attention should be paid to all aspects. After each link of construction is completed, it should be checked again and then proceeded to the next step. The process of each link, together with the extensive application of improvement measures, ensures the quality of sloping roofs and promotes the rapid development of the construction industry on the basis of improving the quality of buildings.
Reference
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