Reinforced concrete is a composite, combined material formed by adding reinforcing raw material, reinforcing mesh, steel plates, and fibers to the concrete.
The comprehensive application of steel and concrete has significantly improved the mechanical properties of the low tensile strength of the raw concrete material, and is therefore widely used in the construction of buildings.
1 The importance of reinforced concrete construction technology
At present, the traditional construction technology can no longer meet the needs of modern construction projects, in order to realize the modern construction project fast, high quality, low cost smooth construction, is to use the management function and scientific methods to promote the technical work.
There are various forms of building structures, from the initial wooden structure, gradually developed into brick and concrete frame structure. With the continuous development of structural forms, the rapid development of the science of reinforced concrete construction technology and the gradual improvement of people’s functional requirements for the use of building projects, reinforced concrete and the scope of application is expanding.
Reinforced concrete construction technology is good or bad, directly affect the quality of concrete buildings, a high level of reinforced concrete construction technology can effectively protect the quality of buildings to a certain extent, and then indirectly protect people’s lives and property safety;.
The low level of reinforced concrete construction technology will affect the quality of the building, causing cracks in the walls and other undesirable results, which not only increases the number of rework, invariably increases the cost of construction, waste of human and material resources, but also to lay a hidden danger to people’s safety. Therefore, the importance of reinforced concrete construction technology is self-evident.
2 reinforced concrete building construction technology
2.1 Formwork construction
In the construction of formwork, materials can be used steel plates, steel formwork, plywood, etc.. In the process of construction, it is necessary to meet the following requirements: pre-buried steel pipes, pre-drilled holes, pre-buried parts must not be missed, these structural accessories are fixed on the formwork, these structural accessories should be installed with attention to the deviation to meet the requirements, the location must be accurate, the installation must be solid. Before the concrete is poured, attention should be paid to keep the formwork dry, not to have the phenomenon of water accumulation, and should clean up the debris in the formwork.
At the same time, water should be poured inside the formwork to moisten it. Attention should be paid to keep the joints of the formwork in a sealed state, so that no slurry leakage can occur; the contact surface between the concrete and the formwork should not use those isolating agents that hinder the construction of decoration works or affect the performance of the structure, but should use those non-toxic and harmless isolating agents.
2.2 Treatment of reinforcement joints
Rebar joints should be set in the less stress, the same longitudinal stress reinforcement should not set two or more joints. Before welding the reinforcing steel shall be test welded, the welder shall have the corresponding induction certificate, and the welded reinforcing steel shall be sampled and tested according to the regulations. When mechanical connection or welding of reinforcing steel is used, the joints set in the same member should be staggered, the welded joints should not be less than 10 times the diameter of the reinforcing steel from the bend, and should not be set at the maximum bend of the reinforcing steel, the beam end, column end of the hoop encryption area should not be set within the joint.
Usually two kinds of joints can be used: welded joints and lap joints, which should be designed according to the characteristics of the actual situation, under the premise of quality assurance, taking into account both economic and progress aspects.
In the same member, the lap joints of adjacent longitudinal reinforcement should be staggered, and the percentage of the joint area to the total reinforcement area should not exceed 25% in the tension zone and 50% in the compression zone. The intersection of the reinforcement should be wire-tied, and the lap joint of the reinforcement should be wire-tied at the center and both ends.
In addition to the intersection of the two rows of reinforcement near the periphery, the intersection of the middle part can be staggered and tied at intervals, but it must ensure that the reinforcing bars are not displaced, and the two-way reinforcement must be tied firmly. The hoop bars of beams and columns shall be set perpendicular to the stressing reinforcement unless the design has special requirements.
2.3 Pouring of concrete
Each layer of structural concrete is poured twice, the first time for columns, the second time for beams and slabs. The free falling height of concrete should not exceed 2 meters, otherwise, stringers and chutes should be applied to ensure that the concrete will not be segregated. Column casting height greater than 3.0m, in 1.8 ~ 2.0m high on one side or both sides of the formwork to open the Siemens plate, concrete from the Siemens plate at the sloping groove or platform into the column mold, the use of high-frequency pounding bar from the top into the vibrating, according to 300-500mm thick layered casting. The beams with greater height should also be poured in layers.
Pouring should focus on the control of pouring height and vibrating rod into the spacing, depth, order. The vibrating rod should be inserted quickly and slowly, and the insertion points should be evenly arranged, moving point by point and in sequence without missing, and the moving spacing should not be 30-40mm in general. when pouring concrete, the formwork, reinforcement, pre-drilled holes and embedded parts should be checked and observed frequently, and problems should be corrected in time.
Pumping concrete should be equipped with sufficient vibrating machinery and personnel according to the pouring speed, and should keep a certain amount of concrete (more than 20cm thick) in the hopper continuously, so as not to inhale air to cause the backflow of concrete to form a blockage. When pumping, the pumping effect should be observed at any time, and the water should be changed once every 2h to wash the tank, and the stroke of the pump cylinder should be checked and adjusted in time if any changes are found.
2.4 Maintenance works
After the concrete is poured, the most important thing is to maintain it in time to provide a certain humidity to the surface of the concrete specimen. To ensure that the concrete can establish the conditions required for its own adequate strength. Curing can be divided into two ways, natural curing and steam curing, depending on its method.
Natural curing is to place the building in the atmosphere, by artificially pouring water to ensure its required humidity, after a certain period of time, so that the components gradually build up strength, and eventually reach the predetermined strength requirements. Steam curing is a curing method used in the production of specimens in prefabricated component plants, where such components can build up strength in a more suitable environment.
However, this is a form limited to those used in precast plants, and most sites now use natural maintenance, watering the members at certain intervals, and this time should be in accordance with the minimum time specified in the construction specifications, as well as certain measures to prevent water evaporation.
2.5 Defect treatment
The defects in the appearance of concrete structure or members, some destroy the structural integrity, reduce the stiffness of the members and affect the structural bearing capacity, while some have little effect on the bearing capacity, but can cause corrosion of reinforcement, reduce durability, or occur leakage, affecting the use.
Therefore, according to the size of the concrete appearance defects, the nature of the difference between the situation, timely processing. For defects such as structural geometric deformation, mold running, etc., without affecting the building’s function and without deformation of the reinforcement, the excess can be chiseled, chiseled fine and flat, without repair; for smaller defects such as slurry leakage and misplaced platform, the rough part can be removed with a flat shovel.
For small areas of leakage, leakage vibration, slag and other defects, can be timely repair, repair material is appropriate to use the same mortar with the structure of the concrete ratio; larger areas of honeycomb, exposed stones and exposed reinforcement, should be chiseled away weak concrete layer and individual protruding aggregate particles, and then choose wire brush or pressurized water rinse the surface, local support mold, fill with a higher strength level of fine aggregate concrete than the original concrete, and carefully pounding.
With the increasing diversification of building shape and building function requirements, there are still many problems in the construction management of reinforced concrete. There are many problems to pay attention to in the construction of reinforced concrete buildings, as a large number of engineering practices illustrate.
Only in the design and construction process for each influencing factor to consider comprehensively and carefully, strictly comply with the design and construction specifications, pay special attention to the construction of reinforced concrete to prevent the impact of common problems on the quality of the project, strengthen the standard management, in order to make better, higher quality engineering, so that the project quality control objectives can be achieved.