引起裂缝的原因与防治办法 Causes and prevention of cracks caused by reinforced concrete drainage pipes
With the continuous deepening of urban construction, the quality requirements for drainage pipes are becoming higher and higher, especially for the leakage. Therefore, more and more projects choose drainage pipes with flexible interfaces, and cracks in the drainage pipe are one of the main causes of leakage of the pipe. A crack in the drainage pipe will also affect the structural safety, service life, strength and appearance of the pipe. Many aspects such as quality have an adverse effect. The national standard GB / T11836-1999 "Reinforced and Reinforced Concrete Drainage Pipes" clearly stipulates that no cracks are allowed on the outside of reinforced concrete pipes, and the width of cracks on the inside and outside must not exceed 0.05mm. In addition, the concrete material is a heterogeneous brittle material. Although it has high compressive strength and good durability, it has low tensile strength, very simple cracking, and many drainage pipes with cracks. The problem of cracks is imperative. Most of the cracks are subtle, and some are hard to find with the naked eye, and have strong concealment, so they are simply ignored by the production enterprises. There are many reasons for cracks in the drainage pipe, and some are the result of the effects of several factors together. In view of this situation, it is necessary to analyze specific problems and take necessary preventive measures.
First, cracks caused by the disassembly of the reinforced concrete drainage pipe mold
1. Low concrete strength
Due to its own characteristics, whether it is a cement pipe mold or the pipe body, the socket end component is much larger than the socket end component. During the demolishing process, when lifting the upper mold half and lifting the pipe body by lifting the bolt, the ends are unbalanced, and the socket end is often lifted easily, but the socket end cannot be lifted, which causes the pipe body to be pulled. . Therefore, if the strength of the socket drainage pipe does not meet the planning requirements, it will simply present a quality problem. In the production process, the factors that cause the concrete strength to be low are mainly the following aspects.
(1) The concrete cooperation ratio is unreasonable, and the intensity of the plan cannot meet the requirements
In order to save costs, some manufacturers plan that the strength of the concrete is relatively low. When the drainage pipe is demolded, the strength required for demolding cannot be achieved. Perhaps the quality management level is low, the strength stability of concrete is not good, the standard deviation is large, and the strength of some formed concrete is too high, while others cannot meet the strength requirements. As a result, concrete cracks are formed during disassembly or transportation.
(2) There are quality problems in the raw materials, and the concrete cannot reach the planned strength
Poor quality of raw materials such as cement, sand, stones, and admixtures will cause the strength of the concrete to decrease, not reaching the strength required for drainage pipe planning.
(3) uneven mixing of the materials, affecting the strength of the concrete
Suspended roller method produces drainage pipes. Because of the use of dry and hard mixtures, the quality of concrete mixing is relatively high, and the mixing is relatively difficult. The main factors affecting the quality of the mixing are the type of mixing machine, the mixing time, the speed of the mixing machine and the order of feeding. The short mixing time of concrete is a common reason. The mixture is not fully mixed, not only the strength of the concrete does not meet the requirements, but also the work function is poor.
(4) The time of the net roll is short, the speed of the suspension roll is low, and the density is not good.
The strength of the drainage pipe and concrete produced by the suspension roll method is directly related to the rolling moment and rolling speed. In order to hurry, the operator may be afraid of the deformation and damage of the reinforcing steel frame, artificially shorten the time of the suspension roll or reduce the speed to form the compactness of the concrete, and the strength of the concrete cannot meet the planning requirements.
The maintenance system is unreasonable. Although the maintenance system is reasonable, it may not be done strictly in accordance with the system and the planned demolding intensity cannot be achieved.
(1) The bolts are incomplete, the mold is difficult to tighten, the force is uneven, and part of the force is too large, which causes the mold to deform.
(2) The mold is not cleaned properly, or there is a problem with the release agent, the isolation effect is not good, the mold is stuck, and the disassembly and assembly are subjected to external forces beyond the limit.
(3) The configuration of the reinforcing steel skeleton is unreasonable, or manual lashing is selected, and the longitudinal structure reinforcement is too small.