Influence of construction process on quality

Engineering quality is formed in the process of construction, not by the final inspection. In order to check the project quality after engaging in the project, turn to pre-control and achieve the purpose of "prevention first", it is necessary to strengthen the quality control in the construction process. First, the concept of process quality control The construction process of an engineering project is composed of a series of interrelated and mutually restrictive processes. Process quality is the foundation, which directly affects the overall quality of the project. To control the quality of the construction process of an engineering project, we must first control the process quality. Process quality includes two aspects: one is the quality of process activity conditions; Second, the quality effect of process activities; From the point of view of quality control, the two are interrelated. On the one hand, it is necessary to control the quality of process conditions, that is, whether the input quality of each process (that is, the quality of people, materials, machines, methods and environment) meets the requirements; On the other hand, it is necessary to control the quality of process activities, that is, whether the engineering products completed in each process meet the relevant quality standards. Process quality control is the quality control of process activity conditions and process activity effects, so as to realize the quality control of the whole construction process. The principle of process quality control is to count and analyze part (sub-sample) data of the process through mathematical statistics to judge whether the quality of the whole process is stable and normal. If it is unstable, countermeasures and measures should be taken in time to improve the abnormal situation, so as to realize the control of process quality. The control steps are as follows: (1) actual measurement: the quality of the extracted process samples is tested by using necessary testing tools and means. (2) Analysis: Use histogram method, Pareto diagram method or management diagram method to analyze the data obtained from the inspection, and understand the laws followed by these data. (3) judging: according to the analysis result of data distribution law, such as whether the data conforms to the normal distribution curve; Whether it is between the upper and lower control lines; Whether it is within the range specified by the tolerance (quality standard); In a normal or abnormal state; Quality variation caused by accidental factors or systematic factors. , judge the quality of the whole process, so as to determine whether the process meets the quality standards. If there is an abnormal situation, we can find out the reasons and take countermeasures and measures to prevent it, so as to achieve the purpose of controlling the quality of the process. Second, the content of process quality control When controlling process quality, we should focus on the following four aspects. 1. Strictly abide by the process regulations, construction technology and operation regulations, which are the basis and regulations of construction operation and the premise of ensuring process quality. Anyone must strictly enforce it and must not violate it. 2. Active control of process activity conditions The quality process activity conditions include many contents, mainly referring to five factors affecting quality: construction operators, materials, construction machinery and equipment, construction methods and construction environment. As long as these factors are effectively controlled, make them in a controlled state, ensure the quality of process input and avoid the changes of system factors, the quality of each process can be guaranteed to be normal and stable. 3. The quality of process activity effect in time is the measure to evaluate whether the process quality meets the standard. Therefore, it is necessary to strengthen quality inspection, conduct comprehensive statistics and analysis on quality status, and grasp quality trends in time. Once quality problems are found, study and deal with them immediately, so that the quality of process activities meets the requirements of specifications and standards from beginning to end. 4. Setting process quality control points refers to the key points, key parts or weak links that need to be controlled in order to ensure the process quality, so as to strengthen management in a certain period and under certain conditions and make the process in a good control state. Third, the setting of quality control points The setting principle of quality control points is determined according to the importance of the project, that is, the influence of quality characteristic values on the quality of the whole project. Therefore, when setting quality control points, first of all, we should make a comprehensive analysis and comparison of the engineering objects under construction and make clear the quality control points; Then, it further analyzes the possible quality problems or the causes of quality hidden dangers in the construction of the set quality control points, and puts forward corresponding preventive countermeasures. It can be seen that setting quality control points is a powerful measure to pre-control the engineering quality. Quality control points cover a wide range. According to the characteristics of the project, depending on its importance, complexity, accuracy, quality standards and requirements, it may be a project with complex structure, a structural member with high technical requirements and great construction difficulty, or a sub-item or sub-item project, or a working procedure or several working procedures that affect the quality. In a word, operation, materials, mechanical equipment, construction sequence, technical parameters, natural conditions, engineering environment, etc. Can be set as quality control points, mainly depending on their impact on quality characteristics and the degree of harm. This is listed as follows: 1. Human behavior Some processes or operating points should control human behavior to avoid quality problems caused by human mistakes. For example, for aerial work, underwater work, dangerous work, inflammable and explosive work, heavy component hoisting or multi-machine hoisting, mechanical work with complex movements and fast operation, processes with high precision and operation requirements, and processes with great technical difficulties, operators should be comprehensively assessed from the aspects of physical defects, psychological activities, technical ability and ideological quality. Repeated disclosure should be made in advance to remind matters needing attention and avoid wrong behavior and violation of discipline and discipline. 2. The state of the object In some processes or operations, the state of the object should be the focus of control. If the machining accuracy is related to construction machines and tools; Measurement is not allowed to be related to measuring equipment and instruments; Hazard sources involve instability, overturning, corrosion, toxic gas, vibration, impact, sparks, explosion, etc. It is also related to interchangeability and multiple work-intensive workplaces. That is to say, according to the characteristics of different processes, some focus on controlling machinery and equipment, some focus on preventing instability, overturning, overheating, corrosion and other hazards, and some focus on the workplace. 3. The quality and performance of materials are the main factors that directly affect the engineering quality; Especially in some processes, the quality and performance of materials should be the focus of control. Such as prestressed reinforcement processing, it is required that the reinforcement is uniform, the elastic modulus is consistent, and the sulfur (S) content and phosphorus (P) content should not be too large to avoid hot brittleness and cold brittleness; N-grade steel bars have poor weldability and are easy to be hot brittle. When they are used as prestressed tendons, welding joints should be avoided as far as possible, and electric heating should be carried out after welding. For example, petroleum asphalt coiled materials can only be paved with petroleum asphalt cold priming oil and petroleum asphalt glue, but not with tar asphalt cold priming oil or tar asphalt glue, otherwise the quality will be affected. 4. The key operations such as prestressing tendon stretching are as follows: overstretching, loading for 2min. The purpose of overstretching is to reduce the elastic compression and creep of concrete, and to reduce the stress loss caused by steel bar relaxation, hole friction and anchor deformation. The purpose of holding load for 2min is to accelerate the early development of steel bar relaxation and reduce the stress loss of steel bar relaxation. In operation, if you don't overstretch and keep the load for 2 minutes, you can't reliably determine the prestress value. If the tension stress control is inaccurate, too large or too small, the prestress value cannot be established reliably, which seriously affects the quality of prestressed members. 5. Some working procedures or operations in the construction sequence must be strictly controlled. Such as cold-drawn steel bar, it must be cold-drawn after butt welding, otherwise it will lose its cold strength. When fixing the roof truss, it is necessary to weld diagonally at the same time to avoid the inclination of the corrected roof truss caused by welding stress. The demoulding by plate hanging method starts from the four corners, the back four sides and the middle, that is, the plate hanging on the four corner columns starts at the same time, and the time is controlled as lOs, which is about 5~8mm higher. Then, the plate lifts on the four side columns and the plate lifts on the middle column should be started in turn in the same way to separate the plates, and then adjust the height difference and lift the whole plate synchronously, otherwise the plates will be broken. Or start from one row and lift it row by row, that is, start the elevator on the first row of columns, about lOs, then start the elevators on the second row and the third row of columns in turn, and then lift the whole synchronously after dividing the plates in the same way. Lifting plate demoulding is the key to the success or failure of lifting plate construction. If the demoulding sequence is not followed and the whole board is lifted at the beginning, the board will be damaged due to excessive adsorption and adhesion between the boards. 6. Technology gap The technology gap between some processes is very time-sensitive, and if it is not strictly controlled, it will also affect the quality. If the concrete is poured in layers, the upper concrete must be poured before the initial setting of the lower concrete. After the leveling layer is dried, the waterproof roof with priming oil coiled material can be brushed cold, and then the coiled material can be laid. After bricklaying, before plastering, there must be 6~ 1Od time for the wall to fully sink, stabilize and dry. After the plastering layer is dried, it can be painted and brushed. 7. Technical parameters Some technical parameters are closely related to quality and must be strictly controlled. Such as the dosage of additives, the hydration degree of concrete, the heat resistance of asphalt glue, the optimum water content of backfill soil and concrete, the fullness of mortar joint, the anti-mixing label of waterproof concrete, etc. , will directly affect the strength, compactness, impermeability and frost resistance, and should also be used as process quality control points. 8. Common quality defects Common quality defects, such as water seepage, water leakage, shelling, sanding and cracks. , are related to the process operation, so we should study countermeasures in advance and put forward preventive measures. 9. Application of new technologies, new processes and new materials When new technologies, new processes and new materials have passed the appraisal and test, but the construction operators are inexperienced and it is the first time to carry out construction, it is also necessary to strictly control their technological operations as the focus. 10. For the processes with unstable quality and many quality problems, the statistics of quality data show that the processes with large quality fluctuation and high unqualified rate should also be set as quality control points. 1 1. Special land foundations and special structures should be specially controlled for the treatment of special land foundations such as collapsible loess, expansive soil and red clay, as well as the construction links and important parts with great technical difficulties such as long-span structures and towering structures. 12. Problems that have a significant impact on the quality in the construction method, such as controlling poor hoisting in the construction of lifting plate method to prevent the instability of group columns; Hydraulic slipform construction, unstable support rods, concrete cracking and collapse, and buildings tilting and twisting; The stability and assembly of formwork are the key points of quality control in the construction of large formwork. To sum up, the setting of quality control points is a powerful measure to ensure the quality of the construction process and an important means of quality control.