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Key points for quality management and acceptance in the construction of prefabricated buildings. Prefabricated buildings are being promoted vigorously through various policies; however, due to a lack of theory and experience, many projects still face numerous issues related to quality management and acceptance during on-site construction. Based on the engineering practices of China State Construction Seventh Engineering Bureau, this article summarizes the approaches to quality management and acceptance in the construction of prefabricated concrete buildings, for reference in implementation. 1 The construction unit of the quality management system shall establish a sound and reliable technical and quality assurance system. Equip with appropriate quality management personnel to conscientiously implement various quality management systems, regulations, and relevant standards. The construction entity and the supervision entity shall establish strict quality supervision and management measures, regularly hold regular supervision meetings to coordinate work arrangements, review the project progress, and inform about any quality or safety issues present in the project, thereby urging the construction entity to make necessary corrections. http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/225a992ff7408e0641a3a5adc50e4280.png2 Quality management requirements: During construction, the “three-inspection” system must be strictly followed. After each task is completed, it must first undergo self-inspection by the work team, mutual inspection, and handover inspection to ensure it meets the standards; thereafter, a professional quality inspector shall conduct another review. The relevant documentation must then be completed, and the work must be submitted to the supervision engineer for approval before moving on to the next stage of construction. All components are subject to quality inspection before being brought on site, and can only be used after passing the inspection. Before carrying out sleeve grouting, the quality of component installation must be submitted to the supervisor for inspection; grouting can only proceed once the inspection is successful. Additionally, the entire grouting process must be supervised, and records of the grouting work must be kept. Before pouring ready-mixed concrete, it is necessary to check the documentation accompanying the concrete delivery. Only after obtaining approval from the supervisor and signing the concrete pouring order can the pouring proceed. 3. Acceptance of prefabricated components upon arrival: Reliable transport vehicles and specialized storage racks are used for transporting the components. All components arriving on site must be accompanied by relevant production documents, and a comprehensive inspection must be conducted regarding their appearance, dimensions, and embedded parts/preparations. http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/8486f792bcce9b0e30dd879a308e3b50.jpghttp://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/7015f83f7352d9466f3b3c8e864fd374.jpghttp://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/6dd630cdf07cfe50da1814b267250013.jpghttp://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/3eb11f36045f4b755a7119d73da8ca85.jpg4 Lifting requirements: For the construction of prefabricated concrete buildings, it is advisable to use tool-based, standardized construction systems. Before construction of prefabricated concrete structures, it is advisable to select a representative unit for a trial installation of prefabricated components. Based on the results of this trial installation, the construction techniques should be adjusted in a timely manner and the construction plan refined. http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/f63332ecba9607b3dcfca4ae0634cfac.jpg Lifting frame http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/05f44af1bfe0531a4b3deaf1702f8ed2.jpg Trial installation 5 Quality control requirements for reinforcement sleeve grouting: During construction, strict control must be exercised over the on-site preparation process of the grouting material; a dedicated person should supervise the grouting process to ensure its quality, and records of the grouting work must be kept. http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/231470b738b913f2bace50dff088ff14.png Inspection of grouting material http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/a1427279275e2a32153a56d8eae9c6d6.png Retention of grouting material test blocks http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/ba60bd4b15936766137accd2be50948d.jpg Plugging after grouting is completed 6 Process quality control and inspection http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/fe9a47d5d27aa99633562c253b263990.jpg Inspection of wall installation quality http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/6c4b8691ff406430c33ff9fb028cd9df.jpg Inspection of cast-in-place joints http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/c542936b97f46134fcb2ba5ed34501be.jpg Inspection of wall positioning lines 7 Supervision and acceptance http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/0952febbbeb823c8453fd3c02cca41d3.jpg Acceptance of wall installation quality [Appendix] Regulations for quality acceptance of prefabricated concrete buildings I. General provisions 1 The construction of prefabricated concrete buildings shall be carried out in accordance with the relevant provisions of the current **standard “Unified Standard for Quality Acceptance of Construction Projects” GB 50300, with regard to the classification of unit projects, sub-projects, sub-items, and inspection lots, as well as their quality acceptance. 2 The sub-projects such as decoration and finishing, as well as mechanical and electrical installation in prefabricated concrete buildings shall be subject to quality inspection in accordance with **current relevant standards. 3 The prefabricated concrete structure works shall be inspected and accepted in accordance with the sub-divisional works for concrete structures. The prefabricated concrete structure components shall be inspected and accepted as separate items within the sub-divisional works for concrete structures, while the other items within this sub-divisional category shall comply with the relevant provisions of the current standard \"Code for Acceptance of Construction Quality of Concrete Structures\" GB 50204. 4 The raw materials, components, and parts used in the construction of prefabricated concrete structures shall be inspected and accepted upon arrival in batches. 5 Before pouring concrete for the connection joints of prefabricated concrete structures and composite members, a concealed work inspection should be carried out. The acceptance of concealed works should include the following main aspects: (1) the quality of the rough concrete surface, as well as the dimensions, quantity, and location of the keyways ； (2) Grade, specification, quantity, position, and spacing of steel bars; bending angle of stirrup hooks and length of the straight sections ； (3) Methods of steel bar connection, joint locations, number of joints, percentage of joint area, lap length, anchorage methods, and anchorage length ； (4) Specifications, quantities, and locations of embedded parts and reserved pipelines ； (5) Waterproofing and fireproofing measures at the joints of precast concrete elements ； (6) Thermal insulation and construction of its joints ； (7) Other concealed items. 6 When conducting the acceptance of the concrete structure sub-project, in addition to providing the documents and records required in accordance with the current **standard \"Code for Acceptance of Construction Quality of Concrete Structures\" GB 50204, the following documents and records shall also be provided: (1) Engineering design documents, construction drawings for the installation of precast components, and detailed fabrication drawings ； (2) Quality certification documents for prefabricated components, main materials, and accessories, on-site acceptance records, and sampling reinspection reports ； (3) Construction record of prefabricated component installation ； (4) Inspection reports on the grouting type of rebar sleeves, process inspection reports, and construction inspection records; construction inspection records for grout-anchored lap joints ； (5) Inspection and acceptance documents for concealed works at the post-poured concrete sections ； (6) Strength test report of post-poured concrete, grouting material, and bedding mortar ； (7) Inspection records for the construction quality of exterior wall waterproofing ； (8) Quality acceptance documents for individual items of prefabricated structures ； (9) Plans for addressing major quality issues in prefabricated construction projects and inspection records ； (10) Other documents and records related to prefabricated construction. II. Key control items for prefabricated components: For prefabricated components produced by specialized enterprises, quality certification documents should be checked upon arrival at the site. Inspection quantity: 100% inspection. Inspection method: Check the quality certification documents or quality acceptance records. When prefabricated components produced by specialized enterprises arrive at the construction site, their structural performance must meet the following requirements: (1) For simply supported bent prefabricated components such as beams and slabs, structural performance tests must be conducted, and these tests must comply with the following provisions: 1) The structural performance tests must adhere to the relevant regulations of current standards as well as the design requirements; the testing requirements and methods shall conform to the relevant provisions of the current standard \"Code for Acceptance of Construction Quality of Concrete Structures\" GB 50204. 2) Reinforced concrete members and prestressed concrete members permitted to develop cracks shall be tested for bearing capacity, deflection, and crack width ； Prestressed concrete members that are not allowed to develop cracks must undergo tests for bearing capacity, deflection, and crack resistance. 3) For large components and those with proven practical experience, only crack width, crack resistance, and deflection tests may be conducted. 4) For components that are used in small quantities, structural performance testing may be omitted if reliable evidence is available. 5) For prefabricated components of the same type used in multiple projects, the structural performance tests can be commissioned jointly, and the results are valid for all such projects. (2) For precast floor slabs that are composite and cannot be used alone, structural performance testing may not be required. For composite beam members, whether to conduct structural performance tests and the method of such tests shall be determined according to the design requirements. (3) For other prefabricated components other than those specified in paragraphs 1 and 2 of this article, structural performance testing may not be required upon arrival, unless there are specific design requirements. (4) For prefabricated components for which structural performance testing is not required as stipulated in paragraphs 1, 2, and 3 of this article, the following measures shall be taken: 1) A representative from the construction unit or the supervision unit shall be stationed at the factory to supervise the production process. 2) When there is no on-site supervision, physical inspections should be carried out on prefabricated components upon their arrival at the site, to check the quantity, specifications, spacing of the main load-bearing rebars, thickness of the protective layer, and concrete strength. Number of specimens for testing: For prefabricated components of the same type, no more than 1,000 components per batch are considered as one batch; 1 component is randomly selected from each batch for structural performance testing. Inspection method: Check the structural performance inspection report or physical inspection report. Note: “Same type” refers to the same steel grade, the same concrete strength grade, the same production process, and the same structural form. When selecting prefabricated components, it is advisable to choose those with the highest design loads, the most unfavorable stress conditions, or the largest production volume. 3. The concrete appearance quality of precast components shall have no serious defects, and there shall be no dimensional deviations that affect the structural performance or the functions of installation and use. Inspection quantity: 100% inspection. Inspection method: Observation, measurement ； Check the processing records. 4. The bonding performance between the pre-applied decorative tiles, stones, and other finishes on the surface of prefabricated components and the concrete must comply with the design requirements as well as the provisions of **current relevant standards. Inspection quantity: Inspect by batch. Inspection method: Check the pull strength test report. For item 5 of the general requirements, precast components shall have no general defects in appearance; for any such defects that do occur, the component manufacturer is required to address them in accordance with the technical treatment plan, followed by re-inspection and acceptance. Inspection quantity: 100% inspection. Inspection method: Observation, examination of the technical treatment plan and treatment records. 6. The appearance quality of the rough surface of prefabricated components, as well as the appearance quality and quantity of keyways, shall meet the design requirements. Inspection quantity: 100% inspection. Inspection method: Observation, measurement. 7. The appearance quality of prefabricated components with pre-applied decorative tiles, stones, and other finishes, as well as decorative concrete finishes, shall meet the design requirements or the provisions of **current relevant standards. Inspection quantity: Inspect by batch. Inspection method: Observation or light tapping for inspection ； Compare with the template. 8. The specifications, models, and quantities of embedded parts, reserved rebar, pre-drilled holes, and embedded pipelines in prefabricated components shall meet the design requirements. Inspection quantity: Inspect by batch. Inspection method: Observation, measurement ； Check the product certificate of conformity. 9. The dimensional tolerances and inspection methods for precast slabs, wall panels, and beam-column components shall comply with the provisions specified in the table below respectively. Allowable deviations in the dimensional specifications of precast floor elements and inspection methods: http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/3dd07e24c39f894f69eddc07a6fadfdc.jpg http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/e926455f9105c746b7ca61980fe15745.jpg http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/6bbdc9bc6ecf355789763a1487625f7a.jpg Allowable deviations in the dimensional specifications of precast wall elements and inspection methods: http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/5ce4926d119990b13a5aae01f24a9a19.jpg http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/3abe8b9433f120b54d560fe27fb541a1.jpg http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/1767ca1ad631159b645083c62a1ebae0.jpg Allowable deviations in the dimensional specifications of precast beams, columns, and trusses and inspection methods: http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/bbfaa74b25743f37a9a141dc8b4570fa.jpg http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/4f0f42712b1c14f8f10113a6557129e5.jpg Number of inspections: For each batch of components that arrive at the site, the number of samples taken for inspection from components of the same specification (type) should be no less than 5% of the total number of such components, and at least 3 pieces. 10. The dimensional tolerances of the decorative appearance of the decorative components and the inspection methods shall meet the design requirements ； When there are no specific design requirements, the provisions in the following table shall be complied with. Permissible deviations in the external dimensions of decorative components and inspection methods: http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/cb72208e6b1147a5bdb86b3e877c939a.jpg http://img.civilcn.com/d/file/zhishi/gcgl/2020-05-26/3cd44c51063d4c51eba32d8d53562853.jpg Inspection quantity: In accordance with the incoming inspection batches, for components of the same specification (type), the number of samples inspected each time should be no less than 10% of the total quantity of that specification (type), and at least 5 pieces. III. Key control items for the installation and connection of prefabricated components 1 The temporary fixing measures for prefabricated components shall comply with the requirements of the design, the specific construction plan, and the provisions of **current relevant standards. Inspection quantity: 100% inspection. Inspection method: Visual inspection; check the construction plan, construction records, or design documents. 2 When a prefabricated structure is connected using post-poured concrete, the strength of the post-poured concrete at the joints between the components shall meet the design requirements. Inspection quantity: Inspect by batch. Testing method: It shall comply with the relevant provisions of the current **standard, ‘Code for Testing and Evaluation of Concrete Strength’ GB/T 50107. 3 When steel bars are connected by sleeve grouting or grout-anchored lap joints, the grouting should be full and dense, with grout flowing out from all outlets. Inspection quantity: 100% inspection. Inspection method: Check the construction quality inspection records and relevant inspection reports for grouting. The strength of the grout used for 4 rebar sleeve grouting connections and grout-anchored lap joints shall comply with the provisions of **current relevant standards and design requirements. Inspection quantity: Inspected in batches, with each layer constituting one inspection batch ； One set of rectangular specimens measuring 40mm×40mm×160mm should be prepared per working shift, with no less than 3 sets per layer; compressive strength tests are conducted after 28 days of standard curing. Inspection method: Check the grouting material strength test report and evaluation records. 5 The grouting strength of the joints at the bottom of prefabricated components shall meet the design requirements. Inspection quantity: Inspected in batches, with each layer constituting one inspection batch ； For each working shift, one set of cubic specimens with an edge length of 70.7 mm should be prepared using the same mix ratio, and no less than 3 sets per layer should be made; compressive strength tests are conducted after 28 days of standard curing. Inspection method: Check the strength test report and evaluation records of the grouting material. 6 When mechanical connections are used for steel bars, the quality of the joints must comply with the relevant provisions of the current industry standard \"Technical Specifications for Mechanical Connections of Steel Bars\" JGJ 107. Number of inspections: It shall comply with the relevant provisions of the current industry standard \"Technical Code for Mechanical Connection of Steel Bars\" JGJ 107. Inspection method: Examine the construction records of mechanical reinforcement connections and the strength test reports of parallel specimens. 7 When steel bars are connected by welding, the quality of the weld joints must meet the design requirements and shall comply with the relevant provisions of the current industry standard \"Code for Welding and Inspection of Steel Bars\" JGJ 18. Inspection quantity: It shall comply with the relevant provisions of the current industry standard \"Code for Welding and Inspection of Steel Bars\" JGJ 18. Inspection method: Check the quality acceptance records for the inspection lot of steel bar welding joints. 8 When prefabricated components are connected by welding steel sections, the quality of the welds at these joints must meet the design requirements, and must also comply with the relevant provisions of the current standards **\"Code for Welding of Steel Structures\" GB 50661 and \"Code for Acceptance of Construction Quality of Steel Structure Projects\" GB 50205. Inspection quantity: 100% inspection. Inspection method: It shall comply with the relevant provisions of the current **standard, the Code for Acceptance of Construction Quality of Steel Structure Projects GB 50205. 9 When prefabricated components are connected using bolts, the material, specifications, and tightening torque of the bolts must meet the design requirements as well as the relevant provisions of the current standards: the \"Code for Design of Steel Structures\" GB 50017 and the \"Code for Acceptance of Construction Quality of Steel Structure Projects\" GB 50205. Inspection quantity: 100% inspection. Inspection method: It shall comply with the relevant provisions of the current **standard, the Code for Acceptance of Construction Quality of Steel Structure Projects GB 50205. 10 The visual quality of the prefabricated structure sub-projects shall have no serious defects, and there shall be no dimensional deviations that affect the structural performance and functional use. Inspection quantity: 100% inspection. Inspection method: Observation, measurement ； Check the processing records. 11 The waterproof performance of the exterior wall panel joints shall meet the design requirements. Inspection quantity: Inspected by batch. Each 1,000 m2 of exterior wall area (including windows) shall be considered as one inspection lot; if the area is less than 1,000 m2, it shall still be regarded as one inspection lot ； For each inspection batch, at least one spot check shall be conducted. The inspected area shall be the horizontal and vertical cross-joint regions formed by 4 wall panels in two adjacent layers, with an area of no less than 10 m². Inspection method: Check the on-site water spraying test report. For general item 12, the construction dimension tolerances and inspection methods for prefabricated structure sub-projects shall meet the design requirements ； When no requirements are specified in the design, the provisions of Table 10.4.12 of this standard shall be complied with. Number of inspections: Divide into inspection batches by floor, structural joint, or construction section. Within the same inspection batch, for beams and columns, 10% of the total number of components shall be sampled, with a minimum of 3 components ； For walls and panels, 10% should be sampled randomly from representative rooms, with a minimum of 3 rooms ； For large-scale spatial structures, walls can be divided into inspection areas based on heights of around 5 meters between adjacent axes, while slabs can be divided into inspection areas using vertical and horizontal axes. 10% of these areas should be inspected randomly, with no fewer than 3 such areas in total. 13 The finish appearance quality of prefabricated concrete buildings shall meet the design requirements and shall comply with the relevant provisions of the current **standard «Code for Acceptance of Construction Quality of Building Decoration Works» GB 50210. Inspection quantity: 100% inspection. Inspection method: Observation and comparative measurement.