The construction period of the concrete main structure shall not be less than 5 days/layer!

Source: Dongguan Municipal Bureau of Housing and Urban-Rural Development, Guangdong Provincial Construction Management

On August 27, the Dongguan Municipal Bureau of Housing and Urban-Rural Development issued a notice on strengthening the quality management of concrete for construction projects. Explicit:

• The construction period of the main concrete structure shall not be less than 5 days/layer.
• If all parties to the project confirm that it needs to be implemented according to 5 days/layer, a construction plan to ensure the quality and safety of the project shall be formulated, and it can only be implemented after being approved by experts.

Attached original text:

Notice on strengthening the quality management of concrete for construction projects

Housing and Urban-Rural Development Bureaus of all parks, towns (streets), and all relevant units (enterprises):

In order to prevent quality and safety production accidents caused by the concrete strength of the main structure in the construction project due to the failure to meet the design requirements, reduce the quality problems such as floor cracking and thickness not meeting the design requirements, improve the safety performance of the building, further strengthen the construction quality management of the concrete structure of the city's housing construction projects, and ensure the quality and structural safety of housing construction projects, according to the "Construction Law", "Regulations on the Quality Management of Construction Projects", "Regulations on the Management of Construction Project Safety Production", " Notice of the Ministry of Housing and Urban-Rural Development on the Implementation of the Primary Responsibility for the Quality of Construction Units (Jian Quality Gui [2020] No. 9), combined with the actual situation of our city, the notice on strengthening the construction quality management of concrete structures in construction projects is as follows:

1. Implement the quality responsibility of the main project of all parties involved

The main body of responsibility for the construction should strictly implement the main responsibility of the project quality, establish and improve the quality assurance system and mechanism, strengthen the process management of the project quality, enhance the quality awareness of all parties involved, and ensure the quality and structural safety of the project. The construction unit shall implement the primary responsibility, scientifically and reasonably determine the construction period and cost of the project, and it is strictly forbidden to blindly rush the construction period and rush the schedule, and shall not force other participating units of the project to simplify the process and reduce the quality standards. The construction contractor shall reasonably arrange the schedule and carry out the construction in strict accordance with the design documents and construction technical quality standards and specifications. The design unit should improve the design quality of concrete structure engineering, and formulate structural measures in strict accordance with the requirements for the prevention and control of common quality problems. The supervision unit shall inspect and inspect the process of acceptance of ready-mixed concrete by the construction unit, strengthen the supervision of the concrete construction process, and strictly implement the responsibility of side station and parallel inspection. The testing unit should strengthen the internal management of the receipt and testing of concrete specimens, and strictly prohibit fraud.

2. Scientifically and reasonably arrange the construction period of the project

Reasonable determination and effective control of the construction period of construction projects is an important part of project management, and it is necessary to firmly establish the awareness of "red line" to ensure the quality and safety of the project. The determination and control of the construction period must follow the principles of safety first, quality first, technical feasibility, economic rationality and environmental protection. The construction unit shall be responsible for the determination and control of the construction period, and shall not arbitrarily compress the construction period. The construction period of the main concrete structure shall not be less than 5 days/layer. If all parties to the project confirm that it needs to be implemented according to 5 days/layer, a construction plan to ensure the quality and safety of the project shall be formulated, and it can only be implemented after being approved by experts.

3. Strengthen the quality management of ready-mixed concrete production

Ready-mixed concrete production enterprises are responsible for the production quality of ready-mixed concrete, and should further improve the quality management system, product quality assurance system and product quality tracking system, and organize production in strict accordance with relevant laws, regulations and technical standards.

(1) Do a good job in the quality inspection of raw materials

All ready-mixed concrete production enterprises should strengthen the inspection and quality control of raw materials, establish and improve the raw material procurement management system and raw material use ledger, and realize the traceability of the use of raw materials. The inspection of raw materials should be strengthened, and the inspection batches should be divided in strict accordance with the requirements of the specifications and standards, and the performance indicators of relevant projects should be inspected to ensure that they must be inspected before use, and the use of unqualified raw materials is prohibited.

(2) Strictly control the concrete mix ratio

All ready-mixed concrete production enterprises should strictly follow the national standards and supply contracts, and design the mix ratio according to the concrete strength grade, durability and working environment requirements to ensure that the actual production mix ratio is consistent with the mix ratio report. Each enterprise should ensure at least once a quarter of the common mix verification, in the use of the standby common mix ratio, should be verified or adjusted in the process of enablement, in the case of raw material varieties, quality changes or concrete performance has special needs, should be re-designed for the mix ratio.

(3) Strengthen the management of concrete delivery and transportation

All ready-mixed concrete enterprises should strengthen the factory inspection of ready-mixed concrete, and provide ready-mixed concrete invoices and factory quality certificates according to regulations to ensure the quality of ready-mixed concrete products. It is strictly forbidden to add water during the transportation of ready-mixed concrete, reasonably control the transportation time, and fully understand the road, traffic and construction conditions before transportation, and take effective technical measures for the situation that the transportation time is greater than 90 minutes, and should ensure that the concrete performance meets the design requirements through test verification. In strict accordance with the supply and demand contract with the use of units to do a good job of delivery acceptance, delivery acceptance should focus on the confirmation of concrete category, quantity and mix ratio, mixing time, mixer truck entry time and unloading time confirmation, concrete collapse and expansion determination and other main contents.

(4) Standardize the management of concrete supply

All ready-mixed concrete production enterprises shall strictly implement the management of supply ledgers, strengthen source control, and shall not sell commercial concrete to illegal construction projects that have not gone through construction permits or supervision and registration procedures in accordance with the regulations, and will be seriously dealt with once found.

Fourth, strengthen the quality control of the concrete construction process

(1) Do a good job of preparing for concrete pouring

The construction unit should formulate a concrete construction plan before pouring concrete, determine the location of the post-pouring belt and construction joints together with the design unit, clarify the pouring time of the concrete after the pouring belt, the treatment method of the post-pouring belt and the construction joint, and do a good job of technical disclosure to ensure that the concrete can be poured in time after passing the inspection. Ensure the stability of supports and supports, and prevent cracks in cast-in-place floor slabs; The support system of the post-pouring belt must be set separately and all painted with red eye-catching paint, reminding the operator not to dismantle at will, and it is strictly forbidden to return to the top after dismantling.

(2) Strengthen the management of the concrete pouring process

The construction unit shall strictly follow the requirements of the "Dongguan Construction Engineering Quality Prevention and Control Manual" and the "Dongguan Construction Engineering Quality Standardization Manual", strengthen the concrete construction management of important parts, and carry out the whole process of quality control:

1. It is strictly forbidden to add water during concrete pumping and pouring.

2. Strictly control the thickness of the floor slab and the thickness of the protective layer of the reinforcement. The cushion block, the negative reinforcement support of the slab and the concealed pipeline shall be set up according to the requirements of the specification to ensure the thickness of the floor slab and the effective height of the floor reinforcement. The floor slab shall not be loaded within 24 hours after the completion of pouring.

3. Comply with the key points of concrete pouring and vibrating construction of wall columns and beams. When the strength grade of wall, column, beam and slab concrete is different, effective interception measures should be taken to prevent the mixing of high and low grade concrete. The connection parts of walls and slabs, beams and columns should be poured with high strength grade concrete first, and concrete with low strength grade should be poured after the initial setting of concrete with high strength grade.

4. The post-pouring belt and construction joint treatment method should meet the requirements of the specification, and be poured according to the time required by the design and specification. The supervision unit should do a good job in the whole process of concrete pouring in important parts.

(3) Strengthen concrete curing

After the concrete pouring is completed, it should be ensured that the concrete has enough curing time with mold, moisturizing and curing in time, and the curing time and thermal insulation and covering measures should comply with relevant regulations. The bare surface of the foundation large-volume concrete should be covered and cured, and the large-volume concrete curing process should have reliable temperature control measures, and the concrete curing method should comply with the provisions of the "Code for Construction of Concrete Structure Engineering". During the maintenance of cast-in-place floor slabs, when the strength is less than 10 MPa, heavy objects should not be lifted or stacked on cast-in-place floor slabs. The supervision unit shall inspect the maintenance of concrete.

5. Strengthen the quality pre-control and acceptance management of ready-mixed concrete

The construction unit shall be at the construction site in accordance with the requirements of the "Code for Acceptance of Construction Quality of Concrete Structure Engineering" (GB50204-2015) to retain the concrete strength specimens and the same conditions of curing specimens, and the supervision unit shall complete the work of writing engineering information into chips and implanting chips in specimens in accordance with the requirements of the "Notice on Officially Enabling the "Dongguan Ready-Mixed Concrete Quality Dynamic Supervision Information System" (Dongjian Quality Letter [2019] No. 18) to ensure the authenticity of concrete specimens. The construction unit shall conduct a self-inspection of the strength of the solid concrete, and the supervision unit shall conduct a parallel inspection of the strength of the structural concrete components by batch, and if there is a problem with the strength of the solid concrete, it shall be reported to the engineering quality supervision agency in a timely manner. For the concrete construction of important parts, the relevant responsible entities should carry out video surveillance and save them as important image data of the project. Before the quality acceptance of the main division (concrete structure subdivision), the main structure entity quality supervision and sampling test should be carried out in accordance with the "Notice on Carrying out the Quality Supervision and Sampling of Concrete Structure Entities of Construction Projects" (Dongjian Qian'an [2016] No. 262).

6. Strengthen daily supervision and strictly investigate violations of laws and regulations

(A) the parks, towns (streets) construction administrative departments and engineering quality supervision agencies to increase the quality supervision of cast-in-place concrete structure engineering. Focus on spot checks on the implementation of concrete quality responsibilities of construction, construction, supervision units and ready-mixed concrete production enterprises, spot check the concrete strength of engineering entities, and spot check the quality behavior of all parties. In the process of daily supervision of the project, the quality supervision agency should urge the supervision unit to conduct parallel inspection of the aged concrete according to the batch, and if there is a problem, the responsible entity shall be required to deal with it accordingly in a timely manner.

(B) to increase the handling of cast-in-place concrete construction bad behavior. If the following violations are found in the daily supervision work of the quality supervision agency, the points shall be deducted from the bad behavior of the relevant responsible entities and dealt with in accordance with the law:

1. There is water addition in the process of concrete transportation and construction;

2. Failure to implant chips in concrete specimens as required;

3. There is fraud in the concrete specimen;

4. When the strength level of walls, columns, beams and slabs is different, no effective interception measures are taken;

5. The setting and treatment methods of post-pouring belts and construction joints do not meet the requirements;

6. Cast-in-place concrete is not cured in accordance with the regulations;

7. There are major quality problems such as serious cracks in the concrete floor slab.

(3) Strengthen the linkage management of quality supervision and linkage of concrete physical engineering. Strictly investigate the problem that the concrete strength does not meet the design strength grade or the thickness of the floor slab does not meet the design requirements. When the concrete strength of the vertical or horizontal components is found to be less than the design strength level and the thickness of the horizontal components (i.e., the floor slab) does not meet the design requirements, it shall be dealt with in accordance with the annex of the Notice on Carrying out the Physical Quality Supervision and Sampling of Concrete Structures of Construction Projects (Dongjian Qian'an [2016] No. 262). For concrete strength lower than the design strength of more than 1 grade, the supervision agency shall be responsible for the relevant responsible entities and ready-mixed concrete enterprises to deduct points for bad behavior, concrete strength is lower than the design strength of more than 2 grades, administrative punishment shall be imposed in accordance with the law; If the thickness of the floor slab does not reach 90% of the design floor thickness, the supervision agency shall deduct points for the bad behavior of the relevant responsible entities.

(4) Strictly investigate the act of arbitrarily compressing the reasonable construction period. The quality supervision agency shall include the inspection of the arbitrary compression of the construction period into the scope of daily supervision, and if it is found that there are violations, it shall carry out physical quality supervision and sampling tests on all involved parts, and deduct points for the bad behavior of the relevant responsible entities. If there are potential quality and safety hazards in the project due to arbitrary compression of the construction period, the project will be suspended and punished. If the construction period of the standard floor slab concrete of the residential project does not meet the above requirements, the issuance or withdrawal of the pre-sale certificate of the commercial housing of the project will be suspended.

(E) due to arbitrary compression of reasonable construction period affecting the quality and safety of the project, resulting in quality and safety accidents, the competent department of housing and urban-rural construction will be in accordance with the provisions of the regulations on the quality management of construction projects, Article 55 of the regulations on the management of production safety in construction projects, and other laws and regulations, order the construction unit to correct, and impose a fine of not less than 200,000 yuan but not more than 500,000 yuan; Where a major safety accident is caused and a crime is constituted, the directly responsible personnel shall be investigated for criminal responsibility in accordance with the relevant provisions of the Criminal Law; and where losses are caused, they shall be liable for compensation in accordance with law.

Dongguan Municipal Bureau of Housing and Urban-Rural Development