Does the concrete for post cast construction with a higher grade of concrete have to be poured?

Technical specification for concrete structures of high-rise buildings JGJ 3-2002》 When a rigid waterproofing scheme is adopted, the foundation of the same building should avoid setting deformation joints. A post-construction pouring joint that penetrates the roof, bottom plate and wall plate can be left every 30 40m along the length of the foundation, and the width of the joint should not be less than 800mm, and it should be arranged in the middle range of the column spacing in three equal parts. Additional waterproof layer should be used for the bottom plate and external wall at the post-pouring joint; The concrete should be poured after two months after the concrete on both sides of the concrete is poured, and its strength grade should be increased by one level, and it is advisable to use the concrete with early strength and compensating for shrinkage.

Explanation of standard terms:

1. It means that it is very strict and must be done: the positive word is "must", and the negative word is "strictly prohibited".

2. It means that it is strict, and it should be done under normal circumstances: the positive word should be "shall", and the negative word should be "should not" or "shall not".

3. It means that a slight choice is allowed, and the first thing to do is when conditions permit: the positive word is "appropriate" or "may", and the negative word is "unsuitable". Indicates that there is a choice, and that this can be done under certain conditions, the word "may" is used.

In the specification, "should" is not "must", and the normal situation should be done at a higher level, but if you have a good relationship, there are special circumstances, or the quality requirements are not high, you can not use the higher level, as for the micro-expansion (compensating for shrinkage) specification, you can use "appropriate", and the quality requirements are not high.

Not only to be higher, but also to add an expansion agent, which is the so-called expansion concrete.

Yes, it is necessary to use expanded concrete one grade higher.

Yes, it must be marked one year higher.

In order to prevent cracks between the old and new concrete, the formation of weak spots.

The post-pouring belt is a temporary construction joint left at the corresponding position of the foundation floor, wall and beam in accordance with the requirements of the design or construction specifications in order to prevent the harmful cracks that may occur in the cast-in-place reinforced concrete structure due to its own uneven shrinkage or uneven settlement in the building construction.

The post-pouring belt temporarily divides the structure into several parts, and after the internal shrinkage of the components, the concrete of the construction joint is poured after a certain period of time, and the structure is connected into a whole zone. The pouring time of the post-pouring belt should be selected when the temperature is low, and the cement or cement can be mixed with a trace amount of aluminum powder concrete, and its strength grade should be one level higher than the strength of the component, so as to prevent cracks between the new and old concrete and the formation of weak parts.

Design requirements for post-pouring belt pouring.

1) The retention width of the post-pouring belt is generally 700-1000mm, and there are three common types: 800mm, 1000mm and 1200mm.

2) There are four types of joints in the post-pouring belt: straight seam, stepped seam, notch seam and X-shaped seam.

3) The steel bar in the post-pouring belt is fully disconnected and then lapped, and there is a provision for additional reinforcement without opening.

4) The re-pouring time of post-pouring with concrete, "Technical Regulations for Concrete Structures of High-rise Buildings" (JGJ3-2010) stipulates that it is poured after 45 days. The third edition of the Concrete Structure Construction Handbook China Architecture & Building Press stipulates that it is 28 days.

5) The concrete preparation and strength of the post-pouring belt, and the original concrete grade is increased by one level to compensate for shrinkage concrete pouring.

It is a grade higher than the slab of the indwelling post-pouring belt, and the impermeable expansion concrete is used, for example, your board is C35, and the post-pouring belt is C40P8

A post-pouring belt for micro-expanded concrete pouring that is one grade stronger than the original concrete. See General Description of Structural Design.

Hello dear, here is the reason why you can find out that the post-pouring belt is a temporary construction joint set up in order to overcome harmful cracks due to temperature, shrinkage and settlement during the construction of cast-in-place concrete structures. The joint needs to be retained for a period of time according to the design requirements before pouring, and the setting distance of the pouring belt after connecting the whole structure into a whole should be determined by calculation under the condition of considering the effective reduction of temperature difference and shrinkage stress. Under normal construction conditions, the general spacing is 30 50m, and after taking special measures, it can be increased appropriately.

The retention time of the post-pouring belt should be determined according to the design, if there is no design requirement, it is generally retained for at least 28 days. The width of the post-pouring belt is generally 70 200cm, and the steel bars in the post-pouring belt should be well protected. Before the construction of the post-pouring belt, the entire concrete surface must be treated in accordance with the requirements of the construction joint.

The concrete filled with the post-pouring belt can be made of micro-expansion or low-shrinkage concrete, and the concrete strength grade should be increased by one level compared with the original structural concrete strength grade, and the wet curing must be maintained for more than 14 days.

The post-pouring belt is a concrete belt left in the corresponding position of the foundation floor, wall and beam in accordance with the requirements of the design or construction code in order to prevent the harmful cracks that may occur in the cast-in-place reinforced concrete structure due to its own uneven shrinkage or uneven settlement in the building construction, which has the following classifications:

1. In order to solve the settlement difference between the main building and the podium of high-rise buildings, the post-pouring construction belt is called the settlement post-pouring belt.

2. In order to prevent the concrete from cracking due to temperature changes, the post-pouring construction belt is called the temperature post-pouring belt.

3. In order to prevent the structure from shrinking and cracking due to excessive construction area, temperature changes, and concrete shrinkage, the post-pouring construction joint is an expansion and post-pouring belt.

Dear, hello, I'm glad to answer for you: can the concrete of the first and second layers of post-pouring belt be poured at one time Answer, pro: No, 1. When pouring the belt after pouring temperature, it cannot be poured at one time, and it should be poured twice.

Because according to the requirements of the specification, it needs to be set up only after a length of more than 50 meters, and the concrete can be poured after 28 days when it is completely stable before it can be poured again, so it needs to be poured after 28 days. Moreover, it is easy to be affected by thermal expansion and contraction in the early stage, and it is also necessary to do a good job in maintenance. 2. If you choose to pour at one time, it will affect the strength, mainly by the temperature, and cracks are easy to appear between the new and old concrete, we need to take into account the temperature factor, and can not be poured at one time.

2. Problems related to pouring belt after pouring temperature 1. After pouring temperature pouring belt, first of all, it is necessary to strictly control the fit, which will affect the strength of the later formation. If it is a C20 strength grade, the water-glue ratio should be reached, in which the composition of water is 168 kg, cement 210 kg, sand 753 kg, stone 1230 kg, and water reducer kg. If it is not proportioned according to the proportion, it will affect the qualification of the concrete base mu.

2. The selection of materials is also very important, and the amount of water added should be strictly controlled to mix and leak slag concrete. If the hard concrete is less than 30%, and the fluidity concrete is only 20%, it will affect its strength if it is mixed with excess water, and there is more water, which will lead to early shrinkage and surface cracking. 3. The selection of sand and gravel is also very important, generally speaking, coarse sand should be chosen.

The medium sand is selected, the grade should be better, the mud content should not exceed 3%, and the particle size should be controlled between 5 and 30 mm.

<> post-pouring belt is a temporary construction joint set up to overcome harmful cracks that may occur due to temperature and shrinkage during the construction of cast-in-place reinforced concrete structures. The joint needs to be retained for a period of time according to the design requirements before being poured, so as to connect the entire structure into a whole.

The setting distance of the post-pouring belt should be calculated under the condition of effectively reducing the temperature difference and shrinkage stress. Under normal construction conditions, the relevant specifications stipulate that if the concrete is placed indoors and in the soil, it is 30m; In the open air, it is 20m.

The retention time of the post-pouring belt should be determined according to the design, and if the design is not required, it is generally retained for at least 28 days.

The width of the post-pouring belt should be considered to be simple to avoid stress concentration. Generally its width is 70 100 cm. The reinforcement in the post-pouring belt should be well preserved.

Figure 10-32: Structural drawing of post-pouring belt (a) Flat joint; (b) tongue and groove; (c) Stepped type.

Before pouring concrete, the entire concrete surface must be treated in accordance with the requirements of the construction joint. Filled post-pouring concrete can be made of micro-expansion or non-shrinkage cement, or ordinary cement can be mixed with the corresponding admixture, but the strength grade of the filled concrete must be increased by one level than the original structural strength, and at least 15 days of wet curing must be maintained.