Is there a specific point in the scheme of large volume concrete layered construction, a large raft

The foundation raft is 70m long and 15 thick, which belongs to the large-volume concrete construction, what measures should be taken to ensure that the raft is not out of your family, the construction organization should pay attention to continuous pouring, and the upper layer should be poured before the initial setting of the lower layer when pouring in layers, and when pouring in parallel, the stubble should also be completed before the initial setting. The process should be subjected to secondary vibration, to avoid leakage vibration, timely maintenance, maintenance time, maintenance methods should be noted. In terms of measures, temperature control measures should be taken, monitoring the temperature difference between inside and outside, and the temperature difference between internal adjacent points, if it is not satisfied, timely measures should be taken, such as borehole water circulation and external insulation.

The most important material is to pay attention to the mix ratio, especially the water-cement ratio is not easy to be too large, affecting the strength, forming shrinkage cracks, and it is not easy to be too small, the hydration heat is large to form expansion cracks, important projects should be matched, the admixtures used, the mixture, aggregates, water should control the alkali content, and the alkali active aggregate reaction will produce expansion cracks. Hope it helps.

Summary. General raft floor with C25 or C30 concrete, in accordance with the construction engineering concrete design code and construction engineering concrete construction specification, in the conventional design, the designer of the design unit generally through the calculation, basically adopt the above-mentioned concrete number is the design, and for the strength of the raft floor and the thickness of the bottom plate has specific requirements, is conducive to the construction period and economic interests in the construction.

Raft foundation also belongs to a kind of extended foundation, generally used for high-rise frame, frame shear, shear wall structure, when the use of strip foundation can not meet the bearing capacity requirements of the foundation, or when the building requires the foundation to have enough rigidity to adjust the uneven settlement. Raft foundations are divided into beam slab raft foundations and flat plate raft foundations.

Classify. The raft foundation is also called the raft foundation, that is, the full foundation. It is to connect all the independent foundations or strip foundations under the column with contact beams, and then pour the bottom plate as a whole.

The raft foundation is divided into a flat raft base and a beam plate raft base, and the flat raft base supports local thickened raft types; The beam-plate raft base supports two forms: upper flat and lower flat rib beam. Generally speaking, when the bearing capacity of the foundation is uneven or the foundation is weak, a raft type foundation is used. Moreover, the buried depth of the raft foundation is relatively shallow, and it can even be used as a non-buried deep foundation.

After the raft foundation construction and concrete pouring are completed, the time for sprinkling and curing should be (the bottom plate concrete is impermeable concrete, and the curing period is not less than 14 days).

General raft floor with C25 or C30 concrete, in accordance with the construction engineering concrete design code and construction engineering concrete construction specification, in the conventional design, the designer of the design unit generally through the calculation, basically adopt the above-mentioned concrete number is the design, and for the strength of the raft floor and the thickness of the bottom plate has specific requirements, is conducive to the construction period and economic interests in the construction. Raft foundation also belongs to a kind of extended foundation, generally used for high-rise frame, frame shear, shear wall structure, when the use of strip foundation can not meet the bearing capacity requirements of the foundation, or when the building requires the foundation to have enough rigidity to adjust the uneven settlement. Raft foundations are divided into beam slab raft foundations and flat plate raft foundations.

Classification raft foundation is also called raft foundation, that is, full foundation. It is to connect all the independent foundations or strip foundations under the column with contact beams, and then pour the bottom plate as a whole. The raft foundation is divided into a flat raft base and a beam plate raft base, and the flat raft base supports local thickened raft types; The beam-plate raft base supports two forms: upper flat and lower flat rib beam.

Generally speaking, when the bearing capacity of the foundation is uneven or the foundation is weak, a raft type foundation is used. Moreover, the buried depth of the raft foundation is relatively shallow, and it can even be used as a non-buried deep foundation. After the raft foundation construction and concrete pouring are completed, the time for sprinkling and curing should be (the bottom plate concrete is impermeable concrete, and the curing period is not less than 14 days).

Hope it helps, dear

The reason for the layered pouring of concrete of raft foundation is that the thickness is large, the area is wide, and the one-time pouring is not conducive to construction, and the excessive heat of hydration is not conducive to the effective strength of the structure.

Before pouring, the garbage, soil, oil stains and other debris on the steel bar in the formwork should be removed, and the cement mortar cushion block and plastic cushion block of the steel bar should be checked to see if they are well mated. If wooden formwork is used, it should be watered to make the formwork moist. The sweeping port of the column formwork should be closed after removing debris and stagnant water.

Vibrating requirements. 1.The free falling height of the concrete self-feeding port shall not exceed 2 meters, and measures must be taken when it exceeds 2 meters.

2.When pouring concrete, it should be carried out in sections and layers, and the pouring height of each layer should be determined according to the structural characteristics and the density of the reinforcement, and the general layered height is the length of the vibrator part, and the maximum is not more than 50 cm.

3.The use of plug-in vibrator should be quickly plugged and unplugged slowly, and the insertion points should be evenly arranged, moved point by point, and carried out in sequence, and should not be omitted, so as to achieve uniform vibrating. The moving distance is not greater than the multiple of the radius of the vibrating rod (generally 30 40cm).

When vibrating the upper layer, the lower layer should be inserted 5cm to eliminate the gap between the two layers.

4.Pouring concrete should be carried out continuously. If intermittent is necessary, the intermittent time should be shortened as much as possible, and the secondary concrete should be poured before the initial setting of the pre-layer concrete.

5.When pouring concrete, we should often observe whether the formwork, steel bars, reserved holes, embedded parts and inserts are moved, deformed or blocked, and the pouring should be stopped immediately if the problem is found, and the poured concrete should be corrected before it is set.

Not all raft concrete is poured in layers, and this method is only used when pouring large volumes of concrete. But this is not the only method, there is also segmented pouring, layered segmented pouring.

1. Not all raft concrete should be poured in layers, and raft thickness less than 500mm is generally poured without layers. Layered pouring is mainly for large-volume concrete, to prevent the concentration and excessive heat of cement hydration, resulting in temperature cracks. Layered pouring can reduce the peak of hydration heat, facilitate heat dissipation, and vibrate in place.

2. The reason for layered pouring: 1) There is a vibrating process when pouring concrete, and vibrating is to ensure the compactness of concrete, and the amplitude of the existing vibrating equipment is limited, and it is too thick to exceed the working range of the vibrator, and it is easy to produce hollowing phenomenon. If the one-time pouring is too thick, the air in the concrete is not easy to be discharged in the vibration, and the vibration time is too long, which will cause the segregation of the concrete, that is, the separation of debris and stone, which affects the strength of the concrete.

2) The cement in the large-volume concrete should release a certain amount of heat in the hydration process, and the large-volume concrete structure has a thick section and a relatively small surface coefficient, so the heat generated by the cement is not easy to lose in the structure. In this way, the heat of hydration inside the concrete cannot be dissipated in time, so that the accumulation is higher and higher, so that the temperature difference between the inside and outside increases. The heat of cement hydration released per unit time of concrete is related to the amount of cement and cement variety per unit volume of concrete, and increases with the age of concrete.

Layered pouring and timely heat dissipation are conducive to reducing temperature cracks in large-volume concrete.

3. The layered pouring method is shown in the following figure:

1 The height of the foundation raft slab pillars should rise above the concrete surface and should be between meters.

2 The foundation raft is a large-area foundation that bears the weight of the building and distributes it into the foundation, while the columns support the superstructure of the building.

The height of the foundation raft column rising from the concrete surface should be between the meters of the Zen beat, because too high will affect the aesthetics of the building, and at the same time, it will also increase the wind area of the building, increase the stress of the structure, and too low may lead to insufficient force on the column, thus affecting the safety of the building.

3 In addition, the height of the foundation raft column rising from the concrete surface also needs to be adjusted according to the specific situation of the building, such as the height of the building, the weight, the bearing capacity of the foundation and other factors need to be considered.

Therefore, when carrying out the basic design, it is necessary to conduct a comprehensive analysis according to the specific situation to ensure the rationality and safety of the basic design.

1 The foundation raft pillars should rise about 15 cm above the concrete surface.

2 The main function of the foundation raft is to carry the weight of the building and disperse it into the foundation soil, while the columns are the supporting structure of the building.

In order to prevent the bottom of the column from being eroded by the soil, it must be raised to a certain height, and the height of the foundation raft should be the same as the height of the column, so it is generally about 15 cm.

3 In addition, the height of the foundation raft column rising from the concrete surface needs to be adjusted according to the specific situation, such as the height of the building, the groundwater level and the stability of the soil and other factors will affect the design and implementation of the foundation.

Therefore, in the process of architectural design and construction of Jianfeng stove, full consideration and meticulous calculation are also required to ensure the safety and stability of the building.

The height at which the foundation raft pillars should rise above the concrete surface should be determined on a case-by-case basis. In general, the height of the raft column should not be less than 100mm above the concrete surface, so as to facilitate the reinforcement and anti-corrosion treatment of the column after the concrete is poured. In some special circumstances, such as high groundwater level and unstable soil layer, the height of the concrete surface should be adjusted accordingly according to the specific situation, generally above 100mm.

In addition, when carrying out the foundation design, the height of the raft column rising from the concrete surface should be determined according to the load, usage, nature of the foundation soil and other factors of the building. During the construction process, the construction should be carried out in accordance with the design requirements, and the height of the circular difference of the concrete surface should be strictly controlled to avoid deviations and ensure the stability and safety of the foundation.

In construction, the foundation should rise at least 10 cm above the concrete floor. This ensures that the foundation is separated from the ground and avoids moisture and decay. However, in specific cases, such as in areas where it is necessary to avoid the flow of water into the basement of a building, it is advisable to raise the foundation to a higher height.

The building designer should determine the lifting height of the raft column on a case-by-case basis.

The concrete surface of the reinforced concrete slab column should be lifted at least 30mm on the concrete foundation in order to leave a gap between the concrete foundation and the shinosa column, so as to avoid contact between the concrete foundation and the shinosa column, so as to prevent damage to the concrete foundation. In addition, the concrete surface of the concrete should be adjusted according to the actual situation, so that the compressive strength of the shinoha column can be effectively played.

The raft foundation of high-rise buildings belongs to the bulk of concrete.

According to the "Code for the Construction of Large-volume Concrete" GB50496-2009, the minimum geometric size of the concrete structure is not less than 1m, or the concrete that is expected to cause harmful cracks due to the temperature change and shrinkage caused by the hydration of the cementitious material in the concrete, is called large-volume concrete.