Problems encountered during the foundation construction process

Crack problem

Concrete is a heterogeneous body composed of different materials, and external loads and environmental influences can cause complex phenomena such as initial stress, internal transfer, and diffusion inside. Therefore, concrete may experience cracking problems during construction. The characteristics of large volume concrete are that the concrete pouring surface and pouring volume are large. When the concrete is poured, the highest temperature inside the concrete will reach its maximum in a short time due to the influence of cement hydration heat. At this time, if the temperature difference between the inside and outside of the concrete exceeds 25 ℃, surface cracks and shrinkage cracks are prone to occur during the heating and cooling stages. Cracks can be divided into surface cracks and deep cracks according to their depth. Surface cracks generally pose less harm, while deep cracks have relatively greater harm and may sometimes damage the integrity and stability of concrete structures. According to other aspects, the causes of cracks can be divided into cracks caused by temperature changes, cracks caused by foundation changes, cracks caused by design reasons, cracks caused by steel corrosion, cracks caused by the quality of construction technology, etc. Cracks in large volume concrete are generally caused by temperature, which is partly due to internal factors of the concrete: the high temperature inside the concrete caused by the hydration heat of cement leads to temperature shrinkage cracks when the surface temperature of the concrete is significantly different from the air temperature. The expansion coefficient of concrete is 0 per degree Celsius 00001, for every 10 ℃ temperature change, the concrete will produce 0 01% expansion or contraction first. In addition, if concrete is constrained to deform, stress will be generated in the structure. Concrete has tensile strength, also known as temperature cracking performance. When the stress exceeds this performance of concrete, the foundation will deform and crack. The vertical or horizontal displacement caused by uneven settlement of the foundation generates additional stress structures, in addition to the tensile strength of the concrete structure, leading to structural cracking. In order to prevent steel corrosion, the crack width should be controlled according to the specifications for design, and an appropriate protective layer thickness should be adopted. There are also cracks caused by the quality of construction technology. During the construction process, the requirements for concrete construction technology are relatively high. If the construction technology department standardizes during the construction process, the possibility of cracks occurring in later use will increase.

Other problems encountered during the construction of large volume concrete

Firstly, during the construction process, the pouring and vibration of large volume concrete should ensure that a new layer of concrete is covered and vibrated before the initial setting of each part of the concrete, and the influence of factors such as the size of the structure, the density of steel bars, the retention of embedded pipes and anchor bolts, the supply of concrete, and hydration heat should also be considered. Secondly, during the curing stage of large volume concrete, attention should be paid to controlling the temperature difference between the inside and outside of the concrete, which requires maintaining appropriate temperature and humidity to promote the normal development of concrete strength and prevent the occurrence of concrete cracks and their development. The curing of large volume concrete should not only meet the needs of strength growth, but also prevent cracking of concrete caused by temperature deformation by controlling the temperature of the damaged material. Finally, when removing the formwork for large volume concrete, the temperature difference of the concrete should not exceed 20 ℃.