With the rapid development of ready-to-use concrete, there are more and more cases where the supply and demand sides are arguing with each other due to the low strength of structural concrete. Since the ready-made concrete industry belongs to the buyer's market, in order for the supply side to recover the payment in time, in order to continue to cooperate with the demand side Cooperation, most enterprises had no choice but to make concessions and passively assume part of the economic responsibility. According to the author's detection of the strength of structural concrete, the main reasons for the low strength of structural concrete are as follows:
1.1 Current status of concrete maintenance
(1) The cast-in-place slab is covered with a plastic film to prevent early cracks, but most construction sites remove the film before laying out the construction line, and then change it to watering maintenance; most construction sites do not have a dedicated person responsible for the maintenance work, just arrange Odd workers maintain several times when they have spare time.
(2) It is better to wrap the concrete columns with plastic film, but there are a few construction sites that have not adopted it.
(3) Most of the concrete shear walls are maintained by sprinkling water after the formwork is removed, but there is no special person responsible for it, the number of sprinkling water is too small, and the maintenance time is too short, which cannot meet the specification requirements.
(4) Especially in recent years, there are more and more high-rise buildings. After more than ten floors, the water pressure cannot be reached, and water pumps can only be installed for secondary pumping. Some water pipes are not enough, and some water tanks cannot be lifted up in time, resulting in poor maintenance. In time, the higher you go, the more difficult it becomes, and the curing of the concrete gets worse.
1.2 Hidden dangers of poor curing to concrete
Due to the lack of maintenance of the newly poured concrete, the strength of the concrete will be significantly reduced, and the reduction will reach 25% to 35%, leaving hidden dangers to the safety of the structure; in addition, the surface of the concrete is not dense, the carbonization speed is fast, and the carbonation depth is large In some projects, when the structure rebounds, the carbonation depth of C30 concrete has reached 6-10mm in less than half a year after pouring. This situation is enough to show that the part has not been maintained at all. If the carbonation depth is too large, the protection ability of concrete to steel bars will be reduced, and the durability of concrete structures will be shortened.
Drilling core detection is not standardized:
Some testing units cannot strictly follow the requirements of the “Core Drilling Regulations” during the core drilling testing process. After cutting the core samples, they do not process the pressure test, resulting in a 20% to 50% reduction in the compressive strength of the core sample concrete than the actual strength. There are also units whose grinding machine does not meet the requirements of the regulations. The grinding machine does not have a device for clamping the core sample. Hold the core sample with both hands and grind it on the grinding wheel. How can such a grinding machine smooth the pressure surface of the core sample? ?
