What is the 2 calendering of concrete construction

Secondary calendering: The coagulant of cement is gypsum, and after the plaster absorbs water, it becomes raw gypsum.

The cement is added with water and mortar before use, and the density is increased by the rolling of the trowel, so that the excess water accumulates in the upper layer, so that the water content of the mortar in the upper layer is high, and the moisture content is stagnant for a period of time.

When it is reduced to a certain proportion, a second rolling increases the density of the mortar, making it hard and smooth.

Calendering refers to the last process of concrete and plastering, which is made of "iron plate" (made by self-made with band saw blades), such as the concrete surface layer must master the heat before "calendering", and the water stains must go sand before drying. However, now if the concrete pavement adopts vacuum water absorption, the surface is compacted (calendered) and can be mechanical. The purpose is to make the ground sand-free; Make the concrete and plastering surface layer smooth and smooth.

Concrete water collection is the first time after pouring, and the water that comes out of the concrete is scraped off by the way. The second calendering and trowel of concrete is to do the above process after the initial setting of the concrete, before the final setting, use the calender to preliminarily smooth it, and then use the ash knife to smooth it.

The secondary plastering process of concrete refers to the technical measures taken to compact, smooth and prevent cracking of the surface layer concrete of the structure or component in two different periods before the initial setting and the final setting of the concrete in order to control the non-structural surface cracks and surface layer smoothing caused by its subsidence and water collection and ensure the apparent quality of the concrete just after the concrete is vibrated and completed, and its main role is to control the development of surface cracks.

That is, after the concrete is poured, the rough surface, after the bubbles are squeezed out, wait for the concrete to solidify quickly and then calender, once to remove the bubbles, the second time is to ensure calendering, it is not good to calender directly, it is easy to bubble again, and it is not easy to wipe, I don't know what you mean, I don't know if you don't want to review my comments.

Secondary calendering refers to leveling once after concrete pouring, and the last leveling calendering after initial setting.

Cement ground, after the concrete is laid and vibrate, it should be flattened with a ruler, and the height is about 5mm higher than the ash cake. When the initial setting is 80%, the second height is the same as the ash cake, and the wood is used to wipe the foam twice before 60% to shape the ground. When the cement is 90% solid, then press it with an iron trowel for the first time, (depending on the situation, you can also sprinkle a little dry cement), and when it is in a 95% state, the ground of the second construction is calendered, and it is very solid after completion, with a bright surface and a smooth finish.

The main thing is that it is not easy to get sand.

The purpose of calendering and collecting concrete is to maintain the hardening strength of concrete.

Concrete is mainly divided into two stages and states: the plastic state before setting and hardening, that is, fresh concrete or concrete mixture; The hard state after hardening, i.e., hardened concrete or concrete.

The concrete strength grade is divided by the standard value of cubic compressive strength, and the strength grade of ordinary concrete in China is divided into 14 grades: C15, C20, C25, Qiaopei C30, C35, C40, C45, C50, C55, C60, C65, C70, C75 and C80.