1. Raw material selection of ready-mixed concrete
Because you are familiar with cement and sand, today we focus on the selection of two raw materials: concrete admixtures and admixtures.
The types of concrete admixtures are mainly water reducing agent, pumping agent, antifreeze, waterproofing agent, early strength agent, retarding agent, expansion agent, air entraining agent, etc., in winter construction concrete often mixed with antifreeze, antifreeze is mainly composed of antifreeze, early strength, air entraining, water reduction and other components. Its main component is sodium nitrite, they can reduce the freezing point of concrete mix, prevent concrete in winter construction under negative temperature caused by frost damage, to ensure the normal construction of concrete under negative temperature. It is strictly prohibited to use salt instead of sodium nitrite, because salt contains chloride ions, which will corrode the steel bar.
The commonly used concrete admixtures include fly ash, slag powder and volcanic ash. Especially, Grade I fly ash, slag powder and silica fume have good application effect. In engineering practice, "double-mixing" technology is often used, that is, mixing fly ash and slag powder at the same time, so as to prepare ordinary, high-strength and high-performance concrete, which can save cement, improve the workability, strength and durability of concrete, and significantly reduce the heat of hydration of mass concrete, which can meet the construction technical requirements of different projects.
2. Quality control of concrete pouring process
(1) It is strictly prohibited to add water in the process of concrete transportation, transportation and pouring.
(2) When two kinds of strength grades of concrete are poured at the same time, the concrete transport vehicle should be equipped with strength grade signs, first pouring high strength grade, then pouring low strength grade, pump and construction personnel should also keep close contact with each other to prevent mispouring of concrete.
(3) Before the final setting of concrete, the plaster treatment on the pouring surface is beneficial to restrain surface cracks and improve the surface quality of concrete. In particular, after the floor concrete pouring, the wooden trowel should be rubbed more than two times to eliminate the early cracks before the final concrete setting.
