Ready-mixed concrete is made from four to five or more materials of different properties, such as cement, water, fine granules, coarse granules and selected admixtures (which may include blast furnace slag, fly ash, chemical admixtures), which are pre-mixed in a plant. The raw materials are produced, transported, stored and mixed during production and delivered to the site via ready-mix trucks.
I Stagnant water method
II Watering sprinkling method
III Covering method
when pouring and leveling, deliberately build a dike around the concrete surface to stagnate water.
After the placement is completed, water is sprinkled on the concrete surface continuously or intermittently.
Use of a cover to keep concrete wet and delay the hardening and setting of the concrete surface
Apply liquid compound agent to the concrete surface to form an impermeable film to prevent the evaporation of water from the concrete.
Needs high early-stage strength. In cold areas concrete needs to be heated to promote the hydration of concrete.
The general concrete maintenance method is mostly applied after the whole casting work is completed, which has lost the best opportunity to suppress plastic shrinkage cracks, so it cannot effectively suppress the cracks. If the maintenance is implemented during the casting process, it will cause problems such as inconvenience in concrete construction and rough or sandy surface after construction. If the water sprinkler head can be distributed evenly over the whole working plane, the water sprayed will slowly and finely fall on the concrete surface in the form of water mist, which can effectively inhibit the formation of plastic shrinkage cracks.
According to CNS3090 A2042 "Ready-mixed Concrete", the specifications of ready-mixed concrete are based on the compressive strength, slump and the nominal maximum particle size of coarse grains, which are listed in the following table with the "O" symbol.
The specifications of custom-made products are agreed between the buyer and the seller: the specifications in the above table may not meet the requirements of the project, and the owner (buyer) may set his own specifications according to the needs of the project, such as the slump requirements of self-filled concrete, or zero-slump concrete for pavement and bridge decks, etc.
The degree of difficulty in the application of concrete is called workability, provided that the materials are not separated. Judgment of workability should be based on the construction method, construction site, project structure, machinery and equipment and other conditions and have different standards of judgment. Therefore, the workability is not necessarily determined by the slump size, but the best way is to produce concrete with lower slump as much as possible to meet the requirements of workability. Slump and flow are one of the simpler ways to measure the "quantitative" workability of concrete.
The degree of difficulty in the application of concrete is called workability, provided that the materials are not separated. Judgment of workability should be based on the construction method, construction site, project structure, machinery and equipment and other conditions and have different standards of judgment. Therefore, the workability is not necessarily determined by the slump size, but the best way is to produce concrete with lower slump as much as possible to meet the requirements of workability. Slump and flow are one of the simpler ways to measure the "quantitative" workability of concrete.
Nowadays, the application of self-filled concrete or high-flowing concrete is very common, and if the slump alone is used to express the workability of concrete, it is not enough to show the unique properties of this special concrete. Therefore, "slump flow test" has been introduced to address this issue, which is to measure the diameter of concrete slump and diffusion after slump test, with the diffusion range (D) value as shown below called "slump flow".
