Concrete made with excess water also experiences greater shrinkage, which typically adds to more cracking. If high slump concrete is essential to the success of the project, you can produce it by using one of the high range water reducer admixtures, also called super-plasticizer. These admixtures greatly increases the workability of the concrete for as much as 30 minutes, after which the concrete returns to its original form. Recommended maximum slump. Hand consolidating includes rodding and spading.
Mechanical vibration permits stiffer mixes.
Durability and strength for air-entrained concrete Application Approx. Adding extra water rapidly lowers durablity and strength. Placing of Concrete A concrete slab on grade starts with a properly prepared site. Concrete requires no special soil as long as the soil is homogeneous and provides uniform support for the slab. A moist subgrade is especially important to prevent too rapid extraction of water from floors and similar work are being placed in hot weather.