Plastic shrinkage, 4.27

Plastic shrinkage is dependent on many factors, such as plastic density, stock temper-... 

The following is a list of recommendations that builders can use to utilize the foundation as a mechanical barrier to radon entry. Foundation walls and floor slabs are often constructed of poured concrete. Plastic shrinkage, and therefore cracking, is a natural function of the drying process of concrete. Many factors, such as the water/cement/aggregate ratio, humidity, and temperature, influence the amount of cracking that occurs in a poured concrete foundation. Cracking may be minimized by... 

The increased tendency for plastic shrinkage caused by rapid evaporation due to high mix temperature and low relative humidity. 

Fig. 7.36 Effect of temperature on plastic shrinkage (Soroka and Ravina [94]).

HOT-WEATHER CONCRETING (PLASTIC SHRINKAGE IN FLAT-SLABS DUE... 

Fig. 7.47 Plastic shrinkage of retarded and unretarded cement mortars of plastic consistency and OPC content of 550 kg m-3. Air temperature 30 C, wind velocity of 20 km h-i and IR irradiation (Soroka and Ravina [94]).

Example of plastic shrinkage without and with glass fiber... 

Early load damage Plastic shrinkage Plastic settlement... 

Plastic shrinkage D Diagonal Roads and slabs Rapid early drying Low rate of bleeding 30 min to 6 h... 

The surface of the concrete substrate has to be prepared to provide sufficient bond of the repair material. Factors that may affect the bond are the strength and integrity of the substrate, the cleanliness of the surface, and the roughness. The surface should be rough and dust or incoherent residues should be removed (for instance by sandblasting or waterblasting). This operation is usually not necessary if hydro-demohtion has been used. If the cementitious repair material is appHed directly on the surface of the concrete, the surface should be saturated by water in order to avoid absorption of water from the substrate and subsequent plastic shrinkage and incomplete hydration of the repair material, which will result in loss of bond. 

Another research effort in this area focused on the use of waste nylon fibers to reduce plastic shrinkage cracking ... 

At early age of cement paste reaction with water the plastic shrinkage occurs, which consists in evaporation of water from the surface layers of concrete [108]. The volume of fresh concrete is thus reduced. This process is not related to the properties of cement itself however it can also result in the formation of cracks. This situation is the consequence of substantial humidity gradient in concrete. The plastic shrinkage, equal 2.5 mm/m, observed in the 7 cm thick surface layer of concrete, was two times higher than the shrinkage in the core of element [108]. 

---