Plastic shrinkage cracking

Environmental conditions such as ambient temperature, relative humidity and wind velocity during curing are very critical. An increase in ambient temperature, a drop in relative humidity and an increase in wind velocity encourage the development of shrinkage cracking. 

ACI 30SR-99. Farmington Hills, Ml American Concrete Institute, 2000 and CCAA, Plastic Shrinkage Cracking. Australia Cement Concrete and Aggregates, 2005.) 

Plastic shrinkage cracks do not seem to cause problems in some situations, but in other cases, they provide an entry for de-icing salts and may contribute to freezing and thawing damage (Pool 2005). 

Plastic shrinkage cracking can be avoided by taking extra care during early curing. 

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

Soroushian P, Mirza F and Alliozaimy A. Plastic shrinkage cracking of polypropylene fiber reinforced concrete. ACI Materials Journal 1993 92(5) 553-560. 

The addition of fibres affects the plastic and hardened properties of concrete. The properties that improved are plastic shrinkage cracking and tensile and flexural strength. The addition of fibres also enhances the ability to resist cracking and spalling and to reduce crack propagation. 

Plastic settlement and plastic shrinkage cracks - occur within a few hours of casting. 

Other studies on the use of polypropylene fibers from carpet waste in concrete [81], used tire cords in concrete [82, 83], and using recycled nylon fibers to reduce plastic shrinkage cracking in concrete [84] have also been reported and reviewed [85]. Gordon et al. [86] used the waste nylon fibers and ground carpet to stabilize asphalt concrete. Increase of asphalt content in asphalt concrete is favorable because it leads to more durable roads. But it is limited by the resultant flushing and bleeding of pavements and possible permanent deformation of the pavement. Addition of 0.3 wt% waste fibers increased the allowed asphalt content by 0.3-0.4 wt%. 

Groom J. L., Holmquist D. V. and Yarbrough K. Y. (1993), Use of waste nylon fibers in Portland cement concrete to reduce plastic shrinkage cracking , in Proc. Recovery Effective Reuse of Discarded Materials and By-Products for Construction of Highway Facilities, Denver, CO, Oct. 19-22,179-183. 

Pelisser, F, Neto, A.B.S.S., La Rovere, H.L., Pinto, R.C.A., 2010. Effect of the addition of synthetic fibres to concrete thin slabs on plastic shrinkage cracking. Construction and Building Materials, 24(11), pp. 2171-2176. 

Banthia, N., Gupta, R. (2006) Influence of polypropylene fiber geometry on plastic shrinkage cracking in concrete . Cement and Concrete Research, 36 1263-7. 

The influence of polypropylene (PP) fibres on early shrinkage (plastic shrinkage) cracking was tested by many authors. A rather low fibre content, 1.0 kg/ or so, is considered sufficient to prevent early shrinkage cracking. Various kinds of synthetic fibres are used to control cracking (cf. Section 5.6). 

Heavy desiccation of newly cast concrete can result in plastic shrinkage cracks in the concrete surface. The desiccation rate of a wet concrete surface is generally determined by the wind velocity at the surface and of the difference between the partial pressure of water vapour at the wet concrete surface pc and the partial pressure of water vapour in the ambient air pa. For a concrete surface, pc corresponds to the partial pressure of saturated water vapour at the concrete temperature 0c. The partial pressure of water vapour in the ambient air is determined by the air temperature 0a and the relative humidity of the air RH. Desiccation of the concrete takes place if pc > Pa- The following thermodynamic standard values have been taken from the table... 

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