Plastic Shrinkage Cracking

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Title: Plastic Shrinkage Cracking

Author(s): Dan Ravina and Rahel Shalon

Publication: Journal Proceedings

Volume: 65

Issue: 4

Appears on pages(s): 282-292

Keywords: cement content;crack width and spacing;cracking (fracturing);evaporation; fresh concretes;hot weather construction;humidity;mortars (material);plastic shrinkage;shrinkage;temperature;tensile strength;tensile stress;wind velocity; workablity.

Date: 4/1/1968

Abstract:
Plastic shrinkage cracking of mortars exposed to different conditions, as prevalent in hot-dry climates, was investigated under controlled conditions. The variables studied were air temperature and humidity, wind velocity, mortar tempera-ture, type and content of cement, and consistency. Shrinkage, tensile strength and tensile stress of fresh mortars, evaporation and time of cracking were measured. Width, depth, and length measurements of the cracks were also taken. The results confirm that rapid evaporation has a predominant effect on plastic shrinkage cracking. Other con-clusions are that plastic shrinkage cracking is not a direct function of water loss, evaporation rate or shrinkage, and that semiplastic mortar did not crack under high evaporation conditions which brought about severe cracking of plastic and wet mortars. It was also established that the first crack coincides with the transition from the intensive, prac-tically unrestrained, linear shrinkage of fresh mortar to the much slower rate due to restraint on stiffening of the mortar.