Influence of restraint on the early age cracking of concrete with and without fibres

Author(s): R. Combrinck, W.P. Boshoff
Paper category: Conference
Book title: 8th RILEM International Symposium on Fiber Reinforced Concrete: challenges and opportunities (BEFIB 2012)
Editor(s): Joaquim A.O. Barros
Print ISBN: 978-2-35158-132-2
e-ISBN: 978-2-35158-133-9
Publisher: RILEM Publications SARL
Pages: 86 - 99
Total Pages: 13
Language: English

Abstract: The restraint of freshly cast concrete is ever present through factors such as reinforcing steel and non-uniform concrete depth. The influence of these restraints on the early age cracking of concrete such as plastic settlement cracking (PSeC) and plastic shrinkage cracking (PShC) is of great importance, since these cracks are both unsightly and can cause severe durability and maintenance issues early in the life of a concrete structure. PSeC is caused by the differential vertical settlement of a concrete mix, whereas PShC is caused by the horizontal contraction of the concrete mix due to evaporation. The exact influence of these two types of cracking on each other is still unclear. However, since the same settlement/bleeding and restraint influence both cracking types, it is imperative to determine how these cracks influence each other. With this in mind, this paper investigated the influence of a specific restraining condition on both PSeC and PShC as well as the interaction between the two cracking types. The restraining condition promoted both PSeC and PShC. The results indicated that under extreme environmental conditions with high evaporation rates, PSeC can force the early and unexpected development of the majority of cracking mainly due to the combined effect of PSeC and PShC. For normal environmental conditions with low evaporation rates, PSeC can occur without any capillary pressure build up or air entry. The results also showed a significant increase in the vertical settlement due to capillary pressure build up. Finally, the addition of a low volume (0.6 kg/m³) of polypropylene fibres seemed to have no influence on the PSeC or the interaction between PSeC and PShC at extreme environmental conditions.

Online publication: 2013
Publication Type: full_text
Public price (Euros): 0.00