DBPapers
DOI: 10.5593/sgem2017/12/S02.023

CONTROL OF CRACKING IN REINFORCED CONCRETE MAT FOUNDATIONS IN INTERACTION WITH SUBSOIL

J. Bilcik, R. Sonneschein, K. Gajdosova
Sunday 10 September 2017 by Libadmin2017

References: 17th International Multidisciplinary Scientific GeoConference SGEM 2017, www.sgem.org, SGEM2017 Conference Proceedings, ISBN 978-619-7105-99-5 / ISSN 1314-2704, 29 June - 5 July, 2017, Vol. 17, Issue 12, 175-182 pp, DOI: 10.5593/sgem2017/12/S02.023

ABSTRACT

This article summarizes and analyses some of the recent developments in strategies to prevent or reduce the effects of restrained volume changes on the behaviour of concrete mat foundations. Mat foundations are usually restrained to some degree externally or internally. For the evaluation of the influence of external restraint in mat foundations, friction and interaction models are introduced. Early-age cracks due to restrained thermal contraction can be serious because, unlike flexural cracks, they can extend through the full thickness of the mat. Mitigation strategies to prevent the formation and propagation of early-age through cracks discussed in this paper. In order to minimize the external restraint in mat foundations the sliding friction between the mat and the subsoil should be reduced to a minimum. In general, when assessing the risk of early-age cracking, drying and autogenous shrinkage may be ignored. Thus, the use of checkerboard sequence of concrete placement can significantly reduce the early-age thermal stresses.
Reinforcement is used to reduce crack spacing and limit crack width. The results of crack width calculation according to EN 1992-1-1 [1] with local variations included in National Annexes are analysed on the basis of key criteria. A comparative study revealed differences in the required reinforcement area and differences in the level of crack width measurement. The crack width is calculated on the concrete surface or at the level of reinforcement bar. The latter allows savings of around 20 % on reinforcement.
Despite of the large amount of research work addressing the early age cracking, the designers have not been overly successful in preventing these cracks.

Keywords: watertight concrete, mat foundation, restrained contractions, cracking.