Early Thermal Cracking Control of Concrete Structures in Qatar

Abstract

Thermal cracks can occur in concrete elements at early stages during the hardening process. Also, the impact of thermal contraction and drying and autogenous shrinkage, may lead to excessive tensile strains and as a result cracks will occur. Consequently, an increase in reinforcements may be required to satisfy Early Thermal Cracking (ETC). ETC remains a major concern for concrete structures, especially for structures with high demand of water tightness. Considering the significance of water leaking in underground structures and the rising of the groundwater table in Qatar in the recent years, the Public Works Authority (ASHGHAL) has set the criteria to control early thermal cracks for Highway and Drainage Structures. This paper aims to present a comparison between the Early Thermal Cracking (ETC) codes and guidelines aiming towards providing sustainable and efficient design. This study compares the design method and parameters considered in BD 28/87, CIRIA C660 and CIRIA C766 currently used in Qatar for ETC calculations such as crack width permissible limit, minimum area of reinforcements, temperature change at early age, long term ambient temperature, autogenous shrinkage, drying shrinkage and restraint conditions. In addition, ETC calculations are carried out for a tunnel reinforced concrete box section with wall and top slab thicknesses ranging from 300mm to 1000mm. The least required area of reinforcements (As,req) for wall subject to edge restraint was by CIRIA C766 and for top slab subject to end restraint was by BD 28/87.