ABSTRACT
The need for stronger, stiffer, more durable and cost effective materials for bridges have led to an increasing interest in high-strength concrete (HSC) in the last decades. The use of HSC, in its turn, has introduced a number of changes: (i) due to economic considerations, the traditional 28-day specified compressive strength has been replaced by strengths specified at later ages such as 56 or 90 days; (ii) production of HSC depends on low water/cementitious ratios, stronger aggregates, higher cement contents, chemical and mineral admixtures, and strict quality control; (iii) testing procedures have demanded stiffer machines and smaller test specimens; and (iv) design codes have been revised to accommodate the mechanical properties of this material and the resulting structural behavior. While most of the aforementioned issues have been thoroughly scrutinized, the use of specified compressive strengths for design based on 56 or 90 days has not yet received enough consideration.
