Specified density concrete : A transition

Applications of Specified Density Concrete (SDC) are increasing in the US, Canada and Europe. The use of SDC is driven by engineers' decisions to optimize concrete density to improve structural efficiency (the strength to density ratio), reduce transportation cost, and to enhance the hydration of high cementitious concrete mixtures with very low w/c ratios .2600 kg/m 3 , SG >2.60) with either coarse or fine Low Density Aggregates (LDA) (generally <1600 kg/m 3 , SG <1.60). Examples of optimizing the design by using SDC include more structurally efficient members in bridges and buildings, improved buoyancy in marine structures, and reduced transportation costs of consumer products like wallboard, imitation stone, precast element, masonry, etc. SDC is defined as concrete with a range of density less than what is generally associated with Normal Density Concrete (NDC) and greater than the lowest density possible when using all LDA. This paper will focus on the 1800-2200 kg/m 3 (112-137 lb/f 3 ) density range. The American Concrete Institute Standard Building Code (ACI 318) provides structural engineers with adequate guidance when designing with structural LDC over the strength range of 20-35 Mpa (2900-5080 psi). ACI 318 precisely defines the differing engineering properties of NDC and LDC including reduced elastic modulus, reduced tensile shear and torsion capacities, increased development length..,etc. The increased use of SDC is creating an urgent need for comprehensive, industry wide investigations into the physical properties and engineering characteristics of concretes with strength/density combinations outside of traditional ranges. Future code revisions should include a seamless transition of engineering criteria for concrete properties of all practical achievable strengths with density ranges from 1200-2500 kg/m 3 (75-156 lb/ft 3 ).