Lightweight Aggregates and Shrinkage-Reducing Admixtures for Low-Cracking Concrete

Cracks in bridge decks facilitate the penetration of chlorides that induce corrosion of reinforcing steel. Formation of cracks is related to the shrinkage and properties of the concrete and the restraints to movement. Lightweight concrete with a low modulus of elasticity, high creep, and water in the aggregate pores for internal curing has a reduced cracking potential. To control cracking, shrinkage of concrete can be reduced by using a shrinkage-reducing admixture (SRA). A recent study at the Virginia Department of Transportation (VDOT) investigated the performance of both lightweight concretes and concretes with SRA containing normalweight aggregates in the field and found that these concretes had no cracks or fewer cracks than were typical of decks constructed with normalweight aggregates over the past 20 years. VDOT developed a new specification that included lightweight concretes or concretes with normalweight aggregates and SRA and this specification is being used successfully to reduce cracking in bridge decks. This paper summarizes the work conducted to develop the new specification and includes information on field applications. Keywords: durability; lightweight concrete; low cracking; permeability; shrinkage; shrinkage-reducing admixture.