The report points out that cracks in bridge decks can be due to many factors related to environmental effects, chemical reactions, and structural loads. To reduce cracking, shrinkage must be reduced; however, cracking also depends on other factors such as modulus of elasticity, creep, tensile strength, and restraint.
Lightweight concrete (LWC) has a lower modulus of elasticity, higher inelastic strains, a lower coefficient of thermal expansion, a more continuous contact zone between the aggregate and the paste, and more water in the pores of aggregates for continued internal curing when compared to normal weight concrete. “These properties tend to reduce cracking in the concrete and are highly desirable in bridge decks,” said the report.
Virginia Department of Transportation (VDOT) has been successfully using LWC in bridge structures. In most, the coarse aggregate has been lightweight and the fine aggregate is normal weight natural sand.
Seven bridges from six VDOT districts were included in the study. Three bridge decks each were constructed in 2012 and 2013, and one was constructed in 2014.
Among the conclusions were that bridge decks with reduced or no cracks can be constructed with LWC mixtures. The study found satisfactory resistance to cycles of freezing and thawing in properly air-entrained LWC made with high-quality lightweight aggregate. Pre-soaking of the lightweight aggregate is very important in obtaining consistent quality LWC and reducing cracking.
The report is available at http://www.trb.org/Main/Blurbs/174244.aspx (link opens in new tab).
A lightweight concrete deck on Route 269 after 34 years
