A Kansas DOT research project used three types of lightweight aggregate to develop lightweight concrete mixtures for a bridge deck and for prestressed bridge girders.

Two of the lightweight aggregates were expanded shale obtained locally from the Buildex Company. One deposit was located in Marquette, Kansas, and the other in New Market, Mo. The third lightweight aggregate source was expanded slate obtained from the Stalite Co. in North Carolina.

Aggregate properties including absorption, gradation, and L.A. Abrasion were evaluated. Over 150 lightweight concrete mixtures were created and tested and several mix design variables such as water-to-cement ratio, cement content, and coarse-to-fine aggregate ratio were evaluated.

From these results, optimized bridge deck and optimized prestressed concrete mixtures were developed for each type of lightweight aggregate.

Special concerns for lightweight aggregate concrete are addressed. These optimized concrete mixtures were then tested for KDOT acceptability standards for the concrete properties of compressive strength, tensile strength, modulus of elasticity, freeze-thaw resistance, permeability, alkali-silica reactivity, drying shrinkage, and autogenous shrinkage.