Investigation of Concrete Mixtures to Reduce Differential Shrinkage Cracking in Inverted T Beam System

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Virginia Tech

The inverted T-beam system provides an accelerated bridge construction alternative. The system consists of adjacent precast inverted T-beams finished with a cast-in-place concrete topping. The system offers enhanced performance against reflective cracking and reduces the likelihood of cracking due to time dependent effects. Differential shrinkage is believed to be one of the causes of deck cracking in inverted T-beam systems. The objective of this study was to develop mix designs that exhibit lower shrinkage and higher creep compared to typical deck mixtures, recommend a prescriptive mix design and a performance criterion to VDOT that can be further investigated and used in the inverted T-beam system to combat effects of differential shrinkage.

Ten different mix designs using different strategies to reduce shrinkage were tested for their compressive strength, splitting tensile strength, modulus of elasticity and unrestrained shrinkage. The four best performing mixes were selected for further study of their time dependent properties. The test data was compared against the data from various prediction models to determine the model that closely predicts the measured data. It was observed that ACI 209.2R-08 model best predicted the time dependent properties for the four mixes tested in this project. Tensile stresses in the composite cross-section of deck and girder, created due to difference in shrinkage and creep are quantified using an age adjusted effective modulus method.

In this analysis, it was observed that mixes with normal weight coarse aggregate (NWCA) developed smaller stresses compared to those of mixes with lightweight coarse aggregate (LWCA). Mixes with fly ash as supplementary cementitious material (SCM) developed smaller stresses at the bottom of deck when compared to mixes with slag as the SCM.

Differential Shrinkage, Creep, Concrete Bridge deck, Reflective cracking