Effect of Concrete Composition on Splitting Cracks in Prestressed Concrete Railroad Ties: Application of Fracture Mechanics

Abstract

The effect of concrete composition on end-splitting cracks in pretensioned concrete members was investigated. Specific parameters included the effect of aggregate shape and content, water-to-cementitious (w/cm) ratio, fly ash, paste and air void content. For each mixture evaluated, prisms were load tested in three-point bending at 4000, 6000 and 8000 psi to determine the effect of concrete compressive strength on crack growth potential. Corresponding splitting tensile tests were also conducted on samples at each compressive strength for all mixtures. Results show that increasing angularity, aggregate size distribution, and decreasing w/cm ratio improve fracture toughness by as much as 28% whereas changing other parameters had little effect. All improving factors were seen to be most effective at low strengths. A statistical model predicting fracture toughness was developed, and the results correlated well with observed cracking in pretensioned concrete members.