Fracture Parameters of Cement Mortar with Different Structural Dimensions Under the Direct Tension Test

Area of Science:

• Materials Science
• Civil Engineering
• Fracture Mechanics

Background:

• Understanding the fracture properties of cementitious materials is crucial for structural integrity.
• Cement mortar, a key component in construction, exhibits complex fracture behavior.
• Previous studies often focused on concrete, leaving mortar's specific fracture characteristics less explored.

Purpose of the Study:

• To accurately measure the fracture properties of cement mortar using direct tension tests.
• To determine the tensile strength, fracture energy, and characteristic length of mortar specimens.
• To investigate the size effects on the fracture behavior of cement mortar.

Main Methods:

• Direct tension tests were performed on four double-notched mortar bar specimens of varying dimensions.
• Load, crack mouth opening displacement, and elongation were recorded under displacement control.
• Fractured surfaces were scanned to calculate key fracture parameters.

Main Results:

• The average ratio of total fracture energy (G_F) to specific fracture energy (G_f) was 1.94, lower than concrete's typical 2.5.
• Mortar specimens exhibited a smaller fracture process zone and a reduced tail in the softening branch, contributing to the lower G_F/G_f ratio.
• Linear elastic fracture mechanics (LEFM) predictions for size effects were not fully supported, with a slope of 1/0.727 observed instead of the expected 1/2.

Conclusions:

• Cement mortar's fracture properties, particularly its fracture energy ratio and size effect behavior, differ from those typically observed in concrete.
• The smaller fracture process zone in mortar is a key factor influencing its fracture energy ratio.
• Discrepancies in size effect predictions may stem from differences in testing methods (tension vs. bending) and material heterogeneity (aggregate size and distribution).