Experimental characterization of mechanical properties of the cement-aggregate interface in concrete

• Published in: Construction & building materials 2018-02, Vol.161, p.16-25
• Main Authors: Jebli, M., Jamin, F., Malachanne, E., Garcia-Diaz, E., El Youssoufi, M.S.
• Format: Article
• Language: English
• Subjects: Aggregates (Building materials); Analysis; Cement-aggregate interface; Chemical properties; Civil Engineering; Concrete; Concretes; Direct shear tests; Direct tensile tests; Engineering Sciences; Experimental characterization; Matériaux composites et construction; Mechanical properties; Phase interfaces; Shear strength; Strength (Materials); Tensile strength
• ISSN: 0950-0618; 1879-0526
• DOI: 10.1016/j.conbuildmat.2017.11.100

•Characterization of the mechanical behavior at cement-aggregate interface by direct tensile and shear tests.•Mechanical properties evolution of the cement-aggregate interface during hydration.•Determination of local cohesion (c) and local friction angle of the cement-aggregate interface.•The mechanical properties of the cement-aggregate interface are lower than those of the cement paste. The microstructure of the Interfacial Transition Zone (ITZ) between the aggregates and the cement paste is characterized by a higher porosity than that of the bulk paste. The particular properties of this zone strongly influence the mechanical behavior of concrete. Microscopic cracks, which develop during subsequent loading, appear either in the matrix (cement paste or mortar) or along the cement-aggregates interface. Cracks could be caused by either tensile, shear strengths or by combinations of both. In this work, the mechanical properties of the cement paste – aggregate sample are experimentally studied. The experimental tests are performed on parallelepipedic samples at classical aggregate scale (one centimeter sections). These samples are composed of limestone aggregates and Portland cement paste, hereafter named “composite”. The cement paste is prepared with a water/cement ratio of 0.5. The shape of the prepared composites makes them convenient for direct tensile and shear tests. At different stages of hydration, we performed direct tensile and shear tests on the composites by means of specific devices. The same tests were carried out on the cement paste in order to compare with the composite results. The analysis of the experimental results showed that the tensile strength of the cement-aggregate interface was about 30% lower than that of the cement paste tensile strength. Also, the shear strength of the cement-aggregate interface was smaller than the shear strength of the cement paste. In the same way as macroscopic Mohr–Coulomb criterion, we observed an increase of shear strength when normal stress increased. It provides access to a local cohesion (c) and a local friction angle (Φ) at classical aggregate scale.