Experimental characterization of mechanical properties of the cement pasteaggregate interface in concrete

M Jebli,E Malachanne,M.S El Youssoufi,E Garcia-Diaz,F Jamin,F Radjai,S Nezamabadi,S Luding,J.Y Delenne

doi:10.1051/epjconf/201714012014

Abstract

Granular materials are extensively used in the field of civil engineering. These materials are either used in their dry state, or mixed with water or with a binder. In the case of concrete, the binder could be cement or mortar. For ordinary concretes, it is generally admitted that there is a thin heterogeneous zone of paste, with a thickness of about 15-60 μ m, surrounding the aggregates surface. This zone, commonly named the Interfacial Transition Zone (ITZ), is characterized by a higher porosity than the bulk paste and a high concentration of the portlandite crystals. Some of these crystals react with the aggregates’ surface (limestone aggregates), leading to a good adhesion. In this work, the mechanical properties of the cement paste and of the cement-aggregate interface are experimentally analyzed. Experimental tensile and shear tests are performed on parallelipipedic samples. These samples are made by linking limestone aggregates with Portland cement paste using a water / cement ratio of 0.5. The results show that the cement-aggregate interface is the weak zone in the composite.

Highlights

Concrete is a composite material of aggregate particles and cement paste
It is proposed to present the experimental results obtained from the direct tensile and shear tests, on cement paste and the composite
For all the tensile and shear tests, it is observed that all the breaks on the composite occur at the cement-aggregate interface (Fig. 4), which represents the weakest zone

Summary

Introduction

Concrete is a composite material of aggregate particles and cement paste. The mechanical properties of concrete depend on the properties of the cement paste, the aggregates and the cement paste-aggregate interface. The cementaggregate interface is characterized by a higher porosity than that found in the bulk paste. For this reason, the mechanical properties of this zone are considered different than those of the cement paste. There is ample evidence that the properties of concrete, such as the tensile strength, modes of failure and the permeability; are significantly influenced by the nature of the existing interfaces between the cement paste and the aggregates. Due to lack of understanding about these interfaces, very little attempts have been made to characterize the mechanical properties of this zone. Some studies have been devoted to the direct characterization of the mechanical properties of the interface between aggregates and cement paste, by using tensile and shear tests

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Results

Conclusion