Graubohm, Markus1; Raupach, Michael2 and Brameshuber, Wolfgang†3

1 Masonry Research Engineer, Dipl.-Ing., RWTH Aachen University, Institute of Building Materials Research, Chair of Building Materials, 52062 Aachen, Germany, graubohm@ibac.rwth-aachen.de
2 Professor and Head of Institute, Dr.-Ing., RWTH Aachen University, Institute of Building Materials Research, Teaching and Research Field of Building Maintenance and Repair, 52062 Aachen, Germany
3 Professor and Head of Institute, Dr.-Ing., RWTH Aachen University, Institute of Building Materials Research, Chair of Building Materials, 52062 Aachen, Germany († 16th September 2016)

ABSTRACT
Masonry is a construction method primarily suited for building structures under compressive load. The decisive characteristic to assess the load bearing capacity of such building members is their compressive strength. In Eurocode 6, presently the masonry compressive strength can only be determined by approximation on the basis of test results, applying an empirical equation which only considers the uniaxial compressive strength values of unit and mortar. However, numerous investigations on the load bearing and fracture mechanisms of masonry under compressive load already showed that the masonry compressive strength does not only depend on the strength of the single components but also on their different deformation behaviours. Usually, the mortar has a significantly higher lateral strain than the masonry unit which is, however, restrained by the bond between both materials. The obstruction of the lateral expansion of the mortar results in additional compressive stresses in the mortar joint and tensile stresses in the unit, normal to the loading direction. This leads to a triaxial state of stress in the unit which can decrease the masonry strength depending on the height of the lateral tensile stresses in the unit and the lateral deformability of the mortar. Thus, the Poisson’s ratios and the elastic moduli of unit and mortar can be specified as essential influencing parameters. Furthermore, the interaction between the suction behaviour of the masonry unit and the water retention of the mortar considerably influences the properties of the joint mortar. Therefore, extensive tests were conducted to examine the influence of the water absorption of masonry units on the mortar properties in the joint using the example of calcium silicate masonry.

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