Laboratory Characterization of Type N Mortar

Personnel of the Geotechnical and Structures Laboratory, U.S. Army Engineer Research and Development Center, conducted a laboratory investigation to characterize the strength and constitutive property behavior of type N mortar. A total of 45 mechanical property tests were successfully completed two hydrostatic compression tests, four unconfined compression UC tests, 18 triaxial compression TXC tests, four direct pull DP tests, six reduced triaxial extension RTE tests, two uniaxial strain UX tests, four uniaxial strain loadbiaxial strain unload UXBX tests, and five uniaxial strain loadconstant volume strain loading UXCV tests. In addition to the mechanical property tests, nondestructive pulse-velocity measurements were obtained on each specimen. The TXC tests exhibited a continuous increase in maximum principal stress difference with increasing confining pressure. A compression failure surface was developed from the TXC test results at nine levels of confining pressure and from the results of the UC tests. The results for the DP and RTE tests were used to determine the tensile strength of type N mortar and develop an extension failure surface. Type N mortar can withstand more deviatoric stress in compression than extension before failure occurs. During UXBX tests, the test specimens recovered approximately one third of their peak compressive volumetric strain. During most of the CV loading, the stress path followed closely to the failure surface developed from the TXC tests, therefore validating the compression failure surface.