Two resistive-strip bulk Micromegas detectors have been installed in the Gamma Irradiation Facility
at CERN in 2015. The primary goal was to assess the performance of the detectors after long
term irradiation. This study is particularly relevant in view of the adoption of the Micromegas
technology for future upgrades, as in the ATLAS inner muon system. In this region the expected
accumulated charge in 10 years of HL-LHC operation has been estimated to be 0.2 C/cm$^2$. After
3 years of continuous irradiation more than 0.3 C/cm$^2$ have been accumulated, allowing to draw
clear conclusions concerning ageing effects on the detectors. During this period, the detector
currents have been monitored and the performance of the detectors has been studied by combining
the photon background with muon beam available at the facility. In particular, the spatial
resolution and detector gain have been studied up to about 70 kHz/cm$^2$.