[en] Sulfate-attack and gamma-irradiation tests were carried out on three Portland cement mortars. For the sulfate attack work an accelerated test was used involving alternate immersion in Na₂SO₄ solution and oven drying of the samples. Attack was monitored through length-change measurements. Cement mortar containing silica fume gave unexpectedly poor resistance to attack. Reasons for this behavior are unclear. Gamma irradiation was found to cause losses in compressive strength at low doses in the 10⁷ rad range. The irradiation time is a major factor in the strength-loss mechanism, whereas the dose rate is of secondary importance for the testing conditions studied. 10 refs., 19 figs., 6 tabs