Experimental and numerical investigations to evaluate the structural integrity of concrete beams exposed to an aggressive coastal environment

•Incipient detection of SO42− deterioration by nondestructive modal analysis.•Correlation of numerical, mechanical, and microstructural results (by SEM and XRD)•Difficulty in detecting damage, by natural frequencies, due to the action of Cl−.•Nondestructive modal identification of SO42− effects after 240 days of exposure.•Predominance of Cl− in incipient combined exposure, reducing the SO42− distress.