This experimental work aims to better understand the hardening process of limestone tuff after compaction when water content varies. Indeed, the pavements built with wet calcareous crust or tuff are hardened by the effect of compaction followed by water evaporation but this cohesion after compaction disappears completely by total saturation. In order to classify the materials according to geotechnical specifications related to limestone crusts, tuff from Faidh el Botma area was studied by following the change of compressive strength measured on specimens prepared at different water contents and stored for several days either under air (for fast drying) or in non-hermetic bags (for slow drying). The first series of specimens appeared more resistant than the second one. As explanation of the hardening, the possible precipitation of new phases such as carbonate during the fast drying is discussed based on chemical and microstructural observations as well as the effect of suction than could change the microstructural arrangement of tuff particles when the moisture content varies.