The five studied Algerian reservoir sludges are mainly composed of SiO2, Al2O3, Fe2O3 and CaO, and three of them (samples SLD2-SLD4) have a high CO2 content. The mineralogical composition of the sludges is complex, with quartz as the major crystalline phase, except in the case of SLD5, where the presence of phyllosilicates (smectite and muscovite) leads to a very low crystallinity value. All the sludges present a very high BET specific surface area and high pozzolanic activity. SLD5 is the most active sample and shows similar behavior to silica fume, one of the most active pozzolans used in the cement industry.
The blended cements prepared with 20% of each sludge show higher consistency values than OPC (except SLD4) due to the increased water demand of the pozzolans. The setting time is also higher due to the typical dilution effects of pozzolanic additions. With regard to compressive strength, the blended cements show lower values than OPC, except for SLD5, whose compressive strength is not only similar to that of the reference OPC at 28 days of reaction but even higher after long curing times (90 days).
Considering all of the above, it may be concluded that these sludges can be used as active additions to prepare blended cements with suitable properties. However, it is necessary to obtain a deeper knowledge of their behavior and to test the durability of the resulting blended cements in order to ensure the good behavior of the sludges in future cementing matrixes.