Abstract: A cement slurry having a density between 750 kg/m3 and 1,000 kg/m3, comprising a solid fraction comprising: either 75%-90% (by volume) of lightweight particles having a mean particle size between 10 and 60 &mgr;m; 10%-25% (by volume) of Portland cement having a mean particle size of between 10 and 50 &mgr;m, or micro-cement having a mean particle size between 0.5 and 5 &mgr;m; or: 20%-50% (by volume) of lightweight particles having a mean particle size between 10 and 60 &mgr;m; 10%-25% (by volume) of Portland cement having a mean particle size of between 10 and 50 &mgr;m, or micro-cement having a mean particle size between 0.5 and 5 &mgr;m; 35%-65% (by volume) of lightweight particles having a mean particle size between 100 and 200 &mgr;m; and a liquid fraction present in an amount of 37%-50% (by volume) of the total volume. Such cements have remarkable mechanical properties due to their very low porosity in spite of having very low density.