Effects of mixing time and nano silica on some properties of superfine-tailings cemented paste backfill

•The optimal mixing time makes the strength and fluidity of SCPB reach the best.•The mixing time can change the degree of influence of NS on thixotropy.•NS can catalyze the hydrolysis of gypsum and generate more hydration products.•NS reacts with CH to form C-S-H gel with low C/S and H/S.