Compressive strength, setting time, and flowability of OPC mortar mixtures modified with a composite of Nano carbon and partially de-aluminated metakaolin.

Nano-black carbon (NC) and partially de-aluminated kaolinitic clay (PDK) composite blend was investigated as an additive to mortar fabrication for improving of the compressive strength. PDK was obtained from aluminum sulphate of Egypt (ASCE). PDK was grounded with nanocarbon. PDK achieved a good pozzolanic activity, it reached 120 %. The experimental protocol included chemical and physical properties of the PDK/Nano-carbon (NCPDK) and the produced mortars. The effect of five weight ratios of NCPDK (0, 5, 10, 15 and 20 %) on the properties of the formed OPC mortars was investigated. Each ratio was tested with three contents of Nanocarbon (1, 2 and 3 %) by weight. The accelerating effect of NCPDK was clear on the initial setting time whereas it reduced by about 31 % and the final setting time reduced by 23 % at 10 % NCPDK. The reduction in the initial flowability of OPC mortar reached 2.7 and 6 % for 10 and 20 % replacement respectively of the OPC by NCPDK and After 60 minutes from mixing, the relative flowability loss was 68 % at 10 % NCPDK and 88 % at 0 % replacement. The compressive strength values of the produced mortars ranged between 46.2 and 50.7 MPa (EN 196-1), with a maximum improvement equal to 14.4 % using 10 % NCPDK. There was no significant change in the pH values of the mortar mixtures. According to the obtained results the composite NCPDK can be used as an additive material in mortar fabrication. The structure of the hardened mortar modified with 10% NCPDK was investigated by XRD, FTIR and TGA that assured formation of more CSH. Incorporation of Nano-carbon enhanced the compressive strength. [ABSTRACT FROM AUTHOR]