Effects of Selected Media on Novel Portland Pozzolana Cement

Abstract

Cement is subject to degradation by aggressive media found in the environment. Durability tests are therefore necessary for any cementitious material in a given environment. The work reported in this thesis involved the study of the effects of selected aggressive media on a cement, made from inter-mixing Ordinary Portland Cement (OPC), dried acetylene lime sludge (DALS) and an incinerated mix of reject bricks (BB), spent bleaching earth (SBE) and rice husks. The cement was labelled Portland Combined DALS Cement (PCDC). Initial tests showed that PCDC met the Kenya Standard requirements for Portland Pozzolana cement (PPC). PCDC was subjected to various media which included sea water, distilled water, chloride and sulphate solutions in a laboratory set-up. The experiments were carried alongside OPC, 25 % Pulverised Fuel Ash substituted OPC (OPC + PF A) and commercial Pl'C. The study was carried out in two phases; cement mortar moulded into 100 mm cubes subjected to the media and reinforced mortar cubes subjected to a wet and dry alternate environment of 3.5 % sodium chloride solution. PCDC exhibited continued compressive strength gain in all media except in chloride solutions. PCDC exhibited comparable gain in compressive strength and selected ions intake/leach to PPC in sulphate solutions and distilled water. PCDC exhibited higher strength gain than OPC in distilled water. Except in chloride solutions, PPC exhibited higher strength gain than OPC. In Corrosion tests, the PCDC mortar rebars showed early attainment of active corrosion coupled with higher corrosion rates over a short period of time than OPC as w/c ratio was increased. The PCDC showed a decreased chloride penetration than OPC as w/c and depth of cover increased. PCDC showed the lowest apparent chloride diffusion coefficients. The resistivity of PCDC in the aggressive media suggested that it required greater depths of cover, where reinforcement was to be used, and long term curing to improve on its resistivity. The tests showed that PCDC can be used for general construction work in the tested media in a similar manner to Pl'C,