ABSTRACT
An enormous gap exists between the production capacities of the Cement Manufacturing Plants and the demand for cement in Nigeria. Prior to 2010, Nigeria could only produce between 4 and 6.5 million tons annually as against the domestic demand of about 18 million tons. There is the need therefore to augment the local cement production by the introduction of Natural Pozzolans of volcanogenic origins as partial replacements of the Ordinary Portland Cement (OPC) in concrete mixtures. The study thus focused on experimental works on the pozzolanic characteristics of Jos Plateau volcanic deposits as potential pozzolans for partial replacements of the OPC in concrete mixtures. The laboratory experimental studies evaluated the chemical characteristics of the volcanic materials and the pozzolanic characteristics of concrete made with the volcanic materials in partial replacement of the Portland cement in the concrete mixtures. The results of the chemical analysis indicated that the oxides of SiO2, Al2O3 and Fe2O3 are substantially present in all the samples tested. The sum of these oxides varied from 71.45 (JP14) to 95.31% (JP3). The average sum of the minor oxides obtained was 3.16%. However ASTM C (2001) recommends that sum of the minor oxides should not be more than 5% by weight. The average values of CaO, MgO, and SO3 were 0.29 %, 1.81 %, 0.53 % respectively of the 20 samples of materials tested. Furthermore alkalis (Na2O and K2O) average values were 0.25 % by weight of the samples tested. All the materials samples studied have no trace of carbon in any of the samples investigated. The results of test indicated that the LOI and the MC of the 12.3 and 2.3 % respectively. The MC values were within the ASTM C 109/C 109M (2001) maximum recommendations of 3%. While those of the LOI were slightly above the 10% recommendation of ASTM C 618 (2005).The result of the study further indicated that the Initial Setting and Final Setting Times were 2 hours 35 minutes and 3hours 30 minutes respectively. The result of soundness test tests of the Portland pozzolan cement paste showed the changes in volume varied from zero to 0.40%. ASTM C 618 (2005) recommended a maximum of 0.80%. The control cube had compressive strengths of 26.0 N/mm2 at 28 days curing. The results of the partial replacements of 5, 10, 15 and 20% of OPC with the volcanic materials were all above 75% of the control strength. The investigation established that Pozzolanic Activity Index with Portland Cement (PAIC) at 28 days for 5% to 20% replacement of OPC showed a sliding from an average index of 105 to 81.ASTM C 595(2006) minimum specification is an index of 75 for a pozzolan to be used Portland Pozzolana Cement in concrete mixtures. The volcanic materials can be used for cement Type IP Type P and (ASTM C 595 (2006).It is conclusive that the volcanic deposits possess pozzolanic characteristics as natural pozzolans for use in concrete.