Use of Jebel Marra Natural Pozzolana as a Replacement Material in Production of Low Cost Blended Cement

Abstract

The need for low cost natural materials to be used as supplementary material in blended cement, and concrete in rural areas of Sudan, and especially in Darfur, was the main reason for carrying out this study. The study mainly focuses on characterization of the locally available natural pozolanic materials and their utilization in low cost cement, to facilitate shift from pure Portland cement which can be used in low cost concrete blocks, mortar, concrete and plaster In this research samples of Volcanic ash materials from Jebel Maraa, were taken namely from Nyertity (NVA), Melem (MVA) Tina (TVA) and Kotrum (KTVA), and evaluate their efficiency as supplementary cementitious materials to Portland cement. Each material was characterized for its chemical and physical properties, using various techniques. Then they were used to prepare different blends using different substitution levels such as 10, 20 and 30% the blended were tested to determine their compliance with Standards. A replace mix of pure O.P.C was also prepared and tested to compare blends with it. The potential use of these materials to facilitate the shift from pure Portland cement to blended cement in mortar, concrete and concrete hollow blocks was then investigated. The chemical and physical analysis of the samples showed that they are congruent with other materials used as supplementary materials, around the world. In physical analysis results, including standard consistencies and setting times for all blends, showed an increase in water demand with increasing substitution level. The results also indicated that addition of these pozzolanic materials retarded the setting, however this retardation was negligible and was within the limitations. The reactivity of volcanic ash was found to be within the limit of standards. The strength activity indexes of the pozzolanic materials were found to be 113% for NVA, 98% for MVA, 105% for TVA and 110% for KTVA, compared with the requirement of 75% and 80% specified by ASTM C-618 and Indian standard IS: 1344, respectively. Result of permeability of blended cement in mortar showed that increasing the level of substitution decreases the permeability. Results of compressive strength of blended cements showed that, in general, increasing the level of substitution contributed to a reduction in compressive strengths. This is especially noticeable at early ages and for higher (greater than 20%) substitution levels. All blended cements showed a trend for increasing strengths with time, with the increase from 7 to 28 days greater than the increase from 28 to 90 days for 20% or less substitution levels. The optimum substitution level obtained from the compressive strength and confirmed by normalized compressive strength, was therefore 20% for volcanic ash in concrete and matching with previous studies. The 30% substitution, despite resulting in strength reduction, gave acceptable strength values according to standards. Blended cement with 30% substitution level was used successfully in mortar and concrete hollow blocks. Accordingly the studies volcanic ash substitution can be safely used in reinforced concrete with 20%substitution level and in mortar and concrete hollow blocks using 30% substitution level. There substitution will greatly reduce the cost of cementing building materials. This was confirmed by comparing the cost of a typical house built with OPC and blended cement of 30% replacement, where they were used for blockwork (mortar), plastering and block production. The reduction found to be about 22%. Furthermore chemical analysis and resulting calculation of mineralogical composition of blended cement at 20% replacement showed that these blends are identical to type Ι cement (OPC) and close to type ΙV cement(low heat cement).