Welded tuff as cement replacement material for concrete production – A case study.

The demand for concrete is increasing rapidly with the growth of construction industries, which leads to the huge usage of binding materials (especially cement) in Ethiopia. The depletion of natural sources due to the extraction of aggregates is a major environmental problem affecting the ecosystem. The cement industries in Ethiopia face many transformation challenges to overcome environmental degradation; thus, finding suitable alternatives become mandatory for them. Welded Tuff is a pyro-clastic type of rock and cementation of volcanic ash or dust, unruffled volcanic ejecta. It can be used as a substitute for cement in the construction sector to attain the optimum binder content. The porous structure of the welded Tuff is an added advantage to lower the freezing temperature and act as the insulation material. In the current study, the characteristics of welded Tuff and its effects on the tangible property have been examined to check its suitability as a partial cement alternative for producing C-25 concrete. The Welded Tuff was oven-dried and sieved by 150 µm to remove the coarser particle. The percentage of cement replacement with Welded Tuff varied from 0% to 20% concerning the cement in incremental steps of 5%. The experimental program was designed to explore Welded-tuff's behavioural tendency over the cement setting time, workability, density, and compressive strength of concrete. The workability of each sample was measured before the specimens cast and cured at a standard temperature, and the test was accomplished on it for 7 and 28 days respectively. A total of thirty (30) 150 x 150 x 150mm concrete test cubes were cast using a coherence mix of 1:2:3 and applied a constant W/C ratio of 0.6. The result indicated that adding Welded Tuff in adhesive cement glue as partial replacement of cement increase both the initial and final setting times of cement. However, the workability and density of concrete diminish with the augment in Welded-tuff content of the mix. Regarding the limit state of compressive stress, increasing the Welded-tuff content (upto10%), there is a continuous enrichment in compressive strength of concrete mixes. Upon completing the minimum curing period (7 days), the concrete containing 5% and 10% Welded Tuff as cement gained 6.3% and 1.09% of strength while at 15% and 20% replacement levels concrete loosed 10.18% and 18.91% of strength respectively. Although the replacement of 10% of Welded Tuff still boosts the compressive strength of special concrete compared with the control concrete, for obtaining accuracy on results, the 5% of Welded Tuff was taken as the optimum replacement level. Eventually, the results encourage using Welded Tuff as pozzolanic material for partial cement substitution in producing conventional concrete and reimburse the impacts of cement production towards environmental, technical, and economic factors. [ABSTRACT FROM AUTHOR]