Evaluating the performance of a “ Volcanic-Ash-Lime-Gypsum “ Binder in blocks

Abstract

Cement productivity refers to the strength obtained from a unit of cement used. Results from a case study in Dar es Salaam show that cement is poorly used in the main application of sandcrete blocks. The relative cement productivity was found to range within 20-30% a very low value compared to when used in the production of mass concrete (Isaksson and Buregyeya, 2020). With low cement productivity, cement consumption is high in order to achieve a desired strength. Increased cement consumption means high prices and a high carbon footprint since cement is the major driver of costs and carbon emissions (Mrema and Isaksson, no date). To improve cement productivity, there is need to change the products used in making the sandcrete blocks or shift to hollow blocks (Isaksson and Babatunde, 2019). This study seeks to apply an alternative binder system that is based on a ternary mix of volcanic ash, lime and gypsum together with OPC and test its productivity in blocks. Volcanic ash was sourced from Nyarurambi volcanic ash deposit in Rutooga village ,Rubanda district and characterization tests carried out on it to determine its composition. Calcium hydroxide (Lime) and gypsum (Plaster of Paris) were bought from Cheap hardware in Kasubi Kampala and hardware world Kampala respectively .Volcanic ash, lime and gypsum were then mixed in ratios according to the design of experiments factorial method. They were mixed in different proportions of 75:20:5; 60:30:10; 70:25:5 and 65:20:15 VA: Lime Gypsum respectively. Binder i.e. setting time and compressive strength tests were carried out on the VALG mix and a mix of VALG and Ordinary Portland Cement (CEM 1) in order to obtain the optimum binder ratio. Using the optimum binder ratio, blocks were produced using the VALG mix at 5.5%, 10% and 15% and OPC (CEM1) at 5% and subjected to ordinary curing at the plant by sprinkling them with water until the testing period. The blocks were then tested for compressive strength at 3,7and 28days and the productivity of the binder assessed. The results obtained showed that blocks from VALG have a higher productivity 43% as compared to the blocks from OPC, which had a relative productivity of 36%. The blocks from the blend of VALG and OPC had a productivity between 20% and 35%. The blocks were classified as grade A density blocks and compressive strength results at 28 days according to the binder percentages were as follows; 10.5% ;6.3Mpa, 15% ;4.4Mpa, 20%;6MPa, VALG 15%;5.17Mpa, and OPC 7%;6.89Mpa. The results from the cost and carbon footprint computations show that blocks produced from VALG and the blend of VALG and OPC have an economic and environmental advantage compared to those from OPC alone.