Abstract

The proportion of electricity generated by coal-fired thermal power plants has been rising in Japan as a result of the nuclear plant accident caused by the Great East Japan Earthquake of 2011. Coal-fired electricity generation has a large environment impact, so the commercial application of integrated coal gasification combined cycle (IGCC) has been promoted. IGCC is an efficient generating method combining a steam turbine and a gas turbine. However, IGCC plants generate coal gasification molten slag (CGMS) and it is necessary to establish effective utilization methods for this slag for further promotion of IGCC technology. In this paper, the fresh properties, hardened properties and durability of concrete containing CGMS as fine aggregate are investigated. The results show that, in comparison with concrete using conventional fine aggregate, the air content introduced by an air-entraining agent is lower and bleeding is increased when CGMS is used as a fine aggregate. As for the hardened properties, compressive strength is slightly lower, while freeze-thaw resistance is significantly reduced. In additional tests, it is found possible to improve freeze-thaw resistance by increasing the air content

Abstract

Technical experts in construction industries are trying to improve the quality, ease of using materials in different forms, and increasing structure performance. However, in the changing cost of each item, quality of works could be sacrificed. In Ethiopia, the practice of using alternative ingredients to produce materials was observed weak in some scenarios. It was because ignoring the right procedures to perform the required material requirements for construction materials. It is known that Ambo area has a scarcity of natural sand or rivers sand which can be extracted from the river bed. Notably, if available, the quality is not good due to the presence of silt and clay. Once it used, it adversely affects the structural integrity of concrete structures. The primary objective of the research is to evaluate the suitability of Ambo Sandstone Fine Aggregate (ASFA) as an alternative replacement of river sand in normal concrete production. Samples extracted from Senkele and Aleltu quarry sites of Ambo Area. Results showed that fine aggregates from Senkele quarry site indicated 14.28% silt content, while from the Aleltu quarry site indicated 12.28% silt content, all of which exceeded 6% based on Ethiopian Standard Specification. It means the samples must be rejected or appropriately washed before use as a part of a concrete mix. After performing the procedure to remove silt content, it found out that the silt content reduced to 5.3%, less than the allowable maximum of 6%. Hence, Ambo Sandstone Fine Aggregates (ASFA) are suitable for concrete mix production and strength determination. There were nine samples of concrete cubes prepared and tested at 7th, 14th, and 28th days for concrete compressive strength with a mix ratio of 1:2:3 and water to cement ratio of 0.50. Based on the laboratory test results with full replacement of river sand by Ambo Sandstone Fine Aggregate (ASFA), the mean compressive strengths at 7th day was 16.61 MPa, while at the 14th day was 19.62MPa, and at 28th day was 25.59 MPa. It means at 28th day; it satisfied the minimum requirement for C-25 grade concrete. Likewise, the cost of production of the fine aggregate of the Ambo Sandstone quarry site is 140 ETB per cubic meter, while the price of river sand from Legeher Market is 300 ETB-400 ETB per cubic meter. Therefore, Ambo Sandstone Fine Aggregate (ASFA) is cheaper than the river sand. However, it must be given emphasis that the Ambo Sandstone Fine Aggregates must wash thoroughly before use in construction projects.