Study on the behaviour of high strength palm oil fuel ash (POFA) concrete

Abstract

Many researchers have studied the use of agro-waste ashes as constituents in concrete. These agro-waste ashes contained an amount of silica which could be used as a pozzolanic material. Palm Oil Fuel Ash (POFA) is a by-product produced in palm oil mills. This ash has pozzolanic properties that not only enables the replacement of cement but also plays an important role in making strong and durable concrete. Collected POFA was dried and then sieved through a 300 µm sieve. Ashes passing through 300 µm sieve were ground in a modified Los Angeles abrasion test machine. The fineness of the POFA was checked by sieving through 45µm sieve at every half an hour grinding. For this research, total of five mixes were made of OPC as a control mix, OPC replaced with 20% and 30 % of POFA 10 µm and OPC replaced with 20 and 30 % of POFA 45 µm respectively. For compressive strength, six cubes of 100 mm tested at 7, 28, and 90 days. For flexural strength, three prisms of 100 x 100 x 500 mm were tested at 28 days. Five cylinders of 100 x 200 mm were tested for indirect tensile strength at 28 days for each mix. The slump test and compacting factor test were employed in measuring the fresh concrete. POFA concrete exhibit lower value of slump compared to slump of OPC concrete. Among POFA results, the finer the POFA, the lower the slump and hence lower degree of compaction. Although strength of POFA concrete did not exceed that of OPC, 58 MPa was achieved when using 20 % of POFA 10 µm. The flexural strength of POFA concrete is slightly lower than that of OPC. The higher was the replacement of OPC; the lower the flexural strength. Like that of flexural strength, indirect tensile strength of concrete containing POFA developed in a similar way. TG Analysis lead to the fact that the amount of Ca(OH)2 increased with curing age indicating the progress of cement hydration reaction. And reduction in weight loss attributed to dehydroxylation of calcium hydroxide, and subsequent increase in compression is indicative of pozzolanic reaction. From the microstructural analysis (FESEM), radiating clusters of C-S-H gel have lead to a densification of the structure, and an increase in strength. Hexagonal platelets of Ca(OH)2 could be observed in some samples.