The production of lightweight aggregates from pulverised fuel ash as the main material
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Date
2006
Authors
Ismail, Khairul Nizar
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Abstract
The present study covers the production of lightweight aggregates using pulverized fuel
ash. The main aim of this research was to produce lightweight aggregates which can
be used as replacement for normal (natural) aggregates in structural concrete.
Pulverised fuel ash was the main raw material used in this study and among the
wastes which can cause disposal and environmental degradation problems.
Lightweight aggregates produced from pulverised fuel ash, will have low density, high
strength and it will reduce the dead weight and material handling costs for construction
work.
The production processes of lightweight aggregate from pulverised fuel ash
involved grinding, mixing of raw materials, agglomeration and sintering process for
hardening and binding of the particles. It also involved study on the physical,
mechanical and chemical properties of raw materials such as pulverized fuel ash,
expanded clay, quarry dust and rice husk ash. Quarry dust, clay and rice husk ash
were also used as additional raw materials in this process. The effect of sintering at
temperatures between 1180 0C and 1250 0C on density, apparent porosity, percent of
water absorption, mineralogy and microstructure of lightweight aggregates was
examined. The samples were characterized by X-ray diffraction (XRD), X-ray
fluorescence (XRF) and the morphology was examined by scanning electron
microscope (SEM).
Chemical analysis showed that pulverized fuel ash used, was F class with an
average particle size of 6.92 μm. It contained siliceous glass phase together with the
crystalline quartz phase, hematite and mullite. The best lightweight aggregates
obtained from this study consisted of 50 % pulverized fuel ash, 30 % rice husk ash,
10% quarry dust and 10 % expanded clay (PQR 1) and was used for further study.
Result obtained showed that at the sintering temperature of 1230oC, the lightweight
aggregate PQR 1 had particle bulk density of 1.388 g/cm3 and loose bulk density of
990 kg/m3 for coarse aggregates. The 24 hours water absorption for aggregate PQR 1
was 0.24 % and contained 27.15 % porosity. Based on the XRD result, it was found
that the graphite phase that contained carbon was absent and had decomposed as
carbon dioxide gas. This result was further supported by the microstructure of the
aggregate which showed the existence of voids in the cross section of the aggregate
with increasing sintering temperature. This result has satisfied the specification of
British Standard BS 3797, Part 2 (1976) for lightweight aggregate. Lightweight concrete
using the lightweight aggregates PQR 1 was produced and the compressive strength,
density and microstructure of the lightweight aggregate concrete were studied up to 28
days. The average 28-day compressive strength was recorded as 30.5 N/mm2 (30
MPa) while, the average density was 1867.56 kg/m3.
Description
PhD
Keywords
Materials and Mineral Resources Engineering , Fuel ash