The document discusses the properties and testing of sludge ash as an aggregate material for lightweight concrete. It finds that sludge ash has a high specific gravity but low unit weight due to its porous nature, making it suitable for lightweight concrete. Testing shows the concrete made with sludge ash has low water absorption and good thermal insulation properties. Additional fire resistance testing found that beams made with sludge ash concrete maintained strength longer when exposed to fire compared to normal concrete beams.

1. • This high SG value can be attributed to the fact that the sludge ash contains compounds of
various metals that are fused together when the sludge reaches the pyroplasticity stage during
the incineration process.
• Although the sludge ash has a high SG value, its inherent porous nature provides the desired
characteristic of low unit weight that is typical of lightweight concrete aggregates.
• This particularly low water absorption value can beexplained by the fact that a major portion of
the porosity of the sludge ash coarse aggregate is formed by fairly large interconnected cells,
which therefore do not retain much absorbed water. Also, the solids content of the sludge ash
consists of much of the fused portion of the various metal compounds, thus causing it to have a
relatively poor affinity for moisture.
• To determine the suitability of lightweight concrete made with sludge ash as a heat-insulation
material, two concrete panels, each having dimensions of 300 mm X 300 mm X 50 mm, were
cast using no-fines lightweight concrete having a cement-to-coarse sludge ash aggregate ratio of
1:6 by weight and a water-cement ratio of 0.5 by weight. The procedure to measure the thermal
conductivity of the lightweight concrete panels was carried out in accordance with ASTM C518-
76 (Steady-State Thermal Transmission Properties by Means of Heat Flow Meter).
• To carry out the fire-resistance test on the sludge ash lightweight concrete, two sets of three
reinforced beams, each of dimensions 100 mm x 100 mm x 500 mm, were cast. The first set of
three beams were cast using lightweight concrete having a sand-to-sludge ash ratio of 1:1.5 by
weight, a water-cement ratio of 0.5 by weight, and a cement content of 400 kg/m3 of fresh
concrete. The second set of three beams, serving as specimens for comparison, were cast using
crushed granite as coarse aggregate and the concrete batched in the same proportions as the
lightweight concrete.
Eachbeam was reinforced longitudinally with two 6-mm diameter, mile steel reinforcements.
• One beam from each set of three had thermocouples mounted on the reinforcement before
casting. All beams were continuously watercured for 28 days and then air-cured for another
seven days, so as to con-
• dition their moisture content to be in equilibrium with the atmosphere before testing them.
• The procedure for the fire-resistance test as specified in BS 476 (Fire Tests on Building Materials
and Structures) was modified for this study. Gas burners were used as heating devices instead of
a furnace with temperature controls.
• Fig. 1 shows the schematic setup for the modified fire-resistance test.
• From each set of beams, two were load tested to determine the average ultimate load-bearing
capacity due to a point load at the center of the simply

2. • supported beam. The remaining beam was subjected to burning for 30 min, while being
loaded under a constant midspan load of 60% of its respective determined ultimate load-
bearing capacity. Throughout the burning period, the rise in temperature of the reinforcement
bars was recorded.
• At the end of the burning period, the beam was loaded to failure to determine its ultimateload-
bearing capacity.
•