Absolute Procedure Essay

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3.5.2. CONCRETE MANUFACTURE

This is a process that describes the making of fresh concrete cubes and testing for compressive strength. The test cubes had a nominal size of 150mm and maximum aggregate size of 20mm. Making test cubes from fresh concrete procedure was in accordance to BS 1881: Part 108: 1983 (cited in Ministry of works, 2000).

EQUIPMENT USED
• Moulds of cast iron or steel, with removable base plate were prepared. The depth of the mould and the distance between the two pairs of opposite internal side faces had nominal size of 150 ± 0.15mm.
• A steel compacting bar weighing 1.8kg, 380mm long and having a ramming face 16mm diameter.
• Sampling tray
• Shovel

Mixing
The concrete was mixed by hand, the coarse aggregate were batched
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Test Procedure
Firstly, the inner surface of the mould was cleaned. The bottom of the mould was placed on a clean, smooth, horizontal, firm and non-absorbent surface steel plate.

Secondly, while firmly holding the mould, it was filled with fresh concrete within 2 minutes after mixing. The mould was filled in three layers, each approximately one-third of the height of the mould when tamped. Thereafter, each layer was tampered with 25 strokes of the tamping rod; the strokes were distributed uniformly over the cross-section of the layer. Each layer was tampered to its full depth.
After tampering, the concrete was heaped above the mould before the top layer was tamped. When the top layer had been tamped, in a sawing motion of the tamping rod, the top level of the mould with concrete was strake off. With the mould still held down, the excess concrete found on the outside of the mould was cleaned away.

The mould was removed from the concrete by raising it vertically, slowly and carefully, in 5 to 10 seconds. The entire operation from the start of filling to the removal of the mould was carried out without interruption and was completed within

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