Title: Slump of Fresh Concrete
Aim: To measure the slump or workability of fresh concrete
• 1 Electronic scale (capacity 8100g accurate to 0.1g, inherent error ± 0.05g)
• Stainless steel tamping rod(diameter =5/8˝, length =18˝)
• Metal scoops
• Slump cone
• Plastic bucket
• Fine aggregate(4.75 mm)
• Coarse aggregate (25mm)
• Tap water
• Ordinary Portland cement(manufactured 7/02/2011)
• 100ml of Admixture (Air Entrain)
1. The cone was dampened and placed on a flat surface.
2. The cone was then filled in three layers with the operator standing on the foot pieces, rodding 25 times for each layer.
3. The top of the concrete in the cone was leveled off to the cone
4. The cone was lifted vertically, without any sideway or vibration motions, until it was clear of the concrete.
5. The cone was then set beside the concrete sample; the rod was placed perpendicularly to the top of the cone and the decrease in height of the concrete sample measured.
Fresh concrete is a homogenous mixture of water, cement, aggregates (coarse and fine), air and in some cases admixtures may be used. Admixture is used in certain cases to control rheology, rate of setting, hardening and durability. After mixing the constituent materials to produce a uniform blend, operations such as transporting, compacting, placing and the finishing of fresh concrete can all affect the properties of hardened concrete. It is important that the constituent materials remain s uniformly distributed within the concrete mass during the various stages of its handling and also that full compaction is achieved. Whenever these conditions are not satisfied the properties of the resulting hardened concrete are adversely affected for example its strength and durability.
There are three (3) properties that define fresh concrete. Workability is a measure of the ease or difficulty in placing concrete, consolidating and finishing within the form without harmful segregation. Consistency is the ability of the concrete to flow. The usual measure of consistency is the slump test. Plasticity is the property which determines the ease of molding.
The slump test is a test used extensively on construction site all over the world. The slump test does not measure the workability of concrete, although it has been described as a measure of consistency, but the test is very useful in detecting variations in the uniformity of a mix of nominal proportions. The slump test is very useful on site as a check on the batch-to-batch or hour –to-hour variation in the materials being fed into the mixer. An increase in slump may mean that the moisture content of aggregate has unexpectedly increased; another cause would be a change in the grading of the aggregate. Too high or too low a slump gives immediate warning and enables the mixer operator to remedy the situation. The application of the slump test as well as its simplicity is responsible for its wide spread use.
The mould for the slump test is a frustum of a core 300mm (12in) high. It is placed on a smooth surface with the smaller opening at the top which is then filled with concrete in three layers. Each layer is tamped 25 times with a standard 16mm (5/8˝) diameter steel rod, rounded at the end. After the three layers have been compacted, the top surface is struck off by means of sawing and rolling motion of the tamping rod. The mould must be firmly held against its base during the entire operation this is facilitated by handles and footrest brazed to the mould.
Immediately after filling the cone is lifted slowly, the unsupported will slump – hence the...