3.6.1 Chemical Admixtures They reduce the cost of construction, modify the properties of concrete and improve the quality of concrete during mixing, transportation, placing and curing.
Some of the chemicals admixtures are:
1. Air-entrainment
2. Water-reducing
3. Set-retarding
4. Accelerating
5. Super-plasticizers
6. Corrosion-inhibitors
3.6.2 Mineral Admixtures These are inorganic materials that also have pozzolanic or latent hydraulic properties. These very fine-grained materials are added to the concrete mix to improve the properties of concrete (mineral admixtures), or as a replacement for Portland cement (blended cement).
Fly ash: A by-product of coal-fired electric generating plants which is used to partially replace Portland
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Workability depends on water content, aggregate (shape and size distribution), cement content and age (level of hydration) and can be modified by adding chemical admixtures, like super plasticizer. Raising the water content or adding chemical admixtures will increase concrete workability. Excessive water will lead to increase bleeding (surface water) and segregation of aggregates (when the cement and aggregates start to separate), with the resulting concrete having reduced quality. Workability of fresh concrete is determined by following …show more content…
The slump test result is a measure of the behavior of a self-compacted inverted cone of concrete under the action of gravity. It is a measure of the concrete's workability or the dampness of concrete. Slump test as per IS: 1199 – 1959 is followed. The apparatus used for doing slump test are Slump cone and tamping rod.
Procedure to determine workability of fresh concrete by slump test:
• The internal surface of the mould is thoroughly cleaned and applied with a light coat of oil.
• The mould is placed on a smooth, horizontal, rigid and non absorbent surface.
• The mould is then filled in four layers with freshly mixed concrete, each approximately to one-fourth of the height of the mould.
• Each layer is tamped 25 times by the rounded end of the tamping rod (strokes are distributed evenly over the cross section).
• After the top layer is tamped, the concrete is struck off the level with a trowel.
• The mould is removed from the concrete immediately by raising it slowly in the vertical direction.
• The difference in level between the height of the mould and that of the highest point of the subsided concrete is measured.
• This difference in height in mm is the slump of the
Depending on the thickness of the materials to be joined, they would next be put through one of two machines; either a three million pound press, or a series of rollers, known as levelers for the thinner material.
they're not. Concrete is to cement as a cake is to flour. Concrete is a mixture
strips was put into each tube and then timed with a stop clock and the
He will have the patient put the prosthetic on and walk around. After walking a few times, he will ask if there are any spots that are too tight or too loose. If there are any spots that are too tight or too loose, heat the prosthetic up and push the mold in or out. Once he has the fitting right on the patient, he will then have the patient walk again. This time he will look to see if it is balanced or not.
When the slip is ready, pour the slip into a pitcher. From the pitcher, the slip has to be poured into the mold until the mold is filled to the top. Once the slip reaches the top, tap the sides of the mold to ensure there are no bubbles. If the slip goes down into the mold slightly, add more to the mold. (5 minutes)
floor, a four-foot base of cement was laid and an iron cage sunk into it.
3) Super workable concretes have the ability to fill the heavily reinforced sections without internal or external vibration, without segregation and without developing large sized voids
Fill the wheelbarrow simplest as complete as you may clean take care of. Wear good work gloves while coping with the concrete as the broken edges are all sharp and jagged. Once all the concrete has been broken and eliminated, re-degree the earth or stone below the slab. You more significant than in all likelihood misplaced a small amount of underneath slab stone with the concrete, Add something quantity is essential to bring the earth/floor returned level with the bottom of the existing slab. Compact the earth/stone to guarantee there will be no settlement afterward as a way to sink and permit the new concrete to re-crack.
Aggregate: in cement concrete to gain good quality aggregates are used in two groups. Sand and coarse
In this report, we will introduce and illustrate on precast concrete, pre-stressed concrete, ready-mix concrete, reinforced concrete, terrazzo and Urbanite in details.
Fairly stiffed texture is mixed with clay body which is loaded into extruder worm screw force it into a die through pushing it along a barrel .depending upon how much clay will shrink in drying and firing process the die is made larger considering this The clay emerges as a continuous brick shaped column. Initially this is smooth but it can be modified by removing a thin sliver from the top and sides using a taught wire to produce a ‘wiredrag’ effect or by placing textured rollers over the column to create a rusticated effect or even by blasting the column with sand. The clay column is then cut into single bricks and palletised ready for the dryers or in some factories, are loaded directly onto kiln cars.
...of slurry to dry in between. This will then be dried and a dipping process will be repeated until a certain thickness has been achieved. The entire pattern will then be placed in an oven and the wax melted leaving a hollow cavity within the mould which matches exactly the shape of the assembly. Before casting the ‘skin’ or shells will be fired in an oven, where the heat will burn out any remaining wax and prepare the mould for the molten metal. The metal will be poured a shell through a funnel-shaped cup and flows down the Sprue channel and pass the gates into the part cavities. Once the metal cools the gates, Sprue and parts will become one solid casting. When the casting has cooled the shell will be broken off. After a few finishing operations, the castings which are exact replicas to the wax patterns are ready for shipment to the customer and for certification.
Compaction was done as per IS 516: 1959. The moulds were filled with concrete in three layers and after every layer compaction was done with the tamping rod by tamping 25 times. After complete filling moulds were compacted using vibration machine to ensure a symmetrical distribution of concrete.
During the forming phase, slip composed of a mixture of ceramic powders is poured into a mould. The mould porosity allows water filtration so leading to the deposition of a clay layer in adherence to the mould surfaces. When such layer reaches the desired thickness (4–7 mm) the water is removed. Pressured air is injected, slightly desaturating the clay, so providing the minimum mechanical strength needed to extract the formed product from the mould and allowing it to support its self weight. At this stage the product is called green
The previous test also produced results for the permanent deflection of the slab. As a result of the simulated weak foundation the initial deflection was quit sever when viewed to next to the deflection present in the later stages of the test. The results reported by this test showed that samples had deflected considerably more than those that included RAP and there was a direct link between an increase of RAD and a decrease in the level of deflection.