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
Then we filled the molds about 25 to 30 percent full and closed the molds with the mold nuts.
Wax is poured into the mould using a machine and the wax takes the shape of the design and final wax piece is formed.
One special subset is called architectural and decorative concrete, which refers to a substance that provides an aesthetic finish and structural capabilities in one. This material is made to be seen. Whether creating broad expanses or minute details, concrete permanently captures the chosen look. Achieving an architectural or decorative appearance usually requires that something different be done to the concrete. Whether that involves special forms, special finishing techniques, or special ingredients, the variety of effects is almost unlimited.
INJECTION OF THE PLASTIC MELTS INTO THE MOULD: In stage 1, the mould is closed and the nozzle of the extruder is pushed against the sprue bushing of the mould. The screw, not rotating at this point, is pushed forward so that the plastic melt in front of the screw is forced into the mould.
Aitcin P.C, “Cements of yesterday and today Concrete of tomorrow”, Cement and Concrete Research, Vol. 30, (2000), pp 1349 - 1359.
2) While many High Performance Concretes exhibits rapid stiffening and early strength gain, other’s may have long set times and low early strengths.
Around the 2nd century BCE, they have learned that by mixing the other concrete ingredients with volcanic sand called pulvis puteolanus made the product stronger and in addition to that it would
[17] BS 4550-3.4:1978. Methods of testing cement, Physical tests, Strength tests. British Standards Institution ; 2007.
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.
The process of proper and accurate measurement of concrete ingredients for uniformity of proportion, is known as ………………………………………
In use from the 1940s onwards, dense aggregate blocks are very much the work-horse of the construction industry. Their distinctive properties of durability and strength make them an ideal and cost-effect solution for all types of load-bearing walls. Dense aggregate concrete blocks are manufactured from cement, sand and aggregates.
...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.
The splitting tests are well known as indirect tests used for determining the tensile strength of concrete. And sometimes it is referred to as split tensile strength of concrete. The split tensile strength is a more reliable technique to evaluate tensile strength of concrete (lower coefficient of variation) compared to other methods. The split tensile strength specimen of 150 mm diameter and 300 mm or 150 x150 mm cube specimen are placed between two plates with two pieces of 3 mm thick, as shown in figure (2.25). The test consists of applying a compressive line load along the opposite generators of a concrete cylinder placed with its axis horizontal between the compressive platens. (ESS 203)
Continuous casting process starts by molten steel flows from a ladle through a tundish into the molder.