Considerable bad experience has been encountered when alkali reactive aggregates have been used.Low alkali cement is normally required to protect against disruptive
Expansion of concrete which occurs generally due to alkali-aggregate reaction.(a chemical reaction between alkali’s in the cement and reactive aggregates.Another means of of controlling alkali-aggregate reactions is by the use of suitable fly ash or natural pozzolan.If a highly reactive aggregate have to be used then it is necessary to use a low alkali cement and a pozzolan.
Another design recommendation is the type of the cement to be used.Type-2 cement is normally used by the Bureau of Reclamation in mass concrete dams.Limitations on the
Heat of hydration of this cement are specified when determined necessary to minimize cracking in the concrete structure.Use of Type-2 cement will generally reduce the heat of hydration of cement to an acceptable level, particularly when type-2 cement is used in conjunction with other methods of heat reduction.These include use of lower cement content and using pozzolan as part of the cementitious material,use of pipe cooling system and use of a specified maximum temperature for placing of concrete,which may be as low as 50 degF.Use of all or some of this methods usually reduce or eliminate the need for stringent limitations on heat of hydration of concrete.However a limitation of 58% on Tricalcium Aluminate plus Tricalcium Silicate content of Type-2 required where
Heat of hydration must be kept low.Further limitation on heat of hydration,if more stringent control of heat is needed can be obtained with a Type-2 cement by providing a maximum limitation on the cement of 70 calories per gram at 7 days or 80 calories per gram at 28...
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Conveying concrete whose aggregate size is less than 7.5 cm.Pumping of concrete is to be done in such way that concrete without air pockets or interruptions is delivered.
Placing of Concrete:
Concrete has to be placed at a uniform rate through out the placing of the concrete.
Each layer is compacted well before placing of the other layer.Generally thickness of layers shall not exceed the following limits.
Reinforced Concrete-25 cm.
Vibrated Concrete-45 cm.
Hand compacted mass concrete-30 cm.
Concrete is placed vertically above the other layer so as to avoid damage,segregation and air pockets.Compaction should be done as quickly as possible after placing.When concrete is placed in the forms temperature may go high as suggested by some previous studies so measures have to be taken in order to reduce such effects.They are
(Mazzassa – Lea's science). Calcium silicate hydrate is the fundamental result of lime-pozzolan response. Calcium aluminous hydrate, hydrated gehlenite, calcium carboaluminate, ettringite and calcium aluminous monosulfate are a percentage of alternate items that outcome from the lime-pozzolan response notwithstanding calcium silicate hydrate. (Admixtures for cement T.erdogan). The hydration between slica of pozzolans and calcium hydroxide are given by mathematical statement.
Most people may not realise but concrete plays a vital part in our lives daily. It shapes and creates the built environment in which we are surrounded by, such as schools, bridges, roads, housing, hospitals, dams and so much mores. Concrete is the most used man made material in the world, averaging around 3 tonnes annually for each person. In comparison with other building materials such as wood, steel, plastic and aluminium, over twice as much concrete is used globally than any of these materials. It is the material choice of most purposes due to its strength, durability, thermal mass and its cost.
In this paper we have studied compressive strength of concrete by replacing natural aggregate with recycled aggregate by 25%, 50% and 75%.This mixture formed in the sample of cubes of dimension 150x150x150mm3.
Aitcin P.C, “Cements of yesterday and today Concrete of tomorrow”, Cement and Concrete Research, Vol. 30, (2000), pp 1349 - 1359.
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
[20] BS Part 116: 1983. Testing Concrete and determination of compressive strength. British Standards Institution ;
Aggregate: in cement concrete to gain good quality aggregates are used in two groups. Sand and coarse
(I): Rock masses yielding low water (WPT) and cement takes (CT) are practically tight and need no treatment:
In this report, we will introduce and illustrate on precast concrete, pre-stressed concrete, ready-mix concrete, reinforced concrete, terrazzo and Urbanite in details.
Throughout the construction industry, technology plays a role to help ease the completion of a project to all of the parties involved. The amount of technology application in the industry supports the belief that technology has a positive impact on project productivity. One of the main materials used in the construction industry that surrounds us every day, in which we overlook, is concrete. Concrete is an art form, in which it takes time and talent in order for it to be used efficiently, to produce its high strength and longevity. However, the downfall of this material is that it is extremely costly and nearly impossible to form it to an aesthetically pleasing surface. In spite of this, what if I told you that there is hope? That the dream of a material made of concrete, producing the same qualities, can be formed to any shape, and used anywhere was a reality.
In these cases, such as building a reservoir, a huge number of concrete trucks are generally brought in in a caravan, and they pour their concrete into the forms that have been constructed onsite. In some cases, this order will put a concrete plant out of commission for a period of time due to the demand, and as such it must obviously be coordinated ahead of time.
...nd Calderwood 1978; Suaris and Shah 1984), because it requires higher energy to split the fibers from the concrete.
Author observed that overall performance of concrete was increased and there is huge reduction in water absorption [19]
Previous study about the Ordinary Portland Cement (OPC), High Performance Concrete (HPC), And Ultra High Performance Concrete(UHPC) there are different result about the penetration of chloride ions to the specimen. This because, the reinforced concrete are exposed to harsh environment yet often expected to last with little or no maintenance for a long periods of time. The lacking maintenance of the concrete may cause this problem become worse and the concrete may not suitable to used.
Laboratory experiments have shown that cement degrades would occur once exposed to such CO2 rich environments [10]-[12], [16], [22], [72]-[74], [30]. It tends to degrade rapidly once exposed to such acid gas by reacting with Ca(OH)2 and C-S-H. The mechanism of degradation process starts when CO2 gas is exposed in a wet environment, it will...