Module 5 Lecture - 3 Fresh Concrete : Role of Admixtures

Lecture Series on Building Materials and Construction by Dr .B.Bhattacharjee, Department of Civil Engineering,IIT Delhi. For more details on NPTEL visit nptel.iitm.ac.in

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CONCRETE SLUMP TEST DEMO BY SACHU

Slump Test- This method of test specifies the Procedure to be adopted, either in the laboratory or during the progress of the work in the field, for determining, by the Slump test the consistency of concrete, where the nominal maximum size of aggregate does not exceed 38mm. Demonstration of the Test conducted in Concrete Lab, Department of Civil Engineering, Bharath University, Chennai - 73

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Module 7 Lecture - 3 Durability of Concrete

Lecture Series on Building Materials and Construction by Dr .B.Bhattacharjee, Department of Civil Engineering,IIT Delhi. For more details on NPTEL visit nptel.iitm.ac.in

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Lecture - 39 Concrete Pavement Design PCA and AASHTO Methods

Lecture Series on Introduction to Transportation Engineering by Prof. Bhargab Maitra and Prof. K. Sudhakar Reddy, Department of Civil Engineering, IIT Kharagpur. For more details on NPTEL visit nptel.iitm.ac.in

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Precast Concrete Retaining Wall

A precast concrete retaining wall is normally used to retain earth or similar materials. It is also used to divide agricultural buildings such as a grain sheds or waste transfer stations to create storage bays.

Concrete retaining walls have gained in favour over in-situ concrete walls or timber walls and are very popular for civil engineering projects. They tend to be more economical, easier to install and more environmentally sound than other options. There are two main methods for fixing the retaining wall in place; embedding them into a concrete floor, or alternatively, using a ground fixing kit. The advantage of the latter solution is that the concrete retaining wall can be moved at a later date.

One of the most important things to consider when building a concrete retaining wall is the force at which the retained material is attempting to move forward and slide due to the force of gravity. This creates a lateral earth pressure behind the wall. Earth pressures will push the wall forward or overturn it if not properly looked at. Also, any groundwater behind the wall that is allowed to build up will cause an additional horizontal pressure on the wall. This problem can be solved by placing suitable drainage holes in the wall. While it can be an unwanted expense, getting a design from a structural engineer is very important and can save a lot of time and expense further down the line.

There are a range of products suitable for use as a concrete retaining wall. The most suitable product will depend on a number of factors including; the material retained, the height of the wall, site restrictions and budget. A few products that are worth considering; concrete panels (either used horizontally or vertically), L shape retaining wall units or concrete crib wall units. While the material costs can look expensive, after taking into account the savings in terms of installation, it often works out as the desired solution.

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Module 5 Lecture - 1 Fresh Concrete

Lecture Series on Building Materials and Construction by Dr .B.Bhattacharjee, Department of Civil Engineering,IIT Delhi. For more details on NPTEL visit nptel.iitm.ac.in

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Concrete Ingredients: Cement & Mineral Admixtures

What is Portland Cement?

Portland cement (PC) is the principal binder that, upon hydration and setting, holds aggregates (coarse and fine) together in concrete. It has the ability to stand in water and increase its strength over time. This ability elicits the term hydraulic cement for this type of cement.

What is the Composition of PC?

PC is a manufactured product formed within narrow confines of specific elements and subjected to heat treatment to form a semi-finished product called clinker. Raw materials used include: Limestone, Shale, Iron Ore and Sand.

The principal elemental ingredients in the raw materials are:

o Calcium Oxide (CaO)

o Silicon (SiO2)

o Aluminum Oxide (Al2O3)

o Iron Oxide (Fe2O3) in addition to other elemental oxides.

It is possible sometimes to have all these elemental oxides in some limestones. Where the principal source, limestone, is deficient in any of the elemental oxides then the other ingredients are added in the right proportion in preparation for the manufacturing process.

The latter process comprise of three phases:

1. Grinding the materials into a powder form

2. Heating the powdered material in a kiln up to about 2700°F

3. Grinding the clinker formed with gypsum to form PC

When PC is mixed with water either to form a cement paste or concrete, in a process called hydration, a chemical reaction takes place and for simplicity sake two principal products are formed: 1) calcium silicate hydrate, C-S-H and 2) calcium hydroxide

Calcium Silicate Hydrate (C-S-H) is insoluble in water. It gives the title hydraulic to set PC's ability to stand in water without any detriment. Calcium hydroxide is soluble in water and leaches out of set concrete and in a two step approach first, the solution is drawn to the exterior wall of the structure and secondly, react with carbon dioxide of the atmosphere to form chalk, the white, efflorescence salt found on concrete walls.

MINERAL ADMIXTURE - Mineral admixtures used in concrete formulations contain oxides of silica and other oxides that are found in Portland cement. Examples of mineral admixtures include fly ash, silica fume and volcanic ash.

Mineral admixtures used in concrete may be referred to as Pozzolans, or materials that won't harden in water but in the presence of lime, react and harden to form a stone-like mass.

One important use of mineral admixtures in concrete is the ability of the silica component to react with the soluble calcium hydroxide formed in the hydrating cement to form an insoluble calcium silicate hydrate thus helping to form a dense, compact concrete/cement paste.

Concrete formulated with mineral admixtures are not likely to form efflorescence salts. The use of mineral admixtures in concrete helps resist sulfate attack and alkali-silica reactivity. In the fresh concrete the presence of mineral admixtures often improve the workability of the mix.

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Module 9 Lecture -2 Mix Design Of concrete IS Method

Lecture Series on Building Materials and Construction by Dr. B. Bhattacharjee, Department of Civil Engineering,IIT Delhi. For more details on NPTEL visit nptel.iitm.ac.in



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Antiwashout Underwater Concrete

Antiwashout underwater concrete is an underwater concrete that has improved resistance to segregation as a result of adding an antiwashout admixture. Antiwashout underwater concrete (or underwater antiwash concrete) shall have the required strength, durability, compactness, and ability to protect steel materials, and the scatter in quality shall be small. Also, the concrete shall have a workability suitable for the placing operation and shall not cause water pollution.

As in the case of ordinary concrete, antiwashout underwater concrete should have the desired strength and durability, as well as the capacity to protect steel materials from corrosion. However, when a large unit water content is needed to obtain the required fluidity, i.e. greater than 200 kg/m3, the amount of cement as determined from the water-cement ratio sometimes exceeds 400kg/m3. It is therefore necessary to thoroughly examine not only the fluidity and strength needed for the structure, but also the temperature rise due to heat of hydration and whether it is proper to use various admixtures, etc. Furthermore, since the final quality of the concrete depends not only on fluctuations in the quality of the materials and measurement errors, but also on the effects of underwater drop height, underwater flow distance, and water currents in the area of construction, consideration should also be given to these points. That is, the final quality of antiwashout underwater concrete is greatly affected by the construction conditions as well as the materials used and the mix proportion, so it is important that these factors be comprehensively considered if a structure of the required performance is to be obtained.

There are a variety of types of antiwashout admixtures, such as those based on the cellulose system and the acrylic system. Also, the degree of antiwashout property and flow property differs depending on the brand of antiwashout admixture, even though the main Ingredient may be the same.

It is thus important to comprehend the performance of the antiwashout admixture to be used using available reference materials, as well as to confirm that the required quality can be obtained by conducting tests in advance using the chosen materials.

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