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Friday, February 15, 2013

PowerPoint Presentation On ADMIXTURES


ADMIXTURES Presentation Transcript:
1. What Are Admixtures?
Admixtures are chemical substances (other than fine and coarse aggregates, cement, or water), which are added in small amounts just before or during the mixing stage to concrete products.

Over decades, attempts have been made to obtain concrete with certain desired characteristics such as high compressive strength, high workability, and high performance and durability parameters to meet the requirement of complexity of modern structures.

To improve workability of fresh concrete
To improve durability by entrainment of air
To reduce the water required
To accelerate setting & hardening & thus to produce high early strength
To aid curing
To impart water repellent / water proofing property

4. To cause dispersion of the cement particles when mixed with water
To retard setting
To improve wear resistance (hardness)
To offset / reduce shrinkage during setting & hardening
To cause expansion of concrete and automatic prestressing of steel
To aerate mortar / concrete to produce a light-weight product

5. To impart colour to concrete
To offset or reduce some chemical reaction
To reduce bleeding
To reduce the evolution of heat

6. Types of Admixtures
Chemical admixtures
Mineral admixtures

Water-reducing admixture / Plasticizers
They achieve a higher strength by decreasing the water cement ratio at the same workability as an admixture free mix. To achieve the same workability by decreasing the cement content so as to reduce the heat of hydration in mass concrete. To increase the workability so as to ease placing in accessible locations

8. Water reduction is more than 5% but less than 12% The commonly used admixtures are Ligno-sulphonates and hydrocarbolic acid salts. Plasticizers are usually based on lignosulphonate, which is a natural polymer, derived from wood processing in the paper industry

9. Super Plasticizers
These are more recent and more effective type of water reducing admixtures also known as high range water reducer. They increase fluidity and following properties: Flowing Self-leveling Self-compacting concrete Penetration and compaction around dense reinforcement

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1. CLIMATE CHANGE is already having
measurable / computable consequences and future impacts are expected to be wide-ranging and costly. How can we adapt to such changes or limit their extent?

2. What makes the climate change……..?
How is climate changing and how has it changed in the past ? How is the climate going to change in the future ? What impacts has already been observed ? What impacts are expected in the future ? How can we adapt to this climate change phenomena ? What are the current trends in greenhouse gas emissions ? What actions can be taken to reduce greenhouse gas emissions ? How can governments create incentives for mitigation ?

ADAPTATION – A change in eco systems or inhuman societies that allows them to adjust to the changing conditions of the environment.
AEROSOL – Collection of microscopique particles solid or liquid,suspended in a gas. Natural sources of aerosols include salt particles from sea spray, dust and clay particles from the weathering of rocks. Human activities are often considered pollutants.
ATMOSPHERE – The mass of air surrounding the Earth. The atmosphere consists of nitrogen (78%), oxygen (21%), and traces of other gases such as argon, helium, carbon dioxide, and ozone. It plays an important role in the protection of life on Earth; it absorbs ultraviolet solar radiation and reduces temperature extremes between day and night. CONT…..

Defined by the United Nations Convention on Climate Change as “Change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods”
GREENHOUSE GAS – A gas in Earth’s atmosphere, be it of natural or human origin, that absorbs heat radiated by the earth and warms the atmosphere, creating what is commonly known as the greenhouse effect. Water vapour (H2O), carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4), and ozone (O3) are the primary greenhouse gases in the Earth’s atmosphere.
LAND USE – The human use of a piece of land for a certain purpose. Changes in land use may have an impact on the properties of the surface, which can have implication for the climate at a local or a global scale.

5. Climate Change…….?
A long term shift in the statistics of the weather (including its averages). Normal expected average values for temperature and precipitation for a given place and time of year from one decade to the next. Last 2 decades have been the warmest period in the entire global instrumental temperature record, starting in the mid-19th century.

6. 5 Interglacial Periods…..
The Greenland Ice Cores reveal Warm Period 1450–1300 BC, Roman Warm Period 250–0 BC, Mediaeval Warm Period 800–1100 AD, Little Ice Age and the late 20th Century, Warm Period 1900–2012 AD.

7. Climate Changing …….
Natural variability Interactions among the Atmosphere Ocean Land Changes in the amount of Solar Radiation reaching the earth.

8. The Earth’s climate is influenced by……………..
Energy coming from the sun Properties of the Earth’s surface, which determine how much of this solar energy is retained or reflected back to space. Amount of GREENHOUSE GASES & AEROSOLS in the atmosphere Carbon Dioxide (CO2), Methane(CH4) & Nitrous Oxide (N2O) have increased since the beginning of industrial revolution. Human activities Burning of fossil fuels, land use change and agriculture. Atmospheric concentration of CO2 is highest in the last 6,50 ,000 years and has been growing faster in the last 10 years, since the beginning of measurements around 1960

9. Overall human activities since 1750 ………..
Increasing air and ocean temperatures, widespread melting of snow and ice, and rising sea levels. Over the last 100 years global temperature has increased by 0.74°C. Global sea level has risen by 17 cm during the 20th century, due to melting of snow and ice. Change in - Arctic temperatures and ice, ocean salinity, wind patterns, droughts, precipitations, frequency of heat waves and intensity of tropical cyclones. Most of the increase in global temperature observed over the past 50 years is very likely due to human emissions of greenhouse gases.

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