2. Cement/Concrete?
What’s the Difference?
• Cement is an ingredient of concrete.
• Cement : Concrete = Flour : Cake
• Concrete is basically a mixture of
aggregates and paste.
• Aggregates are sand and gravel or
crushed stone.
• The paste is water and portland cement.
3. Stronger and Harder
• Cement comprises from 10 to 15 percent
of the concrete mix, by volume.
• Through a process called hydration, the
cement and water harden and bind the
aggregates into a rocklike mass.
• This hardening process continues for
years meaning that concrete gets stronger
as it gets older.
4. Curing & Temperature
• Curing is one of the most important steps in
concrete construction, because proper curing
greatly increases concrete strength, hardness
and durability.
• Curing requires hydration: the chemical
reaction between cement and water.
• Hydration occurs only if water is available
and if the concrete's temperature stays within
a suitable range – between 10 and 50 °C.
• This can last from five to seven days.
6. Concrete Structure
• Concrete is strong in compression, but
weak in tension.
• To prevent the concrete from cracking
when in tension, it is reinforced with steel
rods (REBAR) or steel mesh.
• The steel rods or mesh are strong in
tension and prevent the concrete from
cracking.
7. Composite Material
• Concrete floors that are two inches or
more in thickness are often reinforced with
fibreglass mesh instead of rebar.
• Composites are made of two structures
– The matrix or main component – concrete
– and the reinforcement – rebar or mesh
8. Why Test Concrete?
• Concrete is tested to ensure that the material
that was specified and bought is the same
material delivered to the job site.
• Slump is a measure of consistency, or
relative ability of the concrete to flow.
• Air content measures the total air content in a
sample of fresh concrete.
• Density measures mass/volume.
• Compressive strength is tested by measuring
the force needed to break the concrete.
10. Pascal’s Law
• Pascal's law states that pressure exerted in a fluid
is transmitted equally in all directions throughout
a confined fluid.
• Pressure due to concrete pushes in all directions.
• The weight of concrete causes it to push down
more at the bottom.
• Pressure (Pascal) = Force (Newton)
Area (m2)
• P = F
• A
11. Example
• Calculate the Pressure if 10 Newtons of Force
are applied over an area of 2 m2
• P = Force = 10 Newtons
• Area 2 m2
• = 5 Pascals
12. Archimedes’
Principle
• Archimedes' principle indicates that the
upward buoyant force that is exerted on a
body immersed in a fluid is equal to the
weight of the fluid that the body displaces.
13. What are changes in matter?
• All matter is subject to change either physically, chemically,
or through nuclear transformations.
• Physical Changes are changes in which only the state of
the substance has changed: solid > liquid > gas.
• The atoms and molecules do not change – only their
appearance.
• Chemical Changes involve new substances being created
and change the nature of the matter.
• The bonds between atoms are rearranged to form different
molecules. The characteristic properties are altered.
• Nuclear Changes or Transformations affect the nucleus of
the atom where it splits to form new elements. The
particles are rearranged.
14. Chemical Changes
• In these reactions, the chemical bonds
between reactants are broken and new bonds
formed.
• New products form and have new
characteristic properties.
• Signs that a chemical change has occurred:
– Gas bubbles form
– Heat or light is given off
– Change in colour
– Precipitate forms
– New substance is created
– pH change
– Change is difficult to reverse
15. Conservation of Mass
• Antoine Lavoisier (1743-1794) showed that
the masses of the products of a chemical
reaction were the same as the mass of the
reactants.
• Mass of the reactants = Mass of the products
• E.g. CH4 + 2 O2 CO2 + 2 H2O
• 16g + 64g 44g + 36 g
• 80g 80g
• Q. If you reacted 48 g of methane with 192
g of oxygen, how many grams of product are
16. Conservation of Energy
• Energy is neither created nor destroyed,
but it can change from one energy form to
another.
• % Efficiency is a measure of how much
energy is used compared to how much
energy is supplied.
• %E = Useful Energy (J) x 100%
Total Energy Supplied (J)
17. Exam Question
The diagram shows what happens to the Sun's radiation when it falls on a panel of solar cells.
http://www.s-cool.co.uk/gcse/physics/energy-calculations
i)What is the overall efficiency of the transfer of light energy from the Sun to electrical energy?
A) 15%
B) 56%
C) 71%
D) 100%
ii) If 4 320 000 joules of solar energy hit 1 m2
of solar panel each day, how much solar energy
would be transformed into electrical energy?
18. Balancing Chemical Equations
• Tally the number of atoms of each element on the
Reactant side and the Product side.
• The only way we change the number is by using a
large number called a coefficient which is placed at
the front of the molecule.
• The small # attached to the atoms is called the
subscript # and it NEVER changes.
• E.g. Unbalanced: Mg + O 2 Mg0
• Tally Mg - 1 Mg - 1
• O - 2 O - 1
• Balanced: 2 Mg + O 2 2 Mg0
• Tally Mg - 2 Mg - 2
• O - 2 O - 2
19. Endothermic vs Exothermic Reactions
• Exothermic Reactions release energy to
the environment, often causing
temperatures to increase.
• E.g. a fire burns, and the heat created is
enough to continue the reaction.
• Endothermic Reactions absorb energy
from the environment, often causing
temperatures to decrease.
• E.g. a cake baking absorbs heat from the
oven.
SE
20. Exam Question
Which of the following is a form of energy?
A) Temperature
B) Heat
C) Heat and temperature
D) Neither heat nor energy
Heat energy moves from
A) a warmer area to a cooler area
B) a cooler area to a warmer area
C) a heavier object to a lighter one
D) a solid to a gas
21. 5 Types of Chemical Change
• 1. Synthesis is a reaction where 2 or more reactants
combine to form a new product
( A + B AB)
• 2. Decomposition is a reaction where a compound
separates into two or more compounds or elements.
(AB A + B)
• 3. Precipitation occurs when two solutions are
combined and an insoluble substance (precipitate)
forms.
(Solution + Solution Solid)
• 4. Acid Base Neutralization occurs when an acid
(pH1-6) and a base (pH 8-14) react to produce salt
and water.
(Acid +Base Salt + Water)
• 5. Oxidation occurs when substances react with the
oxygen. E.g. Combustion, rusting, respiration
(HydroCarbon + Oxygen Carbon Dioxide + Water)
22. Exam Question
Which of the following depict a decomposition reaction? (SE)
A)
B)
C)
D)
SE
23. Particle Theory Question
Methane gas is burned in oxygen to form the products of carbon dioxide and water.
It is expressed using the following balanced chemical reaction.
CH4 + 2 O2 CO2 + 2 H2O
Express the above reaction using the following symbols. Draw the symbols in the box below.
C: H: O:
+ +
24. Combustion• 3 types:
– Rapid: spectacular and in a short time, it releases a lot of energy
in the form of heat or light;
– E.g. candle, log fire
– Spontaneous: rapid and without energy from outside source;
unpredictable
– E.g. dry wood catches fire by itself, hay heats
– Slow: occurs over a long period of time and energy is released
gradually into environment.
– E.g. decomposition, fermentation, cellular respiration, metal
corrosion.
25. Exam Question
Which of the following is a product of coal combustion?
A) Oxygen
B) Hydrogen
C) Carbon dioxide
D) Sodium chloride
Which of the following is NOT an example of oxidation?
A) Photosynthesis
B) Burning wood
C) Rusting iron
D) Cellular respiration
26. The Fire Triangle
Three conditions are needed for combustion to occur:
• fuel (something to burn);
• an oxidizing agent (causes fuel to react, e.g.
oxygen)
• the ignition temperature.
If one is removed then there cannot be a fire.
27. Exam Question
• In the combustion of wood, _____ is the fuel
and ______ is the oxidant.
• A) Carbon dioxide, wood
• B) Oxygen, wood
• C) Wood, carbon dioxide
• D) Wood, oxygen
28. Fire Triangle Exam Question
Use the fire triangle to explain each of the following:
A) How a forest fire can be stopped by clearing sections of trees;
B) How a stove top oil fire can be stopped by placing a wet tea towel across the pan;
C) How a fire can be extinguished by using a carbon dioxide fire extinguisher.
29. Photosynthesis
• Is an endothermic chemical reaction
• Plants (producers) use the sun’s energy to make
glucose and oxygen from carbon dioxide and
water.
• It releases oxygen and is needed for maintaining
oxygen levels in the air.
• Glucose is a source of energy.
30. Cellular
Respiration
• Is an exothermic chemical reaction
• Is a type of slow combustion/oxidation
• Glucose and oxygen generate energy in
cells
and produce carbon dioxide and water.
31. Activity
• Work on pages 1&2, 3 & 4 of the handout.
• Concrete Boat Float Lab
• Concrete Beam Lab
• Page 132, Q 1-7
• Ascent of Man – Episode 4
• Cosmos
