Cement is an ingredient of concrete.
Cement : Concrete = Flour : Cake
Concrete is basically a mixture of aggregates
Aggregates are sand and gravel or crushed
The paste is water and portland cement.
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
Curing is one of the most important steps in
concrete construction, because proper curing
greatly increases concrete strength, hardness
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
This can last from five to seven days.
Temperature extremes make it difficult to
properly cure concrete.
On hot days, too much water is lost by
evaporation from newly placed concrete.
If the temperature drops too close to freezing,
hydration slows to nearly a standstill.
Under these conditions, concrete ceases to
gain strength and other desirable properties.
In general, the temperature of new concrete
should not be allowed to fall below 10 ⁰C during
the curing period.
Concrete is strong in compression, but weak in
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.
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.
All matter is subject to change either chemically, physically 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 and different molecules form. The characteristic
properties are altered.
Nuclear transformations affect the nucleus of the atom where
it splits to form new elements. The particles are rearranged.
In these reactions, the chemical bonds between
reactants are broken and new bonds formed.
New products form and have new characteristic
Signs that a chemical change has occurred:
Gas bubbles form
Heat or light is given off
Change in colour
New substance is created
Change is difficult to reverse
Antoine Lavoisier (1743-1794) observed 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
The nature of the atoms involved in the reaction are not
altered but the bonds between the atoms are changed.
We start by counting the number of atoms of each
element based on the formula.
The reactant side must equal the product side in total #
of individual atoms.
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. This number affects every individual
The small # attached to the atoms is called the subscript
# and it does not change.
E.g. Mg + O 2 Mg0
Mg - 1 Mg - 1
O - 2 O - 1
2 Mg + O 2 2 Mg0
Chemical reactions are classified as:
1) Endothermic – absorbing energy; e.g. a cake
baking absorbs heat from the oven.
2) Exothermic - releasing energy; e.g. a fire burns
and the heat created is enough to continue the
Exothermic reactions release energy which is then
absorbed by the environment often increasing
temperatures while endothermic reactions absorb
energy from the environment causing temperatures to
The amount of energy needed to break or form
chemical bonds varies based upon its type.
There are 5 basic ways in which chemical changes occur:
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)
This occurs when two solutions are combined and an
insoluble substance forms which is called a precipitate.
4. Acid Base Neutralization occurs when an acid and a base
react to produce salt and water. (Acid +Base Salt + Water)
Many substances oxidize when they react with the oxygen in
the air or a substance with similar properties to oxygen.
Combustion is a form of oxidation that releases a large
amount of energy.
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;
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
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.
Is a chemical reaction
Is an endothermic reaction
Plants (producers) use the sun’s energy to
make glucose and oxygen from carbon dioxide
It releases oxygen and is needed for
maintaining oxygen levels in the air.
Glucose is a source of energy.
Is a chemical reaction where glucose and oxygen
generate energy which also produces carbon dioxide
Is a type of slow combustion
Takes place in cells of living things.
Energy released disperses in the tissues in the form of
heat; human body temperature is ~37⁰C
The energy allows cells to carry out tasks essential in
Work on pages 1&2, 3 & 4 of the handout.
Concrete Temperature Lab
Concrete Boat Float Lab
Concrete Beam Lab
Page 132, Q 1-7