Civil Engineering Materials
(DCC1023)
Prepared By:
Norzainariah Binti Abu Hassan
Civil Engineering Department, Politeknik Melaka
Topic 1 : Concrete
Materials and Mixture
• Generally, concrete mix can be divided into 2 states;
• Plastic state (
fresh / liquid form
)• Concrete can flow/volatile,
workable & should be free from segregation (separation of
coarse aggregate) and bleeding (separation of cement).
• Hardened state
• Concrete should be hard,
strong, durable, impermeable, minimum dimensional changes and most important it has
achieved the required compressive strength.
Concrete are grade based on its compressive strength (N/mm
2) at 28 days described in BS8110 as shown in the table below:
Grade Characteristics Strength(N/mm2)
Lowest grade suitable for specific purpose
7 10
7 10
Mass & lean concrete
15 15 Reinforced concrete using light weight
aggregates
20 25
20 25
Reinforced concrete using compact aggregates
30 30 Pre-stress & post tension concrete
40 50
40
50 Pre-stress & post tension concrete
CONCRETE MIXING RATIO
Types of concrete mix ratio:
1. High Strength Concrete Mix Ratio
This concrete mix ratio will give you high strength concrete plus water tight properties making it great for ponds, and structural uses such as concrete panels and
building slabs.Cement = 1 part Sand = 2 parts
Stone or gravel = 3 parts
There are many different types of concrete and uses but the most common
are high strength and water tight, general use and foundations.
2. General Use Concrete Mix Ratio
This concrete mix ratio will give you concrete that is great for
paths , floors , general land scraping and driveways.
Cement = 1 part Sand = 2.5 parts
Stone or gravel = 3 parts
3. Foundations and large volume Concrete Mix Ratio
Foundations are the main use for this concrete mix ratio where a large
amount of concrete is used to fill up strip footings trenches.
This concrete mix is used in house foundations, to make it solid and
stable, when filling from bed rock to ground level.
Cement = 1 part.
Sand = 3 parts.
Stone or gravel = 5 parts.
4. Mortar Mix Ratio
• Mortar is a mix of sand, cement, lime and water.
• When mixed properly it forms a bond between
masonry surfaces such as
bricks and concrete blocks of all different sizes.
Cement = 1 part.
Sand = 6 parts.
Lime = 1 part.
Concrete Mixture
Prescribed mix
Designed
Mix Nominal Mix
• Concrete cubes are not required to be tested.
• Prescribed concrete is a mix for which the purchaser prescribes the exact composition and
constituents of the concrete and is responsible for ensuring that these proportions produce a
concrete with the required performance.
• Effectively the purchaser selects the materials and mix
proportions to satisfy the
required strength and durability needs.
The purchaser must state:
1. The type of cement
2. Types of aggregates and their maximum size
3. Mix proportions by weight 4. Degree of workability
(slump/water-cement ratio)
• In these mixes the performance of the concrete is specified by the designer but the mix proportions are
determined by the producer of concrete.
• Concrete mixes that produce concrete with the desired strength, economics
& fulfilled statistical testing requirements.
However, the designed mix does not serve as a guide since this does not guarantee the correct mix proportions for the prescribed performance.
For the concrete with undemanding
performance nominal or standard mixes (prescribed in the codes by quantities of dry ingredients per cubic meter and by slump) may be used only for very small jobs, when the 28-day strength of
concrete does not exceed 30 N/mm2.
• These mixes of fixed cement- aggregate ratio which ensures adequate strength are termed nominal mixes.
• These offer simplicity and under normal circumstances, have a
margin of strength above that specified.
• However, due to the variability of mix ingredients, the nominal
concrete for a given workability
varies widely in strength.
INTRODUCTION of ADMIXTURE
Specific effects generally vary with:
• Type of cement
• Mix composition
• Climatic condition (temperature)
• Its dosage
• Job requirements Substances introduce
into batch of concrete immediately before or during mixing in order to alter or improve the properties of the fresh or hardened concrete or both.
• Knowledge of main active ingredients
• On available
performance data
• On trial mix
Suitability should be evaluated
based on:
PURPOSES OF ADMIXTURES
To improve workability of fresh concrete
To improve durability by entrainment of air
To reduce the water required
To accelerate setting and
hardening
To aid curing
To impart water repellent or water proofing property
To reduce bleeding
Liberation/release of heat
Formation of pores
Development of gel structure
Including improved quality
Acceleration or retardation of
setting time
Enhanced frost and sulphate
Control of
strength Enhanced
finishability.
TYPES OF ADMIXTURES
Catalyzing substances
Retarding substances
Water decreasing substances
Plasticizing substances
Air trapping
additive
Easy mixing additive
AIR-ENTRAINING AGENTS
Improve the durability of concrete, resistance to the effects of frost and de-icing
salts.
A process whereby many small air bubbles are incorporated into concrete and become part
of the matrix that binds the aggregate together in the
hardened concrete.
Improve the workability and cohesiveness of fresh
concrete, reduce bleeding and segregation, reduces
freezing/thawing problems.
Useful when aggregates with poor grading are used, concrete will be exposed to
freeze/thaw conditions, deucing salt applications or
sulphate attack.
Adverse effect – reduction in concrete strength (each 1% of
air may result in 5% decrease in compressive strength).
ACCELERATORS
Reduce setting time and suitable for repair work involving water leakage.
To increase the rate of both setting and early strength development.
Allowing a cold-weather pour, reduce the time required for proper curing and protection, early removal of forms and early surface finishing.
The most common admixture for this purpose is Calcium Chloride (CaCl2) and NaCl.
Higher dosage of CaCl2 increase drying shrinkage, reduced resistance to
sulfate attack and increased risk of corrosion of steel reinforcement.
A most effective and economical material for plain concrete under
winter condition, for emergency repair work or early removal of formwork required.
RETARDERS
Function :
to delay the setting time of cement
paste in concrete.
Slow the hydration of concrete
Have a long term
strength.
They are used mainly in hot countrywhere
high temperature
(cause an increased rate of
hardening and early stiffening )
can reduce the normal setting and hardening
timesand usually apply in
highway industry, especially in the
construction of bridge decks.
The effect is depend on
dosage, cement type
and mix proportions
used.
Application in situation where large
concrete pour, sliding formwork or
ready mix concrete
used.
Retarders keep concrete
workable during placement and delay the
initial set of concrete.
Most retarders also
function as water reducers and
may entrain some air in
concrete.
WATER REDUCER
To achieve a higher strength by decreasing the water/cement ratio at the same as an admixture.
To achieve the same workability by decreasing the cement content and to reduce the heat of hydration in mass concrete.
To increase the workability so as to ease placing in inaccessible locations and also tend to retard the setting time of the concrete.
Used to reduce the amount of water (reduces water demand 7-10%) necessary to produce a concrete of given consistency.
Water reducers are mostly used for hot weather concrete placing and to aid pumping.
The effectiveness at given dosage is dependent on cement type,
aggregate type and grading, mix proportion and ambient temperature.
Freeze-thaw resistance and other durability aspects can also be improved.
SUPERPLASTICISER
Commonly used to produce flowing concrete without having
to change the original mix composition and without causing a strength reduction.
Suitable for heavily reinforced and inaccessible section or
where rapid placement of concrete is required.
Flowing characteristics of a mix are retained only for a short period of time (about 30 min) after addition of superplasticiser.
To achieve high strength at a given workability, the use of
superplasticiser can result a reduction in water content up to
25%.
OTHER
ADMIXTURES
2. Water-repelling Agents• These are the least-effective of all admixtures.
• Based on metallic soaps or vegetable or mineral oils.
• Gives a slight temporary reduction in concrete permeability.
1. Bonding Admixtures
• These are organic polymer
emulsions used to enhance the bonding properties of concrete.
• Use for patching and remedial work.
• To increase the abrasion
resistance of concrete and its tensile strength but some
reduction in compressive strength also occurs.
3. Pigments
• In powder form
• Used in concrete for architectural purposes.
• Best effect when inter ground with the cement clinker rather than added during mixing.
• Formulated from both natural and synthetic material.
4. Pore fillers
• In active finely ground materials (bentonite, kaolin or rock flow).
• To improve workability, stability and impermeability of concrete.
• Used in poorly graded aggregate.
• Result in some reduction in concrete strength.
5. Pozzolanas
• Most commonly used are pumicite and pulverized-fuel ash (PFA).
• Can improve the durability.
• Often retard the rate of setting and
hardening & rate of heat evolution
• Useful in mass concrete work.
• PFA can result in a saving in the PC content.
• Economical (PFA cheaper than cement).
