COMPOSING CONCRETE Presented by: George Evans PPC Cement Your - - PowerPoint PPT Presentation

COMPOSING CONCRETE

Presented by:

George Evans

PPC Cement

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THE PERFECT CONCRETE?

• There’s no such a thing…
• Many well-designed concrete mixes for a

given application, but some are better than

• thers
• Flows easily?
• Easy to finish?
• Meets the strength requirements?
• Perhaps, but time will tell how durable, and

therefore how good the concrete really is…

THE PERFECT CONCRETE?

• It is the best possible compromise between:
• plastic properties
• structural properties
• durability
• What we want is concrete that is easy to

place, strong and durable for the life of the structure,

• will look good when you're finished

TERMINOLOGY

• Workability:
• Describes the ease of transporting, placing

and compacting the concrete without segregation

• It is not measurable and has no units
• In simple terms it is the user friendliness of

the concrete

• Plasticity:
• The mouldability or deformation of

concrete

TERMINOLOGY

• Mobility:
• The fluidity of a concrete
• Consistence:
• The viscosity, cohesion, thickness, etc. of

a concrete

• Rheology:
• The flow, flexibility, manoeuvrability,

transportability of concrete

REQUIRED WORKABILITY

• Workability is often a function of the intended

placing and compaction methods:

• Placing techniques
• Compaction techniques
• Self compacting
• Internal vibration
• External vibration
• Very heavy vibration and pressure

• Concrete is used in almost every structure

built

• Amazing number of illnesses
• Is making good, consistent concrete a

miracle?

• Most variables can be controlled
• Good concrete is the result of good planning

involving everyone in the chain.

GOOD CONCRETE

MAKING GOOD CONCRETE

THE CONCRETE PROCESS

• Good concrete is the result of good

equipment, processes and people

• taking good decisions at every step to

create the concrete that arrives on your site.

• Your thoughts may be focused on what

comes down the chute.

• What went on before the concrete got to the

site?

AGGREGATES

• Good concrete depends on good aggregate.
• Coarse aggregate can be as much as 75% of

the volume in a mix.

• The best aggregate is made from hard,

durable parent rock with low to moderate absorption.

• The worst aggregate to make concrete is

friable, weak matrix and high absorption.

AGGREGATES

• Crushing and screening equipment
• Aggregate stockpiles
• Drainage
• Contamination
• Inter-mixing

AGGREGATES

• Coarse aggregates:
• Gap-graded or continuously graded
• Particle shape
• Maximise stone content; This helps to

produce high-strength concrete with less shrinkage, better workability, and superior durability. Coarse aggregate is stable, mostly, the paste shrinks, so if there’s less paste, there’s less shrinkage.

CEMENTITIOUS MATERIALS

• In the past, the best concrete was made with

all-portland cement, BFA&S!

• Fly ash and Slag being a way to make

cheaper concrete.

• Fact: SCM’s, such as FA, slag, or silica

fume, in combination with portland cement produce concrete that may be superior to what portland cement can achieve on its

• wn.

CEMENTITIOUS MATERIALS

• Cement Type and Source
• Fly Ash generally improves the workability
• f the mix. Has the performance changed?
• Slag improves the workability (but not

necessarily the slump) of the concrete.

• Silica fume reduces the workability of

concrete and increases cohesion.

• Cement Content?

CEMENTITIOUS MATERIALS

• Sustainable concrete mixes (lower carbon

footprint) - 30% or higher replacement of portland cement.

• Caution if you follow that kind of reasoning.
• Rather design your concrete to optimise the

advantages of each ingredient.

• The goal should be a durable concrete with

fresh properties suited to the installation methods.

ADMIXTURES

• In the past - negative attitudes about using

admixtures.

• Snake oils?
• a way to reduce cost by removing the

cheapest component?

• Water was the magic admixture:
• add water to increase slump, extend open

time, make the concrete easy to strike off and finish.

ADMIXTURES

• But now, admixtures are essential to make

good concrete.

• The use of PCE superplasticizers, viscosity

modifying admixtures (VMA), and set- retarding/accelerating admixtures have become synonymous with concrete production.

• Think of admixtures as smart concrete

management tools.

• Perhaps steriods for concrete?

DESIGNER CONCRETE?

• CVC:
• Pavements, Pumping, Sliding, HES

Precast, Matched casting, vertical/horizontal casting

• SCC:
• Applications not suited to CVC, Special

finishes, Appearance, Aesthetics, Repairs

• RCC:
• High volumes, Mass, lower HOH, lower

shrinkage

COMPOSITION ANALOGY

COMPOSITION

• Coarse aggregates = Skeleton
• Cement = Muscles
• Fine aggregates = Organs
• Water = Blood
• Admixtures = Performance enhancers
• Curing = Exercise
• Cube specimens = Babies

MAKING GOOD CONCRETE

• Good concrete is made of blends of quality

ingredients.

• Good control of water additions and proper

blending of the materials.

• Good equipment

Together, the above = consistent quality.

MAKING GOOD CONCRETE

• Quality control
• Testing at the batching plant
• Testing at the site
• Planning
• Discharging
• Placing

• Checklist to ensure failure:
• Fail to plan
• Order or supply the wrong concrete
• Use dihydrogen oxide
• Avoid curing at all cost

BAD CONCRETE

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