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

COMPOSING CONCRETE Presented by: George Evans PPC Cement Your Organisation Logo here

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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 others  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

GOOD CONCRETE  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.

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 own.

CEMENTITIOUS MATERIALS  Cement Type and Source • Fly Ash generally improves the workability of 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

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

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