2.13 special concretes low cost light weight heavy weight underwater ultra high strength ultra...

2.13 SPECIAL CONCRETES• Low Cost• Light Weight• Heavy Weight• Underwater• Ultra High Strength• Ultra Durable• Architectural• Low Noise• Reduced environmental impact• Fast setting• Placing without formwork• Bulk fill• Self compacting

Low Cost

• Cement replacement with PFA - also helps durability and workability.

• Cement replacement with GGBS - helps durability but may increase bleeding.

• Water (and cement) reduction with a water reducer - helps with durability.

• Cementitious content reduction with CSF - do not do it.

Light Weight• Light weight aggregate - some

strength reduction, good thermal properties.

• Foamed concrete - very low strength.

• No-fines concrete

• Fig.2.13.1 Shows routes to producing light weight concrete and fig.2.13.2 shows the achievable densities.

Foamed concrete

Lightweight aggregates

Lightweight concrete and mortar

Heavy weight (for shielding)

• Heavy weight aggregate

• Steel shot - high cost and segregation.

Underwater concrete

• CSF - OK to use it for this - good cohesive mix.

• Non dispersal admixtures.

• Note that any concrete may be placed under water if precautions are used to avoid washout.

Ultra high Strength

• Superplasticisers (high range water reducers)

• CSF

• In-situ de-watering (for slabs)

• Must have strong aggregate

Ultra high performance concrete

Advantages of High Strength Concrete (HSC) • High durability (e.g. abrasion and carbonation

resistance)• High strength to weight ratio, particularly for

lightweight HSC• High early strength allows faster construction and

formwork reuse• Increased elastic modulus and lower creep• Very tall buildings become feasible• Lower column costs for concrete and steel• Smaller columns allow for more floor space• Box girder and solid girder bridge spans may be

increased and designs simplified

Disadvantages of HSC• Increased cost per unit volume• More stringent quality control of materials and construction

needed• CSF mixes may self-desiccate giving failure at day joints.• Workability difficult to define and often declines rapidly with

time after mixing• Timing of concrete delivery and addition of admixtures

becomes critical.• High heat evolution may necessitate use of low heat binders

(e.g. PFA) and cooling measures.• Stiffness (modulus) does not increase in proportion to strength.• More than 28 days may be required to reach specified strength• Structural members may exhibit brittle failure.• Use of HSC not covered by codes

Ultra durable concrete

• Ultra high strength with good curing

• Controlled permeability formwork

• Coated or stainless rebar

• Silanes or siloxanes

• (Glass fibre in surface)

Fragmentation resistance with glass fibre

Concrete with good appearance (Architectural concrete)

• Avoid plain surfaces• Exposed aggregate: Surface retarded,• Bush hammered, • Worked before final set,• Hand placed aggregate• Board finish• Brush finish• Ribbed finish• Imprints etc.• White cement, pigments etc.• Note that a highly textured surface may collect dirt

and moss.

Needs a feature to hide colour change



and moss.

Exposed aggregate finish



and moss.

Board finish

Patterned board finish



and moss.

Brush Finish



and moss.

Profiled (ribbed) finish

Profiles to hide day joints

Deep profiles on wall

Ribbed (profiled) finished spoiled by unevenly applied mould release oil.



and moss.

Imprinted concrete



and moss.

White concrete (being cleaned)

Pigmented Concrete



and moss.

Low noise concrete for roads

• Random grooves

• Exposed aggregate

Concrete with reduced environmental impact

• Cement replacements such as PFA or GGBS save 850kg of CO2 for every tonne of portland cement saved

• No-fines concrete is also known as "pervious" concrete and can reduce or eliminate run-off from roads and prevent flooding and pollution.

• A bright white concrete surface with GGBS will reduce the "heat island" effect of cities in hot climates.

• Magnesia or Alumina Cements to replace calcium silicate

Placing “pervious” concrete

Concrete with reduced environmental impact

• Cement replacements such as PFA or GGBS save 850kg of CO2 for every tonne of portland cement saved

• No-fines concrete is also known as "pervious" concrete and can reduce or eliminate run-off from roads and prevent flooding and pollution.

• A bright white concrete surface with GGBS will reduce the "heat island" effect of cities in hot climates.

• Magnesia or Alumina Cements to replace calcium silicate

Fast Setting Concrete for Precasting

• Superplasticisers to reduce the water content are often as effective as accelerators.

• High temperature curing - but this can cause delayed ettringite formation

• Autoclaved concrete (high temperature and pressure) for rapid production but the hydration products are very different.

Placing without formwork

• Shotcrete

• Often used with fibres.

Bulk Fill

• Foamed concrete

• Controlled Low Strength Material (CLSM) is a flowable fill

• Below about 1MPa it can be re-excavated with a hydraulic excavator

• Can be made without cement

CLSM.Waste gypsum and steel slag (no cement)

Self Compacting Concrete

• Requires viscosity modifier to prevent segregation

• Reduces labour required

• Reduces noise

• Reduces risk of white-finger

• Costs about £30/m3 more

2.13 special concretes low cost light weight heavy weight underwater ultra high strength ultra...

Documents

low strength

light weight concrete

self compacting slide

mortar slide

simplified slide

strength reduction

lightweight concrete

low cost cement replacement