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.
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
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
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
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
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.
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
Ultra high Strength
• Superplasticisers (high range water reducers)
• CSF
• In-situ de-watering (for slabs)
• Must have strong aggregate
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
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
Ultra durable concrete
• Ultra high strength with good curing
• Controlled permeability formwork
• Coated or stainless rebar
• Silanes or siloxanes
• (Glass fibre in surface)
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
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.
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.
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.
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.
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.
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.
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.
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.
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
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
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
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
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
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.
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
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
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
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