Fly ashes from cocombustion as a filler material in concrete production

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Fly ashes from co-combustion as a filler material
in concrete production
By Hillevi Sundblom, Civil engineer, Vattenfall
Utveckling AB
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The goals

• Investigate the potential of using fly ashes from
  co-combustion as a filler material in crushed
  aggregate concrete

• Identify and test suitable fly ashes from
  different fuel mixes and boiler types

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Questions

• Why use fly ashes from co-combustion as a filler
  material in concrete production?

• Increased demand of filler material when changing
  from natural aggregate to crushed aggregate

• A reduction of CO2 discharge

• Reduce of cost
• Decreases the amount of cement in the concrete
• A cheap raw material

• What type of concrete ?

• According to the standard is the typical Swedish
  fly ash not a fly ash.
• C20/25-C25/30, with no demands of water-cement
  ratio

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Background

• Increased use of crushed aggregate
• SFF (Svenska Fabriksbetongförening) has decided
  to limit the production of concrete with natural
  aggregate

• The quality of the Swedish fly ashes
• Complex fuel mixes (dominating bio fuels)
• The ash producers has an interested of creating a
  useful product to the concrete production

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Ash investigation

• Requirements

• Chemical composition
• The total amount chloride in the concrete lt 0,1
  wt (0,2wt)
• LOI lt 9 (1000 C)
• Soundness
• Compressive strength
• Consistency of the fresh concrete
• The fresh concrete must be consistent the first
  hour after mixture

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Ash investigation

• Furnace type and fuel mix of the ashes
  investigated

• Sludge and bio fired fluidised bed boilers, paper
  mills
• Bio and peat fired fluidised bed boilers
• Pulverized peat/coal firing furnaces
• Bio and peat grate-fired boiler

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Laboratory and field investigation

• Chemical composition, Ash analyses

• Soundness, Le Chatelier EN 196-3

• Morphological investigation, SEM

• Scanning test at Sydsten
• Slump cone
• Compressive strength

• Rheological experiments

• Full-scale demonstration
• Skanskas levelling concreting. A preparation for
  a bridge construction at Timjanvägen in Lund

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Results

• Chemical composition
• Some of the ashes in the investigation did not
  fulfil the requirement of chloride content.
  (Higher than 0,6 wt)
• Generally did the fly ash from grate boilers have
  a high level of LOI

• Soundness
• All the ashes fulfilled the soundness requirement
  with an large marginal

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Results

• Morphological investigation

• Ash from bio fired CFB-boiler

• Ash from a pulverized peatfired furnace

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Results

• Scanning test at Sydsten

• Concrete type Crushed aggregate, C25/30-16-HF,
  40-60 kg ash/m3
• Slump cone, 150-200 mm
• Compressive strength, preferably 33-34 MPa

• Loss of consistency
• Few ashes demonstrated, depending on the amount
  of ash introduced, a loss of consistency the
  first hour after mixture

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Results

• Rheological investigation

• Concrete type Crushed aggregate, C25/30-16-HF,
  40-60 kg ash/m3

• Parameters investigated
• Viscosity and yield point

• Loss of consistency
• Few ashes demonstrated, depending on the amount
  of ash introduced, loss of consistency the first
  hour after mixture

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Results

• Full-scale demonstration
• Concreting in Lund, Sweden with ashes from a
  pulverised peat fired furnace in a C25/30-16-HF.

• Did not demonstrate loss of consistency

• Good workability

• Sufficient compressive strength

Levelling plane for a bridge construction
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Discussion

• Fly ashes from co-combustion can be used as a
  filler material in crushed aggregate concrete if
  they fulfil specified requirements.

• The loss of consistency probably depends on
  following factors.
• The morphology of the ash grains
• The amount of unburnt carbon
• The early aluminate reactions depending on the
  amount of Al2O3, CaO and alkali sulphates

• Full scale test did not show any loss of
  consistency.
• The scale effect
• Concrete were transported in agitating equipped
  truck.

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Conclusion

• Fly ashes from co-combustion have big potential
  to be used in crushed aggregate concrete
  production
• Full-scale demonstration
• The experience of Sydsten (35-40)

• It is necessary to define requirements concerning
  the different ash parameters influences on the
  properties of fresh concrete

• Future research needs
• Investigate important parameters that causes the
  early loss of consistency of the fresh concrete.

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Thank you for the attention