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Eco-mechanical performances of concrete made with recycled aggregates
Alessandro P. Fantilli
Bernardino Chiaia
FUTURE CONCRETE 2014December 2, 2014, Grand Hyatt, Doha
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2Eco-mechanical performances of concrete made with recycled aggregates
Outline Motivation
Is there an alternative to current certification? Current strategies to reduce the impact of concrete Application to 12 concrete mixtures
Sustainability assessment Traditional approach and refinements Introduction of the non-dimensional chart
Selection of the best concrete Application to tunnel linings Conclusions
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Certification of sustainability
Some companies (third-party) certify buildings as sustainable.
Inspection and document production, as well as review and verification, take up a lot of time and work energy.
The procedure can be very expensive. Designers do not analyze their own green
building methods, in order to fulfill environmental benchmarks.
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4Eco-mechanical performances of concrete made with recycled aggregates
Reducing the impact Reducing the mass of clinker (Habert & Roussel,
2009) Material substitution strategy: cement is substituted
by mineral additives (e.g. fly ashes) Material performance strategy: consists of increasing
the strength and ductility of concrete
Reducing CO2/kg of concrete by usingsustainability reporting instruments: Green Labels based on Life Cycle Assessment (LCA):
which compute the impact of a product, by analysingall the phases of the product life, from raw materialacquisition to the end-of-life (e.g. Recycled concreteaggregate - RCA).
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12 concrete mixtures
Which of them is the most sustainable?The best mechanical performances with
the lowest environmental impact
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Mechanical performances Generally referred to compressive strength
Concrete 6A shows the highest fc
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Environmental impact Is traditionally based on the carbon footprint
= quantity of CO2 /1m3 of concrete
2cf
(Habert & Roussel 2009)
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The impact of a column Column of a frame (H=2.7 m) subjected to P=100kN
P
P
H
c
PV Hf
Volume of concrete =
Reference
Lower environmental impact
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9Eco-mechanical performances of concrete made with recycled aggregates
Refinement In a more comprehensive evaluation of the
environmental impact, also embodied energyand water consumption should be taken intoaccount.
A new Ecological Index, EI, can be introduced:
= amount (in kg) of carbon dioxide (CO2) = embodied energy (in GJ) = volume of water (m3)
EI is referred to 1 m3 of concrete
EI
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10Eco-mechanical performances of concrete made with recycled aggregates
The new impact of a column Column of a frame (H=2.7 m) subjected to P=100kN
P
P
H
c
PV Hf
Volume of concrete =
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Further refinement
In some cases, verybrittle explosive spalling,instead of a localizeddamage (quasi-brittle),can be observed in thepost-peak responseunder compression.
It depends on the heightH of the columns
6A 3A, 3B, 4A, 4B
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Further refinement
It is possible to define a critical value for theheight, Hcr, depending on the post-peak response: If H<Hcr localized damage If H>Hcr explosive spalling
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13Eco-mechanical performances of concrete made with recycled aggregates
The values of Hcr
Hcr is computed by using the fracture toughnessof the post-peak response of uniaxial compressiontest.
Only 3A and 3B can be accepted.
Hc =2700 mm
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14Eco-mechanical performances of concrete made with recycled aggregates
Mechanical index A new Mechanical Index, MI, can be defined:
mpm= mechanical parameter of concrete material = fc mps= mechanical parameter of concrete structure = Hcr
m sMI mp mp
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The non-dimensional chart If the lower bound value MIinf and the upper
bound value EIsup are required
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The non-dimensional chartLow mechanical performances; high ecological performances
Low mechanical performances; low ecological performances
high mechanical performances; high ecological performances
high mechanical performances; low ecological performances
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Selection of the concrete If EIsup is that of concrete 1A If Miinf = 25 MPa × 2700 mm = 67500 N/mm
Only 3A and 3B can be accepted:- Steel fibers- Replacement of cement with fly ash- 3B contains RCA- Environmental impact reduced of
about 25%
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In the case of tunnel Thin tubes subjected to external pressure p Longitudinal cross-section subjected to
circumferential compression
A critical value of the radius Rcr is defined
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Application to Torino metro
R=3.5 m Only 3B (the best concrete for columns)
can be accepted
R =3500 mm
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20Eco-mechanical performances of concrete made with recycled aggregates
Conclusions Environmental impact (EI) and mechanical
performances (MI) of concrete cannot beassessed separately.
Carbon footprint, embodied energy and waterconsumption define the ecological index EI.
The product of fc and Hcr is MI. In order to have a practical design tool, a non
dimensional diagram has also been introduced. To tailor the best concrete, fly ash, steel fibers
and RCA need to be used, both for columns andlinings.
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Other recycled materials Lightweight aggregates from end-of-life vehicles
Rubber from tires Fluff
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Consultancy services
A innovative company was started up from Politecnico di Torino: ARCOS ENGINEERING
The company provides unconventional consultancy in the field of geotechnics, structures, building materials (durability, eco-compatibility, etc)
Clients in the Gulf Area: Etihad Rail, ENI Spa, SAIPEM
