Page 7 - Open-Access-February-2020

TECHNICAL PAPER

3.1.2 Electricity Grid Mix Process of materials and energy, a Maintenance Factor was built into
the model. The Maintenance Factor is input as a percentage of
The electricity grid mix is based on the Canadian electricity the initial material and energy inputs (ex. a value of 20% means
grid mix process from the GaBi Extension database XVII: Full that over the life of the concrete, 20% more of the materials and
US, which includes biogas, biomass, hard coal, heavy fuel oil, energy required for initial placement must be input to maintain
hydropower, natural gas, nuclear, photovoltaics, wind and the concrete). A value of 20% was selected and is applied to all
waste-to-energy. To increase the geographical and temporal of the mix designs included in this study.
correlation to the scope of this work, the ratio of the individual
types of generation was modified to reflect the supply mix of 3.1.7 End-of-Life Process
Ontario in 2014 (shown in Figure 2).
‘End of life’ is the final stage in a cradle-to-grave LCA. The
3.1.3 Water Treatment Process potential disposal options for concrete products include
recycling, landfill, and reuse. This study considers that concrete
Racoviceanu et al. [16] used the economic input-output life- is typically crushed in place for reuse as fill. This activity, as with
cycle assessment model and the GHGenius model to quantify all on-site activities, is assumed to be powered by diesel. The
the energy use and greenhouse gas emissions for the City of energy required to crush one tonne of concrete is estimated 34
Toronto municipal water treatment system. Several processes MJ [18] . The emissions were estimated using the emission factors
were considered including chemical manufacturing, chemical according to Athena .
[4]
transportation, and water treatment facility operation.
3.2 Processes Included in the Life Cycles of
3.1.4 Aggregate Processes
Alternative Concrete Constituents
Four aggregate processes are integrated in the LCA model:
i) fine aggregate production, ii) coarse aggregate production, 3.2.1 Slag Processing and Transportation
iii) fine aggregate transportation, and iv) coarse aggregate Processes
transportation. To build each of these processes, data for energy SL, a by-product of the steel industry, requires processing
requirements, raw material requirements, atmospheric emissions before it can be incorporated into concrete. Energy and
and liquid effluents were collected for the extraction, processing, emissions for this processing are quantified by Marceau, Nisbet
[4]
and transportation of the fine and coarse aggregates . Based & VanGeem [19] . Upstream energy, raw materials, and emissions
[4]
on a previous LCI , road transportation by diesel-powered truck are not included in this process as SL is generated regardless of
requires 1.18 MJ/t-km. Emissions factors for road transportation whether it is incorporated into concrete, disposed of in a landfill,
by truck are taken from Athena . For this work, where all the or any other usage. Using SL in concrete is environmentally
[4]
transportation processes use the same mode (truck), the route beneficial, and so excluding upstream processes is conservative.
with the longest distance indicates the worst-case transportation This is an assumption commonly used in concrete LCAs [20, 21] .
scenario (200 km for fine and coarse aggregates). The corresponding emissions factors are taken from Athena
[4]
and the worst-case transportation scenario is from Hamilton
3.1.5 Concrete Production Process (Ontario, Canada) via Picton (Ontario, Canada) to Toronto
The concrete production process represents the stage in the (Ontario, Canada) (498 km).
life cycle where the various concrete constituents, including
water, cement, fine aggregate and coarse aggregate, are 3.2.2 Fly Ash Transportation Process
combined in order to create concrete. The mix proportions are FA is a by-product of coal burning. It is a fine powder that
entered into the parameterized model according to the mix does not require further processing before it is incorporated
designs described in Table 1. In addition to the raw material into concrete as cement replacement. As with SL, upstream
requirements, the batching and mixing processes require energy, raw materials, and emissions are not included in this
energy; Prusinski et al. [17] calculated a value of 247 MJ for the process, which is a common and conservative assumption [18, 19] .
production of a cubic metre of concrete. FA transportation is modeled based on FA sources and modes
of transportation that are typical. The corresponding emissions
3.1.6 Concrete Maintenance Process factors are shown in Athena and the worst-case transportation
[4]
Concrete maintenance activities are highly dependent on the scenario is from Pleasant Prairie (Wisconsin, USA) to Toronto
specific concrete application and environmental conditions that (Ontario, Canada) (937 km).
the concrete is exposed to over its life. In terms of life cycle
assessment, however, they can be represented as additional 3.2.3 Silica Fume Transportation Process
quantities of materials and energy that are required over the SF is a by-product of silicon production. Physically, it is a very
entire life of the concrete. In order to estimate these impacts fine powder that does not require further processing before it is

12 The IndIan ConCreTe Journal | FeBruarY 2020