Comparative Life Cycle Assessment (LCA) of 'green' concretes versus conventional concrete is known to depend on how service life is treated: Marinković, Carević and Dragaš (2021) showed for carbonation-exposed reinforced-concrete members that two equally defensible functional-equivalence conventions — same member volume with impacts normalized by modeled service life (Approach A) versus volume/cover-depth adjusted so all alternatives reach the same service life (Approach B) — produce opposite environmental rankings, with only 7–20% more volume flipping normalized impacts by a factor of 6–7. The objective is to make whole-life environmental (and economic) comparison of concrete alternatives reliable when durability differs. Concretely: establish and validate a service-life-integrated whole-life LCA framework that (i) treats durability endogenously through performance-based probabilistic service-life models for at least carbonation and chloride-induced corrosion, (ii) accounts for full life-cycle CO2 uptake including end-of-life re-carbonation of demolition debris, (iii) propagates parameter and model uncertainty from mix-to-durability relations, service-life model parameters, and life-cycle inventory choices, and (iv) determines whether green-versus-conventional concrete rankings are robust or convention-dependent across deterioration mechanisms, exposure regimes and climates, member types, and whole structural systems. Probabilistic whole-life LCA with life-cycle costing, carbonation uptake and climate scenarios (Malami et al. 2024), performance-based chloride-exposed concrete selection with cover-depth optimization (Moro, Keßler and Torrent 2025), and dynamic national-scale CO2-uptake stock-flow models (Sawa et al. 2025) address components of this agenda, but durability-integrated, uncertainty-quantified LCA with standardized functional units remains an open methodology, and the cross-mechanism validation of the ranking inversions has not been delivered.

Background

Concrete is the world's most used construction material, and the production of its binder, Portland cement clinker, accounts for roughly 7% of global anthropogenic CO2 emissions (Javadpour et al. 2026). Life Cycle Assessment (LCA) is the standard framework for quantifying the environmental impacts of a product system over its life cycle, from raw-material production through use to end of life; in comparative LCA the compared alternatives must be functionally equivalent, which is enforced through the functional unit (FU) — the quantified performance of the product system to which the LCA results refer (for example, 'a reinforced-concrete slab member providing a given characteristic strength and a 50-year service life in a specified exposure').

'Green' concretes reduce clinker content by replacing Portland cement with supplementary cementitious materials (SCMs, pozzolanic or hydraulic industrial by-products such as fly ash from coal power plants) or by reusing construction-and-demolition waste as recycled aggregate (recycled aggregate concrete, RAC). A prominent example is high-volume fly ash concrete (HVFAC), in which fly ash replaces a large share of the cement. These substitutions cut production-stage emissions but typically also reduce resistance to deterioration, so a green-concrete structure may need more material (deeper cover, larger sections) to last as long as a conventional one.

Durability of reinforced concrete is dominated by corrosion of the steel reinforcement, which begins once the steel's protective passive film is destroyed (depassivation). The two dominant depassivation mechanisms are carbonation — penetration of atmospheric CO2, which reacts with cement hydration products, lowers the pore-solution pH, and, as a side effect, reabsorbs part of the CO2 earlier released by cement manufacture — and chloride-induced corrosion, in which chloride ions from marine exposure or de-icing salts penetrate the concrete to the reinforcement. Design codes therefore treat service life (the period during which the structure performs its intended function; ISO standards call it design working life) as a design quantity. The fib Model Code 2010, the international model code for structural concrete, provides full-probabilistic service-life models; for carbonation the depth of the carbonated front grows in time tt as xc(t)=2 kekc (ktRACC−1+εt) Cs t W(t)x_c(t)=\sqrt{2\,k_e k_c\,(k_t R^{-1}_{ACC}+\varepsilon_t)\,C_s\,t\,W(t)}, where the inverse effective carbonation resistance RACC−1R^{-1}_{ACC} of a mix is derived from accelerated carbonation tests, CsC_s is the environmental CO2 concentration, and the remaining factors correct for curing and environment. Depassivation is treated as a limit state g=c−xc(t)g=c-x_c(t), with cc the concrete cover depth, evaluated with structural-reliability methods such as the First-Order Reliability Method (FORM), which computes the probability that the limit state is violated within the design life.

Marinković, Carević and Dragaš (2021) coupled exactly this kind of probabilistic carbonation service-life model with production-stage LCA for 94 literature-derived mixtures of conventional concrete (CC) and HVFAC, with European-average life cycle inventory (LCI) data for most processes and a site-specific Serbian inventory for fly ash (LCI denotes the catalogued inputs and emissions of each unit process). Their LCA used midpoint indicators such as global warming potential (GWP, in kg CO2-equivalent). Comparing reinforced-concrete slabs and beams, they tested two ways of enforcing functional equivalence: Approach A keeps the same member volume for both materials (so the green concrete, with its shorter modeled service life under carbonation, must be re-impacted per year of service life), while Approach B adjusts the FU volume — mainly by increasing cover depth and section height, at a 7–20% volume penalty — so that both alternatives attain the same target service life. The two approaches gave opposite rankings: under Approach B all normalized impact indicators of HVFAC members were 6–7 times lower than under Approach A, implying that the choice of functional-equivalence convention, not the material alone, can decide which concrete is 'greener'. The paper closed with four unresolved research directions, which share one objective — making such whole-life comparisons reliable and decision-ready — and jointly require: predictive full life-cycle CO2-uptake models for green concretes; frameworks coupling structural-design adaptation with environmental and cost assessment in multicriteria optimization; quantified propagation of parameter and model uncertainty; and validation of the comparative Approach A versus Approach B modeling across other deterioration mechanisms (notably chloride-induced corrosion), exposures, climates, member types, and whole structural systems.

Problem Statement

Establish and validate a service-life-integrated whole-life LCA methodology for concrete structures that makes comparative environmental and economic assertions between conventional and green concretes reliable when the alternatives differ in durability — and determine the generality and limits of the ranking inversions demonstrated by Marinković, Carević and Dragaš (2021). Four linked results serve this single objective: (1) predictive CO2-uptake (carbonation reabsorption) models for green concretes such as high-volume fly ash concrete and recycled-aggregate concrete that consistently cover the service life, the end-of-life stage, and the size and processing of demolition debris, so that carbonation reabsorption is accounted for across the full life cycle; (2) a life-cycle integrated assessment framework that couples structural-design adaptation (section geometry, reinforcement, cover depth) with environmental impacts and economic costs in multicriteria analysis, quantifying the trade-off between modest increases in material quantity and whole-life environmental and monetary outcomes; (3) quantification and propagation of parameter and model uncertainty — the empirical relation between mixture proportions and compressive strength (cement-content variability for a given mean strength fcmf_{cm}), the probabilistic service-life model parameters and their distributions (fib Model Code parameters), and life-cycle inventory choices such as allocation rules for by-products like fly ash, transport assumptions, and regional variability — to bound decision-relevant uncertainty; and (4) extension and validation of the comparative modeling under the two functional-equivalence conventions (same-volume FU normalized by service life versus FU volume adjusted to attain equal service life) across other deterioration mechanisms, notably chloride-induced corrosion, other exposure regimes and climates, and a wider set of structural member types and full structural systems. All four linked results are jointly required for completion — none of them alone resolves the objective — and they must be established and validated for both carbonation- and chloride-induced corrosion. Result (4) concerns both carbonation- and chloride-induced corrosion, several exposure/climate regimes, several member types, and whole structural systems. For each combination the framework must determine, under propagated parameter and model uncertainty, whether the ranking is robust or convention-dependent. The question to be answered is: under which mechanisms, exposures, climates, and structural systems do the two conventions agree or conflict — that is, are green-versus-conventional concrete environmental rankings robust or convention-dependent — and what unified, uncertainty-quantified framework makes such rankings decision-ready?

References

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