Aapo Räsänen

Structural reliability of hollow-core slabs is critical in both new construction and reuse-oriented projects. Load testing is a central verification method, though its purpose differs between these contexts. In new construction, quality control is primarily based on material testing, with load testing serving as a voluntary method to confirm product consistency and the applicability of the resistance model used. In reuse-oriented projects, however, load testing becomes essential because material properties cannot be altered, and quality assurance relies on existing information and test results from a finite population of slabs. This study identifies the statistical uncertainty associated with the number of samples in HCS shear testing, using 188 full-scale test results from the literature and from this research. The results show substantial variation even among slabs with identical design parameters, and no correlation between variability and production year, slab height, concrete compressive strength, or strand cover depth was found. Increasing the number of samples significantly improves the estimated characteristic resistance value, while finite-population effects remain minor except in very small populations. The findings highlight the need to account for statistical considerations when making preliminary decisions about the required number of samples.

Reusing reinforced concrete structures within a Circular Economy offers substantial environmental benefits, but requires reliable assessment of their remaining service life. Conventional approaches to concrete durability, based on prescriptive design parameters for new structures or carbonation depth measurements in existing ones, are insufficient to ensure reuse for an additional 50 or 100 years. This study addresses this gap by introducing a performance-based probabilistic framework for evaluating carbonation‑induced corrosion, tailored to circular construction. The study incorporates parametric analysis and probabilistic modeling of corrosion initiation and propagation phases, and assesses two precast concrete buildings located in Nordic climates. The study also examines how storage period before reuse, changes in exposure class after deconstruction, altered carbonation rates during a second service life, and repair interventions, affect service life. Monte Carlo simulations are used to estimate the total service life under various conditions, with outdoor carbonation rates reflecting typical Nordic exposures. Corrosion propagation is modelled following fib Model Code 2020 and fib Bulletin 112. The results demonstrate that reused concrete elements can achieve service lives comparable to new structures, provided that performance-based assessment and appropriate repair interventions are applied. The proposed framework supports data-driven decisions on service life, repair, and reuse strategies for structural concrete, considering exposure classes and performance. It can be complemented by non-destructive testing and durability indicators. It provides a scientific basis for extending the service life of reused concrete elements and supports design for circularity and resource efficiency, thereby advancing circular construction and the transition toward a sustainable built environment.

This study addresses how many samples are sufficient to reliably estimate the cover depth of reinforcement and the carbonation depth of indoor load-bearing concrete elements. A Monte Carlo simulation with 10,000 iterations for extreme values of real cases was used to evaluate the standard error of the mean for different numbers of samples. To evaluate the cover depth of reinforcement, the simulation results suggest that 150 measurements are statistically sufficient for a certain reinforcement type and for each element type. However, hollow-core slabs can be treated as a distinct population due to their consistently low variability in cover depth. Reliable preliminary estimate can be obtained with only 10 measurements, while 30 measurements are sufficient to achieve high statistical reliability. To estimate the carbonation depth, 12-14 samples are recommended. The carbonation depth varies between elements and among samples, so the utmost care should be taken when determining sampling spot and the value for an individual sample.

Reusing reclaimed concrete elements is not a widespread practice, although it could help to decrease the carbon footprint of new construction significantly. As reuse needs to be safe, the properties and reusability of the element intended for reuse need to be ensured reliably. When the current statistical method to evaluate characteristic compressive strength with a small number of samples is used, overestimation of the strength has occurred. Moreover, the issue has been considered by only a few studies. Therefore, this study considers the sufficient number of samples and the suitability of the statistical method for the evaluation of the characteristic compressive strength with core samples. With statistical analysis and representative cases, it finds that 12–15 samples should be sufficient for a reliable assessment of a population. However, the compressive strength must be determined on a case‐to‐case basis for each building and element type. The results also highlight that the statistical method for characteristic compressive strength can give significant overestimations from 1 up to 10 MPa. Some modifications are thus needed to the method. The paper presents correction factors for the statistical method to determine characteristic compressive strength.

This paper explores the environmental impacts of retaining or replacing buildings by extending the consequential replacement framework (CRF) for life-cycle assessment (LCA) from individual buildings towards the urban scale. It addresses a gap in previous studies by examining the broader consequences of building-level retention or replacement decisions in the built environment, namely greenhouse gas (GHG) emissions from associated infrastructure construction. The case study, which is located in Finland, investigates alternative ways to densify a growing city, some of which can be achieved within the urban structure, while others require greenfield construction elsewhere in the city. The results reveal that refurbishing and extending already existing buildings is worthwhile in terms of GHG emissions, even if some of the additional floor area targeted in densification were to be built on a greenfield site. After 50 years, the accumulated GHG emissions of scenarios that develop existing buildings are 0.2–12% less than those from replacement scenarios, depending on whether the targeted densification is minor or major and the amount of infrastructure construction involved. This is primarily due to the 11–35% smaller upfront embodied GHG emissions of refurbishment compared with new construction—which 50 years do not offset. Policy relevance This paper reinforces the notion from previous research that developing the existing building stock holds major emission-savings potential, even more so than replacement with energy-efficient new build. It highlights the potential contribution of existing building stocks in low-emission city development, even in growing city contexts. The case study results challenge the common belief in urban planning that if replacement involves densification, it must be a more low-emission alternative than retention, and conversely, if retention leads to greenfield construction, it must be higher in emissions than replacement. Low-emission urban planning should base its conclusions on urban LCA. This paper introduces an infrastructure-extended CRF that accounts for building retention and replacement scenarios, ensuring methodological robustness. The approach is essential for policymakers to base their decisions on evidence and prioritise low-emission development alternatives. Which policymakers hold power over such decisions and which instruments are suitable to pursue these goals depend on the context.