This study investigates the mechanical properties and microstructural characteristics of five concrete mixtures specifically designed for application in low and intermediate-level nuclear waste repositories. These repositories necessitate construction materials that not only offer durability and strength but also maintain a long service-life under the underground environmental conditions over extended period. The concrete mix design was formulated with a focus on optimizing durability and sustainability, incorporating supplementary cementitious materials such as silica fume and slag to enhance the concrete durability. Comprehensive microstructural analyses using petrographic analysis and Micro x-ray fluorescence (μ-XRF) provided insights into the hydrate phases and pore structure evolution, revealing that the concrete exhibits dense microstructures and low permeability, essential for reducing leaching and sulfate attack risks. Mechanical testing demonstrated high compressive strength and modulus of elasticity, showing the suitability of concrete mixtures for structural components in repository environment. Overall, the findings highlight the potential of this designed concrete mixture in meeting the demands of low and intermediate level nuclear waste storage, ensuring safety and stability while also supporting environmental sustainability using eco-friendly materials.
Chloride binding plays a major role with respect to chloride ingress. On one hand, engineering models often rely on "apparent" diffusion coefficients, which account for both the diffusion of chlorides in the pore solution and chloride binding. On the other hand, mechanistic models intend to consider the two phenomena separately. However, the inputs to model chloride binding are quite complex to acquire, because they require dedicated experiments that are usually only conducted for research purposes.In this paper, an approach is proposed to estimate binding parameters from chloride ingress profiles. First, the effective diffusion coefficient is measured with a chloride migration test. Then, a chloride profile from a diffusion test is fitted with a model where transport of free chlorides follows Fick's second law, and free and bound chlorides are linked by a Freundlich equation. Finally, the surface concentration and the Freundlich parameters are adjusted to obtain the best possible fit. The derived Freundlich parameters are fairly close to the ones measured in dedicated chloride binding experiments. A case study applying this approach to concrete elements exposed to seawater in a Danish harbour is also presented.
This study examines the benefits and limitations of different supply chain models for recycled concrete aggregates (RCA), a highly resource- and CO2-intensive material. Focusing on Sweden, it combines material science insights with policy analysis and logistics modelling to assess the potential of RCA in construction. RCA demonstrate strong reuse potential in both bound (new concrete) and unbound (road and backfilling) applications, with life cycle assessments indicating lower climate impacts than virgin aggregates. However, barriers to achieve circularity persist, including fragmented regulations, limited infrastructure, and weak market demand. Using qualitative data from industry actors and quantitative modelling, three scenarios are developed: high-utility reuse of elements, consolidated recycling into bound and unbound applications, and low-utility recycling for backfilling. Results highlight the importance of selective demolition, traceability, procurement models, and strategic placement of concrete material terminals. The study concludes that coordinated policy, logistics planning, and procurement practices are critical to scaling RCA adoption.
Calcium Sulfo-Aluminate (CSA) clinkers are predominantly tailored for specialized markets that require distinct properties such as accelerated strength development and shrinkage compensation, both of which are primarily associated with the presence of the ye’elimite phase. The commercial CSA clinkers constitute a high ye’elimite content from the use of raw materials such as pure alumina or bauxite, which is listed as a critical raw material by the European commission and therefore significantly increasing the production costs. This economic limitation renders CSA cement substantially more expensive than Ordinary Portland cement (OPC), thereby confining its use to small-scale application. These challenges may be addressed by exploring alternative alumina-rich industrial by-products or Al-rich residues characterized by Fe2O3 and SiO2 contents below 5% and Al2O3 content above 60 %, which hold the potential to fully substitute pure alumina or bauxite. Therefore, maintaining the high ye’elimite content of the CSA clinkers without the use of pure alumina or bauxite. However, incorporating Al-rich residues from the aluminium industry may pose a risk to the human health during clinker production due to its high dioxin content of ~ 35 ng TEQ kg−1, higher than the limit proposed by SINTEF of 10 ng TEQ kg−1. Therefore, future research direction should focus on initially the degradation technologies for dioxin removal from the raw material followed by evaluating the feasibility of using Al-rich industrial residues as the sole source of alumina in CSA clinker production, aiming to optimize their processing and performance while minimizing reliance on pure alumina or bauxite.
The simplest way to reduce global CO2 emissions linked to cement productions is to reduce the amount of clinker by partially replacing it with supplementary cementitious materials (SCMs). The availability of the most common used SCMs (e.g. fly ash), is, however, expected to decrease in the coming years. Extensive research is conducted to find new alternatives and ensuring long-term durability of concrete incorporating new materials is crucial for implementation. The impact of novel SCMs from Nordic countries on fresh and hardened properties as well as durability performance in mortar and concrete was studied. The composite cements analysed had a composition of 78 wt.% Portland cement, 18 wt.% SCM and 4 wt.% limestone. The investigated SCMs include natural materials such as clays and volcanic rocks (rhyolite and hyaloclastite), and industrial products such as fly ash, slag, oil shale ash, bio-fuel ash or bio-coal fly ash. All SCMs except oil shale ash had comparable performance to fly ash in terms of resistance to carbonation and chloride ingress, resistance to freeze-thaw scaling and mitigation of ASR. Concretes prepared with oil shale ash had considerably higher chloride ingress and no mitigating effect on ASR expansion.
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.
This paper presents the results of a large and systematic experimental investigation of structural concrete cast with recycled concrete aggregates (RCA) at high replacement ratios. The experimental campaign included determination of modulus of elasticity, compressive strength, and tensile strength, and was divided into two series comprising a total of 312 test specimens. The first series investigated the influence of the replacement ratio (RR) at a fixed target compressive strength, whereas the second series examined varying target strengths at a fixed RR. Proportioning of all concrete mixtures was based on achieving maximum packing density, and the RCA was well-characterised regarding water absorption capacity, density, compressive strength, and aggregate types, the latter two often unspecified in previous studies. The experimental campaign shows that even at considerably higher RRs than current recommendations in standards and the literature, RCA is a viable alternative to natural aggregate (NA) with no increase in cement content nor pre-treatment of the RCA, provided systematic handling of mixture design and production.
Effective repair and protection of concrete structures prolong their service life. This is well documented. There are various repair and protection categories ranging from mechanical repair to electrochemical repairs and surface treatments. The service life of these repairs as such is, however, less studied and documented. There are several parameters that can be used to estimate to what extent the repairs retain their protective properties over time. This paper summarises these parameters and gives a short state of the art review of published English literature over the last 35 years regarding service life of concrete repairs and protection. A call to improve the procedures linked to concrete repair is also presented.
A roadmap for low-carbon concrete was prepared in Finland. The aim of the roadmap was to identify possible options for CO2-emission reductions in concrete production. The calculations were made to correspond the situations in 2030, 2040 and 2050. The calculations were based on the maximum saving potential and the degree of utilization of the options. The roadmap covers the whole Finnish concrete industry and individual companies in different product segments. It is well known that cement has the largest potential for CO2 saving, but the roadmap reveals several other potential options as well. The most potential options vary between the product segments. The roadmap also confirms that concrete can reach very low CO2-emission level in the future.
Steel-concrete composite bridges are commonly designed with full composite action between the steel girders and the concrete deck to enhance structural efficiency and durability. This composite action is achieved through shear connectors, which transfer shear forces and ensure that both materials act as a single unit. While full composite action is preferred, partial composite action may be sufficient in certain cases, depending on interlocking effects between steel and concrete. One strategy to improve the performance of composite bridges is the implementation of horizontal trusses between the lower flanges of the steel girders, which enhance load distribution and lateral stability.Although previous research has investigated the effects of horizontal trusses on global load distribution, their influence on shear force distribution, particularly at shear connectors, remains largely unexplored. Studies on monorail track beams indicate that transverse shear forces significantly affect shear connectors, reducing their capacity and altering failure mechanisms. A similar effect may occur in composite bridges with twin girders and horizontal trusses.This paper presents a case study of a single-span steel-concrete bridge in Sweden, examining the impact of a torsional rigid structure with a semi-closed cross-section on local shear flow distribution. The study also investigates how shear connector rigidity affects force distribution along the steel-concrete interface.
Concrete waste is utilized in Sweden mostly for backfilling in road applications and building landfills. The techniques for recycling concrete to replace natural aggregates are in place and makes it possible to produce circular and climate reduced concrete. This paper explores concrete crushed aggregates (CCA) from rest concrete, produced using industrial crushing methods. Also, the regulatory framework supporting recycling has been discussed. The Swedish concrete standard is implementing to a lower grade the use of CCA in new concrete in comparison to other European standards specially regarding the use of fine CCA fractions. Results for CCA water absorption and apparent density from lab scale and industrial crushing are shown. The CCA fulfills claims for aggregates for indoor concrete. With further improvements in the crushing process, CCA is fit for applications in outdoor concrete.
The ratio of bending stiffnesses at different critical points in the continuous prestressed concrete beam exerts an influence on the redistribution of internal forces, generally moment from support to field. The increasing load will result in the formation of a large number of cracks in the maximum moment regions. This, in turn, leads to a reduction of the flexural stiffness of the member and finally the formation of plastic hinges. Four continuous two-span concrete beams prestressed with unbonded tendons were constructed and loaded up to failure at the laboratory of Civil Engineering in Tampere University. This article focuses on the examination of the flexural stiffness of the test beams during the loading tests. The average bending stiffness of the test beams, as determined through the measured deflections, was clearly less than the elastic value EcmIg, even at the low loading levels. The calculated rotation values in the centre support exhibited a good correlation with experimental results. However, these values remained below the observed values because, in the plastic hinge regions, the stiffness underwent a more rapid decrease. The total plastic rotation obtained from test results was approximately three times the plastic rotation capacity calculated using the Eurocode.
This study presents a novel method to assess the freeze-thaw exposure of concrete structures. The new Relative Freeze-Thaw Exposure index (RFE) is based on regression model that considers location-related actual freeze-thaw damage observations, number of freeze-thaw cycles and both annual and cycle-related amount of wind-driven rain (WDR) before cycles. The RFE index is then used to compare location-, direction- and climate-related freeze-thaw exposure levels.It can be concluded that the amount of WDR before each cycle has the most significant effect on freeze-thaw damage. Freeze-thaw exposure level is highest in present climate and remains the highest in Finland's coastal area regardless of the used climate change scenario. In Finland's coastal area and southern Finland, the exposure level increases more from eastern and western directions than southern which indicates that the exposure level is getting more evenly distributed. However, the southern direction remains with the most severe exposure in almost every studied case in every location.Freeze-thaw exposure for outdoor concrete structures is not getting less severe with the changing climate in Finland. The quality of concrete (e.g. success of air-entrainment) and protecting concrete from free water remain the main methods against the initiation of freeze-thaw damage.
We collected testimonials about cases ending up in the need for rework. People working at construction sites and from a provider of insurances gave us the information. Some of the cases show how damp when released from young concrete results in the need for rework. Other cases show how leakages not only result in repair for membranes, roofs and faulty pipes but also need for drying of concrete and replacement of damaged material. When slopes and altitudes in the structures or in the sewer lines are faulty considerable costs for rework will follow. The trade rules for plumbing work point out actions that could help to avoid some of the problems that recurrently occur among the cases in the testimonials. Education is a way to avoid rework in case of skill-based reasons. When violation to any instruction or principle is the reason responsibility should be placed with the person who can influence the outcome. All cases show the need for great care in the construction process.
With statistical methods and by analysing a comprehensive database of concrete facade condition investigation reports and utilising the newly developed Relative Freeze-Thaw Exposure (RFE) Index, this article presents a novel service life model to estimate the probability of freeze-thaw damage initiation as a function of time. The model provides property owners with cost-effective baseline information for scheduling facade repairs and planning the extent of necessary restoration work.The model considers different geographical locations, facade directions and used surface type. It was initially applied to current climate conditions, but it also allows to calculate the probability of freeze-thaw damage initiation with future climate scenarios.The results showed that freeze-thaw damage initiates most rapidly in painted concrete facades. In contrast, the damage occurs significantly later in unpainted plain concrete facades, due to their greater ability to dry between rain events. This highlights the issue of neglected maintenance in painted concrete facades, as they should be recoated approximately every 15 years. The second shortest service life was predicted for clinker-tiled surfaces. This is due to their characteristic tendency to allow wind-driven rain to penetrate the concrete through the seams, while the dense tiles prevent the concrete dry efficiently.
This is a study about damage resulting in rework in residential construction in Sweden. They are assorted under 13 headings that mention physical facts without taking a position on cause of the problem. This second part of the report presents information considering water freezing in the building envelope, water in the facades, stained facades, construction parts that not fulfil the system performance anticipated and also real disasters. Preparation before casting concrete takes care because any need for demolishment consumes considerable resources. In general, to avoid damage it is good to; have up to date knowledge about problems that emerge; have a leadership that favours commitment to a well-built product; and to follow up the details that are critical, like those that could result in leakage of water. We also think it is good to be open about things that go wrong. In case skill is missing, education would contribute to a better outcome and less need for rework. In case violation to any instruction or principle is the reason, it should be very clear who is responsible, and important to place responsibility with the person who can influence the outcome.
The strength of existing concrete structures can be evaluated and quantified where necessary with non-destructive and destructive testing methods. The aim is to determine the structural adequacy of existing concrete structures and to test the integrity of the concrete structures based on their strength evaluation.This paper investigates the procedure for the estimation of the in situ compressive strength and characteristic in situ compressive strength of concrete in structural components using direct methods (drilled core) and non-destructive testing methods using Ultra-sonic Pulse Velocity (UPV) and rebound hammers.By carrying out the experimental investigation, it helped us to create an understanding of the procedure of determining properties of the hardened reinforced concrete. The procedure should be done systematically, where analysing the results of the first preliminary examination can lead to the next needed examination method.As a result of this research, a flowchart was produced. The flowchart was produced in respect with standard EN 13791 [1] clause 8 and its Finnish application standard SFS 7508:2024 [2]. The scope of the flowchart was to introduce how many cores need to be extracted with possible indirect testing, considering the size of test region and the examination method.
A recycling pathway using flat glass waste as a supplementary cementitious material (SCM) leads to circularity in concrete production through industrial symbiosis. By incorporating glass waste, the environmental impact of cement can be reduced, contributing to the goal of climate-neutral concrete by 2045. This review study highlights the pozzolanic, chemical and physical properties of glass powder (GP) activated through a mechanical process. The relationship between particle size of GP and the strength activity index as well as the hydration phases and its potential to reduce alkali-silica reactions (ASR) are discussed.
Moisture plays a critical role in several degradation mechanisms affecting the structural components of nuclear power plants. It also significantly influences the long-term structural behaviour of reactor containments. This study presents a novel hygrothermal model that uses the relative humidity as the transport potential and accounts for the presence of a thermal gradient across the containment wall. The model is applied to predict moisture conditions in a concrete reactor containment after 30 years of operation. For evaluation, its predictions are compared with both long-term measurement data from a Swedish pressurised water reactor (PWR) and previously published results obtained using an established moisture transport model based on air vapour content. These published results demonstrate that the established model, while adequate under isothermal conditions, yields inaccurate predictions when a temperature gradient is present. In contrast, the proposed model shows good agreement with the measurement data. To capture thermal effects, the model incorporates novel methods for estimating the temperature dependence of sorption isotherms and moisture transport properties—an essential improvement when modelling moisture behaviour under non-isothermal conditions.
Recycled concrete coarse aggregates (RCCA) offer a sustainable alternative to virgin aggregates in concrete production, addressing both environmental and economic concerns. This study evaluates the mechanical properties and freeze-thaw resistance of concrete with 50% and 100% RCCA replacement percentages, using aggregates sourced from demolished structures in Finland. A total of eleven concrete mixes were tested, categorized into four groups based on testing objectives: mechanical strength, elastic properties, creep and shrinkage, as well as freeze-thaw resistance. The results show that compressive strength decreased with higher RCCA replacement, but the extent of the reduction varied across mixes and testing ages. At 100% RCCA, the strength reduction was more noticeable, but it still varied depending on the mix. Young’s modulus declined with increasing RCCA content, while creep strain increased, particularly at 100% RCCA replacement. In contrast, freeze-thaw resistance remained comparable to the control, with minimal internal damage and low surface scaling. These findings underscore the feasibility of RCCA in concrete applications, highlighting both its potential and performance limitations.
