Abstract 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.

Abstract 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.

Abstract 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.

Abstract 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.

Abstract 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.

Abstract 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.

Abstract 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.

Abstract 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.