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In recent decades, new techniques have been developed to produce concrete. Such a technology is self-compacting concrete (SCC) and another is 3D-printed concrete. In both cases, compaction through vibration, which is a labour-intensive moment, is omitted. In the present research project, both techniques have been combined. Traditionally, concrete columns are produced by pouring concrete into a column mould or form that is either made of wood or steel. The steel mould can be used many times while the wooden mould can at best be used maybe two or three times. Building and then dismantling the formwork takes time and costs money. It also leads to increased material use and increased transport. An alternative is columns with a lost form. Steel pipe columns filled with concrete is a proven technique, but it is rarely used. The steel must be protected from corrosion and in buildings also fire protected. A new alternative – which is being studied in the present project – is a lost 3D-printed concrete form in which a core of SCC is cast. The project included load tests on four composite and two homogeneous concrete columns. The columns were 3 m high and had a circular cross-section with a diameter of 300 mm. The composite columns consisted of a 40 mm thick, 3D-printed concrete form that was filled with SCC. The homogeneous columns were cast with the same SCC. All columns were reinforced with four vertical F8 mm bars and ten stirrups F5 mm. In the load tests, the compressive strength was 56 and 44 MPa for the concrete for the 3D-printed forms, respectively. the self-compacting concrete. The composite columns achieved failure loads as high as the corresponding homogeneous columns. However, there was a difference between columns whose entire cross section was loaded (Group A) and columns where only an inner part (corresponding to the size of the SCC core) of the cross section was loaded (Group B). The failure load for Group B was only 60% of the failure load for Group B. A pos, QC 20240828

Extrusion-based 3D concrete printing (3DCP) is a promising technique for fabricating complex concrete elements without formwork, offering advantages like cost reduction and enhanced design flexibility by decoupling manufacturing costs from part complexity. However, this extended formal freedom is still constrained by the fabrication process and material properties. This paper presents a novel method for applying topology optimisation internally i.e. preserving the external boundaries of the concrete element while reducing material use and weight. This method adapts the extrusion thickness along the part according to the expected stresses, reducing the material use while enhancing structural performance. To validate this method, three different unreinforced 3DCP beams are tested in three-point bending. Results show that beams with optimised material distributions presented a higher strength-to-weight ratio, averaging 47% and 63% compared with the conventional 3D printed beam. This paper demonstrates the potential of internal topology optimisation for improving the efficiency and sustainability of 3DCP., QC 20240515This project has received support from Hesselmanska Foundation, the Development Fund of the Swedish Construction Industry (SBUF) 13791, and the strategic innovation program Smart Built Environment (2020-00257), which is part of the strategic innovation areas initiative funded by Vinnova — the Swedish Innovation Agency, Formas — a Swedish Research Council for Sustainable Development and the Swedish Energy Agency. Printable material for 3DCP experiments was supplied by Sika (Sika Sverige AB).

Transverse joints are introduced in jointed plain concrete pavement systems to mitigate the risk of cracks that can develop due to shrinkage and temperature variations. However, the structural behaviour of jointed plain concrete pavement (JPCP) is significantly affected by the transverse joint, as it creates a discontinuity between adjacent slabs. The performance of JPCP at the transverse joints is enhanced by providing steel dowel bars in the traffic direction. The dowel bar provides reliable transfer of traffic loads from the loaded side of the joint to the unloaded side, known as load transfer efficiency (LTE) or joint efficiency (JE). Furthermore, dowel bars contribute to the slab’s alignment in the JPCP. Joints are the critical component of concrete pavements that can lead to various distresses, necessitating rehabilitation. The Swedish Transport Administration (Trafikverket) is concerned with the repair of concrete pavement. Precast concrete slabs are efficient for repairing concrete pavement, but their performance relies on well-functioning dowel bars. In this study, a three-dimensional finite element model (3D-FEM) was developed using the ABAQUS software to evaluate the structural response of JPCP and analyse the flexural stress concentration in the concrete slab by considering the dowel bar at three different locations (i.e., at the concrete slabs’ top, bottom, and mid-height). Furthermore, the structural response of JPCP was also investigated for several important parameters, such as the joint opening between adjacent slabs, mispositioning of dowel bars (horizontal, vertical, and longitudinal translations), size (diameter) of the dowel bar, and bond between the slab and the dowel bar. The study found that the maximum LTE occurred when the dowel bar was positioned at the mid-depth of the concrete slab. An increase in the dowel bar diameter yielded a 3% increase in LTE. Conversely, the increase in the joint opening between slabs led to a 2.1% decrease in LTE, QC 20240516

In concrete structures, material performance is typically determined at the level of the concrete mix (the microscale) and the overall shape and dimensions of a building element (the macroscale). However, recent developments in the field of 3D Concrete Printing (3DCP) are demonstrating that the design of concrete now also can take place at a previously impossible intermediate scale involving the shaping and placement of the material at the level of the printing nozzle (the mesoscale). By focusing directly on the design of print paths, advanced surface effects and internal porous material distributions can be achieved that significantly affect the aesthetic experience and structural performance of 3DCP structures. This ability to design the distribution of concrete according to local architectural, structural, and functional design criteria is an especially interesting application of 3DCP that could be exploited to customise material performance while at the same time optimising material use and reducing the self-weight of building elements. This paper specifically examines how four different three-dimensional print patterns produce distinct material structures at the mesoscale (mesostructures) and presents an experimental procedure for evaluating their load-bearing capacity., QC 20240206

Climate change is highly visible. Since industrialism started around 1800, the carbon dioxide content in the atmosphere has increased from 280 to 420 ppm and the global average temperature by just over 1°C. In a series of agreements, the world's countries have sought to agree on various climate goals. That the temperature rise should be limited to 1.5°C is perhaps the most well-known goal. In order to reach the goals, many measures are required, and extensive research is often behind them. Research on climate change is usually divided into mitigation and adaptation. Until now, research to mitigate the magnitude of climate change has strongly dominated research to adapt society to climate change. Concrete is the world's most used man-made material and concrete production (actually cement production) accounts for 5-8% of global CO2 emissions, which is why it may be justified to exemplify how research has changed over time to deal with climate change. In the mid-1960s, it was established that reinforced concrete does not have an eternal lifespan. Research into durable concrete increased rapidly. Durable concrete has a longer life span reducing the extraction of natural resources, which is an example of a measure towards mitigation of climate change, even if it was not formulated that way. Research into creating more environmentally friendly cement and concrete (or a concrete with lower CO2 emissions) began in the 1990s and has been completely dominant in mitigation ever since. It is primarily about replacing parts of the Portland cement with various industrial by-products (Supplementary Cementitious Materials, SCM) that would otherwise end up in landfill. There is less and less evidence that we can stop climate change. It will probably be difficult to reach the 1.5 degree target and there is a risk that the global average temperature will increase by more than 2°C sometime in the 21st century. Spends on mitigation will not be sufficient. Measures to adapt society, its, Klimatförändringarna är högst påtagliga. Sedan industrialismen startade kring 1800 har koldioxid­halten i atmosfären ökat från 280 till 420 ppm och den globala medeltemperaturen med drygt 1°C. Världens länder har i en serie avtal sökt enas kring olika klimatmål. Att temperaturökningen skall begränsas till 1,5°C är kanske det mest kända målet. För att nå målen krävs många åtgärder och bakom dessa ligger ofta omfattande forskning. Forskningen om klimatförändringar brukar indelas i minskning och anpassning eller mitigation och adaptation som de heter på det internationella forskningsspråket. Hittills har forskningen för att minska klimatförändringarnas storlek kraftigt dominerat över forskningen för att anpassa samhället till klimatförändringar. Betong är världens mest använda av människan tillverkade material och betongproduktionen (egentligen cementtillverkningen) står för 5-8 % av de globala CO2-utsläppen varför det kan vara motiverat att exemplifiera hur forskningen förändrats över tid för att hantera klimat­förändringar. I mitten av 1960-talet konstaterades att armerad betong inte har evig livslängd. Forskningen om beständig betong tog fart. Beständig betong har längre livslängd vilket gör att uttaget av naturresurser kan minskas vilket i sin tur är ett exempel på en åtgärd för att minska klimat­förändringarna även om man inte formulerade sig så. Forskningen om att skapa miljö­vänligare cement och betong (eller en betong med lägre CO2-utsläpp) inleddes på 1990-talet och har varit helt dominerande inom minskning sedan dess. Det handlar i första hand om att ersätta delar av cementet med olika industriella biprodukter (tillsatsmaterial) som annars skulle ha hamnat på deponi. Allt mindre tyder på att vi kan stoppa klimatförändringarna. Det torde bli svårt att nå 1,5-gradersmålet och risk finns att den globala medeltemperaturen kommer att öka med mer än 2°C någon gång på 2100-talet. Då räcker det inte att satsa på minskning. Åtgärder för att anpassa samhället, dess by, QC 20231002

Post-cast application of hydrophobic agents onto hardened concrete is successful at reducing external ion diffusion into cement paste, this work examines pre-cast application of hydrophobic admixtures in fresh concrete. Concretes, with water to cement ratios (w/c) 0.45 and 0.50 (CEM I; low C3A), were mixed. Adding alkyltrialkoxysilane or triacylglycerol admixtures ranging from 1 to 3 wt%cem in these concretes were evaluated. Increasing the dosage of hydrophobic admixtures decreased the compressive strength. The usage of these admixtures did not hinder the further development of the microstructure as all concretes gained strength after one year, but not in the same percentage increase as the reference concrete. Chloride ion diffusion, after exposure to 3 wt% NaCl solution at 20 °C for 91 days, in concretes with 1 wt%cem admixture showed slight reductions in diffusion rate (8-17%) compared to the reference. At 3 wt%cem, triacylglycerol admixtures showed better hindering effects of inward chloride diffusion, this was especially evident in w/c = 0.45. Equivalent addition of alkyltrialkoxysilane-based admixtures increased the diffusion of chloride ions transferred into the cement matrix., QC 20230405

As a pavement material, concrete has several advantages compared to asphalt but it is hardly used on Swedish highways. In fact the youngest one is already 17 years old. This paper starts with the history of Swedish concrete pavements, continues with the current status of existing ones and discusses the reason that concrete has difficulties to compete with asphalt. The modern Swedish concrete highway consists of a 200-220 mm two-layer jointed plain concrete pavement on a cement- or asphalt-treated base. The paper summarizes the experiences from the five most recent Swedish concrete pavement projects. By selecting wear-resistant aggregates and high strength of the top layer, the concrete pavement has been shown to resist wear from the studded tires that are allowed on Swedish private cars during the winter season. In recent years, focus on low investment cost and low CO2 emissions has increased. In order to meet these goals, the Swedish concrete pavement research is oriented towards optimizing the concrete mix and prolonging the service life of existing concrete pavements by adopting foreign repair technologies. The paper ends with a summary of on-going Swedish research and research needs in the area of concrete pavements., QC 20230825

Pavements are essential for the country's development and comprise significant investments. Thewell-operating pavement networks sustain society for a long time. Asphalt and concrete are twocompetitive paving materials used for pavements. In Sweden, the major part of road infrastructureconsists of asphalt due to the strong asphalt industry, while only 1% of pavement networks areconcrete. Concrete pavements are common in the United States (US) and European countriessuch as Germany, Switzerland, Belgium, Austria and France.The intensity of traffic loads has increased exceptionally with time, demanding high wear-resistantpavements. Concrete pavements are superior for highways subjected to the high number of loadrepetitions or for heavy traffic volume roads. Concrete pavements are stiff, durable, wear-resistant,do not deform under permanent and concentrated loads, and have a longer service life. Damagesare rare on concrete pavement, but sooner or later, rehabilitation may be needed. Various types ofconcrete pavement exist, but this paper is limited to the jointed plain concrete pavement as it is themost common pavement system used in Sweden.The rehabilitation of concrete pavements is challenging in heavy traffic volume roads due to trafficcongestion, and if cast-in-place concrete is used, it will substantially affect traffic throughdisruptions. However, it is now possible to repair concrete pavement during shortened work–window. A technology has been introduced internationally based on precast concrete slabs and iswidely used in the US and Canada. The research in this Ph.D project aims to adapt the USexperience with precast technology to Swedish conditions, i.e., geology, studded tire effect, rulesand traditions of procurement etc. The strategy to adapt the existing experience of this innovativetechnology to Swedish conditions includes a literature survey, numerical simulation and field testsof precast concrete slabs, which will be discussed in this paper., QC 20230825

The most frequent method to produce bridge columns is to erect a form and fill it with concrete. The construction of formwork is time-consuming and despite possibilities to reuse the wooden or steel formwork a small or large number of times, respectively, there are always increased material costs. In this pilot research project, we have investigated the possibilities to instead create permanent or lost formwork by using 3D concrete printers. The formwork will then constitute a part of a composite column and contribute to both the load-carrying capacity and durability. If Self Compacting Concrete (SCC) is used for the interior concrete, two efficient technologies will be combined, 3D-printed (3DP) concrete and SCC. Two promising BSc thesis works have been conducted at KTH The Royal Institute of Technology in co-operation with Luleå Technical University (LTU) and the companies ConcretePrint and Betongindustri. A literature review shows that the number of publications within this narrow research field is small. A couple of scientific journal papers deals with the aesthetical possibilities that the 3D-printing procedures provide. In a journal paper from 2021, six Chinese researchers summarize tests on cylindrical 3DP concrete forms filled with concrete. Based on the research outcome, they show that such a composite column is able to develop as high load-carrying capacity as corresponding homogeneous concrete column. The first BSc thesis work was carried out during the spring 2021 at KTH. It covered four, almost wall-shaped, specimens with rectangular cross-section and the height 1,08 m. Two of the 3DP forms were filled with conventional concrete C40/50 and two other ones with SCC. Both 3DP and casting worked well and the forms sustained the casting without any cracking or leakage. Cores were drilled out of the specimens and among other measurements a bond strength between form and interior concrete of almost 1 MPa was obtained. This is of the same magnitude that usual, QC 20220609

Crushed rock aggregates may lead to unhealthy concentrations of radon gas in concrete buildings. The radon exhalation rate isdependent not only on the concrete mixture but also on its microstructure. Carbonation changes the microstructure, and it also influences the radon exhalation rate. With the guidance of the standard carbonation test, EN 12390-3:2019, and radon exhalation rate tests as specified in ISO-EN1165-7, it is found that carbonation has a significant effect on the radon exhalation rate, being reduced by approximately 25% for ordinary portland cement (OPC) after carbonation. In concretes with a substitution of supplementary cementitious materials(SCMs), the radon exhalation rate increased by approximately 30% after carbonation. Conclusively, concretes containing OPC and concretes containing SCMs (fly ash and slag) showed opposite trends as a result of increased carbonation ingress into the concrete mixtures. Diffusion measurements of OPC concrete and concrete containing slag (SCM) support this hypothesis., QC 20221011

Bridges constitute an important part of the infrastructure. For bridges to have the longest possible service life with minimum repairs, the maintenance is of great importance. One type of bridge maintenance that is rarely researched is the continuous preventive maintenance. The continuous preventive maintenance consists of removal of vegetation, cleaning of bridge joints and drainage systems as well as high-pressure washing of the structure. The effect of washing is discussed but not properly researched. A study on the effectiveness of high-pressure washing on concrete is therefore being conducted. An accelerated test method is being developed to mimic field testing. The method has been developed through tests on small concrete specimens subjected to fluctuating temperature, fluctuating moisture, and repeatable exposure to de-icing salt during several cycles. The specimens are of two recipes where one represents an old concrete bridge with rather high water-cement ratio (0.6) and the other one represents a new concrete bridge with a low water-cement ratio (0.4). The first two versions of the method are described. The second version shows promising results, but the method needs further development to incorporate additional factors., QC 20230227

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3D printing concrete (3DPC) is a fairly new technology that is being developed in many countries around the world. The aim is to (i) increase the productivity on site, (ii) improve the quality by reducing the number of errors due to the human factor and (iii) make more advanced member shapes possible. The 3DPC technology is most competitive for making slender and thin structural members. In cases where massive concrete members are needed, 3DPC will have difficulties to compete with cast concrete, e.g., self-compacting concrete (SCC). In many cases, the combination of 3DPC and SCC might be the best solution. One example is columns where the 3DPC constitutes the (permanent or lost) formwork that in a second step is filled with SCC. In an ongoing research project at KTH, composite concrete columns of this type are investigated through a literature survey and laboratory tests. The literature is scarce but promising. Two B.Sc. projects were conducted during spring and autumn 2021. 3DCP forms of a maximum height of 2,4 m were able to withstand the form pressure from SCC without cracking, leakage or any other damage. Bond strength measurements on one of the composite columns showed values between 0,3 and 1,4 MPa, i.e., in the same range as frequent values in the field. This project constitutes the platform for further tests where higher composite columns will be subjected to load-carrying capacity tests as well as durability tests. If also these tests will be successful, it will be possible to save both natural resources and costs by making the 3DPC in high performance concrete and the SCC in a lower strength class with a reduced cement content., Part of proceedings ISBN 978-294064315-8QC 20221109

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Functionally graded materials (FGMs) describe composite materials with a gradual change in properties along one or several axes. A major advantage with this approach is the avoidance of discontinuities between different layers of material. 3D Printing offers the possibility to control the material composition and spatial placement along the printing process to create structures with graded properties. However, there are very few examples of the application of this approach to 3D concrete printing (3DCP). This paper presents a review of the current approaches of and methods to grade the material properties of a 3DCP structure, as well as a review of similar methods used in other 3D printing processes. Finally, the potential applicability of these principles into concrete are presented and discussed., QC 20220728

3D-utskrivning av betong och självkompakterande betong (SKB) är två tekniker med rötter i 1990-talet och som båda kan leda till högre produktivitet och bättre arbetsmiljö. De kanske inte skall konkurrera utan istället komplettera varandra. Här sammanfattas två lovande examensarbeten som visar hur man kan skriva ut pelarformar och därefter fylla dem med SKB och därmed skapa en samverkanspelare med kvarsittande form., QC 20230825

The origin of the author’s paper is a redesign of a Swedish pile-supported steel fiber concrete (SFC) slab for Friend’s Arena in Stockholm, Sweden, where the two different design methods summarized in the paper were compared. The design thickness of the slab was calculated to 350 mm (14 in.) and 450 mm (18 in.), respectively. This comparison was presented at the fib Symposium in 2012 in Stockholm in a paper coauthored by the author and one of the debaters.2 The real slab is 350 mm thick and as far as the author knows it works still perfectly well. On the other hand, the author has recently taken part as an invited expert in a couple of damage investigations where SFC floors have cracked severely due to insufficient thickness and/or too heavy loading. In Sweden, the two design methods still compete. According to the author’s opinion, contractors should compete by selecting and offering different technical solutions with connecting bids, but not by calculating in different ways. The attempt of the CI paper was to try to find probable explanations that the design method leading to smaller thicknesses often work well but not always. The author fully agrees with the debaters that we have to minimize the global waste of resources and not make the floors thicker and containing more fibers than necessary., QC 20230825

In concrete design, material performance is typically defined by the composition of the concrete mix (micro scale) and the overall shape and design of building elements (macro scale). However, recent developments in the field of 3D concrete printing (3DCP) are demonstrating that the design of concrete now also can take place at an intermediate scale involving the spatial organization of the material at the level of the printing nozzle. A growing body of work is showing how the additive process can result in novel material configurations through the programming of print paths. This paper specifically examines the relationship between the spatial organization of concrete at the mesoscale and its overall structural performance and presents an experimental procedure for evaluating the load bearing capacity of a selection of generated mesostructures., QC 20230825