Grijs beton bestaat niet

Beton is wereldwijd een belangrijk constructiemateriaal met een rijke historie. Het inzicht in het gedrag van betonconstructies is, dankzij vele jaren van onderzoek, sterk toegenomen. Trends en ontwikkelingen in onze samenleving stellen ons echter telkens weer voor nieuwe eisen en bieden ook uitdagende nieuwe kansen. Meer dan eens met een groot maatschappelijk belang. Hierbij kan worden gedacht aan constructieve veiligheid, duurzaamheid en ketenintegratie. Maar ook aan ontwikkelingen op het gebied van ICT. De leerstoel betonconstructies bevindt zich in het midden van twee ketens. In één keten geflankeerd door de disciplines ontwerp en uitvoering, in de andere door mechanica en betontechnologie. Het is juist op de raakvlakken tussen de leerstoel en deze disciplines, waar, gegeven de genoemde trends, de beste prikkels tot nieuwe onderzoeken ontstaan. In zijn intreerede bespreekt Theo Salet deze prikkels en de betekenis hiervan voor het onderwijs en onderzoek, vanuit de leerstoel toegelicht. Het zal niet verwonderen dat ook nieuwe betonsoorten hierbij een rol spelen

Kleurrijk grijs

In het boek ‘Misleid door toeval’, stelt Taleb dat we de rol van het toeval in ons leven steeds weer onderschatten. Pech is het verdiende loon, geluk een verdienste. Ons brein geeft liever een verklaring, dan te berusten in stom geluk. Het gaat te ver om het ontstaan van gewapend beton alleen toe te schrijven aan geluk. Ongewapend beton werd immers al in de Romeinse tijd met veel succes toegepast. We zullen echter nooit weten wat er was gebeurd, als de Franse tuinman Joseph Monier op een goede dag in 1867 geen schoon genoeg had gekregen van steeds weer lekkende tuinbakken. Hij zocht de oplossing voor dit probleem in vernieuwing en maakte plantenbakken van gevlochten ijzerdraad en beton

Numerical analysis of sandwich beams

This paper describes the development of a numerical model for the physical nonlinear analysis of simply supported sandwich beams, specifically with foamed-concrete cores and concrete faces. The long-term behaviour is included in view of creep and shrinkage of both faces and core. The structural behaviour of sandwich beams is described by a fourth-order differential equation in the deformation w and a second-order differential equation in the shear deformation of the core γk. The flexural stiffness of the core is taken into account. The general-solution procedure is based on the finite-difference method, together with a successive-substitution algorithm using the secant flexural moduli of the core and faces and the secant shear modulus of the core. The option of tension stiffening is incorporated to represent the nonlinear behaviour of reinforced concrete in tension. The tension stiffening is numerically calculated from a distributed tensile load instead of a load acting on both ends of the reinforced bar. Creep and shrinkage are calculated separately from the differential equations with an algorithm based on increments of time. With the presented model, the time-dependent deflection along the axis of the beam and the state of stress in every fibre can be calculated

Potentials and challenges in 3D concrete printing

Reinforced concrete structures have constantly become more safe and durable over the past century and the materials properties have improved tremendously, but the design and construction method have not changed much over time. Concrete structures face a series of challenges like a new degree of freedom for architecture, sustainability, health, increased productivity and a better integration to BIM models. 3D Concrete printing has the potential to meet these demands, although it is not clear yet which type of structures will benefit most from this additive type of manufacturing. However, in order to explore the benefits, the first task of research is to make the print process robust. This is needed since the load bearing capacity of a structure depends on the design and the printing strategy. Besides, the issue of a lack of reinforcing steel must be solved to ensure safe structures, for example by developing new and ductile types of concrete.</p

Potentials and challenges in 3D concrete printing

Reinforced concrete structures have constantly become more safe and durable over the past century and the materials properties have improved tremendously, but the design and construction method have not changed much over time. Concrete structures face a series of challenges like a new degree of freedom for architecture, sustainability, health, increased productivity and a better integration to BIM models. 3D Concrete printing has the potential to meet these demands, although it is not clear yet which type of structures will benefit most from this additive type of manufacturing. However, in order to explore the benefits, the first task of research is to make the print process robust. This is needed since the load bearing capacity of a structure depends on the design and the printing strategy. Besides, the issue of a lack of reinforcing steel must be solved to ensure safe structures, for example by developing new and ductile types of concrete

Numerical analysis of sandwich beams

This paper describes the development of a numerical model for the physical nonlinear analysis of simply supported sandwich beams, specifically with foamed-concrete cores and concrete faces. The long-term behaviour is included in view of creep and shrinkage of both faces and core. The structural behaviour of sandwich beams is described by a fourth-order differential equation in the deformation w and a second-order differential equation in the shear deformation of the core γk. The flexural stiffness of the core is taken into account. The general-solution procedure is based on the finite-difference method, together with a successive-substitution algorithm using the secant flexural moduli of the core and faces and the secant shear modulus of the core. The option of tension stiffening is incorporated to represent the nonlinear behaviour of reinforced concrete in tension. The tension stiffening is numerically calculated from a distributed tensile load instead of a load acting on both ends of the reinforced bar. Creep and shrinkage are calculated separately from the differential equations with an algorithm based on increments of time. With the presented model, the time-dependent deflection along the axis of the beam and the state of stress in every fibre can be calculated.</p

Mechanical properties and self-sensing ability of graphene-mortar compositions with different water content for 3D printing applications

There is an increasing ongoing research on concrete compositions with enhanced properties such as self sensing given by the use of carbon nanomaterials. Carbon nanotubes-cement composites have been studied for over a decade to produce smart materials, with interesting results. However, since first synthetized in 2004, Graphene is rapidly growing in popularity due to similar conductive properties, high stiffness and strength, lower environmental impact and ease of production and lower production prices. More recent studies have tried to incorporate this material into concrete compositions with positive results. On the other hand, the construction industry is moving towards more automated production processes and new technologies such as 3D printing concrete are gaining popularity. However, there is little research on the effects of nanomaterials in 3D printable concrete compositions. In this paper, the effects of Graphene nanoplatelets (GnPs) on a the mechanical properties and conductivity of a printable mortar are investigated. Five different compositions with different water content and graphene content were prepared to create cast and printed samples with dimensions 40x40x160 mm3 that were tested to evaluate the mechanical strength and the resistivity change between unloaded and loaded to failure conditions. A linear regression model using Matlab was created to have an overview on the strength and resistivity change depending on the water-cement ratio (w/c) and Graphene nanoplatelet content (GnP). The results showed that in cast samples, GnPs improve the compressive strength and the self sensing ability of the material, while in printed samples, GnPs has a detrimental effect on the compressive strength and the self sensing ability depends heavily on the printed layers direction. Future studies should concentrate on the effect of interlayer adhesion on the self sensing and mechanical properties, and on the additives necessary to improve the printability of GnP-mortar compositions