1,721,767 research outputs found
Fibre Reinforced Cementitious Composites with adapted rheology: from state of art knowledge towards new boundaries for structural concrete applications
No full textFibre Reinforced Self-Compacting Concrete (FR-SCC) combines the benefits of highly flowable concrete in the fresh state with the enhanced performance in the hardened state in terms of crack control and fracture toughness provided by the dispersed fibre reinforcement. A “holistic” approach can be conceived to the design of structure made with highly flowable/self consolidating FRC, which encompasses the influence of fresh state performance and casting process on fibre dispersion and orientation, and the related outcomes in terms of hardened state properties. In this framework, this paper, after a review of the current state of the art on the aforementioned topics based on the research performed by the author in the last decade, the research needs will be discussed which have to be urgently tackled in order to address the use of this kind of advanced cement based materials for high end structural applications
High performance fibre reinforced cementitious composites: Six memos for the XXI century societal and economical challenges of civil engineering
Full text linkWorldwide increasing consciousness for sustainable use of natural resources has made “overcoming the apparent contradictory requirements of cost and performance effectiveness a challenging task” as well as a major concern. High Performance Fibre Reinforced Cementitious Composites, by providing tailored and multiple functionalized performance can represent an asset for the construction industry to face the challenges imposed by the needs of our continuously and fast evolving society. The paper, moving from a parallel with “Six memos from the next millennium” by Italo Calvino, the author will provide his own perspective on the current state on the topic, trying to highlight the benefits achievable through a reliable and consistent incorporation into a design and construction practice for both new and existing buildings and structures
Self-healing cement based materials: 5 years of research experience at Politecnico di Milano
No full textWorldwide increasing consciousness for sustainable use of natural resources has made “overcoming the apparent contradictory requirements of low cost and high performance a challenging task” and a major concern. The importance of sustainability as a requisite which has to inform structure concept and design has been also highlighted in Model Code 2010. Self-healing technologies, by repairing “early-stage cracks in concrete structures”, could prevent “permeation of driving factors for deterioration”, and, in case, even provide partial recovery of engineering properties relevant to the application, thus extending the structure service life.
The author’s research group has undertaken a comprehensive research project, focusing on both experimental characterization and numerical modelling of the self-healing capacity of a broad category of cementitious composites, including normal strength concrete and high performance cementitious composites reinforced with either steel or natural fibres. Both autogenous and engineered healing have been considered. Dedicated experimental methodologies have been employed to characterize the healing capacity of the different investigated materials, based on comparative evaluation, in a pre-cracking and a post-conditioning stage, of the mechanical performance. Influence of exposure conditions and duration has been considered. The healing capacity has been quantified by means of “healing indices”, based on the recovery of the load bearing capacity, stiffness, ductility, toughness, correlated to the amount of crack closure, measured by means of optical microscopy and also “estimated” through a suitable indirect methodology.
As a further step a predictive modelling approach, based on modified micro-plane model, has been formulated. The approach incorporates the self-healing effects, in particular, the delayed cement hydration, as well as the effects of cracking on the diffusivity and the opposite repairing effect of the self-healing on the micro-plane model constitutive laws.
The work represents a comprehensive and solid step towards the reliable and consistent incorporation of self-healing concepts into a durability-based design framework
Quality control of plant produced SCC for precast prestressed roof elements
No full textSelf compacting concrete (SCC) is gaining more and more popularity in the building and civil engineering construction field. Precast industry is looking at it with continuously growing interest, the elimination of vibration contributing to significantly improve the quality of its products and the efficacy of production processes, with positive effects also on the “friendliness” of the working environment (e.g. reduction of noises) and consequently on the wellness of workers.
The possibility, now widely investigated, of successfully replacing a not negligible portion of the higher cement content with waste by-products, reducing the total cost for cubic meter, can give a further impulse to the use of SCC also for large scale and series production of structural elements. The higher cost, due to a higher demand of cementitious material and of high-range water reducing and viscosity enhancing admixtures, and which stand as the main drawback for a more and more widespread use of SCC in precast construction, can be in fact successfully reduced by a proper selection of finely ground materials, which enhancing packing density also enables for the reduction of water and HRWRA demand to achieve a required deformability and contemporary the VEA dosage necessary to guarantee stability, without any significant effect on strength. To the author’s knowledge scarce data are so far available on the statistical properties of self compacting concrete, being it relatively new to precast industry and its production, at the present time, having been mainly “limited” to dedicated, even if significant, structural applications. The possibility of extrapolating existing data on conventional concretes (1,2) has hence to be checked, mainly in the sight of extending to SCC quality control procedures calibrated on conventional concretes (3) and assessing material partial safety factors (strength reduction factors) as prescribed in current design codes (4,5,6).
In this work data of quality control on steam-cured plant-produced SCC for precast prestressed long span roof elements are analyzed: one year of continuing production has been taken as a reference (01/11/2001-31/10/2002). The examined SCC is targeted class C45 (45 MPa characteristic compressive strength at 28 days) according to European Standards (7). Statistical evaluations on short-term and 28-days compressive strength have been performed, also in the sight of extending to SCC currently available models for evolution of concrete strength with time. An evaluation of material partial safety factor has been also performed, according to current Italian and International code prescriptions
Edificio a struttura intelaiata in zona non sismicain Guida alll'uso dell'eurocodice 2 con riferimento alle Norme tecniche per le costruzioni - volume 2
No full textIl capitolo intende fornire con riferimento ad un edificio con struttura intelaiata in calcestruzzo armato in zona non sismica, descritto ed illustrato nel successivo paragrafo, un esempio completo di applicazione delle Norme Tecniche per le Costruzioni (NTC), di cui al Decreto del Ministero per le Infrastrutture del 14 gennaio 200
Statistical properties of steam-cured plant-produced SCC for prestressed precast applications
No full textSelf-consolidating concrete (SCC) has been in the last years increasingly used by precast construction industry due to its superior fresh state performance which may significantly optimize the whole manufacturing process.
As a matter of fact for prestressed elements accelerated curing is performed to rapidly achieve the strength required for prestressing release. In this paper a comparative study on the strength development due to accelerated heat curing has been performed with reference to an ordinary and a self consolidating concrete, designed for the same target strength (fck = 45 N/mm2 at 28 days) and employed for precast prestressed roof elements. With reference to 15 months of continuing concrete production (April 2007-June 2008) data referring to fresh state properties (slump/slump flow and air entrainment) and compressive strength tests at different ages (16 hours, 7 and 28 days) have been analyzed in order to calibrate a strength development law and assess the role of mix constituents (limestone filler) and seasonal temperature variations on the strength development as well as on the robustness of the production. This also in the sight of a better calibration of strength reduction factors for the limit state design in the framework of the Eurocode approach.
The study is the first part of a wider investigation aimed at assessing the effect of heat curing on the physical and mechanical properties of self consolidating concrete for precast application with reference to ordinary concrete
Tailoring the orientation of fibres in high performance fibre reinforced cementitious composites: Part 2 -correlation to mechanical properties and design implications
Full text linkCitius, altius, fortius/faster, higher, tougher: pushing ahead the boundaries of structural concrete through fiber reinforced cementitious composites with adapted rheology
No full textFiber-reinforced self-compacting concrete (FR-SCC) combines the benefits of highly
flowable concrete in the fresh state with the enhanced performance in the hardened
state in terms of crack control and fracture toughness provided by the dispersed fiber
reinforcement. Thanks to the suitably adapted rheology of the concrete matrix, it is
possible to achieve a uniform dispersion of fibers, which is of the foremost importance
for a reliable performance of structural elements. Balanced viscosity of concrete
may also be helpful to drive the fibers along the concrete flow direction. An ad
hoc designed casting process may hence lead to an orientation of the fibers
“tailored” to the intended application, which is along the anticipated directions of
the principal tensile stresses within the structural element when in service. This converges
toward a “holistic” approach to the design of structure made with highly
flowable/self-consolidating fiber-reinforced concrete (FRC), which encompasses the
influence of fresh state performance and casting process on fiber dispersion and orientation,
and the related outcomes in terms of hardened state properties. A thorough
understanding is required of the mechanisms underlying the connection between
mix-design and fresh state performance, on one hand, and the dispersion and
orientation of the fibers on the other hand, also in the context with monitoring and
prediction to achieve the anticipated structural performance. In this framework, this
article, after a review of the authors’ main research results on the aforementioned
topics, will focus on the research needs which have to be urgently tackled in order
to address the use of this kind of advanced cement-based materials for high-end
structural applications
Tailoring the orientation of fibres in high performance fibre reinforced cementitious composites: Part 1 -experimental evidence, monitoring and prediction
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