High-Performance Cementitious Materials, Metallic and FRP Reinforcements, and Special Fastening Systems

Research focus

The Peer review has evaluated this group as Good

The introduction of a new material, whatever its field of application may be, requires a multifaceted investigation. In Civil Engineering, the development of high-performance cementitious materials has been made possible by the joint effort of many researchers active in different fields, such as chemistry, mechanics and material science. Nowadays these materials can be designed or tailored to different requirements by controlling their microstructure. These new materials, usually designated as “high-performance concretes” (HPC), are extending the frontiers of the design and construction of large-scale structures, such as tall buildings, large-span bridges, off-shore platforms and containment shells, but other special applications should be mentioned, such as pavements, runways, pipes and safe deposits. The interest in these materials started in the early 90s, when the emphasis was mostly on the mix design (adjuncts, additives, fibers,....) and on the mechanical and physical behavior of these materials. Later the attention turned to the structural implications of the new materials, with specific reference to some basic problems, e.g. size effect, steel-concrete bond and fracture. Fracture of quasi-brittle materials is influenced by the development of an intrinsic “fracture process zone” in the form of a localized region of densely-packed microcracks. This zone has a fundamental importance in controlling the structural behavior in terms of capacity (i.e. peak load, which exhibits size effect) and post-peak softening. These aspects were investigated experimentally by means of specific techniques such as Electronic Speckle Pattern Interferometry (ESPI) and Acoustic Emission. The influence of structural size, fiber type and fiber content (steel, polypropylene or hybrid fibers) was also investigated with reference to high temperature. The investigations on structural behavior have been mainly devoted to highlighting the differences between ordinary concrete and HPC, with particular reference to the extension of standard design codes to HPC and also to Self Compacting Concrete (SCC). Applications of SCC to slabs-on-grade and airport runways were studied as well, and a rather interesting opportunity was offered by the tests performed for improving the performance of the main runway of the city airport of Linate (Milan). These tests and the ensuing investigation were instrumental in proposing a research project on the possible structural advantages of SCC. This project is the joint effort of 6 groups representing as many universities, under the coordination of the group of Politecnico. Among the topics studied in Politecnico, bar-concrete bond and shear in RC beams should be mentioned (the beams are reinforced with a variety of steel products, such as bars, strands and encased steel profiles). For applications in Civil Engineering (mainly RC and PC structures) new metallic and non-metallic materials (fibre-reinforced polymers - FRP) were developed in cooperation with a few steel and composite-materials producers. The combination of these new materials (either high-performance concretes or steel and FRP, bars and anchors) were extensively tested in a variety of situations in order to ascertain their mutual compatibility. In order to address the mechanical behavior of polymeric materials such as those which are used in laminated glass panels, an investigation was made which studied the effects of molecular alignmenon the relaxation behavior of amorphous plastics. The main objectives of this research topic are: - Steel-concrete bond: testing and modeling (HPC, SCC, with/without fibers, different bar diameters) under monotonic loading. 83 - Structural anchors: testing and modeling (mechanical and chemical anchors, HPC, SCC, different embedment lenghts and distances from the edges), in order to refine and extend the actual code provisions. - RC beams in bending and shear: testing and modeling (with/without shear reinforcement, with/without steel fibers), in order to improve the actual code provisions. - One-way RC and PC slabs: testing under fatigue loading in order to measure the strains in the reinforcement, to monitor crack evolution and to evaluate the cumulative damage. - New testing methods and testing equipments: this is crucial for (a) FRP materials, and (b) mechanical and chemical anchors, since – in the latter case – the compliance with EOTA Guidelines has to be checked (EOTA = European Organization for Technical Approvals). The Anchor Lab operated by this research group, together with the Quality Assurance Center of Politecnico di Milano, is responsible for the in-situ inspections concerning the production (in Italy and abroad) of mechanical and chemical anchors, in accordance with EOTA Guidelines. - RC and PC members reinforced with FRP bars and tendons: (a) modeling of their behavior in bending and shear, up to failure, to clarify the pros and cons with respect to steel bars and tendons; and (b) testing and modelling of the different techniques to anchor FRP reinforcement to the concrete. - Contribution to the development of national standards.

Departments

Dipartimento di Ingegneria Strutturale (DIS)

Professors

Full Professors
Biolzi Luigi
Franchi Alberto
Rosati Gianpaolo
Pisani Marco Andrea
Mola Franco
Assistant Professors
Sara Cattaneo