Material behavior and durability of R/C and P/C structures

Research focus

The Peer review has evaluated this group as Excellent

This research is mainly focused on the characterization and modeling of material behavior of concrete and special cementitious composites paying attention to their structural applications. One of the major issues concerning both ordinary concrete (NSC) and special cementitious composites (high- and ultra high-performance concretes and mortars, HPC and UHPC) is their behavior under severe environmental conditions (corrosion, high and low temperatures) since the mechanical decay of the material properties is detrimental to structural performance. Concrete cracking and porosity as a vehicle for reinforcement corrosion – followed by bond decay and by sectional modifications in the reinforcing bars – is one of the most extensively-investigated topic at the Politecnico. The current trend is to use the information coming from the various decay sources to give weathered or damaged structures a “condition rating” as a tool to identify the best possible rehabilitation techniques. Fire and high temperature are also a major factor with regard to the decay of concrete properties, even more so with HPCs and UHPCs which tend to be more heat-sensitive than NSCs. Thermal and mechanical characterization at high temperature has been performed on several different cementitious materials, both at high temperature and after cooling, and different experimental techniques are being developed to this end, including a split-furnace for testing loaded specimens at high temperature. At the same time, structural modeling under fire has been performed on single elements and frames, where stability issues have been treated as well, and innovative nondestructive methods for the assessment of material decay and structural safety after a fire have been developed. Among the construction materials, Fiber-Reinforced Cementitious Composites (FRCCs) have been extensively investigated at the Politecnico. Several countries are introducing in their National Codes specific recommendations in order to allow designers to use these materials, which can be subdivided into three main classes: (1) medium-strength FRC for massive members (Shotcrete and Self-Compacting Concrete), where FRC may be coupled with ordinary reinforcement (P/C and R/C); (2) High-Performance FRC, exhibiting a hardening behavior in bending for precast elements, mainly used to reduce the structural weight and to increase durability and fire and impact resistance by increasing the local toughness; and (3) Ultra High-Performance FRC characterized by a hardening behavior in uniaxial tension used for structural repair, as well as for connections or for any specific application where the required performance cannot be guaranteed by ordinary reinforcement. The mechanical properties in both the fresh and hardened states have been investigated, with different types of fibers (alkali-resistant glass, polypropylene and steel), in order to work out the constitutive laws for structural analysis. Non-metallic textile reinforcement has been considered as well. A sizable part of the activity concerning cementitious materials and structures subjected to impact and fire and interacting with soil is focused on the many issues related to Civil Protection, since one sub-group (active in the Campus of Lecco) has some joint projects with researchers working in different fields, such as topography, geotechnics and geophysics. At the mesostructural level, the research group is also interested in the constitutive modeling of cementitious materials by means of both continuous and discrete models. A microplane constitutive model for cracking damage in concrete has been generalized in nonlocal terms. The model has been applied to the analysis of different cases of practical interest, such as mechanical and chemical anchors and pre-stressed pre-cast reinforced concrete beams. An extension of this model to FRC, in order to take into account low amounts of steel fibers, has been developed and validated. A new type of mesolevel mechanical model has also been developed for the description of concrete behavior under complex stress states. This model randomly generates the coarse aggregates inside the material and approximately describes the effects of the other components (cement paste, medium 69 and fine aggregates, and interfacial transition zone) through the constitutive relations of the struts connecting the coarse aggregates. Moreover, the prediction of the structural behavior of concrete at early ages (critical in massive members) requires the modelling of complex chemo-physical phenomena that cause considerable non-uniform deformations (self-heating, autogenous selfdesiccation and drying processes) and consequently high tensile stresses and material cracking, especially in HPC and UHPC. In the modelling of the hygro-thermal and mechanical behavior of concrete, a phenomenological approach has been used and a novel numerical model based on the coupling of hygro-thermo-chemo-mechanical phenomena has been developed for the analysis of concrete elements still in the hardening phase.

Dipartimento di afferenza

Dipartimento di Ingegneria Strutturale (DIS)

Docenti afferenti

Full Professors
Luigi Cedolin
Marco di Prisco
Pietro Gambarova
Associate Professors
Roberto Felicetti
Assistant Professors
Dario Coronelli
Giovanni Di Luzio
Liberato Ferrara