Effects of autogenous healing on the recovery of mechanical performance of High Performance Fibre Reinforced Cementitious Composites (HPFRCCs): Part 1

[EN] This paper presents the results are shown of a thorough characterization of the self-healing capacity of High Performance Fibre Reinforced Cementitious Composites (HPFRCCs). The capacity of the material will be investigated to completely or partially re-seal the cracks, as a function of its composition, maximum crack width and exposure conditions. The analysis will also consider different flow-induced alignments of fibres, which can result into either strain-hardening or softening behaviour, whether the material is stressed parallel or perpendicularly to the fibres, respectively. Beam specimens, initially pre-cracked in 4-point bending up to different values of crack opening, were submitted to different exposure conditions, including water immersion, exposure to humid or dry air, and wet-and-dry cycles. After scheduled exposure times, ranging from one month to two years, specimens were tested up to failure according to the same test set-up employed for pre-cracking. Outcomes of the self-healing phenomenon, if any, were analyzed in terms of recovery of stiffness, strength and ductility. In a durability-based design framework, self-healing indices quantifying the recovery of mechanical properties were also defined and their significance cross-checked.The support of Politecnico di Milano - Young Researchers 2011 grant to the project Self-healing capacity of cementitious composites is gratefully acknowledged. The authors also thank Matteo Geminiani, Raffaele Gorlezza and Gregorio Sanchez Arevalo for their help in performing experimental tests along different time steps of the project, in partial fulfilment of the requirements to obtain their MScEng degrees.Ferrara, L.; Krelani, V.; Moretti, F.; Roig-Flores, M.; Serna Ros, P. (2017). Effects of autogenous healing on the recovery of mechanical performance of High Performance Fibre Reinforced Cementitious Composites (HPFRCCs): Part 1. Cement and Concrete Composites. 83:76-100. doi:10.1016/j.cemconcomp.2017.07.010S761008

A FRACTURE TESTING BASED APPROACH TO ASSESS THE SELF HEALING CAPACITY OF CEMENTITIOUS COMPOSITES

The self healing capacity of cementitious composites employed for either building new or repairing existing structures opens challenging perspectives for the use of a material intrinsically able to recover its pristine durability levels, thus guaranteeing a longer service life of the designed applications and a performance less sensitive to environmental induced degradation. One possibility of achieving the aforementioned self-healing capacity stands in the use of additives featuring a “delayed crystalline” activity, which, when in contact with water or atmosphere humidity, form chemical compounds which are able to reseal the cracks thus guaranteeing the recovery of a pristine level of mechanical performance. In order to quantify this self healing ability, either in presence of not of the aforementioned additives, and its effects on the recovery of mechanical properties of concrete a methodology has been developed and will be presented in this paper: it allows the recovery of material properties to be evaluated in terms of stiffness, maximum load and effective crack opening and “self healing” indices to be defined and quantified in a “durability based” design framework

Self healing capacity of concrete with crystalline additives: natural vs. accelerated exposure conditions

The presence of cracks may significantly affect the life-cycle of structures, as a results of its influence on the designed structural response vs. persistent or even severe accidental load and exposure conditions, when requested. Repairing damaged concrete in existing structures needs important investments to recover the pristine level of serviceability and extend their designed service life. In this respect, the ability of cementitious composites to \u93self-repair\u94 the cracks, because of autogenous or suitably engineered mechanisms, is a challenging opportunity, making concrete more and more attractive in future sustainable developments of civil engineering. In this study a methodology will be presented to assess the aforementioned capacity, based on three point bending tests on un-cracked and pre-cracked beams, upon exposure to suitable environmental conditions. The paper will focus on the difference between accelerated exposure, in a climate chamber, and \u93natural conditioning\u94 in air; comparison with immersion in water will also be performed

A numerical model for the self-healing capacity of cementitious Composites

The self-healing capacity of cementitious composites, i.e. their capacity to completely or partially re-seal cracks, is studied in this paper. This phenomenon is investigated with reference to a previous experimental campaign dealing with a normal strength concrete which is kept in water after cracking (Ferrara and Krelani 2013, Ferrara et al. 2013). With reference to 3-point bending tests performed up to controlled crack opening and up to failure, respectively before and after exposure/conditioning, the recovery of stiffness and stress bearing capacity has been evaluated to assess the self-healing capacity. The SMM model (Di Luzio and Cusatis 2013) for concrete, which makes use of a modified microplane model M4 and the solidification-microprestress theory, is able to reproduce, as demonstrated, all the major effects of concrete behavior, such as creep, shrinkage, thermal deformation, aging, and cracking starting from the initial stages of its maturing up to the age of several years. The moisture and heat fields, as well as, the hydration degree are obtained from the solution of the hygro-thermal-chemical problem (Di Luzio and Cusatis 2009a, Di Luzio and Cusatis 2009b). This model is extended to incorporate the self-healing effects, in particular, the delayed cement hydration, which is the main cause of the self-healing for young concrete, as well as the effects of cracking on the diffusivity and the opposite repairing effect of the self-healing on the microplane model constitutive laws. A numerical example is presented to validate the computational model developed and to show its robustness

Environmental sustainability of precast and cast-in-situ concrete structures: a case-study comparison based on built supermarket facilities

Environmental sustainability is assuming a growing role in the strategic plans of several countries worldwide. In order to switch to more sustainable solutions in the construction field, many researchers and efforts are focusing on the material level, mainly concerning solutions aimed at partially or fully replacing the most impacting components with alternative or recycled solutions characterised by a lower carbon footprint or a higher durability, in view of a life-cycle assessment. Alongside these positive efforts, another instrument to reduce the environmental impact of construction materials, often less tackled by researchers, is reduction of material consumption by structural optimisation, often ensured by innovative technologies possibly employing high-performance materials that might even have, assuming same volume, higher impact than traditional ones. This concept is analised in the present paper by comparing the computed environmental equivalent carbon footprint of two similar single-storey supermarket facilities, designed and built in the Po valley, Northern Italy, with different technologies: precast and cast-in-situ concrete. Having at disposal the final consumptive volume of materials employed for both buildings concerning the superstructure frame without cladding, the comparison based on Global Warming Potential (GWP) certified by material producers, computed per square metre covered, allowed to evaluate the actual impact of the structure of the two solutions. Moreover, the environmental-related benefits provided by the replacement of the most impacting components (steel and cement) with alternative environmentally friendly solutions further allows to quantify and target the most effective strategies to enhance the sustainability of structural bodies

Numerical simulation of self-healing in cementitious composites

This paper presents a study of the self-healing capacity of cementitious composites, i.e. their capacity to completely or partially re-seal cracks. This phenomenon is investigated with reference to an experimental campaign dealing with a normal strength concrete, in which with reference to 3-point bending tests performed up to controlled crack opening and up to failure, respectively before and after exposure/conditioning, the recovery of stiffness and stress bearing capacity has been evaluated. The SMM (solidification-Microprestress- Microplane model M4) model for concrete, which makes use of a modified microplane model M4 and the solidification-microprestress theory, is able to reproduce all the major effects of concrete behavior, such as creep, shrinkage, thermal deformation, aging, and cracking starting from the initial stages of its maturing up to the age of several years. The moisture and heat fields, as well as, the hydration degree are obtained from the solution of the hygro-thermal-chemical problem. This model is extended to incorporate the self-healing effects, in particular, the delayed cement hydration, which is the main cause of the self-healing for young concrete, as well as the effects of cracking on the diffusivity and the opposite repairing effect of the self-healing on the microplane model constitutive laws. A numerical example is presented to validate the proposed computational model

Zero-Thickness Interface Formulation For Fracture Analysis Of Self-Healing Concrete

A discontinuous-based porosity-based model for concrete subjected to time- evolution self-healing phenomena is presented in this work. The model represents an extension of a fracture energy-based elasto-plastic interface formulation which now in- cludes porosity evolution induced by self-healing mechanisms. The formulation accounts for the characterization of concrete failure behavior in mode I and II fracture types. The post-cracking response is considered by means of specic work softening rules in terms of work spent and porosity evolution. The eects of the aforementioned phenomenon on the recovery of stiness and load bearing capacities have been evaluated by means of three-point bending (3PB) tests performed up to controlled crack opening and up to failure, respectively, before and after conditioning. Experimental tests are employed as benchmark to validate the proposed model formulation. Particularly, after outlining the mathematical formulation of the constitutive model for interface elements, numerical analysis are compared against test data