Experimental Investigation on the Durability of fibre Reinforced Cementitious Materials for Strengthening of Masonry

This dissertation is the product of a research project which focused on the behaviour of Fibre Reinforced Cementitous Matrix (FRCM) for the reinforcement of masonry structures in service conditions and its latest applications. The research was conducted both experimentally and analytically, first considering the results from a preliminary state of the art investigation and then providing an original contribution regarding the durability and new applications of FRCM. Based on the literature and existing regulations on fibre reinforcements for masonry structures and their durability in service conditions, it appears clear that although in the past two decades much work has been done on this subject, still very little is known. Specific conversion factors are provided in a Bulletin on Technical Recommendations for Constructions composed by the Italian National Research Council pertaining to service conditions and Fibre Reinforced Polymers (FRP). Although there are currently no specific guidelines regarding the environmental effects on FRCM, these are to be carefully considered and evaluated before designing these systems. The first step towards a better understanding of the physical behaviour of such systems is through experimentation, but experimental investigations on FRCM systems when subjected to environmental conditions are virtually non-existent. Hence the original contributions of this work, as resulting from four experimental campaigns. The methodology of the procedure for durability testing on FRCM analysed in the present dissertation was derived from the literature review of the testing performed on FRP systems. The first two campaigns are directed toward investigating the behaviour of fibres combined with cementitious matrices after they have been subjected to artificial ageing. In the first campaign freeze/thaw cycles are carried out whereas in the second campaign specimens are subjected to wet/dry cycles in sodium chloride solutions. The third and the fourth campaigns regard durability testing on masonry reinforced FRCM subjected to wet/dry cycles, specifically on small pilasters reinforced through glass and steel fibres, and masonry panels reinforced with a new FRCM technique known as Reticolatus. For the numerical analysis of masonry panels with the reticolatus technique a non-linear procedure has been proposed, which implements the non-linearity of the material in an iterative numerical technique correcting the elastic-linear solution after having evaluated it, step by step, pursuing the final goal of respecting congruence. Every mortar joint is represented in discrete form as a curtain of trusses positioned perpendicularly to the interface of the block and one truss placed in a tangential direction. The trusses perpendicular to the interface of the blocks are able to transmit only compressive strength and therefore the deformations are comparable to elastic cushions interposed between the masonry blocks. The reinforcement is constituted by a mesh made by a steel wire of limited section (ca 1mm) in such a way that it can pass through the scraped mortar joints and the clutch in the steel bars inserted in the panel. Since the section of the wire is limited it can sustain only tensile strength, and therefore the reinforcement is modelled as a sequence of trusses connected to each other and fixed at the ends on the nodes. FEM modelling was used and an iterative calculus process was proposed for the numerical analysis of this specific type of FRCM. Three model panels were calculated with the proposed iteration model, with random positioning of the reinforcement wire, in order to check the method of the analysis. All model panels were subjected to a diagonal compression impressed only on the upper right corner and then tested. The second step of the numerical analysis was to recalculate the panels using the modified strength values found from the experimental campaigns described above. The conclusions drawn about FRCM reinforcing systems for masonry in this dissertation are able to answer questions about these reinforcements that are important in the renovation and restoration of historical structures, such as how long the reinforcement will be able to function effectively and how much time passes between onset of the degradation of the system and the need for replacement.