International Concrete Abstracts Portal

The increasing demand for sustainable building products with lower carbon footprints is a huge global challenge that can hardly be faced by conventional cementitious mixtures. In this context, the use of alternative primary binders, such as hydraulic lime, should be explored. Research in this direction should aim at the development of innovative eco-friendly materials with suitable mechanical performance. For the retrofitting of masonry structures, for instance, it may be necessary to improve their mechanical properties by incorporating supplementary cementitious materials (SCMs), further reducing, at the same time, their environmental impact.

This study investigates the effects of silica fume and metakaolin included either individually or together alongside natural hydraulic lime. The mechanical performance of such binary and ternary binders has been characterized in terms of flexural and compressive strength. Moreover, scanning electron microscopy (SEM) has been used to study the microstructure of the mixtures. Finally, a preliminary investigation concerning the effect of curing time in lime-based mixtures with combined silica fume and metakaolin has been performed to investigate the possible benefits of this approach. The results highlight the superior pozzolanic efficacy of silica fume compared to metakaolin and point towards the proper dosages of SCMs to achieve optimal mechanical performance.

In the last decades, the devastating effects of earthquake events in seismic prone regions increased the attention on the vulnerability of existing constructions. Masonry walls especially experienced severe damage, both considering out-of-plane and in-plane mechanisms. To increase their resistance to horizontal forces, different strengthening systems can be applied. The objective of the present work is to study the efficiency of an innovative strengthening solution, involving the use of fiber reinforced polymer (FRP) pultruded bars. An experimental campaign is presented, in which clay-brick single-leaf masonry panels are retrofitted by carbon FRP rebars, inserted into grooves cut within the masonry panel with a cementitious mortar, and CFRP sheets applied on the panel external surfaces. A total of seven direct shear tests (ST) and four diagonal compression tests (DC) were performed on unreinforced and strengthened samples. The results of the tests showed that the strengthening technique can be effective for the improvement of the shear sliding and diagonal cracking resistances, also allowing to deepen the knowledge of the principal failure mechanisms characterizing the FRP-retrofitted masonry elements.

his paper presents an experimental study on the discontinuous confinement of small-scale masonry columns using a FRCM system. The study aims to investigate the effectiveness of the FRCM in enhancing compressive strength and ductility under axial loading condition. In detail, the adopted FRCM system was composed of a cementitious matrix reinforced with PBO mesh. It was applied to the masonry columns using a discontinuous wrapping technique, which involved wrapping the FRCM material around the column in segments, leaving gaps between the segments itself.

More in deep, the experimental program included twelve specimens, ten (i.e. five couples) of which were wrapped with the PBO-FRCM system using the discontinuous wrapping technique, while the remaining two columns were left unconfined and served as the control group. The columns were measured concerning the load-displacement behavior, ultimate strength and failure mode and then compared between the FRCM-confined and unconfined columns. In particular, the amount of fiber in the vertical direction was kept constant, while the scheme of confinement was varied by both changing the strip width and spacing. In total, five different schemes of discontinuous confinement were proved. The performed research aims to contribute to the knowledge in the field of FRCM-masonry confinement, mainly focusing on the influence of the mentioned parameter.

Unreinforced masonry buildings (URM) are particularly vulnerable to local out-of-plane failure mechanisms of the walls during earthquakes. This study investigates the effectiveness of a relatively novel class of inorganic composite materials, namely Fibre Reinforced Mortars (FRM), for the out-of-plane strengthening of masonry walls. Experimental tests by using a setup to perform out-of-plane tests on masonry panels, part of an enlarged ongoing testing campaign, are presented herein. Two types of masonry walls are investigated: solid clay brick masonry walls and tuff masonry walls. The specimens are subjected to compressive axial load and out-of-plane horizontal actions according to a “four-point bending test” scheme. Two specimens are reinforced before testing with FRM in double-side configuration, while other two specimens are tested in their bare configuration. Experimental results in terms of capacity curves and deformed shapes are reported and discussed. The preliminary results attest that FRMs are effective in increasing the out-of-plane capacity of masonry walls and in postponing the activation of the out-of-plane failure mechanism.

Masonry structures are very sensitive to out-of-plane mechanisms under horizontal actions. A common traditional technique to avoid or mitigate the activation of these mechanisms is represented by injected anchors made of steel bars aimed to improve the connections between orthogonal masonry walls or between floors and masonry walls. The bars are usually embedded in the masonry by means of cement-based grout in holes realized inside the elements to be connected. Recently, an increased interest has developed in the scientific community about the use of Fibre Reinforced Plastic (FRP) bars as alternative to the steel ones for injected anchors, mainly because of their high tensile strength and inertia to corrosion, which can give them high durability, in addition to the use of high-performance grouts. The paper reports the results of experimental pull-out tests realized by the Authors on several types of FRP bars used as injected anchors in small masonry specimens made of yellow tuff blocks. A hydraulic lime and pozzolana-based grout is used to fix the bars in holes realized in the masonry specimens along an embedded length of 250 mm. The set-up is realized in order to apply pure tension to the bars and shear stresses along the bar-grout and the grout-masonry interfaces. The results are analysed in terms of maximum pull-out forces, failure modes and force-displacement relations in order to evidence the global performance of each tested system, especially in relation with the diameter and the surface treatment of the bars. Some comparisons with literature formulation for predicting the pull-out force are developed too.