PSI - Issue 78

Francesco Ascione et al. / Procedia Structural Integrity 78 (2026) 1334–1341

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number of cords (six). A minimum of three specimens were tested for each reinforcement type. In what concern the inorganic matrix, the eco-friendly mortars were prepared using three main constituents: (i) a reactive binder based on GGBFS; (ii) alkaline activators; and (iii) silica sand. The chemical composition of the slag, determined by energy dispersive X- ray spectroscopy (EDS), was as follows: CaO (43.04%), SiO₂ (36.13%), Al₂O₃ (10.19%), MgO (6.72%), SO₃ (1.75%), and K₂O (0.69%). The a lkaline activation system consisted of sodium metasilicate powder (Sigma Aldrich), with a declared purity of 97% and a weight composition of 49.6% SiO₂ and 50.4% Na₂O, and sodium carbonate monohydrate (Carlo Erba), also with a purity of 97%. A commercially available dried silica sand, with particle sizes ranging from 0.1 mm to 1 mm, was used as the fine aggregate. The water-to-binder and sand-to-binder ratios were fixed at 0.62 and 2.7 (with respect to the weight), respectively. The eco-friendly mortar mixture achieved a flow diameter of 10.3 cm, indicating satisfactory consistency. With regard to mechanical performance, flexural and compressive strength tests were carried out at 28 days in accordance with EN 12190 (2000). The “ green ” mortar exhibited an average flexural strength of 2.2 MPa and a compressive strength of 20.1 MPa. For comparison, a commercial reference lime-based mortar was tested under the same conditions, yielding similar results: an average flexural strength of 3.7 MPa and a compressive strength of 15.42 MPa. Concerning the composite, the B-TR specimens measured 500 mm in length and 50 mm in width, while the S-TR coupons had dimensions of 500 mm × 40 mm. Both TR composites featured a nominal thickness of approximately 10 mm. Specifically, each TR sample was produced by embedding a single layer of textile between two layers of inorganic mortar, with individual mortar layer thicknesses of approximately 5 mm. This configuration was adopted in line with the specifications provided by the material manufacturer. Afte r casting, the composite specimens (both commercial and “green”) were cured for 28 days in an uncontrolled laboratory environment at ambient conditions. All TR specimens exhibited a characteristic strain hardening response under uniaxial tension, consistent with the typical behaviour of textile-reinforced systems. For each configuration, a minimum of three specimens were tested, and the reported tensile properties represent average values. In terms of ultimate tensile strength, the commercial S-TR system achieved the highest performance, with an average strength exceeding 2500 MPa, and failed by fibre rupture — an indicator of effective bond quality and near complete exploitation of the textile. In contrast, the “ green ” S-TR specimens reached a significantly lower average tensile strength of approximately 1205 MPa, failing predominantly due to slippage of the steel cords within the matrix. This failure mode was attributed to inadequate textile impregnation and inefficient load transfer, resulting in limited composite action. As for the basalt-based systems, both the commercial and “ green ” B-TR specimens achieved comparable average tensile strengths of approximately 713 MPa and 726 MPa, respectively. Their failure modes were governed by progressive textile slippage followed by yarn rupture — commonly referred to as telescopic failure — suggesting only partial utilisation of the reinforcement. These results emphasise the critical influence of the matrix – textile bond on mechanical performance, particularly in alkali-activated systems. 2.3. TR strengthened clay brick masonry columns: Preparation and test procedure The strengthening procedure started with a thorough cleaning of the column surfaces to remove any dust or debris. After this stage, an initial 5 mm-thick layer of repair mortar was then applied. Onto this first layer, basalt or steel textiles were laid while being gently tensioned by hand to ensure uniform adhesion to the substrate. A second mortar layer, also approximately 5 mm thick, was subsequently applied, serving as the finishing layer of the composite system. For all strengthened specimens, the mesh overlap length was kept constant at 250 mm, corresponding to one side of the column’s square cross -section. Axial compression tests under monotonic loading were then performed on both confined and unconfined specimens. Loading was applied under displacement control, at a constant rate of 0.2 mm/min. Each test was halted once the load dropped by at least 20% from its peak value, a condition adopted as the failure criterion for the columns. Two linear variable displacement transducers (LVDTs) were mounted on opposite sides to measure the relative displacement between the two rigid plates of the testing machine across the full height of the column (Fig.1.b). Additionally, throughout the loading process, the hoop strains were also monitored. Four LVDTs were used for this purpose, placed at mid-height and arranged symmetrically. 3. Experimental results Fig.2 illustrates the stress – strain responses of confined and unconfined columns, presented in terms of both axial