The use of shotcrete or sprayed mortar is a common construction alternative to retrofit unreinforced brick masonry (URM), and extensive research has already been carried out in this area. However, most studies have been conducted on lateral strength, for example, eccentric compression or seismic forces. On the other hand, there are few studies about uniaxial compression, and the results of most studies confirm a strong relationship between the thickness of the retrofitting layer and whether it is a double-sided retrofitting section. However, most studies are exclusively experimental, with few samples, and lack numerical analysis; therefore, deeper research is required on this issue. In this sense, this paper combined experiments and finite element (FE) simulations to further study the uniaxial compression. A series of cyclic uniaxial compression experiments on URM retrofitting with sprayed mortar were performed. The experimental results were used to calibrate the FE model. Using these calibrated FE models, more variable parameters were run so that more reference results could be obtained. Moreover, the resulting damageable model of FE will be useful for studying the behavior in the inelastic phase. Results found that the compression strength of most composite walls retrofitted with sprayed mortar increases with the thickness of the sprayed layer and can improve the construction defects of the masonry itself. An over-thin sprayed layer reduces the range of the elastic phase of the composite wall. This phenomenon tends to stabilize with increasing thickness. The ultimate strength of the composite masonry is generally positively correlated with the overall increase in the thickness of the sprayed mortar but may cause a negative contribution to the ultimate strength of the composite masonry when the sprayed layer is too thin. The contribution of double-sided spraying to the ultimate strength of the composite wall was not as large as expected, but the contribution to the improvement of the elastic modulus of the wall was significant.

(English) This thesis investigates the adhesion behavior between sprayed mortar and masonry substrates, focusing on the influence of compressive strength, mortar age, and surface roughness on adhesion strength. Through detailed experiments and comprehensive analysis, it seeks to better understand these factors and their impact on rehabilitation techniques for masonry structures. The results of this investigation not only expand theoretical knowledge about the adhesion behavior between mortar and masonry but also provide practical recommendations to improve the durability and effectiveness of retrofitting interventions. Experiments were conducted on samples with different compressive strengths (15 MPa, 30 MPa, and 45 MPa) to assess how these factors affect both tensile and shear adhesion strength. It was observed that the tensile adhesion strength decreases with increasing compressive strength of the masonry due to the brittle nature of high-strength materials. Specifically, masonry with a compressive strength of 15 MPa showed tensile adhesion strength ranging from 0.2 to 1 MPa, while masonry with a compressive strength of 40 MPa showed values concentrated between 0 and 0.1 MPa. This behavior is due to the fact that high-strength masonry tends to fail more abruptly, reducing its capacity to maintain adhesions under tension. On the other hand, the shear adhesion strength showed a positive correlation with compressive strength. Substrates with higher compressive strength provided greater shear capacity due to better mechanical interlocking facilitated by surface roughness. Experimental results demonstrated that the shear adhesion strength was almost double that of the tensile strength, highlighting the importance of surface texture in adhesion performance. The age of the mortar is also a crucial factor. Tests were conducted at 7 and 28 days to evaluate the development of adhesion strength over time. At 7 days, the adhesion strength was relatively low due to the ongoing hydration process and incomplete development of the mortar's mechanical properties. However, at 28 days, the adhesion strength increased significantly as the mortar achieved higher levels of hydration and improved mechanical properties. This underscores the importance of allowing adequate curing time in practical applications to ensure the longevity and effectiveness of reinforced structures. Surface roughness is a determining factor in adhesion strength. We measured roughness using the Joint Roughness Coefficient (JRC) and the arithmetic mean deviation (Ra) to quantify its impact. It was found that rougher surfaces facilitated better mechanical interlocking, improving adhesion strength. This finding highlights the importance of surface preparation in rehabilitation applications, where increasing the substrate's roughness can significantly enhance adhesion performance. The experiments revealed three typical modes of failure: adhesion disconnection, specimen fracture, and adhesion material fracture. Adhesion disconnection occurred when the adhesion strength was weaker than the individual strengths of the mortar and masonry, resulting in a clean separation at the interface without significant damage. Specimen fracture was mainly observed in samples with a fragile surface layer developed during mortar curing. Adhesion material fracture involved the rupture of the adhesion material itself, highlighting the impact of shear stress on adhesion integrity. (Català) Aquesta tesi investiga el comportament de l'adhesió entre morter projectat i substrats d’obra de fàbrica, centrant-se en la influència de la resistència a la compressió, l'edat del morter i la rugositat de la superfície sobre la resistència de l'adhesió. A través d'experiments detallats i una anàlisi exhaustiva, es busca entendre millor aquests factors i el seu impacte en les tècniques de rehabilitació d'estructures d’obra de fàbrica. Els resultats d'aquesta investigació amplien el coneixement teòric sobre el comportament de l'adhesió entre morter i maçoneria, i proporcionen recomanacions pràctiques per millorar la durabilitat i efectivitat de les intervencions de retrofitting. Els experiments es van realitzar en mostres amb diferents resistències a la compressió (15 MPa, 30 MPa i 45 MPa) per avaluar com aquests factors afecten la resistència a la tracció i al tall de l'adhesió. Es va observar que la resistència a la tracció de l'adhesió disminueix amb l'augment de la resistència a la compressió de l’obra de fàbrica a causa de la naturalesa fràgil dels materials d'alta resistència. En particular, l‘obra de fàbrica amb una resistència a la compressió de 15 MPa va mostrar una resistència a la tracció que varia entre 0,2 i 1 MPa, mentre que l’obra de fàbrica amb 40 MPa de resistència va mostrar valors concentrats entre 0 i 0,1 MPa. Aquest comportament es deu al fet que l’obra de fàbrica d'alta resistència tendeix a fallar de manera més abrupta, reduint la seva capacitat per mantenir adhesions sota tensió. D'altra banda, la resistència al tall de l'adhesió va mostrar una correlació positiva amb la resistència a la compressió. Els substrats de major resistència a la compressió proporcionaven una major capacitat de tall a causa del millor encaix mecànic facilitat per la rugositat en la interfície. Els resultats experimentals van demostrar que la resistència al tall de l'adhesió era gairebé el doble que la resistència a la tracció, subratllant la importància de la textura superficial en el rendiment de l'adhesió. L'edat del morter també és un factor crucial. Es van realitzar proves als 7 dies i als 28 dies per avaluar el desenvolupament de...

A series of experiments were conducted mainly to investigate the effect of unreinforced brick masonry (URM) retrofitting on strength and modulus of elasticity, and eventually to be able to propose an empirical formula to estimate a similar situation. Direct axial compression tests were central to the overall investigation, and the mechanical properties of various materials were additionally tested to obtain the required data to support finite element (FE) analysis. To obtain more reliable results, a series of FE simulations were performed to supplement the data from the experimental part. First, the load-bearing capacity of most composite walls retrofitted with sprayed mortar increases with the thickness of the sprayed mortar layer and can improve the construction defects of the masonry itself. The test results also showed that the compression behavior of the composite masonry under low deformation conditions basically follows the composite material mechanics that the modulus of elasticity of composite wall increases linearly with increasing thickness of the sprayed mortar. A method for elastic approach is proposed, and by comparing the data, this method can effectively predict the stress-strain behavior at small deformation stages. For the ultimate strength, according to the data analysis results, the ultimate strength of the composite masonry is also positively correlated with the overall increase in the thickness of the sprayed mortar but may cause a negative contribution to the ultimate strength of the composite masonry when the sprayed layer is too thin or at certain specific thicknesses. The cause of these phenomena may be caused by the retrofitting using the sprayed mortar which changes the local stress state of the masonry. Similarly, a possible approximation method for predicting composite walls is proposed. It is also interesting to note that the ultimate strength of the bilaterally sprayed composite appears to be related only to the thickness of each side and not to the total thickness, as this was demonstrated in the experiments.