Search Results (8)

This paper presents the results of an experimental investigation on a steel-reinforced polyurethane (SRPU) composite system with a mineral interlayer, designed for the protection of existing structures. The composite SRPU was reinforced with unidirectional steel textile embedded in polyurethane matrix PS. In the study, SRPU was applied to a brick substrate via a layer of lime- or cement-based mortar of a thickness of 3 mm, 6 mm, or 10 mm. Single-lap shear tests (SLSTs) were carried out on specimens with and without a mortar interlayer. The reference specimens without a mineral interlayer carried higher loads than the specimens with an interlayer. An increase in the interlayer thickness reduced the shear bond strength. The stiffness of the bond under shear of the tested systems was unaffected by the presence of the mineral interlayer. The mechanical properties of the applied mortars influenced the observed failure modes. The tested SRPU system demonstrated notable efficiency in monotonic testing, outperforming previously reported results. Full article

Civil engineering structures are subject to both static and dynamic loadings. This applies especially to buildings in seismic areas as well as bridges, viaducts, and road and railway structures loaded with road or rail traffic. One of the solutions used to repair and strengthen such structures in the event of emergency damage are fibre-reinforced polyurethanes (FRPUs). The article proposes a laboratory method for determining the dynamic complex modulus of FRPU composite tape. The theoretical basis for determining the complex modulus for the tested material is presented. Laboratory tests were carried out using the tensile method for four cyclic loading frequencies and a cyclic load ratio equal to 0.5. Under the assumed test conditions, the material showed a viscoelastic performance with a dominant elastic part (storage modulus). For a frequency of 0.1 Hz, the viscous part (loss modulus) was about 8% of the storage modulus value, while for a frequency of 10 Hz, this value was about 5%. For a loading frequency of 0.1 Hz, the elastic part of the complex modulus was about 1160 MPa, while for a frequency of 10 Hz, it was about 1790 MPa. With the increase in loading frequency, the absolute value of the complex modulus increased. Full article

Polymeric foams are used in many applications, from packaging to structural applications. While polymeric foams have good mechanical performance in compression, they are brittle in tension and bending; fibre reinforcement can enhance their tension and flexural behaviour. This work reports a novel investigation of the mechanical properties of fibre-reinforced polyurethane (FRPU) foams with natural henequen fibres. Pull-out tests were performed with 10 mm fibres and various foam densities to identify the optimal density of 100 kg/m³. Thus, FRPU foams with this density and fibre contents of 1, 2 and 3 wt% were manufactured for mechanical testing. Compression tests showed an increase in the elastic modulus of the FRPU foam specimens compared to the unreinforced PU foam. The FRPU foams also exhibited higher yield stress, which was attributed to the reinforcing effect of the fibres on the cell walls. A maximum increase of 71% in the compressive yield stress was observed for the FRPU foam specimens with a fibre content of 2%. In addition, FRPU foam specimens absorbed more energy for any given strain than the unreinforced PU foam. Flexural tests showed the FRPU foams exhibited increased flexural strength compared to the unreinforced PU foam. A maximum increase of 40% in the flexural strength was observed for the FRPU foam with a fibre content of 1%. The findings reported here are significant because they suggest that FRPU foams incorporating natural henequen fibre exhibit promising potential as sustainable materials with enhanced mechanical properties. Full article

Using 10-(2,5-dihydroxyphenyl)-10-hydrogen-9-oxo-10-phosphine-10-oxide (DOPO-H Q), N,N-diethyl-bis(hydroxyethyl) aminomethylene phosphate diethyl (FRC-6), and (6-oxo- 6H-dibenzo[c,e][1,2]oxphosphine-6-yl) hydroxylmethyl-thiophene (DOPO-SF) as reactive flame retardants, the flame-retardant polyurethane pressure sensitive adhesive (FRPU-PSA) were prepared. The fourier transform infrared (FTIR), thermogravimetric analysis (TG), limiting oxygen index (LOI), vertical combustion (UL 94), 180° peeling, and inclined ball rolling were used to characterize and investigate the properties of FRPU-PSA. It was found that the LOI of PU/50mol%DOPO-HQ, PU/50mol%FRC-6, and PU/20wt%DOPO-SF were 30.7%, 29.3%, and 25.0%, respectively, the peel strength of PU/50mol%DOPO-HQ and PU/50mol%FRC-6 were 3.88N/25 mm and 3.42N/25 mm, respectively. FRPU-PSA not only had good bond strength, but also had good flame retardant performance. Full article

This study focused on characteristic cases of recently tested real-scale RC framed wall infilled structures with innovative seismic protection through polyurethane joints (PUFJ) or polyurethane-impregnated fiber grids (FRPU). The frames revealed a highly ductile response while preventing infill collapse. Herein, suitable 3D pseudo-dynamic FE models were developed in order to reproduce the experimental results. The advanced Explicit Dynamics framework may help reveal the unique features of the considered interventions. Externally applied double-sided FRPU jackets on OrthoBlock infills may maintain an adequate bond with the surrounding RC frame as well as with the brick infill substrate at up to a 3.6% drift. In a weak four-column RC structure, the OrthoBlock infills with PUFJ seismic joints may increase the initial stiffness remarkably, increase the base shear by three times (compared with the bare structure) and maintain a high horizontal drift of 3.7%. After this phase, the structure may receive FRPU retrofitting, reveal the redistribution of stress over broad infill regions, including predamaged parts, and still develop a higher initial stiffness and base shear (compared with the bare RC). The realization of a desirable ductile behavior of infilled frames through PUFJ of only 20 mm thickness, as well as through FRPU jacketing, may remarkably broaden the alternatives in seismic protection against the collapse of structures. Full article

The behaviour of reinforced concrete frames with masonry wall infills is influenced a lot by the stiffness and strength difference between the frame and the infill, causing early detrimental damage to the infill or to the critical concrete columns. The paper reports the results from shake table seismic tests on a full-scale reinforced concrete (RC) frame building with modified hollow clay block (orthoblock brick) infill walls, within INMASPOL SERA Horizon 2020 project. The building received innovative resilient protection using Polyurethane Flexible Joints (PUFJs) made of polyurethane resin (PU), applied at the frame-infill interface in different schemes. Further, PUs were used for bonding of glass fibre grids to the weak masonry substrate to form Fibre Reinforced Polyurethanes (FRPUs) as an emergency repair intervention. The test results showed enhancement in the in-plane and out-of-plane infill performance under seismic excitations. The results confirmed remarkable delay of significant infill damages at very high RC frame inter-story drifts as a consequence of the use of PUFJs. Further, the PUFJ protection enabled the resilient repair of the infill even after very high inter-story drift of the structure up to 3.7%. The applied glass FRPU system efficiently protected the damaged infills against collapse under out-of-plane excitation while they restored large part of their in-plane stiffness. Full article

Polyurethane flexible joints (PUFJ) and fiber reinforced polyurethanes (FRPU) have shown great potential in the repair and protection of masonry and concrete structures. However, some questions have been raised about the durability of such solutions. The accelerated weathering and thermal stability tests carried out so far have shown the mechanical stability of PS-polyurethane in temperatures up to 100 °C and some UV-induced surface degradation. The paper reports the results from tensile tests of PS-polyurethane, used in the technologies mentioned above after being subjected to aging in different corrosive factors, a thermal analysis of unaged polymer which consists of DSC-TGA and dilatometry studies, and SEM-microscopy observation of the specimens with the indication of the elemental composition (EDS). PS-polyurethane showed low sensitivity to weathering with exposition to UV-radiation, some reactiveness to aqueous environments of a different chemical nature, and resistivity to soil and freezing in both air and water. SEM observations indicated changes in the composition of mineral fillers as the main effect of immersion in different water solutions. DSC-TGA studies showed the thermal stability of PS-polyurethane up to 200 °C and degradation proceeding in five stages. Dilatometry studies revealed that the first-degree thermal degradation over 200 °C causes a serious loss of mechanical properties. Full article

A flame retardant rigid polyurethane foam (RPUF) system containing functionalized graphene oxide (fGO), expandable graphite (EG), and dimethyl methyl phosphonate (DMMP) was prepared and investigated. The results show that the limiting oxygen index (LOI) of the flame-retardant-polyurethane-fGO (FRPU/fGO) composites reached 28.1% and UL-94 V-0 rating by adding only 0.25 g fGO. The thermal degradation of FRPU samples was studied using thermogravimetric analysis (TG) and the Fourier transform infrared (FT-IR) analysis. The activation energies (E_a) for the main stage of thermal degradation were obtained using the Kissinger equation. It was found that the fGO can considerably increase the thermal stability and decrease the flammability of RPUF. Additionally, the E_a of FRPU/fGO reached 191 kJ·mol⁻¹, which was 61 kJ·mol⁻¹ higher than that of the pure RPUF (130 kJ·mol⁻¹). Moreover, scanning electron microscopy (SEM) results showed that fGO strengthened the compactness and the strength of the “vermicular” intumescent char layer improved the insulation capability of the char layer to gas and heat. Full article