Polymer Grid Research Articles

Experimental study on flexural shear strengthening effect on low-strength RC beams by using FRP grid and ECC

This paper investigates the shear behaviour of reinforced concrete (RC) beams by using engineered cementitious composite (ECC) and fibre reinforced polymer (FRP) grid as a composite reinforcement layer. A total of seven RC beams, including one control beam and six strengthened beams, were tested to reveal their shear behaviour and strengthening effect. The test variables in the experiments included different reinforcement amounts of FRP grids and shear span ratios of RC beams. As a result, the shear strengthening effect of the FRP grid-ECC layer for RC beams is obvious. However, the strengthening effect of the specimen with two-layer FRP grids did not perform better due to premature debonding. Furthermore, through regression analysis on the experimental data, a formula is proposed to predict the angle of the critical inclined cracks in RC beams strengthened with ECC-FRP grids.

Experimental study on bond behavior of interface between fiber-reinforced polymer grids and concrete substrate

The aim of this study is to investigate the bond behavior of the interface between fiber-reinforced polymers (FRP) grids and concrete substrate. The examined parameters were as follows: (a) FRP grid widths (50, 100, and 150 mm); (b) FRP grid types (basalt, glass, and carbon FRP grids); (c) bonding material types (polymer cement mortar and epoxy resin); (d) FRP product types (FRP grids and sheet). Sixty bonded joint specimens were fabricated and subjected to single-shear experimental tests. The results indicated that the bond behavior of the FRP grid–concrete interface was significantly influenced by the width ratio of the FRP grids to concrete specimen, FRP grid stiffness, and bonding material type. In comparison with the FRP sheet-concrete interface, the FRP grid–concrete interface possessed significantly higher interfacial fracture energy, even though the stress transfer mechanism of this interface was more complicated. Additionally, based on the regression analysis of experimental data, empirical models for the width factor, bond–slip relationship, effective bond length, and bond strength of the FRP grid–concrete interface were developed.

Innovative Approach to Repair Corroded Steel Piles using Ultra-High Performance Concrete

Steel H-piles are a common structural system in existing bridges. Many steel H-piles have been corroded as a result of severe weather and acid/alkaline salt exposures, causing a reduction in the axial load capacity. This paper experimentally investigates the use of ultra-high performance concrete (UHPC) encasement as a novel repair method for corroded steel H-pile. UHPC displays better tensile strength, early compressive strength, workability, and durability compared with conventional concrete. The proposed repair is used to bridge the corroded section in H-pile using either a cast-in-place or precast UHPC elements. A series of push-out tests was conducted on eight full-scale piles to assess the axial force that can be transferred through shear studs and bond between the UHPC and steel piles. The test parameters include the type of casting of the UHPC, that is, cast-in-place versus precast elements, thickness and shape of the UHPC elements, an inclusion of carbon fiber reinforced polymer (CFRP) grid, number and grade of bolts, an inclusion of washer, and applying torque on the bolts. The experimental work demonstrated that the UHPC precast repair can be easily implemented. Moreover, using 57 mm (2.25 in.) thick UHPC plates reinforced by two layers of the CFRP grid was capable of transferring up to 81% of the squash load of the H-pile.

Development of thin precast concrete sandwich panels: Challenges and outcomes

The development of thin precast concrete sandwich panels presents many structural, thermal and practical challenges. This study outlines the design, testing and production of novel panels constructed of two layers of high strength, fibre-reinforced concrete that sandwich a layer of high performance insulation. The layers are connected with fibre reinforced polymer grid connectors in an effort to achieve composite action. Thin precast concrete sandwich panels offer weight and material savings over standard reinforced concrete panels, that enable manufacturing, transport and onsite efficiencies, as well as reduced embodied energy. Much current research, focused on reduced concrete section thickness, prioritise the use of textile reinforced concrete which requires specialist equipment and manufacturing methods. This work instead presents a solution that is suitable for production in standard precast facilities. The design development and testing of different design iterations is outlined. Ten samples of 3 m high panels are tested structurally using flexural tests. The panels are tested thermally using experimental techniques and finite element analysis. A case study is presented on a demonstration building. It achieved bending moment capacities in excess of the design wind load requirements, a measured U-value less than 0.18 W∙m−2∙K−1 and post cracking residual strength ensuring a ductile failure. Hence, the final panel design is deemed to achieve both structural and thermal requirements of a high performing cladding element. The panel was developed at scale in a precast facility for practical implementation on a building in-use.

Experimental investigation on shear behavior of RC beams strengthened by CFRP grids and PCM

This paper presents the experimental results of four-point bending tests for reinforced concrete (RC) beams strengthened by carbon fiber reinforced polymer (CFRP) grids and sprayed polymer-cement-mortar (PCM). The reinforced arrangements of CFRP grids, stirrups and longitudinal steel rebars were selected as changing parameters. The maximum loads, mid-span deflections and strains for the PCM, longitudinal steel rebars, stirrups and CFRP grids were obtained. The mechanical behavior of CFRP grids and the cooperation work performance between CFRP grids and steel rebars were investigated emphatically. The research results indicated that the shear strengthening effect of the CFRP grid-PCM reinforcing layers bonded along both sides of RC beams was sufficient. The shear contribution of the vertical CFRP grid was similar to that of the stirrup, but the stress distribution of vertical CFRP grid was not uniform due to the resistant action of grid points. Moreover, the vertical CFRP grids bore the lateral extruding action with opposite directions in tension and compression zones due to the compressive and tensile behavior of horizontal CFRP grids, resulting in the complex stress state of the vertical grid which differs from the stirrup. There exists the cooperation work between CFRP grids and steel rebars in shear strengthening RC beams. So as to clarify the shear mechanism of RC beams strengthened by CFRP grids and PCM, the complex stress state of vertical CFRP grid, influence of the horizontal CFRP grid and the preconditions for the normal work of CFRP grid should be taken into account. The proposed shear capacity calculation formula based on truss-arch model could satisfy the design requirements.

Flexural performance of Reinforced Concrete One-way Slabs Strengthened by FRP Grid

Fiber reinforced polymer (FRP) grid is a kind of two-way fiber material. Its transverse reinforcement and longitudinal reinforcement have the same physical characteristics. Experiments on the reinforced concrete one-way slabs strengthened by FRP grid were conducted to study the influences of bonding area and FRP anchors on its flexural performance. The results showed that the flexural capacity of reinforced concrete one-way slabs strengthened by FRP grid is increased by 7% - 21%. FRP grid can effectively slow down the crack expanding, increases the stiffness and improve the flexural behavior of the slab.

Punching shear behaviour of concrete slabs reinforced with CFRP grids

Punching shear action has been a focus for research in the field of civil engineering and using a fiber-reinforced polymer (FRP) grid is a novel configuration of the engineering materials. We present the test results of an experimental program on the punching shear performance of carbon-fiber-reinforced polymer (CFRP) grid reinforced concrete slabs. Six full-scale 1600 × 1600 × 150 mm slab specimens including one control steel reinforced concrete (RC) slab and five CFRP reinforced concrete slabs were fabricated and tested under monotonic loading till failure. The experiment aimed to investigate the effects of CFRP grids as flexural reinforcement and shear reinforcement on the punching behaviour of concrete slabs. Furthermore, three different shear reinforcement layouts were devised to verify which arrangement is better. Compared with the control RC specimen, the concrete slab with CFRP grids as flexural reinforcement reached almost the same punching strength with a lower reinforcement ratio. Moreover, adding extra shear CFRP grids was beneficial for improving the resistance of the concrete slab to punching. Among the three topological schemes of shear CFRP gird arrangements, the perpendicular layout was proven to be more effective than radial and rectangular arrangements.

Experimental investigation and numerical analysis of RC beams shear strengthened with FRP/ECC composite layer

Five Reinforced Concrete (RC) beams strengthened with Basalt Fiber Reinforced Polymer (BFRP) grid in conjunction with Engineered Cementitious Composite (ECC) were tested along with one conventional RC beam for reference to investigate their performance improvement, particularly in shear capacity, due to strengthening. The test results highlighted that the failure modes of the tested beams were dominated with shear-compression failure in the shear/bending moment regions and concrete crushing in the compression part of the pure bending zone. A good bonding performance between the BFRP-ECC composite and concrete substrate was exhibited during the testing process, which can effectively suppress the propagation of diagonal cracks in the shear/bending moment regions. The shear capacity of strengthened RC beams was greatly improved with the increase of BFRP grid reinforcement ratio. Moreover, the reinforcement effect of this strengthening technique was much more effective with the increase of shear-span ratio of the tested RC beams. Furthermore, finite element analyses based on ABAQUS/Standard software were conducted to provide analytical estimations of the shear capacity of the strengthened RC beams. The analytical results revealed that the predicted values agree very well with the test data, which can effectively predict the shear capacity of RC beams strengthened with BFRP-ECC composite.

Flexural behavior of RC beams strengthened with prestressed and non-prestressed BFRP grids

This study was aimed to investigate the flexural behavior of reinforced concrete (RC) beams strengthened with a thin composite layer consisting of a basalt fiber-reinforced polymer (BFRP) grid and polymer cement mortar (PCM). Ten RC beams were tested in the four-point flexural experiments, and following variable parameters were examined: (1) the FRP grid type, (2) amount of FRP grid, (3) types of bonding materials, (4) prestress, and (5) number of prestress release. The experimental results demonstrated that the BFRP grid effectively improved the serviceability and ultimate behavior of RC beams. The prestressed BFRP grid further improved the cracking load, yield load, and flexural stiffness of the RC beams owing to its higher strength utilization efficiency. Moreover, the failure mode of the prestressed beams changed from “concrete cover separation” to “concrete crushing” or “BFRP grid rupture” when the number of prestress release increased. Based on the strain compatibility and classical flexural theory of RC members, the prediction of the ultimate load of the FRP grid-strengthened beams exhibited a good agreement with the experimental results.

Axial behavior of reinforced concrete column with ultra-high performance concrete stay-in-place formwork

This paper presents the experimental and numerical study on the axial compressive behavior of a novel composite column that consists of a prefabricated grid-reinforced ultra-high performance concrete (UHPC) stay-in-place (SIP) formwork and post-cast concrete. Eight specimens, including six composite columns and two reinforced concrete columns were tested. The test variables included the type and number of grid layers as well as the thickness of UHPC formwork. According to the test results, the composite columns showed both higher axial load carrying capacity and elastic modulus, whereas the brittle nature of UHPC caused a decrease in ductility and toughness. The use of carbon fiber reinforced polymer (CFRP) grid could provide a more sufficient lateral confinement than stainless steel (SS) grid to achieve a strain hardening behavior and thus increased the ductility and toughness of the specimens. The use of more layers of SS grids could also have a positive effects on brittleness reduction. Furthermore, an analytical model was developed using a finite element (FE) program to simulate axial compressive response of the column. The whole failure process of the composite column and almost all the key characteristics of the load-strain curves were reasonably captured, and a good agreement was found between the calculated and measured load-strain curves, indicating the capability of the proposed FE model to predict the axial compressive behavior of the composite columns.

A modified model for predicting cyclic stress–strain relationship of fiber reinforced polymer grid reinforced engineered cementitious composites

AbstractTo verify the universality of the cycling model of carbon fiber reinforced polymer (CFRP) grid reinforced engineered cementitious composite (CFRP‐ECC) material, a complementary experiment was carried out to investigate the cycling behavior of basalt fiber reinforced polymer (BFRP) grid reinforced ECC (BFRP‐ECC) composite material using both traditional measurement and digital image correlation system. Elastic modulus, layers, and surface treatment of BFRP grid and the loading schemes were considered as the major variables in the experiment. Compared with the CFRP‐ECC, BFRP‐ECC had better ultimate and residual deformation capabilities. Test results also showed that the effective strain of the internal BFRP grid reached 80–90% of the ultimate material strain, therefore, higher loading capacity of BFRP‐ECC material was obtained. A unified model was proposed to analyze the cyclic stress–strain behavior for both BFRP‐ECC and CFRP‐ECC materials. The validation of the analysis model was verified through comparisons between the predicted values and the test results.

Experimental study and modeling of bond of carbon-fiber-reinforced polymer grids to polymer mortar at room and elevated temperatures

Carbon-fiber-reinforced polymer grids encased with polymer mortar have received much attention lately as an effective technology for strengthening concrete structures. The objective of this study was to investigate the bond-slip behavior of carbon-fiber-reinforced polymer grids to polymer mortar at room and elevated temperatures. First, 20 pull-out specimens were tested at room temperature of 20°C, and the investigated parameters included the type of carbon-fiber-reinforced polymer grids, the embedment length of longitudinal bar, and the transverse bar length. Based on the experimental results, a two-branch bond-slip model at room temperature was proposed, with the characteristic bond stress and the corresponding slip determined by the regression analysis of test data. Second, 24 pull-out specimens were tested at elevated temperatures over a range of 20°C–300°C, and the investigated parameters included the type of carbon-fiber-reinforced polymer grids and the testing temperature. Based on the experimental results, a bond-slip model at elevated temperatures was further proposed by modeling the temperature-dependent reduction factors. The two proposed bond-slip models will be particularly useful in the theoretical analysis of structures with carbon-fiber-reinforced polymer grids and polymer mortar strengthening system under both room and elevated temperatures.

Effect of an acidic environment on a glass fibre reinforced polymer grid

The article deals with the effect of an acidic environment on the mechanical properties of a Glass Fibre Reinforced Polymer (GFRP) grid. GFRP composites are prone to the absorption of surrounding media which are either of a liquid or gaseous state, and this may result in the degradation of their mechanical properties. The effect of an acidic environment is examined on specimens cut from a GFRP grid. The specimens were stored in an acidic bath (pH scale 2 – 2.5) for a period of 0 (reference specimen), 1000, 2000 and 6000 hours. The temperature of the acidic bath was 60°C. The specimens were then tested using three‒point bending and the interlamination shear strength test. During the tests, the load and deformation of the specimens were monitored and flexural strength instead and modulus of elasticity were determined. The characteristics of the specimens exposed to the acidic environment were compared with those of the reference specimen. The experiment demonstrated the effect an acidic environment can have on the properties of GFRP material.

Experimental Investigation of the Fatigue Behavior of Basalt Fiber Reinforced Polymer Grid‐Concrete Interface

Fatigue behavior is an important factor for mechanical analysis of concrete members reinforced by basalt fiber reinforced polymer (BFRP) grid and polymer cement mortar (PCM) and plays a critical role in ensuring the safety of reinforced concrete bridges and other structures. In this study, on the basis of the static loading test results of concrete specimens reinforced by BFRP grid and PCM, a series of fatigue tests with different loading levels were conducted on interfaces between BFRP grid and concrete to investigate the fatigue behavior of BFRP grid‐concrete interfaces. The test results indicate that with high loading level, the fatigue failure mode of interface is interfacial peeling failure while it transforms to the fatigue fracture of the BFRP grid under low loading level. The fatigue life (S-N) curves of BFRP grid‐concrete interface are obtained and fitted in stages according to different failure modes, and the critical point of the two failure modes is pointed out. The relative slip evolution of interface during fatigue is further revealed in different stages with two failure modes, and the law of interface strain is studied with the increase of fatigue times. The relation of effective bonding length of interface and fatigue times is also described.

Изучение активности полимеро-ферментных комплексов на основе пероксидазы

The work is devoted to the study of methods of immobilization of peroxidase (KF 1.11.1.7) in the polymer matrix of acetylcellulose and polyacrylamide, as well as in the gel structure of polyvinylpyrolidone. Modifying agents were used to efficiently incorporate the enzyme into the polymer grid. such as chitosan, glutaric dialdehyde. 2,2-Azino-bis-(3-ethylbenzthyosoline-6-sulfonic acids) diammonium salt (ABTS) was used as a substrate in the study of the activity of the immobilized enzyme obtained. Experimental data showed a high activity of the enzyme included in the matrix of polyvinylpyrrolidone: the degree of binding was 85%, the activity expressed by the Michaelis constant Km=14×10−3 mmol/L. The results obtained allow us to recommend the use of enzymes immobilized in polymer matrices of polyvinylpyrrolidone, acetylcellulose, polyacrylamide to create highly sensitive electrodes.

Polycatenation and self-penetration in nitrobenzene-detecting zinc and cadmium 4-carboxylatomethylbenzoate coordination polymers with dipyridylurea coligands

Hydrothermal reaction of zinc or cadmium nitrate, 4-(carboxylatomethyl)benzoic acid (cmbH2), and bis-(4-pyridyl)urea (bpu) generated a pair of coordination polymers that were isolated and subsequently structurally characterized by single-crystal X-ray diffraction. {[Zn2(cmb)2(bpu)2]·2H2O}n (1) shows a 2D + 2D → 3D parallel polycatenated pattern of sawtooth (4,4) coordination polymer grids. In contrast, {[Cd3(cmb)3(bpu)2(H2O)4]·3H2O}n (2) manifests [Cd3(cmb)3(H2O)4]n slab motifs threaded and linked by bpu ligands into an unprecedented self-penetrated 3,3,4,4-connected 3D network with (6·7·8)(627)(627·83)(7383) topology. Thermal decomposition of the new phases is discussed. Both 1 and 2 underwent visible light luminescence upon ultraviolet irradiation, and acted as luminescent “turn-off” sensors for nitrobenzene absorption in ethanol suspension.

Composite Polymer Mesh For Masonry

With the development and introduction of technologies for the production of composite materials for construction purposes in Russia appeared composite flexible ties, anchors, fittings, etc. These materials and products are not fundamentally new and have previously been studied for use for reinforcing concrete or structural elements. However, for increasing the bearing capacity of stone structures as masonry meshes they were practically not used, while masonry mesh is one of the most demanded materials in construction. The article presents experimental studies of composite meshes of different types and performance technology used in masonry. Experimentally substantiated and normalized values of physical and mechanical characteristics of rods for composite polymer grids are obtained. The evaluation of efficiency of composite meshes in masonry is made, the values of crack forming and rupture loads are determined, the peculiarities of the stress-strain state of composite grids as flexible ties are revealed, the fields of application are formulated.

Optimal seismic retrofitting techniques for URM school buildings located in the southwestern Iberian peninsula.

This paper aims to study different seismic retrofitting techniques to test the reduction of the seismic vulnerability of unreinforced masonry buildings. Three techniques have been considered in a case study: adding steel or carbon fibre reinforced polymer grids in the walls and steel encirclements in the openings. The performance-based method has been used to that purpose. Nonlinear static analyses have been performed to obtain the capacity and fragility curves, the performance point and the damage level states. Moreover, an analysis of the cost-benefit ratio has been carried out. Results have shown that the three techniques have produced considerable improvements. The addition of encirclements has reduced the deformation resulting in a slight increase of the structure’s stiffness. Adding steel grids has produced the maximum peak strength increase while adding polymer grids has produced the largest ultimate displacements. Adding encirclement has had the best cost-benefit ratio.

Oxygen Barrier Composite Membrane for Li-Air Battery Using Cuboid LiAlTiPO4 in Orthogonal Array

The Li-Air batteries which convert the electrochemical reactions of lithium and O2 into electrical energy have high theoretical gravimetric capacity (3861 mAh/gLi) that is ten times higher than that of lithium ion batteries (372 mAh/gc). Its potential to generate high energy density makes it a promising candidate to replace the lithium ion in the electric vehicle applications. To meet the requirements of the electric vehicle applications, the technical barriers that limit the cycle life such as oxygen permeation, electrolyte and cathode instability and low rate capability need to be overcome. Especially the consumption/de-activation of Li metal is accelerated when oxygen in cathode side moves into Li metal side through the electrolyte, which is one of the most significant factors preventing long-term operation of the system. Ceramic solid state electrolyte (SSE) separator has a remarkable gas blocking capability, but it should be thick and heavy (~0.3 mm) to be used as a gas barrier of Li-Air battery due to fragile property. This leads to a sharp decrease in energy density. We fabricated composite membrane consisting of micron-sized SSE particles arrayed in matrix shape and polymer grid. Here SSE particles and polymer have functions of lithium ion conduction and gas blocking, respectively. Cuboid particles were synthesized using silicon wafer template with cuboid pattern on it in size of 50 ~ 200um. Interface energy between particle and polymer was controlled by bimodal surface modification for better mechanical strength of membrane. Compared to amorphous particles, composite membrane using cuboid LATP particle has many benefits in high ionic conductivity, uniform thickness, light weight and flexibility. In this presentation, how to fabricate cuboid SSE particles in matrix shape array and characterization of composite membrane using it will be discussed.

Composite behaviour of fibre-reinforced concrete sandwich panels with FRP shear connectors

The flexural behaviour of a precast concrete sandwich panel constructed of high performance fibre reinforced concrete wythes and foam insulation, connected together with carbon fibre reinforced polymer grid connectors, is investigated in this paper. This study tests and analyses the thin concrete cladding system which omits conventional steel reinforcement, the use of which requires concrete cover to the reinforcement layer that typically dictates the minimum thickness of the concrete wythes. A total of four full height panels are constructed in a precast concrete facility and are tested by way of three point bending. To complement the experimental study, finite element analysis is used to better understand the bending behaviour beyond what was discerned from the results obtained through experimentation. The experimental results showed that the thin concrete sandwich panel is a plausible solution for precast cladding systems with ultimate moment capacities in excess of those required to meet design wind loads. Ductile behaviour was observed in all of the four tested panels as a result of the high dosage of small 24 mm coated glass fibres used in the mix design for the concrete wythes. The experimental results showed no evidence of the FRP grid connector providing any significant degree of composite action. Finite element analysis suggests that this is due to, one or a combination of, the insulation′s stiffness being too low or because the tensile members in the grid connector being under an initial compressive strain and not fully engaged during initial loading.