Permanent Formwork Research Articles

Interfacial bonding properties of 3D printed permanent formwork with the post-casted concrete

The rapid construction of prefabricated components of reinforced concrete structures using 3D printing concrete as a permanent formwork is a promising way to organically combine 3D printing with traditional construction technology. The bonding property of the contact interface between the 3D-printed permanent formwork and internal post-cast concrete is crucial for the 3D-printed structure to maintain the overall mechanical performance. In this study, the roughness of 3D-printed formwork (10 mm, 15 mm, 20 mm) and the age difference between the formwork and post-cast concrete (1 d, 3 d, 7 d, and 14 d) were set as variables to investigate their influence on the interfacial tensile and shearing bonding properties. Additionally, computerised tomography (CT) scanning was used to visualise the meso-structure of the interfacial zones and the pore characteristics were quantified. The microstructure and hydration products of the bonding interface were detected, and the gradient structure of the interface transition zone of the 3D printing formwork was presented. A plastic limit analytical mechanical model of the interfacial shear strength was established. The results show that the tensile and shear properties of the bonding interface were the best when the layer height of the printing formwork was 20 mm, and it is recommended to cast internal concrete materials after 7 d of 3D printing formwork moulding.

Experimental and analytical investigation of UHPC confined concrete behavior

Ultra-High Performance Concrete (UHPC) is a self-levelling cementitious material with enhanced mechanical and durability properties when compared to normal strength concrete. Accelerated construction of concrete columns can be realized using a precast hollow UHPC shell as permanent formwork. Also, as a retrofit solution, UHPC can be placed around existing concrete columns with deficient confinement details. The continuous confinement provided by UHPC shell to both the concrete core and longitudinal reinforcement could be used to improve the seismic behavior of columns or reduce the amount of confining hoop reinforcement required in traditional column designs. An experimental and analytical study is performed with a main objective of quantifying the confinement effect provided by plain UHPC shell. The experimental investigation compressed of axial testing of 228 mm (9 in.) and 280 mm (11 in.) dia circular columns, 203 mm (8 in.) and 305 mm (12 in.) square columns confined with UHPC shell. Experimental investigation included a total of two normal strength concrete column specimens as control specimens and 11 column specimens confined with 1 in. and 2 in. thick UHPC shell. All the specimens were tested to failure under axial compression and were extensively instrumented. The confinement provided by the unreinforced UHPC shell improved the peak compressive stress and the crushing strain values of the core concrete by 15%–30% and 26%–46% respectively. The effectiveness of plain UHPC shell to provide confinement was found to considerable in circular columns compared square columns. A detailed 3D FEA models were developed in ATENA software and were validated using the experimental data. The FEA models captured observed responses accurately and provided insight into the observed experimental behavior. Based on the experimental and analytical study, it is recommended to include some transverse reinforcement in UHPC shells, especially for non-circular cross-section for improved confinement effect.

Novel FRP micro-bar reinforced UHPC permanent formwork for circular columns: Concept and compressive behavior

In this study, a novel form of tubular permanent formwork that is made of ultra-high-performance concrete (UHPC) internally reinforced with fiber-reinforced polymer (FRP) micro-bars (herein referred to as FRP-UHPC tubular permanent formwork or simply FRP-UHPC tubular column) is developed. The axial compression test results of FRP-UHPC tubular columns with and without in-filled concrete are presented and discussed. Effects of the FRP micro-bar spiral pitch, the steel fiber addition in the UHPC, the tube thickness and the presence of external FRP confinment are investigated. The test results confirmed that the FRP-UHPC tubular columns have an excellent compressive strength, and the strength and ductility of existing concrete columns jacketed with an FRP-UHPC composite tube are substantially enhanced due to the confinement and axial contribution of the FRP-UHPC tube. The proposed FRP micro-bar-reinforced UHPC composite tubes are attractive in structural applications as pipelines or permanent formworks for columns, as well as external jackets (can be prefabricated in the form of two halves of composites tubes) for strengthening deteriorated reinforced concrete columns.

Longitudinal shear bond strength of profiled deck composite slab: An experimental and analytical investigation

In recent years, composite slabs with concrete topping and profiled/ re-entrant decking sheets have gained popularity as they are faster, more economical, and lightweight construction techniques. In a composite floor, profiled/re-entrant decking sheets serve a dual purpose: they serve as permanent formwork during the construction phase and as main reinforcement after the concrete topping has hardened. Horizontal shear bond strength is a crucial parameter in the design of the composite floor. Presently, the m-k and PSC methods are the most commonly used techniques to calculate the horizontal shear bond strength of the composite slab. In this study, four full-scale composite slabs were cast and tested for four distinct shear spans under four-point loading conditions. The influence of shear span was investigated. Short and long shear span specimens were investigated. Three alternative approaches (the modified partial shear connection method, the force equilibrium method, and the composite beam partial shear connection method) were adopted to evaluate the horizontal shear bond strength of the profiled deck composite slab. Load- displacement behavior, horizontal shear bond strength, and failure modes were used to assess the structural performance of composite slab specimens. The results of all three methods were compared. The horizontal shear bond stress evaluated by the slenderness and force equilibrium methods were in close agreement, whereas the composite beam partial shear connection method approach may underestimate the longitudinal shear bond strength, but it may still be employed as an alternative method.

Performance Evaluation of Reinforced Concrete Beam with 3d-Printed Permanent Formwork

Performance Evaluation of Reinforced Concrete Beam with 3d-Printed Permanent Formwork

Compressive Behavior of FRP Grid-Reinforced UHPC Tubular Columns.

In this study, a novel form of tubular columns that is made of ultra-high-performance concrete (UHPC) internally reinforced with fiber-reinforced polymer (FRP) grid (herein referred to as FRP grid-UHPC tubular column) was developed. The axial compression test results of FRP grid-UHPC tubular columns with and without in-filled concrete are presented and discussed. Effects of the number of the FRP grid-reinforcing cages, the presence of in-filled concrete, and the presence of external FRP confinement were investigated. The test results confirmed that the FRP-UHPC tubular columns have a satisfactory compressive strength, and the strength and ductility of FRP-confined concrete-filled FRP grid-UHPC tube columns are enhanced due to the confinement from the FRP wrap. The proposed FRP grid-reinforced UHPC composite tubes are attractive in structural applications as pipelines or permanent formworks for columns, as well as external jackets (can be prefabricated in the form of two halves of tubes) for strengthening deteriorated reinforced concrete columns.

Seismic performance of PVA textile cementitious composites used as permanent formwork in full-scale circular RC columns

The strength, stiffness and ductility capacity of structural systems must be protected under seismic effects. In the presence of lateral reinforcement, the confinement effect provides these critical properties to reinforced concrete (RC) structures. Textile reinforced cementitious composites (TRCC) have very good tensile, flexural and long-term performance. The effect of confinement will occur in RC columns by using these multilayer composites as permanent formwork. In addition, thanks to the permanent formworks, the service life will be extended against the drawbacks of structural defects. In this study, TRCC circular permanent formworks were manufactured by using a newly developed PPR (Pull-Pour-Roll) technique and machine. A cementitious mortar was designed and 4 & 6 layers of PVA textile were selected for the production of composite permanent formworks. The most important feature of permanent formworks is that they are hollow, thin sectioned and three-dimensional structural elements. Four full-scale circular column specimens were tested in the laboratory under the combination of constant axial load and reversed cyclic lateral load. Two of the columns were constructed as permanent formwork, while others were reference specimens built by temporary formworks. Composite formwork columns and one of the reference specimens include insufficient lateral reinforcement whereas the other reference column has adequate lateral reinforcement. This study was conducted to evaluate the effects of TRCC permanent and conventional temporary formworks in RC columns on key parameters of confinement. These parameters are respectively the hysteretic response, strength, displacement ductility, stiffness degradation, energy absorption capacity, damping ratio, residual displacement, crack pattern and failure mechanism. Extensive experimental studies have shown that the lateral load capacities, ductility, initial stiffness and energy dissipation in composite formwork columns have increased considerably compared to conventional columns. Thus, the TRCC permanent formwork increases the efficiency of confinement. Consequently, there is a great potential for use of TRCC permanent formworks as an alternative for conventional formworks in the RC columns.

PIPE-CONCRETE CENTRALLY-LOADED SUB-COLUMN OF A STEEL COLUMN FOUNDATION

A new progressive solution is considered, which consists in improving the design and static calculation of the strength of the elements of the sub-column part of a pipe-concrete foundation, in simplifying the design of a sub-column made of structural concrete of increased and high strength and a thin-walled metal pipe, using it in the form of a permanent formwork as a working element of a composite structure, in reduction of labor intensity and terms of performance of works of the zero cycle. An algorithm is proposed for designing elements of a precast-monolithic reinforced concrete foundation for a column, including a pipe-concrete sub-column, its fl ange connection with a steel column from above and with a foundation slab from below. Thin-walled pipe metal is an economical casing for in-situ concrete.

Numerical study on seismic performance improvement of composite wide beam-column interior joints

This study aims to improve the seismic performance of a post-tensioned precast wide U beam-column interior joint system, consisting of a precast column, a precast wide U beam as permanent formwork with post-tensioned and cast-in-situ concrete in the joint region, through a numerical approach. The numerical model was verified by simulating a tested half-scale precast wide U beam-column interior joint (PWUBCIJ) system. After the methodological validation, numerical analyses were performed for full-scale and modified wide beam-column joints subjected to lateral cyclic loading. The modified joint models were developed to eradicate or delay diagonal shear cracks and concrete crushing of the tested control specimen. Since the wide precast U beam-column joint system possesses typical and unique joint details, improvement in reinforcement detailing was performed by varying reinforcement patterns. Moreover, a study to reduce the number of A-truss rows was performed to optimize the numbers of A-trusses used. Therefore, a series of FE analyses are performed to elucidate the contribution of each parameter in enhancing the joint strength and drift capacity of the structure. Enhanced load capacity, increased energy dissipation, and higher ductility are achieved using transverse reinforcement and transverse tendons. This is considered due to the formation of the strut-and-tie mechanism, which results in a better force and moment transfer path and from the overall confinement of the system due to the presence of transverse steel and prestressing tendon. As per numerical results, the modified full-scale precast wide U beam-column interior joint was proved to be able for application in the highest seismic zone of Thailand.

Manufacturing of fiber-reinforced concrete bridge arches

Objective. A new method of manufacturing arches for a fiber-reinforced concrete bridge in the form of an analogue of permanent formwork is considered. Within the framework of this work, research results have been obtained that confirm the effectiveness of the system for the construction of bridge arches of various configurations.Method. The proposed developments will improve the strength characteristics of the bridge arch for small and medium bridges by optimizing the shape and size of the cross section in accordance with the change in the bending moment along the length of the arch. At the same time, reduce its metal consumption by several times.Result. The results obtained confirmed the effectiveness of electrostatic spraying of dry concrete mixture with simultaneous moisture up to moisture, which contributes to the work of capillary forces for compaction of concrete layers and the manufacture of a profiled strong shell (analogue of non-removable reinforced formwork) from reinforced fiber-reinforced concrete.Conclusion. By varying the shape and dimensions of the cross- section, the thickness of the shell and the degree of its reinforcement, as well as filling this shell with high-strength fiber-reinforced concrete, it is possible to design and manufacture bridge arches for various loads.

Application of pre-fabricated geopolymer permanent formworks (PGPFs): A novel approach to provide durability and mechanical strength of reinforced concrete

Permanent formworks (PFs) are elements which remain after construction for various applications including improving strength parameters or thermal and acoustic insulation. In aggressive coastal environments, the quality of concrete may decrease due to difficult operating conditions. In this research, a novel application of PFs for enhancing the durability of concrete structures is discussed.To begin with, important evaluation criteria were set for the PFs. Thanks to the desirable properties, a suitable geopolymer mixture was selected to make PFs. Hence, mechanical and durability performance of the samples were examined by several experiments. Subsequently, the connection means between the formwork and the substrate (conventional concrete) were studied by pull-off and Bi-surface experiments. In this way, various treatments were carried out on the surface of the PFs to ensure a suitable bond in the joints. At last, boundary between the PFs was found as a threat to the penetration of chloride ions. So that, different adhesives were applied to seal the PFs borders to finally suggest the desired option.The findings of this study indicate that the approach of using prefabricated PFs can be effective in ensuring the durability of reinforced concrete structures, especially against chloride ions penetration. The mechanical properties of the structure can also be improved with the help of PFs. The use of polyurethane mastic is recommended to protect the seam between the PFs and also the surfaces indentation through a (square) lattice as well as ridging the squares are suggested options for better connection of PFs to the substrate.

Experimental investigation on concrete-filled corrugated steel tubular column under constant axial load and cyclic load

Concrete-filled corrugated steel tubular (CFCST) structure is a novel composite member with significant potential serving as an offshore bridge pier or a sub-sea underground column. The anti-corrosive galvanized corrugated steel tube (CST) is versatilely utilized as a peripheral protecting shell, an external restraint material for the concrete, and a permanent formwork. A considerable body of preliminary experimental and numerical work has been conducted on the static performance of CFCST, however the investigations of its seismic behaviour are rather limited. This paper therefore presents experimental investigations on CFCST columns subjected to constant axial load and cyclic load. The designs and fabrications of the test setup are introduced in detail. With the discussion of failure modes, hysteretic curves, ductility, energy dissipation capacity, and stiffness degradation, the seismic behaviour of CFCST are studied comparatively. The test results indicate that the seismic behaviour of CFCST is more competitive than that of conventional RC columns while similar to those of TRC columns. With the increase of axial compression ratio, the lateral load was increased but the deformability was reduced. Both the strength and ductility of CFCST can be improved with the increase of confinement factor. The analysis of non-uniformly distributed strain of CST indicates that the loading paths do not affect the work mechanism of CST. The CST mainly provides transverse confinement and its contribution to flexural capacity was negligible. The modified equations can be roughly employed to predict the N-M interaction relationships of the CFCST columns. More experimental or numerical work should be conducted in the future to further evaluate the seismic behaviour of CFCST quantitatively.

Research on the mechanical properties of assembled TRC permanent formwork composite columns

To further promote the prefabricated development of textile-reinforced concrete (TRC) permanent formworks, in this paper, the effects of TRC formwork form, assembly method and assembly direction on the mechanical properties of composite columns with TRC permanent formworks are studied by performing axial compression tests. The results show that the failure of these composite columns is divided into three typical failure modes, namely, corner fracture failure, bolt hole shear failure, and splicing joint crack failure. Compared with plain concrete columns, TRC permanent formwork composite columns can better control the development of cracks and improve the crack development mode under compression. A comparison of different forms of TRC formworks shows that the ultimate bearing capacity of a composite column with flat-plate TRC formworks is higher than that of composite columns with L-shaped formworks. Compared with other assembly methods, the composite column with a bolt, angle steel and high-strength nonshrinkage grouting material achieves the maximum ultimate bearing capacity. Furthermore, the bearing capacity of the composite column with the TRC formwork assembled in two directions is weaker than that of the composite column with the TRC formwork assembled in only one direction. Finally, by analyzing the bearing mechanism of the TRC permanent formwork composite column, the calculation model of the ultimate bearing capacity of the composite column is obtained, and the calculated value is in good agreement with the test value.

Study on Permanent Thermal Insulation Formwork of Mass Concrete Prepared by Different Types of Nano-modified Lightweight Aggregate

Aiming at the problems of low strength, flammability, easy falling off, and aging of traditional organic thermal insulation materials, inorganic thermal insulation materials of different types of nano-modified lightweight aggregates were prepared in this paper. The feasibility of preparing permanent thermal insulation formwork of mass concrete with nano-modified lightweight aggregate was studied through experiments and calculation analysis of mechanical, durability, and thermal properties. The results show that the water absorption of shale ceramsite modified by nano-permeable hydrophobic agent is reduced to 1.21%, and the water absorption rate of inorganic precast hollow aggregate produced by nano-silica powder is lower, which is 0.79%. Inorganic precast hollow aggregate concrete, modified shale ceramsite concrete, and organic foamed aggregate concrete have the characteristics of high strength, fire resistance, aging resistance and low thermal conductivity. Inorganic precast hollow aggregate concrete and modified shale ceramsite concrete have excellent impermeability and frost resistance. Organic foamed aggregate concrete has the lowest thermal conductivity and good thermal insulation effect and its durability can be improved by surface protection technology. According to the principle of equivalent surface heat release coefficient, it is feasible to use lightweight aggregate precast formwork as permanent insulation formwork of mass concrete with thickness between 50 and 100 cm. The permanent thermal insulation formwork of nano-modified lightweight aggregate concrete can also be used as the formwork for concrete construction to realize the temperature control measures of tracking thermal insulation and slow cooling of mass concrete, reduce the risk of cracking, and improve the construction efficiency.

Reinforced concrete structural elements cast into wood-chip cement formworks subjected to compression and out-of-plane bending

The mechanical response of reinforced concrete walls cast into permanent woodchip-cement formworks and subjected to eccentric compression has been assessed with experimental tests of full-scale panels and an analytical approach has been proposed. The load-bearing capacity of the wall panel is assured by the inner reinforced concrete grid structure, composed of vertical columns and horizontal ribs, reinforced with vertical and horizontal steel bars. The experimental specimens were realized varying the concrete cross-section and tested varying the eccentricity of the applied vertical load. Both reinforced and non-reinforced panels were tested. An analytical model is proposed to evaluate the load-bearing capacity, based on dimensionless curves, which provide reduction coefficients of strength based on eccentricity and slenderness, considering second-order effects. The analytical model demonstrates a reliable prediction of the experimental peak loads.

Experimental investigation on interface shear strength of composite PVC encased macro-synthetic fibre reinforced concrete walls

Over the past decade, Polyvinyl Chloride (PVC) stay-in-place formwork has become a popular alternative for conventional formwork in concrete construction industry due to its relatively lower cost of construction and ease of assembly. The PVC panels are joined using connectors and serve as a permanent formwork into which fresh concrete is poured to form composite PVC encased concrete walls. This study has experimentally investigated the effects of using macro-synthetic fibre reinforced concrete on the interface shear strength of composite PVC encased walls in comparison with composite PVC encased walls filled with conventional plain concrete and reinforced concrete. Nine composite PVC encased concrete wall specimens were cast and tested using direct shear tests. Based on the load–deflection curves obtained from the direct shear tests, the maximum shear loads and interface shear strength values were determined for three different cases including i) test specimens filled with plain concrete, ii) test specimens filled with macro-synthetic fibre reinforced concrete, and iii) test specimens filled with reinforced concrete. The determined parameters as well as the measured load–deflection curves for the three cases were compared and the final findings have been discussed. Based on the outcomes of this study, it has become apparent that the tested composite PVC encased macro-synthetic fibre reinforced concrete wall specimens can noticeably exhibit higher interface shear strength values compared to the tested wall specimens filled with plain concrete. Since AS 3600 (2018) does not prescribe the shear plane surface coefficients for determining the interface shear strength of composite PVC encased concrete walls, in order to enable structural designers to determine the interface shear strength for those panels using AS 3600 (2018), those coefficients have been extracted from the test results for the three mentioned cases and proposed for practical applications.

Harnessing 3D Printing of Plastics in Construction-Opportunities and Limitations.

Additive manufacturing has been of increasing interest to the construction industry for the last ten years. The subject of the research is the printing of concrete, metals, and plastics. In their analysis and research, authors have focused on printing plastics. 3D printing of reinforcement of concrete elements made of plastics can significantly improve the efficiency of their erection, reduce the amount of waste, and optimize their shape. In this paper, recent developments in the 3D printing of plastics for construction are reviewed. Various applications were discussed, including unconventional spatial reinforcement (impossible to achieve in a traditional way), printed permanent formwork, etc. The challenges for further research and practical applications of such solutions were also discussed.

Experimental and analytical models of flexural behavior of U-shaped reactive powder concrete permanent beam formworks

The primary purpose of this study was to analyze the application of reactive powder concrete (RPC) in U-shaped permanent beam formworks. Experiments were conducted to investigate the mechanical (compression and tensile) properties of RPC and the flexural capacity of permanent formworks. Six U-shaped permanent beam formworks were tested under four-point flexural loading until failure. Additional parameters such as side wall thickness, bottom board thickness, and the reinforcement ratio were analyzed to investigate the flexural behavior of the formworks before pouring. The moment capacity, load-deformation curve, and failure process and mode of the specimens were examined. All the specimens failed the flexural test and exhibited a bending failure mode similar to that of concrete beams. The test results revealed that increasing the thickness of the bottom board of the U-shaped RPC permanent formwork was effective in delaying the cracking moment of the U-shaped formwork. We created analytical models to calculate the cracking moment of U-shaped RPC permanent beam formworks. A comparison of the analytical and experimental results revealed that our simplified analytical model predicts the experimental results better than existing models do.

Experimental testing of a composite structural system using tile vaults as integrated formwork for reinforced concrete

Tile vaults are unreinforced masonry structures made of thin bricks (tiles) and fast-setting mortar that can be constructed without the need of a formwork, except at the boundaries, making them inherently economic. Their slenderness and finishing make them also efficient and expressive. These qualities of tile vaulting can be enhanced by combining it with reinforced concrete creating a new composite system. The tile vault can be integrated in the final solution, as a permanent formwork, reducing construction costs and waste. A top layer of reinforced concrete rises up the strength of the composite system, whereas reinforcement reduces the thickness and opens the possibility to build structures with a formal language well beyond what is typically associated with masonry architecture. Therefore, several advantages make the system competitive compared to traditional reinforced concrete shells. This paper presents experimental research on the materials of this composite system and load tests on composite barrel vaults. The construction of full-scale prototypes has allowed a critical review of the construction process and has demonstrated the feasibility of the technique and its successful structural performance. Moreover, the analysis of this composite structures is carried out using Extended Limit Analysis of Reinforced Masonry (ELARM), provided that the reinforcement guarantees sufficient ductility. Furthermore, the data collected from the experimental research becomes a benchmark for the calibration of eventual further structural models.

A new calculation method for the temperature of the components of composite slabs under fire

Composite steel-concrete slabs are structural elements composed of a profiled steel deck which acts as a permanent formwork to the concrete topping. This layer is commonly reinforced with individual rebars and an anti-crack mesh. The Annex D of the EN 1994-1-2 provides guidelines for the calculation of the temperature of the steel components of composite slabs subjected to the standard fire. However, no revisions were made to these calculation rules during the last years. This paper proposes a new method for the estimation of the temperature of the parts of the steel deck and the rebars as well. The proposed methodology is derived from numerical analyses using a 3-D finite element model, considering perfect thermal contact between the materials.