Formwork Surfaces Research Articles

Flexural behavior and numerical simulation of reinforced concrete beams with a UHPC stay-in-place formwork

To overcome the shortcomings of traditional concrete structures such as long construction cycle, high construction cost and poor durability, seven composite beams with a UHPC stay-in-place formwork (UCB) and one reinforced concrete (RC) beam were designed. An experimental study was conducted to investigate the flexural behavior of composite beams under the static load. The research parameters include formwork thickness, reinforcement rate, and formwork surface treatment. The results revealed that roughening the surface of UHPC formwork has a positive impact on enhancing the integrity of composite beams. The utilization of UHPC stay-in-place formwork can effectively improve the stiffness, cracking load, and peak load of members. Compared with that of the RC beam, the cracking load and peak load of composite beams increased by 63% ~ 103% and 6% ~ 15%, respectively, and the yielding stiffness increased by 23% ~ 41%. Different from the RC beam, new cracks occurred on one side of the initial crack's end and continued to extend upwards rather than along the original crack. The existence of a significant quantity of tiny cracks in composite beams effectively slowed down the increase in the width of pre-existing cracks in the early stage of loading. Due to the multi-crack pattern exhibited by the UHPC formwork, the strain concentration of the steel bars was effectively mitigated. When subjected to the same load level, the strain of the longitudinal steel bars in composite beams was smaller than that of the RC beam. The formula for calculating the flexural bearing capacity of composite beams is established through theoretical analysis. In addition, the numerical model of the composite beam is established by the finite element method (FEM). The influence of the contact method of the UHPC-NC interface on the flexural performance of the composite beam is explored. The supplementary analysis of the parametric study of the reinforcement rate and the UHPC formwork thickness is carried out. When using ABAQUS for the numerical analysis of the composite beam, it is appropriate to adopt the cohesion model or the Tie model for the UHPC-NC interface, and it is not appropriate to use the Coulomb friction model.

Effect of typical formworks and release agents on aesthetical surface quality of concrete

This work involved investigating formwork surface characteristics and concrete surface quality. The results show that release agent types and formwork materials have a great impact on the wettability of a formwork–concrete interface, although all the formwork surfaces, with or without release agents, are hydrophilic. Remarkably, inhomogeneous roughness characteristics are only observed for a steel formwork. Plywood and steel formworks have almost the same roughnesses; however, the roughness profile of plywood is sharper than that of steel. Mineral oil always correlates with larger surface voids and higher surface void ratios (SVRs). Steel formworks significantly increase SVR, compared with plywood and plastics formworks. When SVR < 1‰ and the proportion of small voids (<500 μm) > 50%, the concrete surface appears to be bughole-free. Rusty stains left by a steel formwork aggravate concrete discoloration, especially when water-soluble release agents are applied. To improve concrete surface quality, plywood formwork is more favourable, although release agents and vegetable-oil-based emulsion are more suitable for plastics formworks. The surface area roughness of concretes is mainly determined by that of formworks. The typical microgroove feature on a formwork surface leaves no trace on the formed concrete surface; this might be owing to the difference in dimension between microgrooves and cement particles and the presence of release agents.

Circular, zero waste formwork - Sustainable and reusable systems for complex concrete elements

The construction sector contributes significantly to global carbon emissions, leading to a new need and demand for sustainable and material-efficient construction technologies. Digital form-finding, simulation, and optimization methods are advancing, resulting in highly efficient, but often geometrically complex components. Concrete construction, which is currently dominant worldwide and crucial for sustainable material savings due to its large market volume, still faces challenges in implementing complex geometries. The significant requirements for formwork material and limitations in feasibility and cost at the current state of the art contribute to these challenges. This research presents a zero waste process using recyclable and reusable digitally fabricated formwork made from waste ingredients that can be immediately implemented in the construction industry. Residual sands (quartz and ceramics) were investigated as a basic moulding material in combination with biogenic binders (bentonite, eco-resin, sodium silicate, starch) for the production of stable formwork composites. The material compound were shaped into precise complex forms using 5-axis milling, and the removed material was recycled in a closed material cycle. Testing and characterization methods for evaluating mechanical properties such as compressive forces (20.1 N/mm2), surface roughness (Ra 9.1 μm), tolerances (0), and moulding processes indicate that the presented procedure conforms to common industry standards. Demonstrating feasibility, complex ultra-thin 1:1 concrete prototypes were designed and manufactured under industrial conditions using prefabricated formworks made of researched bio composite. The resulting high-resolution formwork surfaces and exposed concrete precast elements correspond to the highest fair-faced concrete class (SB04), with line roughness values of Ra 14.4 μm. The developed circulation concept allows reproducibility of different geometries and repeated concreting of formwork moulds. The formwork process is free from harmful additives, enabling recycling through grinding and reintegration into a closed material cycle. Sustainability has been continuously monitored and evaluated through a life cycle assessment. This system utilizes standard machines and offers an accessible and easily integrated approach for a holistic zero waste solution, suitable for efficient industrial applications.

Improvement of the durability of cement-based material through surface modification with nano-engineered releasing agents

• Modified releasing agent with NS/NT to make nano-engineered releasing agent. • NS and NT increased the contact angle of releasing agent and help their adhesion on mold. • Reduction of the surface porosity (within 2 mm thick). • Nano-engineered releasing agent can achieve durable concrete surface. Aggressive substances can gain access to the inner structure of cement-based materials through the surface, resulting in deterioration of the structure. This work developed an effective way of improving the quality of cement-based materials surface by applying nanoSiO 2 -/nanoTiO 2 -engineered releasing agents (nSRa/nTRa) on the formwork surface. Continued with our previous work, the positive effects of nSRa/nTRa on cement hydration were used to improve the surface quality of the cement-based samples through its spraying on the mold surface. This work firstly characterized the adhesive properties of these agents on mold surface (contact angle and viscosity measurement), and then their effects on the surface microstructure and the durability of cement-based materials such as 1) sulfate resistance, 2) chloride resistance, and 3) freeze–thaw resistance were determined. Results showed that nanoparticle addition increased the contact angle of releasing agents and helped their adhesion to mold. Applying nSRa/nTRa on cement-based samples benefited the reduction of surface porosity (within 2 mm thick) by 14.2 %, 19.4 %, 8.6 %, and 18.9 % in the nS2Ra-, nS4Ra-, nT4Ra- and nT16Ra-engineered samples. After 120 days of sulfate attack, mortar samples cast in Ra-, nS4Ra-, and nT16Ra-coated molds showed reductions in compressive strength loss of 1.57 %, 0.73 %, and 0.23 %. Noticeable reductions in the chloride migration coefficient of 23.9 % and 26.6 % were found in the nS4Ra-/nT16Ra-modified mortar sample, while their relative dynamic modulus elasticity was 6.72 % and 12 % higher than Ra-sample after 200 freeze–thaw cycles. This work proved that nano-engineered releasing agents can effectively improve the durability of the concrete structure.

Effect of formwork surface texture features on surface morphology, roughness parameters, and the demolding force of cementitious materials

Effect of formwork surface texture features on surface morphology, roughness parameters, and the demolding force of cementitious materials

콘크리트 양생용 거푸집의 온도분포 최적화를 위한 유도가열 코일 배열 및 배치 비교평가

This paper proposes coil design conditions of a concrete curing system based on induction heating method for efficient concrete curing. The concrete curing method using an induction heating coil has the advantage of low energy consumption by using a high-efficiency system compared to the existing methods that undergoes several stages of energy conversion. When the induction heating coil is used, it is important to obtain uniform temperature surface on the formwork temperature. When a temperature difference occurs in the vertical section of a concrete form due to an uneven temperature distribution during concrete curing, it may cause a decrease in concrete strength. In this paper, in order to efficiently heat the concrete formwork surface, the temperature distribution according to the arrangement of the induction heating coil was analyzed and the current strength flowing through the coil was studied. The design conditions and results of the induction heating coil were presented using FEM simulation to obtain a uniform temperature distribution. Based on the proposed two-turn induction coil, the temperature distribution inside the formwork was analyzed using the distance between the formwork and the coil and the distance between the coil turns as design parameters. In addition, the simulation results were verified through an induction heating experiment using an experimental formwork.

Characterizing tribological behavior of fresh concrete against formwork surfaces

Concrete walls are constructed by pouring fresh concrete in-between formworks. The lifespan of these formworks is limited due to the abrasive nature of concrete. The present work investigates the wear of metallic and polymeric-coated plates in contact with fresh concrete. Two formulations were studied: standard concrete and self-consolidating concrete. A plane-plane tribometer was used to control the fresh concrete friction against the plates. This device reproduces the implementation of concrete in the formwork. Results revealed a Coulomb friction law within the range of tested normal pressures. The friction testing induced changes in the surface topography of the plates. The evolution in topography were associated to two underlying wear mechanisms: a granulate-formwork solid-solid friction and a capillary-dominated friction.

The influence of new and used formwork coated with different release agents on the appearance of the formed concrete surface

The influence of silicon oil and liquid wax based release agents on the formation of surface voids and colour variation in cast-in-place concrete was studied. The performance of the said release agents was compared to conventional release agents based on water-soluble emulsion and mineral oil. In addition, new and used formwork panels made of plywood and steel were used in the research to determine the effect of release agents on contact angle values. The quality of surface finish was evaluated in terms of concrete surface void ratio using the standard image analysis methodology, and in terms of colour variation using a new digital colour reading method. The formed concrete surface category was evaluated according to CIB, ACI, DBV and ÖVBB standards in order to know the applicability limits of liquid wax and silicon oil based release agents. The results revealed that the amount of release agent used and the contact angle values on the facings analysed depend on the formwork surface roughness, i.e. the release agents can lodge inside the formwork surface asperities and trap air bubbles at the formwork/concrete interface. Furthermore, the results showed that plywood coated with silicon oil and liquid wax limited the achievement of the formed concrete surface category that is higher than the surface finish satisfying normal requirements. Steel coated with liquid wax did not produce the formed concrete surface of higher than normal quality either, while the surface voids ratio of concrete cast against steel formwork coated with silicon oil did not satisfy the requirements even of the lowest classification according to ACI, DBV and ÖVBB standards. Colour variation analysis revealed that the formwork with higher absorbing capacity produced a darker colour with visual blackness varying in the range from 45% to 60%, whereas the formwork with low absorbing capacity produced a lighter colour with visual blackness varying in the range from 25% to 35%. Rougher surfaces of the formwork absorb more hydrophilic release agents. This has an effect on concrete surface colour variation and on concrete's hue, mainly on the yellow hue with redness or the green hue with yellowness.

Factors influencing the surface quality of architectural concrete

Architectural concrete has wide opportunities to be used both for exteriors and interiors in different buildings. Architectural concrete is the type of concrete which is usually not subjected to finishing, therefore higher standards are declared for its surface quality. According to normative documents, architectural concrete needs to have a uniform colour tone, texture, minimal defects and porosity of the surface. The present research demonstrates the concrete surface quality obtained in the course of varying different factors such as the presence of stabilizing admixture, granulometry of aggregates, usage of fly ash and workability of the concrete mixture. In the course of the research, the testing of raw materials and concrete in the fresh and hardened state were performed according to standard methodologies. The assessment of concrete surface quality was provided through the analysis of concrete surface photo 50x50 cm size. Based on the experimental results, it can be stated that better quality of the concrete surface was obtained in case of usage of gravel with two fractions of 4/16 and 2/8 and fly ash in the dosage of 25 % cement weight in the presence of plasticizing and stabilizing admixtures. The concrete mixture with high workability showed better filling of formwork and mixture particles packing on the formwork surface which led to a better quality of the concrete surface.

Influence of the formwork removal by polarization on the facing aesthetics in reinforced concrete

Formwork removal by means of polarization offers an alternative solution to compensate for some of the disadvantages and risks of using mineral-based oil due to its petrochemical origin. This technique consists of applying an electrical current between the steel reinforcing bars and the metal formwork wall in order to obtain a thin water film at the concrete/formwork interface and allow for formwork removal. This paper focuses on the facing quality of the reinforced concrete and formwork surface at various temperatures for both conventional and self-compacting concretes. A series of experimental tests have been conducted in the laboratory to determine the optimal polarization parameters (voltage value, time and duration of its application). On-site tests were then performed to observe the scaling effect. Results indicate that the proposed polarization technique can indeed provide an effective means to separate the concrete from its formwork without requiring demoulding oil. Concrete mixtures implemented both in the laboratory and on-site display high-quality facing without the presence of any attachment points. A chromatographic analysis of the concrete pore solution and water transported by electro-osmosis shows that ion concentrations remain unaffected. This polarization approach can thus be used as an alternative to avoid the use of oils of a chemical or petrochemical origin.

Characterization of the surface of formworks – Influence of the surface energy and surface texture parameters on the demolding forces

Adhesion between concrete and formwork is ruled by the chemical and physical phenomena emerging by contact of these two surfaces. The objective of this work is to understand how the adhesion between concrete and formwork is influenced by the morphological and thermodynamic surface properties of the formwork. Different formwork surfaces are considered: metallic with and without demolding agent, polished and coated surfaces. Surface texture parameters and surface energy of these surfaces are determined by interferometry and measurement of contact angle, respectively. A demolding procedure is developed and allows the evaluation of the demolding performances in relation to the formwork surface properties.

Influence of fresh concrete pressure on cover porosity investigated by single-sided proton nuclear magnetic resonance

In this study, single-sided proton nuclear magnetic resonance (1H NMR) was used to quantify the porosity of the concrete cover. Laboratory concrete samples were prepared with different formwork surfaces as well as varying fresh concrete pressures. Furthermore, to separate the influence of aggregates on porosity, hardened cement paste and mortar samples of otherwise similar composition were prepared. All samples were tested with single-sided 1H NMR, allowing depth-resolved porosity profiles of up to 18 mm. Differences in the porosity between hardened cement paste, mortar and concrete samples were primarily assigned to the formation of the interfacial transition zone. In concrete samples, the inhomogeneous distribution of the porous hardened cement paste as well as porosity and pore size variations with concrete depth appear. With increasing fresh concrete pressure, a reduction of porosity in the concrete cover can be observed, especially on surfaces made with controlled permeability formwork.

Quantitative and representative adherence assessment of coated and uncoated concrete-formwork

Nowadays buildings construction is performed by pouring concrete into molds called formworks that are usually prefabricated metallic modules. Defects such as stripping may possibly form during the removal of the formwork if the interfacial bonding between the concrete and the formwork is high. Making use of a new pull-off tensile test designed in our laboratory, a correlation has been established between the formwork surface functional signatures and its adherence propensity to concrete. The originality of this near-to-surface test was to characterize the concrete-to-formwork adherence by measuring the required force to pull the concrete from the formwork surface. The design of the test coupon was validated by finite element analysis that proves the small deformation of the tested formwork specimen under the tensile loading and the homogeneity of the applied tensile stress at the interface. The interfacial bonding to concrete has been compared between bare and coated formwork. Both metallic and polymer coatings have been studied. The analyses of the pull-off test results enabled us to understand the bonding mechanisms at the concrete-coating interfaces. The pull-off tensile test was proven capable of ranking formwork coatings according to their adherence to concrete.

Progress to understand influence of reinforcement density on SCC lateral pressure

In addition to material properties, casting conditions, and formwork characteristics, presence and density of reinforcing bars can play a role on the resulting lateral pressure exerted by self-consolidating concrete (SCC) on formwork system. The effect of density of vertical reinforcement and spacing between reinforcing steel and formwork surface (concrete cover) on SCC lateral pressure were investigated in this study using laboratory-scale columns measuring 1.4 m in height. The effect of casting rate and concrete structural build-up at rest were also considered. A model was proposed to estimate SCC lateral pressure taking into consideration reinforcement density and concrete cover. A 6-m high column cast as part of field experimental study was used to validate the laboratory results. The results showed that the increase in steel reinforcement density placed at relatively small cover of 25 mm can reduce the maximum lateral pressure. At casting depth of 3 m and a concrete cover of 25 mm, increasing the reinforcement density from 0.5 to 4%, can reduce lateral pressure from 4 to 22%. The lateral pressure reduction is less significant when concrete cover increases to 50 mm or at deeper casting depths. A 2–17% pressure reductions for the 50-mm concrete cover, and 1–7% for the 5-m casting depth can be estimated. Based on the obtained results, a factor accounting for lateral pressure reduction due to the inclusion of vertical reinforcement was introduced in the pressure prediction models proposed by Khayat and Omran (State-of-the-art review of form pressure exerted by self-consolidating concrete, 2. http://www.concretesdc.org/projects/SCCreport.htm).

Effect of Formwork Characteristics on SCC Lateral Pressure

Lateral pressure exerted on vertical formwork by fresh self-consolidating concrete (SCC) controls its design. Several factors, including material properties, placement conditions, and formwork characteristics, can affect formwork pressure. This paper presents the influence of formwork width (0.20–1.0 m), shape (circular versus square), and surface material (PVC, plywood, steel, and polyester filter membrane) of formwork on lateral pressure characteristics. The diameter of the pressure sensor used to evaluate lateral pressure characteristics is also investigated. The results showed that the increase in formwork width can increase the initial lateral pressure and delay the time needed for the formwork removal. Correction factors accounting for the changes in the formwork width on the initial pressure and pressure decay were developed. The formwork surface materials did show significant effect on initial formwork pressure, and different pressure decay responses were observed for each formwork material. The longest time for pressure cancellation was obtained for the steel formwork, and the shortest one for the polyester filter membrane.

CHARACTERIZATION OF THE INTERFACE BETWEEN FRESH CONCRETE AND FORMWORK

Concrete surface quality is generally linked to the development conditions of concrete close to the formwork. This work aims to study the influence of the nature of release agent and the quantity of fine elements on the chemical interactions at the concrete/oil/formwork interface. Five concretes were prepared at 28, 30, 32, 34, and 36% of paste to study the influence of paste volume on the friction between formwork and fresh concrete. The friction tests were performed using an apparatus which can reproduce the same conditions of construction sites. In addition, a physicochemical investigation was achieved to identify the effect of fine elements on the ability to form the interstitial mediums at the interface. The formation of soap in the vicinity of the formwork surfaces was also studied as a function of the content and the nature of oils. The results showed that the friction between fresh concrete and formwork depends on the pore solution content present at the interface.

Importance of quantification of steel fibre orientation for residual flexural tensile strength in FRC

The orientation of steel fibres affects the flexural performance of fibre-reinforced concrete. In this paper, selected experimental methods for the characterization of fibre orientation are evaluated and the relationship between residual flexural tensile strength and fibre orientation is discussed. To illustrate the applicability of the methods, the impact of the formwork surface on fibre orientation in slabs cast with fibre-reinforced self-compacting concrete (slump-flow class SF1 according to EN206) was investigated for the cases of formwork surfaces with slip, semi-slip and rough condition. The comparison of fibre orientation quantification methods showed good agreement between X-ray computed tomography and image analysis of sections from sawn beams. The variation in fibre orientation over the slab thickness was strongly influenced by the flow and the roughness of the formwork surface. The Thorenfeldt model for the impact of the fibre orientation factor on residual flexural tensile strength (used in the Norwegian proposal for fibre concrete guidelines) was verified and showed good agreement.

COMPARATIVE ERGONOMIC ASSESSMENT OF SLAB FORMWORK SYSTEMS

The economic efficiency of formwork systems does not depend only on the cost of the product; the achievable performance on the construction site has also a big influence on the selection process. This performance is connected to various factors, such as the number or weight of the individual items, or the required height of the formwork surface. In the course of this research project, four different slab formwork systems performing similar jobs were investigated, enabling a comparison based on an ergonomic assessment. The evaluation of the different systems proved that results and expectations correspond, in this case tasks were reviewed separately for individual systems. Comparing the systems directly, by using the calculated points of the ergonomics evaluation for an average work process, the results display that the least onerous system achieved the highest individual score values. These results led to the assumption that ergonomic scores should not be the sole base for a decision; therefore the performance progress was included and relative ergonomic values for a typical formwork surface were calculated. The result of this evaluation is in line with expectations for the strain of individual systems. The different results between single-task and performance-related evaluations illustrated that, for the assessment of health and safety issues combined with economic factors, not only was the single-task evaluation important, but also an overall view should be taken for a typical scope of work.

Influence of Paste Volume, Type of Release Agents, and Contact Pressure on the Quality of Concrete Surfaces

Each concrete component plays a very important role on tribological behavior in the vicinity of the formwork surfaces. The objective of this paper was to understand the influence of paste volume, type of release agent, and contact pressure on the mechanisms that occur at the concrete-formwork interface. Two concretes with 28 and 34% of paste were formulated to study the influence of fines content on the friction of fresh concrete against formwork wall. Friction tests were performed using an apparatus that can reproduce the conditions of job sites. The effect of interface lubrication on friction and on the quality of concrete surfaces was studied using two release agents (vegetable oil and mineral oil). The results show that the friction is governed by the cement grains and the cement’s water content. Moreover, the tearing of concrete at hardness state was directly linked to the friction intensity.

Influence of formwork surface on the orientation of steel fibres within self-compacting concrete and on the mechanical properties of cast structural elements

The influences of formwork surface on the final orientation of steel fibres immersed in self-compacting concrete and on the resulting mechanical response of the cast structural elements are investigated. Experimental observations of fibre orientation within cast slabs, obtained via computed tomography, indicate that fibres tend to orient according to the flow patterns during casting, but such tendencies are suppressed near rough formwork surfaces. Fibre orientation, in turn, affects the mechanical properties of the concrete as demonstrated by the load testing of beams extracted from the cast slabs. These processes and results are simulated using a computational fluid dynamics model of the casting process, in tandem with a lattice model of the fracture of the beam specimens. The computational fluid dynamics model determines the coordinates of each fibre within the concrete, which serve as input to the lattice model. Through comparisons with the experimental data, it is shown that these simulations correctly predict the phenomena of interest. We conclude the paper by highlighting a relationship between the number and orientation of the immersed steel fibres crossing the fracture plane and the mechanical response of the structural elements.