Textile Reinforced Concrete Elements Research Articles

Intelligent carbon-based TRC as self-strain sensor

Abstract: This study investigates the monitoring capabilities of a carbon yarn embedded in a cementitious matrix as an intelligent strain sensor by means of a gauge factor (GF). In the proposed configuration, the yarn simultaneously functions as the structural system and as the sensory platform, yielding efficient and intelligent concrete elements. The concept of the smart self-sensory system is based on monitoring changes in the electrical properties of the carbon yarn, namely: resistance, inductance, or impedance, and correlating them to the structural health. These capabilities were investigated in carbon yarns that were inserted within textile-reinforced concrete (TRC) structural elements, in which the correlation yielded important information in the macro-structural level. The integrative measurements were used to estimate the structural state associated with cracking and straining along the element. Yet, to fully understand the structural-electrical mechanism and to further enhance the development of the smart carbon-based sensor, it is essential to explore the electrical-micro-structural mechanism at the component level. Therefore, the study offers to explore the correlation between straining and cracking at the component level by means of GF. Separately investigating strained or cracked zones at the yarn’s level will provide vital information on the monitoring capabilities of the carbon yarn. To answer these goals, the study will perform an experimental investigation of carbon-based TRC elements subjected to a designated pull-out test based on a uniaxial tensile setup. The proposed setup aims to correlate between changes in the electrical properties characterizing the carbon yarn and the micro-structural mechanism associated with the degradation of the structural health associated with the propagation of the crack. The outcomes of this study aim to enhance the understanding of the structural-electrical correlation, which paves the way for the development of intelligent strain sensors for TRC structures.

Locating cracks in smart TRC elements based on the TDR concept

The current study aims to handle the challenge of identifying the location of cracks in carbon-based textile reinforced concrete (TRC) elements by using their smart self-sensory capabilities. To answer this challenge, the study offers to adopt the concept of the Time Domain Reflectometer (TDR) analysis. Yet, direct implementation of the TDR analysis to smart sensory carbon yarns is not a straightforward act and requires facing some inherent challenges. Therefore, the study offers an advanced monitoring methodology that handles the various challenges. A special electrical setup is proposed that uses a pair of carbon yarns, in which one yarn is used as the electrical conductor that transmits the electrical current, and the other as insulation. Two calibration processes that consider the unique micro-structural mechanism and its correlation to the electrical characterization are developed. The efficiencies of the calibration processes are investigated by a designated identification technique. Results from this study demonstrate the potential and capabilities of the proposed smart self-sensory carbon-based TRC concept to monitor its health by detecting the cracks’ locations.

Material‐minimised construction with extruded textile reinforced concrete

AbstractThe use of textile reinforced concrete (TRC) is particularly suitable for producing sustainable, material‐minimised components, as it allows for a significant reduction in the amount of concrete cover required compared to steel reinforced concrete (SRC). Instead of steel, fibres made of glass, aramid or carbon are used as reinforcement, which are processed from rovings into textiles with a polymer or mineral impregnation. Among these, carbon reinforcements have the highest tensile strength and alkali resistance, making them the most durable in concrete and requiring less maintenance over time. An innovative approach is the production of TRC structures by means of extrusion, in which the stiff, fresh concrete is continuously pressed through a shaping mouthpiece, giving the product its final shape. Within the scope of the CRC/Transregio 280, a new mouthpiece was developed that enables the horizontal introduction of stiff, impregnated textiles. The carbon TRC produced in this process showed a textile stress of up to 4,000 MPa. Additionally, solutions are presented that allow the characterization of stiff, fresh concrete and technical limits for shaping fresh, extruded TRC elements. The potential of this new production method is illustrated through the example of a compound component made of extruded TRC elements.

Comparative evaluation of textiles for use in textile reinforced concrete

Textile reinforced concrete (TRC) offers many advantages over traditional, steel bar reinforced concrete. The biggest advantage is the corrosion resistance of textiles, which leads to a reduced minimum cover with concrete. This allows for significantly thinner concrete elements, which are also easier to shape because of the excellent draping properties of textiles. For producers of technical textiles there is a need for a quick and easy method to test their products for suitability for use in TRC. In this paper, such a method is proposed: Novel textiles can be evaluated by comparing their properties to those of existing textiles already in use in the construction industry. Three different characteristic values crucial to the suitability of textiles for use in TRC are identified: tensile stress–strain behavior and alkaline resistance of the textiles and the tensile stress–strain behavior of TRC components. For each characteristic value a test method is identified. To validate these test methods and to provide a database for future comparison, the tests are performed on three different impregnated biaxial non-crimp fabrics that are already approved for and used in TRC. These consist of a styrene butadiene rubber impregnated carbon fiber textile, an epoxy resin impregnated alkaline resistant glass textile and a polyvinyl alcohol fiber textile. From these validation tests, key figures that allow for a ranking of new textiles in comparison to the already available textiles are inferred; The tensile strength of the textiles ranges from 880 to 2900 MPa, the alkaline strength degradation is at maximum −0.17 %/day and the tensile strength of the TRC elements ranges from 770 to 2310 MPa. The comparison of these values with those of a new textile enables a quick initial evaluation of the suitability of the new textile for the use in TRC.

State-of-the-Art Review on Experimental Investigations of Textile-Reinforced Concrete Exposed to High Temperatures

Textile-reinforced concrete (TRC) is a promising composite material with enormous potential in structural applications because it offers the possibility to construct slender, lightweight, and robust elements. However, despite the good heat resistance of the inorganic matrices and the well-established knowledge on the high-temperature performance of the commonly used fibrous reinforcements, their application in TRC elements with very small thicknesses makes their effectiveness against thermal loads questionable. This paper presents a state-of-the-art review on the thermomechanical behavior of TRC, focusing on its mechanical performance both during and after exposure to high temperatures. The available knowledge from experimental investigations where TRC has been tested in thermomechanical conditions as a standalone material is compiled, and the results are compared. This comparative study identifies the key parameters that determine the mechanical response of TRC to increased temperatures, being the surface treatment of the textiles and the combination of thermal and mechanical loads. It is concluded that the uncoated carbon fibers are the most promising solution for a fire-safe TRC application. However, the knowledge gaps are still large, mainly due to the inconsistency of the testing methods and the stochastic behavior of phenomena related to heat treatment (such as spalling).

Tensile response of textile reinforced concrete

Textile Reinforced Concrete (TRC) is a cementitious composite material where a carbon or glass fabric is embedded as reinforcement. The use of TRC allows building thin and light structures, with reduced concrete covers and an enhanced durability due to the absence of corrosion problems. In this article, the response of TRC elements subjected to tension is reviewed by means of an experimental and theoretical investigation. A test programme comprising 28 specimens reinforced with uncoated and coated carbon textile fabrics is presented. Detailed measurements were performed by using Digital Image Correlation allowing to investigate on the crack development and failure in tension of the specimens. On this basis, a comprehensive approach to address the tensile response of TRC is presented based on a coaxial ring model incorporating different constitutive laws for the core and sleeve filaments and their interfaces. The model is observed to consistently predict the various responses measured experimentally, both in terms of the stabilised cracking phase and failure load, avoiding the need to consider empirical efficiency factors. The results are finally compared to available tests in the scientific literature showing consistent and fine agreement.

New insights into the splitting failure of textile-reinforced concrete

Textile-reinforced concrete is ideally suited to complement ordinary steel-reinforced concrete, as the use of textile reinforcement with its outstanding mechanical properties and durability allows the construction of slender, lightweight structural elements. Despite the increased interest in this innovative composite material making it a subject of various research projects carried out during the past two decades, questions regarding its specific properties remain. An economically driven trend towards using rovings with a high yarn count and coated with a stiff impregnation material has surfaced in recent years, which has led to an increased occurrence of splitting failures in textile-reinforced concrete elements. This paper describes investigations aimed at clarifying the theoretical background of this failure mode. Preliminary experimental studies were carried out to identify and quantify the impact of several influencing parameters thought to be responsible for inducing longitudinal cracking in textile-reinforced concrete. In subsequent numerical computations with a particular focus on bond behaviour, the stress distribution in the concrete during fibre strand pull-out was visualised. The analysis of the different investigations carried out by the authors showed that the geometric characteristics of the fibre strands have a significant influence on bond behaviour and particularly on splitting failure in textile-reinforced concrete.

Thin‐walled shell structures made of textile‐reinforced concrete

AbstractThe present paper describes a design approach for textile‐reinforced concrete (TRC) shells which reflects the interaction between normal forces and bending moments based on the cross‐sectional strength characteristics of the material determined experimentally. The influence of oblique loading on the composite strength of TRC elements with flexible reinforcement is included in a normalized interaction diagram for combined loading. As an example, the design approach is applied to the ultimate limit state assessment of a TRC shell in double curvature. Furthermore, the general applicability of the design approach is discussed in the light of the non‐linear loadbearing behaviour of TRC. Due to its strain‐hardening tensile response, stress redistributions within the shell result in loadbearing reserves. Details of the structural design and production solutions developed and applied during the realization of the TRC shell structure are described in the companion paper (Part I).

Designed Textile Reinforced Concrete Elements for Architectural Facade Applications

By now the application of Textile Reinforced Concrete (TRC) for facade constructions can be considered as state of the art. Especially ventilated curtain walls made of TRC and sandwich elements made in combination of TRC-layers and foam cores recently are realized in pilot projects, which are predominantly located in Aachen, Germany. Textile reinforced concrete elements for architectural facade applications give new chances for architects and engineers design.

Discrepancy between the desired aesthetic appeal and functionality of materials, taking into account the adressee effect

By now the application of Textile Reinforced Concrete (TRC) for facade constructions can be considered as state of the art. Especially ventilated curtain walls made of TRC and sandwich elements made in combination of TRC-layers and foam cores recently are realized in pilot projects, which are predominantly located in Aachen, Germany. Textile reinforced concrete elements for architectural facade applications gives new chances for architects and engineers design. The effect of shapes and colors, smells, sounds and materials is resulted from a combination of physiological and psychological events. Through the integration of the recorded information in an experiential conditional reference system, on the outer color appearance follows an internal reaction. That influences the human psyche. That can cause measurable responses to metabolic and organ function regardless. Numerous studies on modes of action of colors, shapes, smells and materials are represented in the color and morphology, the classical association psychology, in the symbolism of perception, learning and shape psychology, neuroscience, the approaches of the socio-cultural experiences and cognition.

Unsymmetrical Fibre-Reinforced Plastics for the Production of Curved Textile Reinforced Concrete Elements

A new constructive and technological approach was developed for the efficient production of large-dimensioned, curved freeform formworks, which allow the manufacturing of single and double-curved textile reinforced concrete elements. The approach is based on a flexible, multi-layered formwork system, which consists of glass-fibre reinforced plastic (GFRP). Using the unusual structural behavior caused by anisotropy, these GFRP formwork elements permit a specific adjustment of defined curvature. The system design of the developed GFRP formwork and the concrete-lightweight-elements with stabilized spacer fabric was examined exhaustively. Prototypical curved freeform surfaces with different curvature radii were designed, numerically computed and produced. Furthermore, the fabric’s contour accuracy of the fabric was verified, and its integration was adjusted to loads.

Textile reinforced concrete (TRC) shells for strengthening and retrofitting of concrete elements: influence of admixtures

The mechanical behavior under impact loading of concrete elements strengthened with shells of textile reinforced concrete (TRC) was studied. The strengthening shells were made of either alkali- resistant glass or polyethylene (PE) fabrics that were impregnated with several cementitious matrices mod- ified by common admixtures. Testing the strengthened elements for impact loading (strain rate from 0.4 to 1s -1 ) at flexure showed that the TRC reinforced elements conferred improved load capacity and impulse absorption. For glass strengthened TRC elements, the extent of the improvement depended on admixture grain size, such that smaller grain sizes were associated with better performance. For PE strengthened TRC elements, no similar dependency was found. These results correlate well with the behavior of the standalone TRC shells and with the properties of the fabrics themselves. PE TRC strength- ened elements were found, via impulse loading tests, to have load carrying capacities comparable to those of elements strengthened with glass TRC, but without matrix additives. These findings suggest that low cost, commercially available PE textile could be used in TRC applications.