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Kraft R, Kahnt A, Grauer O, Thieme M, Wolz DS, Schlüter D, Tietze M, Curbach M, Holschemacher K, Jäger H, Böhm R. Advanced Carbon Reinforced Concrete Technologies for Façade Elements of Nearly Zero-Energy Buildings. Materials (Basel) 2022; 15:ma15041619. [PMID: 35208159 PMCID: PMC8878493 DOI: 10.3390/ma15041619] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/14/2022] [Revised: 02/11/2022] [Accepted: 02/14/2022] [Indexed: 02/01/2023]
Abstract
The building sector accounts for approx. 40% of total energy consumption and approx. 36% of all greenhouse gas emissions in Europe. As the EU climate targets for 2030 call for a reduction of greenhouse gas emissions by more than half compared to the emissions of 1990 and also aim for climate neutrality by 2050, there is an urgent need to achieve a significant decrease in the energy use in buildings towards Nearly Zero-Energy Buildings (nZEBs). As the energy footprint of buildings includes the energy and greenhouse gas consumption both in the construction phase and during service life, nZEB solutions have to provide energy-efficient and less carbon-intensive building materials, specific thermal insulation solutions, and a corresponding design of the nZEB. Carbon reinforced concrete (CRC) materials have proven to be excellent candidate materials for concrete-based nZEBs since they are characterized by a significantly lower CO2 consumption during component production and much a longer lifecycle. The corresponding CRC technology has been successively implemented in the last two decades and first pure CRC-based buildings are currently being built. This article presents a novel material system that combines CRC technology and suitable multifunctional insulation materials as a sandwich system in order to meet future nZEB requirements. Because of its importance for the life cycle stage of production, cost-efficient carbon fibers (CF) from renewable resources like lignin are used as reinforcing material, and reinforcement systems based on such CF are developed. Cutting edge approaches to produce ultra-thin lightweight CF reinforced concrete panels are discussed with regard to their nZEB relevance. For the life cycle stage of the utilization phase, the thermal insulation properties of core materials are optimized. In this context, novel sandwich composites with thin CRC layers and a cellular lightweight concrete core are proposed as a promising solution for façade elements as the sandwich core can additionally be combined with an aerogel-based insulation. The concepts to realize such sandwich façade elements will be described here along with a fully automated manufacturing process to produce such structures. The findings of this study provide clear evidence on the promising capabilities of the CRC technology for nZEBs on the one hand and on the necessity for further research on optimizing the energy footprint of CRC-based structural elements on the other hand.
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Affiliation(s)
- Robert Kraft
- Faculty of Civil Engineering, Structural Concrete Institute, Leipzig University of Applied Sciences, PF 30 11 66, 04251 Leipzig, Germany; (R.K.); (A.K.); (O.G.); (M.T.); (K.H.)
- Faculty of Engineering, Leipzig University of Applied Sciences, PF 30 11 66, 04251 Leipzig, Germany
| | - Alexander Kahnt
- Faculty of Civil Engineering, Structural Concrete Institute, Leipzig University of Applied Sciences, PF 30 11 66, 04251 Leipzig, Germany; (R.K.); (A.K.); (O.G.); (M.T.); (K.H.)
| | - Otto Grauer
- Faculty of Civil Engineering, Structural Concrete Institute, Leipzig University of Applied Sciences, PF 30 11 66, 04251 Leipzig, Germany; (R.K.); (A.K.); (O.G.); (M.T.); (K.H.)
| | - Mike Thieme
- Institute of Lightweight Engineering and Polymer Technology, TU Dresden, 01307 Dresden, Germany; (M.T.); (D.S.W.); (H.J.)
| | - Daniel Sebastian Wolz
- Institute of Lightweight Engineering and Polymer Technology, TU Dresden, 01307 Dresden, Germany; (M.T.); (D.S.W.); (H.J.)
- Research Center Carbon Fibers Saxony (RCCF), TU Dresden, 01307 Dresden, Germany
| | - Dominik Schlüter
- Institute of Concrete Structures, TU Dresden, 01062 Dresden, Germany; (D.S.); (M.C.)
| | - Matthias Tietze
- Faculty of Civil Engineering, Structural Concrete Institute, Leipzig University of Applied Sciences, PF 30 11 66, 04251 Leipzig, Germany; (R.K.); (A.K.); (O.G.); (M.T.); (K.H.)
- Institute of Concrete Structures, TU Dresden, 01062 Dresden, Germany; (D.S.); (M.C.)
| | - Manfred Curbach
- Institute of Concrete Structures, TU Dresden, 01062 Dresden, Germany; (D.S.); (M.C.)
| | - Klaus Holschemacher
- Faculty of Civil Engineering, Structural Concrete Institute, Leipzig University of Applied Sciences, PF 30 11 66, 04251 Leipzig, Germany; (R.K.); (A.K.); (O.G.); (M.T.); (K.H.)
| | - Hubert Jäger
- Institute of Lightweight Engineering and Polymer Technology, TU Dresden, 01307 Dresden, Germany; (M.T.); (D.S.W.); (H.J.)
- Research Center Carbon Fibers Saxony (RCCF), TU Dresden, 01307 Dresden, Germany
| | - Robert Böhm
- Faculty of Engineering, Leipzig University of Applied Sciences, PF 30 11 66, 04251 Leipzig, Germany
- Research Center Carbon Fibers Saxony (RCCF), TU Dresden, 01307 Dresden, Germany
- Correspondence: ; Tel.: +49-341-3076-4177
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Tekle BH, Hertwig L, Holschemacher K. Setting Time and Strength Monitoring of Alkali-Activated Cement Mixtures by Ultrasonic Testing. Materials (Basel) 2021; 14:ma14081889. [PMID: 33920174 PMCID: PMC8069208 DOI: 10.3390/ma14081889] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/19/2021] [Revised: 04/03/2021] [Accepted: 04/05/2021] [Indexed: 11/16/2022]
Abstract
Alkali-activated cement (AAC) is a promising binder that replaces ordinary Portland cement (OPC). In this study, the development of setting time and strength of AAC mixes were studied using ultrasonic testing method. The test results were compared with traditional Vicat setting time and compressive and flexural strengths. The findings showed that setting times and strengths have a strong correlation with ultrasonic velocity curve. The initial setting time corresponds well with the ultrasonic velocity curve’s dormant period, and the final setting time with the time it takes to reach the velocity curve’s maximum acceleration. Both setting times also showed a correlation with the value of the maximum acceleration. An exponential relation was found between the ultrasonic velocity and the compressive and flexural strengths. The effect of binder content, alkaline solid to binder ratio (AS/B), sodium silicate to sodium hydroxide solids ratio (SS/SH), and total water to total solid binder ratio (TW/TS) on the strength and setting time are also studied using Taguchi method of experimental design. AS/B ratio showed a significant influence on the setting time of AAC while TW/TS ratio showed only a minor effect. The ultrasonic velocities were able to capture the effect of the different parameters similar to the compressive strength. The velocity decreased mainly with the increase of TW/TS ratio and binder content, while AS/B and SS/SH ratios showed a lower influence.
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Kaeseberg S, Messerer D, Holschemacher K. Experimental Study on Concrete under Combined FRP-Steel Confinement. Materials (Basel) 2020; 13:ma13204467. [PMID: 33050141 PMCID: PMC7601914 DOI: 10.3390/ma13204467] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/07/2020] [Revised: 09/29/2020] [Accepted: 10/03/2020] [Indexed: 11/24/2022]
Abstract
The confinement of reinforced concrete (RC) compression members by fiber-reinforced polymers (FRPs) is an effective measure for the strengthening and retrofitting of existing structures. Thus far, extensive research on the stress–strain behavior and ultimate limit state design of FRP-confined concrete has been conducted, leading to various design models. However, these models are significantly different when compared to one another. In particular, the use of certain empirical efficiency and reduction factors results in various predictions of load-bearing behavior. Furthermore, most experimental programs solely focus on plain concrete specimens or demonstrate insufficient variation in the material properties. Therefore, this paper presents a comprehensive experimental study on plain and reinforced FRP-confined concrete, limited to circular cross sections. The program included 63 carbon FRP (CFRP)-confined plain and 60 CFRP-confined RC specimens with a variation in the geometries and in the applied materials. The analysis showed a significant influence of the compressive strength of the confined concrete on the confinement efficiency in the design methodology, as well as the importance of the proper determination of individual reduction values for different FRP composites. Finally, applicable experimental test results from the literature were included, enabling the development of a modified stress–strain and ultimate condition design model.
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