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During the last years, incorporation of nano-constituents into cement-based construction materials has been increasingly spreading thanks to their unique physicochemical properties which enable both nano- and micro-mechanical improvement of cementitious composites. It has been well established that besides increasing concretes strength, refinement of pore size occurs causing a significant reduction in total porosity values and improvement in specimens durability. The present work aims at the analysis and performance evaluation of nanocellulose (NC) enriched Ultra High Durable Concretes (UHDC) exposed to aggressive environmental conditions (i.e. chemical attack - XA environmental exposure class). To this purpose, two reference UHDC materials containing crystalline admixtures and steel fibers were compared with mixes holding also cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) into their structures. In all cases, NC loading remained constant and equal to 0.15% (by %wt of cement amount).The excellent reinforcing capabilities of NCs are demonstrated by the enhanced fracture resistance properties of the cementitious matrix. Additionally, microstructural analysis results of as derived specimens suggest that the use of NCs can lead to the development of materials with advanced textural and morphological characteristics and therefore widen their application prospects to aggressive environmental conditions.

During the last years, incorporation of nano-constituents into cement-based construction materials has been increasingly spreading thanks to their unique physicochemical properties which enable both nano- and micro-mechanical improvement of cementitious composites. It has been well established that besides increasing concretes strength, refinement of pore size occurs causing a significant reduction in total porosity values and improvement in specimens durability. The present work aims at the analysis and performance evaluation of nanocellulose (NC) enriched Ultra High Durable Concretes (UHDC) exposed to aggressive environmental conditions (i.e. chemical attack - XA environmental exposure class). To this purpose, two reference UHDC materials containing crystalline admixtures and steel fibers were compared with mixes holding also cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) into their structures. In all cases, NC loading remained constant and equal to 0.15% (by %wt of cement amount).The excellent reinforcing capabilities of NCs are demonstrated by the enhanced fracture resistance properties of the cementitious matrix. Additionally, microstructural analysis results of as derived specimens suggest that the use of NCs can lead to the development of materials with advanced textural and morphological characteristics and therefore widen their application prospects to aggressive environmental conditions.

Flowable concretes can differ significantly from traditional vibrated concrete. Concrete types like selfcompacting concrete (SCC), ultra-high performance concrete (UHPC) and high performance fibre reinforced cementitious composites (HPFRCCs) require novel mix design approaches. This has consequences for the production and the performance in the hardened state. Mix designs for flowable concretes can incorporate a wide variety of innovative admixtures or components: e.g. superplasticisers increase the flowability and allow for significant reduction of the water content, shrinkage compensating admixtures or superabsorbent polymers support sound and damage free curing processes, viscosity modifying admixtures enhance the robustness, and new fibre types allow for sophisticated and tailored structural performance. The new Model Code has limitations regarding the application of flowable concrete, e.g. thresholds for the minimum aggregate size and the maximum strength. Provisions are added to include fibres for structural design. fib Task Group 4.3 aims at facilitating the use of innovative flowable materials for designing concrete structures and considers three aspects of flowable concrete: material properties, production effects and structural boundary conditions and performance. This paper reports about the progress of fib TG 4.3 related to the mix design of flowable concrete and discusses the present stateof-the art concerning admixtures and robustness., Civil Engineering and Geosciences

Stress and strain interaction is of vital importance for concrete structures as it has an influence on cracking, deflection and prestressing loss. With the increased range of compressive strengths and flow characteristics, the mixture composition of nowadays concretes often differs considerably from Vibrated Concrete (VC) with regard to paste strength, paste composition and paste volume. As a result, the viscoelastic properties of concrete are altered as well and some of the established stressstrain-relations valid for VC have to be questioned or at least reconfirmed for new concrete types like Self-Compacting Concrete (SCC), Ultra High Performance Concrete (UHPC) and Engineered Cementitious Composites (ECC). This paper discusses time- and load-dependent characteristics of flowable concrete as an outcome of a workgroup within fib Task Group 4.3 that aims at facilitating the use of innovative flowable materials for the design of concrete structures., Structural Engineering, Civil Engineering and Geosciences

Flowable concretes can differ significantly from traditional vibrated concrete. Concrete types like selfcompacting concrete (SCC), ultra-high performance concrete (UHPC) and high performance fibre reinforced cementitious composites (HPFRCCs) require novel mix design approaches. This has consequences for the production and the performance in the hardened state. Mix designs for flowable concretes can incorporate a wide variety of innovative admixtures or components: e.g. superplasticisers increase the flowability and allow for significant reduction of the water content, shrinkage compensating admixtures or superabsorbent polymers support sound and damage free curing processes, viscosity modifying admixtures enhance the robustness, and new fibre types allow for sophisticated and tailored structural performance. The new Model Code has limitations regarding the application of flowable concrete, e.g. thresholds for the minimum aggregate size and the maximum strength. Provisions are added to include fibres for structural design. fib Task Group 4.3 aims at facilitating the use of innovative flowable materials for designing concrete structures and considers three aspects of flowable concrete: material properties, production effects and structural boundary conditions and performance. This paper reports about the progress of fib TG 4.3 related to the mix design of flowable concrete and discusses the present stateof-the art concerning admixtures and robustness., Civil Engineering and Geosciences

Stress and strain interaction is of vital importance for concrete structures as it has an influence on cracking, deflection and prestressing loss. With the increased range of compressive strengths and flow characteristics, the mixture composition of nowadays concretes often differs considerably from Vibrated Concrete (VC) with regard to paste strength, paste composition and paste volume. As a result, the viscoelastic properties of concrete are altered as well and some of the established stressstrain-relations valid for VC have to be questioned or at least reconfirmed for new concrete types like Self-Compacting Concrete (SCC), Ultra High Performance Concrete (UHPC) and Engineered Cementitious Composites (ECC). This paper discusses time- and load-dependent characteristics of flowable concrete as an outcome of a workgroup within fib Task Group 4.3 that aims at facilitating the use of innovative flowable materials for the design of concrete structures., Structural Engineering, Civil Engineering and Geosciences

With the tendency to apply concrete with a higher workability and the use of new concrete components more options are available to design concrete. New concrete types like self-compacting concrete (SCC), ultra-high performance fibre reinforced concrete (UHPFRC) and high performance fibre reinforced cementitious composite (HPFRCC) also require adopted mix designs and in case, a new engineering approach. Flowable concrete not only is an innovative material, but its application can lead to innovative structures, combinations of building materials and alternative and efficient production methods. fib Task Group 8.8 aims at facilitating the use of innovative flowable materials for the design of concrete structures and considers three aspects of flowable concrete for structural design: material properties, production effects and structural boundary conditions. The main objectives of this group of experts are to combine research findings with practical experience and to write a state of-the-art report and a recommendation on the structural design with flowable concrete. Areas of structural design where flowable concrete differs from traditional vibrated concrete have to be identified. This paper reports about the progress of fib TG 8.8 and discusses important aspects related to flowable concrete., Structural Engineering, Civil Engineering and Geosciences

Structural Engineering, Civil Engineering and Geosciences

With the tendency to apply concrete with a higher workability and the use of new concrete components more options are available to design concrete. New concrete types like self-compacting concrete (SCC), ultra-high performance fibre reinforced concrete (UHPFRC) and high performance fibre reinforced cementitious composite (HPFRCC) also require adopted mix designs and in case, a new engineering approach. Flowable concrete not only is an innovative material, but its application can lead to innovative structures, combinations of building materials and alternative and efficient production methods. fib Task Group 8.8 aims at facilitating the use of innovative flowable materials for the design of concrete structures and considers three aspects of flowable concrete for structural design: material properties, production effects and structural boundary conditions. The main objectives of this group of experts are to combine research findings with practical experience and to write a state of-the-art report and a recommendation on the structural design with flowable concrete. Areas of structural design where flowable concrete differs from traditional vibrated concrete have to be identified. This paper reports about the progress of fib TG 8.8 and discusses important aspects related to flowable concrete., Structural Engineering, Civil Engineering and Geosciences

Structural Engineering, Civil Engineering and Geosciences

The presence of cracks may significantly affect the life-cycle of structures, as a results of its influence on the designed structural response vs. persistent or even severe accidental load and exposure conditions, when requested. Repairing damaged concrete in existing structures needs important investments to recover the pristine level of serviceability and extend their designed service life. In this respect, the ability of cementitious composites to “self-repair” the cracks, because of autogenous or suitably engineered mechanisms, is a challenging opportunity, making concrete more and more attractive in future sustainable developments of civil engineering. In this study a methodology will be presented to assess the aforementioned capacity, based on three point bending tests on un-cracked and pre-cracked beams, upon exposure to suitable environmental conditions. The paper will focus on the difference between accelerated exposure, in a climate chamber, and “natural conditioning” in air; comparison with immersion in water will also be performed.

The presence of cracks may significantly affect the life-cycle of structures, as a results of its influence on the designed structural response vs. persistent or even severe accidental load and exposure conditions, when requested. Repairing damaged concrete in existing structures needs important investments to recover the pristine level of serviceability and extend their designed service life. In this respect, the ability of cementitious composites to “self-repair” the cracks, because of autogenous or suitably engineered mechanisms, is a challenging opportunity, making concrete more and more attractive in future sustainable developments of civil engineering. In this study a methodology will be presented to assess the aforementioned capacity, based on three point bending tests on un-cracked and pre-cracked beams, upon exposure to suitable environmental conditions. The paper will focus on the difference between accelerated exposure, in a climate chamber, and “natural conditioning” in air; comparison with immersion in water will also be performed.