High-performance Fiber-reinforced Cement Research Articles

Influence of Ground Granulated Blast Furnace Slag on the compressive strength and ductility of Ultra High-performance fibre reinforced cementitious composites

The mechanical properties of Ultra High Performance Fibre Reinforced Cementitious Composite (UHPFRCC) is basically influenced by the type of fibres and reactive binders used. Fibres primarily influence the ductility whereas reactive binders influence the compressive strength of UHPFRCC. Among the commonly used reactive binders, Ground Granulated Blast Furnace Slag (SL) with its vitreous nature has the ability of influencing both the compressive strength and ductility of UHPFRCC. This study discussed the microstructure and mechanical properties of six different mixtures made up of 0%, 20%, 40%, 60% 75% and 90% cement replacement of SL. The XRD results indicated that, increased levels of C-S-H and ettringite retard the hydration process leading to lower compressive strength and vice versa. The SL-cementitious composite can achieve a compressive strength of up to 108.1MPa and ductility of up to 1.67% without the use of fibres. The maximum compressive strength and ductility were achieved with 40% SL replacement of cement whereas the minimum compressive strength and ductility were achieved with 60% and 20% SL contents, respectively. Moreover, the optimum mechanical properties (i.e. compressive strength, tensile strength, flexural strength, and tensile strain) were achieved with a 40% SL replacement of cement in the cementitious composite.

Mechanical properties and self-healing capacity of Ultra High Performance Fibre Reinforced Concrete with alumina nano-fibres: Tailoring Ultra High Durability Concrete for aggressive exposure scenarios

The effects of alumina nano-fibres are investigated in this paper on the mechanical performance of Ultra High Performance Fibre Reinforced Cementitious Concrete and their efficacy in enhancing the durability of the cementitious composite when exposed to extremely aggressive conditions, with main reference to the stimulated autogenous crack sealing and self-healing capacity. A tailored characterization of the flexural and tensile behaviour of the composite has been first of all performed, also with the purpose of validating an experimental and analytical approach for the identification of the tensile stress vs. strain/crack opening constitutive relationship, which makes use of a purposely conceived indirect tensile test methodology, called Double Edge Wedge Splitting test. Secondly the crack sealing and self-healing capacity have been investigated, considering the recovery of both mechanical flexural performance and durability properties (water permeability) and cross analysing the results for a thorough validation. Microstructural investigations have complemented the aforementioned experimental programme to confirm the efficacy of alumina nano-fibres in enhancing the durability performance of the investigated composites. Superior performance of the mix with alumina nano-fibres with respect to parent companion ones has been highlighted and explained through both a nano-scale reinforcing effects which helps in controlling the cracking process since its very onset as well as through their hydrophilic nature which is likely to foster cement and binder hydration reactions, which can usefully stimulate crack sealing and performance healing recovery at both the macroscopic and mesoscopic fibre-matrix interface) level.

High performance fibre reinforced cementitious composites: Six memos for the XXI century societal and economical challenges of civil engineering

Worldwide increasing consciousness for sustainable use of natural resources has made “overcoming the apparent contradictory requirements of cost and performance effectiveness a challenging task” as well as a major concern. High Performance Fibre Reinforced Cementitious Composites, by providing tailored and multiple functionalized performance can represent an asset for the construction industry to face the challenges imposed by the needs of our continuously and fast evolving society. The paper, moving from a parallel with “Six memos from the next millennium” by Italo Calvino, the author will provide his own perspective on the current state on the topic, trying to highlight the benefits achievable through a reliable and consistent incorporation into a design and construction practice for both new and existing buildings and structures.

Response of rc columns strengthened with composite materials

The use of High Performance Fibre Reinforced Cementitious Composite (FRCC) systems as a repair/strengthening of RC columns is an innovative technique for increasing their capacity and preventing brittle failures when a seismic event occurs. This study presents and discusses the results of an experimental program carried out on nine scaled RC columns under compressive axial load. In particular, six columns were strengthened with FRCC, two columns were confined with uniaxial carbon fibres (CFRP) and one unstrengthened coloumn was used as control specimen. The strengthening with FRCC consisted of the total replacing of the existing concrete cover with a thin layer of FRCC for the entire length of the specimen. The behaviour of columns strengthened with FRCC is compared with the two columns confined by using CFRP. The effectiveness of the FRCC repair/strengthening technique was investigated by means of comparisons with the response of the control specimen and columns confined with CFRP. The specimens’ response has been analysed in terms of failure modes and strength/deformation capacity.

Properties of high-performance cementitious composites containing recycled rubber crumb

Concrete containing rubber crumb from waste tyre has been investigated previously and enhancement of material performance, for example, energy absorbing, has been observed. However, at the same time, the degradation of compressive and flexural strength, as well as some other physical properties are also inevitable. In this study, physical, mechanical properties and durability of High Performance Cementitious Composites containing rubber crumb (HPCC-R) were assessed. Moreover, 2% volume fraction of micro steel fibres were added to form High Performance Fibre Reinforced Cementitious Composites (HPFRCC-R) to increase its integrity. Experimental results were then compared to those of the base material without rubber crumb. The impact of different mix design methodologies, grading of rubber particles, and different curing conditions were investigated.It was observed that the drying shrinkage is neglectable after hot water curing at either 90°C or 60°C for HPCC-R. Under normal curing condition, drying shrinkage development follows the similar trend as the base material but end up with approximately 20% higher shrinkage at 28days’ age. The compressive strength and flexural strength of both HPCC-R and HPFRCC-R decrease significantly with the increase of the amount of rubber crumb. Applying hot water curing at 90°C and pre-treatment of rubber crumb using Na(OH) were identified as effective approaches to compensate the compressive strength loss. However, it was observed that impacts of different curing conditions are insignificant on the flexural strength development. The rapid chloride permeability test (RCPT) results of HPFRCC-R material under different curing conditions were at the same level, and as good as that of the base material. Mixing scheme of using rubber crumb as filler material instead of replacement of fine sand lead to better material performance regarding its compressive strength versus density ratio at a relatively high replacement ratio of 40% by volume. It is recommended to use “Addition” mixing scheme when a large amount of rubber crumb being used in HPFRCC in the future.

Performance of Two-way RC Slabs Retrofitted by Different Configurations of High Performance Fibre Reinforced Cementitous Composite Strips

Introduction:Considering the promising results gained from several studies using cementitious composites with strain hardening behaviour (High Performance Fibre Reinforced Cementitious Composites, HPFRCC) for repair and retrofitting concrete flexural members, in this paper the possibility of using HPFRCC for retrofitting two-way RC slabs is investigated.Methods:A total of five two-way slabs were made and tested to failure. Three slabs were retrofitted with a variety of different types of retrofit configurations and two other slabs, having low and conventional reinforcement ratios, were used as control slabs. A novel technique of bonding, designated NSM-HPFRCC, is proposed. Flexural responses of all slabs are evaluated and the bonding behaviour and associated failure modes are investigated.Results and Conclusion:It is shown that the proposed retrofit configurations, especially when accompanied by the NSM-HPFRCC technique, can greatly improve the flexural performance of retrofitted slabs; hence, they can be used successfully to retrieve the flexural reinforcement deficiency of weak slabs.

Tensile Behaviour and Durability Issues of Engineered Cementitious Composites with Rice Husk Ash

ABSTRACT The Engineered Cementitious Composites (ECC) is a special type of High Performance Fibre Reinforced Cementitious Composite (HPFRCC) characterized by a high tensile ductility with a 2% maximum volume of micro fibres. ECC has a tensile strain-hardening performance that leads to multiple cracking behaviour, thus providing the high ductility to the concrete. One of the main applications of ECC is as structural reinforcement in the construction or rehabilitation of rigid and flexible pavements. In order to adapt the ECC to the Brazilian environment, polypropylene fibres have been used instead to PVA fibres. Moreover, rice husk ash (RHA) has also been used as a partial replacement to cement, aiming to produce an environmentally friendly and a more economically viable version of the ECC. This work presents the results obtained for ECC mixtures containing 10%, 20% and 30% (by volume) of non-processed rice husk ash, as a replacement to cement. An experimental study has been carried out to investigate the tensile behavior and durability issues of these ECCs. The results indicate that the use of RHA is technically viable and that the replacement of 30% cement by RHA leads to the most promising performance in terms of high ductility, resistance to crack propagation, decrease in the water absorption and voids content and heat at hydration.

Effects of autogenous healing on the recovery of mechanical performance of High Performance Fibre Reinforced Cementitious Composites (HPFRCCs): Part 1

This paper presents the results are shown of a thorough characterization of the self-healing capacity of High Performance Fibre Reinforced Cementitious Composites (HPFRCCs). The capacity of the material will be investigated to completely or partially re-seal the cracks, as a function of its composition, maximum crack width and exposure conditions. The analysis will also consider different flow-induced alignments of fibres, which can result into either strain-hardening or softening behaviour, whether the material is stressed parallel or perpendicularly to the fibres, respectively. Beam specimens, initially pre-cracked in 4-point bending up to different values of crack opening, were submitted to different exposure conditions, including water immersion, exposure to humid or dry air, and wet-and-dry cycles. After scheduled exposure times, ranging from one month to two years, specimens were tested up to failure according to the same test set-up employed for pre-cracking. Outcomes of the self-healing phenomenon, if any, were analysed in terms of recovery of stiffness, strength and ductility. In a durability-based design framework, self-healing indices quantifying the recovery of mechanical properties were also defined and their significance cross-checked.

Autogenous healing on the recovery of mechanical performance of High Performance Fibre Reinforced Cementitious Composites (HPFRCCs): Part 2 – Correlation between healing of mechanical performance and crack sealing

This paper is the second part of a companion paper study focused on the autogenous self-healing capacity of High Performance Fibre Reinforced Cementitious Composites (HPFRCCs). In part 1 investigation has focused on the capacity of the material to completely or partially re-seal the cracks, as a function of its composition, maximum crack width and exposure conditions. Different flow induced alignment of fibres, with respect to the applied bending stresses have been also considered. The outcomes of the self-healing phenomenon, have been analyzed in terms of recovery of stiffness, strength and ductility, as measured by means of 4-point bending tests, performed before (pre-cracking) and after the conditioning exposure. In a durability-based design framework, self-healing indices quantifying the recovery of mechanical properties were also defined and their significance cross-checked. In this paper the crack closure will be evaluated, both through visual image analysis of the healed cracks as well as through a tailored indirect method, proposed by the first authors in a previous study. This method is based on the comparative analysis of the damage evolution curves built for both the pre-cracked and the healed stages from the evaluation of the flexural stiffness. Recovery of mechanical properties will hence be correlated to the identified amount of crack closure. In the authors' opinion, this step represents a fundamental contribution in order to reliably and consistently incorporate the effects of self-healing into tailored durability-based design approaches, based, e.g., on a “healable” crack width threshold concept.

Development of a new Ultra High Performance Fibre Reinforced Cementitious Composite (UHPFRCC) for impact and blast protection of structures

Ultra High Performance Fibre Reinforced Cementitious Composites (UHPFRCCs) represent a class of cement composites which have superior characteristics in terms of material properties. Their mechanical and fracture behaviour is substantially enhanced compared to other types of concrete. The aim of the specific paper is to present the results of an extended work focused on the development of the first UHPFRCC with the use of constituent materials available in Cyprus. The paper presents results on a broad variety of mechanical properties and the effect of several parameters on the strength development and the rheological characteristics of the produced material. Furthermore, the developed material should have certain properties and specifications, so as to have a sufficient response against blast and impact loading conditions. The optimum mixture has a water–binder ratio equal to 0.16 and volume fraction of steel fibres equal to 6%. The average compressive strength and specific fracture energy obtained for this mixture were around 175MPa and 26000N/m, respectively.

Experimental field investigation of impact and blast load resistance of Ultra High Performance Fibre Reinforced Cementitious Composites (UHPFRCCs)

Ultra High Performance Fibre Reinforced Cementitious Composites (UHPFRCCs) represent a class of cement composites which have superior characteristics in terms of material properties. These materials have, however, a significant increase in cost compared to conventional and even High Performance Concrete and it is therefore appropriate to identify applications which will fully utilise their mechanical properties and performance characteristics. A new class of UHPFRCC material has been developed through the experimental work of a research project entitled “Mix Design, Mechanical Properties and Impact Resistance of UHPFRCCs”, designated UHP-CY. The material is characterised by high compressive strength, high tensile/flexural strength and high-energy absorption capacity. The research work presented in this paper focused on the experimental investigation of the quality and the behaviour of this material in a highly demanding application, such as the impact and blast resistance of structures. The impact resistance of UHP-CY slabs was experimentally verified in a range of real firing shots, using several weapons and projectile types. A purpose-built experimental setup was developed for this work. It was observed that relatively thin slabs made of this material can be an outstanding protective overlay of existing structures, since they can prevent the penetration of strong projectiles without shaped charges. Moreover, these panels can also minimise the damage of retrofitted Reinforced Concrete structures, hit by projectiles with shaped charges. The presence of a high volume fraction (i.e. 6%) of steel fibres in UHP-CY overlays contributes substantially to the control of the back face spalling and fragmentation of the RC walls.

Evaluation of toughness of textile concrete

High Performance Fibre Reinforced Cementitious Composites (HPFRCC) are characterized by a stress–strain response in tension that exhibits strain-hardening behaviour accompanied by propagation of multiple cracks. This process is often referred to as pseudo-ductility due to multiple cracking with relatively large energy absorption capacity. The cracking characteristics are dependent on matrix strength, fibre/matrix bond, fibre volume fraction and the aspect ratio of the fibre used in the composite. The matrix cracking strength and interfacial bond vary with the degree of hydration of cement in the matrix, which is time and environment dependent. This study analyses the multiple cracking patterns formed in weathered Textile Concrete (TC) samples due to direct tensile testing, and links the cracking patterns to the tensile behaviour. The specimens used for the study were thin laminates which were produced by casting six layers of specially made polypropylene (PP) textile in fine-grained mortar. The samples were cured under controlled laboratory conditions for 28 days, and thereafter exposed to different weathering regimes for different periods. The weathered samples were tested in direct tension in a Universal Testing Machine (UTM) over a range of stresses. For all the samples tested, it was observed that the tensile behaviour was characterised by strain hardening and multiple cracking, which gave high tensile strains in excess of 20% at final failure. It was further found that the cracking patterns varied mainly with age, weathering history and stress levels. Other factors that contributed to the cracking characteristics were moisture state of the specimen and the fibre/matrix bonding strength. A strong bond and dense matrix resulted in wide crack spacings compared with samples with a weaker bond which developed closely spaced cracks. A general trend of increasing crack widths and crack spacings with ageing was observed which was accredited to increased hydration accompanied by an increase in fibre/matrix bond strength.

Tensile Response and Fracture Process of High-Performance Hybrid Fiber-Reinforced Cement Composites

Five twisted steel fibers (steel cord, SC) are used to improve the post-cracking behavior of cement composites. In addition to these steel cord macrofibers, microfibers are used to enhance the pre- and post-cracking strength and behavior. The three specific hybrid fiber blends pursued in this investigation are SC and polyethylene (PE), SC and polypropylene (PP) as well as SC and polyvinyl alcohol (PVA) fibers. The research results show that SC macrofibers with high ultimate strain, strength and bond stress can bridge the macrocracks in the matrix. Therefore, cement-based composites reinforced with SC fibers exhibit a pseudo-strain hardening in tension as a result of the formation of multiple cracks. The microfibers improved pre-peak mechanical performance, strength, and fracture process by delaying the formation of a macrocrack. The tensile strength, energy consumption capacity and ductility of SC macrofibers and high elastic modulus microfiber PE reinforced cement-based composites are tremendously improved compared to SC macrofibers with lower elastic modulus microfibers PVA and PP.

Proposed classification of HPFRC composites based on their tensile response

The tensile response of fiber reinforced cement (FRC) composites can be generally classified in two distinct categories depending on their behavior after first cracking, namely, either strain-hardening or strain-softening. Within the strain-softening category, one can distinguish between deflection-hardening and deflection-softening behavior. Several standard tests (ASTM, JCI, RILEM) are available to assess the characteristics of mostly strain-softening FRC composites through bending tests, but no standard test is currently available to characterize strain-hardening response in tension. Such composites have been described as high performance FRC or HPFRC composites. In this paper a proposal is put forth to characterize the response of strain-hardening FRC composites based on the results of direct tensile tests. The classification is based on several parameters which include a minimum value of elastic modulus, a minimum value of peak strain after first cracking, and the tensile strength level. While one of the key obstacles remains, that is, to develop a realistic and meaningful tensile test standard, some requirements on minimum specimen size, fiber size and aggregate size are also suggested.