Influence of the chloride attack on the post-cracking behavior of Recycled Steel Fiber Reinforced Concrete

The main purpose of the present work is to study the mechanical behavior and durability performance of recycled steel fiber reinforced concrete (RSFRC) under a chloride environment. To this end, the effect of chloride attack on the load-carrying capacity of pre-cracked RSFRC round panels is investigated by performing round panel tests supported on three points (RPT-3ps), considering the influence of the crack width and the fiber distribution/orientation profile. In addition, the influence of the adopted chloride exposure conditions on the post-cracking constitutive laws of the developed RSFRC is also assessed by performing numerical simulations for the prediction of the long-term performance of RSFRC under these aggressive conditions. The tensile stress–crack width relationship of RSFRC is derived by performing an inverse analysis with the RPT-3ps results. The obtained experimental and numerical results show a negligible effect of the chloride attack on the post-cracking behavior of RSFRC for the chloride exposure conditions and pre-crack width levels adopted in this study.This research was funded by C.F. research grant PD/BD/113638/2015 provided by Fundação para a Ciência e a Tecnologia (FCT) through the Doctoral Program in Eco Construction and Rehabilitation–EcoCoRe, and J.B. through the project ICoSyTec (POCI-01-0145-FEDER-027990) financed by FCT and co-funded by FEDER through Operational Competitiveness and Internationalization Programme (POCI)

An experimental investigation on the post-cracking behaviour of Recycled Steel Fibre Reinforced Concrete

Steel fibres resulting from the industry of tyre recycling can be efficiently employed for the reinforcement of concrete structures. Recycled Steel Fibre Reinforced Concrete (RSFRC) is a promising candidate with technical, environmental and economic benefits for the development of ductile, high strength and durable constructive systems, as it is required for breakwater elements used on the protection of coastal zones. For assessing the potentialities of recycled steel fibres (RSF) as concrete reinforcement, an experimental program was performed in the present work by comparing the following properties of concrete reinforced with industrial steel fibres (ISF) and with RSF: compressive strength, modulus of elasticity, flexural strength, flexural toughness and indirect tensile strength. Under chloride attack, the durability performance of RSFRC requires the assessment of its corrosion resistance. To evaluate the corrosion effects on the post-cracking response of RSFRC, double edge wedge splitting tensile tests were conducted in RSFRC specimens previously exposed to aggressive chloride environment. The obtained results demonstrate that, for the adopted industrial and recycled fibres, the last ones had not inferior post-cracking strengthening performance than the first ones. The corrosion action caused a slight decrease of the average post-cracking tensile strength of the RSFRC. The small percentage of rubber attached to RSF surface had a negligible effect in the corrosion resistance of RSFRC.FCT through PTDC/ECMEST/2635/2014 project, as well as the collaboration of CiviTest Company in the production of concretes. The first author would like to thank the FCT for the financial support through the Research Grant PD/BD/113638/2015. The supplying of RSF and ISF from Twincon and Maccaferri Companie

An experimental study on the corrosion susceptibility of Recycled Steel Fiber Reinforced Concrete

Steel fibers resulting from the industry of tire recycling can be efficiently employed in concrete to improve its mechanical performance, such as post-cracking load bearing and energy absorption capacity. Under chloride attack, an important aspect of Recycled Steel Fiber Reinforced Concrete (RSFRC) durability is its corrosion resistance. However, the insufficient knowledge on this domain contributes for a conservative design philosophy, which can compromise the cost competitiveness of RSFRC and prevent its application in elements where this occurrence, even eventual, is not acceptable. In the present work, an experimental program was performed with the aim of assessing the corrosion susceptibility of RSFRC including the characterization of the micro-mechanical properties and the corrosion resistance of recycled steel fiber (RSF) by means of nano-indentation testing, electrochemical monitoring techniques and scanning electron microscopy (SEM) analysis. The influence of the small rubber debris attached to the RSF surface was also analyzed by using two distinct pre-treatment methods. The adhesive bond behavior between the RSF and the surrounding self-compacting concrete (SCC) matrix was analyzed by performing monotonic RSF pullout tests. Double edge wedge splitting (DEWS) tests were conducted for evaluating the corrosion effects on the post-cracking response of RSFRC.CiviTest Company and the Scientific and Technological Research Assistance Centre (CACTI) of the University of Vigo. The first author would like to thank the FCT for the financial support through the Research Grant PD/BD/113638/2015. The third author acknowledges the grant SFRH/BSAB/114302/2016 provided by FCT. Part of this work is supported by FCT with the reference project UID/EEA/04436/2013, COMPETE 2020 with the code POCI-01- 0145-FEDER-006941. Finally the support of the FCT through the project PTDC/ECM-EST/2635/201

Durability of Recycled Steel Fiber Reinforced Concrete in Chloride Environment

For structural elements exposed to chloride environments, an important aspect of Recycled Steel Fiber Reinforced Concrete (RSFRC) durability is the corrosion resistance. In the present work, an experimental program was carried out to evaluate the long-term effects of chloride attack on the post-cracking behavior of RSFRC by performing splitting tensile tests and round panel tests. Two RSFRC mixtures defined based on the packing density optimization were produced with a fiber content of 0.8% and 1% per volume of concrete. The influence of different periods of chloride immersion was investigated, as well as the influence of fiber dispersion at crack surfaces of the specimens. Additionally, a simplified prediction of the long-term chloride penetration depth into uncracked RSFRC under immersion aggressive chloride exposure conditions was estimated. The RSFRC revealed high susceptibility to surface corrosion under the chloride exposure conditions adopted. However, the post-cracking resistance of RSFRC was not significant affected. The addition of RSF had a negligible effect in the diffusion of chloride ions into concrete, and the critical chloride content was higher than that found in conventional reinforced concrete structures

Technical and environmental potentialities of recycled steel fiber reinforced concrete for structural applications

The use of recycled materials and industrial by-products as sustainable constituents of cementbased materials could be an environmentally and technically promising solution for application to structural elements. In the present work, the technical and environmental impact of using recycled steel fibers as an alternative to industrial steel fibers for concrete reinforcement was assessed at material level. Numerical simulations were performed to derive the post-cracking constitutive laws of the developed Recycled Steel Fiber Reinforced Concrete (RSFRC) and Industrial Steel Fiber Reinforced Concrete (ISFRC) by inverse analysis of experimental results obtained from three-point notched beam bending tests (3PNBBT), round panel tests supported in three points (RPT-3ps) and double edge wedge splitting tests (DEWST). These simulations were able of fitting with high accuracy the experimental results and consequently to derive the tensile stresscrack width relationships of RSFRC and ISFRC that was used to numerically simulate the bending response of a T-cross section steel RSFRC beam failing in shear. The environmental impact of the incorporation of RSF in concrete in comparison with ISFRC was evaluated using Life Cycle Assessment methodology. The reduction of the environmental impact of the production of RSFRC compared to ISFRC with the same concrete strength class is demonstrated.The 1st author would like to thank the FCT for the financial support through the Research Grants PD/BD/113638/2015 under the Doctoral Program in Eco Construction and Rehabilitation – EcoCoRe

Fertilizantes nitrogenados de eficiência aumentada e ureia na cultura do milho

A ureia é o principal fertilizante nitrogenado utilizado na adubação de cobertura no milho; no entanto, apresenta elevada suscetibilidade às perdas de N por volatilização de amônia. Uma alternativa é o tratamento da ureia com inibidor de urease ou revestimento com camadas de polímeros, classificados como fertilizantes nitrogenados de eficiência aumentada. Neste contexto, o presente trabalho objetivou avaliar o efeito da aplicação de doses de nitrogênio na forma de fertilizantes nitrogenados de eficiência aumentada e ureia em cobertura na cultura do milho. Utilizou-se o delineamento em blocos casualizados em esquema fatorial 3 x 4 + 1. As fontes utilizadas foram: ureia comum; ureia tratada com inibidor de urease e ureia revestida com polímeros testados nas doses de 32,5, 65, 130 e 260 kg ha-1 de N. A massa de cem grãos e a massa seca de parte aérea de plantas aumentaram de forma linear com as doses de N. O teor de nitrogênio na folha e a produtividade de milho foram superiores quando se utilizou ureia tratada com inibidor de urease ou revestida com polímeros, principalmente nas doses de 130 e 260 kg ha-1 de N. Neste sentido, a utilização de fertilizantes nitrogenados de eficiência aumentada não apenas aumentou mas também melhorou o suprimento de N para o milho aumentando ainda a produtividade de grãos

Innovative prefabricated lightweight slab system of high structural performance

This paper presents a new pre-fabricated lightweight slab system where the relatively high post-cracking tensile capacity of steel fibre reinforced concrete (SFRC) is combined with the high ductility and tensile strength of optimized shape profiles made by cold formed steel sheets for a synergetic result in terms of structural performance. The SFRC fills the longitudinal steel profiles (girders) that have openings in the web for materializing SFRC shear mechanisms that provide very high shear resistance to the slab. This slab system (designated by PreSlabTec) includes a SFRC deck of 40 mm thickness and lightweight blocks serving as permanent moulds to the SFRC and thermal insulation. The transversal stiffness is assured by thin wall tubular steel profiles that remained anchored in the girders due to their openings. PreSlabTec is simple and fast of executing and was conceived for being produced in an automation process of prefabrication industry. For assessing the performance of the PreSlabTec in serviceability and ultimate limit state conditions, an extensive program with almost real scale prototypes was executed and tested under loading configurations for flexural and shear failures. For the flexural loading configurations, the PreSlabTec demonstrated a very high load carrying capacity and ductility performance. The PreSlabTec never failed in shear, despite the very exigent shear loading configurations adopted. The long-term deflection was also experimentally evaluated for the standard design requirement for slabs of residential buildings, and a relatively low average creep coefficient of 0.13 was obtained. Finally, the theoretical approach for the design of PreSlabTec is described and its good predictive performance is demonstrated.The authors would like to acknowledge the financial support provided by the ‘Incentive System for Business R&DT – Demonstration Projects in Co-Promotion and co-financing by the ERDF – European Regional Development Fund’, through NORTE 2020 (NORTE-01-0247-FEDER-033690)