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 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

description of the methodological approach

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Influence of Water-Repellent Admixtures on the Water-Resistance of Unstabilized and Stabilized Compressed Earth Blocks

 The low durability of water action has been the main issue of earth construction since ancient times. In this way, sustainable solutions are needed to improve the earthen building materials water-resistance performance without significantly changing their appearance and eco-friendly nature. This study aims at characterizing the water-resistance of compressed earth blocks (CEB) produced with or without different types of colorless water-repellent admixtures. To this end, different types of unstabilized and 8% cement stabilized CEB were protected with two post-surface treatments, namely a silane-siloxane based surface water-repellent (SWR) and a natural linseed oil (LO), as well as one olein based integral water-repellent (IWR). Unprotected reference CEB were also considered for comparison purposes. More sustainable CEB were produced with 20% replacement of earth by recycling waste building materials. The CEB were tested in terms of compressive and flexural strength, capillary water absorption, immersion absorption, water permeability, low-pressure water absorption, and water erosion resistance from drip and spray tests. The influence of the moisture content on the compressive strength was also analysed. The cement-stabilization and water-repellent treatments were able to overcome the non-water-resistant nature of unstabilized CEB. In general, the best performance was attained with SWR, followed by IWR. The LO was less effective in reducing the long-term absorption but was able to protect unstabilized CEB from light rainfall simulated conditions. Under severe water erosion, the surface treatments were less effective, but water penetration was reduced up to near 40%. The mechanical strength, total porosity, water permeability and immersion absorption were not significantly affected by water-repellent products. Moreover, the mechanical strength reduction of stabilized CEB after saturation was about 30%, regardless of the water-repellent treatment. The main contribution of water-repellent admixtures occurred in all properties involving capillary absorption

Influence of carbon dioxide as a mixture component on the cement hydration

Concrete is the most widely material used in the construction industry. However, it has a great environmental impact, mainly because of cement manufacture and the inherent CO2 emissions into the atmosphere. This research intends to contribute to the reduction of the environmental impact of the concrete industry through the uptake of CO2 during the concrete production phase. The few research works on this issue report contradictory results regarding the impact of CO2 when added during the mixing phase. These results report an acceleration of the reactions [1], a reduction of the time setting [2] and either an increase or a decrease in the amount of hydration products, depending on the CO2 amount [3, 1]. Thus, this research aims at understanding the impact of CO2 amount on the hydration reactions of cement in order to enable its adoption as a component mixture. To achieve this purpose, 4 cement pastes were produced with different amounts of CO2. The pH of the mixture was measured to evaluate the impact of CO2 on its alkalinity reduction. Compressive strength, XRD and SEM analysis were also performed to assess the influence on the hydration reactions and also on the degree of carbonation. Results suggest that CO2 can increase the mechanical resistance at early ages if used in a little amount. However, the reduction in pH due to CO2 appears to compromise this performance at longer ages

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