Multimodal analysis of GRC ageing process using Nonlinear Impact Resonance acoustic Spectroscopy

Glass fibre Reinforced Cement (GRC) is a composite material composed of Portland cement mortar with low w/c (water/cement) ratio and high proportion of glass fibres. This material suffers from the ageing process by losing its strength with time because of its exposure to severe weather conditions. Ageing process damages the fibre surface and decreases the mechanical properties of the structural components made of this material. It reduces the elastic modulus and toughness of GRC. Fracture toughness is traditionally measured by four point bending tests. In a previous study by the authors it was observed that ageing related deterioration or damage of GRC could be monitored by Non Destructive Testing (NDT) techniques such as Non-linear Impact Resonance Acoustic Spectroscopy (NIRAS) and other ultrasonic techniques. The scope of this paper is to corroborate previous investigations and offer early damage detection capability by generating more experimental data points by optimizing location of the point of strike and thus generating more resonance vibration modes in NIRAS tests.The authors acknowledge the financial support of the Ministerio de Ciencia e Innovacion MICINN, Spain, and FEDER funding (Ondacem Project: BIA 2010-19933).Genovés Gómez, V.; Riestra García-San Miguel, C.; Borrachero Rosado, MV.; Eiras Fernández, JN.; Kundu, T.; Paya Bernabeu, JJ. (2015). Multimodal analysis of GRC ageing process using Nonlinear Impact Resonance acoustic Spectroscopy. Composites Part B: Engineering. 76:105-111. https://doi.org/10.1016/j.compositesb.2015.02.020S1051117

Concretos secos produzidos com agregados reciclados de RCD separados por densidade

ResumoO uso de agregados reciclados de resíduos de construção e demolição (RCD) em blocos de concreto permite compatibilizar as diferentes características de composição e porosidade desses agregados com os diferentes níveis de exigência mecânica em uso dos blocos. Paralelamente, concretos secos são pouco estudados porque a energia de prensagem obtida em vibroprensas não é facilmente reprodutível em escala de laboratório; porém, parte dessa limitação pode ser superada, realizando-se a avaliação do comportamento da mistura (sob confinamento) com prensas de laboratório com controle de deformação. Assim, o objetivo deste artigo foi analisar o comportamento do concreto seco (no estado fresco e endurecido) produzido com agregados de RCD (separados ou não por densidade), empregando-se esse método laboratorial de prensagem. Com substituição total do agregado natural pelo agregado reciclado misto obtido por processo de jigagem obteve-se resistências à compressão comparáveis às dos concretos de referência. A influência das características dos agregados e das formulações de concretos secos foi identificada pela técnica de compactação laboratorial. A redução da porosidade do agregado reciclado e a otimização da granulometria da mistura seca (cimento e agregados) foram os parâmetros mais importantes para o incremento de resistência observado

Critical Grain Size of Fine Aggregates in the View of the Rheology of Mortar

The aim of this research was to investigate the validity of the Krieger-Dougherty model as a quantitative model to predict the viscosity of mortar depending on various aggregate sizes. The Krieger-Dougherty model reportedly predicted the viscosity of a suspension, which includes cement-based materials. Concrete or mortar incorporates natural resources, such as sand and gravel, referred to as aggregates, which can make up as much as 80% of the mixture by volume. Cement paste is a suspending medium at fresh state and then becomes a binder to link the aggregate after its hydration. Both the viscosity of the suspending medium and the characteristics of the aggregates, therefore, control the viscosity of the cement-based materials. In this research, various sizes and gradations of fine aggregate samples were prepared. Workability and rheological properties were measured using fresh-state mortar samples and incorporating the various-sized fine aggregates. Yield stress and viscosity measurements were obtained by using a rheometer. Based on the packing density of each fine aggregate sample, the viscosity of the mortar was predicted with the Krieger-Dougherty model. In addition, further adjustments were made to determine the water absorption of fine aggregates and was transferred from successful experiment to simulation for more accurate prediction. It was also determined that both yield stress and viscosity increase when the fine aggregate mean size decreases throughout the mix. However, when the mean size of the fine aggregates is bigger than 0.7 mm, the yield stress is not affected by the size of the fine aggregate. Additionally, if aggregate grains get smaller up to 0.3 mm, their water absorption is critical to the rheological behavior

Probabilistic approach of carbonation-induced corrosion initiation via a surrogate model

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Coupled carbonation-rust formation-damage modeling and simulation of steel corrosion in 3D mesoscale reinforced concrete

WOS:000356194200011International audienceThis paper presents a modeling strategy to simulate the corrosion of steel reinforcement in atmospheric environment due to carbonation of concrete. Its principal objectives are to analyze the effects of the progressive formation of corrosion products at the steel/concrete interface on concrete cover cracking. The approach is based on modeling studies carried out independently on carbonation, corrosion and creep. These models are coupled and integrated into a numerical 3D simulation procedure for investigating the behavior of concrete mesostructures. A viscodamage model is used to reproduce both creep and damage behaviors of mortar, and the approach is applied to the simulation of a 3D reinforced concrete mesostructure including explicitly the coarse aggregates. The numerical results highlight the influence of aggregates and the effects of creep on crack initiation and propagation. (C) 2015 Elsevier Ltd. All rights reserved

Genetic programming for granular compactness modelling

The prediction of granular mixtures compactness is a recurring question common to many technical and scientific domains. Knowing the theoretical difficulties to predict the ideal solution, the general approach consists in seeking via an experimental approach, which is based on ideal grains distribution curves, an optimal mixtures. In this context, and faced to the empiricism of current approaches, several models have been developed. These models allow predicting granular mixture compactness to some extent. The compressible packing model which is an improved version of the solid suspension model based on the linear model of compactness is one of predictive models allowing the estimation of compactness on the basis of components characteristics and the compaction mode. However, this model in its initial form loses its predictive power because its use requires the measurement of some parameters based on the derivative of experimental curves. In this context, this study aims to present a model which allows predicting the granular mixtures compactness using the intrinsic parameters of components, easily accessible to experiment. The model is issued from the application of the genetic programming (GP) approach. This work presents a double interest: proposing a predictive model of granular mixture compactness with a new approach and demonstrating the GP reliability as a revolutionary tool which forms part of the machine learning algorithms, in complex phenomena modelling

A coupled carbonation- rust formation-mechanical damage model for steel corrosion in reinforced concrete

WOS:000341010300007International audienceThis paper aims at presenting a strategy to simulate the corrosion of steel reinforcement due to carbonation of concrete in atmospheric environment. We propose a model coupling drying, carbonation, diffusion of oxygen, formation of rust and mechanics to describe these phenomena. The rust layer is assumed to be composed of two sub-layers with different elastic modulus. An unstable layer with a low modulus (from 0.1 to 5 GPa) is located next to the transformed medium, and another more stable one with a higher modulus (from 100 to 150 GPa) at the interface with steel reinforcement. This model is applied to a numerical mesostructure composed of 4 phases: mortar matrix, randomly distributed aggregates, steel rebar and rust layers to underline the effect of aggregates on damage initiation and corresponding crack pattern of concrete cover

Probabilistic modelling of calcium leaching in a tunnel for nuclear waste disposal

This works aims at studying, through the Monte-Carlo method, the influence of the leaching kinetics parameters spatial variability on the lilfespan of a concrete structure. The considered structure is a tunnel for nuclear waste disposal. It is observed that the expected value for the lifespan estimated when considering the material spatial variability is significantly lower than the lifespan estimated with a single simulation considering uniform parameters fields, equal to the expected value for each parameter