Ahmed Loukili

Ahmed Loukili
Ecole Centrale de Nantes | EC Nantes · Department of Mechanics, Materials and Civil Engineering

Prof. Dr.

About

219
Publications
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Publications

Publications (219)
Article
Analyzing concrete microscopic images is difficult because of its highly heterogeneous composition and the different scales involved. This article presents an open‐source deep learning‐based algorithm dedicated to air‐void detection in concrete microscopic images. The model, whose strategy is presented alongside concrete compositions information, i...
Article
Designing printable cement-based materials aims to achieve targeted properties to fulfill the specific performance criteria. At fresh state, the material should satisfy particular rheological requirements to achieve a tradeoff between its workability (W), extrudability (E), and buildability (B). Given the printability criteria to be fulfilled, the...
Article
Ultra-High Performance Concrete (UHPC) exhibits high autogenous shrinkage (AS) which significantly increases the risk of early age cracking. To predict the risks of early age shrinkage cracking of environmentally friendly CEM III-based UHPC, a numerical model originally developed for early age crack assessment of ordinary concrete, has been further...
Chapter
The prediction of the early age behavior of cementitious materials is a difficult task, because many of the material properties are very sensitive to curing conditions as it is the case for High Performance Concrete (HPC), which usually has a very low water to cement ratio (0.2 < w/c ≤ 0.3). Early age cracking, a common problem for HPC, is caused b...
Article
The present work analyses the impact of the substitution of natural coarse gravel and sand by recycled gravel and sand on the concrete behavior under free and restrained condition since setting. The methodology presented in this paper associates a Temperature Stress Testing Machine (TSTM) with free shrinkage tests and other experimental advanced te...
Conference Paper
Early age cracking, a common problem for Ultra-High Performance Concrete (UHPC), is caused by Autogenous Shrinkage (AS) and self-desiccation arising from the chemical shrinkage during the cement hydration reactions when the deformation is restrained. However, to avoid the crack development initiated by AS, several solutions can be adopted; one exam...
Article
This paper presents the influence of natural hydraulic lime (NHL) on the behavior of cement-based materials at fresh and hardened states. Two reference mortars with and without limestone filler (LF) and with water-to-cement ratio of 0.6 were considered. For each reference mixture, cement was replaced by NHL with increasing mass proportions of 12.5%...
Chapter
Delayed deformations of concrete are known to induce a risk of cracking in structures and excessive bending. Delayed deformations are mainly of two types: shrinkage and creep. The shrinkage tests were carried out for two substitution rates of natural aggregates with 30% and 100% recycled aggregates (RA). State-of-art and the experimental results sh...
Article
This paper aims to identify the parameters influencing the curling phenomenon, and to understand the influence of cement substitution by increasing proportions of Natural Hydraulic Lime (NHL) on the kinetics and the final curling magnitude. The developed experimental approach shows that the curling is mainly driven by the progress of the drying fro...
Article
Full-text available
In the sustainable development context, the use of demolition waste increases in the building industry. Recycled aggregates from the demolition of concrete structures are then mixed in new concrete. Furthermore, the performance evaluation of a these recycled aggregate concrete (RAC) mix is not only limited to the determination of its conventional m...
Article
Full-text available
This paper describes a comprehensive approach for modelling mechanical and fracture behavior of concrete using discrete element method. Concrete is modelled at mesoscale as three phase material composed of aggregates, mortar and interface. Full aggregate grading curve is considered. A systematic approach has been used in this study to determine DEM...
Article
Full-text available
L'objectif de l'approche expérimentale décrite ici est d'étudier le lien entre le séchage progressif des structures et les déformations macroscopiques engendrées (tuilage et retrait). L'étude présentée vise aussi à identifier les principaux gradients qui apparaissent au sein d'une dalle soumise dès le jeune âge à un séchage par une seule face. Pour...
Article
The concrete structures are under heavy loads once they are set up. The effect of this early loading particularly in terms of creep deformations could be very significant. In order to evaluate the effect of these deformations on the cracking risk of concrete, many studies on early-age creep have been conducted in the last decades. These studies con...
Article
Full-text available
This paper presents the influence of natural hydraulic lime (NHL) on setting and early-age hydration of cement-based materials. A reference mortar was designed with a water-to-cement ratio of 0.6. At a constant paste volume, cement was replaced with increasing mass proportions of 12.5%, 25% and 50% of NHL. The freshly mixed mortars were tested for...
Article
The drying shrinkage of cementitious materials is a complex phenomenon that is very sensitive to boundary conditions such as relative humidity (RH). Its evolution in the range of high RH is well-known and strongly related to the capillary pressures. However, for a range of lower RH, the pressures induced by interfaces become more significant and th...
Article
A partial replacement of the clinker by latent hydraulic or pozzolanic materials is encouraged due to environmental and specific technical requirements. Such substitution remains limited to a relatively low level (less than 30% by mass of cementitious materials). An experimental research work was carried out on mortars made with binary and ternary...
Article
The shape of the specimen or structure has a direct impact on the behavior of drying concrete. This effect is not taken into account in most of shrinkage models and codes. Only the current B4 model and its previous version B3 model incorporate a shape factor. The determination of this coefficient is based on the nonlinear moisture diffusion analysi...
Article
The evolution of technical and environmental requirements fosters the development of geopolymer based grouts for soil reinforcement. Geopolymer based materials actually have several advantages but the improvement of their rheological performances remains a challenging task, as the raw materials, especially sodium silicate and metakaolin, do not hav...
Article
Full-text available
ABSTRACT The shear strength of reinforced concrete beam remains an issue of great interest in structural engineering. For structural members without transverse reinforcements, the application of simple models (Strut and tie model, for instance) results an unsafe design. Also, most of the design codes are based on empirical formulas to design such m...
Article
The nanostructure of alkali-activated materials is now better understood. However, very few studies have been carried on grouts. These highly diluted systems are used to improved soil properties for instance. In this study, the evolution of their local structure was monitored via 29Si and 27Al NMR to understand the formation of the binding phase an...
Article
The service life of concrete structures is primarily affected by cracking. Concrete with a lower cracking potential is consequently more sustainable. In order to estimate the risk of shrinkage-induced cracking, at least four properties should be studied: shrinkage, Young's modulus, creep/relaxation and tensile strength. A mixed experimental and num...
Chapter
In civil engineering, the control of creep has a major role in concrete structure design. Indeed, the viscoelasticity of concrete leads to delayed deformations which could be at the origin of cracking in structures. So, these delayed strains have an impact on their safety margin and life time, especially when they are subjected to high loads. For e...
Article
ESA performance testing protocols are mainly a set of exposure conditions, monitoring strategy, and specimens configuration. Although the large feedback on the representativeness of exposure conditions and the relevance of monitored parameters, the effect of specimen configuration still deserved to be studied. In order to investigate the effect of...
Article
This paper presents the main results of a research carried out to analyze the mechanical properties, intrinsic permeability, drying shrinkage, carbonation, and the self-healing potential of concrete incorporating recycled concrete aggregates. The recycled concrete mixtures were designed by replacing natural aggregates with 0%, 30%, and 100% of recy...
Article
Full-text available
The natural, e.g. autogenous, healing capacity of cementitious materials in concrete is a promising path to overcome the ecological problems and durability preoccupations inherent to civil engineering. But, recovery of mechanical from autogenous healing are due to ongoing hydration reactions highly dependent on the binder. In this study, the healin...
Article
Slabs are subjected to many important drying effects due to their large exchange surface area, particularly plastic and drying shrinkage. The use of suitable mineral additions with shrinkage reducing properties is necessary to improve cement-based materials behavior. The aim of the experimental work carried out is to investigate the influence of na...
Article
This paper aims to study the relation between drying and the development of damage from concrete surface. For that reason, the experimental study aims to measure the internal relative humidity in four different locations during 500 days. In parallel, total shrinkage is monitored for 250 days in different positions of the specimen. Under drying cond...
Article
The study presented in this paper aims at defining a procedure to study the efficiency of models used to extrapolate long-term shrinkage from experimental data. The approach allows estimating the minimum duration of measurements required to reach a given accuracy. The drying shrinkage of three Self-Consolidating Concretes (SCC) was monitored during...
Article
The use of recycled aggregates in concrete mixtures is a part of waste recovery strategy. The French national project RECYBETON aims at developing scientific knowledge to facilitate the use of recycled aggregates into concrete. In this experimental study, two exposure conditions were combined to analyse the behaviour of fresh and hardening concrete...
Article
Full-text available
Fracture in quasi-brittle materials like concrete is mainly governed by two processes: energy dissipation and discontinuous displacement fields or discrete cracks. In this study we discuss the simultaneous development of both types of fracture. Energy dissipation and crack openings are analyzed during the fracture development by acoustic emission a...
Article
Normal and recycled aggregate concrete differ significantly in their fracture characteristics. The cracking in recycled concrete initiates earlier; the fracture length is generally larger and the use of high proportion of recycled aggregate results in higher strain gradients in the fracture process zone. However, in spite of the negative influences...
Article
Full-text available
La formulation de mortiers autonivelants vise un compromis entre la fluidité et la stabilité requise pour éviter les problèmes de ségrégation. L'utilisation d'additions minérales appropriées avec des propriétés de rétention d'eau s'avère nécessaire pour améliorer l'homogénéité. L'objectif de l'approche expérimentale décrite ici est d'étudier l'infl...
Article
The influence of sealed curing on long-term drying behaviour and durability of concrete is investigated in this experimental study. Two concretes were cured for 16 h, 24 h, 48 h, and 1 month then exposed to drying at 20 °C and 50% RH. Mass-loss, total and autogenous shrinkage were monitored. Hydration and microstructural development were studied by...
Article
A new monitoring approach was developed to enhance the analysis of performance tests and provide new sulfate resistance criteria. Even in the case of low degradation rates or non-swelling materials exposed to external sulfate attacks, the method allows detecting microscopic evolutions via a set of easily accessible monitored parameters. The monitor...
Article
Full-text available
This study aims at improving the analysis of drying tests and taking better advantage of the measurements, by studying the influence of the specimen size. One self-consolidating concrete (SCC) was studied during three years. Drying started 24 hours after casting. The tests were carried on three sizes of cylinders: Φ78mm, Φ113mm and Φ163mm, under th...
Article
The requested thermal efficiency for new buildings leads to use new materials. In recent years, many researchers have conducted studies on the phase change materials (PCM) concrete composite. Fire safety in buildings has become an important requirement and building materials should have good fire behaviour in order to be used in certain application...
Article
External sulfate attacks induce severe deterioration of concrete because of several phenomena: leaching, precipitation of expansive products, aggregates loss, and cracking. A new methodology has been developed to assess sulfate resistance of cement-based materials. We can actually estimate the nature of leached and precipitated minerals, and the mi...
Article
This paper presents the results of experimental research on recycled concrete at early age and long term. It consists in studying the effect of initial water saturation of recycled concrete gravel (RG). Five mixtures were investigated, one mixture with natural aggregates only (reference concrete) and the second with 100% of RG using four initial wa...
Article
Geopolymers have gained much interest recently as a promising alternative to cementitious materials in some applications. However, research is still needed to use this technology for soil reinforcement grouts. The specifications of grouts mainly consist in rheological properties, strength and permeability. Grouting actually requires a low viscosity...
Article
This paper presents the results of experimental research on recycled concrete at early age. The influence of recycled gravel and sand (RG and RS) and initial water saturation of RG on plastic shrinkage and cracking sensitivity was investigated. Four initial water saturations were studied: 30%, 70%, 100% and 120% of saturated surface dried (SSD). Th...
Article
Underground concrete structures may be subjected to external sulfate attack and their long-term performance is of concern. A coupled transport/chemical numerical model has been compared to experimental data obtained on a cement paste exposed to external sulfate attack thanks to recent developments in experimental analysis such as scanning electron...
Conference Paper
Full-text available
Since Self-Consolidating Concrete (SCC) does not need any vibration; its use results in better filling of formworks and safer conditions for workers on the construction sites. For these reasons, SCC is taking a more significant market share in France and worldwide. However, some problems associated with vibrated concrete remain, and one of them sta...
Article
In this paper, the fracture process zone (FPZ) is investigated on unnotched and notched beams with different notch depths. Three-point bending tests have been realized on plain concrete under crack mouth opening displacement (CMOD) control. Crack growth is monitored by applying the acoustic emission (AE) technique. The comparison with a numerical m...
Article
This paper focuses on mechanical regains that can be obtained due to self-healing of cementitious materials. Experimentally, small cracks with a width of around 10 μm were healed by water immersion and corresponding regains were assessed by means of three-point-bending tests. A general discussion about stiffness and strength regains is provided wit...
Article
This study aims at rationalizing the analysis of drying shrinkage tests and taking better advantage of the measurements, by studying the influence of the specimen size. Three self-consolidating concrete and one vibrated concrete mixes were studied during 3 years. Drying started 24 h after casting. The tests were carried on three sizes of cylinders:...
Article
Full-text available
The fracture process zone (FPZ) was investigated on unnotched and notched beams with different notch depths. Three point bending tests were realized on plain concrete under crack mouth opening displacement (CMOD) control. Crack growth was monitored by applying the acoustic emission (AE) technique. In order to improve our understanding of the FPZ, t...
Article
Full-text available
The fracture process zone (FPZ) was investigated on unnotched and notched beams with different notch depths. Three point bending tests were realized on plain concrete under crack mouth opening displacement (CMOD) control. Crack growth was monitored by applying the acoustic emission (AE) technique. In order to improve our understanding of the FPZ, t...
Conference Paper
The quality of curing is a significant initial condition, which changes regularly during construction. A longer sealed curing results in higher strength and stiffness of concrete. It also provides a better durability and a lower carbonated depth. However, few studies deal with the influence of the duration of sealed curing on the long-term drying s...
Conference Paper
This paper presents the results of experimental research on recycled concrete at early age and long term. It consists in studying the effect of the proportion of recycled gravel (RG) on shrinkage and cracking risk. Three mixtures were investigated to study the effect of substitution of natural gravel (NG) by the recycled gravel (0% RG, 30% RG and 1...
Article
The study presented in this paper deals with the influence of the measurement technique on autogenous shrinkage. A state of the art shows that many setups based on different techniques have been designed to measure autogenous deformations. In this experimental study, four different setups and setting devices were gathered in the same laboratory. Al...
Conference Paper
In order to understand the interaction between creep and damage, some experimental methods were developed to follow the microcracking evolution during creep tests as the acoustic emission technique. However, these techniques are unable to analyze the real coupling between creep and damage. In fact, the creep deformations lead to the damage which in...
Conference Paper
The creep behavior of concrete structures at long term depends on the initial state and therefore on an eventual damage of the main material. Most studies were interested in creep phenomenon of mature concrete while a few works were carried out on young concrete. However, the concrete structures may be solicited earlier as the tensioning of the pre...
Article
Full-text available
Within the CEOS.FR national research project, several experiments on massive concrete structures were conducted to improve the knowledge on the cracking phenomenon. In this paper, experiments where deformations at early age are restrained are presented. Testing bodies are I-shaped and two largely dimensioned steel struts are placed laterally betwee...
Article
Abstract The use of municipal solid waste incineration (MSWI) electrostatic precipitator fly ash (ESPFA) as partial replacement of cement was studied in this work in order to provide a method to assess its potential reactivity in presence of cement. Thermal fly ash (TFA) and ground sand (GS), respectively pozzolanic and chemically inert materials,...
Conference Paper
Full-text available
Concrete's intrinsic ability to heal, called autogenic healing, has been reported for many years. This natural process is being improved and supplemented for some years by promising engineered additions such as mineral additions, capsules containing healing agents, minerals producing bacteria, or fibres limiting the crack width. However, a deeper u...
Conference Paper
Full-text available
Self-healing of concrete cracks is a potential way to increase durability of structures. Even if the natural, autogenic, healing capacity of concrete is rather well understood, both from a mechanical and a permeability point of view, non-destructive techniques are required to supplement destructive tests to assess and monitor the healing efficiency...
Article
An experimental investigation is performed to study the degradation of reinforced concrete beams by employing two experimental techniques simultaneously i.e. digital image correlation and acoustic emission. The former method gives very precise measurement of surface displacements, thus crack openings and crack spacing are determined. In order to co...
Article
Full-text available
Les comportements mécaniques à la rupture de bétons constitués de granulats recyclés (BGR) et de sables recyclés (BSR) ont été étudiés en utilisant une analyse synchronisée d'essais en flexion trois points avec la technique de corrélation d'images. Les profils d'ouverture de fissure et les zones de localisation des déformations (ZLD) ont été calcul...
Chapter
Sulfate-rich groundwater and seawater can be considered as chemically aggressive environments where external sulfate attacks may affect the durability of concrete. The consequences of sulfate attacks are leaching, expansion, cracking and softening of concrete. This chapter focuses on external sulfate attacks, i.e. the chemical action of sulfate ion...