Bacterial self-healing is an innovative technology allowing repairing open micro-cracks in concrete by CaCO3 precipitation. This bio-technology improves the durability of the structure. In this ...paper, peptone, yeast extract and Bacillus Subtilis were added as microbial adjuvant in concrete mix design. This led to a decrease in porosity resulting in an increase of strength, dynamic modulus as well as a reduction of water uptake, gas permeability and chloride permeation. Scanning electron microscopy, energy dispersive spectroscopy and raman spectroscopy showed that the microbial precipitations in the crack were CaCO3. Moreover, the morphology of calcite crystals was a needle-like, bouquet-like and rhombohedral-shaped. At 44 days, 400 μm crack surface width was completely filled. Hence, peptone, yeast extract and Bacillus Subtilis could be considered as a promising concrete admixture in enhancing durability and mechanical properties of concrete. Furthermore it is established that Eurocode 2 could be applied with confidence for predicting properties of bacterial concrete.
This research investigates the effectiveness of bio-sourced flax fiber-reinforced polymer in comparison with a traditional system based on carbon fiber-reinforced epoxy polymer in order to confine ...recycled aggregate concretes. The experimental investigation was conducted on two series of concrete including three mixtures with 30%, 50%, and 100% of recycled aggregates and a reference concrete made with natural aggregates. The concrete mixtures were intended for a frost environment where an air-entraining agent was added to the mixture of the second series to achieve 4% air content. The first part of the present work is experimental and aimed to characterize the compressive performance of confined materials. The results indicated that bio-sourced composites are efficient in strengthening recycled aggregates concrete, especially the air-entrained one. It was also found that the compressive strength and the strain enhancement obtained from FRP confinement are little affected by the replacement ratio. The second part was dedicated to the analytical modeling of mechanical properties and stress-strain curves under compression. With the most adequate ultimate strength and strain prediction relationships, the full behavior of FRP-confined concrete can be predicted using the model developed by Ghorbel et al. to account for the presence of recycled aggregates in concrete mixtures.
This work is devoted to the study of fresh and hardened properties of concrete containing recycled gravel. Four formulations were studied, the concrete of reference and three concretes containing ...recycled gravel with 30, 65 and 100 % replacement ratios. All materials were formulated on the basis of S4 class of flowability and a target C35 class of compressive strength according to the standard EN 206-1. The paper first presents the mix design method which was based on the optimization of cementitious paste and granular skeleton, then discusses experimental results. The results show that the elastic modulus and the tensile strength decrease while the peak strain in compression increases. Correlation with the water porosity is also established. The validity of analytical expressions proposed by Eurocode 2 is also discussed. The obtained results, together with results from the literature, show that these relationships do not predict adequately the mechanical properties as well as the stress–strain curve of tested materials. New expressions were established to predict the elastic modulus and the peak strain from the compressive strength of natural concrete. It was found that the proposed relationship
E
–
f
c
is applicable for any type of concrete while the effect of substitution has to be introduced into the stress–strain (
ε
c1
–
f
c
) relationship for recycled aggregate concrete. For the full stress–strain curve, the model of Carreira and Chu seems more adequate.
Modern concrete mix design is a complex process involving superplasticisers, fine powders, and fibres, requiring time and energy due to the high number of trial tests needed to achieve rheological ...properties in the fresh state. Concrete batching involves the extensive use of materials, time, and the testing of chemical admixtures, with various methodologies proposed. Therefore, in some instances, the required design properties (physical and mechanical) are not achieved, leading to the loss of resources. The concrete equivalent mortar (CEM) method was introduced to anticipate concrete behaviour at fresh and hardened states. Moreover, the CEM method saves time and costs by replacing coarse aggregates with an equivalent sand mass, resulting in an equivalent specific surface area at the mortar scale. This study aims to evaluate the performance of fibre in CEM and concrete and determine the relationships between the CEM and the concrete in fresh and hardened states. Steel and polypropylene fibres were used to design three series of mixtures (CEM and concrete): normal-strength concrete (NSC), high-strength concrete (HSC), high-strength concrete with fly ash (HSCFA), and equivalent normal-strength mortar (NSM), high-strength mortar (HSM), and high-strength mortar with fly ash (HSMFA). This study used three-point bending tests and digital image correlation to evaluate load and crack mouth opening displacement (CMOD) curves. An analytical mode I crack propagation model was developed using a tri-linear stress–crack opening relationship. Post-cracking parameters were optimised using inverse analysis and compared to actual MC2010 characteristic values. The concrete slump is approximately half of the CEM flow; its compressive strength ranges between 78% and 82% of CEM strength, while its flexural strength is 60% of CEM strength. The post-cracking behaviour showed a significant difference attributed to the presence of aggregates in concrete. The fracture energy of concrete is 28.6% of the CEM fracture energy, while the critical crack opening of the concrete is 60% of that of the CEM.
•Pozzolanic materials may improve the mortar's frost resistance.•The treated clay has not improved the mortar’s behavior when exposed to 300 F-T cycles.•Despite its pozzolanic potential, damage ...increased with the clay content.•The clay fineness (only 3870cm2/g) was the main factor of its low efficiency.•The F-T cycles have favored the progress of cement hydration reactions.
This paper presents an assessment of the frost resistance, after 300 freeze – thaw cycles, of mortars made from cements having different amounts of pozzolan addition. Calcined Algerian clay was used, as clinker replacement, at 0, 10, 15 and 20% by weight. In order to limit its physical pozzolanicity, the fineness of the treated clay, at 700°C for 5h, was chosen very close to that of clinker. The aim of this work is to study the influence of the pozzolanic addition on the physical, mechanical and thermal properties of mortars undergoing this kind of cyclical loading. Experimental results show that compressive strength and thermal conductivity decreased, while porosity, water absorption and hydration progress increased. The deteriorations were in an absolute increase with the increase of treated clay level. Although the variant with 10% of addition was the least affected, it was found that whatever the substitution level, the clay fineness has not led to an improvement in pozzolan mortars behavior against the frost attack compared with the control CEM I.
The aim of this work is to study the possibility to reuse the tunnel excavated earth in order to elaborate earth-based mortar for rammed earth reparation. The tunnel excavated earth-based mortars ...were compared with raw earth based-mortars, largely used in practice. The cement was used as stabilizer and the hemp fibers were used to diminish the cracking due to shrinkage. The mechanical, thermal and hydric properties of mortars were characterized after 28 days. The mortars were maintained in hydrothermal chamber at controlled conditions, 20 ± 2 °C and 50 ± 5 HR. The obtained results show that the mechanical performances increase with the increase of cement by earth ratio. While, the increase of cement content affects negatively the thermal conductivity of earth-based mortars. Whereas, the thermal properties were improved with the addition of natural fiber. The excavated earth-based mortars show higher mechanical performances and good thermal properties compared to raw earth-based mortars.
The performance of reinforced concrete beams in the presence of cathode-ray tube (CRT) glass waste is examined. Four concrete mixes containing 0%, 10%, 20%, and 30% CRT glass waste as partial ...replacement of sand were prepared. The compressive and flexural strength as well as the modulus of elasticity of concrete were determined. Reinforced concrete beams with varying amounts of CRT glass were prepared and the three-point bending test was conducted. The load-deflection curve as well as the strain distribution along the depth of the beams were determined. Concrete containing CRT glass showed an increase in compressive strength, flexural strength, and modulus of elasticity especially at 10% replacement level. The load carrying capacity of reinforced concrete beam is higher when 10% of sand is replaced with CRT glass compared to the control beam and the beams with 20% and 30% CRT glass substitution. The failure mode of the reinforced concrete beams is flexural failure, and the failure pattern is similar for all beams. Strain distribution showed a better ductility at control beam where the deflection was higher than the other beams at the same load. Numerical analysis was conducted, and comparison was made with the experimental results. The comparison showed the accuracy of the software used, where the results of maximum load capacity and maximum deflection were very similar, and the difference did not exceed 5%. In addition, the tensile damage generated by the numerical analysis was very similar to that obtained by the experimental study.
In this paper the effects of the strain rate on the inelastic behavior and the self-heating under load conditions are presented for polymeric materials, such as polymethyl methacrylate (PMMA), ...polycarbonate (PC), and polyamide (PA66). By a torsion test, it was established that the shear yield stress behavior of PMMA, PC, and PA66 is well-described by the Ree-Eyring theory in the range of the considered strain rates. During the investigation, the surface temperature was monitored using an infrared camera. The heat release appeared at the early stage of the deformation and increased with the strain and strain rate. This suggested that the external work of deformation was dissipated into heat so the torsion tests could not be considered isothermal. Eventually, the effect of the strain rate on the failure modes was analyzed by scanning electron microscopy.
► Optimisation of the formulation of epoxy polymer concretes, PC. ► The optimum polymer content combining the best performances and the lowest cost is about 13%. ► Cement concrete samples are ...designed with the same aggregates and the same ratio G/S. ► Ordinary cement concrete, OCC, has lower mechanical properties compared to polymer concrete. ► PC exposed to temperatures up to 225
°C is still more efficient than OCC.
This research deals with polymer concrete, PC, based on epoxy resin hardened with a modified polyamines. The used aggregates are sand graded from 0 to 4
mm (S0/4) and gravel graded from 4 to 10
mm (G4/10). Four formulations were fabricated differing by the polymer content which ranged from 6% to 16%. The evolution of the elastic moduli obtained through ultrasonic wave’s propagation method, the thermal conductivity, the porosity and the mechanical strengths in flexure and compression show that the optimum polymer content that guarantees obtaining a polymer concrete with the highest mechanical performances and the lowest cost is about 13%.
The optimum polymer concrete is then exposed to temperature less than 250
°C for 3
h and the obtained results were compared to those of an ordinary cement concrete. When exposed to temperatures higher than 150
°C, the epoxy polymer concrete shows a significant loss of strengths mainly due to the thermo-oxidative degradation of the epoxy polymer and to the debonding between aggregates and the binder. These degradations are accompanied by a gas release.
Cement based concrete has lower mechanical properties compared to polymer concrete. Results show that when exposed to temperatures less than 250
°C the epoxy polymer concrete is still more efficient than cement based concrete.
Classical models based on the thermodynamics of irreversible process with internal variables dedicated to the inelastic analysis of metallic structures are modified and then used for modeling the ...mechanical behavior of polymers. The major difference comes from the expression of the yield criterion. Indeed, a generalized yield criterion, based on the parabolic Drucker and Prager criterion, is proposed including the first invariant of the stress tensor as well as the second invariant and the third invariant of the deviatoric part of the stress tensor. Close agreement between experimental data and yielding predictions is obtained for various polymers loaded under different states of stress. It has been established that the temperature
T, the strain rate
s
˙
, the critical molecular mass
M
c and the degree of crystallinity
X
c do not affect the parameter
m of the proposed yield function. Furthermore, viscoplastic constitutive equations are developed in the framework of the general principles of thermodynamics with internal variables for generalized materials considering only the kinematic hardening rule. Experimental data obtained under different loading conditions are well reproduced by the proposed model. An accurate identification of the model parameters and the introduction of the isotropic hardening variable into the yield function and the drag stress will improve the predictions of the overall mechanical behavior of polymers especially the unloading path.
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