Sofiane Amziane

Influence of compactness and hemp hurd characteristics on the mechanical properties of lime and hemp concrete

ABSTRACT Research on concrete made with hemp is part of a sustainable development policy in the building field. The very low apparent density of the hemp hurds confers to lime and hemp concrete lightness and low thermal conductivity, however compared to usual construction materials, it has low mechanical strength. The presence of fibres in the hemp, the optimization of the granular to binder ratio, and the compaction during the casting process represent parameters which could significantly increase the compressive strength and change the mechanical behaviour of the material. A brief study of these parameters is presented and discussed in this paper.

Effect of compaction on mechanical and thermal properties of hemp concrete

ABSTRACT Some preliminary studies, dealing with the process optimisation of pre-cast building elements made of Lime and Hemp Concrete (LHC), have shown that compression during casting lead to significant improvements: better mechanical characteristics and facing. However, this compaction leads to an increase of the weight to volume ratio and to a decrease in porous volume. Thus, the amount of entrapped air inside material, which contributes to decrease the thermal conductivity, is lower. Our data actually show a slight increase in thermal conductivity when compactness increases. The goal of this study is to compare the effect of compaction during casting on both mechanical and thermal characteristics of hardened specimens in order to evaluate the relevance of such a process.

Cementitious Paste Setting Using Rheological and Pressure Measurements

For construction schedules, such as placement and formwork removal, to be controlled, how mechanical characteristics of concrete evolve during the setting period needs to be measured. Cement paste and mortar setting time measurement is usually done through the standard Vicat test, which does not determine when concrete pumping or extrusion may occur because of insufficient information (initial and final set time). Hydraulic form pressure and intrinsic material parameter (plastic viscosity and yield stress) variation effects on cement paste setting period are studied. Hydraulic and rheological (shear rate sweep and stress growth) measurements allowed setting monitoring. The authors discuss experiment results and compare them with the cement paste Vicat Test. The study shows that the Vicat test is less sensitive to cement paste setting evolution than the proposed tests, which provide useful information at an early age.

Efficiency of Beam-Column Joint Strengthened by FRP Laminates

The recent earthquakes have shown that the vulnerability and the defects of the concrete joints in beam– column framed structures were the main causes for many building collapses. Such vulnerability and defects are in general the consequences of many factors. External strengthening with composite materials represents an alternative and a sound and efficient technique to improve the performances and aptitude to withstand seismic action. However, while the use of such strengthening technique offers many advantages, it has some disadvantages, particularly a remarkable loss of ductility. The present study examines the effects of an external strengthening of reinforced concrete beam–column joints against cyclic loading using CFRP laminates and GFRP sheet. The experimental program is constituted of three beam–column reinforced concrete joints at a scale of one to three (1/3) tested under the effect of a prestressing axial load acting over the column. The beams were subjected at their ends to a reverse cyclic loading under displacement control to simulate a seismic action. Strain and cracking fields were monitored with the help a digital recording camera. Following the analysis of the results, a comparison was made concerning the performances in terms of ductility, strength and mode of failure of the different strengthening solutions.

A novel settling and structural build-up measurement method

A new device, consisting of a rough plate immersed in the fluid sample, was developed to enable a simpler measurement of the sedimentation and yield stress increase of non-Newtonian suspensions. Due to the deformation of the material at rest or due to changes in the solid volume concentration by sedimentation along the vertical axis, the plate apparent mass varies with time. The apparent yield stress value of a fluid and the sedimentation rate could be calculated from this measurement.

Measurement of Workability of Fresh Concrete Using a Mixing Truck

The main objective of this study is to evaluate the workability of fresh portland cement concrete while it is still in the mixing truck by determining fundamental rheological parameters (plastic viscosity and yield stress). Nine concrete mixtures with different values of yield stress and plastic viscosity were tested in a concrete truck. The measurements made with the truck were based on the typical method of determining the flow behavior in a traditional fluid rheometer; that is, the shear rate in the mixing truck was swept from high to low by varying the rotation speed of the drum. The results of these experiments are discussed and compared with data provided by the ICAR rheometer, a portable rheometer designed for measuring concrete rheology. The test results indicate that the mixing truck equipment is sufficiently sensitive to detect differences in yield stress, slump, and plastic viscosity. However, the plastic viscosity determined by the truck measurement did not correlate with plastic viscosity as measured by the ICAR rheometer, while the yield stress determined by the truck measurement did correlate well with the measured slump and the ICAR rheometer results Suggestions are given on how to improve the mixing truck for better use as a rheometer.

Bio-aggregates Based Building Materials

Global warming, energy savings, and life cycle analysis issues are the factors that have contributed to the rapid expansion of plant-based materials for buildings, which can be qualified as environmental-friendly, sustainable and efficient multifunctional materials. These materials are obtained from the processing of hemp, flax, miscanthus, pine, maize, sunflower and bamboo. The work of the Technical Committee (TC 236-BBM) was dedicated to the study of construction materials made from plant particles. Are concerned building materials containing as main raw material renewable, recyclable and easily available plant particles. However, the work was relatively centred on hemp because hemp shiv is the bio-aggregate that is the most widely used in building materials and the most studied in the literature. This state-of-the-art report reflects the current knowledge on the assessment of the chemical, physical and mechanical properties of bio-aggregate and vegetal concrete. It presents an overview on the several possibilities developed worldwide about the use of plant aggregate to design bio-based building materials. The first five chapters relate to the description of the vegetal aggregate. Then, hygrothermal properties, fire resistance, durability and finally the impact of the variability of the method of production of bio-based concrete are assessed on Chaps. 7-9.

Influence de la rhéologie des bétons renforcés de fibres métalliques sur leurs propriétés mécaniques

ABSTRACT This paper presents the results of an experimental study on the effect of rheology on the orientation of steel fibers. It then studies then the influence of the orientation of a volume of 0.5% of steel fibers on the mechanical properties of a fluid ordinary concrete and a self-compacting concrete (low yield stress) and of a concrete with high performances figure (high yield stress). The results show that the fluidity of the concrete followed by the wall effects are essential parameters of the orientation and distribution of fibers. Since one obtains an orientation in the direction of the mechanical effectiveness, a flexural behavior clearly improved is observed, including for ordinary concrete. On the other hand, we observed in the case of a high performances concrete that a bad orientation of fibers cancels their mechanical contributions in bending (ductility). Compressive strength is not affected.

Effects of the Transverse Reinforcement on the Shear Behaviour of High Strength Concrete Beams

This paper presents the results of an experimental investigation dealing with the effects of transverse reinforcement on the crack patterns, the ultimate carrying capacity and the ductility of beams made of high strength concrete and normal strength concrete for comparison purposes. The test results are analyzed and compared with the shear provisions in the four major universal codes (ACI-318; BS-8110; Eurocode 2; BAEL 99). Twenty six reinforced concrete beams with and without transverse reinforcement were constructed using different shear-span to depth ratios (a/d = 1.5, 2.0 and 3.0) and different compressive strengths of concrete (44 MPa, 65 MPa and 86 MPa). The test results indicate that the presence of transverse reinforcement had controlled efficiently the crack width by enhancing the aggregate interlocking on the crack surface, increased moderately the shear strengths of the beams by factors ranging from 1.14 to 1.86, and increased appreciably the ductility of beams at the ultimate state. It should be noted, however, that the beams failed at shear strength contributions of transverse reinforcement (Vs) considerably lower than the values predicted by the models used in the four major universal codes. This translates that the existing universal design codes may not be rationally safe against shear design of high strength concrete beams containing transverse reinforcement.

Geometrical Effect on the Behavior of CFRP Confined and Unconfined Concrete Columns

The present contribution aims at highlighting the behavior of square-section and cylindrical specimens confined by carbon fiber reinforced polymer fabrics. For this purpose, 48 cylindrical concrete moulds of 110 × 220 mm 2 dimensions and 24 prismatic concrete moulds of 100 × 100 × 200 mm3 dimensions were tested for uniaxial failure under compression. The forms of rupture observed are all similar, no matter the shape of the section of the test-specimen (circular or square). Without confinement, a superiority of 14% in terms of compressive strength is confirmed for the square-section specimen in comparison with the circular-section specimens. With confinement, we observe a very significant advantage of circular-section specimens compared to square-section specimens. The performance of an fiber-reinforced polymer confinement is, however, largely better for a cylindrical specimen comparing to the prismatic specimen. With a rate of confinement of 1 and 3 layers, the compressive strength is increased, respectively, by 58% and 236% for the cylindrical test-specimen and by 20% and 95% for the square specimen. Moreover, the concrete shows an additional deformability proportionally to the confinement rate. The stress-strain curves obtained showed a tri-linear behavior; the first and the second part of the curve depend on the resistance of the non-confined concrete, whereas the third part was directly dependent on the confinement rate and its stiffness. Extension of analytical modeling of Wu et al. (Wu, G., Wu, Z.S., Lu, Z.T. and Ando, Y.B. (2008). Structural Performance of Concrete Confined with Hybrid RP Composite, Journal of Reinforced Plastics and Composites, 27(12): 1323-1348) is proposed to take into account the effect of geometry.