Mongi Ben Ouezdou

Experimental Study of Steel Fiber Concrete Slabs Part I

This article aims to study the effects of adding steel fibers to concrete on the mechanical behavior of steel fiber concrete (SFC) slabs. After formulating the SFC, an experimental work was, first, conducted on 160 × 320 mm cylindrical specimens and 70 × 70 × 280 mm prisms. Then, this study was carried out on 20 rectangular 1,100 × 1,100 × 60 mm small slabs submitted to a distributed load. Two types of fibers with hooked ends were used: long fibers (LF) of a length of 50 mm and short fibers (SF) of a length of 35 mm. The studied parameters are compressive and tensile strengths and Youngs modulus. Plain concrete (PC) small slabs were also prepared to be compared to the SFC specimens. The results showed that the compressive strength of SFC increased up to 25% while the splitting tests showed an improvement of the SFC reaching 45%. Tests on SFC small slabs also showed that a smaller deflection is obtained with respect to PC, which indicates an improvement in strength (up to 100%), in ductility and in resistance to cracking. The LF gives a better improvement in strength than the SF for a 70% kg/m³ of steel proportioning.

Incorporation of Crushed Sands and Tunisian Desert Sands in the Composition of Self Compacting Concretes Part II

This paper is interested in the incorporation of crushed sand and desert sand in the composition the self compacting concretes (SCC). Desert dune sand, which has a fine extra granulometry, and the crushed sand, which contains an important content of fines, can constitute interesting components for SCC. Part II consists in studying the behaviour of SCC containing various sands with different origins. These sands, with different sizes, consist of several combinations of rolled sand (RS), crushed sand (CS) and desert sand (DS). The study examines the influence of the granular combination of sands on the characteristics in the fresh and the hardened state of SCC. The results of the experimental tests showed an improvement of the workability of the fresh SCC by combining sands of varied granulometry. The addition of the DS to CS or to RS allowed the increase of the mixture viscosity but decreased the mechanical strengths. Furthermore, the CS-RS combinations increased the compressive and the tensile strengths of the studied SCC. The optimized formulations of sands gave the highest performances of the SCC.

Incorporation of CrusHed Sands and Tunisian Desert Sands in the Composition of Self Compacting Concretes Part I: Study of Formulation

This paper examines the incorporation of the crushed sand (CS) and desert sand (DS) in the formation of self compacting concrete (SCC). These sands have been substituted for the rolled sand (RS), which is currently the only sand used in concretes and which is likely to run out in our country. DS, which comes from the Tunisian Sahara in the south, is characterized by a tight distribution of grains size. CS, a by-product of careers containing a significant amount of fines up to 15%, is characterized by a spread out granulometry having a maximum diameter of around 5mm. These two sands are considered as aggregates for the SCC. This first part of the study consists in analyzing the influence of the type of sand on the parameters of composition of the SCC. These sands consist of several combinations of 3 sands (DS, CS and RS). The method of formulation of the adopted SCC is based on the filling of the granular void by the paste. The CS substitution to the RS made it possible, for all the proportions, to decrease the granular voids, to increase the compactness of the mixture and to decrease the water and adding fillers proportioning. These results were also obtained for a moderate substitution of DS/CS (

Prediction and Measurement of the Bending Strength of the RCC

The present work deals with the prediction, through models and experimental evaluation, of the bending strength of roller compacted concrete (RCC) for pavement applications. This concrete was manufactured using low cement proportioning (150 to 250 kg/㎥). The characterization of hardened RCC was carried out by experimental measurements of bending strengths. The predictions of these characteristics were achieved using empirical models. Comparison, of the values found in experiments with those empirically obtained, was made in order to choose and to propose the adapted and the most reliable models of prediction. The study showed that the bending strengths of the RCC mixture, experimentally found, can be also identified by models.

Chloride Diffusion in Mortars - Effect of the Use of Limestone Sand Part II: Immersion Test

In order to determine the effect of the use of limestone sand on chloride ion ingress in mortar, specimens were cast with two different sands: siliceous sand (used as reference) and limestone crushed sand (used for this study). To compare and assess the resistance of this mortar to chloride penetration, two different diffusions tests were employed: slow migration and rapid migration (AASHTO test). In this study, calculation of the effective diffusion coefficient is proposed using a model based on Nernst?Planck equation. The diffusion coefficients from each sample were compared. The results for all tests show that the diffusion coefficients for siliceous sand mortar are larger than those obtained with limestone sand. It appears also that the diffusion coefficient varies as a function of the W/C ratio.

Modeling of creep in GFRP RC beams

The laws of creep following the Eurocode 2 recommendations are investigated. Analytical study was also conducted including creep under constant stress; successions of increasing stress superposition principle equivalent time and the return creep reloading. The results of this study revealed that in the case of a very short unloading phase, which would be of little influence, this leads to an overestimation of creep deformation. In the limit by succession of very short loading -unloading cycles application of BPEL led to grossly overestimated deformations. This investigation should guide the civil engineer/designer for a better understanding creep phenomenon in GFRP reinforced concrete members.

Study of the Anisotropy of the Roller Compacted Concrete (RCC) for Pavement

The roller compacted concrete (RCC) is supposed to be isotropic, whereas the compaction of this material, which is achieved using the same machines used for the soil, appears only unidirectional, making the RCC an anisotropic material. In this experimental work, the influence of the phenomenon of compaction on the isotropy of the RCC is studied. This study was carried out through an evaluation of the compressive strengths and ultrasonic tests which were used for measurements of the elastic modulus and the dynamic Poissons ratio of the RCC as well as a qualitative judgement of the RCC aspect at the hardened state. The results of this work proved the anisotropy of the RCC and they showed the sensitivity of the mechanical strengths and the elastic modulus to the compaction direction.