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

Abdelhamid Rmili,Mongi Ben Ouezdou,Mhamed Added,Elhem Ghorbel 한국콘크리트학회 2009 International Journal of Concrete Structures and M Vol.3 No.1

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.

Primary user localisation and uplink resource allocation in orthogonal frequency division multiple access cognitive radio systems

Haewoon Nam,Saeed, Nasir,Ben-Ghorbel, Mand,Alouini, Mohamed Slim IET 2015 IET COMMUNICATIONS Vol.9 No.8

<P>In cognitive radio networks, secondary users (SUs) can share spectrum with primary users (PUs) under the condition that no interference is caused to the PUs. To evaluate the interference imposed to the PUs, the cognitive systems discussed in the literature usually assume that the channel state information (CSI) of the link from a secondary transmitter to a primary receiver (interference link) is known at the secondary transmitter. However, this assumption may often be impractical in cognitive radio systems, since the PUs need to be oblivious to the presence of the SUs. The authors first discuss PU localisation and then introduce an uplink resource allocation algorithm for orthogonal frequency division multiple access-based cognitive radio systems, where relative location information between primary and SUs is used instead of CSI of the interference link to estimate the interference. Numerical and simulation results show that it is indeed effective to use location information as a part of resource allocation and thus a near-optimal capacity is achieved.</P>

Incorporation of CrusHed Sands and Tunisian Desert Sands in the Composition of Self Compacting Concretes

Abdelhamid Rmili,Mongi Ben Ouezdou,Mhamed Added,Elhem Ghorbel 한국콘크리트학회 2009 International Journal of Concrete Structures and M Vol.3 No.1

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 (< 40%) and a weak ratio of DS/RS (20%). For higher proportions, the addition of DS to CS or RS did not improve the physical characteristics of the SCC granular mixture.

Incorporation of Crushed Sands and Tunisian Desert Sands in the Composition of Self Compacting Concretes Part Ⅱ: SCC Fresh and Hardened States Characteristics

Abdelhamid Rmili,Mongi Ben Ouezdou,Mhamed Added,Elhem Ghorbel 한국콘크리트학회 2009 International Journal of Concrete Structures and M Vol.3 No.1

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

Rmili, Abdelhamid,Ouezdou, Mongi Ben,Added, Mhamed,Ghorbel, Elhem Korea Concrete Institute 2009 International Journal of Concrete Structures and M Vol.3 No.1

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 (< 40%) and a weak ratio of DS/RS (20%). For higher proportions, the addition of DS to CS or RS did not improve the physical characteristics of the SCC granular mixture.

Incorporation of Crushed Sands and Tunisian Desert Sands in the Composition of Self Compacting Concretes Part II: SCC Fresh and Hardened States Characteristics

Rmili, Abdelhamid,Ouezdou, Mongi Ben,Added, Mhamed,Ghorbel, Elhem Korea Concrete Institute 2009 International Journal of Concrete Structures and M Vol.3 No.1

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.

Production and Biochemical Characterization of α-amylases from Bacillus mojavensis A21 Grown on Chicken Feathers Medium

Noomen Hmidet,Hana Maalej,Hanen Ben Ayed,Sofiane Ghorbel,Habib Kriaa,Moncef Nasri 한국생물공학회 2011 Biotechnology and Bioprocess Engineering Vol.16 No.4

Extracellular α-amylases produced by a newly isolated feather degrading bacterium strain Bacillus mojavensis A21 was optimized and characterized. Zymography showed that the A21 strain produced at least two α-amylases. Higher α-amylase production was achieved in the presence of 10 g/L chicken feathers and 1 g/L yeast extract. The growth of B. mojavensis A21 using chicken feathers as the nitrogen and carbon source resulted in its complete degradation after 48 h incubation at 37°C. However,maximum α-amylase activity was attained after 24 h. The optimum temperature and pH for crude α-amylase activity were 60°C and 6.5, respectively, and its activity was inhibited by EDTA. The end products of starch hydrolysis were maltose, maltotriose, and maltotetraose. α-Amylases from the A21 strain also catalyzed transglycosylation reactions when maltotetraose and maltopentaose were used as substrates and formed higher molecular weight maltoligosaccharides from G5 to G8. The maltooligosaccharide forming endo-α-amylases is useful in bread making as an anti-staling agent and can be produced economically using a low-cost medium with chicken feathers as the substrate.