Effect of Molecular Weight and Carboxylic Density of Polycarboxylates Ether Superplasticizer on Its performance in Cement Pastes

The main difficulty encountered in the formulation of high performance concrete (HPC) consists in choosing the most efficient cement-superplasticizer pair allowing to obtain maximum water reduction, good workability of the concrete in the fresh state and very good mechanical resistance in the hardened state. The aim of this work is to test the efficient of three polycarboxylate ether based superplasticizers (PCE) marketed in Algeria with CEMI 52.5 R cement and to study the effect of chemical structure of PCE on zeta potential, rheological and mechanical properties of cement pastes. The property of the polymers in cement was tested by a Malvern Zetasizer 2000 apparatus and VT 550 viscometer. Results showed that the zeta potential and its rheological properties are related with the molecular weight and the carboxylic density of PCE. The PCE with a moderate molecular weight and highest carboxylic groups had the best dispersion (high value of zeta potential) and lowest viscosity. The effect of chemical structure of PCEs on mechanical properties are evaluated by formulation of cement mortar with this PCEs, the result shows that there are a correlation between zeta potential of polymer and compressive strength of cement paste

Effect of Molecular Weight and Carboxylic Density of Polycarboxylates Ether Superplasticizer on Its performance in Cement Pastes

The main difficulty encountered in the formulation of high performance concrete (HPC) consists in choosing the most efficient cement-superplasticizer pair allowing to obtain maximum water reduction, good workability of the concrete in the fresh state and very good mechanical resistance in the hardened state. The aim of this work is to test the efficient of three polycarboxylate ether based superplasticizers (PCE) marketed in Algeria with CEMI 52.5 R cement and to study the effect of chemical structure of PCE on zeta potential, rheological and mechanical properties of cement pastes. The property of the polymers in cement was tested by a Malvern Zetasizer 2000 apparatus and VT 550 viscometer. Results showed that the zeta potential and its rheological properties are related with the molecular weight and the carboxylic density of PCE. The PCE with a moderate molecular weight and highest carboxylic groups had the best dispersion (high value of zeta potential) and lowest viscosity. The effect of chemical structure of PCEs on mechanical properties are evaluated by formulation of cement mortar with this PCEs, the result shows that there are a correlation between zeta potential of polymer and compressive strength of cement paste

Effect of Calcium Sulphate on the Geotechnical Properties of Stabilized Clayey Soils

An experimental investigation was undertaken to study the effect of calcium sulphate (CaSO4.2H2O) on the behaviour of the grey clay (GS) and red clay (RS) soils stabilized with lime (L), natural pozzolana (NP) and their combination (L-NP). In this study, the geotechnical properties investigated are respectively, the Atterberg limits on samples cured for 1 to 30 days to assess the diffusion time effect of CaSO4.2H2O (DTC) in the soil paste and the unconfined compressive strength (UCS) on samples cured for 7 to 120 days. The results show that both GS and RS samples can be successfully stabilized with L alone or with L-NP which substantially reduce their plasticity index (PI) and increase their UCS. On the other hand, a negligible effect was reported when the NP is used alone. However, when combining a fraction of CaSO4.2H2O to samples containing L or L-NP, a further decrease in the PI is observed. In addition, higher UCS values are recorded

A hybrid multi-objective algorithm to predict the characteristics of soil profiles from seismic ground motion records

The underlying goal of this study is to present an efficient algorithm to identify soil parameters such as thicknesses, shear wave velocities, damping and others parameters of subsurface layers, and site amplification characteristics (natural frequencies, peak amplitudes) from a given pair of seismic records. It is a hybrid procedure combining the stochastic genetic algorithms (GAs) optimization method, to find a point close to the global optimum in the global search phase, and a gradient based local determinist method (Levenberg-Marquardt: LM), to refine the solution. To improve the performance of the global search phase, a multi-objective optimization algorithm is used to minimize the errors between some characteristics of the theoretical amplification function and the experimental one of vertical array records. The weighted sum method which combines the weighted objectives into a single objective function is used to solve the optimization problem. The efficiency of the present algorithm is proven by several examples. Results show that the scheme works well and the curve fitting was always satisfying. Also, the proposed procedure leads to good approximations, requiring a lower computational effort, yet with good rates of convergence. Moreover, neither the growing number of parameters nor the vastness of the search space reduces the efficiency of the algorithm in predicting the characteristics of soil profiles and site amplification commonly required in seismic risk mitigation

Modelling of non-linear seismic ground response using elasto-plastic constitutive framework within a finite element soil column model

The prediction of seismic ground response is conditioned by the knowledge of each material behavior of soil deposits. The recourse to plasticity criterion to simulate cyclic behavior of soils under seismic loading is becoming more realistic. In this study, an elasto-plastic constitutive equation is cast within the framework of one dimensional finite element (FE) soil column model to account for the spatial and material nonlinearity of the secant shear modulus. To account of the spatial non linearity, shear modulus is written in terms of rigid base shear modulus and height of the soil column, while for material nonlinearity, the shear modulus degradation is deducted by the application of the isotropic evolution of the Von Misès criterion. Obtained results proved the efficiency of the proposed methodology and the predictive capability of the elaborated elastoplastic model which captures both small- and large-strain behaviors. They likewise highlight the important roles that play the spatial and material shear modulus variation in the prediction of the seismic soil responses

Stabilization of Algerian Clayey Soils with Natural Pozzolana and Lime

Cohesive soils with a high plasticity index present difficulties in construction operations because they usually contain expansive clay minerals. However, the engineering properties of soils can be improved by different techniques. The aim of this paper is to study the effect of using lime, natural pozzolana or a combination of both lime and natural pozzolana on plasticity, compaction and shear strength of two clayey soils classified as CH and CL according to the unified soil classification system (USCS). The obtained results indicated that for CH class clay soil, the plasticity index decreased significantly for samples stabilized with lime. On the other hand, for the soil classified as CL class clay, a high decrease in the plasticity index value was observed for samples stabilized with natural pozzolana compared to those stabilized with lime. Also, both the cohesion and internal friction angle in lime added samples were demonstrated to increase with time. The combination of lime and natural pozzolana exhibits a significant effect on the enhancement of both the cohesion and  internal friction angle at later stages. The lime-natural pozzolana combination appears to produce higher shear strength parameters than lime or natural pozzolana used alone

Influence des Superplastifiants à base d’Ether Polycarboxylique EPC sur les Propriétés Rhéologiques des Pâtes Cimentaires

The main difficulty encountered in the formulation of Self-Compacting Concrete (SCC) (SCC) consists in choosing the most effective cement-superplasticizer pair allowing obtaining maximum water reduction, good workability and satisfactory rheology of the concrete during the setting time implemented. Achieving the greatest workability depends on the compatibility between the admixture and the cement used. The purpose of this work is to verify the compatibility of two superplasticizers based on polycarboxylic ether PCE with CEM II 42.5 cement and to study the influence of PCE on the rheological properties of a cement paste. The experimental study is based on the measurement of the flow time in the Marsh cone of a cement grout with and without the addition of silica fume by varying the W/C ratio, the dosage and the type of PCE. A full factorial design was proposed in this paper to study the cement-PCE interactions, and to optimize the choice and the dosage of superplasticizer for the studied cement. Good fluidity was obtained with PCE1 for a W/C ratio = 0.4 and a superplasticizer dosage of 1.25%. The compatibility between the two PCEs and the cement mixed with 10% silica fume (SF) has already been studied. SF increases the saturation dosage of PCE1 from 1.25 to 1.5, and decreases their fluidifying power.La principale difficulté rencontrée dans la formulation des bétons autoplaçants (BAP) consiste à choisir le couple ciment-superplastifiant le plus efficace permettant d'obtenir une réduction maximale de l'eau, une bonne ouvrabilité et une rhéologie satisfaisante du béton pendant le temps de mise en œuvre. L’obtention de la plus grande ouvrabilité dépend de la compatibilité entre l'adjuvant et le ciment utilisé. Le présent travail a pour but de vérifier la compatibilité de deux superplastifiants à base d’éther polycarboxylique (SP EPC) avec le ciment CEM II 42.5 et d’étudier l’influence des SP EPC sur les propriétés rhéologiques d’une pâte cimentaire.  L’étude expérimentale s’articule sur la mesure du temps d’écoulement dans le cône de Marsh d’un coulis de ciment avec et sans ajout de fumée de silice en faisant varier le rapport E/C, le dosage et le type de SP EPC. Un plan factoriel complet a été proposé dans cette étude pour étudier les interactions ciment-EPC, et optimiser le choix et le dosage en superplastifiant pour le ciment étudié. Une bonne fluidité a été obtenue avec EPC1 pour un rapport E/C= 0.4 et un dosage en superplastifiant de 1.25%. La compatibilité entre les deux SP EPC et le ciment mélangé avec 10% de fumée de silice (FS) a été déjà étudiée.  La FS augmente le dosage de saturation de SP EPC1 de 1.25 à 1.5, et diminue leur pouvoir fluidifiant

Effect of Molecular Weight and Carboxylic Density of Polycarboxylates Ether Superplasticizer on Its performance in Cement Pastes

The main difficulty encountered in the formulation of high performance concrete (HPC) consists in choosing the most efficient cement-superplasticizer pair allowing to obtain maximum water reduction, good workability of the concrete in the fresh state and very good mechanical resistance in the hardened state. The aim of this work is to test the efficient of three polycarboxylate ether based superplasticizers (PCE) marketed in Algeria with CEMI 52.5 R cement and to study the effect of chemical structure of PCE on zeta potential, rheological and mechanical properties of cement pastes. The property of the polymers in cement was tested by a Malvern Zetasizer 2000 apparatus and VT 550 viscometer. Results showed that the zeta potential and its rheological properties are related with the molecular weight and the carboxylic density of PCE. The PCE with a moderate molecular weight and highest carboxylic groups had the best dispersion (high value of zeta potential) and lowest viscosity. The effect of chemical structure of PCEs on mechanical properties are evaluated by formulation of cement mortar with this PCEs, the result shows that there are a correlation between zeta potential of polymer and compressive strength of cement paste

TGF-ß Regulates Enamel Mineralization and Maturation through KLK4 Expression

Transforming growth factor-ß (TGF-ß) signaling plays an important role in regulating crucial biological processes such as cell proliferation, differentiation, apoptosis, and extracellular matrix remodeling. Many of these processes are also an integral part of amelogenesis. In order to delineate a precise role of TGF-ß signaling during amelogenesis, we developed a transgenic mouse line that harbors bovine amelogenin promoter-driven Cre recombinase, and bred this line with TGF-ß receptor II floxed mice to generate ameloblast-specific TGF-ß receptor II conditional knockout (cKO) mice. Histological analysis of the teeth at postnatal day 7 (P7) showed altered enamel matrix composition in the cKO mice as compared to the floxed mice that had enamel similar to the wild-type mice. The µCT and SEM analyses revealed decreased mineral content in the cKO enamel concomitant with increased attrition and thinner enamel crystallites. Although the mRNA levels remained unaltered, immunostaining revealed increased amelogenin, ameloblastin, and enamelin localization in the cKO enamel at the maturation stage. Interestingly, KLK4 mRNA levels were significantly reduced in the cKO teeth along with a slight increase in MMP-20 levels, suggesting that normal enamel maturation is regulated by TGF-ß signaling through the expression of KLK4. Thus, our study indicates that TGF-ß signaling plays an important role in ameloblast functions and enamel maturation