Ahmed S. Mohammed

Smart cement modified with iron oxide nanoparticles to enhance the piezoresistive behavior and compressive strength for oil well applications

In this study, smart cement with a 0.38 water-to-cement ratio was modified with iron oxide nanoparticles (NanoFe2O3) to have better sensing properties, so that the behavior can be monitored at various stages of construction and during the service life of wells. A series of experiments evaluated the piezoresistive smart cement behavior with and without NanoFe2O3 in order to identify the most reliable sensing properties that can also be relatively easily monitored. Tests were performed on the smart cement from the time of mixing to a hardened state behavior. When oil well cement (Class H) was modified with 0.1% of conductive filler, the piezoresistive behavior of the hardened smart cement was substantially improved without affecting the setting properties of the cement. During the initial setting the electrical resistivity changed with time based on the amount of NanoFe2O3 used to modify the smart oil well cement. A new quantification concept has been developed to characterize the smart cement curing based on electrical resistivity changes in the first 24 h of curing. Addition of 1% NanoFe2O3 increased the compressive strength of the smart cement by 26% and 40% after 1 day and 28 days of curing respectively. The modulus of elasticity of the smart cement increased with the addition of 1% NanoFe2O3 by 29% and 28% after 1 day and 28 days of curing respectively. A nonlinear curing model was used to predict the changes in electrical resistivity with curing time. The piezoresistivity of smart cement with NanoFe2O3 was over 750 times higher than the unmodified cement depending on the curing time and nanoparticle content. Also the nonlinear stress–strain and stress–change in resistivity relationships predicated the experimental results very well. Effects of curing time and NanoFe2O3 content on the model parameters have been quantified using a nonlinear model.

XRD and TGA, Swelling and Compacted Properties of Polymer Treated Sulfate Contaminated CL Soil

In this study, the effect of up to 4 % calcium sulfate contamination on the soil properties of a natural clay with low liquid limit (CL) soil with and without polymer treatment was investigated and compared to 6 % lime treated soil. X-ray diffraction (XRD) and thermogravimetric analysis (TGA) methods were used to identify and quantify the changes in the contaminated CL clay soil. XRD analyses showed the major constituents of the soil were calcium silicate (CaSiO3), aluminum silicate (Al2SiO5), magnesium silicate (MgSiO3), and quartz (SiO2). With 4 % calcium sulfate contamination, the liquid limit (LL) and plasticity index (PI) of the CL soil increased by 30 and 45 %, respectively. The addition of calcium sulfate resulted in the formation of calcium silicate sulfate (Ternesite Ca5(SiO4)2SO4) and aluminum silicate sulfate (Al5(SiO4)2SO4). TGA analyses showed a notable reduction in the weight of calcium sulfate contaminated soil between 600 and 800°C, possibly due to changes in soil mineralogy. In addition, the total weight loss at 800°C for 1.5 % polymer treated soil was about 40 % less than the 4 % calcium sulfate contaminated soil, and it was similar to the weight loss observed in the uncontaminated CL soil. The maximum dry density of compacted soil decreased and the optimum moisture content increased with 4 % of calcium sulfate. The addition of 4 % calcium sulfate increased the free swelling of compacted soil by 67 %. The addition of 6 % lime resulted in the formation of ettringite (Ca6Al2 (SO4)3(OH)12·26H2O). Polymer treatment decreased the LL, PI, swelling index, and optimum moisture content of the soil and increased the compacted maximum dry density. Behavior of sulfate contaminated CL soil with and without treatment was quantified using a unique model that represented both linear and nonlinear responses. Also the model predictions were compared with published data in the literature.

Vipulanandan failure models to predict the tensile strength, compressive modulus, fracture toughness and ultimate shear strength of calcium rocks

AbstractIn this study, over 1000 data from the literature were used to characterize and compare the density, strengths, modulus, fracture toughness, porosity and the ultimate shear strengths of the...

Statistical Variations and New Correlation Models to Predict the Mechanical Behavior and Ultimate Shear Strength of Gypsum Rock

Abstract In this study, over 1000 data from the several research studies was used to characterize and compare the density, strengths, modulus, flexural strength, porosity and the ultimate shear strengths of the calcium rocks. The gypsum rock data were statistically analyzed, quantified and compared with the limestone rock data. The ranges of the densities for gypsum rock (CaSO4·2H2O) and limestone rock (CaCO3) were 2.10 to 2.83 gm/cm3 and 1.70 to 2.75 gm/cm3, respectively. The compressive and tensile strengths of the gypsum and limestone rocks varied from 2 MPa to 250 MPa and 1.8 MPa to 25 MPa, respectively. Vipulanandan correlation model was effective in relating the modulus of elasticity, flexural strength, with the relevant strengths of the rocks. A new nonlinear Vipulanandan failure criterion was developed to better quantify the tensile strength, pure shear (cohesion) strength and predict the maximum shear strength limit with applied normal stress on the gypsum and limestone rocks. The prediction of the failure models for the two rock types was also compared to the Mohr-Coulomb failure model. The Vipulanandan failure model predicted the maximum shear strength limit was, as the Mohr-Coulomb failure model does not have a limit on the maximum shear strength. With the Vipulanandan failure model based on the available data, the maximum shear strengths predicted for the gypsum and limestone rocks were 64 MPa and 114 MPa, respectively.