Ahmed Mohammed

Bio: Ahmed Mohammed is an academic researcher from University of Sulaymaniyah. The author has contributed to research in topics: Compressive strength & Cement. The author has an hindex of 26, co-authored 106 publications receiving 1877 citations. Previous affiliations of Ahmed Mohammed include University of Houston & American University.

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

Abstract: 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.

Compressive and Tensile Behavior of Polymer Treated Sulfate Contaminated CL Soil

Abstract: In this study, the compressive and tensile behavior of polymer treated sulfate contaminated CL soil was investigated. Based on the information in the literature, a field soil was contaminated with up to 4 % (40,000 ppm) of calcium sulfate in this study. In addition to characterizing the behavior of sulfate contaminated CL soil, the effect of treating the soil with a polymer solution was investigated and the performance was compared to 6 % lime treated soil. In treating the soil, acrylamide polymer solution (15 g of polymer dissolved in 85 g of water) content was varied up to 15 % (by dry soil weight). Addition of 4 % calcium sulfate to the soil decreased the compressive and tensile strengths of the compacted soils by 22 and 33 % respectively with the formation of calcium silicate sulfate [ternesite Ca5(SiO4)2SO4)], magnesium silicate sulfate (Mg5(SiO4)2SO4) and calcium-magnesium silicate (merwinite Ca3Mg(SiO4)2). With the polymer treatment the strength properties of sulfate contaminated CL soil was substantially improved. Polymer treated sulfate soils had higher compressive and tensile strengths and enhanced compressive stress–strain relationships compared to the lime treated soils. Also polymer treated soils gained strength more rapidly than lime treated soil. With 10 % of polymer solution treatment, the maximum unconfined compressive and splitting tensile strengths for 4 % of calcium sulfate soil were 625 kPa (91 psi) and 131 kPa (19 psi) respectively in 1 day of curing. Similar improvement in the compressive modulus was observed with polymer treated sulfate contaminated CL soil. The variation of the compacted compressive strength and tensile strength with calcium sulfate concentrations for the treated soils were quantified and the parameters were related to calcium sulfate content in the soil and polymer content. Compressive stress–strain relationships of the sulfate soil, with and without lime and polymer treatment, have been quantified using two nonlinear constitutive models. The constitutive model parameters were sensitive to the calcium sulfate content and the type of treatment.

Soil and clay stabilization with calcium- and non-calcium-based additives: A state-of-the-art review of challenges, approaches and techniques

Abstract: Soil stabilization is a technique to improve the engineering and geotechnical properties of soils such as mechanical strength, permeability, compressibility, durability and plasticity. Much has been learned about soil stabilization techniques and additives over the past century. The state of the practice in stabilization techniques and challenges is presented with a discussion. Moreover, available studies regarding the effects of various types of stabilizing agents on the engineering and geotechnical properties of stabilized soils are reviewed here. These stabilizing agents include both calcium-based and non-calcium-based additives. Eco-friendly additives as alternative materials to conventional stabilizing agents are also discussed in this paper. In addition, the problems associated with the presence of disruptive salts and sulfate as well as the techniques to overcome these problems in soil stabilization projects are reviewed.