Dr. Girum Urgessa

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Academic Career Length

19Years (2008-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

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7 February 2023 in Construction Materials

Journal Article

Strength, Porosity and Permeability Properties of Porous Concrete Made from Recycled Concrete Aggregates

Due to expansion in infrastructure and increased development of urbanization in Ethiopia, most of the places are covered either by impermeable cement concrete or bitumen that blocks the percolation of water from rainfall. A porous concrete made of zero fine aggregates, creating a pore that permits the concrete to be water permeable, is highly desirable. Similarly, the demand for natural coarse aggregates remains high, while natural resources are being depleted. Therefore, this study aims to investigate the properties of porous concrete using recycled concrete aggregate as a partial replacement for natural coarse aggregate. Experimental tests were conducted on cement setting time, workability of concrete, compressive, split tensile, porosity, and permeability of porous concrete. The properties of porous concrete at different ratios—0, 15, 30, 45 and 60%—revealed that RCA is suitable for use as coarse aggregate. The optimum replacement percentage of recycled aggregate for porous concrete in terms of strength is 30%, with 28th-day compressive strength of 17.37 MPa. However, slight increments were observed in porosity and permeability coefficient. Therefore, the concrete produced in this study is structural concrete, which is suitable for walkways and other concrete flat works, whereby heavy vehicle traffic loads do not exist.

28 September 2018 in Polymers

Journal Article

Internal Relative Humidity, Autogenous Shrinkage, and Strength of Cement Mortar Modified with Superabsorbent Polymers

Girum Urgessa

Ki-Bong Choi

Jung Heum Yeon

Laboratory evaluations were performed to investigate the effect of internal curing (IC) by superabsorbent polymers (SAP) on the internal relative humidity (IRH), autogenous shrinkage, coefficient of thermal expansion (CTE), and strength characteristics of low water-cement ratio (w/c) mortars. Four types of SAP with different cross-linking densities and particle sizes were used. Test results showed that the SAP inclusion effectively mitigated the IRH drops due to self-desiccation and corresponding autogenous shrinkage, and the IC effectiveness tended to increase with an increased SAP dosage. The greater the cross-linking density and particle size of SAP, the less the IRH drop and autogenous shrinkage. The trend of autogenous shrinkage developments was in good agreement with that of IRH changes, with nearly linear relationships between them. Both immediate deformation (ID)-based and full response-based CTEs were rarely affected by SAP inclusions. There were no substantial losses in compressive and flexural strengths of SAP-modified mortar compared to reference plain mortar. The findings revealed that SAPs can be effectively used to reduce the shrinkage cracking potential of low w/c cement-based materials at early ages, without compromising mechanical and thermal characteristics.

1 July 2010 in Journal of Engineering Mechanics

Journal Article

Dynamic Response of Retrofitted Masonry Walls for Blast Loading

Girum Urgessa

Arup K. Maji

A full-scale blast test was conducted on eight masonry walls reinforced with two and four layers of carbon fibers and two types of polymer matrices. The walls were then subjected to a 0.45-kg pentolite booster suspended from the ceiling of a test structure. The pressure-time history caused by the blast and the resulting displacement response were measured during the test. This paper presents a summary of the test program and the corresponding results from a nonlinear single degree of freedom analysis. The results provide a basis for determining effective means of retrofitting existing masonry walls and designing new structures to withstand blast loads. The paper also outlines a fiber-reinforced polymer retrofit design procedure for walls subjected to blast loading.

1 October 2008 in Journal of Aerospace Engineering

Journal Article

Full-Scale Testing and Analysis for Blast-Resistant Design

Arup K. Maji

Jay P. Brown

Girum Urgessa

A full-scale blast test was conducted on a structure representing a mailroom, constructed with unreinforced masonry walls. The four walls were retrofitted with different quantities of glass fiber-reinforced polymers (GFRP) on the outside face to increase their resistance to the blast load. In addition, shotcrete was added to the inside face of the two long walls. The objective of this test was to validate a method of analysis that can be used to design effective retrofit techniques to contain blast loads. A blast load was produced by the detonation of a 0.91 kg (2 lb) equivalent TNT charge placed near the center of the room. Instrumentation on individual walls monitored the blast pressure and the consequent displacement and velocity of the walls. Although the walls sustained extensive internal damage and plastic deformation, the retrofit was able to withstand the blast load. It was observed through the postmortem analysis of the test that the stiffness of the walls is completely lost at an early stage and...

4 April 2023 in Structures

Journal Article

Finite element analysis of the response of conventional and special reinforcement detailed concrete beams subjected to impact loads

Solomon Abebe Derseh

Girum Urgessa

Tesfaye Alemu Mohammed

1 November 2020 in Journal of Materials Research and Technology

Journal Article

Analysis and modeling of uniaxial compressive creep of MMA-modified unsaturated polyester polymer concrete

Kwan-Kyu Kim

Girum Urgessa

Jung Heum Yeon

About Me

Girum Urgessa is a tenured professor in the Sid and Reva Dewberry Department of Civil, Environmental, and Infrastructure Engineering (CEIE) at George Mason University. He received his MS (2002) and PhD (2006) from the University of New Mexico, and his BS (2000) from Addis Ababa University. Before coming to Mason, he was a research engineer in the Applied Science Division of Weidlinger Associates (now Thornton Tomasetti) and a structural engineer at Dekker/Perich/Sabatini. Over the past 12 years, he has taught ten different structural engineering and mechanics courses and received the university's Teaching Excellence Award in 2015 He has played active roles in faculty governance at Mason, including serving on the faculty senate, the faculty handbook revision committee, the term faculty task force, and several academic program review committees. He has also chaired the Faculty Matters Senate standing committee. Outside of Mason. Dr. Urgessa is currently a member of the sub-committee on Retrofit of Structures under Dynamic Loads under the Committee on Dynamic Effects of the American Society of Civil Engineers. He was a voting member of the American Concrete Institute Committee on Blast and Impact Load Effects and the Transportation Research Board Committee on Field Testing and Nondestructive Evaluation of Transportation Structures. Dr. Urgessa is a licensed professional engineer in the State of Maryland.

Dr. Girum Urgessa

Dr. Girum Urgessa

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