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Performance Evaluation of Ethiopian Cements: physical, chemical, thermodynamic and mechanical aspects Performance Evaluation of Ethiopian Cements: physical, chemical, thermodynamic and mechanical aspects

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DR. ESAYAS G.YOUHANNES

Associate Prof. of Concrete Materials & Structures, Executive Director, AAU-AAiT with the Rank of V/President for AAU, Head of Construction Materials Lab AAU, AAiT, ETHIOPIA
 

Challenges associated with hot weather concreting, salty environment and scarcities of appropriate materials are tackled systematically in the Ditcheto-Galafi-Belho rigid concrete pavement road project, being constructed to connect Ethiopia with the port of Tadjoura in Djibouti. The project area is located in the afar region where typical conditions of hot weather prevail with combination of high ambient temperature, low relative humidity, high wind speed and intense solar radiation. Concreting in very hot weather results in undesirable problems that could impair the properties and serviceability of concrete. The development of high concrete temperatures could cause a number of effects that have been shown to be detrimental to long-term concrete performance. High concrete temperatures increase the rate of hydration, thermal stresses, the tendency for drying shrinkage cracking, and permeability and decrease long-term concrete strengths and durability as a result of cracking. This paper presents the result of a comprehensive experimental work aimed at evaluation the effect of ambient air temperatures on the water demand, setting time, early age thermal cracking, slump loss, shrinkage, flexural strength and compressive strength of concrete having a wide range of water-cement ratios. Relationships between the flexural strength, early age thermal stress and various influencing factors are investigated.


Remedies intended to eliminate the adverse effects of rapid setting by selecting temperature dependent optimal dosage of a water-reducing and set retarding admixtures are described. Means are described for reducing concrete temperature by proper attention to ingredients particularly cooling of aggregates, water and use of low to medium heat cement produced locally; methods of production and delivery; and care in placement, protection, and curing. Due attention is given on the use of admixtures to reduce mixing water requirements and curing compound to reduce the curing water requirements. With the aim of lowering the risk of thermal cracking, sulfate attack and corrosion modified cement with low to medium heat generation and lower proportion of Tricalcum alumunate is used. Data from the Ditcheto-Galafi-Belho rigid concrete pavement road project were analyzed to reveal the difference in the conditions of the pavement segments at different ambient temperatures. The results of the analysis emphasize the importance of Mix design and concrete temperature control during concrete pavement construction in hot weather conditions.

 

 

Associate Professor Esayas is a faculty member in the school of Civil and Environmental Engineering, Addis Ababa University, Institute of Technology, since 2001. He obtained his MSc. and PhD degree from the University of Tokyo, Japan. His interests relate to nonlinear analysis of reinforced concrete, constitutive modeling, Shrinkages and Creep, performance assessment, supplementary cementitious materials, and corrosion of reinforcing bars in concrete. Dr. Esayas has published 25 papers on concrete mechanics. He received the ACT outstanding paper Award in 2008 and 2012, and received best researcher award in AAU in 2013. He is a founding member of the Ethiopian young Academy of Sciences. He is currently serving as an Executive Director of the Addis Ababa Institute of Technology and a member of the Concrete materials and structure chair.