Publications

Investigation on the Properties of Porous Concrete Using Recycled Concrete Aggregate as Partial Replacement of Coarse Aggregate

Infrastructure department is the second-largest economic sector in Ethiopia after the agriculture industry. Due to expansion in this infrastructure and increased development of the country, most of the places are covered either by impermeable cement concrete or bitumen surfaces that blocks the percolation of water from rainfall or any other sources. It is significantly desired to produce eco-friendly concrete to reduce environmental issues for sustainable development. One of these concretes is porous concrete made up of zero fine aggregate, creating a significant pore that allows the concrete to be water permeable. However, this type of concrete has not been considered in the Ethiopian market. Similarly, the demand for natural coarse aggregate is still high whereas natural resources are depleting. Hence, recycling of construction and demotion wastes in to secondary concreting materials is a sustainable solution that reduces the gap between demand and supply of fresh aggregate as well as waste disposal land. Therefore, the study aims to investigate the properties of porous concrete experimentally using recycled concrete aggregate as partial replacement of natural coarse aggregate. The test results for engineering properties of recycled concrete aggregate at different ratios of 0%, 15%, 30%, 45%, and 60% revealed that the material is suitable to be used as coarse aggregate. To determine the behavior of the concrete, both Workability and fresh density at fresh state, compressive strength, split tensile strength, porosity and permeability of the concrete were examined at 7, 14, and 28 curing days using specimen cube size of 150mm* 150mm* 150mm and cylinders of 200mm* 100mm. The experimental result indicates that replacement of recycled concrete aggregate by natural coarse aggregate improves the porosity and permeability of the concrete. Also, the optimum replacement percentage of RCA for porous concrete strength is at 30% with 28 th day compressive strength of 17.37MPa which is greater than the suitable value. A regression model was also developed to determine the degree of workability using compacting factor test. From the result, coefficient of determination (R 2 ) shows that compacting factor test values are 88% accurate to govern the workability of fresh porous concrete. Generally, the finding of this experimental study indicates that the use of recycled concrete aggregate as coarse aggregate for porous concrete production is practicable.

Effect of shell spacing on mechanical behavior of multi-span soil-steel composite structure

This study analyses the effect of lateral shells on central shell at a different spacing in a multi-span soil-steel composite structure subjected to quasi-static moving loads. The displacements and internal forces of the central shell during consecutive truck passages over the structure are investigated by finite element (FE) analysis. Field measurements from a site in Niemcza, Poland, are used to calibrate input parameters. Next, the simulations for different spacing between the shells are investigated. The backfill soil is modeled as elastic-perfectly plastic, while the shells and sheet piles are linear elastic. The non-linear contact zone between the shell and the soil backfill is assumed to reflect an elastic-plastic constitutive model. The analysis reveals that both vertical and horizontal displacements increase significantly when the ratio of shell spacing to span length is less than 0.5. Maximum stress occurs when the shells are placed adjacent to each other, i.e., without spacing. The stress is almost doubled in this position compared to the reference case—a single-span structure. The shifting of extreme deflections and stress is observed in the direction of truck movement. Nevertheless, the influence of lateral shells on the central shell's performance under moving loads is nearly negligible when the spacing-to-span ratio exceeds 0.5.

Investigating the Effects of Coarse Aggregate Physical Properties on Strength of C-25 Concrete

The strength of concrete mostly depends on the strength and properties of coarse aggregate since the major volume of concrete was covered by coarse aggregate. The physical properties of coarse aggregates do grossly affect the workability and structural performance of concrete. This study considered the effects of physical properties of coarse aggregate on properties of concrete and the difference in strength of concrete made from four different types of coarse aggregates namely crushed basalt, crushed marble, river graver and surface gravel which were collected from different areas near to Nekemte town. For each types of collected coarse aggregate their physical properties are determined by performing necessary laboratory tests to attain the objective of the study. For proportioning of concrete making materials the ACI concrete mix design was followed. Total of 36 cubes and 12 beam molds were casted for determination of compressive strength flexural strength of C-25 concrete made from the four aggregate samples. The results indicate physical properties and types of coarse aggregate have effects on the strength of concrete. The four coarse aggregate samples have different physical properties and produced concrete having different compressive and flexural strength. Thus, it concludes, the compressive and flexural strength of concrete was greatly influenced by the physical properties and strength of coarse aggregate.

Developing Construction Labor Productivity Model for Concreting Activity Using Artificial Neural Networks

There are various modeling techniques adopted for predicting the labor productivity that incorporate the influence of various factors, but neural networks are found to have strong pattern recognition and higher accuracy to get reliable estimates. To develop a construction labor productivity (CLP) model for concreting activities, data were collected through a questionnaire. The most critical influencing parameters were ranked according to their relative importance index (RII). Then the strength of the relationship between CLP and influencing parameters was analyzed using correlation coefficient results generated in Python program. Finally, the CLP model which represents the output of the crew within a certain factor was successfully developed using artificial neural networks (ANNs). Five objectives and six subjective critical influencing parameters were selected using RII. Crew experience, age of workers, and placement technique are the top three influencing parameters that have a strong relation with CLP with correlation coefficient values of 0.5681, 0.5349, and 0.5227 respectively. The developed model within these influencing parameters has a higher capability to predict the output of labor with a 92% coefficient of determination (R2) and a mean squared error of 0.316%. Therefore, the application of such a model for the accurate estimation of labor productivity is recommended.

Deterioration Envelopes for Predicting Concrete Bridge-Deck Deterioration Due to Chloride Exposure

Bridge decks are exposed to chloride ingress from deicing salts, freeze–thaw cycling, and repeated wetting and drying, which gradually degrades the concrete over time. Many existing models treat concrete conditions as static and do not capture time-varying chloride exposure. This study develops deterioration envelopes for concrete bridge decks to predict long-term loss of compressive strength and internal integrity by integrating accelerated laboratory wet–dry and freeze–thaw testing with in-service bridge-deck core measurements from Delaware bridges. The model is supported by three data sources: accelerated laboratory tests, cores from in-service bridges provided by the Delaware Department of Transportation (DelDOT), and climate and asset datasets from the National Oceanic and Atmospheric Administration (NOAA) and the Federal Highway Administration’s (FHWA) InfoBridge™ database. Laboratory specimens (n = 300) were reproduced based on Delaware mix designs from the 1970s and 1980s and were tested in accordance with ASTM and ACI protocols. Environmental conditioning applied wet–dry and freeze–thaw cycles at chloride contents of 0, 3, and 15 percent to replicate field exposure within a shortened test period. Measured properties included compressive strength, modulus of elasticity, resonance frequency, and chloride penetration. The results show a gradual, near-linear reduction in compressive strength and resonance frequency with increasing chloride content over 160 cycles, which corresponds to about 2 to 5 years of service exposure. Resonance frequency was the most sensitive indicator of internal damage across the tested chloride contents. By combining test results, core data, and bridge inspection history into a single durability index, the deterioration envelopes forecast long-term degradation under different chloride exposures, providing a basis for prediction that extends beyond visual inspection.

Effect of Specimens’ Height to Diameter Ratio on Unconfined Compressive Strength of Cohesive Soil

The undrained shear strength (Su) and cohesion (Cu) of cohesive soils are frequently determined using an unconfined compression test. However, the test results are heavily dependent on specimen size. This causes uncertainty in geotechnical analyses, constitutive models, and designs by overestimating or underestimating the shear strength of cohesive soils. Therefore, the study aims to assess the effect of the height-to-diameter ratio on the unconfined compressive strength (UCS) of cohesive soil. The soil specimen was tested on a compacted cylindrical specimen at the maximum dry density and optimum moisture content with a height to diameter (H/D) ratio of 1–3 for 38, 50, and 100 mm specimen diameters. Disturbed sample specimens were considered for the laboratory program. Accordingly, the standard Proctor compaction test determines soil classification and compaction characteristics. The unconfined compression test was performed for undisturbed and compacted remolded states of various diameters of cohesive soil specimens to investigate the strength variation with the specimen variation in H/D ratio. The laboratory test results revealed that cohesive soil's unconfined compression strength value drops rapidly with height-to-diameter ratios and the soil specimens’ diameter increases. However, the UCS value was stable at H/D ratio from 1.75 to 2.25. As the specimens’ diameter and H/D ratio increased, the peak UCS value axial strain decreased. Similarly, the gap between the axial strains of peak UCS value for the smallest and the most significant H/D ratio decreased with increase in the specimens’ diameter.

Numerical modeling of wave-induced loads on coastal bridges using a Coupled Eulerian– Lagrangian analysis

Numerical analysis of soil–steel composite structure performance at ultimate load: impact of stiffening ribs and geotextile reinforcement

This study investigates soil–steel composite structures, emphasizing the role of stiffening ribs and geotextile reinforcement through comprehensive n

Investigation on the Properties of Porous Concrete Using Recycled Concrete Aggregate as Partial Replacement of Coarse Aggregate

Due to expansion in infrastructure and increased development urbanization in Ethiopia, most of the places are covered by impermeable cement concrete that blocks the percolation of water from rainfall or any other sources. It is significantly desired to produce porous concrete made up of zero fine aggregate, creating a significant pore that allows the concrete to be water permeable. Similarly, the demand for natural coarse aggregate is still high whereas natural resources are depleting. Hence, recycling of construction and demotion wastes in to secondary concreting materials is a sustainable solution that reduces the gap between demand and supply of fresh aggregate as well as waste disposal land. Therefore, the study aims to investigate the properties of porous concrete experimentally using recycled concrete aggregate as partial replacement of natural coarse aggregate. The test results for engineering properties of recycled concrete aggregate at different ratios of 0%, 15%, 30%, 45%, and 60% revealed that the material is suitable to be used as coarse aggregate. To determine the behavior of the concrete, both Workability and fresh density at fresh state, compressive strength, split tensile strength, porosity and permeability of the concrete were examined at 7, 14, and 28 curing days using specimen cube size of 150mm* 150mm* 150mm and cylinders of 200mm* 100mm. The experimental result indicates that replacement of recycled concrete aggregate by natural coarse aggregate improves the porosity and permeability of the concrete. Also, the optimum replacement percentage of RCA for porous concrete strength is at 30% with 28th day compressive strength of 17.37MPa which is greater than the suitable value. A regression model was also developed to determine the degree of workability using compacting factor test. From the result, coefficient of determination (R2) shows that compacting factor test values are 88% accurate to govern the workability of fresh porous concrete. Generally, the finding of this experimental study indicates that the use of recycled concrete aggregate as coarse aggregate for porous concrete production is practicable.

Experimental Study on the Suitability of Waste Plastics and Glass as Partial Replacement of Fine Aggregate in Concrete Production

Solid waste management is a major environmental challenge, especially in developing countries, with increasing amounts of waste glass (WG) and waste plastics (WP) not being recycled. In Ethiopia, managing WG and WP requires innovative recycling techniques. This study examines concrete properties with WG and WP as partial replacements for fine aggregate. Tests were conducted on cement setting time, workability, compressive strength, splitting tensile strength, and flexural strength. Concrete grade C-25, with a compressive strength of 25 MPa, was prepared using an optimum ratio of 14% WG and 6% WP. Mechanical properties were tested at 7 and 28 days of curing. At 20% replacement, workability decreased at water-cement ratios of 0.5 and 0.6 but remained stable at 0.4. Thus, a 0.4 ratio was used. For 10% replacement, compressive strength increased by 12.55% and 6.44% on the 7th and 28th days, respectively. At 20% replacement, compressive strength decreased by 14.35% and 0.73% on the 7th and 28th days, respectively. On the 28th day, splitting tensile strength at optimum replacement was 4.3 MPa, an 8.5% reduction from the control mix. However, flexural strength increased by 19.7%, from 12.46 MPa to 15.52 MPa. Overall, WG and WP improved flexural strength but slightly reduced splitting tensile strength.

Experimental Study on the Suitability of Waste Plastics and Glass as Partial Replacement of Fine Aggregate in Concrete Production

Solid waste management is a major environmental challenge, especially in developing countries, with increasing amounts of waste glass (WG) and waste plastic (WP) not being recycled. In Ethiopia, managing WG and WP requires innovative recycling techniques. This study examines concrete properties with WG and WP as partial replacements for fine aggregate. Tests were conducted on cement setting time, workability, compressive strength, splitting tensile strength, and flexural strength. Concrete of grade C-25, with a target compressive strength of 25 MPa, was prepared by partially replacing fine aggregate with WP and WG. The mechanical properties were evaluated after 7 and 28 days of curing. At a 20% replacement level, workability decreased at water–cement ratios of 0.5 and 0.6 but remained stable at 0.4, leading to the selection of the 0.4 ratio for further testing. A 10% replacement of fine aggregate, using a ratio of 3% WP and 7% WG, was found to be optimal, resulting in an increase in compressive strength by 12.55% and 6.44% at 7 and 28 days, respectively. In contrast, a 20% replacement led to a decrease in compressive strength by 14.35% and 0.73% at 7 and 28 days, respectively. On the 28th day, the splitting tensile strength at the optimal replacement level was 4.3 MPa, reflecting an 8.5% reduction compared to the control mix. However, flexural strength improved significantly by 19.7%, from 12.46 MPa to 15.52 MPa. Overall, the incorporation of WG and WP in concrete enhances flexural strength but slightly reduces splitting tensile strength.

Influence of geotextile soil reinforcement layout on the deformation of a model soil-steel composite structure

Geotextiles have become a subject of scientific research in recent years due to their ability to reduce pressure on soil masses and buried structures. However, the effective optimal of geotextiles above the crown of the shell of a soil-steel composite structure (SSCS) is not well described in the literature. This article presents an analysis of the impact of geotextile placement at different locations in the ground cover over the crown of the shell on the behaviour of the steel shell. The tests were carried out under different static loads. In the article, a comparative analysis of the results obtained on a natural scale with those obtained using the finite element method (FEM) is presented. For the purpose of the analysis, an experimentally verified computational model was developed and implemented in the commercial FE code, namely, the Zsoil numerical programme. The result demonstrated a significant reduction in maximum displacements and stresses upon employing a single-layer geotextile. The most significant reduction in vertical displacement, amounting to 37%, was observed when the geotextile was positioned at a shallower depth, closer to the load's zone of influence. Furthermore, it was found that vertical displacements in the crown can be reduced by up to 40% with the application of a double layer of geotextile. Furthermore, analysis of the effect of the position of the geotextile layer revealed that reinforcement is more effective when placed at a shallower depth, closer to the zone of influence of the load. These findings provide valuable information for designers who want to optimise geotextile placement for enhanced performance in SSCS designs.

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.

Enhanced Rail Track Modeling and Modulus Estimation Using DIC-Calibrated Finite Element Analysis

Deterioration Envelopes for Predicting Concrete Bridge Deck Deterioration due to Chloride Exposure

Bridge decks are exposed to chloride ingress from de-icing salts, freeze-thaw cycling, and repeated wetting and drying, which gradually degrades the concrete over time. Many existing models treat concrete conditions as static and do not capture time-varying chloride exposure. This study develops deterioration envelopes for concrete bridge decks that predict loss of compressive strength and internal integrity by combining accelerated laboratory testing with in-situ bridge core data extracted from Delaware bridges. The model is supported by three data sources: accelerated laboratory tests, cores from in-service bridges provided by the Delaware Department of Transportation (DelDOT), and climate and asset datasets from the National Oceanic and Atmospheric Administration (NOAA) and the Federal Highway Administration's (FHWA) InfoBridge™ database. Laboratory specimens (n = 300) were reproduced based on Delaware mix designs from the 1970s and 1980s and were tested in accordance with ASTM and ACI protocols. Environmental conditioning applied wet-dry and freeze-thaw cycles at chloride contents of 0, 3, and 15 percent to replicate field exposure within a shortened test period. Measured properties included compressive strength, modulus of elasticity, resonance frequency, and chloride penetration. Results show a gradual, near-linear reduction in compressive strength and resonance frequency with increasing chloride content over 160 cycles, which corresponds to about 2 to 5 years of service exposure. Resonance frequency was the most sensitive indicator of internal damage across the tested chloride contents. By combining test results, core data, and bridge inspection history into a single durability index, the deterioration envelopes forecast long-term degradation under different chloride exposures, providing a basis for prediction that extends beyond visual inspection.

Effect of Shell Spacing on Mechanical Behavior of Multi-Span Soil-Steel Composite Structure

This paper analyses the effect of lateral shells on the central shell at a different spacing in a multi-span soil-steel composite structure subjected to live loads. The displacements and internal forces of the central shell during consecutive truck passages over the structure are investigated by finite element (FE) analysis. The results of a field measurement on the structure located in Niemcza, Poland, are used to calibrate the input parameters. Next, the simulations for different spacing between the shells are investigated. The constitutive model for the backfill soil is elastic-perfectly plastic and linear elastic for the shell and sheet piles. The analysis shows that both vertical and horizontal displacements are significantly increased when the ratio between shell spacing and span length is less than 0.5. Maximum stress is observed when the shells are assumed adjacent to one another, i.e., without spacing. The stress is almost doubled in this position compared to that in the reference case, that is, the single-span structure. The shifting of extreme deflections and stress is observed in the direction of the vehicle movement. Nevertheless, the effect of the lateral shell on the performance of the central shell under moving load is almost negligible at a spacing-to-span ratio of not less than 0.5.

Effect of Geotextile Reinforcement on Corrugated Steel Culvert Behavior During Construction