Experimental Investigation into Strength Properties of Ribbed Mild Steel Reinforcing Bars (RMSRBs) Produced by Local Companies in Ghana

The construction of high-rise buildings has increased the production and demand of ribbed mild steel reinforcing bars (RMSRBs) in Ghana. This study aimed at investigating the strength properties of RMSRBs manufactured in Ghana from scrap metals. Three steel-producing companies were considered for this study. A total of 90 samples of 12, 16, and 20mm diameters with lengths of 500, 50, and 20mm were used for the study. The prepared specimens were subjected to tensile strength test, chemical composition analysis, micro-hardness test, and microstructure analysis. The results indicate that the average tensile strength of between 576.00 and 768.40N/mm 2 were above the minimum tensile strength of 250N/mm 2 recommended by ASTM E8/E8M-16a. The carbon equivalent values (CEVs) of between 0.287 and 0.333% obtained were almost within the range of 0.3 to 0.55% recommended by ASTM A706/A706M-09b. It was also identified that the average Vickers hardness values of between 255.76 and 295.38HV were acceptable. The microstructural images showed good distribution of the pearlite and ferrite of the core. One Way ANOVA results indicated that the differences in the tensile strength values for 12mm (p-value ˂ 0.000) and 16mm (p-value =0.001) were statistically significant, however, the 20mm (p-value =0.138) was not statistically significant. The study, therefore, concludes that the strength properties of the 12, 16, and 20mm diameters of the RMSRBs produced by the three different companies in Ghana meet the standard requirements, and are recommended for use by contractors for the production of reinforced concrete.


INTRODUCTION
The increase in the population of human settlements globally has contributed to increased infrastructural development.This has resulted in high demand for ribbed mild steel reinforcing bars (RMSRBs) to counteract tensile stresses in concrete structures.As reported by previous studies (Danso & Akwaboah, 2021; Danso 2018 and 2013), the use of local materials needs to be supported and reinforced to provide sufficient strength with adequate quality to withstand the effects of climate conditions.According to Abioye and Billihaminu (2016), reinforcement is a method of increasing the strength properties of concrete structural members.Steel bars of different diameters have been prescribed for use in reinforcing concrete.The choice of steel bars is based on strength, cost, accessibility, ease of erection, aesthetics, sustainability, and other environmental concerns (Ede et al., 2015).The performance of reinforced concrete as structural material depends strongly on the properties of the steel bars and concrete (Boateng et al. 2023).The ribbed steel bars have the advantage of increasing the bond strength at the concrete steel interface to improve the tensile and compressive properties of the reinforced concrete.
Structures are designed to ensure that they do not fail prematurely, whether collapse or service failure.Unfortunately, cases of premature structural failure are on the increase.In Ghana, reported cases of structural failure have recently become frequent, especially for buildings (Danso & Boateng, 2015).Ayodele (2009) examined the role of reinforcement in the collapse of buildings in Nigeria.The study revealed that the physical, chemical, and mechanical properties of different ribbed mild steel bars produced by different companies were different and some did not meet the acceptable standard.This is confirmed by Ayininuola and Olalusi, (2004) that the use of poor quality and substandard steel bars are among the causes of building failure in the construction environment.The variation in scrap feeds and impurities present in the scraps may contribute to a decline in the strength of ribbed mild steel bars which affects the quality (Atsbeha, 2017).
A study by Assiamah et al. (2023) evaluated the physical characteristics of reinforcement bars available in Ghana and concluded that local milling companies producing mild steel reinforcing bars should improve on the standardization of the diameter of reinforcing bars they produce.Dzogbewu and Arthur (2013) carried out comparative studies of locally produced and imported low-carbon steels on the Ghanaian market with two different batches of samples (rebars) from local and foreign producers with 12mm bars only.Kankam and Adom-Asamoah (2002) studied the strength and ductility characteristics of reinforcing steel bars milled from scrap metals and found that the tensile strength was high with very little elongation value of 9.6, 10.6 and 11.8 for the company A, B and C respectively leading to limited ductility compared with standard mild steel bars.They used an Avery Denison universal testing machine to perform the mechanical test, and the mode of failure indicated little or no necking and brittle behaviour of the steel.
Adebisi and Ndaliman (2015) studied the influence of process parameters (reinforcement fraction, stirring speed, The above studies focused on the physical and ductility properties of reinforced bars and 12mm diameter bars.There is a need to study the strength properties of various sizes of RMSRBs produced by different manufacturers.Therefore, this study focused on the strength properties of 12, 16, and 20mm diameters of RMSRBs produced by three different producers.The study further examined the chemical compositions and the hardness of ribbed mild steel reinforcing bars, and the microstructure analysis of ribbed mild steel reinforcing bars RMSRBs produced by local companies in Ghana.These were done to ascertain the conformity of RMSRBs' properties to standards.

MATERIALS AND METHODS
An experimental research design was used in sourcing data for analysis in this study.This section of the paper presents the materials, procedures, and methods that were used in the experimental work.

Materials
The main materials that were used in this experimental study are ribbed mild steel reinforcement bars (RMSRBs).These RMSRBs were obtained from three major local manufacturing companies in Ghana.The local manufacturing companies that manufacture the RMSRBs are Sentuo Steel Company (STS), Ferro Fabrik Limited (FFL), and Tema Steel Limited (TSL).For the purpose of identification, STS, FFL, and TSL are denoted by letters A, B, and C, respectively.Samples of the RMSRBs used for the study are shown in Figure 1.(12,16, and 20mm diameters) of grade 250N/mm 2 of the RMSRBs were randomly selected and used for the experimental work.Five specimens of lengths 20, 50, and 500mm were prepared as samples for testing as shown in Figure 1.A total of ninety (90) specimens were used for the testing of the properties of the RMSRBs.Forty-five (45) of the specimens were used for tensile strength test, fifteen (15) each for chemical composition test, micro-hardness test, and microstructure analysis as shown in Table 1.For the chemical composition test, microhardness test, and microstructure analysis only the 16mm diameter RMSRBs were prepared for the study.The specimens were tested after the preparation.The tests that were conducted are tensile strength, chemical composition, hardness, and microstructure.

Tensile Strength Test
The tensile strength test was conducted following the ASTM A706/A706M-09b (2022) test standard.The universal testing machine (model WAW-1000H) was used to carry out the tensile strength test of the RMSRBs as shown in Figure 2a.The test machine was linked to a computer-controlled system in which the load and extension data were graphically displayed together with the calculations of stress and strain.A total of 45 test specimens comprising 15 each specimen of 12, 16, and 20mm were tested.Each specimen was placed in the upper and the lower jaws (well gripped) of the test machine, and the uniaxial load was applied at both ends at the rate of 5mm/min till the specimen failed (Figure 2b).The ultimate tensile strength, Young's Modulus, percentage elongation, and fracture stress data were obtained from the test machine.Equation 1 was used for the ultimate tensile strength test calculation.
Where, s=ultimate tensile strength, P=force required to break RMSRBs, and A= cross-sectional area.

Chemical Composition Test
The chemical composition of the RMSRBs was determined using the Angstrom V-950 Spectrometer apparatus shown in Figure 3a.Specimens of length 50mm (see Figure 3b) were cut to the cross section of the RMSRBs perpendicular to the axis and grounded flat for spectrometry.Each specimen was placed in position and the spark pointer positioned on the grounded surface of the specimen.The percentage chemical composition data were tabled automatically by the computer connected to the Spectrometer.

Hardness Test
The Vickers hardness test was conducted following the ASTM E92-17 (2017) test standard.This study employed a Vickers hardness tester to measure the scratch hardness of the RMSRBs.Figure 4a shows the experimental setup for the micro-hardness test.The Vickers hardness tests method was made to utilize test forces ranging from 9.807 x 10-13 to 1176.80 N (1gf to 120 kgf).A diamond indenter in the form of a right pyramid of a square base of an angle of 136° between opposite faces under a load (F) parallel to the axis of the specimen was applied to the surface.Each hardness test was carried out on a fresh surface of RMSRBs specimen as shown in Figure 4b.Vickers hardness values were found to be higher for indentation made closer to the axis of RMSRBs than for other surface regions.This suggests that smaller indentations produce higher value.The equation used in VH is shown in equation 2.
Where, VH=Vicker hardness value, F= load applied and D =the area of indentation.
where F = ANOVA coefficient, MSB = mean sum of square between groups, and MSE= mean sum of errors.

RESULTS AND DISCUSSION 3.1 Tensile Strength of RMSRBs
The average tensile strength results of the RMSRBs are presented in Table 2.The results also show the average modulus of elasticity and the average elongation percentage of company A, B, and C.  2002) obtained 560, 500, and 550 N/mm 2 average tensile strength.These gave corresponding elongation values of 9.6, 11.8, and 10.6 for the three samples.The findings of this study are consistent with the findings of Shunichi and Morifumi (2006).The results obtained from this study (between 582.20 and 768.40N/mm 2 ) imply that the RMSRBs produced in Ghana were above the minimum tensile strength of 250N/mm 2 recommended by ASTM E8/E8M-16a (2019) and ASTM E8/E8M -22 (2022).Tensile strength of 20mm diameter RMSRBs specimen tends to be lower than the 12mm and 16mm diameter specimens because of shear-lag effect.Due to uneven stress distribution next to the jaw of the test machine, moreover, not all the area of cross section were directly gripped in the jaw.This contributed to fracture not occurring at the mid-span of the RMSRBs as shown in Figure 2b.The failure mechanism occurred when the stress (load) increases beyond the elastic limit of the RMSRBs undergo deformation which is known as the yield point.Further increase of stress beyond the ultimate strength point reduces the cross-sectional area called necking, which means a breaking stage.At this stage, the RMSRBs breaks, thus the curve drops as shown in Figure 7.The chemical composition was analysed using carbon equivalent value (CEV).Carbon equivalent value combines seven chemical elements (Carbon, Manganese, Chromium, Molybdenum, Vanadium, Nickel, and copper) in a relationship that can be used to conclude based on their percentage.The comparison of the chemical composition in terms of CEV is shown in Figure 8. CEV of 0.287, 0.323, and 0.333% were obtained, respectively for company A, B, and C specimens.The CEV of company A, which was 0.287% can be run off to 0.3%.Companies B and C had all ten samples within the excellent range.Only two samples from company A were below the excellent range.Company B and C exhibited acceptable percentages because the carbon and phosphorus content in the material met the minimum percentage (0.25 and 0.040 respectively) as specified by ASTM A706/A706M-09 (2010).The CEVs obtained were within the range of 0.3 to 0.55% recommended by ASTM A706/A706M-09b (2010).According to ASTM A706/A706M-09 (2022), the CEV in the range of 0.3 to 0.55% shows much better mechanical performance than a steel bar.A study by Ssempijja (2019) also obtained CEV within the range of 0.3 to 0.55%.Therefore, the tensile strength values obtained from the current study which are higher than the minimum recommended values can be attributed to the acceptable CEV of the RMSRBs that are manufactured in Ghana.5 presents the One-Way ANOVA results.The p-value of tensile strength of 12mm (˂0.000) 16mm (0.001) and 20mm (0.138) indicate that the differences in the tensile strength for 12 and 16mm specimens were less than the specified significant level of 0.05.Therefore, the differences in the tensile strength values obtained for 12 and 16mm are statistically significant.However, the p-value of tensile strength of 20mm (0.138) indicates the differences in the tensile strength were not statistically different.It can also be seen from the ANOVA analysis results in Table 5 that the p-value of hardness value of 16mm (0.572) was greater than the specified significant level of 0.05 and therefore, the difference is statistically not significant, while the CEV p-value of 0.030 was less than 0.05 and therefore, the difference is statistically significant.1.The study found that the average tensile strength of between 576.00 and 768.40 N/mm 2 was obtained from the 12, 16, and 20 mm RMSRBs produced by the three companies in Ghana.These strength values are above the minimum tensile strength of 250N/mm 2 recommended by ASTM E8/E8M-16a. 2. Chemical composition for the 16mm diameter RMSRBs of carbon equivalent values (CEVs) of between 0.287 and 0.333% were obtained from the three manufacturing companies in Ghana.The CEVs obtained were within the range of 0.3 to 0.55% recommended by ASTM A706/A706M-09b.3. The study found that the average hardness values of between 255.76 and 295.38HV for RMSRBs produced by the three companies in Ghana.These Vickers hardness values are above the 150HV recommended by previous studies.4. The microstructural images of the RMSRBs showed good distribution of the pearlite and ferrite of the core.This is the reason why the RMSRBs produced by the three companies in Ghana obtained high tensile strength.5.The One-Way ANOVA results indicated that the differences in the tensile strength values for 12mm (p-value ˂0.000) and 16mm (p-value =0.001) were statistically significant, however, the 20 mm (p-value =0.138) was not statistically different.The difference in the hardness value of 16mm (p-value =0.572) was found to be statistically not significant, while the difference in the CEV value (p-value =0.030) was found to be statistically significant.6.The study, therefore, concludes that the strength properties of the 12, 16, and 20mm diameters of the RMSRBs produced from three different companies in Ghana meet the standard requirement, and are recommended for use by contractors for the production of reinforced concrete.

Figure 1 :
Figure 1: Untreated ribbed mild steel reinforcing bars 2.2 Preparation of Specimens Three different sizes(12,16, and 20mm diameters) of grade 250N/mm 2 of the RMSRBs were randomly selected and used for the experimental work.Five specimens of lengths 20, 50, and 500mm were prepared as samples for testing as shown in Figure1.A total of ninety (90) specimens were used for the testing of the properties of the RMSRBs.Forty-five (45) of the specimens were used for tensile strength test, fifteen (15) each for chemical composition test, micro-hardness test, and microstructure analysis as shown in Table1.For the chemical composition test, microhardness test, and microstructure analysis only the 16mm diameter RMSRBs were prepared for the study.

Figure 3 :
Figure 3: Determining the chemical composition of the RMSRBs: (a) setting up angstrom V-950 Spectrometer (b), prepared specimen for chemical composition test.

Figure 4 :Figure 5 :
Figure 4: Determining the hardness of the RMSRBs: (a) set up for Vickers hardness test, (2) prepared specimen for Vickers hardness test.2.3.4Microstructural TestSpecimens of lengths of 20mm were cut from the cross section of the ribbed steel bars perpendicular to the axis of RMSRBs and were used for microstructural analysis.The surfaces of the specimens were micro-polished with aluminium oxide powder and etched by a mixture of 2% nitric acid with 98% ethanol.Micrographs of the etched surfaces were obtained using Olympus-412 photomicroscope as shown in Figure5using a magnification of 100×, and the micrographs were used to analyse the microstructure of the specimens.

Figure 6 :
Figure 6: Tensile strength of the RMSRBs

Figure 7 :
Figure 7: Stress-strain graph of the RMSRBs 3.2 Chemical Composition of RMSRBs The results of the chemical composition test of 16mm diameter RMSRBs are presented in Table 3. From the table, the chemical compositions of the steel bars are slightly different from each other.The combined effect of the alloying elements of the steel bars and their carbon equivalent values (CEV) were calculated using the standard formula in equation 4 (Guo et al., 2013): CE =  +  6 + ++ 5

Figure 8 :
Figure 8: Carbon equivalent value (CEV) of the RMSRBs 3.3 Micro-Hardness of RMSRBs The micro-hardness test results are shown in Table4.The hardness test was performed to identify the hardness strength of the RMSRBs.Hardness test results comparison for companies A, B, and C are illustrated in Figure9.It can be observed that the average hardness values are 295.38,291.16, and 255.76HV, respectively for companies A, B, and C RMSRBs.Comparing the hardness value with the CEV, it can be observed that, the higher the hardness value the lower the carbon equivalent value.Company A had the lowest CEV of 0.287% with the highest average hardness value of 295.38.Company C had a higher CEV of 0.333 with the lowest hardness value of 255.76HV.The results show that the Vickers hardness values for all the companies were higher than the recommended hardness value of 150HV(Totten, 2007;Ponle et al., 2014).According toTotten (2007), the hardening capacity of steel depends mainly on its carbon content and to a lesser extent on its content of alloying elements and the grain size of austenite grains.Average Vicker hardness value of 295.38, 291.16 and 255.76 as obtained in this study depicted the hardness level of RMSRBs.

Figure 9 :
Figure 9: Vickers hardness value of the RMSRBs3.4Microstructural Analysis of RMSRBsThe core zone micro-structure of RMSRBs was analysed with Photo Microscope at a 100× magnification lens as shown in Figure10.All the RMSRBs, regardless of chemical composition and strength levels, exhibited a composite microstructure consisting of ferrite and pearlite phases in the core.The micro-graphs showed ferrites are the white patches that are not clearly visible, and the pearlites are the dark patches that are more visible.The relatively uneven distribution of phases is visible around some areas in the core of the images of specimen A. The images of specimens B and C had a good distribution of the pearlite and ferrite of the core.This could be the reason why RMSRBs from company A obtained higher tensile strength than companies B and C. Martensite was not detected in any of the specimen therefore, the results are similar to the results of previous studies(Chen et al., 2017;Balogun et al., 2009).Dzogbewu and Arthur (2013) also found similar pattern of ferrite and pearlite in the micro-graph images.

Table 1 :
Number of Ribbed mild steel reinforcing bars sampled.

Table 2 :
Average strength results of RM.The results indicate that the tensile strength of company A obtained the highest average tensile strength among the 12 and 16mm RMSRBs and company C obtained the highest for the 20mm.There were corresponding elongation values of 11.24, 10.03, and 17.08 (see Table 2) for 12, 16, and 20mm, respectively.A study by Kankam and Adom-Asamoah (

Table 3 :
Results of chemical compositions of RMSRBs

Table 4 .
Totten (2007);Ponle et al., 2014)o identify the hardness strength of the RMSRBs.Hardness test results comparison for companies A, B, and C are illustrated in Figure9.It can be observed that the average hardness values are 295.38,291.16,and255.76HV,respectively for companies A, B, and C RMSRBs.Comparing the hardness value with the CEV, it can be observed that, the higher the hardness value the lower the carbon equivalent value.Company A had the lowest CEV of 0.287% with the highest average hardness value of 295.38.Company C had a higher CEV of 0.333 with the lowest hardness value of 255.76HV.The results show that the Vickers hardness values for all the companies were higher than the recommended hardness value of 150HV(Totten, 2007;Ponle et al., 2014).According toTotten (2007), the hardening capacity of steel depends mainly on its carbon content and to a lesser extent on its content of alloying elements and the grain size of austenite grains.Average Vicker hardness value of 295.38, 291.16 and 255.76 as obtained in this study depicted the hardness level of RMSRBs.

Table 5
examined the strength properties of 12, 16, and 20mm diameters of ribbed mild steel reinforcing bars (RMSRBs) produced with scrap metals from three different companies in Ghana.The study further determined the chemical compositions, hardness, and microstructure properties of the RMSRBs.The findings of the study are summarized below.