Civil Engineering

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Anaerobic co-digestion of abattoir and textile industry wastewater in a UASB reactor
(2015-04) Ondari, James Maati; Ndege, Maurice S.; Aoyi, Ochieng
Textile industry effluents are carcinogenic and highly recalcitrant hence difficult to degrade especially through biological methods. Abattoir effluents are classified under high-strength wastewaters because of their characteristic high organic load hence highly biodegradable. Anaerobic co-digestion is the concept of degrading two effluent streams with complementary characteristics in order to improve the substrate removal rate. The feasibility of co-digesting abattoir and textile wastewater in a UASB reactor was evaluated at mesophilic and ambient temperature conditions. Preliminary experiments were conducted in 500 ml batch reactors to evaluate the optimum abattoir to textile synthetic wastewater ratio. The effect of COD, TVFA, alkalinity and pH on biogas yield was examined at both ambient and mesophilic temperatures. Anaerobic co-digestion of abattoir to textile wastewater in the ratio determined in the batch process was carried out in a 3 L UASB reactor by a continuous process. The continuous biodegradation process was executed at three different HRTs (22, 18 and 14 hrs) over a 60 day operation period. UASB reactor efficiency was achieved at organic loads ranging from 3.0 – 10.8 gCOD L-1 day-1. Continuous mode experiments were carried out at influent flow rates which corresponded to HRTs ranging between 1 to 8 days in order to evaluate the steady state operating parameters for the co-digestion process. The abattoir to textile effluent ratio was found to be 60:40 respectively. The COD, TVFA, alkalinity and pH and biogas yield followed a similar pattern over time at both mesophilic and ambient temperature conditions. Experimental data adequately fit the Grau first order kinetic model and average COD removal efficiencies of 85% and BOD5 of around 96% were achieved. The average biogas yield remained essentially constant, around 0.19 L/g CODremoved. The co-digested mixture was found to be biodegradable judging from the BOD:COD ratio of 0.53. TCOD removal efficiency decreased from 93% to 16% as HRT decreased from 8 days to 1 day. The kinetics of a UASB reactor co-digesting the mixture of synthetic abattoir and textile wastewater was evaluated in this study using Grau second order multicomponent substrate removal kinetic model. The Grau second order kinetic model, whose kinetic coefficient (ks) was 0.389, was found to be suitable for predicting the performance of a lab-scale UASB reactor.
Application of integrated water resources management in computer simulation of River Basin's status - case study of River Rwizi
(2012-03-28) Atim, Janet; Ngirana-Katashaya, G.; Ndambuki, J. M.
During the last few years, concern has been growing among many stakeholders all over the world about declining levels of surface water bodies accompanied by reduced water availability predominantly due to ever increasing demand and misuse. Furthermore, overexploitation of environmental resources and haphazard dumping of waste has made the little water remaining to be so contaminated that a dedicated rehabilitation/remediation of the environment is the only proactive way forward. River Rwizi Catchment is an environment in the focus of this statement. The overall objective of this research was to plan, restore and rationally allocate the water resources in any river basin with similar attributes to the study area. In this research, Integrated Water Resources Management (IWRM) methodology was applied through Watershed/Basin Simulation Models for general river basins. The model chosen and used after subjection to several criteria was DHI Model, MIKE BASIN 2009 Version. It was then appropriately developed through calibration on data from the study catchment, input data formatting and its adaptation to the catchment characteristics. The methodology involved using spatio-temporal demographic and hydrometeorological data. It was established that the model can be used to predict the impact of projects on the already existing enviro-hydrological system while assigning priority to water users and usage as would be deemed necessary, which is a significant procedure in IWRM-based environmental rehabilitation/remediation. The setback was that the available records from the various offices visited had a lot of data gaps that would affect the degree of accuracy of the output. These gaps were appropriately infilled and gave an overall output that was adequate for inferences made therefrom. Several scenarios tested included; use and abstraction for the present river situation, the effect of wet/dry seasons on the resultant water available for use, and proposed projects being constructed on and along the river. Results indicated that the river had insufficient flow to sustain both the current and proposed water users. It was concluded that irrespective of over exploitation, lack of adequate rainfall was not a reason for the low discharge but rather the loss of rainwater as evaporation, storage in swamps/wetlands, and a considerable amount of water recharging groundwater aquifers. Thus, the proposed remedy is to increase the exploitation of the groundwater resource in the area and reduce the number of direct river water users, improve farming methods and conjunctive use of groundwater and surface water - the latter as a dam on River Rwizi. The advantage of the dam is that the water usage can be controlled as necessary in contrast to unregulated direct abstraction, thus reducing the risk of subsequent over-exploitation.
Determining the efficiency of selected vegetated biofilters in reducing nutrients from urban stormwater in the city of Ekurhuleni, South Africa
(Vaal University of Technology, 2021-11) Bvumbi, Mulalo Justice; Rwanga, S. S., Dr.; Ochieng, G. M., Prof.
Over time, the quality standard of stormwater in the City of Ekurhuleni (CoE) has deteriorated due to industrial, commercial, residential and farming activities. Stormwater quality directly impacts the treatment chain of potable water, and therefore, it should be kept in check at all stages. Innovations in the biofiltration process can provide useful, practical solutions to overcome crucial stormwater pollution problems. In 2013, the CoE developed stormwater design guidelines and standards to be implemented for the design of stormwater management, which include the principles of Water Sensitive Urban Design (WSUD) and Sustainable Urban Drainage Systems (SuDS) in particular. The CoE stormwater design guidelines and standards do not provide details on how the city plans to implement SuDS treatment trains to reduce stormwater pollution experienced by the city. This study aimed to verify the efficiency and effectiveness of vegetated biofilters on the stormwater treatment using CoE – Olifantsfontain's natural stormwater and to determine the most suitable vegetation to be used in the region. The CoE experimental case study was conducted to assess the efficiency of selected vegetated biofilters in lowering the concentration of orthophosphate (PO4-3), ammonium (NH4+), and nitrate (NO3-) from Tembisa/Olifantsfontain stormwater. In the experimental setup, six selected plant species were planted into 30 vegetated biofilter columns, namely: Agapanthus praecox (Dryland plant), Carpobrotus edulis (Dryland plant), Stenotaphrum secundatum (Dryland plant), Zantedeschia aethiopica (Wetland plant), Typha capensis (Wetland plant) and Phragmites australis (Wetland plant). The six species were grouped according to general habitats, i.e. three wetland and three dryland plants. Wetland plants were planted into fifteen vegetated biofilters, and dryland plants were also planted on another fifteen vegetated biofilters. The biofilters contained layers of sandy loam soil, coarse and and gravel sand. Each biofilter had a designated inlet and outlet section fitted with a gate valve to control retention time. The raw stormwater consisting of natural nutrient pollutants was applied to each vegetated biofilter through the inlet section. The samples were collected from the inlet and outlet of the six grouped vegetated biofilters during the month of June. All six plant species reduced outflow concentrations of PO4-3 and NH4+ by an average of 99% and 98%, respectively. The results also show that all plant species excluding Phragmites australis were able to reduce NO3- with outflow concentrations being reduced by an average of 58%. From the results obtained, it may be concluded that all the six plant species may be suitable variants to be applied as biofilter material for the purposes of treating urban stormwater in the CoE. The reason is that the determined removal efficiencies for bio-retention fall within 50% – 60% for PO4-3, and 40% - 50% for NH4+ and NO3- respectively. The results also show that if the plant species were applied for SuDs in the CoE, there could be a great improvement in the urban stormwater quality with the consequent improvement in both surface and groundwater quality of the receiving water bodies in the area. Regardless of the nutrient removal by selected plant species, the inclusion of vegetation in a field setting would slow flow rates and thus encourage infiltration into the soil, improve water quality, and support urban biodiversity. In the CoE, all the selected species could be used in the SuDS treatment trains targeting PO4-3, NH4+ and/or NO3-. The case study results provide a informed records for the CoE in the future/intended application SuDs in the upgrade/rehabilitation of its stormwater system.
Development of pavement management systems for road network maintenance
(2012-11-01) Mapikitla, David; Ndambuki, Julius M.
In the past thirty years there has been a rapid deterioration of the road network in South Africa. As an attempt to address this challenge, a study was conducted on R34 between Vrede and Bothmas Pass Border. The aim of the study was to develop a pavement management system for road network maintenance to serve as a decision support tool to assist to improve the efficiency of making decisions, provide feedback as to the consequences of these decisions, ensure consistency of decisions made at different levels and improve the effectiveness of all decisions in terms of efficiency of results. The study focused on developing and testing pavement management system for road network maintenance. Consequently, visual condition inspections, non-destructive and semi-destructive tests were conducted on the field, data acquired, processed and analysed in accordance with guidelines stipulated in the Draft Technical Recommendations for Highways (TRH) 22 in order to draw conclusions. The data acquired included the surfacing assessments, structural assessments, functional assessments, traffic surveys, riding quality, falling weight deflectometer, mechanical rutting, material investigations and dynamic cone penetration. After analysis of the data, visual condition index was then calculated to be 40%. Visual condition index was then used to determine the action required towards rehabilitating the road. After consultation with guidelines contained in the TRH22, it was concluded that the pavement treatment needed for the road was Rehabilitation. It was then concluded that PMS developed would provide key performance indicators to assist with decision support system and that it is also suitable for road network applications ranging from national roads, provincial roads, regional or district arterial and collector / distributor networks in SA. The municipalities and other road maintenance agencies were then recommended to utilise the “easy to use” developed pavement management system as a decision support tool in their maintenance programmes.
Effect of land-use change on traffic peak hour factor
(Vaal University of Technology, 2012-01) Phahlane, Motsepe Herbert; Salim, W. R., Dr.; Ndambuki, J. M., Prof.
Growth in land development in South Africa resulted in large increase in traffic volumes. A Traffic Impact Assessment (TIA), as a traffic engineering tool, is commonly used to assess the possible effects of a land development project on the transportation and traffic system. During the TIA process, capacity analysis is performed to indicate the measures of effectiveness of the intersection. Intersection capacity analysis in South Africa by engineers is done on the basis of default values of the Peak Hour Factor (PHF) provided by the Highway Capacity Manual (HCM) or limited traffic counts. However, the default value of PHF may be significantly affected by new developments in the neighbourhood of the intersection. This study aimed at investigating the impact land-use change has on the existing intersection PHF, thus predicting values per land-use type. Intersections with traffic counts conducted before and after land-use change in vicinity were selected and investigated. The results showed that change in land-use has an impact on the existing PHF. They also assist in identifying the appropriate intersections to predict the PHF per land-use type. Intersections were identified and analysed, and this led to the development of a design chart showing the predicted PHF per land-use type selected and measures to consider during traffic analysis. Intersection capacity analysis was performed to compare the results using the predicted PHF and the HCM default values. The results showed that traffic flow rate was adjusted by up to 26% when using the default values, 0.92 and 0.95. The results also showed that the default values could overestimate the volume to capacity ratio and the average delay by up to 15% and 35%, respectively. It was then concluded that the use of HCM default values of the PHF for every land-use type will have an effect of the final roadway design results. The computed PHF values for each land-use type were then recommended to be used to ensure fairness and consistency in traffic analysis.
The evaluation of project management practices relationship with the project performance outcome of reconstruction development programme (RDP) and subsidy housing
(Vaal University of Technology, 2022-06) Tseladikae, Tshepo; Ochieng, G. M., Prof.; Agumba, J. N., Prof.
As citizens migrate from rural to urban locations, coupled with the population growth in South Africa, housing supply remains an imperative task. Regarding this migration and housing need, the South African government, shortly after the dawn of democracy, has been providing housing to its previously disadvantaged citizens due to the apartheid government. The housing typology that the government delivers to its citizens is the Reconstruction Development Programme (RDP) and subsidy housing. The construction industry has difficulties achieving satisfactory project performance, especially with the current delivery of the Reconstruction Development Programme and subsidy housing projects in South Africa. Most housing projects are never completed satisfactorily as contractors either abandon the project or deliver it late. They incur cost overruns and poor quality, making it an expensive and wasteful process for the beneficiaries and the government. As a result, this dissertation investigated the relationship between project management practices (PMPs) usage and project performance outcomes for the RDP and subsidy housing in South Africa. The research design was quantitative in nature, using primary data and the data were analysed using the IBM Statistical Package for Social Sciences (SPSS). The main statistical parameters used to present and analyse data results were mean score, correlation and factor analysis. The researcher used a questionnaire survey to gather the primary data and address the objective of this study, which is a deductive research approach. A convenience non-probability sampling method was used for sampling the participants. The questionnaire was administered to Gauteng-based small and medium contractors undertaking the RDP and subsidy housing projects. A total of 116 questionnaires were returned for analysis. However, one questionnaire was removed from further analysis because it was a large contractor as per the Department of Trade and Industry definition. As per the results, the majority of the respondents were males; 14 percent were females and 86 percent were males. The majority had a minimum qualification of a diploma, which represented 50.9 percent. The challenges faced by contractors were ranked using the mean score. The findings indicated that late payment of contractors was deemed a significant challenge. Furthermore, factor analysis established that the challenges stated were a three-factor model, categorised as project management, environmental and financial factors. The 86 PMPs identified in the literature were analysed using exploratory factor analysis (EFA). The results from the EFA established a ten-factor model in line with the theory of the knowledge areas of the Project Management Body of Knowledge (PMBOK). The mean score was performed to determine the usage level and results showed that one project management practice, namely a bar chart, was used every time in the RDP and FLIP housing projects (mean = 4.25 and Std. Deviation = 0.77), ranking first. Eighty-two other PMPs were used almost every time, as their mean scores were in the range of 3.41 to 4.20. On the contrary, Pareto, flow chart and fishbone were almost never used as they were in the range of 1.81 to 2.60. The final part of the results determined the performance outcome of the project and the relationship between the usage of the PMPs and the project performance outcome. The identified performance outcome measures were analysed using EFA and three components of the performance outcome measures were identified: compliance and financial performance, contractor process and employee satisfaction and contractor process and employee satisfaction. Spearman’s rho correlation, which is non-parametric, was used to evaluate the relationship between the three project performance outcomes and the 10 PMPs. From the results, the hypotheses tested indicated that nine of the PMPs, namely scope, schedule, cost, quality, integration, stakeholder, resources, communication and risk management, significantly correlate with one of the three project performance outcomes. However, the procurement management practice established no significant correlation with any of the three project performance outcomes. In conclusion, PMP has a relationship with the project outcome and each area of project management affects a different aspect of performance; for instance, cost management practices showed a relationship with compliance and financial performance component whereas stakeholder was customer performance component, the following recommendations were made: Relevant PMPs found to correlate with the performance outcomes of the project should be made compulsory for every RDP and subsidy housing project; qualified personnel should be employed to care for a project management role and not be a passive role given to anyone; training in PMPs should be compulsory for all those involved in the construction of RDP and subsidy housing projects.
Flash flood risk management in a South African township: a case study of Alexandra
(Vaal University of Technology, 2022) Fadupin, Adekunle Oluwatosin; Ndege, M., Prof.; Ochieng, G. M., Prof.
Several studies have been carried out on improvement of flood risk assessment and management in South Africa. Despite all these studies, the problem of F lash Flood (FF) persists. This study was designed to determine the most appropriate Flash Flood Inundation Model that could be applied in flash flood risks management in a South Africa Township: a case study of Alexandra. Alexandra Township being a FF prone area was chosen for this study from where a sample of 30 respondents was purposively selected. A survey (Questionnaire) and document search were used to collect relevant quantitative data and qualitatively based secondary information from the sample population respectively. Also, data were collected through in-depth interviews of senior officials in the Disaster Management Services for more well-rounded information. Content analytical method was used to process the qualitative information. The study adopted complementary analytical tools, namely, R-programming and appropriately selected tools from the Statistical Package for Social Sciences (SPSS version 21.0) to analyze the quantitative data and to determine the most appropriate Flash Flood Inundation Model. In search of mitigating the risk of the FF in Alexandra Township, a FF inundation model was determined. People were educated on FF not to build shacks along Juskei River and were trained to prepare for and manage FF. Early Warning messages were sent and community volunteers were trained on managing risks related to FF. The main observed risk factors of FF where building of shacks without abiding by the rules and regulation, blocking of drainage system by illegal dumping of solid waste and growth in population. The major risk factors the respondents agreed to cause FF where annual rainfall intensity (70.0%), poor drainage (56.7%) and human settlement (50.0%). The three Principal Components identified to be contributing to FF in Alexandra Township were terrain, soil texture and poor drainage system. This factors contributed 82.0% of FF risk factors in Alexandra Township. The model revealed that appropriate solid waste disposal, construction of sewers, dredging of Jukskei River, and construction of Gabions along Jukskei River will mitigate flash flood risk and related hazards in Alexandra Township.
Investigation of the performance of fibre reinforced polymer re-bars in structural foundations
(2012-11-01) Labana, Beltran; Wanjala, Salim; Ndambuki, J. M.; Masu, L. M.
This research focused on the structural performance of Fibre Reinforced Polymer (FRP) re-bars in structural foundation compared to steel reinforcement re-bars. The corrosion of steel re-bars is the main reason of deterioration of reinforced concrete. However, use of FRP re-bars as alternative reinforcement will address the deterioration of reinforced concrete. Carbon and Glass Fibre Reinforced Polymer re-bars were used as reinforcing bars and traditional steel reinforced concrete was used as the reference. Thirty six specimens of reinforced concrete bases were tested for flexural capacity at different ages. The simulation of Soil Bearing Pressure of this study was derived from the model of beam finite length on elastic foundation. The foundation base was treated as a beam while the soil was modelled as series of timber elements acting as springs. The mathematical model to reflect the model was as documented by Timoshenko (1976:18) and Den Hartog (1952:160). Results showed that stress in the steel re-bars of reinforced concrete was higher than that of Carbon Fibre Reinforced Polymer (CFRP) and Glass Fibre Reinforced Polymer (GFRP) re-bars by 227 MPa (5.99 percent) and 284 MPa (7.61 percent), respectively. The stress in CFRP re-bars was 57 MPa or 1.53 percent higher compared to GFRP re-bars of FRP reinforced concrete. Furthermore, the experimental ultimate moments of CFRP and GFRP reinforced concrete foundation – bases on the 28th day were 23.917 kNm (79.0 percent) and 23.529 kNm (77.7 percent) higher than the theoretical ultimate moments, respectively. However, steel reinforced concrete foundation – bases had the higher calculated deflection than FRP reinforced concrete. With high resistance to corrosion as a property, FRP re-bars appeared to be a better alternative reinforcement to steel in corrosion in an aggressive environment.
Modelling of Pressurised Water Supply Networks that May Exhibit Transient Low Pressure - Open Channel Flow Conditions
(Vaal University of Technology, 2011-03) Byakika, Stephen Nyende; Ndambuki, Prof. J. M.; Ngirane-Katashaya, Prof. G.
Growing demand for water due to increasing populations, industrialisation and water consuming lifestyles puts stress on existing water supply systems. To cater for the rising demand, water distribution networks are expanded beyond their design capacities and this creates transient “low-pressure-open-channel flow” (LPOCF) conditions. Current water supply models use “demand driven approach” (DDA) methodology which is not able to simulate transient LPOCF conditions, that poses an impediment to management/analysis of pressure-deficient networks. With a case study of the water supply network of Kampala City, LPOCF conditions were studied in this research. A “pressure/head driven approach” (PDA/HDA) was used in order to determine what demand is enabled by particular nodal pressures. Conversion of free surface to pressurised flow was analysed and modelled, with a view to clearly understanding occurrence of this phenomenon. The research demonstrated that if adequate pressures and flows are to be maintained, effectiveness of the water distribution network should be given as much attention as water production capacity. The research also indicated that when network pressures are low, the head-driven approach to water distribution modelling gives more accurate results than the traditional demand-driven methodology. Coexistence of free-surface and pressurised flow in networks prone to LPOCF conditions was confirmed and modelled. Results obtained highlighted the advantages of developing fully dynamic and transient models in the solution of transient LPOCF conditions in water distribution networks. Models developed allow application of PDA/HDA and DDA methodologies in systems that may exhibit LPOCF conditions thus enabling identification, understanding and analysis of the status of all sections of the network. These culminated in the development of a DSS to guide operational decisions that can be made to optimise network performance.
Monitoring and modelling of water quality characteristics along a reticulation system: a case study of modimolle reticulation network
(2012-01) Mehlo, Mahlomola; Wanjala, R. Salim, Dr.; Ndambuki, J. M., Prof.
Potable water quality can deteriorate immensely from point of treatment to point of usage. This change in quality along a bulk distribution main may be attributed to numerous factors, such as the ingress of storm water. Furthermore, water utilities experience challenges in terms of the microbiological organisms that are not attributed to operational practices. For example, drinking water bulk distribution mains may be a shelter for these microorganisms that are sustained by organic and inorganic nutrients present within the pipe itself. These microorganisms may be active in the water being transported by the pipe, and can cause a significant drop in the water quality. In order to deal with the problem of deteriorating water quality, sufficient information within the bulk main is required, so that the consumer can be protected from ingesting contaminated water or water of poor quality. Hence, the overall objective of this study was to investigate and model water quality characteristics within the Modimolle reticulation network. Water samples were collected from various points throughout the entire system for quality analysis. Different sampling points were established along the main pipeline as well as within the Modimolle distribution system. Water quality software, EPANET, was then used to model the water quality deterioration for both the bulk line and the reticulation network of Modimolle extension 11. Residual chlorine was the main parameter which was monitored. This study presents results of a research on water quality variation within a long distribution mains conveying water up to 87 km. Results show that raw residual chlorine is constantly depleted along the pipeline, and is therefore unable to be maintained at the required level of 0.2 mg/l, as stipulated by the Department of Water Affairs. This means that if any harmful contaminants should enter the water, the residual chlorine in the water will not be able to protect the consumers from the contaminants.
Optimal modelling of non-revenue water: A case study of Lebohang extension 9 and 10 in Govan Mbeki Municipality, Mpumalanga, South Africa
(Vaal University of Technology, 2023-01-15) Mlangeni, Ready Victor; Ochieng, G. M., Prof.
South Africa was declared a water scarce country with an annual runoff that is estimated to be less than 13 percent against the world average. South African municipalities are in position of providing accurate water balance data which is necessarily to measure the level of NRW. However, majority of them don’t keep accurate records of their input volume or billed consumption. The study done by South African Water Research Commission which analysed 62 system has estimated total water losses (real and apparent) to be 31 percent of total supplied water. (McKenzie: 2014) The global volume of non-revenue water (NRW) or water losses is overwhelming. Each year more than 32 billion m3 of treated water is lost through leakages from the distribution networks. An additional 16 billion m3 per year is delivered to consumers but not invoiced due to various reasons such as of theft, poor metering, inadequate billing systems, or illegal use. In some low-income countries this loss represents 50 -60 percent of water produced, with a global average estimated at 35 percent. Saving just this amount would supply water to an additional 100 million people without further investment in water production and distribution systems. (Simbeye I: 2010) Many studies conducted proved that water loss in South Africa is generally considered high between 30 percent and 70 percent and the cause of these high losses is defined in various studies (McKenzie & Seago: 2007). Many reasons have been tabled as contributing factors to the cause of high level of non-revenue water in general. The reasons include amongst others and not limited to poor planning, pressure management control, insufficient funds, and poor water network implementation. The factors further include inadequate actions in place to address optimization of services, leakage control, inadequate tariff, and collection systems. (Muhamad Shahbani Abu Bakar: 2005) The major challenges towards efficient and effective water delivery to all urban people are usually poor governance, financial constraints, poor network design, poor customer services, and inadequate infrastructure. It is obvious that high levels of NRW result from volumes of water lost through physical leaks or administrative losses from poor customer accounting and billing. This seriously affects the financial sustainability of water service providers. (Simbeye I: 2010)
Rubber tyre and plastic waste use in asphalt concrete pavement
(2015-12) Onyango, Felix Odhiambo; Salim, R. W.; Ndege, M.
Modified asphalt concrete is one of the important construction materials for flexible pavements. The addition of polymers and natural hydrocarbon modifiers to enhance the properties of asphalt concrete over a wide temperature range in paving applications has been the common practice. Currently these modified asphalt mixtures are relatively expensive. However, recycled polymers and rubber added to asphalt have also shown similar results in improving the performance of road pavements. In this study, an attempt has been made to use low density polyethylene (LDPE) obtained from plastic waste and crumb rubber obtained from worn out vehicle tyres. The aim was to optimise the proportions of LDPE in the bitumen binder using the ‘wet process’ and crumb rubber aggregates in the hot mix asphalt (HMA) using the ‘dry process’. The Marshall method of bituminous mix design was carried out for varying percentages of LDPE namely 2%, 4%, 6%, 8% and 10% by weight of bitumen binder and 1%, 2%, 3%, 4% and 5% crumb rubber by volume of the mineral aggregates. The characteristics of bitumen modified with LDPE were evaluated. The modified asphalt mix was also evaluated to determine the different mix characteristics. The results from laboratory studies in terms of the rheological properties of the LDPE modified bitumen binder showed an increase in viscosity, softening point and stiffness of the binder. The optimum Marshall stability values for HMA mixtures containing 2% crumb rubber tyre and 4% LDPE were found to be 30% higher than the conventional asphalt concrete mix. The wheel tracking test done at 50ºC was 9.81mm rut depth showing a good rutting resistance of the optimized mixture compared to the conventional asphalt mixes. The Modified Lottman test gave a Tensile Strength Ratio value of 0.979 which indicates a low degree of moisture susceptibility of the modified asphalt mix. The above results showed improved properties of the asphalt mixture. The economic assessment done using the present worth of costs indicated a reduction in maintenance cost due to the extended service life of the modified asphalt pavement.
Structural bond behaviour of ribbed GFRP rebars in concrete beams under dynamic loading
(Vaal University of Technology, 2019-09-19) Mukalay, J. N.; Masu, L. M., Prof.; Rwanga, S., Dr.; Salim, R. W., Prof.
This research investigated the structural bond strength of GFRP rebars in concrete beams under dynamic loading with the aim to characterize the structural bond behaviour and evaluate the limitations of the GFRP rebars under dynamic loading. The dynamic loading in this study was set at 500 repeating cycles to simulate a more realistic dynamic loading scenario such as earthquake since most dynamic loading studies are carried under ten repeating cycles. The experimental work was divided into 2 main tests which were firstly, the tensile tests of the GFRP rebars in order to evaluate the tensile strength of the rebars and characterize their properties. Secondly, the flexural tests of GFRP and steel reinforced concrete beams in order to evaluate the bond strength of GFRP and steel rebars, to characterize the average bond strength of GFRP and steel reinforced concrete beams under dynamic loading and finally to compare the average bond strength of GFRP rebars to Steel rebars in both dynamic and static loadings. The tensile tests were carried out using a Universal Testing Machine (UTM) and the results of the tensile tests of the GFRP rebars showed that the average experimental tensile strength of GFRP rebars was only 56.65% of the nominal tensile strength provided on the supplier data sheet. As for flexural tests, they were carried out through a four-point bending test using a UTM in conjunction with a universal dynamic shaker to create the dynamic loading set up. Steel reinforced concrete beams were used as control beams during the tests and factors such as the tensile strength of the GFRP rebars, the slip of the rebars, the load-deflection relationship and the stress-strain relationship were investigated. The results of the tests showed that the tensile strength of the GFRP rebar is strongly proportional to the maximum beam load bearing capacity and the maximum stresses of GFRP reinforced concrete beams. The results also showed that the average bond strength of GFRP rebars in static loading (8.44 MPa) was only 80% of the average bond strength in dynamic loading (10.95 MPa). Moreover, the experimental work showed that the failure of GFRP reinforced concrete beams depicted large deflections (19 mm) and slips (5 mm to 12.5 mm) when compared to steel reinforced concrete beams (for which the maximum deflection was 9.66 mm at failure and slippage values of 2 mm to 10 mm). Based on that it could be stipulated that the tensile strength of GFRP rebars is one determinant factor to the bond strength behaviour of GFRP rebars in concrete. Hence, the structural bond behaviour of GFRP rebars could be well-defined if more studies were done on the bond behaviour of GFRP rebars in concrete beams under dynamic loading using another type of GFRP rebars that would consist of a relatively high tensile strength as compared to the ones used in this study and different surface texture.

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