Journal of Civil Engineering, JKUAT

Causes of Early Deterioration of Coastal and Marine Structures in Temperate African Countries and Design Approaches to Improve their Service-Lives

V. S. Kamara, X. L. Liu — Mon, 01 Mar 2004 00:00:00 +0000

The introduction of western civilization in most Africa Countries starting from the mid 20th century has brought about the implementation of varieties of foreign design codes of practice in the construction of marine and coastal reinforced concrete structures. Variation in environmental and climatic conditions and lack of routine maintenance and monitoring system has resulted in the premature deterioration and failure of a large percentage of these vital structures. The large sums of money used in repairs, rehabilitation and rebuilding of these structures has not only resulted to low economic growth, but also endangered lives and material wealth. This paper identifies key design parameters, which because of their absence during the design process have contributed to the early failure of concrete structures exposed to aggressive environments especially those in coastal and temperate countries. Based on extensive research on existing marine and coastal concrete structures, recommendation and approaches on how to ensure a more accurate design process of marine and coastal structures so that a prolonged service-life of these structures can be achieved. Guidelines on how this can be possible are presented.

(Journal of Civil Engineering, JKUAT: 2002 8: 1-12)

Rice Husk Ash Cement – An alternative pozzolana cement for Kenyan building Industry

B. Waswa-Sabuni, P. M Syagga, S. O Dulo, G. N Kamau — Mon, 01 Mar 2004 00:00:00 +0000

A survey was carried out to assess the quantities of rice husks at the rice milling plants in the country. Mwea, Ahero, West Kano and Bunyala rice growing areas were visited. Large deposits of husks exist at rice milling plants in these areas with Mwea leading. Samples of rice husks from Mwea Rice Mills were used to confirm the pozzolanic properties of rice husk ash (RHA). Chemical analysis of the ash showed high silica (SiO2) content (more than 50%) which is a requirement for a good pozzolanic material. The engineering properties of the cement resulting from a mixture of OPC plus RHA and lime plus RHA were satisfactory with addition of up to 50% RHA. The RHA improved greatly the compressive strength of lime. The cost of producing RHA was considered in pricing the resulting binder and it showed that the use of RHA to supplement OPC and lime reduced the overall cost of the binder.

(Journal of Civil Engineering, JKUAT: 2002 8: 13-26)

Properties of Periwinkle-Granite Concrete

Bamidele I. O Dahunsi — Mon, 01 Mar 2004 00:00:00 +0000

The suitability of the shells from periwinkle, a small gastropod sea snail (mollusc), for use as partial replacement of granite in concrete was investigated. Physical and mechanical properties of the shells and well-graded granite chippings were determined and compared. Concrete cubes were prepared using 1:0, 1:1, 1:3, 3:1 and 0:1 proportions of periwinkle shells and granite chippings by weight, as coarse aggregate. Compressive strength tests were carried out on the periwinkle-granite concrete cubes. The bulk density of the periwinkle shells was found to be 1353kg/m3 while that for granite was 2644kg/m3. The ten percent fines and aggregate crushing values were 26KN and 64% respectively for periwinkle shells while for granite they were 114KN and 18%. Concrete cubes with periwinkle shells alone as coarse aggregate were lighter and of lower compressive strengths compared to those with other periwinkle:granite proportions. The 28-days density and compressive strength were 1824kg/m3 and 12.12N/mm2 respectively. Density, workability and the compressive strength of periwinkle concrete increased with increasing inclusion of granite chippings. It could be concluded from this study that periwinkle shells could be used as partial replacement for granite in normal construction works especially in places where granite is in short supply and periwinkle shells are readily available.

(Journal of Civil Engineering, JKUAT: 2002 8: 27-36)

Engineering Structures and Environment During this Fast Changing Climatic and Human Thought

V. S. Kamara, X. L. Liu — Mon, 01 Mar 2004 00:00:00 +0000

Advancements in science and technology has resulted in an improved human life style and fashionable engineering structures that have allowed modern engineers to pay less attention to how design codes can be modified in respond to growing changes in climatic conditions. This, together with disproportionate use of building materials and mix ratio in concrete structures, has not only given rise to a dramatic decline in the durability and safety of structures but has caused the use of billions of individual country's currency in repairs, maintenance and rehabilitation especially corrosion related deterioration. This paper throws light on the usefulness of up-to-date design codes, problems facing modern structures and what need to be done to accurately handle this growing phenomena so as to ensure safer structures as the unpredictable changes in climatic condition continues in the 21st century. A mathematical model to calculate the effective diameter of deteriorating beam with delaminated reinforcements and the vulnerability of structural systems are presented and useful recommendations made.

(Journal of Civil Engineering, JKUAT: 2002 8: 37-46)

Interim Project Financing in the Nigerian Construction Industry

N. Aniekwu, W. A. Osedeme — Mon, 01 Mar 2004 00:00:00 +0000

Out of the 47 variables identified through a structured survey, that can adversely affect the construction industry in Nigeria, “the difficulties in securing credit for interim construction finance on reasonable terms”, is ranked as the 6th most important factor, while “client's unwillingness to pay for advance for mobilization and purchase of equipment”, was ranked 13th, resulting in the inability of most local capacities to be utilized in the local construction industry. Given that the growth of any industry in any economy is necessarily related to the local participation in that economy and the ability to integrate the local capacities in the developmental process, this paper looks at the implication of the current policies on lending and mobilization fees and postulates that the payment of mobilization fees and or material advances should be encouraged but with enough safeguards to protect the client.

(Journal of Civil Engineering, JKUAT: 2002 8: 47-60)

Characteristic Strength and Treatability of a Recycled Paper Mill Wastewater in a UASB Reactor

E. Nyangeri Nyanchaga, Mustafa A. Elkanzi

The characteristic strength of wastewater from a recycled paper mill in Nairobi, Kenya and its suitability for treatment in a UASB (upflow anaerobic sludge blanket) reactor at ambient temperature were assessed. TheBOD5/COD relationship showedthat the wastewater is of high strength, biodegradable and has a potential to increase in strength with time. The effluent is acidic and deficient in basic inorganic nutrients such as nitrogen and phosphorus which are required for biological treatment. The effluent has less sulphate and total solids as compared to wastewater from paper mills using virgin wood pulp and is thus suitable for treatment by anaerobic process. In a UASB reactor, about 63 per cent COD removal and total biogas production rate of 0.2 l/g COD were attained at a load of 12 to 15 KgCOD/m3/day. A well-pelletized sludge was formed in the reactor over a period of 4 months.

(Journal of Civil Engineering, JKUAT: 2002 8: 61-78)

Fluoride Contamination in Drinking Water in the Rift Valley, Kenya and Evaluation of the Efficiency of a Locally Manufactured Defluoridation Filter

E. Nyangeri Nyanchaga, Tiffani Bailey — Mon, 01 Mar 2004 00:00:00 +0000

A survey of the amount of Fluoride in ground, potable water in Njoro division, Nakuru district and some parts outside the division was conducted to determine the concentration of Fluoride the residents are consuming through water. This area is situated in the Great Rift Valley of East Africa, which is known to have high levels of the anion in the water due to the volcanic eruptions that occurred thousands of years ago. Water samples were collected from 18 sources and analysis was performed using an ion selective electrode (ISE). Concentration levels ranged from 0.78 mg/L (river water) to 11 mg/L (borehole water). A locally manufactured de-fluoridizer made of charred bone particles was evaluated for its ability to remove F- from water. Generally, more than 99% F- was removed by the de-fluoridizer. Apart from removing the target anion, F-, some metal cations are also removed at various extents, while others are added into the water apparently from the bone char through leaching.

(Journal of Civil Engineering, JKUAT: 2002 8: 79-88)

Modelling of Suspended Sediment Discharge for Masinga Catchment Reservoir in Kenya

W. W. Saenyi, M. C. Chemelil

Masinga reservoir is experiencing high rates of siltation due to accelerated soil erosion in the catchment occasioned by rapid deforestation. There is need, therefore, to devise sediment management strategies both for the reservoir and the catchment to minimize the siltation rate. To give meaningful suggestions on techniques for sediment management, the priority is to model the sedimentation process in the reservoir. Sedimentation models however, require suspended load as the basic input data. For Masinga reservoir, there is no reliable suspended sediment data. Only scanty information on suspended solids is available. Because of this data scarcity, an integrated approach was used to model both the soil erosion from the catchment and the sedimentation process in the reservoir. The Water Erosion Prediction Project (WEPP) model was applied to Masinga catchment to estimate soil loss due to surface runoff. Modelling of the sedimentation process in the reservoir was accomplished by using a semi-two-dimensional model for water and sediment routing, GSTARS 2.1. Through erosion modelling, Sediment-rating curves for both Tana and Thika arms of the reservoir were obtained and used as input into the sedimentation model. The output from the sedimentation model showed preferential siltation in the old river channels, at the two mouths of the reservoir, at the confluence, and near the dam wall. Based on this spatial sediment distribution information, sediment management strategies are proposed. Dredging out fine sediments, construction of sedimentation basins at the two mouths of the reservoir and flushing out sediments through bottom outlet gates are suggested to provide solution to Masinga's myriad siltation problems.

(Journal of Civil Engineering, JKUAT: 2002 8: 89-98)

Through Thickness Ultrasonic Testing and Its Use in Characterising the Mechanical Properties of Various Types of Limestone

Maina Maringa

The stiffness coefficients of different types of limestone were determined using the through thickness ultrasonic test and measurements of size and weight, and the results obtained verified using aluminium specimens of known mechanical properties. The values of density and stiffness coefficients obtained for the various types of limestone were consistent with their different formation processes. The stiffness coefficients for each specimen were different, exhibited directional properties and were significantly lower in one of the three mutually orthogonal directions in which tests were conducted, a clear confirmation of the heterogeneous and layered nature of limestone. Clearly, therefore, while the through thickness ultrasonic test easily yielded through thickness values of stiffness coefficient, complete characterisation of limestone, would require the use of more complex ultrasonic testing equipment and methods.

(Journal of Civil Engineering, JKUAT: 2002 8: 99-110)