African Journals Online
Journal of Civil Engineering, JKUAT

Abstracts of papers in the current issue: JCE-JKUAT 
VOLUME 7, MARCH 2002

Engineering properties of common subgrade soils below pavement structures in Kenya

Sixtus K. Mwea ¹⁾ and Francis J. Gichaga ²⁾

1) Senior Lecturer, Department of Civil Engineering, University of Nairobi, KENYA

2) Professor and former Vice Chancellor of the University of Nairobi, and current Chairman, Kenya National Council of Science and Technology, KENYA

Abstract

This paper reports findings of laboratory testing of common sub-grade soils in pavement structures in Kenya. The materials were collected from different parts of the country. The results are intended to form a database for use by practicing engineers and researchers in the field of pavement engineering. The investigated materials include the expansive black soils, silty clayey soils, sandy loamy clayey soils and lateritic gravels. In addition the properties of lime improved gravels are reported. For the fine-grained soils the plasticity index was found to be linearly proportional to the liquid limit. In all the investigated soils the optimum moisture content was found to be inversely proportional to the maximum dry density. The increase in the strength of lime improved materials was found to increase with lime content at a diminishing effect.

Investigation of causes of failures of flexible pavements: a case study of Nairobi -Thika highway

S.M. Mulei1), J.K.Z. Mwatelah2), E. Asano3)

1) Lecturer, Department of Civil Engineering, Jomo Kenyatta University of Agriculture and Technology, KENYA

2) Senior Lecturer, Department of Civil Engineering, Jomo Kenyatta University of Agriculture and Technology, KENYA

3) Associate Professor, Setsunan University, JAPAN

Abstract

Failures of flexible pavements (bituminous roads) have been prevalent in many developing countries, a trend causing concern to both the road users and the roads authorities. In this regard, it was found necessary that an investigation be initiated to determine the possible causes of such failures, and a case study was carried out on Nairobi-Thika Highway in Kenya. The investigations were conducted in several categories to determine the pavement characteristics such as structural strength by Benkelman Beam Deflection Test (BBDT), skid resistance by British Pendulum Tester (BPT). Traffic loading by Axle load measurements, Traffic volumes by traffic counting and ageing characteristics of the type of the bitumen used by cutting cores and extracting the bitumen for the standard tests, such as penetration, ductility, bitumen content, air voids, softening point and CBR using the Light Drop Weight Tester (LDWT). The visual inspection of the pavement showed that due to the hardening of the bitumen and overloading, cracks and potholes were very common for the whole stretch of the road. Axle load data revealed that, there has been a tendency to exceed the maximum allowed axle load limits, especially until 19^th august, 1999, after that the enforcement of axle load limits was tightened. This fact together with the revelation that the road is a very busy one as depicted in the traffic counts, could be one of the major causes of the road's fast deterioration.

Burnt clay waste as a pozzolanic material in Kenya

Laban U. Shihembetsa1) and Benedette Waswa-Sabuni2)

1) Director, Housing and Building Research Institute, University of Nairobi, KENYA

2) Chief Technologist, Housing and Building Research Institute, University of Nairobi, KENYA

Abstract

Building materials account for about 60 percent of the total construction cost of a house. Cement is one major element of the building materials that account for 20-35 percent of the materials cost and is the most important element since it binds the building together. In Kenya, there are two binders commonly used, i.e., Portland Cements (PC) and Lime. The Portland cements, which include Ordinary Portland Cement (OPC) and Portland Pozzolana Cement (PPC) are the most widely used cements because of their fast curing properties. The introduction of PPC has not reduced the cost of cement in the country and the use of alternative cements, which are cheaper specifically for masonry works, should be encouraged. This paper presents findings of on-going research work since 1998 on alternative cement blended with burnt clay waste pozzolana, which is a by-product from burnt clay products. The research findings show that burnt clay waste contains pozzolanic properties for production of alternative pozzolana cement. It is therefore, recommended that small scale production enterprises be set up in areas that produce burnt clay products in order to process the pozzolana from the wastes to produce alternative pozzolanic cement, hence reduce the cost of cement in construction.

What controls the failure process of irregularly-shaped reinforced concrete columns

Paul Nibasumba¹⁾ and Xila Liu²⁾

1) Tsinghua University, Beijing, 100084, PEOPLES REPUBLIC OF CHINA

2) Professor, Tsinghua University, Beijing, 100084, PEOPLES REPUBLIC OF CHINA

Abstract

This paper presents the results of an experimental study of six irregularly-shaped reinforced concrete columns. The column specimens were subjected to a cyclic loading varying in time and to a constant concentrically applied axial load. Steel reinforcement and concrete strains together with maximum lateral deflection were recorded as the lateral load was varying during the experimental test. Envelopes of hysteretic load-deflection curves are plotted. Through load-deflection curves, the failure process of the tested columns is described. The experimental results demonstrate that the concrete column's failure is a process and not a fixed point. The failure process starts with the cracking of the tensile concrete at the critical cross-section. It is found that the maximum load point is the peak of the failure process while the maximum bending moment occurs later. The first point represents the stability failure, while the second corresponds to the material failure of the columns. The test results show that the columns' failure is caused by instability rather than the loss of strength.

The effects of resin content variation on the physical and mechanical properties of coffee husks/tannin particleboards

W.O. Ogola¹⁾, E.T.N. Bisanda²⁾, and J.V. Tesha³⁾

1) Department of Industrial and Energy Engineering, Egerton University, P.O. Box 536, Njoro, KENYA, E-mail: [email protected] 

2) Department of Engineering and Technology, Faculty of Science, University of Namibia, Private Bag 13301,Windhoek, NAMIBIA, E-mail: [email protected]

3) Department of Mechanical Engineering, University of Dar es Salaam, P.O. Box 35131, Dar es Salaam, TANZANIA, E.mail: j_tesha@hotmail .com   

Abstract

Particleboard industries have been heavily relying on woods' existence and the synthetic resins such as urea formaldehyde (UF), phenol formaldehyde (PF) and melamine for their survival and existence. While in use, these synthetic resins emit formaldehyde, which is harmful to human health. In addition, their resources have been depleted making them scarce and expensive. Research developments have revealed that it is possible to produce particleboards using natural resins such as cashew nut shell liquid (CNSL), hydrolyzed tannin etc as the binders. In this research, two particleboards of different densities were made from coffee husks as the reinforcement and varied resin content of hydrolyzed tannin from 4-16% of the dry weight of the particles. Results indicated that both mechanical and physical properties were improved as the resin content was increased. This was found to be in agreement with what other researchers have done.

Application of high strength plate bolts in friction grip joints

Antony Monda¹⁾

1) Jomo Kenyatta University of Agriculture and Technology, Nairobi, KENYA

Abstract

High Tension Bolts (HTB) are known to exert a significant influence on the strength characteristics of connections and have a significant influence on the ductility and behaviour of the joint. Normally HTB failure occurs in the shape resultant high stress concentration neck and thread areas resulting in relatively low ductility characteristics. Creep and relaxation occur after HTB tightening causing shaft tension loss and further stress redistribution in the connected components. Past research has shown that waisting the HTB shaft diameter reduces stress concentrations, shaft tension loss and increases ductility. With the further modification of making the HTB head plate shape counter sunk, a plate HTB with an aesthetically pleasing flat surface less susceptible to rain corrosion results. In this research, tensile, relaxation and friction grip joint slip experiments were done on waisted shank, counter sunk plate head HTB to ascertain the ductility improvement, the resulting decrease in shaft tension loss and its magnitude, as well as their applicability in friction grip steel connections. Apart from significant shaft tension loss reduction, no detrimental effects are induced in the slip coefficient results when these HTBs are applied in friction grip joints. Within these experimental parameters, the closest to ideal HTB shape is proposed.

Computer simulation of orthokinetic flocculation in a filterbed

P.M.A. Odira¹⁾

1) Civil Engineering Department, University of Nairobi, KENYA

Abstract

The rational for application of direct filtration in water treatment with omission of the conventional coagulation processes has been a subject of discussion since the inception of direct filters. Among the questions asked is whether the filterbed facilitates sufficient flocculation of the raw water necessary for adequate water treatment. This paper studies, through a computer simulation process, the orthokinetic flocculation that is likely to occur in a filterbed. The results of the study clearly indicate that mathematical modelling based upon well-established theoretical interpretations and experimental data, predicts that under typical filter conditions, orthokinetic flocculation of particles in the filterbed is significant. This result should form a firm basis for design and promotion of direct filtration, which would save costs in drinking water treatment.

Flow-through hydraulic flocculator

Wangai J. Ndirangu¹⁾, Tuitoek Daniel²⁾, Menzwa David ³⁾, Klaveren Paul Van⁴⁾

1) Batiment-IPS Consultants, P.O. Box 127, Uhuru Gardens, Nairobi – 00517, KENYA

2) Egerton University, Department of Water & Environmental Engineering, P.O. Box 536, Njoro

3) Moi University, Department of Chemical & Processing Engineering, P.O. Box 3900, Eldoret

4) BKH Consulting Engineers, Poortweg 10, P.O. Box 5094, 2600GB Delft, NETHERLANDS

Abstract

Slow mixing is a basic and important process in physico-chemical water treatment plants, for induction of tapered orthokinetic flocculation in the formation of flocs that would be suitable for sedimentation. Hydraulic mixing gives certain advantages in terms of maintenance and energy saving, a fact that would make them preferable in many instances in water and wastewater treatment plants particularly in the developing countries. However field experiences with hydraulic flocculators have been far from satisfactory. Where an increase in the sizes of the flocs has been expected, floc break up has been observed instead. This study therefore was used to document and confirm the problems associated with hydraulic flocculators as a starting point in addressing these shortcomings. A 17.2-m³/day pilot plant with velocity gradient induced by round-the-end baffle mixing was used to investigate flow through a hydraulically mixed flocculator. Sodium chloride tracer was introduced instantaneously at the inlet of flocculator and the slug of the tracer detected on-line using a conductivity meter. Visual monitoring of tracer dye was used to complement and corroborate the tracer salt measurements. The results obtained showed that hydraulic mixing achieves reasonable dissipation. However the flow regime was not stable and resulted in the formation of dead zones in the centre and corners of the flocculator, short-circuiting and excessively high velocities at the 180-degree bend that disintegrated the flocs formed.

The impact of the 1997/98 El-Nino rains on the water quality of Lake Naivasha, Kenya

K. S. Makhanu ⁽¹⁾, E. C. Mwachiro ⁽²⁾, C. K. Kamau ⁽³⁾, and A. Gachanja ⁽⁴⁾

(1) Senior Lecturer, Department of Civil Engineering, JKUAT

(2) Senior Lecturer, Department of Zoology, JKUAT

(3) Senior Research Officer, Division of Research, Production and Extension, JKUAT

(4) Senior Lecturer, Department of Chemistry, JKUAT

Jomo Kenyatta University of Agriculture and Technology, P.O Box 62000, Nairobi, KENYA

Abstract

Lake Naivasha and its environs is host to a fast expanding flower and horticultural industry of great economic value to Kenya. These activities however pose significant environmental impact on the lake ecosystem due to the nature of chemicals used in the production and processing of such products. The fact that Lake Naivasha is a Ramsar site of immense ecological and bio- diversity values to the entire world community makes continuous monitoring of the Lake's environmental quality a necessary exercise. In conjunction with the Lake Naivasha Riparian Association (LNRA), researchers from the Jomo Kenyatta University of Agriculture and Technology carried out an intensive study of the Lake water quality between June to September 1998. This time frame has major significance as the Lake level had risen substantially from the recent El- Nino rains. The lake level at the turn of the 20^th Century had in fact been restored. We discuss the variation of the Lake water quality through an environmental quality index (EQI) from published data over the years before the El- Nino rains and immediately after the El- Nino rains. From the two sets of data, the effect of the El- Nino rains on the EQI is clearly evident as the general long term general variation of the Lake's EQI. Through our study we have isolated pertinent physico-chemical parameters which can easily be incorporated in a simple water quality-monitoring model for long-term evaluation of the environmental status for the entire Lake ecosystem. With such tools in place, the current status of the entire Lake ecosystem can be known within a time frame as short as one week.

Prediction of parametric numbers in filterbed flocculation

P.M.A. Odira¹⁾

1) Civil Engineering Department, University of Nairobi, KENYA

Abstract

This paper reviews the various geometric and hydrodynamic representations of flow in granular beds and proposes a model for prediction of the parameters that are pertinent in flocculation process in a filter bed – the velocity gradient G, residence time tr and the product Gtr. The proposed model is applied to direct filtration data and compared to actual measurements taken from the filter beds. The results indicate that values of the flocculation parametric numbers obtainable in the filter beds are quite similar to those used in conventional flocculation practice. This finding clearly discounts the commonly held view that the setbacks experienced in the use of direct filters (e.g. poor effluent quality, turbidity breakthrough, etc) are due to insufficient flocculation in the filter bed. Such setbacks are probably due to the limited pore volume in the filter bed that would necessitate the settlement of flocculated water to reduce the sediment load applied to the filter.

After disaster: the role of surveying in the assessment of building structural integrity

Galcano C. Mulaku¹⁾ and Peter C. Wakoli²⁾

1) Senior Lecturer, Department of Surveying, University of Nairobi, KENYA

2) Lecturer, Department of Surveying, University of Nairobi, KENYA

P.O. Box 30197, Nairobi, KENYA

Abstract

Disasters, whether natural (such as earthquakes, typhoons, etc) or man-made (such as war bombardment, terrorist bomb attacks, etc) always leave building infrastructure in their wake destroyed or destabilized to a certain degree. The cost of subsequent recovery efforts can be minimized by rehabilitating as much as possible what is destabilized rather than rebuilding afresh, provided that the destabilized buildings still conform to the structural specifications in force. Surveying has an important role to play in the geometrical evaluation of such buildings before they are either condemned to demolition or recommended for rehabilitation. This paper describes the role that surveying played in evaluating Cooperative House, one of the taller buildings in Nairobi, Kenya, for rehabilitation following severe damage to it by a terrorist bomb blast at the neighbouring US embassy in 1998.