African
Journals Online
Journal of Civil Engineering, JKUAT
Volume 8, March 2003
ABSTRACTS
Causes of Early Deterioration of Coastal and Marine Structures in
Temperate African Countries and Design Approaches to Improve their
Service-Lives
V. S. Kamara1 and X. L. Liu1
1Department
of Structural Engineering, School of Civil Engineering, Tsinghua University,
Beijing, 100084, China (P.R)
Abstract
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.
Rice Husk Ash Cement – An alternative
pozzolana cement for Kenyan building
Industry
B. Waswa-Sabuni1, P.M Syagga2,
S.O Dulo3, G.N Kamau4
1Housing and Building Research Institute (HABRI),
University of Nairobi
2Department of Land Development, University of
Nairobi
3Department of Civil Engineering, University of
Nairobi
4Department of Chemistry, University of Nairobi
Abstract
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.
Properties of Periwinkle-Granite Concrete
Bamidele I. O Dahunsi 1
1Department
of Civil Engineering, University of Ibadan, Nigeria.
Abstract
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.
Engineering Structures and Environment
During this Fast Changing Climatic and Human Thought
V. S. Kamara1 and X. L. Liu1
1 Department of Structural
Engineering, School of Civil Engineering, Tsinghua University, Beijing, 100084,
China
Abstract
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.
Interim Project Financing in
the Nigerian Construction Industry
N.
Aniekwu1and W. A. Osedeme2
1Member, Nigerian Institute of Construction
Management (MNIConst.M)
2Member, Nigerian
Institution of Civil Engineers (MNICE) Civil
Engineering Department, University of Benin, Benin City, Nigeria
Abstract
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.
Characteristic
Strength and Treatability
of a Recycled Paper Mill Wastewater in a UASB Reactor
E. Nyangeri Nyanchaga1 and Mustafa
A. Elkanzi2
1 Senior Lecturer, Department
of Civil Engineering, University of Nairobi, P.O Box 30197, Nairobi, Kenya
2 M.Sc. Researcher, Department
of Civil Engineering, University of Nairobi, P.O Box 30197, Nairobi, Kenya
Abstract
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.
Fluoride Contamination in Drinking Water in
the Rift Valley, Kenya and Evaluation of the Efficiency of a Locally
Manufactured Defluoridation Filter
W. J. Mavura1 and Tiffani
Bailey2
1Egerton University, P.O. Box 536,
Njoro, Kenya
2Hampton University, Hampton
Virginia,VA 23668, USA
Abstract
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.
Modelling of Suspended Sediment Discharge
for Masinga Catchment Reservoir in Kenya
W.W. Saenyi1 and M.C. Chemelil2
1Department
of Water and Environmental Eng., Egerton University, P.O. Box 536 Njoro, Kenya
Department of
Agricultural Engineering, Egerton University, P.O. Box 536 Njoro, Kenya
Abstract
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.
Through Thickness Ultrasonic Testing and Its Use in Characterising the
Mechanical Properties of Various Types of Limestone
Maina Maringa1
1Lecturer, Department of Mechanical
Engineering, Jomo Kenyatta University of Agriculture and Technology, P. O. Box
62000, Nairobi, KENYA, EAST AFRICA
Abstract
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.
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