Waste Concrete as a Source of Aggregate for New Concrete

Three concrete mixes of widely differing water cement ratios were made using crushed waste concrete as coarse aggregate. The properties investigated include the physical properties of the recycled aggregate, the compressive and flexural strengths of the concrete. These properties were compared with those of similar concrete specimens made with conventional natural aggregate. Also tested was the compressive strength of concrete cubes cut from the waste concrete. Results of the tests suggest that the strength of concrete made from recycled waste concrete aggregate is dependent on the strength of the original concrete from which the recycled aggregate is derived. It is concluded that recycled aggregate can be used to produce quality concrete when the strength of concrete required is not greater than the strength of the original concrete from which the recycled aggregate is derived

The Potentials of Cassava Flour as a Set-Retarding Admixture in Concrete

The potentials of cassava flour as a set-retarding admixture in concrete were investigated. Concrete mix proportion of 1:2:4 by weight of cement, sand and coarse aggregate and, water/cement ratio of 0.46 was made with six different dosage levels of cassava flour as admixture. The properties tested include setting time, workability of the fresh concrete and compressive strength of the hardened concrete. These properties were compared with those of similar concrete mix made without cassava flour admixture. It was observed that cassava flour considerably improved the workability of the fresh concrete and delayed the setting time of cement by up to 6 hours. Results of the tests also show that while cassava flour reduced the early strength of concrete, the long-term strength was improved. Cassava flour dosage level of 3% was also found to be the optimum level of addition of the admixture

ESTIMATING FORMWORK STRIKING TIME FOR CONCRETE MIXES

In this study, we estimated the time for strength development in concrete cured up to 56 days. Water-cement ratios adopted range from 0.44-0.57. Nonlinear regression analysis performed on each experimental data set produced Strength-Age (S-A) curves from which Duration-Strength (D-S) models were deduced to estimate approximate time in hours for a particular strength development. A quick reference table for soffit formwork striking time and removal of props was produced. The time to attain the characteristic strengths for C20, C25, C30 and, C35 concrete were 247.04 hours (10.3 days), 285.57 hours (11.90 days), 484.54 hours (20.20 days), 481.58 hours (20.10 days) and, 267.72 hours (11.16 days), 338.74 hours (14.11 days), 560.67 hours (23.36 days), 482.49 hours (20.10 days) for medium and high slump range respectively. Faster construction scheduling operations can be achieved by using lower water-cement ratios and higher grades of concrete.   http://dx.doi.org/10.4314/njt.v35i1.

COMPARATIVE ANALYSIS OF MECHANICAL AND MANUAL MODES OF TRAFFIC SURVEY FOR TRAFFIC LOAD DETERMINATION

Traffic survey was carried out to obtain data that are necessary for traffic study and evaluation. One of the most important characteristics of a traffic stream is its volume which can be defined as the number of vehicles passing through a section of a road per unit time.  The road project which is approximately 75 km in length consists of a number of traversed roads, but the traffic study is focused only on the 6 major intersections. The surveys of traffic were conducted using volume count from 7am to 7pm each day because working at night is very unsafe in this area, by using an automatic traffic recorder (Trax 1 Plus) and road tube installation for collecting accurate data with manual counting for comparison. This study aims to analyze the current road traffic data collection methods - comparing both mechanical and manual mode of Traffic Survey simulation - in terms of capabilities and limitations on Nigeria roads using Ogoja (Mbok) Junction and Mfum road in Cross River State as a case study. The tendency of the mechanical counting machine to withstand nonstop24hrs-continuous counting was noted during the exercise compared to manual counting, since security at night cannot be predicted on manual.  The design equivalent standard axle load (ESAL) generated from the result shows that Ikom-Cameroon Junction has the highest value with a difference of (0.999x10^6 ) between the mechanical and manual, this value shows  a downward effect using manual data for the pavement structural thickness evaluation, this can further degenerate to the structural failure at the earlier stage, tensional fatigue, cracks etc. However, traffic study for the period 2015 to 2035 was considered in the analysis, the equivalent standard axle load (ESAL) generated along the section of the corridor and the pavement thickness shows that automatic counter machine is more accurate than the manual. Nonetheless the mechanical counter is more advantageous compared to the manual counter to this reasons the mechanical counter should therefore be employed during the raw data traffic survey. Manual on the other hand less useful for traffic survey in predicting the feature traffic analysis. http://dx.doi.org/10.4314/njt.v35i2.

Effects of Flexural Rigidity of Reinforcement Bars on the Fundamental Natural Frequency of Reinforced Concrete Slabs

An understanding of the orthotropic plates' behavior in their dynamic regime is essential because the loading can cause severe damage in the plates, such as: - cracking, loss of aesthetic, fear to the occupants, etc. To this end, a new set of stress - strain relations for. Orthotropic plates were derived. The principle of force of inertia was introduced, yielding the corresponding dynamic governing equation of orthotropic plate. The solution of the equation was obtained by numerical method, and the results show that the flexural rigidity of the bars has significant effect on the fundamental natural frequency of heavily reinforced concrete sections

Modeling the Effect of Contact and Seepage Forces at Equilibrium on the Failure of Water Borehole

There have been records of failures and quicksand conditions in boreholes in recent times impeding the performance and operation of boreholes which may have resulted from various factors ranging from construction problems, drilling inaccuracies, fitting and installation problems, some chemical effects within the aquifer medium etc, but it has been ignored that a factor of great benefit to the operation of water boreholes; seepage force could get to a considerable which becomes unsafe for the well operation thereby causing dislodgement of sand particles and sandstones resulting boiling. This research work has investigated the contribution of contact force and seepage force to the failure of boreholes. This necessitated the use of combined finite-discrete element method to generate model expressions from contact and seepage forces considered to be the major forces contributing to the flow of fluid through soil mass and boiling or quicksand effect results when seepage force becomes more in effect under critical hydraulic gradient and / or critical hydraulic head. A mathematical/laboratory model was used and an expression for calculating the critical hydraulic head causing critical seepage deduced as = and the equilibrium model has deduced an expression for the safe hydraulic head during well pumping as =. These have been verified using a laboratory investigation; borehole prototype well failure test. It has been established that there is strong agreement between model result and the laboratory study result from the correlation analysis conducted which has shown correlations of 1.00975 and 0.989879999701 for the critical state condition and equilibrium state condition respectively. For purposes of future calculations, borehole performance monitoring and designs, the standard critical hydraulic head of the system from Table 3 and Fig.7 is 2.92E-8 which has the strongest agreement with 2.59E-8 of the laboratory study with a deviation of 3.3E-9. The deduced models can be used to design and monitor the performance of boreholes. For safe pumping and corresponding yield in the bore hole system, inter-granular force between granular particles should equal the seepage force and this is achieved by ensuring that the deduced model expression is used to determine the safe hydraulic head. Finally, irrespective of the fact that an increase in hydraulic head increases discharge, the system should be operated at a head safe for the performance of the well and as long as the model hydraulic head expression deduced is used under the above conditions, safe pumping can be achieved at any voltage between 150volts and 240volts.http://dx.doi.org/10.4314/njt.v34i3.3

Potentials of Cement Kiln Dust in Sub-Grade Improvement

The ever increasing cost of construction materials in Nigeria and other developing countries has created the need for research into locally and readily available materials and also on how to convert materials considered to be waste by-product such as cement kiln dust (CKD) for use in construction and soil improvement. To achieve this, soil samples collected from Sankwalla - Busiri road, Obanliku, Cross River State classi ed as an A-2-7 soil on AASHTO classi cation were stabilized with 2-24% cement kiln dust (CKD) by weight of the dry soil. The investigation includes evaluation of properties such as compaction, consistency limits and strength of the soil. The results obtained show that the increase in CKD content increases the Optimum moisture content (OMC) with a reduction in plasticity. There was also improvement in the California Bearing Ratio (CBR) and Uncon ned Compressive strength (UCS) with increase in the CKD content. A predictive model was developed and found to reasonably predict the relationship between properties of soil and the proportion of CKD used. The coecients of correlation were high showing a strong relationship between the measured and predicted values. The study concluded that CKD can be used to improve the properties of soil for construction purposes and 24% CKD content was observed to yield maximum improvement for CBR and UCS.Keywords: cement kiln dust (CKD), compaction, consistency, California bearing ratio, uncon ned compressive strength, subgrad

Gender Accessibility and Equality in Education: The Implication to Manpower Development in Nigeria

There seem to be a global progress made regarding equity between men and women in the field of education. In spite of this, the educational gap between both sexes has not been bridged in Nigeria. Even with the universal declaration of Human Rights in 1948, article 26 for instance, estimates reveal that more than half a billion adult women aged 15 and above were illiterate in 1990, which is 63 percent of all illiterates in the world. It is in recognition of this that the UNICEF strongly raised the issue of removing constraints and disparities that will place the girl child education at a disadvantaged position. This paper appraises the gender differences in education accessibility and equality of Nigerians. It equally assessed some of the constraints to gender equality in education and concludes that gender imbalance in education accessibility and equality if not addressed will have an adverse effect to manpower development in Nigeria

Models for Prediction of Structural Properties of Palmnut Fibre-Reinforced Cement Mortar Composites

An analytical study was carried out to investigate the structural properties of palmnut fibre reinforced cement-based composites. Explicit expressions were derived for the flexural, compressive and elongation behavior of composites using a two-phase constitutive model and verified using results obtained from literature. The predicated and measured values were found to agree favourably. Both the predicted and measured composite specimens showed increasing flexural strength up to the optimum fibre volume fraction while the compressive strength decreases with increase in fibre volume fraction. The correlation coefficients were high showing the effectiveness of the two-phase constitutive models in the analysis and design of palmnut fibre-reinforced cement composites

A New Approach to Concrete Mix Design Using Computer Techniques

Concrete is an essential part of most civil engineering works. Mix design of concrete is usually specified in terms of prescription or performance. The purpose of this work is to develop a model that is capable of reproducing any expected concrete strength within a specified range of cement content. In addition such a model can be used to generate data on mix proportions and their corresponding compressive strength, thereby furnishing useful information for general purpose, safe-ready-to-use mix design. Such data were generated and checked against values obtainable from standard mix design practice and found to agree very well within the limits of experimental error. A test of the statistical significance of the developed model using F-statistic shows that the regression as a whole is highly significant. The work culminated in the development of a concrete mix design chart which presents mix proportions for various grades of concrete ranging from compressive strength values of 10N/mm2 to 50N/mm2. This chart is expected to be of immense help to site supervisors involved in concrete production since the use of the chart as a guide to batching the ingredients of concrete, will eliminate the need for tedious mix design procedures and at the same time ensure that correct quantities of the required materials are used for concrete production