Contributions to the Physio-Chemical Characterization of Mezam Sand
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Sand is an inert construction material which is as important as the other constituents that make up mortar and concrete. Since this material is found in natural form around Mezam, it demands an urgent study, so as to rule it out in the recent structural failures observed in the locality.
With the present crises, we are witnessing another disturbing phenomenon, that of the use of sand from a source that was earlier claimed to be unfit for construction.
A good number of samples were collected at Mbatu, Chomba, Dreamland rock quarry, Mezam and even Menchum rivers. The physical analysis was mostly carried out at GTHS Bamenda laboratory and NPUI laboratory meanwhile the chemical analysis was conducted at LABOGIENIE Yaounde and CATUC chemical Lab in Baham.
In the physical analysis of the samples, it was very imperative that a group of helpers be sorted for efficiency and efficacy, not leaving out timeframe. Level 200 students, about 20, were used and also evaluated, so that care is taken to give us the desired results.
After all the analysis, the various samples were classified so that users can choose their desired types for their various works. For one physical analysis, 16 samples where analyzed before concluded on the property of that particular sample. As for the chemical analysis, four samples where used to draw the conclusion on one sand type.
One thing we discovered is the scarcity in the chemical analysis and even the laboratories, which explains why one test could cost up to 50 000 FRS and this let to delays and plenty of setbacks to the progress of the research.
With the rapid growth in infrastructure of the country, the construction industry is booming and thus the demand for building materials has increased manifolds. The demand for high rise buildings in Mezam is beginning to see the light of day, of course, due to space constraints, rapid urbanization and growth in population.
This has led to increase in demand for better performing materials like high performance/strength concrete and its composites.
The performance of structural concrete is dependent on its strength and durability which in turn is dependent on the characteristics of the mortar, aggregate and mortar-aggregate bond.
For same quality of mortar mix, the type, texture and mineralogy of aggregate affects the various parameters of concrete in its hardened and fresh state. The effect of aggregate type is more prominent in high strength concrete due to limitation on water/cement ratio.
Different properties of aggregate such as its size, shape, texture, petrography, mineralogy etc, have an effect on the properties and behavior of the Interfacial transition zone. It should be noted that the interfacial transition zone is the region of the cement paste around the aggregate particles which is perturbed by the presence of the aggregate.
A lot of studies have been done on the bond strength due to the shape and surface texture of the aggregate however the type of aggregate also attributes to the bond that aggregate makes with mortar. The mineral constituents of the aggregate can lead to chemical reaction between cement and aggregate thereby strengthening or weakening the bond.
The primary cause of micro cracks development is the difference in modulus of elasticity of the aggregate and cement mix. The differential shrinkage in the two regions, because of difference in modulus of elasticity, is a big reason behind low tensile strength of concrete.
Hence the quality plays an important role in the tensile strength of concrete specifically for high strength concrete. The compressive strength of concrete is primarily controlled by the quality of mortar and the bond properties of aggregate.
However, the influence of aggregate type is relevant in high strength concrete as the quality of mortar improves in them. Apart from the properties discussed above, modulus of elasticity of concrete is also a matter of concern from the design and strength perspective.
The use of high strength concrete helps in reducing the dead load of the structure due to use of thinner sections to carry load so therefore the requirement of higher modulus of elasticity has increased. The modulus of elasticity of concrete is directly related to the type of aggregate.
Thus, the type and mineralogy of aggregate affects various properties of concrete and hence it should not be treated as an inert material. A careful petrographic study of the aggregate should be conducted before its use in high performance concrete. We will be focusing our study on Mezam division, the regional headquarter of the North west region of Cameroon.
Cement in Cameroon is tested and certified before it reaches the consumers. Steel is supposedly tested too before distributing to consumers in Cameroon. Gravel in Mezam is also supplied through standard certified sources but sand is not tested or having any norm as of now.
We do admit that studies have been conducted on it but the significance is so small and the study for the production of high quality concrete for mega projects like dams, stadiums and high-rise buildings and even bridges is not available. Findings have proven that only 5% of structures in Mezam have had sand tested before use and the rest 95% is left to faith.
Sand is one of the constituents of concrete or mortars whose roles are;
- to sub-divide the paste of binding materials into thin films and allow it to adhere and spread,
- fill up the gap between the building blocks and spreads the binding material,
- adds to the density of the mortar,
- prevents the shrinkage of the cementing material,
- allows carbon dioxide from the atmosphere to reach some depth and thereby improve setting power,
- the cost of cementing material per unit volume is reduced as this low cost material increase the volume of the material.
- Silica of sand contributes to formation of silicates resulting into the hardened mass.
The most common material that constitutes the sand is the silicon dioxide. The size of a sands particle normally ranges from 0.0625mm to 5mm and if the size of the particle exceeds this range, it is called gravel. If it is smaller than 0.0625mm, then it is generally called silt.
A study on the quality of sand in a mix will lead to an increase in the quality of mortar or concrete, densify the mix thereby increasing the compressive strength of the concrete, reduces shrinkage and improves the durability of the structure to the desired time frame.
Though most of the sand is generally made of silica (silicon dioxide), not all of it is composed in the exact some way.
This is why the careful study of sand is very important as it will expose the actual characteristics of the material and consequently minimize building failure. With a study on the main sand sources in Mezam, the 1.8million tons that is approximately use in the division yearly will result in safer and doubtless structures.
Sand is available in three forms in Mezam Division;
– River sand, obtained principally from river Mezam, Mbengwi, Wum, and Babanki, where sand is collected from river beds and banks.
– Pit sand available in Mbatou, where the sand is excavated and washed
– Quarry sand obtainable from Edge quarry, dreamland and Kendely rock quarry, here, it is the residues from crushed gravel which passes through 5mm sieves.
In a standard concrete mix, we have four constituents; cement, sand, gravel and water and also reinforcement for R.C. All constituents have been very well studied and standards arrived at except for sand whereas sand plays a very important role in a mix design especially for concrete used in high rise buildings.
Secondly, we have structures with early degradation, cracks on floors and walls, dampness and collapse in extreme cases such as was the case with a GF+1 storey building in Ntahsen Nkwen, a GF+3 storey building in Bambili and others. Sand could be one of the causes of these failures.
Thirdly, Engineers in the country have been given the task to help derive a building code for Cameroon and studying the sand from Mezam is certainly one of the requirements.
Finally, there is a cacophony with regards to the quality of sand in Mezam as was observed during a site visit to the quarries, some miners claimed that only sand from Mezam river was good for quality building works and justified it to the fact that all major building projects in the division have been suspended due to the blockage of the road for three years now.
But if we sample building across the Division especially Bamenda town, we see a geometric rise in building works.
How do you check scientifically the quality of sand used for construction works?
Does the sand in Mezam meet these standards?
How should the sand be tested in order to avoid engineering problems such as those aforementioned?
The variables in our work are: the sand equivalent, the percentage of impurity, the particle size distribution, specific gravity, the sand pH, the carbon content and the sulfate content.
- GENERAL OBJECTIVE
The general objective of the study is to value the physico-chemical characteristics of sand from Mezam sources.
- SPECIFIC OBJECTIVES
- Do a physical characterization of each sand sample
- Do a chemical characterization of each sample
- Present the properties of each sample visa vice standard references.