Browsing by Author "Atiemo, Eugene"

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    Evaluation of clay pozzolanas as partial replacement of cement for shelter construction
    (1998-02-14) Atiemo, Eugene
    The issue of housing in Ghana has become a national problem due to overpopulation and high cost of building materials, especially cement. Whereas the materials for the production of cement are imported, there exist alternative and durable local materials for the production of both ordinary and composite or blended cement. Pozzolana cement is one of such blended cements. The study focused on the evaluation of pozzolanic properties of clay samples from four (4) deposits at Asokwa (near Obuasi), Nkonsia (7km from Wenchi), Mankesim and Hwereso (25km from Kumasi) for the production of pozzolana cement in Ghana. The clays were calcined at 600°C - 1000°C, milled and passed through 75μm standard sieves. The burnt clays were then used to replace 20% - 40% of cement and moulded into mortar cubes. Also, pozzolana lime mortars at three different mix ratios were moulded. On calcination, Asokwa and Mankesim clays became highly pozzolanic at 800°C, Hwereso and Nkonsia clays were at 900°C and 600°C respectively. The 28-day compressive strength at 20-40% replacement of cement by mass showed that Nkonsiaa clay pozzolanas can replace cement up to 40%, Asokwa and Mankesim clays up to 30% and Hwereso at 25%. 1:2:6 lime pozzolana sand mortar cubes gave appreciable 28-day dry compressive strength. The water absorption of the pozzolana cement was not different from the ordinary cement but they set faster than ordinary portland cement. All the clays were highly siliceous, containing more than 60% silica. Minerologically, all the clay samples are kaolinite with some amount of quartz. Of the four clays, Mankesim and Asokwa pozzolana cement products were mildly affected by sulphate attack whilst Nkonsia and Hwereso products were seriously damaged, showing the least resistance. Their compressive strengths were greatly reduced after one year in sulphate solutions. It is shown that using 25% of the total cement used in Ghana from pozzolana cement would save the country at least $6.7m (about 15.1 billion cedis) in foreign exchange per annum, generate employment for the youth and provide revenue to both the central government and local authorities. The pozzolana cement from Asokwa, Mankesim and Nkonsia clays can be used for general construction, including concrete works, up to 30% replacement of cement and up to 40% replacement for masonry works and production of sandcrete blocks. For Hwereso clay pozzolana cement, it can only be used for masonry works and sandcrete blocks with up to 25% replacement of cement.
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    Studies on the Effect of Selected Local Admixtures on Essential Properties of Cement for Housing Construction
    (2012-06-15) Atiemo, Eugene
    Current trend in cement production is to introduce inorganic admixtures to improve the technical properties such as workability and reduced cracks in concrete. In addition, replacement of clinker or cement greatly reduces environmental pollution due to release of greenhouse gas emissions such as carbon dioxide, carbon monoxide, Nitrogen oxides (Nox) and Sulphur dioxide (SO2)during cement production. Cement replacement also reduces the high energy cost associated with clinker production and this leads to reduced price of cement. The objective of this study was to determine the effect and suitability of four local inorganic materials; namely, clay, limestone, clam shells and steel slag (all obtained in Ghana) as mineral admixtures in cement for construction purposes. Blended cements, ranging from binary to quinternary mixes, were produced. The soundness of the blended cement samples were less than 2.0mm. Water permeability tests showed clearly that addition of the admixtures, except slag, reduced the porosity of the cement by at least 4% and as much as 20%. The water demand of the blended cements ranged from 24.5% to 34.5% and that it increased as the percentage replacements of cement were increased. The water demand of the blended cements ranged from 24.5% to 34.5% and that it increased as the percentage replacements of cement are increased. The setting times of all the blended cements were within the standard limits. iv The infrared spectrometry, X-ray Diffraction(XRD), Scanning Electron Microscopy/Energy Dispersive X-ray (SEM/EDX) and Thermogravimetric (DTA/TG) analysis of the study clearly showed that the presence of the four admixtures reduced Ca(OH)2 content considerably and improved impermeability of concrete. The Infrared analysis indicated that when the admixture content was increased from binary to ternarythe accelerating effect of admixtures on hydration was enhanced. This effect manifested in high early strength of the blended cement, especially the CaCO3-based blended cement samples. The ettringite and monosulphonate of CaCO3-based admixtures (that is, limestone and shell cement) bands were almost flat or disappeared compared to others, indicating increased reactivity between CO32- and SiO44- ions. Significantly, the study showed that a combination of three admixtures (5% each) or all four (2.5% each) in the cement almost eliminated portlandite content as compared to 36.9% in the reference cement as provided from the X-ray diffraction (XRD) analysis. This is a novel revelation and it was sufficiently corroborated by the EDX and TG/DTA analysis.The EDX and X-ray analysis also showed increased silica and oxygen composition of the blended compared to the control indicating increasing amounts of calcium silicate components. The mortar compressive strength tests showed that blending 5%x, 5%x5%y, 2.5%x2.5%y2.5%z and 2.5%x2.5%y2.5%z2.5p by mass of the admixture(s) produced Class 42.5N cement. These cements can therefore be used for early strength concrete v works and all types of construction works. 1:2:4 blended cement concretes with water cement ratio of 0.6 reached the targeted strength value of 20 ± 2 MPa at 28 days. The study showed that the effect of seawater (NaCl) and Na2SO4 on strength was reduced as the number of admixtures in the cement were increased. In all, the quinternary (2.5%x2.5%y2.5%z2.5%p) cement provided the best blend that could resist the deleterious effect of both seawater and sulphate solution negative action. These give ample proof that a combination of three or four admixtures in cement greatly influenced the reductionofportlandite content leading to high resistance to acidic attack. Economically, replacing 15% of total clinker imports by these admixtures would amount to a capital saving of at least $33.43 million per annum to Ghana.