ABSTRACT
Metakaolin (MK) is one of the most sustainable cementitious construction materials, which is derived through a direct heating procedure known as calcination. Calcination process takes place substantially lower temperatures than that required for Portland cement, making it a more environmentally sustainable alternative to traditional cement. This procedure causes the removal of hydroxyl water from the naturally occurring kaolin clay (Al2Si2O5(OH)4 with MK (Al2O3·2SiO2) as its product. Kaolin naturally exists in large amount within 5°29'N-5°35'N and 7°21'E-7°3'E geographical coordinates surrounding Umuoke, Obowo, Nigeria. Alumina and silica are the predominant compounds in MK, which provide it with the pozzolanic ability, known as the 3-chemical pozzolanic potential (3CPP), with high potential as a cementitious material in concrete production and soil stabilization. Over the years, researchers have suggested the best temperature at which MK is derived to have the highest pozzolanic ability. Prominent among these temperature suggestions were 800 °C (3CPP of 94.45%) and 750 °C (3CPP of 94.76%) for 2 h and 5 h' calcination periods, respectively. In this research paper, 11 different specimens of Kaolin clay obtained from Umuoke, Nigeria, were subjected to a calcination process at oven temperatures from 350 to 850 °C in an increment of 50 °C for 1 h each to derive 11 samples of MK. The MK samples and Kaolin were further subjected to X-ray fluorescence), scanning electron microscopy (SEM) and X-ray diffraction (XRD) Brunauer-Emmett-Teller (BET) tests to determine the microstructural behaviour and the pozzolanic properties via the 3CPP as to exploit the best MK with the highest cementing potential as a construction material. The results show that the MK heated at 550 °C and 800 °C produced the highest pozzolanic potentials of 96.26% and 96.28%, respectively. The enhancement in pozzolanic potential at optimum calcination temperature is attributed to an increase in the specific surface area upon calcination of kaolinite confirmed by BET results. The SEM and XRD results further supported the above result with the strengthened crystal structure of the MK at these preferred temperatures. Generally, 550 °C is more preferred due to the less heat energy needed for its formulation during 1 h of calcination, which outperforms the previous results, that suggested 750 °C and 800 °C in addition to longer hours of heat exposure.
ABSTRACT
BACKGROUND: Acute gastroenteritis (AGE) is a major cause of morbidity and mortality in children world-wide with the highest incidence in the developing countries. The persistence and effect of this condition require a study of the features and characteristics of the disease especially, within any (each) locality in order to offer possible control solutions. AIM: To determine, the clinical and social characteristics associated with AGE among children seen in the University of Nigeria Teaching Hospital, Enugu. SUBJECTS AND METHODS: A hospital-based population study in which children admitted in the children emergency room of the University of Nigeria Teaching Hospital whose parents/caregivers gave their consent were enrolled, over a 7 month period. Appropriate statistical tools: Chi-square, t-tests, correlation and logistic regression were used to determine significant values and associations. RESULTS: A total of 76 children with AGE were enrolled; 69.7% (53/76) were males. The mean age of the subjects was 11.3 (6.6) months. Majority 94.7%, (72/76) of cases of AGE occurred in children less than 24 months, with children 6-11 months contributing the highest percentage 42%, (32/76). The study population was predominantly urban dwellers; 78.9%, (60/76, P = 0.40) and water cistern constituted 77.6% (58/76) of waste disposal method. Those who had potable water supply were 23.7%, (18/76, P = 0.30) and 19.7% of the children were exclusively breast fed. Fever and vomiting were the commonest associated symptoms, occurring in 82.9% (63/76) and 73.7% (56/76) of the subjects respectively. A good percentage of the subjects 64.5%, (49/76) had ORS before presentation. CONCLUSION: AGE is more common in older infants among those who were not exclusively breast-fed and the severity was unrelated to place of domicile and waste disposal habits.
