Mechanical and Microstructural Characterization of Alkali-Activated Coconut Shell Ash Mortar

In this paper, potential of alkaline activation of coconut shell ash (CSA) as binder in mortar was investigated. Coconut shells were collected and calcined at temperature ranges between 500 and 900°C at interval of 100 for 30, 60 and 90 minutes to determine optimum burning condition that produces ash of higher silica content. Chemical composition of the ashes was then determined using X-ray Florescence (XRF) technique. Sodium hydroxide (NaOH) of different concentrations of 10, 12, 14 and 16 Molar (M) was used as alkaline activator, while mortar of mix ratio 1:3 was produced, while ratio of the alkali to CSA was of 0.5.  Mortar prisms of size 40 mm  40 mm  160 mm were cast and cured in an oven at a temperature of 80  for 7, 28, 56, 90 and 120 days. Thereafter, flexural and compressive strengths were determined at the end of each curing ages, following standard procedures. Scanning Electron micrographs of the hydrated mortar at 120 days were obtained using scanning electron microscopy (SEM) The results showed the oxide composition did not follow any pattern with increase in temperature but CSA produced at 800 for 1h gave the highest combined silica, alumina and ferric oxides above 70%, which is accepted as minimum value for pozzolanic materials.  Both compressive and flexural strengths of the activated mortar samples were found to increase with increase in activator concentration up to 14M and decline thereafter. At 120 days, the compressive strength was 13.9 N/mm2 while the flexural strength was 6.88 N/mm2. These values were higher than the strengths recommended by Nigerian Industrial Standard (NIS) for load bearing blocks. It was concluded that activation of CSA with NaOH could be used as binder for non-structural use. The SEM results indicated that mortar made from 14 M had structure that was densely packed compared to other mortar samples produced from other concentrations

Review of Selected Bio-Wastes as Potential Materials for Alkali-Activation for Cement-Based Products

There is growing need to finding alternative binder for Ordinary Portland Cement (OPC) as a result of the environmental hazards associated with its production. This paper presents the result of the review of selected bio-wastes as potential materials for alkali-activation in cement-based products. Studies carried out by several authors on the use of ashes from rice husk, cassava peel, sugarcane straw, corn cob and coconut shells were critically reviewed, while their chemical compositions as well as other criteria for alkali activation were identified. The review showed that the combined composition of SiO2, Al2O 3 and Fe2O3 were in the ranges of 67.90 – 93.60, 46.59 – 72.25, 73.79 – 83.02, 41.13 – 78.30 and 71.3 – 77.57 % for rice husk ash, cassava peel ash, sugarcane straw ash, corn cob ash and coconut shell ash, respectively. These values met the requirement of ASTM 618 for materials to be considered as pozzolan, while the hydraulic coefficients of the ashes were also found comparable to notable industrial wastes that have been utilized for alkali-activation. It was also found that these materials are still not explored for alkali-activation. The paper concluded that the ash from these materials could be alkali activated to produce binders in cement-based products due to their potential properties

Radiological and related chemical health impact assessments of uranium in pipe borne water from some waterworks in Lagos metropolis, Nigeria

The common purifying technique of water for public (human) consumption in Nigeria is by chlorination which only eliminates the microbial contaminants, but the radioactive contaminants remain unaffected. There had been no serious radiological and related chemical health impact assessments of pipe borne water in the country. Water samples were collected from five waterworks across Lagos Metropolis and a single crystal NaI (Tl) detector was used to determine the activity concentration of 238U radionuclide in the water. The radiological health impact assessment determined includes annual effective dose rates and risk of incurring cancer. Using activity concentrations obtained and the relation from United State Environmental Protection Agency (USEPA), the chemical health impact such as life average daily dose (LADD) and hazard quotient (HQ) due to ingestion of 238U in water were determined and data were analyzed using descriptive statistics. The mean 238U activity concentrations were 15.3±4.1 Bql-1, 14.6±5.2 Bql-1, 9.7±2.0 Bql-1, 11.0±2.9 Bql-1 and 11.3±1.8 Bql-1 for Agege, Shomolu, Iju, Saka and Amuwo respectively. The least mean effective dose, 0.3±0.1 mSvy-1 was obtained in Iju while the highest, 0.5±0.2 mSvy-1 was obtained in Agege and Shomolu. The least mass concentration of 174.2±35.7μgl-1 was obtained in Iju and the highest of 274.9±73.3 μgl-1 was obtained in Agege. The highest mean cancer mortality and morbidity risks, (0.6±0.2) x10-3 and (0.9±0.2) x10-3 respectively were obtained in Agege. The activity concentrations of radionuclide in the water were low hence the morbidity and mortality risks in the study were low when compared to the world average value of 1.0x10-3. The result showed high radioactivity and chemical levels therefore caution and control should be taken to avoid any health crisis later in future.Keywords: uranium impact assessment, pipe born water, water works, Lagos metropolis, Nigeri

Ionospheric foF2 morphology and response of F2 layer height over Jicamarca during different solar epochs and comparison with IRI-2012 model

Diurnal, seasonal and annual foF2 variability and the response of the F2-layer height over Jicamarca (11.9◦S, 76.8◦W, 1◦N dip) during periods of low (LSA), moderate (MSA) and high (HSA) solar activities was investigated. The relative standard deviation (VR) was used for the analysis. The F2-layer critical frequency pre-noon peak increases by a factor of 2 more than the post-noon peak as the solar activity increases. The variability coefficient (VR) is lowest during the day (7–16%) for the three solar epochs; increases during nighttime (20–26%, 14–26%, and 10–20%, respectively for the LSA, MSA and HSA years); and attained highest magnitude during sunrise (21–27%, 24–27%, and 19–30%, respectively in similar order). Two major peaks were observed in VR – the pre-sunrise peak, which is higher, and the post-sunset peak. Generally, the variability increases as the solar activity decreases. Annually, VR peaks within 23–24%, 19–24% and 15–24% for the LSA, MSA, and HSA periods, respectively. The ionospheric F2-layer height rises to the higher level with increasing solar activity. The foF2 comparison results revealed that Jicamarca is well represented on the IRI-2012 model, with an improvement on the URSI option. The importance of vertical plasma drift and photochemistry in the F2-layer was emphasized