Near - surface study of a hot spring site in Fiji

A geophysical investigation of a hot spring system located in Rabulu, Fiji, was carried out from October 2014 to March 2015. The investigation covered a survey area of 6075 m2. Self-potential (SP), ground temperature and soil carbon dioxide (CO2) concentrations were measured and investigated for their distribution characteristics and inter-linkages. Results indicated obvious anomalous zone at the hot spring discharge site. The SP profile analysis highlighted thermal water upwelling zones and elevation-driven subsurface groundwater pathways. Measurement of subsurface temperatures up to 1 m depths revealed increasing temperatures, indicating potentially high thermal gradients in the area. Surface soil CO2 distributions also agreed with SP and ground temperature results. The overall result of the study demonstrated that synchronised measurements of SP, ground temperature and soil CO2 can be instrumental in identifying anomalous zones near the hot spring sites. Other parameters such as spring water temperature, discharge rate and energy flux estimates from the spring were calculated and analysed. The high-dense multi-parameter data coverage allowed interpretation of geothermal features at a scale never conducted in Fiji before. The near-surface investigations reported in this study corroborate previously suggested steady geothermal activity in the region, deserving further detailed investigation

Rebar corrosion due to chlorides in synergy with sodium, potassium, and magnesium

The ability of steel reinforced concrete to withstand long service life is ensured by the strong binding between the concrete and the rebar. Although rebar corrosion deterioration in the presence of chlorides is well known, it is important to note that these anions are never present in isolation, i.e., other cations are also present within the exposed environment. Consequently, a study was conducted to investigate the rebar deterioration due to chlorides in the presence of different cations. A well-controlled laboratory experiment for assessing the corrosivity of sodium chloride, potassium chloride and magnesium chloride was conducted. The galvanostatic pulse technique was used to investigate the concrete-steel interfacial structure, which was modelled after a modified Randles circuit. Analysis revealed influences of the associated cations during the rebar corrosion process. A normalisation approach was used to compare chloride attacks on the rebar due to different salt solutions. Results suggest that chloride attacks in the presence of sodium cations are relatively corrosive

Corrosion behaviour of sinter forged aluminium composites during hot deformation

A galvanostatic pulse technique was used to determine corrosion behavior of sinter-forged aluminium composites. Specimens were prepared using powder metallurgy (P/M) manufacturing techniques, with two different initial relative density and various carbide reinforcements such as titanium carbide (TiC), molybdenum carbide (Mo2C), iron carbide (Fe3C) and tungsten carbide (WC). The specimens were machined and molded in a thermo-plastic material so that a surface area of 1 cm2 is exposed in a solution of 3.5wt% water solution of NaCl during the corrosion test. The corrosion behavior of the sinter-forged aluminium composites were studied alongside microstructure studies to expose corrosion dynamics and presented in this report

Denoising time - domain induced polarisation data using wavelet techniques

Time-domain induced polarisation (TDIP) methods are routinely used for near-surface evaluations in quasi-urban environments harbouring networks of buried civil infrastructure. A conventional technique for improving signal to noise ratio in such environments is by using analogue or digital low-pass filtering followed by stacking and rectification. However, this induces large distortions in the processed data. In this study, we have conducted the first application of wavelet based denoising techniques for processing raw TDIP data. Our investigation included laboratory and field measurements to better understand the advantages and limitations of this technique. It was found that distortions arising from conventional filtering can be significantly avoided with the use of wavelet based denoising techniques. With recent advances in full-waveform acquisition and analysis, incorporation of wavelet denoising techniques can further enhance surveying capabilities. In this work, we present the rationale for utilising wavelet denoising methods and discuss some important implications, which can positively influence TDIP methods

Neutron activation analysis of atmospheric aerosols from a small Pacific Island country: a case study of Suva, Fiji Islands

A systematic study was developed to investigate the quality of air in Suva, the capital city of Fiji Islands. This is the first work of its kind in the South Pacific Islands and was aimed at characterizing the elemental abundances in total suspended particulate (TSP) matter in Suva 19s air. Aerosol samples were collected from 11 locations in Suva during the period 2000 132003 using a high-volume sampler. Concentrations of some heavy metals and other trace elements in these atmospheric aerosols were investigated by neutron activation analysis and gamma spectrometry. Concentrations of total suspended particulates for residential, traffic and industrial areas were found to be in the range 9-43, 20-58 and 33-91 ;Cg/m3, respectively. The elements sodium, iron and zinc have been observed in relatively higher concentrations than other elements. Moreover, calculated enrichment factors for some elements (such as arsenic, bromine, cobalt, chromium and antimony) reveal possible anthropogenic inputs into air mainly through automobile exhaust emissions

Spectral Induced Polarization Techniques in Soil Corrosivity Assessments

We presented a laboratory method for investigating the spectral induced polarization (SIP) response of soil samples and the implications for overall soil corrosivity. This study was important in order to advance the understanding of soil electrical properties, which can be used diagnostically to assess infrastructure integrity. Presently, isolated measurements of soil resistivity are the only (electrical) parameters that are routinely used to identify soil corrosivity. Our work showed that the low frequency soil spectral properties may lead to better soil corrosivity assessments when coupled effects from clay and salinity were present. In particular, unfolding and interpreting the soil spectral properties using the Cole-Cole model revealed that the normalized chargeability parameter mn was highly appropriate for identifying the character of potentially corrosive soils

Measurement of corrosion in soil using the galvanostatic pulse technique

The galvanostatic pulse technique was applied in the soil environment, allowing the characterisation of corrosion rate and the double layer capacitance formed at the metal/soil interface. A well-controlled laboratory framework for assessing potential corrosivity amongst different soil samples was presented. The galvanostatic pulse technique and the suggested framework were used to evaluate the effect of varying clay and chloride contents on corrosion of common ferrous pipeline alloys. A coupled moisture-chloride effect induced by clay was used to explain the features of the electrical double layer. The study provides a reference for calibrating future corrosion experiments in soil media

Self-potential and soil temperature profiling: Case study of Tavua hot spring, Fiji

Studies on hot spring regions in Fiji have been conducted by several workers such as (Cox 1982), (Healy 1960) and (Autar 1996). These studies identified several distributions patterns that require further investigation and analysis. There are almost no published works continued from the efforts of previous workers. In the present work, a geophysical investigation of a hot spring was conducted using advanced geophysical techniques to build upon conclusions from preceding works. The Tavua hot spring site, located in northern Viti Levu within the Nakauvadra range was investigated using several geophysical techniques. Self-potential (SP) and soil temperature profiling were carried out within the hot spring. The SP study provided useful information on subsurface fluid flow, clearly delineating upward and downward flows. Good correspondence between SP and soil temperature was also observed. Other hydrological parameters viz., discharge rate and outflow water temperature were evaluated to determine the energy flux of the hot spring. The present methodological study aims to a) investigate the distribution of various geophysical parameters within this area, and b) provide a baseline investigation so that feasibility of further detailed explorations can be determined. To our knowledge, there is no recent published literature concerning geophysical studies on hot springs making this the first of its kind investigation in Fiji