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<p> In this study the experiments were designed to measure the geochemical and surface charge (zeta potential) changes with time for two crushed samples of feldspar (Na-fs and K-fs) over the pH range of most natural waters (5 to 9). These experiments show: </p> <p> (a) the importance of adsorption/desorption phenomena in both short-term and long-term feldspar dissolution, and probably for chemical weathering in general; </p> <p> (b) that the generalized curve which characterizes the geochemical data (an initial rapid rise to a peak followed by a decrease to a lower, either constant or later increasing value) is consistent with a consideration of the adsorption/desorption process (i.e., the formation of the double layer) taking place at the feldspar surface and with the simple dissolution of the mineral; </p> <p> (c) that the cation-silica ratios (Na₂O/SiO₂, K₂O/SiO₂, CaO/SiO₂) of the solution compared to those in the original feldspar indicate an initially incongruent dissolution which tends towards congruency during the latter part of the experiments. </p> <p> From information in the Iiterature and the results of these experiments. it may be concluded that: </p> <p> (a) the most important or master variables in chemical weathering are abrasion, minerologic or crystallographic factors such as twinning, exsolution regions, impurities, fractures and grain size, and solution composition and concentration. pH does not appear to be a master variable in most natural waters, especially for long-term weathering, and the chemical composition of the mineral phase is also not a good criterion for predicting weathering behaviour; and </p> <p> (b) the most extreme chemical weathering should occur in a high energy environment, either for physical reasons (i.e., high abrasion due to extreme relief) or for chemical reasons (i.e., high rainfall). </p> / Thesis / Master of Science (MSc)

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Many failures of external walls made of porous buildingmaterials are caused by excessive moisture content,particularly after driving rain and under long duration ofmoist conditions. Lack of sufficient protection againstexposure conditions is one of the reasons for external wallsprematurely demonstrating failures, i.e. properties andperformance above/below critical levels. Silicon-based waterrepellants are increasingly used in order to improve theperformance of both old and new buildings. Water repellants areexpected to prolong the service life and improve the durabilityof wall components by preventing or minimising water ingressinto the structure and thus delaying the deteriorating effectsof the atmosphere. To date, various kinds of water repellantshave been developed. However, only limited research has beencarried out, particularly on the long-term field exposuretesting. Existing research is mainly focused on the performanceof surface treatments of concrete structures and the protectionof historical buildings built of stone, brick and wood, and isprimarily based on short-term laboratory testing. The aim ofthis research work is to study the long-term performance,degradation processes and ageing characteristics of renderedautoclaved aerated concrete (AAC) with and without waterrepellants. Investigations are carried out by physical andchemical analysis of fresh samples, samples naturally weatheredby long-term field exposure and samples artificially aged byshort-term accelerated laboratory tests. Two differentapplication of water repellants are employed: impregnation ofrendering surface with an aqueous product and as additive inpowder form mixed into the fresh rendering mortar. Continuousmoisture and temperature monitoring of naturally exposed testsamples are also included in the study. Wetcorr sensors andresistance-type nail electrodes are used to measure the surfacemoisture and the moisture content in the material,respectively. This thesis describes the experimental set-upand presents the results from site monitoring and laboratorytests of unexposed, naturally and artificially exposed samples(freeze-thaw and UV+water). The results from the continuousmoisture measurements are compared with the results obtainedfrom the full-scale test cabin built within the EUREKA-projectE 2116 DurAAC. The test cabin has the same basic measurementinstruments for continuous monitoring of moisture andtemperature. An attempt has been made to develop methods forlong-term performance assessment of water repellants to be usedin service life prediction. The combination of data obtainedfrom the field measurements with data obtained from thelaboratory tests and analysis may also meet practical needs ofthe end-users.

<p>Many failures of external walls made of porous buildingmaterials are caused by excessive moisture content,particularly after driving rain and under long duration ofmoist conditions. Lack of sufficient protection againstexposure conditions is one of the reasons for external wallsprematurely demonstrating failures, i.e. properties andperformance above/below critical levels. Silicon-based waterrepellants are increasingly used in order to improve theperformance of both old and new buildings. Water repellants areexpected to prolong the service life and improve the durabilityof wall components by preventing or minimising water ingressinto the structure and thus delaying the deteriorating effectsof the atmosphere. To date, various kinds of water repellantshave been developed. However, only limited research has beencarried out, particularly on the long-term field exposuretesting. Existing research is mainly focused on the performanceof surface treatments of concrete structures and the protectionof historical buildings built of stone, brick and wood, and isprimarily based on short-term laboratory testing. The aim ofthis research work is to study the long-term performance,degradation processes and ageing characteristics of renderedautoclaved aerated concrete (AAC) with and without waterrepellants. Investigations are carried out by physical andchemical analysis of fresh samples, samples naturally weatheredby long-term field exposure and samples artificially aged byshort-term accelerated laboratory tests. Two differentapplication of water repellants are employed: impregnation ofrendering surface with an aqueous product and as additive inpowder form mixed into the fresh rendering mortar. Continuousmoisture and temperature monitoring of naturally exposed testsamples are also included in the study. Wetcorr sensors andresistance-type nail electrodes are used to measure the surfacemoisture and the moisture content in the material,respectively. This thesis describes the experimental set-upand presents the results from site monitoring and laboratorytests of unexposed, naturally and artificially exposed samples(freeze-thaw and UV+water). The results from the continuousmoisture measurements are compared with the results obtainedfrom the full-scale test cabin built within the EUREKA-projectE 2116 DurAAC. The test cabin has the same basic measurementinstruments for continuous monitoring of moisture andtemperature. An attempt has been made to develop methods forlong-term performance assessment of water repellants to be usedin service life prediction. The combination of data obtainedfrom the field measurements with data obtained from thelaboratory tests and analysis may also meet practical needs ofthe end-users.</p>

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This study refers to a qualitative and quantitative weathering characterization of a gneiss rock mass (weathering profile, intact rock and discontinuity) in a tropical region. The rock mass was excavated for a construction of an unlined railway tunnel, which during its useful life began to present block instability problems linked to the weathering and the time of exposure of the rock. The weathering of the rock mass and its weathering grades are approached in the geological and geotechnical points of view, covering bibliographical review on the subject, field inspection, direct and indirect investigations, and laboratory tests: petrographic analysis, X-ray diffraction, physical properties and durability index, sclerometry, ultrasonic test, uniaxial and diametral compression. / Este estudo se refere à caracterização qualitativa e quantitativa do intemperismo de um maciço rochoso gnáissico (perfil de intemperismo, rocha intacta e descontinuidades) em uma região tropical. O maciço foi escavado para a construção de um túnel ferroviário não revestido, que ao longo da vida útil começou a apresentar problemas de instabilidade de blocos vinculados ao intemperismo e ao tempo de exposição da rocha. O intemperismo do maciço rochoso e os seus graus de alteração foram abordados do ponto de vista geológico e geotécnico, levando-se em consideração uma ampla revisão bibliográfica sobre o tema, inspeção de campo, investigações diretas e indiretas, e os seguintes ensaios laboratoriais: análise petrográfica, difratometria de raios X, índices físicos e de durabilidade, esclerometria, ultrassom, compressão uniaxial e diametral.

<div><div><div><p>The radionuclide 10Be is produced in the atmosphere and is delivered to Earth’s surface in meteoric rain and aerosols. The stable nuclide 9Be is present in trace concentrations within rocks in Earth’s crust and is released via chemical weathering. Together, these two isotopes have been employed to study a wide range of Earth processes. Here I explore new terrestrial archives of Be isotopes: cave speleothems and terrestrial Mn-oxides. Until this point, these archives have barely been studied. Only one published dataset of Be isotopes in cave speleothems exists (Lundblad, 2006), and to my knowledge, terrestrial manganese oxides are yet to be explored. However, since speleothems and Mn-oxides precipitate from groundwater, they have the potential to encode temporal variations in the 10Be/9Be ratio of water and colloids in the vadose zone.</p><p>I develop a framework for using the 10Be/9Be ratio in the dissolved phase and/or secondary weathering products as a metric of chemical weathering rate. I am motivated by several over-arching questions:</p><ol><li><p>1) Which factor, or factors, is/are dominant in controlling Be isotopes in speleothems and terrestrial Mn-oxides?</p></li><li><p>2) Can Be isotopes in speleothems be used as a metric of weathering rate over time, particularly across glacial/interglacial cycles?</p></li><li><p>3) Can Be isotopes be used to date the formation of terrestrial Mn-oxides?</p></li></ol><p>I measure Be-isotope concentrations in speleothems from Soreq Cave, Israel. By applying an equation that I derive in this thesis, I use the temporal variation in the speleothem10Be/9Be ratio to calculate chemical weathering rates over the last 168 ka. Chemical weathering varies with independent proxies for temperature. The weathering-temperature relationship can be fit to an Arrhenius relationship, and the calculated activation energy (Ea) matches other field-based estimates for feldspar, an abundant mineral in the soil above the cave. In the Appendices I present additional results of Be-isotope measurements in a flowstone from Buffalo Cave in South Africa, as well as Mn-oxides from the Appalachians.</p></div></div></div>

One of the most essential resources for life on our planet is water. A concern for water resource sustainability has shifted towards the sustainable development of clean water body resource (SWDF, 2009). Data for the Vaal River water chemistry is in abundance. However, research on the historic natural conditions influencing the inorganic water quality, is not as extensive. Inorganic data was obtained from the Department of Water Affairs, for the period 1972 to 2011, for identified monitoring stations along the Vaal River. Water quality was evaluated using various geochemical techniques to analyse the data. The results of the study indicate that the water chemistry of the Vaal River is controlled by: 1. Chemical weathering of siliceous sediment, intrusive igneous rocks and metamorphic rocks (Na+, K+, Mg2+, Ca2+ and (HCO3)-). 2. Anthropogenic influences increasing the sulphate (SO4) concentration There is no major increase in ion concentrations for the stations. However the concentrations of bicarbonate (HCO3)- and SO4 change as it progresses downstream from the first upstream station to the last downstream station. Based on the chemical characterisation, three groups have been identified. (1) Group 1 stations appear to suggest a higher influence in chemical weathering than the group 2 stations. (2) Group 2 stations appear to suggest a greater influence from SO4. (3) Group 3 stations appear to suggest an influence from both the bicarbonate and the SO4 influences. Geographically the chemical weathering is an indication of the three different groups with strong anthropogenic influences in the middle group. The water chemistry for the Vaal River is controlled by two processes, namely chemical weathering and anthropogenic influences. The prominent indication of the difference in these two influences can be seen between group 1 and group 2. A secondary conclusion indicates that a total dissolved solid (TDS) alone is not an accurate representation of anthropogenic influence (or poor water quality) on inorganic water quality of the Vaal River. The natural weathering or geological influences appears to play a more dominant role in certain sections or catchments with lower contributions from anthropogenic influences. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015