title: Effects of activator powders on hybrid binders based on volcanic ash and portalnd clinker based cement

authors: Hettiya Kandage, Havanjana Lanka Fernando

subjects: sustainable material

abstract: Concrete remains the most widely used construction material worldwide. However, the high energy consumption and CO₂ emissions associated with Portland cement production have driven the search for more sustainable alternatives. Volcanic ash (VA), a naturally occurring pozzolan found in abundance in regions such as Tauranga, New Zealand, presents promising potential as a partial replacement for cement. 

This thesis investigates the performance of value-added products from the Takitimu North Link (TNL) site, using chemical activation with sodium sulphate (Na₂SO₄) and calcium hydroxide (Ca(OH)₂) in hybrid binder systems. A central composite experimental design was employed to systematically vary the VA content and activator dosages. 
Mortar mixes with 25%, 50%, 75%, and 100% VA replacement were tested (Series A), with particular focus on the 25% blend. This composition underwent further testing with varying activator dosages to determine the optimal Na₂SO₄/Ca(OH)₂ (NS/CH) ratio (Series B). Compressive strength tests were conducted at 7, 28, and 90 days to assess mechanical performance. 

Additionally, microstructural characterization techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) were used to identify hydration products and evaluate binder densification. 

The results showed that a 25% replacement of Portland cement with VA, activated with 14% Na₂SO₄ at an NS/CH ratio of 1, delivered optimal compressive strength and microstructural development. While higher replacement levels generally reduced early-age strength due to weaker pozzolanic activity, appropriate activator dosages improved long-term performance significantly. 

Overall, the study demonstrates that chemically activated volcanic ash can substantially improve the sustainability profile of concrete by reducing Portland cement usage and its environmental impacts. The use of optimized hybrid binders incorporating volcanic ash offers a viable solution for developing sustainable, resilient, and cost-effective construction materials in New Zealand and other volcanic regions worldwide.

text: Effects of activator powders on hybrid binders based on volcanic ash and portalnd clinker based cement Concrete remains the most widely used construction material worldwide. However, the high energy consumption and CO₂ emissions associated with Portland cement production have driven the search for more sustainable alternatives. Volcanic ash (VA), a naturally occurring pozzolan found in abundance in regions such as Tauranga, New Zealand, presents promising potential as a partial replacement for cement. 

This thesis investigates the performance of value-added products from the Takitimu North Link (TNL) site, using chemical activation with sodium sulphate (Na₂SO₄) and calcium hydroxide (Ca(OH)₂) in hybrid binder systems. A central composite experimental design was employed to systematically vary the VA content and activator dosages. 
Mortar mixes with 25%, 50%, 75%, and 100% VA replacement were tested (Series A), with particular focus on the 25% blend. This composition underwent further testing with varying activator dosages to determine the optimal Na₂SO₄/Ca(OH)₂ (NS/CH) ratio (Series B). Compressive strength tests were conducted at 7, 28, and 90 days to assess mechanical performance. 

Additionally, microstructural characterization techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) were used to identify hydration products and evaluate binder densification. 

The results showed that a 25% replacement of Portland cement with VA, activated with 14% Na₂SO₄ at an NS/CH ratio of 1, delivered optimal compressive strength and microstructural development. While higher replacement levels generally reduced early-age strength due to weaker pozzolanic activity, appropriate activator dosages improved long-term performance significantly. 

Overall, the study demonstrates that chemically activated volcanic ash can substantially improve the sustainability profile of concrete by reducing Portland cement usage and its environmental impacts. The use of optimized hybrid binders incorporating volcanic ash offers a viable solution for developing sustainable, resilient, and cost-effective construction materials in New Zealand and other volcanic regions worldwide.

year: 2025-05-08

title: The power output of spine and fan magnetic reconnection solutions

authors: Craig, Ian J.D.

subjects: MHD—plasmas

abstract: The ability of three-dimensional magnetic “spine” and “fan” reconnection solutions to provide flarelike energy release is discussed. It is pointed out, on the basis of exact analytic solutions, that fast dissipation is possible only if the hydromagnetic pressure in the reconnection region becomes unbounded in the limit of small plasma resistivities. The implication is that some “saturation” of the power output is inevitable for realistic coronal plasmas. Estimates of the saturated power, based on limiting the flux pileup in the field, suggest that the geometry of the spine reconnection mechanism precludes significant flare energy release. However, the current sheet structures involved in fan reconnection seem able to release sufficient magnetic energy fast enough to account for modest flares, even under the conservative assumption of classical plasma resistivities.

text: The power output of spine and fan magnetic reconnection solutions The ability of three-dimensional magnetic “spine” and “fan” reconnection solutions to provide flarelike energy release is discussed. It is pointed out, on the basis of exact analytic solutions, that fast dissipation is possible only if the hydromagnetic pressure in the reconnection region becomes unbounded in the limit of small plasma resistivities. The implication is that some “saturation” of the power output is inevitable for realistic coronal plasmas. Estimates of the saturated power, based on limiting the flux pileup in the field, suggest that the geometry of the spine reconnection mechanism precludes significant flare energy release. However, the current sheet structures involved in fan reconnection seem able to release sufficient magnetic energy fast enough to account for modest flares, even under the conservative assumption of classical plasma resistivities.

year: 1997-08

title: Death and homelessness on the streets of Aotearoa New Zealand: Sustaining life

authors: Charvin-Fabre, Sandrine

abstract: In high-income countries, homeless people die 20 to 35 years earlier than domiciled populations. Despite this enduring reality, the issue of death inequality remains underexplored, especially in indigenous homeless contexts, facing the ongoing effects of colonisation. This study centres on the perspectives and aspirations of a Māori street homeless community, known as the “Peeps”. Its objective is twofold: to spotlight to unjust, untimely, and avoidable mortality impacting homeless communities in Aotearoa New Zealand, and to understand how life can be sustained against the adversity of street life. The thesis diverges from conventional public health approaches, which often dichotomise early deaths prevention through improved healthcare access during homelessness, and palliative care provision at the end of life of homeless people. This thesis explores “the temporal space of life prior to death”. Within that temporal realm, the omnipresent “risk of dying” that infiltrates the lives of homeless people, disrupting the linear progression toward death observed in domiciled populations, is recognised. This temporal space is understood as a zone of uncertainty and potentiality, wherein complex life-death dynamics operate, revealing broader political, societal and cultural tensions. This study encountered significant challenges, including the dearth of prior death-related research in Māori homeless contexts, and my non-Māori identity. In response, an indeterminate approach, rooted in relational ethics and complexity and systems thinking — aligned with Māori worldviews — was adopted.  

Part I of the thesis is conceptual and contextual. Part II invites the readers into the fragile “temporal space of life prior to death” and the cyclical research process. Cycle 1 focuses on understanding the local context of death inequality, through relational fieldwork and statistical analysis of coroners’ reports. This analysis uncovers a 30-year life expectancy disparity with domiciled populations, exacerbated by three-quarters of avoidable mortality, mainly due to chronic conditions and suicide. Subsequent cycles sustain relational fieldwork, using collaborative and critical performance ethnography. Cycle 2 reveals the Peeps’ resistance to access healthcare, rooted in experiences of transgenerational trauma and marginalisation of Māori beliefs and values in relation to death and dying within mainstream healthcare institutions. Collaboration with the Peeps leads to the co-creation of a drama, intended to initiate conversations with health professionals from the Peeps’ perspectives and aspirations, to improve the quality of care. This cycle also highlights the impact of disconnection processes with whānau (family, extended family) experienced by the Peeps. Progressing further, cycle 3 illuminates healing processes with whānau using Advance Care Planning, envisioned as a relational space, providing the Peeps with a sense of belonging, and spiritual continuity in the perspective of death and dying. 
 
In addition to shedding light on the profound death inequality that affect Māori homeless people, this thesis argues for homelessness to be recognised as “complex life-threatening conditions associated with serious-related health suffering”. Accordingly, the thesis advocates the shift toward comprehensive care, inclusive of a concurrent prevention and palliation approach over the course of homelessness, to mitigate its impact on the lives of Māori homeless people and enhance holistic wellbeing.

text: Death and homelessness on the streets of Aotearoa New Zealand: Sustaining life In high-income countries, homeless people die 20 to 35 years earlier than domiciled populations. Despite this enduring reality, the issue of death inequality remains underexplored, especially in indigenous homeless contexts, facing the ongoing effects of colonisation. This study centres on the perspectives and aspirations of a Māori street homeless community, known as the “Peeps”. Its objective is twofold: to spotlight to unjust, untimely, and avoidable mortality impacting homeless communities in Aotearoa New Zealand, and to understand how life can be sustained against the adversity of street life. The thesis diverges from conventional public health approaches, which often dichotomise early deaths prevention through improved healthcare access during homelessness, and palliative care provision at the end of life of homeless people. This thesis explores “the temporal space of life prior to death”. Within that temporal realm, the omnipresent “risk of dying” that infiltrates the lives of homeless people, disrupting the linear progression toward death observed in domiciled populations, is recognised. This temporal space is understood as a zone of uncertainty and potentiality, wherein complex life-death dynamics operate, revealing broader political, societal and cultural tensions. This study encountered significant challenges, including the dearth of prior death-related research in Māori homeless contexts, and my non-Māori identity. In response, an indeterminate approach, rooted in relational ethics and complexity and systems thinking — aligned with Māori worldviews — was adopted.  

Part I of the thesis is conceptual and contextual. Part II invites the readers into the fragile “temporal space of life prior to death” and the cyclical research process. Cycle 1 focuses on understanding the local context of death inequality, through relational fieldwork and statistical analysis of coroners’ reports. This analysis uncovers a 30-year life expectancy disparity with domiciled populations, exacerbated by three-quarters of avoidable mortality, mainly due to chronic conditions and suicide. Subsequent cycles sustain relational fieldwork, using collaborative and critical performance ethnography. Cycle 2 reveals the Peeps’ resistance to access healthcare, rooted in experiences of transgenerational trauma and marginalisation of Māori beliefs and values in relation to death and dying within mainstream healthcare institutions. Collaboration with the Peeps leads to the co-creation of a drama, intended to initiate conversations with health professionals from the Peeps’ perspectives and aspirations, to improve the quality of care. This cycle also highlights the impact of disconnection processes with whānau (family, extended family) experienced by the Peeps. Progressing further, cycle 3 illuminates healing processes with whānau using Advance Care Planning, envisioned as a relational space, providing the Peeps with a sense of belonging, and spiritual continuity in the perspective of death and dying. 
 
In addition to shedding light on the profound death inequality that affect Māori homeless people, this thesis argues for homelessness to be recognised as “complex life-threatening conditions associated with serious-related health suffering”. Accordingly, the thesis advocates the shift toward comprehensive care, inclusive of a concurrent prevention and palliation approach over the course of homelessness, to mitigate its impact on the lives of Māori homeless people and enhance holistic wellbeing.

year: 2024