The use of supplementary cementitious materials (SCMs) has increased over the years due to the carbon footprint associated with the production of cement, which contributes to 10% of the total global CO₂ gas emissions. This causes an increase in global warming, and the exponential increase in demand for construction of concrete has caused depletion of natural resources. Furthermore, due to increased urbanisation, large quantities of agro-industrially processed waste materials are generated and dumped into landfills, causing significant land scarcity, environmental issues, and pollution. Therefore, it has become necessary to reduce the CO₂ emissions by reducing our dependency on cement as a binder and developing eco-friendly concrete using alternative binders from agro-industrial waste materials. This study utilises Rice Husk Ash (RHA) as SCM and reinforcing with polypropylene (PP) fibres. The cement content is replaced with 5 to 20% RHA with an increment of 5% while reinforcing with PP fibres ranging from 0.20 to 0.30%. Based upon the results, it can be observed that concrete incorporating 15% RHA and reinforced with 0.25% PP fibres achieved better performance than the specimen with no SCM. However, a further increase in RHA content decreased concrete strength, which could not be recovered entirely with the reinforcement of PP fibres, though concrete with higher (20%) RHA reinforced with PP fibres could be used for non-structural and low-cost construction.

Purpose: This study aims to understand the process, structure and determinants of persistent illegal gold mining in Indonesia.Design/methodology/approach: An exploratory study included a literature review, field observations and in-depth interviews. Fieldwork was conducted at two mining locations in Kalimantan, Indonesia. Sixteen respondents representing key stakeholders: government, mining companies, mining associations and community, including illegal miners, were interviewed. The findings of the literature review were categorized as the push or pull factors within the topics, and field observations verified the literature review results regarding Indonesia. Interview data were analyzed using content analysis methods. A structural diagram of the actors and causal loop diagrams among the determinants of illegal gold mining was created and interpreted.Findings: A complex activity process and structure were revealed involving a range of actors. Politicians, government officials and law enforcement authorities added the complexity to the structure. Six main determinants of persistent illegal gold mining emerged: financial, low entry barrier, regulations and policies, supporting resources availability, politics and power and psychosocial factors.Practical implications: This study provides a deeper understanding for policymakers to consider when formulating policies on natural resources, and insights for mining companies to minimize conflicts with the community.Originality/value: The study contributes to our knowledge of the complex structure and main determinants of illegal gold mining in Indonesia, which supports efforts to curtail this illegal activity.