https://www.um.edu.mt/library/oar/handle/123456789/469 Previously known as Faculty of Architecture and Civil Engineering Tue, 20 Oct 2026 12:21:55 GMT 2026-10-20T12:21:55Z https://www.um.edu.mt/library/oar/handle/123456789/150215 Title: Development of eco-friendly gypsum composite using gypsum binder and gypsum waste aggregates Authors: Vaičiukynienė, Danute; Nizevičienė, Dalia; Mockienė, Jūratė; Vaičiukynas, Vilimantas; Balevičius, Giedrius; Borg, Ruben Paul Abstract: The development of sustainable building materials is increasingly focused on integrating regenerative resources and secondary raw materials obtained through industrial symbiosis. In this context, gypsum composites represent a promising solution for reducing environmental impact in the construction sec-tor. The raw materials used for gypsum composites include not only building gypsum (BG) but also gypsum-based demolition waste (GDW). In this study, gypsum composites were produced using BG binder combined with varying proportions of fine recycled fillers derived from GDW. The primary aim was to evaluate whether incorporating GDW can reduce environ-mental impact while maintaining mechanical performance comparable to reference gypsum composites without recycled material. BG was substituted with 10, 20, 30, and 40 wt% GDW, and the gypsum-to-water (G/W) ratio varied from 0.5 to 0.7. For each composition, nine samples were tested. The structural and mechanical behavior of the composites was assessed using X-ray diffraction (XRD), scanning electron microscopy (SEM), compressive strength tests, hydration temperature measurements, and loss-on-ignition analysis. The results showed that the proportion of recycled fillers significantly influenced the key material properties. Notably, a slight improvement in compressive strength was observed in the eco-friendly composites: the reference sample achieved 13.85 MPa, whereas the composite containing 10 wt% GDW reached 15.95 MPa. However, higher GDW content led to a reduction in com-pressive strength. This increase can be attributed to the micro-filler and nucleation effects of GDW, which produced denser microstructure and improved bonding characteristics. Thu, 01 Jan 2026 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/150215 2026-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/150060 Title: Sustainability of traditional, historical roofs in the Mediterranean : a rediscovered opportunity for a carbon neutral future Authors: Cassar, JoAnn; Galdies, Charles; Muscat Azzopardi, Elizabeth Abstract: As the world grapples with the effects of climate change, there is an urgent need for sustainable solutions to help reduce carbon emissions. Historic urban centres can indicate one possible way forward, and this is because of the way traditional buildings (in this paper centring on the Mediterranean) are built. Their materials and technologies are usually well chosen and adapted to hot climates, while the layout of historic centres, often with quite narrow, winding streets, provide shading and frequently also appropriate direction of cooling winds, especially in marine locations. These often result in these urban cores being cooler than more modern city centres. Traditional roofs, in particular, have over the centuries proved to be reliable and sustainable (when given appropriate maintenance), with layers of porous materials providing inbuilt breathable (evaporative) properties. These lead to a degree of passive cooling and ultimately to less energy consumption (less use of air conditioning for example), thus creating a smaller carbon footprint for each building, and hence also for the urban centre when a number of these buildings are present. This paper is based on a three-year pilot study, where an innovative methodology using a combination of remote data (obtained from Unmanned Aerial Vehicle (UAV) and satellite) with in situ measurements, allows for the remote identification of traditional and modified roofs, as well helping understand the thermal behaviour of such roofs, with this study concentrating on historic centres in the Island of Malta, in the Mediterranean. Ultimately aimed at promoting preservation of these traditional roofs, this study provides data to help address, at least in part, current climatic concerns, whilst also potentially providing some adaptation strategies to address climate change (in particular increased ambient temperatures). Our studies on the behaviour of traditional deffun mortar roofs have shown that they are effective in protecting the internal environment from the external one. This can lead to a reduction in carbon emissions and help create a more carbon-neutral future over an entire historic centre. Therefore, in the long term, with the right management policies in place, traditional roofs on traditional buildings can provide an excellent and cost-effective way of moving towards carbon neutrality in historic urban centres. Sun, 01 Jan 2023 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/150060 2023-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/149388 Title: Machine learning-based prediction of compressive strength and CO2 uptake in CO2-cured cementitious materials Authors: Han, Seongho; Kim, Jayon; Farrugia, Kay; Jun, Heejung; Borg, Ruben Paul; Hong Kim, Jae; Yoon, Jinyoung Abstract: Predicting the compressive strength and CO2 uptake of CO2-cured cementitious materials is challenging because these properties are influenced by complex interactions among mixture composition, curing conditions, and carbonation behavior. Accurate prediction and optimization of CO2 curing efficiency are therefore essential for developing sustainable low-carbon cementitious materials. This study developed a Least Squares Boosting (LSBoost)-based machine-learning framework for predicting and optimizing compressive strength and CO2 Uptake using a literature-derived database consisting of 423 compressive strength datasets and 131 CO2 uptake datasets. The input parameters incorporated binder chemistry through the Steinour formula, mixture proportions, pre-conditioning conditions, and CO2 curing variables. Hyperparameter tuning identified an optimal LSBoost configuration consisting of 10 splits, a minimum leaf size of 3, a minimum parent size of 10, 500 learning cycles, and a learning rate of 0.5. The developed models demonstrated strong predictive performance, with testing correlation coefficients exceeding 0.95 for both compressive strength and CO2 uptake predictions. The compressive strength model achieved a testing mean absolute percentage error of approximately 10.4%, while the CO2 uptake model yielded a testing RMSE of 3.76 despite the presence of zero-uptake datasets. Feature importance analysis revealed that compressive strength was mainly governed by the Steinour formula, water-to-binder ratio, curing duration, and curing age, whereas CO2 uptake was strongly influenced by CO2 concentration, relative humidity, and exposure duration during CO2 curing. Monte Carlo-simulation-based optimization further suggested that CO2 concentrations above approximately 15%, relative humidity above 60%, and curing durations longer than 48 h promoted higher predicted CO2 uptake under the investigated conditions. Thu, 01 Jan 2026 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/149388 2026-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/149376 Title: Effect of Lithium Sulfate on the Hydration Mechanisms and Performance of Ferroaluminate Cement Authors: Zhang, Yuanzhi; Shi, Penghang; Fu, Lifeng; Yang, Yi; Li, Lichen; Tang, Shengwen; Borg, Ruben Paul; Al Qunaynah, Siraj; Liao, Yishun Abstract: The effect of lithium sulfate (LS) admixture on the performance of ferroaluminate cement (FAC) remains poorly understood, and no systematic investigation of the regulatory effects of LS hydration in FAC systems has been conducted. By revealing how LS modulates the macroscopic properties and hydration progression of FAC, this work addresses an important knowledge deficit in the existing literature. This study investigated the performance evolution of FAC pastes with varying amounts of LS addition. It examined the setting time, fluidity, compressive strength, pH and electrical conductivity of the pore solution, as well as X-ray diffraction (XRD) and electrical resistivity. The findings indicate that LS significantly accelerates the early hydration rate of FAC, shortening setting time and reducing paste fluidity as its content increases. Notably, LS inhibits compressive strength development at 12 h, yet it enhances the rate of strength development after 1 day. The analysis of electrical conductivity and pH demonstrated that LS increases ion concentration and alkalinity within the first day, and these parameters stabilize after 28 days. Resistivity measurements indicate that LS raises paste resistivity within 3 h and enhances the peak hydration rate. Quantitative XRD demonstrates that LS induces complex lithium-sulfate coupling effects on ettringite (AFt): LS20 hits the critical $\text{Li}^+$ inhibition threshold, while the sulfate from the higher LS dosage mitigates such negative influences. These findings establish a theoretical foundation for the targeted application of LS in materials based on FAC. Thu, 01 Jan 2026 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/149376 2026-01-01T00:00:00Z