Environmental Engineering: Research @ Brunel

Research published by Brunel staff

Below are recent articles (co-)authored by Brunel academic staff. Please click the title of the article to access the full-text.

• Graph-informed convolutional autoencoder to classify brain responses during sleep
  Zakeri, S. et al
  Frontiers in Neuroscience, Vol 19, Art No. 1525417 (Apr 2025)
  Automated machine-learning algorithms that analyze biomedical signals have been used to identify sleep patterns and health issues. However, their performance is often suboptimal, especially when dealing with imbalanced datasets. In this paper, we present a robust sleep state (SlS) classification algorithm utilizing electroencephalogram (EEG) signals. To this aim, we pre-processed EEG recordings from 33 healthy subjects. Then, functional connectivity features and recurrence quantification analysis were extracted from sub-bands. The graphical representation was calculated from phase locking value, coherence, and phase-amplitude coupling. Statistical analysis was used to select features with p-values of less than 0.05. These features were compared between four states: wakefulness, non-rapid eye movement (NREM) sleep, rapid eye movement (REM) sleep during presenting auditory stimuli, and REM sleep without stimuli. Eighteen types of different stimuli including instrumental and natural sounds were presented to participants during REM. The selected significant features were used to train a novel deep-learning classifiers. We designed a graph-informed convolutional autoencoder called GICA to extract high-level features from the functional connectivity features. Furthermore, an attention layer based on recurrence rate features extracted from EEGs was incorporated into the GICA classifier to enhance the dynamic ability of the model. The proposed model was assessed by comparing it to baseline systems in the literature. The accuracy of the SlS-GICA classifier is 99.92% on the significant feature set. This achievement could be considered in real-time and automatic applications to develop new therapeutic strategies for sleep-related disorders.

• Thermoeconomic performance of a CO₂ heat pump for space and water heating of a 4-bedroom house in the South of England
  Qayyum, U. et al
  Building Services Engineering Research & Technology, Early Access article (May 2025)
  Heat pumps are considered a key technology for the decarbonisation of space and water heating in domestic dwellings in the UK. Heat pumps that employ high-temperature working fluids such as CO₂ have the potential to be used in retrofit applications. This paper presents the characteristics of a CO₂ heat pump developed at Brunel University of London and the simulation results of its application to provide space and domestic hot water heating in a well-insulated four-bedroom semi-detached house with four occupants. The heating system is assumed to employ water thermal energy storage. Analysis has shown that storage volumes between 200 L and 300 L can satisfy the space temperature control requirements of the domestic dwelling if a heat pump capacity of 4.5 kW at 7 degrees C ambient temperature and 60 degrees C water flow temperature is employed. A comparison of the heat pump with a gas boiler reveals that with current gas and electricity prices, running costs for the heat pump can be 91% higher and CO₂ emissions 40% lower than those of the gas boiler. Further design and control optimisation of the heat pump is expected to reduce both its running costs and CO₂ emissions. Practical application: This paper examines the practical application of a 4.5 kW heat pump with water thermal energy storage for domestic heating. The system operates efficiently at 7 degrees C ambient and 60 degrees C water flow temperatures, and can be retrofitted in two-thirds of UK homes without upgrading radiators. For a four-bedroom house, 200-300 L thermal storage volumes are optimal. While running costs are 91% higher than a gas boiler, the heat pump reduces CO₂ emissions by 40%, offering a more sustainable heating solution.

• Influence of alluvial slope on avulsion in river deltas
  Prasojo, O. A. et al
  Earth Surface Dynamics, Vol 13, No 3, p.349-363 (May 2025)
  Changing hydrological regimes, sea-level rise, and accelerated subsidence are all putting river deltas at risk across the globe. One mechanism by which deltas may respond to these stressors is that of avulsion. Decades of delta avulsion studies have resulted in conflicting hypotheses as to whether avulsion timing and location are primarily controlled by upstream (water and sediment discharge) or downstream (backwater and sea-level rise) drivers. Here we use Delft3D morphodynamic simulations to test the upstream-influence hypothesis by varying the initial alluvial slopes upstream of a self-formed delta plain within a range (1.13x10^-4 to 3.04x10^-3 m m^-1) that is representative of global deltas, while leaving all other parameters constant. Avulsion timing and location were recorded in six scenarios modelled over a 400-year period. We measured independent morphometric variables including avulsion length, delta lobe width, bankfull depth, channel width at avulsion, delta topset slope, and sediment load and compare these to natural and laboratory deltas. We find that larger deltas take more time to avulse, as avulsion timing scales with avulsion length, delta lobe width, and bankfull depth. More importantly, we find strong negative correlations between sediment load avulsion timescale and sediment load initial alluvial slope. Sediment load is directly dependent on the upstream alluvial slope, and increases in this slope raise transport capacity and introduce more sediment into a delta plain, leading to higher aggradation rates and, consequently, more frequent avulsions. These results introduce further debate over the role of downstream controls on delta avulsion.

• Energy release and related sensitivity analysis of anisotropic CJBs under compression conditions without and with lateral pressure
  Gong, B. et al
  Bulletin of Engineering Geology and the Environment, Vol 84, No 6, Art No. 297 (Jun 2025)
  The cumulative energy released by micro-cracks when columnar jointed basalts (CJBs) attain peak strength (micro-crack energy index (MCEI)) under compression is a crucial foundation for understanding the mechanical behavior of CJBs and informing engineering strategies for monitoring and reinforcement. Beginning with the construction of detailed CJB images owning varied settings, the meso-scale damage mechanics, stochastic strength principle, and continuum mechanics are integrated. Employing the rock failure process analysis method improved by digital image correlation, the related heterogeneity numerical models are established using the generated images, facilitating a comprehensive scrutiny of the force-deformation features, fracture process, and energy change of CJBs exposed to compression conditions without and with lateral pressure (CCWOLP and CCWLP). Then, the effects of different factors on the micro-crack quantity index (MCQI) and MCEI are investigated, and the sensitivity analysis is conducted to clarify the impact relationships and recognize pivotal variables. The results show that under the CCWOLP and CCWLP, the increased rock homogeneity and larger column diameter lead to the intensified stress concentration at joints and accelerate the occurrence of the MCEI. Conversely, the higher residual strength coefficient of joints can delay the MCEI. The specimen, with the greater joint elastic modulus / no secondary joint set, may release MCEI later, and the MCEI value may be lower, hinging on the specific column dip angle. Under the CCWOLP, the dominant sensitive variables for the MCEI comprise joint constitutive correlation, column diameter, column irregularity degree. However, under the CCWLP, the primary sensitive variables regarding the MCEI contain rock mass restraint state, column irregularity degree, joint mechanical property. Additionally, the corresponding fitting models provide theoretical underpinnings for guiding the monitoring, enhancement, functioning, and servicing of CJB project undertakings.

• The Potential of Wood Ash to Be Used as a Supplementary Cementitious Material in Cement Mortars
  Lescinskis, O. et al
  Buildings, VOl 15, No 9, Art No. 1507 (Apr 2025)
  This study explores the application of wood ash (WA) as a partial replacement for PC in mortar. Three pre-treatment methods were applied to WA to enhance its reactivity, and it was then incorporated into mortar at two different substitution levels of 10 and 30%. Tests on compressive and flexural strength were conducted on the hardened mortar samples. All hardened mortar samples containing WA showed a decrease in mechanical properties compared to the reference sample without WA. The highest compressive and flexural strength of the samples with WA were observed for those containing 10% of sieved and slaked WA. The compressive and flexural strength of these samples after 28 days were 56 and 9 MPa, respectively, whereas those of the reference samples were 62 and 10 MPa, respectively. Based on the results, the best-performing samples on the compressive test underwent additional testing for freeze-thaw resistance to assess their durability. The mass loss of the reference sample and that with 10% of sieved and slaked WA after 56 freeze-thaw cycles was 11,800 and 13,800 g/m², respectively. The findings revealed that increasing the proportion of WA typically led to a decline in the mechanical properties of mortar compared to conventional mixtures. However, with appropriate pre-treatment techniques, the quality and performance of mortar containing WA were significantly improved, demonstrating its potential as a sustainable alternative in reducing the carbon footprint of PC production.

• Mechanical and microstructural properties of glass powder-modified recycled brick-concrete aggregate concrete
  Zhao, Y. et al
  Case Studies in Construction Materials, Vol 22, Art No. e04720 (Jul 2025)
  In order to achieve a better recycling of construction waste and explore the mechanical properties of concrete after incorporating multiple types of construction waste, this paper uses discarded concrete as recycled concrete aggregate (RCA), waste clay bricks as recycled fine brick aggregate (RFBA), and waste glass powder (GP) as an auxiliary cementitious material. Taking fully into account the modification effect of GP on the mortar matrix, a new type of green recycled concrete, namely GP modified Recycled Brick-Concrete Aggregate Concrete (GBCC), is prepared. Through a four-factor, four-level orthogonal experimental design combined with microstructural analyses (XRD, SEM, EDS, MIP), the mechanical properties and synergistic mechanisms of GBCC were systematically investigated. Results demonstrate that under the optimal mix ratio (15 % RCA, 40 % RFBA, 10 % GP, and water-binder ratio of 0.48), the 28-day cube compressive strength of GBCC reaches 39.2 MPa (equivalent to 100 % of C30 concrete), while the axial compressive strength and splitting tensile strength are 29.8 MPa and 2.72 MPa, respectively, meeting the design requirements of C30 concrete. Notably, at 40 % RFBA replacement, GBCC achieves over 90 % of the compressive strength of conventional C30 concrete. Microscopic analysis indicated that C-(A)-S-H gels formed by GP and RFBA reduced the total porosity by approximately 18 % (MIP test) and increased the proportion of harmless pores (<20 nm) to 25 similar to 28 %, effectively refining the pore structure. SEM-EDS observations revealed dense gel filling at the interfacial transition zone, with the Ca/Si ratio of the gel reduced to 0.29, significantly enhancing interfacial bonding. This study pioneers the efficient co-utilization of RCA, RFBA, and GP, and for the first time integrates SEM-EDS microstructural characterization with molecular chemical analysis to elucidate the formation mechanisms of gels.