Journal of building engineering最新文献

The construction industry continuously seeks sustainable alternatives as primary building materials to mitigate environmental impacts and achieve sustainable development. In this study, efforts are been made to develop and test the performance of geopolymer bricks with recycled brick waste (RBW) as a precursor material in the geopolymer. The main objective of the present study is to recycle and reutilize brick wastes from Construction and Demolition (C&D) waste and assess their physico-mechanical, brick-bond strength, and durability properties of recycled brick waste-based geopolymer bricks (RBWB). The trial mix had been prepared using the Taguchi L9 (3³) Orthogonal Array design; three factors and three levels were considered, Molarity (M) 8–12, Alkaline Solution Ratio (ASR) 1.5–2.5, and Curing Temperature (CT) 40–60 $°C$. Statistical analysis of variance (ANOVA) and multi-response optimization were conducted to identify optimal parameters. Prediction analysis and confirmation experiments were performed and validated within a 95 % confidence interval (CI). According to multi-response analysis, the optimal parameters for enhancing the performances of bricks were 10M, 2.5ASR, and 60 °C CT. RBWB showed only a 3.1%–5.87 % reduction in compressive strength at 400 $°C$ and 7.1%–8% at 1000 $°C$, indicating that they are highly thermally stable and can be suitably used for high-temperature applications. The weight and compressive strength reductions of RBWB in the range of 3.1%–9.2 % and 3.1%–35.73 %, respectively, were recorded after exposure to a solution of 5 % H₂SO₄ for 7–180 days. Further, the exposure of RBWB to a 5 % Na₂SO₄ solution resulted in weight change from 1.4 % to −1.1 % and compressive strength from 2.74 % to −13.2 % for 180 days. These results further reveal RBWB as a viable and sustainable substitute for traditional bricks, offering significant environmental benefits with improved characteristics for building applications.

Public toilets are locations to shelter and spread viruses because of the high traffic flow of people. Exposure to virus-carrying aerosol particles is a major way of spreading respiratory disease. This paper focuses on the distribution of human-exhaled aerosols in the toilet. The distribution and temporal variations of aerosol particles within toilet cubicles were investigated through numerical simulation. The percentage of suspended, deposited, and escaped particles was 28.43 %, 21.06 %, and 50.51 % under top evacuation. Higher volume ventilation and different ventilation modes were conducted to explore the efficient removal method. An infection risk assessment based on the Wells-Riley model was conducted and the back-side ventilation had the best performance. Random Forest, Light Gradient Boosting Machine (LightGBM), and Multilayer Perceptron (MLP) models are employed to reveal the connection between particle size, density, time, and suspension rate. Residual analysis is utilized to determine the best machine learning model. The Random Forest model has the best performance, with the residual obeying normal distribution. Its Mean Absolute Error (MAE) and Mean Squared Error (MSE) are the lowest, at 0.0249 and 0.0011. Finally, the SHapley Additive exPlanations (SHAP) value explores the effects of particle size and density on the spread of aerosols. With the study's results, more efficient ventilation or disinfection techniques can be adopted to lower the risk of infection and prevent the spread of respiratory disorders.

CFD is a valuable tool for assessing Wind-Driven Rain (WDR) loading, one of the most important environmental loads for façade design. The majority of previous studies on this topic have primarily concentrated on simple building configurations, i.e., stand-alone buildings. Hence, prior findings may not be applicable to consider the impact of upstream buildings in urban areas, which significantly alter wind flow field, consequently, change WDR loadings on downstream building facades compared to the stand-alone building. Part A: four different steady-state RANS models (i.e., standard $k-\omega$, realizable $k-\epsilon$, RNG $k-\epsilon$, and standard $k-\epsilon$) coupled with the Eulerian Multiphase (EM) technique (RANS-EM) are compared and implemented using OpenFOAM-7. These models are validated and verified based on wind-tunnel and field measurement data obtained from the literature for a six-story mid-rise residential building located in an urban area in Vancouver, Canada. The study considers 13 distinct rainfall events, for the test building with/without overhangs. All four RANS models are deemed suitable for modeling WDR in urban areas, while the steady-state standard k-ω RANS-EM approach without incorporating turbulent dispersion showing slightly better performance, thus utilized for the reminder of the study. Part B: a sensitivity analysis is presented on how the upstream buildings influence the WDR loading on a downstream building, denoted as Obstruction Factor. A comparison between the CFD and ISO semi-empirical model shows significant discrepancies, potentially reaching up to factors of 5. Thus, updated Obstruction Factors are suggested to enhance the ISO model for more accurate estimation of WDR loads.

This paper presents a pilot study investigating the manufacturing process and properties of novel bio-based materials intended for insulation in building walls. Panels with a thickness of $20\mathrm{mm}$ were fabricated by mixing grass, water, and potato starch, followed by pressing and heating. Various combinations of coarse, medium, and fine Cynodon dactylon particles, along with three starch-to-water ratios (1:3, 1:4, and 1:5), were explored. The panels underwent characterization in terms of density, quasi-static compressive behavior, quasi-static flexural strength, high-strain compressive strength, sound absorption coefficient, thermal conductivity, and degradation under external environmental conditions. Results indicate that density is influenced by particle size and micro-structure arrangement, while static compressive stiffness is affected by both particle size and starch-to-water ratio. The panels exhibit low damage and effective dissipation under compressive high-strain deformation. The sound absorption test reveals superior capabilities (Class III of ISO 11654:1997) due to the porous structure. Thermal conductivity values ranging from 0.075 to 0.092 $W{m}^{-1}{K}^{-1}$ support the application as a thermal insulation material. Furthermore, the study demonstrates that reducing particle size and increasing starch-to-water ratio enhance mechanical properties while slightly diminishing acoustic and thermal performance. Under external environmental conditions, the panels lasted more than 1 months, demonstrating acceptable resistance to rain and humidity. Comparative analysis with other natural bio-based materials shows that Cynodon dactylon-starch panels possess similar or superior physical, mechanical, acoustic, and thermal characteristics. These findings suggest that these panels could serve as environmentally friendly alternatives in the insulation materials sector within the building industry.

The demand for lithium batteries in electronic products is constantly increasing, and a large amount of solid waste is generated during the production of lithium batteries. These wastes are not only harmful to the environment, but more importantly, the cost of processing the wastes is very high. To reduce the harm caused by lithium slag waste and increase the chloride ion penetration resistance of concrete, this paper designs C20, C30, C40, and C60 concrete with lithium slag contents of 0 %, 10 %, 20 %, and 30 %. The effects of different lithium slag contents on the compressive strength, electric flux, and porosity of concrete specimens were studied. The study found that for C20, C40, and C60 concrete, the compressive strength decreases with the increase of lithium slag content. For C30 concrete, the compressive strength shows a trend of increasing first and then decreasing with the increase of lithium slag content. For the electric flux of C20, C30, and C40 concrete, it shows a trend of decreasing with the increase of lithium slag content. For the porosity of C20, C30, and C40 concrete, it shows a trend of first decreasing and then increasing with the increase of lithium slag content. Combining Fick's second law and the law of conservation of mass, a chloride ion penetration model of lithium slag concrete under the action of different lithium slag contents was established. The results show that the penetration performance of chloride ions in the immersion environment conforms to the experimental law; the maximum error between the simulation results and the test results is at 360 min of C30-30LS, and the error value is 14.49 %.

Alkali-activated lunar regolith (AALR) has become one of the most promising lunar building materials, offering the potential to support the construction of large-scale lunar structures. This paper presents a comprehensive experimental investigation on the fresh properties, physical properties, mechanical performance and microstructural characteristics of alkali-activated lunar regolith simulant (AALRS) considering the effects of lunar environments (high-temperature, vacuum and coupled high-temperature and vacuum), alkaline activators (sodium hydroxide and sodium silicate) and curing age. The results show that AALRS under high-temperature environment exhibits higher strength while the strength development is limited. However, AALRS under vacuum environment exhibits lower strength but the strength increases as the curing time increases. In terms of pore structure, the volume fractions of macro voids for SH-V and SS-V account for up to 50.94 % and 63.64 %, respectively, which are 12.22 % and 7.95 % higher than those of SH-H and SS-H. Regarding the impact of coupled high-temperature and vacuum environment, the compressive strength of SH-HV-7 is reduced by 47.8 % compared to that of SH-H-7, while the compressive strength of SS-HV-7 exhibits a 57.2 % increase over that of SS-H-7. The sodium hydroxide-activated (SH-activated) system and sodium silicate-activated (SS-activated) system demonstrate fundamentally intrinsic differences in terms of reaction products, structure build-up and pore structure. The positive optimization mechanism and reverse degradation effect of vacuum environment on the performance of AALRS paste were revealed. Finally, the evolution of structural characteristics of AALRS paste under different environments was elucidated.

Engineered geopolymer composites (EGC) have garnered significant attention from researchers as a new environmentally friendly building material with superior tensile properties, impact resistance, and high-temperature resistance. This study focuses on the investigation of the dynamic mechanical properties of a hybrid fiber reinforced lightweight EGC containing ceramsite (LW-EGC) after exposure to elevated temperatures and multiple impacts. The effects of temperature, steel fiber content, and ceramsite types were taken into consideration. The analysis encompassed multiple impact stress-strain curves, dynamic peak stress and strain evolution, energy absorption, damage evolution, damage morphology, and microstructure changes following exposure to elevated temperatures. The experimental results revealed a significant decrease in the number of impacts endured by LW-EGC-M as the temperature increased. After 200 °C, the LW-EGC-M experienced 15 impacts, while after 800 °C, it only endured 2 impacts. Both cumulative energy absorption and cumulative damage of LW-EGC exhibited an exponential growth pattern with an increasing number of impacts. Microstructural analysis unveiled the emergence of a new nepheline phase after exposure to elevated temperatures, while the calcite in the matrix demonstrated gradual decomposition. Moreover, elevated temperatures led to a decreased Si/Al ratio in the matrix. The complete melting of PVA fibers after exposure to elevated temperatures resulted in the production of numerous interconnected pores in the matrix, leading to a decline in the mechanical strength of LW-EGC. This phenomenon also contributed to the reduction of internal pore pressures and the release of local vapor pressure generated by elevated temperatures.

The bimetallic steel bar (BSB) is a new type of corrosion-resistant reinforcement material composed of carbon steel and stainless steel, which can effectively improve the durability of structures. Reinforced concrete structural strength depends on the bond between steel bars and concrete. This mechanism can be compromised after exposure to a fire, but it has been less considered in research, and is not addressed in concrete design codes. To evaluate the residual bearing capacity of BSB reinforced concrete structures after a fire, it is necessary to clarify the bonding performance between BSBs and concrete after exposure to high temperatures. In this study, 45 BSB-seawater concrete (BSBSC) pull-out specimens were prepared, and the bonding performance of BSBSC after high temperature was studied by heating treatment and pull-out tests. The results showed that the BSBSCs changed from bluish-gray to grayish-yellow with the increase in heat treatment temperature. After exposure to 400 °C, cracks appeared on the surface of BSBSCs. As the heat treatment temperature increased, the slope of the rising and descending stages for the bond stress-strain curve decreased gradually. In addition, as the thickness of the concrete cover increased, the bonding strength of BSBSCs also improved. The higher the heat treatment temperature, the less significant the improvement effect. Based on test results, a predictive model for the bonding performance characteristics of BSBSCs after high temperature was proposed, and a constitutive model for bonding stress-slip relationship was established.

This study aims to investigate the specimen size effect of compressive strength in 3D printed concrete containing coarse aggregate (3DPCA). Firstly, we compare the specimen size effect of compressive strength in mold-cast concrete (CC) and 3DPCA. Through X-CT scans and image analysis, the underlying mechanisms of this specimen size effect in 3DPCA are revealed. The results indicate that 3DPCA exhibits a less pronounced specimen size effect on compressive strength when loaded along the Z direction compared to CC, due to the presence of interlayer weak zones that mitigate the influence of size variations. Specifically, when the water-binder ratio varies between 0.3 and 0.5, the size coefficient of printed sample is reduced by 0.01–0.07 compared to cast sample. Similarly, variations in coarse aggregate content result in a size coefficient for printed sample that is 0.01–0.05 lower than cast sample. Higher porosity increases the specimen size effect of 3DPCA, but good printing quality can mitigate this influence. A modified Weibull model integrating water-binder ratio and coarse aggregate content was proposed, providing precise predictions of the specimen size effect on 3DPCA's compressive strength, with a correlation coefficient exceeding 93 %.

Phase change materials (PCMs) offer significant potential for building energy management, but are limited by poor heat transfer rates. This study investigates charging/discharging performance optimization of a shell-and-multi-tube heat storage system using high-enthalpy PCM (RT70HC) with differentiated fin configurations. The key novelty of the work lies in its thorough examination of geometric mutations within this system, specifically targeting building energy applications. A validated numerical model simulated charging and discharging processes, comparing finned and plain tube designs. Key performance metrics analyzed here include melting times, heat storage rates, phase transition velocities, and temperature profiles. Results reveal the finned tube design enables a 268 % higher heat storage rate (1421 W vs 387 W) and 74.5 % faster melting time (196 min vs 770 min) compared to the plain tube. Detailed analysis of the 10-h charging process exposes intricate thermal stratification patterns. The inclusion of dedicated discharging finned tubes significantly enhances heat distribution. During the 20-h discharge, heat transfer rates decrease from 2000 W to 100 W, providing crucial insights into solidification dynamics. These quantified findings highlight the potential of optimized finned tube arrays to substantially improve thermal performance of shell-and-multi-tube heat storage systems for building energy applications.