Evaluation of the Performance and Microstructure of Ecofriendly Construction Bricks Made with Fly Ash and Residual Rice Husk Ash

This research presents the engineering performance and the microstructural characterization of ecofriendly construction bricks that were produced using a binder material made from a mixture of class-F fly ash (FA) and residual rice husk ash (RHA). Unground rice husk ash (URHA) was used as a partial fine aggregate substitute (0–40%). The solid bricks of 220 × 105 × 60 mm in size were prepared by mixing FA and RHA with an alkaline solution and fine aggregates, formed by compressing the mixture in a steel mold under 35 MPa of forming pressure, and then cured at 35°C and 50% relative humidity until the required testing ages. The tests of compressive strength, water absorption, and bulk density were conducted in accordance with relevant Vietnamese standards in order to estimate the effect of the URHA content on the engineering performance of the hardened bricks. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) were performed to determine the microstructure and the phase composition of the brick samples. The results show that properties of these bricks conformed to relevant Vietnamese standards. Therefore, FA and RHA are potential candidate materials for producing ecofriendly construction bricks using geopolymerization technology

Improving Corrosion Resistance and Prolonging the Service Life of High-performance Concrete Structures Using Fly Ash and Ground Granulated Blast-furnace Slag

This study investigates the impact of ground granulate blast-furnace slag (GGBFS) and fly ash (FA) on both the corrosion resistance of steel reinforcement, assessed through the accelerated macrocell corrosion test (AMCT), and the durability characteristics of high-performance concrete (HPC). Additionally, the study encompasses an analysis of various concrete properties, including the pH of fresh concrete mixtures as well as water absorption, chloride permeability, and surface resistivity (SR) in hardened concrete specimens. Microstructure analysis on HPC specimens as well as the service life prediction of RCS were also performed in this study. Test results show that the HPC incorporating 35% GGBFS or 35% GGBFS + 20% FA as cement replacement resulted in a lowered pH of fresh mixtures while water absorption and chloride permeability of these specimens increased significantly. In addition, the incorporation of 35% GGBFS or 35% GGBFS + 20% FA concurrently enhanced the SR of HPC specimens. Moreover, these HPC specimens exhibited better corrosion resistance ability as their respective AMCT values were about 1.54 and 1.45 times higher than that of the control specimen. Further, the research highlighted a substantial extension in the corrosion initiation time of concrete structures employing 35% GGBFS or 35% GGBFS + 20% FA, about 3 and 6 times longer than the HPC without GGBFA and FA, respectively. The experimental results, confirmed by the substantial microstructural enhancement in the HPC containing GGBFS and FA, also demonstrated a close interplay between durability and other concrete properties such as water absorption, chloride permeability, and SR

An Early-age Evaluation of Thermal Cracking Index of Heavy Concrete Applying for Airport Pavement

Industrial waste management has been an integral part of many countries in the world, including in Vietnam. In which, bottom ash (BA) has been used as a pozzolanic additive in compositions of the heavy concrete applying for airport concrete pavement (ACP), which allows reducing the hydration heat, the cost, and the thermal cracking of the concrete during the construction process. The purpose of this study is to summarize the experimental laboratory results of the heavy concrete samples containing 35 % BA sourced from a thermal power plant in Vietnam. The mechanical and thermal properties of the heavy concrete samples were determined at different curing ages. Besides, the heat of cement hydration during the preparation of the heavy concrete in the laboratory was measured using a "TAM AIR" isothermal calorimeter. Moreover, the Midas civil computer software based on the finite element method was used to analyze the temperature field and thermal cracking index of the ACP at the early ages. As the results, the heavy concrete had the respective thermal conductivity and the average of specific heat of 1.1 W/(m.°C) and 878.35 J/(kg.°C). Moreover, the value of thermal cracking index indicates that no cracking occurred on the ACP at the early ages. Furthermore, the results of the present study can be considered as a useful reference source for future projects that are associated with the construction of the ACP

Performance Evaluation of Pre-foamed Ultra-lightweight Composites Incorporating Various Proportions of Slag

This research examines the feasibility of using a mixture of cement, fly ash, ground granulated blast-furnace slag, and river sand to manufacture pre-foamed ultra-lightweight composite (PULC). Four PULC specimens were prepared with the substitution of cement by slag at 0, 10, 20, and 30 % by weight. The engineering properties of PULC samples were evaluated through the tests of compressive strength, dry density, water absorption, drying shrinkage, and thermal conductivity. Besides, numerical simulation of heat transfer through the PULC brick wall and the microstructure observation were performed. The performance of PULC mixtures incorporating slag showed higher effectiveness than merely used cement. The substitution of 20 % cement by slag resulted in the highest compressive strength as well as the lowest value of water absorption of the PULC samples. Also, the efficiency of the thermal conductivity was in inverse proportion with the density of PULC specimens and it was right for water absorption and drying shrinkage. Moreover, numerical simulations showed that the temperature distribution values in the wall made by PULC material were smaller than in the wall made by the normal clay brick in the same position. Besides, the microstructure analysis revealed that the existence of slag generated a more dense structure of PULC samples with the addition of calcium-silicate-hydrate (C-S-H) gel, especially for a mix containing 20 % slag. Thus, the results of this study further demonstrated that a 20 % slag was the optimal content for the good engineering properties of the PULC samples

A Modified Reactive Powder Concrete Made with Fly Ash and River Sand: An Assessment on Engineering Properties and Microstructure

Containing a high quantity of both fine powders and steel fiber makes reactive powder concrete (RPC) a unique kind of ultra-high strength concrete. However, the cost of manufacture, shrinkage, and hydration heat are increased when silica fume and cement are used in significant amounts. To mitigate these negative consequences and the environmental impact, this study assessed the use of fly ash (FA) with high volume combined with natural-fine river sand (NFRS) in the manufacturing of RPC. FA was utilized to partially substitute cement at 0, 20, 40, and 60 wt% in RPC mixtures that had a set water/binder ratio of 0.2. Thermal conductivity, porosity, water absorption, and compressive strength tests were performed. Furthermore, RPC's microstructure was examined using a scanning electron microscope (SEM). This study also included a cost and global warming potential analysis of RPC production. Test results indicated that a modified RPC with a 60 MPa compressive strength value could be created by using NFRS and a large amount of FA. In comparison to the reference mixture, a higher compressive strength, reduced water absorption, and lesser porosity were observed in RPC when the FA replacement amount was less than 40%. Many FA particles did not engage in the hydration reaction when the FA replacement level was more than 40%, which had a detrimental impact on the RPC's characteristics. In general, using FA to produce RPC has certain benefits for the economy and the environment. It is recommended that 40% of FA be used in actual practice

Effect of Microwave Curing on the Performance of High-volume Fly Ash Concrete

Concrete curing significantly impacts mechanical properties and durability, yet traditional methods face efficiency challenges. Microwave curing (MC) offers a promising alternative, providing rapid and uniform concrete curing. However, fully understanding the impact of MC on concrete performance, particularly in high-volume fly ash concrete (HVFC), remains a research gap. This study addresses this gap by investigating the effect of MC on key properties of HVFC, including compressive strength, drying shrinkage, chloride ion penetration, and resistance to sulfate attack. Concrete specimens underwent MC at varied energies (200–1000 W) and durations (10–30 min) to evaluate their mechanical and durability characteristics. Results show that MC significantly boosts early-stage concrete strength, notably at high applied energy. The specimen cured at 1000 W for 30 min (MC1000-30) achieved the highest 1-day strength of 23.68 MPa. However, the normal curing specimen exhibited the highest strength of 32.07 MPa at 28 days while the strength value of the MC1000-30 specimen declined to 20.25 MPa, indicating a 36.85% decrease. Although declining strength was observed after 28 days, the MC1000-30 specimen demonstrated improved durability with significantly reduced drying shrinkage (by 83.12%) and chloride ion penetration (by 31.6%). The study underscores the feasibility of utilizing MC for HVFC as it demonstrated significant enhancements in both early-stage concrete strength and durability at a later stage. Careful parameter optimization can ensure sustained effectiveness over time, offering a viable alternative to traditional curing methods

Experimental Evaluation on Engineering Properties and Drying Shrinkage of No-Cement Mortar Produced by Alkaline Activation of Fly Ash-Slag Mixtures

Turning locally available industrial by-products such as fly ash (FA) and ground granulated blast-furnace slag (GGBFS) into cement-free materials has been recently received much attention from researchers. Following this trend, the present study produces alkali-activated mortars (AAFS) using a mixture of FA and GGBFS as a precursor activated by an alkaline solution of sodium hydroxide and sodium silicate. Five AAFS mixtures were prepared for the evaluation of engineering properties, drying shrinkage, and microstructural observation using various FA/GGBFS ratios of 30/70, 40/60, 50/50, 60/40, and 70/30. The experimental results show that the proportions of FA and GGBFS significantly affected the performance of the AAFS in both fresh and hardened stages. Higher GGBFS content resulted in a reduction in flowability and higher fresh unit weight. The GGBFS-rich AAFS developed its mechanical strength faster than the FA-rich AAFS and the strength gain of the GGBFS-rich AAFS was significantly higher than that of the cement-based mortar at only 1-day old, confirming the applicability of AAFS as a structural material and its potential to replace cement in the no-cement mortar production. The AAFS sample incorporating 60% of GGBFS and 40% of FA exhibited the highest strength, lowest water absorption, and less drying shrinkage with a relatively dense microstructure among the AAFS samples

Evaluation of mechanical strength and durability characteristics of eco-friendly mortar with cementitious additives

The mechanical strength and durability of eco-friendly mortars used in the repair of marine concrete structures exposed to freshwater and seawater environments were evaluated in this paper. The eco-friendly mortar samples were produced using various ratios of fly ash (FA), ground granulated blast-furnace slag (GGBFS), and silica fume (SF) as cementitious materials. Seven mixtures of eco-friendly mortars, including a control mixture; three mixtures with respective substitutions of GGBFS for Portland cement of 10, 20, and 30% by cement mass; and three mixtures with respective additions of SF of 5, 10, and 15% by total binder mass, were used to produce the samples. Tests, including compressive strength, flexural strength, ultrasonic pulse velocity (UPV), electrical surface resistivity (ESR), rapid chloride ion penetration (RCP), thermal conductivity (TC), and microstructure analysis, were conducted to determine the mechanical strength and durability values of the samples. The experimental results show that replacing Portland cement with GGBFS negatively affected the properties of the mortars by reducing the mechanical strength, UPV, ESR, and TC while increasing the RCP in the samples. Also, adding an appropriate amount of SF could improve the mechanical strength and durability characteristics of the eco-friendly mortars. As a result, the mortar sample containing 30% GGBFS and 10% SF earned compressive and flexural strength values of approximately 49.2 and 13.8 MPa, respectively, at 56 days of curing age. Mortar samples with UPV values >3660 m/s were identified as "high quality". The corrosion resistance of all of the samples was found to be high, particularly in chloride-contaminated environments, due to relatively low (1000 - 2000 Coulombs) RCP values. The best overall performance was recorded for the sample containing 30% GGBFS and 10% SF.Web of Science24455254

Assessing the readiness for electric vehicle adoption: A study of clean energy infrastructure and transformation in Ho Chi Minh City

Zero-emission transportation is the ultimate goal for many countries around the world. The decreasing availability of fossil fuels and global climate change have compelled governments to take immediate action on energy transformation. This study investigates public perception of electric vehicle (EV) adoption and the concerns that people may have regarding this transformation, including commuting and travel, willingness to switch to EVs, decision-making criteria, and charging infrastructure. Results indicate that 51.16 % of survey respondents trend towards switching to EVs within the next 5 years, while others are satisfied with their current motorcycles. The investigation identified the most significant concerns affecting clean vehicle transformation, including battery performance (41.03 %), accessibility of charging infrastructure (20.36 %), and maintenance costs (18.9 %). Moving towards a net-zero emissions future, plug-in electric vehicles represent the best alternative for transportation, offering significant environmental benefits. However, the transition to EVs faces practical challenges due to obstacles in charging infrastructure, battery-related issues, initial purchase costs, and other factors. Additionally, the study identifies promotional services and tax incentives as potential levers to boost EV adoption

Spatiotemporal evolution of SARS-CoV-2 Alpha and Delta variants during large nationwide outbreak of COVID-19, Vietnam, 2021

We analyzed 1,303 SARS-CoV-2 whole-genome sequences from Vietnam, and found the Alpha and Delta variants were responsible for a large nationwide outbreak of COVID-19 in 2021. The Delta variant was confined to the AY.57 lineage and caused >1.7 million infections and >32,000 deaths. Viral transmission was strongly affected by nonpharmaceutical interventions