Performance of Sustainable and Low-Carbon Cementitious Composites under Aggressive Environmental Conditions

University of Technology Sydney. Faculty of Engineering and Information Technology.Pozzolanic materials, like fly ash (FA) and ground granulated blast-furnace slag (GGBFS), are considered promising binder materials as they are industrial by-products, helping to decrease ordinary Portland cement (OPC) demands and further lessen greenhouse emissions. Therefore, the total or partial replacement of pozzolanic materials for OPC to fabricate sustainable and low-carbon cementitious composites (LCC) has garnered extensive attention for providing enormous environmental benefits for infrastructure and offshore construction. In addition, the durability of LCC under aggressive environmental deterioration (such as fire, acid, and marine environments) is a progressively significant property for concrete structures due to the increasing demand for extended service life and less maintenance. For total pozzolanic materials replacement for OPC, this work has estimated the performance of fly ash/GGBFS-based geopolymer under combined mechanical loads and aggressive environmental conditions (fire and sulfuric acid attack). For partial pozzolanic materials replacement for OPC, this work has also assessed the performance of cementitious composites with GGBFS under the marine environment. The synergistic effects of seawater and undesalted sea sand on the properties of cementitious composites have been firstly analyzed. And then, the fire resistance of GGBFS-based cementitious composites with seawater and undesalted sea sand has been examined. Finally, the chloride-binding capacity of GGBFS-based cementitious composites in seawater and chloride solutions has also been observed. The results showed that fly ash/GGBFS-based geopolymer with 20 wt.% GGBFS could be regarded as a remarkable alternative for OPC to achieve extraordinary fire resistance by considering the strength and compatibility variations. The fly ash/GGBFS-based geopolymer with cyclic preloading was also confirmed to exhibit less severe performance deterioration even after 18-month exposure to sulfuric acid attacks. In addition, the results illustrated that the chloride, sulphate, and magnesium ions in seawater and/or undesalted sea sand were assessed to lead to the phase changes of cementitious composites, including the formation of Friedel’s/Kuzel’s salts, magnesium hydroxide, and magnesium silicate hydrate, etc. The addition of 30 wt.% GGBFS and 1.0 wt.% glass fibers was also supposed to improve cementitious the fire resistance of cementitious composite with seawater and undesalted sea sand. Additionally, the cementitious composite with 30 wt.% GGBFS and 1.0 wt.% NS having the highest value of chloride-binding ratio was expected to enhance the long-term chloride-binding capacity. Overall, this thesis improves the current understanding of the performance of low-carbon cementitious composites under aggressive environmental environments to produce more reliable data and ensure the reliability and sustainability of LCC-based construction

Property degradation of seawater sea sand cementitious mortar with GGBFS and glass fiber subjected to elevated temperatures

Effects of ground granulated blast-furnace slag (GGBFS) and glass fiber on the property degradation of seawater sea sand mortar (FSSM) after elevated temperature exposure were investigated in this study. The physical properties and mechanical strength of FSSM were compared with that of cementitious mortar prepared with demineralized water and river sand (FRRM). The results showed that when the mortars were exposed to normal temperature, the compressive strength of FSSM was higher than that of FRRM. GGBFS increased both the compressive and flexural strengths of FSSM, while glass fiber increased the flexural strength but slightly decreased the compressive strength. The maximum flexural strength of FSSM was achieved with 1 wt.% glass fiber and 30% GGBFS. After exposed to temperatures of 200 °C and 400 °C, the flexural and compressive strength losses of FSSM were lower than that of the corresponding FRRM, while the FSSM with glass fiber exhibited more compressive strength loss but less flexural strength loss compared to the FRRM. Additionally, GGBFS could densify the microstructure of FSSM, and decrease the losses of flexural and compressive strength after exposed to elevated temperatures. The calcium aluminosilicate hydrate (C–A–S–H) gels with higher ratios of Si/Ca and Al/Ca in the FSSM with GGBFS were significantly more stable at the temperature of 700 °C compared to the calcium silicate hydrate (C–S–H) gels with lower ratios of Si/Ca and Al/Ca in the FRRM or FSSM without GGBFS. Therefore, it can be included that the high temperature or fire resistance of FSSM can be improved by glass fibers and GGBFS.This article is published as Qu, Fulin, Wengui Li, Zhuo Tang, and Kejin Wang. "Property degradation of seawater sea sand cementitious mortar with GGBFS and glass fiber subjected to elevated temperatures." Journal of Materials Research and Technology 13 (2021): 366-384. DOI: 10.1016/j.jmrt.2021.04.068. Copyright 2021 The Author(s). Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). Posted with permission

Efficiency Analysis of Electric Vehicles with AMT and Dual-Motor Systems

With the rapid development of automobiles, energy shortages and environmental pollution have become a growing concern. In order to decrease the energy consumption of electric vehicles (EVs), this study aims to improve EV efficiency with AMT and dual-motor systems. Firstly, the paper establishes an Automated Manual Transmission (AMT) model for EVs, which is then simulated using MATLAB R2022a software. In order to eliminate the impact of gear ratio selection, the genetic algorithm is used to optimize the AMT gear ratios. Meanwhile, a dual-motor EV model is constructed, and three different torque distribution schemes are simulated and analyzed. The results indicate that due to the elongation of the energy transmission chain in AMT-equipped EVs, energy losses increase, leading to some improvement in optimized power consumption. However, these EVs remain inferior to those with only a single-stage main reducer. The study also found that the torque distribution based on optimal efficiency further improves results

Anti-cracking and shrinkage performance of sustainable concrete incorporating high-volume natural pozzolans: A case design for high-speed railway concrete slab tracks

This investigation was conducted to examine the effect of the designed composite agent (DCA) on the shrinkage performance of the concrete high-volume natural pozzolans (PHVNC). Based on an economic-cost analysis, it was determined that natural pozzolans (NP) were a suitable replacement for fly ash (FA) in the production of sustainable concrete for high-speed railway concrete slab track design. The results confirmed that the inclusion of DCA effectively improved the early-age shrinkage performance of PHVNC with 30% or 50% NP content. As a result, the concrete containing high-volume NP and DCA (PHVNDC) exhibited a smaller crack density compared to PHVNC, and even outperformed concrete with a high volume of FA (PHVFC). In terms of the effect of DCA on the drying shrinkage performance of mixes containing NP, a similar trend was observed, where the mixes that included both NP and DCA exhibited lower levels of dry shrinkage and mass loss at 28 days compared to mixes with either NP or FA. The results from phase transformation and microstructure analysis further indicated that adding DCA can enhance the mechanical and shrinkage performance of the mixes containing high-volume NP. This enhancement is attributed to the optimization of the hydration reaction rate, increased production of hydration products, and an overall improvement in the microstructure performance of the mixes with NP. Hence, DCA can serve as a valuable support in preserving the characteristics of NP-based mixtures, making it a valuable discovery for implementing high-volume NP in practical engineering projects with abundant NP resources

Research on Optimization of Intelligent Driving Vehicle Path Tracking Control Strategy Based on Backpropagation Neural Network

To enhance path tracking precision in intelligent vehicles, this study proposes a lateral–longitudinal control strategy optimized with a Backpropagation (BP) neural network. The strategy employs the BP neural network to dynamically adjust prediction and control time-domain parameters within an established Model Predictive Control (MPC) framework, effectively computing real-time front-wheel steering angles for lateral control. Simultaneously, it integrates an incremental Proportional–Integral–Derivative (PID) approach with a meticulously designed acceleration–deceleration strategy for accurate and stable longitudinal speed tracking. The strategy’s efficiency and superior performance are validated through a comprehensive CarSim(2020)/Simulink(2020b) simulation, demonstrating that the proposed controller adeptly modulates control parameters to adapt to various road adhesion coefficients and vehicle speeds. This adaptability significantly improves tracking and driving dynamics, thereby enhancing accuracy, safety, stability, and real-time responsiveness in the intelligent vehicle tracking control system

Phase transformation and microstructure of in-situ concrete after 20-year exposure to harsh mining environment: A case study

The phase transformations and microstructural properties of a drilled cylinder specimen from a C40 concrete dam used for mining wastewater disposal were evaluated in this study, covering a span of up to 20 years. Various analysis methods, including PT, ICP-MS, XRD, FTIR, TGA, MIP, and SEM-EDS, were employed to assess the performance of powder samples obtained through layer-by-layer grinding. The results obtained from XRD, FTIR, and TGA analyses indicated that the presence of calcite in all ground powder samples, suggesting that carbonation can occur in all layers, even including the inner layers. Moreover, the MIP and SEM-EDS results illustrated that the microstructural properties of the concrete could be influenced by phase transformations induced by various ions present in the mining wastewater, resulting in increased porosity and looser interfacial transition zones (ITZs) in the sample closer to the outer layer. The PT results confirmed the penetration of chloride into the concrete, although the relative chloride content decreased with the increasing depth of the layers. It was observed through TGA analysis that a portion of the chloride ions could attribute to the formation of Friedel’s salts, derived from ettringite or calcium aluminate monosulfate. Additionally, SEM-EDS examination revealed that some chloride ions could bind to the C-S-H gels. The presence of different ions, particularly magnesium ions in the mining wastewater could lead to decalcification of the hydrated gels. These research findings provide significant support for the safety assessment of the concrete structure exposed to mining environments

Durability deterioration of concrete under marine environment from material to structure : a critical review

Durability deterioration of cementitious concrete and reinforced concrete (RC) is critical to durability, safety, and sustainability of infrastructures, especially for offshore concrete structures under marine environment. In this paper, the effects of marine environment on the deterioration mechanism, performance, and durability of concrete materials and structures are systematically reviewed. For the deterioration mechanism, the effect of various chemicals in seawater and different marine exposure zones on the cementitious concrete and reinforced concrete is firstly analyzed and compared. At material level, this paper discusses the characterizations of cementitious concrete, including compressive strength, chloride diffusion, carbonation depth, and pore structure. On the other hand, the performance of cementitious concrete with the addition of supplementary cementitious materials was also compared when exposed to marine environment. At structure level, the durability of RC structures, including beams and slabs and other elements with corrosion protection under marine environment is evaluated. This paper also assesses some cases studies of RC structures after many years of exposure to marine environment. Furthermore, prospectives are proposed for practical applications on concrete under marine environment. The conclusions are of great benefit to the researchers and engineers in the concrete-related industry who aim to develop durable and sustainable concrete infrastructures under marine environment

Investigation on early-age hydration, mechanical properties and microstructure of seawater sea sand cement mortar

Using seawater for concrete manufacturing promisingly provides significant economical and environmental benefits. In this study, ordinary Portland cement (OPC) hydration in distilled water and seawater and the corresponding evolution of solid phases was investigated by heat evolution, hydrated phase, hydration kinetics, and microstructure characterization. The results show that seawater can promote the early hydration of tricalcium silicate (C3S) during the hydration acceleration period. The hydrated phase assemblage was affected by the dissolved ions in seawater. Friedel’s salt was detected as a specific hydration phase in seawater, which was formed by chemical combination between the aluminate ferrite monosulfate (AFm) phase and chloride ions. The monocarboaluminate can be converted into a stable phase as Friedel’s salt in the seawater, due to the reaction with chloride ions. Furthermore, the ettringite becomes more stable when coexists with Friedel’s salt than that with monocarboaluminate, and thus ettringite formed in seawater remains 67% higher than that formed in distilled water at the later curing age. Moreover, additional unhydrated cement and less amorphous calcium silicate hydrate (C-S-H) were formed in seawater, which might be responsible for the slightly lower compressive strength of cement mortar prepared by seawater and sea sand. A modeled evolution of the solid phase and pore solution have been established, which agrees well with the characteristics of the dissolution of mineral phase, precipitation of hydration products and changes of pore solution. The related results can provide an insight into the applications of seawater and sea sand concrete for marine infrastructures

Chloride-binding capacity of cement-GGBFS-nanosilica composites under seawater chloride-rich environment

The effects of granulated blast furnace slag (GGBFS) and nano-silica (NS) on the chloride-binding capacity of cement paste after 6-month exposure to seawater chloride-rich solutions were investigated in this paper. The pH, chloride-binding ratio (CBR), leaching behavior, and phase transformation were investigated by various experimental and analysis methods. Thermodynamic modeling was also used to study the phase assemblages for the Portland cement-GGBFS-NS composites exposed to the NaCl and MgCl2 solutions. It was found that for all cementitious composites, more chlorides were bounded in samples exposed to the salt solutions with sodium ions than that with magnesium ions. Proper additions of GGBFS and NS can enhance the chloride-binding capacity of cementitious composites. The results confirm that the addition of GGBFS can improve the chemical chloride-binding capacity because of the increased amount of chloroaluminate. The increased amount of hydrated gels in the cementitious composites with GGBFS also improved the physical chloride-binding capacity. The addition of NS increased the physical chloride-binding capacity due to the more formation of C-S-H/C-A-S-H gels, while the excessive addition of NS left less aluminum phase available for the formation of chloroaluminate, thus further decreased the chemical chloride-binding capacity. Magnesium ions in solutions increased the amount of chloride in the diffuse layer of C-S-H gels and hydrotalcite. The related results provide novel insight into the influences of GGBFS and NS on the chloride-binding capacity of cementitious composites under chloride-rich environments.This is a manuscript of an article published as Qu, Fulin, Wengui Li, Yipu Guo, Shishun Zhang, John L. Zhou, and Kejin Wang. "Chloride-binding capacity of cement-GGBFS-nanosilica composites under seawater chloride-rich environment." Construction and Building Materials 342 (2022): 127890. DOI: 10.1016/j.conbuildmat.2022.127890. Copyright 2022 Elsevier Ltd. Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). Posted with permission

The Role of Bainite in Wear and Friction Behavior of Austempered Ductile Iron

The austempered ductile iron was austenitized at 900 °C for 1 h and quenched in an isothermal quenching furnace at 380 °C and 280 °C, respectively. This paper aims to investigate the effects of bainite on wear resistance of austempered ductile iron (ADI) at different loads conditions. The micro-structure and phase composition of ADI was characterized and analyzed by metallographic microscope (OM), X-ray diffractometer (XRD) and scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS). The results showed that the volume fraction of retained austenite in ADI is reduced with the increase of austenitizing temperature. Meanwhile, the two kinds of ADI samples showed varied wear resistance when they were worn at different loads conditions. For wearing at a load of 25 N, the wear resistance of ADI mainly depends on matrix micro-hardness. Thus, ADI with lower bainite structure has higher hardness and leads to better wear resistance. When wearing at a load of 100 N, the increase of micro-hardness of upper bainite was significant. As a consequence, upper bainite showed superior friction and wear behavior. It was also found that the form of wear behavior of ADI changed from abrasive wear to fatigue delamination as the wear load increased from 25 N to 100 N according to the observation on worn surface