Dynamic Mechanical Properties and Microstructure of Graphene Oxide Nanosheets Reinforced Cement Composites

This paper presents an experimental investigation on the effect of uniformly dispersed graphene oxide (GO) nanosheets on dynamic mechanical properties of cement based composites prepared with recycled fine aggregate (RFA). Three different amounts of GO, 0.05%, 0.10%, and 0.20% in mass of cement, were used in the experiments. The visual inspections of GO nanosheets were also carried out after ultrasonication by transmission electron microscope (TEM) atomic force microscope (AFM), and Raman to characterize the dispersion effect of graphite oxide. Dynamic mechanical analyzer test showed that the maximum increased amount of loss factor and storage modulus, energy absorption was 125%, 53%, and 200% when compared to the control sample, respectively. The flexural and compressive strengths of GO-mortar increased up to 22% to 41.3% and 16.2% to 16.4% with 0.20 wt % GO at 14 and 28 days, respectively. However the workability decreased by 7.5% to 18.8% with 0.05% and 0.2% GO addition. Microstructural analysis with environmental scanning electron microscopy (ESEM)/backscattered mode (BSEM) showed that the GO-cement composites had a much denser structure and better crystallized hydration products, meanwhile mercury intrusion porosimetry (MIP) testing and image analysis demonstrated that the incorporation of GO in the composites can help in refining capillary pore structure and reducing the air voids content

Evaluation of Residual Flexural Behavior of Corroded Fiber-Reinforced Super Workable Concrete Beams

This Study Investigates the Effect of Macro Synthetic Fiber (MSF) Volume and Crack Widths on Corrosion of the Reinforcing Bars and Residual Flexural Behavior of Fiber-Reinforced Super-Workable Concrete (FR-SWC) Beams Exposed to Accelerated Corrosion. FR-SWC Beams Prepared with 0, 0.33%, and 0.66% MSF Were Pre-Cracked at 0.2-, 0.4-, and 0.75-Mm Widths Before Corrosion Testing. the Controlled Crack Width Was Initiated in One Set of Beams that Were Then Unloaded. the Crack Width Was Maintained for Another Set of Beams during Corrosion Testing by Inserting a Shim. Test Results Showed that the Use of 0.33% and 0.66% MSF Reduced Crack Development and Crack Propagation, Delayed Corrosion Initiation Time, and Significantly Increased the Residual Flexural Strength of Beams Subjected to Accelerated Corrosion. the Beams Reinforced with 0.66% MSF Enhanced Residual Ultimate Load, Residual Yield Load, and Residual Flexural Toughness by 10%–45%, 38%–113%, and 42%–150% Compared to the Corresponding Non-Fibrous Beams. the Improved Flexural Performance of Beams Made with MSF after Accelerated Corrosion Can Be Attributed to the Ability of MSF to Reduce Crack Width Due to Corrosion Damage. Crack Width Lower Than 0.2 Mm Showed No Significant Effect on the Residual Flexural Behavior of Beams after Corrosion Testing. However, the Pre-Crack Width over 0.2 Mm Showed a Significant Influence on the Crack Initiation and Residual Flexural Behavior after Accelerating Corrosion. the Pre-Cracked Beams with a 0.75 Mm Crack Width Retained the Ultimate Load of 65%–76%, Yield Load of 47%–80%, and Toughness of 38%–83%, Respectively, compared to their Corresponding Uncracked Beams Subjecting to Accelerated Corrosion. the Un-Shimmed Beams Allowed Partial Closure of Cracks Due to the Presence of MSF after Initial Loading and Increased the Residual Ultimate Load, Yield Load, and Flexural Toughness by 7%–45%, 27%–82%, and 3%–56%, Respectively, Compared to their Corresponding Shimmed Beams. a Correlation between the Residual Flexural Behavior and the Rate of Cross-Sectional Area Loss of Reinforcing Bars Due to Corrosion Was Developed. Furthermore, a Mechanism Was Proposed to Explain the Effect of MSF in Improving the Residual Flexural Performance in the Cracked FR-SWC Beams

Synergistic Effect of HEDP.4Na and Different Induced Pouring Angles on Mechanical Properties of Fiber-Reinforced Alkali-Activated Slag Composites

The Poor Flexural and Damping Properties of Building Materials Damages Concrete Structures and Affects their Service Life When Concrete Structures Are Subjected to Dynamic Loads. Three Different Dosages (I.e., 0%, 0.3%, and 0.6%) of Organic Phosphonates (HEDP.4Na) and Different Pouring Methods (I.e., Conventional Pouring Method, 90°-Induced Pouring Method, and 150°-Induced Pouring Method) Were Designed to Improve the Flexural and Damping Performance of Fiber-Reinforced Alkali-Activated Slag Composites (FR-AASC). the Enhanced Mechanism of HEDP.4Na Was Revealed by Phase Analysis (X-Ray Diffraction, XRD), Pore Structure Analysis (Mercury Intrusion Porosimetry, MIP), the Heat of Hydration, and Scanning Electron Microscopy (SEM) Analysis. the Results Showed that 0.3% HEDP.4Na Combined with the 150°-Induced Pouring Angle Can Significantly Improve the Mechanical Properties of the FR-AASC Sample Compared with the Reference Group. the Sample with 0.3% HEDP.4Na Cast by the 150°-Induced Pouring Angle Increased Compressive and Flexural Strength, Damping Energy Consumption and Storage Modulus by 20%, 60%, 78%, and 30%, Respectively, Compared with the Reference Sample Cast by the Conventional Pouring Methodology. HEDP.4Na Reduced the Early Hydration Heat and Total Porosity of the FR-AASC Matrix, Modified the Fiber–matrix Interface Transition Zone, and Increased the Frictional Energy Consumption of Steel Fibers. overall, the Synergistic Effect of HEDP.4Na and the Induced Pouring Methodology Significantly Improved the Flexural and Damping Properties of FR-AASC. This Study Can Provide a Guidance for Improving the Flexural and Damping Capacity of FR-AASC and Promote the Application of FR-AASC in Construction Engineering

Effect Of Competitive Adsorption Between Specialty Admixtures And Superplasticizer On Structural Build-up And Hardened Property Of Mortar Phase Of Ultra-high-performance Concrete

This study aims to enhance structural build-up of ultra-high-performance concrete (UHPC) without influencing the initial flowability, which is critical in repair applications (e.g., use of UHPC in thin bonded overlays for bridge deck rehabilitation). Specialty admixtures, such as a viscosity-modifying admixture (VMA), have been used to enhance the structural build-up at rest. However, the use of specialty admixtures can increase superplasticizer (SP) demand to maintain proper flowability; the synergistic effect of these admixtures on structural build-up is not well understood as the coupled admixture content can reverse the net effect on yield stress, viscosity, and thixotropy. In this study, VMAs including welan gum (WG), diutan gum (DG), and cellulose ether (CE) were used. Styrene-butadiene rubber (SBR) and acrylic ester (AE) latex polymers (LPs) that can enhance structural build-up and bond strength were also incorporated. The competitive adsorption between these specialty admixtures and SP and its effect on structural build-up, early-age hydration, compressive and pull-off strengths, porosity and entrapped air content of UHPC mortar (i.e., without fiber) were systematically investigated. Test results indicated that the incorporation of anionic WG and DG that exhibited high competitive adsorption with SP led to a 275%–450% enhancement in structural build-up despite the 55%–135% increase of SP demand. Such increase was limited to 130% when using CE, SBR, or AE that cannot effectively adsorb onto cement particles in the presence of SP. This was because the high competitive adsorption between specialty admixtures and SP strengthened the particle flocculation and promoted the cement hydration in the first hour; the latter resulted in 20%–40% enhancement in non-reversible component of structural build-up. Furthermore, the use of LP at low and moderate dosages secured high bond strength to normal strength mortar despite 8%–33% decrease in compressive strength given the increased capillary porosity. The use of VMAs increased the entrapped air and resulting 5%–15% lower compressive strength, while the bond strength was not influenced

Prediction of Dynamic Mechanical Behaviors of Coral Concrete under Different Corrosive Environments and its Enhancement Mechanism

The marine structures are usually exposed to dynamic loadings within short periods and chemical attacks, resulting in severe dynamical damage or failure to concrete structures. The study of the time-dependent changes in the dynamic mechanical behavior of coral concrete under different corrosive environments and low-frequency waves is limited. For the safety and reliable use of coral concrete in the marine environment, different corrosion environments (chloride ions, sulfate ions, and mixed chloride-sulfate ions) and low-frequency waves (0.5–2.0 Hz) were designed to evaluate the dynamic properties of concrete. A model considering the effect of corroded age is formulated to predict the damping capacity of coral concrete. Testing results indicate that sulfate attack shows the most significant effect to influence the dynamic behaviors of coral concrete, while the effect of chloride ion penetration is negligible. The loss factor of coral concrete under corroded environments increases by 59.5% compared with ordinary concrete, even though the loss modulus and storage modulus of coral concrete reduce by 38.5% and 51.8%. It was attributed to coral concrete showing a low ability to resist sulfate attack, resulting in more cracks and pores in the matrix. Coral aggregate with high porosity and interconnected pores in coral concrete works like a cushion to dissipate more external energy. The proposed prediction model (R2 = 0.89) can accurately describe the relationship between erosion age and damping capacity in different corrosion environments, which can guide the application of coral concrete in marine and vibration environments

Multi-task deep neural network acoustic models with model adaptation using discriminative speaker identity for whisper recognition

This paper presents a study on large vocabulary continuous whisper automatic recognition (wLVCSR). wLVCSR provides the ability to use ASR equipment in public places without concern for disturbing others or leaking private information. However the task of wLVCSR is much more challenging than normal LVCSR due to the absence of pitch which not only causes the signal to noise ratio (SNR) of whispers to be much lower than normal speech but also leads to flatness and formant shifts in whisper spectra. Furthermore, the amount of whisper data available for training is much less than for normal speech. In this paper, multi-task deep neural network (DNN) acoustic models are deployed to solve these problems. Moreover, model adaptation is performed on the multi-task DNN to normalize speaker and environmental variability in whispers based on discriminative speaker identity information. On a Mandarin whisper dictation task, with 55 hours of whisper data, the proposed SI multi-task DNN model can achieve 56.7% character error rate (CER) improvement over a baseline Gaussian Mixture Model (GMM), discriminatively trained only using the whisper data. Besides, the CER of the proposed model for normal speech can reach 15.2%, which is close to the performance of a state-of-the-art DNN trained with one thousand hours of speech data. From this baseline, the model-adapted DNN gains a further 10.9% CER reduction over the generic model