Cementitious composites incorporating well-dispersed carbon nanotubes (CNTs) have demonstrated significant mechanical performance enhancements, however, there has only been limited investigation into ...the nanocomposite microstructure and pore structure. In this study, the effects of (i) CNT dispersion with and without the assistance of a dispersant, (ii) CNT dose at 0.05–0.25 wt% of cement, and (iii) CNT dispersion quality upon the composite microstructure after 7- and 28-days' hydration were investigated using quantitative image analysis of backscattered electron microscopy and X-ray computed microtomographic datasets. Results show that dispersed CNTs promoted the formation of low- and higher-density hydration products within 7 days of hydration and reduced the pore size distribution by 28 days, although 3D X-ray results showed some large CNT agglomerations formed in the nanocomposite. Further, poorly-dispersed CNTs increased the 28-day pore size distribution, but had a beneficial effect, similar to well-dispersed CNTs, upon the microstructural composition of the hydrated phases.
Multiwalled carbon nanotubes have outstanding mechanical properties that, when combined with Portland cement, can provide cementitious composites that could lead to the innovative construction of ...stronger, lighter, and thinner built infrastructure. This paper addresses a knowledge gap that relates to the durability of CNT–cement composites. The durability to corrosive chloride, uptake of water by sorption, and flow of the permeability of water acting under high water pressure are addressed. Flow simulations were undertaken through segmented 3D pore networks, based on X-ray computed microtomography measurements, the creation of a virtual microstructure, and fluid simulations that were compared with larger-scale samples. The investigation showed decreased water sorptivity of CNT–cement mixtures, indicating improved durability for the cover zone of concrete that is prone to the uptake of water and water-borne corrosives. Chloride diffusion of CNT–cement composites provided up to 63% improvement compared with control samples. The favourable durability bodes well for the construction of long-life CNT-reinforced concrete infrastructure.
Significant quantities of soil are adversely impacted by organic contaminants, including per- and poly-fluoroalkyl substances (PFAS). One proven technology for remediating PFAS affected soils is ...excavation and heat-treatment which destroys the PFAS, but renders the soil as an industrial waste that is normally diverted to landfill. This study investigated alternative uses for heat-treated industrial waste (HIW) soils as components in concrete, as aggregate replacement and as partial substitution of cement binder. At a replacement rate of 100% fine aggregate and ≈15% coarse aggregate, concretes made with HIW soil exhibited a strength of 47.2–48.3 MPa after 28 days’ curing, compared with a reference concrete of 49.7–53.1 MPa, making the HIW ideal for aggregate replacement. Overall, the study demonstrated a novel, holistic approach to (1) remediating PFAS-affected soils, (2) diverting contaminated soil away from landfill, (3) reducing the use of high quality quarried concrete aggregates and (4) producing normal-strength concretes with a lower embodied carbon footprint than existing approaches. This study reveals that in Australia, up to 93% of all contaminated soil currently sent to landfill annually could instead be used a resource for mid-strength concretes, suitable for many applications.
•Heat-treated industrial waste (HIW), in which PFAS compounds were destroyed, was assessed for application in concrete.•Aggregates replaced (100% fine and ≈15% coarse) with HIW resulted in compressive, indirect tensile strengths comparable to reference concrete.•Pozzolan activity of clay in HIW potentially reduces the embodied CO2 footprint of concrete.•Nearly all soils contaminated by PFAS can be diverted from landfill and used in concrete after heat-treatment.
The addition of carbon nanotubes (CNTs) to cementitious nanocomposites have demonstrated significant mechanical performance enhancements, however, there has been only limited research of the effects ...of CNTs upon hydration kinetics. Isothermal calorimetry was used to study in detail (i) CNT dispersion with and without a polycarboxylate-based superplasticiser, (ii) CNT dose at 0.05–0.25 wt% of cement, and (iii) CNT dispersion quality upon cement hydration. Results show a 45-min acceleration and 17% increase in principal hydration peak at a CNT dose of 0.1 wt% without superplasticiser, indicating enhanced nucleation with CNTs. Varying CNT dose, delaying effects of the superplasticiser dominated, although there was an increase in hydration peak of 17% with 0.25 wt% CNTs. Finally, it was found that CNT content, not ‘good’ or ‘poor’ dispersion quality, had a greater effect upon the overall nanocomposite hydration and microstructural development, facilitating further optimisation of CNT dispersion and microstructural development for CNT-cement nanocomposites.
•Proprietary pre-dispersed CNT admixture used to produce carbon nanotube-reinforced concrete.•Longer mixing time significantly improved compressive strength of CNT-reinforced concrete.•Enhanced fresh ...properties with dosage, increased workability and significantly reduced bleed.•CNT-reinforced concrete had up to 46% higher strength at 1 day, and up to 37% at 28 days.
This study evaluated the effects of a pre-dispersed carbon nanotube (CNT) liquid admixture on the fresh and hardened performance of CNT-reinforced concrete (CNTRC) dosed at 2.5, 5 and 10% (bwoc), using high-early strength (HE) and Portland cement (OPC) binders. The effect of mixing time, admixture dosage and water-to-binder ratio sensitivity on rheology, bleed and compressive strength after 1-, 7- and 28-days’ curing of CNTRC mixes were assessed, addressing a knowledge gap in workability and early-age performance of the concrete nanocomposite. 10% admixture addition imparted significant strength enhancements at 1 day – up to 40% with OPC, 46% with HE binders – and 28 days – up to 21% for OPC and 37% for HE binders. Results highlighted the benefits of an extended mixing time upon improved CNT homogenisation, compressive strength and reduced bleed. This research demonstrates the significant, applications-ready benefits to early-age and 28-day concrete performance with a pre-dispersed CNT liquid admixture.
A new method of direct‐write nanolithography that is able to rapidly etch silica surfaces under a scanning atomic force microscopy (AFM) probe in tapping mode (TM) is reported. In this lithography ...technique, silica surfaces are etched using a recently described electro‐chemo‐mechanical phenomenon of frequency enhanced electrochemical pressure solution (FEEPS). In FEEPS, the tapping of the AFM tip generates oscillations of the Stern potential at the silica‐water interface that can accelerate the silica dissolution kinetics by more than 5–6 orders of magnitude when surface resonance states are achieved; i.e., when the oscillation frequency is in phase with the dynamics of interfacial chemical reaction steps. By scanning silica surfaces in TM, silica is selectively dissolved below the tapping tip as it is scanned. The FEEPS accelerated silica dissolution rates can generate etched features with depths of more than 60 nm in a single AFM tip pass. The rate of etching can be controlled easily by varying the scanning rate or by modulating the tapping frequency. This fine control over the silica etching process and because material is removed (dissolved) rather than displaced as with nanoscratching, the FEEPS process lends itself to gray‐scale nanolithography which is demonstrated.
This work details a new method of atomic force microscopy (AFM)‐based lithography which utilizes a new chemical phenomenon of “frequency enhanced electrochemical pressure solution” (a.k.a. “FEEPS”) that greatly enhances the rate of silica dissolution under an oscillating AFM tip undergoing tapping in pure water. FEEPS greatly reduces tip wear and eliminates unwanted features like hillocks common to other AFM lithography techniques like nanoscratching.
Agricultural systems models worldwide are increasingly being used to explore options and solutions for the food security, climate change adaptation and mitigation and carbon trading problem domains. ...APSIM (Agricultural Production Systems sIMulator) is one such model that continues to be applied and adapted to this challenging research agenda. From its inception twenty years ago, APSIM has evolved into a framework containing many of the key models required to explore changes in agricultural landscapes with capability ranging from simulation of gene expression through to multi-field farms and beyond.
Keating et al. (2003) described many of the fundamental attributes of APSIM in detail. Much has changed in the last decade, and the APSIM community has been exploring novel scientific domains and utilising software developments in social media, web and mobile applications to provide simulation tools adapted to new demands.
This paper updates the earlier work by Keating et al. (2003) and chronicles the changing external challenges and opportunities being placed on APSIM during the last decade. It also explores and discusses how APSIM has been evolving to a “next generation” framework with improved features and capabilities that allow its use in many diverse topics.
•APSIM is an agricultural modelling framework used extensively worldwide.•It can simulate a wide range of agricultural systems.•It begins its third decade evolving into an agro-ecosystem framework.
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