Rheological behavior of fresh inorganic polymer paste: Polymer bridging effect of the alkali silicate solution

Inorganic polymers (IP), produced by alkali activation of a glassy precursor, have been mainly investigated on their microstructure and mechanical strength properties. However, it is important to understand how the IP flow behaves under shear conditions, in particular when pumping is required. The activating solution is one of the main parameters influencing rheology. Therefore, the physical effect of the silicate structure on the rheology was investigated by varying the SiO2/Na2O molar ratio from 1.4 to 2.0 in the activator. The elastic and rheological properties of the IP were measured with a rheometer. In order to investigate the activator silicate structure and IP polymerisation development, Fourier Transform Infrared Spectroscopy (FTIR) and Nuclear Magnetic Resonance Spectroscopy (NMR) were performed. A decrease in elasticity was monitored for IP with a low SiO2/Na2O ratio as a result of the dissolved species, which can be correlated to NMR. The FTIR spectra implied that an activating solution with a higher SiO2/Na2O ratio resulted in the formation of a 3D silicate network with Q3 and Q4 crosslinks. The presence of a network modifier in the activating solution, such as Na, resulted in more Q1 and Q2 crosslinks. A higher stress, at a shear rate of 0.1 s-1; was observed in IP which consisted of a 3D silicate network as a result of the polymer bridging effect between the particles. A stronger shear thinning was observed in an IP with a higher SiO2/Na2O ratio, due to the steric hindrance from the entangled silicates. The rheological data of the IP can be fitted with the Herschel-Bulkley model

Recent progress in low-carbon binders

The development of low-carbon binders has been recognized as a means of reducing the carbon footprint of the Portland cement industry, in response to growing global concerns over CO2 emissions from the construction sector. This paper reviews recent progress in the three most attractive low-carbon binders: alkali-activated, carbonate, and belite-ye'elimite-based binders. Alkali-activated binders/materials were reviewed at the past two ICCC congresses, so this paper focuses on some key developments of alkali-activated binders/materials since the last keynote paper was published in 2015. Recent progress on carbonate and belite-ye'elimite-based binders are also reviewed and discussed, as they are attracting more and more attention as essential alternative low-carbon cementitious materials. These classes of binders have a clear role to play in providing a sustainable future for global construction, as part of the available toolkit of cements

The development and assessment of alkali activated paving blocks

In recent years great attention has been placed by the building sector on alkali-activated technology based on metakaolin, fly ash and ground granulated blast furnace slag (GGBFS), but also on emerging precursors such as by-products from non-ferrous metallurgy. The present work focuses on the development of alkali-activated binders from two slags, one from primary and one from secondary copper production, which were finely milled, blended with GGBFS, and activated with K-based alkali silicate solution with a 1.7 SiO2/K2O molar ratio. The aggregate to paste mass ratio was 2. The mixtures were cast, and cured for a designated time at room temperature and 60% RH. The so-obtained paving blocks were then tested in accordance with European standard for concrete paving blocks. The following properties were measured: splitting tensile strength, abrasion resistance, slip and skid resistance, resistance to freeze-thaw and resistance to freeze-thaw in the presence of de-icing salts. Their properties were compared to those of commercially available concrete paving blocks, and it was found that the performance of the alkali-activated pavers was generally comparable with the concrete pavers, while certain properties (e.g., abrasion resistance, freeze-thaw resistance and freeze-thaw resistance in presence of de-icing salts) were considerably better

Inorganic polymers from a plasma convertor slag: Effect of activating solution on microstructure and properties

Plasma processing of materials is a technology now also employed in the management of municipal solid wastes, often mixed with industrial residues. The specifics depend per case, but typically the process delivers energy, in the form of a gas or heat, a metal-rich fraction as well as a slag. The slag, containing mainly Si-, Fe-, Ca- and Al-oxides, is almost completely amorphous after rapid cooling and thus could possibly be used as precursor in the synthesis of inorganic polymers (IP). The latter is explored in the present work. Slag resembling the composition of refuse-derived fuel ash was mixed with various Na-silicate activating solutions, and the effect of SiO₂/Na₂O as well as H₂O/Na₂O molar ratio on the synthesis and mechanical properties of the prepared IP was investigated. It was found that for SiO₂/Na₂O molar ratios of 1.2 and H₂O/Na₂O molar ratio of 30.8, the mechanical strength of casted IP reached almost 90 MPa after 90 days. Further decrease in the SiO₂/Na₂O ratio, accompanied by decrease in the H₂O/Na₂O ratio, increased the early strength and the released reaction heat, but had no effect on the late strength. In addition to that, crack formation was pronounced. The increase of the concentration of activating solution, by means of reducing the water content level, i.e. H₂O/Na₂O, resulted in an increase of the released reaction heat as well as an increase of the mechanical strength, up to 112 MPa at 90 days. The above results are relevant to a range of metallurgical slags and other vitreous by-products and contribute towards more high added-value applications.status: publishe

Innovation in ICT course provision : Meeting stakeholders’ needs

ICT companies face problems in recruiting a workforce with ICT skills to meet an increasing demand driven by business growth and innovation. Typical degree courses offered by universities have failed to keep up with this demand, with the number of graduates failing to provide a sufficient supply of suitably-qualified employees. There is also often a mismatch between the degrees offered and the requirements of companies in the ICT industry. There is a need to develop new approaches to address these challenges with sustainable effect. This paper presents three case studies from three different countries. These case studies describe approaches taken by universities, government and industry in developing ICT courses using co-creation method. We consider the role of the different stakeholders and identify areas of commonality and challenges for the future

On the foaming kinetics for the synthesis of porous inorganic polymers

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Reactivity of Crystalline Slags in Alkaline Solution

© The Minerals, Metals & Materials Society 2019. Slags with varied amorphous and crystalline content, typical of iron and steel production, are generally underutilized. One promising reuse pathway for these wastes is chemical activation, producing alternatives to conventional building materials with lower embodied energy. The formation of a hardened binder is dependent on the slag mineralogy and, specifically, the reactivity of relevant phases. Reactivity can be understood by monitoring elemental dissolution rates through inductively coupled plasma (ICP-OES) analysis. Post-dissolution ICP analysis of activating solution and spectroscopic analysis of remaining solids was performed on several highly crystalline slags and on relevant synthetic minerals to track changes in chemical and phase composition. Amorphous and ionic phases have been observed as more reactive than other crystalline phases. This work aims to inform future studies on waste blending in alkali-activated systems, a promising avenue for valorization of industrial wastes with varied physicochemical properties. To this end, dissolution tests with varied initial Si, Al, and Ca concentrations in activating solution were also performed

Towards Sustainable Inorganic Polymers: Production and Use of Alternative Activator

Inorganic polymers are considered to have a much smaller CO2 footprint than traditional Portland cements. The possible environmental impact reduction was calculated to be up to 77% of a CEMI ordinary Portland cement (OPC)-based mortar, while the CO2 emissions were reduced by up to 83%. The highest contribution to the total CO2 footprint of inorganic polymers is related to the manufacturing of alkali activators. Within this context, the current work discusses the synthesis of inorganic polymers made from Fe-rich precursor and alternative silicate solutions. The obtained results indicate that there is no significant difference between an inorganic polymer prepared from alternative and commercially available solutions, which confirms that the waste glass can be use as alternative raw material in the production of sodium silicate

Herpes Simplex Keratitis in Patients with SARS-CoV-2 Infection: A Series of Five Cases

Herpes simplex virus type 1 (HSV-1) is a leading cause of infectious blindness worldwide. Most of the initial infection cases manifest as acute epithelial keratitis. Reactivation of herpesviruses is common in critically ill patients, including patients with severe Coronavirus disease (COVID-19). However, the data on COVID-19-related ocular infections is sparse, despite recent observations that more than 30% of COVID-19-infected patients had ocular manifestations. We report five cases of HSV-1 keratitis in COVID-19 patients. In total, five COVID-19 patients underwent ophthalmic examination, showing similar symptoms, including photophobia, tearing, decreased vision, eye redness, and pain. After initial assessment, tests of visual acuity and corneal sensitivity, a fluorescein staining test, and complete anterior and posterior segment examinations were performed. A diagnosis of HSV-1 keratitis was confirmed in all cases. Therapy was initiated using a local and systemic antiviral approach together with local antibiotic and mydriatic therapy. The complete reduction of keratitis symptoms and a clear cornea was achieved in all patients within 2 weeks. SARS-CoV-2 infection may be a risk factor for developing HSV-1 keratitis, or it may act as a potential activator of this ocular disease