Consequences of omitting some important factors in the environmental analyses of commercial sodium silicate/sodium hydroxide use for alkaline activation in the light of comparison with cement-based composites.

Alkali-activated materials (AAMs) based on various waste precursors were considered mostly as a sustainable alternative to Portland cement-based composites to date. However, a narrow focus on carbon dioxide savings in the environmental assessment of AAMs may not be sufficient to achieve a truly sustainable solution. Therefore, this paper provides a detailed insight into midpoint impact categories related to the production of AAMs based on waste precursors and conventional activators, as compared with common cement-based materials. The obtained results point to a higher environmental load of AAMs in several categories, such as ozone layer depletion, primary resource consumption, and terrestrial and aquatic ecotoxicity. In a hypothetical scenario, it is demonstrated that 10 % replacement of global concrete production by AAMs may result in notably increased emissions of ozone depletion substances (+35 %) and damage to the aquatic environment (+ 40 %). The risk for human health can then be higher. As for the aquatic environment, eutrophication can also lead to a significant increase in indirect emissions of CH4 and N2O having a high impact on the greenhouse effect. Hence, the importance of robust interdisciplinary research in the environmental assessment of AAMs should be emphasized, together with the need to use alternative alkaline substances, which would be more environment-friendly than conventional activators.

Assessment of Clayey Freshwater Sediments as Suitable Precursors for Alkaline Activation.

One of the biggest challenges in the construction industry in recent times is the mitigation of the environmental impact of this sector, the reduction in dependence on primary raw materials, and the reduction in CO2 production while maintaining functional properties. Alkaline activation of a number of waste products represents a promising way to achieve the above-mentioned goals, but the availability of a number of waste products changes over time, especially in Europe. While freshwater sediments were in the past widely utilized as an agricultural fertilizer, recent precautions have significantly decreased such application, and thus new destinations must be delivered. To explore the potential of freshwater sediments, select samples from various locations were subjected to detailed characterization to verify the applicability of the material for alkali activation. As recognized, the selected sediments contain a substantial volume of desired mineralogical compounds that can serve, after 900 °C curing, as suitable precursors. Such samples have consequently activated the mixture of alkaline activators to obtain dense structures and were subjected to detailed investigation aimed at understanding the mechanical parameters. The obtained mechanical results ranging between 14.9 MPa and 36.8 MPa reveal the engineering potential of sediments for valorization through alkali activation and outline new research challenges in this area.

Experimental and Environmental Analysis of High-Strength Geopolymer Based on Waste Bricks and Blast Furnace Slag.

The rationalization of material flows, together with the utilization of waste raw materials for the production of alternative binders, became a very attractive topic during the last decades. However, the majority of designed materials can be used as a replacement for low-performance products. In this work, the waste materials (brick powder and blast furnace slag) are valorized through geopolymerization to design high-performance material as an alternative to high-performance concrete. Designed mixtures activated by sodium silicate and waste-originated alkali solution are characterized by the meaning of the chemical and mineralogical composition, evolution of hydration heat, and mechanical strength test. To contribute to the understanding of the environmental consequences and potential benefits, the carbon footprint and embodied energy analysis are provided. Obtained results highlight the potential of end-of-life bricks for the design of high-performance composites if mixed together with more reactive precursors. Here, even values over 60 MPa in compressive strength can be achieved with the dominant share of low-amorphous brick powder. The higher crystalline portion of brick powder may lead to the reduction of drying shrinkage and preservation of flexural strength to a greater extent compared to used slag. Performed environmental analysis confirmed the CO2 emission savings; however, the embodied energy analysis revealed a huge impact of using alkaline activators.

Effects of Secondary Porosity on Microstructure and Mechanical Properties of SAP-Containing Lime-Based Plasters.

Despite the many benefits associated with the utilization of superabsorbent polymers (SAPs), several drawbacks have been reported. In particular, the effect of SAPs on microstructure, together with its consequences for mechanical properties, is not fully understood yet for some composite materials. This study analyzes the role of SAPs in the formation of the microstructure of lime composites, taking into account their chemical composition. The obtained experimental results show that the particle size and cross-linking density of used SAPs are crucial parameters affecting both the microstructure and mechanical performance of the analyzed composites. Coarser SAPs with low cross-linking density in the dosage of 0.5 and 1 wt.% are found as the most suitable solution, leading even to a slight improvement of mechanical parameters. The secondary porosity formed by swelled hydrogels is identified as a very significant factor since hydrogel-filled voids do not contribute to the strength parameters. The formation of the affected zone around SAP cores depends on the chemical composition of SAPs considerably as the higher cross-linking density influences the desorption rate. Based on achieved results, utilization of SAPs in building materials should be studied at a more detailed level with particular importance on the definition of SAP-related voids and affected zone around SAP particles.

Glucagon increase after chronic AT1 blockade is more likely related to an indirect leptin-dependent than to a pancreatic α-cell-dependent mechanism.

AT1 blockers (ARB) prevent diabetes by improving pancreatic ß cell function. Less is known about whether α cells are affected although they express angiotensin II (AngII) receptors. We aimed to investigate glucagon release upon AngII stimulation. We determined glucagon release after AngII stimulation (0.01-100 µM) in α cells (InR1G9) and isolated murine islets. We determined plasma glucagon in rats that were chronically treated with AngII (9 µg/h) or the ARBs telmisartan (8 mg/kg/day) and candesartan (16 mg/kg/day) and correlated glucagon with additional hormones (e.g. leptin). Glucagon was only released from InR1G9 cells and islets at the highest AngII concentrations (>10 µM). This was not inhibited by losartan or PD123319. Ang(1-7) and AngIV were also almost ineffective. AngII did not alter glucagon secretion from islets. Plasma glucagon increased when obese Zucker rats were treated with AngII or candesartan and also when Sprague Dawley rats were treated with telmisartan in parallel to high-calorie feeding. Plasma glucagon and leptin negatively correlated in ARB-treated rats. The glucagon release from InR1G9 cells or islets after AngII, AngIV or Ang(1-7) is unspecific since it only occurs, if at all, after the highest concentrations and cannot be blocked by specific inhibitors. Thus, the AngII-dependent increase in plasma glucagon seems to be mediated by indirect mechanisms. The negative correlations between plasma leptin and glucagon confirm findings showing that leptin suppresses glucagon release, leading us to suppose that the increase in plasma glucagon is related to the decrease in leptin after ARB treatment.

Chronic blockade of angiotensin AT1 receptors improves cardinal symptoms of metabolic syndrome in diet-induced obesity in rats.

BACKGROUND AND PURPOSE: AT1 receptor antagonists decrease body weight gain in models of murine obesity. However, fewer data are available concerning the anti-obesity effects of these antagonists, given as a treatment after obesity had been established. EXPERIMENTAL APPROACH: In spontaneously hypertensive rats, obesity was established by cafeteria diet (CD) feeding for 19 weeks. Rats were then were treated with telmisartan (8 mg·kg⁻¹·d⁻¹) or amlodipine (10 mg·kg⁻¹·d⁻¹; serving as blood pressure control) or telmisartan + amlodipine (2 + 10 mg·kg⁻¹·d⁻¹; to control for dose-dependency) for 17 weeks. Rats receiving only chow (C(chow)) or CD-fed rats treated with vehicle (C(CD)) served as controls. KEY RESULTS: The CD feeding induced obesity, hyperphagia, hyperlipidaemia, and leptin and insulin resistance. Telmisartan reduced the CD-induced increase in body weight and abdominal fat mass. Whereas energy intake was higher rather than lower, the respiratory ratio was lower. After telmisartan, leptin-induced energy intake was reduced and respiratory ratio was increased compared with C(CD) rats. Telmisartan also decreased plasma levels of triglycerides, free fatty acids and low-density lipoprotein. Amlodipine alone or the combination telmisartan + amlodipine did not affect body weight and eating behaviour. Telmisartan, but not amlodipine and telmisartan + amlodipine, improved glucose utilization. The decrease in BP reduction was almost the same in all treatment groups. CONCLUSIONS AND IMPLICATIONS: Telmisartan exerted anti-obesity effects and restored leptin sensitivity, given as a treatment to rats with obesity. Such effects required high doses of telmisartan and were independent of the decrease in blood pressure.