Water resistance and thermal behavior of metakaolin-phosphate-based geopolymer cements

The main target of this work was to investigate the thermal behavior and water resistance of geopolymer cement made from metakaolin as an aluminosilicate source using phosphoric acid solution (10 M) as a hardener. The obtained geopolymer cements were cured at room temperature for 28 days, the one part was treated at 200°C, 400°C, 600°C, 800°C and 1000°C, and the others were soaked in water for 28 days. The geopolymer cements were characterized by microstructural properties using X-ray diffractometry, infrared spectroscopy, microstructure, physical property based on water resistance and thermo-mechanical properties (thermal analysis, compressive strength). The results show that the compressive strength of the unheated geopolymer cement was 87.96 MPa. The ones soaked in water revealed a strength of 40.71 MPa. This indicates that the specimens soaked in water lose about 54% of their strengths. The X-ray patterns of heated geopolymer cements showed the formation of crystalline phases even at relatively low temperatures. It was typically found that the compressive strength of metakaolin-phosphate-based geopolymer cements decreases due to the hydrolysis of Si-O-P bonds in the presence of water

Low-temperature alkaline activation of feldspathic solid solutions: Development of high strength geopolymers

Most of the natural solid solutions, as a result of the history of their formation and crystallization, present a fraction of amorphous or metastable materials that may easily be dissolved or activated in alkaline media. In this work, trachyte, granite, pegmatite and sand for comparison are used as principal solid precursors for the design of high strength geopolymers. The particularity of the solid-solution based geopolymers is the high fraction of crystalline phases incongruently dissolved that may react essentially at the surface, thus developing very resistant bonds. While working with 100 wt% of solid solution is almost unrealistic for the production of geopolymers, it was found that 15 to 30 wt% of metakaolin in replacement of the solid-solution powder conducts to low porosity (10 vol.%), high flexural strength (20-30 MPa) and compact microstructure. Preliminary resonance-based mechanical tests showed that the elastic modulus of the investigated samples ranged between 11-15 GPa, as also confirmed by instrumented micro-indentations. It was concluded that a high strength and durable matrix are a result of chemico-mechanical equilibrium of phases contained within the composites including the pore volume and pore-size distribution, which are significant for the life cycle of geopolymer composites

Investigation of the relationship between the condensed structure and the chemically bonded water content in the network of geopolymer cements

The main objective of this work was to investigate the relationship between the condensed structure and the chemically bonded water content in the metakaolin-based geopolymer network. The kaolinite clay used in this work as an aluminosilicate source was transformed to metakaolin by calcination at 700 °C. The powder of the waste glass and the silica fume were used as silica sources for the synthesis of the hardeners. The obtained hardeners were characterized by infrared spectroscopy and MAS-NMR 29Si. The metakaolin and the hardeners were used for producing geopolymers cements. The synthesized products were characterized by X-ray diffractometry, infrared spectroscopy, mercury intrusion porosimetry, scanning electron microscopy, MAS-NMR 29Si and 27Al, thermal analyses (TG and DSC) and compressive strength. The results show that the compressive strength of geopolymer cements using hardener from silica fume and the one from waste glass are 62 and 26 MPa, respectively. The microstructure (SEM observations) geopolymer cements obtained using hardener from silica fume are homogeneous, compact and dense with an average pore diameter around 10 nm. Whereas, the one obtained using hardener from waste glass are heterogeneous and contains larger pores (170 nm). MAS-NMR 29Si and 27Al results show that the specimen obtained using hardener from the silica fume contains more aluminum in four-fold coordination in its network than waste glass geopolymer, GWG. This indicates a higher degree of crosslinking of poly(sialate-siloxo) chains which could lead to a smaller pore sizes and a higher water uptake in the structure of the sample. The amount of chemically bonded water contained in the network of geopolymer cements using hardeners from waste glass and silica fume were 6.82 and 11.23%, respectively, as determined from weigth loss in the range 100-300 °C. All these results indicate that the higher content of chemically bonded water in the network of geopolymer obtained using hardener from silica fume is related to the much smaller average pore size diameter and the hydrophilic character of aluminum, which reveals obviously better mechanical and microstructural properties of the specimen. This could indicate here a higher degree of condensation using silica fume based hardeners for geopolymerisation. Please click Additional Files below to see the full abstract

Microstructure and mechanical, physical and structural properties of sustainable lightweight metakaolin-based geopolymer cements and mortars employing rice husk

This work focuses on an in-depth investigation of the formation of pores in the structure of lightweight geopolymer cements and mortars using rice husk as a foaming agent. The hardener used in this study was sodium waterglass. Metakaolin was replaced by 0, 10, 20, 30 and 40 % by mass of husk and the obtained powders were used to produce lightweight geopolymer cements and mortars. The formation of pores in the lightweight geopolymer cements was monitored using X-ray diffractometry and infrared spectroscopy while those in the mortars were assessed using apparent density and compressive strength measurements, mercury intrusion porosimetry and optical and scanning electron microscopy. The values for the compressive strength and apparent density were in the ranges of 28.92\u20130.75 MPa and 1.88\u20131.70 g/cm 3 , respectively. The results indicated that the values for the compressive strength and apparent density of geopolymer mortars decreased while those of the cumulative pore volume increased with increases in the metakaolin replacement level. Stereomicroscopic and scanning electron microscopic images showed the presence of rice husk and fibres of rice husk, respectively, in the networks. It was found that rice husk can be used as a foaming agent for producing sustainable lightweight geopolymer mortars

Meta-halloysite to improve compactness in iron-rich laterite-based alkali activated materials

In this paper, the results of the experimental investigation were used to understand the effect of fine meta-halloysite on the reactivity, mechanical and microstructural properties of laterite-based geopolymers. Laterite was replaced by 0, 20, 30 and 50 wt% of meta-halloysite in order to improve the physico-chemical performance. Meta-halloysite was prepared by calcination of natural halloysite at 600 °C. The moduli (molar ratio SiO2/Na2O) of the activating solutions were 1.04, 0.92, and 0.75 with H2O/Na2O = 9.78, 10.45 and 12.04, respectively. The results indicated that calcined laterite has a high specific surface area (43.00 ± 0.12 m2/g), notwithstanding a high average particle size (d50 = 45.20 μm) compared to meta-halloysite with a smaller average particle size (d50 = 8.40 μm) and a specific surface (29.80 ± 0.16 m2/g). The compressive strength of geopolymers increased upon the addition of meta-halloysite from 12 MPa to 45 MPa at 28 days. While the setting time and water absorption decrease with increase in the of meta-halloysite content as well as with increase in Si/Al, Si/Fe, Al/Fe and Na/Al molar ratios used in the synthesis of geopolymers. The use of fine meta-halloysite resulted in better efficiency and improved mechanical performance of synthesized products

Engineering properties, phase evolution and microstructure of the iron-rich aluminosilicates-cement based composites: Cleaner production of energy efficient and sustainable materials

This paper investigates the direct transformation of laterites (natural iron-rich aluminosilicates) to cementitious composites with principal mineral phases being Gismondine and Stratlingite. The effects of particles size distribution and cement content (2 to 8 wt%) on the mechanical properties and microstructure of laterite-cement composites are assessed. Four grades of granulometry with various percentages of fine and coarse particles were considered. The Environment Scanning Electron Microscopy (ESEM), Mercury Intrusion Porosimetry (MIP), Fourier Transformed Infrared Spectroscopy (FT-IR) and X-ray Powder Diffractometry (XRD) were performed after 1, 90 and 365 days, to assess the phase's evolution, mechanical performance and the microstructure of the laterite-cement composites. It is found that fines particles, essentially pozzolanic and amorphous, are responsible for the bonding strength while coarse particles improve the compressive strength. Dense and compact microstructure, water absorption under 18% and flexural strength above 6 MPa (compressive strength > 30 MPa) could be achieved as from 4 wt% of cement making the laterite-cement composite appropriate as building and construction materials. The choice of a highly corroded class of laterite and the selection of the particle size distribution allows the production of optimum composite that is presented as energy-efficient and sustainable. Thus, corroded or indurated laterites are considered as “green metakaolins” which do not require any energy for their transformation unlike clayey materials

Moisture Control Capacity of Geopolymer Composites: Correlation of the Bulk Composition\u2013Pore Network with the Absorption\u2013Desorption Behavior

Abstract: Porous composites with the principal class of porosity in the range of those presented in the literature as ideal for the moisture control capacity of building environment are described. In the course of the design of the matrices, micrometric pores are introduced to give to the pore systems a bi- or multimodal characters with the aim of improving the phases percolation during the course of desorption and make the moisture accumulation\u2013desorption behavior of the porous composites essentially function of weather and environment. The porous composites present size of pores in the range 0.001-1\u3bcm for the gel pores and peak centered at 10\u3bcm for the micrometric pores which insure the matrices efficiency in moisture control capacity and durability. The results of cycles of moisture absorption\u2013desorption in the course of various seasons of the year permit to identify the activities of gel pores meanly efficient in the extreme environment: absorption when the temperature is under 11 18C; relative humidity is >60% and desorption when the temperature is above 18 18C. At ambient conditions, the pores more active are micrometric pores, while gel pores enter in activity only in the extreme environment conditions. The proposed porous geopolymer composites appeared promising candidates for the management of the moisture while improving the thermal insulation of residential building particularly in the regions with important fluctuation of weather. The use of geopolymerization process for the production of those porous composites, the choice of recycling industrial and municipal inorganic wastes appears ideal solution, environmentally friendly, eco-efficient and sustainable for the design of newly materials for the moisture control capacity in building environment. Graphical Abstract: [Figure not available: see fulltext.]

Genetic Selection of Low Fertile Onchocerca volvulus by Ivermectin Treatment

Onchocerca volvulus is the causative agent of onchocerciasis, or “river blindness”. Ivermectin has been used for mass treatment of onchocerciasis for up to 18 years, and recently there have been reports of poor parasitological responses to the drug and evidence of drug resistance. Drug resistance has a genetic basis. In this study, genetic changes in β-tubulin, a gene associated with ivermectin resistance in nematodes, were seen in parasites obtained from the patients exposed to repeated ivermectin treatment compared with parasites obtained from the same patients before any exposure to ivermectin. Furthermore, the extent of the genetic changes was dependent on the level of ivermectin treatment exposure. This genetic selection was associated with a lower reproductive rate in the female parasites. The data indicates that this genetic selection is for a population of O. volvulus that is more tolerant to ivermectin. This selection could have implications for the development of ivermectin resistance in O. volvulus and for the ongoing onchocerciasis control programmes. Monitoring for the possible development and spread of ivermectin resistance, as part of the control programmes, should be implemented so that any foci of resistant parasites can be treated by alternative control measures

Mechanical properties of cotton fabric reinforced geopolymer composites at 200-1000 °C

Geopolymer composites containing woven cotton fabric (0–8.3 wt%) were fabricated using the hand lay-up technique, and were exposed to elevated temperatures of 200 °C, 400 °C, 600 °C, 800 °C and 1000 °C. With an increase in temperature, the geopolymer composites exhibited a reduction in compressive strength, flexural strength and fracture toughness. When heated above 600 °C, the composites exhibited a significant reduction in mechanical properties. They also exhibited brittle behavior due to severe degradation of cotton fibres and the creation of additional porosity in the composites. Microstructural images verified the existence of voids and small channels in the composites due to fibre degradation

Genome-wide association study of REM sleep behavior disorder identifies polygenic risk and brain expression effects

Rapid-eye movement (REM) sleep behavior disorder (RBD), enactment of dreams during REM sleep, is an early clinical symptom of alpha-synucleinopathies and defines a more severe subtype. The genetic background of RBD and its underlying mechanisms are not well understood. Here, we perform a genome-wide association study of RBD, identifying five RBD risk loci near SNCA, GBA, TMEM175, INPP5F, and SCARB2. Expression analyses highlight SNCA-AS1 and potentially SCARB2 differential expression in different brain regions in RBD, with SNCA-AS1 further supported by colocalization analyses. Polygenic risk score, pathway analysis, and genetic correlations provide further insights into RBD genetics, highlighting RBD as a unique alpha-synucleinopathy subpopulation that will allow future early intervention