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Protection of concrete against aggressive influences from the surrounding environment becomes an important step to increase its durability. Today, alkali silicate solutions are advantageously used as pore-blocking treatments that increase the hardness and impermeability of the concrete's surface layer. Among these chemical substances, known as concrete densifiers, lithium silicate solutions are growing in popularity. In the present study, the chemical composition of the lithium silicate densifiers is put into context with the properties of the newly created insoluble inorganic gel responsible for the micro-filling effect. Fourier-transform infrared spectroscopy was used as a key method to describe the structure of the formed gel. In this context, the gelation process was studied through the evolution of viscoelastic properties over time using oscillatory measurements. It was found that the gelation process is fundamentally controlled by the molar ratio of SiO2 and Li2O in the densifier. The low SiO2 to Li2O ratio promotes the gelling process, resulting in a rapidly formed gel structure that affects macro characteristics, such as water permeability, directly related to the durability of treated concretes. [ABSTRACT FROM AUTHOR]

This study investigates the relationships between the hydration kinetics of waterglass-activated slag and the development of its physical-mechanical properties, as well as its color change. To modify the calorimetric response of alkali-activated slag, hexylene glycol was selected from various alcohols for in-depth experiments. In presence of hexylene glycol, the formation of initial reaction products was restricted to the slag surface, which drastically slowed down the further consumption of dissolved species and slag dissolution and consequently delayed the bulk hydration of the waterglass-activated slag by several days. This allowed to show that the corresponding calorimetric peak is directly related to the rapid evolution of the microstructure and physical-mechanical parameters and to the onset of a blue/green color change recorded as a time-lapse video. Workability loss was correlated with the first half of the second calorimetric peak, while the most rapid increase in strengths and autogenous shrinkage was related to the third calorimetric peak. Ultrasonic pulse velocity increased considerably during both the second and third calorimetric peak. Despite the modified morphology of the initial reaction products, the prolonged induction period, and the slightly reduced degree of hydration induced by hexylene glycol, the overall mechanism of alkaline activation remained unchanged in the long-term perspective. It was hypothesized that the main issue of the use of organic admixtures in alkali-activated systems is the destabilizing effect of these admixtures on soluble silicates introduced into the system with an activator. [ABSTRACT FROM AUTHOR]

Belite-rich cement is a low carbon footprint binder. However, its use is accompanied by a low initial rate of hydration. This can be partially eliminated by grinding to a high specific surface or through the addition of admixtures (mineralizators or activators). The influence of alkaline activators CaSO4, Na2SO4 and Na2CO3 (in the amount of 5 wt.% related to the clinker weight) on the hydration course, as well as the quantity of hydration products in belite-rich cements, were investigated in this paper. Belite-rich clinker was laboratory-synthetized and ground together with activators to prepare various belite-rich cements. Next, the hydration kinetics and the hydrated phase assemblage were investigated using isothermal calorimetry, X-ray powder diffraction and thermogravimetric and differential thermal analyses. The use of selected admixtures allowed us to obtain belite-rich cements with higher hydraulic activity in the initial period. [ABSTRACT FROM AUTHOR]

The aim of this study was to explore the influence of ethylene glycol in a wide range of polymerization degree, i.e. from monomer (EG) up to polyethylene glycol (PEG) with molecular weight of about 35,000, on properties of alkali-activated slag mortars. Changes in molecular weight and dose of all tested glycols had only minor effect on compressive strength, while drying shrinkage was significantly affected by both these factors. EG had negligible impact on drying shrinkage, but other tested glycols reduced it significantly with PEG2000 and PEG10000 being the most effective. Such different shrinkage behavior was attributed to the changes in surface tension and pore structure. All tested glycols reduced the total heat released during the hydration and interestingly modified the heat flow depending on their molecular weight. [ABSTRACT FROM AUTHOR]

• Lignosulfonate efficient for NaOH activation regardless of the time of addition of paste components. • Calorimetry of alkali-activated slag with low silicate modulus of activator (0; 0.10; 0.25, 0.50). • Effect of lignosulfonate on rheology greatly related to its retarding effect on hydration. • The use and evaluation of strain amplitude sweep tests after different time discussed. • Hump on loss modulus curve for the pastes with significant precipitation of products. One of the crucial issues of alkali-activated materials is the application of conventional plasticizers. Lignosulfonate plasticizer (LS) works well for sodium hydroxide-activated slag but loses its efficiency in sodium waterglass-activated slag because of competitive adsorption with silicates. Therefore, the effects of the timing of LS and activator addition on the structural build-up and breakdown of AAS pastes with low-silicate moduli activator (0 to 0.50) were investigated, particularly by means of non-traditional strain sweep tests, which are thoroughly discussed. The rheological tests were correlated with the Vicat needle test and isothermal calorimetry. The results showed the high efficiency of LS in NaOH-activated slag paste over time, regardless of the order of addition of the components of the paste. It was accompanied by a considerable retardation effect of LS on the hydration of AAS. The beneficial effect of LS on the rheological parameters and hydration kinetics decreased rapidly with an increase of the silicate modulus of the activator. The delayed addition of the concentrated silicate-containing activators completely counteracted the slightly beneficial effect of LS and even accelerated the initial structural build-up. [ABSTRACT FROM AUTHOR]

The fixation of heavy metals (Ba, Cu, Pb) in an alkali-activated matrix was investigated. The matrix consisted of fly ash and blast furnace slag (BFS). The mixture of NaOH and Na-silicate was used as alkaline activator. Three analytical techniques were used to describe the fixation of heavy metals—X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), and X-ray powder diffraction (XRD). All heavy metals formed insoluble salts after alkaline activation. Ba was fixed as BaSO4, and only this product was crystalline. EDS mapping showed that Ba was cumulated in some regions and formed clusters. Pb was present in the form of Pb(OH)2 and was dispersed throughout the matrix on the edges of BFS grains. Cu was fixed as Cu(OH)2 and also was cumulated in some regions and formed clusters. Cu was present in two different chemical states; apart from Cu(OH)2, a Cu–O bond was also identified. [ABSTRACT FROM AUTHOR]

Significant drying shrinkage is one of the main limitations for the wider utilization of alkali-activated slag (AAS). Few previous works revealed that it is possible to reduce AAS drying shrinkage by the use of shrinkage-reducing admixtures (SRAs). However, these studies were mainly focused on SRA based on polypropylene glycol, while as it is shown in this paper, the behavior of SRA based on 2-methyl-2,4-pentanediol can be significantly different. While 0.25% and 0.50% had only a minor effect on the AAS properties, 1.0% of this SRA reduced the drying shrinkage of waterglass-activated slag mortar by more than 80%, but it greatly reduced early strengths simultaneously. This feature was further studied by isothermal calorimetry, mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Calorimetric experiments showed that 1% of SRA modified the second peak of the pre-induction period and delayed the maximum of the main hydration peak by several days, which corresponds well with observed strength development as well as with the MIP and SEM results. These observations proved the certain incompatibility of SRA with the studied AAS system, because the drying shrinkage reduction was induced by the strong retardation of hydration, resulting in a coarsening of the pore structure rather than the proper function of the SRA. [ABSTRACT FROM AUTHOR]

The aim of this paper is the introduction of a sophisticated testing method, X-ray photoelectron spectroscopy (XPS), used to study the interface between the hydrated cement phase and polymer after mechanochemical activation, which is fundamental for the creation of macro-defect-free (MDF) composites. The XPS results clearly explain the hypothesis of a chemical reaction mechanism in the interphase regions affecting the final properties of the MDF materials. [ABSTRACT FROM AUTHOR]

Workability improvement of alkali-activated materials by common plasticizers used for ordinary Portland cement is usually an issue, but certain effectiveness is often found for lignosulfonate-based plasticizers (LS), especially for activation with sodium hydroxide (its silicate modulus considered as zero). Therefore, the action of LS depending on the silicate modulus of the activator (0, 0.10, 0.25, 0.50) was studied in this paper, using non-traditional oscillation strain sweep tests. The results showed that LS works for silicate moduli of 0 and 0.10 especially in terms of great reduction in the viscoelastic moduli due to a significant decrease in zeta potential magnitude. However, LS had a marginal effect for the silicate moduli of 0.25 and 0.50, which was attributed to the competitive adsorption of LS and silicates from waterglass onto the slag grains. Although splitting of LS chains in NaOH was proven using X-ray photoelectron spectroscopy, electrostatic repulsion of smaller fragments is preserved. [ABSTRACT FROM AUTHOR]

Alkali-activated systems (AAS) represent an ecologically and economically sustainable inorganic binder as an alternative to ordinary Portland cement (OPC). One of the main benefits of AAS is their durability in aggressive environments, which can be equal or even better than that of OPC. In this paper, the influence of the type of alkaline activator in alkali-activated blast furnace slag (AAS) in terms of resistance to sulfur dioxide corrosion was investigated. The durability testing process was based on the CSN EN ISO 3231 standard and simultaneously compared with mortar samples prepared by using Blastfurnace cement CEM III/A 32.5R. The degradation progress was evaluated by employing several different methods such as observing the compressive strength development, weight change evaluation, non-destructive testing methods like ultrasound or impact echo technique, or visual phenolphthalein technique. Subsequently, fundamental characterization of samples by the XRD method was performed during the degradation test. The obtained results indicate that none of the testing methods used could be prioritized over others to determine the resistance of AAS against the action of sulfur dioxide. For this reason, the durability testing of AAS remains an issue, and the development of specific standards considering the behavior of AAS seems necessary. [ABSTRACT FROM AUTHOR]

Hybrid systems represent a new sustainable type of cement combining the properties of ordinary Portland cement and alkali-activated materials. In this study, a hybrid system based on blast furnace slag and Portland clinker was investigated. The economic aspects and appropriate waste management resulted in the usage of technological waste from water glass production (WG-waste) as an alkaline activator. Although the Portland clinker content was very low, the incorporation of this by-product significantly improved the mechanical properties. Nevertheless, the high amount of alkalis in combination with possible reactive aggregates raises concerns about the risk of alkali–silica reaction (ASR). The results obtained from expansion measurement, the uranyl acetate fluorescence method, and microstructure characterization revealed that the undesirable effects of alkali–silica reaction in mortars based on the hydration of hybrid cement are minimal. [ABSTRACT FROM AUTHOR]

• Amino alcohol surfactants reduced the surface tension of AAS pore solutions. • Surfactants had a minor effect on autogenous shrinkage. • Drying shrinkage was reduced mainly thanks to hydration retardation caused by surfactants. • Decrease in surface tension does not necessarily lead to decrease in shrinkage. • Adsorption of surfactants on slag particles were observed. One of the most important technological problems associated with alkali-activated materials is high shrinkage. In this study, shrinkage reducing admixtures (SRAs) based on amino alcohols were used in alkali-activated slag (AAS) as strong surfactants that should, in terms of capillary pressure theory, decrease shrinkage via the decrease in surface tension. Although the surface tension of the pore solution was reduced by SRAs, autogenous shrinkage was not affected in the long run, while drying shrinkage was noticeably reduced and simultaneous weight changes were dramatically increased. The expected retardation effect of SRAs on hydration was confirmed using isothermal calorimetry, strength development, mercury intrusion porosimetry and scanning electron microscopy. The obtained results suggest that the observed effect of SRAs on drying shrinkage was caused by coarser pore structure rather than by a decrease in surface tension of the pore solution. Since the decrease in surface tension does not necessarily lead to decrease in shrinkage, the application of capillary pressure theory in AAS can sometimes be an issue. [ABSTRACT FROM AUTHOR]

Cement kiln by-pass dust (CKD) is a fine-grained by-product of Portland clinker manufacturing. Its chemical composition is not suitable for returning back into feedstock and, therefore, it has to be discharged. Such an increasing waste production contributes to the high environmental impact of the cement industry. A possible solution for the ecological processing of CKD is its incorporation into alkali-activated blast furnace slag binders. Thanks to high alkaline content, CKD serves as an effective accelerator for latent hydraulic substances which positively affect their mechanical properties. It was found out that CKD in combination with sodium carbonate creates sodium hydroxide in situ which together with sodium water glass content increases the dissolution of blast furnace slag particles and subsequently binder phase formation resulting in better flexural and compressive strength development compared to the sample without it. At the same time, the addition of CKD compensates the autogenous shrinkage of alkali-activated materials reducing the risk of material cracking. On the other hand, this type of inorganic admixture accelerates the hydration process causing rapid loss of workability. [ABSTRACT FROM AUTHOR]

Alkali-activated matrices are suitable materials for the immobilization of hazardous materials such as heavy metals. This paper is focused on the comparison of immobilization characteristics of various inorganic composite materials based on blast furnace slag and on the influence of various dosages of the heavy metal Pb on the mechanical properties and fixation ability of prepared matrices. Blast furnace slag (BFS), fly ash, and standard sand were used as raw materials, and sodium water glass was used as an alkaline activator. Pb(NO3)2 served as a source of heavy metal and was added in various dosages in solid state or as aqueous solution. The immobilization characteristics were determined by leaching tests, and the content of Pb in the eluate was measured by inductively coupled plasma optical emission spectroscopy (ICP-OES). The microstructure of matrices and distribution of Pb within the matrix were determined by scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). Increasing the dosage of the heavy metal had negative impacts on the mechanical properties of prepared matrices. The leaching tests confirmed the ability of alkali-activated materials to immobilize heavy metals. With increasing addition of Pb, its content in eluates increased. [ABSTRACT FROM AUTHOR]

The presented research investigates the application of the organosilicon admixtures based on triethoxyoctylsilane (OTES) on the hydration of the cement-based material with addition of supplementary cementitious materials (SCM) such as blast furnace slag and microsilica. The influence of silane-based admixtures on the kinetics of hydration was investigated by isothermal calorimetry. The calorimetric results disclosed that applied admixtures affect the hydration process of cement paste with SCM. The DTA/TG analysis provided the information about impact of triethoxyoctylsilane on the composition and formation of the mineral phases. The DTA/TG measurements showed noticeable changes in the thermal decomposition of the tested materials and amount of bounded water. The impact of OTES on the microstructure and pore size distribution of pastes was examined by mercury intrusion porosimetry. The result showed significant changes in the range of pore diameters. The influence of organosilicon admixtures on the compressive strength of mortars after 2, 7, 28, 56 and 90 days was also investigated. The effect depended on the mineral additive used. In case of blast furnace slag, the development of compressive strength was only delayed, however, in the case of microsilica, it was stopped. [ABSTRACT FROM AUTHOR]

Humic acids isolated from seven lignite samples from six European coal basins were characterized using spectral methods and elemental analysis and compared with each other. X-ray photoelectron spectroscopy and fluorescence spectrometry are not commonly used for the investigation of lignite humic acids, although they may provide relevant information. Comparison of the examined lignite humic acids shows that they are very similar to each other in chemical nature regarding the at least degree of aromaticity, molecular weight, and the distribution of functional groups. Fluorophores of lignite humic acids lie within the A region with typical maxima centred in the range 255–265/460–510 nm. EEM spectra have the character of fingerprints for humic acids, and lignites (as the starting material). In this work, the capacity of lignite as a parent source of humic acids for agricultural applications is appreciated mainly on the base of extractability and ash content. [ABSTRACT FROM AUTHOR]

There are many highly variable approaches to mix proportioning of alkali-activated materials (AAMs), which considerably contribute to their great complexity and often incomparability of the obtained results. Therefore, this paper suggests one specific approach, based on the molarity of the activator and the volume fraction of the precursor. First, an inherently simple calculation procedure is introduced to obtain the weights of the raw materials required to prepare a desired volume of AAM paste and possibly mortar or concrete. Second, the rationale for this approach is demonstrated using calorimetric experiments conducted on alkali-activated slag pastes, activated with sodium and potassium hydroxides, waterglasses, and carbonates in wide ranges of molarities. Third, the applicability and impact of the presented approach are discussed in-depth, considering practical applications. The overall outcome is a complex set of information emphasizing the importance of molarity, precursor volume fraction, and space-filling ability of the reaction products for different activators. • Mix designing of AAM based on activator molarity and precursor volume fraction • Space-filling ability of products for each activator also considered • Reaction kinetics of AAS mapped over the concentrations of six common activators • Molarity of 2 to 4 M Na+ or K+ recommended for slag activation • Impact of the presented approach and data discussed in a wide practical and scientific context [ABSTRACT FROM AUTHOR]

The present paper deals with the study of pH buffer influence (pH + ions) on hydration course of tricalcium aluminate (CA), monocalcium aluminate (CA), monocalcium di-aluminate (CA) and dodecacalcium hepta-aluminate (CA). These calcium aluminate phases were synthesized at 1450 °C (CA and CA), 1600 °C (CA) and 1360 °C (CA), respectively. The purity of synthesized products was controlled by X-ray diffraction (XRD). Then, different calcium aluminate phases were hydrated at 25 °C in excess of water at pH 6 and with buffers to keep the pH values at 9, 11 and 13. The evolution of hydration heat was monitored by isothermal calorimetry for 48 h. After this period, hydration was stopped and the products were cross-characterized with different techniques: XRD, high-temperature X-ray diffraction, combined differential thermal analysis-thermogravimetry-effluent gas analysis. It was found out that the hydration course and the nature of hydration products of different calcium aluminate phases are strongly dependent on the hydration environment (pH + ions). [ABSTRACT FROM AUTHOR]

The performance of immunosensing devices crucially depends on the methodology of antibody or antigen immobilization on the sensor surface. Hence, the stable intermediate layers capable of specific and reproducible binding of antibodies are required. Herein, we introduce the amine rich (NH x concentration of 6 at.%) layers prepared by pulsed plasma polymerization of cyclopropylamine (CPA) for functionalization of the quartz crystal microbalance (QCM) surface by the antibody specific to human serum albumin. In these layers the amine groups serve as anchor for the antibody binding. The sensitivity of QCM sensors prepared in this way surpasses the one for the previously reported sensors functionalized by the thiol-based self-assembled monolayers by the factor of 2. Our results thus show that CPA plasma polymers have a significant potential for further development of the active layers for biosensing applications. [ABSTRACT FROM AUTHOR]

This work deals with the use of laser-induced breakdown spectroscopy (LIBS) for determining the surface density of titanium in ultrathin layers, particularly in ultrathin layers on a steel sheet. The results obtained by LIBS spectroscopy were compared with those obtained by wavelength dispersive X-ray fluorescence spectroscopy (WDXRF), X-ray photoelectron spectroscopy (XPS) and laser ablation inductively coupled plasma time of flight mass spectrometry (LA-ICP-TOF-MS). A simple, cheap and efficient method for the determination of the surface density of titanium in thin layers has been developed. [ABSTRACT FROM AUTHOR]

The very early stages of alkaline activation of slag control its rheology and setting, but also affect its hydration, which occurs later. Simultaneously, these parameters are dictated by the nature and dose of the alkaline activator. Therefore, we investigated and compared the changes in slag particles (SEM, BET, laser diffraction), as well as in the pore solution composition (ICP–OES), pH, and conductivity, of alkali-activated slag (AAS) pastes containing the three most common sodium activators (waterglass, hydroxide, and carbonate) and water during the first 24 h of its activation. To ensure the best possible comparability of the pastes, a fairly nontraditional mixture design was adopted, based on the same concentration of Na+ (4 mol/dm3) and the same volume fraction of slag in the paste (0.50). The results were correlated with the pastes' hydration kinetics (isothermal calorimetry), structural build-up (oscillatory rheology), and setting times (Vicat). Great differences were observed in most of these properties, in the formation of hydration products, and in the composition of the pore solution for each activator. The results emphasize the role of the anionic groups in the activators and of the pH, which help predict the sample's behavior based on its calorimetric curve, and offer data for further comparisons and for the modelling of AAS hydration for specific activators. [ABSTRACT FROM AUTHOR]

Herein, we presented electromagnetic interference shielding characteristics of NiFe2O4 nanoparticles—in-situ thermally-reduced graphene oxide (RGO)—polypropylene nanocomposites with the variation of reduced graphene oxide content. The structural, morphological, magnetic, and electromagnetic parameters and mechanical characteristics of fabricated nanocomposites were investigated and studied in detail. The controllable composition of NiFe2O4-RGO-Polypropylene nanocomposites exhibited electromagnetic interference (EMI) shielding effectiveness (SE) with a value of 29.4 dB at a thickness of 2 mm. The enhanced EMI shielding properties of nanocomposites with the increase of RGO content could be assigned to enhanced attenuation ability, high conductivity, dipole and interfacial polarization, eddy current loss, and natural resonance. The fabricated lightweight NiFe2O4-RGO-Polypropylene nanocomposites have potential as a high performance electromagnetic interference shielding nanocomposite. [ABSTRACT FROM AUTHOR]