Aggregation Reaction Research Articles

Mechanical Properties of the Interface between Reactive Powder Concrete and Aggregates at Different Temperatures

Mechanical Properties of the Interface between Reactive Powder Concrete and Aggregates at Different Temperatures

Effect of alkali silica reaction on the performance of hooked bars

The Alkali-silica reaction (ASR) is a deterioration phenomenon that causes undesirable expansion and cracking in hardened concrete. This reaction usually occurs between certain types of reactive aggregates and high-alkali cement and is reported in a notable number of reinforced concrete (RC) structures worldwide, for which assessing the residual performance is critical. Many of these structures employ hooked bars to provide anchorage, especially in their joint regions. This paper examines the pull-out behavior of hooked bars in RC beam-column joints affected by ASR to help assist with safety evaluation of RC structures impacted by this reaction. A set of 7 full-scale RC columns was fabricated with concrete containing reactive fine aggregates, which incorporated different hooked bar diameters and amounts of transverse reinforcement. The specimens were subjected to pull-out of their hooked bars either in control conditions or after curing in a relative humidity of 100 % and a temperature of 50°C for up to 303 days to achieve different levels of ASR-induced expansions. Results showed that up to an unrestrained uniaxial expansion level of 0.2 %, the ASR-affected hooked bars showed an increase by up to 22 % in their ultimate pull-out capacity but a notable reduction in their ductility. Despite distributed cracking in ASR-affected specimens, their failure mode was relatively similar to that in the control specimen and remained a combination of side and front failure.

Effect of pore solution alkalinity on alkali–silica reaction (ASR) in metakaolin‐based geopolymer

AbstractGeopolymer concretes have shown better resistance against alkali–silica reaction (ASR) than ordinary Portland cement concretes, which was attributed to the low pore solution alkalinity of the geopolymer. However, the alkalinity of the geopolymer pore solution depends on the concentration and volume of the activating solutions used and age of the geopolymer. The main objective of this study was to investigate the effects of pore solution alkalinity on the ASR expansion of the metakaolin‐based geopolymer concrete. The chemistry of the pore solution of metakaolin‐based geopolymer was studied, and its reaction with reactive and non‐reactive aggregates was investigated. The concrete prism expansion tests showed no ASR‐induced expansion in geopolymer despite sufficient pore solution alkalinity to attack the reactive aggregates. The SEM and XRD characterizations confirmed that no ASR‐related gel was formed during the reaction between reactive aggregates and extracted pore solution. The chemical structure of the reaction product between aggregates and pore solution was characterized using MAS NMR and revealed no difference in the reaction products with reactive and non‐reactive aggregates. The results suggest that the pore solution alkalinity is not the sole governing parameter for ASR expansion in the geopolymer.

Assessment of possibility of decreasing alkali reactivity of aggregates by using pozzolanic materials

Assessment of possibility of decreasing alkali reactivity of aggregates by using pozzolanic materials

Alkali-Silica Reaction and Residual Mechanical Properties of High-Strength Mortar Containing Waste Glass Fine Aggregate and Supplementary Cementitious Materials

This paper presents the influence of supplementary cementitious materials (SCMs), such as fly ash (FA), silica fume (SF), ground granulated blast furnace slag (GGBS), and waste glass fine aggregate (GA), on the alkali-silica reaction (ASR) in high-strength and normal-strength mortar using an accelerated mortar bar test (AMBT). Residual mechanical properties and scanning electron micrographs were used to assess the changes in the matrix. GA reduced the mechanical properties of both normal-strength (NGA_OPC) and high-strength mortars (HGA_OPC), contributing to a decline in overall performance. This phenomenon was a result of the slipping of the GA from the matrix owing to its smooth surface. However, the inclusion of reactive SF and GGBS in the HGA improved the slip phenomenon of the GA, leading to a significant enhancement in its mechanical properties. Following the ASR expansion measurement, HGA_OPC demonstrated an ASR expansion rate approximately three times higher than that of NGA_OPC. This was attributed to the dense structure of HGA_OPC, which resulted in greater expansion than that of NGA_OPC. However, with the incorporation of SCMs into both HGA and NGA, a significant reduction in ASR expansion was observed. This was attributed to the delayed ASR of GA due to alkali activation or the pozzolanic reaction of the SCMs. Continuous exposure to the AMBT environment can lead to the destruction of GA. This was caused by the inner ASR that originated from the surface crack of the GA, which resulted in a reduction in the flexural strength of the mortar. The HGA with SF exhibited the highest resistance to ASR expansion and residual mechanical properties’ degradation. Therefore, various durability and long-term performance-monitoring studies on ultra-high-performance concrete or high-strength cementitious composites with very high SF contents and GA can be conducted.

A NEW APPROACH TO THE ACCELERATED METHOD FOR ASSESSING THE ALKALI REACTIVITY OF DOMESTIC AGGREGATES

In Poland, the prevailing protocols for examining the alkali reactivity of aggregates are based on indirect methodologies such as petrographic appraisal, in addition to direct methodologies including the measurement of expansion in mortar and concrete specimens containing the aggregate under investigation. The available research methods exhibit certain deficiencies, which have been mitigated under the experimental conditions delineated in the novel accelerated approach for ascertaining the reactivity of aggregates, otherwise known as the MCPT – Miniature Concrete Prism Test. The methodology of MCPT has the potential to become an alternative for the existing procedures of quality assessment for both fine and coarse aggregates. This work presents the assessment results of the alkaline reactivity of indigenous fine quartz aggregate, examined in accordance with the protocols established by the Polish General Directorate for National Roads and Motorways along together the novel, expedited MCPT methodology.

Enhancing the Reactivity of an Aromatic cyclo-P5 Ligand via Electrophilic Activation.

Electrophilic activation of the aromatic cyclo-P5 ligand in [Cp*Fe(η5-P5)] is demonstrated to drastically enhance its reactivity towards weak nucleophiles. Unprecedented functionalized, contracted as well as complexly aggregated polyphosphorus compounds are accessed utilizing [Cp*Fe(η5-P5Me)][OTf] (A), highlighting the great potential of this underexplored mode of reactivity. Addition of carbenes to A affords novel 1,2- or 1,1-difunctionalized cyclo-P5 complexes [Cp*Fe(η4-P5(1-L)(2-Me)][OTf] (L=IDipp (1), EtCAAC (2), IiPr (3 b)) and [Cp*Fe(η4-P5(1-IiPr)(1-Me)][OTf] (3 a). For the first time, the much smaller IMe4 leads to the contraction of the cyclo-P5 ligand and formation of [Cp*Fe(η4-P4(1-IMe)(4-Me)] (4). DFT calculations shed light on the delicate mechanism of this type of reaction, which is reinforced by the experimental identification of key intermediates. Even the comparably weak nucleophile IDippCH2 reacts with A to form [Cp*Fe(η4-P5(1-IDippCH2)(1/2-Me)][OTf] (6 a/b), highlighting its explicitly more reactive nature. Moreover, exposure of A to IDippEH (E=N, P) leads to a unique aggregation reaction affording [{Cp*Fe}2{μ2,η4:3:1-P10Me2(IDippN)}][OTf] (8) and [{Cp*Fe}2{μ2,η4:1:1:1-P11Me2(IDipp)}][OTf] (9), respectively.

Effect of low-heat cement Portland cement on alkali-silica reaction of aggregates with different alkali-reactivities

This study investigated the impact of cement clinker percentages on the alkali-silica reaction (ASR) mechanisms of aggregates with varying alkali-silica reactivity. Experimental findings indicated that the low-heat Portland cement (LHC) mitigated the development of the ASR process in soda-lime glass aggregate (SLGA) concrete. The ASR in ordinary Portland cement (OPC) mainly initiated within the SLGA, leading to crack propagation through the matrix. The in-situ X-ray micro-computed tomography test indicated that LHC altered the manifestation of ASR in concrete containing SLGA, leading to different destructive forms. Specifically, ASR between the LHC and SLGA primarily occurred at the periphery of the SLGA. The in-situ quantity analysis results illustrated that the LHC mitigated the ASR-induced cracks in the SLGA concrete. For the less alkali-reactive natural aggregate, the effect of LHC cement on ASR was diminished. ASR still only occurred within the natural aggregate concrete, distributing in highly alkali-reactive phases inside the aggregates. The chemical analysis results supposed that the differing ASR pathways could be attributed to the interaction between the calcium content in the LHC and the spatial distribution of alkali-reactive phases within the aggregates. These findings help interpret the mechanism of the slower ASR process in the belite-rich cement concrete.

Upcycling Spent Waterglass Foundry Sand into Reactive Fine Aggregates for Alkali-Activated Slag to Achieve Enhanced Compressive Strength

Upcycling Spent Waterglass Foundry Sand into Reactive Fine Aggregates for Alkali-Activated Slag to Achieve Enhanced Compressive Strength

Suppressing of alkaline aggregate reaction (AAR) through waterproofing of concrete surface, aggregates, and mortars

Water is necessary for the alkali aggregate reaction to occur and this study investigates the impact of waterproofing on alkali-aggregate reaction (AAR) in concrete by separating water from alkali reactive aggregates through surface, aggregate, and matrix treatments. Accelerated mortar bar tests (AMBT) are conducted to analyze the expansion caused by alkali aggregates. Furthermore, the suppressive mechanism of waterproofing on AAR is explored using scanning electron microscopy (SEM), while the influence of waterproof concrete aggregate and matrix on pore characteristics and hydration products is assessed using nuclear magnetic resonance (NMR) and X-ray diffraction (XRD). The results demonstrate that surface waterproofing with silane and polyvinyl alcohol (PVA) effectively suppress AAR. Moreover, PVA-coated aggregates significantly enhance the compactness of the interfacial transition zone (ITZ) in concrete. Based on these findings, an improved model considering waterproofness is proposed to quantify the degree of alkali aggregate reaction. These findings offer valuable guidance for controlling AAR.

Influence of enforced carbonation on alkali-silica reaction: Performance and multi-scale mechanisms

Alkali-silica reaction (ASR) has emerged as one of the major concrete deterioration issues. Despite the extensive effort investments in ASR mitigation, the interaction between ASR and carbonation remains unclear. To investigate the role and mechanisms of early-age enforced carbonation in ASR, enforced carbonation conditions at 50 °C and 95 % RH with different CO2 concentrations up to 20 % were employed at two stages. The ASR mitigation efficacy was evaluated by monitoring the volume expansion and cracking behavior of mortars containing reactive aggregates. A comprehensive understanding was obtained by analyzing the evolutions of ASR gel's composition, molecular structure, and hygroscopicity. The results indicate that ASR can be effectively suppressed under carbonation with a 97.9 % decrease in ASR-induced volume expansion and fully suppressed cracking when the mortars were cured at 20 % CO2 for 30 days. The decreases in the Q3 polymerization sites and [K + Na]/Si ratios of the ASR products, as well as the 30.3 % reduction in water uptake capacity of ASR gels under carbonation, uncovered the underlying mechanisms for the mitigated ASR at multiple length scales.

High entropy Prussian Blue Analogues assisted by reduced graphene oxide for enhancing the lifespan of Sodium-ion batteries

In recent years, Prussian blue analogues (PBAs) have been regarded as one of the most promising cathode materials for Sodium-ion batteries (SIBs) due to their open structure, low cost, and high theoretical capacity. However, the problem of capacity degradation caused by phase transitions during the charge/discharge process has so far limited the applicability of PBAs. While the high entropy strategy can alleviate capacity decay induced by phase transitions, challenges such as low conductivity, material aggregation, and severe interface reactions between electrode materials and electrolytes still persist. Therefore, we used a simple and scalable one-step co-precipitation method to grow high entropy Prussian blue analogues (HEPBA) on reduced graphene oxide (rGO) to address these problems. The rGO not only inhibits material agglomeration but also separates the electrolyte from the electrode material to prevent severe interface reactions. Meanwhile, the Warburg impedance is reduced and the Na+ diffusion performance is improved. When high entropy Prussian blue grown on an rGO matrix (HEPBA@rGO) is utilized as the cathode in a half-cell, it exhibits high discharge specific capacity (115.2 mAh g−1 at 100 mA g−1), long cycling stability (retaining 84.6 mAh g−1 after 1000 cycles), and good rate capability (62 mAh g−1 at 15 C). The full battery with HEPBA@rGO as the cathode and hard carbon as the anode has a high specific discharge capacity (100.12 mAh g−1 at 100 mA g−1), good stability (capacity retention rate of 81 % after 150 charge/discharge cycles), and good rate performance (72.5 mAh g−1 at 5 C). This study provides valuable insights for the development of SIBs.

Electromagnetic wave absorption performance of porous geopolymer: Dual effects of fly ash on alkali activation and microwave dissipation

The simultaneous occurrence of aggregation reactions in fly ash (FA) facilitates the uniform dispersion of internal ferrite into the geopolymer. Considering the excellent impedance matching and multiple reflection effects of foam concrete, this paper develops a ‘zero-absorber’ foam geopolymer-based electromagnetic absorbing material. The effects of different densities (400, 600, 800, 1000, 1200 kg/m3) and FA contents (40 %, 50 %, 60 %, 70 %, 80 %) on the electromagnetic absorption performance of foam geopolymer are investigated, respectively. Combined with the iron element distribution and 3D pore structure by SEM and X-CT analysis, the dissipation mechanism of electromagnetic energy by FA and pore structure in foam geopolymer are further explored. Experimental results show that FA can uniformly disperse inherent ferric ions from the matrix into the geopolymer during the polymerization reaction, leading to excellent magnetic losses through magnetic moment orientation adjustment and intermolecular friction interactions without adding external absorber. Additionally, the uniformly dispersed porous structure consumes incident electromagnetic energy through reflection, scattering, coherent attenuation, and interference resonance loss effects. It shows multi-scale electromagnetic absorption effects in the ‘zero-absorber’ foam geopolymer-based electromagnetic absorbing material, including pore structure multiple reflections (millimeter scale), inter-pore wall interference resonance (micrometer scale), and ferric ion magnetic loss (nanometer scale). For the foam geopolymer with 1000 kg/m3 density and 50 % FA, it achieves the optimal electromagnetic absorbing performance with the minimum reflection loss (RL) of −34.9 dB and the effective absorption bandwidth of 14.1 GHz (RL below −10 dB) in 2–18 GHz range.

On the Importance of Solar Radiation and Shading for the Alkali–Aggregate Reaction Prediction of Concrete Arch Dams

On the Importance of Solar Radiation and Shading for the Alkali–Aggregate Reaction Prediction of Concrete Arch Dams

U-Pb dating of Barra Velha carbonates reveals the influence of Santos Basin sedimentary and tectonothermal history on pre-salt carbonate ages

The depositional age and diagenetic history of the Upper Barra Velha carbonates are poorly understood. To clarify the geochronology of these events and the behavior of the U-Pb isotopic system in carbonates, we conducted an integrated petrographic, QEMSCAN imaging, and in situ U-Pb dating study of calcites and dolomites from the Barra Velha Formation, in the central Santos Basin (SE Brazil). Our results span three geochronological intervals, which are ∼125 Ma, ∼116-114 Ma, and ∼105-100 Ma. The U-Pb isotopic system of calcite allochems was disturbed, yielding ages of ∼115 Ma and ∼105-100 Ma. These ages coincide with magmatic and hydrothermal events in the pre-salt. Dolomites showed that geochronological disturbance of carbonate components may not be pervasive but rather related to fluid-rock interactions and properties of rocks and their constituents such as mineralogy, porosity and permeability. This is evidenced by the U-Pb system of non-porous, non-permeable, and less reactive dolomitic aggregates remaining undisturbed. Eodiagenetic microcrystalline and fine dolomite rhombs provided evidence of Barremian ages, challenging the belief that the Upper Barra Velha deposits are Aptian. Other eodiagenetic dolomites occur as ∼117 Ma eodiagenetic lamellar dolomites, as pseudomorphic dolomites that underwent U-Pb alteration at ∼100 Ma, and as ∼112 Ma pervasive rhombohedral dolomites associated with Mg-rich fluids percolation in the Upper Barra Velha carbonates. Blocky dolomite and saddle dolomite cements have ages of ∼100 Ma, with saddle dolomite constraining the latest silicification event as > 100 Ma. This research elucidates significant geological events, processes, and factors (including magmatic activity, hydrothermal alteration, fluid-rock interactions, and petrographic and mineralogical controls) that influenced the ages of the Upper Barra Velha carbonates. Moreover, it aids in reconstructing the depositional and diagenetic history of the Barra Velha Formation and enhances the understanding of the Santos Basin tectonothermal evolution.

Calcium nitrate effectively mitigates alkali–silica reaction by surface passivation of reactive aggregates

AbstractCalcium nitrate (CN: Ca(NO3)2) has been shown to mitigate alkali–silica reaction (ASR) in concrete. Such ASR mitigation has been suggested to be on account of precipitate (i.e., barrier or passivation layer) formation‐induced dissolution inhibition of reactive/dissolving aggregate surfaces. Herein, we examine the ability of CN to mitigate ASR across two cements (Type I/II and Portland Limestone Cement), for aggregates of varying reactivity, and across different types and dosages of SCMs (supplementary cementitious materials, i.e., amorphous steel slag and Class C and Class F fly ashes). Based on expansion measurements carried out as per ASTM C1260/C1567, it is observed that CN, as a function of dosage, substantively mitigates ASR in mortar formulations across aggregate types. Careful microstructural examinations, dissolution studies, and thermodynamic calculations indicate that CN induces the formation of C–S–H, portlandite (Ca(OH)2), and calcite (CaCO3) precipitate mixtures, which form on aggregate surfaces at the expense of typical ASR gels. Such precipitates create a dissolution barrier and inhibit ASR in both SCM‐free and SCM‐containing formulations. The outcomes indicate that CN is an efficient and cost‐effective ASR mitigation additive (∼$250–$600 per tonne), particularly in a time of dwindling fly ash supplies and unaffordable lithium prices (>∼$12 000 per tonne).

The shear rate promotes pinocytosis of extracellular dextran in platelets.

Several conventional studies focused on platelet pinocytosis for possible utilization as drug delivery systems. Although platelet pinocytosis is important in such utilization, the impact of the shear rate on pinocytosis is unclear. Our objective was to investigate the relationship between shear rate and platelet pinocytosis in vitro. In addition, this study addressed the change in platelet aggregation reactivity with adenosine diphosphate (ADP) stimulation after pinocytosis. Porcine platelet-rich plasma was mixed with fluorescein isothiocyanate (FITC)-conjugated dextran and incubated for 15 min under shear conditions of 0, 500, and 1500 s-1. After incubation, confocal microscopic scanning and three-dimensional rendering were performed to confirm the internalization of FITC-dextran into platelets. The amount of FITC-dextran accumulated via platelet pinocytosis was compared using flow cytometry at each shear rate. In addition, light transmission aggregometry by ADP stimulation was applied to platelets after pinocytosis. The amount of intracellular FITC-dextran increased with higher shear rates. Platelets with increased amounts of intracellular FITC-dextran did not show changes in the aggregation reactivity to ADP. A higher shear rate promotes platelet pinocytosis, but enhanced pinocytosis does not affect aggregation sensitivity, which is stimulated by ADP.

The role of shear forces in primary and secondary nucleation of amyloid fibrils

Shear forces affect self-assembly processes ranging from crystallization to fiber formation. Here, the effect of mild agitation on amyloid fibril formation was explored for four peptides and investigated in detail for A[Formula: see text]42, which is associated with Alzheimer's disease. To gain mechanistic insights into the effect of mild agitation, nonseeded and seeded aggregation reactions were set up at various peptide concentrations with and without an inhibitor. First, an effect on fibril fragmentation was excluded by comparing the monomer-concentration dependence of aggregation kinetics under idle and agitated conditions. Second, using a secondary nucleation inhibitor, Brichos, the agitation effect on primary nucleation was decoupled from secondary nucleation. Third, an effect on secondary nucleation was established in the absence of inhibitor. Fourth, an effect on elongation was excluded by comparing the seeding potency of fibrils formed under idle or agitated conditions. We find that both primary and secondary nucleation steps are accelerated by gentle agitation. The increased shear forces facilitate both the detachment of newly formed aggregates from catalytic surfaces and the rate at which molecules are transported in the bulk solution to encounter nucleation sites on the fibril and other surfaces. Ultrastructural evidence obtained with cryogenic transmission electron microscopy and free-flow electrophoresis in microfluidics devices imply that agitation speeds up the detachment of nucleated species from the fibril surface. Our findings shed light on the aggregation mechanism and the role of detachment for efficient secondary nucleation. The results inform on how to modulate the relative importance of different microscopic steps in drug discovery and investigations.

Elucidating the role of magnesium in alkali-silica reaction: Performance and mechanisms

Alkali-silica reaction (ASR) is a major concrete deterioration causing volume expansion, cracking, and hence degradations in the strength and permeability of concrete structures. Despite a variety of ASR mitigation approaches having been investigated, the successful use of chemical admixture is limited to lithium salts, which have negative impacts on cement hydration and shrinkage behavior of concrete. To explore alternative substances for effective and economic ASR mitigation, the role of magnesium nitrate in mortars containing reactive aggregate is investigated at varying Mg/alkali ratios from 0 to 3.0 in terms of volume expansion, cracking behavior, silica dissolution, and modifications of ASR products. The results indicate that, at a Mg/alkali ratio of 0.74, the expansion and surface cracking density of the ASR-impacted mortar were decreased by 21.1 % and 39.1 %, respectively, which is superior to the efficacy of lithium nitrate. The 51.3 % less silica dissolution from aggregate, suppressed ASR gel formation, fewer Q3 polymerization sites in the silicate chains, less packed structure, and reduced alkali/Si ratio of the reaction products elucidate the underlying mechanisms across multiple length scales.

Plumbagin accelerates serum albumin's amyloid aggregation kinetics and generates fibril polymorphism by inducing non-native β-sheet structures

The ligand-induced conformational switch of proteins has great significance in understanding the biophysics and biochemistry of their self-assembly. In this work, we have investigated the ability of plumbagin (PL), a hydroxynaphthoquinone compound found in the root of the medicinal plant Plumbago zeylanica, to modulate aggregation precursor state, aggregation kinetics and generate distinct fibril of human serum albumin (HSA). PL was found to moderately bind (binding constant Ka ∼ 10−4 M−1)) to domain-II of HSA in the stoichiometric ratio of 1:1. We found that PL-HSA complex aggregation was accelerated as compared to that of HSA aggregation and it may be through an independent pathway. We also detected that fibril produced in the presence of PL is wider in diameter, contains a higher amount of β-sheet (∼18%) and disordered (∼46%) structures, and is less stable. We concluded that the acceleration of aggregation reaction and generation of fibril polymorphism was mainly because of the higher extent of unfolding and high content of non-native β-sheet structure in the aggregation precursor state of PL-HSA complex. This study offers opportunities to explore the ability of ligand binding to modulate aggregation reactions and generate polymorphic protein fibrils.