Aggregation Reaction Research Articles

Development of prediction models for evaluation of alkali-silica reaction in concrete

Alkali-silica reaction (ASR) and expansion induced are one of the major concerns over durability of concrete structures. It causes an increase in internal stresses and hence deteriorating mechanical properties, reducing load capacity, and compromising structures’ serviceability. Factors governing ASR include water-to-cement ratio, alkali content, the content of reactive aggregate, exposure temperature, relative humidity, etc. Previous prediction models for ASR expansion focus on the measurements under particular conditions and these models are suffering from the neglect of effects of some factors. This study aims to propose a back-propagation neural network (BPNN) model to predict ASR by considering both mix compositions and environmental conditions. In this paper, by adopting two different training functions, namely Levenberg-Marquardt function (LM) and Bayesian regularisation backpropagation (BR), two models of LM-BPNN and BR-BPNN were developed and proposed. To achieve this, a database containing 168 pairs of data from 25 studies was established, its data includes water-to-cement ratio, cement content, alkali fraction, content of non-reactive and reactive fine/coarse aggregate, temperature, and relative humidity. Results indicate that both LM-BPNN and BR-BPNN models can produce reasonable estimates for ASR expansion at 180 days with MSE and R of 0.00209%, 0.002753%, 0.926 and 0.912, respectively. Results reveal that fraction of reactive fine/coarse aggregate is dominant on ASR expansion while alkali content and humidity have a significant correlation with expansion. Water-to-cement ratio, cement content, and content of non-reactive fine/coarse aggregate have low impact on ASR expansion based on the results.

Dip Coating of Water‐Resistant PEDOT:PSS Films Based on Physical Crosslinking

AbstractWater‐resistant poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films are valuable in biomedical applications; however, they typically require crosslinkers to stabilize the films, which can introduce undesired aggregation or phase separation reactions. Herein, a dipping‐based process to prepare PEDOT:PSS films on nonplanar surfaces without crosslinker is developed. Sequential soaking of a dip‐coated PEDOT:PSS film in ethanol and water imparts water resistance to the film. Microscopic and spectroscopic techniques are used to monitor the process and confirm that the ethanol soaking elutes the excess PSS from the film bulk, which stabilizes the film prior to the water‐soaking process. The obtained films act as conductors and semiconductors on curved surfaces, including 3D‐printed objects. A film deposited on a curved surface is successfully applied as the channel layer in a neuromorphic organic electrochemical transistor. This approach can enable integrated bioelectronic and neuromorphic applications that can be readily deployed for facile prototyping.

Failure criteria and microstructure evolution mechanism of the alkali–silica reaction of concrete

Abstract In this study, the influence of two distinct reactive aggregate dosages on the alkali–silica reaction (ASR) of concrete was investigated. The expansion ratio, axial compressive strength, splitting tensile strength, and relative dynamic elastic modulus (RDEM) of concrete were considered as the main parameters to study the failure criteria of concrete induced by ASR at 40°C. Microscopic experiments, such as scanning electron microscopy and X-ray computed microtomography, were applied to analyze the damage induced by ASR on the concrete prisms and the propagation of internal cracks of the reactive aggregates in nanospace. The results showed that the two ranges can be used as the failure criteria produced by the ASR of concrete containing 3 and 6% dosages of reactive aggregates at 40°C, respectively, when the RDEM of concrete was reduced to 70‒75% and 85‒90%. Additionally, the results of CT indicated that microcracks tended to extend from the initial defects of aggregate to the cement slurry. Meanwhile, ASR gel packed with the pores, which reduced the porosity. It was noteworthy that the adhesive force between the ASR gel and the cement matrix after filling pores could not make up for the loss of the mechanical properties of concrete.

Use of Coal Mine Overburden as Sustainable Fine Aggregate in Cement Mortar

The natural aggregate crisis is an alarming concern for the construction industry worldwide. This study provides a detailed investigation of coal mine overburden (OB) from opencast mine dumps, to evaluate its potential as a sustainable alternative to natural aggregate. The microproperties, including mineralogy, morphology, and chemistry, were evaluated, and the macroproperties, including alkali–aggregate reaction, soundness, durability, flow value, ultrasonic pulse velocity, and other mechanical properties of crushed OB, OB-based mortar, and concrete, were determined. OB was found to be mineralogically more stable (55%–77% SiO2), mechanically comparable, and durable (volume change 3%–8%) than other alternatives of natural aggregate. The toxicity characteristic due to leaching was found to have no hazardous effects on local and regional soil and water quality. The cement mortar prepared using OB had similar performance in terms of fresh and hardened density, flowability (>0.6 w/c), and durability [slake durability index (SDI) >95%] as other industrial by-products. The compressive strength of the mortar with OB was found to be comparable to that of mortar with river sand. OB-based mortar and concrete were found to have good corrosion resistance. For bulk utilization of OB, a pilot-scale study is recommended to assess its performance under real-world exposure conditions.

Expansion and Mitigation of Alkali-Silica Reaction in Binary Blended Concrete Confining Potentially Reactive Aggregates

Without a cure but preventable, Alkali-Silica Reaction (ASR), dubbed the “Concrete Cancer,” happens when alkali in cement bonds with silica in aggregates to form an expansive gel. This research aims to investigate expansion and influence mitigation of ASR in concrete by identifying potentially reactive aggregates causing its onset and using binary blended cement to slow down unwanted gel expansions through the mitigative ability found in its fly ash component. This research also observed variations in expansive behavior and the physical changes that arose after the experiments. Aggregate samples were collected from different quarries in Davao, Philippines, denoted as Deposit A, Deposit B, Deposit C, and Deposit D. These deposits were tested according to the ASTM C1260: Accelerated Mortar Bar Tests (AMBT) to identify a reactive group. Three aggregate groups, Deposit A, Deposit B, and Deposit C, were tagged as reactive due to exhibiting more than a 0.1% increase in lengths, indicating unideal expansion. Additional sets of AMBTs were done for the identified aggregates using blended cement as a binder to test the combinations' ability to minimize expansion. This resulted in an average expansion decrease per set of approximately 78%, 82%, and 85% for A, B, and C, respectively, further strengthening the reputation of fly ash as an effective mitigating SCM against ASR.

Preparation of reactive urchin-like recycled concrete aggregate by wet carbonation: Towards improving the bonding capability of the interfacial transition zone in recycled aggregate concrete

To enhance the bonding capability between recycled concrete aggregate (RCA) and paste, an innovative carbonation method was developed to modify the surface characteristic of RCA by promoting the formation of needle-like aragonite using accelerated carbonation in Mg(NO3)2 solution under an elevated temperature (75 °C). The evolution of surface microstructure, phases and reaction kinetics was investigated using multiple testing methods including scanning electron microscopy, nanoindentation, X-ray diffraction, etc. The results revealed that reactive urchin-like RCA could be prepared within less than an hour after exposing to CO2. The urchin-like wrapping with a thickness of about 100 μm was seen rapidly grown on the surface of RCA, consisting of an outermost layer of aragonite coating, a thin layer of brucite and a silica-rich layer. The mineral wrapping induced by carbonation significantly modified the roughness, topography and geochemistry of RCA's surface entirely, contributing to enhanced bonding strength between RCA and new mortar (33.54%).

Study of the mechanism of inhibiting alkali-aggregate reaction and self-healing in concrete materials

Concrete is one of the most widely used materials in the world; however, several pathological manifestations can be associated with the design, execution, and selection of its constituent materials. Cracks, one of these pathological manifestations, are caused by the alkali-aggregate reaction (AAR). This is a chemical phenomenon in which silica, which is present in aggregate, reacts with alkali ions of the cement paste to produce an expansive silica-alkali gel. Herein, the clogging mechanism of the pathological cracks, which form during AAR, was investigated using a reference mortar trace, in order to select innocuous and reactive aggregates. Expansion in the mortar mix was examined using these two types of aggregates: (i) a potentially reactive aggregate, which can promote the formation of pathological cracks during AAR, and (ii) an innocuous aggregate to establish a reference trace without any expansive reaction. Subsequently, a concrete mix was characterized and reactivities of its constituents evaluated. In addition, fine and coarse granulometry analyses were performed. The concrete mix was dosed with the mortar mix, which comprised potentially reactive aggregate, and the bars were molded for the expansion tests. The crystalline mineral additive was added in these concretes to observe the clogging of the cracks. Comparative evaluation of the concrete mix, with and without reactive aggregate, suggested the occurrence of clogging because of the autogenous healing caused by chemical reactions, resulting in a reduction in the expansion of the concrete bars, with crystalline additive, at day 56.

Comparative study on the effect of different supplementary cementitious materials on Alkali-silica reaction of self-compacting concrete

Self-compacting concrete (SCC) has been increasingly used in construction industry especially in prefabricated concrete applications. Alkali-silica reaction (ASR) is a deleterious reaction between reactive aggregate and alkalis in cement. This reaction can lead to serious expansion and cracking in concrete, causing major structural problems. The deployment of supplementary cementitious materials (SCMs) emerges as a promising solution to counter ASR effects. Therefore, it is important to understand the role SCMs can play to eliminate the effect of ASR in SCC. In this study, the effect of ground granulated blast-furnace slag (GGBS), fly ash (FA) and limestone powder (LSP) on the potential of ASR in SCC was assessed. To evaluate ASR, two standardized methodologies, RILEM AAR-4 and ASTM C1260, were adopted. Additionally, assessments encompassed fresh and hardened properties, alongside transport dynamics such as permeability and capillary absorption. It was found that the properties of fresh and hardened concrete are greatly affected by the type of SCMs used. The main findings of the study showed that SCC-GGBS outperformed other SCMs against ASR.

CORROSION RATE OF REINFORCED CONCRETE WITH COMBINED DETERIORATION BY CHLORIDE ATTACK AND ASR

Chloride ions destroy the passive film of steel bars in concrete and induce corrosion. Moreover, the alkali-silica reaction (ASR) produces map cracks in concrete through the formation and expansion of a hygroscopic gel around aggregates. Some existing structures simultaneously experience these two types of deteriorations. In this study, the corrosion rate of steel embedded in mortar with this combined deterioration was evaluated. That is, the presence or absence of reactive aggregates and chloride ions was set as experimental parameters, and specimens with single or combined deterioration of chloride attack and ASR were produced. Cracks and rebar corrosion rates were measured and the influences of chloride ions and ASR on rebar corrosion were discussed based on the polarization curves and resistivity. As conclusions, compared with chloride attack alone, concrete with combined deterioration had more oxygen supply through ASR cracks and a faster corrosion rate. Furthermore, the presence of chloride ions facilitated the formation of electric circuits. In contrast, ASR cracks hindered the formation of an electric circuit. Therefore, the mortar resistivity was the lowest in the case of chloride attack alone, the highest in the case of ASR alone, and intermediate in the case of combined deterioration.

A comparative study of ethylenediamine tetraacetic acid induced gas-solid and liquid-solid accelerated carbonation for enhancement of steel slag aggregates

Accelerated carbonation is an effective technique to enhance the hydration reactivity and volume stability of steel slag aggregates (SSA). However, due to limitations in CO2 transport and carbonation kinetics, carbonation of SSA is frequently carried out using pure CO2 under high pressures. In this study, carbonation under 10% CO2 concentration and ambient temperature and pressure was employed to treat SSA. To accelerate the carbonation of SSA, ethylenediamine tetraacetic acid (EDTA)-induced gas–solid (dry) and liquid–solid (wet) carbonation processes were proposed. Effect of EDTA on the physical and mechanical properties and microstructure of carbonated SSA; and the performance of resulting concrete with a selected mix design were examined. Dry carbonation of SSA, prior to which EDTA was sprayed on the surface of SSA, resulted in a denser carbonated layer and consequently higher specific gravity compared to uncarbonated SSA. Concrete samples involving carbonated SSA, on which 0.1 mol/L EDTA was sprayed at 50% of water absorption mass of SSA, followed by carbonation curing for 24 hrs, revealed 24% increase in strength and 75% reduction in expansion when compared to those containing uncarbonated SSA. Wet carbonation of SSA, during which CO2 was injected into SSA-EDTA solution, promoted both carbonation and hydration of SSA, especially in 0.2 mol/L EDTA solution, resulting in the consumption of periclase and enabling the formation of brucite. While strength improvement was not obvious in the presence of brucite that weakened the interfacial transition zone (ITZ) of concrete, expansion was further reduced by the reduced periclase in SSA. Comparatively, EDTA-induced dry carbonation was more effective and required only 0.4 kg EDTA per tonne of SSA.

Petrographic Evaluation of Aggregate from Igneous Rocks: Alkali–Silica Reaction Potential

A thorough petrographic evaluation of aggregates from igneous rocks in terms of their alkali–silica reaction (ASR) potential is crucial in ensuring the durability and long-term performance of concrete structures, especially those where access to additional alkalis is possible, such as from de-icing agents. The aim of the research was to assess the potential reactivity of aggregates from igneous rocks, as only such aggregates are used for concrete airport pavements in Poland. Petrographic analysis was conducted to identify the reactive minerals in the aggregate, and it was extended by quantitative image analysis. The strained, microcrystalline and cryptocrystalline quartz were found to be reactive components but significantly differed in content. It was found that aggregates from igneous rocks were characterized by different susceptibility to ASR and that methods to mitigate the occurrence of ASR should be considered to be used in airfield concrete. A relationship between the content of analyzed reactive minerals and the expansion of mortar bars in AMBT, as well as of the concrete prism in the CPT method, was revealed.

Concrete Alkali–Aggregate-Reactivity-Induced Steel Reinforcement Corrosion

The alkali–aggregate reactivity (AAR) of concrete, long known for mass concrete, can also induce corrosion of steel in reinforced concrete structures. Several examples are given for which the origin of observed reinforcement corrosion and loss of concrete cover originally was attributed to chloride-induced or to carbonation-induced reinforcement corrosion. Critical reviews of these cases, using available information, suggest that, more likely, the observed crack patterns and concrete deterioration are the result of long-term AAR-induced concrete matrix expansion and loss of concrete strength and that these effects occurred prior to the eventual initiation of reinforcement corrosion. This proposition is supported by finite element and other stress analyses of various concrete–steel ensembles. They show that concrete expansion produces tensile stresses localised at and near exterior concrete surfaces or relative to the reinforcement. The locations of high-stress and -strain zones so produced correlate with field observations of long-term concrete cracking and delamination. The present interpretations highlight that AAR may be a significant contributor to initiation and subsequent long-term development of reinforcement corrosion in structurally reinforced concretes.

Efficient degradation of chloroquine phosphate by peroxymonosulfate activated using reusable lanthanide cobalt-copper perovskite-cerium dioxide composite catalyst: Performance, mechanism and degradation pathway

In recent years, chloroquine phosphate (CQP) has been widely used as a specific drug for treating COVID-19. Because of its biological toxicity, the release of CQP into water is bound to have a potential impact on human health. It is urgent to find a reusable and efficient catalyst to treat a large number of CQP wastewater. Currently, perovskite-type catalysts are gradually entering the field of advanced oxidation process, but there are still some problems such as high particle aggregation and limited reaction contact. Here, LaCo0.5Cu0.5O3-CeO2 was prepared by sol-gel method and used to activate peroxymonosulfate (PMS) to degrade CQP for the first time. The LaCo0.5Cu0.5O3-CeO2 material has better stability, larger specific surface area and more uniform pore structure. Under the conditions of 0.2 g/L catalyst and 1.0 mM PMS, 20 mg/L CQP can be completely degraded within 8 min and is suitable for a wide pH range and complex water quality. Superoxide free radical (·O2-) and the singlet oxygen (1O2) are the main free radicals to degrade CQP. The addition of CeO2 makes Ce4+/Ce3+ participate in the redox cycles between Co3+/Co2+ and Cu2+/Cu+, realizing the multipath electron transfer. In addition, LaCo0.5Cu0.5O3-CeO2/PMS system can degrade CQP into low toxicity products through different pathways, ultimately mineralizing it into inorganic small molecules. In general, LaCo0.5Cu0.5O3-CeO2 has more reasonable structure, efficient and durable catalytic performance, anti-interference ability and low ion leaching level, which provides a new idea for preparing heterogeneous catalyst to activate PMS to treat pharmaceutical wastewater, and has broad practical application prospects.

Evaluating the efficiency of SCMs to avoid or mitigate ASR-induced expansion and deterioration through a multi-level assessment

It is widely accepted that Alkali-Silica Reaction (ASR)-induced expansion and deterioration may be prevented by the appropriate use of supplementary cementing materials (SCMs). Nevertheless, the correlation between microscopic/macroscopic damage degree and features of SCMs-made concrete is still not fully understood. Moreover, more research needs to be conducted to understand the impact of SCMs on the elastic properties of ASR-secondary products. This research presents the results of a multi-level assessment of ASR-induced damage development in concrete incorporating a wide range of reactive aggregates and SCMs at selected unrestrained expansion levels (i.e., 0.00 %, 0.05 %, 0.12 %, 0.20 % and 0.30 %). Furthermore, a thorough discussion is made on the damage generation and propagation at distinct locations of affected concrete: aggregate particles, ITZ and cement paste. Results indicate that higher volumes of SCMs can slightly change ASR damage development by lowering the formation of cracks in the cement paste and altering ASR reaction products' chemo-mechanical properties.

Multimerizations, Aggregation, and Transfer Reactions of Small Numbers of Molecules.

Chemical equilibria of multimerizations in systems with small numbers of particles exhibit a behavior seemingly at odds with that observed macroscopically. In this paper, we apply the recently proposed expression of equilibrium constant for binding, which includes cross-correlations in reactants' concentrations, to write an equilibrium constant for the formation of clusters larger than two (e.g., trimer, tetramer, and pentamer) as series of two-body reactions. Results obtained by molecular dynamics simulations demonstrate that the value of this expression is constant for all concentrations and system sizes, as well as at an onset of a phase transition to an aggregated state, where densities in the system change discontinuously. In contrast, the value of the commonly utilized expression of equilibrium constant, which ignores correlations, is not constant and its variations can reach few orders of magnitude. Considering different paths for the same multimer formation, with elementary reactions of any order, yields different expressions for the equilibrium constant, yet, with exactly the same value. This is also true for routes with essentially zero probability to occur. Existence of different expressions for the same equilibrium constant imposes equalities between averages of correlated, along with uncorrelated, concentrations of participating species. Moreover, a relation between an average particle number and relative fluctuations derived for two-body reactions is found to be obeyed here as well despite couplings to additional equilibrium reactions in the system. Analyses of transfer reactions, where association and dissociation events take place on both sides of the chemical equation, further indicate the necessity to include cross-correlations in the expression of the equilibrium constant. However, in this case, the magnitudes of discrepancies of the uncorrelated expression are smaller, likely because of partial cancellation of correlations, which exist on both the reactant and product sides.

Diagnosis of durability-related problems in concrete structures through comprehensive analysis and non-destructive testing: a case study

ABSTRACT The present study investigated concrete durability problems at the National University of Sciences and Technology,Pakistan, through comprehensive analysis and non-destructive testing. During the visual inspection of concrete structures, different deterioration mechanisms such as alkali-silica aggregate reaction (ASR), carbonation, abrasion and drying shrinkage were found. After visual inspection, the data on ingredients used in the construction of various structures were collected, revealingthat different brands of cement used in construction contained high alkali-equivalent content. Fine aggregates were used from two different quarries during construction. The available literature and X-ray Diffraction (XRD) results showed that both the quarries’ aggregates have the potential for alkali-silica reactivity. Furthermore, the XRD results of gel-type material collected from mapped cracking indicated the presence of delhayelite, similar to alkali-silica gel, suggesting ASR. The XRD curves of the whitest powder collected from various sites showed the presence of sodium sulfate and calcium carbonate peaks, indicating salt hydration attacks. The carbonation rate in concrete ranges from 4.33 to 5.77 mm/year. The results of the rebound hammer and pulse velocity test indicated that concrete used in parking has low strength which is the main cause of abrasion. Based on these findings a few recommendations have been presented to avoid durability-related problems in future structures.

Effects of Bamboo Leaf Ash on Alkali-Silica Reaction in Concrete

The construction industry is generally faced with so many challenges of which deterioration in concrete structures caused by Alkali-silica reaction (ASR) is one of the pressing challenges. This reaction induces expansion in concrete, resulting in its eventual cracking and subsequent failure. Research direction is being geared towards obtaining properties of pozzolanic concrete of recently discovered different biogenic pozzolans such as bamboo leaf ash (BLA). BLA has been proven to be acceptable in terms of compressive strength and some other properties but few researches have been performed on the impacts of ASR on BLA concrete structures. This research work focuses on investigating the properties of BLA through X-ray diffraction and fluorescence analyses, and its effectiveness in resisting or eliminating ASR that may be present in concrete. Tests were performed on concrete bars soaked in NaOH at a temperature of 80 oC to determine the possible reactivity of aggregates to ASR. In addition, workability and the compressive strengths of BLA concrete at different percentage levels were determined after curing for 7, 28 and 56 days. The findings of the research show that BLA improves the workability of fresh concrete, however, it causes a decline in the compressive strength of concrete when compared with the strength of conventional concrete. Also, BLA has no detrimental effect on the linear expansion of concrete. This study recommends that a 5% partial replacement of cement with BLA will give effective performance when used in areas where strength is not the major priority. Alkali-silica reaction, bamboo leaf ash, compressive strength, concrete, construction, linear expansion, pozzolans

Preventing ASR-induced deteriorations with hydrophobic aggregates- a feasibility study

Concrete deterioration due to alkali-silica reaction (ASR) is one of the main durability concerns. This study explores the feasibility of minimizing ASR-induced deterioration by enhancing aggregates' hydrophobicity. Mortar samples with highly reactive aggregates were prepared. The aggregates were modified through coating with hexamethyldisilazane (HMDS) pretreated fumed silica for improved hydrophobicity. The ASR progression of the specimens prepared with nontreated (control-NHA), washed-coated (WHA), and non-washed coated aggregates (HA) was assessed using compressive strength, linear expansion, and dynamic modulus of elasticity tests. In addition, an ASR detection reagent was used to study the extent of deterioration of the mortar specimens. Furthermore, the microstructure and chemical compositions of the ASR-affected mortar were studied using scanning electron microscopy (SEM) and energy-dispersed X-ray analysis (EDX). The research found that although using hydrophobic aggregates may reduce the compressive strength, increasing the hydrophobicity of aggregates can significantly reduce ASR-induced expansion, minimize cracking, and prevent warping.

Formation and stability of fibers obtained by cold gelation of pea protein isolate aggregates in a hydrodynamic spinning process

Using plant protein sources in the formulation of food products is an important option to reduce the overall carbon footprint of the human diet. However, the ability to convert plant proteins into functional ingredients can hamper their use by the food industry. Our objective was to assemble pea protein isolate (PPI) aggregates into edible fibers. They were obtained by co-injection of a suspension of PPI aggregates with a solution of calcium chloride by means of physico-chemical bonds, i.e. in the absence of thermal treatment or chemical reaction. As soon as specific hydrodynamic conditions were met, homogeneous fibers of few hundreds μm diameter and few cm length were obtained. Small angle X-ray scattering showed that the building blocks of these fibers were dense aggregates of 400 nm radius. Calcium and PPI concentrations required for the processing of fibers were roughly given by the sol-gel state diagram of PPI aggregates. Compared to their dairy protein based equivalent, PPI fibers were obtained with a low mass fraction of protein (3% w/w) and were stable regardless of the concentration of calcium chloride used. We concluded that the robustness of the hydrodynamic spinning process was attributed to the strong reactivity of PPI aggregates with calcium ions and the low tendency of PPI gels to syneresis.

Ultrastiff Amyloid-Fibril Network of α-Synuclein Formed by Surface Seeding Reaction Confirmed by Multichannel Electrodeless Quartz-Crystal-Microbalance Biosensor.

We developed a multichannel wireless quartz-crystal-microbalance (QCM) biosensor for mechanically studying the on-surface aggregation reaction of α-synuclein (α-syn). We find a quite unusual change in the resonant frequency that eventually exceeds the baseline, which has never been observed during seeding aggregation reaction. By incorporating a growth-to-percolation theory for fibril elongation reaction, we have favorably reproduced this unusual response and found that it can be explained only with formation of an ultrastiff fibril network. We also find that the stiffness of the fibril network grown from artificially prepared twist-type seeds is significantly higher than that from rod-type seeds. Furthermore, the stiffnesses of fibril networks grown from seeds derived from brain tissues of Parkinson's disease (PD) and multiple system atrophy (MSA) patients show a very similar trend to those of rod and twist seeds, respectively, indicating that fibrils from MSA patients are stiffer than those from PD.