Silica Reaction Research Articles

The influence of lithium compounds on alkali – silica reaction in calcium aluminate cement mortars subjected to the deicing salts attack

Paper presents the results of research on the effect of the lithium nitrate and carbonate addition on the alkali – silica reaction in calcium aluminate cement mortars, subjected to the a deicing salts attack. Mortars with the addition of quartz glass as the reactive aggregate were immersed in 4.5 molar sodium acetate, chloride and hydroxide solutions according to the modified ASTM C1260 method. In all cases, the mortars exhibited expansion, the highest for samples immersed in the acetate solution, and the lowest in the hydroxide solution. The addition of 1% of lithium carbonate in respect to the cement mass slightly reduces the expansion of mortars immersed in sodium acetate and hydroxide solutions. The addition of 1.86% and 3.73% of lithium nitrate increases the expansion of mortars immersed in both solutions. The addition of 1.86% lithium nitrate reduces the expansion of the mortar stored in sodium hydroxide solution, while 3.73% of this addition increases the expansion of this mortar. Changes in the microstructure were also presented.

Reaction-probe infrared investigation on drastic change in reactivity of mesoporous silica for acetalization of cyclohexanone with methanol; pore-size dependence

Abstract Small-pored ( O stretching band appeared at lower frequency side on MCM-41 at a small amount of adsorption in addition to that observed on SBA-15. This result indicates the presence of the stronger interaction of cyclohexanone with MCM-41 than that with SBA-15. When the time course of the reaction was observed by in-situ IR observation, the consumption of activated carbonyl groups and the generation of 1,1-dimethoxycyclohexane, the reaction product, were confirmed. The presence of the activated cyclohexanone was most probably due to the adsorption on two (or more) OH groups in vicinity, while a non-activated species occupied a single OH group. The reaction probe IR method is thus, a direct and effective approach to extract the small differences in catalysis.

Durability performance of high volume fly ash roller compacted concrete pavement containing crumb rubber and nano silica

ABSTRACT This study investigated the effect of a hybrid of crumb rubber and nano silica on the durability performance (Porosity and Permeability) and skid resistance of high volume fly ash (HVFA) roller compacted concrete (RCC) pavement. The HVFA RCC pavement was developed with 50% cement by volume replaced using fly ash. Crumb rubber was used to partially replace fine aggregate at varying percentages, i.e. 0%, 10%, 20%, and 30% by volume replacement. Nano silica was added by weight of cementitious materials at variations of 0%, 1%, 2%, and 3%. The Vebe consistency, water absorption, and mercury intrusion porosimetry were used to measure the consistency, permeability, and porosity of the HVFA RCC pavement, respectively. The skid resistance was measured in terms of the British Pendulum Number (BPN) using the British Pendulum Tester (BPT). The result findings showed that the HVFA increased the consistency, rate of water absorption, and porosity of the RCC pavement. Furthermore, the consistency, water absorption, and porosity of the HVFA RCC pavement increased with an increase in the partial replacement of the fine aggregate with crumb rubber. On the contrary, the addition of nano silica decreased the consistency, rate of water absorption, and porosity of the HVFA RCC pavement. This was due to the larger surface area, finer size, and physiochemical reaction of the nano silica which resulted in pore structure refinement in the hardened matrix of the HVFA RCC pavement by filling the voids within the interconnected pores thereby breaking the interconnectivity and reducing its diameter. The results of the skid resistance showed that incorporation of 10% crumb rubber as the replacement to fine aggregate and addition of up to 2% nano silica by weight of cementitious materials increased the skid resistance of the HVFA RCC pavement.

Role of test method in detection of alkali–silica reactivity of concrete aggregates

The risk of alkali–silica reaction of concrete aggregates in many parts of the world remains largely unexplored. In particular, a suitable approach for testing aggregates with marginal to moderate alkali–silica reactivity has not been clearly identified. In this study, the mineralogical compositions of aggregates from five different quarries were investigated. Mortar bar expansion for these aggregates was tested as per the guidelines of both C 227 and C 1260. Although the tested aggregate sources proved non-reactive under ASTM C 227 test conditions, ASTM C 260 identified one group of aggregates as potentially reactive. Scanning electron microscopy imaging confirmed that two sources of aggregates were reactive. The compressive and flexural strength test results of aged specimens with reactive aggregates indicated that the strength reduction of those subjected to 1 month of ASTM C 260 exposure was similar to those of specimens under 6 months of ASTM C 227 exposure. Based on the experimental results, it appears that aggregates with potential alkali–silica damage may be characterised as non-reactive if the appropriate test method is not adopted. The findings indicate that the ASTM C 1260 procedure is more effective in determining the reactivity potential of marginally to moderately reactive aggregates.

Application of resin and NH4NO3 as an ion exchange agent for microspherical preparation of nanostructured kaolin-SAPO-34 catalyst for methanol to light olefins reaction in a fluidized bed reactor

The aim of this research is to investigate the influence of various ion exchange methods in the assembly of nanostructured kaolin-SAPO-34 catalyst using silica sol as binder by spray drying for conversion of methanol to light olefins in a fluidized bed reactor. Physiochemical properties of the catalysts were identified by XRD, FESEM, EDX, BET, NH3-TPD and FTIR techniques. The results of XRD analysis exhibit typical SAPO-34 and kaolinite phase for all the three spray dried samples. It represents the successful spray drying that the crystallite structure of the shaped samples assumes by the spray dryer that is composed of both kaolinite and SAPO-34 phase. With the comparison of FESEM results of the samples, it can be implied that use of resin as an ion-exchange agent resulted in smoother and larger particles. According to NH3-TPD results at high calcination temperatures, the reaction of silica from the binder with the extra-framework alumina of kaolin or SAPO-34 results in new acid sites. The catalysts mechanical strength was evaluated by the fluidized bed attrition test. MTO Performance tests were carried out to study the activity of the catalysts in a fixed bed reactor. The optimized catalyst was also tested in a fluidized bed reactor. The optimal shaped sample showed excellent activity of near 22 h during MTO reaction in a fluidized bed reactor.

A Literature Review on Alkali Silica Reactivity of Concrete

Deterioration of concrete structures with time is well understood. One of the major reasons of deterioration is reaction between cement paste and reactive siliceous aggregates which is known as alkali silica reaction (ASR). This article reviews the studies on ASR in concrete. Although a vast literature is available on mechanisms and preventive measures against ASR, however there are still a lot of deficiencies regarding the test methods to detect the ASR potential in concrete. The aim of this article is to discuss different factors affecting ASR, consequences of ASR and different challenges encountered by researchers in the detection of ASR. The study revealed that alkali content of cement, aggregates grading, mineralogical combinations, testing methods and testing conditions are all the challenges, researchers face during evaluation of ASR potential in concrete.

Sustainable Materials for Transportation Infrastructures: Comparison of Three Commercially-Available Metakaolin Products in Binary Cementitious Systems

Metakaolin is the only major natural pozzolan to be specified for use as a supplementary cementitious material in the United States. As a result, the metakaolin market for concrete has grown dramatically in the past 20 years. As of now, the specifications of up to 16 state departments of transportation allow for the use of commercially-available and high-reactivity metakaolin products. However, to the best of the authors’ knowledge, no study has been performed to evaluate whether these products are comparable in their performance. Three commercially-available (U.S.) metakaolin products, each replacing 10%, 15%, and 20% of the cement content in concrete and mortar mixtures are studied. Concrete mixtures contained a cementitious content of 422 kg/m3, a coarse aggregate fraction of 985 kg/m3, and a water-to-cementitious ratio equal to 0.43. Varying levels of a superplasticizer were used to maintain a uniform workability between mixtures. Each mixture was subjected to the following tests: compression, split-cylinder tension, modulus of rupture, dynamic elastic modulus, rapid chloride-ion penetrability, alkali–silica reactivity, sulfate resistance, the coefficient of thermal expansion, and drying shrinkage. Benefits from the inclusion of metakaolin were highly product-dependent and include increases in mechanical strength. All metakaolin supplemented concrete mixtures benefitted from decreased permeability and increased resistance to chemical attacks, with the exception of the sulfate resistance of mortars including a metakaolin product with high fineness. The inclusion of any metakaolin at any replacement level increased the coefficient of thermal expansion of concrete specimens. Reasons for difference in performance between products are discussed, and predictors of quality are recommended.

Effect of mechanical activation of red mud on the strength of geopolymer binder

The growing interest in utilization of industrial waste and green construction has motivated the present work. Red mud is an industrial waste produced in the process of extraction of aluminum from bauxite by Bayer’s process. The paper presents the studies conducted to assess the influence of mechanical activation of red mud and curing methods on the strength of red mud-fly ash geopolymer paste. Red mud was used in both unprocessed and pulverised form and the alkali activated paste samples were cured thermally as well as in ambient condition. The percentage of red mud varied from 0 to 90% and alkalinity from 6 M to 12 M NaOH solution. X-ray diffraction (XRD) was carried out to identify the mineral phases in pulverised and unprocessed red mud. SAED (selective area diffraction diagram) test was done on the red mud, along with SEM (scanning electron microscopy), TEM (transmission electron microscopy) and HRTEM analysis (high resolution transmission electron microscopy) to study the effect of mechanical activation and validate the experimental findings. Mechanical activation increased the reactivity of silica and the hematite phase of red mud as reflected in the silica reactivity and Fourier transform infrared spectroscopy (FTIR) test results. Use of pulverised red mud enhanced the mechanical properties of ambient cured paste and the specimens possessed maximum 7 day compressive strength of 40 MPa at 6 M alkalinity with 30% mechanically activated red mud content.

Regularities of Sol-Gel Processes in the Preparation of Polysilicates

The regularities of sol-gel processes in the preparation of potassium polysilicate based on silica hydrosol (Ludox AS-40) are studied. The potassium hydroxide–silica molar ratio (silicate modulus M = [SiO2]/[Me2O]) is set by introducing potassium hydroxide into the sol. The addition of alkali at the initial stage induces sol coagulation. The mechanism of alkali effect is considered taking into account the reactivity of silica (the polycondensation and depolymerization reactions) and the aggregative stability of the colloidal system.

Alkali-reactivity of a Swiss siliceous limestone caused by finely dispersed quartz

The present study was conducted to provide a better understanding of the alkali-silica reactivity (ASR) of siliceous limestones in concrete applications. A Swiss siliceous limestone, which is potentially reactive, was subjected to a series of tests. Microbar tests were first conducted to classify the limestones reactivity with respect to ASR. Two other methods were then used to characterize the amount of SiO2 present. First, an analysis of the chemical composition with petrographic and mineralogical characterizations was carried out, and second, a model reactor was used to characterize the silica reactivity. The results showed a siliceous reactive limestone. In petrography, three main types of carbonate lithology were outlined according to their SiO2 and glauconitic content. The emphasis was placed on the types of SiO2 and their sizes: a finely dispersed micro- to crypto-quartz has been highlighted by SEM and TEM, and analysed as quartz. The reactive free SiO2 content, obtained by a mineralogical calculating method, completes the petrographic results. The proportion of reactive free SiO2 could be essentially attributed to the presence of finely dispersed micro- to crypto-quartz from TEM observations which is probably very reactive towards the ASR due to its small-size. The presence of finely dispersed micro- to crypto-quartz is important to consider, due to its potential effects on the concrete mixture. The grain size of SiO2 seems to be a supplementary key parameter, in addition to crystallinity and strain, since it can promote ASR development with some siliceous aggregates.

Influence of ground waste expanded perlite on the reaction of siliceous aggregates with sodium and potassium hydroxides

Paper presents results of investigation on the influence of ground waste expanded perlite on the mitigation of alkali – silica reaction in cement mortars. Crushed quartz glass was used as model reactive aggregate. Natural reactive aggregate containing radiolarite was also used. Obtained results showed, that addition of ground waste expanded perlite to mortars containing reactive aggregates resulted in significant reduction of alkali – silica reaction. Expansion of mortars soaked in sodium hydroxide at elevated temperature, according to modified ASCT C1260 test was markedly lower comparing reference samples without perlite addition. Examination of mortars and pastes with ground waste expanded perlite addition confirmed its pozzolanic properties. Increased C-S-H phase content together with decreased permeability of the mortars and decreased calcium hydroxide content are most probably the reasons for better durability of perlite bearing mortars towards alkali – silica reaction.

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Evaluation of the pozzolanicity of nanostructured sol-gel silica and silica fume by electrical conductivity measurement

The present paper evaluates the pozzolanic activity of two nanostructured silicas with high specific surface area, synthetized by sol-gel technique, in comparison with silica fume. The materials were characterized by X -ray diffraction, scanning electron microscopy and nitrogen sorption. Electrical conductivity tests were performed in calcium hydroxide saturated solutions. Results revealed that both nanostructured sol-gel silicas have great pozzolanic reactivity, much higher than silica fume, especially in the early stage of the reaction. Hence, the pozzolanic reactivity of silica is affected by its specific surface area. Moreover, silica amount, test temperature and average pore size also seems to alter the silica reactivity. The reaction rate of silicas with small average pore size is reduced along the pozzolanic reaction.

Cement Type Influence on Alkali-Silica Reaction in Concrete with Crushed Gravel Aggregate

Alkali-silica reaction is one of the chemical reactions which have a significant influence for durability of concrete. During alkali and silica reaction, silicon located in aggregates of the concrete, reacts with high alkali content. This way in the micropores of concrete is forming hygroscopic gel, which at wet environment, expanding and slowly but strongly destroying concrete structures. The goal of this paper- to determine the influence of cement type on alkali-silica reaction of mortars with crushed gravel. In the study crushed gravel with fraction 4/16 mm was used and four types of cements tested: CEM I 42.5 R; CEM I 42.5 SR; CEM II/A-S 42.5; CEM II/A-V 52.5. This study showed that crushed gravel is low contaminated on reactive particles containing of amorphous silica dioxide. The expansion after 14 days exceed 0.054 %, by RILEM AAR-2 research methodology (testing specimen dimension 40×40×160 mm). Continuing the investigation to 56 days for all specimens occurred alkaline corrosion features: microcracking and the surface plaque of gel. The results showed that the best resistance to alkaline corrosion after 14 days was obtained with cement CEM I 42.5 SR containing ash additive, and after 56 days with cement CEM II/A-V 52.5 containing low alkali content. The highest expansion after 14 and 56 days was obtained with cement CEM I 42.5 R without active mineral additives.

Solid-state reaction route to synthesis of ordered mesoporous β-Zn2SiO4:Mn-SiO2 composites with ultraviolet and yellow emission

Ordered mesoporous Mn-doped β-Zn2SiO4-SiO2 composites are synthesized by solid state reaction at 800 °C using mesoporous silica as assisted template and silicon source. The formation temperature of β-Zn2SiO4 doped with Mn2+ is much lower than that of conventional solid state reaction, which is ascribed to the high reactivity of mesoporous silica with large surface area and porous structure. Mn-doped β-Zn2SiO4 crystals disperse in the mesoporous silica frameworks which play roles in supporting the mesoporous structure and restraining the phase transformation from β- to α-Zn2SiO4, contributing to enhancing the stability of composites. Excitation spectra of the composites show the zinc silicate absorption around 210 nm and the charge transfer band around 245 nm. Mn-doped β-Zn2SiO4-SiO2 composites exhibit an ultraviolet emission at 390 nm attributed to silica and a strong yellow emission around 575 nm driven by 4T1 to 6A1 radiative transition of Mn2+. No obvious concentration quenching is observed at high doping level of 0.08, proving the homogeneous doping of Mn2+ in the composites. This route exhibits a significant advantage of lowering the reaction temperature, facilitating easy doping and preventing concentration quenching.

Efficiency of waste marble powder in controlling alkali–silica reaction of concrete: A sustainable approach

Recycling of wastes in building materials is gaining a lot of attention worldwide. This not only conserves natural resources but also enhances the properties of existing building materials leading to economical and environment friendly construction. The main aim of this study was to explore the efficiency of waste marble powder (WMP) in controlling alkali silica reactivity (ASR) of concrete. For this purpose, WMP was obtained from a marble industry. To initiate the ASR phenomena, reactive aggregate was used in the study. Mortar bar specimens prepared with WMP as cement replacement material at 10%, 20%, 30% and 40% replacement levels (by cement weight) were evaluated in the standard ASTM C1260 test method. Compressive strength and thermal analysis tests were performed to investigate the effect of WMP on strength development of concrete. Results of compressive strength and thermal analysis showed improved strength after 10% of cement replacement with WMP. Moreover, 28% and 50% reduction in mortar bar expansion was observed after replacing 10% and 40% of cement with WMP, respectively. Scanning electron microscopic images also showed no signs of ASR cracking for mortar bars incorporating WMP. However, presence of cracks due to ASR was observed in control specimens. Furthermore, energy disperse X-ray spectroscopy (EDS) showed that amount of alkalies reduced after replacing cement with WMP, leading to overcome ASR expansion. Therefore, based on the results WMP can be effectively used to control ASR expansion leading to durable, sustainable and economical construction.

Urushiol-derived non-silane coupling agent

Sulfur was chemically incorporated into urushiol in one step to afford an oligomeric sulfurized urushiol (SU). About 53% of the linkages between urushiol monomer units are cleavable multi-sulfidic bonds. Surface modification of silica with SU can be achieved either in a suspension before rubber compounding or in situ during rubber compounding. SU performs better when added in situ into the rubber compound than when used to pre-modify silica. Mooney viscosity and Payne effect studies of the uncured rubber compounds show that SU is as effective as TESPT to promote filler dispersion during mixing. The increased bound rubber content and suppressed filler flocculation demonstrate that SU does indeed generate covalent filler-rubber interactions during mixing in contrast to our previously reported hydrogenated urushiol, which only act as a covering agent. However, SU is less effective than TESPT as a coupling agent. The dynamic mechanical properties of the SU-containing vulcanizate are intermediate between the TESPT-containing standard and the hydrogenated urushiol-containing standard. When SU is used to replace 50% TESPT, mechanical and dynamic mechanical properties of the two vulcanizates are essentially identical. Noteworthy is that the reaction between SU and silica during rubber compounding produces water instead of ethanol, which the reaction of silica and TESPT produces, as a volatile organic compound.

Control over Silica Particle Growth and Particle-Biomolecule Interactions Facilitates Silica Encapsulation of Mammalian Cells with Thickness Control.

Over the last twenty years, many strategies utilizing sol-gel chemistry to integrate biological cells into silica-based materials have been reported. One such strategy, Sol-Generating Chemical Vapor into Liquid (SG-CViL) deposition, shows promise as an efficient encapsulation technique due to the ability to vary the silica encapsulation morphology obtained by this process through variation of SG-CViL reaction conditions. In this report, we develop SG-CViL as a tunable, multi-purpose silica encapsulation strategy by investigating the mechanisms governing both silica particle generation and subsequent interaction with phospholipid assemblies (liposomes and living cells). Using Dynamic Light Scattering (DLS) measurements, linear and exponential silica particle growth dynamics were observed which were dependent on deposition buffer ion constituents and ion concentration. Silica particle growth followed a cluster-cluster growth mechanism at acidic pH, and a monomer-cluster growth mechanism at neutral to basic pH. Increasing silica sol aging temperature resulted in higher rates of particle growth and larger particles. DLS measurements employing PEG coated liposomes and cationic liposomes, serving as model phospholipid assemblies, revealed electrostatic interactions promote more stable liposome-silica interactions than hydrogen bonding and facilitate silica coating on suspension cells. However, continued silica reactivity leads to aggregation of silica coated suspensions cells, revealing the need for cell isolation to tune deposited silica thickness. Utilizing these mechanistic study insights, silica was deposited onto adherent HeLa cells under biocompatible conditions with micron scale control over silica thickness, minimal cell manipulation steps, and retained cell viability over several days.

Göksun Ofiyolitine ait (Kahramanmaraş-Türkiye) Yayla ilişkili Volkanik Kayaçların Alkali-Silika Reaksiyonu Potansiyeli

The alkali-silica reactivity is one of the most important problems that can occur in concrete structures. Because of their wide spectrum of mineralogical compositions and phases, volcanic rocks are more likely to cause alkali-silica reactivity. In this study, alkali-silica reactivity potentials of the rocks representing the upper levels of the crustal section of the Late Cretaceous suprasubduction-type Goksun ophiolite in the Tauride ophiolitic belt have been investigated. The Goksun ophiolite displays and intact ophiolite pseudostratigraphy with the thick layer of volcanic section characterized by a different composition of rock units such as basalt, basaltic-andesite, andesite, dacite and rhyolite. Firstly, the petrographic determinations of the samples derived from these volcanic units were made and then geochemical analyzes carried o ut o n t he s ame s pecimens t o c ontrol t he a ccuracy o f t he petrographic analyzes and the rocks were classified according to trace elements. Finally, the accelerated mortar bar method was applied on the concrete bars produced from same rock samples to compare the variation of Alkali-Silica Reactivity (ASR) with lithology. The test results yielded that the intermediate volcanics have much Alkali Silica Reactivity (ASR) potential than basic and acidic volcanics (basalts, rhyolites and dacites). It is estimated that the glassy matrix of the intermediate volcanics is partly responsible for the alkali-silica reactivity. SiO2, TiO2, Al2O3, Na2O a nd K 2O values have show positive correlation with the amounts of expansion in the andesite and basaltic andesites, whereas the major oxide contents of acidic and basic volcanic rocks have no clear relation with the expansion ratios.

Preparation of Al–Si composite from high-alumina coal fly ash by mechanical–chemical synergistic activation

High-alumina coal fly ash (HAFA) is a special solid waste because it contains more than 45% alumina and 35% silica. This material can be applied to prepare Al–Si series ceramics if the impurities can be removed and the Al/Si mass ratio can be elevated to a high level. In this work, a new mechanical–chemical synergistic activation–desilication process is proposed and optimized. During the synergistic activation, the morphology, ironic leaching ratios, efficient desilicated ratio (EDR), and mineral phases of different treatments are investigated. The reactivity of amorphous silica can be elevated to a high level (EDR>11%). After the desilication process, the contents of different impurities can be lowered up to less than 1%, and the Al/Si mass ratio can be elevated from 1.26 to 2.71. Mullite refractories are prepared from desilicated HAFA by forming and sintering process, and the bulk density and apparent porosity can reach to 2.85g/cm3 and 2.07%, respectively.