Kinetics Of Pozzolanic Reaction Research Articles

The engineering properties and pozzolanic reaction kinetics of quaternary blended binder high strength mortars optimized by the Taguchi method

The Taguchi method has been applied for the experimental design of the mixture proportions of quaternary blended cement mortars on the basis of four factors. The design of experiment derived mixture proportions have been examined on four levels, comprising supplementary cementitious materials (SCMs) viz: ultra-fine treated palm oil fuel ash (u-TPOFA; at 4 levels of 30, 35, 40, and 45%), ground granulated blast furnace slag (GGBFS; at 4 levels of 12.5, 15, 17.5, and 20%), metakaolin (MK; at 4 levels of 7.5, 10, 12.5, and 15%) as partial replacement of ordinary Portland cement (OPC), and water to binder ratio (W/B; at 4 levels of 25, 26, 27, and 28%), in order to achieve an optimum mixture. The response factors employed were compressive strength (CS), porosity (P%), and water absorption (Abs%) at the ages of 3, 7, 14, and 28 days. By utilizing the L16 array as proposed by the Taguchi method, the specimens prepared were analyzed using 16 experiments. The results obtained showed that the response values of the optimized mixture using the Taguchi method were much better than the plain cement mortar mix and those proposed in the initial 16 series. The workability of the optimum mix increased by about 6% over the plain cement mortar mix. The relative CS results of the optimum mix was 116.92% at 28 days of curing. Likewise, the relative P% and Abs% results of the optimum mix exhibited notable reductions at 28 days of about 40.0% and 45%, respectively. Further analyses were carried out using thermogravimetric (TG) and x-ray diffraction (XRD) analyses to quantify the contribution of the SCMs and their chemical reaction which was reflected by the remaining amount of the unreacted portlandite in the mix. According to the results, the optimum quaternary blended binders mortar mix which utilized only 37.5% of cement by volume (i.e., a reduction from 882.22 to 330.83 kg/m3) portrayed improved physical properties, chemical reaction, enhanced workability, better CS, as well as lower P% and Abs% compared to the plain cement mortar.

Effect of fineness on the pozzolanic reaction kinetics of slag in composite binders: Experiment and modelling

In this study, the kinetics of the pozzolanic reaction of slag with various levels of fineness was characterized by experimental analysis and model simulation. The maximum reaction rate of ultrafine slag at the main pozzolanic reaction peak was found to be 67% larger than that of ordinary slag, with this gap becoming even larger (228%) at a high curing temperature. The early pozzolanic reaction degree was found to increase by 40%–60% due to increased slag fineness. At late ages, the pozzolanic reaction degree was still increased by approximately 40%–70% at room temperature but only by 20% at a high curing temperature due to increased slag fineness. The parameters for the kinetic model illustrate that slag fineness has little influence on the nucleation rate and linear growth rate of the product per unit surface area. However, the increase in the total surface area results in a large number of nuclei for the pozzolanic reaction products, leading to a large amount of product and a high reaction degree for ultrafine slag. The apparent activation energy for the pozzolanic reaction of ultrafine slag was found to be identical to that of ordinary slag, showing that an increase in slag fineness does not change the mechanism governing the pozzolanic reaction.

Kinetics of pozzolanic reaction and carbonation in ceramic – lime system: Thermogravimetry and solid-state NMR spectroscopy study

Waste red-clay ceramic powder (RCC) is a pozzolanic material which is currently not commercially used, but high amount of “brick fraction” of construction and demolition waste may become a source for a cheap pozzolanic additive for Portland cement and lime-based binders. A sort of specific of RCC, compared to other pozzolans, is the higher content of non-reactive minerals. Pozzolanic reaction, taking place in lime-based system, is inevitably accompanied by carbonation of the lime; these two processes are concurrent with respect to the lime consumption. Products of hydration (C–S–H and calcium aluminate hydrate phases) and carbonation (CaCO3) are contributing to the strengthening of the system. The goal of this research has been to evaluate the rate and mechanism of hardening of the RCC – lime mixtures. The relative rate of pozzolanic reaction and carbonation was studied over one-year period in RCC – lime pastes by help of thermal analysis and 23Na, 27Al and 29Si Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy (MAS NMR), accompanied by porosimetry and compressive strength determination. The kinetics of lime conversion to hydration products and CaCO3 was determined by the help of thermogravimetry and described by Jander's equation. The highest rate of pozzolanic reaction, as well as the highest strength, reached mixture of 70% of RCC and 30% of lime; such high effective pozzolana content is caused by the phase composition of ceramic powder – it contains lower amount of reactive species, compared to metakaolin or other pozzolans. The formation of AlVI hydration products (AFm and AFt phases) took place within initial 3 days in all mixtures, while the content of C–S–H hydrates grown over the whole year of the experiment.

Use of ceramic industry milling and glazing waste as an active addition in cement

AbstractThe beneficial effects of pozzolans on cement manufacture have encouraged their use in that industry. Traditional natural pozzolan have become less available of late, however, due to a decline in quarrying intensity aimed at minimizing the impact on the landscape. At the same time, environmental policies pursue the reduction or elimination of spoil heaps by valorizing industrial waste and by‐products as raw materials, in keeping with the principles of the circular economy. The quest for new types of waste and by‐products with pozzolanic properties has consequently become a priority line of research. This study explored the valorization of one such by‐product, the ceramic sludge resulting from fired clay industry milling and glazing, as a component in new, more eco‐sustainable cements. The sludge was characterized physically, chemically, morphologically, and mineralogically to determine its suitability as a pozzolanic addition in cement. The findings showed that ceramic sludge consists in clustered particles ranging in size from 100 μm to 1 μm. SiO2, Al2O3, and Fe2O3 together comprise over 70% of the total composition, while the reactive silica content is greater than the 25% required by the existing legislation. The predominant minerals are quartz, kaolinite, and muscovite, with some zircon. A study of pozzolanic reaction kinetics in the ceramic sludge/lime system revealed that over time this waste can fix lime, generating products such as calcium aluminate hydrates and C–S–H gels. The cements made with ceramic sludge proved to be standard‐compliant in terms of water demand, setting, drying shrinkage and mechanical strength.

Monitoring of Kinetics of Pozzolanic Reaction

The pozzolanic additions are widely used as concrete component for numerous technical, economic and environmental reasons. Obviously the hydration process in a pozzolana containing system differs from hydration of Ordinary Portland Cement (OPC) what is indicated macroscopically by slower increase of strength and lower hydration heat. This paper aims to study pozzolanic reaction from perspective of chemical kinetics. From this point of view pozzolanic reaction and carbonation are two parallel reactions which are competing for portlandite (Ca (OH)2). The rate of each of these two reactions is characterized by rate constant and order of reaction. The system under study was 1:1 mixture lime – ceramic powder. The course of reaction was primarily studied by thermogravimetry which results were further subjected to kinetic analysis. MAS NMR spectroscopy was used for study of structural changes taking place in material in the course of pozzolanic reaction.

Effects of the pozzolanic reactivity of nanoSiO2 on cement-based materials

The aim of this work is to understand the characteristics of the pozzolanic reactivity of nanoSiO2 from studies of its pozzolanic reaction kinetics, morphology and structure of the hydrates and the influences of these features on the properties of cement-based materials, so as to explore a more targeted way of using nanoSiO2 in cement or concrete. It revealed that the pozzolanic reaction of nanoSiO2 is of the first-order and the apparent reaction rate constant of nanoSiO2-4nm is about one order of magnitude bigger than that of silica fume, but the specific reaction rate constant is about one half to that of silica fume. A compacter gel structure and poorer crystallinity of the hydrates of nanoSiO2 to those of silica fume are found, as well. The rate of hydration of cement at very early ages is enhanced by nanoSiO2, but the rate slows down with aging due to the compact gel structure. To make the use of the high pozzolanic reactivity and ultrafine particle size of nanoSiO2, as well as its resulting compact gel structure, colloidal nanoSiO2 was applied onto the hardened cement mortar by brushing technique and a less permeable surface was resulted, which shows the potential of using nanoSiO2 as a surface treatment material for cement-based materials.

Kinetics of lime/bentonite pozzolanic reactions at 20 and 50 °C: Batch tests and modeling

The effects of duration (1–100days) and temperature (20 and 50°C) were assessed from batch tests for Ca-bentonite mixed with 10wt.% lime. The pozzolanic processes were monitored over time by 29Si NMR (Cement Concr. Res. 42, 2012), TGA-DTA, XRD and chemical analysis. Modeling considered kinetics and thermodynamics of mineralogical transformations and cation exchange. Kinetic laws were dependent on pH and temperature (Arrhenius energy).Lime hydration occurs within hours, modifying the bentonite exchangeable population and increasing the pH. These alkaline conditions initiate the pozzolanic reactions in a second stage. The rate-limiting step is the dissolution kinetics of the bentonite minerals, i.e. a relatively fast and total consumption of cristobalite in parallel to a long-term slower dissolution of montmorillonite. First C–S–H and then C–A–S–H are formed consequently. Temperature speeds up the pozzolanic reaction kinetics by a factor 5 from 20 to 50°C, corresponding to an apparent activation energy of 40–50kJ/mol.

Pozzolanic behaviour of a bagasse ash from the boiler of a Cuban sugar factory

The paper presents a study of the pozzolanic reaction kinetics between calcium hydroxide and sugar cane bagasse ash (SCBAB) from the boiler of a sugar factory. A pozzolanic activity method (conductometric method) based on measurement of the electrical conductivity of the SCBAB/calcium hydroxide solution as the reaction proceeds is applied and the kinetic parameters are then quantified by applying a kinetic–diffusive model to the process. The kinetic parameters that characterise the process (in particular, the reaction rate constant and the free energy of activation) were determined with relative accuracy in the fitting process of the model. The pozzolanic activity is quantitatively evaluated according to the obtained values of the kinetic parameters. Other experimental techniques, such as X-ray diffraction and scanning electron microscopy, are also employed. Comparison with another bagasse ash calcined under controlled conditions in the laboratory is carried out. The results show the good pozzolanic properties of the SCBAB from the boiler of the sugar factory.

The effect of binary pozzolan mix on the mineralogical changes in the ternary activated paper sludge–fly ash–Ca(OH)2 system

This paper presents for the first time the influence of mixing different thermally activated paper sludges (APS) and fly ash (FA) on the pozzolanic reaction kinetics in APS–FA–Ca(OH)2 systems as a previous step to manufacture the future commercial ternary blended cements. In this study, two paper sludge wastes from different origins and activation conditions (laboratory (LS) and industrial (IS) scale) have been investigated, once mixed with fly ash at a ratio of 1:1 by weight. The results indicated that binary blends of pozzolans exhibited a high pozzolanic activity, showing that the hydrated phases produced during the pozzolanic reaction depend on the origin and activation conditions of clay wastes. At all times of reaction, the predominant phase turn out to be the LDH structures when LS pozzolan was used; meanwhile for the IS pozzolan the C4AC¯H12 along with the LDH were the main phases during the first 28days.

On the kinetics of pozzolanic reaction in metakaolin–lime–water system

The kinetics of pozzolanic reaction metakaolin–lime is studied in the present work. Metakaolin is prepared by calcination of enriched kaolin (deposit “Senovo”, Bulgaria) at temperature of 830 ± 10 °C in a labscale muffle oven. The reaction is performed in intensively stirred water suspension at different temperatures in the range 20–100 °C. The kinetics is analyzed by comparing the experimental data with theoretical curves, derived according to appropriate kinetic and diffusion models taking into account the grain size distribution of metakaolin. The macroscopic mechanism and activation energy of the reaction are determined. It is found, that the activation energy decreases gradually from 71 to 45 kJ/mol[Ca(OH)2] with the increase of the reaction degree from 0.2 up to 0.6, respectively, which is a characteristic for transition regime reactions.

On the kinetics of pozzolanic reaction in the system kaolin–lime–water

The kinetics of the pozzolanic reaction of enriched kaolin from the “Senovo” deposit (Bulgaria) with lime is the object of this article. The kaolin contains kaolinite as a major clay mineral as well as admixtures of quartz and illite. The experimental data of pozzolanic activity at temperatures of 100 and 23 °C are obtained for different reaction times. The reaction degrees of kaolinite and lime at 100 °C are determined from the pozzolanic activity data using a powder X-ray diffraction analysis. The kinetic analysis is performed by joint presentation of theoretical and experimental data in dimensionless coordinates having in mind the influence of particle size distribution on the reaction rate. It is found by the kinetic analysis that the rate of entire reaction is limited by the rate of chemical reaction on the reaction surface up to degree of reaction near to 0.4. The rate of penetration of the chemical reaction into the kaolinite particles for this area—from the beginning to degree of reaction 0.4, is determined to be equal to 2.10−11 m/s.

Pozzolanic reaction kinetics of coal ashes

The pozzolanic reactivity was determined by the hydration kinetics of pozzolanic reaction based on the fact that the hydration products of active SiO2 and Al2O3 with lime were soluble in dilute hydrochloric acid. The results show that the pozzolanic reaction of active SiO2 and Al2O3 of coal ashes follows apparent first-order kinetics. The reaction rate constant of FBC ashes is greater than that of PC ashes, while the activation energy of the former is lower than that of the latter. It is confirmed that the pozzolanic activity of fluidized bed combustion(FBC) ashes is significantly higher than that of PC ashes, and the reaction barrier of the former is lower than that of the latter, because the microstructures of FBC ashes, such as mineralogical composition, morphology and polymerization degree of [SiO4] and [AlO6] are more favorable to the pozzolanic activity development than those of PC ashes.

Study of the pozzolanic reaction kinetics in sugar cane bagasse–clay ash/calcium hydroxide system: kinetic parameters and pozzolanic activity

This paper presents a study of the pozzolanic reaction kinetics between calcium hydroxide and a mixture of sugar cane bagasse with 20 and 30% of clay, burned at 800 and 1000°C (SCBCA) by electrical conductivity measurements. A kinetic–diffusive model produced in previous studies by some of the authors was used. The model was fitted to the experimental data, which allowed the computation of the kinetic parameters of the pozzolanic reaction (reaction rate constant and free energy of activation) that rigorously characterised the pozzolanic activity of the materials. The results show that SCBCA demonstrated reactivity and good pozzolanic qualities in the range 800–1000°C.

Kinetics of pozzolanic reaction for preparation of flue gas desulfurizer from fly ash and Ca(OH)2

A kinetic model of the pozzolanic reaction for the preparation of flue gas desulfurizers from fly ash and Ca(OH)2 was deduced on the basis of solid phase reaction kinetic theory. Kinetic expressions and parameters were obtained and verified by experiment. A comparison of calculated results with experimental results showed that precision in kinetic expressions was good. The apparent reaction rate constants of the pozzolanic reaction could be raised by increasing the specific surface area of fly ash and the hydration temperature, and by using a suitable additive.

An evaluation of different kinetic models for determining the kinetic coefficients in sugar cane straw–clay ash/lime system

The paper presents a comparative study in which different kinetic models were applied to describe the reaction kinetics of a mixture of sugar cane straw with 20 and 30% of clay, burned at 800 and 1000°C (SCSCA), and hydrated lime [calcium hydroxide (CH)]. Classical models, such as the Jander, Jander Modified and Zuravlev models were applied. These models were compared with a kinetic-diffusive model previously published by some of the present authors. The models were fitted to the experimental data by computerised methods, which allowed the computation of the kinetic parameters that rigorously characterise the pozzolanic activity of the materials. The results showed that Jander, Jander Modified and Zuravlev models did not describe the pozzolanic reaction kinetics in this system correctly, whereas the model proposed by the authors gave the best results with respect to fitting to the experimental data. This demonstrated that the model proposed by the authors was the most adequate for describing the reaction kinetics in the SCSCA system.

Validation of a kinetic-diffusive model to characterize pozzolanic reaction kinetics in sugar cane straw-clay ash/lime systems

A kinetic-diffusive model proposed by the authors in previous papers to describe pozzolanic reaction kinetics in sugar cane straw-clay ash (SCSCA)/calcium hydroxide (CH) systems is validated in this study. Two different methods (direct and indirect) for determining pozzolanic activity were applied and their effect on pozzolanic reaction rate kinetic constants evaluated. Determined by fitting a model to the data, these constants are used to quantitatively characterize pozzolanic activity. The values of the kinetic constants calculated with the model were similar for the two methods. Classic kinetic models, such as the Jander, modified Jander and Zhuravlev models, were also applied to the system studied and the results were compared to the figures calculated with the model proposed. The kinetic-diffusive approach proposed was found to be valid regardless of the method for determining pozzolanic activity used, and to be the most suitable model for describing pozzolanic reaction kinetics in the SCSCA/lime system.

Pozzolanic reaction in the presence of chemical activators: Part I. Reaction kinetics

This study has examined the effect of activators (Na 2SO 4 and CaCl 2) on pozzolanic reaction kinetics in a lime-pozzolan blend, which consists of 80% ground volcanic ash and 20% hydrated lime, at 23, 35, 50, and 65°C. The addition of 4% Na 2SO 4 increased both the early and later strengths of lime-pozzolan pastes from 23 to 65°C. The presence of 4% CaCl 2 · 2H 2O decreased the early strength but increased the later strength at 23°C, and increased both the early and later strengths of the paste from 35 to 65°C. Measurement of free Ca(OH) 2 in hardened pastes indicated that the presence of Na 2SO 4 and CaCl 2 accelerated the consumption of Ca(OH) 2. A fair linear correlation could be established between measurable compressive strength and the degree of reaction of Ca(OH) 2 regardless of activators. Kinetic analyses using modified Jander's equation suggest that the pozzolanic reaction process in the lime-pozzolan pastes could be divided into three phases: Phase I, controlled by the pozzolanic reaction rate; Phase II, controlled by the diffusion of reactants through a layer of porous hydration products; and Phase III, controlled by the diffusion of reactants through a layer of dense hydration products