A method for measuring reactivity of pozzolanic materials and correlating their reactivity to strength development in composite cement

Abstract

The invention relates to a method for measuring the reactivity of pozzolanic materials and correlating this reactivity with strength development in composite cement. The method comprises dissolving pozzolanic materials in an alkaline solution and preparing a 1.0–5.0 M Sodium Hydroxide (NaOH) solution. This solution, containing the dissolved materials, is placed on a flow cell, configured to accommodate particles up to 100 µm. The flow cell is heated between 20 °C and 70 °C, and optical images of the particles are collected using an optical microscope. Particle count and area are measured by image processing with spatial and morphological filters to identify particles in the solution over time. The change in particle count or area is computed, and the normalized count represents dissolution plotted over time, describing the dissolution rate. This particle dissolution behaviour is correlated with compressive strength data obtained from samples tested within 1–28 days.

Description

[0001] A method for measuring reactivity of pozzolanic materials and correlating their reactivity to strength development in composite cement

[0002] FIELD OF THE INVENTION

[0003] This invention relates to a method for measuring reactivity of pozzolanic materials and correlating their reactivity to strength development in composite cement.

[0004] BACKGROUND OF THE INVENTION

[0005] Pozzolanic materials - alumino-silicates in their composition - are substances that, when combined with an alkaline source (e.g. Calcium, Sodium, and Potassium hydroxides) and water, form compounds possessing cementitious properties. Examples of pozzolanic materials include fly ash, silica fume, natural pozzolana, calcined clay, volcanic ashes, to mention a few. The addition of pozzolanic materials to cementitious systems contributes to strength development via pozzolanic reactions, i.e. the pozzolanic materials react with alkalis in the presence of water to form cementitious compounds, such as calcium silicate hydrates (C-S-H), calcium aluminate hydrates (C-A-H), and calcium alumina silicate hydrates (C-A-S-H). These compounds contribute to the binding and strength development of the hydrated cement matrix, hence, pozzolanic materials are used in blended cements or composite cements.

[0006] The variability in pozzolanic materials' composition can significantly affect the blended cement properties, therefore, its quality. Factors such as chemical composition, reactivity, and physical properties vary depending on the material source and processing. This impacts properties such as compressive strength. Quality control measures are crucial to ensure consistency and predictability in cement performance. Standardization and specifications help mitigate variability, ensuring reliable use in materials that compose cementitious systems. In the case of strength development of cementitious systems comprising pozzolanic materials (or any cement), compressive strength measurements take up to 28 days to be available. This is because the current standard on cement (EN 197-1.2011 Cement - Part 1: Composition, specifications, and conformity criteria for common cements) requires compressive strength tests on cast samples. Therefore, attempts to characterize strength development of cementitious systems comprising pozzolanic materials (or any other substitution material such as fillers and slags) in a shorter timeframe have been proposed. The most widespread case is by isothermal calorimetry (ASTM C1897-20:

[0007] Standard test methods for measuring the reactivity of supplementary cementitious materials by isothermal calorimetry and bound water measurements). Nonetheless, this method still requires at least 7 days of continuous measurement to provide data that can be used to predict the reactivity of a pozzolanic material, which is then correlated to the compressive strength of blended cements at 28 days. In summary, there is a long lead time between producing blended cements and quantifying their strength.

[0008] To mitigate the above-mentioned limitations in terms of test frequency, it is desired to characterize the strength development of blended cements (cementitious materials) comprising pozzolanic materials as quickly as possible. This helps reduce the lead time between material production and test results, providing a more granular (i.e. regular or frequent) response to production systems.

[0009] OBJECT OF THE INVENTION

[0010] It is an object of the present invention to overcome or at least alleviate one or more of the above problems / limitations of the prior art and / or provide the consumer with a useful or commercial choice. It is an object of the present invention to provide a method for measuring reactivity of pozzolanic materials and correlating their reactivity to strength development in composite cement.

[0011] It is an object of the present invention to provide a method for predicting the evolution of strength of a blended cement based on a nomogram, which can also be converted in a set of equations in a software.

[0012] It is an object of the present invention to provide an apparatus for use of the method for measuring reactivity of pozzolanic materials and correlating their reactivity to strength development in composite cement.

[0013] It is a further object of the present invention to provide an alternative to the prior art.

[0014] SUMMARY OF THE INVENTION

[0015] In a first aspect, the invention relates to a method for measuring reactivity of pozzolanic materials and correlating their reactivity to strength development in composite cement, said preferably method comprising the steps of

[0016] - dissolving pozzolanic materials in an alkaline solution,

[0017] - placing a 1.0 to 5.0 Molar Sodium Hydroxide - Na(OH) - solution obtained by dissolving the pozzolanic materials in the alkaline solution on a flow cell or a thin glass sheet, said flow cell configured to accommodate pozzolanic particles up to 100pm, - heat the flow cell at 20 to 70°C, collecting one or more optical images of the particles using an optical microscope,

[0018] - measuring the pozzolanic materials (particle) count and area by image processing using a set of spatial and morphological filters to identify the particles distributed in the solution over time,

[0019] - compute the change in particle count or area over time; the normalised particle count is interpretated as dissolution - which is plotted over time, describing the particle dissolution rate over the measurement time, and

[0020] - correlate the particle dissolution over time with compressive strength data generated from samples tested in a range from 1- 28 days

[0021] The advantage of this setup is that it enables a fast characterization method to assess the quality of a pozzolanic material regarding its contribution to strength development in blended cement.

[0022] Additional advantages include the use of this setup for a) commissioning equipment used to produced pozzolanic materials such as calcined clay, specifically, on the measurement of the product quality and adjustment of process parameters; b) the same setup can be used to control the process of producing a pozzolanic material; and c) adjustment of cement blend compositions in cement mills by measuring the reactivity of the pozzolanic materials and correcting the proportions of clinker replacement in the final composite cement blend.

[0023] While collecting one or more optical images of the particles for data collected at 20 to 70 degrees Celsius, the measurement may be performed in the range of 5 to 240 minutes, depending on the reactivity of the tested material. The correlation of the total particle dissolution with compressive strength data is preferably generated from samples tested at 28 days, but data from 1 to 28 days can also be used. Similarly, data from tensile strength and flexural strength at 1 to 28 days can be used.

[0024] In a second aspect, the invention relates to an apparatus utilizing the method according to any of the above-mentioned embodiments.

[0025] The apparatus preferably comprises a computing device. The computing device may be configured for receiving inputting digital signals from sensors and analysis, preferably configured for making mathematical operations with the signals and for outputting digital signals that convert the observed changes in particle count or particle size or area over time into a relative measure of particle dissolution, i.e. changes in particle count or particle size or area normalized in relation to the initial count or size of the particles at the start of the test.

[0026] The apparatus may be used for measuring particle reactivity of pozzolanic materials.

[0027] In a third aspect, the invention relates to a cement factory, comprising the apparatus according to the second aspect of the invention.

[0028] The first, second, and third aspect of the present invention may be combined.

[0029] In the present context, a number of terms are used in a manner being ordinary to the skilled person. Some of these terms are detailed below:

[0030] Supplementary Cementitious Materials (SCM): materials that can partially replace clinker in Portland cement composition and / or replace Portland cement in a concrete mix, improving workability, reducing permeability, and increasing strength and durability over time. They are often composed of siliceous, aluminous, or pozzolanic compounds. The latter reacts chemically with calcium hydroxide in the presence of water. Common examples of SCMs include fly ash (a by-product of coal combustion), calcined clay (thermally activated raw clays), ground granulated blast-furnace slag (from iron manufacturing), silica fume (from silicon metal production), and natural pozzolans (such as volcanic ash).

[0031] Ordinary Portland Cement (OPC): Ordinary Portland Cement (OPC) is a hydraulic cement that sets and hardens when mixed with water, primarily composed of calcium silicates, along with smaller amounts of calcium aluminates and calcium ferrites.

[0032] Blended Cement (or Composite Cement): Composite cements are a type of cement that combines Ordinary Portland Cement (OPC) with supplementary cementitious materials (SCMs) and / or other additives to enhance performance, sustainability, and workability.

[0033] Dissolution rate: The dissolution rate refers to the speed (rate) at which a substance dissolves in a solvent, typically measured as the amount of solute that dissolves per unit time. It is influenced by factors such as temperature, agitation, surface area of the solute, and the properties of the solvent.

[0034] Apparent dissolution: a relative metric of particle dissolution based on changes in particle count or particle size or area normalized in relation to the initial count or size of the particles at the start of the test (i.e. prior to dissolution taking place). The apparent dissolution rate describes the changes in apparent dissolution over time. The terms particle dissolution and apparent dissolution are used interchangeably.

[0035] BRIEF DESCRIPTION OF THE FIGURES

[0036] The figures show one way of implementing the present invention and are not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set. Embodiments of the invention, by way of example only, will be described with reference to the accompanying figure in which:

[0037] Figure 1 schematically illustrates the method according to the present invention.

[0038] Figure 2 schematically illustrates the application of the method to derive a nomogram that is used in the prediction of the evolution of compressive strength of a cementitious mix produced with a composite cement comprising Ordinary Portland Cement and calcined clay.

[0039] DETAILED DESCRIPTION OF THE INVENTION

[0040] In a first aspect, the invention relates to a method for measuring reactivity of pozzolanic materials and correlating their reactivity to strength development in composite cement.

[0041] The method comprises the steps of

[0042] - dissolving pozzolanic materials in an alkaline solution,

[0043] - placing a 1.0 to 5.0 Molar Sodium Hydroxide - Na(OH) - solution obtained by dissolving the pozzolanic materials in the alkaline solution on a flow cell or a thin glass sheet, said flow cell configured to accommodate pozzolanic particles up to 100pm,

[0044] heat the flow cell at 20 to 70°C, collecting one or more optical images of the particles using an optical microscope, - measuring the pozzolanic materials (particle) count and area by image processing a set of spatial and morphological filters to identify the particles distributed in the solution over time,

[0045] - compute the change in particle count or area over time; the normalised particle count is interpretated as dissolution - which is plotted over time, describing the particle dissolution rate over the measurement time, and

[0046] - correlate the particle dissolution over time with compressive strength data generated from samples tested in a range from 1- 28 days

[0047] While collecting one or more optical images of the particles for data collected at 20 to 70 degrees Celsius, the measurement is performed in the range of 5 to 240 minutes.

[0048] The correlation of the total particle dissolution with compressive strength data is generated from samples tested at 28 days.

[0049] The method according to the present invention predicts the evolution of compressive strength of a blended cement based on a nomogram (FIG. 2) that comprises 3 curves: Curve 1 (1, FIG.2) - particle dissolution rate of a pozzolanic material measured via optical microscope as a function of time; Curve 2 (3, FIG.

[0050] 2) - Compressive Strength evolution of a blended cement mortar as a function of time; and Curve 3 (2, FIG. 2) - Correlation curve between particle dissolution rate and strength development rate of a blended cement.

[0051] Part 1 : The pozzolanic material (fine powder) is dissolved into a 1 to 5 molar alkaline solution (Sodium Hydroxide and Water) and heated to 20 to 70°C. The samples solution is then observed for a time period from 15 to 240 minutes using an optical microscope and the rate of particle dissolution is measured by means of computer vision - item 4 in FIG. 2 depicts the experimental data for a calcined clay sample. The dissolution rate is computed either as (a) the number of particles dissolved in relation to the initial particle count (4, FIG. 2) or (b) the change in the total of particles dissolved in relation to the total area of particles at the start of the test. This composes curve 1 (1, FIG. 2) that displays the dissolution of particles as a function of time.

[0052] Part 2: The pozzolanic material is mixed with Ordinary Portland Cement at any given mass proportion (e.g. one that matches the proportions from the blended cement that will be produced in a cement plant) and the strength development of this mix is measured up to 28 days based on the test method EN196-5: Methods of testing cement - Part 5 Pozzolanicity test for pozzolanic cement. This composes a curve 2 (3, FIG. 2) that displays the rate of strength development as a function of time. For item 3 in FIG.2, the experimental data (5, FIG. 2) is obtained from a mix produced with a composite cement that comprises 80% Ordinary Portland Cement and 20% Calcined clay (mass fraction of total binder, i.e. cement and SCM).

[0053] Part 3: Curves 1 (1 , FIG. 2) and 2 (3, FIG. 2) are correlated - i.e. a time scale is applied to match the dissolution test time with the strength development time using a linear interpolation. This composes the correlation curve between particles dissolution rate and strength development (2, FIG. 2)

[0054] Part 4: Curves 1 (1 , FIG. 2) to 3 (3, FIG. 2) are grouped to form a nomogram (FIG. 2) that serves as basis to predict the strength development of a cement blend with a given percentage of pozzolanic materials in its composition as a function of particle dissolution.

[0055] In another aspect, the invention related to an apparatus utilizing the method according to any of the above-mentioned embodiments.

[0056] The apparatus comprises a computing device, being configured for receiving inputting digital signals from sensors and analysis, configured for making mathematical operations with the signals and for outputting digital signals that convert the observed changes in particle count or particle size or area over time into a relative measure of particle dissolution, i.e. changes in particle count or particle size or area normalized in relation to the initial count or size of the particles at the start of the test.

[0057] The apparatus can be used to measure particle reactivity of pozzolanic materials.

[0058] The apparatus is preferably installed in a cement factory.

[0059] Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. It should also be understood that the form of this invention as shown is merely a preferred embodiment. Various changes may be made in the function and arrangement of parts; equivalent means may be substituted for those illustrated and described; and certain features may be used independently from others without departing from the spirit and scope of the invention as defined in the following claims.

Claims

CLAIMS1 : A method for measuring reactivity of pozzolanic materials and correlating their reactivity to strength development in composite cement, said method comprising the steps of- dissolving pozzolanic materials in an alkaline solution,- placing a 1.0 to 5.0 Molar Sodium Hydroxide - Na(OH) - solution obtained by dissolving the pozzolanic materials in the alkaline solution on a flow cell or a thin glass sheet, said flow cell configured to accommodate pozzolanic particles up to 100pm,- heat the flow cell at 20 to 70°C, collecting one or more optical images of the particles using an optical microscope,- measuring the pozzolanic materials (particle) count and area by image processing a set of spatial and morphological filters to identify the particles distributed in the solution over time,- compute the change in particle count or area over time; the normalised particle count is interpretated as dissolution - which is plotted over time, describing the particle dissolution rate over the measurement time, and- correlate the particle dissolution over time with compressive strength data generated from samples tested in a range from 1- 28 days2: A method according to claim 1 , when the collecting of one or more optical images of the particles for data collected at 20 to 70 degrees Celsius, the measurement is performed in the range of 5 to 240 minutes.3: A method according to claim 1 , wherein the correlation of the total particle dissolution with compressive strength data is generated from samples tested at 28 days.4: An apparatus utilizing the method according to any of the claims 1-3, said apparatus comprises a computing device, said computing device configured for receiving inputting digital signals from sensors and analysis, configured for making mathematical operations with said signals and for outputting digital signals that convert the observed changes in particle count or particle size or area over time into a relative measure of particle dissolution, i.e. changes in particle count or particle size or area normalized in relation to the initial count or size of the particles at the start of the test.5: An apparatus according to claim 4, for use to measuring particle reactivity of pozzolanic materials.6: A cement factory, comprising the apparatus according to claims 4 or 5.

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