The authors would like to acknowledge partial financial support from the Kiewit Transportation Institute and the Federal Highway Administration (FHWA) through DTFH61-12-H-00010. All of the laboratory work presented herein was performed at the Kiewit Transportation Institute at Oregon State University.

1. Pore Solution Expression13
<ol>
	<li>Make sure the individual components of the pore solution extractor are clean and dry.</li>
	<li>Use a new cellulose filter (with an average pore diameter of 0.45 &#181;m) for each expression.</li>
	<li>Assemble the pore solution extractor, as shown in Figure 1.</li>
	<li>Check that there are no visible deformations in the cellulose filter.</li>
	<li>Add the fresh cementitious paste into the main chamber, leaving it empty for at least 1 cm from the top. 
	NOTE: The term fresh paste indicates any cementitious paste still in a plastic state. Cementitious pastes are generally made by mixing cement, supplementary cementitious materials, water, and chemical admixtures. The volume ratios of these constituents can vary depending on the properties desired.</li>
	<li>Connect the pore solution extractor to the nitrogen source and seal the main chamber.</li>
	<li>Align the expression device with the plastic canister to temporarily collect the extracted pore solution.</li>
	<li>Open the valve of the nitrogen tank and regulate the pressure using the pressure regulator, so that a pressure of approximately 200 kPa is applied to the paste inside the main chamber. 
	NOTE: For safety, a pressure regulator must be utilized.</li>
	<li>Maintain constant pressure for a period of 5 min, during which the pore solution will be collected in the plastic canister.</li>
	<li>After 5 min from the start of the expression, close the main valve so that the pressure inside the main chamber drops to atmospheric pressure.</li>
	<li>Remove the canister from under the extractor and transfer the pore solution to a 5-mL syringe, making sure not to suck in any air bubbles in the process.</li>
	<li>Seal the syringe with its needle cap and move it inside a 5 &#177; 1 &#176;C chamber to be stored till the time of testing.</li>
	<li>Wait until the pressure gauge shows that there is no additional pressure inside the main chamber and, then, disassemble the pore solution extractor.</li>
	<li>Clean the pore solution extractor parts using deionized water and paper towels.</li>
	<li>Discard the cellulose filter.</li>
</ol>
2. Assembly of the Solution Containers
<ol>
	<li>Make sure that the plastic cylinders are clean and dry.</li>
	<li>Place the polypropylene film (commercially available with 0.4-&#181;m thickness, 90 mm in diameter) flat on top of the larger cylinder (commercially available with a 35-mm diameter).</li>
	<li>Insert the smaller cylinder (commercially available with a 32-mm diameter) completely on top of the larger cylinder, pushing down and pressing the film in-between both cylinders to create a plastic container with a polypropylene film base.</li>
	<li>Ensure that the film is smooth and has no tears or deformations.</li>
</ol>
3. XRF Application Development and Solution Calibration
<ol>
	<li>Create an application file on the XRF software. The application has to be for solution samples and has to be able to detect the main ionic species in pore solution: sodium (Na+), potassium (K+), calcium (Ca2+), and sulfide (S2-).</li>
	<li>Calibrate the solution application with solutions of known concentrations.
	<ol>
		<li>Prepare the standard solutions using varying concentrations of &#62; 99% pure sodium chloride (NaCl), potassium chloride (KCl), calcium chloride (CaCl2), and aluminum sulfate (Al2[SO4]3) to accurately quantify the element studied. 
		NOTE: The concentrations of the standards can vary depending on the materials of interest. As an example, it has been observed that the concentrations of Na+ varied between 0 and 0.5 mol/L, the concentrations of K+ between 0 and 0.9 M, the concentrations of Ca2+ between 0 and 0.05 M, and the concentrations of S2- between 0 and 0.25 M; however, exceptions that exceed these limits might occur depending on the system14. The elements defined and measured in the calibration of the application must include all elements used in the calibration standards: sodium (Na+), potassium (K+), calcium (Ca2+), sulfide (S2-), calcium (Cl-), and aluminum (Al3+).</li>
		<li>For each calibration solution, measure 6 g of that solution inside the assembled testing container.</li>
		<li>Seal the container with the corresponding lid.</li>
		<li>Leave the testing container with the standard solution on a paper towel for 2 min to ensure that the film has no leaks that could potentially damage the XRF device.</li>
		<li>Place the sealed testing containers with the standard solutions inside the XRF sample holders and close the XRF.</li>
		<li>Measure each standard solution using the XRF. The intensities of characteristic fluorescent X-rays of elements from each of the solutions, measured in counts per minute (cpm), are detected by the XRF. 
		NOTE: Varying conditions sets for different groups of elements are needed. Refer to a previously published article for parameters such as measuring time and excitation energies6.</li>
		<li>Note the concentration in parts per million (ppm) of each element in each standard solution as defined in the software and related to the intensity in counts per minute (cpm) measured by the XRF.</li>
		<li>After the standard solutions are measured, use a matrix correction model from the XRF software used (linear, alphas, fundamental parameters (FP)) that will yield the minimum relative RMS (%) for each element in the calibration to create the best linear fit for the calibration.</li>
		<li>Verify that the application yields accurate results by testing solutions of known concentrations of sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca[OH]2), and aluminum sulfate (Al2[SO4]3) at different concentration levels within the calibration range. 
		NOTE: The application should yield accurate results if the error is within 5%.</li>
	</ol>
	</li>
</ol>
4. XRF Analysis
<ol>
	<li>Inject at least 2 g of the pore solution sample in the assembled testing container.</li>
	<li>Seal the container with the corresponding lid.</li>
	<li>Leave the container with the solution on a paper towel for 2 min to ensure that the film has no leaks that could potentially damage the XRF device.</li>
	<li>Place the testing containers with the solutions inside the XRF sample holders and close the XRF.</li>
	<li>On the XRF software, select the XRF application that was previously developed.</li>
	<li>Use the application interface on the software to select the XRF sample holders that are going to be subjected to the X-ray fluorescence analysis. 
	NOTE: It is recommended to name the new file for each selected sample holder based on the solution being tested.</li>
	<li>Start the XRF application to measure the ionic concentrations of the solutions. 
	NOTE: The results from the XRF analysis will show the concentration of sodium (Na+), potassium (K+), calcium (Ca2+), and sulfide (S2-).</li>
</ol>
5. Ionic Concentration Calculation
<ol>
	<li>Use stoichiometry to calculate the concentration of sulfate (SO42-) using equation 2. 
	<img alt="Equation 4" src="/files/ftp_upload/58432/58432eq04.jpg" style="opacity: 0.9;" />&#160; (2) 
	Here, 
	<img alt="Equation 5" src="/files/ftp_upload/58432/58432eq05.jpg" />&#160;= the measured ionic concentration of sulfide ions from XRF in ppm; 
	<img alt="Equation 6" src="/files/ftp_upload/58432/58432eq06.jpg" />&#160;= the molecular weight of sulfide in g/mol; 
	<img alt="Equation 7" src="/files/ftp_upload/58432/58432eq07.jpg" />&#160;= the measured ionic concentration of sulfate ions from XRF in ppm; 
	<img alt="Equation 8" src="/files/ftp_upload/58432/58432eq08.jpg" />&#160;= the molecular weight of sulfate in g/mol.</li>
	<li>Use a charge balance to calculate the concentration of hydroxides (OH-) using equation 3. 
	<img alt="Equation 9" src="/files/ftp_upload/58432/58432eq09.jpg" style="opacity: 0.9;" />&#160; (3) 
	Here, 
	<img alt="Equation 10" src="/files/ftp_upload/58432/58432eq10.jpg" />&#160;= the hydroxide ions concentration in ppm; 
	<img alt="Equation 11" src="/files/ftp_upload/58432/58432eq11.jpg" />&#160;= the sodium ions concentration in ppm; 
	<img alt="Equation 12" src="/files/ftp_upload/58432/58432eq12.jpg" />&#160;= the potassium ions concentration in ppm; 
	<img alt="Equation 13" src="/files/ftp_upload/58432/58432eq13.jpg" />&#160;= the calcium ions concentration in ppm; 
	<img alt="Equation 14" src="/files/ftp_upload/58432/58432eq14.jpg" />&#160;= the sulfate ions concentration in ppm.</li>
	<li>Convert the ionic concentrations from ppm to mol/L using equation 4 and assuming a density (&#961;) of 1,000 g/L. If desired, more accurate density information may be obtained from textbooks15 or thermodynamic software and used. 
	<img alt="Equation 15" src="/files/ftp_upload/58432/58432eq15.jpg" />&#160; (4) 
	Here, 
	<img alt="Equation 16" src="/files/ftp_upload/58432/58432eq16.jpg" />&#160;= the ionic concentration of a single ionic species in mol/L; 
	<img alt="Equation 17" src="/files/ftp_upload/58432/58432eq17.jpg" />&#160;= the ionic concentration of a single ionic species in ppm obtained from XRF; 
	<img alt="Equation 18" src="/files/ftp_upload/58432/58432eq18.jpg" />&#160;= the density of the solution in g/L; 
	<img alt="Equation 19" src="/files/ftp_upload/58432/58432eq19.jpg" />&#160;= the molecular weight of a single ionic species in g/mol; 
	<img alt="Equation 20" src="/files/ftp_upload/58432/58432eq20.jpg" />&#160;= a single ionic species.</li>
</ol>
6. Resistivity Calculation
<ol>
	<li>Use the model developed by Snyder et al.16, expressed in equations 5 - 7, to calculate the electrical resistivity of the pore solution. 
	<img alt="Equation 21" src="/files/ftp_upload/58432/58432eq21.jpg" />&#160;(5) 
	<img alt="Equation 22" src="/files/ftp_upload/58432/58432eq22.jpg" />&#160; (6) 
	<img alt="Equation 23" src="/files/ftp_upload/58432/58432eq23.jpg" style="opacity: 0.9;" />&#160; (7) 
	Here, 
	<img alt="Equation 24" src="/files/ftp_upload/58432/58432eq24.jpg" />&#160;= electrical resistivity of the solution in &#8486;m; 
	<img alt="Equation 25" src="/files/ftp_upload/58432/58432eq25.jpg" />&#160;= the equivalent conductivity of a single ionic species in cm2 S/mol; 
	<img alt="Equation 26" src="/files/ftp_upload/58432/58432eq26.jpg" />&#160;= the valence concentration of a single ionic species; 
	<img alt="Equation 17" src="/files/ftp_upload/58432/58432eq17.jpg" />&#160;= the molar concentration of a single ionic species in mol/L; 
	<img alt="Equation 27" src="/files/ftp_upload/58432/58432eq27.jpg" />*&#160;= the equivalent conductivity of ionic species at infinite dilution in cm2 S/mol; 
	<img alt="Equation 28" src="/files/ftp_upload/58432/58432eq28.jpg" />*&#160;= the empirical conductivity coefficient of a single ionic species in (mol/L)-1/2; 
	<img alt="Equation 29" src="/files/ftp_upload/58432/58432eq29.jpg" />&#160;= the ionic strength (molar basis) in mol/L; 
	<img alt="Equation 20" src="/files/ftp_upload/58432/58432eq20.jpg" />&#160;= a single ionic species. 
	Empirical values can be found in Table 1. 
	NOTE: The formation factor can then be estimated as the ratio of the electrical resistivity of concrete and the electrical resistivity of pore solution (equation 1)3. As the formation factor is a fundamental descriptor of the concrete microstructure, the determination of the formation factor is an important step in moving a traditionally prescriptive industry toward performance-based specifications. The formation factor has been linked to various transportation phenomena, such as diffusion, absorption, and permeability, and could be used to predict concrete service life1,2,4,5,17,18.</li>
</ol>

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E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+electrical+resistivity+log+as+an+aid+in+determining+some+reservoir+characteristics.">The electrical resistivity log as an aid in determining some reservoir characteristics.</a> Society of Petroleum Engineers. 142 (1), 54-62 (1942).</li><li>Spragg, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Factors+that+influence+electrical+resistivity+measurements+in+cementitious+systems.">Factors that influence electrical resistivity measurements in cementitious systems.</a> Transportation Research Record: Journal of the Transportation Research Board. 2342, 90-98 (2013).</li><li>Spragg, R. P., Bu, Y., Snyder, K. A., Bentz, D. P., Weiss, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrical+Testing+of+Cement-Based+Materials:+Role+of+Testing+Techniques,+Sample+Conditioning,+and+Accelerated+Curing.">Electrical Testing of Cement-Based Materials: Role of Testing Techniques, Sample Conditioning, and Accelerated Curing.</a> Joint Transportation Research Program Technical Report. , (2013).</li><li>Tsui-Chang, M., Suraneni, P., Isgor, O. B., Trejo, D., Weiss, W. 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R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> CRC Handbook of Chemistry and Physics. , (2018).</li><li>Snyder, K. A., Feng, X., Keen, B. D., Mason, T. 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A., Lukovic, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Toward+Performance+Specifications+for+Concrete:+Linking+Resistivity,+RCPT+and+Diffusion+Predictions+Using+the+Formation+Factor+for+Use+in+Specifications.">Toward Performance Specifications for Concrete: Linking Resistivity, RCPT and Diffusion Predictions Using the Formation Factor for Use in Specifications.</a> , 2057-2065 (2017).</li><li>Andersson, K., Allard, B., Bengtsson, M., Magnusson, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemical+composition+of+cement+pore+solutions.">Chemical composition of cement pore solutions.</a> Cement and Concrete Research. 19 (3), 327-322 (1989).</li><li>Barneyback, R., Diamond, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Expression+and+analysis+of+pore+fluids+from+hardened+cement+pastes+and+mortars.">Expression and analysis of pore fluids from hardened cement pastes and mortars.</a> Cement and Concrete Research. 11 (2), 279-285 (1981).</li><li>Nicoleau, L., Schreiner, E., Nonat, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ion-specific+effects+influencing+the+dissolution+of+tricalcium+silicate.">Ion-specific effects influencing the dissolution of tricalcium silicate.</a> Cement and Concrete Research. 59, 118-138 (2014).</li><li>Rajabipour, F., Sant, G., Weiss, W. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interactions+between+shrinkage+reducing+admixtures+(SRA)+and+cement+paste's+pore+solution.">Interactions between shrinkage reducing admixtures (SRA) and cement paste's pore solution.</a> Cement and Concrete Research. 38 (5), 606-615 (2008).</li></ol>

The authors have nothing to disclose.

Since this is a sensitive chemical analysis method, it is imperative to have laboratory practices that prevent contamination. For this method, it is critical that the calibration standards are specifically performed with high-purity chemicals (&#62; 99%). When transferring the pore solution into the syringe, make sure that no visible cement grains are present in the solution to avoid any changes in the pore solution. When stored in a sealed syringe at a constant temperature of 5 &#177; 1 &#176;C, the pore solution has been observed to maintain an unaltered chemical composition for up to 7 days.
One of the main limitations of this protocol is that the method of expression outlined can only be used for fresh paste specimens and is not suitable for later age samples. For later age or hardened samples, a method of expression using a high-pressure extraction die20 is needed. Another limitation is that a minimum amount of 2 g of solution is needed to test in the XRF since an amount less than 2 g does not provide a constant sample height that can cover the entire bottom face of the container. This last limitation applies to the particular set-up that was used in this study. A different set-up would probably allow a reduction in the minimum amount of pore solution required for the testing. Another limitation is that the model is not likely applicable to systems containing slag-rich cements since species such as bisulfide (HS-) may be present, as discussed by Vollpracht et al.14.
Since XRF is a commonly used technique in the cement industry, this method could potentially enable cement manufacturers to use a tool already at their disposal to provide more information about the cementitious pore solution, such as the chemical composition and resistivity for numerous applications and at a lower cost and testing time than conventional methods. For example, when comparing sample preparation and testing time between ICP (a commonly used testing method for pore solution composition), the testing time is reduced from 50 min per sample to 8 min per sample using XRF. This method could extend the applications for XRF and could potentially be implemented fairly quickly in the industry.
XRF can be used to determine the main elemental concentrations in the pore solution. This suggests the use of XRF for applications such as (i) determining the composition of pore solutions to study the dissolution kinetics of cementitious phases21 or (ii) determining the effect of chemical admixtures22. Early age pore solution and concrete resistivity measurements could be used as a measure of the water-to-cement ratio of concrete, which could potentially be used in quality control.

The transport properties of concrete are determined by its formation factor, which is a fundamental measure of the microstructure1. The formation factor is defined as the inverse of the product between the connectivity and the porosity of a concrete2. The formation factor can be calculated from the ratio of the electrical resistivity of concrete and the electrical resistivity of pore solution as presented in equation 13.
<img alt="Equation 1" src="/files/ftp_upload/58432/58432eq01.jpg" />&#160; (1)
Here,
<img alt="Equation 2" src="/files/ftp_upload/58432/58432eq02.jpg" style="font-size: 14px;" />&#160;= electrical resistivity of bulk or concrete (&#937;m);
<img alt="Equation 3" src="/files/ftp_upload/58432/58432eq03.jpg" style="font-size: 14px;" />&#160;= electrical resistivity of pore solution (&#937;m).
The bulk electrical resistivity of concrete may be easily determined on hardened concrete using a resistivity meter, following approaches outlined in AASHTO PP84-17 Appendix X2 and other literature4,5. The purpose of this article is to provide instructions for expressing the pore solution from fresh paste and analysis of the solution ionic composition using X-ray fluorescence (XRF) spectroscopy. The expressed pore solution is tested in the XRF using commercially available materials (cylinders and film). The ionic composition detected by the XRF can be used for multiple concrete durability applications and can also be used to calculate the electrical resistivity of pore solution, to ultimately determine the formation factor6.
Current methods to determine the chemical composition of pore solution, such as inductively coupled plasma (ICP)7, atomic absorption spectroscopy (AAS)8, and ion chromatography (IC)9, can be costly, time-consuming, and quite laborious. Additionally, in some cases, a combination of various methods must be used in order to obtain a complete characterization of the main ionic species in pore solution10. XRF can be used as an alternative to these methods, where the composition of pore solution can be obtained at a relatively lower cost and shorter testing time compared to conventional methods.
XRF is a technique commonly used in the cement industry as it is primarily used to analyze the chemical composition of the manufactured materials for quality control and quality assurance throughout the cement manufacturing process11,12. Therefore, this method will describe how that technique can be used to enable cement manufacturers to use this tool to provide more information about the pore solution composition of different cement batches. Overall, using XRF for pore solutions could potentially extend the use of this technique for multiple applications and could be implemented in the industry relatively quickly.

<table><tbody><tr><td>Energy Disperssive X-Ray Fluorescence Benchtop Spectrometer</td><td>Malvern PANalytical</td><td>Epsilon 3XLE or Epsilon 4</td><td></td></tr><tr><td>35 mm Sample Cups for Liquids</td><td>Malvern PANalytical</td><td>9425 888 00024</td><td>Panalytical Consumables Catalogue 2016 for XRF Accessories and Consumables Catalog</td></tr><tr><td>4 micron Polypropylene Film</td><td>Malvern PANalytical</td><td>9425 888 00029</td><td>Panalytical Consumables Catalogue 2016 for XRF Accessories and Consumables Catalog</td></tr><tr><td>Syringe, 5 mL</td><td>VWR</td><td>53548-005</td><td>HSW Norm-Ject Sterile Luer-Slip syringes, Air-Tite</td></tr><tr><td>Needle, 16Gx1&#039;&#039;</td><td>VWR</td><td>89219-334</td><td>Premium Veterinary Hypodermic Needles, Sterile, Air-Tite</td></tr><tr><td>Container</td><td>VWR&amp;nbsp;</td><td>15704-092</td><td>VWR Specimen containers, Polypropylene with Polyethylene Caps</td></tr><tr><td>Pressurized Filter Holder</td><td>EMD Millipore</td><td>XX4004700</td><td>100 mL capacity, 47 mm filter diameter</td></tr><tr><td>MCE Membrane Filter</td><td>PALL</td><td>63069</td><td>47 mm diameter, 0.45 &amp;mu;m pore size</td></tr><tr><td>Silicone Funnell</td><td>SpiceLuxe</td><td>SLP-122513-F1</td><td>Top opening 2 1/2&amp;Prime;, Bottom opening 3/4&amp;Prime;, Height 2 3/4&amp;Prime;</td></tr></tbody></table>

expression of cementitious pore solution and the analysis of its chemical composition and resistivity using x-ray fluorescence

The goal of this method is to determine the chemical composition and electrical resistivity of cementitious pore solution expressed from a fresh paste sample. The pore solution is expressed from a fresh paste sample using a pressurized nitrogen gas system. The pore solution is then immediately transferred to a syringe to minimize evaporation and carbonation. After that, assembled testing containers are used for the X-ray fluorescence (XRF) measurement. These containers consist of two concentric plastic cylinders and a polypropylene film which seals one of the two open sides. The pore solution is added into the container immediately prior to the XRF measurement. The XRF is calibrated to detect the main ionic species in the pore solution, in particular, sodium (Na+), potassium (K+), calcium (Ca2+), and sulfide (S2-), to calculate sulfate (SO42-) using stoichiometry. The hydroxides (OH-) can be calculated from a charge balance. To calculate the electrical resistivity of the solution, the concentrations of the main ionic species and a model by Snyder et al. are used. The electrical resistivity of the pore solution can be used, along with the electrical resistivity of concrete, to determine the formation factor of concrete. XRF is a potential alternative to current methods to determine the composition of pore solution, which can provide benefits in terms of reduction in time and costs.

In this section, representative outcomes of each major step in the methodology are presented. This is done in order to obtain an idea of what is expected at the end of each step and provide useful tips to ensure a correct application of the method.
The first important step consists in the expression of the pore solution from the fresh paste sample. Figure 2 shows a pore solution that is correctly extracted and sealed in a 5-mL syringe. The pore solution in the figure was expressed from a fresh ordinary Portland cement paste with a water-to-cement ratio of 0.36. The sample was mixed 10 min before the image was taken. The pore solution is expected to be clear; however, the color can vary depending on the type of cementitious materials that were used and the age of the sample at the time of the expression.
Before the XRF measurement of the extracted pore solution, it is necessary to calibrate the instrument. In particular, each element whose ionic concentration will be measured needs to be calibrated. A representative calibration plot of the potassium (K+) ions is shown in Figure 3. The figure shows the fitting performed by the software on the intensities measured by the XRF. Note that the root mean square (RMS) error of the fitting should stay below 5%.
After calibration, it is recommended to test a solution of known ionic concentration to determine the accuracy of the machine. The measured composition of the ions using XRF is compared to the theoretical composition of both solutions. According to our experience, assuming a correct preparation of the ionic solutions, this checking step should yield a percentage of errors lower than &#177; 5%. Figure 4 shows the composition results for the spot-checking of the solutions. When the spot-checking yields a percentage of errors higher than &#177; 5%, repeat the calibration of the XRF device.

Table 2 shows a representative set of results for composition and resistivity. While the ionic concentration of the pore solution can vary widely depending on the chemical composition of the cement, the water-to-cement ratio of the system, and the presence of supplementary cementitious materials19, reference values can be obtained from the literature20 for the main ions, as shown in Table 1.

Finally, when calculating the resistivity of a sample, values for early age pore solutions are typically expected to be within 0.05 and 0.25 &#937;m14. Now that the resistivity of the pore solution is known, the bulk resistivity can be obtained using other methods, like uniaxial resistivity, in order to, ultimately, calculate the formation factor, which is typically over 2,000 for good quality concrete4,5,18.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/58432/58432fig1.jpg" /> 
Figure 1: Assembly of the pore solution extraction system. The system consists of a main expression device, a nitrogen tank and tube with a safety pressure gauge and regulator, and a collection container. Always refer to the manufacturer&#39;s instructions and safety precautions for the specific system used. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58432/58432fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/58432/58432fig2.jpg" /> 
Figure 2: Correctly extracted and sealed extracted pore solution in a 5-mL syringe. The extracted pore solution should appear clear (i.e., no visible particles) and should be sealed with no air bubbles within the syringe.&#160;
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/58432/58432fig3.jpg" /> 
Figure 3: Representative calibration plot of potassium (K+). The x-axis shows the imputed (known) concentrations in ppm, and the y-axis shows the detected (measured) intensities with XRF in cpm. The calibration line calculated from one of the correction models in the software should have the smallest RMS (%), as discussed in section 3 of the protocol. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58432/58432fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/58432/58432fig4.jpg" /> 
Figure 4: Sodium ion (Na+) and potassium ion (K+) verification plot. The dashed line represents a 1:1 ratio.The verification plot should show a good correlation (almost a 1:1 relationship with a high R-squared value) between the known concentrations of the sodium and potassium ions and the detected concentrations using XRF. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58432/58432fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Ionic Species (i)</td>
			<td>Equivalent conductivity at infinite dilution (&#955;&#730;i)</td>
			<td>Empirical conductivity coefficient&#160;</td>
		</tr>
		<tr>
			<td>(i)</td>
			<td>(z&#955;&#176;i)</td>
			<td>(Gi)&#160;</td>
		</tr>
		<tr>
			<td></td>
			<td>(cm2 S/mol)</td>
			<td>(mol/L)-1/2</td>
		</tr>
		<tr>
			<td>Sodium (Na+)</td>
			<td>50.1</td>
			<td>0.733</td>
		</tr>
		<tr>
			<td>Potassium (K+)</td>
			<td>73.5</td>
			<td>0.548</td>
		</tr>
		<tr>
			<td>Calcium (Ca2+)</td>
			<td>59</td>
			<td>0.771</td>
		</tr>
		<tr>
			<td>Hydroxide (OH-)</td>
			<td>198</td>
			<td>0.353</td>
		</tr>
		<tr>
			<td>Sulfate (SO42-)</td>
			<td>79</td>
			<td>0.877</td>
		</tr>
	</tbody>
</table>
Table 1: Equivalent conductivity at infinite dilution (<img alt="Equation 30" src="/files/ftp_upload/58432/58432eq30.jpg" />) and empirical conductivity coefficients (<img alt="Equation 31" src="/files/ftp_upload/58432/58432eq31.jpg" />&#8203;) for each ionic species&#160;obtained from the literature11. These values are used in order to calculate the electrical resistivity of the pore solution.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Ionic Species&#160;</td>
			<td>Concentration&#160;</td>
		</tr>
		<tr>
			<td>(i)</td>
			<td>(mol/L)</td>
		</tr>
		<tr>
			<td>Sodium (Na+)</td>
			<td>0.16</td>
		</tr>
		<tr>
			<td>Potassium (K+)</td>
			<td>0.39</td>
		</tr>
		<tr>
			<td>Calcium (Ca2+)</td>
			<td>0.02</td>
		</tr>
		<tr>
			<td>Hydroxide (OH-)</td>
			<td>0.18</td>
		</tr>
		<tr>
			<td>Sulfate (SO42-)</td>
			<td>0.2</td>
		</tr>
		<tr>
			<td>Resistivity (&#937;m)</td>
			<td>0.156</td>
		</tr>
	</tbody>
</table>
Table 2: Representative results for the composition and resistivity of a cement paste with a water-to-cement ratio of 0.36 at 10 min. The values in this table are examples of the results obtained using this method.

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Expression of Cementitious Pore Solution and the Analysis of Its Chemical Composition and Resistivity Using X-ray Fluorescence

This protocol describes the procedure to express fresh pore solution from cementitious systems and the measurement of its ionic composition using X-ray fluorescence. The ionic composition can be used to calculate pore solution electrical resistivity, which can be used, together with concrete electrical resistivity, to determine the formation factor.

The goal of this method is to determine the chemical composition and electrical resistivity of cementitious pore solution expressed from a fresh paste ...

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Unit 1

Introduction to Concrete

Method Development and Sampling Techniques

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9.1K Views.  Oregon State University. Het algemene doel van deze procedure is om een methode te beschrijven om verse porieoplossing van een plastic cementitious basissysteem te beschrijven gebruikend een roestvrij staal onder druk gezet stikstofgasfilter en de chemische samenstelling van de porieoplossing te meten gebruikend een energie dispersieve spectroometer van de vloeispuitenfluorescentiebank. De chemische ionische samenstelling gemeten door de XRF kan worden gebruikt het berekenen van de elektrische weerstand van de porie ...

Video: Expression of Cementitious Pore Solution and the Analysis of Its Chemical Composition and Resistivity Using X-ray Fluorescence

Reservoir Condition Pore-scale Imaging of Multiple Fluid Phases Using X-ray Microtomography

X-ray microtomography was used to image, at a resolution of 6.6 &#181;m, the pore-scale arrangement of residual carbon dioxide ganglia in the pore-space of a carbonate rock at pressures and temperatures representative of typical formations used for CO2 storage. Chemical equilibrium between the CO2, brine and rock phases was maintained using a high pressure high temperature reactor, replicating conditions far away from the injection site. Fluid flow was controlled using high pressure high temperature syringe pumps. To maintain representative in-situ conditions within the micro-CT scanner a carbon fiber high pressure micro-CT coreholder was used. Diffusive CO2 exchange across the confining sleeve from the pore-space of the rock to the confining fluid was prevented by surrounding the core with a triple wrap of aluminum foil. Reconstructed brine contrast was modeled using a polychromatic x-ray source, and brine composition was chosen to maximize the three phase contrast between the two fluids and the rock. Flexible flow lines were used to reduce forces on the sample during image acquisition, potentially causing unwanted sample motion, a major shortcoming in previous techniques. An internal thermocouple, placed directly adjacent to the rock core, coupled with an external flexible heating wrap and a PID controller was used to maintain a constant temperature within the flow cell. Substantial amounts of CO2 were trapped, with a residual saturation of 0.203 &#177; 0.013, and the sizes of larger volume ganglia obey power law distributions, consistent with percolation theory.

We present a methodology for the imaging of multiple fluid phases at reservoir conditions by the use of x-ray microtomography. We show some representative results of capillary trapping in a carbonate rock sample.

X-ray microtomography was used to image, at a resolution of 6.6 &#181;m, the pore-scale arrangement of residual carbon dioxide ganglia in the pore-space ...

Dynamic Pore-scale Reservoir-condition Imaging of Reaction in Carbonates Using Synchrotron Fast Tomography

Underground storage permanence is a major concern for carbon capture and storage. Pumping CO2 into carbonate reservoirs has the potential to dissolve geologic seals and allow CO2 to escape. However, the dissolution processes at reservoir conditions are poorly understood. Thus, time-resolved experiments are needed to observe and predict the nature and rate of dissolution at the pore scale. Synchrotron fast tomography is a method of taking high-resolution time-resolved images of complex pore structures much more quickly than traditional &#181;-CT. The Diamond Lightsource Pink Beam was used to dynamically image dissolution of limestone in the presence of CO2-saturated brine at reservoir conditions. 100 scans were taken at a 6.1 &#181;m resolution over a period of 2 hours. The images were segmented and the porosity and permeability were measured using image analysis and network extraction. Porosity increased uniformly along the length of the sample; however, the rate of increase of both porosity and permeability slowed at later times.

Synchrotron fast tomography was used to dynamically image dissolution of limestone in the presence of CO2-saturated brine at reservoir conditions. 100 scans were taken at a 6.1 &#181;m resolution over a period of 2 h.

Underground storage permanence is a major concern for carbon capture and storage. Pumping CO2 into carbonate reservoirs has the potential to dissolve ...

Two-way Valorization of Blast Furnace Slag: Synthesis of Precipitated Calcium Carbonate and Zeolitic Heavy Metal Adsorbent

The aim of this work is to present a zero-waste process for storing CO2 in a stable and benign mineral form while producing zeolitic minerals with sufficient heavy metal adsorption capacity. To this end, blast furnace slag, a residue from iron-making, is utilized as the starting material. Calcium is selectively extracted from the slag by leaching with acetic acid (2 M CH3COOH) as the extraction agent. The filtered leachate is subsequently physico-chemically purified and then carbonated to form precipitated calcium carbonate (PCC) of high purity (&lt;2 wt% non-calcium impurities, according to ICP-MS analysis). Sodium hydroxide is added to neutralize the regenerated acetate. The morphological properties of the resulting calcitic PCC are tuned for its potential application as a filler in papermaking. In parallel, the residual solids from the extraction stage are subjected to hydrothermal conversion in a caustic solution (2 M NaOH) that leads to the predominant formation of a particular zeolitic mineral phase (detected by XRD), namely analcime (NaAlSi2O6&#8729;H2O). Based on its ability to adsorb Ni2+, as reported from batch adsorption experiments and ICP-OES analysis, this product can potentially be used in wastewater treatment or for environmental remediation applications.

A protocol for the parallel production of precipitated calcium carbonate and zeolitic material from blast furnace slag via mineral carbonation and alkaline hydrothermal conversion, respectively, is presented. The performance of the zeolitic material towards nickel adsorption is tested.

The aim of this work is to present a zero-waste process for storing CO2 in a stable and benign mineral form while producing zeolitic minerals with ...

Detecting the Water-soluble Chloride Distribution of Cement Paste in a High-precision Way

To improve the accuracy of the chloride distribution along the depth of cement paste under cyclic wet-dry conditions, a new method is proposed to obtain a high-precision chloride profile. Firstly, paste specimens are molded, cured, and exposed to cyclic wet-dry conditions. Then, powder samples at different specimen depths are grinded when the exposure age is reached. Finally, the water-soluble chloride content is detected using a silver nitrate titration method, and chloride profiles are plotted. The key to improving the accuracy of the chloride distribution along the depth is to exclude the error in the powderization, which is the most critical step for testing the distribution of chloride. Based on the above concept, the grinding method in this protocol can be used to grind powder samples automatically layer by layer from the surface inward, and it should be noted that a very thin grinding thickness (less than 0.5 mm) with a minimum error less than 0.04 mm can be obtained. The chloride profile obtained by this method better reflects the chloride distribution in specimens, which helps researchers to capture the distribution features that are often overlooked. Furthermore, this method can be applied to studies in the field of cement-based materials, which require high chloride distribution accuracy.

A protocol for obtaining a water-soluble chloride profile by using a high precision milling method is presented.

To improve the accuracy of the chloride distribution along the depth of cement paste under cyclic wet-dry conditions, a new method is proposed to obtain a ...

Atom Probe Tomography Analysis of Exsolved Mineral Phases

Element diffusion rates and temperature/pressure control a range of fundamental volcanic and metamorphic processes. Such processes are often recorded in lamellae exsolved from host mineral phases. Thus, the analysis of the orientation, size, morphology, composition and spacing of exsolution lamellae is an area of active research in the geosciences. The conventional study of these lamellae has been conducted by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and more recently with focused ion beam (FIB)-based nanotomography, yet with limited chemical information. Here, we explore the use of atom probe tomography (APT) for the nanoscale analysis of ilmenite exsolution lamellae in igneous titanomagnetite from ash deposits erupted from the active Soufri&#232;re Hills Volcano (Montserrat, British West Indies). APT allows the precise calculation of interlamellar spacings (14&#8211;29 &#177; 2 nm) and reveals smooth diffusion profiles with no sharp phase boundaries during the exchange of Fe and Ti/O between the exsolved lamellae and the host crystal. Our results suggest that this novel approach permits nanoscale measurements of lamellae composition and interlamellar spacing that may provide a means to estimate the lava dome temperatures necessary to model extrusion rates and lava dome failure, both of which play a key role in volcanic hazard mitigation efforts.

Analysis of the morphology, composition, and spacing of exsolution lamellae can provide essential information to understand geological processes related to volcanism and metamorphism. We present a novel application of APT for the characterization of such lamellae and compare this approach to the conventional use of electron microscopy and FIB-based nanotomography.

Element diffusion rates and temperature/pressure control a range of fundamental volcanic and metamorphic processes. Such processes are often recorded in ...

Environment

Analysis of Minerals Produced by hFOB 1.19 and Saos-2 Cells Using Transmission Electron Microscopy with Energy Dispersive X-ray Microanalysis

This video presents the use of transmission electron microscopy with energy dispersive X-ray microanalysis (TEM-EDX) to compare the state of minerals in vesicles released by two human bone cell lines: hFOB 1.19 and Saos-2. These cell lines, after treatment with ascorbic acid (AA) and &#946;-glycerophosphate (&#946;-GP), undergo complete osteogenic transdifferentiation from proliferation to mineralization and produce matrix vesicles (MVs) that trigger apatite nucleation in the extracellular matrix (ECM).
Based on Alizarin Red-S (AR-S) staining and analysis of the composition of minerals in cell lysates using ultraviolet (UV) light or in vesicles using TEM imaging followed by EDX quantitation and ion mapping, we can infer that osteosarcoma Saos-2 and osteoblastic hFOB 1.19 cells reveal distinct mineralization profiles. Saos-2 cells mineralize more efficiently than hFOB 1.19 cells and produce larger mineral deposits that are not visible under UV light but are similar to hydroxyapatite (HA) in that they have more Ca and F substitutions.
The results obtained using these techniques allow us to conclude that the process of mineralization differs depending on the cell type. We propose that, at the cellular level, the origin and properties of vesicles predetermine the type of minerals.

We present a protocol to compare the state of minerals in vesicles released by two human bone cell lines: hFOB 1.19 and Saos-2. Their mineralization profiles were analyzed by Alizarin Red-S (AR-S) staining, ultraviolet (UV) light visualization, transmission electron microscopy (TEM) imaging and energy dispersive X-ray microanalysis (EDX).

This video presents the use of transmission electron microscopy with energy dispersive X-ray microanalysis (TEM-EDX) to compare the state of minerals in ...

Chemistry

Synchrotron X-ray Microdiffraction and Fluorescence Imaging of Mineral and Rock Samples

In this report, we describe a detailed procedure for acquiring and processing&#160;x-ray microfluorescence (&#956;XRF), and Laue and powder microdiffraction two-dimensional (2D) maps at beamline 12.3.2 of the Advanced Light Source (ALS), Lawrence Berkeley National Laboratory. Measurements can be performed on any sample that is less than 10 cm x 10 cm x 5 cm, with a flat exposed surface. The experimental geometry is calibrated using standard materials (elemental standards for XRF, and crystalline samples such as Si, quartz, or Al2O3 for diffraction). Samples are aligned to the focal point of the x-ray microbeam, and raster scans are performed, where each pixel of a map corresponds to one measurement, e.g., one XRF spectrum or one diffraction pattern. The data are then processed using the in-house developed software XMAS, which outputs text files, where each row corresponds to a pixel position. Representative data from moissanite and an olive snail shell are presented to demonstrate data quality, collection, and analysis strategies.

We describe a beamline setup meant to carry out rapid two-dimensional x-ray fluorescence and x-ray microdiffraction mapping of single crystal or powder samples using either Laue (polychromatic radiation) or powder (monochromatic radiation) diffraction. The resulting maps give information about strain, orientation, phase distribution, and plastic deformation.

In this report, we describe a detailed procedure for acquiring and processing&#160;x-ray microfluorescence (&#956;XRF), and Laue and powder ...

Multimodal Analysis of Bone Formation Using Explant Models

Comprehensive Characterization of Tissue Mineralization in an Ex Vivo Model

The extensive characterization of tissue mineralization in the context of bone regeneration represents a significant challenge, given the numerous modalities that are currently available for analysis. Here, we propose a workflow for a comprehensive evaluation of new bone formation using a relevant large animal osseous ex vivo explant. A bone defect (diameter = 3.75 mm; depth = 5.0 mm) is created in an explanted sheep femoral head and injected with a macroporous bone substitute loaded with a pro-osteogenic growth factor (bone morphogenetic protein 2 - BMP2). Subsequently, the explant is maintained in culture for a 28-day period, allowing cellular colonization and subsequent bone formation. To evaluate the quality and structure of newly mineralized tissue, the following successive methods are set up: (i) Characterization and high-resolution 3D images of the entire explant using micro-CT, followed by deep learning image analyses to enhance the discrimination of mineralized tissues; (ii) Nano-indentation to determine the mechanical properties of the newly formed tissue; (iii) Histological examinations, such as Hematoxylin/Eosin/Saffron (HES), Goldner's trichrome, and Movat's pentachrome to provide a qualitative assessment of mineralized tissue, particularly with regard to the visualization of the osteoid barrier and the presence of bone cells; (iv) Back-scattering scanning electron microscopy (SEM) mapping with internal reference to quantify the degree of mineralization and provide detailed insights into surface morphology, mineral composition, and bone-biomaterial interface; (v) Raman spectroscopy to characterize the molecular composition of the mineralized matrix and to provide insights into the persistence of BMP2 within the cement through the detection of peptide bonds. This multimodal analysis will provide an effective assessment of newly formed bone and comprehensive qualitative and quantitative insights into mineralized tissues. Through the standardization of these protocols, we aim to facilitate interstudy comparisons and improve the validity and reliability of research findings.

Author Spotlight: Advanced Techniques for Characterizing Tissue Mineralization in Bone Regeneration Research

The proposed protocol entails a global approach to assess bone formation in the context of bone regeneration using multimodal analyses. It aims to provide qualitative and quantitative information on new bone formation, enhancing the rigor and validity of basic and pre-clinical investigations.

The extensive characterization of tissue mineralization in the context of bone regeneration represents a significant challenge, given the numerous ...

Bioengineering

X-ray Fluorescence (XRF)

Source: Laboratory of Dr. Lydia Finney &#8212; Argonne National Laboratory
X-ray fluorescence is an induced, emitted radiation that can be used to generate spectroscopic information. X-ray fluorescence microscopy is a non-destructive imaging technique that uses the induced fluorescence emission of metals to identify and quantify their spatial distribution.

X-ray Fluorescence XRF: Elemental Analysis by Emitted Fluorescent X-Ray

Source: Laboratory of Dr. Lydia Finney &#8212; Argonne National Laboratory
X-ray fluorescence is an induced, emitted radiation that can be used to ...

JoVE Science Education

Porosity in Cement Paste

The porosity of concrete is a measure of the void spaces within its structure. These spaces impact its strength and durability significantly. When water and cement interact, a chemical reaction called hydration creates a semi-solid paste. This paste includes combined water, making up approximately 23% of the cement&#39;s dry mass, and gel water, which fills minuscule voids known as gel pores, accounting for about 28% of the cement gel volume.
The balance of water to cement in the mix is critical&#8212;it influences the extent of hydration and, thereby, the porosity and strength of the cured concrete. In an ideal hydration process, extra space not occupied by solid hydration products forms capillary pores, representing around 18.5% of the original cement volume. As the concrete cures, continuous hydration can fill the capillary pores with hydration products, increasing the density of the material.
For complete hydration and optimal strength, the curing process must be managed carefully. It allows for additional hydration, reducing porosity by filling the capillary spaces with more stable hydration products and, as a result, densifying the paste. This meticulous process is crucial for achieving durable, high-quality concrete that is less susceptible to environmental and mechanical degradation.

As fresh cement paste sets, it transitions from a fluid state to a solid mass, entrapping water in various forms, such as gel water, capillary water, and ...

Expression of Cementitious Pore Solution and the Analysis of Its Chemical Composition and Resistivity Using X-ray Fluorescence

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