The sample preparation for BSE-SEM was more laborious. First the specimen needed to be broken
and placed in a small plastic container, approximately 1.5 cm in diameter. Then in a cup enough
resin to cover the specimen was made at a ratio of 25:3 g of EpoFix Resin to EpoFix Hardener
(Figure 30a). The resin was introduced into the container under a vacuum to ensure the minimum
amount of air bubbles got stuck with the resin (Figure 30b). Once the resin completely covered
the specimen, the specimen was put aside, and the resin was allowed to harden over a period of 24
hours (Figure 30c). A Struers Accutom-50 diamond saw was used to cut the specimen such that
it had a planar surface (Figure 30d-e). A Struers grinding polishing machine was then used to
polish the specimen through a series of decreasing grain size (Figure 30f-h). After polishing the
specimen was set aside for another 24 hours to allow enough time for the polishing alcohol residue
to evaporate (Figure 30i). The specimen was then coated with a carbon coater (Leica) to create a
conductive surface on the plane (Figure 30c).
(a) (b)
54
(c) (d)
(e) (f)
55
(i) (j)
Figure 30 Sample Preparation for back scattering electron scanning electron microscopy.
4.5. Mercury Intrusion Porosimetry
Mercury intrusion porosimetry (MIP) was used to characterize the pore structure of the CNF-
UHPC composites. This technique is based on the intrusion of a non-wetting fluid (mercury) into
the connected pore structure under increasing pressure. The Washburn equation is used to relate
the pressure to the entry pore size. Samples were crushed to obtain a mass of 1g. The dried samples
were placed in the dilatometer and the air was removed. The measurement was in two steps for
two different populations of the pores. In the first step a pressure of 100kPa was applied to intrude
the larger pores. In the second step, the pressure was increased up to 400 MPa which allowed the
mercury to intrude pore entries down to 2 nm.
4.6. Inverse Gas Chromatography
A Hewlett-Packard gas chromatograph fitted by Surface Measurement Systems (SMS) with a
flame ionization detector (FID) was used for the Inverse Gas Chromatography (IGC)
measurements. Glass columns of 30 cm in length and 4 cm in diameter were packed with a tap-
and-fill method with specimens that were grounded up by hand and then sieved through a #200 or
#140 sieve. Each column was packed with 100 mg – 150 mg of material. Before the columns
56
were at 60°C with an injection flow rate of 10 sccm. The probes listed in Table 9 were selected
based off the limited literature on IGC and cement [146,162-164]. The dead-time was determined
by methane injection. A Flame Ionization Detector (FID) was used to determine retention times.
Table 9 Selected probes used in this study.
Probe Molecule Type Probe Molecule Type
Benzene aromatic Methane n-alkane
Chloroform aromatic Octane n-alkane
Ethyl acetate polar Nonane n-alkane
Methanol polar Decane n-alkane
Acetonitrile polar Undecane n-alkane
4.7. Dynamic Light Scattering
The concentration of particles remaining in the filtered interstitial pore fluid after mixing and
filtering was determined by Dynamic Light Scattering (DLS). Measurements were performed
using a Zetasizer nano S from Malvern Instruments, operating at an incident light wavelength of
633 nm, scattered light detection angle of 173°, and constant temperature of 25 °C. The value of
the scattered intensity was computed from the average of five independent measurements. DLS is
generally used to measure the size distribution by intensity of particles or polymer coils in a liquid
medium. In this work, the measured scattered intensity was further used to study the nanoparticles
in cement pore solution and estimate their concentration.
Plotted in Figure 31a, the size distribution by intensity of cement pore solutions solution at
different relative concentrations obtained through calcium hydroxide dilution. The calcium
hydroxide solution (i.e. lime) was prepared by adding to distilled water 0.85g/L of Ca(OH)2 . The
presence of nanoparticles with a size around 130nm can be seen. Figure 31b shows that the light
intensity scattered by these nanoparticles, which corresponds to the peak area from 30 nm to 1000
57
work, the concentration of nanoparticles in the pore solution will be estimated by measuring the
scattered intensity (i.e. peak area).
Figure 31 (a) The size distribution by intensity of cement pore solutions at different relative
concentrations (i.e. the ratio between concentration of the solution after dilution with calcium
hydroxide solution and the concentration of the initial solution) and (b) the corresponding peak
area as a function of the relative concentration. The pore solution is obtained from a cement
paste prepared at W/C=0.3, containing 0.4% PCE and mixed at the speed of 840 rpm.
4.8. Adsorption Isothermals
Total Organic Carbon (TOC) analysis was used to measure the adsorption of the PCE on the
surfaces of the cement or quartz powders. The TOC analyzer in this study was manufactured by
Shimadzu. The adsorption levels of different dosages of PCE on the mineral phases of the powder
were found by taking the difference between the total organic carbon content of a reference PCE
solution and the amount of PCE extracted from the pore solution of a cement or quartz powder
paste. The amount of organic carbon content in the powders from the production process cannot 0.0E+00 2.0E+04 4.0E+04 6.0E+04 8.0E+04 1.0E+05 1.2E+05 1.4E+05 1.6E+05 10 100 1000 In te n sity (k cp s) Radius (nm) Relative concentration =0.4 Relative concentration =0.5 Relative concentration =1 y = 715720x R² = 0.99 0.0E+00 1.0E+05 2.0E+05 3.0E+05 4.0E+05 5.0E+05 6.0E+05 7.0E+05 8.0E+05 0.20 0.70 1.20 In te n sity (k cp s) Relative concentration (-)
58
be neglected as it strongly affects the measurements if left aside. The subsequent measurements
were taken from pastes with incremental increases in PCE dosage. The adsorption isotherms were
then computed to determine the saturation levels of the PCE on the surfaces of the cement or quartz
powders.
4.9. Isothermal Calorimetry
The thermal power and heat of hydration of the cement pastes were monitored for the first 48 hours
using a TAM Air microcalorimeter (Thermometrics) at a constant temperature of 20 ºC. Samples
were mixed according to the mixing procedure and then 5g of paste was placed inside the
calorimeter cell. All samples were balanced with a reference cell having the same heat capacity.