Surface properties of clinker phases and clay minerals characterized by inverse gas chromatography (IGC) and their link to reactivity

[Description of methods used for collection/generation of data] IGC measurements at infinite dilution (IGC-ID) and finite dilution (IGC-FD) were carried out using a PerkinElmer Clarus 400 chromatography meter coupled with an Agilent AMD 1000 flowmeter to control the gas injections. The analysis of recorded chromatograms to obtain the isotherms was conducted using the CGI-CF V 709G software from Adscientis. For the determination of energy distribution functions, the FDRJ 07.5.F software from Adscientis was used. For the measurements at infinite dilution (IGC-ID), C3S-I, C3S-II and C3A samples were placed in a 6.4 mm (1/4 in.) measuring column, with an internal diameter of 4 mm and a length of 10 cm. Approximately 2 g of powder were placed in the columns for measurement. Due to the poor handling properties of the kaolinite and metakaolin powders, compaction, crushing and sieving was carried out beforehand. This procedure ensured a suitable gas flow rate in the IGC column. To do this, kaolinite and metakaolin samples were compacted in a pelletizing mold under a pressure of 1 ton for 2 minutes. Afterwards, the pellets were crushed and sieved. A 3.2 mm (1/8 in.) measuring column, with an internal diameter of 2 mm and a length of 10 cm, was filled with pieces with a size between 250 to 450 m. Approximately 0.35 grams of kaolinite and metakaolinite were used in each case. Before conducting the measurements, the surface of the samples inside the column was conditioned for the tests using a flow of dry helium at 5 mL/min during 16 h at 30°C. Measurements were conducted at 30°C for all samples, except kaolinite. In this case, the retention times observed were extremely long, and the measurement temperature was increased to 80°C on this sample to achieve full elution over a reasonable timeframe. Hexane, heptane, octane, nonane, isooctane, 2,2-dimethyl-hexane (2,2-DHM) and cyclooctane were used as n-alkane probes to determine the dispersive surface energy. Isooctane, 2,2-dimethyl-hexane (2,2-DMH) and cyclooctane were used as branched and cyclic probes to measure the surface nanoroughness. Acetone, acetonitrile (CH3CN), tetrahydrofuran (THF), ether, chloroform (CHCl3) and benzene were also used as polar probes to determine the acid-base character of the different cementitious materials. For IGC-FD measurements, water and isopropanol were used as probes over the set of samples with helium as carrier gas in both cases. Water was initially used over C3A and C3S-I samples. In this case, P/P0 values from 0.15 to 0.64 were explored. A strong interaction of water with the surfaces was observed, and consequently isopropanol was selected as a more suitable adsorbate to conduct further experiments. Measurements with isopropanol were done for C3A, C3S-I, C3S-II, C3S-II Ann, C3S-II-TEA, Kaolinite, MK and MK-TEA. For these measurements, the injected amount of isopropanol was fixed so to achieve a P/P0 up to 0.2, with a minimum of 3 injections. All isopropanol injections were preceded by injection pulse of methane (CH4), used as a reference to compute the retention times (TR) at each point of the chromatogram. All measurements were conducted at 30°C. For all cement phases, a 6.4 mm (1/4 in.) measuring column, with an internal diameter of 4 mm and a length of 10 cm was used. The columns were filled with 1.6-2 g of sample. In the case of C3S-II Annealed, a shorter column (3 cm, filled with 0.6 g of sample) with the same diameter was used to decrease the observed retention time. In the case of clay minerals, a 3.2 mm (1/8 in.) measuring column, with an internal diameter of 2 mm and a length of 5 cm was used, filled with 0.13 to 0.18 g of sample. The clay powders were pelletized in the same way as for the IGC-ID measurements. Isothermal calorimetry was used to characterize the reactivity of the different cement phases. Paste samples were prepared by mixing 15 g of powder with distilled water at a water-to-solids ratio of 0.35. A high shear mixer was used at 1600 rpm for 2 minutes. Afterwards, 10 grams of sample were placed in a glass ampoule and sealed. A TAM Air isothermal calorimeter was used to monitor the heat release of the samples for 7 days at 20°C. Isothermal calorimetry was also used to assess the reactivity of the different clay minerals. For this purpose, the R3 test (ASTM C1897) [16] was selected due to its reliability and ease of interpretation. In this procedure, the different clays are mixed with portlandite, calcium carbonate, potassium sulphate, potassium hydroxide and water at 40 °C, and put into glass ampoules inside the calorimeter at 40 °C. The total heat evolved is taken as a measure of the reactivity of the clays.