[BBG02-04] Characteristics of organic matter as inhibitor of calcium silicate hydrate formation
Keywords:Soil organic matter, C-S-H, Formation inhibition
Alkaline activated soils were made with two dredged soils E and H collected from ports of Japan and a steel slag. Their mixtures are named as mixture 1E and 1H, which were cured for three days under hermetical condition at 25 °C. Uniaxial compressive strengths of 1E and IH were 288 kPa and unmeasurable due to its soft property after curing, respectively. This difference may be attributed by C-S-H formation in 1E and C-S-H formation inhibition in 1H. C-S-H was not detectable under X-ray diffraction of the cured samples, yet its formation was underpinned by geochemical analysis and thermodynamic calculations.
To directly analyze the interaction of C-S-H with organic matters, lignosulfonate, with similar composition to the soil organic matters that consist of macromolecule compound of aliphatic and aromatic carbon with acidic functional groups, is doped to C-S-H synthesis. C-S-H was synthesized from Ca(OH)2, portlandite, and amorphous silica in coexistence with lignosulfonate of 0.29 and 0.56 g/g addition ratio to unreacted inorganic reagents in 100 rpm shaker at 50 °C for 10 days. The X-ray diffractograms of the sample with 0.29 g/g addition of lignosulfonate consisted of C-S-H whereas 0.56 g/g addition of lignosulfonate consisted of portlandite and amorphous silica, which C-S-H formation was inhibited.
Carbon chemical state imaging acquired by scanning transmission X-ray microscopy (STXM) showed grains in 1E and the synthetic C-S-H of 0.26 g/g lignosulfonate addition coexisted with phenolic and carboxylic carbon similar to the bulk organic carbon entity in each systems, whereas grains in 1H and C-S-H formation inhibited products with 0.56 g/g lignosulfonate addition had a tendency to coexist with aromatic carbon and less carboxylic carbon relative to C-S-H formation systems. Aromatic carbon may be favorable to coexist in C-S-H formation inhibited grains, which may directly play a key role or indirectly state the effect of organic matter on C-S-H formation inhibition. These data with further organic matter’s characterization and geochemical analysis on alkaline activated soils could infer the possible mechanisms of C-S-H formation inhibition caused by natural organic matters in relation with their specific components.