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Alkali-activated slag materials are known for their high Chloride penetration resistance. This makes them potentially applicable as repair systems for damaged steel-reinforced concrete structures, which are exposed to chloride attack. For this purpose, the influence of the activator composition, i.e. the SiO2 and Na2O concentration of the alkaline solution on a) the compressive strength, b) shrinkage and mass change and c) the resistance against chloride penetration of four alkali-activated slag mortars (AASM) were studied. An ordinary Portland cement-based mortar was used as the reference sample. Increasing SiO2 and Na2O concentrations increased the strength, shrinkage and mass loss of the AASMs. The resistance of the mortars against chloride penetration was evaluated using the non-steady-state migration coefficient Dnssm obtained from NT BUILD 492. The results indicate that the Dnssm is related to differences in the pore solution of the AASMs rather than to differences in their microstructure. An upcoming study of the authors is going to evaluate this hypothesis by the accelerated chloride penetration (diffusion) test.
Shrinkage measurement of miniaturized low temperature co-fired
ceramics (LTCC) samples under load typically leads to a collapsing of
the sample due to the softening of the glassy phase, which hampers
the characterization of shrinkage up to full densification. In practical
sintering processes in contrast, LTCC panels are sintered under axial
loads of up to 1 MPa without lateral shrinkage or collapsing of the
structure. To characterize the shrinkage behavior during such
processes, a measurement setup was developed, which allows for in-situ
thickness shrinkage measurements of practical, large LTCC panels
during pressure-assisted sintering in a sintering press. Using this setup,
the shrinkage behavior of two commercial LTCC tapes (GreenTape 951
and Ceramtape GC) has been measured under loads of up to 1 MPa.
No crushing of the specimens was observed and reproducible
characterization of shrinkage up to full densification has been
performed. Based on comparisons to thermomechanical analyzer
measurements in this and other studies, it is concluded that the in-situ
approach is much better suited for shrinkage characterization of LTCC
under load.