This paper evaluates the efficiency of polypropylene fibers in improving the tensile and flexural characteristics of fiber-reinforced alkali-activated slag composites with strain-hardening behavior. Several different composites were produced and the mechanical properties of the composites were investigated during compressive and flexural tests. Furthermore, the mid-span curvature of the beams was measured by applying the digital image correlation technique to the flexural tests, and the curvature-deflection diagrams of the composites were analyzed and demarcated by structural mechanics. Finally, an analytical model considering strain-hardening behavior was proposed by fitting the calculated moment-curvature diagrams to the experimental results to recognize the tensile behavior of composites more precisely than the existing indirect methods. The results showed that an ultra-high tensile strain capacity was obtained for composites cured under laboratory conditions. Also, it was found that the fiber interfacial bond with the matrix was improved by using slag with lower Al₂O₃ content. Moreover, weakening the interfacial transition zone between the fine aggregate and the paste, the heat-treatment curing reduced the fracture energy of the composites which is favored to make strain-hardening cementitious composites.

Carbonated wollastonite-based clinker is proposed as a potential novel supplementary cementitious material. The clinker can be synthesized from limestone and a silica source, and exhibits a CO₂-footprint after carbonation, which is approximately 60-70% less than the one of Portland cement. When carbonated, a silica-rich amorphous phase forms besides various polymorphs of calcium carbonate. When the carbonated clinker is blended with Portland cement, hydration is accelerated, and a significant pozzolanic reaction of the silica-rich amorphous phase takes place. This leads to a positive contribution to compressive strength. In a blend with 30% replacement of Portland cement by the carbonated wollastonite-based clinker almost the same mortar compressive strength is reached after 28 days compared to the plain Portland cement. Further investigations, especially regarding the production of the carbonated clinker, the durability of concrete incorporating this novel material, and life cycle analyses as well as economical assessments are needed.

Moisture transport is the key phenomenon indicating the deterioration of the durability and structural performance of concrete structures. Although various studies have attempted to evaluate moisture transport in concrete, an anomalous behavior, which does not follow the root-t law compared to other porous material, was not explicitly taken into account. To quantitatively evaluate anomalous moisture transport, this study developed a couple of numerical methods between the truss-network model (TNM) and the rigid-body-spring model (RBSM) for this purpose. The colloidal behavior of calcium-silicate-hydrate (C-S-H), which is the major phase of cement-based material, was introduced to consider the anomalous behavior and mechanical response regarding the microstructural change of cement paste as well as cracks that significantly accelerate the moisture transport in concrete. The numerical results indicated that both microstructural change of cement paste and rapid absorption through cracks cause anomalous behavior. In addition, the numerical results suggest that volumetric change of cement paste should rely on water content related to the colloidal behavior of C-S-H in order to reproduce the realistic expansion and the closure of cracks during a rewetting process that affects structural performance and durability of concrete.