Abstract: Tuning microstructures by adding nanoparticles is a promising way of improving the performance of cementitious composites. In this study, nanoclay was introduced to polyvinyl alcohol (PVA) fiber reinforced ultra high toughness cementitious composites (UHTCCs). The mechanical properties, crack patterns, water permeation resistance, and microstructures of UHTCCs with different dosages of nanoclay were studied. The addition of a proper dosage of nanoclay shows few effects on the compressive strength of UHTCCs, however, the compressive strength is decreased when an excessive amount of nanoclay is added. The flexural deformation capacity of UHTCCs is independent of nanoclay dosage, whereas the flexural strength generally decreases with an increasing dosage of nanoclay. Different cracking patterns were observed in the ultra high toughness cementitious composites containing nanoclay (NC-UHTCC) specimens subject to bending tests. A UHTCC with 1% (in weight) nanoclay shows the best water permeation resistance and the lowest water permeability. Variations in the mechanical properties and the water permeation resistance of UHTCCs containing different dosages of nanoclay could be ascribed to the synthetic effects of filling and heterogeneous nucleation of nanoclay at low dosages and the agglomeration effect of nanoclay at high dosages. This study is to optimize the water permeation resistance of UHTCCs, paving a path for the future application of UHTCCs in the fields of construction, decoration, and repair.

Key words: Nanoclay; Water permeability; Pore structure; Cementitious composites; Strain hardening

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