Nano-modified cementitious composites reinforced with basalt fiber pellets and their potential for repair/overlay applications

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Azzam, Ahmed
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Under loading and environmental conditions, the brittle nature of conventional concrete flatwork infrastructure (e.g. pavements/bridge decks) may negatively affect its performance due to susceptibility to excessive cracking, requiring costly rehabilitation or replacement of damaged sections. Thus, this thesis aimed at developing and testing a novel type of high-performance cementitious composites. Nano-modified cementitious composites comprising 50% fly ash or slag and reinforced with an innovative type of macro-fibers [basalt fiber pellets (BFP)] were developed and extensively studied. The consistency and flowability/flowability retention of the composites as well as setting times were investigated. The mechanical performance of the composites was tested under static and dynamic (Split Hopkinson Pressure Bar) loading schemes. Moreover, the performance of the cementitious composites under aggravated (alkaline and salt-frost) exposures was comprehensively explored. To investigate potential of these composites for repair and overlay applications in concrete flatwork, thermal, elastic, and mechanical compatibility of the cementitious composites with conventional concrete paving mixture as well as their suitability for bonded overlay systems were experimentally and numerically studied. The results showed that the nano-modified composites with 6% nano-silica exhibited enhanced mechanical performance at both early- and late-ages. Moreover, they revealed the efficacy of BFP in reinforcing the cementitious composites and highlighted their role at enhancing the post-cracking performance in terms of energy absorption capacity and strain at failure. While alkaline exposure provided favorable conditions for the binders’ reactivity, this was accompanied by reduction of ductility of composites due to pellets’ degradation. The matrix of the composites deteriorated physically and/or chemically under the salt-frost exposure, albeit to different extents according to the binder type. The composites showed high thermal, elastic, and mechanical compatibility with concrete substrate even after aggravated exposures. Furthermore, the cementitious composites showed significant efficacy in bonded overlay systems, even with pre-cracked substrate concrete layer. The synoptic outcomes of this thesis highlighted the promising fresh, mechanical, and durability properties of the nano-modified cementitious composites, particularly the slag-based composites, as well as their compatibility with normal concrete paving mixture. Thus, they may present a viable option for high-performance repair/overlay applications at critical and heavy-duty locations in concrete pavements and bridge decks.
Nanomodified cementitious composites, Basalt fiber pellets, Post-cracking behavior, Single pellet pullout, Impact loading, Durability, Aggravated Exposure, Partial depth repair, Overlay