Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | Department of Civil and Environmental Engineering | en_US |
| dc.contributor.advisor | Yu, Tao (CEE) | en_US |
| dc.contributor.advisor | Zou, Fangxin (AAE) | en_US |
| dc.creator | Hussain, Abasal | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/14509 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | Nanocarbon black-based ultra-high-performance concrete with self-sensing capability : development and durability | en_US |
| dcterms.abstract | Concrete structures are inevitably affected by different loads and environmental conditions during their service life, and the resulting structural cracks and damage significantly reduce the durability and serviceability of the structures. Therefore, there is an increasing demand for real-time monitoring of the stress state and deformation in concrete structures. Smart cementitious composites (SCCs) have emerged as a promising technology that aims to develop an intrinsic sensing system to replace conventional sensors which are generally expensive, often incompatible with concrete structures, and may suffer from durability issues. However, the existing SCCs still face many challenges, including their relatively high costs, dispersion issues of piezoresistive materials, inferior mechanical properties, durability and/or serviceability. | en_US |
| dcterms.abstract | Against this background, this PhD study aims to develop a new type of SCC with ultra-high strength, excellent durability, and an incredible strain sensing capability while being highly cost-effective. Ultra-high-performance concrete (UHPC) has exceptional mechanical and durability properties due to its dense and well-compacted microstructure. The dense microstructure of UHPC, however, makes it challenging for the development of sensing capability as it hinders the mobility of piezoresistive materials. In this study, UHPC with sensing capability was developed by incorporating nanocarbon black (nCB) in the cement matrix. Nanocarbon black is a highly conductive and low-cost material, with its unit cost being less than 1% of that of carbon nanotubes, and the use of nCB makes the cement matrix conductive by its branched structure through a quantum tunnelling mechanism. The resulting UHPC is termed herein nCB-UHPC. | en_US |
| dcterms.abstract | This study started with investigations on the effect of the structures of nCB on the mechanical and piezoresistive properties of cementitious matrix. Three different nCB structures were investigated, and nCB with the most suitable structure was identified. The selected nCB was then used for a comprehensive experimental programme, in which it was incorporated into UHPC by up to 2.0% of the binder mass. The experimental programme included the formulation of proper mix designs and evaluation of the fresh, hardened mechanical properties and microstructure of nCB-UHPC under different curing environments. In addition, the piezoresistive properties of the nCB-UHPC, including the percolation threshold, strain sensitivity and conductive mechanism, were examined. The test results show that by incorporating nCB of a proper content (e.g., 1.0-1.5%), the resulting nCB-UHPC can have an ultrahigh 28-day compressive strength (>140 MPa), sufficiently good workability (slump spread ≥170 mm) and excellent strain-sensing capability (gauge factor >130) at the same time. | en_US |
| dcterms.abstract | Moreover, UHPC with 1.50% nCB was further investigated for its durability under different working conditions. The effects of multiple curing conditions and long-term aggressive environmental exposure on the mechanical, piezoresistive and microstructural properties of the UHPC were examined. The test results showed that the nCB-UPBC developed in this study possesses a highly durable and well-synchronized response and is less influenced by the aggressive environment. | en_US |
| dcterms.abstract | Furthermore, nCB was incorporated into UHPC with seawater and sea-sand (i.e., ultra-high-performance seawater sea-sand concrete or UHPSSC), leading to the so-called nCB-UHPSSC. The use of seawater and sea-sand offers significant benefits, especially for construction of coastal/marine infrastructure; by replacing river sand with sea-sand, the environmental impact caused by excessive sand mining in riverbeds can also be mitigated. A comprehensive experimental programme was conducted, involving the development of new mix designs of UHPSSC with varying concentrations of nCB (up to 1.80% by binder mass) as well as investigations of its mechanical, microstructural and piezoresistive properties with different curing conditions. In addition, the piezoresistive behaviour was studied in a fully saturated state and after drying treatment. The test results indicated that the nCB-UHPSSC has comparable mechanical properties to nCB-UHPC. The piezoresistive behaviour of nCB-UHPSSC is characterized by a precisely synchronized response with a low percolation zone, and the nCB-UHPSSC in a saturated state has a higher sensitivity than that in a dry state due to the dissolved ions in the former. | en_US |
| dcterms.abstract | While the initial findings were incredibly promising, the durability performance of nCB-UHPSSC considering practical applications was further evaluated. A comprehensive experimental programme was conducted on UHPSSC with 1.40% nCB by binder mass, which is the percolation threshold of nCB-UHPSSC. The investigations encompassed electromechanical properties under various curing conditions and exposure durations, as well as the microstructure analysis. Besides, the impact of different in-situ temperatures on the piezoresistive properties was also explored to gain insights into the sensitivity and reliability of the self-sensing UHPSSC. The result indicated that the strain sensitivity of nCB-UHPSSC increases with the temperature due to the thermal energy which allows more charge carriers to flow easily within a system. | en_US |
| dcterms.abstract | In summary, this PhD study has successfully developed two new types of UHPCs with self-sensing capability (i.e., nCB-UHPC and nCB-UHPSSC) and has systematically investigated their mechanical, piezoresistive properties and durability. The two types of UHPCs, with their demonstrated excellent properties, can be used as high-performance constructional materials as well as a real-time monitoring measure for civil infrastructure. | en_US |
| dcterms.extent | xxxi, 255 pages : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2025 | en_US |
| dcterms.educationalLevel | Ph.D. | en_US |
| dcterms.educationalLevel | All Doctorate | en_US |
| dcterms.accessRights | open access | en_US |
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