{"id":{"repo_id":"cambridge","oai_identifier":"oai:www.repository.cam.ac.uk:1810/364253"},"canonical_url":"https://search.dev.ndltd.org/etd/cambridge/oai:www.repository.cam.ac.uk:1810/364253","repository":{"repo_id":"cambridge","name":"Cambridge University","base_url":"https://api.repository.cam.ac.uk/server/oai/request"},"display":{"title":"Self-healing strain-hardening cementitious composites (SH2CC) for cyclic loading environments","abstract":"Cyclic loading is ubiquitous and frequently encountered in various infrastructure. However, the widely used construction material, concrete, is inherently brittle and could be poor at sustaining cyclic stress (especially those involving tensile stress). Although reinforcement can help avoid structural failure, large cracks are unavoidable which would reduce the durability of the material. In this case, timely retrofit or repair of damaged or cracked infrastructure due to cyclic loading is crucial, which can however be difficult and costly. Aiming to reduce structural damage and repair costs due to cyclic loading, self-healing techniques could be applied in combination with fibre-reinforced strain-hardening cementitious composites (SHCC); the former enables cementitious materials to heal cracks without human intervention, and the latter features much higher ductility than traditional concrete due to effective fibre bridging based on micromechanical design. Accordingly, this research develops novel materials based on SHCC which achieve 1) high deflection capacity (around 5 mm, equivalent to an estimated tensile strain capacity around 1.92%) under cyclic loading with different strain rates, 2) effective crack width (CW) control (below 30 μm regardless of sample sizes) and enhanced self-healing ability to fully recover mechanical properties within 3 weeks after damage caused by low-rate cyclic loading. Three main challenges are dealt with in this research. Firstly, uniform fibre distribution in SHCC is the prerequisite for developing and producing SHCC with robust mechanical performance, and appropriate rheological status of the fresh mortar is the key to it, which could however be difficult to achieve and guarantee with the existing trial-and-error methods. Therefore, a quantitative method for effective rheology control of fresh SHCC using combined chemical admixtures was first developed based on rheometer testing and regression modelling, which was further validated by four-point bending tests. The developed models were able to predict rheological parameters with high confidence and provide guidance for rheology optimisation for achieving robust deflection-hardening behaviour of SHCC. Secondly, either cyclic loading or high loading rates has been reported to reduce the ductility of SHCC in most cases, while the performance of SHCC under cyclic loading with different loading rates has not been sufficiently studied. It is also necessary to develop SHCC with enhanced cyclic endurance especially at varying or elevated strain rates for targeted applications. Results show that either cyclic loading or high loading rates could increase the tendency of fibre rupture, thus reducing the ductility of SHCC; combined elevated-rate and cyclic loading posed an even larger negative effect on the SHCC ductility due to accelerated degradation of fibres and fibre-matrix interfaces. Nevertheless, the impact could be minimised through matrix tailoring. Two SHCC mixes with improved rate-cyclic endurance were developed through increasing fly ash (FA) content or incorporating triethanolamine (TEA) based on micromechanical models, which showed reduced tendency of fibre rupture and thus improved ductility under the high-rate reversed cyclic loading. Thirdly, traditional SHCC has exhibited satisfying CW control below 100 μm which could promote autogenous healing after cracking, while this process can be slow and insufficient especially for aggressive loading conditions. Considering this, the healing efficiency of SHCC can potentially be enhanced and accelerated through incorporating engineered healing agents. Non-encapsulated mineral and/or polymer admixtures were found to be more compatible without harming the deflection-hardening property of SHCC. Based on this, five SHCC mixes for enhancing self-healing efficiency (named SH2CC) were developed by applying expansive mineral substitutes (MS, including reactive magnesia pellets, or reactive magnesia powder, combined with quicklime) and/or TEA additive in high-volume-FA-SHCC, and their self-healing performance after low-rate cyclic damage (up to 50% of ductility) was investigated. All the SH2CC showed almost 100% recovery regarding various mechanical properties after the 3-week healing conditioning, and SH2CC with MS presented 70 – 90% CW reduction. MS could promote mechanical recovery through hydration and pozzolanic reaction with water supply, and more prominently accelerate crack sealing through enhanced carbonation at crack tips. TEA addition was able to pause the initial hydration/carbonation process of SH2CC under air curing, thus resuming the process upon water contact and boosting both mechanical recovery and crack sealing. Accordingly, SH2CC with combined MS and TEA additive exhibited the highest healing efficiency which was attributed to 1) improved CW control (≤ 20 μm), 2) the production of larger amounts of mixed types of healing products (various hydrates and carbonates) both in cracks and fibre-matrix interfaces for crack filling and enhancement of fibre bonding strength.","abstract_html":"Cyclic loading is ubiquitous and frequently encountered in various infrastructure. However, the widely used construction material, concrete, is inherently brittle and could be poor at sustaining cyclic stress (especially those involving tensile stress). Although reinforcement can help avoid structural failure, large cracks are unavoidable which would reduce the durability of the material. In this case, timely retrofit or repair of damaged or cracked infrastructure due to cyclic loading is crucial, which can however be difficult and costly. Aiming to reduce structural damage and repair costs due to cyclic loading, self-healing techniques could be applied in combination with fibre-reinforced strain-hardening cementitious composites (SHCC); the former enables cementitious materials to heal cracks without human intervention, and the latter features much higher ductility than traditional concrete due to effective fibre bridging based on micromechanical design. Accordingly, this research develops novel materials based on SHCC which achieve 1) high deflection capacity (around 5 mm, equivalent to an estimated tensile strain capacity around 1.92%) under cyclic loading with different strain rates, 2) effective crack width (CW) control (below 30 μm regardless of sample sizes) and enhanced self-healing ability to fully recover mechanical properties within 3 weeks after damage caused by low-rate cyclic loading. Three main challenges are dealt with in this research. Firstly, uniform fibre distribution in SHCC is the prerequisite for developing and producing SHCC with robust mechanical performance, and appropriate rheological status of the fresh mortar is the key to it, which could however be difficult to achieve and guarantee with the existing trial-and-error methods. Therefore, a quantitative method for effective rheology control of fresh SHCC using combined chemical admixtures was first developed based on rheometer testing and regression modelling, which was further validated by four-point bending tests. The developed models were able to predict rheological parameters with high confidence and provide guidance for rheology optimisation for achieving robust deflection-hardening behaviour of SHCC. Secondly, either cyclic loading or high loading rates has been reported to reduce the ductility of SHCC in most cases, while the performance of SHCC under cyclic loading with different loading rates has not been sufficiently studied. It is also necessary to develop SHCC with enhanced cyclic endurance especially at varying or elevated strain rates for targeted applications. Results show that either cyclic loading or high loading rates could increase the tendency of fibre rupture, thus reducing the ductility of SHCC; combined elevated-rate and cyclic loading posed an even larger negative effect on the SHCC ductility due to accelerated degradation of fibres and fibre-matrix interfaces. Nevertheless, the impact could be minimised through matrix tailoring. Two SHCC mixes with improved rate-cyclic endurance were developed through increasing fly ash (FA) content or incorporating triethanolamine (TEA) based on micromechanical models, which showed reduced tendency of fibre rupture and thus improved ductility under the high-rate reversed cyclic loading. Thirdly, traditional SHCC has exhibited satisfying CW control below 100 μm which could promote autogenous healing after cracking, while this process can be slow and insufficient especially for aggressive loading conditions. Considering this, the healing efficiency of SHCC can potentially be enhanced and accelerated through incorporating engineered healing agents. Non-encapsulated mineral and/or polymer admixtures were found to be more compatible without harming the deflection-hardening property of SHCC. Based on this, five SHCC mixes for enhancing self-healing efficiency (named SH2CC) were developed by applying expansive mineral substitutes (MS, including reactive magnesia pellets, or reactive magnesia powder, combined with quicklime) and/or TEA additive in high-volume-FA-SHCC, and their self-healing performance after low-rate cyclic damage (up to 50% of ductility) was investigated. All the SH2CC showed almost 100% recovery regarding various mechanical properties after the 3-week healing conditioning, and SH2CC with MS presented 70 – 90% CW reduction. MS could promote mechanical recovery through hydration and pozzolanic reaction with water supply, and more prominently accelerate crack sealing through enhanced carbonation at crack tips. TEA addition was able to pause the initial hydration/carbonation process of SH2CC under air curing, thus resuming the process upon water contact and boosting both mechanical recovery and crack sealing. Accordingly, SH2CC with combined MS and TEA additive exhibited the highest healing efficiency which was attributed to 1) improved CW control (≤ 20 μm), 2) the production of larger amounts of mixed types of healing products (various hydrates and carbonates) both in cracks and fibre-matrix interfaces for crack filling and enhancement of fibre bonding strength.","abstract_has_math":false,"creators":["Tang, Zixuan"],"institution":"University of Cambridge","degree_name":"Doctor of Philosophy (PhD)","degree_level":"Doctoral","degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Al-Tabbaa, Abir"],"committee_chairs":[],"committee_members":[],"year":2023,"date_issued":"2023-03-01","date_published":"2023-03-01","updated_at":"2026-07-22T22:23:59Z","subjects":["composite material development","crack width","cyclic loading","fibre dispersion","mechanical recovery","micromechanics","microstructural analysis","mineral and chemical admixtures","regression modelling","self-healing","strain-hardening"],"languages":["eng"],"rights":[],"rights_urls":["https://www.repository.cam.ac.uk/bitstreams/6a0e9d51-316c-42f8-b99e-fee8f33d583e/download","https://www.rioxx.net/licenses/all-rights-reserved/"],"identifier_entries":[{"key":"dc:creator.authoridentifier","label":"Author Identifier","values":["0000000243341898"],"render_values":[{"text":"0000-0002-4334-1898","href":"https://orcid.org/0000-0002-4334-1898","code":true}]}]},"links":{"outbound_url":"https://doi.org/10.17863/CAM.105997","outbound_label":"DOI","outbound_source":"dc:identifier.doi"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Al-Tabbaa, Abir"]},{"key":"dc:contributor.sponsor","label":"Sponsor","values":["(1) Engineering and Physical Sciences Research Council (EPSRC): Resilient Materials for Life (RM4L) Programme Grant (EP/P02081X/1) (2) Cambridge Commonwealth, European and International Trust (CCEIT) Scholarship"]},{"key":"dc:creator","label":"Author","values":["Tang, Zixuan"]},{"key":"dc:creator.authoridentifier","label":"Author Identifier","values":["0000000243341898"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.issued","label":"Date","values":["2023-03-01"]},{"key":"dc:publisher.institution","label":"Dc Publisher Institution","values":["University of Cambridge"]},{"key":"dc:relation.isreferencedby.uri","label":"Dc Relation Isreferencedby URI","values":["https://www.repository.cam.ac.uk/handle/1810/364253"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["Doctoral"]},{"key":"dc:type.qualificationname","label":"Dc Type Qualificationname","values":["Doctor of Philosophy (PhD)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["composite material development","crack width","cyclic loading","fibre dispersion","mechanical recovery","micromechanics","microstructural analysis","mineral and chemical admixtures","regression modelling","self-healing","strain-hardening"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["https://www.repository.cam.ac.uk/bitstreams/6a0e9d51-316c-42f8-b99e-fee8f33d583e/download","https://www.rioxx.net/licenses/all-rights-reserved/"]},{"key":"dc:rights.embargodate","label":"Dc Rights Embargodate","values":["2027-02-08"]},{"key":"dc:rights.embargotype","label":"Dc Rights Embargotype","values":["embargo"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.doi","label":"DOI","values":["https://doi.org/10.17863/CAM.105997"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://www.repository.cam.ac.uk/bitstreams/264be2ea-6a54-4099-9526-63d0a696e2e6/download"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Cyclic loading is ubiquitous and frequently encountered in various infrastructure. However, the widely used construction material, concrete, is inherently brittle and could be poor at sustaining cyclic stress (especially those involving tensile stress). Although reinforcement can help avoid structural failure, large cracks are unavoidable which would reduce the durability of the material. In this case, timely retrofit or repair of damaged or cracked infrastructure due to cyclic loading is crucial, which can however be difficult and costly. Aiming to reduce structural damage and repair costs due to cyclic loading, self-healing techniques could be applied in combination with fibre-reinforced strain-hardening cementitious composites (SHCC); the former enables cementitious materials to heal cracks without human intervention, and the latter features much higher ductility than traditional concrete due to effective fibre bridging based on micromechanical design. Accordingly, this research develops novel materials based on SHCC which achieve 1) high deflection capacity (around 5 mm, equivalent to an estimated tensile strain capacity around 1.92%) under cyclic loading with different strain rates, 2) effective crack width (CW) control (below 30 μm regardless of sample sizes) and enhanced self-healing ability to fully recover mechanical properties within 3 weeks after damage caused by low-rate cyclic loading. Three main challenges are dealt with in this research. Firstly, uniform fibre distribution in SHCC is the prerequisite for developing and producing SHCC with robust mechanical performance, and appropriate rheological status of the fresh mortar is the key to it, which could however be difficult to achieve and guarantee with the existing trial-and-error methods. Therefore, a quantitative method for effective rheology control of fresh SHCC using combined chemical admixtures was first developed based on rheometer testing and regression modelling, which was further validated by four-point bending tests. The developed models were able to predict rheological parameters with high confidence and provide guidance for rheology optimisation for achieving robust deflection-hardening behaviour of SHCC. Secondly, either cyclic loading or high loading rates has been reported to reduce the ductility of SHCC in most cases, while the performance of SHCC under cyclic loading with different loading rates has not been sufficiently studied. It is also necessary to develop SHCC with enhanced cyclic endurance especially at varying or elevated strain rates for targeted applications. Results show that either cyclic loading or high loading rates could increase the tendency of fibre rupture, thus reducing the ductility of SHCC; combined elevated-rate and cyclic loading posed an even larger negative effect on the SHCC ductility due to accelerated degradation of fibres and fibre-matrix interfaces. Nevertheless, the impact could be minimised through matrix tailoring. Two SHCC mixes with improved rate-cyclic endurance were developed through increasing fly ash (FA) content or incorporating triethanolamine (TEA) based on micromechanical models, which showed reduced tendency of fibre rupture and thus improved ductility under the high-rate reversed cyclic loading. Thirdly, traditional SHCC has exhibited satisfying CW control below 100 μm which could promote autogenous healing after cracking, while this process can be slow and insufficient especially for aggressive loading conditions. Considering this, the healing efficiency of SHCC can potentially be enhanced and accelerated through incorporating engineered healing agents. Non-encapsulated mineral and/or polymer admixtures were found to be more compatible without harming the deflection-hardening property of SHCC. Based on this, five SHCC mixes for enhancing self-healing efficiency (named SH2CC) were developed by applying expansive mineral substitutes (MS, including reactive magnesia pellets, or reactive magnesia powder, combined with quicklime) and/or TEA additive in high-volume-FA-SHCC, and their self-healing performance after low-rate cyclic damage (up to 50% of ductility) was investigated. All the SH2CC showed almost 100% recovery regarding various mechanical properties after the 3-week healing conditioning, and SH2CC with MS presented 70 – 90% CW reduction. MS could promote mechanical recovery through hydration and pozzolanic reaction with water supply, and more prominently accelerate crack sealing through enhanced carbonation at crack tips. TEA addition was able to pause the initial hydration/carbonation process of SH2CC under air curing, thus resuming the process upon water contact and boosting both mechanical recovery and crack sealing. Accordingly, SH2CC with combined MS and TEA additive exhibited the highest healing efficiency which was attributed to 1) improved CW control (≤ 20 μm), 2) the production of larger amounts of mixed types of healing products (various hydrates and carbonates) both in cracks and fibre-matrix interfaces for crack filling and enhancement of fibre bonding strength."]},{"key":"dc:format.checksum.md5","label":"Dc Format Checksum Md5","values":["d6f238ba8fb1c75aac0ab051aa71a09c","87eda9de84448d1f82354d60eee3eb5f"]},{"key":"dc:title","label":"Title","values":["Self-healing strain-hardening cementitious composites (SH2CC) for cyclic loading environments"]}]}],"canonical_facts":{"dc:contributor.advisor":["Al-Tabbaa, Abir"],"dc:contributor.sponsor":["(1) Engineering and Physical Sciences Research Council (EPSRC): Resilient Materials for Life (RM4L) Programme Grant (EP/P02081X/1) (2) Cambridge Commonwealth, European and International Trust (CCEIT) Scholarship"],"dc:creator":["Tang, Zixuan"],"dc:creator.authoridentifier":["0000000243341898"],"dc:date.issued":["2023-03-01"],"dc:description.abstract":["Cyclic loading is ubiquitous and frequently encountered in various infrastructure. However, the widely used construction material, concrete, is inherently brittle and could be poor at sustaining cyclic stress (especially those involving tensile stress). Although reinforcement can help avoid structural failure, large cracks are unavoidable which would reduce the durability of the material. In this case, timely retrofit or repair of damaged or cracked infrastructure due to cyclic loading is crucial, which can however be difficult and costly. Aiming to reduce structural damage and repair costs due to cyclic loading, self-healing techniques could be applied in combination with fibre-reinforced strain-hardening cementitious composites (SHCC); the former enables cementitious materials to heal cracks without human intervention, and the latter features much higher ductility than traditional concrete due to effective fibre bridging based on micromechanical design. Accordingly, this research develops novel materials based on SHCC which achieve 1) high deflection capacity (around 5 mm, equivalent to an estimated tensile strain capacity around 1.92%) under cyclic loading with different strain rates, 2) effective crack width (CW) control (below 30 μm regardless of sample sizes) and enhanced self-healing ability to fully recover mechanical properties within 3 weeks after damage caused by low-rate cyclic loading. Three main challenges are dealt with in this research. Firstly, uniform fibre distribution in SHCC is the prerequisite for developing and producing SHCC with robust mechanical performance, and appropriate rheological status of the fresh mortar is the key to it, which could however be difficult to achieve and guarantee with the existing trial-and-error methods. Therefore, a quantitative method for effective rheology control of fresh SHCC using combined chemical admixtures was first developed based on rheometer testing and regression modelling, which was further validated by four-point bending tests. The developed models were able to predict rheological parameters with high confidence and provide guidance for rheology optimisation for achieving robust deflection-hardening behaviour of SHCC. Secondly, either cyclic loading or high loading rates has been reported to reduce the ductility of SHCC in most cases, while the performance of SHCC under cyclic loading with different loading rates has not been sufficiently studied. It is also necessary to develop SHCC with enhanced cyclic endurance especially at varying or elevated strain rates for targeted applications. Results show that either cyclic loading or high loading rates could increase the tendency of fibre rupture, thus reducing the ductility of SHCC; combined elevated-rate and cyclic loading posed an even larger negative effect on the SHCC ductility due to accelerated degradation of fibres and fibre-matrix interfaces. Nevertheless, the impact could be minimised through matrix tailoring. Two SHCC mixes with improved rate-cyclic endurance were developed through increasing fly ash (FA) content or incorporating triethanolamine (TEA) based on micromechanical models, which showed reduced tendency of fibre rupture and thus improved ductility under the high-rate reversed cyclic loading. Thirdly, traditional SHCC has exhibited satisfying CW control below 100 μm which could promote autogenous healing after cracking, while this process can be slow and insufficient especially for aggressive loading conditions. Considering this, the healing efficiency of SHCC can potentially be enhanced and accelerated through incorporating engineered healing agents. Non-encapsulated mineral and/or polymer admixtures were found to be more compatible without harming the deflection-hardening property of SHCC. Based on this, five SHCC mixes for enhancing self-healing efficiency (named SH2CC) were developed by applying expansive mineral substitutes (MS, including reactive magnesia pellets, or reactive magnesia powder, combined with quicklime) and/or TEA additive in high-volume-FA-SHCC, and their self-healing performance after low-rate cyclic damage (up to 50% of ductility) was investigated. All the SH2CC showed almost 100% recovery regarding various mechanical properties after the 3-week healing conditioning, and SH2CC with MS presented 70 – 90% CW reduction. MS could promote mechanical recovery through hydration and pozzolanic reaction with water supply, and more prominently accelerate crack sealing through enhanced carbonation at crack tips. TEA addition was able to pause the initial hydration/carbonation process of SH2CC under air curing, thus resuming the process upon water contact and boosting both mechanical recovery and crack sealing. Accordingly, SH2CC with combined MS and TEA additive exhibited the highest healing efficiency which was attributed to 1) improved CW control (≤ 20 μm), 2) the production of larger amounts of mixed types of healing products (various hydrates and carbonates) both in cracks and fibre-matrix interfaces for crack filling and enhancement of fibre bonding strength."],"dc:format.checksum.md5":["d6f238ba8fb1c75aac0ab051aa71a09c","87eda9de84448d1f82354d60eee3eb5f"],"dc:identifier.doi":["https://doi.org/10.17863/CAM.105997"],"dc:identifier.uri":["https://www.repository.cam.ac.uk/bitstreams/264be2ea-6a54-4099-9526-63d0a696e2e6/download"],"dc:language":["eng"],"dc:publisher.institution":["University of Cambridge"],"dc:relation.isreferencedby.uri":["https://www.repository.cam.ac.uk/handle/1810/364253"],"dc:rights":["https://www.repository.cam.ac.uk/bitstreams/6a0e9d51-316c-42f8-b99e-fee8f33d583e/download","https://www.rioxx.net/licenses/all-rights-reserved/"],"dc:rights.embargodate":["2027-02-08"],"dc:rights.embargotype":["embargo"],"dc:subject":["composite material development","crack width","cyclic loading","fibre dispersion","mechanical recovery","micromechanics","microstructural analysis","mineral and chemical admixtures","regression modelling","self-healing","strain-hardening"],"dc:title":["Self-healing strain-hardening cementitious composites (SH2CC) for cyclic loading environments"],"dc:type":["Thesis"],"dc:type.qualificationlevel":["Doctoral"],"dc:type.qualificationname":["Doctor of Philosophy (PhD)"]},"updated_at":"2026-07-22T22:23:59Z"}