Dr Benyi Cao

Lecturer in Civil and Environmental Engineering; Sustainability Fellow at the Institute for Sustainability
+44 (0)1483 689280
01A AA 02


My qualifications

BEng in Civil Engineering
Tongji University
MEng in Civil Engineering
Supervisor: Prof. Shijin Feng
Tongji University
PhD in Engineering
Supervisor: Prof. Abir Al-Tabbaa
University of Cambridge

Previous roles

Research Assistant Professor
Nanjing Institute of Environmental Sciences
Research Associate
University of Cambridge


Research interests


Postgraduate research supervision



A large amount of energy consumed globally is done by buildings, also, buildings are responsible for a great portion of greenhouse gas emissions. With progress in smart sensors and devices, a new generation of smarter and more context-aware building controllers can be developed. Consequently, zone-level surrogate artificial neural networks are used herein, where indoor temperature, occupancy, and weather data are the inputs. A new metaheuristic optimization algorithm, called Chaotic Satin Bowerbird Optimization Algorithm (CSBOA) is employed for the minimization of energy consumption. 24-hour schedules of the heating setpoint of each zone are created for an office building located in Edinburgh, Scotland. Two modes of optimization including day-ahead and model predictive control are applied for each hour. The consumption of energy decreased by 26% during a test week in Feb in comparison to the base case approach of heating. By definition of a time-of-use tariff, the cost of energy consumption is decreased by around 28%.

Benyi Cao, Jian Xu, Fei Wang, Yunhui Zhang, David O'Connor (2021)Vertical Barriers for Land Contamination Containment: A Review, In: International journal of environmental research and public health18(23)12643 Mdpi

Soil pollution is one of the major threats to the environment and jeopardizes the provision of key soil ecosystem services. Vertical barriers, including slurry trench walls and walls constructed with soil mix technology, have been employed for decades to control groundwater flow and subsurface contaminant transport. This paper comprehensively reviewed and assessed the typical materials and mechanical and permeability properties of soil-bentonite, cement-bentonite and soil mix barriers, with the values of mix design and engineering properties summarized and compared. In addition, the damage and durability of barrier materials under mechanical, chemical, and environmental stresses were discussed. A number of landmark remediation projects were documented to demonstrate the effectiveness of the use of barrier systems. Recent research about crack-resistant and self-healing barrier materials incorporating polymers and minerals at Cambridge University and performance monitoring techniques were analyzed. Future work should focus on two main areas: the use of geophysical methods for non-destructive monitoring and the optimization of resilient barrier materials.

Benyi Cao, Jingtao Chen, Abir Al-Tabbaa (2021)Crack-resistant cement–bentonite cut-off wall materials incorporating superabsorbent polymers, In: Canadian geotechnical journal58(6)pp. 800-810 NRC Research Press

Preserving the integrity of cement–bentonite cut-off walls, particularly in aggressive environments, is critical to their serviceability in polluted sites. The hardened cement–bentonite material in cut-off walls is highly susceptible to desiccation and wet–dry cycles, commonly leading to cracking. The objective of the work presented in this paper was to develop crack-resistant cement–bentonite cut-off wall materials subject to wet–dry cycles. Superabsorbent polymers (SAPs), which are cross-linked polymers that can absorb and retain a large amount of water and swell as a result, were employed for this purpose. It is found that the added SAPs increased the compressive strength by decreasing the water-to-cement ratio and that the strain at failure also increased due to energy dissipative and reinforcement effects. In addition, crack resistance was greatly improved under the imposed wet–dry cycles as the matrix suction was reduced as a result of the reduction of the contact between the free pore water and cement–bentonite particles and the increase of the pore size in the matrix. The morphology and microstructure of the interconnected foam network formed by the SAP films in the matrix were identified with SEM-EDX and micro-CT scan analyses. The results demonstrated the significant potential for SAPs in the development of crack-resistant cement–bentonite cut-off wall materials.

Benyi Cao, Livia Ribeiro de Souza, Abir Al-Tabbaa (2020)Organic Contaminant-Triggered Self-Healing Soil Mix Cut-Off Wall Materials Incorporating Oil Sorbents, In: Materials13(24)5802 MDPI

Soil mix cut-off walls have been increasingly used for containment of organic contaminants in polluted land. However, the mixed soil is susceptible to deterioration due to aggressive environmental and mechanical stresses, leading to crack-originated damage and requiring costly maintenance. This paper proposed a novel approach to achieve self-healing properties of soil mix cut-off wall materials triggered by the ingress of organic contaminants. Oil sorbent polymers with high absorption and swelling capacities were incorporated in a cementitious grout and mixed with soil using a laboratory-scale auger setup. The self-healing performance results showed that 500 µm-wide cracks could be bridged and blocked by the swollen oil sorbents, and that the permeability was reduced by almost an order of magnitude after the permeation of liquid paraffin. It was shown by micro-CT scan tests that the network formed by the swollen oil sorbents acted as attachments and binder, preventing the cracked mixed soil sample from crumbling, and that the oil sorbents swelled three times in volume and therefore occupied the air space and blocked the cracks in the matrix. These promising results exhibit the potential for the oil sorbents to provide soil mix cut-off walls in organically-contaminated land with self-healing properties and enhanced durability.

Cong Zhang, P Hu, Qing Liu, Zeyu Lu, Benyi Cao, Yuxin Tang, Tianwei Hao (2023)Biopolymer recovery from waste activated sludge toward self-healing mortar crack, In: The Science of the total environment858(Pt 3)160107 Elsevier

Activated sludge (AS) offers great potential for resource recovery considering its high organic and nutrient content. However, low recovery efficiency and high costs are directing the focus toward the high-valuable resource recovery. This study extracted 71.5 ± 5.9 mg/g VSS of alginate-like exopolysaccharides from AS (ALE/AS) and applied it to mortar as a novel biopolymer agent for crack self-healing. With a mortar crack of 120 μm, addition of 0.5 wt% ALE/AS yielded a high crack closure ratio of 86.5 % within 28 days. In comparison to commercial healing agents, marginal flexural strength reduction with ALE/AS addition (17.9 % vs 30.2-50.5 %) was demonstrated. The abundance of COO group in GG blocks of ALE/AS resulted in a higher cross-link capacity with Ca , while the reduction of hydrophilic residues (e.g., COO and OH) after complexation engendered a lower swelling capacity, which facilitated self-healing and flexural strength maintenance. Molecular dynamics (MD) revealed that lower Ca diffusivity, arising from the stronger electrostatic interactions between the COO groups and Ca , resulted in a high Ca concentration around the cracks, leading to CaCO deposition and healed cracks. The outcomes of this study provided light on ALE-based mortar crack healing and presented a possibility for multi-level AS resource recovery.

Benyi Cao, L. P. Souza, Fei Wang, Jian Xu, Chrysoula Litina, A Al-Tabbaa (2023)The first microcapsule-based self-healing cement-bentonite cut-off wall materials, In: Géotechnique73(2)pp. 105-114 Ice Publishing

Despite the extensive use of cement-bentonite in contaminated land containment applications, there are still many challenges related to durability. The development of self-healing cement-bentonite materials could provide more resilient, sustainable and reliable cut-off walls with significantly enhanced durability, reduced maintenance costs, enhanced safety and protection against sudden or undetected failure. The objective of this study was to develop self-healing cement-bentonite cut-off wall materials incorporating microcapsules. Microencapsulated sodium silicate, as a healing agent, would be released into cracks when the microcapsules rupture as a result of any damage incurred, and would react with the cement-bentonite matrix to fill and heal the cracks. Novel microcapsules with switchable mechanical properties developed for self-healing cement applications were employed here. The results demonstrated the enhanced average crack mouth healing and recovered permeability performance provided by the microcapsules compared to control cement-bentonite samples. X-ray microcomputed tomography and scanning electron microscopy were applied to investigate the self-healing process of the microcapsule-containing cement-bentonite system. The microstructural analysis confirmed the survivability, uniform dispersion and crack-triggered rupture of the microcapsules, as well as the release of the healing agent and the generation of hydration products within the cracks. These are promising results for the application of the microcapsule-based system for self-healing cement-bentonite cut-off wall materials.

Yunhui Zhang, Fei Wang, Benyi Cao, Hailong Yin, A Al-Tabbaa (2022)Simultaneous removal of Pb and MTBE by mixed zeolites in fixed-bed column tests, In: Journal of environmental sciences (China)122pp. 41-49 Elsevier B.V

•Co-removal feasibility of MTBE and Pb with PRB was assessed in column tests.•Column performance of mixed zeolite reactive media was evaluated.•Clinoptilolite granule and powder were used to examine the effect of particle size.•Removal capacity of clinoptilolite powder almost tripled granule (130.6 vs 45.3 mg/g).•The minimum thickness and longevity became higher with clinoptilolite powder. The co-contamination of metals and organic pollutants, such as Pb and methyl tert-butyl ether (MTBE), in groundwater, has become a common and major phenomenon in many contaminated sites. This study evaluated the feasibility of their simultaneous removal with permeable reactive barrier (PRB) packed with mixed zeolites (clinoptilolite and ZSM-5) using fixed-bed column tests and breakthrough curve modeling. The effect of grain size on the permeability of PRB and removal efficacy was also assessed by granular and power clinoptilolite. The replacement of granular clinoptilolite by powder clinoptilolite largely reduced the breakthrough time but increased the saturation time nearly fourfold. The column adsorption capacity of clinoptilolite powders almost tripled that of clinoptilolite granules (130.6 mg/g versus 45.3 mg/g) due to higher specific surface areas. The minimum thickness and corresponding longevity of PRB were calculated as 7.12 cm and 321.5 min when 5% of granular clinoptilolite was mixed with 5% ZSM-5 and 90% sand as mixed PRB reactive media compared with 10.86 cm and 1230.2 min for the application of powder clinoptilolite. This study is expected to provide theoretical support and guidance for the practical application of mixed adsorbents in PRBs. Graphical Abstract [Display omitted] .

Yunhui Zhang, Benyi Cao, Hailong Yin, Lite Meng, Wei Jin, Fei Wang, Jian Xu, A Al-Tabbaa (2022)Application of zeolites in permeable reactive barriers (PRBs) for in-situ groundwater remediation: A critical review, In: Chemosphere (Oxford)308136290 Elsevier Ltd

Permeable reactive barrier (PRB) is one of the most promising in-situ groundwater remediation technologies due to its low costs and wide immobilization suitability for multiple contaminants. Reactive medium is a key component of PRBs and their selection needs to consider removal effectiveness as well as permeability. Zeolites have been extensively reported as reactive media owing to their high adsorption capacity, diverse pore structure and high stability. Moreover, the application of zeolites can reduce the PRBs fouling and clogging compared to reductants like zero-valence iron (ZVI) due to no formation of secondary precipitates, such as iron monosulfide, in spite of their reactivity to remove organics. This study gives a detailed review of lab-scale applications of zeolites in PRBs in terms of sorption characteristics, mechanisms, column performance and desorption features, as well as their field-scale applications to point out their application tendency in PRBs for contaminated groundwater remediation. On this basis, future prospects and suggestions for using zeolites in PRBs for groundwater remediation were put forward. This study provides a comprehensive and critical review of the lab-scale and field-scale applications of zeolites in PRBs and is expected to guide the future design and applications of adsorbents-based PRBs for groundwater remediation. [Display omitted] •A comprehensive and critical review on applications of zeolites in PRBs is provided.•Treatability testing for zeolites as reactive media is comprehensively reviewed.•The lab-scale and field-scale applications of zeolites in PRBs is reviewed.•This review can guide the future design and application of adsorbents-based PRBs.

Benyi Cao, A Al-Tabbaa (2022)Reactive MgO-based self-healing slag-cement-bentonite slurry walls, In: Cement & concrete composites131104565 Elsevier Ltd

Despite the common use of slag-cement-bentonite slurry trench walls for geotechnical and geoenvironmental applications, the materials deteriorate under mechanical, chemical and environmental stresses. Providing the slurry wall with the capacity of self-healing cracks, could address the concerns. This study proposes and investigates, for the first time, the self-healing slag-cement-bentonite incorporating reactive MgO pellets. The incorporation of the MgO pellets slightly increased the UCS and stiffness, without any significant adverse effects on the engineering properties of the slurry wall material. The crack closure percentages after hydration and carbonation reached over 50% and 80%, when the MgO pellets were added at a dosage of 5% and 10%. The post-healing permeability was as low as 8.4 × 10−9 m/s, satisfying the requirement for slurry walls. TGA and SEM-EDX results show that brucite and hydrated magnesium carbonates produced by the hydration and carbonation processes are the main healing products in the MgO-containing specimens. The uniform dispersion of MgO pellets and healing products was confirmed by micro-CT analysis, and it was observed most of the cracks could be at least partly blocked. The results have collectively demonstrated the great potential of reactive MgO pellets as an effective self-healing agent for the development of more reliable and resilient slag-cement-bentonite slurry walls.

Benyi Cao, Yunhui Zhang, Jian Xu, A Al-Tabbaa (2022)Use of superabsorbent polymer in soil-cement subsurface barriers for enhanced heavy metal sorption and self-healing, In: The Science of the total environment831154708 Elsevier B.V

Conventional subsurface barrier materials for contamination containment deteriorate in aggressive environments and only have a limited exchange/adsorption capacity for heavy metals. This study focused on the potential use of superabsorbent polymer (SAP) in soil-cement subsurface barriers for enhanced heavy metal sorption and self-healing. The SAP adsorption results for lead, copper, zinc and nickel were well fitted by the Langmuir model. The SAP had the highest adsorption capacity for lead at 175 mg/g, and plays a key role in the removal of the heavy metals in an acidic environment. In addition, the incorporation of SAP in soil-cement increased the ductility and had negligible adverse effects on mechanical and permeability properties. When cracks propagate in the matrix, the SAP is exposed to the ingress of water and swells, and this swelling reaction seals the cracks. The SAP-containing soil-cement demonstrated enhanced self-healing performance in terms of the recovery of permeability. The uniform dispersion and the 3D network of the SAP were observed using micro-CT scanning, and good bonding and self-healing mechanism were confirmed by SEM-EDX analysis. The results suggest the significant potential for the SAP-based approach for the development of more resilient subsurface barriers with enhanced heavy metal sorption and self-healing. [Display omitted] •The SAP adsorption were well fitted by Langmuir model with Pb(II) sorption at 175 mg/g.•Brittle stress-strain behaviour of soil-cement changes to a ductile response with SAP addition.•After self-healing, the permeability of SAP-containing soil-cement recovered to the undamaged level.•SAP-based subsurface barriers have enhanced heavy metal sorption and self-healing performance.

Benyi Cao, Yunhui Zhang, A Al-Tabbaa (2022)SEBS-Polymer-Modified Slag-Cement-Bentonite for Resilient Slurry Walls, In: Sustainability (Basel, Switzerland)14(4)2093 Mdpi

In spite of the well-established design and construction approaches of slag-cement-bentonite slurry walls, the materials deteriorate inevitably in contaminated land. The development of effective materials which are sustainable, resilient and self-healing over the lifetime of slurry walls becomes essential. This study, for the first time, adopts a styrene-ethylene/butylene-styrene (SEBS) polymer to modify slag-cement-bentonite materials to enhance mechanical and self-healing performance. The results show that the increase in SEBS dosage results in significantly increased strain at failure, indicating the enhanced ductility thanks to the modification by the deformable polymer. The increased ductility is beneficial as the slurry wall could deform to a greater extent without cracks. After the permeation of liquid paraffin, the SEBS exposed on the crack surface swells and seals the crack, with the post-healing permeability only slightly higher than the undamaged values, which exhibits good self-healing performance. Scanning electron microscopy and micro-computed tomography analyses innovatively reveal the good bonding and homogeneous distribution of SEBS in slag-cement-bentonite. SEBS acts as a binder to protect the slag-cement-bentonite sample from disintegration, and the swollen SEBS particles effectively seal and heal the cracks. These results demonstrate that the SEBS-modified slag-cement-bentonite could provide slurry walls with resilient mechanical properties and enhanced self-healing performance.

Benyi Cao, L. P. Souza, Jian Xu, Wenting Mao, Fei Wang, A Al-Tabbaa (2021)Soil Mix Cutoff Wall Materials with Microcapsule-Based Self-Healing Grout, In: Journal of geotechnical and geoenvironmental engineering147(11) Asce-Amer Soc Civil Engineers

Over the last three decades, cutoff walls using soil mix technology have been developed and deployed to deliver in situ containment of contaminated sites. The aggressive contaminated soil environment imposes significant long-term stresses on wall materials, and underground cracking is very difficult to detect and can compromise the integrity of walls. A recent relevant development is the concept of self-healing materials that can be triggered by damage and self-heal without the need for external intervention. This laboratory study developed, for the first time, a microcapsule-based self-healing soil mix cutoff wall material and demonstrated its performance in the healing processes, recovery of compressive strength, and hydraulic conductivity. The developed microcapsule-based cementitious grout was mixed with a sand soil using a laboratory-scale auger, and the embedded microcapsules were triggered upon cracking and released a sodium silicate cargo that healed the cracks. Micro-computed tomography (micro-CT) scan analysis verified the good survivability and uniform distribution of the microcapsules during the auger mixing process. Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) and thermogravimetric analysis (TGA) revealed that the released sodium silicate microcapsule cargo reacted with the cementitious matrix to produce healing products in the form of calcium silicate hydrates. The microcapsule-containing posthealing specimens regained 44% of initial compressive strength and showed a recovered hydraulic conductivity only slightly higher than that of the undamaged specimens. The results demonstrated the great potential of microencapsulated sodium silicate as a self-healing agent for cement mixed soil, which could provide more resilient and reliable soil mix cutoff walls.

Chrysoula Litina, Benyi Cao, Jingtao Chen, Zijing Li, Ioanna Papanikolaou, Abir Al-Tabbaa (2021)First UK Commercial Deployment of Microcapsule-Based Self-Healing Reinforced Concrete, In: Journal of materials in civil engineering33(6) Asce-Amer Soc Civil Engineers

Consolidating previous research on the development of novel microcapsules for self-healing in cementitious systems, this work forms a base for developing an implementation strategy and guidance for microcapsule-based self-healing technology. The study presents details of the first commercial deployment of this technology, as a ready-mix self-healing additive for commercial application. This involved the on-site construction of two slabs in a new development at the University of Cambridge. This paper describes the optimization of the mix, the structural concept and design, and processing and casting procedures. Prior to application, the compliance and compatibility of the healing additive with the concrete according to specifications and requirements of the design were investigated, validating the use of the developed system. These were complemented by large-scale laboratory testing of the healing efficiency under damage scenarios identified as critical for the on-site application. The performance of the site installation was monitored over 12 months through a combination of nondestructive testing methods. Results are presented with durability indicators confirming the in situ enhanced performance of the proposed self-healing system.