Christopher K Y Leung

• Hong Kong University of Science and Technology

Engineered Cementitious Composites also known as Strain‐hardening cementitious composites (SHCCs) has unique cracking patterns like cracks that have tiny widths and showcase high density. All of this makes it difficult and laborious to compute crack parameters from crack patterns. Unfortunately, this is an essential part of assessing durability and...

Glass fiber reinforced polymer (GFRP) has been considered as an advanced material to replace conventional steel reinforcements in concrete structures to address the corrosion issue. The degradation of GFRP rebars, which may threaten both the durability and safety of infrastructures, is a major concern. To predict the 100-year strength retention of...

Strain-hardening Cementitious Composites (SHCC) exhibit unique tensile strain-hardening behavior accompanied by closely spaced cracks. Recent research has shown that incorporating Carbon Fiber-Reinforced Polymer (CFRP) laminate strips together with SHCC in the tensile zone can effectively enhance/recover the load-bearing capacity of RC beams. Addit...

Lightweight concrete offers numerous advantages for modular construction, including easier construction planning and logistics, and the ability to offset additional dead loads induced by double-wall and double-slab features. In a previous study, authors proposed incorporating lightweight aggregate into foamed concrete instead of adding extra foam t...

Reactive magnesia cement (RMC) is an emerging class of low-alkaline and CO2-sequestering binder, which can mitigate the deterioration of GFRP reinforcements induced by a high-alkaline environment, e.g., in Portland cement. This study investigated the slip behavior of GFRP rebar embedded in RMC composite, which varies with carbonation depth signific...

With increasing demand for sustainable and long-lasting materials, seawater sea-sand engineered cementitious composite (SS-ECC) has emerged as a promising alternative to conventional concrete in near-ocean construction projects. Glass fiber reinforced polymer (GFRP) bar with excellent corrosion resistance is an ideal choice for these applications....

Tensile performance of strain hardening cementitious composites (SHCC) is determined from uniaxial tensile specimens, in which the fiber orientation can vary with sample size and processing method. However, when interpreting the laboratory-determined tensile behaviors, synthetic fibers in SHCC are usually assumed to be randomly oriented without exp...

Glass fiber reinforced polymer (GFRP) rebars are commonly considered as a substitute for conventional steel reinforcements in concrete structures to avoid possible steel corrosion. However, the tensile strength of GFRP rebars may degrade with time due to the degradation of glass fibers under H 2 O/OH-attack in a moist concrete with a high pH level...

The construction sector is responsible for about 40% of energy-related emissions worldwide. Utilizing low-carbon concrete materials (LCCMs) has been recognized as an efficient way to reduce embodied carbon (EC). However, there is a lack of systematic understanding and a unified comparison of the LCCMs’ EC reduction potentials. This paper identifies...

REC-15 Polyvinyl alcohol (PVA) fibers are the most widely used fibers in engineered cementitious composites (ECC). To reduce the high cost of fibers and also to restrain the crack width, local PVA (C-PVA) fibers and Polyethylene terephthalate (PET) fibers are hybridized to replace the REC-15 PVA fibers. Single fiber pullout tests of C-PVA and PET f...

The adoption of modular buildings has been promoted around the world in recent years, especially in densely populated areas such as Hong Kong that require a large number of new housing units to be quickly constructed. In modular construction, it is important to minimize the cast-in-place joints between prefabricated modules for a variety of reasons...

Lowering water-to-cement (w/c) ratio is a conventional method for reducing the diffusion rate of chlorides in concrete and hence reducing the corrosion risk of internal steel reinforcements. However, the potential effect of w/c ratio on the mechanical performance of glass fiber reinforcement polymer (GFRP) is unknown. In this study, concrete mix de...

Glass fiber reinforced polymer (GFRP) rebars can be utilized as a substitute for steel reinforcements in concrete structures to eliminate possible steel corrosion. However, embedded GFRP rebars may also degrade with aging time due to the high concrete alkalinity (pH ~ 13). Previous studies only focused on the GFRP degradation in extreme conditions...

Strain-Hardening Cementitious Composites (SHCC) have demonstrated superior mechanical performance, which could potentially solve the challenges of adding reinforcement in 3D-printed concrete structures. This study investigates the tensile performance of 3D-printed SHCC. Preliminary studies are conducted to investigate the effects of nanoclay dosage...

The development of modular construction is surging in recent years. It has been popularized worldwide due to better quality control, environmental-friendliness and potential construction time and cost savings. A specific challenge associated with reinforced concrete modular construction is the design of inter-module joint. Minimizing the size of in...

Mechanical properties of engineered cementitious composites (ECC) are highly dependent on the pore structural characteristics and fibre-matrix interaction. The relationship between them has not been extensively explored. This paper proposes a practical micromechanical analytical model accounting for pore structure characteristics and crack-bridging...

Understanding the water diffusion process in glass fiber reinforced polymer (GFRP) is critical to bridging the gap between the long-term degradation performance of GFRP composite and the retained strength of glass fibers under water attack. In this study, the water diffusion in GFRP with consideration of defects is systematically investigated throu...

To overcome the highly brittle nature of cementitious materials, our study aims to explore the potential of incorporating nano-engineered polyvinyl alcohol (PVA) latex in cement mortars. Hydroxyl carbon nanotubes (CNT-OH) were used to enhance the mechanical properties of PVA latex, and the resulting CNT-OH/PVA latex was used to improve the mechanic...

Glass fiber-reinforced-polymer (GFRP) composites have been considered a good alternative to conventional steel rebars in structures. However, the high-pH value (∼13) of normal concrete would lead to severe degradation of GFRP rebars. Yet limited research seems to have investigated the durability of GFRP rebars embodied in low-pH concrete. In this s...

Engineered Cementitious Composites (ECC, also known as Strain-Hardening Cementitious Composites or SHCC) are a family of high-performance fibre-reinforced cement-based materials. With the ultimate tensile strain of over 1% and the self-controlled crack width of less than 100 μm, ECC enables high damage tolerance and outstanding durability under var...

This paper presents an experimental approach to investigate the long‐term durability of vinyl ester (VE) used in civil/structural engineering. Various alkaline (pH = 7, 11, 12, and 13) and temperature (23, 40, and 60°C) conditions were considered for accelerated aging over 12 months. The test results reveal only slight changes in water absorption c...

Strain Hardening Cementitious Composites (SHCC) are materials featuring multiple cracking and strain hardening behavior. The variation of SHCC’s tensile performance, especially the tensile strain capacity, has long been a puzzle for civil engineers who seek broader infrastructural application of this advanced material. The tensile performance of SH...

Strain hardening cementitious composites (SHCCs) are a type of cementitious material reinforced with randomly distributed short fibers that exhibit tensile strain hardening behavior and prominent crack resistance. The tensile behavior of SHCCs could be significantly affected by the distribution of the fiber orientation. In large-scale specimens, th...

Conventionally, a soil nail is a piece of steel reinforcement installed inside a hole drilled into the slope and filled with cement paste (CP) grout. Chloride penetration is a major deterioration mechanism of conventional soil nails as the CP grout is easy to crack with an uncontrollable crack opening when the soil nail is subject to loading or gro...

Tomographic reconstruction is an important step toward visualization, identification and quantification of local damage through of structural elements. We have developed mathematical guiding principles for passive wave tomography. We have then utilized these guiding principles to develop a novel technique: Fast Tomography for computational and info...

Characterization of surface cracks is one of the key steps towards condititional assessment and understanding the durability of strain hardening cementitious composites (SHCCs). Under laboratory conditions, surface crack statistics can be obtained from images of specimen surfaces through manual inspection. This is subjective, time consuming and lab...

Developing seawater sea-sand concrete can address the challenges arising from the lack of freshwater and river/manufactured sand for making concrete on-site for sustainable marine and coastal construction. To eliminate the corrosion risk of steel fibers while maintaining the high ductility of concrete, this study aims to develop a new type of ultra...

Seawater sea-sand Engineered Cementitious Composites (SS-ECC) is a new version of ECC for marine constructions facing the scarcity of freshwater and river/manufactured sand. This study aims to assess and model the crack characteristics of SS-ECC, which are critical for its applications with non-corrosive reinforcements. The influence of sea-sand si...

Hong Kong discards between 4-6 million disposable face masks every day. The global figure is estimated in the billions. The bulk of the discarded face masks are sent to the landfill along with Municipality Solid Waste (MSW). Based on the estimation that each face mask weighs two to three grams, the face masks disposed of at landfills every day weig...

Marine infrastructures play an important role in the social-economic development of coastal cities. However, the shortage of river/manufactured sand and fresh water is a major challenge for producing concrete on site, as the transportation of these materials is not only costly but also environmentally unfriendly, while desalination of sea-sand and...

Engineered Cementitious Composite (ECC) is an advanced fiber-reinforced concrete exhibiting multiple-cracking and strain-hardening under tension. This study aims to explore the feasibility of producing high-strength seawater sea-sand Engineered Cementitious Composites (SS-ECC) for marine and coastal applications facing the shortage of freshwater an...

Strain hardening cementitious composites (SHCC) are a class of fiber reinforced materials exhibiting tensile strain hardening behavior up to strain of several percent, accompanied by the formation of fine multiple cracks with openings below 50 μm. To model the full stress-strain relation of SHCC (which governs ductility and energy absorption) and t...

Technology development and adoption are slowest in a conservative sector such as construction. The traditional approach to product development has been inefficient and unproductive in terms of commercialisation. On the other hand, management by process rather than function with a multi-functional project team approach has gained wide acceptance. Su...

Strain Hardening cementitious composites (SHCCs) have been known to produce excellent crack width control and very good tensile strain capacity. As a result, strategically introducing SHCCs would lead to significant carbon saving through the creation of structures that are durable and could potentially undergo autogenous self-healing. However, for...

Engineered Cementitious Composites (ECC) have great potential in marine and coastal applications to extend the service life of infrastructures. In this study, the feasibility of using seawater and sea-sand to produce both normal-and high-strength ECC was explored. Some fundamental properties of seawater sea-sand ECC (SS-ECC) were evaluated, includi...

Strain-hardening cementitious composite (SHCC) was widely recognized as a material that possesses great potential in the repair and strengthening of reinforced concrete (RC) structures. SHCC can usually achieve high ductility with multiple cracking behavior and it also has excellent durability. Moreover, high tensile strength can also be achieved w...

Engineered Cementitious Composites (ECC) showing multiple-cracking and strain-hardening under tension are appealing for the construction industry, but the high cement content in conventional ECC leads to high environmental impacts. Recently, the limestone and calcined clay (LCC) blend has been proposed as a promising alternative of Supplementary Ce...

Accurate Time of Arrival (TOA) detection is essential for successful wave and vibration-based structural health monitoring (SHM) system including Acoustic Emission (AE). AE is the foremost among passive wave-based monitoring systems. During high burst rate results, AE waves could overlap. Overlapping of AE waves leads to overlap in both time and fr...

Engineered Cementitious Composite (ECC) with unique tensile strain-hardening and multiple-cracking properties is an advanced construction material that can enhance resiliency and durability of structures. However, the high cost of the constituents limits the wide spread application of ECC. A relatively low-cost ECC formulation having adequate compr...

In strain-hardening cementitious composites, the bridging effect of fibers can control crack openings to very small values so the cracks can be self-healed in the presence of water. To rely on autogeneous self-healing to enhance the durability of structures, a method to assess the state of self-healing is required. A new strategy is presented in th...

Using nano-silica (NS) in cement-based materials has attracted extensive attention. However, whilst most studies focused on the hydration, fresh, mechanical and durability properties, there is limited information on the effect of NS on the fracture properties of fiber-reinforced high-volume fly ash mortars (HVFAM). In our paper, a series of experim...

The behavior of Strain-Hardening Cementitious Composites (SHCC) is often studied at different scales, from single fiber to single crack and further to the composite material. Establishing a model that can link SHCC behavior at different scales is crucial for the design of SHCC through the proper selection or tuning of properties at the microscale....

This study aims to investigate the pozzolanic strength activity of three kinds of Supplementary Cementitious Materials (SCMs) a limestone-calcined clay from India and Class F fly ashes from China as well as India. Using the ASTM C311 strength activity index test method, the effect of the different pozzolan replacement levels of cement (0%, 20%, 50%...

Use of smart cementitious materials is becoming increasingly critical for enhanced serviceability of structures. Addition of carbon fibers, carbon nanotubes and various nanopowders such as nano-silica, carbon black and graphite giving cementitious materials electrical properties that can be used for self-sensing has been known for almost two decade...

We are pleased to bring to you the first-ever special issue of the ICJ exclusively focused on Engineered Cementitious Composites (ECC) with an objective to introduce and encourage more research and application in this field. A book authored by Prof. Victor C. Li titled Engineered Cementitious Composites (ECC): Bendable Concrete for Sustainable and...

This study develops a novel graphene oxide (GO) coated polyethylene (PE) fiber (GO/PE fiber) by simply mixing PE fibers in GO aqueous solution at a certain temperature. The experimental results indicate that due to the different thermal expansion behavior, the shrinkage of GO at a higher temperature facilitates the formation of a 3D cover around th...

This study aims to investigate the pozzolanic strength activity of three kinds of Supplementary Cemntitious Materials (SCMs) – a limestone-calcined clay from India and Class F fly ashes from China as well as India. Using the ASTM C311 strength activity index test method, the effect of the different pozzolan replacement levels of cement (0%, 20%, 50...

Engineered Cementitious Composites (ECC) are a special class of fibre-reinforced cementitious materials exhibiting strain-hardening and multiple-cracking under tension; therefore, ECC have clear advantages over normal concrete for many construction applications. However, ECC are also well known to have a lower elastic modulus compared to plain conc...

Recently, hybridizing fibers with distinct properties in cementitious materials has gained much attention due to their advantage over single-type fiber reinforcements. However, for Strain-Hardening Cementitious Composites (SHCC), most existing studies only compared hybrid-fiber SHCC (HySHCC) with conventional concrete or introduced additional steel...

Recent studies show that high strength strain-hardening cementitious composite (SHCC) can serve as a potential repair material for deteriorated reinforced concrete structures due to its excellent properties in terms of strength, ductility and durability. However, a major problem of high strength cementitious mix is the excessive shrinkage after har...

This study evaluated the mono and hybrid effects of hydroxyl carbon nanotubes (CNTs-OH) and polyvinyl alcohol (PVA) on the corrosion behavior of steel rebars embedded in concrete under accelerated chloride attack by an impressed voltage technique. The contents of CNTs-OH and PVA were fixed at 0.5% and 1% by weight of cement, respectively. Mechanica...

Strain-Hardening Cementitious Composites (SHCC) exhibit multiple-cracking behavior under tension. Theoretically speaking, the distribution of matrix inherent flaws results in variation in cracking strength of SHCC, and the cracking strength decreases accordingly with increasing flaw size. Therefore, for a SHCC specimen under tension, it should show...

This study aims to investigate the hydration and strength characteristics of green cementitious mortars with ultrahigh-volume limestone-calcined clay as well as two kinds of Class F fly ash. Using the ASTM C311 strength activity index test method, the effect of different pozzolan replacement levels of cement (0%, 20%, 50%, and 80%, by weight) were...

This paper presents the experimental investigation of uniaxial tensile and flexural properties as well as fibre-matrix pull-out resistance of ultra-high-toughness cementitious composites (UHTCC). Specimens of UHTCC containing high-volume fly ash were fabricated using polyvinyl alcohol (PVA) fibres and subjected to uniaxial tensile test and four-poi...

Aggregation of graphene oxide (GO) in cement matrix greatly reduces its reinforcing efficiency to the mechanical properties of cement-based materials. However, current technology is too difficult to distinguish the aggregated GO from the complex components in hardened cement matrix, so how does the GO aggregation influence the mechanical properties...

A new model for calculating the bridging stress of inclined fiber is developed in this paper. While the full debonding/pullout behavior can be derived from the model, particular focus is placed on the situation with small crack opening, which is the operating condition for Strain- Hardening Cementitious Composites (SHCC). The model reveals the phys...

As the cracking mode (tensile or shear) of a crack is related to the underlying physical mechanisms, crack mode classification is a very useful method to identify the damage state of a structure for proper maintenance to enhance structural safety and durability. Acoustic Emission (AE) is a passive structural health monitoring technique based on the...

Greenhouse gas emissions and its impact on climate change has a significant dependence on use of ordinary Portland cement with its substantial carbon footprint. Since the global cement consumption is dominated by China and India, it is of particular importance that industrial wastes such as fly ash and low carbon pozzolans including limestone calci...

Automatically adding or even printing steel reinforcements into a 3D-printed concrete structure is antithetical to the design freedom as well as construction ease and efficiency. Strain-Hardening Cementitious Composite (SHCC) is a kind of short random fibre reinforced cementitious composites exhibiting robust tensile strain-hardening and multiple c...

Greenhouse gas emissions and its impact on climate change has a significant dependence on use of ordinary Portland cement with its substantial carbon footprint. Since the global cement consumption is dominated by China and India, it is of particular importance that industrial wastes such as fly ash and low carbon pozzolans including limestone calci...

Acoustic emission is a powerful experimental Structural health Monitoring (SHM) technique for determining the location of cracks formed in a member. Pinpointing wave arrival time is essential for accurate source location. Conventional arrival detection technique's accuracy deteriorates rapidly in low Signal to Noise Ratio (SNR) (5-40dB) region thus...

As tensile crack-bridging constitutive relations play an important role in the multiple cracking behaviors of Strain-Hardening Cementitious Composites (SHCCs), careful control of the crack-bridging relations is the key to a successful design of the materials. This study theoretically explores the crack-bridging relations of SHCCs with fixed total v...

As an important portion of the total plastic waste bulk but lack of reuse and recycling, the enormous amounts of polyethylene terephthalate (PET) solid wastes have led to serious environmental issues. This study explores the feasibility of recycling PET solid wastes as short fibers in Strain-Hardening Cementitious Composites (SHCCs), which exhibit...

SHCC is a new class of materials with high tensile ductility and excellent crack control. Conventionally, mix design of SHCC has been based on the direct tensile behavior. In particular, compositions with higher tensile ductility are considered to be better. However, recent experimental results have shown that the tensile stress-strain curve itself...

The mechanical behavior of fiber-reinforced cementitious composites (FRCC) is strongly dependent on the bridging of cracks by fibers. While fiber bridging effect on the tensile behavior of FRCC has been widely studied, little attention has been paid to the effect of fibers on the shear transfer behavior of cracked FRCC. In this study, a micromechan...

Strain hardening cementitious composites (SHCC) are materials exhibiting high deformation capacity and excellent crack control, which have shown great potential for various engineering applications. In our previous study, a new discrete model is proposed for SHCC, with the use of continuum element for matrix damage/cracking behavior, truss element...

Strain-Hardening Cementitious Composites (SHCC) are materials featuring strain-hardening behavior accompanied by formation of multiple cracks. The distribution of fiber orientation in SHCC members is affected by member thickness due to the limited freedom of rotation for fibers near the surfaces. This paper first demonstrates how to acquire fiber o...

The behavior of Strain-Hardening Cementitious Composites (SHCC) is strongly affected by the relationship between fiber bridging stress and crack opening width. When the fiber is inclined to the crack surface, the fiber is under the combined action of pulling and bending. This paper treats the fiber on each side of the crack as a continuously suppor...

With advent of Smart Civil Engineering Infrastructure, Structural Health Monitoring (SHM) is becoming increasingly critical for enhanced durability and serviceability of structures. Self-sensing and self-healing cement-based materials are an integral part of such an approach that have been subject of increasing research interest. Addition of carbon...

Acoustic Emission has been used widely to monitor the health of structures. Typically AE wave parameters such as Event, Count, Peak Amplitude and Duration have been used as Damage Indicators (DIs) to qualitatively identify the initiation of non-reversible change (damage) in a structure as they can be efficiently computed at real time. However, the...

This study explored the potential benefits of employing hybrid polyvinyl alcohol (PVA)/steel fibers in Strain-Hardening Cementitious Composites (SHCCs) at the single-crack level. Due to the multiple-cracking nature of SHCCs with tight crack spacing, direct measurement of the crack-bridging constitutive relation for a single crack is challenging, as...