Shan He

Delft University of Technology | TU · Faculty of Civil Engineering and Geosciences (CEG)

A novel idea of using carbon nanofibers (CNFs) to strengthen the interface transition zone (ITZ) and to enhance the interface frictional bond strength between polyethylene (PE) fibers and cement-based matrix was proposed and realized by coating CNFs on surface of PE fibers through hydrophobic interactions. A strain hardening ultra-high performance...

A new approach to characterize ITZ between microfiber and cement matrix is reported. Results show that microstructure of hydrated cement paste is highly modified in the vicinity of microfibers, with higher porosity and less anhydrous cement. ITZ can extend up to 100 μm from the interface into the matrix. The larger extent of ITZ suggests that pertu...

Variability of concrete properties has strong influences on design and conformity assessment. However, variability of residual flexural strengths of steel fiber-reinforced concrete (SFRC) has yet been statistically investigated. In this study, a large number of SFRC specimens was sampled from a central mix concrete plant manufacturing precast SFRC...

This study investigated the evolution process of high-volume slag cement (HVSC) paste from a chemo-mechanical standpoint. HVSC specimens with a 70 w.t. % slag replacement rate were studied at various ages. Evolution of phase assemblage, microstructure development, and micromechanical properties were analyzed using TGA/XRD/MIP/SEM-EDS and nano-/micr...

This study investigates the bond-slip behavior of micro steel fibers embedded into an Ultra-High-Performance Concrete (UHPC) matrix as affected by the self-healing of the same matrix in different exposure conditions. The UHPC matrix contains a crystalline admixture as a promoter of the autogenous self-healing specially added to enhance the durabili...

In the current study, experiments and numerical simulations were carried out to investigate the cracking behavior of reinforced concrete beams consisting of a very thin layer (i.e., 1 cm in thickness) of SHCC in the concrete cover, tension zone. A novel type of SHCC/concrete interface that features a weakened chemical adhesion but an enhanced mecha...

We propose a new numerical method to analyze the early-age creep of 3D printed segments with the consid-eration of stress history. The integral creep strain evaluation formula is first expressed in a summation form usingsuperposition principle. The experimentally derived creep compliance surface is then employed to calculate thecreep strain in the...

This paper presents an experimental study on the interface bonding properties of polyvinyl alcohol (PVA) fiber in alkali-activated slag/fly ash (AASF) pastes. Three interface bonding properties (i.e., the chemical bonding energy, the initial frictional bond strength, and slip-hardening behavior) were determined using single-fiber pullout tests. The...

In the current study, experiments were carried out to investigate the cracking behaviour of reinforced concrete beams consisting of 1-cm-thick layer of Strain Hardening Cementitious Composite (SHCC) in the concrete cover zone. The hybrid SHCC/concrete beams with different types of interfaces were tested and compared with control reinforced concrete...

In the current study, experiments were carried out to investigate the structural performance of reinforced concrete (RC) beams with a self-healing cover zone. The cover zone consists of a 1.5-cm-thick layer of bacteria-embedded strain hardening cementitious composite (SHCC) for a combination of crack width control and crack healing. The aim is to b...

This paper employs computer vision techniques to predict the micromechanical properties (i.e., elastic modulus and hardness) of cement paste based on an input of Backscattered Electron (BSE) images. A dataset comprising 40,000 nanoindentation tests and 40,000 BSE micrographs was built by express nanoindentation test and Scanning Electron Microscopy...

This study aims to experimentally investigate the autogenous deformation and the stress evolution in restrained high-volume ground granulated blast furnace slag (GGBFS) concrete. The Temperature Stress Testing Machine (TSTM) and Autogenous Deformation Testing Machine (ADTM) were used to study the macro-scale autogenous deformation and stress evolut...

Limestone-calcined clay-cement (LC3), as one of the most promising sustainable cements, has been under development over the past decade. However, many uncertainties remain regarding its rheological behaviors, such as the metakaolin content of calcined clay. This study aims to investigate the effect of increasing the content of fine-grained metakaol...

The properties of the interfacial transition zone (ITZ) between microfiber and cement-based matrix are of primary significance for the overall behavior of strain hardening cementitious composites (SHCCs). However, due to the relatively small diameter of polymeric microfibers (e.g., PVA fiber), it is technically difficult to obtain quantitative and...

Early‐age stress (EAS) is an important index for evaluating the early‐age cracking risk of concrete. This paper encompasses a thermo‐chemo‐mechanical (TCM) model and active ensemble learning (AEL) for predicting the EAS evolution. The TCM model provides the data for the AEL model. First, based on Fourier's law, Arrhenius’ equation, and rate‐type cr...

A good bond between the layers of 3D printed cementitious materials is a prerequisite for having high structural rigidity for the printed elements. However, the influence of printing process on an interlayer bond is still not well understood. This study investigates the influence of curing methods (i.e., air curing, plastic film covering, wet towel...

Cracking is one of the main causes for deterioration of concrete structures. Self-healing concrete with 3D-printed vascular networks has excellent potential for autonomous self-healing. This approach is scarcely investigated: no studies have been devoted to the influence of printing parameters on the properties of vascular based self-healing concre...

Strain hardening cementitious composite (SHCC) is a special class of ultra-ductile material which has autogenous self-healing capability due to its intrinsic tight crack widths. To further improve its healing ability, healing agent (HA) can be incorporated in SHCC, enabling it also the autonomous self-healing mechanism. In this study, the effects o...

Stress evolution of restrained concrete is a significant direct index in early-age cracking (EAC) analysis of concrete. This study presents experiments and numerical modelling of the early-age stress evolution of Ground granulated blast furnace slag (GGBFS) concrete, considering the development of autogenous deformation and creep. Temperature Stres...

This paper aims to provide a systematical review of the available printing strategies, sustainable cementitious materials and characterization methods for extrusion-based 3D concrete printing (3DCP). The printing strategies, consisting of printing setup, process, and material requirements, were summarized initially. In the material aspect, the high...

This paper aims to investigate the influences of high Portland cement substitutions (>60 wt%) by low-grade calcined clay (CC) and limestone (LF) on 3D concrete printability, stiffness evolution and early-age hydration. Results show that, with the same dosage of admixtures (superplasticizer and viscosity modifier), increasing LF and CC content reduc...

The interfacial transition zone (ITZ) governs the mechanical properties and durability of fiber-reinforced cement-based composites. It has been reported that strategic strengthening of the ITZ by simple coating of carbon nanofibers (CNFs) on microfibers resulted in a 22% enhancement of the fiber/matrix bond. In the current study, ingenious methods...

Magnesium-silicate-hydrate (M-S-H) cement has emerged as an alternative binder with potentially lower energy requirements and emissions. Due to the intrinsically low pH values of its matrix, however, normal steel reinforcement is not appropriate for M-S-H system. To toughen the matrix and to overcome the brittle nature of the material, a new strain...

This study examines autogenous healing of interface between micro polymeric fiber and hydraulic cement matrix. Experiments were carried out to evaluate the healing-induced recovery of fiber/matrix interface bond strength and to characterize the morphology and chemical compositions of the healing products. Results show that interface frictional bond...

In this study, the interface transition zone (ITZ) between CNF-coated polyethylene (PE) fiber and cement paste matrix was characterized. The microstructure and mechanical properties of CNF-strengthened ITZ were investigated and compared with the control ITZ between pristine PE fiber and cement paste. Specimens embedded with one singe fiber were pre...

This paper reviews the research and development of micromechanics-based design theory of strain hardening cementitious composites (SHCC) at different scale, linking the microstructure at micro scale with the composite tensile behavior at macro scale through fiber bridging properties at meso scale. Micromechanics relates macroscopic properties of SH...

In this study, high strength and high ductility cementitious composites were developed by incorporating carbon nanofibers (CNFs) coated polyethylene (PE) fibers. The CNFs were coated on the PE fiber surface through hydrophobic interaction to strengthen the interface transition zone (ITZ) between PE fibers and cement-based matrix. The resulting comp...