Carbon-based conductive fillers have recently been incorporated into a cement matrix to develop an intrinsic self-sensing concrete for data monitoring without the need for embedded, attached, or remote sensors while maintaining or improving its mechanical properties and durability. This paper studies cementitious composites filled with graphite as a novel self-sensing construction material. Experiments were systematically conducted to investigate the dispersion, chemical, mechanical, electroconductivity and piezo-resistivity properties of the composites. Experimental results showed an effective mixing with uniform dispersion of the graphite which acted as an inert filler in the mix and did not alter the microstructure of cement hydration products. Isothermal calorimetry, TGA and rheology tests showed good hydration and adequate workability of the composites with low graphite concentration (≤ 10%), while the effect of adding graphite on the compressive strength is insignificant for graphite concentrations of up to 10%. Monotonic and cyclic compressive test results indicated a repeatable piezo-resistivity performance for low graphite concentration cementitious composites whose stress sensitivity values vary from 0.75 to 7.25%/MPa, and strain sensitivity/gauge factor (GF) 150–1250 with some hysteresis. These combinations showed a stable and reliable piezo-resistivity and the ability to detect damage upon failure.

This study investigates the microstructural changes of cement paste due to the inclusion of polymeric microfiber at different water-to-cement (w/c) ratios. A procedure to quantify the porosity of epoxy impregnated interfacial transition zone (ITZ) is also presented. Results show that the microstructures of the ITZ beneath and above a microfiber, with respect to the gravity direction, are largely different. Though the ITZ at both sides of the fiber are more porous than the bulk matrix, the porosity of the lower ITZ (i.e., the ITZ beneath a fiber) is significantly higher than the upper side (i.e., the ITZ above a fiber). This difference can be attributed to the combined effects of fiber on the initial packing of surrounding cement grains and on the settlement of the fresh mixture. The porosity gradients of the upper ITZs are found to be nearly identical for all the tested w/c ratios, while the porosity gradients of the lower ITZs become steeper when the w/c is higher. The lower side is also found to be the preferred location for the precipitation of calcium hydroxide crystals. Results of energy-dispersive X-ray spectroscopy (EDS) and nano-indentation analyses confirm that the chemical and mechanical properties of the ITZ are also asymmetric.

In the present work, the synergetic effect of fly ash (FA) and ground granulated blast furnace slag (GGBS) on the early compressive strength and microstructure development of CO2-cured mortars was investigated. A rim of several micrometers was found around carbonated cement particles, which contained not only silica-rich gel but also crystal calcium carbonate. The calcium carbonate formed around the cement particles were surrounded by an amorphous layer of around 3 nm, while no layers were observed around the calcite formed on FA or GGBS particles. The calcite formed on FA particles were hexagonal plate shaped, while the one on GGBS particles were rhombohedral shaped. The use of FA resulted in the increase of crystal size and crystallinity of calcite, while GGBS decreased the crystal size of calcite. The incorporation of FA and GGBS increased the calcite content and polymerization of silica-rich gel. However, this didn't result in a higher compressive strength. This was due to the looser microstructure and nanopores within the carbonation products compared to the pure ordinary Portland cement sample. The compressive strength of the ternary binder system showed linear relationship with capillary pores and the crystal size of calcite. Moreover, the effect of GGBS on the compressive strength reduction was more obvious than that of FA.

An electromagnetic Pulse-Induced Acoustic Testing (EPAT) method was investigated for evaluating debonding between rebar and concrete. Debonding specimens were prepared by wrapping polystyrene foam around a rebar to induce debonding between the concrete and rebar. An acoustic emission sensor was placed on the concrete specimen surface to collect elastic wave signals. A powerful pulsed electromagnetic force was applied to the specimens and the elastic waves of the rebar were analyzed. By comparing the differences in signal reach time of the elastic waves between specimens with and without a debonding, it was demonstrated that EPAT is useful for non-destructive evaluation of debonding. Finite element simulations were also conducted, validating the reliability of EPAT for examining debonding in reinforced concrete.

This research studies the effect of incorporating a surrogate molten salt radioactive waste (labelled as MS, composed of a mixture of carbonates, chlorides and sulphates) on the mechanical, mineralogical and microstructural features of two types of cementitious systems: i) Portland cementitious systems and ii) a novel “one-part geopolymer”. As Portland cementitious systems, a CEM I/42.5 SR and a CEM III/B 32.5, were selected. The “one-part” geopolymer was prepared with mixtures of metakaolin and blast furnace slag as precursors, and NaOH and Na2SiO3 powders, as solid activators. Results shown that the MS interacts with both cementitious matrixes, affecting the hydration/activation and promoting the crystallisation of sodium/calcium carbonate hydrated phases. Mechanical strengths substantially declined and the microstructure was clearly affected, especially in samples containing 30% of the MS. Some lines of action are suggested to improve the cementation treatment of MS minimising its effect in the development of the different cementitious materials.

Reactive amorphous aluminum silicates dominate the reactivity of fly ash in alkali cement; however, the quantitative characterization of valid chemical compositions and structures information is highly challenging due to the heterogeneity and complexity of these phases. To acquire this information, in this work, Class F fly ash was treated with 1% hydrofluoric acid, followed by step-by-step analysis using a scanning electron microscope with an energy dispersive spectrometer (SEM-EDS), solid-state magic angle spinning nuclear magnetic resonance (MAS-NMR), and Fourier transform infrared (FT-IR) spectroscopy. Based on the acidolysis method, along with SEM-EDS statistical analysis, four amorphous aluminum silicate phases with relatively higher reactivity were successfully separated and quantitatively showcased, along with their respective average atomic percentage compositions (i.e., Si, Al, Ca, Fe, Na, K, and Mg%). In addition, the use of MAS-NMR and FT-IR analyses allowed for further quantitative insight into the reactive chemical structures and their associations with reactivity. The proposed characterization techniques have unique advantages for acquiring detailed reactive amorphous chemistries, which are difficult to obtain using conventional analysis procedures in alkali systems.

To alleviate the storage of red mud (RM) and the resulting pollution, this study presented an encapsulation-based strategy for the safe management of RM, and adopted ultra-high performance concrete (UHPC) as an encapsulating material due to its superior impermeability and chemisorption properties. It is noteworthy to find that encapsulated material suffered from a selective chemisorption and density functional theory (DFT) calculations were innovatively employed to investigate the selective chemisorption mechanism. The simulation results suggested that distinct bonding forms lead to the selective chemisorption of heavy metals, with Pb being adsorbed by Si–O–Pb chemical bonds and a strong Si–O–Pb–O–Si long chain, while As and Cr only form relatively weak As–O and Cr–O bonds through their attraction to O atoms. With the thickness of the encapsulating material increases, the synergistic effect of chemical solidification and physical package is provided to achieve a stronger stabilization effect. The leaching results indicated that the encapsulated RM exhibited exceptionally low concentrations of hazardous components (i.e., Na at 1.580 mg/L, As at 0.003 mg/L, Cr at 0.027 mg/L, and undetected levels of Pb in encapsulated RM with a thickness of 1.5 mm), far below the limits set by the United States Environmental Protection Agency (EPA). This study opening a new window for the sustainable and efficient management of hazardous solid waste.

The use of capsule-based technology for self-sealing and self-healing cementitious systems has been extensively investigated for both macro- and microencapsulated additions. In this study, macrocapsules, produced using a novel technique were characterised and compared, evaluating mechanical triggering, bonding with the cementitious matrix, and self-sealing efficiency upon integration into cementitious mortar specimens. Macrocapsules containing a commercially available water repellent agent were produced in two ways. Stereolithographic additive manufacturing (3D printing) was used to produce novel rigid acrylate macrocapsules as well as alumina ones. Cementitious macrocapsules produced with a rolling technique were also used as a comparison. The capsules were characterised in terms of watertightness, water uptake, and shell morphology. Following this, the capsules were integrated into cement mortar prisms and subjected to controlled cracking by three-point bending to evaluate the triggering and subsequent self-sealing effect. The results highlighted influential process parameters that can be optimised and explored for further capsule-based self-sealing in structural applications.

Micro-defects in UHPFRC, inevitably generated from the manufacturing to engineering service stage, impact its durability under extreme service environments. However, relevant understanding is still insufficient. This work assesses the corrosion risk and corrosion-induced deterioration in UHPFRC containing initial micro-defects, simulated by a combination of mechanical pre-loading and thermal treatment. Analytical analyses include electrochemical tests (OCP, Tafel, EIS), SEM, MIP, compressive strength measurements, etc. Results show that initial defect degree and steel fiber contents have significant effects on the corrosion resistance and mechanical performance of UHPFRC. Micro-cracks and pores are the major channels to deepen fiber corrosion risk, degrading mechanical performance up to 52%-56% in the most severely damaged UHPFRC. The porosity is increased by the corrosion/increased defects and fiber contents up to a growth rate of 35%, 56% and 78%, respectively, as corrosion triggers the occurrence of new defects (e.g., fiber splitting, newborn micro-cracks, pores). The present results provide a reference for predicting the corrosion potential of the defective UHPFRC.

Spent fluidized catalytic cracking catalysts (SC) are considered toxic solid waste due to it is contained heavy metal ions, which can be polluting for the environment and harmful to humans. Since conventional disposal methods can be harmful to both the environment and people, therefore, new disposal methods need to be developed. In this study, 80 kg/m3 and 150 kg/m3 of SC are incorporated into the design of high-density cement-based materials (HDCM). The mechanical properties, hydration kinetics, durability, and environmental characteristics of HDCM containing SC are evaluated. The results shown that the HDCM has good mechanical properties, with a 6.62% increase in compressive strength at 28 days for HDCM containing 80 kg/m3 of SC. Furthermore, the HDCM containing SC has better long-term volumetric stability, with a 44.55% reduction in dry shrinkage compared to the reference. Further, the HDCM has a good immobilizing ability for heavy metal ions. The leaching concentrations of Ni and V from C1 are only 0.203 mg/L and 0.282 mg/L, and the immobilizing rate is 99.08% and 98.26%, respectively. For the C2, the leaching concentrations of Ni and V are 0.198 mg/L and 0.402 mg/L, the immobilizing rate is 99.31% and 98.25%.

Cement-based mortars are commonly modified with Waterborne Epoxy Resin (WER). However, the curing kinetics of WER in mortars has never been quantified up to now. This study proposed using 1H low-field nuclear magnetic resonance (1H LF-NMR) to quantitatively determine the curing kinetics of WER in polymer-cement composite. The distribution and curing of WER in repair systems was also explored using 1H LF-NMR. To avoid the interference of the NMR water signal, heavy water was used to prepare repair mortar. It was found that the curing reaction of WER in a mortar was significantly influenced by the cement hydration. It starts to accelerate when the cement hydration stepped into an acceleration period. Moreover, the 1D spatial NMR signal distribution showed that WER in the repair materials permeated into the substrate with water, which is affected by both the W/C of the repair and the RH of the substrate. The WER was enriched at the interface between the substrate and the repair mortar and exhibited a gradient in the distribution both upwards into the repair mortar and downwards into the substrate.

The study of the rheological properties of cement-based materials is essential to the processes directly linked to the flow performance of the fresh mixture. As well, the use of micro- and nano-cellulose-based materials is gaining visibility in its application within cementitious matrices. Despite the great potential represented by those materials, there are still informational gaps to be filled. This work aims at exploring the rheological behavior of cement pastes with micro- and nano-materials beyond the single-point testing customarily presented. An experimental program was developed to characterize and discuss the effects of microcrystalline cellulose (MCC) and nanofibrillated cellulose (NFC) on the rheological behavior of cement pastes. The investigation included both dynamic and static regimes, with a specific range of percentages of MCC and NFC. During the dynamic evaluation both MCC and NFC presence resulted in stiffer cement pastes, with increases in yield stress of up to 136% with 0.040% of NFC and 94% of MCC. MCC-specimens showed non-monotonic behavior regarding the static yield stress values. The rheological characteristics of the NFC gel itself affected the general behavior of the cement paste. The water present in the gel was found to be only partially available as mixing water.

Alkali-activated slag (AAS) has attracted huge attention worldwide for its low CO2 emission. However, the high water sorptivity of AAS is an obstacle before its practical application, while conventional methods can hardly solve this issue. In this study, the water sorptivity of AAS was decreased using a novel admixture, and the admixture shows a little effect on compressive strength at long ages. In order to clarify causes for its working mechanisms, the reaction process, reaction products and pore structure were investigated. The results suggest that sodium stearate (NaSt) plays an instrumental role in reaction process of AAS. Primarily, Na+ can provide a high alkaline environment, which is conducive for the dissolving of slag and increases compressive strength at the long term. Secondly, C17H35COO− can dramatically limit the movability of ions in the liquid phase due to its long molecular chain and thus, regulates precipitation of coagulation structure, improving the of ordering structure of C(N)-A-S-H and promoting formation of hydrotalcite-like phases (LDHs), from which the pore structure is upgraded by coarsening the pore diameters at the level of harmless and less harmful pores and decreases the pore connectivity.

Dynamic cyclic loading commonly encountered in engineering practice can pose great threat to the integrity and durability of concrete infrastructures. Ductile materials with enhanced self-healing performance could provide a promising solution under such conditions. This study proposes and investigates, for the first time, as self-healing SHCC (SH2CC) for dynamic reversed-cyclic (DRC) applications through incorporating a mineral substitute (MS) comprising of reactive MgO and quicklime and triethanolamine (TEA) additive in a high-volume-fly-ash matrix. Different DRC preloads were considered. Results indicated that applying 5% MS combined with 1.5% TEA additive showed optimal crack width control below 12 μm under up to 5 cycles of DRC preloading and the highest potential for mechanical strengthening of modulus of rupture, first cracking strength and flexural stiffness reaching up to 160%, 137% and 210% respectively after healing. Moreover the highest crack sealing efficiency was observed up to 88% under 14d water immersion. Microstructural analysis revealed that MS produced additional hydrates and promoted more carbonates to form in cracks during healing, while TEA effectively paused hydration under air curing but resumed the process upon water contact for massively enhancing crack healing (especially mechanical strengthening). Combining MS and TEA in SH2CC produced complementary healing products both in cracks and fibre-matrix interfaces indicating better filling and bridging of the cracks and demonstrating great potential for enhancing healing performance under aggressive loading conditions.

Quick mixing technology at the nozzle is a potential approach to avoiding the opposing requirements for pumpability and buildability and improving productivity in 3D concrete printing. However, the addition of rheological modifiers poses a challenge in quickly achieving a uniform mix while minimizing mixing energy. This study investigated two common rheological modifiers, including polymeric carboxymethylcellulose (CMC) and nano-clay. Their effects on the liquid bridge of mixing water and the mixing evolution and yield stress of concrete were investigated. Results show that the resistance of mixing concrete with CMC reduced with mixing time after a peak whereas that with nano-clay exhibited an opposite trend. An increase in modifier dosages enhanced the liquid bridge force and rupture energy, increasing mixing resistance; the CMC was more influential than nano-clay. Furthermore, the quick mixing method resulted in better dissolution (or dispersion) of these modifiers and higher yield stress but cost more mixing energy.

This study investigates the impact of steel fiber geometrical properties on the interfacial bond and tensile behavior of ultra-high-performance alkali activated concrete (UHP-AAC). Two types of steel fibers, straight and hooked-end, with aspect ratios of 65, 97.5, and 125 were examined. Results showed that the hooked-end steel fiber exhibited the highest average and equivalent bond strengths in the UHP-AAC matrix, measuring 15.13 and 11.46 MPa, respectively, which were approximately 66% and 94% higher than those of straight steel fibers in the same matrix and bonding area. The best tensile performance of UHP-AAC was achieved using straight steel fibers with an aspect ratio of 97.5, demonstrating the highest tensile strength and strain energy density of 12.28 MPa and 55.24 kJ/m3, respectively, and the second highest strain capacity of 0.533%. Straight steel fibers were more effective in increasing the tensile strength of UHP-AAC than hooked-end steel fibers with the same aspect ratio. Higher fiber aspect ratios resulted in larger microcrack widths, with the straightened end-hooks acting on the crack plane to transmit tensile force more effectively, contributing to increased microcrack width and deformability.

Due to the low density and the distinct surface hydrophobicity of EPS, EPS are prone to float in the mixing and forming process of EPS concrete and to distribute unevenly in the process of concrete hardening, which finally results in the poor mechanical properties of EPS concrete. To improve EPS hydrophilicity, a new modification method was proposed in this paper to graft Pluronic (PEO) and ammonium chloride (NH4Cl) with hydrophilic groups on EPS surface, thereby converting EPS from hydrophobicity to hydrophilicity. The effects of modification on both the EPS hydrophilicity and the working performance and mechanical properties of EPS concrete were studied. The results suggest that both the modified EPS hydrophilicity and the EPS concrete fluidity and uniformity were significantly improved, with the minimum hydrophilic angle of EPS of 29°, and the minimum quality difference between the upper and lower concrete parts of 4.7%. While at the final failure, unmodified EPS concrete presented the most severe damage, however, modified EPS concrete, remained relatively intact. Compared with unmodified EPS concrete, modified EPS concrete cube increased its compressive strength by 26.64%, and its flexural strength by 16.12%. The ascending section of the stress-strain curve shows a regular linear distribution, whereas its descending curve jittered down with slight fluctuations in load, owning to the resilience of EPS. In addition, each stress-strain curve was fitted by a two-stage method, which indicates a high overall fitting degree.

Formulation of strain hardening cementitious composites typically engage 2% or more fiber by volume, resulting in higher cost and difficult processing. This study presents the development of strain hardening magnesium-silicate-hydrate composite with an extremely low fiber volume fraction of 0.5% via micromechanics-guided design approach. The developed composite demonstrated a tensile strain capacity of 7.2% with a tensile strength of 2.24 MPa, and a compressive strength of 86.1 MPa. The fiber/matrix interfacial bond was characterized using single fiber pullout test. The microstructural characterization of fiber surface and fiber tunnel in the matrix was carried out to understand the fiber/matrix interface properties. The micromechanics-based assessment of critical fiber volume fraction required to achieve strain hardening was also conducted. The material sustainability of the developed composite was evaluated and compared with existing Portland cement-based strain hardening cementitious composites, and strategies to further reduce embodied carbon and primary energy were proposed.

Corrosion can lead to deterioration of the bonding properties at anchor-mortar interfaces, affecting the durability of the anchored structures. Therefore, it is essential to establish an accurate analytical model of the anchor-mortar interface bond to estimate the interface bond strength under corrosion. Steel corrosion occurs via electrochemical reactions, that is, anode and cathode formation in different potential zones on the steel surface, resulting in an electrical potential difference that facilitates constant cation migration and the generation of corrosion products with anions. In this study, electrochemical impedance spectroscopy, taking into account electrochemical theory, was carried out to analyse the kinetics of the electrode processes. Based on electrochemical parameters such as pore solution resistance and charge transfer resistance, a function relating electrochemical parameters to the material properties was established. The traditional theoretical model of a thick-walled cylinder was modified to obtain an analytical model of the bond strength of the anchor-mortar interface in pull-out damage mode under the effect of corrosion. The accuracy of the estimated values of the analytical model was verified via pull-out test results. The estimated values obtained from the analytical model were in good agreement with the test values, indicating that the model was able to describe the corrosion state at the anchor-mortar interface and estimate the interfacial bond without damaging the specimen.

The thermal conductivity (λ-value) of cementitious materials with steel fibers is not always better than that of plain cementitious materials due to the interface between the steel fiber and cementitious materials and the increased porosity. A mesoscale finite element (FE) model considering both fiber-matrix interface and pore effects was developed to quantify the influences of porosity, pore water saturation degree, fiber-matrix interface property, fiber content, fiber length, fiber shape, and fiber orientation on the λ-value of cementitious materials, which can explain well the various relationships between the λ-value of cementitious materials and steel fiber content reported in the literature. In the FE model, cementitious materials containing steel fibers were divided into two scales where Scale I included solid phase and pore, and Scale II was made up of the homogenous composites from Scale I and steel fibers. To achieve a more accurate representation of the pore structures, the pores at Scale I were created randomly without specifying their geometry. The fiber-matrix interface in cementitious materials at Scale II was modelled as a zero-thickness interface with constant interfacial thermal conductance. It is found that the λ-value of cementitious materials decreases linearly with increasing porosity but increases linearly with increasing pore water saturation degree. The influence of steel fiber on the λ-value of cementitious materials depends on the fiber-matrix interface property. When the fiber content or fiber length increases, the λ-value will increase for good fiber-matrix interfaces with high interfacial thermal conductance; while poor interfaces with low interfacial thermal conductance lead to an opposite trend. Fiber geometry has a limited impact on the λ-value. The fiber orientation can affect the λ-value of cementitious materials. When the fiber rotational angle with respect to the direction of temperature gradient increases, the λ-value of cementitious materials with the same fiber-matrix interface property will decrease.