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Cement‐based sensors (CBSs) have demonstrated potential in structural health monitoring (SHM) despite rare applications due to their poor flexibility and sensing accuracy/protection with robustness. Herein, a promising strategy is reported to design a waterborne epoxy resin (WEP)‐modified cement‐based composite coating sensorcapable of simultaneous stable SHM and durable protection. The interpenetrating network (IPN) formed by WEP within cement paste is bionic to the toughness and crack resistance of biological muscle tissue and balances the ion permeation performance and polarization of hydration products. The polymerization‐redispersion progress and mechanism of calcium silicate hydrate (C‐S‐H) gel modified with [3‐(2‐aminoethylamino)‐propyl]trimethoxysilane silsesquioxane (C‐POSS) are characterized and revealed. The results show that the muscle‐like IPN increases the cement‐based coatings' maximum deflection angle to 30° and improves the monitoring accuracy of compressive, tensile, and fatigue microchanges of concrete structures to more than 95%. The POSS···Ca2+···C‐S‐H interaction in C‐POSS partially transferred the intra‐adhesive hydrogen bonds surrounding the nanoconducer into electrostatic bridging ones to maintain an excellent electromechanical conductive dispersion. [ABSTRACT FROM AUTHOR]

Supplementary cementitious materials (SCMs) are usually employed to replace partial cement and the pore-solution chemistry of blended cements is extremely essential for their cement hydration and durability. In this work, the pore-solutions of cement pastes with various water-to-cement (w/c) ratios and SCMs (fly ash, ground granulated blast-furnace slag and silica fume) are extracted for observing their ions and conductivities. The results illustrate that Na+, K+, OH−, Ca2+ and SO42− are the main and their concentrations are declined by the improving w/c ratios and SCMs dosages and thus decreasing their conductivities. The conductivity evolution shows three typical periods: induction (<5 h), acceleration (5 h-7d) and deceleration (>7d). The pore-solution conductivities of pastes with various w/c ratios are predicted well by the model established (R2 > 0.90) while the SCMs decline the model effectiveness. The OH−, K+ and SO42− provide the conductivities over 90% of the whole with the contributions in decreasing order. [ABSTRACT FROM AUTHOR]

Accurate prediction of transport properties for cementitious materials remains a challenge since it is difficult to experimentally obtain the realistic three-dimensional (3D) pore network of cement paste. In this study, the 3D pore network of cement paste is quantitatively characterized using nano X-ray microtomography coupled with the metal centrifugation porosimetry (MCP). First, the MCP technique is carried out to impel the liquid metal into the pore network of cement paste. Subsequently, the 3D pore network of cement paste with the intruded metal is reconstructed using high-resolution X-ray microtomography. Finally, based on the X-ray microtomography images, the transport properties of cement paste including ionic diffusivity and fluid permeability are simulated using a set of lattice Boltzmann transport models. The results show that the metal alloy can significantly enhance the contrast between the pore network and solid phase, and the realistic 3D pore network can be successfully reproduced. For the cement pastes with water-to-cement (w/c) ratios of 0.5 and 0.6, the transport properties are dramatically increased with the improving w/c ratio. A similarly dramatic growth evolution of transport properties also occurs when the effective porosity of cement pastes raises from 27.56% to 36.11%. [ABSTRACT FROM AUTHOR]

• Nano X-CT combined with metal centrifugation porosimetry (X-MCP) is developed. • The 3D pore structure is visualized by the novel X-MCP and CEM3D simulation methods. • The pore parameters obtained by X-MCP and CEM3D are evaluated by the traditional MIP. • The critical pore diameters obtained by X-MCP and CEM3D are higher than those by MIP. • The porosity values obtained by the three methods are accordant with each other. Cementitious material is a vital composite for infrastructure, its 3D pore-structure determines its cement hydration as well as structural performance. However, the quantitative characterization of 3D pore-structure has yet been investigated in depth. In this study, the 3D pore-structure in hardened cement-paste is investigated systematically using innovative experiment and simulation methods. The experiment implements nano X-ray techniques combined with metal centrifugation porosimetry (X-MCP) for visualizing the 3D pore-structure and compared to that obtained by CEM3D-based model. The 3D pore-structure parameters containing the critical pore-diameter (d c) and porosity by X-MCP and CEM3D are counted and compared to those by mercury intrusion porosimetry (MIP). The results show that the d c values by X-MCP and CEM3D are both higher than those by MIP, and the porosity values obtained by the three methods agree with each other. [ABSTRACT FROM AUTHOR]

• A new avenue to prepare rGO suspension with excellent comprehensive was developed. • The mechanical and functional properties of samples were significantly improved. • The percolation threshold of rGO was determined by comparing different performance. • The functional mechanism of rGO to mortar was analyzed by comparing different model. For modern concrete materials and structures, how to realize the multifunctional application is still a challenge. The introduction of functional components into concrete materials is the most effective method. The present study successfully develops a new avenue to prepare rGO suspension with excellent dispersibility and stability through the combination of dispersant and ultrasonic pre-dispersion. This rGO suspension is added to the cement-based material, resulting in the improvement of mechanical and functional properties. The compressive and flexural strength of mortar are increased by 45% and 50% at 3 days, respectively. Meanwhile the hydration heat and pore structure are improved up to doping 2.00 wt% rGO. Moreover, the resistivity and thermal conductivity of mortar are decreased by 45% and increased by 23%, while the electromagnetic shielding effectiveness of cement paste is increased by 45%. In addition, the pressure-sensitive property of mortar increases first and then decreases with the increases of rGO content, wherein the largest stress and strain sensitivity coefficient can reach up to 1.28%/MPa and 147.80 with 2.00 wt% rGO. These results demonstrate that doping rGO is a promising approach to the improvement of the functionality of cement-based materials resulting from the doping rGO is attributed to, the formation of a conductive network structure with the continuous phase in the cement matrix when rGO content reached percolation threshold. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a centrifuge device is proposed to facilitate the intrusion of a low-melting point metal alloy into the pore space of hardened cement paste. X-ray microtomography is combined with metal centrifugation porosimetry (MCP) to quantitatively investigate 3D pore structure. The low-melting-point metal alloy is melted and introduced into pore space in pastes with water cement ratio of 0.5 and 1.0 at a temperature of 65 °C. 3D pore structure is quantitatively analyzed by X-ray microtomography after the molten metal alloy has been consolidated. A new threshold value segmentation method for pore space was proposed using conversion coefficient on region of interest (ROI). Porosity and pore size distribution are tested by MCP and compared with the results based on mercury intrusion porosimetry (MIP). The results show that the contrast between pore space and solid phase in the X-ray microtomography device image is improved. The total porosity obtained by MCP was found to be consistent with the results obtained by MIP. Highlights • Metal alloy was intruded into pore space to enhance the contrast in imaging. • 3D pore structure of hardened cement paste investigated with X-ray microtomography. • 3D pore structure of cement paste successfully imaged and quantitatively analyzed. [ABSTRACT FROM AUTHOR]

A novel green cement which was prepared with superfine Portland cement and high volume solid wastes (fly ash and blast furnace slag) was investigated in this study. The mechanical performance, heat of hydration, particle packing density, evolution of hydration products and microstructure of this novel blended cement were studied and compared to the conventional blended cement. Moreover, the energy consumption and carbon emission of novel green cement were calculated. The effects of superfine cement in blended cement were systematically studied and compared to Portland cement (PC). Test results showed that a notable improvement in the mechanical properties of novel green cement was achieved compared to conventional blended cement. Even the mechanical properties and workability of novel green cement were very close to PC. The calculation based on mixtures indicated that the energy consumption and carbon emissions of novel green cement containing 70 wt% mineral admixtures only reached 47.3% and 40.9%, respectively, of those of PC. The analysis suggested that the superfine cement increased the packing density of blended cement and effectively accelerated the hydration of mineral admixtures to form a refined and dense microstructure, which is key for preparing high-performance green cement. This research provided guidance for developing low carbon and environmentally friendly cement. [ABSTRACT FROM AUTHOR]

• A structural kinetics model was developed by combining a kinetic equation of the structural parameter λ and the relationships between yield stress τ y. • Yield stress is more suitable to characterize the structural build-up of fresh cement paste than viscosity and rheological index. The test of the yield stress needs to consider the structure of the rheometer. • When the specific area of limestone exceeds 600 m2·kg−1, it can accelerate the establishment rate of the dynamic structure. When the specific area is 400 m2·kg−1, the content of limestone corresponding to the maximum structuration rate is reduced. The structural build-up of fresh cement-based materials is of great significance to the early forming and later performance. A structural kinetics model (SKM) used to indicate the structural build-up was developed by combining a kinetic equation described by structural parameter (λ) and a relationship between yield stress (τ y) and λ in the paper. SKM transforms the structuration rate (A thix ) in linear Roussel model and the characteristic time (t c) in non-linear Perrot model into more specific indicators such as initial solid volume fraction (ϕ 0) , rate of hydration during induction period (α ̇ ind) , and shear rate (γ.). The yield stress (τ y) obtained by RHEOLAB QC rotary viscometer was explored the dynamic and static structural build-up of fresh cement paste. The yield stress of fresh cement paste (W/C = 0.4) exhibits a quasilinear pattern with rate of 0.42 Pa/s for 210 min of mixing, with rate of 0.88 Pa/s for 100 min of resting after 4 min of mixing. The static yield stress of fresh cement paste evolves from linear to non-linear patterns within 100 min of resting after beyond 30 min of mixing. The fitting results show that SKM can well fit the evolution of yield stress including linear and nonlinear phases. Comparing with the dynamic structural build-up, the effect of limestone powder on the static structural build-up of cement paste is more obvious. When the mixing process is longer than 60 min, the content of limestone powder less than 20 wt% is beneficial to the structural build-up of fresh paste. Additionally, a declined rate of cement hydration in the induction period with increasing mixing time indicates that the rising yield stress, in this case, cannot be attributed entirely to the contribution of hydration to structural build-up. [ABSTRACT FROM AUTHOR]

The formation of the interpenetrating polymer network (IPN) structure within the cement-polymer system has been revealed by experiments from 2 dimensional to 3-dimensional scales. However, the microstructure design and performance prediction of IPN as a function of specific C-S-H/polymer components or ingredients' parameters e.g. water to cement ratios (w/c), polymer to cement ratios (p/c), monomer components, degree of polymerization (DP), etc. is by far not available. Here we developed a mesoscale model for IPN visualization based on the Flory-Huggins interaction theory which was applied to cement science for the first time. All the ingredients in the micro-structure were considered as soluble beads with rational sizes based on their properties obtained by molecular dynamic methods. The interaction parameters of each bead were then determined based on their element ratios and chemical backbones. The model was validated with the waterborne epoxy-cement material (WECM) in which a novel waterborne epoxy resin (WEP) was prepared and impregnated. The verification results on the 2D-3D scale show that the developed model predicts the WECM's IPN structures by rule and line concerning DP, w/c, and p/c in the mixture. The C-S-H beads were progressively scaled in size which alters the C-S-H texture to have completely different dissolution characteristics. Beads of diameter ~6 Å are more unstable and soluble which enable them to form a continuous phase in water or a composite structure with WEP. In contrast, beads with diameters larger than 10 Å have different properties with stronger nucleation effects. The results also suggest the impregnation content of WEP in cement-based material should be limited to 10% vol. to prevent the polymer IPN from decomposing into discrete clusters. The application of Flory-Huggins theory in cement-based composites demonstrates great potential in performance prediction and microstructure design. [ABSTRACT FROM AUTHOR]