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Solid wastes have become used to manufacture high ferrite cement clinker (HFCC). However, the behavior and effect of common heavy metal in solid wastes, i.e., lead during calcination process are still lacking. And understanding the solidification behavior of lead and its action mechanisms on phase reconstruction and hydration processes is crucial for rational utilization of lead-containing solid waste. Hence in this study, the distribution and solidification form of lead during HFCC calcination are explored and the effect of solidified lead in clinker on mineral phase composition, liquid phase properties, microstructures, and hydration properties of HFCC are systematically studied using various experimental and modelling methods. Results indicate that nearly all the Pb ions are solidified in the inherent phase structures, among which the majority are dissolved in the silicate phase. Due to the unstable phase configurations formed by lead substitution and the unmatched electronic structure, the Pb elements are subject to enter C 3 S, C 2 S, and C 4 AF in the form of interstitial solid solution. The solidification preference of the Pb element in the single crystal is C 2 S > C 4 AF > C 3 S as a result of the larger interstitial voids of C 2 S. The solidified Pb elements in HFCC mainly affect the mineral phase composition by varying the liquid phase properties. The formation of a eutectic mixture reduces the viscosity and formation temperature of the liquid phase, resulting in an increased interstitial phase content. Additionally, the high-energy-activated state of the Pb-formed interstitial solid solution increases the hydration activity of HFCC and the Pb elements in the voids of the tetrahedral silicate phase will not be released through chemical bond rupture. Thus, the solidification of Pb ions in clinker accelerates the hydration reaction of HFCCs and eventually leads to a higher ultimate hydration heat and the postponing effect on induction period is relatively low. • The mechanism of Pb element participating in high-temperature mineral phase reconstruction was revealed. • Most Pb ions solidified in the voids of the tetrahedral silicate phase in the form of an interstitial solid solution. • The high-energy-activated state of the Pb-formed interstitial solid solution increases the hydration activity of HFCC. • The low dissolution content of solidified Pb ions results in a low postponing effect on induction period. [ABSTRACT FROM AUTHOR]

Apparent gas-permeability (k a) of concrete highly depends on pore-structure and medium. However, the effects of gas-medium on permeability have yet been investigated in depth. In this work, concrete with various water-to-cement ratios and fly-ash/slag dosages is prepared for k a testing. Various gas-mediums (CO 2 and O 2) are applied for analyzing their effects on the k a. Meanwhile, pore-structure characteristic, inner gas-pressure, and gas-absorption in concrete are observed for exploring permeation mechanism. The results illustrate that the narrowing pore-scale effect and surface-diffusion contribution derived from gas-absorption of CO 2 and O 2 both have minor impacts on the k a. The k a of O 2 (k O2) is higher than that of CO 2 (k CO2) and their relative permeability (k O2 / k CO2) ranges from 1.18 to 2.29. These deviations are mainly caused by significantly different Knudson diffusion occurring in the area near the concrete outlet-gas side (approximately 5%). • Gas permeability of concrete is measured by various osmotic-mediums (CO 2 and O 2). • Inner gas-pressure distribution of concrete is obtained under steady-state flow. • The apparent gas-permeability of concrete tested by O 2 is higher than that by CO 2. • Gas absorption of CO 2 and O 2 has minor impacts on apparent gas-permeability. • The deviation of apparent permeability is mainly caused by Knudson diffusion. [ABSTRACT FROM AUTHOR]

This study focused on the modification of a mixture of a lime-based composite cementitious material (LCM) by using chemical admixtures to increase the mechanical performance of the LCM. The different types and amounts of chemical admixtures including NaOH and Na 2 SO 4 were used as activators to prepare the novel modified LCM. The mechanical strength, hydration kinetics, assemblage of hydrates and microstructure of the modified LCM were systemically explored and compared to conventional LCM. The experimental results indicated that Na 2 SO 4 had better effects on the improvement of LCM strength compared to NaOH when used alone as the activator. The composite activator that was composed of Na 2 SO 4 and NaOH showed the optimal effects on the increase of the LCM strength. The composite activator effectively increased the hydration rate of the LCM, and more hydrates were formed during the hydration process of the LCM. Furthermore, the U-phase was formed only in the hydration products of the LCM containing the composite activator. A large amount of U-phase as crystals effectively occupied and filled the space in the LCM paste and led to the formation of a compact microstructure with fewer macro-pores. Thus, the presence of U-phase in the paste increased the strength of the LCM. [ABSTRACT FROM AUTHOR]

The use of solid waste to produce low carbon, high ferrite cement clinker (HFCC) with favorable durability delivers potential application prospects. However, the semivolatile heavy metals Zn and Cd in solid waste not only restrict its utilization ratio but also cause potential environmental pollution. In this study, the migration and solidification behavior of Zn and Cd during calcination and their action mechanisms on phase reconstruction are systematically studied. The reaction sequence and conditions of Zn were revealed by experimental tests and phase diagram simulation. Zn2+ will firstly solidify in the C 2 S phase by the solid-phase reaction. After liquid phase forms, Zn2+ is more inclined to substitute Fe3+ in the C 4 AF phase with 4-coordination in the [FeO 4 ]. Only a small amount of Zn2+ enters the C 3 A and C 3 S phases in the form of interstitial solid solution. Zn promotes the formation of the liquid phase and C 3 S phase. And HFCCs indicate a favorable solidification effect on Zn. While due to low volatilization temperature and high volatility of Cd, even at a low sintering temperature, the HFCC cannot greatly reduce the volatilization of Cd. Cd2+ mainly exists in HFCC by substituting Ca2+ in the C 3 S, C 2 S and C 4 AF phases with a 6-coordination number in [CaO 6 ] to form the spatial configuration of octahedral complexes. • Reaction sequence and reaction condition of Zn during sintering were revealed. • Compared with OPC, high ferrite cement clinker (HFCC) has a stronger solidification ability for Zn. • Solidification priority depends on liquid phase content, elements volatilization and lattice distortion. [ABSTRACT FROM AUTHOR]

With the extension of service time, infrastructure is in growing urgency for repair and reinforcement due to its deterioration in safety and durability over the years. Normal cement concrete has shortcomings, e.g., high brittleness and low flexural-tensile strength, that fail to meet the requirements of construction repair. In this paper, a novel waterborne epoxy-concrete composite repair material (WECM) was prepared by using self-synthesized water-based epoxy resin based on the molecular structure-activity relationship. The mechanisms of waterborne epoxy (WEP) and WEP-fiber synergy on the improvement of concrete performance were clarified. The results show that the defects of high brittleness and poor ductility of concrete are significantly improved by WEP and that the ductility of WECM is increased by 300%–600% compared with the control concrete. The fiber and WEP in the WECM exhibited a synergistic effect on the tensile strength, ductility, and crack resistance of concrete in which the fiber coating layer mixed with WEP and embedded cement particles (inlay) provided fiber protection as well as an interfacial bonding enhancement. The P/C of 0.2 is the turning point of the flexural and tensile strength of the WECM, which is related to the continuous phase formation of the WEP-interpenetrating polymer network (WEP-IPN). [ABSTRACT FROM AUTHOR]

The inherent brittle fracture characteristics of cement limit the application of cement-based materials in fields such as building repair, thin-layer coating, and the preparation of deformable components. The blending of polymers alleviates this characteristic to a certain extent, but the flexibility and toughness still need to be further improved. We prepared a multi-scale toughener (MST) by applying a hydrothermal method to improve the dispersion performance of the nano-silica (NS) aqueous while constructing the multi-component silane molecular cages (SMC) by using 3-glycidyloxypropyl trimethoxysilane (GPTMS). The mechanical properties and micromorphology of the waterborne epoxy-cement repair material (WECM) with MST were characterized. The zeta potential analysis, laser particle size analysis (LPSA), gas chromatography-mass spectrometry (GCMS), gel permeation chromatography (GPC) and molecular dynamics simulation were used to characterize and explain the basic questions that persist in the theory of particle dispersibility and hydrolysis-condensation effects within the MST system. The results show that the hydrothermal treatment is more efficient than mechanical dispersion in dispersing performance while surging the GPTMS' reaction rate by ~1000 times as well as the transformation from monomers to the caged multimers. The ductility of MST modified WECM radically increased by 300%–400%. The microscopic morphology reveals that the MST effectively induced multi-slit cracking (cracks of ~5 μm in length and ~1 μm in width, the aspect ratio of 6: 1 ~ 4: 1) effects with a noticeable rugged morphology observed. The obtained results include parameters to improve the mechanical properties of composites with MST and this simple and effective organic-inorganic nano toughener has a good application prospect in the field of polymer modified cement-based materials. [ABSTRACT FROM AUTHOR]