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The water transport behaviors of cement-based materials are altered after hydrophobic modification. The influence of hydrophobic modification on the water transport behaviors of mortar was investigated through 1H NMR and the absorption test. The results indicate that the incorporation of paraffin significantly reduces both the capillary and moisture absorption masses of mortar. The ratio of moisture absorption mass to capillary absorption mass increases with higher hydrophobicity, attributed to the paraffin coverage around the pores and the subsequent increase in contact angle. When incorporating 10 wt% paraffin, the increase in capillary absorption mass of mortar is mainly attributed to vapor diffusion and capillary condensation, accounting for 90.3 %. And the content of interlayer water, gel water, and inter-hydrate water in the two mentioned specimens is approximately equal, attributed to increased resistance to the ingress of liquid water. The reinforcement corrosion protection performance improves by one to two orders of magnitude due to the alteration of water transport behaviors. • Hydrophobic modification alters the proportion of various water transport behaviors. • 1H NMR is employed to characterize the distribution of water content in different water absorption environments. • When the hydrophobicity of the mortar increases, the capillary and moisture absorption specimens exhibit similar mass increments and absorption rates. [ABSTRACT FROM AUTHOR]

The water status within concrete under low air pressure (AP) condition has been reported to affect the long-term properties of concrete in plateau regions, however, the underlying mechanism for the microstructural changes is not fully understood yet. In this paper, the confined water statuses within cement pastes curing at 98% RH and different APs (i.e. 101 kPa, 60 kPa, and 20 kPa) were first demonstrated and then correlated to the nanomechanical property changes of calcium-silicate-hydrates (C-S-H) phase by means of the 1H NMR relaxometry and nanoindentation techniques. The results show that low AP conditions increase the evaporable water content and drive the water movement from interlayer spaces to gel pores during wetting at 98% RH. According to the nanoindentation investigations, low AP conditions increase the volume fraction of high-density (HD) C-S-H and improve the nanomechanical and creep characteristics and bending strength of hardened cement pastes, which is attributed to the water redistribution within C-S-H phase. • Water statuses within cement pastes were identified by 1H NMR relaxometry. • Low air pressures drove water redistribution from interlayer space to gel pores. • Low air pressures changed nanomechanical characteristics of cement pastes. • Nanomechanical characteristics changed with water statuses of cement pastes. [ABSTRACT FROM AUTHOR]

The impact of polymer admixtures on the performance of cementitious materials is certainly dependent on their molecular structures. This paper aims to elucidate the influence and mechanism of polyacrylamide (PAM) molecular weight on the workability of cement paste. The surface charge property and adsorption behavior of modified cement paste were quantified. Additionally, the assembly morphology of three molecular weight PAMs and the viscoelasticity of their solutions were monitored, so as to provide new insights into the underlying mechanisms. The findings indicate that the growth of PAM molecular weight causes a significant drop in fluidity and an improvement in plastic viscosity of modified cement paste. PAM with higher molecular weight can be adsorbed as a larger size of assembly aggregates on the cement particles, thus promoting the bridging effect. Besides, after the incorporation of PAM, the electrostatic repulsion between cement particles is decreased, whereas a higher PAM molecular weight causes a greater drop. Therefore, it is important to consider not only the dosage of PAM but also its molecular weight in practical engineering. [ABSTRACT FROM AUTHOR]

Highlights • Rheological properties have a good relation with the absorption of SAP. • The thixotropy shows the effect of SAP absorption behavior compared with plastic viscosity and maximum shear stress. • Large SAP's particles led to a high absorption rate and a long absorption time. Abstract Superabsorbent polymer (SAP) is an important internal curing agent for concrete with low or ultra-low water-to-binder ratio (w/b). When SAP is added, it will absorb water from fresh concrete fast. Thus, water absorption of SAP will affect the rheological properties of cement-based materials, especially at low w/b. Moreover, SAP with different particle size has a different absorption rate which will also affect the rheological properties. In this paper, two SAPs with different particle size are used to investigate its effects on the maximum shear stress, yield stress, plastic viscosity and thixotropy of cement-based materials within 80 min. Basic w/b of 0.18 was specified as reference values. Rheological results show that the absorption of SAP changed the evolution of yield stress, plastic viscosity and thixotropy of fresh mortar with time. Large SAP's particles led to a high absorption rate and a long absorption time which increased the yield stress and plastic viscosity. The above effects of SAP are closely related to the availability of water near SAP in cement mortar which causes to be a nonlinear relationship between the amounts of SAP and extra water required. In addition, the amount of extra water should be adjusted according to particle size of SAP and the addition level of SAP. [ABSTRACT FROM AUTHOR]

Structural build-up is of great importance in many concrete applications, such as formwork pressure, multi-layers casting, slip form paving, stability, and 3D printing. In this paper, the growth of static yield stress (τ s ) and thixotropic area were used to characterize the structural build-up of cement paste. The effects of different mineral admixtures, i.e. silica fume (SF), ground slag (GS), fly ash (FA), attapulgite (AG), nano calcium carbonate (NC), and nano silica (NS) on the structural build-up of cement pastes were studied. Calorimetric curves, zeta potential and conductivity of the pastes were also measured. Results showed that thixotropic behavior characterized by the growth of τ s and thixotropic area gave different ranking on cement pastes with various mineral admixtures. NS, AG, NC and SF increased the growth of τ s over 120 min, and NS was the most effective one. FA and GS decreased the growth of τ s over 120 min. Hydration of cement played a dominant role in the structural build-up of cement paste. However, high hydration rate didn’t always lead to high structural build-up rate. [ABSTRACT FROM AUTHOR]

The structural build-up of cement-based materials is often characterized by the determination of the evolution of static yield stress with time. This property is crucial to many applications of concrete. However, the measurement of static yield stress may disturb the structure of cement-based material. As a consequence, the true structural build-up of the materials may not be detected. In this paper, the evolution of static yield stress and storage modulus (G′) determined by small amplitude oscillatory test was determined to characterize the evolution of the structural build-up of cement pastes. Results showed that G′ and static yield stress developed similarly with time. When the tests were carried out on the same sample, the measurement of static yield stress disturbed the structure of cement paste and had a significant effect on the following measurement of G′, but a slight effect on the following measurement of static yield stress. [ABSTRACT FROM AUTHOR]

It has been long recognized that low air pressure (AP) affects the moisture transfer in concrete, and thus its microstructure and bulk property, but less is known about the thermodynamic mechanism. This research investigated the microstructure evolution of young white Portland cement paste during wetting or drying at different APs (i.e. 101 kPa, 60 kPa, 20 kPa), the experimental and numerical analyses reveal the moisture transfer changes at low APs, which matters for the microstructural features of hardened cement paste. It was found that low APs increase the water vapor diffusion and convective mass transfer coefficients, and the intrinsic permeability of cement paste sample, which results in higher water contents within cement paste during wetting at 98 % RH but more rapid water losses during drying at 43 % RH. Owing to the distinct moisture transfer behaviors, the C-S-H structures were linked with water contents within confined pores. [ABSTRACT FROM AUTHOR]

In this paper, the effects of asphalt-to-cement ratio (A/C) and water-to-cement ratio (W/C) on the elastic modulus E c of cement asphalt (CA) binder were studied through measuring the stress-strain curves and phase volume fractions of various CA binder specimens. The results illustrate that the CA binder with high asphalt content (A/C ⩾ 0.6) is a two-phase composite with complicated microstructure formed by both cement hydrates and asphalt agglomerates. The elastic modulus of CA binder decreases with the increase of A/C and W/C, especially A/C. A composite model that describes the CA binder in terms of the properties of asphalt and volume fractions of cement phases is suggested, and E c of CA binder can be predicted by this model according to A/C, W/C and properties of asphalt. [ABSTRACT FROM AUTHOR]

This paper elucidated the temperature dependence of cement setting by comparing the storage modulus (Gʹ) evolutions under different temperatures ranging from 10 to 55 °C. The temperature-induced changes in cement hydration and colloidal interaction were also explored to reveal the underlying physio-chemical effects. It was found that the increase in temperature significantly accelerates the growth of Gʹ in all the stages of setting process, which mainly arises from the promotion of forming "calcium silicate hydrates (C–S–H) bridges" and compressing the electrical double layer of particles. For the same hydration degree, the rise of temperature leads to a greater Gʹ of cement paste. It was attributed to the diminution of the electrostatic repulsive force between particles caused by not only the direct effect of rising temperature but also the higher SO 4 2-/Ca2+ concentration ratio of interstitial solution in the paste cured at the higher temperature. [ABSTRACT FROM AUTHOR]

• The early properties of cement pastes modified by anionic, cationic and nonionic PAM were contrastively studied. • The absorption and hydration of cement pastes with different ionic PAMs were investigated. Polyacrylamide (PAM) has been widely applied as a viscosity modifier to optimize the workability of cement-based materials, but PAMs with different ionic types may show various effects, which is often ignored in practical engineering. In this paper, the early properties including the rheology, flowability, and setting of cement pastes modified by three ionic PAMs (anionic APAM, cationic CPAM, and nonionic NPAM) were contrastively studied. The absorption and hydration of cement pastes with different ionic PAMs were further investigated. Moreover, the contributions of physical flocculation and chemical hydration on the structural build-up of cement pastes were quantified by combining the static yield stress and heat release at the same time scale. The results indicated that three ionic PAMs showed different effects on the structural build-up, fluidity and setting of fresh cement pastes, which were dominated by the different physical flocculation and hydration retardation effects of three ionic PAMs on the cement pastes. The order of flocculation and hydration retardation effects of these three ionic PAMs was APAM ≫ NPAM > CPAM, which was concentration-dependence and evolved over times. The reason is mainly due to the distinct molecular structures and physicochemical properties of three ionic PAMs and their different adsorption behaviors with cements particles. [ABSTRACT FROM AUTHOR]

AC impedance spectroscopy (ACIS) is a promising technique for monitoring the microstructure evolution of fresh cement paste in real-time. This paper compared the change of bulk electric resistivity (ρ bulk) obtained from ACIS with the developments of storage modulus (G′) and the mean transverse relaxation times (T 2) of fresh Portland cement pastes within 5 h. It was found that the three different phases (Phase I, II, and III) on the microstructural build-up process of fresh paste can be accurately distinguished by analyzing ρ bulk , as well as G′ and T 2. The use of ρ bulk fails to characterize the microstructural changes in Phase I due to the great sensitivity on the electrical conductivity of the interstitial solution. However, it can successfully reflect the developing features of microstructure in Phases II and III, and reliably evaluate the impacts of water to cement ratio, superplasticizer, and supplementary cementitious materials on the microstructural development. [ABSTRACT FROM AUTHOR]

Abstract: This paper reviews the chloride binding of cement-based materials subjected to external chloride environments. Chloride ion exist either in the pore solution, chemically bound to the hydration products, or physically held to the surface of the hydration products. Chloride binding of cement-based material is very complicated and influenced by many factors, such as chloride concentration, cement composition, hydroxyl concentration, cation of chloride salt, temperature, supplementary cementing materials, carbonation, sulfate ions and electrical field etc. Four different types of binding isotherms, namely linear, Langmuir, Freundlich and BET binding isotherm have been proposed to describe the relationship between free and bound chloride, none of which can accurately express the relationships between free and bound chloride within the whole concentration range. Freundlich binding isotherm seems to be the most approximate one. However, some field data fit linear isotherm well. This may be ascribed to the leakage of hydroxyl ion. Many service life prediction models based on diffusion mechanism alone have been proposed during the past two decades. If chloride ion binding is not considered in the models, it underestimates the predicated service life. [Copyright &y& Elsevier]

• The early-age deformation behaviors of CA mortar with AP and/or UEA were studied. • Deformation results from the graduated flask method and the buoyancy method were compared. • Four deformation stages of CA mortar were found and the underlying mechanisms were discussed. Early-age deformation of cement emulsified asphalt mortar (CA mortar) is a key parameter for its application in the CRTS I and CRTS II slab ballastless tracks of China. In this paper, the buoyancy method was used to measure the early-age deformation behaviors of CA mortars with aluminum powder (AP) and/or U-type expansive agent (UEA). The results indicate that the buoyancy method accurately and stably reflects the early-age deformation of CA mortar. The deformations of CA mortars with AP and/or UEA are composed of four stages: slight shrinkage stage, fast expansion stage, gradual shrinkage stage, and stable stage. Further analyses of relative expansions of samples reveal that different mechanisms of AP and UEA take effect at the gradual shrinkage stage of CA mortar deformation. Thermal effect induced by internal heat accumulation increases the air pressure in voids entrained by AP in CA mortar, thereby increasing the peak deformation values. Then the deformation tends to decrease with heat dissipation at the gradual shrinkage stage. Similar shrinkage stage is also observed in field tests. The buoyancy method can reflect the entire early-age deformation process of CA mortar with AP. This method is more suitable for engineering applications than the graduated flask method which is standardized in the specifications of China. [ABSTRACT FROM AUTHOR]

• The hydration, structural build-up and strength development of cement pates with different accelerators were investigated. • Accelerators increase the structural build-up rate by different mechanisms. • Mechanical efficiency of C-S-H may give wrong ranking on the efficiency of C-S-H. Fast structural build-up and strength development of fresh/hardened cement-based materials are always desired in many scenarios, where accelerators are often used. In this paper, the hydration, structural build-up and strength development of cement pates with different accelerators were investigated. The growth of static yield stress was used to characterize the structural build-up of fresh cement paste with 1% nano silica. Calorimetric curves, zeta potential and conductivity of pastes and strength development of mortars were also measured. Results showed that accelerators promote the reaction of C 3 S or C 3 A at different stages and in different mechanisms. Mechanical efficiency of C-S-H determined by growth of elastic modulus or yield stress over cumulated hydration heat may give wrong ranking on the efficiency of C-S-H. Apart from formation of C-S-H gel, structural build-up may originate from other sources. [ABSTRACT FROM AUTHOR]

The major crystalline phases in magnesium oxychloride cement (MOC) have been extensively studied, but the other phases have not been studied due to the difficulty in identifying them. In the current study, we focused on the effect of chlorine‐containing phases other than crystalline oxychlorides on the strength of cured MOC materials. The alcohol leachable chloride (ALC) was proposed to characterize the other phases containing chlorine, and the absolute ethanol leaching test was developed to determine ACL content in a cured MOC paste. The results showed that either decreasing MgO/MgCl2 molar ratio or increasing H2O/MgCl2 molar ratio led to an increase in ALC content in cured MOC slurry, but adding a small amount of phosphoric acid resulted in very little or almost no ALC in the modified MOC slurry. In addition, increasing ALC content has been shown to significantly reduce the compressive strength of hardened MOC pastes. Thus, the modified MOC pastes had high strength, compared with the corresponding common MOC pastes. According to the experimental results, the relationship between the ALC content and the compressive strength of cured MOC materials was established. Therefore, a low ALC content was proposed as a characteristic index of high‐quality MOC materials. [ABSTRACT FROM AUTHOR]

Highlights • The effect of temperature on the structural buildup of cement pastes with various mineral admixtures was studied. • The hydration kinetics of cement paste was studied by boundary nucleation and growth model. • The relation between hydration kinetics and structural buildup was analyzed. Abstract The temperature dependence of structural build-up is of great importance to some new concrete technologies, such as 3D printing and slip-form casting concrete. In this paper, the structural build-up of cement paste with various mineral admixtures, characterized by the growth of static yield stress, were measured at 10, 20 and 40 °C. They were related with the calorimetric curves of cement paste at various temperatures. Nucleation kinetic (K N) and growth kinetic (K G) were introduced to analyze the hydration dynamics. The results showed that the addition of fly ash and slag were unfavorable for the structural build-up of cement paste at 10 and 20 °C, however, a favorable phenomenon was observed at 40 °C. The additions of nano-CaCO 3 or nano-SiO 2 had positive effect on structural build-up at all temperatures. The incorporation of silica fume had negative effect on structural build-up at 10 °C, while positive effect at 20 and 40 °C. Both the K N and K G played important roles on the structural build-up rate of cement paste. K G contributed more to the temperature dependence of structural build-up than K N. [ABSTRACT FROM AUTHOR]

• The performance of calcined CSMR as a new SCM was corroborated. • Fresh and hardened properties of blended cement-based materials were examined. • Calcined CSMR exhibited higher reactivity than siliceous fly ash. • Cement composites with 20% calcined CSMR showed desired engineering performances. • Adding calcined CSMR reduced the environmental footprints of the final products. Supplementary cementitious materials (SCMs) have been widely used in modern concrete technology to improve the sustainability and performance of concrete, but the concern over the decreasing supply of conventional SCMs in the future raises a need to explore their alternatives. This study aims to corroborate the performance of a calcined solid waste, i.e., cutter soil mixing residue (CSMR), as a new SCM in sustainable cementitious materials. The rheological behaviors, hydration kinetics, pore structures, physico-mechanical properties, and durability of cement paste and mortar blended with calcined CSMR were experimentally investigated. Results showed that the calcined CSMR powders with a lower specific surface area than the cement particles could improve the flowability of the cement paste. The calcined CSMR exhibited higher reactivity than the coal fly ash and could accelerate the cement hydration, create additional hydrates, and refine pore structures. Adding 20% calcined CSMR in the cement mortar had negligible adverse effects on the compressive strength, dry shrinkage resistance, electrical resistivity, and sulfate attack resistance. Meanwhile, the incorporation of 15–30% calcined CSMR reduced the embodied energy and carbon emissions of the cement mortar by around 13–25%. Overall, this research demonstrated the possibility of using calcined CSMR as a new SCM to develop greener cementitious materials without compromising the engineering properties. [ABSTRACT FROM AUTHOR]

This paper focuses on developing strain-hardening cementitious composites (SHCCs) with a new alkali-activated cement (AAC). The AAC was synthesized with a calcined solid waste, i.e., cutter soil mixing residue (CSMR), as a primary precursor. The test variables included the water-to-binder (w / b) ratio and silica modulus (M s) of alkali activators. The binder chemistry, mechanical performances, and micromechanical parameters of the new SHCCs were investigated. Results demonstrated that a moderate w / b ratio with a high M s value favored the trade-off between the quantity of alkali-activated hydrates, matrix properties, and fiber bridging behaviors, leading to optimal overall macroscopic performances of the composites. The SHCCs with proper mix design exhibited high tensile strain capacities of 4.43–5.13% and sufficient compressive strengths at 3 days (23.6–28.9 MPa) and 28 days (32.7–56.3 MPa). Compared to Portland cement-based SHCCs, the new SHCCs achieved comparable mechanical properties, while possessing around 20% less embodied energy and 40% less CO 2 emissions. [ABSTRACT FROM AUTHOR]

Air bubble stability in cementitious materials in low air pressure (AP) environments is influenced by the Ostwald ripening process, which causes coarsening behavior of air bubbles. This research reports the enhancement of air bubble stability in low AP via the adoption of rheology and surface tension methods. Besides, the evolution of air bubbles during the cement early hydration process is proposed. It was found that incorporating viscosity-modifying agents (VMAs) and shrinkage-reducing admixtures (SRAs) resulted in improving air bubble stability by 37.7 % and 23.4 %, upon undergoing AP change from 100 to 60 kPa. Calculation of air bubbles via ripening equations under low AP revealed that VMA induced a notable decrease in the effective diffusion flux within fresh cement mortar, leading to a reduction of 9.8 % in air bubble ripening within 120 min. Conversely, SRAs were primarily aimed at reducing the initial dimensions of air bubbles. [ABSTRACT FROM AUTHOR]

Pore solution expression (PSE) is the most commonly used method to obtain the aqueous phase in cementitious material. However, the high pressure applied on the sample during PSE can affect the composition of the solid phase. An experimental study on the chemical and mineral composition of cement paste before and after PSE was conducted. The results indicate that a small part of the alkali contained in the samples was excluded during PSE, depending mainly on the alkali concentration in the pore solution. Due to the expulsion of interlayer water in calcium silicate hydrate under high pressure, PSE reduced the bound water content (measured by thermogravimetric analysis (TGA)). The portlandite content determined by TGA was not affected by PSE, but it led to an overestimation of portlandite by means of quantitative X-ray diffraction, because of the enhanced preferred orientation of the (001) plane under the applied high pressure. In addition, the size of the portlandite crystals decreased to some extent due to the creep caused by pressure. The content of the hemicarbonate phase was found to decrease slightly after PSE, which may be due to increased solubility under high pressure. [ABSTRACT FROM AUTHOR]

Workability and early-ages mechanical properties are important indicators of magnesium potassium phosphate cement (MKPC) as a repair material. The effect of metakaolin (MK) on the setting time, fluidity and early-ages strength of MKPC paste was studied, and its influence mechanism was analyzed through pore structure, microstructure and nanomechanical properties. The results show that 10% and 20% of MK prolong the setting time of MKPC paste, but excessive MK shortens the setting time of MKPC paste. Meanwhile, incorporating MK reduces the fluidity of MKPC paste, and the early-ages strength of MKPC specimens increases when the substitution ratio of MK is 10%. When 10% of MK is incorporated to the MKPC paste, the 30-d shrinkage of the sample is only 69% of the control group. Meanwhile, a proper amount of MK can improve the pore structure of the MKPC specimen and make its microstructure denser by generating amorphous aluminosilicate phosphate gel. It is observed from the nano-scale characteristics that incorporating 10% MK can reduce the content of pore phase and unreacted MgO phase, and increase the volume fraction of hydration products. [ABSTRACT FROM AUTHOR]

• Mechanical properties of PVA-FRCCs with calcined CSMR were investigated. • Binder chemistry, matrix properties, and fiber bridging behaviors were studied. • Calcined CSMR can significantly improve the tensile strain-hardening properties. • Enhanced fiber–matrix interface by calcined CSMR was demonstrated. In this paper, a cutter soil mixing residue (CSMR), which is a soil–cement solid waste, was calcined and then used as a partial cement replacement in polyvinyl alcohol fiber reinforced cement composites (PVA-FRCCs). The binder chemistry was characterized using XRD, TGA and FTIR. The fiber–matrix interfacial properties were examined with SEM. The composite mechanical properties, including compressive strength, flexural properties and tensile behaviors and fiber bridging stress-crack opening relationships, were investigated. Results showed that the calcined CSMR can produce additional hydrates to aid the strength gain and densify the fiber–matrix interface. With a cement replacement level up to 40%, the tensile strength was not compromised, while the tensile strain capacity significantly increased to a maximum value of 3.2%. The micromechanical analysis revealed that the improved strain capacity is mainly attributed to the optimized fiber–matrix interface yielding enhanced pseudo strain-hardening indices. The results obtained in this study indicate that calcined CSMR is an attractive novel supplementary cementitious material for developing greener strain-hardening cementitious composites. [ABSTRACT FROM AUTHOR]

• The effect of roughness on bonding performance between old OPC concrete and new MPC concrete was studied. • Fractal dimension was used to define the roughness of the bonding surface. • Roughness has significant influence on the bonding strength and microstructure of interface between new and old concretes. This paper investigated the bonding performance between magnesium phosphate cement concrete (MPC) and ordinary portland cement concrete (OPC) with different roughness. The bonding interface was characterized using fractal dimension, backscattered electronic microscopy, and microhardness. The optimal mixture proportion of MPC is selected with the mass ratio of MgO-KH 2 PO 4 (M/P) by 3:1 and Na 2 B 4 O 7 ·10H 2 O-MgO (B/M) by 40%, which has the compressive strength of 52.8 MPa and the initial setting time of 24 min 20 s. It is found that the roughness indicated by fractal dimension has a positive correlation to rough depth and the bonding performance. The bonding interface can be categorized into two forms that either MPC paste bonds to OPC paste or bonds to the aggregate. Micro-analysis shows that the former has denser hydration products and lower porosity, providing better chemical bonding and the latter contributes to the mechanical interlocking which is the major form of the bonding force. MPC is a potential material for the field application of wet joints of the floating slab tracks. [ABSTRACT FROM AUTHOR]

• The limited fractal behavior in cement paste is discussed. • Two modules of ordinary and multiscale fractal are adopted. • Pore structure in cement paste is well reconstructed. The fractal nature of cement paste has been discussed a lot in recent decades. Most of studies are concentrated on ordinary fractal dimension of a complete fractality, while an incomplete or limited fractality is exhibited in fact. This paper presents some results towards a comprehensive understanding about the limited fractal behavior in cement paste upon the mercury intrusion porosimetry test. To that end, two modules of analysis are adopted, i.e., the ordinary fractal and the multiscale fractal. Moreover, ordinary and multiscale fractal models are introduced to simulate pore structure, and pore size distributions are compared among ordinary fractal model, multiscale fractal model and test. Results indicate that multiscale fractal provides a much richer and preciser way than ordinary fractal to describe the limited fractal behavior in cement paste even it may deviate far from perfect fractaltiy. [ABSTRACT FROM AUTHOR]

Pore solution expression is a widely accepted approach to extract pore solution of cement-based materials by appllying high pressure. In this study, the variations of pore solution distribution and chloride content in cement pastes before and after pore solution expression were examined. The results showed that the value of chloride concentration index N c were mostly higher than 1.0 for cement pastes immersed in NaCl solution, and decreased with the chloride concentration of soaking solution and water-to-binder (w/b) ratio. During the pore solution expression, the pores larger than 40 nm were totally removed and the porosity of smaller pore was decreased. Based on a proposed physical model on structure of cement paste, the value of N c was calculated according to the variations of pore structure and chloride content during pore solution expression. The calculated results showed similar trend as the experimental results obtained by pore solution expression method. [ABSTRACT FROM AUTHOR]

The workability of cement asphalt (CA) mortar plays a key role in the construction quality and durability of the parking layers in the slab track structure of high speed railways of China. Whereas, the workability of CA mortar is mainly controlled by the rheology of CA paste. In the present paper, the rheological curves of CA paste were measured at 25 °C using a rotating coaxial cylinder viscometer. The Bingham, modified Bingham, Herschel–Bulkley and Casson rheological models were used to fit the data of shear stress–shear rate. The mechanism of the rheological behavior of CA paste was analyzed. The results show that the Hereshel–Bulkley model, which is usually applied for cement pastes, is also the most suitable model for CA paste. The yield stress, consistency index and non-Newton index of CA paste are influenced by the Zeta potential of particles and strengthen of flocculated structure. [ABSTRACT FROM AUTHOR]

This review summarizes the interaction between cement and asphalt emulsion from two aspects: the adsorption of asphalt emulsion on cement grains and the destabilization of asphalt emulsion by cement hydration. [Display omitted] • The adsorption abilities of cement for two types of asphalt emulsion are analyzed. • Both of the physical and chemical interaction mechanisms are summarized. • Effect of interaction on various properties of CA paste are evaluated. • Future research is recommended to develop the high-performance CA composites. Cement asphalt emulsion (CA) composites which integrate the advantages of both rigidity and flexibility, have been widely used as the key materials in ballastless slab track, semi-flexible base, cold recycling of asphalt pavement. The critical properties of both fresh and hardened CA paste are greatly depended on the interaction between cement and asphalt emulsion, which is reviewed in this paper. The interaction mechanisms are summarized from two aspects: the adsorption of asphalt emulsion on cement grains and the destabilization of asphalt emulsion by cement hydration. The main influencing factors and evaluation methods for both the physical and chemical adsorption of asphalt emulsion, and interaction with Ca2+ are introduced. Meanwhile, the influencing mechanisms of interaction on asphalt emulsion demulsification, cement hydration and rheology of CA pastes are analyzed. Last, the prospective direction for research is also suggested. [ABSTRACT FROM AUTHOR]

• The XCT and MIP tests provide a quantitative description of pore structure. • A general modeling framework of molecular diffusion is proposed. • A two-level hybrid analytical-numerical algorithm is implemented. Diffusion phenomena such as the ingress of various deleterious ions are of crucial importance to the service life of reinforced concrete. A physical parameter, i.e., the molecular diffusion coefficient or diffusivity is often used to define the diffusion rate. To date, the determination of molecular diffusivity remains a challenging issue, though numbers of laboratory tests and modeling methods have been developed. This paper is to present a general modeling framework of molecular diffusivity in cement paste. The necessary inputs come from the usual tests of X-ray computed tomography and mercury intrusion porosimetry, while a two-level hybrid analytical-numerical algorithm is proposed. At the voxel level, a general expression of modified Archie's equation is derived upon a combination of tortuosity model and fractal theory. At the cement paste level, a finite element method is adopted for the sake of homogenization. It is shown that the general modeling framework can be a good alternative to predict the molecular diffusivity in cement paste from the knowledge of structural feature as determined through experiments. [ABSTRACT FROM AUTHOR]

• A-PAM can be adsorbed onto the surface of cement particles until a saturation point is reached. • The retardation and bridging effect generated from A-PAM jointly affect the early properties of cement. • The relationship between the adsorption, retardation of A-PAM and the early properties of cement paste was discussed. Deep understanding of the influence and mechanism of A-PAM on the early properties of the cement-based materials is of both scientific and practical importance. In this paper, the effects of anionic polyacrylamide (A-PAM) with different mass ratios on the early properties of cement, including hydration, structural build-up, setting time and early strength development were studied. The interaction between A-PAM and cement particles was also investigated. The relationship between the adsorption, retardation of A-PAM and the early properties of cement paste was then discussed. The results showed that the retardation and bridging effect generated from A-PAM jointly affect the early performances of cement. A-PAM can be adsorbed onto the surface of cement particles until a saturation point is reached. When the A-PAM dosage is below the saturation point, A-PAM mainly acts as flocculant, bridging cement particles and increasing the connection between cement particles. This accelerates the structural build-up and setting of cement paste. When the A-PAM dosage is above the saturation point, the dominant role of A-PAM is retarder, which highly retards the cement hydration and setting, thus slows down the structural build-up and reduces the early strength. [ABSTRACT FROM AUTHOR]

Water extraction method has been widely applied to determine the free chloride content in cement-based materials. This paper studies the effects of different extraction time, curing ages and w/b ratios on the obtained free chloride content of seawater cement paste with low water-binder ratio by water extraction method. An appropriate testing process of water extraction method for pore solution acquisition and measurement of cement paste with low water-binder ratio is determined and the results are compared with that obtained by pore pressing method. The results show that the water extraction test is suitable for free chloride measurement of cement-based materials with low water-binder ratio by controlling the extraction time within a certain range about 3 min. The obtained results by water extraction with 3 min of extraction time are comparable to those obtained by pore pressing method. However, the physically bound chloride content decreases after water extraction and pore pressing tests, which indicates that the water extraction and pore pressing methods overestimates the free chloride content in cement-based materials. The effect of w/b ratio and curing age on the accuracy of this method is not evident. [ABSTRACT FROM AUTHOR]

• This study focused on the microstructure deterioration of MKPC in solutions. • LF-NMR was introduced for the first time to observe the degradation process of MKPC. • The coarsening process of micropores in MKPC was detailed by LF-NMR in-situ. Low-field 1H nuclear magnetic resonance (LF-NMR) is applied to investigate water instability of magnesium potassium phosphate cement (MKPC) mortar immersed in neutral and alkaline solutions, aiming to introduce a in-situ monitoring of microstructure to demonstrate the deterioration process of MKPC mortar. By tracking the evolution of water bearing pore, the deterioration is well characterized, and mainly attributed to the coarsening of micro-pores in the K-struvite network. Compared with tap water, 2.5 wt% NaCl and MgSO 4 solutions, dramatical deterioration of strength and microstructure are detected in the MKPC mortar exposed in 2.5 wt% NaOH solution. In addition, the millimeter sized water cavity is formed due to the opening of the spherical closed pores in the later exposure stage in both neutral and alkaline solutions. [ABSTRACT FROM AUTHOR]

• SCE method is a convenient, reliable and environmental friendly method. • SCE method can determine sulfate ion content in CSA cement based materials. • SCE method is improper for PO cement due to sulfate ion could be trapped by C-S-H. The penetration of sulfate ions into the concrete often causes durability problems such as spalling, cracking, and strength loss. Traditional methods for sulfates content test in cement-based materials, a large number of toxic and high-risk chemical reagents such as hydrochloric acid, barium chloride, barium chromate are used. In this research, the sodium carbonate extraction (SCE) method was used to determine the sulfates content in Ordinary Portland cement (OPC) and Calcium sulphoaluminate (CSA) cement while the gravimetric method was used as standard method to evaluate the accuracy of SCE method. The optimum SCE method operation conditions were determined as 0.30 mol/L sodium carbonate solution, liquid–solid ratio at 100:1 and particle size smaller than 500 μm. The results indicated that the replacement of gravimetric method with SCE method for sulfates content test is acceptable in CSA cement but improper for Portland cement system. Through the FTIR, XRD, and TG-DSC analysis, it was found that the absorption of sulfate ions by C-S-H gels was responsible for the failure of SCE method in Portland cement system. [ABSTRACT FROM AUTHOR]

In this study, the sulfate attack on uncarbonated cement paste partially exposed to Na2SO4 solution was experimentally investigated and compared with that on carbonated specimens with the same exposure regime and uncarbonated specimens without exposure. N2 was used to protect specimens from carbonation throughout the sulfate exposure period. The effects of the water-to-cement (w/c) ratio and the fly ash as cement replacement on the sulfate attack were evaluated. Portland cement paste specimens with different w/c ratios of 0.35, 0.45, and 0.55 or fly ash replacement rates of 10%, 20%, and 30% were prepared. These specimens were partially immersed in 5% Na2SO4 solution for 50 d and 100 d exposure periods. The micro-analysis was conducted to evaluate the effect of the partial sulfate attack on the uncarbonated cement paste using X-ray diffraction (XRD) and thermo-gravimetric (TG) techniques. The results confirmed that, for uncarbonated cement paste, the chemical attack rather than the physical attack is the deterioration mechanism and is responsible for more severe damage in the evaporation zone (dry part) compared with the immersed zone (immersed part). When the effect of carbonation is well excluded, there is an optimal w/c ratio of 0.45 for minimizing the sulfate attack, while incorporating fly ash tends to reduce the sulfate attack resistance. [ABSTRACT FROM AUTHOR]

The paper compared the tensile strength and elongation at break of cement–emulsified asphalt–standard sand (CAS) mortar and cement–emulsified asphalt–rubber particle (CAR) mortar. The tensile properties of CAS and CAR mortars were investigated. Microscopic analysis was carried out by Environmental Scanning Electron Microscopy and Energy Dispersive Spectrometer. The test results showed that the tensile strength of the CAR mortar at 7 days improved by about 9.09% higher than that of the CAS mortar, and further increased to 17.76% higher at 28 days The values of elongation at break of the CAR mortars at 3 days, 7 days, and 28 days increased by about 70% higher than those of the CAS mortars. Microscopic analysis showed that in the hardened CAS mortar, an obvious bubble accumulation layer with many pores appeared at the interfacial transition zone (ITZ). In the hardened CAR mortar, asphalt wrapped both cement hydration products and rubber particles and formed an integrated structure where a relatively dense and strong ITZ was formed as a result. This paper proves that the CAR system has superior tensile properties and has a promising future in waste rubber disposal. [ABSTRACT FROM AUTHOR]