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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]

Epoxy adhesives for concrete cracks repair may necessitate the addition of reactive diluent to decrease their viscosity. However, research on the effect of different reactive diluents on the various properties of epoxy adhesives remains insufficient. In this paper, three reactive diluents, including monofunctional alkyl C12–C14 glycidyl ether (AGE), butyl glycidyl ether (BGE) and difunctional 1,4-butanediol diglycidyl ether (BDDE) are utilized to comparatively study the different effects on the viscosity, exothermic temperature, mechanical properties, and bond strength with cement mortar of the adhesives. The results show that the addition of BDDE increases the maximum curing temperature of the adhesives, whereas AGE and BGE both causes a decrease. The epoxy adhesive with AGE or BGE shows greater ultimate tensile strain, but a more obvious reduction in Young's modulus than that with BDDE at the same concentration. BDDE improves the bond strength of the adhesive-mortar interface whereas AGE and BGE both decrease it. Moreover, the bond strength shows a positive correlation with the hydroxyl content on the surface of cured epoxy. Comparing with AGE and BGE, BDDE increases the hydroxyl content, resulting in the strongest bond strength. [ABSTRACT FROM AUTHOR]

• The leaching kinetics and related changes in mechanical behavior and microstructure of CA mortar were studied. • Three distinct zones in term of local calcium content in the direction of radius of the specimen were found. • Compressive behavior was modelled by the combination of compression damage model degradation damage model. Calcium leaching is an important durability problem for cement asphalt (CA) mortar used in ballastless slab track. In this paper, calcium leaching in CA mortar was accelerated by immersing in 6 mol/L ammonium nitrate solution. The leaching kinetics and related changes in mechanical behavior and microstructure of CA mortar were studied. Results showed that calcium leaching followed the Fick's law. The calcium leaching led to the formation of three distinct zones in term of local calcium content in the direction of radius of the specimen. Due to the leaching of calcium hydroxide and the progressive decalcification of C S H, the three zones had different chemical compositions. The compressive mechanical behavior was modeled by a compression damage model derived from Weibull distribution. The degradation damage model was established on the distribution of local elastic modulus. The combination of these two models can well predict the compressive behavior of partially leached CA mortar. [ABSTRACT FROM AUTHOR]

Cement asphalt (CA) mortar, a porous and organic-inorganic composite, has been widely used in high-speed rail. Since the high content of asphalt and its low strength, mercury intrusion porosity (MIP) may not be applicable to measure the complete pore structure of cement asphalt (CA) mortar. In this paper, nuclear magnetic resonance (NMR) relaxometry method was used to measure the pore structure of CA mortar with various water-to-cement (W/C) ratio and asphalt to cement (A/C) ratio. The porosity obtained by MIP under the pressure of 0–0.4 MPa was used to infer the surface relaxivity which is a key parameter for the calculation of pore size in NMR relaxometry method. Results showed that a value of 40 μm/s can be adopted as the surface relaxivity of CA mortar. Pore size distribution of CA mortars presented three peaks. The peaks did not shift with w/c ratios, but got higher with the increase in W/C ratios. Low A/C ratio leads to coarser pore structure of CA mortar. [ABSTRACT FROM AUTHOR]

Superabsorbent polymers (SAPs) combined with air-entraining agents (AEAs) were used to improve the frost resistance of mortar pepared under low air pressure in this study. Effects of SAPs combined with AEAs on the pore structure and frost resistance of mortar were investigated. Results showed that the combined use of SAPs and AEAs could improve the frost resistance of mortar made under low air pressure efficiently. This is further clarified by the changes of the pore structure. SAPs had a better performance in air-entraining as well as internal curing under low air pressure than those under a normal atmosphere. In addition, SAPs combined with AEAs could greatly optimize the pore structure of mortar prepared at low air pressure, especially reduce the number of pores larger than 200 nm. Moreover, correlations between pore characteristic parameters and frost resistance were discussed based on the linear fitting method and grey correlation analysis method. Finally, a modified hydraulic pore pressure model considering the influence of air pressure was established, and calculation results showed that the hydraulic pore pressure during freezing decreased due to low air pressure. • Effects of low air pressure on the pore structure and frost resistance of mortar were analyzed. • SAPs combined with AEAs were used to improve the performance of mortar made at low air pressure. • Correlations between pore structure and frost resistance of mortar made at low pressure were investigated. • A modified hydraulic pore pressure model considering the influence of air pressure was established. [ABSTRACT FROM AUTHOR]

Air entrainment in cement-based materials is believed to be affected by low air pressure (AP) which is the atmospheric characteristic in high plateaus, and thus the rheology may be affected. This paper attempts to study rheology and air entrainment of fresh Portland cement mortar in simulated low APs. The results indicate that the rheological responses with the varying AP gradients are relevant to the air entrainments in fresh mortar mixtures. The volume changes of air voids in fresh mortars are linearly related to the varying APs, which is owing to not only the AP difference between the inside and outside air voids but also the additional pressure on the liquid films of air voids stemming from the surface tension changes. Moreover, the Bingham capillary number is calculated to account for the air void deformability. Then rheological parameters are correlated to the content and deformability of air voids in fresh mortars. [ABSTRACT FROM AUTHOR]

The mix proportioning of extrusion-based 3D-printed cementitious material should balance printability and hardened properties. This paper investigated the effects of three key mix proportion parameters of 3D-printed alkali-activated fly ash/slag (3D-AAFS) mortar, i.e., the sand to binder (s/b) ratio, fly ash/ground granulated blast-furnace slag (FA/GGBS) ratio, and silicate modulus (Ms) of the activator, on extrudability, buildability, interlayer strength, and drying shrinkage. The results showed that the loss of extrudability and the development of buildability were accelerated by increasing the s/b ratio, decreasing the FA/GGBS ratio, or using a lower Ms activator. A rise in the s/b ratio improved the interlayer strength and reduces the drying shrinkage. Although increasing the FA/GGBS mass ratio from 1 to 3 led to a reduction of 35% in the interlayer bond strength, it decreased the shrinkage strain by half. A larger silicate modulus was beneficial to the interlayer bond strength, but it made shrinkage more serious. Moreover, a simple centroid design method was developed for optimizing the mix proportion of 3D-AAFS mortar to simultaneously meet the requirements of printability and hardened properties. [ABSTRACT FROM AUTHOR]

• 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]

• Buildability of 3D printing mortar was evaluated by the deformation of stacking layers. • A deformation monitoring device was designed to monitor the deformation of printing layer. • An equation between the optimal interval time and structural build-up rate was proposed. The buildability of fresh concrete is of great importance to 3D printing technology. In this paper, the buildability of 3D printing mortar was evaluated from the perspective of deformation of fresh mortar during the process of printing. A deformation monitoring device was designed to monitor the change of deformation of printing layer with stacking. The physical and chemical effects on the evolution of structural build-up were evaluated by the growth rate of static yield stress and penetration resistance. Results showed that the chemical effect was more effective than the physical effect, and the combination of physical and chemical effects was the most effective one. The growth of penetration resistance had a linear relationship with the growth of static yield stress, and both of them can be used to characterize the structural build-up of fresh mortar. The deformation value and optimal printing interval time could be obtained by simulating the printing process using the deformation monitoring device. An equation between the optimal interval time and the growth rate of static yield stress was established. [ABSTRACT FROM AUTHOR]

• The rheological properties of AAS pastes have been improved by low surface free energy mineral admixtures. • The surface free energy properties of low surface free energy mineral admixtures have been determined by IGC method. • The interparticle forces were calculated to reveal the mechanism for rheological improvement. This study investigates the effect of low surface free energy mineral admixtures (CaF 2 -dominated fluorite (FL) and fluorine-containing lithium slag (LS)) on the rheological behavior of alkali-activated slag (AAS) pastes. The fluidity, rheological behavior, surface charge properties and surface free energy properties were tested. The interparticle forces based on extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) theory were calculated to understand the mechanism for the rheological behavior improvement. The results revealed that both FL and LS could improve the fluidity and decrease the yield stress and plastic viscosity of AAS pastes. Furthermore, the attraction is manifested by the sum of electrostatic, van der Waals, and Lewis acid-base forces, and this value decreases with increasing LF or LS content, implying that the particle dispersion in AAS pastes is improved. Furthermore, observing flocculent structures captured by the metallographic microscope proves the better dispersion of AAS pastes after adding FL and LS. Moreover, incorporating LS or FL decreases the flexural and compressive strengths of AAS mortars. [ABSTRACT FROM AUTHOR]

Highlights • Effects of rotational shearing on rheology of mortars with glass fiber are investigated. • The shear-induced behavior of mortar with glass fiber depends on the matrix composition. • Fresh mortars with glass fibers easily exhibit shear-thickening behavior. Abstract Shear stresses are always applied to fresh concrete during mixing and transporting processes, which have significant influences on the dispersion and agglomeration of cement particles. In this study, the effects of rotational shear mixing on rheological properties of fresh short glass fiber reinforced mortars with different mineral admixtures (containing fly ash and silica fume) were experimentally investigated. The shear rates of 50 s−1, 100 s−1 and 150 s−1 were selected as the rotational shearing rates. The Herschel-Bulkley model was used to characterize the rheological behavior of fresh glass fiber reinforced mortar. Results showed that the shear-thickening intensity increased with the increase of glass fiber volume fraction for the cement-fly ash binary mortar, while the addition of glass fiber resulted in the rheological behavior of cement-silica fume binary mortar changed from shear-thickening to shear-thinning response. After subjecting to rotational shear mixing, the measured shear stress was significantly increased and the fresh mortars with glass fibers easily showed shear-thickening behavior. [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 study aims to formulate solid and aqueous compositions of hydrated Portland cement incorporated with reactive alumina (RA) via thermodynamic modeling, with the goal to prevent alkali–silica reaction (ASR). Based on SEM/EDS point analysis, the uptake of Al into C–S–H was corrected in the thermodynamic modeling to improve the accuracy. The predicted solid and aqueous compositions were validated by means of XRD, TGA, and ICP. An accelerated mortar bar test was also carried out to confirm the ASR mitigating efficiency, and a preliminary relationship among the ASR expansion, solid assemblage, and aqueous species was established. The critical content for RA is around 5.75% in the studied systems, above which katoite precipitates, resulting in increased Al concentration in the pore solution (∼0.8 mmol/L); hence, ASR can be effectively inhibited. [ABSTRACT FROM AUTHOR]

Water treatment sludge (WTS) management is a growing global problem, which is often disposed as a hazardous material in landfill space. This paper aims to use modified WTS as a novel supplementary cementitious material, by determining the effects of calcined WTS addition on the composition and performance of Portland cement composites. The effect of WTS to replace cement partially by weight on the mechanical properties and drying shrinkage of specimens has experimentally been studied, and the internal microstructure is also determined by scanning electron microscope and nanoindentation techniques. The results showed that mortar with 10% modified WTS presented higher 90-day compressive strength although specimens with 20% and 30% modified WTS showed 10.54% and 16.20% reduction compared to the control group. Meanwhile, the modified WTS has pozzolanic activity and can react with cement hydration products to increase the compactness of the microstructure, thereby reducing the drying shrinkage of the pastes (10% modified WTS). When 10% of the cement was replaced by modified WTS, the volume fraction of unhydrated clinker and pore phase in the matrix decreased significantly, while the volume fraction of C–S–H phase increased. In addition, the interface transition zone (ITZ) width of the specimen (10% WTS) is the smallest, and as the replacement rate of modified WTS increases, the ITZ width of the specimen increases significantly. This paper proves that the modified WTS, as a supplementary cementitious material, can be considered a feasible and sustainable alternative for use in the building materials. Image 1 • The modified WTS can be considered a feasible and sustainable alternative for use in the Portland cement. • The nano-scale characteristics of the mortar mixed with modified WTS are investigated by nanoindentation technology. • Mortar mixed with 10% modified WTS has good microstructure and mechanical properties. [ABSTRACT FROM AUTHOR]

• The bonding behaviors of the new-old mortar interface were studied. • The deterioration of the new-old mortar interface after coupled cycles was studied. • The microstructures of the new-old mortar interface were characterized. A well-bonded interface between concrete substrate and repair materials is of great significance for the durable repaired concrete. In this paper, the performance of the new-old mortar interface and deteriorations after wet-dry or heat-cool cycles were investigated by mechanical tests and microstructural analyses. Slant shear test, four-point bending strength test, back scattering electron microscopy (BSEM), microhardness test and thermogravimetric analysis (TGA) were carried out to characterize the interface deterioration. The results show that the slant shear test is suitable for evaluating the new-old mortar bond strength. The constituents of repair mortars affect the bond strength, but have little impact on the bending strength of composite beams. After cycled treatments, coupled effect of wet-dry and heat-cool cycles result in severer deteriorations of new-old mortar interface than heat-cool cycles do. Effect of heat-cool cycles is mainly attributed to reduction of interlocking point, while reductions in both interlocking point and chemical bond force are responsible for the interface deterioration after coupled cycles. The microstructural analyses further reveal the characterization of the new-old interface zone. [ABSTRACT FROM AUTHOR]

• Mortar bar incorporated with 30% glass powder exhibits good volume stability during external sulfate attack (ESA) test. • The pozzolanic reaction of glass powder significantly elevates the Na concentration and pH. • Elevated alkalinity of pore solution in sample with 30% glass powder leads to the dissolution of monosulfate. • The Pitzer model could give a reasonable estimation of the dissolution and/or precipitation trend of products formed during ESA test. Due to the presence of high alkali content, it is inferred that the improvement of sulfate attack resistance for blend with glass powder should not be solely ascribed to the refinement of microstructure. This study aims to explore the effect of glass powder on the pore solution and its relationship with the chemical sulfate attack process. Paste samples blended with 30 % wt. glass powder and quartz powder were prepared and subjected to a simulated external sulfate attack (ESA) test. To eliminate the effect of microstructure on sulfate ingress and alkali leaching, the pressed paste grains (after pore solution extraction) were immersed in test solution consisting of 5 % Na 2 SO 4 and extracted pore solutions during the ESA test. The evolution of the chemical composition of test solution and phase assemblage of pressed paste grains during the ESA test were quantitatively characterized. Results indicate that the improvement of sulfate attack resistance is related to the increase in alkalinity of pore solution. The high alkalinity of pore solution leads to the dissolution of monosulfate, which suppresses the formation of ettringite. The maintained high alkalinity reduces the saturation degree of ettringite, monosulfate and gypsum with respect to the pore solution, preventing it from precipitating even at a high sulfate ions concentration up to 0.5 M. This study highlights the effect of glass powder on alkalinity of pore solution and its relationship with stability of ESA products. [ABSTRACT FROM AUTHOR]

The stress relaxation behavior of cement and asphalt mortar (CA mortar) under different initial strain levels was investigated. Results show that the stress relaxation of CA mortar can be divided into two parts: the attenuation stress relaxation stage and stable stress relaxation stage. With the increasing strain levels, the relaxed stress, stress relaxation rate, stress relaxation modulus and specific stress relaxation of CA mortar increase gradually. Under the same initial strain level, the relaxed stress of type I CA mortar and type II CA mortar are little different, whereas the specific stress relaxation of type I CA mortar is much greater than that of type II CA mortar. In the strain range of 0.32–0.80%, the isochronous stress-strain relation of type I CA mortar is linear. When the strain is greater than 0.80%, the isochronous stress-strain relationship concaves to the strain axis gradually. The isochronous stress-strain relationship of type II CA mortar show linear increase in the strain range of 0.47–1.42%. A stress relaxation model based on thermodynamic theory was established, which agrees very well with the experimental results. [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 study aims to explore the impacts of alkali ions and aqueous Al species in pore solution on alkali-silica reaction (ASR). Wrapped accelerated mortar bar test (100% RH, 38 °C) was carried out on mortars prepared with binders containing various metakaolin (0% and 5%) and alkali content (Na 2 O eq = 0.65%, 1.25%, 2.25%, and 2.75%); solid and aqueous compositions of the corresponding hydrated pastes were analyzed using XRD and ICP-OES. A combined effect of alkali ions and aqueous Al species on ASR is identified, which can be characterized by a ratio of alkali (Na + K) to aluminum concentration in pore solution, and ASR expansion increases with this ratio. This finding provides new insights in understanding the relationship between pore solution composition and ASR, and indicates alternative approaches in controlling ASR, other than limiting alkalis content. [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]

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]