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To explore the modification of rheological behavior of fresh cement paste by in situ polymerization, the rheological properties of fresh in situ polymerization modified cement (IPMC) pastes with various acrylamide (AM) monomer dosages and resting time were investigated by rheology test in this paper. The interaction mechanism between inorganic-organic components of IPMC paste and its influence on rheology are also discussed. The results revealed that the yield stress and plastic viscosity of fresh IPMC paste decreased as the AM dosage increased, and rose rapidly with the resting time when the AM dosage was more than 5%. The time-dependent rheological properties of IPMC paste were associated with various periods of AM polymerization reaction. This paper also found that the dispersing effect produced by the AM adsorption and the flocculating effect generated from the polyacrylamide (PAM) microgels bridging would jointly impact the structural buildup of IPMC paste; the former improved the rheological properties and fluidity, while the latter acted contrary. Our results provide the underlying insights needed to guide the dynamic regulation of rheological properties of cement-based materials by in situ polymerization modification. [ABSTRACT FROM AUTHOR]

Magnesium oxychloride cement (MOC) is an eco-friendly cementitious material with a fine prospect in construction and protection engineering. A full understanding of the time-dependent rheological behavior of MOC paste is crucial to many applications. In this study, the shear flow curves of MOC pastes with various H 2 O/MgCl 2 molar ratios were tested at different reaction times. The setting process of MOC paste was characterized by the time evolution of storage modulus (G′). Results indicate that the rise of the H 2 O/MgCl 2 molar ratio reduces the dynamic yield stress and plastic viscosity while leading to a more prominent shear-thinning behavior. The formation of crystalline 5-phase greatly accelerates the development of rheological parameters. The evolution of G′ reveals that the setting process of MOC paste includes five stages, which are governed by the gradual rigidification of 5-phase linkages among particles and the dynamic evolvement of electrostatic repulsion induced by the ionic composition changes of interstitial solution. Moreover, the rise of the H 2 O/MgCl 2 molar ratio is found to weaken the mechanical efficiency of 5-phase in the setting process. • The impact of 5-phase crystallization on the rheological properties of MOC paste was investigated. • The setting process of MOC paste was characterized by the growth of storage modulus. • The evolution of storage modulus derives from the 5-phase linkage formation and the changing electrostatic repulsion. • The rise of H 2 O/MgCl 2 molar ratio weakens the mechanical efficiency of 5-phase during setting. [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]

Pumping changes the rheological properties, workability and construction performance of fresh concrete. However, there were limited knowledges on influences of discharge rates and pumping distances on the fresh properties of concrete. In this paper, effects of various discharge rates and pipeline lengths on rheological properties of self-consolidating concrete (SCC) after pumping were studied. A total of 12 SCC mixtures with the slump flow of 650–745 mm were pumped in pipelines with measured lengths of 342 m, 545 m, and 1044 m by constant discharge rates ranging between 5.1 and 11.4 L/s. Rheological properties were measured before and after pumping. Physical conditions of SCC during pumping, including pressure, shear, and temperature were estimated theoretically and experimentally. Moreover, the total organic carbon in the pore solution of SCC mixtures was measured to evaluate the change of superplasticizer adsorptions after pumping. Test results indicated that, due to pumping, the yield stress increased; the initial tangential viscosity decreased and the shear-thickening phenomenon was eliminated. The changes of yield stresses and viscosity were encouraged by discharge rates. Besides, lower initial slump flow of SCC exhibited a larger slump flow loss after pumping due to a higher shear rate experienced during pumping. The yield stress and viscosity after pumping increased with the increase of pipeline length at similar discharge rates, but decreased with the pipeline length under similar pumping pressures. The adsorption of superplasticizer increased after pumped at relative low discharge rates (5.2–5.7 L/s), but decreased at discharge rates of 7.7–10.8 L/s. [ABSTRACT FROM AUTHOR]

• The rheological properties of LHC pastes with MEA and SRA were studied. • The variations of dynamic yield stress and plastic viscosity were estimated by response surface methodology. • The roles of MEA and SRA on the static yield stress development of LHC pastes were investigated. The combined use of low heat Portland cement (LHC), MgO-based expansive agent (MEA) and shrinkage reducing admixture (SRA) is beneficial to reduce the cracking risk of concrete. In this study, the effects of MEA and SRA on the rheological behaviour of LHC paste were investigated using dynamic and static shearing tests. The response surface methodology was used to estimate the effects of MEA, SRA, and superplasticizer on dynamic rheological parameters, while the zeta potential, calorimetric, and solid phases tests were conducted to explore the mechanisms of time-dependent rheological behaviour. Results indicate that MEA contributes to higher dynamic yield stress and plastic viscosity, while the effect of SRA is dependent on its dosage. MEA promotes the static yield stress development for accelerating the hydration of blends and the formation of Mg(OH) 2. SRA retards the hydration of LHC and blended paste and reduces the number of main hydration products. However, the static yield stress is further increased by SRA, showing a consistent changing trend with the surface area of hydrated particles. [ABSTRACT FROM AUTHOR]

• Resistivity evolution of fresh HSC were measured to characterize the early age hydration process in HSC. • Influence of pumping on early age hydration in HSC were evaluated. • Changes in dynamic yield stress of HSC after pumping were related to corresponding changes in hydration process. The pumping process exerts high pressure and strong shearing on fresh concrete, which may affect the hydration process and rheological behavior of concrete. In this paper, full-scale pumping circuits with lengths of 348-, 600-, and 924-m were established to evaluate the effect of pumping on hydration and rheology of concrete. Electrical resistivity measurement was employed to indirectly evaluate the hydration process of concrete. Ten high-strength concrete (HSC) mixtures with slump flow of 680 ± 50 mm and strength grades of C60-C100 were pumped, and HSC mixtures were sampled before and after pumping for rheological properties and electrical resistivity measurements. Findings indicated that the hydration process, determined by the electrical resistivity evolution, was accelerated after pumping. The end of the dormant period of fresh concrete was decreased by 10.3%-27.3%, and the end of the setting period was shortened by 15.6%-28.4% after pumping. The reduction in the dormant period can be well correlated with the drop in slump flow or increase in dynamic yield stress after pumping. [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]

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]

Pumping is a widely used placement means for concrete construction, but both fresh and hardened property changes in concrete due to pumping. In this review, the effects of pumping on both the fresh and hardened properties of various concrete mixtures are presented in terms of each specific characteristic. Analyses of data from the published literature showed that the air content of fresh concrete is altered after pumping. The general trend in the change in rheological properties of fresh concrete due to pumping was also determined, and the mechanisms of this trend were discussed. Moreover, the improvement in the compressive strength of hardened concrete was investigated, which is considered to result from the pumping-induced hydration acceleration and the air content variation. Finally, changes in the durability of hardened concrete were discussed, and future research topics were suggested. [ABSTRACT FROM AUTHOR]

The influence of pumping on the rheological properties of self-consolidating concrete (SCC) is widely recognized, but there is still limited understanding of its behavior within the pipeline. In this study, we propose a novel approach using equilibrium distances to investigate the evolution of rheological properties along the pipeline. Full-scale horizontal pumping circuits spanning 328 m were established to assess the axial development of SCC's rheological properties. Thirteen mixtures, with water-to-cement (w/c) ratios ranging from 0.22 to 0.27, were pumped at discharge rates varying from 5.77 to 12.69 L/s. Our findings show that for pumping setups and material studied, both the w/c ratio of SCC and the discharge rate significantly affected the influence of rheological equilibrium distances on pressure loss gradient changes. In all tested samples, viscosity values required the entire length of the pipeline to reach post-pumping levels, while yield stress values rapidly achieved their fully developed state upon entering the pipeline. Importantly, the predicted pressure loss displayed a strong correlation with experimental measurements, with an accuracy of 89.42% across all tested mixtures. Our predictive model showed an average improvement of 4.6% in accuracy compared to the linear approach, with the most significant enhancement observed in samples with higher w/c ratios. This research sheds new light on the behavior of SCC during pumping and provides valuable insights for optimizing the pumping process. • The equilibrium distance of rheology is introduced to describe SCC flow behavior along the pipeline. • Horizontal pumping circuits spanning 328 m is used. • Factors affecting the equilibrium distance of rheology are discussed. • The prediction accuracy of the model is validated. [ABSTRACT FROM AUTHOR]

The pumping pressure loss of fresh concrete has traditionally been modeled as a linear function of the pumping distance. However, previous studies have suggested that this relationship is nonlinear in nature. This research has identified that the nonlinearity is due to changes in the rheological properties of fresh concrete during pumping. In this study, a new prediction equation has been proposed for the loss of pumping pressure for concrete mixtures with w/c ratios between 0.17 and 0.46, and an equivalent horizontal pipe length between 328 and 912 m. The equation provides a linear approximation of the nonlinear relationship of pumping pressure loss. To account for the effect of rheological changes during pumping, an empirical coefficient related to the initial slump flow of the concrete has been incorporated. The new function can improve the prediction accuracy of pressure loss by 25 % and 4.2 % for horizontal and vertical pumping, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • The role of CGS on the workability of cement paste with and without PCE was investigated. • The decrease of interparticle force leads to the improvement of fluidity when added CGS. • The aggregation of PCE in pore solution leads to its efficiency decrease in the cement pastes blended with CGS. Coal gasification slag (CGS) is the main by-product of coal gasification technology, and the utilization of CGS as mineral admixture is environmentally sound. In this paper, the effect and mechanisms of CGS on the workability (i.e., fluidity and rheological behaviors) of ordinary Portland cement (OPC) paste with and without polycarboxylate superplasticizer (PCE) were studied. The zeta potential and surface free energies of OPC and CGS were tested to calculate the electrostatic force and Van der Waals force variations due to the addition of CGS particles. The results revealed that CGS mainly decreases the van der Waals attraction force between binder particles, enhancing the fluidity and reducing cement pastes' yield stress and plastic viscosity. When blended with PCE, the dissolution of CGS mainly increased the ionic concentrations of Si(OH) x (4-x), which promoted the aggregation of PCE and decreased its adsorption, thus decreasing the fluidity and increasing the rheological parameters. [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]

Fresh concrete needs vibration to compact, fill the mould and reach a dense state. During the compaction process, coarse aggregates (CAs) tend to settle, affecting the homogeneity and eventually the long-term durability of hardened concrete. In this study, a 3-D, multi-phase numerical model for fresh concrete is developed for better understanding the CA settlement under vibration. The settlement rate of the CA in vibrated concrete is considered based on the Stokes law, and the calibrated rheological parameter of mixtures is determined by the segmented sieving method. The model prediction shows that the vibration time has the greatest effect on CA settlement, followed by the particle size of CAs, whereas the density of CAs and the plastic viscosity of mixtures contribute a little compared with the aforementioned factors. Through experimental tests, the validity of prediction results is well verified. The proposed model provides a new method to understand and estimate the settlement behaviour of CAs. [Display omitted] • A rheological problem of cement-based materials has been studied both experimentally and numerically. • Numerical method is developed for the first time to investigate aggregate settlement in vibrated concrete. • The proposed model is verified by the experiments based on segmented sieving method. • Grey relational analysis is performed to study the influence of related factors on CA settlement. [ABSTRACT FROM AUTHOR]

Many alkali-activated materials (AAMs) exhibit poor workability in mixing owing to great viscosity of the paste and fast setting. Chemical admixtures commonly used in Portland cement-based materials, such as rheology control additives and superplasticizers, show lower efficiency in AAM systems. Understanding the rheological features of various AAMs and their control can lead to a valuable guidance for their application in large-scale, especially in the field of pumping and placement, grouting and 3D printing, etc. This paper aims to deliver a comprehensive review of the effects of composition factors including activators, precursors, admixtures, additions, aggregates and fibers on the rheology of AAMs, as well as models for describing their rheological behavior. The current progress has shown that the large knowledge gap needs substantial research from scientific mechanisms to robust formulations of paste, mortar and concrete to meet both workability and mechanical requirements. [ABSTRACT FROM AUTHOR]