Properties Of Fresh Cement Paste Research Articles

C–S–H-PCE nanoparticles and anionic surfactants as nucleation agent in cement based materials: Focus on the antagonism

The small solid particles and surfactants inclusion have the potential to furnish abundant nucleation sites, yet the concurrent operation mechanisms in cement remain unclear. Thus, calcium-silicate-hydrate-polycarboxylate ether (C–S–H-PCE) nanoparticles and calcium stearate (CaSt2) all were introduced as composites nucleation agents in this work, and then the properties of fresh cement paste, hydration process and microstructure of hardened pastes were especially investigated. Experimental results demonstrated that C–S–H-PCE and CaSt2 enhanced cement hydration by utilizing their ability to provide nucleation sites, but they were less compatible. Therefore, the combination showed the antagonistic effects: a decrease in fluidity and compressive strength. The decrease in fluidity was mainly attributed to the lowered particle dispersion. The decrease in compressive strength was associated with a lower overall density and increased cumulative porosity of the C–S–H gels. This work establish the theoretical foundation for selecting components of green composite nucleation agents.

Impact of aragonite coral powder on hydration, strength, and rheology of cement paste

Understanding the intricate bonding mechanism between coral reef surfaces and C–S–H is crucial for advancing large-scale engineering applications. This study conducts a comprehensive analysis of the impact of coral powder (CP) on cement paste. Initially, zeta potential experiments were performed to probe ion adsorption from the cement pore solution at the CP interface. We propose a novel model to quantify the adsorption of Ca2+ by CP. Subsequently, the study delves into the morphological properties of C–S–H nucleation and growth at this interface and formulates an equation elucidating the CP and Ca2+ adsorption relationship. Then, the crack extension behavior of cementitious materials was scrutinized. Finally, an examination of CP effects on the rheological properties of fresh cement pastes is presented. The findings indicate that CP particles exhibit a notably weaker adsorption affinity with Ca2+ compared to their interaction with SO42−. Compared to limestone (LP), CP exhibited a 32.1 % reduction in Ca2+ adsorption in Ca(OH)2 solutions, 44.2 % reduction in Ca(OH)2 + 10 mmol/L K2SO4, and 40.6 % reduction in Ca(OH)2 + 50 mmol/L K2SO4 solutions. Higher zeta potential values correspond to stronger Ca2+ adsorption and broader surface coverage of Ca2+. The inferior surface characteristics of CP hinder C–S–H nucleation and growth, leading to a low CH orientation index in cement paste containing CP. These pastes exhibit cracks more frequently between CP and hydration products. An attractive force is observed between CP and cement particles, decreasing cement paste flowability.

Rheological Properties of Fresh Cement Paste Modified by In Situ Polymerization of Acrylamide Monomer

Rheological Properties of Fresh Cement Paste Modified by In Situ Polymerization of Acrylamide Monomer

Viscoelastic properties of fresh cement paste: measuring procedures and influencing parameters

Fresh cement pastes behave as viscoelastic materials below the flow onset. The measurements of viscoelastic properties of fresh cement paste provide valuable insight into the dispersion of solid particles as well as the hydration kinetics at early age and its influence on the structural evolution and solidification behavior at quasi-static conditions. Monitoring the development of viscoelastic properties of fresh cement paste using dynamic oscillatory shear measurements can also elucidate the working mechanisms of chemical admixtures. These properties are efficient indicators to guide mixture proportion design and are necessary to understand the rheology and stability of concrete. In this paper, the most common techniques, including dynamic oscillatory measurements, used to assess the viscoelastic properties of fresh cement paste are presented and discussed. The measurement challenges and their effects on the accuracy of the obtained properties are highlighted. On the other hand, the effects of high-range water-reducer, viscosity-modifying admixture, and supplementary cementitious materials are discussed. Furthermore, the use of viscoelastic measurements to assess yield stress and structural build-up of cement paste is presented.

Utilization of coal gangue power generation industry by-product CFA in cement: Workability, rheological behavior and microstructure of blended cement paste

Circulating fluidized bed fly ash (CFA), by-product of coal gangue power generation industry based on circulating fluidized bed combustion technology, differs from ordinary fly ash (OFA) in its physical and chemical properties. This paper aims to investigate the influences of CFA with three particle sizes on the workability and rheological properties of cement paste. The results show that untreated raw CFA (RCFA) can significantly degrade many properties of fresh cement paste. Directly using CFA as a mineral admixture in cement-based materials is not suitable in terms of workability. However, CFA through grinding methods can significantly mitigate the detrimental effect of CFA on the flowability of cement paste. When 15% ultrafine CFA (UCFA) was added, the cement paste exhibited relatively favorable workability and rheological properties. The rheological behavior of cement paste containing CFA with three particle sizes follow the shear thinning, which is in line with the modified Bingham model. Furthermore, the reasons for the impact of CFA on the microscopic level of cement workability are analyzed and discussed. The addition of CFA reduces the amount of free solution in the cement paste, leading to the formation of a flocculated structure and an increase in the thixotropic loop area. Based on the analysis of TOC, BET and TEM, it was determined that numerous polycarboxylate superplasticizer (PCE) molecules are adsorbed onto the rough and porous surface structure of CFA particles, hence the destructive ability of PCE to the flocculation structure caused by cement hydration is weakened. Therefore, the mechanism that CFA affecting the working performance of cement paste can be determined as: the adsorption of free water and PCE molecules.

The impact of coal gasification slag powder on fluidity, rheology and viscoelasticity properties of fresh cement paste

Coal gasification slag (GS) is a potential pozzolanic industrial waste discharged during coal gasification. The study aimed to investigate the effect of finely ground GS powder on the fluidity, rheology and viscoelasticity properties of cement paste, which is essential for utilizing GS as a supplementary cementitious material for building materials. The research revealed that the morphology, physical filling effect, and particle size distribution of GS powder played a vital role in the workability of cement. The particle size distribution of the GS-cement system followed the Rosin-Rammler distribution model, and the width of the particle size distribution negatively correlated with paste fluidity. The rheological characteristics of blended paste transitioned from Bingham to modified Bingham fluid with increased GS powder content, showing shear thinning. Plastic viscosity can predict the fluidity and thixotropy of the paste. GS powder at 10% content broadened the particle size distribution, improved fluidity and rheological properties, with minimal effect on viscoelastic characteristics. With increased GS powder content, plastic viscosity, yield stress, and thixotropy of blended paste increased continuously, resulting in a slow transition from viscosity to elastic solid. Extending mechanical grinding time improved the fineness and activity of GS powder, optimized the particle size distribution, and reduced water demand, minimizing negative effects.

Recycling palm oil wastes for the production of a pozzolanic cement replacement material for concrete

The palm oil industry produces wastes that are harmful to the environment but can be managed. The empty fruit bunch (EFB) and oil palm mesocarp fibres (OPMF) are used as combustibles in Africa. This research focused on identifying the chemical and physical characteristics of EFB and OPMF ashes in order to develop the richest possible pozzolanic composite for use as cement replacement material (CRM). The effects of calcination temperatures and duration were studied for the different ashes. A suitable combination of the two ashes was determined, and its effects on the properties of fresh cement paste were studied. The results showed that a rich pozzolana meeting the established requirement of ASTM C618-19 class N pozzolan can be obtained by combining OPMF and EFB in a ratio of 80/20. Furthermore, it was found that the reactivity of the ashes could be improved by grinding these ashes to reduce their particle sizes.

Rheology and Thixotropy of Cement Pastes Containing Polyacrylamide

In this article, the rheological and thixotropic properties of fresh cement pastes (fcps) with nonionic polyacrylamide (PAM) are investigated through the coaxial rotary method. The B-HB model is resorted to fit the shear stress versus shear rate diagram, from which the slurry plastic viscosity is particularly discussed. The results show that with the development of PAM, the plastic viscosity increases first, then decreases, and then increases again, exhibiting the “up-down-up” trend, which is consistent with the fcps fluidity. The adsorption, lubrication, and entanglement mechanisms of PAM are successfully used to interpret this phenomenon. Combined with the suspension density, the relationship among plastic viscosity, flowability, and density is successfully established follower via a multivariate linear regression method. The Durbin-Watson coefficient, variance inflation factor, μ significance, ρ significance, and R 2 are 2.122, 1.024, 0.014, 0.004, and 0.776, respectively, demonstrating the feasibility of fitting formula. Besides that, the PAM containing slurry which exhibits the explicit thixotropy is also found according to the appeared hysteresis curve during one shearing cycle. With the increase of PAM dosage, the thixotropic indexes including Th1 and Th2 decreased, until the PAM exceeded 0.5%-0.6% dosage, both of them yielded negative values. The phenomenon that the fcps final shear stress exceeds its initial value occurs.

Influence of Waste Fly Ash on the Rheological Properties of Fresh Cement Paste and the Following Electrical Performances and Mechanical Strengths of Hardened Specimens

Waste fly ash (WFA) is a kind of solid waste without reasonable disposition. The WFA with active substance can promote the cement hydration, therefore, WFA may enhance the mechanical strengths of cement-based materials. In this paper, the rheological properties (slump flow and plastic viscosity) of fresh cement paste with WFA ranging from 0% to 25% by mass ratio of cement were studied. The alternating current (AC) electrical resistance and direct current (DC) resistance time curves were determined. The AC impedance spectroscopy curves of the specimens cured for 1 day and 28 days were obtained. Finally, the mechanical strengths of hardened cement paste cured for 1 day, 3 days, 7 days, and 28 days were tested. The results showed that the slump flow was decreased and the plastic viscosity was increased by the addition of WFA and the increasing curing time. The AC electrical resistance increased in the form of the quadratic function with the cuing age. Meanwhile, the addition of WFA demonstrated an enhancing effect on the electrical conduction of cement paste. The variation rate of DC electrical resistance during the testing time increased with the increasing dosages of WFA and the curing age. The mechanical strengths increased with the addition of curing time and the content of WFA. The increasing rate of mechanical strengths increased with the addition of WFA (0~15%) and decreased with curing time. However, when the dosage of WFA increased from 15% to 25%, the increasing rate decreased.

The interaction of sodium citrate and polycarboxylate-based superplasticizer on the rheological properties and viscoelasticity of cement-based materials

The changes of the rheological properties of cement paste containing sodium citrate and polycarboxylate-based superplasticizer (PCE) over time were not fully understood. The interaction of sodium citrate and PCE on the rheological properties and viscoelasticity of fresh cement paste was thus investigated. The mechanism of complicated experimental phenomena was confirmed by means of adsorption measurement and zeta potential test in the fresh cement paste. It was found that the rheological properties of fresh cement pastes varied with the dosage variation of sodium citrate. The citrate with small dosage or high dosage and PCE have synergistic effects or antagonistic effects on the rheological properties of fresh cement pastes, respectively. The fluidity of cement pastes improved with time except those pastes with high dosage of sodium citrate. Microrheological analysis showed that the viscoelasticity evolution of pastes with small dosage of sodium citrate was similar but it increased sharply at initial moment when the dosage of sodium citrate is high. Preferred adsorption of citrate and delayed adsorption of PCE was account for the complicated changes of rheological properties and viscoelasticity of pastes, which leaded to the variation of zeta potential. The complexation between citrate and calcium ion was obvious when the dosage of sodium citrate exceeded 0.1%.

Investigation of the Effect of Seawater and Sulfate on the Properties of Cementitious Composites Containing Silica Fume

Concrete consumes over two billion tons of freshwater every year and 75 % of regions of the world will become water shortages in 2050. Because of increasing freshwater scarcity seawater may become reasonable as an alternative mixing and curing water for concrete. In this study, seawater (SW) was utilized for mixing and curing of concrete and investigated the seawater and sulfate on the properties of cementitious composites containing silica fume (SF). Hence, SF was replaced with the cement at ratios corresponding to 0 %, 2.5 %, 5 %, 7.5 %, 10 %, 12.5 %, and 15 % by weight of cement, and SW and tap water (TW) were used as mixing water in the production of cementitious composites. Thus, the effect of SW on the properties of fresh cement pastes and the flexural and compressive strengths of 7-day, 28-day, and 90-day old cementitious composites were examined. Additionally, the lengthening change values of cementitious composites containing SF that were kept in 5 % Na2SO4 solution for 7-day, 28-day, and 90-day were determined. The SF delayed the setting period while increasing the water requirement of the cement paste. It is determined that the SW accelerated the setting period of cement. In the case when 10 % SF in cementitious composites was used, the maximum compressive and flexural strengths were obtained for cementitious composites produced by mixing with SW and SF fume at an age corresponding to 28-day and 90-day. It was observed that the length change of the cementitious composites decreased due to the increase in the SF replacement ratio.

Structural kinetics constitutive models for characterizing the time-dependent rheologic behaviors of fresh cement paste

The development of microstructure of cement-based materials should be mainly responsible for the time dependences of their rheological properties. In this paper, a series of structural kinetics constitutive models were established to predict the time-evolutions of the rheological properties of fresh cement paste under different working conditions. The models were developed from the Hershel-Bulkley model by combining a kinetic equation of the structural parameter λ and the relationships between rheological parameters and the structural parameter. The effects of shear rate, thixotropy and cement hydration on the structural breakdown and structural build-up were considered in the kinetic equation. Meanwhile, the specific parameters of Portland cement paste in the kinetic equation were estimated according to the experimental data of published literatures. Moreover, the reliability of the new models was further validated by comparing the experimental results with the predicted value of dynamic and static yield stresses of cement pastes under mixing and rest. Thus, the relationship for Portland cement between the development of microstructure and the rheological properties had been established.

Effects of the charge density of anionic copolymers on the properties of fresh cement pastes

In this work, the effects of the charge density of the anionic copolymers on the properties of fresh cement pastes were fully discussed. A series of random copolymers based on anionic acrylic acid (AA) and nonionic N, N-dimethyl acrylamide (DMAA) were prepared by free radical solution polymerization. By varying the initiator concentration, the obtained polymers have different charge densities but similar molecular weights. The adsorption, fluidity, bleeding and rheology of the cement pastes mixed with different polymers were tested, respectively. The results indicate that the anionic and nonionic monomer of the polymers effect on the properties of fresh cement paste cooperatively, and the polymer with medium charge density can effect on the cement paste strongest. Our study is quite beneficial to understand the structure–property relationships and action mechanism of anionic polymers in cement pastes.

The Influences of Cement Hydration and Temperature on the Thixotropy of Cement Paste.

The rheological properties of fresh cement paste are highly influenced by a large number of parameters, among which the most important factors are the applied shear stress, and the shear history, the age of the sample and the temperature. The effects of these parameters on the yield stress (designated as structural limit stress in this work), the viscosity and the structural recovery rate (i.e., the change in dynamic viscosity with time at rest) were studied. In parallel, the changes in ion composition of the carrier liquid, mineral phase content and granulometry were investigated. The results reveal that all investigated rheological parameters exhibit an approximated bi-linear trend with respect to the degree of hydration, with a period of quasi-constant properties until a degree of hydration of approximately 0.07, followed by a non-linear increase. This increase could be attributed to the formation of calcium hydroxide (CH) and calcium-silicate-hydrate (C-S-H) via calorimetry results. With regard to the effect of the shear history of the sample on the rheological properties, the structural limit stress showed a minor dependency on the shear history immediately after the end of shearing, which, however, vanished within the first minute at rest. The same is true for the structural recovery rate. The presented results give detailed insights into the influences of hydration and shear on the rheological properties—especially the thixotropy—of fresh cement pastes.

Adsorption of organic core-shell corrosion inhibitors on cement particles and their influence on early age properties of fresh cement paste

The influence of copolymers on the material properties of cement-based materials is closely related to their adsorption and distribution in cement matrix. In this study, the adsorption of organic core-shell corrosion inhibitors based on poly(ethylene oxide)-b-polystyrene (PEO-b-PS) micelles on cement particles and their influence on the early age hydration and workability of cement paste were investigated. The results showed that the micelles rapidly adsorbed on cement particles surface within 40 s. At mesoscale, the micelles distribution was uniform in cement matrix; at microscale they were preferentially adsorbed on positively charged aluminates phases. Due to the efficient adsorption, the particle dissolution and precipitation of hydration products were impeded, leading to the slightly retarded early hydration of C3A; the workability of cement paste was improved, which was attributed to the better dispersion of cement particles associated with the altered surface potential of cement particles and steric hindrance effect provided by the micelles.

NMR study on bleeding properties of the fresh cement pastes mixed with polycarboxylate (PCE) superplasticizers

This study investigated the bleeding properties of fresh cement paste mixed with various polycarboxylate superplasticizers (PCEs) using low-field nuclear magnetic resonance (NMR). The PCE superplasticizers were synthesized with various acid to ether ratio, molecule weight of methyl allyl alcohol polyoxyethylene ether (HPEG) and functional groups. The bleeding process of fresh cement paste mixed with the PCE superplasticizers was monitored by low-field NMR and the bleeding rate was obtained with the calculation of transverse relaxation time (T2) peaks. Results showed that the proposed NMR method can not only evaluate the bleeding extent, probe the microstructure of fresh cement paste but also provide information about the PCEs concentration of bleeding water. It was found that PCE superplasticizers synthesized with high acid to ether ratio would reduce the bleeding, and PCE superplasticizers synthesized with the HPEG of molecule weight 4400 and functional group of methyl methacrylate (MMA) would lead to less bleeding when the fresh cement paste reached the same fluidity. The T2 relaxation time of bleeding water increased with bleeding rate, which implies the PCEs molecules in bleeding water was diluted during the bleeding process. Furthermore, the results suggest more bleeding water coming out from the pore water results in larger microstructure changes due to sedimentation.

Effect of coral powder on the properties of cement-based materials

In the construction of offshore engineering, a growing number of coral sand and coarse aggregate is used as concrete aggregates in the local construction. Thereupon, a lot of coral powder is left as a solid waste. This work is an attempt to study the potential of the coral powder replacing part of cement as supplementary cementitious materials. The flow properties of fresh cement paste with coral powder were studied, as well as the mechanical properties of hardened cement paste. Experimental results show that the fluidity of cement paste blended with coral powder decrease with the dosage of micro coral powder, due to its high water demand and high adsorption of polycarboxylate superplasticizer (PCE). Replacement of cement by coral powder have positive effects on the cement hydration and mechanical properties of cement paste at early ages. However, at the curing age of 7 days, the addition of coral powders deceases the strength of cement paste regardless of replacement levels.

Rheological characterization of the viscoelastic solid-like properties of fresh cement pastes with nanoclay addition

At sufficiently low applied shear deformation or shear stress, fresh cement paste exhibits viscoelastic solid-like behavior. This solid-like state is particularly important for some applications, such as self-consolidating concrete formwork pressure and 3D concrete printing. In this study, the viscoelastic solid-like behavior of fresh cement pastes is probed using a rheometer. Static yield stress, storage modulus, and cohesion are measured by creep recovery and constant shear rate test, small amplitude oscillatory sweep (SAOS) test and tack test, respectively. The effect of nanoclay addition is studied in various aspects of viscoelastic performance of fresh cement pastes. It is found that nanoclay addition not only enhances yield stress and cohesion, but also stiffness in terms of storage and tangent modulus.

Mechanism of tricalcium silicate hydration in the presence of polycarboxylate polymers

The early-age hydration of cement is inhibited in the presence of comb-shaped polycarboxylate ether (PCE) polymer—a dispersant commonly added to control rheological properties of fresh cement paste. This study employs a series of microcalorimetry experiments and phase boundary nucleation and growth simulations to elucidate the effects of dosage and molecular architecture of PCE on hydration of tricalcium silicate (Ca3SiO5 or C3S in cement notation), the dominant phase in cement. Results show that PCE—regardless of its molecular architecture—suppresses early-age hydration of C3S. PCE-induced retardation becomes increasingly more pronounced as dosage of PCE in the paste increases. Such suppression of C3S hydration has been attributed to adsorption of PCE molecules on silicate surfaces, which inhibit topographical sites of C3S dissolution and C–S–H nucleation, and impede the post-nucleation growth of C–S–H. This study develops a correlation between molecular architecture of PCE and its ability to suppress C3S hydration through quantitative analyses of retardation effects induced by PCEs with different molecular architectures. The numerical equation, describing such correlation, offers a reliable, and, more importantly, a readily quantifiable indicator of PCE’s potential to suppress C3S hydration in relation to its dosage and molecular architecture. In the context of practical application of this study, the aforementioned numerical equation can be used to order and rank PCEs—of various molecular architectures—on the bases of their potentials to suppress C3S hydration, and to select ones that cause the optimum (i.e., user-desired) extent of hydration suppression.

Assessment of Rheological and Piezoresistive Properties of Graphene based Cement Composites

The concrete production processes including materials mixing, pumping, transportation, injection, pouring, moulding and compaction, are dependent on the rheological properties. Hence, in this research, the rheological properties of fresh cement paste with different content of graphene (0.03, 0.05 and 0.10% by weight of cement) were investigated. The parameters considered were test geometries (concentric cylinders and parallel plates), shear rate range (300–0.6, 200–0.6 and 100–0.6 s−1), resting time (0, 30 and 60 min) and superplasticizer dosage (0 and 0.1% by weight of cement). Four rheological prediction models such as Modified Bingham, Herschel–Bulkley, Bingham model and Casson model were chosen for the estimation of the yield stress, plastic viscosity and trend of the flow curves. The effectiveness of these rheological models in predicting the flow properties of cement paste was verified by considering the standard error method. Test results showed that the yield stress and the plastic viscosity increased with the increase in graphene content and resting time while the yield stress and the plastic viscosity decreased with the increase in the dosage of superplasticizer. At higher shear rate range, the yield stress increased while the plastic viscosities decreased. The Herschel–Bulkley model with the lowest average standard error and standard deviation value was found to best fit the experimental data, whereas, Casson model was found to be the most unfitted model. Graphene reduces the flow diameter and electrical resistivity up to 9.3 and 67.8% and enhances load carrying capacity and strain up to 16.7 and 70.1% of the composite specimen as compared with plain cement specimen. Moreover, it opened a new dimension for graphene-cement composite as smart sensing building construction material.