Fresh Cement Research Articles

Innovative strategies for time-release PCE design and cement paste flowability control

Extending the retention time of cement paste flowability with the addition of admixtures containing slow-release components is standard practice for ensuring the continued building quality of cement-based materials. This study aims to control the release rate of PCE and enhance its time-varying dispersion effect in fresh cement paste by utilizing Time-dependent Release PCEs (TRPCEs) with varying side-chain structures. The structural characterization of the synthesized TRPCEs was investigated using GPC (Gel Permeation Chromatography), FTIR (Fourier Transform Infrared Spectroscopy), and 1H NMR (Proton Nuclear Magnetic Resonance) techniques. Furthermore, experiments were carried out on time-varying flowability with different dosages of TRPCEs to investigate the flowability changes under the time-varying release effect. The influence of TRPCEs on cement hydration was examined using isothermal calorimetry by measuring the early hydration heat of cement paste. The time-dependent adsorption behaviors of TRPCEs were also examined using a TOC (Total Organic Carbon) analyzer. The findings show that TRPCEs have a minor effect on the cement hydration process's rapid reaction period but little effect on its induction and acceleration periods because of variations in the initial dispersion effect. Additionally, the adsorption behaviors of TRPCEs on cement particles vary significantly due to the hydrolysis of slow-release groups. The varying adsorption and consumption of TRPCEs on cement particles and hydration products in different hydration phases are key controlling factors for the time-varying flowability changes in cement paste. Finally, this innovative approach offers a novel perspective for designing and preparing new types of PCEs with a strong capability for time-varying flowability retention.

Effect and mechanisms of type, content, and dispersion method of flash graphene on the rheological behaviors of fresh cement pastes

Flash Joule heating provides a facile, low-carbon, and cost-effective method for upscale graphene production, benefiting the application of graphene in modifying cement-based materials. Understanding the effect and mechanisms of flash graphene (FG) type, content, and dispersion method on the rheological behaviors of cement-based materials is essential for designing and controlling cement-based materials in different application scenarios. Therefore, this study explored the rheological behaviors of cement pastes with 2 different types of flash graphene at 4 different content levels (namely 0.1 wt%, 0.2 wt%, 0.3 wt%, and 0.4 wt% of cement mass) using 3 different dispersion methods (namely water reducer dispersion with ultrasonic treatment, dry mixing with water reducer, and mechanical dispersion with water reducer). The results indicated that the addition of FG generally increases the yield stress and plastic viscosity of fresh cement pastes. The water reducer dispersion with ultrasonic treatment and nano-boron doping shows a good effect in dispersing FG. The influence mechanisms of FG on rheological behaviors of fresh cement pastes are a competition between exert replacement, agglomeration, lubrication, and adsorption effects.

Damage localisation in fresh cement mortar observed via in situ (timelapse) X-ray μCT imaging

This paper presents the outcome of a study focused on the evolution of internal damage in fresh cement mortar over 25 h of hardening. In situ timelapse X-ray computed micro-tomography (μXCT) imaging method was used to detect internal damage and capture its evolution in cement mortar hardening. During μXCT scans, the temperature released during the cement hydration was measured, which provided insight into the internal damage evolution with a link to a hydration temperature rise. The measured temperature during cement mortar hardening was compared with an analytical model, which showed a relatively good agreement with the experimental data. Using 20 CT scans acquired throughout the observed cement mortar hardening, it was possible to obtain a quantified characterisation of the porous space. Additionally, the use of timelapse μXCT imaging over 25 h allowed for studying the crack growth inside the meso-structure including its volume and surface characterisation. The results provide valuable insights into cement mortar shrinkage and serve as a proof-of-concept methodology for future material characterisation.

Effect of Different Concentration of CO2 Gas Injected into Fresh Cement Paste Along with the Addition of Superplasticizer on the Mechanical Properties of Cement

This paper focused on examining the impact of injecting varying concentrations of carbon dioxide (CO2) gas on the mechanical characteristics of both the fresh and hardened states of cement paste. This study also considered the influence of the presence or absence of polycarboxylate superplasticizer in cement mixture on these properties. Many researchers discovered the benefit of CO2 gas utilization in cement mixture to accelerate the early strength of cement or concrete hydration by its carbonation that form calcium carbonate (CaCO3). The application method is to directly inject CO2 gas in a curing chamber for air-curing of precast concrete. Alternatively, carbonated water is mixed with cement during concrete mixing. However, the use of CO2 gas does not significantly improve the 28-day strength of concrete. This study explores how to improve the carbonation impact on mechanical properties of cement paste and apply it to ground improvement. In this study, the method adopted is direct injection of CO2 gas during cement slurry mixing with different injection duration. The influence of CO2 in the presence of superplasticizer (SP) in cement slurry was also studied as SP is generally used for grouting. The results showed that the carbonation of cement paste with additional of superplasticizer significantly affect its flow, viscosity and bleeding properties. Unlike samples with SP addition, the samples without SP addition showed higher compressive strength after 28 days of curing up to certain CO2 injection time. For all CO2 gas injection time, smaller porosity rates were observed for 7-day cured samples with SP addition compared to those without SP addition. This is due to accelerated carbonation due to SP presence in cement mixture. From the results, the optimum of CO2 gas injection time for one liter mixture of cement paste to improve its compressive strength (up to 123% increase) have been discovered. It can be inferred that the addition of superplasticizer in cement slurry reduces the amount of CO32- ions and Ca2+ ions during carbonation process of cement hydration products, which are strongly related to the pH level in pore solution. These ions play a significant roles in determining the mechanical properties of cement slurry.

Time-Dependent Properties and Model Analysis of Rheology for Fresh Sulphoaluminate Cement Paste Evaluated by Electrochemical Impedance Spectroscopy

Time-Dependent Properties and Model Analysis of Rheology for Fresh Sulphoaluminate Cement Paste Evaluated by Electrochemical Impedance Spectroscopy

Influence of Rigid Side Chains on the Structural Stability of High-Temperature Resistant Fluid Loss Additives for Oil Well Cements: An Experimental Study and Molecular Simulation

A fluid loss additive (named AAMN) for cementing ultra-deep reservoirs at high temperature (210 °C) was prepared by a free radical copolymerization method using 2-acrylamido-2-methylpropane sulfonic acid (AMPS), acrylamide (AM), acrylic acid (AA), and N-vinyl-2-pyrrolidinone (NVP) as monomers. Filtration tests at 210 °C demonstrated that AAMN reduced the amount of fluid loss by 22% in fresh cement slurry, 23% in 18 wt% NaCl cement slurry, and 16% in 36 wt% NaCl cement slurry compared to AAM (without NVP) when both were added at 6% bwoc ("bwoc" denotes the addition by the weight of the cement). The pore structure was analyzed using the Brenner-Emme-Teller (BET) method and environmental scanning electron microscopy (ESEM), confirming that AAMN could be adsorbed onto the cement particles surfaces, filling the pores and blocking fluid loss channels. The degradation temperatures of the two copolymers were tested by thermogravimetric analysis (TGA-DTGA) and the molecular dynamics behavior of two Amorphous Cell (AC) models (the amorphous structures with randomly arranged Ca2+, Cl−, Na+ and H2O with the AAMN or AAM) built by Materials Studio 7.0 software, were compared: the introduction of five-element NVP side chains didn’t significantly improve the thermal stability of the AAMN relative to the AAM, but resulted in the AAMN molecular chain maintaining a stable geometry at a temperature of 483 K (210 °C). The AAMN also showed more adsorption groups (–SO3 − and –COO−) at the high temperatures, which allowed the AAMN to form a dense "network structure" with Ca2+ and H2O molecules, thus effectively blocking the channels for water molecule loss from the cement slurries.

Liquid nitrogen frozen cementitious material and its potential applications: Inspired by refrigeration industry

Liquid nitrogen frozen cementitious material introduces a novel approach to utilizing cementitious material in engineering construction and maintenance. This process involves the quick-freezing of fresh cement mortar into blocks. Tests were conducted on the thawed cement mortar to evaluate key technical parameters such as compressive strength and fluidity. Microscopic analyses including mercury intrusion porosimetry, scanning electron microscopy, X-ray diffraction and thermogravimetric analysis were conducted for mechanism analysis. The results indicate that quick-freezing with liquid nitrogen has a minimal or negligible impact on the compressive strength and fluidity of cement mortar, with compressive strength decreasing by no more than 4 % and fluidity decreasing by no more than 2 %. The rapid hydration reaction suspended by utilizing the extremely low temperature characteristics of liquid nitrogen is the main contribution. The freezing blocks possess unique properties such as hydration suspending, low-temperature and non-dispersibility as solid, which can be utilized in some special engineering applications such as long-distance transportation, temperature control of large volume concrete or underwater structure repair.

Isocyanate microcapsules recovering automatically impermeability of cement paste through self-hydrophobic broken panels

Cracks are inevitable in the use of cement-based materials. It takes a lot of resources to repair these cracks and prolong the service life of cement-based materials. Self-healing cement-based materials that can automatically repair cracks and improve the self-healing ability of cement-based materials have become the focus of current research. The current self-healing systems achieve impermeability recovery of matrix by the filling cracks. Few scholars have paid attention to the impermeability recovery through self-hydrophobic broken panels. In this paper, SEM, FTIR, core content titration, water flux test and contact angle test were carried out. The morphology, composition, core content and impermeability recovery effect of self-healing cement paste were prepared and characterized. Carbon nanotubes are used to improve the water resistance of isocyanate microcapsules, which possess a diameter of 237.6 ± 59.1 μm, distinct core-shell structure, and good dispersibility. The residual core fraction is 58.2 % after 21 days in Ca(OH)2 aqueous solutions. The microcapsules maintain integrity without breakage when mixed with fresh cement paste and have good bonding compatibility with cement matrix. When microcapsules are embedded into cement paste, the cracks could break the microcapsules releasing isocyanate to wet the broken panels. The isocyanates react with the moisture with the formation of polyurea, changing the contact angle of broken panels from near 0° to 118.4 ± 0.1°. The hydrophobic panels could retard the water penetration and recover the impermeability of cement paste. Based on this, a new self-healing mechanism of self-hydrophobic fracture surface to realize self-healing of impermeability of cement matrix is proposed.

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.

Modeling thixotropic behavior of fresh cement pastes

It is crucial to describe the thixotropic behavior of cement-based materials, which plays an important role during the production process such as mold casting or 3D printing. This study establishes and validates a thixotropic model of fresh cement pastes considering de-flocculation using experimental data with different shear rates and water-to-cement ratios.

Design of a hydrophobic nano-SiO2-modified ER@EC microcapsule: Improving rheology, regulating hydration while preserving self-healing in cementitious materials

Microcapsule-based self-healing concrete chronically suffers from rheology deterioration and hydration stagnation due to the hydrophilic and hygroscopic nature of microcapsules, limiting its efficacy and broader application. To address these issues, a novel hydrophobic nano-SiO2-modified epoxy resin (ER)@ethyl cellulose (EC) microcapsule was developed and characterized. Examinations revealed that both 5 % and 7 % SiO2-modified ER@EC microcapsules displayed favorable fundamental properties for cement-based materials, featuring high core contents (53.08 % and 48.04 %) and water contact angles over 90°. Compared to the unmodified capsules, the incorporation of 7 % SiO2-modified capsules prominently enhanced the rheology and hydration exotherm of fresh cement pastes, attributed to floc disassembly caused by electrostatic repulsion and increased water volume induced by replacement and ball-bearing effects. Moreover, incorporating a 4 % dosage of 5 % SiO2-modified capsules exhibited prominent healing efficiencies of 6.14 % for compressive strength and 35.11 % for chloride diffusion resistance. The hydrophobic nano-SiO2-modified ER@EC microcapsules actively improved rheology and hydration exotherm while preserving the ability to self-heal cracks in cement-based materials.

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.

Improving the air bubble stability of air-entrained mortar in low air pressure environments via adopted rheology and surface tension methods

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.

Kualitas Semen Segar Babi Berdasarkan Umur dan Ras di Kabupaten Kupang

The study aims to see how age and race affect the quality of fresh cement between pigs. The cement sources used in the study came from pigs of different ages of 9 months, 1.4 years, and 2.5 years. The pig races used were Landrace pigs and Duroc. Cemented is collected using the method of massage and then macroscopic and microscopic evaluation. The data from the cement evaluation will be a descriptive analysis presented in the form of the chart. Studies show 2.5-year-old pigs have a better fresh cement quality than a 9-month-old pig and 1.4 years old. The Landrace pig also has better fresh cement quality than the Duroc pigs.

Reducing plug flow effect on measured rheological results of cement-based materials: Image analysis and numerical iteration approach

The rheological properties of cement-based materials (CBM) significantly influence their workability and application in construction. Despite the common use of coaxial cylinder rheometers for measuring these properties, challenges arise, particularly at low shear rates due to plug flow within the tested samples. This study aims to investigate the impact of plug flow on rheological property measurements of CBM and proposes strategies to enhance measurement accuracy. An image analysis method and a novel numerical iteration algorithm were proposed in this study to address plug flow effects. Three series fresh cement paste with different fluidities were prepared to conduct the rheological tests. Through the image analysis method, actual shear radii at different rotor speeds were measured. The corresponding rheological parameters were determined and compared using the complete shear assumption, the image analysis method, and numerical iteration algorithm, respectively. The results indicated the great influence of plug flow on rheological results, especially at low shear rates and low fluidities, highlighting the need for its consideration in rheological parameters calculations. Moreover, the proposed numerical iteration algorithm was verified to calculate the incomplete shear state of CBM and improve the measurement accuracy of rheological parameters. The extensions and limitations of the numerical iteration algorithm in its application were discussed further.

Fresh cement as a frictional non-Brownian suspension

Cement is an essential construction material due to its ability to flow before later setting, however the rheological properties must be tightly controlled. Despite this, much understanding remains empirical. Using a combination of continuous and oscillatory shear flow, we compare fresh Portland cement suspensions to previous measurements on model non-Brownian suspensions to gain a micro-physical understanding. Comparing steady and small-amplitude oscillatory shear, we reveal two distinct jamming concentrations, ϕμ and ϕrcp, where the respective yield stresses diverge. As in model suspensions, the steady-shear jamming point is notably below the oscillatory jamming point, ϕμ<ϕrcp, suggesting that it is tied to frictional particle contacts. These results indicate that recently established models for the rheology of frictional, adhesive non-Brownian suspensions can be applied to fresh cement pastes, offering a new framework to understand the role of additives and fillers. Such micro-physical understanding can guide formulation changes to improve performance and reduce environmental impact.

Gas CO2 foaming and intermixing in portland cement paste to sequester CO2

In this study, concentrated CO2 gas was used to create foamed cement paste, and concentrated CO2 gas was intermixed in fresh cement paste to produce regular cement paste materials that were not foamed. The potential of both methods to form CaCO3 from calcium ions that would form Ca(OH)2 was investigated. After curing the materials for different ages, the Ca(OH)2 and CaCO3 contents were measured using thermogravimetric analysis; the large void size distributions, dynamic modulus, and compressive strength were tested and compared against Control (no gas added), and N2 foamed and N2 intermixed specimens. A 10% increase in dynamic modulus and compressive strength was measured in CO2 foamed specimens compared to N2 foamed specimens. The increase in mechanical properties was the result of both a narrow void diameter distribution and CaCO3 formation in place of Ca(OH)2. The CO2 foamed cement generation method shows the potential to sequester 0.06 ton of CO2 for every ton of cement which is a CO2 emission reduction of 7.0% of the CO2 production associated with cement production. For the CO2 intermixing method, the void content, compressive strength, and dynamic modulus results were consistent between the Control and CO2 intermixed specimens while the N2 intermixed specimens showed a decrease in compressive strength and dynamic modulus. The CO2 intermixing method showed potential to sequester 0.04 ton of CO2 for every ton of cement or a 4.7% CO2 emission reduction of the total CO2 production associated with cement manufacturing. The reported CO2 emissions are not based on life cycle assessment and do not account for emissions associated with CO2 collection, transportation, and intermixing. The present paper does not investigate the mechanisms of hydration under CO2 intermixing.

Using metakaolin to improve properties of aged Portland cement: Effectiveness and the mechanism

Aging of Portland cement, due to its reaction with moisture and atmospheric CO2 prior to regular use, has the potential to severely impair its hydration reactivity. The effectiveness of using metakaolin to improve the properties of aged Portland cement exposed to a laboratory conditions (RH=65 %, 20 °C) as well as the associated mechanism are studied. The incorporation of 5–10 % metakaolin changes the early-stage hydration kinetics of aged cement obviously by enhancing reactions of both C3S and C3A through the filler effect at the early hydration stage, thereby mitigating detrimental influences of aging on setting time and early-age strength development (up to 7 days). Metakaolin exhibits significant effectiveness on enhancing 28-day strength of aged cement, and the enhancement arises from the synergic reaction between metakaolin and CaCO3, which converts CaCO3 resulting from aging into carboaluminate phases and produces secondary C-S-H. The incorporation of 5 % metakaolin increases the 28-day compressive strength of the sample with cement aged for one month to a comparable level as that of fresh cement.

Deformation capacity of fresh cement pastes

Deformation capacity of fresh cement pastes

On the Flow of a Cement Suspension: The Effects of Nano-Silica and Fly Ash Particles.

Additives such as nano-silica and fly ash are widely used in cement and concrete materials to improve the rheology of fresh cement and concrete and the performance of hardened materials and increase the sustainability of the cement and concrete industry by reducing the usage of Portland cement. Therefore, it is important to study the effect of these additives on the rheological behavior of fresh cement. In this paper, we study the pulsating Poiseuille flow of fresh cement in a horizontal pipe by considering two different additives and when they are combined (nano-silica, fly ash, combined nano-silica, and fly ash). To model the fresh cement suspension, we used a modified form of the power-law model to demonstrate the dependency of the cement viscosity on the shear rate and volume fraction of cement and the additive particles. The convection-diffusion equation was used to solve for the volume fraction. After solving the equations in the dimensionless forms, we conducted a parametric study to analyze the effects of nano-silica, fly ash, and combined nano-silica and fly ash additives on the velocity and volume fraction profiles of the cement suspension. According to the parametric study presented here, larger nano-silica content results in lower centerline velocity of the cement suspension and larger non-uniformity of the volume fraction. Compared to nano-silica, fly ash exhibits an opposite effect on the velocity. Larger fly ash content results in higher centerline velocity, while the effect of the fly ash on the volume fraction is not obvious. For cement suspension containing combined nano-silica and fly ash additives, nano-silica plays a dominant role in the flow behavior of the suspension. The findings of the study can help the design and operation of the pulsating flow of fresh cement mortars and concrete in the 3D printing industry.