Properties Of Cement Paste Research Articles

Simultaneously comparing various CO2-mineralized steelmaking slags as supplementary cementitious materials via high gravity carbonation

The integration of accelerated carbonation with the utilization of steelmaking slags presents a vital strategy for CO2 mineralization towards net-zero scheme. This study simultaneously evaluates basic oxygen furnace slag (BOFS), refining slag (RFS), and electric arc furnace reducing (EAFRS) and oxidizing slags (EAFOS) as potential partial replacements for ordinary Portland cement, at substitution levels ranging from 5 % to 15 % as supplementary cementitious materials (SCMs). These slags were pretreated through aqueous accelerated carbonation in a high-gravity rotating packed bed. We assessed several parameters, including carbonation conversion, CO2 capture capacity, workability, strength, and durability. The results demonstrated that EAFRS achieved the highest CO2 capture capacity, reaching 0.193 kg-CO2/kg-slag with a maximum carbonation conversion of 46 % under 197 times high-gravity conditions and a liquid-to-solid ratio of 20. While the incorporation of carbonated slags had minimal impact on the setting properties of cement pastes, higher substitution ratios necessitated increased water demand. The strength of blended cement containing 5 %, 10 %, and 15 % of carbonated BOFS, RFS, and EAFRS met standard requirements at 28th day. Additionally, a mathematical model was developed to predict the mechanical strength of cement mortars. The introduction of carbonated BOFS, RFS, and EAFRS facilitated hydration due to the formation of calcium carbonates, although it resulted in slower strength development kinetics. Notably, the replacement of cement with carbonated EAFOS exhibited a higher expansion rate, likely due to its elevated silicon dioxide and alkaline species content, which may lead to alkali-aggregate reactions, resulting in expansion and cracking.

Rheological properties of cement paste with in-situ polymerization of sodium acrylate: Roles of polymerization and hydration

In-situ polymerization modified cement paste shows a great potential in 3D concrete printing (3DCP) due to its enhanced rheological properties. Unlike direct adding conventional polymer, how in-situ polymerization and cement hydration synergistically regulate the rheology of cement paste with different monomer dosages remains unclear. Here, we investigate the rheological properties of in-situ polymerization modified cement paste with different dosages of sodium acrylate (SA) to reveal the roles of cement hydration and polymerization. When the monomer dosage is lower (1 % and 3 %), the polymerization inhibits the cement hydration without providing sufficient contribution to the structural development of cement paste, resulting in the decreased rheological properties, such as static/dynamic yield stress and structural build-up rate. On the contrary, once the monomer dosage reaches a higher level (5 % and 7 %), the resultant polymers can gradually form a network interwinding within the cement particles, thus leading to enhanced rheological properties, regardless of the more severely inhibited cement hydration.

Self-Compacting Mixtures of Fair-Faced Concrete Based on GGBFS and a Multicomponent Chemical Admixture—Technological and Rheological Properties

The use of superplasticizers in a self-compacting concrete mix without the addition of a foaming agent in practice leads to a well-known problem associated with increased air entrainment and promotes the formation of harmful large bubbles, high-void content, and ununiform appearance. This paper presents research on the properties of cement paste consisting of Ordinary Portland Cement (OPC), powder based on ground granulated blast furnace slag (GBBS), and superplasticizer. The methodology of this study was the estimation of flow diameter and flow time, as well as the evaluation of the rheological characteristics. The influence of ground granulated blast furnace slag and polycarboxylate plasticizer on the flowability and viscosity of cement paste was studied. The effect of superplasticizer (SP) based on polycarboxylate esters (PCE) anti-foaming agent (AFA) based on a glycol ester and air-entraining admixture (AEA) based on an amphoteric surfactant on flowability, viscosity, rheological properties and the strength of the cement paste was evaluated. It was found that the increase of slag content in cement paste (25%) with the presence of superplasticizer (0.64%) significantly changes the flowability and viscosity. It was stated that the addition of 0.04% anti-foaming agents increases flowability (20%) and reduces viscosity (44%) of cement paste. It was stated that the addition of small dosages of glycol ester-based anti-foaming agent (0.02 and 0.04%) significantly changes the rheological properties, decreases the shear yield stress by 2.1–2.8 times, the plastic viscosity by 2.4–2.6 times and apparent viscosity 1.6–2.5 times, improves the compressive strength at the age of 1 and 7 days by 2.5 and 1.4 times, respectively. The addition of air-entraining admixture led to a decrease in the plastic viscosity by 1.2–1.4 times. It was stated that the presence of air-entraining admixture assists in increasing the apparent viscosity by 1.7–2.4 times. It was shown that the presence of complex admixtures of various origins, purposes, and mechanisms of action would assist in predicting the behavior of concrete mixtures under the conditions of the building site and reduce the consumption of polycarboxylate esters due to the enhancing plasticizing effect of anti-foaming agent and air-entraining admixture.

Study of the Structure and Properties of Concrete Modified with Nanofibrils and Nanospheres

The application of modifying nanoadditives in the technology of cement composites is currently a relevant and widely researched topic in global materials science. The purpose of this study was to investigate new nanoadditives—nanofibrils made from synthesized wollastonite (NF) and nanospheres from corundum (NS)—produced by LLC NPK Nanosystems (Rostov-on-Don, Russia) as a modifying additive. During the experimental investigations, the mechanical properties of cement pastes and concrete were examined. This included an analysis of the density, compressive and bending strength, as well as water absorption of concrete that had been modified with NF and NS additives. X-ray phase and microstructural analyses of concrete were performed. It was established that modification of cement composites with NF and NS additives had a beneficial effect on their properties, and the optimal amount for both types of additives was 0.3% by binder weight. The highest recorded enhancements in compressive and flexural strength of concrete with 0.3% NF were 7.22% and 7.04%, respectively, accompanied by a decrease in water absorption by 4.70%. When modifying concrete with 0.3% NS, the increases in compressive and flexural strength were 2.71% and 2.48%, and water absorption decreased by 1.96%. Modification of concrete with NF and NS additives did not have a significant effect on the change in concrete density, which was no more than 1%. Based on the results of phase analysis, it was established that concrete with NF and NS additives were characterized by the presence of five main phases: quartz, portlandite, calcite, larnite, and olivine-Ca. It was found that compositions with 0.3% NF and NS differed from the control composition by the presence of such a phase as olivine-Ca. Microstructural analysis confirmed the effectiveness of NF and NS additives. The microstructure of the modified concretes was distinguished by the extensive occurrence of clusters composed of calcium silicate hydrate zones. The conducted studies prove the possibility of using NF and NS as modifying nanoadditives in the technology of cement composites. The addition of nanofibrils from synthesized wollastonite is the most effective and promising and is recommended for use in real construction practice.

Experimental and theoretical study on the physico-mechanical characteristics and radiation shielding capability of hardened alumina sludge waste-cement pastes containing MnFe2O4-nanoparticles

This research investigates the impact of incorporating low-cost MnFe2O4 spinel nanoparticles (MF-NPs) at varying concentrations (0.5, 1, and 2 mass%) on the mechanical and physical properties of blended cement pastes. These pastes were produced by replacing different proportions (5, 10, and 15 mass%) of ordinary Portland cement (OPC) with activated alumina sludge waste (AAS), to promote sustainability. Also, the research examined the gamma radiation shielding effectiveness of certain hardened composites against a 137Cs gamma radiation source with an energy of 661.64 keV using a NaI (Tl) detector (Oxford Model) with 3″ × 3″, amplifier and 16 k multi-channel analyzer. The linear attenuation coefficient (LAC) of all the studded samples were calculated theoretically using a Monte Carlo code MCNP-5 code. The gamma radiation shielding properties were analyzed in depth using a Monte Carlo code MCNP-5 simulation model. The theoretical and experimental results for LAC were found to be in complete agreement. Phy-X/PSD software was applied to estimate the mass attenuation coefficient (MAC) for gamma radiation at various energies, as well as the effective atomic number (Zeff), mean free path (MFP), half-value layer (HVL), and tenth-value layer (TVL). The findings demonstrated that the addition of 0.5% MnFe2O4 nanoparticles (MF-NPs) to blended cement pastes exhibited the best physical and mechanical characteristics, as well as the most effective gamma radiation shielding.

Fresh and hardened properties of cement paste under the synergistic influence of polycarboxylate superplasticizer and anionic polyacrylamide

The combined impact of anionic polyacrylamide (APAM) and polycarboxylate superplasticizer (PCE) on the fresh and hardened properties of cement paste, including rheological properties, setting time, and compressive strength, was investigated. Then the mechanism was further discussed by conducting the experiments of cement hydration and adsorption measurement. The results showed that the increasing dosage of APAM increased the yield stress of cement paste and led to a tendency from shear thickening to shear thinning. This phenomenon was directly connected with the formation of a network structure and hydration products via the bridging effect of adsorbed APAM. The generated hydration products strengthened the network structure over time, leading to a higher structural build-up rate and shorter setting time. Meanwhile, the increasing dosage of APAM increased the adsorption amount of PCE, indicating that PCE still dispersed cement particles and ensured the hydration rate; thus similar compressive strength was observed.

The Effect of Calcium Sulfate on the Hydration and Properties of Red Mud-Based Calcium Ferroaluminate Cement Clinker.

The hydration of high-alkali red mud-based ferroaluminate cement (RCFA) clinker with calcium sulfate needs to be regulated. This study explored the effects of the calcium sulfate type and dosage on the hydration and properties of high-alkali RCFA clinker. The research results show that when 4% gypsum was added, the 3 d compressive strength of cement was 39.1 MPa, and the 28 d compressive strength was 63.2 MPa. The 28 d strength increased by 61.6% compared with the 3 d strength. The properties of cement paste can be adversely affected by excessive anhydrite content. The exothermic hydration of clinker was accelerated by calcium sulfate at the beginning, but the rate declined as the process progressed. Sufficient sulfur supply can enhance the hydration of ye'elimite, thereby increasing the AFt content in the hydration product. The mass loss of the hydration product is mainly caused by the dehydration of ettringite, monosulfoaluminate, and AH3. In addition, the Na element in the RCFA hydration product is mainly present in monosulfoaluminate and unhydrated cement particles.

Performance Assessment of a Novel Green Concrete Using Coffee Grounds Biochar Waste

An actual scientific problem in current concrete science is poor knowledge of the problem of modifying concrete with plant waste. At the same time, plant waste benefits from other types of waste because it is a recycled raw material. A promising technological approach to modifying concrete with plant waste is the introduction of components based on the processing of coffee production waste into concrete. This study aims to investigate the use of biochar additives from spent coffee grounds (biochar spent coffee grounds—BSCG) in the technology of cement composites and to identify rational formulations. A biochar-modifying additive was produced from waste coffee grounds by heat treatment of these wastes and additional mechanical grinding after pyrolysis. The phase composition of the manufactured BSCG additive was determined, which is characterized by the presence of phases such as quartz, cristobalite, and amorphous carbon. The results showed that the use of BSCG increases the water demand for cement pastes and reduces the cone slump of concrete mixtures. Rational dosages of BSCG have been determined to improve the properties of cement pastes and concrete. As a result of the tests, it was determined that the ideal situation is for the BSCG ratio to be at a maximum of 8% in the concrete and not to exceed this rate. For cement pastes, the most effective BSCG content was 3% for concrete (3%–4%). The compressive and flexural strengths of the cement pastes were 6.06% and 6.32%, respectively. Concrete’s compressive strength increased by 5.85%, and water absorption decreased by 6.58%. The obtained results prove the feasibility of using BSCG in cement composite technology to reduce cement consumption and solve the environmental problem of recycling plant waste.

Effect of chelator on carbon sequestration and mechanical properties of CO2-cured cement pastes with different pore structures

Chelator can accelerate the mineralization reaction of cement-based materials, playing a positive role in reducing CO2 emissions into the atmosphere. Cement pastes with different pore structures were prepared by adjusting the water cement ratio, and effects of chelator on the microstructure, phase composition, carbon sequestration and mechanical properties of CO2-cured cement pastes with different pore structures were investigated in this study. The results indicated that chelator could promote CO2 transport in dense cement paste with more gel pore and transition pore and medium dense cement paste with many transition pore and capillary pore, and induce mineralization reaction to repair larger pores in loose cement paste with more capillary pore and megalopore (LCM). Chelator had the most significant effect on improving the performance of cement paste of LCM, increasing the carbonation sequestration rate and compressive strength of cement paste cured for 48 h by 19.0 % and 28.1 %, respectively.

Çimento Hamur ve Harç Özelliklerine Öğütülmüş Yüksek Fırın Cürufu ile Sönmüş Kirecin Birlikte Etkisinin Araştırılması

Bu deneysel çalışmada, çimento bazlı hamur ve harç karışımlarına yüksek oranda sönmüş hava kireci (SK) ve öğütülmüş yüksek fırın cürufunun (YFC) birlikte kullanımı ile üretilen numunelerin bazı fiziksel ve mekanik özellikleri araştırılmıştır. SK ve YFC ağırlıkça %10SK+%10YFC, %20SK+%20YFC ve %30SK+%30YFC oranlarında Portland çimentosu ile yer değiştirilerek hamur ve harç karışımları hazırlanmıştır. Üretilen harç karışımlarında işlenebilirlik sabit alınmıştır. Üretilen harç karışımlarından elde edilen fiziksel ve mekanik deney sonuçları kendi aralarında ve kontrol numuneleri ile karşılaştırılmıştır. Hamur numunelerde kıvam suyu, priz süreleri ve hacim genleşmesi deneyleri, harç numunelerde ise birim hacim ağırlık, basınç dayanımı ve eğilmede çekme dayanımı deneyleri yapılmıştır. Deney sonuçları, SK ve YFC’nin çimentoya ikame edilmesinin hamur kıvam suyu miktarını artırdığı, priz başı sürelerini azalttığı ancak priz sonu sürelerini artırdığı, birim hacim ağırlığı ve hacim genleşmesini ise azalttığı tespit edilmiştir. Ayrıca %30’a kadar SK ve YFC’nin birlikte ikame edilmesi, numunelerin 7, 28 ve 90 yaş gün eğilme ve basınç dayanımlarını azaltmıştır.

Alteration of cement rheological properties and setting-hardening: Novel insight into the impact of polyaluminum sulfate

The accelerator significantly influences the setting and hardening performance of shotcrete, in order to develop novel setting components, this study investigates the underlying mechanisms through which polyaluminum sulfate (PAS) facilitates the setting of cement paste. QXRD, Isothermal calorimetry, Zeta potential and Rheological test were employed to analyze the effects of PAS addition on the setting and hardening behavior, hydration kinetics, and rheological properties of cement paste. When the dosage of PAS is 10 %, the initial and final setting times are reduced by 54.39 % and 38.57 % respectively, meanwhile the compressive strength after 6 hours increases by 659.09 %. The influence of PAS on cement setting acceleration and rheological properties were analyzed using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and the Water Film Thickness (WFT) theory. PAS leads to an acceleration in particle aggregation rate and an increase in shear stress and plastic viscosity of the cement paste. Furthermore, the accelerated hydration effect of PAS promotes the formation of additional hydration products, strengthens the interparticle connectivity, and facilitates the formation of a rigid network. This study highlights a novel pathway for understanding the rapid setting mechanism of aluminum-based accelerators.

Carbonation mechanism and cementation properties of recycled cement paste based on CO2 injection time and pressure

Current applications of recycled cement paste (RCP) carbonation mainly focus on using carbonized particles as filler materials or enhancing the adhesion of hardened cement paste to aggregates. However, there is limited research on the carbon dioxide (CO2) sequestration effectiveness and strength improvement mechanisms of carbonized waste recycled concrete powder as a cementitious material. This study investigates the carbonation mechanism and cementation properties of RCP under various carbonation conditions. The phase composition and microstructural evolution of RCP are systematically analyzed through detailed characterization tests, exploring the impact of carbonation time and CO2 pressure on the mechanical properties of the RCP samples. These findings demonstrate that prolonged carbonation enhances the formation of calcium carbonate (CaCO3) and crystalline silica (SiO2), which in turn improves particle bonding and reduces porosity. Higher CO2 pressure results in increased carbonation products and tighter interparticle binding. Advanced nuclear magnetic resonance (NMR) analyses indicate that carbonation facilitates the transition of Al from six- to four-coordinated states and the polymerization of SiO4 tetrahedra, leading to enhanced structural cohesion. This study demonstrates the potential of carbonation in reshaping the cementitious properties of RCP, highlighting its environmental and economic benefits for recycling construction waste.

Study on the Modification Mechanism of Soap-Free Latex on the Microstructure and Mechanical Properties of Cement Paste

Abstract In view of problems such as the decline in strength of cement paste and latex exudation caused by the addition of conventional latex, JAS soap-free latex (JAS latex) was prepared by soap-free emulsion polymerization technology. JAS latex had the characteristics of low viscosity, uniform particle size, good dispersity of particles, and good compatibility with cement admixtures. JAS latex had little impact on the fluidity of oil-well cement paste. The free liquid of the cement paste with 10 % JAS latex was 0 %, and its liquid-loss content was 43 mL. When the JAS cement paste was cured at 90°C, its compressive strength was 34.08 MPa. When the curing temperature was 70°C, the bond strength between the paste and metal casing reached 4.95 MPa. Combining the results tested by X-ray diffraction, scanning electron microscopy, and atomic force microscopy showed that JAS latex did not affect the hydration process of oil-well cement, had good film-forming ability in cement paste, and improved the density and impact resistance of the cement paste. It is helpful to improve the sealing integrity and sealing ability of cement sheath in cementing engineering and ensure the safe and efficient development of oil and natural gas resources.

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.

The Contribution of Nano-Alumina to Ultra-High-Performance Cement-Based Systems.

In the last decades, nano-silica (NS), nano-alumina (NA), and nano-calcium oxide (NC) particles have been incorporated into cementitious materials, and it seems that each one of them contributes uniquely to the materials' properties. This research explores the influence of each nanomaterial on the fresh properties of cement pastes and their compressive strength evolution over one year. Low proportions (1.5% by weight) of nanomaterials were added to cement pastes, and their fresh properties, such as heat of hydration and X-ray diffraction patterns in the first hours, were analyzed. The compressive strength and open porosity were also measured long-term. The acceleration of hydration heat in NA-cement pastes is linked to enhanced hydration product formation at early ages. Among the tested nanomaterials, NA increased compressive strength by 10% at later ages. Although the fresh properties of NC-cement pastes remained unaffected, their open porosity decreased by 54% at 28 days. In contrast, the increase in heat of hydration in NS-cement pastes did not result in significant strength improvement. Based on these findings, NA was selected for ultra-high-performance cement (UHPC)-based material use. Its incorporation not only preserved the ultra-high-performance (UHP) properties but also provided additional benefits such as an increase in compressive strength under a CO2 atmosphere. Through detailed analysis, this research establishes that nano-alumina incorporation optimizes the microstructural development and compressive strength of ultra-high-performance cement-based systems, presenting a novel advancement in enhancing the mechanical properties and durability of these materials under various environmental conditions.

Impacts of graphene nanoribbon dispersion and stability on the mechanical and hydration properties of cement paste: Insights from surfactant-assisted ultrasonication

In this study, we aim to evaluate the different dispersion methods that affect the dispersion behavior of graphene nanoribbons (GNRs) and to conduct a contrastive analysis of the different surfactants that influence the dispersion and stability of GNRs in deionized (DI) water and alkaline solution. Moreover, we studied uniformly dispersed GNRs with respect to the hydration, mechanical properties, and microstructure of the cement paste. Owing to the surface defects of the GNRs, electrostatic repulsion was sufficient to overcome the van der Waals force and provide a long-term period of high stability. The results show that by using SPs and 60 min of ultrasonication, the dispersibility of GNRs improved by 8.5 % and 25.7 % in DI water and alkaline solution, respectively. Uniformly dispersed GNRs accelerate the hydration and C-S-H polymerization, resulting in significant increases in compressive strength and splitting tensile strength by 17 % and 33 %, respectively, and reduced porosity by 14.6 % after 28 days of curing.

The adaptability of polycarboxylate superplasticizer in alkaline electrolyzed water (AEW)-based cement composites containing clay: Workability and mechanical properties

Improving the adaptability of polycarboxylate superplasticizers (PCE) in high-clay content mortar is of great significance in enhancing the workability and mechanical properties of mortar containing clay. In this study, the potassium-based alkaline electrolyzed water (AEW) was used as mixing water for cement mortar. The excellent properties of AEW enabled PCE to be more compatible in cement mortar containing montmorillonite (MT) or kaolin (GL), improving the performance of mortar containing clay. The results showed that compared with ordinary tap water (OTW), the adsorption rate of clay minerals on PCE decreased in the AEW environment, and the clay interlayer spacing of MT was also reduced. AEW can inhibit the intercalation and adsorption of PCE molecular side chains by clay minerals to some extent. However, due to its unique crystal structure, the adsorption of MT on PCE was still significantly higher than that of GL. At the same time, increasing the content of clay mineral led to a decrease in mortar performance. Compared with the GL series, the MT series had a more significant negative impact on mortar fluidity and strengths. AEW also can promote hydration reactions, release more hydration heat, and produce more hydration products to encapsulate clay particles, thereby improving the workability and mechanical properties of cement paste containing clay. Furthermore, the high-activity AEW is rich in positively charged metal ions that can interact with clay minerals preferentially over cement particles, which enables the clay interlayer structure to be quickly saturated by AEW water molecules, effectively hindering the adsorption of PCE by clay minerals. However, in both the OTW and AEW environments, the intercalation effect of GL on PCE molecular side chains was not significant. Therefore, AEW has great potential in improving the adaptability of PCE in muddy cement pastes, which can help to enhance the workability and mechanical properties of muddy cement composites. This study provides theoretical references for preparing high-performance anti-clay concrete.

Experimental Study on Improving the Performance of Cement Mortar with Self-Synthesized Viscosity-Reducing Polycarboxylic Acid Superplasticizer

In this study, a viscosity-reducing polycarboxylic acid superplasticizer (VRPCE) was synthesized using methylallyl polyoxyethylene ether (HPEG), acrylic acid (AA), and maltodextrin maleic acid monoester (MDMA) as the main raw materials. The influences of the VRPCE on the microscopic properties of cement paste were studied by gel permeation chromatography (GPC), total organic carbon test (TOC), zeta potential, laser particle size analysis, XRD, MIP, TG, and SEM. Finally, the effects of the VRPCE on the macroscopic properties of cement mortar were evaluated through flow time, slump flow, compressive strength, shrinkage, and creep. The results showed that the VRPCE can improve the hydration degree of the cement, optimize the pore structure, increase the porosity, improve the fluidity, compressive strength, and creep, and decrease the shrinkage resistance of the cement mortar.

Effect of Activated Siliceous Wastes Incorporated as Mineral Admixtures on the Rheological Properties of Cement Paste: Insights into Their Physicochemical Interactions in Suspension.

Mechanical grinding is a common method used to enhance the pozzolanic activity of tailings, and these activated tailings can be used as supplementary cementitious materials in cement production. However, the addition of activated tailings usually reduces the workability of cement paste, and the mechanism of influence of different minerals in tailings on workability varies. In this study, three kinds of principal silicate minerals in tailings-quartz, feldspar, and mica-were mechanically activated. The influence of these activated minerals on the rheological properties of cement paste were studied in the absence or presence of PCE (polycarboxylate ether) superplasticizers, and the influence mechanism was investigated using rheology, TOC, contact angles, zeta potential, XPS, ICP-OES, and XRD. The results showed that quartz has the highest fluidity, and mica has the lowest. An increase in hydrophilicity decreased the flowability of the blended cement paste. The increase in the metal cation dissolution rate was the main reason for the decrease in the fluidity of PCE-blended cement pastes. The knowledge gained provides a valuable reference for the utilization of activated tailings in cement production.

Mechanism of recalcification and its effects on the microstructure and transport properties of cement paste

Calcium leaching involves the removal of calcium ions from the pore solution and hydration products, leading to a decrease in pH, coarsening of pore structure, and, in severe cases, loss of cohesion, shrinkage, and cracking. Recalcification is a restoration process aiming at repairing degraded C-S-H structures by externally supplying calcium ions. However, our understanding of recalcification mechanism, its potential to reverse calcium leaching, and its effects on deteriorated cementitious matrices remains limited. This study aims at enhancing the understanding of the impact of recalcification on calcium leached cement pastes. Our findings demonstrate that calcium leaching can be partially reversed by immersion in a saturated calcium hydroxide solution. Recalcification functions by introducing calcium ions to the degraded matrix, triggering a reaction with the degraded C-S-H. This process reverses silicate polymerization, increases the Ca/Si ratio in the degraded zone’s, and densifies the pore structure. After only 14 days of recalcification, the degraded portion experienced a 50 % reduction in porosity, an increase in pH. By day 28, recalcification halved the permeability of the treated sample and completely consumed all silica gel. Additionally, our findings reveal that higher temperatures adversely affect the structure of C-S-H, hindering the beneficial structural modifications facilitated by recalcification.