Cement Hydration Research Articles

Impact of TiO2 powder type on hydration and photocatalytic NOx degradation in cement paste

This study was aimed at developing novel functional construction materials with NOx removal capabilities using TiO2 powder. To this end, the effects of the chemical composition of TiO2 powder on the hydration process and the mechanical properties of cement were investigated. The hydration characteristics of the cement were assessed by analyzing the setting time and heat of hydration, while the mechanical properties were evaluated by measuring compressive strength at different curing ages. Additionally, the NOx degradation performance was examined. The results demonstrate that TiO2 powder accelerates the hydration of cement, enhancing the compressive strength during the early stages of hydration. Furthermore, the NOx degradation performance of mortar specimens was enhanced with the incorporation of TiO2 powder. However, the extent of these improvements varied significantly depending on the chemical composition of the TiO2 powder, with the composition ratio of anatase and rutile being particularly influential. When utilizing TiO2 powder to enhance the performance of construction materials or impart new functional properties, it is advisable to consider the composition of the TiO2 powder to ensure alignment with the intended performance improvement objectives.

Synthesis of a chitosan-based superabsorbent polymer and its influence on cement paste

To address the challenge of adaptability between cement-based materials and conventional superabsorbent polymers (sodium polyacrylate, Na-PA), a chitosan-based superabsorbent polymer (CSP) with high salt and alkaline resistance was synthesized, and the optimal synthesis process was determined by a single-factor method. The macroscopic performance and microstructure of CSP and Na-PA were compared, and their influences on cement paste were studied. The results show that CSP exhibits a gradual swelling process during water absorption, which is independent of the solution environment. The poriferous structure of CSP allows it to form a network composed of gel membranes. The introduction of amide group enhances the resistance of CSP to salt and alkaline conditions. The autogenous shrinkage of cement paste is mitigated by CSP, with a superior effect compared to Na-PA. The longer desorption time of CSP allows it to promote cement hydration for a longer period, reducing the loss of compressive strength. The heat release, chemically bound water and hydration products (portlandite and amorphous substances) of CSP pastes are higher than those of Na-PA pastes. The water desorption from CSP fills some middle capillary pores and mesopores, leading to the pores in the hardened cement paste being more concentrated in smaller sizes.

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.

Understanding the uneven phase distribution and multi-step reaction mechanism of carbonated γ-C2S-based foam concrete

γ-C2S has been attracting much attention as the role of exclusive or primary binder to fabricate carbonated materials due to its high carbonation reactivity. However, the very limited hydration reactivity of γ-C2S makes it difficult in the production of casting-formed materials such as foam concrete, and this is exacerbated by the presence of bursting-prone foams in the mixture. Given the highly cementitious property of Portland cement (PC), 10 wt% of PC was added to γ-C2S-based foam concrete (CFC) as the supplemented binder to maintain its cellular structure while providing demoulding strength. The compressive strength of the CFC (600 kg/m3), carbonated for 2 h at ambient conditions, impressively peaks at 4.49 MPa, comparable to that of autoclaved aerated concrete with the same density grade, and is three times higher than the standard strength of foam concrete. This is partly attributed to the more uniform air-void size distribution formed by the enrichment of cement hydration products on the void-wall. Furthermore, the presence of cement hydration products positively promotes the dissolution of calcium ions from γ-C2S, forming a mixture of calcium and silicon products. This paper aims to understand the carbonation mechanisms of composite CFC, and also provide guidance for further realizing the reaction process associated with multiple carbonatable phases.

Effect of steam curing on strength, durability and microstructure of concretes with and without mineral admixtures

This research explores the effect of steam curing on the strength, durability and microstructure of concretes with and without mineral admixtures of fly ash (FA) and ground granulated blast-furnace slag powder (SL). Two types of C55 strength grade concretes (one was pure cement concrete, the other was a concrete made by replacing part of the cement with 12% FA and 18% SL) were prepared and their compressive strength, chloride diffusion coefficient and carbonation depth under standard and steam-curing conditions were measured and compared. The phase composition and microstructure of the concretes under the two curing conditions were tested by X-ray diffraction, scanning electron microscopy and mercury intrusion porosimetry. The results showed that, on the one hand, compared with standard curing, steam curing is beneficial to the early strength, but not conducive to the later strength development and chloride permeability resistance of both types of concretes. Furthermore, for the steam-cured concrete, the 28 days carbonation depth of the forming surface is higher than that of the bottom surface. In addition, steam curing can reduce the carbonisation resistance of pure cement concrete and improve the carbonisation resistance of concrete mixed with FA and SL. On the other hand, composite mineral admixtures of FA and SL reduce the early strength and the carbonisation resistance of concrete cured by standard curing, but improve the later strength, the carbonisation resistance and chloride permeability resistance of concrete cured by steam curing. FA and SL are thermally activated under steam curing and can react with the calcium hydroxide formed by cement hydration in the early stage, which produces a larger amount of secondary hydration products to improve the pore structure and interfacial microstructure of the concrete with FA and SL. In this way, the adverse effects of steam curing on later strength and durability of concrete are significantly restrained by composite mineral admixtures of FA and SL.

Effects of Typical Supplementary Cementitious Materials (SCMs) on the Bonding Property of Cement with Casing under Shallow Formation of Deep-Water Environment

Due to low temperature environments and other factors, the performance of cement slurry is affected by deep-water shallow formation cementing, which makes it difficult to ensure the interface bonding quality. The objective of this study is to investigate the effect of fly ash (FA), metakaolin (MK), and microsilica (MS) as supplementary cementitious materials (SCMs) by replacing 5–20% of the cement on the bonding property of cement with casing in the shallow formations of deep-water environments. This is based on the cementing conditions for the 20″ surface casing in the deep-water shallow formation of the LS18-1 well area. Under the 30 °C experimental conditions, the results showed that the compressive and bonding strength of cement with FA and MS decreased gradually as their dosage increased. In contrast, compared with the control group (BG0), the compressive strength of the MK group increased by 25.6%, 32.1%, and 24.2% under the optimal dosages (MK15, MK15, MK20) at 3, 7, and 14 days (d), and the bonding strength increased by 73.6% at 3 d (MK15) and 34.9% at 7 d (MK15). The test analysis showed that MK can promote cement hydration and generate more hydration products, which are conducive to cement-casing interface cementation. Additionally, it can improve the pore structure, reduce the fractal dimension of the pore volume, and ensure a more reasonable distribution of cement stone crack openings.

A closed-loop recycling of wastewater derived from aqueous carbonation of basic oxygen furnace slag in cement paste production

Aqueous carbonation (AC) treatment is a promising method for enhancing the cementitious activity of Ca- and Mg-rich solid wastes, such as basic oxygen furnace slag (BOFS), while also reducing carbon emissions. However, the carbonated filtrate (CF) solution generated during the AC process poses significant environmental challenges and limits its large-scale application. This paper, therefore, explores the feasibility of recycling CF in cement paste production as a strategy for managing AC wastewater. The study examines the impact of CF on the physico-mechanical properties, hydration behavior and microstructure of cement pastes (pure and blended with either 10% as-received or carbonated BOFS), compared to those prepared with tap water (TW) and carbonated water (CW). The results indicate that carbonated solutions (CF and CW) promote the hydration of aluminate phase in cement, with a more pronounced effect observed for CW. The solid suspensions in CF, particularly nesquehonite, restrict the growth space for calcium silicate hydrates (C-S-H) in the paste matrix, resulting in the formation of foil-like Type II C-S-H and lowering compressive strength. However, the additional nucleation sites provided by calcite crystals in carbonated BOFS (C-BOFS) accelerate cement hydration in CF-based pastes and mitigate strength loss by promoting the formation of more fibrillary C-S-H. Furthermore, the addition of a superplasticizer reduces interparticle forces in the C-BOFS-CF paste, further enhancing strength development and achieving a 28-day strength comparable to that of the control sample (OPC-TW paste).

Retardation of Chlorine-36 by Cementitious Materials Relevant to the Disposal of Radioactive Wastes

The activation product chlorine-36 (36Cl) is an important radionuclide within the context of the disposal of nuclear wastes, due to its long half-life and environmental mobility. Its behaviour in a range of potential cementitious encapsulants and backfill materials was studied by evaluating its uptake by pure cement hydration phases and hardened cement pastes (HCP). Limited uptake of chloride was observed on calcium silicate hydrates (C-S-H) by electrostatic sorption and by calcium monosulphoferroaluminate hydrate (AFm) phases, due to anion exchange/solid solution formation. Diffusion of 36Cl through cured monolithic HCP samples, representative of cementitious materials considered for use in deep geological repositories across Europe, revealed a markedly diverse migration behaviour. Two of the matrices, a ground granulated blast furnace slag/ordinary Portland cement blend (GGBS–OPC) and an ordinary Portland cement (CEM I) effectively retarded 36Cl migration, retaining the radionuclide in narrow, reactive zones. The migration behaviour of 36Cl within the cementitious matrices is not strictly correlated to the measured sorption distribution ratios (Rd-values), suggesting that physical factors related to the microstructure can also have a distinct effect on diffusion behaviour. The findings have implications when selecting cementitious grouts and/or backfill materials for 36Cl-bearing radioactive wastes.

Effect of treatment types of recycled concrete aggregates on the properties of concrete

Reusing waste materials such as construction and demolition waste is an environmentally significant task. This article aims to improve the quality of recycled aggregates after the demolition of concrete structures. Two methods, mechanical cleaning and impregnation, were explored to enhance the quality of coarse aggregates. The findings indicate that mechanical cleaning is more effective than soaking in a sodium silicate solution. The compressive strength of concrete made with mechanically cleaned recycled aggregates was 2.3 times greater than that of concrete made with untreated rubble. Concrete with impregnated rubble had a compressive strength 1.1 times greater than that of concrete with untreated aggregates. Infrared spectroscopy was used to study the microstructure, revealing that the type of treatment does not influence the quantity of portlandite and ettringite in hydrated cement. However, the treatment of recycled aggregates alters the interaction in the gel portion of cement hydration products. Concrete with aggregates treated by sodium silicate has more aluminate components. Additionally, there is a shift of the bands assigned to Si-O stretching to higher wave numbers (from 995 cm–1 to 1088 cm–1), which can be attributed to the formation of calcium-silicate-hydrate gel with a lower calcium/silicon ratio.

Carbonized seawater cement slurries for offshore deep cement mixing: Carbonation mechanism, strength enhancement and microstructure evolution

Seawater cement slurry (SCS) is a commonly used binder in offshore deep cement mixing (DCM) construction. Seawater cement slurries are usually prepared before they are grouted into the seabed and mixed with marine clay. The aim of this study is to explore the feasibility of applying carbonation technology to fabricate SCS suitable for offshore DCM while achieving carbon sequestration and obtaining better mechanical properties for stabilised marine sediments.This study demonstrated that after appropriate carbonation, carbonized SCS can be used in DCM to replace conventional SCS. Short-term carbonation promotes cement dissolution and hydration rates under seawater conditions rich in magnesium, calcium, and other inorganic ions. The carbonates include calcite, vaterite and amorphous carbonates, which provide additional nucleation sites for the hydration of SCS, resulting in an increment for amorphous CS(A)H gel with a dense pore structure and binding interaction with soil particles. After carbonation with 20 % CO2 for 5 min (0.5 wt% of cement), the UCS and secant modulus of cement-soil mixtures by 15.7 % and 111 % at the age of 1 day, and by 6.82 % and 10 % at the age of 28 days when treating marine clay with 80 % moisture content at a dosage of 260 kg/m3.

Effect of nano silica-cement paste impregnation-carbonation reinforcement on the properties of low-quality recycled aggregates

The aim of this study was to investigate the impact of a nano silica (NS) -cement paste impregnation-carbonation strengthening technique on both the properties of low-quality recycled aggregates and the recycled aggregate concrete (RAC) they form. First, the changes in the basic properties of recycled concrete aggregates (RCA) after reinforcement were evaluated, followed by pore structure, XRD, thermo-gravimetric analysis, nanoindentation, and SEM tests to explore the microstructure and the mechanism of its influence. The results showed that the crushing value of the recycled aggregate reinforced with NS-cement paste impregnation-carbonation composite were reduced about 35 %, compared to the unreinforced recycled aggregate. The crushing value and water absorption were reduced about 17 % and 28 %, respectively, compared to cement slurry impregnated-carbonated reinforced recycled aggregates. The addition of NS promoted the hydration of cement in the encapsulated slurry, and some unreacted nanoparticles in turn filled the pores of the hardened cement slurry, reducing the porosity of the recycled aggregate. The performance of the ITZ is improved after the aggregate is reinforced. The 28 d compressive strength of recycled concrete formulated with NS-cement paste impregnation-carbonation-reinforced aggregates was increased about 34 % and 52 % for 50 % and 100 % substitution rates, respectively. In conclusion, this study elucidated the mechanism of NS-cement paste impregnation-carbonation strengthening on the properties of recycled aggregates and provided a theoretical basis for the application of NS-cement paste impregnation-strengthening in construction materials.

Electromagnetic absorption properties of composite mortar with graphene and manganese-zinc ferrite

Electromagnetic wave absorption of building structures plays a crucial role in safeguarding information and mitigating electromagnetic radiation. This study delves into the absorption capabilities of composite mortar made with graphene (GR) and manganese-zinc ferrite (MFO) across frequencies of 1–18 GHz. The mechanical strength, microstructural examinations, and numerical simulations to elucidate the underlying mechanisms of wave absorption in the composite mortar are investigated. The results indicate that incorporating 30 % MFO reduces the strength of mortar due to its low bonding capacity and diluting effects, whereas GR enhances the strength of mortar by facilitating cement hydration. Electromagnetic examinations reveal that MFO boosts the magnetic loss performance, while GR augments dielectric loss properties. In addition, the presence of needle, rod, mesh, and flake hydration products in the pores of composite mortar also contributes to increased wave depletion. According to the simulation of electromagnetic absorption based on the finite difference time domain (FDTD) method, the composite mortar with GR and MFO exhibits a superior performance of electromagnetic wave absorption. With the 25 mm thickness of composite mortar with 30 % MFO, an absorption below −10 dB, covering a bandwidth of 1.68–4.34 GHz are obtained, with a peak reflection loss of −22.13 dB at 3.23 GHz. Thus, by combination magnetic loss of MFO, dielectric loss of GR, and the reflective capabilities of porous mortar, a composite mortar with a better electromagnetic wave absorption can be achieved.

Degradation mechanism and strength prediction of aeolian sand concrete under sulphate dry-wet cycles

In this paper, aeolian sand (AS) with different contents (0 %, 25 %, 50 %, 75 % and 100 %) was used as fine aggregate to prepare aeolian sand concrete (ASC). The effects of AS content and dry-wet cycle (DWC) times on the durability of ASC under sulfate (5 % Na2SO4) erosion conditions were investigated by DWC tests. The mass loss rate, compressive strength loss rate and relative dynamic elastic modulus (RDEM) were used as the macroscopic performance evaluation indexes, while the damage degradation mechanism of ASC was revealed by combining the microscopic technical means such as SEM, XRD, TG-DSC and NMR. The results show that the macroscopic properties of ASC under the action of DWC of sulphate all show the first increase and then decrease, as when the dosage of AS is below 50 %, the "bead effect" and "padding effect" of AS can further improve the internal densification of ASC, thus effectively resisting external sulphate erosion. During sulphate erosion, SO42- firstly reacts with cement hydration product Ca(OH)2 to generate erosion products such as Ettringite (AFt) and fills them within the original defects, with short-term rnhancement of macroscopic properties. As the DWC continue, the excessive erosion products accumulated, resulting in the destruction of pore structure and extension through the phenomenon, the matrix compactness is reduced, and the macroscopic properties degraded. The grey entropy correlation analysis yielded that the grey entropy correlation grade of bound fluid saturation, harmless pore percentage and less harmful pore percentage with compressive strength were all above 0.8, and the GM(1,4) strength prediction model established on the basis of the above pore structure parameters has a high prediction accuracy, and the relative errors between the predicted strength values and the actual strength values are within 10 %, and the research results can provide certain theoretical support for the study of the durability of ASC in sulfate erosion environment.

Effect of nano-Ti-Li-Al hydrotalcite-like on the hydration and hardening properties of sulfoaluminate cement-based materials

The use of sulfoaluminate cement-based materials (SCBMs) in grout reinforcement projects is common, and they also perform well in road repair and other facilities. To obtain high workability and permeability, a large water-to-cement ratio is generally used, which reduces the early mechanical properties of SCBMs. The early mechanical properties of cement-based materials can be improved by adding nanomaterials. The cement hydration product monosulfate (AFm) belongs to the hydrotalcite-like family, which is also called layered double hydroxide (LDHs). At present, there is no literature on the influence of nano-Ti-Li-Al layered double hydroxide materials (TiLiAl-LDHs) on SCBMs. In this study, two types of nano -TiLiAl-LDHs with different Ti/Li/Al molar ratios (Ti1Li3Al4-LDHs and Ti2Li3Al4-LDHs) were synthesized. Nano-Ti1Li3Al4-LDHs promoted the hydration of the slurry and improved the early mechanical properties of SCBMs to a greater extent than nano-Ti2Li3Al4-LDHs. However, the cause of this phenomenon remains unclear. Nano-TiLiAl-LDHs act as nucleation sites for ettringite (AFt) and AFm, both of which are cement hydration products. Among them, Ti1Li3Al4-LDHs preferentially provided nucleation sites for AFt, whereas Ti2Li3Al4-LDHs preferentially provided nucleation sites for AFm. Ti1Li3Al4-LDHs and Ti2Li3Al4-LDHs can release titanium, lithium, and carbonate ions in the SCBMs paste, and Ti1Li3Al4-LDHs release more lithium ions (up to 50 mg/L) while Ti2Li3Al4-LDHs release more titanium ions (up to 100 mg/L). Li+ can consume AlO2− and OH− in the slurry and form amorphous lithium aluminum compounds. Although Li+ inhibits the formation of AFt products, it promotes the hydration of anhydrous calcium sulfoaluminate (ye’elimite). Ti4+ reacts with OH− to form a complex that inhibits the formation of AFt, thus reducing the hydration of SCBMs. CO32− promotes the formation of calcium carbonate and indirectly promotes the dissolution of ye’elimite and gypsum. The nucleation effect and release of titanium, lithium, and carbonate ions acted synergistically to influence the hydration and hardening processes of SCBMs. Compared with Ti2Li3Al4-LDHs, Ti1Li3Al4-LDHs has a greater ability to enhance the hydration and mechanical properties of the slurry owing to its strong nucleation and release of higher concentrations of lithium ions and lower concentrations of titanium ions.

Low-grade fly ash in portland cement blends: A decoupling approach to evaluate reactivity and hydration effects

Fly ash with low glass content is often prohibited from use in concrete due to the low reactivity and/or the inclusion of contaminants. However, the scarcity of high-quality fly ash promotes the evaluation of the feasibility of using fly ash with low glass content (e.g., low-grade fly ash) in concrete. This study proposes a decoupling method to quantitatively estimate the degree of reaction of fly ash with extremely low glass content, which partially replaces cement, and the degree of hydration of the hosting cement, simultaneously. The estimation is derived from the contents of calcium hydroxide and chemically bonded water in hydrated binary cement pastes, which can be determined by thermogravimetric analysis-based experiments and theoretically validated stoichiometric parameters. The results exhibit that the fly ash tends to retard the early-age hydration of cement but promotes its later-age hydration, resulting in a higher ultimate degree of reaction of cement than the reference paste. The microstructural and porosity evaluation shows that the fly ash, though has relatively low degrees of reaction due to its low glass content, can result in a more tortuous pore network of the hydrated pastes, which could be potentially more resistant to the penetration of water and aggressive chemicals.

Early-age shrinkage behavior of cement mixtures regulated with metakaolin-based internal conditioning

Shrinkage occurs in concrete during its hardening and strength gain process leading to undesired deformation, cracking, and decreases in strength and durability. While metakaolin-based internal conditioning (MIC) has been validated as a promising technique for modifying cement and mitigating alkali-silica reactions in concrete, its impact on the early-age shrinkage behavior of cement remains unexplored. This study delves into the effects of MIC and its coupling with lithium on the chemical shrinkage, autogenous shrinkage, and drying shrinkage of portalnd cement incorporating 30 % metakaolin with varying degrees of saturation (50 %, 75 %, and 100 %). The results indicate that the hydration of cement can be substantially enhanced by MIC with 29.0 % more heat released and a 32.3 % decrease in calcium hydroxide content. As a result of the enhanced hydration, cement with MIC yielded increased chemical shrinkage. Compared with dry MK, the autogenous shrinkage and drying shrinkage of cement were decreased by 38.0 % and 11.0 %, respectively, in the presence of MIC. A synergistic effect between MIC and lithium was suggested by the higher efficacy in suppressing autogenous shrinkage.

Enhanced pozzolanic reactivity in hydrogen-form zeolites as supplementary cementitious materials

Pozzolans rich in silica and alumina react with lime to form cementing compounds and are incorporated into portland cement as supplementary cementitious materials (SCMs). However, pozzolanic reactions progress slower than portland cement hydration, limiting their use in modern construction due to insufficient early-age strength. Hence, alternative SCMs that enable faster pozzolanic reactions are necessary including synthetic zeolites, which have high surface areas and compositional purity that indicate the possibility of rapid pozzolanic reactivity. Synthetic zeolites with varying cation composition (Na-zeolite, H-zeolite), SiO2/Al2O3 ratio, and framework type were evaluated for pozzolanic reactivity via Ca(OH)2 consumption using ion exchange and in-situ X-ray diffraction experiments. Na-zeolites exhibited limited exchange reactions with KOH and Ca(OH)2 due to the occupancy of acid sites by Na+ and hydroxyl groups. Meanwhile, H-zeolites readily adsorbed K+ and Ca2+ from a hydroxide solution by exchanging cations with H+ at Brønsted acid sites or cation adsorption at vacant acid sites. By adsorbing cations, the H-zeolite reduced the pH and increased Ca2+ solubility to promote pozzolanic reactions in a system where Ca(OH)2 dissolution/diffusion was a rate limiting factor. High H-zeolite reactivity resulted in 0.8 g of Ca(OH)2 consumed per 1 g of zeolites after 16 h of reaction versus 0.4 g of Ca(OH)2 consumed per 1 g of Na-zeolite. The H-zeolite modulated the pore fluid alkalinity and created a low-density amorphous silicate phase via mechanisms analogous to two-step C-S-H nucleation experiments. Controlling these reaction mechanisms is key to developing next generation pozzolanic cementitious systems with comparable hydration rates to portland cement.

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.

Importance of adsorption compared with complexation for retarding C3S hydration via adding sodium gluconate

Adsorption effect on particle surfaces and complexation effect with free Ca2+ mostly determine the retarding performance of organic admixtures on cement hydration. However, it is difficult to identify which effect plays a more important role in retarding hydration by experimental methods. Here, a theoretical model was developed to investigate the retarding mechanisms of sodium gluconate (SG) on hydration of tricalcium silicate (C3S). Based on obstruction theory and complexation reaction kinetics, effects of adsorption and complexation were simulated to examine the retarding performance of C3S hydration with addition of SG. The proposed model well predicted the effect of additional dosing of SG on the retarding performance of C3S hydration. Theoretical parameter studies demonstrated that adsorption ratio contributed much largely to the delays in C3S hydration, compared with rate constant of complex generation. Therefore, it is confirmed that adsorption plays a more important role in regulating the retarding mechanism of C3S hydration.

Durability Assessment for Mortar Containing LDH Additives

Abstract This study investigates the potential of Layered Double Hydroxides (LDH) as additives to improve the durability and physical properties of cement-based mortars, with a focus on freeze-thaw resistance. Three LDH types—MgAl-LDH, CaAl-LDH, and ZnAl-LDH—were synthesized and incorporated into mortar at a 1/1000 w/w ratio. X-ray diffraction (XRD) and wavelength dispersive X-ray fluorescence spectroscopy (WDXRF) were used to characterize the LDHs, and the effects of the additives on mortar density, water absorption, and durability under 30 freeze-thaw cycles were examined. Results revealed that MgAl-LDH provided the best freeze-thaw resistance, likely due to its smaller crystallite size and enhanced cement hydration. CaAl-LDH offered moderate improvements, while ZnAl-LDH negatively impacted the mortar’s mechanical integrity, leading to higher degradation. The study demonstrates the potential of LDH additives—particularly MgAl-LDH—in improving the durability of cementitious materials, although further optimization is required to enhance long-term performance and resistance to environmental stresses.