Tricalcium Aluminate Research Articles

Influence of retarder admixtures on the hydration, rheology, and compressive strength of white Portland cements under different temperatures

White cement is characterized by higher tricalcium aluminate (C3A) contents than conventional Portland cement; thus, it can present a reduced setting time, especially under hot weather conditions, limiting the material's application period. An approach to delay these materials' setting time is using retarder admixtures (RA). Nevertheless, there is a knowledge gap regarding the effect of RA on the rheological properties of white cement. This study aimed to evaluate the effect of two types of RA on the mini-slump, rheological parameters, hydration kinetics, and compressive strength of two white cements. Furthermore, the effect of temperatures of 25 and 40 ⁰C on the performance of the admixtures was also assessed. Both RA showed a dispersing effect, reducing cement pastes' dynamic yield stress and plastic viscosity. Moreover, the admixtures extended the induction period of cement hydration by up to 15.4 h without significantly affecting the 72-h cumulative heat at a temperature of 25 ⁰C. At 40 ⁰C, both RA exhibited a lower dispersing and retarding effect. Although RA delayed the initial hydration reactions of the WC, it enhanced the mechanical performance of the mortars after three days of hydration.

CHLORIDE CORROSION OF REINFORCING STEEL

Introduction. Many years of experience in examining corrosion conditions show the dangerous adverse effects of chloride media on reinforced concrete structures.Although a large number of domestic and foreign publications have been devoted to the aggressive action of chloride salts on reinforcing steel, protection against chloride corrosion remains a relevant issue.Aim. In this work, the state of this problem, along with the methods for determining the chloride content in concrete, was assessed in order to propose the means to increase its protective action in aggressive chloride media.Materials and methods. This article discusses the following issues:– maximum permissible chloride content in concrete;– binding of chlorides by components in the matrix, the role of the mineral composition of cement;– critical evaluation of methods for determining the chloride content in concrete;– reduction of the diffusion permeability of chlorides in concrete as a method of corrosion protection.Results. The article presents the data on moisture tests of reinforced concrete prepared using Portland cement having various contents of alite, belite, and tricalcium aluminate, as well as CaCl2 additive.Indicated were the challenges of identifying aggressive free chlorides in the matrix. The need to develop a standard method for determining free chlorides in concrete was discussed. Until such a standard is developed, the chloride aggressiveness to steel in concrete can be assessed by the electrochemical method. It was shown that concretes of extremely low diffusion permeability obtained using advanced complex additives that reduce the water demand of concrete mixtures and change the charge of the matrix surface can be used as a protection measure against chloride corrosion.Presented are the results of determining the potentials of steel in concrete by electrochemical method, chlorides in concrete by colorimetric method, and diffusion permeability of chlorides in concrete.Conclusion. The corrosion activity of chlorides against reinforcing steel depends on a large number of factors, including the total chloride content and the amount of free, physically, and chemically bound chlorides.Since chloride binding depends on a large number of technological factors, it is recommended to perform electrochemical tests of reinforcing steel in concrete as per GOST 31383 to assess the hazard level of chlorides introduced into concrete with initial materials; a decision on the protective measures for reinforcing steel in chloride environments should be made on the basis of the obtained results.

Chloride binding behaviors and early age hydration of tricalcium aluminate in chloride-containing solutions

Understanding the hydration kinetics and interactions of hydration products of cement components with chlorides is crucial for designing durable cement-based materials. The most reactive component of ordinary Portland cement (OPC), tricalcium aluminate (C3A), was investigated on its hydration kinetics, chloride binding behaviors and hydrated phase assemblages through multiple ex-situ and in-situ methods. The hydrated phases of C3A demonstrated different chloride binding isotherms in NaCl and CaCl2 solutions at different ages. Chloride ions can suppress the formation of calcium aluminate hydrates (OH-AFm and C3AH6) while calcium ions were favorable to increase the content of hydrocalumite (Cl-AFm) and regulate its crystal structure. The carbonation process deteriorated the chloride binding capacity of C3A pastes through producing more calcium mono/hemi-carboaluminate phases (Mc/Hc) or forming a solid solution between Mc and Cl-AFm. These findings can be used as a guide for corrosion protection design of cement-based materials.

JUSTIFICATION FOR THE BUILDING MATERIALS REQUIREMENTS IN THE ASPHALT PAVEMENT REPAIR BY THE CEMENT CONCRETE LAYERS

This scientific text examines the main requirements for the composition of cement-concrete mixtures for pavement layers. In particular, it is noted that to obtain high-strength cement concrete, type I and II Portland cement should be used with the content of tricalcium aluminate (C3A) in an amount of no more than 8% by weight. To increase the strength of concrete, it is recommended to add steel or polypropylene fiber. Coarse aggregate of high-strength modified cement concrete can be crushed stone from dense rocks. To obtain high-strength cement concrete, it is also necessary to take into account the requirements for sand, and entraining additives and calculate the composition of concrete in accordance with the methodology for road cement concrete. Ensuring the necessary frost resistance is achieved by selecting the optimal composition of the concrete mixture and using highly active cement. In addition, the text specifies the requirements for the transportation of the concrete mixture, the slump of the cone, the volume of entrained air, and the preservation of concrete properties. The final technological properties of the concrete mixture are evaluated at the design stage.

Mechanisms of hydration heat inhibitors on the early heat release process of cement

We evaluated the effects of hydration heat inhibitors on the early hydration heat release process of cement and its main mineral components. We used a microcalorimetric method to determine the effects of various proportions and properties of hydration heat inhibitors on the hydration of portland cement, tricalcium silicate, and tricalcium aluminate: concentration (C) = 40% m/m hydroxydiphosphonic acid (HEDP) (1-hydroxyethylidene-1,1-diphosphonic acid) and C = 40% m/m diethylene triamine pentonyphosphonic acid (DTPMPA) (diethylenetriaminepentamethylene phosphonic acid). We also analyzed and tested the heat release rate and cumulative heat release during the hydration of cement and its main mineral components. The hydration heat inhibitors decreased the heat release rate of cementitious materials by means of adsorption, chelation, precipitation, complex formation, and control of calcium hydroxide crystals. Among these materials, the hydration heat inhibitor had the most substantial effect on the composition of tricalcium silicate clinker, reducing the peak temperature at the initial stage of hydration and delaying its occurrence time. These results are pertinent to controlling and selecting the early hydrothermal release process of cement systems.

Efficient models to evaluate the effect of C3S, C2S, C3A, and C4AF contents on the long-term compressive strength of cement paste

The primary chemical compositions of the cement are CaO, SiO2, Al2O3, and Fe2O3, while minor compositions are MgO, K2O, Na2O, and SO3. In this study, 142 data were collected from different research studies. The dataset was analyzed and modeled to forecast the compressive strength of cement paste (cubic sizes). The samples were cured at room temperature (25 °C). The essential input model parameters were tricalcium silicate (C3S%), which ranged from 31.5 to 73.74; dicalcium silicate (C2S%), which varied between 2.73 and 40.78; Tricalcium Aluminate (C3A%) ranged from 0.85 to 12.45, Calcium Aluminoferrite (C4AF%) varied from 4.1 to 14.9, Calcium Oxide (CaO%) varied between 60.12 and 65.74, Silicon Dioxide (SiO2%) ranged from 19.4 to 24.78, Aluminum Oxide (Al2O3%) varied between 1.72 and 6.18, Iron (III) Oxide (Fe2O3%) ranged between 1.35 and 4.9, water to cement ratio varied between 0.25 and 0.7, and curing time ranged from 1 to 90 days. The output parameter was compressive strength with 18 to 57 MPa. A linear, non-linear, multi-linear, full quadratic, and interaction regression model was used to predict the compressive strength of cement paste for the data collected from the literature. Based on statistical tool assessments such as objective function (OBJ), mean absolute error (MAE), coefficient of determination R2 functions, and scatter index, the full quadratic model with the lowest root means square error (RMSE) performed better than the other models in predicting the compressive strength of cement paste. In addition, CaO proved to be the most productive parameter of the compressive strength of cement paste. At the same time, Al2O3 was found to be the least influential variable in terms of the compressive strength of cement paste. The effect of various chemical components such as CaO, SiO2, Al2O3, Fe3O2, C3S, C2S, C3A, C4AF, water-to-cement ratio, and curing time on the long-term compressive strength of cement paste. Also, no study can be found in the literature comparing the efficiency of four models with very good accuracy in predicting the compressive strength of the cement paste. From now towards, researchers and the construction industry can use the developed models in this study with high accuracy (low RMSE and high R) to predict the compressive strength of the cement paste without any cost. They would save lots of time for the experimental lab work.

Chemical-Physical Properties and Bioactivity of New Premixed Calcium Silicate-Bioceramic Root Canal Sealers.

The aim of the study was to analyze the chemical-physical properties and bioactivity (apatite-forming ability) of three recently introduced premixed bioceramic root canal sealers containing varied amounts of different calcium silicates (CaSi): a dicalcium and tricalcium silicate (1-10% and 20-30%)-containing sealer with zirconium dioxide and tricalcium aluminate (CERASEAL); a tricalcium silicate (5-15%)-containing sealer with zirconium dioxide, dimethyl sulfoxide and lithium carbonate (AH PLUS BIOCERAMIC) and a dicalcium and tricalcium silicate (10% and 25%)-containing sealer with calcium aluminate, tricalcium aluminate and tantalite (NEOSEALER FLO). An epoxy resin-based sealer (AH PLUS) was used as control. The initial and final setting times, radiopacity, flowability, film thickness, open pore volume, water absorption, solubility, calcium release and alkalizing activity were tested. The nucleation of calcium phosphates and/or apatite after 28 days aging in Hanks balanced salt solution (HBSS) was evaluated by ESEM-EDX, vibrational IR and micro-Raman spectroscopy. The analyses showed for NeoSealer Flo and AH Plus the longest final setting times (1344 ± 60 and 1300 ± 60 min, respectively), while shorter times for AH Plus Bioceramic and Ceraseal (660 ± 60 and 720 ± 60 min, respectively). Radiopacity, flowability and film thickness complied with ISO 6876/12 for all tested materials. A significantly higher open pore volume was observed for NeoSealer Flo, AH Plus Bioceramic and Ceraseal when compared to AH Plus (p < 0.05), significantly higher values were observed for NeoSealer Flo and AH Plus Bioceramic (p < 0.05). Ceraseal and AH Plus revealed the lowest solubility. All CaSi-containing sealers released calcium and alkalized the soaking water. After 28 days immersion in HBSS, ESEM-EDX analyses revealed the formation of a mineral layer that covered the surface of all bioceramic sealers, with a lower detection of radiopacifiers (Zirconium for Ceraseal and AH Plus Bioceramic, Tantalum for NeoSealer Flo) and an increase in calcium, phosphorous and carbon. The calcium phosphate (CaP) layer was more evident on NeoSealer Flo and AH Plus Bioceramic. IR and micro-Raman revealed the formation of calcium carbonate on the surface of all set materials. A thin layer of a CaP phase was detected only on AH Plus Bioceramic and NeoSealer Flo. Ceraseal did not show CaP deposit despite its highest calcium release among all the tested CaSi-containing sealers. In conclusion, CaSi-containing sealers met the required chemical and physical standards and released biologically relevant ions. Slight/limited apatite nucleation was observed in relation to the high carbonation processes.

Influence of carlin-type gold mine tailings addition on the synthesis temperature, alkali-resistant performance, and hydration mechanism of Portland cement

The massive discharge of carlin-type gold mine tailings (GMT) has caused serious harm to the environment, such as occupying land and building tailings dams. However, GMT is rich in SiO2 and CaO, which is likely to be a material for the synthesis of Portland cement in theory. Thus, this work synthesized four Portland cement with GMT addition of 0.00, 5.00, 10.00, and 15.00 wt%, and investigated their synthesis temperature, mineral phase composition, alkali-resistant performance, and hydration mechanism via the CaO free test, X-ray diffraction, compressive strength ratio, electron microscopy, and thermogravimetric analyzer. Results show that the synthesis temperature decreases by 100 °C when the GMT addition in raw materials exceeds 10.00 wt%. The mineral phase composition of these synthesized Portland cement is alite, larnite, tricalcium aluminate, and tetra-calcium aluminoferrite; their hydration phase is rod-like AFt, nubby CSH, and sheet-like Ca(OH)2; both are the same as that of Portland cement without GMT. Results also show that the Portland cement synthesized with 10.00 wt% GMT performs better on the compressive strength (24.7/18.5 MPa at 7 days and 56.1/48.6 MPa at 28 days) and alkali-resistant (0.75 at 7 days and 0.87 at 28 days) since the highest output of the total AFt and CSH (8.50/13.25 wt% at 7/28 days) and the Ca(OH)2 (5.89/11.57 wt% at 7/28 days). This work proves that GMT as a material for the synthesis of Portland cement is viable, and provides an effective method for the resource utilization of GMT.

Mechanism of activator and pore surface adsorption in aluminum-based flameless ration heaters: A molecular dynamics study

The aluminum-based flameless ration heaters (FRHs) in self-heating food packaging are the heating elements, while water is the activator. Inevitable inadequate reactions can lead to reduced heating capacity and material waste. The transport behavior of activators (water and ions) in the main components of FRHs was investigated with molecular dynamics to study the mechanism of low exothermic efficiency. This paper transported a mixed solution composed of calcium ions, sodium ions, chloride ions, and water in the nanopores with three pore sizes 1.0, 1.5, and 2.5 nm. Results demonstrate that the formation of hydrogen bonds at the surface of tricalcium aluminate (C3A) with water can slow the movement of water molecules. Sodium, calcium ions, and oxygen atoms on the surface of C3A combine competitively through surface chemical bonding, forming Ca-O and Na-O bonds. In addition, as the pore size becomes smaller, the hindering effect of the nano-pore channel becomes stronger. Calcium ions and chloride ions form ion pairs through ionic bonding, which can continuously aggregate to hinder the transport of water molecules and ions. This work provides a basis for understanding the study of the transport and adsorption behavior of liquids in C3A pores and provides a viable idea for subsequent experimental studies.

Solubility of tricalcium aluminate from 10 °C to 40 °C

Fundamental reaction-transport models of Portland cement hydration have been difficult to refine and validate because of the challenge of obtaining accurate data on the reaction rates and solubility of the four major clinker phases. Here we provide the first measurements of the solubility product of cubic tricalcium aluminate (C3A) as a function of temperature between 10 °C and 40 °C. The measurements were obtained by examining dissolution rates as a function of solution saturation and extrapolating the lowest dissolution rates to zero by nonlinear regression. That procedure yields ln Ksp(C3A), for the dissolution: C3A + 2H2O = 3Ca2+ +2AlO2− + 4OH−, of −43.74, −48.02, −49.48 and −50.56 at temperatures of 10 °C, 20 °C, 30 °C and 40 °C, respectively. These Ksp data were regressed to several candidate temperature models used in thermodynamic modeling to estimate the functional dependence of the standard Gibbs energy of dissolution on temperature. The results can be used to refine thermodynamic models of cementitious materials and related simulation approaches for predicting microstructure development of concrete binders.

Deconvolution of main hydration kinetic peaks in properly sulfated Portland cements with boundary nucleation and growth models and relation to early-age concrete strength development

When the hydration kinetics of properly sulfated Portland cements is monitored by heat flow calorimetry, the initial dissolution peak and the dormant period is followed by the main hydration peak – formation of calcium-silicate-hydrates and portlandite, the so-called silicate peak. This main peak is superimposed by a peak associated to further tricalcium aluminate dissolution and a surge in precipitation of sulfoaluminates (the so-called sulfate depletion peak) right after sulfate added for setting control is depleted in the material system. In this paper strategies for the deconvolution of silicate peak and sulfate depletion peak are presented. Hereby, the boundary nucleation and growth model and the classical bulk nucleation and growth model serve as tools for deconvolution of calorimetric data. We discuss obtained kinetic parameters and their temperature dependency. The boundary nucleation and growth model for constant nucleation rate emerged as the most suitable model for the silicate reaction, the bulk nucleation and growth model with an order of three, indicating site saturation, as adequate for the sulfate depletion peak. The reaction enthalpy for tricalcium silicate hydration was obtained as 503 J/g, remarkably close to literature values. Calorimetric data related to the sulfate depletion peak is corroborated by X-ray diffraction analysis of formation history of crystalline hydration products. Furthermore, the history of the (silicate) degree of reaction as predicted by the boundary nucleation and growth model for different temperature histories is related to experimentally obtained early-age strength histories. • Investigation of hydration kinetics of commercial, well-sulfated Portland cement. • Main peak (C-S-H and portlandite formation) superimposed by sulfate depletion peak. • Strategies for deconvolution of peaks with Avrami–Cahn models as tools for analysis. • Degree of silicate reaction history is linked to early-age strength gain.

Synthesis of White Mineral Trioxide Aggregate (WMTA) Using Silica from Rice Husk Ash and CaCO<sub>3</sub> from Limestone

White mineral trioxide aggregate (WMTA) was successfully synthesized using silica from rice husk ash (RHA) and precipitate calcium carbonate (PCC) from limestone. Silica was synthesized from rice husk ash by the sol-gel method with the help of a strong base NaOH to obtain sodium silicate solution. In contrast, PCC in the calcite structure was extracted from limestone by a carbonation method. The limestone powder sample was calcined at 900 °C for 3 hours, dissolved in 0.8 M nitric acid solution, and was followed by carbonation for 60 minutes. The synthesis of WMTA was carried out by mixing silica, PCC, bismuth oxide, aluminum oxide, NH3 solution catalysts and treating the mixture thermally at 950 °C for 3 hours. Products were characterized by Fourtier-Transform Infrared (FTIR) spectroscopy, X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). The results showed that the RHA silica had an amorphous phase that peaked at 2θ= 22°, but the background intensity was irregular. The PCC obtained through isolation from limestone is predominantly calcite structure. WMTA has been successfully synthesized by thermal treatment at 950 °C using NH3 solution catalyst, as evidenced by the presence of tricalcium silicate (C3S), dicalcium silicate (C2S), tricalcium aluminate (C3A), and Bi2O3.

The Composition and Origin of PM1-2 Microspheres in High-Calcium Fly Ash from Pulverized Lignite Combustion

This article presents the results of a systematic study on the composition and origin of PM1-2 microspheres in high-calcium fly ash. The composition of individual microspheres was studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy. It is shown that the compositions of the analyzed microspheres satisfy the general dependency with a high correlation coefficient: [SiO2 + Al2O3] = 88.80 − 1.02 [CaO + Fe2O3 + MgO], r = −0.97. The formation pathway is parallel to the general trend: anorthite, gehlenite, esseneite, tricalcium aluminate, ferrigehlenite, and brownmillerite. The microspheres were classified into four groups depending on the content of major components: Group 1 (CaO > 40, SiO2 + Al2O3 ≤ 35, Fe2O3 < 23, MgO < 16 wt %); Group 2 (30 < CaO < 40, SiO2 + Al2O3 ≤ 40, Fe2O3 < 27, MgO < 21 wt %); Group 3 (CaO ≤ 30, 40 ≤ SiO2 + Al2O3 ≤ 75, Fe2O3 < 10, MgO < 10 wt %); and Group 4 (14 < CaO < 40, SiO2 + Al2O3 < 14, Fe2O3 > 30, MgO ≤ 14 wt %). A comparative analysis of the relationship between major component concentrations suggests the routes of PM1-2 formation from feldspars and Ca–, Mg–, and Fe–humate complexes during lignite combustion.

An accelerated physical sulfate attack test using an induction period and heat drying: First applications to concrete with different binders including ground glass pozzolan and limestone filler

This study aims to investigate an accelerated protocol to test physical sulfate attack on concrete with different types of binders. To speed up the accumulation of sodium sulfate within the binder matrix and the initiation of the mirabilite-thenardite phase transition, the proposed protocol consists of heat drying specimens before and after 15 days of immersion in a concentrated sodium sulfate solution. After this preconditioning, the partial immersion mode under dry-wet cycling regimes was found to result in higher visual damage compared to the full-immersion mode. For similar water absorption rates, concrete prepared with general use cement and high sulfate resisting cement showed similar deterioration rates despite their different tricalcium aluminate contents. Partial replacement of cement with 20% ground glass pozzolan delayed concrete damage contrary to the replacement with 10% limestone which resulted in faster physical sulfate attack.

Hydration behavior and formation of strätlingite compound (C2ASH8) in a bio-cement based on tri-calcium silicate and mono-calcium aluminate for dental applications: influence of curing medium

BackgroundThe aim of this work was to study the influence of simulated body fluid (SBF) and Pseudomonas aeruginosa (in Mueller Hinton Broth, MHB media) on the hydration reactions, formation of strätlingite (C2ASH8) and morphology of a composite material based on nano-size tri-calcium silicate (C3S) and tri-calcium aluminate (CA) phases. The two experimental phases were prepared in laboratory by firing the required molar ratios of chemically pure reactants by solid-state reactions at elevated temperatures. Investigation of setting time, micro-hardness, pH of immersion solution, X-ray diffraction analysis, infrared spectroscopy, scanning electron microscopy and cytotoxicity were also carried out.ResultsThe results emphasized that the hydrated compounds of C3S phase can partly solve the problem of conversion process through the formation of the more stable and highly mechanical stratlingite hydrate (C2ASH8) plates that results in an increase in hardness values for samples cured in distilled water (DW) at 37 °C. The SBF solution showed more strength loss than those cured in Pseudomonas aeruginosa microbe (MHB) medium bacterial solution. SEM and EDAX analyses emphasized the formation of hydroxyapatite at 37 °C.ConclusionsThe prepared cements are promising for dental application.

Influence of liquid accelerator based on sodium aluminate on the early hydration of cement, C3A and C3S pastes

The objective of this study was to explore the influence of an alkali liquid accelerator based on sodium aluminate (ASa) on the early hydration behaviour of cement paste, tricalcium aluminate (C3A) and tricalcium silicate (C3S) and identify its accelerating mechanism. The setting times and mechanical properties of cement paste and mortar mixed with different amounts of ASa were determined. Isothermal calorimetry showed that the addition of ASa increased the first exothermic peak of cement hydration and advanced the second exothermic peak. The morphology of hydration products was analysed by scanning electron microscopy (SEM) and a model for the early hydration of cement paste was established. X-ray diffraction and SEM were also used to analyse the phase composition and morphology changes of C3A and C3S with or without ASa and early hydration models were established. Analysis of the experimental results revealed that the sodium hydroxide produced by ASa hydrolysis had the function of consuming gypsum, breaking calcium silicate hydrate gel film and increasing the calcium hydroxide concentration in the cement paste. The ettringite in the hydration products interweaved together to form a skeleton structure, which was conducive to cement paste hardening.

Influence of the availability of calcium on the hydration of tricalcium aluminate (C3A) in seawater‐mixed C3A–gypsum system

AbstractThis work examined the effects of seawater (SW) on the hydration of tricalcium aluminate (C3A) in C3A–gypsum and C3A–gypsum–Ca(OH)2 systems through the characterization of hydration heat release, the evolution of aqueous phase composition and hydration products with the hydration time. It was found that SW increased the dissolution driving force of C3A and solubility of gypsum, which accelerated the early hydration of C3A and the formation of ettringite (AFt), leading to a higher hydration degree of C3A at an early age compared with the deionized (DI) water–mixed pastes. After gypsum depletion to form AFt, and in the absence of Ca(OH)2, the formation of chloroaluminate hydrates was slower due to the insufficient Ca resulted in an accumulation of Al in solution. This would delay the subsequent transformation of AFt to monosulfate (SO4–AFm) and the formation of hydrogarnet (C3AH6), which would further reduce the hydration degree of the C3A at the later ages. However, in the presence of Ca(OH)2, the hydration degree of C3A–gypsum–Ca(OH)2 at later ages was increased, which was similar to that of the corresponding DI pastes. This can be inferred that the amount of Ca available in SW‐mixed cement concrete can affect the hydration degree of C3A in cement.

Mineralogy of tricalcium aluminate hydration with silica nanoparticles

Formation of siliceous-hydrogarnet (Si-hydrogarnet) and stability of katoite (C3AH6) in tricalcium aluminate (C3A) system in presence of silica nanoparticles (n-SiO2) have been examined in the present study. C3A hydration in presence of n-SiO2 upto 24 h show retardation in hydration due to the surface coverage of C3A grain through calcium-silicate-hydrate (C-S-H)/calcium-alumino-silicate-hydrate (C-A-S-H) (previous study). However, in the present investigation, hydration was studied upto 10 days using QXRD, TGA, FTIR, FESEM, EDS and Mapping and 29Si NMR techniques. QXRD results show that in case of control samples, the katoite content increases from 61 to 73%, while in n-SiO2 incorporated C3A samples, it decreases from 28 to 15% as the hydration proceeds showing katoite phase destabilization in presence of n-SiO2. Further, FTIR results show symmetric stretching vibration of Si-O-Si at ∼784 cm−1 and ∼818 cm−1, while asymmetric stretching vibration of Si–O–Si/Si-O-Al at ∼1028 cm−1 indicating the formation of C-S-H/C-A-S-H and Si-hydrogarnet in presence of n-SiO2. In 29Si NMR results, Q2u peak at −89 ppm confirm the formation of Si-hydrogarnet at 10 days of hydration. The present study is important from performance and durability point of view as formation of C-A-S-H and Si-hydrogarnet can act as an aluminum reservoir, which may prevent severe chloride and sulphate attack.

Portland and Belite Cement Hydration Acceleration by C-S-H Seeds with Variable w/c Ratios.

The acceleration of very early age cement hydration by C-S-H seeding is getting attention from scholars and field applications because the enhanced early age features do not compromise later age performances. This acceleration could be beneficial for several low-CO2 cements as a general drawback is usually the low very early age mechanical strengths. However, the mechanistic understanding of this acceleration in commercial cements is not complete. Reported here is a contribution to this understanding from the study of the effects of C-S-H gel seeding in one Portland cement and two belite cements at two widely studied water–cement ratios, 0.50 and 0.40. Two commercially available C-S-H nano-seed-based admixtures, i.e., Master X-Seed 130 and Master X-Seed STE-53, were investigated. A multi-technique approach was adopted by employing calorimetry, thermal analysis, powder diffraction (data analysed by the Rietveld method), mercury intrusion porosimetry, and mechanical strength determination. For instance, the compressive strength at 1 day for the PC (w/c = 0.50) sample increased from 15 MPa for the unseeded mortar to 24 and 22 MPs for the mortars seeded with the XS130 and STE53, respectively. The evolution of the amorphous contents was determined by adding an internal standard before recording the powder patterns. In summary, alite and belite phase hydrations, from the crystalline phase content evolutions, are not significantly accelerated by C-S-H seedings at the studied ages of 1 and 28 d for these cements. Conversely, the hydration rates of tetracalcium alumino-ferrate and tricalcium aluminate were significantly enhanced. It is noted that the degrees of reaction of C4AF for the PC paste (w/c = 0.40) were 10, 30, and 40% at 1, 7, and 28 days. After C-S-H seeding, the values increased to 20, 45, and 60%, respectively. This resulted in larger ettringite contents at very early ages but not at 28 days. At 28 days of hydration, larger amounts of carbonate-containing AFm-type phases were determined. Finally, and importantly, the admixtures yielded larger amounts of amorphous components in the pastes at later hydration ages. This is justified, in part, by the higher content of amorphous iron siliceous hydrogarnet from the enhanced C4AF reactivity.

Microscopic phase identification of cement-stabilized clay by nanoindentation and statistical analytics

The mechanical properties of cement-stabilized clay (CSC), are significantly inferior to that of concrete and mortar due to the presence of clay minerals. To reveal the interaction between clinker's functional constituent and clay minerals within the CSC matrix to promote the performance of stabilized clay, large data sets cross-scale nanoindentation coupled with thermogravimetric analyses were involved. Two commercially available clays (i.e., kaolin and bentonite, whose dominant clay minerals are kaolinite and montmorillonite, respectively) stabilized by two key functional constituents of cement clinker, i.e., tricalcium silicate (C3S) and tricalcium aluminate (C3A), were investigated to unravel the primary hydration of the cement clinker, pozzolanic reactions with clay minerals, and the microstructure's evolution. Large data sets of elastic modulus and hardness derived from the nanoindentation tests were statistically investigated by two deconvolution methods: probability density function and cumulative distribution function. The results indicated that calcium silicate hydrates (C-S-H) and calcium aluminate hydrates (C-A-H) were the major reaction products for C3S-stabilized and C3A-stabilized clays. However, during the secondary pozzolanic reaction process, the dissolved colloids from the clay minerals and the hydrated products would react and accumulate at the interface between the primary cementitious paste and clay particles to form a new soft, porous phase. The deconvolution and thermogravimetric analysis also indicate that more pozzolanic products and high-density (HD) porous phases were detected in bentonite than in kaolin, suggesting that the pozzolanic reaction in montmorillonite is much more pronounced than that in kaolinite. This understanding can clarify the interaction between clay minerals, hydration products, and distinct CSC for traditional cementitious materials.