Initial Hydration Period Research Articles

Study on the influence of nano-silica substitution of reactive Si on the properties and hydration process of alkali-activated cementitious materials paste

Nano-silica (NS) is one of the most commonly used nanomaterials in alkali-activated materials (AAMs). Differing from other inactive nanoparticles, as an active Si source, the pozzolanic activity of NS has a significant effect on the hydration reaction and properties of alkali-activated materials. In this study, activated Si in the activator was replaced by NS to prepare alkali-activated slag/fly ash cementitious materials. The effects of different dispersion methods (dry-mix (MD), water dispersion (WD), and activator dispersion (AD)) of NS on the fluidity, rheological properties, and setting time of fresh pastes were investigated. Effects of NS and reactive Si in the activator on the hydration process of alkali-activated slag/fly ash paste were investigated using isothermal calorimetry and the Krstulović-Dabić hydration model. ICP-OES was utilized to study the changing behavior of the composition of the fresh paste pore solution during the hydration reaction. The results show that ions in the pore solution change continuously with the hydration time and eventually stabilize. The stabilized pore solution is mainly composed of OH- and Na+. Different NS dispersion methods have significant effects on paste workability, rheology, and setting time. Activator dispersion can elevate the content of active Si in the activator, causing changes in the hydration process of the paste, especially for the initial hydration period. NS has the most significant effect on the hydration process due to its pozzolanic activity compared to nucleation and filling effects. The Krstulovic-Dabic model can roughly simulate the hydration kinetics possessed of alkali-activated NS/slag/fly ash after entering the accelerated period.

Effect of alkali sulfates in clinker on hydration and hardening properties of cement incorporating SCMs

Fly ash and slag are widely used in cement production. The effect of alkali sulfates in clinker on hydration and hardening of cement blended with fly ash and slag is studied. The results of hydration heat evolution, hydrates analysis and mechanical properties indicate arcanite (K2SO4), thenardite (Na2SO4), aphthitalite (3K2SO4·Na2SO4, K3NS4) and Ca-langbeinite (K2SO4·2CaSO4, KC2S3) in clinker could activate the pozzolanic activity of fly ash and slag, facilitating the appearance of the second hydration peak in the initial hydration period, and promote the hydration and hardening properties of blended cement. The adverse effects of alkali sulfates in clinker are alleviated with the addition of fly ash and slag; this can be attributed to the dilution and filler effects of supplementary cementitious materials (SCMs), as well as the effect of the alkali sulfates activating fly ash and slag. Arcanite, thenardite and aphthitalite (K3NS4) provide a better activating effect on mortar with slag than fly ash mortar to increase compressive strength and reduce drying shrinkage when the content of alkali sulfates is less than 0.6% sodium oxide equivalent (Na2Oeq).

Relevance and Efficiency of Using Nanosized Particles in Structuring Cement Pastes

The relevance of the use of nanosized particles in the structuring of cement pastes is due to the ability at the micro level to control the processes occurring during the hardening of cement. And it also provides the ability to purposefully control the composition of hydrated neoplasms. Plasticizer-stabilized aqueous suspensions of nanosized particles of non-hydraulically active materials in a cement matrix cause forced crystallization of hydrated neoplasms from a supersaturated liquid phase. And they act as seeds introduced from the outside, on the surface of which neoplasms are concentrated, that subsequently combine into conglomerates that make up the structure of a cement stone. The formation of the structure of the cement matrix occurs without the formation of large the portlandite fields, which are typical for no additive portland cement. The structure of a cement stone with nanosized particles is represented by poorly crystallized flaky calcium hydrosilicates. It was found that the degree of hydration of cements with suspensions of nanoparticles is 15-18% higher. The efficiency of using nanosized particles in structuring cement pastes is giving the cement paste mobility in the initial period of hydration and the possibility of plasticizing it without blocking the surface of cement particles with surfactants. On the other hand, it makes it possible to obtain dense and durable structures of a cement matrix with improved physical and mechanical characteristics. The porosity of cements with suspensions is lower on 15 - 20%, and after 28 days of hardening it is lower on 20 - 35% than that of non-additive cement. And the strength of the samples after 24 hours increased 1.5 - 1.8 times (from 19.5 to 27 - 34 MPa), at the brand age by 15 - 24% (from 64 to 75 - 80 MPa)

Hydration and Mechanical Properties of Calcium Sulphoaluminate Cement Containing Calcium Carbonate and Gypsum under NaCl Solutions.

Hydration characteristics and mechanical properties of calcium sulphoaluminate (CSA) cement with different contents of CaCO3 and gypsum under NaCl solutions were studied, using the testing methods of isothermal calorimetry, X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), linear shrinkage, and compressive strength. Results show that CaCO3 can promote hydration and reduce the hydration heat of CSA cement. The reaction between gypsum and C4A3 releases a large quantity of heat in the initial hydration period; however, over 3 days of accumulation, the level of hydration heat is reduced. Under NaCl solutions, the aluminate phase has difficulty reacting with CaCO3 to form carbonate phase but combines with chloride ions to form Friedel’s salt. On the contrary, gypsum reduces aluminate phase, and the content of Friedel’s salt is also reduced. Furthermore, CaCO3 and gypsum both increase the total porosity of the CSA cement paste under NaCl solutions during the early curing phase, and over the long-term, pore structure is also optimized. CaCO3 and gypsum reduce the linear shrinkage of CSA cement paste under NaCl solutions. Overall, the compressive strength of CSA cement is reduced with the addition of CaCO3, and the trend will be sharper with the increase in CaCO3. However, when it comes to gypsum, the compressive strength is almost the same during early curing, but in the long-term, compressive strength improves. Essentially, the compressive strength of CSA cement mortar with CaCO3 and gypsum will improve under NaCl solutions.

Microstructure and mechanical properties of activated high-alumina ferronickel slag with carbide slag and alkaline salts

Alkali-activated materials have several remarkable advantages over Portland cement particularly in carbon emission and energy consumption. However, less work has focus on the feasibility of preparing geopolymers from high-alumina ferronickel slag (AFS) with alkaline salts as activators. This article reports the microstructure and mechanical properties of activated high-alumina ferronickel slag (AAFS) with a combination of carbide slag (CS) and Na2CO3 (SC) or Na2SO4 (SS). Results indicate that the AAFS pastes properties are affected by concentration (Na2O equivalent) and nature of activator. The hydration of high-alumina ferronickel slag (FNS) is accelerated as the Na2O equivalent increases from 0.5% to 3% regardless of alkaline salt type, while the early age hydration will be restricted when Na2O equivalent is higher than 3%. The pH of pore solution in SS-activated series is lower than that of SC-activated series. As such, SC-activated FNS pastes have higher exothermic heat in the initial hydration period than SS dosed specimens. Although SC-activated pastes have more gel products and smaller critical pore diameter, the SS-activated specimens can achieve higher compressive strength due to compact interfacial transition zone and reasonable hydration products composition.

Analyzing the early structural build-up of accelerated cement pastes

Extrusion-based additive manufacturing imposes high requirements on the material stability right after the extrusion. Therefore, a thorough understanding of the chemical reactions that determine the early reduction in processability is necessary. Accelerators are especially considered here, which have a major influence on the early reaction. This study contributes to these issues by analyzing the influence of 0.1 wt% TEA (triethanolamine) and 2.0 wt% Ca(NO3)2 on the hydration of two CEM I 52.5 R. The hydration was analyzed by isothermal heat flow calorimetry and in-situ X-ray diffraction. Vicat needle penetration, a penetrometer of own design, and ultrasonic P-wave velocity development were used to monitor the early change in workability. The obtained results indicate that ettringite formation is the main factor influencing workability during the first 60 min of hydration. Afterwards, the influence of ettringite is exceeded by the formation of C–S–H. Ca(NO3)2 was shown to enhance C–S–H formation and had no significant effect on the workability during the first 60 min of hydration while rapidly decreasing workability during the induction period. TEA was shown to increase brownmillerite dissolution and ettringite formation and, consequently, promote the workability loss during the initial hydration period. The time of initial and final setting determined by the Vicat needle test depended mainly on the formation of C–S–H phases.

Investigating factors influencing polymer elution and the mechanism controlling the chemical compatibility of GCLs containing linear polymers

A study was conducted to investigate (1) physicochemical factors that influence polymer elution from GCLs containing a blend of bentonite and linear (water-soluble) polymer (LPB GCLs) and (2) the mechanism that controls the chemical compatibility of LPB GCLs when polymer elutes. A series of hydraulic conductivity (k), free swell and viscosity tests were performed on a commercial LPB GCL using DI water, varying concentrations of NaCl and CaCl₂. Comparable tests were also performed on a conventional bentonite (CB) GCL containing the same untreated bentonite and the same physical properties as the LPB GCL. The LPB GCL showed improved swelling and hydraulic performance compared to the CB GCL when permeated with salt solutions. Total organic carbon analysis of the effluents showed that polymer eluted from the LPB GCL regardless of the permeant solution. However, the rate at which polymer eluted increased as the concentration and valence of the dominant cation increased. The rate at which polymer eluted also increased with hydraulic gradient. The mass of polymer retained inside the GCL matrix did not correlate with the k of the LPB GCL. Free swell tests coupled with chemical analysis suggest that, the improved chemical compatibility of the LPB GCL was due to the ability of the polymer to scavenge cations from the solution which allows the bentonite to undergo adequate swelling during the initial hydration period. Analogous to water-prehydrated CB GCLs, the dispersed structure of the bentonite fabric and increased adsorbed water molecules attained during initial swelling controls the k of the LPB GCL when polymer elutes.

Undissolved Ilmenite Mud from TiO2 Production—Waste or a Valuable Addition to Portland Cement Composites?

This paper presents a method of utilising ilmenite MUD created during the production of titanium dioxide (TiO2) according to the sulphate method as an additive for Portland cement composites. After the production process, undissolved MUD was additionally rinsed with water and filtrated in the factory to make it more useful (R-MUD) for implementation and also to turn back some of the by-products of the production of TiO2. R-MUD is less hazardous waste than MUD. It has a lower concentration of sulphuric acid and some heavy metals. The rinsing process raised the concentration of SiO2, which is a valuable part of R-MUD because of its potential pozzolanic activity. This means that the R-MUD might be a reactive substitute of part of Portland cement in building composites. The article presents the results of research on the pozzolanic activity of R-MUD and other materials with proved pozzolanic activity, such as silica fume, fly ash and natural pozzolana (trass). Tests were performed using thermal analysis techniques. The tests showed that the pozzolanic activity or R-MUD after three days is at the same level as silica fume and after 28 days it is twice as high as the activity of fly ash. Beyond the 180th day of curing, R-MUD had the same level of activity as fly ash. The summary is supplemented by calorimetric tests, which confirm the high reactivity of R-MUD compared to other commonly used concrete additives, already in the initial hydration period. In summary, heat of hydration after 72 h of Portland cement with R-MUD is at the same level as the heat of hydration of Portland cement with silica fume and also pure Portland cement grout. The results confirm that the process of formation of micro-silica contained in R-MUD react with calcium hydroxide to form the C-S-H phase, which is responsible for the microstructure of cement composites.

Investigation of the early-age microstructural development of hydrating cement pastes through electrical resistivity measurements

The non-contact electrical resistivity method was employed to investigate the microstructural development of three grades of cement under a fixed water-to-cement ratio (w/c) and the same curing conditions. The method was verified by measuring the heat of hydration and estimating the degree of hydration of the three pastes. The results showed that the existence of a linear relationship between the compressive strength at 28 d (f 28) and bulk electrical resistivity at 72 h (ρ72); thus, the proposed method can be used to assess the strength of cement. Moreover, the results indicated that the quality of cement can be further distinguished by interpreting the trend in the resistivity curve. The high-strength cement will have lower electrical resistivity values during cement dissolution due to the higher content of ions in the pore solution, while it will have higher resistivity values during cement hardening due to the greater amount of hydrates. The electrical resistivity of the cement solution (ρ0) filtered from the cement paste at an early age was measured to demonstrate the effect of the ionic concentration on the bulk electrical resistivity in the initial hydration period. The measured liquid resistivity of cement can be used as an indication of clinker reactivity; higher-strength cement will always have lower measured values. The rate of electrical resistivity development curve was plotted to elucidate the setting range of cement pastes based on three critical points. The time at the second critical point (C2) coincided with the final setting time determined using a Vicat needle. New general relationships between the gel-space ratio and electrical resistivity were developed. Furthermore, autogenous shrinkage was measured for the three cement pastes, and the behaviour could be anticipated from the electrical resistivity measurements.

Early-age behavior of blast-furnace slag cement pastes produced with carbon nanotubes grown directly on clinker

Abstract Carbon nanotubes are a promising material to solve the low tensile strength and ductility of Portland cement-based materials. Carbon nanotubes (CNTs) synthesized directly on cement clinker particles can also reduce production costs and help dispersion. In this scenario, this paper analyzes the fresh state rheological behavior, as well as the initial hydration period of blast-furnace slag (Brazilian CP III 40 RS) cement pastes produced with CNTs grown directly on clinker. CP III 40 RS was selected since it is one of the most used cement by the construction industry in Brazil. Cement pastes containing 0.1% and 0.3% of CNTs with respect to cement content were compared with CNT-free pastes. No chemical admixtures were used as a dispersant in all cases. The yield stress, plastic viscosity, temperature profile and evolved accumulated heat during the initial hydration period as well as setting times are the properties investigated. The results show that the addition of CNTs does not alter the rheological behavior of the cement pastes considering the employed concentrations, although the yield stress values were larger. The presence of CNTs in the cement pastes did not change the evolved accumulated heat during the first 72 hours of the hydration period.

Structurization of cement systems with nanodispersed silica stabilized with acetate ions

The influence of a modifying additive in the form of silica sol stabilized with acetate ions on the structure and properties of cement stone has been studied. The mechanism of structure formation in the system of “cement-nanodispersed silica (NDS) stabilized with acetate ions” is proposed. It includes two aspects. In the initial period of hydration the crystallization of calcium hydroacetoaluminates occurs, the rate of their formation being higher than the rate of ettringite formation. Their crystals have some micro-reinforcing effect on cement stone, increasing its density and strength. The nanodisperse silica in combination with the calcium hydroacetoaluminates is directly involved in the structurization of cement stone, colmataging the pores. Si4+ atoms, building-in in the structure of portlandite phases, increase the impermeability of cement stone. The generation of calcium hydroacetoaluminates leads to the formation of the primary carcass, providing the strength development of cement stone in the early stages of hardening. It is established that adding the modifier results in pore redistribution in size: a decline in the amount of macropores and an increase in the quantity of the gel pores and submicropores (5-0.1 µm) at a constant micropore volume (0.1-20 µm).

Heat Emission Kinetics and Hydration Behavior of Modified Polymer–Cement Mixtures for 3D Printing Construction

Abstract—The process of heat emission is investigated during the hydration of the binder in polymer–cement mixtures and mixtures modified by phloroglucinol–furfural superplasticizer. The specific binder hydration enthalpy in the presence of a polyvinyl acetate dispersion and redispersible polymer powder is determined. It is established that the specific enthalpy of polyvinyl acetate polymer–cement systems is positive, which indicates the endothermic nature of the overall process. The dependence of the absolute heat emission values in the initial periods of material hardening on the binder hydration time in the presence of organic mixture components (polyvinyl acetate and phloroglucinol–furfural modifier) is studied. It is proved that, when modifying polymer–cement systems, there is a decrease in the heat emission peak, a reduction in the timing of the initial hydration period, and an increase in the duration of the second (induction) period. The heat emission kinetic curves of the modified polyvinyl acetate–cement mixtures are presented, and the hydration behavior of the studied systems is considered. It is established that, in the initial period of hardening, polyvinyl acetate increases and phloroglucinol–furfural superplasticizer reduces the heat emission rate, while when modifying the polymer–cement system with a polymer in the form of a polymer dispersion, this process is partially balanced.

Acceleration of OPC by CAC in binary and ternary systems: The role of pore solution chemistry

In dry-mortar-formulations calcium aluminate cement (CAC) is often used as a set accelerator for ordinary Portland cement (OPC). However, a critical amount of CAC is able to delay not only the silicate reaction but also the renewed C3A dissolution of an OPC. This delay can be counteracted by adding an appropriate amount of calcium sulfate (C$) to the mix OPC/CAC. The initial hydration period is dominated by fast ettringite formation from CA (CAC) and CaSO4 from OPC generating early strength. High aluminum and low calcium concentrations in the pore solution probably hinder C-S-H seeding and precipitation, thus preventing alite dissolution. Aluminum has to be initially removed by precipitating hydrate phases to change the pore solution chemistry. The start of the silicate reaction is then induced by increasing the calcium concentration in the pore solution.

Rheology of hydrating cement paste: Crossover between two aging processes

The roles of applied strain and temperature on the hydration dynamics of cement paste are uncovered in the present study. We find that the system hardens over time through two different aging processes. The first process dominates the initial period of hydration and is characterized by the shear stress σ varying sub-linearly with the strain-rate γ̇; during this process the system is in a relatively low-density state and the inter-particle interactions are dominated by hydrodynamic lubrication. At a later stage of hydration the system evolves to a high-density state where the interactions become frictional, and σ varies super-linearly with γ̇; this is identified as the second process. An instability, indicated by a drop in σ, that is non-monotonic with γ̇ and can be tuned by temperature, separates the two processes. Both from rheology and microscopy studies we establish that the observed instability is related to fracture mechanics of space-filling structure.

Technology Focus: Well Integrity (January 2015)

Technology Focus Cementing operations represent one of the more critical aspects concerning well integrity. Despite the large amount of research and the huge number of operations throughout the years, the industry still faces well-integrity problems during and after cementing operations. These occurrences have been experienced by the petroleum industry worldwide and can happen at any moment of the well life cycle, from the drilling phase to abandonment after the well’s production life. Here, I have categorized these well-integrity issues according to the moment at which they manifest: during the cement displacement inside the well (minutes); after the cement placement (hours to days), and after the cement has been cured (months to years). The first category may result in serious well-control problems, including blowouts (the Macondo blowout was related to cementing operations). According to a survey published by the former Minerals Management Service, during the period between 1992 and 2006, the leading factor contributing to blowouts in the US offshore area was cementing (18 out of 54 blowouts reported). These well-control problems are normally caused by improper design of the cementing operation in terms of hydrostatic pressure of the cement slurries or preflushes, failure when mixing the cement slurry to achieve its planned density, lost circulation during the cement displacement, or failure of casing float equipment. In my opinion, well-control courses must dedicate more time to discussing well-control problems during cementing operations. The second category encompasses those issues normally associated with the loss of hydrostatic pressure of the cement slurry during its initial hydration period and consequent gas flow inside the annulus. This condition also can cause well-control problems, pressure buildup in the annulus between casing strings, and zonal-isolation problems later on. The industry has several ways to mitigate these occurrences that include, but are not limited to, the use of gas-block additives, the design of cement slurries with short transition times, the application of surface pressure on the annulus, the use of external casing packers, and the implementation of multistage cementing operations. Despite the application of these mitigation measures, annular gas flow after cementing is still a recurrent problem, and remedial solutions are normally expensive and difficult. The last category refers to long-term problems normally caused by poor cementing practices, with detrimental effects on zonal isolation. Inadequate drilling-mud removal during the cement-slurry displacement in the annulus, insufficient cement height that may lead to casing leakage and corrosion problems, and the channels that result from the gas flow previously mentioned are some of the factors that can contribute to long-term well-integrity failures. Again, remedial solutions are normally expensive. JPT Recommended additional reading at OnePetro: www.onepetro.org. IPTC 16592 Mitigation of Deepwater Shallow Hazards With Simplified Cement System: South China Sea Case Study by Todd B. Ellis, Baker Hughes, et al. OTC 24369 Well-Integrity Analysis Applied to Workover Prediction by T.C. da Fonseca, Petrobras, et al. SPE/IADC 163474 Automated Alarms for Smart Flowback Fingerprinting and Early Kick Detection by Tarab H. Ali, Baker Hughes, et al.

Hydration of Calcium Aluminate Phases at Different Temperatures

Mayenite (C12A7) and calcium dialuminate (CA2) are both components of Calcium aluminate Cement (CAC). The hydration of these phases depends on initial conditions especially on the temperature. Pure phases were synthesized by solid-state reaction. The hydration was carried out at three different temperatures – 20 °C, 30 °C and 60 °C. The course of hydration was investigated by isothermal calorimetry. The results prove, that higher temperature increase reactivity of phases and decrease their initial period of hydration. The X-ray diffraction analysis (XRD) identified the hydration products of CA2 as katoite (C3AH6) and gibbsite (AH3). The hydration products of C12A7 depends on the temperature. At 20 °C the major products are C2AH8 and CAH10. At 30 °C CAH10 disappears and only C2AH8 remains. At 60 °C the only stable hydrates – C3AH6 and AH3 are formed.

Investigation on early hydration of ternary Portland cement-blast-furnace slag–metakaolin blends

The paper investigates the hydration of ternary blends comprising Portland cement, blast-furnace slag and metakaolin. The isothermal calorimetry and “in situ” X-ray diffraction was used to evaluate the effect of metakaolin and blast-furnace slag on the early hydration of blends. XRD, DTA and SEM were used to analyze the hardened paste after 1month of hydration. Metakaolin influences significantly the kinetics, mechanism and products of hydration at initial period of hydration causing the rapid formation of ettringite. Hemicarbonate aluminate hydrate is formed as a product of ettringite conversion due to the presence of reactive calcite in Portland cement.

The influence of steel slag with high Al2O3 content on the initial hydration of cement

The initial hydration of steel slag with high Al2O3 content and its influence on the initial hydration of cement were investigated in this study. Steel slag with high Al2O3 content may contain much calcium aluminate mineral but very little gypsum. The steel slag hydrates much more quickly than cement in the initial hydration period, producing many flake products which have a great influence on the fluidity, initial setting time, and adsorption level of superplasticizer of paste. Replacing part of cement by steel slag with high Al2O3 content can change the hydration condition of calcium aluminate mineral of the cement by decreasing the gypsum to calcium aluminate mineral ratio, resulting in accelerating the hydration rate of calcium aluminate mineral in the initial hydration period. Paste containing steel slag with high Al2O3 content has a shorter initial setting time, higher adsorption level of superplasticizer, and greater loss in fluidity than the pure cement paste.

Influence of Sn on the hydration of tricalcium aluminate, Ca3Al2O6

Tricalcium aluminate (Ca3Al2O6, C3A) containing 0–5% of Sn was synthesized by solid-state method, and the products were characterized by XRD technique. Differential thermo-analytical technique (DTA) along with X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) were applied to study the hydration behaviour of different C3A samples with and without the presence of gypsum. Results indicate that C3A can accommodate small amount of Sn in its structure and remaining amount forms SnO2. Hydration studies of the synthesized C3A shows that the additions of 0.5 and 1% Sn increase and 2% Sn decrease the reactivity of C3A at the initial period (<3 h) of hydration. Increasing additions of Sn also increase the amounts of amorphous phases and hexagonal calcium aluminate hydrates in the cement pastes. The stabilities of these hydration products also increase with increasing content of Sn in C3A at the experimental conditions. The presence of Sn significantly changes the hydration of C3A and gypsum solid mixture at the initial period of hydration by enhancing the formation of more amounts of AFt and AFm phases. However, at the later stage of hydration (on or after 3 days), the hydration products in C3A and gypsum pastes with and without the presence of Sn are almost similar.

Action Mechanism of Sulfate Compatible Polycarboxylate Type Admixture

Interaction between cement and a kind of sulfate compatible polycarboxylate type admixture (PCA) and action mechanism of the novel water reducer were investigated. Experimental results indicate that adsorption amount of PCA on surfaces of cement particles is lower than that of polynaphthalene sulfonate condensate water reducer (PNS) because of the formation of more ettringite and calcium monosulfoaluminate, and calcium monocarboaluminate when CaCO3 presents in hydration system, even at initial period of hydration. Results from XRD analysis, derivative thermogravimetric (DTG) analysis and chemical analysis all verify the benificial effect of sulfate compatible PCA on initial and early age hydration of C3A. An establishment of electrostatic repulsion by grafting SO3- in molecule structure of PCA may result in a more negative zeta potential in the dispersion system. The improved dispersibility and fluidity retention are the result of a combination action mechanism of electrostatic repulsion cooperating with steric hindrance, and the acceleration effect of sulfate compatible PCA on initial and early age formation of ettringite and AFm phase. A combined high range water reducer mainly consisting of sulfate compatible PCA and PNS was made up based on the experimental and theoretical investigation results.