Hydration Of OPC Research Articles

Alkali-activated calcined clay blended cement: Effect of NaOH activator on performance of HPEG PCEs and on early strength

The effect of NaOH on dispersing performance of HPEG PCE superplasticizers and early strength was studied in a calcined clay (CC) blended cement (OPC:CC = 70:30 wt./wt.). Activator impact on workability and mechanical properties was investigated on mortar via fluidity and strength tests. The results revealed a time-dependent impact. At early ages (16 h – 3 d), the strength of the NaOH-activated OPC/CC blend exceeds that of OPC, while at longer curing times (> 3 d) it is ∼ 30 % below that of OPC. Among the HPEG PCEs tested, the polymer possessing a medium long side chain (nEO = 50) performed best. Generally, NaOH addition prompted significantly increased PCE dosages. Heat flow calorimetry and in-situ XRD measurements suggest that NaOH promotes initial hydration of both OPC and CC, but later delays OPC reaction. Zeta potential measurements confirmed that NaOH significantly reduces the adsorbed amount of PCE on the binder, thus explaining higher dosage requirement.

Preparation of reactive seedings by in-situ precarbonation under power ultrasound-assisted mixing: Enhancing the hydration and mechanical properties of OPC

In this study, a precarbonation process of cement paste was developed using a power ultrasound-assisted mixing method to prepare a highly reactive seedings admixture, which was subsequently added to the remaining cement paste for secondary mixing. The results revealed that power ultrasound greatly facilitated the release of ions from the cement into the pore solution, promoting the formation of calcium carbonate, aluminum hydroxide and C–S–H gels. After the 20 min ultrasound treatment, a substantial quantity of very fine seedings was observed, capturing 7.09 wt% CO2 of the total cement used. These seedings also acted as nucleation sites to accelerate further cement hydration, which shortened the hydration induction period and ultimately formed a more homogenous, denser cement microstructure.

Influence of a dialysed polymer latex on the hydration of OPC – A closer look into adsorption processes

The impact of a dialysed styrene acrylate copolymer on cement hydration was investigated. The retarding and depressing mechanism of the polymer particles on OPC hydration was examined via heat flow calorimetry, in-situ X-ray analysis and pore solution composition measurements. To ensure excessive polymer particles were remaining in the pore solution during the hydration, a high polymer-cement-ratio was chosen. It is found that the physical mechanism, the adsorption, is the most influential cause of the retardation and depression. Both aluminate and silicate reactions are strongly inhibited by the adsorption of polymer particles on hydrate phases. As long as polymer particles are found in the pore solution, newly forming surfaces are directly occupied by the latex particles, thus delaying the reaction. The OPC hydration is kinetically slowed down by polymer particle adsorption even though thermodynamically there is no hindrance for the hydration progression.

Tailored rheological development in OPC systems by controlled ettringite precipitation and its effect on compressive strength

AbstractThe control of rheological properties is gaining in importance to meet the special requirements for cementitious materials in novel technologies such as 3D‐printing. A deeper understanding of the underlying mechanisms of cement hydration is necessary to customize the mix design to the specific application.The hydration of OPC is mainly characterized by the silicate and aluminate reaction. The aluminate reaction is especially relevant for the early rheological development, whereas the formation of C‐S‐H (silicate reaction) is responsible for the later hardening of the hydrating paste.A hydration control agent is used to delay the initial aluminate reaction to a defined point in time. When no additional mixing occurs during this period of rapid ettringite precipitation, the cement paste stiffens to a solid cement stone. However, when the sample is mixed during this period, the workability of the paste is retained. The rheological changes can be correlated directly to the magnitude of ettringite formation. Additionally, the compressive strength and pore size distribution of all systems (reference, HCA, HCA with additional mixing) are investigated to analyze the long‐term properties. These results predict future customized mix designs in various application fields.

C3A Variation in Synthetic Model Cements ‐ Influence on Rheology and Reactivity

AbstractThe amount of early ettringite crystallization is known to influence the rheology of cementitious materials. It is dependent on various factors, e.g., the reaction temperature, the chemical composition of the cement and the amount of PCE. In this study, we investigate the rheology and reactivity of synthetic model cements with different contents of C3S, C3A and β‐hemihydrate (β‐HH). Their reactivity is studied using in‐situ calorimetry and their rheology is studied using a rotational rheometer. Our results demonstrate that higher C3A contents in the clinker increase the early heat release of the cements which is associated with an increased formation of ettringite. Increased C3A contents from 2.5 wt.% to 12.5 wt.% enhance the early heat by four orders of magnitude. The static yield stress of the different cement pastes was determined with an oscillation based rheometry method 17 minutes after contact with water. Interestingly, the static yield stress increases exponentially with the heat of hydration. These findings have implications for the understanding of OPC hydration, as well as for chemical optimization and the design of OPC‐based materials.

Enhancing the aluminate reaction during OPC hydration by combining increased sulfate content, triethanolamine and tartaric acid

Possibilities for enhancing the aluminate reaction were studied in a mix of OPC blended with 7.9 % hemihydrate (HH) or 7.4 % anhydrite (AH) in combination with different triethanolamine (TEA) dosages. Heat flow calorimetry and quantitative X-ray diffraction (XRD) were performed to study the hydration process. Using anhydrite as an additional sulfate carrier allowed a lower TEA dosage compared to hemihydrate systems to enhance the degree of hydration of C3A. High TEA dosages in hemihydrate systems were found to hinder C3S hydration. Nevertheless, it was possible to push the aluminate reaction ahead of the silicate reaction, thereby enhancing the degree of hydration of C3A. Additionally, the degree of hydration of C3S was not strongly affected when anhydrite and a well-balanced TEA dosage were used. The addition of tartaric acid to OPC-anhydrite-TEA systems retarded the subsequent aluminate reaction.

Understanding the effect of MPEG‐PCE's microstructure on the adsorption and hydration of OPC

AbstractPolycarboxylic ethers or polycarboxylate (PCEs) are one of the most employed superplasticizers in construction. However, the understanding of their microstructure–property relationship is still incomplete. Recently, a theoretical model was proposed that relates the microstructure–conformation of the PCE to its effect on the adsorption onto cement particles and cement hydration time. In this work, the effects of a wide range of PCEs with different side chain lengths (P = 5, Group 1; P = 20, Group 2; and P = 45 and 113, Group 3) having flexible backbone worm conformation except one which has stretch backbone worm conformation (P = 113) were experimentally investigated for their effect on adsorption and cement hydration. It is found that PCEs from Group 1 show electrostatic repulsion as dispersing mechanism, unlike PCEs from Groups 2 and 3. Furthermore, the prediction of the theoretical model is also assessed for all the studied PCEs. Only Group 1 PCEs (shortest side chains) showed deviation from the theoretical predictions, and it was attributed to their different behaviors from the standard PCEs for which the theoretical model was developed.

Diatomaceous Earth-Lightweight Pozzolanic Admixtures for Repair Mortars-Complex Chemical and Physical Assessment.

The presented research is focused on the complex assessment of three different types of diatomaceous earth and evaluation of their ability for application as pozzolana active admixtures applicable in the concrete industry and the production of repair mortars applicable for historical masonry. The comprehensive experimental campaign comprised chemical, mineralogical, microstructural, and physical testing of raw materials, followed by the analyses and characterization of pozzolanic activity, rheology and heat evolution of fresh blended pastes, and testing of macrostructural and mechanical parameters of the hardened 28-days and 90-days samples. The obtained results gave evidence of the different behavior of researched diatomaceous earth when mixed with water and Portland cement. The differences in heat evolution, initial and final setting time, porosity, density, and mechanical parameters were identified based on chemical and phase composition, particle size, specific surface, and morphology of diatomaceous particles. Nevertheless, the researched mineral admixtures yielded a high strength activity index (92.9% to 113.6%), evinced their pozzolanic activity. Three fundamental factors were identified that affect diatomaceous earth’s contribution to the mechanical strength of cement blends. These are the filler effect, the pertinent acceleration of OPC hydration, and the pozzolanic reaction of diatomite with Portland cement hydrates. The optimum replacement level of ordinary Portland cement by diatomaceous earth to give maximum long-term strength enhancement is about 10 wt.%., but it might be further enhanced based on the properties of pozzolan.

Effects of Synthetic Hierarchical NaP-Zeolite Addition on Physico-mechanical Properties and Kinetics of OPC Hydration Development

Effects of Synthetic Hierarchical NaP-Zeolite Addition on Physico-mechanical Properties and Kinetics of OPC Hydration Development

The effect of calcined mayenite on the hydration of ordinary Portland cement

The synthesis of mayenite with differences in mineral composition and its influence on the properties of Ordinary Portland cement samples were examined. The synthesis of mayenite precursor was carried out in hydrothermal condition (CaO/Al2O3 = 2.8, w/s = 10) within 1–72 h at 130 °C. It was observed that synthetic precursor which was formed after 4 h remained stable only till 275 °C, and, at a higher temperature (350 °C), it fully decomposed to mayenite. In addition, when the temperature increases, the diffraction peaks typical to mayenite increases and changes mineral composition.It was found that the highest amount of mayenite additive (7.5 wt%) with differences in mineral composition has a positive influence on OPC hydration. It was observed that the mineral composition of additives has influence on the OPC hydration mechanism: at the first stage of hydration, the calcination temperature exerts negative influence on the formation of ettringite; at the second hydration stage, the reaction of gypsum with the additive calcined at 900 °C is more accelerated. The mechanism of hydration (21–60 min) depends mostly on the calcination temperature of the additive. At this stage, ettringite in the systems OPC -mayenite (synthesized at 350 °C) and OPC - mayenite (synthesized at 900 °C) is partially decomposed into monosulfoaluminate and gypsum. Meanwhile, the new exothermic reaction between mayenite and ettringite in the OPC- mayenite (synthesized at 550 °C) system promoted the formation of monosulfoaluminate and hydrated calcium aluminate compounds.

Influence of Alkalis on Natural Carbonation of Limestone Calcined Clay Cement Pastes

Vulnerability to atmospheric carbonation is one of the major durability concerns for limestone calcined clay cement (LC3) concrete due to its relatively low overall alkalinity. In this study, the natural carbonation behaviors of ternary ordinary Portland cement-metakaolin-limestone (OPC-MK-LS) blends containing various sulfate salts (i.e., anhydrous CaSO4, Na2SO4, and K2SO4) are studied, with the aim of revealing the influence of alkali cations (Na+, K+). Detailed analyses on the hydrated phase assemblage, composition, microstructure, and pore structure of LC3 pastes prior to and post indoor carbonation are conducted. The results show that the incorporation of sulfate salts accelerates the setting and strength gain of LC3 pastes, likely through enhancement of ettringite formation, but undermines its later age strength achievement due to the deleterious effect of alkali cations (Na+, K+) on late age OPC hydration. The carbonation resistance of LC3 systems is considerably undermined, particularly with the incorporation of Na2SO4 or K2SO4 salts, due to the simultaneous pore coarsening effect and reduced CO2-binding capacity. The carbonation-induced phase and microstructural alterations of LC3 pastes are discussed and compared with those of reference OPC pastes.

Thermodynamic model for ternary OPC/CAC/Calcium Sulfate binders

Ternary binders combining Portland (OPC) and calcium aluminate (CAC) cements with calcium sulfate (CS-) capitalise on differential setting and hardening properties to compensate for expansion or shrinkage.This study explored hydration over curing times ranging from 1 h to 1 year in nine cements, combinations of OPC, CAC and CS- prepared with a w/c ratio of 0.4. The experimental findings were subsequently applied to corroborate the results of a thermodynamic model for the same compositions.According to the model findings, under thermodynamic equilibrium conditions, in binary blends with a high OPC content, the addition of CS- induces the formation of more ettringite (AFt), but no calcium monosulfoaluminate hydrate (AFm), whereas a higher CAC replacement ratio prompts AFm phase formation and retards OPC hydration. Those two effects were observed to compete in the ternary system, with phase development depending on the initial proportions of the two binders.A thermodynamic hydration model was developed for the OPC/CAC/CS- ternary system in keeping with the experimental data and factoring in cement composition, clinker phase hydration kinetics and geochemical speciation-based thermodynamic equilibrium calculations. The model predictions for phase development correlated well with the experimental findings where hydration was assumed to be ongoing in the 1 year materials.

Reactivity in cement pastes bearing fine fraction concrete and glass from construction and demolition waste: Microstructural analysis of viability

Converting construction and demolition waste (CDW) into secondary raw materials is one of the priorities of environmental policy and circular economy strategy. This study analysed the variation in eco-efficient paste reactivity with OPC replacement ratio (5% to 10%) and hydration time (2 d, 28 d and 90 d). Three types of CDW were explored: two (calcareous and siliceous) consisting of fine (<5 mm) concrete waste and one in laminated glass (<40 mm). Further to the mineralogical phases identified at the aforementioned percentages, the four materials, i.e., the three types of CDW-blended cements and the OPC reference, were similarly reactive. The primary hydration products, C-S-H gels, C4AH13 and C4AcH11, ettringite and portlandite, were the same as observed in OPC hydration. These findings attest to the scientific viability recycling such CDWs as mineral additions in eco-cement manufacture and consequently eliminating the need for stockpiling these materials at recycling/storage plants.

Flue gas desulfurization (FGD) fly ash as a sustainable, safe alternative for cement-based materials

The reduction in fly ash production in coal-fired power plants has created an opportunity to explore alternative types of fly ashes previously deemed unfit for use in concrete. In plants using flue gas desulfurization (FGD) processes, fly ash could contain high amounts of sulfur oxides, making its use in concrete inadvisable. However, the type of sulfur compound present in a fly ash strongly impacts its performance in concrete. In this study, two types of fly ash were used to evaluate the effect of sulfur oxides on mortar mixtures incorporating fly ash as supplementary cementitious material (SCM); one from an FGD unit, with high sulfur oxide content (in the form of hannebachite), and the other generated in a system without FGD, with negligible sulfur oxide. Calorimetry results show that hannebachite can effectively control C3A hydration similar to gypsum; however, its presence in FGD fly ash does not induce deleterious expansion associated with internal sulfate attack in mortars. TGA and XRD analyses suggest that hannebachite has lower reactivity than sulfate. Hannebachite not only maintains the pozzolanic reactivity of the fly ash, but its fineness may promote OPC hydration, increasing compressive strength. The results of this study indicate that FGD fly ash can be used as an SCM, allowing more sustainable concrete production.

Effect of marble slurry as a partial substitution of ordinary Portland cement in lean concrete mixes

AbstractMarble stone is the mostly quarried stone in Rajasthan for its high demand in India and abroad. This quarrying resulted in the generation of waste in a slurry form which was dumped in the nearby landfill sites resulted in a detrimental effect on the soil strata and expanding the landfill area with time. The focus of the study is to explore the outcome of utilization of marble slurry as a partial substitution of ordinary Portland cement by 10%, 20%, 30%, and 40% for lean concrete mixes with an average target compressive strength of 20 MPa or more. To explore the prospect of deployment of marble slurry in cement concrete mechanical properties, durability aspects, and relevant microstructural analysis was performed, and the results have been reported. Though the durability aspect was not purely encouraging, though it was depicted that marble slurry can be utilized as a partial replacement of OPC up to 40% for the purpose for which the investigation has been done.Highlights Marble slurry utilized as a substitution of OPC by 10%, 20%, 30%, 40%. TGA results indicate that marble slurry did not affect the hydration of OPC. Resistance against carbonation decreases with the increment of marble slurry content. UPV results indicates after 40% substitution concrete was in the good quality zone.

Correction to: The influence of the glass transition temperature (Tg) of polymers on early OPC hydration: a complete study of the heat flow, phase evolution, and pore solution chemistry

The article ‘‘The influence of the glass transition temperature (Tg) of polymers on early OPC hydration: a complete study of the heat flow, phase evolution, and pore solution chemistry’’, written by ‘‘D. Jansen, Z. Lu, X.-M. Kong, J. Pakusch, E. Jahns, F. Deschner, Ch. Schmidtke’’, was originally published electronically on the publisher’s internet portal (currently SpringerLink) on 11 December 2019 without open access.

Flexural behaviour of reinforced concrete beams with partial replacements of metakaolin and marble powder

Concrete is the most widely used and versatile building material which is generally used to resist compressive force. By addition of some pozzolanic materials as admixtures, the various properties of concrete can be improved. Many modern concrete mixes are modified with the addition of admixtures, which improve the micro structural properties as well as decrease the calcium hydroxide concentration by consuming it through a pozzolanic reaction. Metakaolin is a cementitious pozzolanic material highly efficient and can react rapidly with the excess calcium hydroxide resulting from OPC hydration by a pozzolanic reaction, to produce calcium silicate hydrate and calcium alumino silicate hydrates. Due to rapid growth of construction activity, the available sources of natural sand are getting exhausted. Therefore, it is necessary to replace natural sand in concrete by an alternate material either partially or completely without compromising the quality of concrete. Waste marble dust is one such material which can be used to replace sand as fine aggregate in concrete. The present study describes an experimental program conducted to investigate the flexural behaviour of Reinforced Concrete beams with metakaolin as partial replacement for cement and marble powder as partial replacement for river sand in preparation of concrete. The percentage replacement of cement by metakaolin considered in this experimental study are 0, 2, 4, 6 and 8% by weight of cement and sand by marble powder are 20, 15, 10, 5 and 0%. The mechanical properties such as compressive and split tensile strength are analysed for conventional and modified concretes, at the age of 7, 14 and 28 days. A total of five RC beams, with dimensions 150 × 200 × 1500 mm was cast and tested under four point loading. The observations made were initial crack load, ultimate failure load and deflection of the beams. The results show that metakaolin and marble powder can be used as alternate construction materials at lower percentage replacement levels.

The acceleration mechanism of nano-C-S-H particles on OPC hydration

In recent decades, a novel concept of accelerating hydration process of cement has been proposed by adding external nuclei into a hydrating cement system, which is called seeding technology. Nano-sized C-S-H particles are prepared and characterized by means of dynamic light scattering (DLS), TEM, XRD, FT-IR and TGA. It has been realized that polycarboxylate superplasticizer (PCE) often leads to lower early strength of hardened cement paste (hcp) due to its retardation action, which is undesired for pre-fabricated concrete and repair mortars industry. The mechanism of nano-C-S-H seeds accelerating cement hydration containing PCE is investigated by isothermal calorimetry. The mortar strength growth with inclusion of seeds is investigated at every curing age of 1 d, 3 d and 28 d. Results show that nano-C-S-H particles significantly promote the early strength development for mortar containing PCE without obvious reduction of 28 d strength. The threshold pore size of hcp is also significantly decreased. The addition of nano-sized seeds decreases [Ca] in the pore solution, which is needed by C-S-H nucleation. More importantly, this paper brings a direct evidence that nano-C-S-H seeds provide more nucleation sites for further generated C-S-H precipitate by separated hydration method. C-S-H gel is identified as the substance growing on nano-C-S-H seeds by FT-IR, XRD and TGA. The separated hydration result firmly indicates that homogeneous nucleation is irrelevant in the blank hydrating cement pastes and the C-S-H hydration product is able to grow on the surface of the added foreign C-S-H seeds.

Synthesis of dispersing agents from starch – Influence on rheological properties and early age hydration of OPC

This study deals with the influence and effectivity of synthesized starch-based superplasticizers on rheological behaviour of cement pastes and on cement hydration. By varying molecular parameters, like molecular weight and the amount of introduced anionic charges, key parameters which induce thickening or liquefying behaviour in cement pastes were identified. Cement hydration was monitored by isothermal calorimetry, ultrasonic measurements and conductivity experiments. The investigations were supplemented by adsorption measurements by the phenol-sulphuric acid method. Results clearly show that low molecular weights and anionic charges in the molecular structure are necessary to create superplasticizers from starch. Also, the amount of anionic charges implemented in the molecular structure by chemical modification is a key parameter for a high dispersing performance. Furthermore, the starch-based superplasticizers delay the hydration of cement pastes, because of adsorption on cement surface, especially on the first hydration products.

The influence of the glass transition temperature (Tg) of polymers on early OPC hydration: a complete study of the heat flow, phase evolution, and pore solution chemistry

The impact of two different dialyzed styrene-acrylate polymer dispersions on the early hydration of OPC was studied. The polymer particles of both dispersions show a similar particle size distribution and high charge due to carboxylic groups on the surface of the particles. Both dispersions also show similar adsorption behavior. The hydration of the OPC was studied at a polymer concentration below the initial adsorption in order to evaluate possible reasons for the interaction of the polymer particles with cement hydration. It can be shown that the polymer particle with the lower glass transition temperature Tg shows a stronger impact on cement hydration, which cannot be explained by any influence on the pore solution composition or the initial dissolution of cement phases. Hence, the adsorption mechanism seems to be the most likely cause of the interaction of the polymers with hydrating cement.