Hydration Of Blended Cements Research Articles

Prediction of the heat of hydration of fly ash concrete by adiabatic temperature rise test and regression analysis

This paper deals with the proposal of a model that can predict heat of hydration of concrete containing fly ash and the adiabatic temperature rise test results that are the basis of the model. For the adiabatic temperature rise tests, total of twelve concrete mixtures were prepared with variables of the percentage of fly ash replacement and w/cm. The test results indicate that the replacement of fly ash significantly reduces the adiabatic temperature rise and delays the early hydration of fly-ash blended cements. Additionally, w/cm was found to influence not only the maximum adiabatic temperature rise but also the slope of the temperature rise. Therefore, a regression analysis was conducted to propose three parameters (hydration time parameter, hydration slope parameter, ultimate degree of hydration) for the heat of hydration model of concrete containing fly ash. The developed heat of hydration model was validated using test data. Models that did not consider w/cm, similar to those proposed by other researchers, failed to accurately predict the test results. However, the final model developed, which incorporates w/cm, accurately predicted the test results, as confirmed through this study.

Influence of Mechanically Activated Silico-Manganese Slag on Hydration and Properties Development of Blended Cement

Influence of Mechanically Activated Silico-Manganese Slag on Hydration and Properties Development of Blended Cement

Thermal Reactivation of Hydrated Cement Paste: Properties and Impact on Cement Hydration.

In this research, the properties and cementitious performance of thermally activated cement pastes (referred to as DCPs) are investigated. Hydrated pastes prepared from Portland cement and slag blended cement were subjected to different thermal treatments: 350 °C for 2 h, 550 °C for 2 h, 550 °C for 24 h and 750 °C for 2 h. The properties and the reactivity as SCM of the DCPs were characterised as well as their effect on the mechanical performance and hydration of new blended cements incorporating the DCPs as supplementary cementitious materials (SCMs). It was observed that the temperature and duration of the thermal treatment increased the grindability and BET specific surface area of the DCP, as well as the formation of C2S phases and the reactivity as SCM. In contrast, the mechanical strength results for the blended cements indicated that thermal treatment at 350 °C for 2 h provided better performance. The hydration study results showed that highly reactive DCP interfered with the early hydration of the main clinker phases in Portland cement, leading to early setting and slow strength gain. The effect on blended cement hydration was most marked for binary Portland cement-DCP blends. In contrast, in the case of ternary slag cement-DCP blends the use of reactive DCP as SCM enabled to significantly increase early age strength.

Effect of nano-SiO2 on rheology and early hydration of cement containing high volume slag

Using nano-SiO2 particles is a viable approach for enhancing early performance of blended cement containing high volume slag. The present research aims to investigate the rheology and early hydration of cement incorporating high volume slag and nano-SiO2. The initial and time-varying rheology of blended cement have been evaluated by testing static/dynamic yield stress, plastic viscosity as well as apparent viscosity. Besides, early hydration of blended cement has also been studied through measuring the setting time and heat of hydration. Results show that nano-SiO2 significantly increases the initial and time-varying rheological value of blended cement, the enhancement effect becomes more obvious with the increased dosage of nano-SiO2. In addition, nano-SiO2 can shorten the setting time of blended cement, which is beneficial to rapid construction of concrete with high volume slag. Further, nano-SiO2 shortens induction period, promote C3S hydration, accelerate the transformation from ettringite (AFt) to monosulfate (AFm). Ultimately, nanosilica decreases the content of C3S+C2S in hardened cement paste, resulting in more hydration products. This paper will provide scientific support for revealing the rheology and early hydration of blended cement with high volume slag and nano-SiO2.

Sulfate consumption during the hydration of Alite and its influence by SCMs

AbstractSCMs with a large specific surface area, such as calcined clays or fine limestone powder, can significantly accelerate the occurrence of the aluminate heat flow peak during the early hydration of blended cements. These systems therefore require a higher amount of sulfate. While this effect has been drawn back to the sulfate incorporation into C‐S‐H, which is formed more rapidly due to the filler effect, it has been recently shown that in systems with high amounts of metakaolin, the sulfate balance is influenced by further mechanisms. This study provides new results on the influence of aluminum‐rich and aluminum‐free SCMs on the early hydration of alite in presence of calcium sulfate. A synthesized alite was blended with 5 wt% of anhydrite and its hydration was investigated by isothermal calorimetry and in‐situ XRD at a w/b ratio of 0.5. It was shown that the formed C‐S‐H is able to take up the calcium and sulfate ions, indicated by a depletion of the solid anhydrite after approximately 20 hours. This process is significantly accelerated by incorporating 30 wt% of a fine limestone filler. The addition of metakaolin leads to an acceleration of the alite hydration compared to the reference as well, but to a significantly lower extend compared to the limestone. However, this system requires a lower degree of alite reaction to reach sulfate depletion. This indicates that in metakaolin‐rich systems, the sulfate demand is influenced by further effects. The results from in‐situ‐XRD reveal that significant ettringite formation is taking place in the metakaolin‐blended system already during the first hours of hydration. Correlations between the degree of alite hydration and the rate of sulfate depletion provide new insights into the mechanisms affecting the sulfate balance and early hydration of blended cements.

Early age hydration and autogenous shrinkage of blended cement containing brick powder

Early age hydration and autogenous shrinkage of blended cement containing brick powder (BP) was investigated using hydration heat, internal relative humidity (IRH) and 1H NMR methods. The results show that BP can promoting the early nucleation and growth process of cement. The unique porous structure of BP gives it water absorption property, which plays a role in internal curing. The internal curing effect of BP reduced the rate of decrease of IRH in cement paste and effectively reduced the autogenous shrinkage of cement paste. These findings suggest that moderate adjustment of the dosage of BP can effectively promote the hydration and control the autogenous shrinkage of cement-based materials.

Hydration and material properties of blended cement with ground desert sand

The potential of existing supplementary cementitious materials (SCMs), such as fly ash and slag, has been dramatically decreased after decades of use. For future development, finding new SCMs to address the sustainability issue of cement and concrete is essential. Due to its global distribution and reserves, and the fact that it has not been officially used for construction, desert sand may become a new option for SCM for cement. Since desert sand has a very fine and uniform particle size, regular milling in the field can conveniently transform it into a powder comparable to cement fineness. This study investigated the technical possibility of desert sand powder as an SCM through physical experiments, thermodynamic modeling, and life cycle analysis. The mechanical strength of blended cement with desert sand powder was generally lower than that of pure cement due to the cement reduction and increased effective water-cement ratio. When the dosage of desert sand powder was within 15%, the 28-day strength of blended cement exceeded 75% of that of pure cement, and the strength development of blended cement was better than that of pure cement after 28 days till long curing ages (112 days). Both the initial and renewed stages of early cement hydration were promoted by desert sand powder. The desert sand powder's leading minerals, quartz and calcite, participated in the cement hydration reactions, generating corresponding hydration products, calcium silicate hydrate (C-S-H) and carbonate-based aluminate ferrite mono-sulfate (AFm). The microstructure showed the interactions between the desert sand powder particles and the hydrated cement matrix, including physical and chemical aspects. In the case of high dosage, the hardened matrix's pore structure was apparent with a less dense matrix due to excess water and reduced hydration products. The thermodynamic modeling theoretically quantified the phase assemblage of hydrated cement with desert sand powder, connecting to the observed reactivity of desert sand powder in cement hydration. The life cycle analysis showed that the carbon emission of desert sand powder was comparable to the conventional SCMs (fly ash and limestone powder). However, if it was proposed to be used outside the desert and surrounding regions, the carbon emission may increase due to the extended transportation distance.

The hydration of ternary blended cements with Fe-rich slag from non-ferrous metallurgy and limestone

Fe-rich slags originating from non-ferrous metallurgy have shown promising properties as a new type of supplementary cementitious material (SCM). However, their combined use with limestone has not yet been investigated in detail. The goal of this study is to elucidate whether this yields a positive effect as observed for aluminosilicate SCMs with limestone. Compressive strength, hydration kinetics and products as well as pore solution concentrations of ternary blended cements with at least 50 wt% replacement of PC by limestone and non-ferrous metallurgy slag are investigated up to 150 days. Although there is no significant change in the reaction degree of clinker or slag upon addition of limestone, a slight compressive strength enhancement and increased bound water content were observed, originating from formation of additional carbonate AFm phases. Finally, partial replacement of slag by limestone appeared to suppress the formation of siliceous hydrogarnet in favor of a (Fe, Mg)-Al-layered double hydroxide.

Hydration of ternary blended cements with sewage sludge ash and limestone: Hydration mechanism and phase assemblage

The hydration kinetics and phase assemblage of ternary blended cements composed of sewage sludge ash (SSA) and limestone were investigated. Isothermal calorimetry reveals an inhibition effect of SSA on the hydration of C3S within the first day, while the hydration degree of C3S in ternary blended cements exceeds that in PC after 3 days. The reaction between SSA and limestone generates additional carboaluminate phases and inhibits the transformation of AFt to monosulfate, increasing the stability of AFt. This reaction is reflected on the second peak in the deceleration period of heat flow curves. The generation of a large amount of carboaluminate phases has a significant effect on porosity refinement and strength development of ternary blended cements. The pozzolanic reaction of SSA generates C-(A)-S-H with high Si/Ca and Al/Ca atomic ratios. Iron from the dissolution of SSA is captured by C-(A)-S-H, leading to the increase in Fe/Ca atomic ratios of C-(A)-S-H.

Effect of Particle Size and Morphology of Siliceous Supplementary Cementitious Material on the Hydration and Autogenous Shrinkage of Blended Cement

Supplementary cementitious material (SCM) plays an important role in blended cement, and the effect of the particle size and morphology of siliceous supplementary cementitious material on hydration should not be ignored. In this study, 0.5 h and 1 h of wet grinding was applied to pretreat iron ore tailing powder (TP), and the divergence in pozzolanic behavior and morphology were investigated. Then, the treated TPs were used to replace the 30% cement contents in preparing blended cementitious paste, and the impact mechanism of morphology on performance was studied emphatically. M, the autogenous shrinkages of pastes were tested. Finally, hydration reaction kinetics was carried out to explore the hydration behavior, while X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were used to characterize the hydration product properties, respectively. Meanwhile, microscopy intrusion porosimetry (MIP) was also carried out to characterize the pore structures of hardened specimens. Results indicated that wet grinding has a dramatic effect on particle size and morphology, but hardly affects the phase assemblages and pozzolanic reactivity of TP, while the particle shape of TP changes from sub-circular to clavate and, finally, back to sub-circular. The results of hydration reaction kinetics, representing the morphology of particles, had a significant effect on hydration rate and total heat, and compared with the sub-circle one, the clavated particle could inhibit the hydration procedure. With the increasing grinding time, the compressive strength of cementitious paste was increased from 17.37% to 55.73%, and the micro-pore structure became denser; however, the autogenous shrinkage increased.

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).

Hydration of blended cement with high-volume slag and nano-silica

Utilization of nano-silica is an effective method to improve the early properties of blended cement containing high-volume slag. In current work, the hydration of blended cement with high-volume slag (40 wt%, 60 wt% and 80 wt%) and nano-silica has been investigated by testing setting time, heat of hydration, compressive strength, hydration products and pore structure. The results illustrate that nano-silica can improve the hydration of slag and cement (including tricalcium silicate (C3S) hydration and transition from ettringite to monosulfate) before 3 d. The increased slag content affects the promotion of nano-silica on cement hydration. Besides, nano-silica inhibits the hydration of cement after 3 d. Furthermore, nano-silica can improve the content of chemically bound water and reduce Ca(OH)2 content. Combined use of appropriate content slag and nano-silica can better optimize the pore structure of hardened pastes, including pore size and cumulative porosity. Ultimately, nano-silica enhances the compressive strength of hardened paste, but the improvement effect of nano-silica gradually weakens with the increase of slag content and the extension of curing time. This paper can provide a theoretical basis for nano-silica modified cement with high-volume slag, and help to improve the early performance of cement with high-volume slag.

Effect of Metakaolin and Lime on Strength Development of Blended Cement Paste

To develop a more reactive pozzolan for supplementary cementitious materials (SCMs), the co-calcination of kaolinite and limestone was investigated for its contribution to hydration of blended cement. Kaolinite (with ~50 wt% quartz impurity) was calcined at 700 °C, and a mixture of kaolinite and limestone was calcined at 800 °C. These activated SCMs were added to ordinary Portland cement (OPC), replacing ca. 30 wt% of the OPC. The compressive strength of these blended cement paste samples was measured after 28 and 90 days, while the hydration products and microstructural development in these blended cement pastes were analyzed by X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The results revealed that adding free lime to OPC, together with metakaolin, led to enhanced compressive strength. The compressive strength of this new blended cement paste reached 113% and 112% of the compressed strength of pure OPC paste after 28 and 90 days of hydration, respectively. Furthermore, this study showed that the improvement was due to the increased consumption of Portlandite (CH), the formation of calcium aluminosilicate hydrate (CASH), and the reduction of porosity in the sample containing free lime and metakaolin.

Impact of C-S-H seeding on hydration and strength of slag blended cement

The impact of C-S-H seeding on the hydration of slag blended cement was systematically investigated, trying to understand and explore the potential of C-S-H seeding in blended cement. Three levels of substitution of cement by slag were investigated: 50, 75 and 95 wt%. Compressive strength, calorimetry, in-situ and fresh disc XRD experiments were carried out. Results show that C-S-H seeding improves the performance of slag blended cement significantly with regards to strength at early and later stage. Quantitative XRD analyses show how C-S-H seeding influences the clinker hydration kinetics. The microstructure of hardened blended cement paste was investigated using electron microscopy and mercury intrusion porosimetry. The results show that C-S-H seeding altered the microstructure dramatically by refining the porosity. Correlation of strength to heat release and pore structure indicates that there is structural impact of C-S-H seeding besides the impact on kinetics in the hardened samples.

Hydration and Mechanical Properties of Blended Cement with Copper Slag Pretreated by Thermochemical Modification.

The application of granulated copper slag (GCS) to partially replace cement is limited due to its low pozzolanic activity. In this paper, reconstituted granulated copper slag (RGCS) was obtained by adding alumina oxide (Al2O3) to liquid copper slag. Blended cement pastes were formulated by a partial substitute for ordinary Portland cement (OPC) with the RGCS (30 wt%). The pozzolanic activity, mechanical development, and the microstructure were characterized. The results show that 5–10 wt% Al2O3 contributes to the increase in magnetite precipitation in RGCS. The addition of Al2O3 alleviates the inhibition of C3S by RGCS and accelerates the dissociation of RGCS active molecules, thus increasing the exothermic rate and cumulative heat release of the blended cement pastes, which are the highest in the CSA10 paste with the highest Al2O3 content (10 wt%) in RGCS. The unconfined compressive strength (UCS) values of blended cement mortar with 10 wt% Al2O3 added to RGCS reach 27.3, 47.4, and 51.3 MPa after curing for 7, 28 and 90 d, respectively, which are the highest than other blended cement mortars, and even exceed that of OPC mortar at 90 d of curing. The pozzolanic activity of RGCS is enhanced with the increase in Al2O3 addition, as evidenced by more portlandite being consumed in the CSA10 paste, forming more C-S-H (II) gel with a higher Ca/Si ratio, and a more compact microstructure with fewer pores than other pastes. This work provided a novel, feasible, and clean way to enhance the pozzolanic activity of GCS when it was used as a supplementary cementitious material.

Particle characteristics of calcined clays and limestone and their impact on early hydration and sulfate demand of blended cement

Supplementary cementitious materials (SCMs) can alter significantly the early hydration behavior of blended cement. While the underlying mechanisms have been intensively discussed in literature, they need to be extended regarding SCMs with complex mineralogy and surface properties, such as calcined clays. In this study, a blended Portland limestone cement was monitored during the first 48 h of hydration using in situ X-ray diffraction and isothermal calorimetry. The influence of a fine limestone and four different calcined clays, which vary in mineralogical composition and particle properties, was investigated at a replacement level of 30 wt%. The sulfate content was gradually adjusted and its influence on heat evolution and phase development was examined. It was shown, that depending on their particle properties, the investigated SCMs influence the aluminate and silicate clinker reaction by different mechanisms and to varying extents. The results underline the importance of proper sulfation of blended cements.

Synchrotron X-ray micro-tomography investigation of the early hydration of blended cements: A case study on CaCl2-accelerated slag-based blended cements

In situ X-ray Micro-Tomography (XMT) analyses with a pixel size of 0.325 µm were conducted on slag-based blended cements containing 75% of Ground-Granulated Blast-Furnace Slags (GGBS) and 25% of Ordinary Portland Cement (OPC), with or without CaCl2 acceleration. Results show the identification of the main cementitious phases and the need to perform data repeatability tests in order to allow their quantification. Investigation of the early hydration during the first 31 h of hydration by image subtraction showed (i) the dissolution of OPC/GGBS, (ii) the precipitation of hydrates including C-S-H, (iii) the accelerating effect of CaCl2, and (iv) phase-identification based on their specific grey level.

Promoting utilization rate of ground granulated blast furnace slag (GGBS): Incorporation of nanosilica to improve the properties of blended cement containing high volume GGBS

Utilization of high volume ground granulated blast furnace slag (GGBS) to produce cement-based materials (CBMs) meets the requirements of sustainable development. However, high volume GGBS will significantly reduce some properties of CBMs. Incorporation of nanosilica is a potentially feasible approach to solve the problem. In present paper, effects of nanosilica (1 wt%, 2 wt% and 3 wt%) on hydration and microstructure of blended cement incorporating high volume GGBS (80 wt%) have been studied by testing setting time, compressive strength, hydration heat, hydration products and pore structure. Results reveal that nanosilica shortens the initial and final setting time of blended cement by 10.75%–20.56% and 10.45%–23.00%, respectively. Furthermore, nanosilica enhances early hydration heat release rate of cement and GGBS. Meanwhile, nanosilica increases cumulative heat release of blended cement by 23.40%–26.46%. However, nanosilica hinders cement hydration after curing for 7 d. Results of thermal analysis indicate that 80 wt% GGBS significantly reduces the content of chemically bound water, while nanosilica improves the parameter by 1.32%–5.91% at 56 d. Additionally, 80 wt% GGBS increases cumulative porosity by 31.89% at 28 d, but nanosilica decreases cumulative porosity by 3.05% at 28 d. Both high volume GGBS and nanosilica can decrease average pore diameter and enhance microstructure of cement paste. Ultimately, nanosilica increases the 28 d compressive strength by 8.27%–19.23%, which partially compensates for the reduction of compressive strength caused by high volume GGBS. This paper can provide the essential foundation for the theory of nanosilica-modified CBMs with high volume GGBS, help to improve the effective utilization rate of GGBS and realize sustainable development of CBMs.

Hydration of blended cement with high volume iron-rich slag from non-ferrous metallurgy

The hydration of blended cements with up to 70 wt% iron-rich slag was investigated. Isothermal calorimetry revealed a retarding effect of the slag on Portland cement hydration during the first day, while from 2 days onwards the reaction extent of C3S, C3A and C4AF increased. The slag reacted to 20–30% after 150 days resulting in AFm phases, as well as a new phase with a layered double hydroxide structure with (Mg + Fe)/Al around 3. Fe was also detected in the C-S-H phase of the blended cements, whereas no clear increase of Fe(III)-containing hydrates was observed. The Ca/Si atomic ratio of C-(A)-S-H in the blended cements decreased with increasing slag content, while the Al/Ca ratio increased only slightly. This study elucidated the fate of iron in cements blended with iron-rich slags and showed the suitability of the latter as SCM with a reactivity similar to the one of siliceous fly ash.

Experimental evidence for the acceleration of slag hydration in blended cements by the addition of CaCl2

Cements with high substitution rates of ground granulated blast furnace slags (GGBS) have the potential to significantly lower CO2 emissions of concrete, but their early age strength is often below those of traditional OPC cements. One way of mitigating this drawback is to use accelerating admixtures. In this study, the effect of CaCl2 additions on the hydration of blended cements was investigated by measuring compressive strength, porosity, heat release and propagation of ultrasound in blends containing 70 wt% of GGBS. The onset of formation of aluminate phases was monitored using in-situ XRD. The effect of CaCl2 on slag hydration was isolated by replacing GGBS by an inert quartz filler. Results showed that compressive strength values at one, two and seven days were increased by 50% by the CaCl2 addition. The increases in compressive strength corresponded to a reduction in pore space. GGBS hydration contributed to the heat development, structuration and compressive strength of the blended cements from 15 h. The addition of CaCl2 led to an earlier onset of the GGBS reaction, at around 10 h, and increased the rate of GGBS hydration during the first seven days. The time of onset of the GGBS contribution was also the moment when AFm precipitation started. In CaCl2-containing blends, Cl was incorporated in AFm.