Early Hydration Research Articles

Effect of ball milling-Ca(OH)2 coupling activation on the cementitious properties of ferrous extraction tailing of nickel slag: Basic properties, hydration mechanism and heavy metal safety

In order to improve the reactivity of ferrous extraction tailing of nickel slag (FETNS), This paper delves into the influence of ball milling-activator Ca(OH)2 on the cementitious activity of FETNS. Furthermore, it assesses the combined activation's impact on the working performance, mechanical properties, shrinkage properties, early hydration process, hydration products, and heavy metal element leaching of the FETNS-OPC composite cementitious system. The results show that the coupling activation significantly enhanced the reactivity of FETNS and prolonged the acceleration period of the composite cementitious system during the hydration process, thereby promoting the hydration reaction. This not only shortened the setting time of the composite cementitious system, but also significantly improved its early compressive strength. The microscopic test results showed that the coupling activation improved the reaction degree of the composite cementitious system, promoted the formation of more reaction products, and increased the compactness of the internal structure. In addition, the coupling activation also enhanced the degree of polymerization of the composite cementitious system, and these factors together led to an increase in compressive strength. However, it is worth noting that with the increase of FETNS reactivity under the coupling activation, the autogenous shrinkage change rate and drying shrinkage change rate of the composite cementitious system also increased accordingly. Finally, the results of the heavy metal leaching test showed that the coupling activation reduced the leaching value of heavy metal elements in FETNS, ensuring the safety of practical application.

Influence of free calcium sulfate levels on the early hydration of sulfate-rich belite sulfoaluminate clinkers: A comparative study with anhydrite and gypsum

In the present study, belite sulfoaluminate (BSA) clinkers containing varying levels of free calcium sulfate (f-CaSO4)—specifically 0 %, 5 %, and 10 %—were synthesized. These clinkers were subsequently mixed with anhydrite and gypsum for comparative analysis. Utilizing a range of analytical techniques such as isothermal calorimetry, X-ray diffraction (XRD), and thermogravimetric analysis (TGA), the early hydration process and the constitution of hydration products were systematically investigated. The experimental data reveal that sulfate-rich BSA clinkers demonstrate enhanced hydration activity, as well as superior early compressive strength. As the f-CaSO4 content escalates, there is a corresponding increase in the cubic crystal sulfoaluminate within the BSA clinkers. This compositional shift has a beneficial impact on both the initial and final setting times, thereby enhancing the 3-day compressive strength. Contrary to ordinary BSA cement clinkers, those rich in sulfate retard the dissolution rate of external gypsum. It is noteworthy that anhydrite, possessing a solubility greater than gypsum, exerts a more pronounced acceleration effect on the early hydration process of sulfate-rich BSA clinkers.

Roles of CO2-BOFS induced CaCO3 in the aluminum-rich GGBS cementitious material system

The objective of this work is to understand the roles of carbonation induced CaCO3 (from basic oxygen furnace slag, BOFS) on the hydration, mechanical properties and microstructural change in the aluminum-rich GGBS cementitious system, and study comparatively with fresh BOFS and conventional limestone. The 1 day compressive strength results show that the composite paste containing 45 wt% GGBS mixed with 15 wt% carbonated BOFS attained only 38 % of the corresponding OPC paste, however, in comparison the presence of nano-sized rhombohedral and cauliflower calcite on the surface of carbonated BOFS (rougher than CaCO3 of limestone) is better to enhance the early hydration of the composite. More importantly, the 28 days compressive strength of carbonated BOFS-GGBS composite paste can reach 97 % of that of OPC paste, attributed to the carbonated BOFS actively grows together with the hydrated cement matrix by consuming the nano-CaCO3 shell and generating in-situ carboaluminates. The formed carboaluminates not only can enhance the bonding behavior of the cementitious matrix but also refine the pore structure as well as the mechanical properties of the composite paste.

Factors influencing the hydration kinetics of ye'elimite; effect of free lime

This study investigates factors influencing the hydration of ye'elimite, comparing stoichiometric ye'elimite-rich clinkers with and without free lime (Y-C and Y, respectively). Although the hydration sequences and products were similar, there were notable differences in their kinetics. Y-C exhibited rapid hydration upon contact with water, followed by a significant slowdown within minutes. Contrary, Y demonstrates a slower early hydration, but reached the main hydration period earlier and proceeded more rapidly thereafter. Solution analyses revealed higher initial calcium and aluminium concentrations for Y-C, while the sulfur concentration was reduced. This was attributed to the rapid dissolution of free lime, along with some ye'elimite, resulting in the instantaneous formation of ettringite and aluminium hydroxide. Consequently, the solution composition was altered, causing delayed onset of monosulfate formation and main hydration period. These findings contribute to understanding the hydraulic reactivity of ye'elimite and its potential implications for cement production processes.

Influence of TiO2 Nanoparticles on the Physical, Mechanical, and Structural Characteristics of Cementitious Composites with Recycled Aggregates.

The aim of this study is to analyze the effect of the addition of TiO2 nanoparticles (NTs) on the physical and mechanical properties, as well as the microstructural changes, of cementitious composites containing partially substituted natural aggregates (NAs) with aggregates derived from the following four recycled materials: glass (RGA), brick (RGB), blast-furnace slag (GBA), and recycled textolite waste with WEEE (waste from electrical and electronic equipment) as the primary source (RTA), in line with sustainable construction practices. The research methodology included the following phases: selection and characterization of raw materials, formulation design, experimental preparation and testing of specimens using standardized methods specific to cementitious composite mortars (including determination of apparent density in the hardened state, mechanical strength in compression, flexure, and abrasion, and water absorption by capillarity), and structural analysis using specialized techniques (scanning electron microscopy (SEM) images and energy dispersive X-ray spectroscopy (EDS)). The analysis and interpretation of the results focused primarily on identifying the effects of NT addition on the composites. Results show a decrease in density resulting from replacing NAs with recycled aggregates, particularly in the case of RGB and RTA. Conversely, the introduction of TiO2 nanoparticles resulted in a slight increase in density, ranging from 0.2% for RTA to 7.4% for samples containing NAs. Additionally, the introduction of TiO2 contributes to improved compressive strength, especially in samples containing RTA, while flexural strength benefits from a 3-4% TiO2 addition in all composites. The compressive strength ranged from 35.19 to 70.13 N/mm2, while the flexural strength ranged from 8.4 to 10.47 N/mm2. The abrasion loss varied between 2.4% and 5.71%, and the water absorption coefficient varied between 0.03 and 0.37 kg/m2m0.5, the variations being influenced by both the nature of the aggregates and the amount of NTs added. Scanning electron microscopy (SEM) images and energy dispersive X-ray spectroscopy (EDS) analysis showed that TiO2 nanoparticles are uniformly distributed in the cementitious composites, mainly forming CSH gel. TiO2 nanoparticles act as nucleating agents during early hydration, as confirmed by EDS spectra after curing.

Impact of Electronic Waste Glass on the Properties of Cementitious Materials

The article analyses the impact of two different types of dispersive glass on cement hydration and compressive strength at 7 and 28 days. The study employed dispersive glass from various LCDs (TV sets, computer monitors, smart phones), characterised by a composition of approximately 8% SrO, and dispersive glass from washing machines, which consists mainly of SiO2, Na2O, and CaO. The chemical composition and particle-size distribution of different types of dispersive glass were analysed. The study compares the effect of electronic waste glass on cement hydration by evaluating the amount and rate of heat released during the process. In addition, the results of X-ray diffraction (XRD), thermogravimetric analysis (TG), and scanning electron microscopy (SEM) are provided. Different types of glass were determined to have a similar effect on the physical and mechanical properties as well as the mineral composition of cementitious samples: density and UPV decrease up to 6% and compressive strength decreases by about 30%, when 5–20% of cement was replaced by glass waste. However, more prominent differences were observed in the workability of the mixtures: the waste glass from home appliances increased the spread by up to 25%, while the waste glass from electronic devices decreased the spread compared to the reference sample by approximately 20%. The mixtures modified with the waste glass of electronic devices had a higher degree of early hydration (96%) due to the higher water absorption of the mixtures compared to the waste glass of home appliances (88%).

Innovative synthesis of low-carbon cemented backfill materials through synergistic activation of solid wastes: An integrated assessment of economic and environmental impacts

The accumulation of large amounts of steel slag (SS) and oil shale residue (OSR) causes serious pollution due to the lack of effective ways to utilize them. In this study, OSR, SS, and soda residue (SR) were used to synergistically prepare all-solid-waste low-carbon cemented backfill material (ALCCB). No cement and chemical additives were added to this material, and synergistic activation enabled full utilization of the solid wastes. The total solid waste utilization rate was 100 %. The mechanical characteristics of the ALCCB and the heavy metal leaching rates were determined. The unconfined compression strength of the ALCCB after 28 days was 5.97 MPa, while the slump was 205 mm. These results met the performance requirements for a filling material. The leaching rates for the heavy metals after 28 days conformed to the guidelines for Class III groundwater quality. The mechanism underlying synergistic hydration of the solid wastes was analyzed at the micro- and macroscale with X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP). The results indicated that hydration of the ALCCB occurred continuously during curing, and the faster early hydration reaction stabilized heavy metal curing at 7 d. In addition, ALCCB offers greater economic and environmental advantages than cementitious materials. Notably, the economic and environmental benefits of ALCCB were found to supersede those of cement-based materials, with a cost reduction of 42.6 % and a CO2 emission reduction of 86.9 %. This innovative low-carbon mine backfill material effectively promotes the utilization of solid waste resources and supports sustainable development.

Synergistic effect of nano silica and metakaolin on mechanical and microstructural properties of concrete: An approach of response surface methodology

Nano and micro materials are both effective individually in enhancing the mechanical and microstructural properties of concrete. The combination illustrates an iconic shift in material engineering to produce concrete with distinctive characteristics. In this work, the combined effect of Nano Silica (NS) and Metakaolin (MK) on the mechanical and microstructure properties were examined by conducting compressive strength, split tensile strength, and Field Emission Scanning Election Microscope (FE-SEM) with Energy-dispersive X-ray (EDX) analysis, X-ray Diffraction (XRD) spectroscopy, Fourier Transform Infra-Red (FTIR) spectroscopy, respectively. The concrete matrix was investigated by varying the concentration of NS and MK with different Water-Binder Ratio (WBR). Further, the Response Surface Methodology (RSM) technique was used to identify the complex interaction between NS (1–3 %) and MK (5–20 %) at different WBR (0.35, 0.40 and 0.45). The synergistic effect between NS and MK resulted in enhanced compressive and split tensile strengths of the concrete. The optimum mix proportion of the concrete was found to be 2 % NS and 12.5 % MK at a WBR of 0.4. The compressive strength enhancements for the optimum mix proportion were 35.75 %, 34.4 %, 33.1 %, and 32.5 %, while the split tensile strength enhancements were 26.56 %, 25.92 %, 20.95 %, and 17.8 %, respectively on the 7th, 28th, 56th, and 90th day. The RSM technique developed for all the mixes has been statistically validated to have less than 5 % of mean error. Moreover, the microstructural analysis revealed early hydration, formation of additional Calcium Silicate Hydrate (C-S-H) products, and presence of dense microstructure resulting in improved microstructural properties. The incorporation of NS and MK in the concrete changes the concrete’s configuration at the nano and micro levels, thus paving the way for the development of novel and sustainable construction materials.

High value-added utilization of desulfurized building gypsum as self-leveling mortar: the comprehensive effect of cement.

The utilization of desulfurized building gypsum as raw material for gypsum-based self-leveling mortar (GSL) is limited by its low strength and poor water resistance. The objective of this study is to enhance comprehensive properties of GSL and prepare qualified desulfurized building gypsum-based self-leveling mortar that can be effectively applied in practical engineering projects. The influence of cement on water consumption rate of initial fluidity (W/M ratio), fluidity, setting time, mechanical strength, and water resistance of GSL were evaluated. Additionally, rheological parameter, heat of hydration, crystal morphology, and pore structure were also analyzed. Cement significantly improved the fluidity of slurry. Moreover, the compressive strength and softening coefficient of GSL reached 20.6MPa and 0.56 at 10% cement, respectively. Furthermore, cement reduced the 30-min-fluidity loss and improved fludity by reducing the yield stress and increasing the plastic viscosity of screed. The transformation of hydration kinetics of GSL could be due to Ca2+ and OH- released by cement, thus resulting in the shortening of initial setting time and the prolongation of the interval between initial and final setting time. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) showed that CSH gel and AFt crystal would generate on the surface of CaSO4·2H2O crystal, making the structure more compact. Mercury intrusion porosimetry (MIP) indicated that cement greatly reduced the porosity through the water reduction effect in the early stage and continuous hydration in the later stage. The continuous hydration of cement also increased the shrinkage rate. This work was expected to provide reference for promoting the application of desulfurized building gypsum as the high value-added screed.

Using metakaolin to improve properties of aged Portland cement: Effectiveness and the mechanism

Aging of Portland cement, due to its reaction with moisture and atmospheric CO2 prior to regular use, has the potential to severely impair its hydration reactivity. The effectiveness of using metakaolin to improve the properties of aged Portland cement exposed to a laboratory conditions (RH=65 %, 20 °C) as well as the associated mechanism are studied. The incorporation of 5–10 % metakaolin changes the early-stage hydration kinetics of aged cement obviously by enhancing reactions of both C3S and C3A through the filler effect at the early hydration stage, thereby mitigating detrimental influences of aging on setting time and early-age strength development (up to 7 days). Metakaolin exhibits significant effectiveness on enhancing 28-day strength of aged cement, and the enhancement arises from the synergic reaction between metakaolin and CaCO3, which converts CaCO3 resulting from aging into carboaluminate phases and produces secondary C-S-H. The incorporation of 5 % metakaolin increases the 28-day compressive strength of the sample with cement aged for one month to a comparable level as that of fresh cement.

Preparation of C-S-H seeds from solid waste and its application as Portland cement accelerator

C-S-H seeds are expected to be a new type of accelerator to cope with the challenges of reduced strength and poor durability of concrete in the later stage caused by high dosage of accelerator. In this study, two solid wastes, rice husk ash and carbide slag, were used as silicon and calcium sources to synthesize C-S-H seeds. By screening the particle size and solid content of C-S-H seeds, the optimum synthesis condition was determined to be stirring at 25 °C for 2 h. The average particle size of synthesized C-S-H seeds approximates this to 320 nm and was mainly composed of C-S-H gel, PCE and sodium nitrate. The effects of C-S-H seeds on the properties of cement paste were studied by experiments such as fluidity, setting time, compressive strength, heat of hydration, XRD, TG and MIP. The results showed that the addition of C-S-H seeds improved the fluidity of cement paste, shortened its setting time, accelerated its early hydration, especially the NG process, and significantly improved its early compressive strength. Meanwhile, it densified the cement paste and improved the compressive strength in the later stage. The C-S-H seeds synthesized in this study not only showed excellent acceleration, but also were based on solid waste as raw material, while the reaction time was short and the equipment requirements were low.

Innovative encapsulation of alkali activators in alkali-activated slag concrete: A sustainable strategy for regulating setting time and durability

The scientific community has devoted considerable attention to alkali-activated slag binder systems, due to the low-carbon footprint and eco-friendly attributes. However, the regulation of setting time poses significant challenges to the widespread application in practical engineering environments. This study proposes an innovative approach to encapsulate alkali activators in capsules or tablets, followed by the incorporation into the alkali slag concrete matrix. This strategy aims to regulate and control the early dissolution and hydration rate of slag, thereby altering the setting time of the alkali-activated material. Specifically, this method can prolong the setting time by approximately 40%. Importantly, this intervention does not significantly damage the mechanical properties of materials over the 28 days due to the continuous outward diffusion of the active ingredients of the alkali activator. This encapsulation technique harbors the capacity for quantitative modulation of the setting time in alkali-activated slag concrete. The findings of this research offer valuable theoretical insights, paving the way for the application of alkali-activated hydration systems in diverse engineering domains.

Thermal performance and applied evaluation of the pre-bored grouting planted nodular pile in warm frozen soil

The thermal effect of pile foundation in frozen ground is crucial for the formation of its bearing capacity. To break through the problems of strong thermal disturbance and slow formation of bearing capacity in the existing pile foundations. In this paper, a new type of pile named Pre-bored Grouting Planted Nodular (PGPN) was first introduced to the permafrost area, which was a prefabricated composite pile. Its unique structure can reduce the amount of cementitious materials and improve the bearing capacity. To reveal the thermal performance of the PGPN pile to warm permafrost, and compare with that of bored concrete pile, the model experiment and numerical simulation of the pile were conducted in this paper. It was found that: 1) The refreezing time and thermal disturbance radius of the PGPN pile were 270 days and 1.8 m, respectively, which were one-third and half of those of cast-in-place pile. The cemented-soil around the PGPN pile could significantly reduce its hydration heat and reduce the thermal disturbance to frozen ground. 2) Because of the high cement concentration in cemented-soil, the early hydration reaction of the pile was strong, and the temporary high temperature provided a favorable environment for the strength maintenance of cemented-soil in frozen soil. On the contrary, the hydration reaction of bored concrete pile lasted a long time, which intensified the degree of thermal disturbance to permafrost; and 3) Affected by the cooling effect of the atmospheric environment and the self-recovery effect of the lower permafrost, the temperature field of the pile foundation refrozen from the upper and lower ends to the middle. The structure of the frozen soil was changed by hydration heat, making it difficult to return to its initial state. The research results can provide data support for the promotion and application of prefabricated pile foundation in permafrost regions.

Use of coal chemical industry by-product coal gasification fine ash as supplementary cementitious materials in cement: Chemical excitation, hydration and hardening characteristics

In order to realize the resource utilization of coal gasification fine ash (CGFA) in cement fields, a key is to solve the problem of low activity of CGFA. This paper studied the performance of CGFA as supplementary cementitious materials in cement. Furthermore, to enhance the activity of CGFA, targeted chemical activators were employed, with triethanolamine (TEA) and simulated high salinity wastewater (SHSW) chosen as representatives of organic and inorganic agents, respectively. It was found that CGFA had a synergistic effect with cement at a low dosage, while the inhibition effect on cement hydration was dominant at a high dosage. TEA promotes the strength development of the CGFA-cement system by promoting early hydration of cement and dissolution of active minerals in CGFA. However, the promoting effect of TEA on cement hydration will change to an inhibiting effect with the development of time, which will have an adverse effect on the development of strength. In general, the optimal dosage of TEA is 0.03 %, which can increase the 28-day activity index of CGFA from 69.1 % to 75.6 %. SHSW accelerates the strength development of the CGFA-cement system by promoting the hydration of cement and facilitating the dissolution and hydration of active minerals in CGFA. In addition, X-ray diffraction results show that a new hydration product, Friedel’s salt, is formed under the excitation of SHSW. But this new hydration product will gradually dissolve as the pH decreases. The 28-day activity index of CGFA can be increased to a maximum of 83.3 % under the excitation of 2 % SHSW.

Investigation on the preparation of low carbon cement materials from industrial solid waste phosphogypsum: Clinker preparation, cement properties, and hydration mechanism

Low-carbon calcium sulfoaluminate (CSA) cement can be prepared with industrial by-product phosphogypsum (PG). This paper uses PG to replace natural gypsum in preparing PG-based CSA (PGCSA) cement as a raw material and mineral admixture, and the mechanical properties and hydration mechanism of PGCSA cement are explored. The results showed that the clinker with ye'elimite mineral content of 67.23% was fired at 1250 °C by mixing 19.52% PG into the raw materials. The participation of PG in hydration can accelerate the hardening of paste and improve the compressive strength of cement. The optimum dosage of PG as a mineral admixture was 20%, and the compressive strength reached 88.4 MPa at 28 days. Added PG promoted the early hydration of ye'elimite, and reaching 60% hydration within 1 day. The hydration mechanism was believed that a large amount of Ca2+ released by PG dissolution increased the ion concentration and promoted the hydration of ye'elimite. The PGCSA cement prepared in this study at 1250 °C had low carbon emission and PG utilization was higher than 40%. In addition, the pH and exothermic hydration of PGCSA cement were reduced about 2 and 100 J/g compared to that of CSA cement. This paper provides a feasible solution for PG resource utilization and carbon reduction.

Role of C-F-S-H/PCE nanocomposites on the hydration of Portland cement with varying gypsum levels

This study delves into the role of C-F-S-H/PCE (calcium-ferrite-silicate-hydrates/polycarboxylate ether) nanocomposites on the cement hydration with varying gypsum levels. It is found that the addition of C-F-S-H/PCE nanocomposites simultaneously promotes the dissolution of cement clinker and gypsum during early hydration. What’ more, the early hydration is further enhanced notably by C-F-S-H/PCE nanocomposites at moderately higher gypsum level without compromising the long-term compressive strength. It merits attention that the compressive strength of cement paste emerges as a factor intricately interwoven with not only its microstructure but also the content of AFt (ettringite) it harbors. Anyway, in the presence of the C-F-S-H/PCE nanocomposites, the faster depletion of gypsum leads to an earlier formation of AFm (monosulfoaluminate) whereas the morphologies of various hydration products remain unaffected. The findings demonstrate that the addition of C-F-S-H/PCE nanocomposites increases the demand for gypsum in cement and provide insights into the production of cement and concrete using seeding materials.

Mechanism underlying effects of CaO-MgO combined expansive agent on hydration kinetics of cement-based systems

With the order of better understanding the early hydration process and reaction mechanism of CaO-MgO combined expansion agent-involved cement-based systems (CMEA-CBS), CMEA dosage, CaO to MgO ratio (Ca/Mg), MgO activity, hydration temperature, and water-binder ratios (w/b) were chosen as the influencing factor. Accordingly, isothermal calorimetry was implemented to analyze the hydration heat release law, and the Krstulovic–Dabic model was applied to investigate the hydration kinetic. Moreover, the activation energy of CMEA-CBS was calculated. The findings of this study are as follows. The incorporation of CMEA can accelerate the hydration of cementitious systems. Hydration temperature increase markedly promote the hydration reaction of CMEA-CBS. The hydration reaction of CMEA-CBS is a complex associated reaction process dominated by multiple reaction mechanisms in sequence. At both 20 °C and 45 °C, the hydration process of CMEA-involved cement-based systems experienced three stages of crystallization nucleation and crystal growth (NG), phase boundary reaction (I), and diffusion (D), and the hydration mechanism was NG → I → D. However, the hydration of CMEA-CBS at 65 °C switched from the NG stage to the D stage directly. The hydration promotion effect of increasing temperature on I and D process of CMEA-CBS is less than I and D process of pure cement. Compared to the other groups, the temperature increase had the least effect on the early hydration process of 10%-C1M1-M-0.4 with the lowest apparent activation energy.

Effects of polycarboxylate superplasticizer and hydroxypropyl methylcellulose on the properties of ferric-rich sulfoaluminate cement

Ferric-rich sulfoaluminate cement (FR-SAC) is a promising low-carbon cement and is usually used to prepare precast products due to its short setting time. However, the fast setting of FR-SAC paste also leads to its poor fluidity and workability. Polycarboxylate superplasticizer (PCE) and hydroxypropyl methylcellulose (HPMC) can improve the fluidity and viscosity but may affect other properties of FR-SAC products. To get a suitable performance of FR-SAC by adding PCE or HPMC, the properties of FR-SAC paste with PCE and HPMC added and their influence mechanism were explored. The results indicate that PCE adsorbs on the surface of positively charged ettringite in the slurry under the electrostatic attraction, which makes the negatively charged or uncharged FR-SAC particles uniformly dispersed in the slurry, thus regulating the rheology and other properties of FR-SAC paste. The compressive strength of FR-SAC paste increases with the increase of PCE addition. PCE slightly retard the early hydration rate of FR-SAC but does not affect the formation of later hydration products. Adding HPMC to FR-SAC paste can decrease the fluidity and increase the viscosity of FR-SAC paste but has little effect on its hydration properties. Therefore, when PCE and HPMC are used to modulate the rheology of FR-SAC paste, it is necessary to combine the utilization process and compressive strength requirements to keep both the rheological parameters and compressive strength in the suitable condition.

Study on the performance of alkali-activated phosphorus slag cemented paste backfill material: Effect of activator type and amount

Effective disposal of phosphorus slag (PS) is crucial for ecosystem protection. Herein, this study proposed that Na2SO4 (SS), Na2SiO3 (NS), Na2CO3 (SC) and NaOH (NH) were performed to prepare alkali-activated phosphorus slag cemented paste backfill material (AAPS-PB). The evolution mechanisms of setting time, rheological behavior and mechanical properties at different contents of various activators were systematically investigated. The mineral compositions, bonding structure, micromorphology and pore structure characteristics of AAPS-PB hydration products were further clarified by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) and mercury intrusion porosimeter (MIP). Results indicated that activators were proved to significantly promote the dissolution of PS at appropriate content. NH had stronger alkali activation ability in the early hydration period, whereas NS sufficiently improved the later strength, enhanced the denseness of hydration products and refined the pore structure characteristics. This study expands the avenues for high-value applications of PS.

Investigation on the early proceeding of cement hydration containing dispersed nano Calcium Silicate Hydrated (CSH) seeds

Steam curing process is a traditional method for accelerating the progression of cement hydration to satisfy the rapid development of compressive strength in precast concrete industry. However, steam curing would release significant amount of CO2 into the atmosphere. In order to avoid the serious environmental pollution caused by the steam curing process, Calcium Silicate Hydrate (CSH) dispersed by comb-like polycarboxylate superplasticizer (PCE), shorted as dispersed nano CSH seed, was utilized to promote the early cement hydration at normal temperature. This investigation aims at disclosing the hydration process of cement and the microstructure evolution of cement paste in the presence of dispersed nano CSH seed during the early stage via setting time, ultrasonic pulse velocity (UPV), compressive strength, conductivity, pH, thermogravimetric (TG), 29Si NMR and nitrogen adsorption/desorption. The results demonstrated that with the dispersed nano CSH seed increasing, the setting process of cement paste was shortened dramatically, the compressive strength and UPV of cement mortar increased significantly especially at 12 h. The variation of conductivity and pH of cement suspension indicated that the ion dissolution process was promoted by dispersed nano CSH seed, which therefore conducive to the precipitation of cement hydration products. TG curves exhibited that the formation of cement hydration products, including CH (Calcium Hydrated), AFt and CSH gel were accelerated by dispersed nano CSH seed. The 29Si NMR (Nuclear Magnetic Resonance) and nitrogen adsorption/desorption results validated that the incorporating dispersed nano CSH seed promoted considerably the polymerization of CSH gel. The aforementioned results are correlated well with the fast formation of microstructure and in turn the rapid development of compressive strength at early age.