Microstructure Of Cement Paste Research Articles

Influence of Nano-SiO2 Content on Cement Paste and the Interfacial Transition Zone.

Nano-SiO2 (NS) is widely used in cement-based materials due to its excellent physical properties. To study the influence of NS content on a cement paste and the interfacial transition zone (ITZ), cement paste samples containing nano content ranging from 0 to 2% (by weight of cement) were prepared, and digital image correlation (DIC) technology was applied to test the mechanical properties. Finally, the optimal NS content was obtained with statistical analysis. The mini-slump cone test showed that, with the help of superplasticizer and ultrasonic treatment, the flowability decreased continuously, as the NS content increased. The DIC experimental results showed that NS could effectively improve the mechanical properties of the cement paste and the ITZ. Specifically, at the content level of 1%, the elastic modulus of cement paste and ITZ was 20.95 GPa and 3.20 GPa, respectively. When compared to that without nanomaterials, the increased amplitude was 73.50% and 90.50%, respectively. However, with the further increase in NS content, the mechanical properties decreased, which was mainly caused by the agglomeration of nanomaterials. Additionally, the NS content did not exhibit a significant effect on the thickness of the ITZ, and its value was maintained at 76.91-91.38 μm. SEM confirmed that NS would enhance the microstructure of both cement paste and ITZ.

Novel application of potassium methylsiliconate in cement-based materials: Retarding of hydration process and improvement of compressive strength

The presented research investigates the application of the organosilicon compound named potassium methylsiliconate (MESI) as a set-retarding admixture for cement-based materials which also provides the strengthening effect. The study concerns the impact of three dosages of MESI (1%, 2% and 3% per cement mass) on the properties of the cement paste, mortar and concrete. The greatest delay of the setting time of cement CEM I 42.5 R and retardation effect, examined by manual Vicat apparatus, was observed for addition of 1% methylsiliconate. The beginning of the setting was prolonged to 23 h. The influence of potassium methylsiliconate on the kinetics of cement hydration was investigated by isothermal calorimetry. The calorimetric results disclosed significant extension of induction period during Portland cement hydration with addition of potassium methylsiliconate as an admixture. It is especially visible in case of addition of 1% of MESI. Moreover, tests performed at 30 °C, 40 °C and 50 °C showed that MESI can also delay the cement hydration at higher temperatures. The influence of potassium methylsiliconate on the compressive strength of cement mortar and concrete after 1, 2, 7, 28 days and72 days was also investigated. In the first days of hydration, the compressive strength of the materials was reduced, but after 28 days of curing the compressive strength was increased by 21% and 16% for cement mortar and concrete, respectively. The impact of MESI on the microstructure and pore size distribution of cement pastes in 2nd, 7th and 28th of hydration was examined by mercury intrusion porosimetry (MIP). The result showed significant delay in the development of the cement pastes microstructure during the first days of hydration. The XRD and DTA/TG analysis provided the knowledge about impact of siliconate on the composition and formation of the cement phases. Both, the XRD and DTGA/TG analyze showed noticeable changes in portlandite formation during the first days of hydration. The conducted research and obtained results reveal the innovative and novel application of potassium methylsiliconate as retarders, which prolongs the workability of fresh mixture and improves the compressive strength of matured concrete and mortar. This admixtures can be a competitive alternative to traditional retarders.

Effective diffusivity of hardened cement paste from 3D microstructures: A critical comparison of real and virtual microstructures

This study compares experimentally obtained hardened cement paste microstructures from μCT and virtual microstructures generated by two hydration models, namely CEMHYD3D and HYMOSTRUC. Several microstructural features (phase volume fractions, connectivity, pore size distribution, and two-point correlation functions) were cross-validated among the microstructures on the basis of image analysis. In addition, the corresponding effective diffusivities in a fully saturated state were compared. The simulated effective diffusivities of the μCT and CEMHYD3D microstructures agree well with the experimental data, where HYMOSTRUC overestimates. However, none of the virtual microstructures can fully capture the actual microstructural features. HYMOSTRUC produces realistic pore size distributions but overly connected capillary pores, whereas CEMHYD3D generates excessive scattering of small pores with low connectivity. The impact of the differences in the pore structure on the output diffusivity is presented.

A facile approach to disperse metakaolin for promoting compressive strength of cement composites

Metakaolin (MK), a highly reactive supplementary cementitious material, is extensively employed in cement composites to improve their compressive strength. Nevertheless, MK suffers from extremely poor dispersion, resulting in agglomerating in the cement-based materials, thus failing to exhibit its positive effects fully. To overcome this drawback, for the first time, this work elaborately developed a facile graphene quantum dots (GQDs)-assisted ultrasonic dispersion approach to improve the dispersity of MK effectively. Furthermore, it investigated effect of as-obtained MK (GMK) on compressive strength of cement composites. More specifically, GMK owned a smaller size and a larger specific surface area and presented a higher dispersity than UMK (namely, MK was identically treated by ultrasonic dispersion only without GQDs) and original MK. And in light of the characteristics of three types of MKs, the dispersing mechanism of MK caused by GQDs-assisted ultrasonic treatment was rationally ascribed to intercalation, exfoliation and surfactant effects of GQDs. Crucially, GMK purely by the incorporation of 1.0 wt.% (by weight of cement) demonstrated a significant enhancement of 31.03% for the 28-day compressive strength of mortar; While UMK had little influence on the compressive strength of mortar under the identical conditions. And based on the comprehensive analyses of hydration heat, phase composition and microstructure of different cement pastes, the most significant positive effect of highly dispersed GMK purely by a dosage of 1.0 wt.% on the compressive strength of cement composites was accredited to the fact that GMK was able to accelerate hydration process, boost the formation of C−(A)−S−H and refine the microstructure. This study firstly provided a facile, efficient and low-cost method to fabricate high-dispersity GMK, and verified its remarkable promotion effect on compressive strength of cement composites. These observations would improve the benefits and reduce the cost of MK-like materials applied to cement-based materials.

Effect of chelator on compressive strength and microstructure of CO2 curing cement paste

In this paper, chelator was used to accelerate CO2 mineralization curing cement paste. The mechanical properties and microstructure of CO2 curing cement paste with chelator were investigated through compressive strength test, low-field nuclear magnetic resonance (NMR) test, and scanning electron microscopy (SEM) observation. Next, the effect of chelator on the content of mineralized products was analyzed through X-Ray diffraction (XRD) test and thermogravimetric analysis (TGA). Finally, the CO2 absorption capacity of cement paste with chelator was evaluated through carbon sequestration rate calculation. The results showed that the chelator could improve the strength of CO2 curing cement paste and accelerate the mineralization reaction rate. With the increase of the chelator dosage, the compressive strength of cement paste presented a trend of first increasing and then decreasing. When the dosage of chelator was 0.5% of the cement content, the improvement effect on compressive strength of cement paste was the best, and under the premise of achieving equivalent mechanical properties, chelator could shorten the CO2 curing period of cement paste by half. NMR showed that chelator could promote the conversion of large pores to small pores in hardened cement paste. CO2 curing for 4 h, the porosity of pores above 40 nm in cement paste with 0.5% chelator decreased by 17.0% compared to ordinary cement paste. Based on the XRD and TGA on the mineralization reaction zone, it was found that the addition of 0.5% chelator could improve the CO2 curing degree of cement paste. CO2 curing for 48 h, the 0.5% chelator could effectively increase the yield of mineralized product CaCO3 by 22.5%. CO2 curing for 4 h and 48 h, the cement paste with 0.5% chelator could increase the carbon sequestration rate by 11.8% and 17.4% compared with ordinary cement paste, respectively.

Insights into the effect of CNTs on cement hydration from the perspective of water evolution

The addition of carbon nanotubes (CNTs) into cement can remarkably enhance the mechanical properties of concrete. To investigate the impact of CNTs addition on the early-stage hydration of cement paste, low-field nuclear magnetic resonance (NMR) was employed to monitor the water evolution and microstructure of cement paste. The relaxation signals obtained from low-field NMR can provide valuable information regarding the state and content of water molecules, thereby indirectly characterizing the microstructural change of cement. Based on the correlation of characteristic transverse relaxation T 2 and water confinement state, low-field NMR can be used to predict the setting time of cement in the early stage. The findings indicated that the addition of CNTs can expedite the initial hydration process of cement, leading to a denser microstructure and shorter setting time. The results of Vicat needle test validated the efficacy of low-field NMR in predicting the setting time of cement. The non-destructive and non-invasive nature of low-field NMR technology renders it particularly advantageous in assessing the impact of CNTs on the early-stage behavior of cement paste.

Analysis of the Microstructure and Porosity of Cement Pastes with Functionalized Nanosilica with Different Contents of Aminosilane.

This research aims to analyze the effect of functionalized nanosilica (NSF) with different levels of amine groups in the formation of hydration products. Four cement pastes were investigated, one reference with Portland cement and three replacing 1% of Portland cement by nanosilica (NS), NSF with a low content of amine groups, and NSF with a high content of amine groups. The heat of hydration of the pastes was evaluated up to 7 days of hydration, the amount of calcium hydroxide (CH) and hydrated phases by means of the thermogravimetric analysis (TGA) test and compressive strength at 2, 7, and 28 days, and porosity through tests of mercury intrusion porosimetry and computed tomography at 28 days of hydration. It was possible to observe that the NSF directly influenced the hydration kinetics of the pastes, delaying the hydration of the Portland cement; however, it demonstrated a similar mechanical performance to the paste with NS at 2 days of hydration and an increase of 10% at 28 days of hydration due to the improvement in the hydration process. Thus, it is possible to conclude that the functionalization of NSF with a low 3-aminopropyltriethoxysilane (APTES) content is promising for use in cementitious materials and may improve hydration and mechanical performance at more advanced ages compared to NS.

The development of sustainable cement pastes enhanced by the synergistic effects of glass powder and carbonation curing

Due to the dilution-induced early-age strength reduction, the glass powder (GP) dosage used in concrete to replace ordinary Portland cement (OPC) is restricted. This study used carbonation curing on GP blended cement pastes to overcome this obstacle. The experimental investigations concluded that mutual improvements could be achieved, where, in comparison to the carbonated OPC batch, not only the compressive strength of 20% GP-incorporated batches was higher for both early-age (increment of 13.4%, 1-day strength of 55.4 MPa) and late-age (increment of 11.2%, 28 days strength of 62.4 MPa), but the carbon sequestration degree was also promoted. According to the characterizations of mineralogy, microstructure, and phase evolution of the blended cement paste subjecting to carbonation curing, the addition of 20% GP induced a higher carbonation degree, smaller calcite crystal size, refined pore structure, and reduced porosity than that of pure OPC control references. The sustainability assessments confirmed that carbonated GP blended cement is a cleaner alternative to OPC.

Measurement and evaluation of cement paste porosity by electrochemical impedance spectroscopy

Porosity is an important part of cement paste microstructure, which significantly influences the mechanical properties (especially durability and strength) of cement-based materials. Electrochemical impedance spectroscopy (EIS) is a non-destructive method used to measure the pore system utilizing a range of frequencies of electric current, which is fed to the cement paste by stainless steel electrodes. The pore volume is obtained from the pore resistance and the matrix capacitance measured by EIS. This paper deals with the evaluation of porosity based on resistance values from EIS on a sample of pure CEM I 42.5R Portland cement paste at 3 different hydration times (age 7, 14, 28 days).

Phase separation of recycled concrete powder during grinding and consequent influences on its hydration behaviors in cement paste

Recycled concrete powder (RCP) collected from waste concrete recycling presents significant variation in both composition and hydration behavior, while available literatures were mainly carried out on RCPs derived from target concrete, mortar, or cement paste, RCPs collected from actual waste concrete is totally different from RCPs reported, their roles has not been clarified yet due to its complexity in components, leading to substantial deviation in understanding the roles of RCP in cement-based materials. In this study, RCP collected from a waste concrete reutilization plant was classified into five fractions, then effects of RCP fractions on heat evolution and mechanical properties of cement pastes were investigated. The results showed that hydration products and un-hydrated clinker were predominantly concentrated in fine RCP fraction, while higher proportion of aggregate grains (mainly quartz, anorthite, and dolomite) in coarse RCP fraction, indicating that cement paste was pulverized or milled into finer particles prior to fine and coarse aggregates due to its diminished elastic modulus. Compared with coarse RCP fraction, fine RCP fraction showed significant acceleration of cement hydration and higher strength contribution, which can be attributed to the remarkable pore refinement of fine particle and conspicuous seeding effect of C–S–H in RCP. Furthermore, increased dissolution of Si4+ and Al3+ from the fine RCP fraction was observed, then more hydration products were generated to densify the microstructure of cement paste. The results provided a deeper insight into the roles of RCP in cement-based materials, and then facilitate the efficient utilization of RCP to achieve resource-conservation development.

Influence of Nanosilica and Superplasticizer Incorporation on the Hydration, Strength, and Microstructure of Calcium Sulfoaluminate Cement Pastes

Influence of Nanosilica and Superplasticizer Incorporation on the Hydration, Strength, and Microstructure of Calcium Sulfoaluminate Cement Pastes

Experimental investigation on effects of polyaniline-modified-lignin on cement-based materials: Strength, hydration and dispersion

The application of lignin dispersants in cementitious materials has been limited due to its strong retarding effect on cement hydration. In this study, polyaniline modified lignin (PL) was prepared to be as a new lignin additive to increase the dispersion of cement system and maintain good mechanical properties of cementitious materials. This investigation systematically revealed that different contents of PL (0%, 0.5%, 1.0%, 2.0%) had various effects on the early hydration, the work performance and the microstructure of cement paste and mortar. Appropriate dosage of PL was beneficial to achieve better dispersion and improve the fluidity of cement system. The retarding effect on cement hydration was significantly reduced by PL, compared to unmodified lignin. When the content of PL was 0.5% and 1.0%, the mechanical properties of the mortar was maintained as well as mortar without PL. However, excessive content of PL (2.0%) decreased the flexural strength and compressive strength significantly. XRD and TG tests exhibited that no new hydration products were generated and the formation of calcium hydroxide was inhibited after the addition of PL. Besides, SEM and MIP results showed that low dosage of PL could decrease the porosity due to the filling effect. When the dosage of PL in cement exceeds 2.0%, the structure was more loose and porous, attributed to the delayed hydration and air entertainment. The dispersion mechanism was also discussed and ascribed to electrostatic repulsion caused by PL adsorbed on the surface of cement particles and the steric effect due to the branched chains of PL. This study provides a new idea for high-value application of lignin and the promotion of low-carbon building materials by using renewable resources.

Analysis of Pore Structure in Cement Pastes with Micronized Natural Zeolite.

The continuous development of urban areas around the world led to an increase in construction material use and demand, with concrete seeing significant market uptake. Although significant progress has been made to reduce the environmental impact of concrete, there is still a stringent need for improvement. One of the most widely used methods to reduce the environmental impact of the cement industry and the construction industry alike is the replacement of ordinary Portland cement (OPC) by supplementary cementitious materials (SCM). Aside from by-products of industry, SCMs could also come from natural sources. Taking into account the porous structure of zeolites and their contribution to the improvement of the mechanical and durability properties of cement-based materials, the analysis of pore structure in cement pastes incorporating micronized natural zeolite is deemed necessary. In this research, the OPC was replaced by zeolite in three different percentages: 10%, 20%, and 30% by mass. The evolution of pore structure was investigated by means of nuclear magnetic resonance relaxometry at the curing ages of 1, 7, and 28 days. The microstructure of cement pastes was assessed by scanning electron microscopy investigations at 1, 7, 14, 21, and 28 days. The obtained results show that smaller pore sizes are present in cement pastes containing zeolites during the first 7 days. However, at the age of 28 days, the reference mix exhibits a similar pore structure to the mix containing 10% micronized zeolite due to the presence of larger amounts of hydration products. Increasing the replacement percentage to 30% results in larger pores, as indicated by larger values of the relaxation time.

Effect of two-dimensional MXene on electrical conductivity of cement pastes

In this study, two-dimensional (2D) MXene cement-based material with high electrical conductivity was prepared. The conductive behavior of cement pastes was measured by electrochemical impedance spectroscopy (EIS) and four-probe method. Besides, the microstructures of cement pastes were examined by scanning electron microscope (SEM), X-ray diffraction (XRD), and mercury intrusion porosimetry (MIP). The results demonstrate that the variation of electrical conductivity corresponds to percolation theory, and curing age exerts a negligible influence on the percolation threshold. Increasing the MXene content leads to both an increase in the electrical conductivity and the compressive strength (at an MXene dosage below 0.5 wt%). SEM analysis reveals that MXene can form a conductive network in the percolation zone of the matrix. Moreover, the hydration degree is promoted with the addition of MXene within 1.0 wt%, reflected by XRD analysis. The MIP results demonstrate that the addition of MXene at 0.7 wt% significantly reduces the porosity.

Fabricated CeO2/ZrO2 nanocomposite to improve thermal resistance, mechanical characteristics, microstructure and gamma radiation shielding of OPC composite cement pastes

The main objective of this study is to utilize the synthesized CeO2/ZrO2 nanocomposite (CZ-NPs) in different concentrations (0.25, 0.5, 0.75, 1, and 1.5%) for improving the mechanical characteristics, microstructural properties, thermal resistance, and gamma radiation shielding of hardened ordinary Portland cement (OPC) composites. CZ-NPs were fabricated via the precipitation method. Various analytical techniques in addition to X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), and Scanning electron microscopy (SEM) analysis were used to investigate the fabricated CZ-NPs and hardened composite pastes. The physico-mechanical features, thermal stability, and radiation resistivity of different OPC-CZ-NPs composite pastes were investigated. The results showed that the composite CZNP1 containing 0.25% CZ-NPs is the best choice for mechanical performance and has the highest gamma-ray shielding efficiency, as it can attenuate 50–90% respectively of gamma rays with energy 660Kev at distances 4 cm and 13 cm, respectively. Also, the composite accommodating of 0.5% CZ-NPs motivates the thermal resistance at 400 °C.

Internal hydrophobization of cement-based materials by means of silanes

The paper shows the opportunity of application of an organosilicon compound such as triethoxyoctylsilane (OTES) containing long, hydrophobic alkyl sidechains (octyl groups – C8H17) attached to the silicon atoms, as the admixtures for internal hydrophobization of cementitious building materials characterized by a porous internal structure. The study included the cement paste, mortar and concrete with three different hydrophobic admixtures based on triethoxyoctylsilane, but with miscellaneous concentration of the triethoxyoctylsilane in the admixture and different dosage in the fresh mix. The impact of organosilicon hydrophobic admixtures on the mechanical properties such as compressive strength, capillary water absorption of the cement mortar and concrete and the microstructure of cement paste was investigated. The hydrophobic, silicon-based admixtures decrease the capillary water absorption coefficient significantly. Even by 81.1% in case of cement mortar. The mechanical strength of cement mortar is also decreased, by 23.6%. The noticeable changes in the internal structure of pores of cement paste only for one admixture is observed.

Hydration and microstructure of cement paste mixed with seawater – An advanced investigation by SEM-EDS method

This study aimed to investigate the microstructural hydration features of Portland cement incorporating with natural seawater (SW). Special attention was paid to characterizing the pore structure, hydrated and anhydrous phases using microscopy techniques, such as secondary electron (SE), backscattered electron (BSE) imaging and energy dispersive spectrometry (EDS) mapping. Through the utilization of algorithms, information extracted from these methods underwent self-corrected, denoising, and imaging calibration, which significantly contributed to the calculation of pore volume, identification and segmentation of various phases, and quantitative characterization. By leveraging the chemical and spatial information from EDS mapping, highly detailed distribution maps of the different cement phases could be obtained, surpassing the conventional BSE grayscale segmentation method in phase identification. Statistical analysis revealed that the deviation of the phase quantification was reduced when using a magnification of 250 times. Higher content of hydrate phases with lower porosity can be observed in SW samples exhibited a higher content of hydrate phases with lower porosity, indicating a stimulated hydration effect. However, accurately determining hydrate phases with small crystal sizes, such as ettringite, necessitated an increase in mapping resolution. Therefore, the use EDS mapping for quantification of various cement phases in submicroscopic and microscopic characterization is both feasible and promising.

Development of ultra-fine SAP powder for lower-shrinkage and higher-strength cement pastes made with ultra-low water-to-binder ratio

Superabsorbent polymer (SAP) as internal curing agent can effectively mitigate the autogenous shrinkage and promote cement hydration of ultra-high performance concrete (UHPC). However, it has a risk of impairing the mechanical performance of UHPC given the macro pores left. This study developed ultra-fine SAP powder aiming at securing the lower shrinkage and higher strength of UHPC. The influence of SAP powder on (average diameter (ds) of 5.78–60.85 μm) the water absorption/desorption characteristics, strength, shrinkage, and microstructure of cement paste with ultra-low water-to-binder ratio (w/b) was systematically studied. The results showed that the reduction of particle size of SAP can reduce the spacing distance of SAP in cement paste, which is beneficial for the internal curing, such as reducing the autogenous shrinkage, improving hydration of cement, and increasing the compressive strength. When the ds of SAP powder was 11.55 μm, it can reduce autogenous shrinkage by 72.4% without any reduction in the compressive strength compared to paste made without SAP powder. Such SAP powder led to about 5% higher hydration degree and 12.5% lower porosity compared to the conventional SAP. A quantitative approach considering the spatial distance and water absorption of SAP was proposed to describe their effect on internal curing.

Synthesis, characterization, and application of graphene oxide and reduced graphene oxide and its influence on rheology, microstructure, and mechanical strength of cement paste

The present study is an attempt in disseminating the influence of graphene-based nanomaterials such as graphene oxide (GO) and reduced graphene oxide (rGO) in cement composites. The improved Hummer's approach was employed to synthesise the GO and rGO. Various characterization techniques involving XRD, FTIR, TGA, TEM, and SEM were utilized to understand the crystalline structure, interlayer spacing, functional groups, and microstructure of GO and rGO nanoparticles and further nanomaterial-doped cement composites. Both GO and rGO were used as 0.01%, 0.02%, 0.03%, 0.04%, and 0.05% by weight of cement. The influence of GO and rGO on rheology, workability, microstructure and mechanical strength were determined. The compressive test results indicated an improvement of compressive strength by 21.72% and 30.26% in 0.03% GO and 0.04% rGO cement composites respectively. The enhancement in physicochemical properties is attributed to the densification of microstructure with the GO and rGO usage in cement composites. Concrete workability, pumpability, and printability depend on rheological parameters such yield stress, viscosity, and thixotropy. The research paper highlights the significance of critical rheological parameters of cement with the addition of nanomaterials. The incorporation of graphene oxide and reduced graphene oxide into cement paste represents a promising avenue for enhancing the material's rheology, microstructure, and mechanical strength, with the potential to revolutionize the construction industry and pave the way for a new generation of high-performance, sustainable building materials.

Study on the damage resistance and deterioration behavior of GO concrete under the harsh environment.

To exploretheeffects of physical, mechanical, anti-deterioration properties of graphene oxide (GO) on cement-based cementitious materials, GO sheet dispersions areprepared by the improved Hummers method and ultrasonic dispersion method. The influence of theGO content on the compressive and flexural strengths of cement paste is investigated, and the penetration process of chloride ions in graphene oxide concrete is discussed by the electric accelerated erosion method. Combined with the rapid freeze-thaw test, the deterioration of graphene oxide concrete ismethodically analyzed. Theobtained results reveal that an appropriate amount of GO improves both the compressive and flexural strengths of cement pastev. In the chloride environment, the chloride diffusion coefficient of 0.03% GO concrete is 18.75% less than that of ordinary concrete.Under the action of freeze-thaw cycles, with the increase of salt freezing times, the deterioration mode of GO concrete is a combination of mortar shedding, micro-crack expansion, denudation, and block shedding; The stress-strain curve of the specimen tends to be flat with the growth of salt freezing times. The peak stress gradually lessens, the peak strain gradually grows, and the elastic modulus remarkably reduces. Compared with ordinary cement paste, theGO is capable of promoting the growth of cement paste hydration crystals, changing the size and shape of crystals, and realizingthe regulation of cement paste microstructure. Incorporating an appropriate amount of theGO could promote the cement hydration process and enhance the chemical water-binding amount in the cement paste. The optimal GO content is reported to be 0.03% of the cement mass.