Microstructure Of Cement Paste Research Articles

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.

Utilization of coal gangue power generation industry by-product CFA in cement: Workability, rheological behavior and microstructure of blended cement paste

Circulating fluidized bed fly ash (CFA), by-product of coal gangue power generation industry based on circulating fluidized bed combustion technology, differs from ordinary fly ash (OFA) in its physical and chemical properties. This paper aims to investigate the influences of CFA with three particle sizes on the workability and rheological properties of cement paste. The results show that untreated raw CFA (RCFA) can significantly degrade many properties of fresh cement paste. Directly using CFA as a mineral admixture in cement-based materials is not suitable in terms of workability. However, CFA through grinding methods can significantly mitigate the detrimental effect of CFA on the flowability of cement paste. When 15% ultrafine CFA (UCFA) was added, the cement paste exhibited relatively favorable workability and rheological properties. The rheological behavior of cement paste containing CFA with three particle sizes follow the shear thinning, which is in line with the modified Bingham model. Furthermore, the reasons for the impact of CFA on the microscopic level of cement workability are analyzed and discussed. The addition of CFA reduces the amount of free solution in the cement paste, leading to the formation of a flocculated structure and an increase in the thixotropic loop area. Based on the analysis of TOC, BET and TEM, it was determined that numerous polycarboxylate superplasticizer (PCE) molecules are adsorbed onto the rough and porous surface structure of CFA particles, hence the destructive ability of PCE to the flocculation structure caused by cement hydration is weakened. Therefore, the mechanism that CFA affecting the working performance of cement paste can be determined as: the adsorption of free water and PCE molecules.

Comparative study on effects of pozzolanic nano-SiO2 and non-pozzolanic nano-TiO2 on the microstructure and macro properties of cement paste subjected to early-age frost attack

The effects of nano-SiO2 (NS) and nano-TiO2 (NT) on the microstructure, strength and chloride diffusivity were compared, and the mechanism of both nanoparticles on early-age frozen cement paste was revealed. The thermogravimetric (TG) results demonstrate that NS effectively increases C-S-H gel content and degree of hydration to make up for hydration loss due to early-age frost attack, while NT had little effect on compensating for hydration loss. The mercury intrusion porosimetry (MIP) results indicate that NS and NT have the same improvement mechanism for frost-damaged pore structures, while NS has a better improvement effect on pore structure than NT. The macro results show that the enhancement effects of NS and NT on strength are similar, while the improvement effect of NS on chloride diffusivity is much better than that of NT. Finally, it is concluded that, in the early-age frozen cement paste, NS promotes cement hydration and optimize pore structure through pozzolanic effect, while NT mainly improves pore structure through nano-filling effect.

Influence of direct electric curing on the hydration and microstructure of cement paste excluding ohmic heating

A modified apparatus based on isothermal calorimetry was employed to determine the influence of direct electric curing (DEC) on the hydration of cement paste other than ohmic heating effect. In addition, the effects of DEC on the microstructure of cured cement pastes were investigated by TG, XRD, NMR, SEM and MIP. The results show that the heat release of DEC samples at early-age is increased significantly due to the electrical power. However, the hydration and microstructure of DEC samples in the isothermal environment are familiar with the normal curing sample. This indicates that, other than OH effect, the impact of DEC on the hydration process and microstructure of cement is negligible. Moreover, a theoretical model for predicting the electric power evolution related to porosity, free water content, hydration degree and initial electric power per unit mass was established which is matched well with the actual measurement results.

Reactivity of C3S and model cement in presence of Na2S2O3 and NaSCN

The impact of NaSCN and Na2S2O3 on the reactivity, microstructure and morphology of C3S and model cement (with a clinker containing 85% C3S and 15% C3A) pastes was systematically investigated. Results concluded that both alkali salts mainly act enhancing the reactivity of the C3S phase while not significant influence on the reactivity of C3A was measured. While both admixtures rose the reactivity of C3S over the studied 7 days of hydration, they only increased the reactivity of model cement pastes up to 14–20 h. NaSCN and Na2S2O3 did not modify the C–S–H stoichiometry but they influenced its morphology. In particular, thicker convergent C–S–H needles were formed in pastes containing Na2S2O3 compared to non-admixed systems, while a higher number of thinner C–S–H needles were formed in presence of NaSCN. Furthermore, greater portlandite clusters and intermixing of AFm and C–S–H were observed in admixed C3S and model cement pastes, respectively, compared to plain systems.

Performance of silica fume slurry treated recycled aggregate concrete reinforced with carbon fibers

The utilization of recycled concrete aggregate (RCA) is a sustainable way to produce concrete. However, using recycled aggregate in concrete results in inferior mechanical performance and durability, mainly due to the weak interfacial transition zone (ITZ) and attached mortar. The research aims to overcome the inferior properties of recycled aggregate concrete (RAC) by treating recycled aggregate with silica fume (SF) slurry and carbon fibers (CF) as reinforcement. A total of thirteen mixes were prepared and tested for workability, water absorption, mechanical strength, elastic modulus and performance against acid attack. To optimize the performance of recycled concrete, carbon fiber and silica fume were employed at 0.5% and 10%, respectively, with 25%, 50%, and 100% substitution levels of recycled aggregates. The aggregate was pre-soaked in SF slurry for 24 h before mixing in concrete to ensure its absorption or adherence to aggregate. Compressive, split tensile, and flexure strengths of recycled aggregate concrete were evaluated at 7, 28, and 56 days. Elastic modulus was examined under axial compression at 28 days of curing age. Experimental results showed that SF improves the microstructure of cement paste and the bonding between binder matrix and carbon fibers. Compressive, split tensile and flexural strength results of 45.2 MPa, 5.4 MPa and 7.8 MPa, respectively were observed by combined utilization of carbon fiber and silica fume at 28-day curing age in 100% recycled concrete i.e., for recycled concrete mix CFSF-RC100, which is 20%, 34%, and 46% more than their corresponding control mix i.e., RC100. Elastic modulus for RC mixes were found to vary between 22 GPa for RC100 mix and 35.6 GPa for CFSF-RC25 mix respectively. Silica fume also contributed to the water absorption reduction of up to 14% in recycled concrete. Carbon fiber-reinforced recycled concrete was more acid attack resistant having only 6.3% mass loss after acid attack and hence 40% reduced mass loss was observed compared to that of recycled aggregate concrete. Hence, strong, durable, and environment friendly concrete was produced.

Effect of Microcrystalline and Nano-Fibrillated Cellulose on the Mechanical Behavior and Microstructure of Cement Pastes

Effect of Microcrystalline and Nano-Fibrillated Cellulose on the Mechanical Behavior and Microstructure of Cement Pastes

Early-Age Properties Development of Recycled Glass Powder Blended Cement Paste: Strengths, Shrinkage, Nanoscale Characteristics, and Environmental Analysis

Recycling solid waste in cement-based materials cannot only ease its load on the natural environment but also reduce the carbon emissions of building materials. This study aims to investigate the effect of recycled glass powder (RGP) on the early-age mechanical properties and autogenous shrinkage of cement pastes, where cement is replaced by 10%, 20% and 30% of RGP. In addition, the microstructure and nano-mechanical properties of cement paste with different RGP content and water to binder (W/B) ratio were also evaluated using SEM, MIP and nanoindentation techniques. The results indicate that the early-age autogenous shrinkage decreases with the increase of RGP content and W/B ratio. While the mechanical strength deteriorates due to the addition of RGP, it can be compensated by reducing the W/B ratio. Although the addition of RGP increases the total porosity of the hardened paste, it reduces the small size porosity (

Efeito de nanotubos de carbono em matrizes de cimento Portland

abstract: This study evaluates the effects of three carbon nanotubes with different geometric characteristics on the rheological behaviour and mechanical performance, as well as on the microstructure of mortars and cement pastes. For nanotube content ranging from 0.025 to 0.2 wt%, the yield stress and viscosity were determined by rotational rheometry, and mechanical performance was evaluated by flexural strength and dynamic modulus of elasticity. The microstructural analysis was performed by X-ray diffraction, thermo-gravimetric analysis and scanning electron microscopy (SEM). The obtained results showed that the yield stress presents a considerable increase as the carbon nanotube content increases. The viscosity was also influenced by the presence of carbon nanotubes. The flexural strength of mortars increases for different amounts of carbon nanotubes, and depending on the geometric characteristics of the carbon nanotubes, the material behaves like a composite. The microstructural analysis showed the nucleation of hydration products on the surface of the carbon nanotubes, and that the better mechanical performance of matrices containing carbon nanotubes is not related to the increase in hydration products.

Influence of hoop restraint on microstructure and phase composite of cement paste filled steel tube under external sulfate attack

The deterioration of cement-based material caused by external sulfate attack (ESA) is a major durability problem affecting concrete structures. This study aims to investigate the effect of hoop restraint of steel tube on microstructure and phase composition of cement pastes prepared with ordinary Portland cement (OPC) and high sulfate-resistance Portland cement (SRPC) under ESA for 540 days. The effects of hoop restraint on the change in micromorphology, phase composition and microstructure of cement hydration products under ESA were investigated by SEM-EDS, XRD, 29Si and 27Al MAS NMR spectroscopy and low-field NMR. Moreover, the effects of hoop restraint on local mechanical properties of the cement pastes under ESA were evaluated by micro-hardness measurement. Results indicate that hoop restraint significantly inhibits the formation of micro-cracking and limits the permeation rate of sulfate ions, leading to a reduction in the amount of ettringite and gypsum crystals. 27Al NMR analysis shows that the hoop restraint has significant “delay effect” on the transfer of Al phase transition from monosulfoaluminate (AFm) and third aluminate hydrate (THA) to ettringite. 29Si NMR test reveals that hoop restraint can significantly slow down decalcification and dealuminization of C-(A)-SH gel, leading to a slow reduction in Al[4]/Si ratio of C-(A)-SH, together with the lower mean chain length (MCL) of the silicate chain. The MCL reduces by 34.7 % and 9.0 %, and Al[4]/Si ratio increases by 41.9 % and 8.3 % for OPC and SRPC pastes with steel tube compared to the equivalent free ones, respectively. Additionally, hoop restraint results in better quality pore structure of cement pastes with steel tube than the equivalent free ones.

Effect of regenerated nano-FeB on mechanical properties of cement paste

Regenerated nano-FeB were prepared from construction waste iron powder, and composite cement paste blocks were prepared.The mechanical and electrical conductivity tests were carried out on the composite cement paste test block,the experimental results show that the regenerated nano-FeB content is 0.075 %, the composite cement paste performance improvement is the best. At 28 days of age, the compressive strength and volume resistivity of the composite cement paste were 53.7 MPa and 2.4 × 104Ω · cm,which were 39.8 % higher and 24.8 % lower than that of the control group.The regulation mechanism of regenerative nano-FeB on cement paste was revealed by using scanning electron microscope (SEM) and Raman spectroscopy.The results showed that an appropriate amount of regenerated nano-FeB could effectively promote the growth of hydration crystals in cement paste, change the shape of hydration products crystals, and effectively improve the internal microstructure of cement paste, thereby improving the mechanical and electrical properties of cement paste.

Characteristics of CSH under carbonation and its effects on the hydration and microstructure of cement paste

This paper investigated the characteristics of synthesized calcium silicate hydrate (CSH) during the carbonation process and the effects of CSH and carbonated C-S-H (CCSH) seeds on the performance of cement pastes. The result showed that the CCSH is composed by 68.4% calcite and 31.6 % silica gel with Ca/Si of 0.09 and can absorb 301 g CO2 per kg C-S-H, which had a high potential for CO2 capture. please modifed to The result showed that the CCSH is composed by 68.4% calcite and 31.6 % silica gel and can absorb 301 g CO2 per kg C-S-H, which had a high potential for CO2 capture. The addition of CCSH showed more significant improvement on the cement hydration due to the higher surface area and the generated calcite and silica gel after carbonation treatment in comparison to CSH. A new hydration product of calcium aluminate mono-carbonate was generated in CCSH sample with the reaction between calcium carbonate and aluminate. Different from the only additional nucleation sites provided by CSH seeds, the generated calcite after carbonation provided nucleation effect, chemical effect and finer effect, and the silica gel had a high pozzolanic reaction degree, which significantly accelerated the hydration and led to a denser pore structure. Therefore, the CCSH seeds significantly accelerated the early hydration and increase the early compressive strength without an obvious decrease of the later compressive strength due to the coupling effect of calcite and silica gel.

Static and dynamic mechanical thermoanalyses of cement paste with highly dispersed graphene oxide

This study investigated the static mechanical properties of cement pastes with highly dispersed graphene oxide (GO), performed a dynamic mechanical thermoanalysis (DMTA), and studied the microstructure of cement pastes after exposure to high temperatures (105, 200, 300, 450, 600, and 750 °C). First, GO was uniformly dispersed in the cement paste with the aid of polycarboxylate-based superplasticizers. Generally, the incorporation of dispersed GO can enhance the residual compressive strengths of the cement pastes. For pastes with 0.04% GO (by weight) exposed to temperatures of 105, 200, 300, 450, 600, and 750 °C, the strengths are 14.84%, 4.83%, 13.35%, 15.71%, 11.91%, and 64.49% higher than that of pastes without GO, respectively. The DMTA results reveal that cement pastes with 0.04% GO have a high storage modulus and low loss factors in the temperature range of 25–350 °C, which improve their thermal resistance. Moreover, the addition of dispersed GO refines the pore structure and decreases the total porosity at high temperatures by suppressing the coarsening of the pore structure of cement pastes.

Effect of Ultrafine Calcium Silicate on the Mechanical Properties of Oil Well Cement-Based Composite at Low Temperature

A low-temperature environment will reduce the hydration rate of oil well cement-based composites, resulting in the slow development of mechanical strength, which cannot meet the requirements of cementing operations. In order to improve the early strength of cement paste under low temperature, the influence of ultrafine calcium silicate powder on the rheological properties, water loss, thickening time and permeability of oil well cement-based composites was evaluated. The compressive strength, flexural strength and impact strength of cement paste with different contents of ultrafine calcium silicate were studied. The hydration process and microstructure of cement paste were analyzed by hydration heat measurement system, X-ray diffraction (XRD) and scanning electron microscope (SEM). The experimental results show that the ultrafine calcium silicate has a certain impact on the rheology and thickening time of cement slurry, and dispersants and retarders are required to adjust these properties when it is used. The ultrafine calcium silicate can improve the stability of cement slurry and reduce water loss and permeability. In addition, under the condition of curing at 20 °C for 24 h, the compressive strength, flexural strength and impact strength of cement paste with 8% ultrafine calcium silicate content increased by 243.0%, 278.5% and 66.3%, respectively, compared with the pure cement paste. The hydration of cement slurry is accelerated by ultrafine calcium silicate, the hydration temperature is enhanced and the heat release of hydration is increased. The ultrafine calcium silicate improves the formation degree of hydration products and makes the structure of cement paste more compact. The research results help to design a low-temperature and early-strength cement slurry system.

Utilizing nano-SiO2 for modifying the microstructure, strength and transport properties of sustainable cementitious materials with waste concrete powder

Using waste concrete powder as an alternative binder in green cementitious materials contributes to reduce the number of construction and demolition waste, and developing an effective method to modify the performance of waste concrete powder blended cementitious materials is necessary. The influences of nano-SiO2 at 0–3% dosage on cementitious materials containing waste concrete powder as partial cement replacement (0–50%), under a ratio of 1:2 for both water-to-binder and binder-to-sand, were investigated in this study with the aspects of micro-structure and macro-performance. The results illustrated that mixing waste concrete powder negatively impacted the hydration reaction and micro-structure of cement paste; however, the mix of nano-SiO2 promoted the secondary hydration reaction and refined pore diameter of waste concrete powder mixed paste. Mixing nano-SiO2 raised the drying shrinkage but reduced the water loss of paste including waste concrete powder. The replacement of cement by waste concrete powder caused the reduction in compressive strength of paste. But at a fixed substitution level of waste concrete powder in paste, the compressive strength rose with the increment of nano-SiO2 content up to 3%. The transport properties rose as waste concrete powder was incorporated in mortar, but the mix of nano-SiO2 significantly reduced the transport properties of waste concrete powder incorporated mortar. Particularly, the effects of nano-SiO2 addition on the decrease in water absorption became more distinct as high content of waste concrete powder was blended. Optimizing the content of waste concrete powder and nano-SiO2 can obtain green cementitious materials owning good strength and low transport properties.

Microstructure and Electrical Conductivity of Cement Paste Reinforced with Different Types of Carbon Nanotubes.

Over the last few years, the addition of small amounts of carbon nanotubes (CNTs) to construction materials has become of great interest, since it enhances some of the mechanical, electrical and thermal properties of the cement. In this sense, single-walled and multi-walled carbon nanotubes (SWCNTs and MWCNTs, respectively) can be incorporated into cement to achieve the above-mentioned improved features. Thus, the current study presents the results of the addition of SWCNTs and MWCNTs on the microstructure and the physical properties of the cement paste. Density was measured through He pycnometry and the mass change was studied by thermogravimetric analysis (TGA). The microstructure and the phases were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Finally, the electrical conductivity for different CNT concentrations was measured, and an exponential increase of the conductivity with concentration was observed. This last result opens the possibility for these materials to be used in a high variety of fields, such as space intelligent systems with novel electrical and electronic applications.

Impacts of microwave on hydration evolution of Portland cement in the perspective of composition and microstructure of hydrates

Effects of microwave curing on the hydration evolution of Portland cement were analyzed, compared with normal curing and steam curing. Hydration products, microstructure of cement paste, and the underlying mechanism were investigated. Results showed that the hydration degree of Portland cement under microwave curing for 45-min radiation was higher than that under steam curing at 80 °C for 4 h and normal curing for 12 h. Steam curing promoted the hydration of C3S, and microwave curing accelerated the hydration of C2S. The main hydration products of C3A under normal, steam, and microwave curing, were AFt, katoite, and AFm, respectively. Microwave curing reduced the content of portlandite (CH), decreased the normal size of the face (001) of CH, and increased the preferred orientation of CH. In comparison with steam curing, microwave curing generated granular C–S–H gel with a high Ca/Si atom ratio in hydrated Portland cement.