Properties Of Portland Cement Paste Research Articles

Algal Biochar-Metal Nanocomposite Particles Tailor the Hydration Kinetics and Compressive Strength of Portland Cement Paste.

Biochar can improve the mechanical properties of portland cement paste and concrete. In this work, we produced algal biochar-zinc (biochar-Zn) and algal biochar-calcium (biochar-Ca) nanocomposite particles and studied their effect on the hydration kinetics and compressive strength of cement paste. Results show that 3 wt % biochar-Zn delayed peak heat evolution during cement hydration from 8.3 to 10.0 h, while 3 wt % addition of biochar-Ca induced a minor acceleration of peak heat from 8.3 to 8.2 h. Both biochar-Zn and biochar-Ca nanocomposite particles increased the compressive strength of cement paste at 28 days by 22.6 and 17.0%, respectively. Data substantiate that retardation or minor acceleration of the reaction kinetics was due exclusively to the presence of Zn and Ca phases, respectively, while the enhanced strength was attributed to a nucleation effect induced by such phases and the internal curing effect of biochar.

Effect of Poly(ethylene glycol)–Poly(propylene glycol) Triblock Copolymers on Autogenous Shrinkage and Properties of Cement Pastes

This study investigates the hydration, microstructure, autogenous shrinkage, electrical resistivity, and mechanical properties of Portland cement pastes modified with PEG-PPG triblock copolymers with varied molecular weights. The early age properties including setting time and hydration heat were examined using the Vicat test and isothermal calorimetry. The hydration products and pore size distribution were analyzed using thermogravimetric analysis (TGA) and nitrogen adsorption, respectively. Mechanical properties and electrical resistivity were evaluated using the compressive strength test and electrochemical impedance spectroscopy (EIS). It was shown that the addition of the copolymers reduced the surface tension of the cement paste pore solution due to the presence of a hydrophobic block (PPG) in the molecular structure of the copolymers. The setting time and hydration heat were relatively similar in the control paste as well as the pastes modified with the copolymers. The results showed that copolymers were able to reduce the autogenous shrinkage in the paste due primarily to a reduction in pore solution surface tension. TGA showed a slight increase in the hydration degree of the paste modified with the copolymers. The compressive strength was reduced in the pastes modified with the copolymers that showed an increased volume of air voids. The addition of copolymers did not affect the electrical resistivity of the pastes except in the case where there was a large volume of air voids, which acted as electrical insulators.

Experimental investigation on the influence of cenosphere on mechanical and rheological properties of Portland cement pastes

Experimental investigation on the influence of cenosphere on mechanical and rheological properties of Portland cement pastes

Synthesis of Aragonite Whiskers by Co-Carbonation of Waste Magnesia Slag and Magnesium Sulfate: Enhancing Microstructure and Mechanical Properties of Portland Cement Paste

This study focused on the synthesis of aragonite whiskers through a synergistic wet carbonation technology utilizing waste magnesia slag (MS) and magnesium sulfate (MgSO4), aiming to improve the microstructure and mechanical properties of ordinary Portland cement (OPC) paste. The influence of MgSO4 concentration on the wet carbonation process, phase composition, and microstructure of MS was investigated. Furthermore, the effect of incorporating carbonated MS (C-MS) on the mechanical properties and microstructure of Portland cement paste was evaluated. Results showed that appropriate MgSO4 concentrations favored aragonite whisker formation. A concentration of 0.075 M MgSO4 yielded 86.6% aragonite with high aspect ratio nanofibers. Incorporating 5% of this C-MS into OPC increased the seven-day compressive strength by 37.5% compared to the control OPC paste. The improvement was attributed to accelerated hydration and reduced porosity by the filling effect and microfiber reinforcement of aragonite whiskers. MS demonstrated good CO2 sequestration capacity during carbonation. This study provides an effective method to synthesize aragonite whiskers from waste MS and use it to enhance cementitious materials while reducing CO2 emissions, which is valuable for the development of a sustainable cement industry.

Influence of gravity on the micromechanical properties of portland cement and lunar regolith simulant composites

Concrete materials utilizing in-situ planetary resources are a promising option for construction on the Moon and Mars but the influence of variables, such as reduced gravity, needs to be understood. In this paper, we investigate the influence of gravity on the micromechanical properties of portland cement pastes that contain the lunar regolith simulant JSC-1A. Samples were prepared by astronauts onboard the International Space Station (ISS) and hydrated in microgravity (μg), lunar gravity (0.17 g), Martian gravity (0.38 g), and a statistical point at 0.7 g. Results were compared to a control sample hydrated on Earth (1.0 g). Specimens were analyzed by statistical nanoindentation and results for the paste suggest that gravity does not influence the in-situ mechanical properties of the hydrated phases. Results for the simulant give insight into the potential performance of lunar regolith as a component in a composite material. These results are critical to the continued development of lunar concrete technology.

Experimental and numerical study on the mitigation of autogenous shrinkage of cementitious material

This study experimentally investigated the effects of surfactants and water-repelling agents on the hydration process, relative humidity, and mechanical properties of Portland cement pastes. Based on the measurement results, the degree of hydration, degree of saturation, capillary tension of autogenous shrinkage, and magnitude of autogenous shrinkage were simulated using a numerical model. In the numerical model, the elastic and creep components of autogenous shrinkage were calculated separately, and the creep component was simulated based on the solidification theory. The simulation results indicated that adding admixtures led to lower degrees of hydration and saturation. The capillary tension of the pure Portland cement was larger than that of the other mixtures. This can be attributed to several factors, including the smaller surface tension of mixtures with surfactants, larger contact angle of mixtures with water-repelling agents, and a lower degree of hydration of mixtures with both admixtures. Analyses of the simulated and measured results for different mixtures also show that creep plays an indispensable role in autogenous shrinkage. Adding a surfactant and a water-repelling agent can effectively mitigate autogenous shrinkage. However, when an excessive amount of water-repelling agent was added, its influence on the mitigation of autogenous shrinkage was insignificant.

Development of a Novel Double-Sulfate Composite Early Strength Agent to Improve the Hydration Hardening Properties of Portland Cement Paste

A novel double-sulfate composite early strength agent (DSA) incorporating aluminum sulfate and sodium sulfate was developed to improve the early strength of Portland cement paste. The effect of the DSA dosage on the setting and hardening properties, hydration process, hydration product composition, microstructure, and pore structure of the Portland cement paste was investigated to reveal its synergistic enhancement mechanism. The results show that the 3 d and 28 d compressive strengths of the Portland cement paste incorporating with 1.0% aluminum sulfate and 1.5% sodium sulfate performed the best, with a 21.3% and 29.7% increase, respectively, compared to the control group. The heat of hydration, XRD, TG, SEM, and MIP tests showed that aluminum sulfate and sodium sulfate acted synergistically, with more AFt (Ettringite) being produced by the synergistic use of 1.0% aluminum sulfate and 1.5% sodium sulfate. Moreover, the hydration of C3S and C2S was accelerated, which resulted in a denser microstructure.

Influence of calcined medium grade clay on the properties of Portland cement pastes

ABSTRACT In the recent decades, the composition of Portland cements has undergone significant changes related to an increase in the range and content of supplementary cementitious materials following development of composite and multicomposite cements. The development of these binders that meet the requirements of sustainability requires the expansion and adaptation of the mineral resource base of cement industry to the production of low-emission binders with a gradual decrease of resource and energy intensities. Efforts to find the widespread sources of pozzolans providing high reactivity and physical–chemical stability have led to intensive studies on thermally treated clays of various chemical–mineralogical composition and their industrial adoption. Due to scarcity and high cost of kaolin clays, great attention is given to medium- and low-grade clays. This article reports on a study to evaluate the effect of calcined clay with 52% of clay minerals on the properties of fresh and hardened pastes, in particular on the resistance to sodium sulfate and nitric acid attacks. The reaction products assemblage of the blended Portland cement pastes was investigated by XRD and thermal analyses. The hardened Portland cement pastes incorporated with thermally treated clay demonstrated better durability performance compared to reference ones.

Blending eco-efficient calcium sulfoaluminate belite ferrite cement to enhance the physico–mechanical properties of Portland cement paste cured in refrigerated and natural winter conditions

The acceleration impacts of calcium sulfoaluminate belite ferrite (CSABF)—a cement produced from industrial side streams—on the hydration and strength development of Portland cement (PC) paste cured at −5 °C with and without pre-curing at room temperature were investigated. The impacts of eco-friendly CSABF cement content and pre-curing on the setting time and hardened properties of pastes were investigated. Freezing point of the paste and the amount of freezable water (FW) decreased with CSABF cement content and pre-curing. Hydration rate increased with CSABF cement content. By adding an optimal CSABF cement content, the compressive strength of paste cured at −5 °C increased by 500%. The effects of pre-curing on the compressive strength of the subzero-cured pastes were highly dependent on CSABF cement content and curing period. After 6 months, the outdoor-cured 70%PC/30%CSABF paste gained compressive strength comparable to that in the 90-day-old pair cured at −5 °C and continuous strength gain was detected up to one-year. The microstructural observations and porosity results are consistent with compressive strength measurements.

Investigation of hydration and setting process in nanosilica-cement blended pastes: In situ characterization using low field nuclear magnetic resonance

In order to characterize the effect of nano-SiO2 addition on early properties of Portland cement paste, low-field nuclear magnetic resonance (NMR) was used to monitor the hydration process and microstructure evolution. The relaxation signals of low-field NMR can provide the information about the water molecules status and corresponding content, thus indirectly revealing the microstructure evolution of cement paste. Based on the relaxation signals, new applications of low-field NMR in predicting the strength and setting time of cement were developed. The results indicate that the increasing nano-SiO2 addition as well as decreasing water-to-cement ratio can accelerate the early hydration process of cement and densify its microstructure, thus shortening the setting time and enhancing the early compressive strength. The effectiveness of low-field NMR in predicting the strength and setting time of cement was confirmed by the results of compression test and Vicat needle test, respectively. Due to the non-destructive and non-invasive characteristics of low-field nuclear magnetic resonance technology, this method shows special advantages in characterizing the influence of nano-silica on the early performance of cement paste.

Synergistic use of sodium bicarbonate and aluminum sulfate to enhance the hydration and hardening properties of Portland cement paste

A novel composite admixture (N-A admixture) including sodium bicarbonate (NaHCO3) and aluminum sulfate (Al2(SO4)3) was developed for the in situ generations of calcium carbonate (CaCO3) nano-reinforced particles in Portland cement paste. The effect of N-A admixture dosage (0%, 1%, 2%, 3%, 4%, 5%) on the hydration and hardening properties of Portland cement paste such as setting time and compressive strength was systematically investigated. The enhancement mechanism of the N-A admixture was also revealed by using XRD, TGA, SEM, MIP, and ICC. The results indicated that the N-A admixture can effectively accelerate the hydration reaction process of Portland cement paste and shorten its setting time. When the N-A admixture was added at 3%, the compressive strength at 1 day was 86.9% higher than that of the control Portland cement paste, and there was no inversion of strength at 90 days. N-A admixture promoted the formation of more hydration products. At the early stage of hydration, in situ CaCO3 with a grain size ranging from 25.53 to 42.98 nm was generated, the amount of which increased with the addition of N-A admixture. Moreover, the in situ CaCO3 also reacted with the aluminum phase to form mono-carbonate (Mc) in the late stage, which effectively reduced the proportion of large pores, resulting in a dense microstructure of the hardened Portland cement paste. The results of this work provide a novel and facile method for the generation of in situ CaCO3, which can be used to greatly improve the performance of cement concrete.

Multiwall carbon nanotubes (MWCNTs) dispersion & mechanical effects in OPC mortar & paste: A review

The incorporation of multiwalled Carbon nanotubes (MWCNTs) and their dispersion procedures such as the use of surfactant agents, functionalization, and ultrasonication have been intensively implemented to improve the mechanical and durability properties of ordinary Portland cement (OPC) mortar and paste. Many studies stated significant enhancements in the mechanical properties of OPC mortar or paste; however, others showed impairments. The review observed the preparation techniques for dispersion and mixing MWCNTs with dry materials such as cement and sand. The recent studies regarding the implementation of MWCNTs on the mechanical properties of OPC paste and mortar were reviewed. These properties include compressive, tensile, flexural strengths, and elastic modulus. A statistical approach was conducted to observe the effects of the MWCNTs' amendment on the mechanical properties of Portland cement paste and mortar. The results showed that there is no consistent preparation technique for the dispersion of MWCNT. The ultrasonication, used in most studies either alone or as a surfactant combination, was the most effective technique for dispersion when the sonication duration was between 20 and 45 min. The statistical mechanical property observations revealed that the majority of compressive strength enhancements were below 40% (approximately 91% of the data) regardless of the MWCNTs %. The improvement in strength below 40% was 74% of the data for tensile/flexural strength of mortar. For cement paste, 50% of the enhancements were equal to or below a 40% increase. However, some studies showed impairments in the mechanical properties of OPC composites when MWCNTs were incorporated. Most reduction in compressive strength was below 40% compared to mortar and cement with 0% MWCNTs.

Evaluation of the effects of bismuth oxide (Bi2O3) micro and nanoparticles on the mechanical, microstructural and γ-ray/neutron shielding properties of Portland cement pastes

This study presents a comparison of the effects of micro-Bi2O3 and nano-Bi2O3 powders on the mechanical, microstructural and gamma / neutron shielding properties of Portland cement pastes. Cement pastes with various ratios of cement (up to 30 wt-%) replaced with Bi2O3 micro and nanoparticles were prepared. Consistency, compressive strength, water accessible porosity and mercury intrusion porosimetry tests were performed, in order to characterize their engineering properties. In addition, experimental and theoretical evaluations of γ-ray and neutron shielding properties were performed. The results showed that the incorporation of Bi2O3 powders gradually leads to a decline in cement pastes’ compressive strength and an increase in their porosity, as the amount of powder is increased. However, the deterioration rate varies depending of type of powder used, in favor of nano-Bi2O3. Gamma attenuation tests results indicate that the addition of Bi2O3 powders enhances the shielding capability of pastes, in the energy range of interest (0.08–2.614 MeV). However, the effects of particle size on γ-ray attenuation are negligible in that energy range. Slow neutron attenuation study showed that the addition of nano-Bi2O3 improved the shielding ability of cement pastes, with enhancements ranging between 15.3% and 25.5% for samples with 5 and 30 wt-% nano-Bi2O3, respectively. In conclusion, this study shows that the addition of nano or micro-Bi2O3 is effective in producing lead-free cementitious composites with improved γ-ray and neutron shielding properties. Unlike gamma shielding, nano-sized Bi2O3 has a better ability to attenuate neutrons, in comparison to their micro-sized counterparts.

Effect of Li2CO3 on the properties of Portland cement paste

In order to increase the application of CO2 in cementitious materials and to develop new additives for cement-based materials, the effect of lithium carbonate (Li2CO3) on the properties of Portland cement (PC) paste was investigated. The hydration heat of fresh paste was tested and the hydration products were characterized using XRD, TG–DTA, SEM and MIP. The results showed that both the initial and final setting time of the PC paste was prolonged with increasing Li2CO3 content. While, the compressive strength of the hardened PC paste at 1 day, 7 days and 28 days increased initially and then decreased. When the content of Li2CO3 was 0.09wt%, the initial and final setting time was increased by 19.8% and 27.7%, and the compressive strength at the age of 1 day, 7 days and 28 days was increased by 47.6%, 21.2% and 14.0%, respectively. Hydration heat, TG–DTA, XRD, SEM, pore structure and other tests showed that Li2CO3 promoted the formation of AFt, and prolonged the arrival time of hydrated calcium silicate peak, but increased the formation of hydrated calcium silicate. Especially when the Li2CO3 content was below 0.09wt%, the pore structure was also optimized. Based on the above results, when the content of Li2CO3 is not greater than 0.09wt%, not only the setting of the Portland cement paste can be retarded, but also the early strength can be enhanced. This can provide a good reference for the use of Li2CO3 in the preparation of new Portland cement-based material admixtures.

Synergistic effect of EVA, TEA and C-S-Hs-PCE on the hydration process and mechanical properties of Portland cement paste at early age

This work investigates the synergistic utilization of EVA, TEA and C-S-Hs-PCE as admixtures in Portland cement. The alteration of hydration process is measured by isothermal calorimetry (ICC) and the effects of admixtures on mechanical properties are evaluated by the development of strengths and apparent density. The mechanism of admixtures acting in cement is revealed via XRD, FT-IR and TGA techniques. Results show that the fluidity of fresh cement paste is significantly improved with the addition of EVA, TEA and C-S-Hs-PCE, and consequently to the increasing in workability. The admixtures accelerate the hydration process and increase the cumulative heat release, deepening the hydration degree of cement paste. Both the improvement of fluidity and promotion of hydration are the important reasons for the enhancement of mechanical properties. Results of XRD, FT-IR and TGA indicate that the CH contents increase evidently with the content of admixtures, which further proves that the deepening of hydration process. This study could provide an experimental reference, which is of great significance to the valuable application of admixtures in cement based materials.

Effect of SiO2 coated leuco-dye based thermochromic pigment on the properties of Portland cement pastes

This study investigates the influence of silica-coated leuco dye-based thermochromic pigment (STC) on the properties of white Portland cement pastes. The surficial-SiO2 coating around thermochromic pigment was generated using the Stober method, followed by assessing the properties of cement pastes prepared using coated thermochromic pigment. The properties such as standard consistency, setting time, temperature change due to hydration reaction, compressive strength, and color stability of cement pastes were assessed. Besides, analytical characterizations such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM), and Energy dispersive X-ray (EDX) analyses were also performed to evaluate the degree of hydration in cement pastes. Analytical characterizations indicate that STC pigment promotes the degree of hydration of cement pastes and accelerates the setting process, which in turn leads to higher compressive strength. SEM analysis revealed the presence of well-intact STC pigment microcapsules, indicating the protective effect of SiO2 coating against a harsh cementitious environment. The colorimetric study results indicate that STC pigment retains its thermochromic response; it can withstand the alkaline cementitious environment, thereby protecting the leuco-dye mixtures from unwanted reactions when exposed to water and high temperature.

The effects of graphene oxide-silica nanohybrids on the workability, hydration, and mechanical properties of Portland cement paste

Although graphene-based materials have attracted much attention as nanoreinforcements for cementitious materials, their effectiveness is significantly dependent on their dispersibility in cement matrix. In particular, graphene hybridization (e.g. with silica) has shown considerable potential to meet this challenge within the broader family of graphene-based materials. In this study, we investigated the effects of silica coated graphene oxide (GOS) nanohybrids on the workability and the mechanical and microstructure properties of Portland cement paste composites. GOS with three different thicknesses of silica coating (5, 10 and 30 nm) were designed via a sol-gel method and characterized using microscopic techniques. We found that the increase in thickness of silica coating resulted in reduced workability of cement paste and a corresponding increase in cement mechanical properties with nanohybrid addition. With the incorporation of GOS, the compressive strength of cement paste was increased by 3.2–34.6% at 7 days and by 7–12.4% at 28 days, proportional to the increasing coating thicknesses. X-ray diffraction and mercury intrusion porosimetry indicated that the reaction of portlandite with the silica coating of the GOS nanohybrids led to pore refinement of the cement matrix, with more pronounced effects in samples with thicker coatings. These results demonstrate that rational design of graphene oxide nanohybrids presents an effective method to obtain stronger and more durable Portland cement composites.

Effect of Magnesium Carbonate on Hydration and Hardened Properties of Portland Cement Paste

The effects of magnesium carbonate on the setting time and compressive strength of Portland cement paste were studied when the content of magnesium carbonate was 0wt%, 0.5wt%, 1wt%, 2wt%, and 3wt% by the weight of cement. The influence mechanism was analyzed through combining with the tests of hydration heat, X-ray diffraction (XRD), differential thermal analysis-thermogravimetric analysis (DTA-TG), and scanning electron microscope (SEM). The results show that magnesium carbonate makes the setting time of cement paste shorten, and makes the compressive strengths of cement paste increase at 1 day and 7 days, but decrease at 28 days. The testing results of the heat of hydration, XRD, SEM, and DTA-TG show that magnesium carbonate promotes the formation of Ettringite (AFt) and the hydration of calcium silicate in the early stage when its content is less than 1wt%, but the addition of magnesium carbonate is unfavorable to the later hydration of Portland cement. Based on the above analysis, it is suggested that the content of magnesium carbonate is not more than 1wt%, which has good reference value for using magnesium carbonate to prepare early strength agent for cement paste.

Time-Stability Dispersion of MWCNTs for the Improvement of Mechanical Properties of Portland Cement Specimens.

This study shows the energy optimization and stabilization in the time of solutions composed of H2O + TX-100 + Multi-Wall Carbon Nanotubes (MWCNTs), used to improve the mechanical properties of Portland cement pastes. For developing this research, sonication energies at 90, 190, 290, 340, 390, 440, 490 and 590 J/g are applied to a colloidal substance (MWCNTs/TX-100 + H2O) with a molarity of 10 mM. Raman spectroscopy analyses showed that, for energies greater than 440 J/g, there are ruptures and fragmentation of the MWCNTs; meanwhile at energies below 390 J/g, better dispersions are obtained. The stability of the dispersion over time was evaluated over 13 weeks using UV-vis spectroscopy and Zeta Potential. With the most relevant data collected, sonication energies of 190, 390 and 490 J/g, at 10 mM were selected at the first and the fourth week of storage to obtain Portland cement specimens. Finally, we found an improvement of the mechanical properties of the samples built with Portland cement and solutions stored for one and four weeks; it can be concluded that the MWCNTs improved the hydration period.

Effect of heat-treated polymineral clays on the properties of portland cement paste

Owing to Portland cement production, an enormous amount of carbon dioxide, which pollutes the environment is released into the atmosphere. It is possible to reduce the amount of emitted carbon dioxide by partially replacing the main component of cement – clinker - with heat-treated clays. During heat treatment of clays, amorphous oxides of silicon and aluminum are formed, which interact with hydrated new growths of cement stone and lead to compaction and hardening of the entire system.The study of composition and structure of polymineral clays makes it possible to choose the optimum parameters of heat treatment at which calcinates are characterized by the highest pozzolanic activity.The effect of heat-treated polymer clays on the properties of Portland cement is investigated. It is established that heat-treated polymineral clays, as well as metakaolin, can act as an alternative replacement for Portland cement clinker. Introduction of heat-treated aluminosilicates in an amount of up to 15% increases strength characteristics (1.5–2 times), the coefficient of water resistance (by 10%) and reduces porosity (by 20%), compared with plain Portland cement.