Calcium Silicate Hydrate Research Articles

Investigation on Key Influencing Factors Affecting Temperature Distribution in Concrete

Concrete is an unavoidable composite material used in buildings and structures. The behavior of concrete under the effect of fire is always critical, causing more structural damage. This research proposes experimental investigation on various factors that affect temperature distribution in concrete when exposed to fire. Water cement ratio, grade of concrete, curing period, type of admixtures, and fibers are the factors taken into consideration. The test was carried out in the temperature range of 100 °C to 600 °C. The temperature was measured at various depths of the specimen and then compared. Results from experiments show that grade of concrete, water-cement ratio, curing period and admixture type significantly influences the temperature distribution in concrete whereas contribution of fiber type is negligible. Comparison of temperature distribution at 25 mm from the bottom of specimen at 600 °C for M20 grade with 0.5 and 0.4 water cement ratio was done. It is found that temperature distribution in concrete goes higher as water cement ratio goes higher. There is an increase of 22.6% of temperature distribution for 0.5 water cement ratio than 0.4. Concrete samples which were cured for 14 days, and 28 days were tested, temperature distribution in concrete cured for 14 days is higher than that cured for 28 days. It is because of the curing time of calcium silicate hydrate (CSH) gel, and it was not fully matured and there was no moisture to finish the hydration process of cement.

Mock-up pragmatic study on the impact performance of self-compacting concrete incorporating sea sand

Self-Compacting Concrete (SCC) allows for the use of non-desalted sea sand as a fine aggregate, but the durability of triple mix SCC with partial sea sand replacement remains unclear. To optimize binder and fine aggregate replacements, tests for consistency, setting times, soundness, compressive strength, and Ultrasonic Pulse Velocity were performed. Six SCC variations, incorporating 30%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\%$$\\end{document} Class F Fly Ash (FA), 5%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\%$$\\end{document} Ground Granulated Blast Furnace Slag (GGBS), and various fine aggregate combinations, were evaluated for their fresh, mechanical, microstructural, and durability properties. Results demonstrated that SCC with 50%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\%$$\\end{document} sea sand and 50%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\%$$\\end{document} manufactured sand achieved superior 90th\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{th}$$\\end{document} day compressive strength. This improvement was attributed to accelerated cement setting and enhanced FA reactivity, leading to better hydration products. Microstructural analysis revealed more hydration products and fewer pores in specimens with 50%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\%$$\\end{document} sea sand, due to the disconnected pore structure from Friedel’s salt formation. Chloride binding in concrete involves both chemical and physical mechanisms. Chemical binding is related to Friedel’s salt, while physical binding depends on Calcium-Silicate-Hydrate (C-S-H) content. Dense C-S-H formation from sea sand, confirmed by Scanning Electron Microscope (SEM) images, results in greater chloride binding. Additionally, aluminum oxide in FA and GGBS enhances chemical binding by forming Friedel’s salt.

Experimental study on the factors affecting cement bond strength at the second interface of oil-gas well

The second interface of cementing refers to the interface formed by the formation and the cement sheath after cementing. The bonding strength of the second cementing interface is mainly generated through the interaction between the cement sheath and the formation. This study employs sandstone and limestone as experimental materials to investigate the influencing factors on the bonding strength of the second cementing interface by altering the water-cement ratio of the cement slurry system, adding ultrafine materials, and incorporating latex materials. In a progressive experimental approach, various types of cement slurries are selected, including pure cement slurry systems under different water-cement ratios (L1, L2), cement slurry systems with added nano-silica on the basis of pure cement systems (L3), and cement slurry systems with latex added (L4). The influence factors of the bonding strength of the second cementing interface of cement sheaths are explored through self-developed bonding strength evaluation molds and micro-characterization of the bonding interface. The results indicate that increasing the water-cement ratio or adding nano-silica can promote the generation of calcium silicate hydrate (C-S-H), resulting in higher early bonding strength but lower later strength under sandstone interfaces; the reaction of latex particles themselves to form a three-dimensional network structure can enhance the bonding strength. This research provides significant insights into the bonding laws of the second cementing interface and is of great importance to the cementing construction process.

Low-cost flash graphene from carbon black to reinforce cementitious composites for carbon footprint reduction

With the merits of high quality, cost-effectiveness, and high yield efficiency, flash Joule heating (FJH) emerges as an efficient means for mass production of flash graphene (FG). It creates prerequisites for the large-scale application of graphene in reinforcing cementitious composites, thus opening innovative possibilities for curbing carbon emissions and fostering the sustainable evolution of cementitious composites. In this study, two types of FGs, including high-purity FG (FG-G) and conductive FG (FG-D), are successfully synthesized via FJH process using carbon black as the carbon source. FG-G features a low ID/IG of 0.52, and exhibits higher graphitization and structural orderliness with fewer defects compared to the FG-D. The addition of 0.25 wt% FG-D increases the compressive strength, flexural strength, and flexural ultimate strain of cementitious composites by 16.48 MPa/16.8%, 1.43 MPa/37.2%, and nearly 2600 με/550%, respectively. The microstructure characterization results reveal that FG reduces the matrix defects, enhances both the matrix microstructure and calcium silicate hydrate gel nanostructure, which is advantageous for matrix refinement, inhibition of microcrack aggregation and propagation, and load transfer efficiency. Its disorderly stacked turbine structure also contributes to robust interface bonding and friction with cement matrix, thus facilitating the strengthening and toughening of cementitious composites. This study introduces a potential avenue to develop widely applicable and versatile silicon-based cementitious composites with high performance and low CO2 emission by using small carbon-based graphene as reinforcement.

Utilization of incense stick ash as a supplementary cementitious material: Effects on strength, cement chemistry, and sustainability

Incense stick ash (ISA), a by-product generated from the combustion of biomass during religious rituals, presents challenges regarding its high-volume disposal despite some emerging technologies offering avenues for its reuse. This study aims to investigate the feasibility of utilizing ISA as a supplementary cementitious material and its impact on fresh and hardened properties, hydration kinetics, microstructure, and environmental and economic aspects of Portland cement (PC) pastes. Results reveal that incorporating 5–20 % ISA increases the cumulative heat release per gram of PC. Specifically, replacing 5 % of PC with ISA enhances the 28-day compressive strength, with an increase of 19.78 % compared to plain cement paste. However, further elevation in ISA substitution leads to a decline in compressive strength. The utilization of 5 % ISA refines the pore structure of samples and elevates the content of calcium silicate hydrate (C-S-H), particularly the proportion of high-density C-S-H. Additionally, carbonates present in ISA react with AFm to form monocarbon calcium aluminate, which stabilizes AFt and enhances the microstructural compactness of cement paste. Compared to plain cement paste, the paste with 5 % ISA exhibits lower coefficients for the cost of pastes per cubic meter, CO2 emission of pastes per cubic meter, and non-renewable energy consumption, underscoring the effective utilization of ISA and its role in promoting sustainability. This study will facilitate the application of ISA in cement-based materials and provide technical guidance for subsequent research.

Hydration process and fluoride solidification mechanism of multi-source solid waste-based phosphogypsum cemented paste backfill under CaO modification

The large-scale, environmentally friendly utilization of phosphogypsum (PG) remains a global challenge. PG cemented paste backfill (PCPB) is a promising method to manage PG, but using ordinary Portland cement as the binder has drawbacks such as high cost, low mechanical strength, and high fluoride leaching risk. This paper presents a multi-source solid waste-based PCPB (MPCPB) material that enhances mechanical properties and reduces fluoride leaching risks. In MPCPB, industrial waste residues like steel slag (SS) and ground granulated blast furnace slag (GBFS) are used as precursors (SS: GBFS = 1:2). Additionally, 4–8 wt% CaO (relative to the dry weight of PG) is used as a neutralizing modifier and alkaline activator. The results indicate that an optimal amount of CaO can neutralize the residual acidity of PG, provide sufficient Ca(OH)2 for MPCPB hydration, and react with PG to produce significant amounts of AFt. Furthermore, CaO promotes the geopolymerization reaction between SS and GBFS, generating more calcium silicate hydrate (C-S-H) and calcium aluminate silicate hydrate (C-A-S-H) gels. Fluoride stabilization in MPCPB results from synergistic effects involving hydration reactions, complexation, ionic mobility, rearrangement, and physical adsorption. Notably, CaO enhances the conversion of free fluoride ions into stable compounds like fluorapatite, fluorite (CaF2), [AlF6]3-, and [FeF6]3- complexes. This approach offers a cost-effective, environmentally friendly, and efficient solution to the PG stockpiling challenge.

Effect of Recycled Asphalt Mixture and Solid Waste-Based Solidification Materials on Performance of Cold-Regenerated Asphalt Mixture

In this study, an aging asphalt mixture was regenerated by a waste-based rejuvenator and cemented by solid waste-based solidification materials (SSMs). A splitting test, wheel tracking test, and three-point bending test were conducted to evaluate the properties of the regenerated asphalt mixture (RAM). The results reveal that the properties of the asphalt mixture were not diminished or were moderately enhanced by the 30% substitution of RAP. With the substitution of RAP to 100%, the splitting tensile strength, dynamic stability, and splitting strength ratio were decreased by 13%, 15%, and 5%, respectively. With the 100% substitution of SSMs for cement, the compressive strength, dynamic stability, flexural strain, and splitting strength ratios of the RAM were increased by 40%, 32%%, 14%, and 8%, respectively. The lightweight components can be supplemented, and low-temperature deformation and interlayer flowability can be improved by the incorporation of the rejuvenator. The generation of hydrated calcium silicate and ettringite for SSMs is greater than those of cement. The massive generation of ettringite has been observed to increase the solid phase volume by 120%, which may facilitate a more complete filling of the remaining pores in the RAM due to water evaporation. The regeneration and cement on green and the high performance of the rejuvenator and the SSM markedly enhanced RAM performance.

The impact of relative humidity on the nanoindentation relaxation in calcium silicate hydrates

Despite extensive research efforts, understanding the time-dependent behavior of concrete remains an enigma due to the complex nature of cement microstructure. In this study, the statistical nanoindentation was employed to investigate the influence of relative humidity (RH) on the relaxation behavior of calcium silicate hydrates (C-S-H) in a cement paste. Our experiments, performed at RH levels of 33 % and 86 %, revealed significant enhancements in both the indentation modulus and hardness of the C-S-H as RH increased. Remarkably, the internal water exerted a significant influence on the asymptotic relaxation behavior, displaying a clear power-law fashion. Further analysis identified the presence of short- and long-term viscoelastic behaviors within the C-S-H, distinguished by a transition observed within the initial seconds. These findings advance the understanding of nanoscale mechanisms driving concrete creep under different humidity conditions.

Study on the chloride ion binding rate of sulfoaluminate cement mortars containing different mineral admixtures

In this study, the chloride ion (Cl−) binding rate of sulfoaluminate cement (SAC) mortars containing different mineral admixtures was investigated. This is essential to improve the durability of concrete structures in high Cl− environments, especially where they are susceptible to Cl− attack such as coastlines and marine structures. The effects of Cl− concentration, curing age, and the type and amount of mineral admixture on the Cl− binding rate of SAC mortars were analyzed. It was found that the content of water-soluble Cl− in SAC mortars decreased with the increase of curing age, while the Cl− binding ratio increased accordingly, indicating that its resistance to internal Cl− permeation increased. The addition of fly ash (FA) and ground granulated blast furnace slag (GGBS) can significantly improve the Cl− binding rate of SAC mortars, and the Cl− binding rate increases to 46.6% with 20% of FA and 38.7% with 40% of GGBS. The effects of mineral admixtures on the microstructure and phase composition of SAC mortars were further investigated by X-ray diffraction (XRD) analysis. The results showed that the addition of FA and GGBS promoted the formation of C-S-H (calcium silicate hydrate) gels and improved the resistance of SAC mortars to Cl− penetration. On the other hand, the excessive addition of silica fume (SF) decreased the Cl− binding rate, whereas a moderate amount of limestone powder (LP) improved the Cl− binding rate. The study of the Cl− binding rate of SAC mortars can help to evaluate their resistance to Cl− erosion in real projects, thus guiding the optimization of concrete formulations and the improvement of durability.

[formula omitted] Affects the crystalline calcium silicate hydrate minerals synthesized by fly ash-based silicon extraction solution and lime milk

When extracting amorphous silicon from fly ash using a strong alkaline solution, other elements such as Al also enter the silicon extraction solution in the form of AlOH4−. To systematically investigate the impact of AlOH4− on the synthesis of typical calcium silicate hydrate crystals in a silicon extraction solution, a specific amount of AlOH4− was added to the silicon extraction solution, and calcium silicate was hydrothermally synthesized at 90℃ and 230℃. Scanning electron microscopy (SEM) and Brunner−Emmet−Teller (BET) analysis revealed that with the increasing in AlOH4− content, microporous calcium silicate gradually loses its microporous morphology. While the specific surface area shows no significant change, the median pore diameter first increases from 1.47 nm to 1.58 nm and then decreases to 1.55 nm. The xonotlite fibers underwent a gradual refinement, diminishing from 0.28 to 0.15 µm. Simultaneously, the specific surface area increases from 28.87 to 56.8 m2/g. At an AlOH4− concentration of 3 mol/L, the microscopic morphology transforms into a sheet-like structure. X-ray diffraction (XRD) analysis reveals that AlOH4− promotes the formation of tobermorite while inhibiting the further development of calcium silicate. Additionally, Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance indicate that Al can replace Si in the calcium silicate hydrate system, primarily substituting positions the Q2 and Q3 sites. Qualitatively, it is suggested that with the increasing incorporation of Al, the polymerization degree of the silicon-oxygen tetrahedra decreases. According to experimental results, the concentration of AlOH4− should be below 0.05 mol/L when synthesizing microporous calcium silicate hydrate and less than 0.2 mol/L when synthesizing fibrous xonotlite-type calcium silicate hydrate.

Synergistic Effects of Polypropylene Fibers and Silica Fume on Structural Lightweight Concrete: Analysis of Workability, Thermal Conductivity, and Strength Properties

Structural lightweight concrete (SLWC) is crucial for reducing building weight, reducing structural loads, and enhancing energy efficiency through lower thermal conductivity. This study explores the effects of incorporating silica fume (SF), micro-polypropylene (micro-PP), and macro-PP fibers on the workability, thermal properties, and strength of SLWC. SF was added to all mixtures, substituting 10% of the Portland cement (PC), except for the control mixture. Macro-PP fibers were introduced alone or in combination with micro-PP fibers at volumetric ratios of 0.3% and 0.6%. The study evaluated various parameters, including slump, Vebe time, density, water absorption (WA), ultrasonic pulse velocity (UPV), thermal conductivity coefficients (k), compressive strength (CS), and splitting tensile strength (STS) across six different SLWC formulations. The results indicate that while SF negatively impacted the workability of SLWC mortars, it improved CS and STS due to the formation of calcium silicate hydrate (C-S-H) gels from SF’s high pozzolanic activity. Additionally, using micro-PP fibers in combination with macro-PP fibers rather than solely macro-PP fibers enhanced the workability, CS, and STS of the SLWC samples. Although SF had a minor effect on reducing thermal conductivity, the use of macro-PP fibers alone was more effective for improving thermal properties by creating a more porous structure compared to the hybrid use of micro-PP fibers. Moreover, increasing the ratio of micro- and macro-PP fibers from 0.3% to 0.6% resulted in lower CS values but a significant increase in STS values.

Performance and mechanism of triethanolamine-triisopropanolamine corrosion inhibitor to deterioration of reinforced concrete under the coupling effect of freeze-thaw cycles and chloride attack

The purpose of this study is to propose an efficient and economical organic triethanolamine-triisopropanolamine corrosion inhibitor (OTTCI) to reduce the corrosion of steel in reinforced concrete. The influence of OTTCI on corrosion of steel in reinforced concrete under the coupling effect of freeze-thaw cycles and chloride attack (FTCs-CA) were characterized by electrochemical impedance spectroscopy (EIS), dynamic electrode potential (PDP), mechanical properties (mass loss rate (M), compressive strength (fn) and relative dynamic elastic modulus value (Pi)), capillary water absorption (CWA), bubble spacing coefficient (BSC) and scanning electron microscope (SEM). The inhibition mechanism of OTTCI was also analyzed and summarized. The results displayed that the dosage of OTTCI delayed the degradation of reinforced concrete under FTCs-CA. After 150 cycles, the M value of specimens with 1.0 % OTTCI reduced by 66.31 % compared to that of specimens without OTTCI, the Pi value increased by 51.9 %, and the polarization resistance and corrosion inhibition efficiency reached 2744.19 Ω cm2 and 92.88 %, respectively. In addition, OTTCI significantly reduced the CWA value and porosity. After 150 cycles, the CWA and porosity with 1.0 % OTTCI decreased by 60.1 % and 54.54 % respectively. The capillary water absorption coefficient increased linearly with the increase of FTCs-CA. SEM tests illustrated that OTTCI inhibited the development of internal cracks and macropores in concrete and promoted the formation of hydrated calcium silicate gels and calcite. The application of this study not only provides a new method to alleviate the deterioration of reinforced concrete, but also offers theoretical and technical support for further investigate on the deterioration characteristics of reinforced concrete in harsh environments.

Synthesis and characterization of calcium silicate hydrate from biomass fly ash

Synthesis and characterization of calcium silicate hydrate from biomass fly ash

Soil utilization of solid waste: Small-strain dynamic properties and microscopic mechanism of phosphogypsum-modified coastal cement soil

Phosphogypsum (PG), a solid waste from the wet process phosphoric acid industry, but the utilization rate is low at present. The effect of phosphogypsum and cement on small strain dynamic characteristics of coastal soft soil was studied by resonance column test, and characterize the micro-mechanisms of the specimens by SEM and EDS test. The results show that the dynamic shear modulu (G) and the damping ratio (D) firstly increase and then decrease with the PG level increasing. PG can motivate the formation of hydrated calcium silicate (C–S–H) gel and react with calcium aluminate to form calcium. The critical value for assessing the dynamic behavior of PCS under small strain is γ = 10−4. The Hardin-Drnevich model eigenmodel can well characterize the dynamics of the PCS. Based on this model, a modified dynamic model is established to describe the dynamic characteristics of PCS. The microscopic results showed that the addition of phosphogypsum promoted the production of hydration products and made the particles more closely arranged. The content of this study provides a new reference for the application of solid waste phosphogypsum in cement soil.

ENVIRONMENTAL ASPECTS OF WASTE-DERIVED BOTTOM BLEND CLAY LINERS INCORPORATING ZEOLITE AND BENTONITE

This research investigated the effects of incorporating bentonite and zeolite into bottom blended clay liners (BBCLs) on their engineering properties and adsorption capacity. BBCLs composed of clay, water treatment residue, and calcium carbide in a 40:40:20 ratio by volume were investigated with the addition of 1, 2, and 3 wt.% bentonite or zeolite. The experimental results indicated that bentonite and zeolite had positive effects on the slake durability index and the equilibrium time for the adsorption of lead (Pb) and chromium (Cr) from the leachate, whereas the unconfined compressive strength (UCS) and coefficient of permeability were negatively affected compared to those of the samples without bentonite and zeolite. At 56 days, the UCS of BBCLs with bentonite and zeolite decreased from 3.4 to 2.2MPa, while the coefficient of permeability of all the samples met the regulatory limit of sanitary landfills, which was given at 1×10-7cm/s. The slake durability index of all samples was lower 50% but it remained higher compared to BBCLs without bentonite and zeolite (approximately doubled). Both additives enhanced the equilibrium time and percentage of Pb and Cr adsorption by about 20% and 200%, respectively. SEM-EDS results show the adsorption of Pb and Cr onto the raw materials, calcium silicate hydrate (CSH), zeolite, and bentonite. Therefore, the addition of zeolite can increase the ability to adsorb heavy metals form leachate, which is suitable for use in secured landfills.

A closed-loop recycling of wastewater derived from aqueous carbonation of basic oxygen furnace slag in cement paste production

Aqueous carbonation (AC) treatment is a promising method for enhancing the cementitious activity of Ca- and Mg-rich solid wastes, such as basic oxygen furnace slag (BOFS), while also reducing carbon emissions. However, the carbonated filtrate (CF) solution generated during the AC process poses significant environmental challenges and limits its large-scale application. This paper, therefore, explores the feasibility of recycling CF in cement paste production as a strategy for managing AC wastewater. The study examines the impact of CF on the physico-mechanical properties, hydration behavior and microstructure of cement pastes (pure and blended with either 10% as-received or carbonated BOFS), compared to those prepared with tap water (TW) and carbonated water (CW). The results indicate that carbonated solutions (CF and CW) promote the hydration of aluminate phase in cement, with a more pronounced effect observed for CW. The solid suspensions in CF, particularly nesquehonite, restrict the growth space for calcium silicate hydrates (C-S-H) in the paste matrix, resulting in the formation of foil-like Type II C-S-H and lowering compressive strength. However, the additional nucleation sites provided by calcite crystals in carbonated BOFS (C-BOFS) accelerate cement hydration in CF-based pastes and mitigate strength loss by promoting the formation of more fibrillary C-S-H. Furthermore, the addition of a superplasticizer reduces interparticle forces in the C-BOFS-CF paste, further enhancing strength development and achieving a 28-day strength comparable to that of the control sample (OPC-TW paste).

Retardation of Chlorine-36 by Cementitious Materials Relevant to the Disposal of Radioactive Wastes

The activation product chlorine-36 (36Cl) is an important radionuclide within the context of the disposal of nuclear wastes, due to its long half-life and environmental mobility. Its behaviour in a range of potential cementitious encapsulants and backfill materials was studied by evaluating its uptake by pure cement hydration phases and hardened cement pastes (HCP). Limited uptake of chloride was observed on calcium silicate hydrates (C-S-H) by electrostatic sorption and by calcium monosulphoferroaluminate hydrate (AFm) phases, due to anion exchange/solid solution formation. Diffusion of 36Cl through cured monolithic HCP samples, representative of cementitious materials considered for use in deep geological repositories across Europe, revealed a markedly diverse migration behaviour. Two of the matrices, a ground granulated blast furnace slag/ordinary Portland cement blend (GGBS–OPC) and an ordinary Portland cement (CEM I) effectively retarded 36Cl migration, retaining the radionuclide in narrow, reactive zones. The migration behaviour of 36Cl within the cementitious matrices is not strictly correlated to the measured sorption distribution ratios (Rd-values), suggesting that physical factors related to the microstructure can also have a distinct effect on diffusion behaviour. The findings have implications when selecting cementitious grouts and/or backfill materials for 36Cl-bearing radioactive wastes.

Effect of metakaolin and lime addition on geopolymerization of construction and demolition waste.

Construction and demolition waste generates the largest amount of waste by volume, which threatens sustainable development and adversely affects the environment. These wastes contain a significant amount of aluminosilicates that have the potential to be used as building materials for value-added applications applicable to alternative construction materials. This study aims to synthesize geopolymers from brick powder using metakaolin/lime as additives and compare their physico-mechanical properties. The compressive strengths of the geopolymer products GP-1, GP-2, and GP-3 developed at 28days from brick powder and metakaolin/lime with the activator solution were found to be 8.35, 21.30, and 25.0MPa respectively, 2.55 and 2.99 times higher when metakaolin and lime were added. FTIR spectra and SEM-EDX micrographs of the reaction products showed structural changes and formation of aluminosilicate hydrate and calcium silicate hydrate gel with Al2O3/Na2O ratios of 0.75, 1.67, and 1.98 respectively. The reaction products containing SiO2/(SiO2 + Al2O3 + Fe2O3) ratios of 0.70 and 0.76 were found to be desirable. The geopolymer product GP-3 was found to have a higher bulk density and mechanical strength than those of GP-1 and GP-2. These products are found to be very hard, with potential applications in construction industries to conserve the environment.

Enhancing anti-carbonation properties of oil well cement slurry through nanoparticle and cellulose fiber synergy

The anti-carbonation property of oil well cement (OWC) is critical for sealing efficiency of wellbores under geological CO2 sequestration. However, gas migration through OWC around wellbores may lead to a deterioration and failure of the entire storage system. Developing carbon-resistant cement has been the emerging trend in the research community. Previous studies mainly focused on nanoparticles alone to enhance performance of OWC, and the purpose of the research is to explore the synergy of nanoparticles and cellulose fiber (CF) in enhancing engineering properties (e.g., carbonation resistance) of oil well cement slurry. The focus was on investigating compressive strength, permeability, pore structure, and carbonation depth associated with the micro-level texture in a CO2 corrosion environment using X-ray diffraction, Scanning Electron Microscopy, and thermogravimetric analysis methods. Four nanoparticles, namely, nano-SiO2 (NS), nano-TiO2 (NT), nano-Al2O3 (NA), and nano-CaCO3 (NC), were selected for the mixture design. Results indicated that the incorporation of 1∼2 % NPs into the OWC paste resulted in a notable decrease in portlandite and an increase in calcium silicate hydrates, thereby enhancing compressive strength and hydration process. In addition, the single admixture of CF could minimize the formation of cracks in the cement matrix and reduce the average carbonation depth by 54 %. More importantly, the synergy of CF and NP significantly improved the resistance of OWC to carbonation, and the OWC mixed with CF and NS displayed the highest carbonation resistance.

Unveiling the dissolution mechanism of calcium ions from CSH substrates in Na2SO4 solution: Effects of Ca/Si ratio

The decalcification behavior of calcium silicate hydrate (CSH) under sulfate attack poses a critical challenge to the long-term durability of cement-based infrastructure, yet understanding its underlying microscopic mechanisms remains elusive. This study employs molecular dynamics to compare the differences in calcium ion dissolution capability of CSH substrates with varying Ca/Si ratios under sulfate solution exposure. The results show that the dissolution amount and dissolution efficiency of Ca are positively correlated with Ca/Si, and the root cause depends on the basic structure of CSH. With the increase of Ca/Si, the electronegativity of CSH decreases, and the adsorption capacity and stability of cations weaken. Meanwhile, Ca ions are less limited by the silicate chain coordination, water molecules are more likely to invade the substrate interior and replace the Ca ions. This research aims to provide a molecular basis for cement production and durability applications in marine engineering.