Development of a kinetic-thermodynamic model for lime-stabilization of Na-bentonite

With the development of nanotechnology, reduced graphene oxide (rGO) has been used to improve the flexural strength of geopolymers. However, the reinforcing mechanism of rGO nanosheets on the flexural strength of geopolymers remains unclear. Here, this reinforcing mechanism was investigated from the perspectives of hydration and chemical composition. The effect of the reduction degree on rGO-reinforced geopolymers was also studied using isothermal calorimetry (IC), X-ray diffraction (XRD), and nuclear magnetic resonance (NMR) tests. Results show that the hydration degree and flexural strength of geopolymers effectively increase due to rGO addition. After alkali reduction at a temperature of 60 °C, rGO nanosheets have maximum reinforcement on the flexural strength of geopolymers with an increment of 51.2%. It is attributed to the promotion of slag hydration, as well as the simultaneous formation of calcium silicate hydrate with low Ca/Si ratio (C-S-H(I)) and calcium aluminosilicate hydrate (C-A-S-H) phases due to the inhibiting effect of rGO nanosheets on Al substitution on the end-of-chain silicates of C-S-H and C-A-S-H gels. In addition, different reduction degrees have almost no effect on the chemical composition of rGO-reinforced geopolymers, while excessive reduction impairs the improving effect of rGO nanosheets on the hydration process and flexural strength of geopolymers due to significant structural defects.

The kinetic of calcium silicate hydrate formation from silica and calcium hydroxide nanoparticles

Strength development of Recycled Asphalt Pavement – Fly ash geopolymer as a road construction material

Calcium silicate hydrate (CSH) formation is a fundamental process required to enhance the density, strength, and durability of cementitious materials. However, there is a gap in the research on the structural, physical, and chemical transformations of CSH. The objectives of this study are to develop a predictive model of CSH formation in cementitious materials and evaluate the effects of gelatin powder (GP), silica fume (MS), ground coffee (SCG), and peanut shell (PS) on CSH formation. Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS) apply to the study of the composite cementitious materials. A multiple linear regression model is proposed to predict the changes of key elements, which improved the qualitative and quantitative understanding of the hydration mechanisms. The results show that GP significantly accelerates CSH formation by increasing the calcium and oxygen contents, while MS enhances pozzolanic activity by increasing the availability of silicon, resulting in structural densification. SCG contributes to the increase of carbon and oxygen by acting as a filler, while PS has minimal effect on hydration or crystallization. A regression model relating cement mix design proportions and CSH shows strong correlations between admixtures and chemical changes, particularly for calcium (R²=0.988) and silica (R²=0.985). To fill the existing research gaps, this study goes beyond previous studies, which primarily focused on individual aspects of CSH formation without considering the convergence of structural and chemical analysis.

The influence of aluminosilicate pozzolanic waste, specifically spent fluid catalytic cracking waste (FCCW) and metakaolin waste (MK) from the expanded glass industry, on the properties of hardened Portland cement paste were analysed. The study involved replacing part of cement with FCCW and MK and observing their impact on the hydration, microstructure, density, and compressive strength of hardened cement paste. Various analysis methods were employed, including X-ray diffraction (XRD), thermogravimetric analysis (TG), and scanning electron microscopy (SEM), to understand the changes in the structure of the hardened cement paste during hydration. The findings revealed that FCCW tends to accelerate the cement hydration process due to its high surface area and pozzolanic activity. Notably, the formation of portlandite crystals was observed on FCCW particle surfaces in a specific direction. These crystals appeared smaller and developed in different directions in compositions containing a composite binder with mixture of FCCW and MK in a ratio 1:1. This could be influenced by pozzolanic reactions activated by fine particles of MK and the formation of calcium silicate hydrates (C-S-H) and calcium alumino silicate hydrates (C-A-S-H) in the presence of portlandite. The XRD and TG results indicated that the specimens containing a composite binder exhibited the least amount of portlandite. The compressive strength of these specimens increased compared to the control specimens, although the amount of cement was 9% lower.

The transportation infrastructure, including low-volume roads in some regions, needs to be constructed on weak ground, implying the necessity of soil stabilization. Untreated and cement-treated lateritic soil for low-volume road suitability were studied based on Malaysian standards. A series of unconfined compressive strength (UCS) tests was performed for four cement doses (3%, 6%, 9%, 12%) for different curing times. According to Malaysian standards, the study suggested 6% cement and 7 days curing time as the optimum cement dosage and curing time, respectively, based on their 0.8 MPa UCS values. The durability test indicated that the specimens treated with 3% cement collapsed directly upon soaking in water. Although the UCS of 6% cement-treated specimens decreased against wetting–drying (WD) cycles, the minimum threshold based on Malaysian standards was still maintained against 15 WD cycles. On the contrary, the durability of specimens treated with 9% and 12% cement represented a UCS increase against WD cycles. FESEM results indicated the formation of calcium aluminate hydrate (CAH), calcium silicate hydrate (CSH), and calcium aluminosilicate hydrate (CASH) as well as shrinking of pore size when untreated soil was mixed with cement. The formation of gels (CAH, CSH, CASH) and decreasing pore size could be clarified by EDX results in which the increase in cement content increased calcium.

Microstructure of cement paste with natural pozzolanic volcanic ash and Portland cement at different stages of curing

Strength properties and microstructural characteristics of clay treated with alkali activated mortar and fiber

Single and dual effects of magnesia and alumina nano-particles on strength and drying shrinkage of alkali activated slag

The thermodynamic stability of sulfate ions on synthesized calcium aluminosilicate hydrate (C-A-S-H) microstructure with different Ca/Si ratios and Al/Si ratios was investigated by XRD, SEM-EDS, 29Si and 27Al nuclear magnetic resonance (NMR) and thermodynamic modeling. The results indicate that sulfate attack leads to both decalcification and dealumination for C-A-S-H gels, and the amount of corrosion products (gypsum and ettringite) decreased gradually with decreasing Ca/Si ratios of C-A-S-H. Sulfate ions can also promote the polymerization degree of C-A-S-H gels, improving its resistance to sulfate attack. Moreover, the 4-coordination aluminum (Al[4]) in C-A-S-H, 5-coordination aluminum (Al[5]), 6-ccordination aluminum (Al[6]) in TAH (third aluminum hydrate) and Al[6] in monosulfate or C-A-H (calcium aluminate hydrate) can be transformed into Al[6] in ettringite by sulfate attack. Furthermore, through thermodynamic calculation, the decrease of Ca/Si ratios and increase of Al/Si ratios can improve the thermodynamic stability of C-A-S-H gels under sulfate attack, which agrees well with the experiment results.

The influence of aluminum additive on the formation mechanism and thermal stability of calcium silicate hydrates was determined. Calcium silicates hydrates were synthesized in the primary mixtures with the molar ratios of CaO/(SiO2 + Al2O3) = 1.5 and Al2O3/(SiO2 + Al2O3) = 0.025 or 0.05. The hydrothermal synthesis has been carried out in unstirred suspensions under saturated steam pressure in argon atmosphere at 200 °C temperature for 4, 8, 16, 24, 48 and 72 h by applying extra argon gas (10 bar). It was determined that Al2O3 additives have a significant influence on the formation mechanism of synthesis products as well as their stability during the isothermal curing. At the beginning of the reaction, this additive retarded the formation of calcium silicate hydrates but stimulated the crystallization of CASH and C2S which remained stable under all experimental conditions. The thermodynamic calculations, in the mixtures with Al2O3/(SiO2 + Al2O3) = 0.025 molar ratio, showed that the greatest possibility that C-S-H(I) and C2S with incorporated Al3+ ions in the structure will crystallize, because the obtained Gibbs free energy value is the lowest (\(\Delta_{\rm r} G_{\rm T}^{0}\) = −80.3 kJ and \(\Delta_{\rm r} G_{\rm T}^{0}\) = −104.5 kJ). Meanwhile, in the mixtures with larger amount of aluminum, there is the greatest possibility that 4CaO·Al2O3·9.5H2O and 4CaO·Al2O3·6.5H2O will be formed. The obtained results were confirmed by the thermodynamic calculations and instrumental analysis data.

This paper presents experimental results and analysis of sulfate-bearing soils treated with ground granulated blast-furnace slag (GGBS). The experiments involve the unconfined compression strength test, shrinkage, free swelling, suction measurements, and microstructural examination. Short- and long-term swelling tests were conducted to inspect the durability of GGBS stabilization against the sulfate-induced heave. The concept of the shrinkage curve was employed to elucidate how GGBS stabilization alleviates soil shrinkage behavior and alters the pore size distribution. The results manifested that 7% GGBS was sufficiently adequate to improve the 28-day strength of the tested sulfate-bearing soils about five times. The GGBS treatment mainly results in the decline of calcium sulfate content and the formation of calcium silicate hydrate, ettringite, and calcite. The results of long-term swelling tests indicated a delayed sulfate-induced heave that started beyond a month from the time of exposing the treated soils to water. The delayed heave was still not significant as compared with that of the untreated control soil specimens. Accordingly, it is recommended that the treated sulfate-bearing soils are tested with the selected GGBS content for any delayed swelling before application in the field. The GGBS treatment has significantly escalated suction magnitude during curing mainly due to the consumption of water in the hydration process and the formation of ettringite.

This study investigated the influence of blended powders of dealuminated metakaolin (DK), limestone (LS), and silica fume (SF) as partial cement replacements on the properties of high-strength concrete (HSC). Nine concrete mixes were designed, including a control mix and mixes incorporating binary, ternary, and quaternary blends of SF, LS, and DK at varying cement replacement levels. The experimental program evaluated the physical properties (slump, setting times, consistency), mechanical properties (compressive and tensile strengths), and microstructure (SEM, XRD, and EDX analysis)of the investigated concrete mixes. Furthermore, radiation shielding properties of the produced concretes were assessed using Monte Carlo (MC) simulations and Phy-X software. The analysis covered both γ-rays and fast neutrons. Results showed that quaternary blends of DK, LS, and SF reduced slump due to higher water demand, while their increased content enhanced compressive and tensile strengths.Optimal strength values were achieved with specific blend ratios: mix 4 (10% DK) for binary blends, mix 6 (15% SF+10% DK) for ternary blends, and mix 9 (15% SF+10% LS+10% DK) for quaternary blends. These optimal mixes exhibited compressive strength increases of 37.3%, 43.35%, and 23.4%, and tensile strength increases of 15.3%, 32.4%, and 22.25%, respectively, compared to the control mix. SEM analysis showed fewer voids and microcracks and a denser microstructure in the optimal replacement mixes. Furthermore, XRD and EDX analyses confirmed that DK, LS, and SF promoted the formation of calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH) through pozzolanic reactions. The γ-ray attenuation tests indicated modest improvement in γ-ray shielding capacity of HSC, with DK10 and SF15LS10DK10 mixes recording the highest linear attenuation coefficients (LAC). This improved performance is attributed to their elevated densities (2.47, 2.45g cm-3) and substantial iron content (1.53% and 1.92%, respectively). Additionally, DK10, SF15LS10, and SF15LS10DK10 mixes exhibited excellent neutron shielding, achieving a removal cross-section (FCS) value of 0.086cm⁻1, with the lowest half value layer (HVLFCS) of 8.059cm, and relaxation length (λFCS) of 11.627cm.

This study evaluated the impact of nano silica (NS) and nano metakaolin (NMK) on high-strength concrete (HSC). Portland cement was partially replaced with varying amounts of NS and NMK, both individually and in combination. Portland cement was partially replaced with varying percentages (1, 2, 3, and 4 wt%) of NS and (2, 4 and 6 wt%) of NMK in individual mixes. Four concrete mixtures were formulated using a combination of NS and NMK. The physical properties (slump, consistency, and setting times), mechanical properties (compressive and tensile strengths at 28 days), and microstructural analysis (X-ray diffraction (XRD) and energy-dispersive X-ray (EDX)) were conducted on both the individual and combined mixtures, along with the control mix. Radiation shielding properties of the concrete were conducted. The Monte Carlo simulation code and the Phy-X program were used to examine the efficacy of these combinations in shielding against ionizing radiation, e.g., gamma rays and fast neutrons. The results showed NS and NMK reduced slump in HSC, primarily due to increased water demand and a denser structure. Combined use led to a more significant reduction than individual. Increased NS and NMK content led to higher water demand but shorter setting times. NS improved compressive and tensile strengths, reaching a maximum of 10.5% and 5.6%, respectively, at replacement 3% NS. NMK increased compressive and tensile strengths of 11.7% and 6.3%, respectively at replacement 4% NMK. The combined mixture 1% NS + 4% NMK mixture, demonstrated enhancement in compressive and tensile strengths by 14.2% and 7.7%, respectively, compared to the control mix. XRD and EDX analyses confirmed that NS and NMK enhanced the formation of calcium silicate hydrate and calcium aluminate hydrate through pozzolanic reactions. The linear attenuation of the concrete samples was NMK4 < CM2 < NS3 < C0. The sample containing NMK demonstrated the best value for the linear attenuation coefficient of gamma rays and a rise in FCS, indicating that it is an excellent barrier against both gamma rays and neutrons. These findings demonstrate that NS and NMK significantly enhance HSC strength and radiation shielding, offering safer and more durable concrete for nuclear and medical facilities.

This study explores the potential use of naturally and locally available pozzolana as an eco-friendly alternative to cement in the manufacture of compressed earth blocks (CEBs). Wet granulometric tests were carried out on samples taken from a construction site in Casablanca to determine their appropriateness for CEB production. CEBs were made with different percentages of pozzolana, both used individually and in combination with cement. Soil was treated uniformly through mixing, compaction, and curing, followed by compressive strength tests to determine mechanical characteristics, and X-ray diffraction (XRD) analysis to examine the mineral composition of the samples. The results were encouraging, as the CEBs stabilized with 4% pozzolana achieved higher compressive strength than those stabilized with 4% cement. The XRD results showed that in the soil-pozzolana mixture, significant mineralogical transformations occurred, such as the formation of calcium silicate hydrates (CSH) and calcium aluminate hydrates (CAH), which strengthen the soil matrix and improve the compressive strength. Such a finding demonstrates the potential of pozzolana to act as a greener stabilizer in low-load structural applications, partially replacing cement with lowering environmental impact. This work highlights the feasibility of using pozzolana as a sustainable, locally adapted solution for construction.