Calcium Aluminum Silicate Hydrate Research Articles

Kinetics of Al uptake in synthetic calcium silicate hydrate (C-S-H)

The effect of equilibration time on the composition, structure and solubility of calcium aluminate silicate hydrate (C-A-S-H) was investigated in 0.5 M NaOH solutions at Al/Si = 0.1. Longer equilibration time led to longer silica chains, to less Na and, to more Ca in C-A-S-H, as well as to an increased fraction of tetrahedral Al(IV) charge-balanced by Ca2+. Aluminium, calcium and silicon concentrations in solution changed rapidly during the first day, while after 14 days only minor changes were observed. The long-term concentrations could be reproduced well by the thermodynamic CASH+ model. Over a longer time span of up to 10 years, a slow redistribution of Si and Al in C-A-S-H as well as the partial replacement of Na+ by Ca2+ in the interlayer space was observed. This study highlights the importance of considering the effect of time on C-A-S-H structure.

Optimization of mechanical performance of limestone calcined clay cement: Effects of calcination temperature of nanosized tubular halloysite, gypsum content, and water/binder ratio

Halloysite is a clay mineral that has a nanosized tubular morphology and high pozzolanic activity, and its calcination product can be used as a supplementary cementitious material in limestone calcined clay cement (LC3). In this study, the effects of the calcination temperature of halloysite, gypsum content, and water/binder (W/B) ratio on the mechanical properties and microstructures of LC3 were evaluated. The results demonstrated that halloysite calcined at the temperature of 650°C–850°C exhibited high pozzolanic activity: LC3 prepared using halloysite calcined above 650°C exhibited a shorter setting times and higher compressive strengths than those prepared with halloysite calcined at 550°C. This is attributable to the formation of more additional calcium aluminate silicate hydrate gel, and a larger amount of hemicarboaluminate and monocarboaluminate at higher temperatures than at lower temperatures, which results in more filling of pores in LC3 under the former conditions than the later conditions. The results also indicated that the optimum content of additional gypsum for LC3 was between 0 wt% and 2 wt%, and overdose gypsum did not substantially alter their setting times but decrease their compressive strengths. In contrast, a decrease in the W/B ratios decreased their setting times, total porosity, and increased their compressive strengths. Overall, in this study, LC3 prepared using halloysite calcined at 750°C, with a W/B ratio of 0.40 and without additional gypsum, exhibited the highest compressive strengths, which were 42.6, 51.7, and 57.1 MPa after 3, 7, and 28 days of curing, respectively. These findings deepen the research on the hydration mechanism of LC3 prepared with calcined halloysite and provide basic data for the wide application of this approach.

Sustainability-driven atomistic model for exploring the mechanical properties of low carbon limestone calcined clay cement (LC3)

Limestone Calcined Clay Cement (LC3) is identified as a promising alternative to cement blends, and it has become an effective way to alleviate the environmental burdens in the cement industry due to its sustainable nature. In this work, we developed the first molecular model to describe the optimized properties of LC3 blend considering its natural sustainability. The proposed model entails the atomistic structures of Calcium-aluminate-silicate-hydrate (C-A-S-H) in LC3, identifying its mechanical properties, tensile deformation behaviors and failure mechanisms. We revealed that the natural atomistic origins contributing to the superior mechanical properties of C-A-S-H in LC3 compared to that in plain cement are: (1) highly polymerized aluminate-silica chain in C-A-S-H enhances its mean chain length and reduces its porosity; and (2) highly activated aluminate monomer strengthens the cross-linked network in C-A-S-H through a series of pozzolanic reactions. Furthermore, we elucidated the failure mechanisms including aluminate-silica chain breakage, nanopore expansion and microcrack evolution of C-A-S-H under tensile loading. Our findings provide atomic insights to uncover the nanoscale structures of C-A-S-H in sustainable LC3, portraying new understandings of their complicated molecular interactions and structural-failure mechanisms and paving ways for the development of sustainable cementitious composites for construction industry with lower environmental impacts.

Research on the mechanical properties and microstructure of fly ash-based geopolymers modified by molybdenum tailings

The environmental and economic problems caused by the accumulation of molybdenum tailings (MT) have become increasingly prominent. Therefore, a cost-effective method is urgently needed to realize the resource utilization of MT. In this paper, the mechanism of action of MT on fly ash-based geopolymers were systematically researched. The effects of MT on the macro-properties of fly ash-based geopolymers were researched in terms of fluidity, setting time, drying shrinkage and mechanical strength. The reaction mechanism of fly ash-based geopolymers modified by MT were analyzed from the perspective of microstructure and micromorphology by using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric (TG) and nitrogen adsorption/desorption (NAD) methods. The results show that the addition of MT could effectively improve the fluidity of fly ash-based geopolymer paste, appropriately delay its setting time and increase its drying shrinkage; When the content of MT was 20%, the bending strength of fly ash-based geopolymers were significantly improved, and the flexural strength at 3, 7 and 28 days were increased by 79.2%, 47.4% and 19% respectively. The SEM, FTIR and TG results confirmed that the main product was glassy sodium calcium aluminum silicate hydrate (N(C)-A-S-H) gel, which was used as a binder to connect residual raw material particles and form hardened geopolymer materials. The XRD results show that the addition of MT would not lead to the formation of new crystal phases in the fly ash-based geopolymers, and when the addition of MT was 20%, the diffraction peak intensity of the crystal phase structure of the fly ash-based geopolymers basically were not changed obviously. The NAD results show that the addition of 20% MT could significantly improve the pore structure of fly ash-based polymers, increased the volume fraction of micropores, and reduced the volume fraction of macropores. The SEM/EDS results show that the MT could be dissolved in alkali activator to form nanorods to fill the pore structure of fly ash-based geopolymers, thus reducing the cracks and defects of fly ash-based geopolymers and improving the compactness of the microstructure.

Bioinspired Super Thermal Insulating, Strong and Low Carbon Cement Aerogel for Building Envelope.

The energy crisis has arisen as the most pressing concern and top priority for policymakers, with buildings accounting for over 40% of global energy consumption. Currently, single-function envelopes cannot satisfy energy efficiency for next-generation buildings. Designing buildings with high mechanical robustness, thermal insulation properties, and more functionalities has attracted worldwide attention. Further optimization based on bioinspired design and material efficiency improvement has been adopted as effective approaches to achieve satisfactory performance. Herein, inspired by the strong and porous cuttlefish bone, a cement aerogel through self-assembly of calcium aluminum silicate hydrate nanoparticles (C-A-S-H, a major component in cement) in a polymeric solution as a building envelop is developed. The as-synthesized cement aerogel demonstrates ultrahigh mechanical performance in terms of stiffness (315.65MPa) and toughness (14.68MJ m-3 ). Specifically, the highly porous microstructure with multiscale pores inside the cement aerogel greatly inhibits heat transfer, therefore achieving ultralow thermal conductivity (0.025W m-1 K-1 ). Additionally, the inorganic C-A-S-H nanoparticles in cement aerogel form a barrier against fire for good fire retardancy (limit oxygen index, LOI ≈ 46.26%, UL94-V0). The versatile cement aerogel featuring high mechanical robustness, remarkable thermal insulation, light weight, and fire retardancy is a promising candidate for practical building applications.

A novel alkali-activated cement from mineral admixture, superabsorbent polymers, and alkali-doped carboxylate glass

In this paper, we introduce a novel approach for the targeted delivery of concentrated alkali required for activation of aluminosilicate-based cements, which avoids exposure to caustic solutions on site. The solid alkali, encapsulated within a water-soluble glass (alkali-doped carboxylate glass) is dry blended with mineral admixtures (ground granulated blast slag and fly ash) and water saturated superabsorbent polymers (SAP, being the only source of mix water in this study). The solubility of alkali-doped carboxylate glasses (ACG) was characterized. The hydration of ground granulated blast slag (GGBS) and fly ash (FA) with different curing times were monitored by SEM, XRD, FT-IR and solid-state MAS NMR, which showed the co-existence of calcium aluminum silicate hydrate (C-A-S-H) gel and sodium aluminosilicate hydrate (N-A-S-H) gel in the hydration products. The mechanical properties of AAC were tested, and the compressive strength of AAC (using ACG as alkali activator, water saturated SAP as water source) reached over 40 MPa after curing for 28 days.

Hydration kinetics of clinoptilolite zeolite blended ternary cementitious materials with fly ash and metakaolin

The typical characteristics of hydration kinetics for the natural zeolite blended cementitious system may be impacted due to the varied sources and compositions of the zeolite particles. Previous research reported that the substitution of portland cement with natural clinoptilolite zeolite substantially minimized the tricalcium aluminate (C3A) peak heat of hydration apart from the regular matrix of the hydration kinetics, an indication of the potential interaction of zeolite particles in the blended system. Therefore, the present study investigated the suitable reasons for minimizing C3A peak heat of hydration in the blended system replacing the portland cement with clinoptilolite zeolite up to 20% by mass. Similarly, class C fly ash and metakaolin were utilized up to 20% by mass to observe the hydration kinetics of the zeolite blended ternary cementitious system. Additional 5% gypsum replaced the portland cement in the zeolite mixed system to verify the undersulfation. The heat of hydration was observed via isothermal conduction calorimetry. Phase identification of hydration products was done by x-ray diffraction (XRD) analysis at an early age of 3 days. Results revealed that the minimized C3A peak heat of hydration was not due to the undersulfation. Results also revealed that the zeolite blended ternary samples (i.e., cement-zeolite-class C fly ash, and cement-zeolite-metakaolin) obtained a relatively higher C3A peak heat flow and an increased duration for the monosulfate formation compared to the binary (i.e., cement-zeolite) samples. Likely, zeolite particles had a relatively slow chemical dissolution compared to the class C fly ash and metakaolin particles which supplied comparatively reduced amounts of alumina in the system in the early ages. The XRD results indicate the potential formation of a new hydration product (calcium-aluminum–silicate-hydrate), which likely consumed a reasonable amount of aluminate leading to a minimized C3A peak heat of hydration in the clinoptilolite zeolite blended system.

Valorization of industrial siliceous wastes in the production of geopolymers binders

To develop a practical alternative to classic cement materials, alkali-activated materials were manufactured from industrial wastes (fly and bottom ash). Microstructural behavior of these blends was investigated through X-ray diffraction, scanning electron microscope, thermal analysis, Fourier-transform infrared spectroscopy and surface response methodology. Natrolite, phillipsite, and calcium aluminum silicate hydrate and sodium carbonate newly formed after alkali activation. Empirical ternary diagrams as well as modeling equations were united to predict the physico-mechanical evolution of the prepared specimens. The used model described well the evolution of the studied properties against the processing factors; temperature, NaOH concentration and curing time. The weight of the effect of each parameter was estimated and factor to factor interaction was considered. NaOH concentrations and ageing temperature had a considerable positive effect on density and mechanical strength, respectively. Water absorption and electrical conductivity were influenced differently by the factors, the electrical conductivity increases as the NaOH concentrations increase, and time and temperature decrease. The response surfaces and their results were correlated with the microstructure of the hardened samples. Overall, alkali activated binders with good engineering properties could be synthesized in the considered conditions. The optimal alkali activation conditions were ∼12 M and the corresponding final properties were as follows: 50 MPa for the compressive strength and 20% for water absorption while density was recorded at a 1.75 g/cm3 value.

The role of nano magnesia in accelerating the early hydration rate of sodium sulfate activated slag

The present work aimed at accelerating the early hydration rate of sodium sulfate (Na2SO4) activated slag via nano magnesia (nM). Slag was activated by two Na2SO4 concentrations equivalent to 1 and 3 wt% Na2O (SS1 and SS3, respectively). The results demonstrated that the addition of nM accelerated the hydration rate and raised the pH of the medium, resulting in a marked enhancement of the early compressive strength of the hardened SS3 mixture. Specifically, the samples containing 0.5, 1.0, and 1.5 wt% nM recorded 3-day compressive strengths 12, 21, and 15 times higher than the control sample (SS3). As time progressed up to 90 days, the strength gap between SS3-nM and SS3 mixtures decreased, but samples containing 0.5 and 1.0 wt% nM still showed higher strengths. By contrast, the mixture containing 1.5 wt% nM recorded lower 90-day compressive strength. Nonetheless, higher nM content bolstered the formation of ettringite and calcium aluminum silicate hydrate phases while simultaneously decreasing both the pore volume and drying shrinkage of Na2SO4-activated slag. Utilizing nM successfully addressed the issue of poor initial performance of Na2SO4-activated slag, leading to improved commercial viability and increased mass production of such binder.

Solidification/stabilization treatment of Hong Kong marine deposits slurry at high water content by ISSA and GGBS

Soft soils have been adopted as a conventional fill material in land reclamation projects, which is quite promising in Hong Kong with a huge mass of dredged marine sediments produced per year. It is proposed to use Hong Kong marine deposits (HKMD) as fill material treated by stabilisation/solidification (S/S) technology with sustainable binding material. In this work, lime, incinerated sewage sludge ash (ISSA) and ground granulated blast furnace slag (GGBS) were selected as the binding materials. The S/S performance of the binders on HKMD slurry was investigated. The results showed that the use of ISSA and GGBS as part of the binder is effective in promoting the strength of HKMD slurry with a high initial water content of 200%. The HKMD slurry treated by 30% binders (30% lime and 70% (ISSA + GGBS) with ISSA: GGBS = 3) gains strength, which became higher with increasing curing time. The results from X-ray diffraction (XRD), thermo-gravimetric (TG) analysis and scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) presented the formations of calcium (aluminium) silicate hydrate (C-(A)-S-H), Friedel’s salt, and ettringite, which are mainly responsible for the strength increase of treated HKMD with their phases filling into the pores, interlocking and reinforcing the particles in the mixture. The porosity of the treated HKMD in bulk and powder state was determined by mercury intrusion porosimetry technique (MIP) and nitrogen adsorption/desorption isotherms (NAI), it is found that the bulk porosity of treated HKMD samples reduces with curing time due to the neoformations, especially the ettringite crystal by SEM results. This work indicates the potential application of lime-activated recycling wastes (i.e., ISSA and GGBS) for S/S treatment of HKMD slurry.

Alkali-silica reactivity of lightweight aggregates in alkali-activated slag cement and ordinary Portland cement systems

For alkali-activated slag cement (AAC), an environmentally-friendly material, high-alkalinity activators are normally utilized for activation, which can lead to possible concrete degradation owing to alkali-silica reaction (ASR) when alkali-active aggregates were used. This study explored the effectiveness of lightweight aggregates in mitigating ASR behaviors of the AAC system. Alkali-reactive expanded perlite and non-alkali-reactive expanded shale were used as lightweight aggregates to compare ASR behaviors in ordinary Portland cement (OPC) and AAC systems. The formation of ASR gel in the expanded perlite was expansive, whereas the higher Ca/Si ratio calcium-aluminate-silicate-hydrate (C-A-S-H) in the non-alkali-reactive expanded shale did not cause expansion. In contrast with the OPC system, the larger amount of lower Ca/Si ratio ASR gel caused more deleterious ASR expansion and cracks in the AAC system. Furthermore, replacing expanded perlite with expanded shale effectively mitigated the ASR expansion. Discussion on the ASR mitigation mechanism of lightweight aggregates was provided for predicting the influence on the concrete.

Effect of high volume tile ceramic wastes on resistance of geopolymer mortars to abrasion and freezing-thawing cycles: Experimental and deep learning modelling

Utilizing industrial and agriculture waste materials to produce a green and sustainable mortar have widely investigated and assessed based on the mechanical and durability properties. Herein, the abrasion and freezing-thawing resistance of fly ash (FA)-ground blast furnace slag (GBFS) based geopolymer mortars incorporating high content of tile ceramic wastes (TCWs) have been evaluated experimentally and mathematically using artificial neural network (ANN). A relatively dilute (4 M) alkaline solution was used to activate the ternary blend. The TCWs was maintained as a relatively large percentage of the total binder, i.e. 50%, 60% and 70%. Once the casting process was complete, curing of the samples was performed at 27 °C. These then underwent testing at day 1, day 3, day 7 and day 28 to provide durability data for various specimen ages. Tests encompassed exposure to abrasion, ability to withstand cyclic freeze-thawing and wet-drying, and permeability to water. Investigations to establish the impact of the high TCWs proportion on the generation of sodium aluminium, calcium aluminium and calcium silicate hydrate (N, C-A-S-H) gels, respectively, included X-ray diffraction, scanning electron microscopy and Fourier-transform infrared spectroscopy. The large percentage of TCWs (70%) generated GPMs that had a minimal effect on the environment and which, by day 28, evidenced a compressive strength above 35 MPa. Augmenting the GBFS and FA content promoted the capacity to withstand freeze-thawing cycles and enhanced durability. Improved performance was also observed in scenarios associated with abrasion resistance. In addition, the proposed models proved their accuracy in which MSE, MAPE, SI were less than 1.93, while R2 of greater than 0.9 confirmed the closeness between predicted and actual results. Substitution of TCWs and FA for GBFS additionally reduced landfill problems of ceramic wastes and achieved the sustainability aims.

Effects of Cl- erosion conditions on Cl- binding properties of fly-ash-slag-based geopolymer

This study aims to investigate the Cl--binding ability of calcium aluminate silicate hydrate (C-A-S-H)/sodium aluminosilicate hydrate (N-A-S-H) gel and fly-ash-slag based geopolymer mortar exposed to different Cl- concentration under 0–56 days exposure ages. The concentration of Cl- was from 0.1 to 1.0 mol/L. The physical phase and corresponding layer spacing, degree of crystallization, crystal structure and thermal stability were measured and the effect of changes in the C-A-S-H/N-A-S-H gel structure on the Cl- binding capacity of the geopolymer was analyzed. The results showed that the C-A-S-H/N-A-S-H gels changed from flake structure to flocculent structure after Cl- invasion, leading to the transformation of the geopolymer from laminar structure to a laminar-flocculent structure with crystallization and non-crystallization coexisting. With the erosion of Cl-, the crystal structure of C-A-S-H/N-A-S-H gels was disrupted and the crystallinity decreased, leading to an increase in the crystalline surface spacing of the geopolymer. In addition, the erosion of Cl- led to a decrease in the glass transition temperature of C-A-S-H/N-A-S-H gels and a decrease in the thermal stability of the geopolymer. The binding of Cl- by geopolymer mortar was divided into two aspects, C-A-S-H/N-A-S-H gel adsorption and chemical binding, with gel adsorption as the main source. With the increase of Cl- concentration or exposure age, the Cl- binding ability of C-A-S-H/N-A-S-H gels first rose rapidly and then gradually decreased, which was similar to that of geopolymer mortar.

The inhibitory effect of excess calcium ions on the polymerization process of calcium aluminate silicate hydrate (CASH) gel.

Calcium ion, as an essential component in CASH, affects the aggregation and formation process of CASH, thereby influencing its microstructure and mechanical properties. However, the mechanism by which calcium ions affect the polymerization process of CASH is not yet fully understood. In this study, the effects of calcium ions on the polymerization process, coagulation state, and microstructure of CASH are investigated via molecular dynamics simulation. The results indicate that the presence of a trace amount of Ca2+ attracts oligomers towards the calcium-rich region, thus speeding up the polymerization to some extent, but as the Ca2+ content increases, more Ca2+ binds to the oxygen atoms in silica-oxygen tetrahedra and aluminum-oxygen tetrahedra, forming tight ion pairs and occupying the hydroxyl binding sites required for the polycondensation reaction. This inhibits the continuous aggregation of CASH gel and slows down the rate of polymerization. Additionally, Ca2+ attracts oxygen atoms from free water molecules and free OH-, forming Ca(OH)2 dispersed in the spatial structure, which hinders the formation of larger clusters. As a result, the higher the Ca ion content in the system, the lower the overall polymerization degree of the CASH gel, resulting in a decrease in the conversion of the Q1 dimer to Q2 and Q3 chain structures, a shorter average chain length, poorer overall connectivity, and a transition from large clusters in a better-aggregated state to dispersed small clusters. This study sheds light on the polymerization reaction mechanism of CASH gels.

The experimental investigation on the geo-polymerization of water-based filtercake at the second interface of the oil-gas well

The quality of bond along the second interface of sandstone oil-gas well is of an utmost important in order to ensure long-term zonal isolation throughout the lifecycle of the well by preventing the potential leakage of hydrocarbon fluids. Attaining effective long-term zonal isolation for the lifetime of oil-gas wells depends on the sealing capacity at second interface (SI). Existence of untreated filtercake at SI acts as weak point of potential leakage of hydrocarbon. Different techniques were developed to improve the situation; however, it is still difficult to cleaned up completely by chemical washes and spacers. Therefore, it is imperious to develop a method that can make a filtercake which can provide an effective bonding between the formation and the cement sheath. The experimental work introduces a novel KN solution developed in the laboratory, simulated wellbore as sandstone formation under the wellbore simulated conditions.The results revealed that the samples treated with KN solution had higher shear bond strength over untreated samples. The bond quality increased with the increase of curing time (3, 7, 14, and 28 days). The improvement was due to geopolymerization of remained water-based filtercake took place which led to formation of cementitious material such as Calcium-Silicate-Hydrate (C–S–H) and FTIR analysis revealed the formation of cementitious material (Calcium-Silicate-Hydrate (C–S–H)) and other geopolymers like Calcium-Aluminium-Silicate-Hydrate (C-A-S-H) and Sodium-Aluminium-Silicate-Hydrate (N-A-S-H)) along the interface which filled the existed pores hence reducing porosity hence high strength of bond at high concentration to treated samples. The untreated samples were observed at low transmittance revealing the low content of inorganic geopolymers hence poor bond quality. Thick water-based filtercake films at second interface, which prevented the complete reaction of cement hydration between rock grains and cement slurry material to form a chemical binder at the interface.This technique is of an utmost important as compared to the other means of improving shear bong strength. This chemical solution tends to convert the clay material into cementitious product (geopolymers) which will enhance the bonding strength. In addition, the formed products are high durable as it can withstand harsh environmental conditions such as higher elevated temperature and salinity condition hence leading to remedial cost reduction.

Morphology and microstructure of waste material-based geopolymer with flyash, eggshell powder, and soft soil

The morphological and microstructural evolution of flyash (FA), eggshell powder (ESP), and soft soil (S) geopolymer was studied. The variable parameters for synthesis was precursor concentration (10 %, 20 %, 30 %, 40 %, and 50 %) in soft soil, whereas ESP:FA ratio as 50:50, Na2SiO3:NaOH ratio as 70:30, and curing condition as 50 °C for 7 days were the fixed parameters. The effect of these parameters on the geopolymerization was explained using field emission gun-scanning electron microscopy including an energy dispersive X-ray spectrometer and mapping. The calcium aluminate silicate hydrate gel co-existed along with the highest cementitious product. The geopolymeric gel structure filled the voids between soft soil particles and reinforced the whole matrix.

A long-term study on structural changes in calcium aluminate silicate hydrates

Production of blended cements in which Portland cement is combined with supplementary cementitious materials (SCM) is an effective strategy for reducing the CO2 emissions during cement manufacturing and achieving sustainable concrete production. However, the high Al2O3 and SiO2 contents of SCM change the chemical composition of the main hydration product, calcium aluminate silicate hydrate (C–A–S–H). Herein, spectroscopic and structural data for C–A–S–H gels are reported in a large range of equilibration times from 3 months up to 2 years and Al/Si molar ratios from 0.001 to 0.2. The 27Al MAS NMR spectroscopy and thermogravimetric analysis indicate that in addition to the C–A–S–H phase, secondary phases such as strätlingite, katoite, Al(OH)3 and calcium aluminate hydrate are present at Al/Si ≥ 0.03 limiting the uptake of Al in C–A–S–H. More secondary phases are present at higher Al concentrations; their content decreases with equilibration time while more Al is taken up in the C–A–S–H phase. At low Al contents, Al concentrations decrease strongly with time indicating a slow equilibration, in contrast to high Al contents where a clear change in Al concentrations over time was not observed indicating that the equilibrium has been reached faster. The 27Al NMR studies show that tetrahedrally coordinated Al is incorporated in C–A–S–H and its amount increases with the amount of Al present in the solution.

Effects of co-calcining kaolinite-rich clay blends with alkali and alkali earth metal hydroxides

The aim of this paper is to investigate the effects of co-calcining kaolinite and montmorillonite clay blends with alkali and alkali earth metal (AAEM) hydroxides as a route to enhance the reactivity of the clay blends. NaOH, KOH, and Mg(OH)2 were added in different dosages (0–20%) to the clay blend and calcined together at 750 °C. When NaOH and KOH added at a dosage <10%, this co-calcination promoted amorphization, increased non-bridging oxygen per tetrahedron (NBO/T), increased dissolution of Si, and therefore improved reactivity. At a higher dosage, these additives decreased reactivities. These clay blends were utilized as a precursor in a seawater-cured lime-pozzolana binder system. The evolution of the microstructures was monitored using XRD, FTIR, 29Si solid-state NMR, 27Al solid-state NMR, ICP-OES, and SEM-EDS for up to 90 days. The maximum compressive strength came from the 5% Mg(OH)2 batch which was 22.1 MPa at 90 days. The 5% dosages of all the AAEM hydroxides showed better performance than that of the control batch. The mineralogy showed the presence of hydrocalumite, ettringite, gehlenite, hydrogarnet, and calcium aluminum silicate hydrate (C-A-S-H) in seawater cured paste samples. The SEM-EDS revealed the presence of plate and needle like C-A-S-H in the seawater cured samples.

Experimental study on modification of water-based filtercake to improve the bonding strength at the wellbore cement-formation interface

The objective of this experimental study is to improve the cementing bond quality of sandstone oil-gas well along the wellbore cement-formation interface (WCFI), so as to ensure long-term zonal isolation throughout the lifecycle of the well by using NSO solution as filtercake modifier which was developed in the laboratory. According to designed experimental method and API RP 10, the effectiveness of filtercake modifier (NSO) on the bonding strength at the WCFI was assessed by using designed simulated wellbore as sandstone formation. The experimental results indicated that the samples which were treated with NSO solution had higher bond strength over untreated samples. The strength generally increased with curing period as for treated samples, 0.198, 0.374, 0.433 and 0.473 MPa for 3, 7, 15, and 30 days respectively while for the untreated samples the bond strength were 0.050, 0.070, 0.81 and 0.100 MPa for the same period. The water-based filtercake modification techniques had significantly enhanced the bonding strength of WCFI by increasing rates above 296%. Improvement of bond strength to the treated sample was due to filtercake modification as a result of formation of cementitious material as revealed in FTIR spectral such as Calcium-Silicate-Hydrate (C–S–H) and other geopolymers like Calcium-Aluminium-Silicate-Hydrate (C-A-S-H) and Sodium-Aluminium-Silicate-Hydrate (N-A-S-H)) along the interface which filled the existed pores hence reducing porosity hence high strength of bond. The low transmittance value for the NSO treated samples revealed that there were more cementitious materials existing at the WCFI which led to improvement of bonding strength as compared to the untreated samples. The lower/poor bond strength for the untreated samples is due to existence of untreated, thick water-based filtercake films at WCFI, which prevented the complete hydration process between rock grains and cement slurry components to make chemical binder of cement slurry material and formation.

Development and characterization of ceramic waste powder-slag blended geopolymer concrete designed using Taguchi method

• Taguchi L16 matrix was used to design the experiments with five factors and four levels. • Taguchi method optimized the mix design of CWP-slag blended geopolymer concrete. • The compressive strength of the optimum mix reached 58.9 MPa. • Mechanical and durability properties were correlated using analytical regression models. • Scanning electron microscopy highlighted the formation of C-A-S-H and N -A-S-H gels. The ability to utilize industrial by-products in the production of cement-free geopolymer concrete is a promising technology. However, the development, characterization, and optimization of geopolymer concrete made with ceramic waste powder (CWP) and ground granulated blast furnace slag (or simply slag) have not been examined yet. This paper investigates the mechanical and durability properties of geopolymer concrete incorporating CWP and slag. Taguchi method was employed to design sixteen CWP-slag blended geopolymer concrete mixes. Five factors with four levels were considered in the design, including binder content, CWP replacement percentage by slag, alkali-activator solution to binder ratio (AAS/Binder), sodium silicate (SS) to sodium hydroxide (SH) ratio (SS/SH), and SH solution molarity. Results showed that geopolymer concrete properties remarkably degraded when CWP served as the sole binding material. However, combining 40 % CWP and 60 % slag yielded superior performance than the control mix made with 100 % slag. Correlations between mechanical and durability properties were developed in the form of regression models. The optimal compressive strength response (58.9 MPa) of CWP geopolymer concrete was attained using 450 kg/m 3 of binder content, 60 % of CWP replacement by slag, 0.5 of AAS/Binder, 1.5 of SS/SH, and 10 M of SH solution molarity. Scanning electron microscope and energy-dispersive X-ray spectroscopy highlighted the formation of calcium aluminum silicate hydrate and calcium silicate hydrate gels. Experimental findings provide evidence of the ability to utilize CWP in the production of structural grade geopolymer concrete.