Cement Formulations Research Articles

Reactivity of MSWI-fly ash in Mg-K-phosphate cement

In this study, the behaviour and reactivity of Municipal Solid Waste Incineration Fly Ash (MSWI-FA), introduced in the formulation of magnesium potassium phosphate cement (MKPC), was investigated by considering the waste either as fully inert or reactive. MSWI-FA induced structural and compositional modifications in MKPC as a consequence of dissolution/precipitation processes which involved many MSWI-FA elements (e.g., Ca, Mg, Al, Si, Zn) and led to the formation of mostly amorphous phosphate secondary products. The reaction path has been described in terms of the early fast dissolution of MSWI-FA, with precipitation of very low solubility phases, and subsequent late precipitation due to pH changes and water subtraction during MKPC gelification. The increase in amorphous content peaked to 50 wt.% and it has been related to the improved behaviour with respect to the leaching of heavy metals (reduced by 70-99%), pointing to this cement as an excellent matrix for their chemical stabilization. The obtained MKPC microstructure exhibited better mechanical performance, with an improvement of up to 60% in compressive strength. All in all, the results indicated that the incorporation in MKPC is a viable recycling opportunity for MSWI-FA, although, for an effective cement formulation, its reactivity must be taken into account.

Preparation and Characterization of Mono- and Biphasic Ca1-xAgxHPO4·nH2O Compounds for Biomedical Applications.

This study aimed to explore the effects of the full-scale replacement (up to 100%) of Ca2+ ions with Ag1+ ions in the structure of brushite (CaHPO4·2H2O). This substitution has potential benefits for producing monophasic and biphasic Ca1-xAgxHPO4·nH2O compounds. To prepare the starting solutions, (NH4)2HPO4, Ca(NO3)2·4H2O, and AgNO3 at different concentrations were used. The results showed that when the Ag/Ca molar ratio was below 0.25, partial substitution of Ca with Ag reduced the size of the unit cell of brushite. As the Ag/Ca molar ratio increased to 4, a compound with both monoclinic CaHPO4·2H2O and cubic nanostructured Ag3PO4 phases formed. There was a nearly linear relationship between the Ag ion ratio in the starting solutions and the wt% precipitation of the Ag3PO4 phase in the resulting compound. Moreover, when the Ag/Ca molar ratio exceeded 4, a single-phase Ag3PO4 compound formed. Hence, adjusting the Ag/Ca ratio in the starting solution allows the production of biomaterials with customized properties. In summary, this study introduces a novel synthesis method for the mono- and biphasic Ca1-xAgxHPO4·nH2O compounds brushite and silver phosphate. The preparation of these phases in a one-pot synthesis with controlled phase composition resulted in the enhancement of existing bone cement formulations by allowing better mixing of the starting ingredients.

Minimizing the particles settling of ilmenite weighted oil well cement using laponite

Cementing operations are fundamental undertakings during the drilling and completion of oil and gas wells, ensuring zonal isolation and structural stability within the wellbore. Ilmenite serves as a dominant weighting material for high-density cement. However, challenges associated with its particle settling have arisen, reporting the potential for various complications within the cement sheath. In this context, the present study used laponite, a synthetic layered clay, to address the issue of particles settling in ilmenite-weighted oil well cement under high pressure and high-temperature curing conditions. The investigation extended to comprehensively assessing the consequences of incorporating laponite on the cement's rheological, mechanical, and petrophysical properties. Varied concentrations of laponite were employed and compared against the base cement, devoid of laponite. A total of six high-density cement samples of 18 ppg at different concentrations of laponite were prepared under a high pressure of 3000 psi and a high temperature of 294 °F. Findings from this work revealed that an optimal laponite concentration of 0.3% by weight of cement (BWOC) appeared to be the most effective. Adding laponite to the cement led to an impressive 83% reduction in particle settling within ilmenite-weighted cement. This deduction was confirmed through the direct density variation method and NMR measurements. Moreover, the inclusion of laponite yielded favorable outcomes in the rheological aspects of oil well cement. Laponite-based cement showed a 40% reduction in plastic viscosity and a 31.5% and 14.5% increase in yield point and gel strength, respectively, compared to the base cement formulation. Mechanically, laponite had a tangible positive impact, evidenced by a 95% and 131% increase in compressive and tensile strengths, respectively and a 16% reduction in Young's modulus, all relative to the base cement sample. Significantly, laponite's role extended to pore space optimization, leading to a decline in cement porosity by 2% and a 25% reduction in permeability.

Suitability of excavated London clay as a supplementary cementitious material: mineralogy and reactivity

This study evaluated the potential of producing supplementary cementitious materials (SCMs) using London Clay excavated from construction activities of the High Speed 2 rail project. A trade-off between enhancing reactivity versus decomposition of impurities (e.g., pyrite, carbonates) present in different London Clay samples was considered in selecting the calcination temperature. The additional reactivity obtained by calcining at 800 °C is deemed to be worth the cost of the small additional process emissions from decomposition of carbonate minerals. Blended cement formulations were developed with the produced SCMs, with replacement levels of 50 and 70 wt%. The optimal gypsum dosage was found to be 1 wt%, which resulted in improved reaction kinetics at early ages. Mortars produced with these binders developed ~50 MPa compressive strength after 90 days of curing even with 70 wt% replacement, which is sufficient for potential production of low to medium strength concretes. These findings demonstrate the excellent potential of London Clays for SCM production and present a systematic approach for characterisation, processing and utilization of excavated mixed clays obtained from infrastructure projects.

Novel surface functionalization of cellulose fibers with polyurethane prepolymers in fiber cement composites: Impact on final properties and potential benefits for the production process

The objective of this research was to perform a deep exploration of cellulose polyurethane (PU) fibers used in fiber cement boards for usage in building applications. Grafting treatment was performed on cellulose fibers with PU-pre-polymers, through a synthesis method using propylene carbonate solvent medium, followed by a cleaning step. Fiber cement boards were prepared thorough cement and limestone dispersion followed by a dewatering process, to roughly mimic the Hatschek production process. The experiments confirmed that grafted cellulose fibers can present lower water absorption (∼10 %) and greater fiber preservation, when embedded in alkaline matrix. Although the mechanical performance of fiber cement composites prepared with cellulose-PU fibers were not appreciably different, superior ability to drain water from the green cement sheet was demonstrated, which can provide great benefits during the production process. It’s worth mentioning that cellulose fiber is added in the air cured fiber cement formulation as a process aid agent to retain fine aggregates, and mechanical reinforcement is mainly carried out by the synthetic fibers. From the fiber cement production perspective, the reduced water retention showed in the green sheet can be beneficial in different production processes, e.g. the Hatschek or flow-on, in two ways: First, by possibly reducing the number of stops, as a lighter green sheet would be less prone to drop from the machine, and second, due to lower vacuum applied, possibly avoiding segregation and producing more homogeneous boards.

Source of quartz cement and its impact on reservoir quality in Jurassic Shaximiao Formation in central Sichuan Basin, China

Quartz cement is an essential authigenic mineral in the tight sandstones of the Shaximiao Formation in the Sichuan Basin, China. Accurately identifying its sources and investigating its impact on reservoir quality is important for understanding diagenetic fluid evolution and pore development in these reservoirs. To address this, we conducted a systematic analysis of the silicon sources in quartz cement employing mineralogical, fluid inclusion, and geochemical data. Quartz cement is characterized by two phases of quartz overgrowth and pore-filling authigenic quartz. Homogenization temperatures of fluid inclusions range from 60 to 150 °C, indicating that quartz cementation occurred from the early diagenetic phase (B stage) to the late mesodiagenetic phase. During the early diagenetic stage, volcanic material was dissolved by meteoric water, resulting in the formation of the earliest quartz cement and smectite. At temperatures of approximately 70–100 °C, smectite illitization, accompanied by K-feldspar consumption and SiO2 precipitation. In the mesodiagenetic stage (temperature approximately 100–130 °C), organic acids led to the dissolution of minerals like feldspar and laumontite, releasing SiO2. In the deep burial stage, clastic quartz grains experienced dissolution due to high stress, providing a limited source of SiO2. Smectite alteration and the dissolution of aluminosilicate minerals represent the primary sources of silicon for quartz cementation, while contributions from volcanic material hydrolysis and pressure solution are relatively minor. The presence of chlorite films inhibits the development of quartz overgrowths, and the limited precipitation of authigenic quartz within the primary porosity has a minimal impact on reservoir quality. Consequently, sandstones rich in chlorite films represent a favorable lithology for the development of high-quality reservoirs.

Mesoporous Bioactive Glass-Incorporated Injectable Strontium-Containing Calcium Phosphate Cement Enhanced Osteoconductivity in a Critical-Sized Metaphyseal Defect in Osteoporotic Rats.

In this study, the in vitro and in vivo bone formation behavior of mesoporous bioactive glass (MBG) particles incorporated in a pasty strontium-containing calcium phosphate bone cement (pS100G10) was studied in a metaphyseal fracture-defect model in ovariectomized rats and compared to a plain pasty strontium-containing calcium phosphate bone cement (pS100) and control (empty defect) group, respectively. In vitro testing showed good cytocompatibility on human preosteoblasts and ongoing dissolution of the MBG component. Neither the released strontium nor the BMG particles from the pS100G10 had a negative influence on cell viability. Forty-five female Sprague-Dawley rats were randomly assigned to three different treatment groups: (1) pS100 (n = 15), (2) pS100G10 (n = 15), and (3) empty defect (n = 15). Twelve weeks after bilateral ovariectomy and multi-deficient diet, a 4 mm wedge-shaped fracture-defect was created at the metaphyseal area of the left femur in all animals. The originated fracture-defect was substituted with pS100 or pS100G10 or left empty. After six weeks, histomorphometrical analysis revealed a statistically significant higher bone volume/tissue volume ratio in the pS100G10 group compared to the pS100 (p = 0.03) and empty defect groups (p = 0.0001), indicating enhanced osteoconductivity with the incorporation of MBG. Immunohistochemistry revealed a significant decrease in the RANKL/OPG ratio for pS100 (p = 0.004) and pS100G10 (p = 0.003) compared to the empty defect group. pS100G10 showed a statistically higher expression of BMP-2. In addition, a statistically significant higher gene expression of alkaline phosphatase, osteoprotegerin, collagen1a1, collagen10a1 with a simultaneous decrease in RANKL, and carbonic anhydrase was seen in the pS100 and pS100G10 groups compared to the empty defect group. Mass spectrometric imaging by time-of-flight secondary ion mass spectrometry (ToF-SIMS) showed the release of Sr2+ ions from both pS100 and pS100G10, with a gradient into the interface region. ToF-SIMS imaging also revealed that resorption of the MBG particles allowed for new bone formation in cement pores. In summary, the current work shows better bone formation of the injectable pasty strontium-containing calcium phosphate bone cement with incorporated mesoporous bioactive glass compared to the bioactive-free bone cement and empty defects and can be considered for clinical application for osteopenic fracture defects in the future.

Utilization of low reactive bottom ash in cement formulation through Na2CO3 triggered pozzolanic reaction

In this study, the use of sodium carbonate anhydrous (Na2CO3) to enhance the reactivity of bottom ash (BA) in the ordinary Portland cement (OPC) system was investigated. The presence of Na2CO3 exerted an interactive effect on the hydration mechanism of the BA-OPC composite, leading to a significant enhancement in the pozzolanic reactions between BA and calcium hydroxide, following the improved silicate reactions. Consequently, remarkable improvements were observed in the mechanical properties of the BA-OPC composite with an extremely small amount of the activator. Specifically, the sample containing 0.025 % Na2CO3 exhibited the highest increase in compressive strength compared to the sample without Na2CO3, showing an improvement of 35.4 % at 7 days and 70.6 % at 28 days. Based on the proposed method, the reactivity of BA and silicate phases can be enhanced which contributes to the sustainable development of BA-OPC composite.

The effect of chlorite rims on reservoir quality in Chang 7 sandstone reservoirs in the Ordos Basin, China

Chlorite rims have been of interest to petroleum geologists over the past several decades, as a significant number of abnormal high-porosity sandstone reservoirs at great depths have been related to chlorite rims. To clarify the contribution of chlorite rims to porosity preservation in sandstones, the relationship between chlorite rims and porosity evolution in Chang 7 sandstones of the Upper Triassic Yanchang Formation in the Ordos Basin in north-central China was investigated using thin sections, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction analyses. Based on the detrital composition and diagenetic evolution pathway analyses, it was concluded that chlorite rims inhibited the formation of quartz cementation. However, in addition to quartz cementation, compaction and other cements (commonly carbonates and clays) also control the porosity evolution of sandstones. In sandstones in which porosity reduction is largely controlled by compaction or other cements, chlorite rims may have a limited effect on porosity preservation. Thus, chlorite rims can play an important role in porosity preservation only in sandstones in which quartz cementation is the main process of porosity destruction. The results of this study indicate that the development of high-porosity sandstones is often controlled by many factors, and the effects of chlorite rims on porosity preservation are not always significant.

Histological evaluation of tissue reaction and new bone formation of different calcium silicate-based cements in rats.

The purpose of this study was to evaluate the local reactions and new bone formation of rat subcutaneous and bone tissue to different calcium silicate cements. In this study, 80 rats were divided into five groups as control, BIOfactor MTA (BIO), NeoMTA Plus (NEO), MTA Repair Hp (REP), Biodentine (DENT) and then into two subgroups according to sacrification times (7, 30 days; n = 8). Polyethylene tubes filled with appropriate materials (test groups); empty tubes (control group) were implanted into the dorsum of each rat subcutaneously. For intraosseous implantation, materials were placed in the cavities created in tibia of rats. Subcutaneous tissue and tibia samples were stained with haematoxylin-eosin and subjected to histopathological analysis. A score (0-3) was used to grade inflammatory reaction and new bone formation. Data were analysed by Kruskal-Wallis and Mann-Whitney U tests (P < 0.05). Inflammatory reaction observed in subcutaneous and intraosseous tissues for 7 days decreased significantly in all groups over time (P < 0.05). It was determined that there was significant increase in new bone formation in REP, BIO, DENT groups over time (P < 0.05). Four contemporary bioceramic materials induced local inflammation and tissues changes shortly after subcutaneous implantation, which were reduced over time. In ıntraosseous implantation, all materials induced new bone formation over time. ADJ-03-23-0134. © 2023 Australian Dental Association.

Optimization of the rice husk ash production process for the manufacture of magnesium silicate hydrate cements

Different types of amorphous, silica-rich materials can be employed as supplemental cementitious materials (SCM) in Portland cement compositions that are more common. SCMs react with Ca(OH)2 in the presence of Portland cement and a water solution to create calcium silicate hydrate (C–S–H). When produced under specific circumstances, rice husk ash (RHA) contains a high concentration of amorphous silicon dioxide and is utilized as SCM in Portland cement formulations. Similar to this, materials high in amorphous silica, like RHA, encourage the production of hydrated magnesium silicate gels (M-S-H) in reactive magnesium aqueous solutions. Studies examining RHA's capacity to generate M-S-H under various temperature settings, however, are scarce. For the creation of cellulose-reinforced cementitious composites, M-S-H cements, which have superior mechanical qualities and reduced alkalinity (pH 9–10) as compared to Portland cement, are a suitable option. Because of this, the current study assesses the hydration reaction of magnesium oxide with silica produced from RHA and processed by various heat treatments (500, 550, 600, and 650 °C) to generate M-S-H. There were tests for mechanical stability, electrical conductivity, calorimetry, XRD, TG, pH, and more. As benchmarks, compositions containing MgO and commercially active silica (SF) were employed. The findings demonstrate that, in comparison to previous thermal treatments, RHA generated at 500 °C (RHA500) enabled the creation of an increased M-S-H concentration. The axial compressive strength of this composition (MgO/RHA500) in the initial phases is comparable to that of the reference composition (MgO/SF). Since the paste consisting of MgO/RHA500 had the lowest pH values at 30 days of curing, even when compared to the pH of the reference composition MgO/SF (pH 10.04), the calcination of RHA at 500 °C is also the best treatment to lower the alkalinity of the created system. The MgO/RHA500 composition's decreased alkalinity will enable the RHA generated at lower temperatures to be applied in a new way. The RHA, which is already a by-product of the agro-industrial sector with some added value, serves as a predecessor for the creation of M-S-H cement, which will promote both technical and environmental benefits for non-conventional cementitious materials.

Influence of Dosage and Modulus on Soluble Sodium Silicate for Early Strength Development of Alkali-Activated Slag Cements

In world practice, the need for high-strength concrete with an intensive gain of early strength is due to an increase in requirements for characteristics of concrete and the desire to shorten the construction period. Alkali-activated cement, based on soluble sodium silicates (SSS), can demonstrate high strength and rapid gain due to the nano-modifying effect of amorphous silica present in SSS. However, the problem with the effective use of such cement compositions is unsatisfactory short setting times. This work investigates the effect of modifying admixtures on the structure formation of alkali-activated slag cement (AASC), its physical and mechanical properties depending on characteristics of SSS and the basicity of the aluminosilicate component (precursor), which was changed by the ratio of the ordinary Portland cement (OPC) clinker and granulated blast furnace slag (GBFS). A positive synergistic effect was noticed from glycerol and trisodium phosphate, as the components of a complex admixture, to control the setting of AASC. This resulted in extending the initial setting time from 1 to 5 min to the values of 21–72 min. The compressive strength of 21–26.3 MPa by 3 h, 36.5–43.4 MPa by 1 day, and 84.7–117.1 MPa by 28 days was obtained. Proper shrinkage deformations were equal to 0.47–0.6 mm/m. It was shown that with an increase in the basicity of the aluminosilicate component, the properties of AASC increased both in the early and late stages of hardening.

Natural hydrogen in low temperature geofluids in a Precambrian granite, South Australia. Implications for hydrogen generation and movement in the upper crust

Natural hydrogen (H2) has the potential to be a low-carbon fuel and energy source, playing a crucial role in achieving a clean, secure, and affordable energy future. However, our understanding of the generation, migration, and accumulation of H2 in the subsurface remains poorly constrained. Increasing evidence suggests that H2 is abundantly and widely present in various geological settings, making them viable targets for exploration of this emerging resource. Reports have indicated the presence of hydrogen-dominated natural gas in vintage boreholes located in the Yorke Peninsula and Kangaroo Island, South Australia. These boreholes were drilled in Cambrian sedimentary cover over Precambrian terranes that host iron ore, copper or gold ore deposits. To gain insight into these occurrences, rock samples were examined from the Roxby Downs granite, a Mesoproterozoic pluton associated with the Hiltaba Suite event (1.59 Ga), belonging to the same magmatic origin as the Yorke Peninsula basement.Our investigation revealed metasomatic fluid circulation, evidenced by alteration of feldspar and mafic grains, as well as discrete cemented fractures within the granite. In some of these fracture-fill cements, we discovered water and gas inclusions containing hydrogen. The formation of the hydrogen-bearing cements occurred at paleo-temperatures ranging from 170 °C to the present-day 55 °C. Analysing the oxygen isotope values of the quartz cements and considering their fluid inclusion temperatures, a marine water signature as the source of water in equilibrium with the quartz cements was identified.To constrain the fluid history, neon and argon isotope signatures from the fluid inclusion gases were measured from the granite and separated quartz grains. Nucleogenic neon isotopes increased with depth along specific production lines. While this is consistent with long-lived fluid within the granite and increasing fluid residence with depth, separated quartz grains show less variation with depth and suggest that younger fluids were introduced, triggering alteration of less robust minerals, visible in bulk granite. Petrographic analyses identified hydrolytic alterations of mafic minerals into magnetite, and subsequently magnetite to hematite, as sources of hydrogen and contributors to the observed increase in pore water salinity. Our findings highlight that natural hydrogen can be produced and retained in granites at low temperatures, expanding beyond the commonly reported alteration processes observed in mafic and ultramafic rocks.

Reconstruction of foot and ankle defects using the vaccum sealing drainage versus the induced-membrane the elderly: A retrospective comparative study.

The purpose of this study was to compare the reconstructive outcomes of soft-tissue defects around foot and ankle with vaccum sealing drainage (VSD) or induction membrane (IM) of cement formation and attempt to provide an optimal strategy for elderly patients. A retrospective review of all continuous patients with foot and ankle reconstruction using different flaps from October of 2016 and October of 2020 was performed. Based on the different way, the patients were divided into two groups: VSD group (n = 26) and IM group (n = 27). Outcomes were assessed according to the size of the defect, frequency of debridement procedures, hospitalization time, duration of healing, the healing rate, major amputation rate, functional outcomes and complications. Immunohistochemistry (IHC) detection of vascular endothelial growth factor (VEGF) was also be completed. We found that there was no difference in demographic characteristics, size of the defect, debridement times and functional outcomes between the two groups (p > 0.05); however, a significant difference in the wound healing time, hospitalization time and complications were noted between them(p < 0.05). The fresh granulation tissue of both groups showed abundant positive expression of VEGF. Thus, the VSD and IM are both available for foot and ankle reconstruction in elderly patients. However, the IM group offers short hospitalization time, duration of healing and lower frequency of postoperative complications. Thus, we advocate the IM for reconstruction of defects of the foot and ankle region in the elderly patients.

Enhanced cement formation for well completion in gas hydrates reservoirs

Natural gas hydrates (NGHs) have abundant reserves and are greener energy source compared to petroleum resources. Intense heat release of cement slurry impacts the stability of NGHs during oil well cementing operations. Conventional low hydration-heat cement slurries significantly reduce the early-stage strength. In this paper, a novel strategy to optimize the exothermic and mechanical properties of cement slurry is proposed with the synergistic effects of various mineral admixtures and additives. The hydration heat and microstructure of cement with different admixtures were studied through isothermal calorimetry (IC), semi-adiabatic temperature test (ST), scanning electron microscopy (SEM), X-ray diffraction (XRD) and mechanical strength tests. The results indicate that the addition of nanosilica (NS) and C–S–H seeds lead to high early-stage strength for cement slurry substituted with high-volume fly ash (FA) and ground granulated blast furnace slag (GGBS), which meets the engineering performance for NGHs cementing. Compared with neat cement, blended cement designed with the new strategy has a 40.46% lower cumulative heat and a 56% higher compressive strength after 24 h. However, ST showed that the separated hydration heat rate peaks recombine together at higher temperature. The thermal storage performance of solid-solid phase change material (SSP) can effectively control the temperature rise due to cement hydration and maintain the separation of hydration heat rate peaks. This study provides novel ideas for the construction of low hydration heat and high early-stage strength cement slurry, and also provides key theoretical and methodological support for the performance control of cement slurry for NGHs cementing.

An investigation of fatigue response of well cement under cyclic loading and impact on zonal isolation performance

Cyclic bottomhole pressure fluctuation is very prevalent in modern well construction and enhanced petroleum recovery applications and poses a great challenge to annular seal integrity and successful zonal isolation, even in cases where the cement seal exhibits excellent initial quality. Thus, annular sealants must be designed to mitigate or minimize the deleterious effects of cyclic pressure fluctuations on the annular seal. Optimal cement designs for this purpose require a proper understanding of damage modes and mechanisms associated with a cyclic pressure regime, as well as the impact of the cement mechanical integrity evolution on the leakage of the cemented annulus. Using four cement formulations with distinct mechanical and microstructural properties, we investigated the mechanical integrity evolution and leakage characteristics of cemented pipe specimens subjected to confinement pressure fluctuations. Via microscopic inspection of the cement/pipe interface after pressure cycling and permeability measurements during pressure cycling, we attempted to correlate cement properties with leakage and suggest a recommendation for optimal cement design and successful zonal isolation in wellbores subjected to cyclic pressure. Test data indicate that under high enough pressure variation, interfacial cracking at the cement pipe interface is unavoidable and the cement seal's ability to maintain zonal isolation will be dependent on the microstructural morphology and microscale mechanical resilience of the cement formulation. Stiffer conventional cements also appear to have a higher chance of leakage through non-interfacial fractures than their more flexible counterparts. Latex cements show great promise for effective zonal isolation under cyclic bottomhole pressure conditions and should be studied in more detail.

Can tundish deskulling waste be used as a magnesium oxide source to develop magnesium phosphate cement?

Ordinary Portland cement (OPC) has a significant environmental impact since approximately 0.81 kg of CO2 is generated for every kilogram produced. Thus, it is mandatory to look for sustainable alternative cements. One of the most promising materials in this sense is magnesium phosphate cement (MPC). This study evaluates the possibility of revaluing a waste obtained from the tundish deskulling (TUN) as a raw material for formulating alternative MPC. This approach aims to promote the circular economy and minimizing the environmental impact of MPC. The tundish working lining is a crucial refractory material used in continuous steel casting. An optimal cement formulation was achieved by maximizing the compressive strength (CS) at 7 days, resulting in the combination of 60 wt% of TUN and 40 wt% of KH2PO4, with a water/cement (W/C) ratio of 0.27. The physical and mechanical properties were evaluated at three different stages: after 1, 7, and 28 days of curing. Furthermore, an exhaustive physicochemical characterization was conducted to investigate the feasibility of using it as an alternative cement. This study confirms the feasibility of formulating MPC using TUN as raw material due to the main product obtained, which is K-struvite. The use of TUN implies important economic savings and enhances sustainability criteria avoiding its management in landfills.

Complex Modulus characterization of an Optimized Binder with SCMs: proposition of an enhanced Cement formulation to improve Stiffness Behavior and Durability of Mortars and Concretes

Complex Modulus characterization of an Optimized Binder with SCMs: proposition of an enhanced Cement formulation to improve Stiffness Behavior and Durability of Mortars and Concretes

Study on the mechanism and controlling method for annulus pressure buildup problems in shale gas wells

The Annulus Pressure Buildup (APB) problems in shale gas wells is mainly caused by the crack at casing-cement interface. The stresses on casing-cement interface and cement-formation interface are calculated by the established model which the constrain of formation rock is considered. The elastic modulus of cement sheath has great effect on the stress on casing-cement and cement formation interface. The radial stress on interfaces changed linearly with fluid pressure. The cement rock is treated as a porous elastic material and the residual strain in cement sheath is mainly caused deformation or collapse of pore structure in the cement rock due to the large radial stress on interfaces. Ultimately, micro-annulus will be generated on the casing-cement interface due to the residual strain of cement sheath. High flexibility cement rock is proposed to decrease the radial stress on the interfaces which can reduce the residual strain of cement sheath. On the other hand, PABP is proposed to offset the decreased radial stress due to residual strain. A model for calculating the stress on interface by considering residual strain of cement sheath and PABP is established. The radial stress on the interfaces caused by PABP is quantitative calculated. The mechanism on how the method for solving APB problems in shale gas wells is clearly explained. The field application certificated the validity of method for solving the APB problems and it also proved the correctness of the calculation method.

Simulation study on the evolution of cement plug sealing capability in CO2 geological sequestration wells

CO2 geological sequestration technology injects CO2 into the target geological formation through a borehole. Usually, cement plugs are used to seal the well after finishing the injection. Ensuring the plugs' sealing capability is the focus after CO2 sequestration, which is also directly related to the final result of the sequestration. Since the cement's mechanical and poroperm behavior under corrosion has yet to be fully considered, this paper developed a 3D finite element model of the plug-formation, which considers the changes of the corrosion zone. This paper simulates the micro-annulus propagation on the bonding surface, quantifies the effects of corrosion time and corrosion environment on the propagation characterivdstics, and discusses the effects of potential changes in bonding strength and corrosion zone Poisson's ratio after corrosion on the plugs' sealing. The simulation results show that: with the increase of corrosion time, the plug is more prone to radial deformation, the micro-annulus propagation pressure decreases as a power function, and the micro-annulus axial propagation distance is longer. Compared with the liquid-phase corrosion environment, the micro-annulus is more easily propagated in the gas-phase corrosion environment, the micro-annulus aperture is larger, and the propagation distance is longer. When the bond strength and corrosion zone Poisson's ratio decrease after corrosion, the plug's sealing capability will weaken further. In CO2 sequestration wells, following the general abandonment requirements is not appropriate. Improving the cement formulation to reduce the corrosion rate, enhancing the cement's strength after corrosion, and extending the plug length will help maintain the plug's long-term sealing. This study explains the effect of CO2 chemical attack on the plug's sealing. The results have important implications for controlling the long-term sealing capability of CO2 geological sequestration wells.