A fluid flow perspective on the diagenesis of Te Aute limestones

Pliocene cool-water, bioclastic Te Aute limestones in East Coast Basin, New Zealand, accumulated either in shelfal shoal areas or about structurally shallow growth fold structures in the tectonically active accretionary forearc prism. Up to five stages of carbonate cementation are recognised, based on cement sequence-stratigraphic concepts, that formed on the seafloor during exposure of the limestones before burial, during burial, uplift, and deformation. Two principal fluid types are identified--topography-driven meteoric fluids and compaction-driven fluids. We have developed conceptual and quantitative models that attempt to relate the physical characteristics of fluid flow to the cement paragenesis. In particular, we have simulated the effects of uplift of the axial ranges bordering East Coast Basin in terms of the degree of penetration of a meteoric wedge into the basin. The dynamics of meteoric flow changed dramatically during uplift over the last 2 m.y. such that the modelled extent of the meteoric wedge is at least 40 km across the basin, and the penetration depth 1500 m or more corresponding with measured freshwater intersections in some oil wells. Cement-fluid relationships include: (1) true marine cements that precipitated in areas remote from shallow freshwater lenses; (2) pre-compaction cements that formed in shallow freshwater lenses beneath limestone "islands"; (3) post-compaction cements derived from compaction-driven flow during burial; (4) early uplift-related fracture-fill cements formed during deformation of the accretionary prism and uplift of the axial ranges; and (5) late uplift-related cements associated with uplift into a shallow meteoric regime

Retention Of Long-Term Interim Restorations With Sodium Fluoride Enriched Interim Cement

Purpose: Interim fixed dental prostheses, or provisional restorations , are fabricated to restore teeth when definitive prostheses are made indirectly. Patients undergoing extensive prosthodontic treatment frequently require provisionalization for several months or years. The ideal interim cement would retain the restoration for as long as needed and still allow for ease of removal. It would also avoid recurrent caries by preventing demineralization of tooth structure. This study aims to determine if adding sodium fluoride varnish to interim cement may assist in the retention of interim restorations. Materials and methods: stainless steel dies representing a crown preparation were fabricated. Provisional crowns were milled for the dies using CAD/CAM technology. Crowns were provisionally cemented onto the dies using TempBond NE and NexTemp provisional cements as well as a mixture of TempBond NE and Duraphat fluoride varnish. Samples were stored for 24h then tested or thermocycled for 2500 or 5000 cycles before being tested. Retentive strength of each cement was recorded using a universal testing machine. Results: TempBond NE and NexTemp cements performed similarly when tested after 24h. The addition of Duraphat significantly decreased the retention when added to TempBond NE. NexTemp cement had high variability in retention over all tested time periods. Thermocycling for 2500 and 5000 cycles significantly decreased the retention of all cements. Conclusions: The addition of Duraphat fluoride varnish significantly decreased the retention of TempBond NE and is therefore not recommended for clinical use. Thermocycling significantly reduced the retention of TempBond NE and NexTemp. This may suggest that use of these cements for three months, as simulated in this study, is not recommended

Residual capability of alkali binding by hydrated pozzolanic cements in long-service concrete structures

An experimental procedure was developed and applied to cement pastes made with two different pozzolanic cements (CEM IV/B (P) and CEM IV/B (V)) in order to ascertain the existence of a residual capability of alkali binding by long-term hydrated pozzolanic cements and, at the same time, to evaluate the alkali retention capability and the concentration of OH- ions in the pore solution of such cementitious matrices. The developed procedure consisted of accelerated curing of cement paste specimens (150 days at 60°C and 100% RH), subsequent leaching tests at 60°C for 30 days by using deionized water or basic solutions (NaOH or KOH at different concentrations) as leaching media, and correlation of the leaching test results with a simple mass balance equation for sodium and potassium ions. The developed procedure was found to be appropriate for evaluating both the pore liquid alkalinity and the alkali retention capability by long-term hydrated pozzolanic cement pastes. A residual capability of alkali binding was also identified for both tested pozzolanic cements, thus indicating their potential ability to prevent (CEM IV/B (V)) or minimize (CEM IV/B (P)) the risk of deleterious expansion associated to alkali-aggregate reaction in long-service concrete structures, like concrete dams

Quality of type I Portland cement from Ghana and UK

Type I Portland cement is general purpose cement found in many countries and it is manufactured by different companies. This study sought to compare the properties of Type I Portland cements from Ghana (less economically developed country) and United Kingdom (more economically developed country) to ascertain whether the quality of Ghana cement is a contributing factor for recent spate of building collapse in the country. The study adopted a laboratory-based experimental approach to determine the properties of three cement samples: one from Ghana and two from the United Kingdom (UK). It was identified that UK cements particles were the fineness, contained more Calcium oxide (CaO), recorded earlier setting times and achieved early strength. Ghana cement on the other hand, had more Alkali (Na2O + K2O) content, higher density, good resistance to water and achieved better late strength development than UK grey cement. The study has revealed that although there are some differences in the properties of Ghana and UK Type I Portland cements, they all meet international standard requirements and therefore, the quality of Ghana cement may not be one of the contributing factors of recent building collapse in the country

Calcium carbonate-calcium phosphate mixed cement compositions for bone reconstruction

The feasibility of making calcium carbonate-calcium phosphate (CaCO3-CaP) mixed cements, comprising at least 40 % (w/w) CaCO3 in the dry powder ingredients, has been demonstrated. Several original cement compositions were obtained by mixing metastable crystalline calcium carbonate phases with metastable amorphous or crystalline calcium phosphate powders in aqueous medium. The cements set within at most 1 hour at 37°C in atmosphere saturated with water. The hardened cement is microporous and exhibits weak compressive strength. The setting reaction appeared to be essentially related to the formation of a highly carbonated nanocrystalline apatite phase by reaction of the mestastable CaP phase with part or almost all of the metastable CaCO3 phase. The recrystallization of metastable CaP varieties led to a final cement consisting of a highly carbonated poorly crystalline apatite (PCA) analogous to bone mineral associated with various amounts of vaterite and/or aragonite. The presence of controlled amounts of CaCO3 with a higher solubility than the apatite formed in the well-developed calcium phosphate cements might be of interest to increase resorption rates in biomedical cement and favor its replacement by bone tissue. Cytotoxicity testing revealed excellent cytocompatibility of CaCO3-CaP mixed cement compositions

Clinkering of calcium sulfoaluminate clinkers: polymorphism of ye'elimite

The manufacture of CSA cements is more environmentally friendly than that of OPC as it releases less CO2. This reduction depends on CSA composition and is due to three factors: i) less emissions from decarbonation in the kilns; ii) lower clinkering temperature, consequently less fuel is needed, and iii) it is easier to grind, implying a depletion in indirect emissions. CSA cements are prepared by mixing the clinker with different amounts of calcium sulfate as a set regulator. Their main performances are fast setting time (followed by a rapid hardening), good chemical resistance and, depending on the amount of the added sulfate source they can work as shrinkage controllers. CSA cements present a wide range of phase assemblages, but all of them contain over 50 wt% of ye'elimite (C4A3s) jointly with belite (C2S), tetracalcium aluminoferrite (C4AF) and other minor components such as CA, Cs, CsH2 and so on [1]. Ye'elimite is also included (~25 wt%) in BYF (Belite- Ye'elimite-Ferrite) or BAY (Belite-Alite-Ye'elimite) clinkers. Ye'elimite has a sodalite type structure with general composition, M4[T6O12]X. Stoichiometric ye'elimite crystal structure at room temperature will be described in detailed. The role of different amounts of minor elements on the synthetic procedure and crystal structures will be also presented [2,3]. This keynote will be also focused on a revision of the effect of raw materials on the mineralogical composition of CSA, BYF and BAY. Specifically, the role of main elements contents in the ye'elimite formation in these systems will be described. Moreover, the effect of minor elements on the polymorphism of both ye'elimite and belite, especially on BYF and BAY clinkers, will be presented [4,5,6].Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Spanish MINECO and FEDER [BIA2017-82391-R] research project and I3 [IEDI-2016-0079] program

Strontium-loaded mineral bone cements as sustained release systems : Compositions, release properties, and effects on human osteoprogenitor cells

This study aims to evaluate in vitro the release properties and biological behavior of original compositions of strontium (Sr)-loaded bone mineral cements. Strontium was introduced into vaterite CaCO3-dicalcium phosphate dihydrate cement via two routes: as SrCO3 in the solid phase (SrS cements), and as SrCl2 dissolved in the liquid phase (SrL cements), leading to different cement compositions after setting. Complementary analytical techniques implemented to thoroughly investigate the release/dissolution mechanism of Sr-loaded cements at pH 7.4 and 37°C during 3 weeks revealed a sustained release of Sr and a centripetal dissolution of the more soluble phase (vaterite) limited by a diffusion process. In all cases, the initial burst of the Ca and Sr release (highest for the SrL cements) that occurred over 48 h did not have a significant effect on the expression of bone markers (alkaline phosphatase, osteocalcin), the levels of which remained overexpressed after 15 days of culture with human osteoprogenitor (HOP) cells. At the same time, proliferation of HOP cells was significantly higher on SrS cements. Interestingly, this study shows that we can optimize the sustained release of Sr2þ, the cement biodegradation and biological activity by controlling the route of introduction of strontium in the cement paste

Efficacy of the Biomaterials 3 wt%-nanostrontium-hydroxyapatite-enhanced Calcium Phosphate Cement (nanoSr-CPC) and nanoSr-CPC-incorporated Simvastatin-loaded Poly(lactic-co-glycolic-acid) Microspheres in Osteogenesis Improvement

Aims The purpose of this multi-phase explorative in vivo animal/surgical and in vitro multi-test experimental study was to (1) create a 3 wt%-nanostrontium hydroxyapatite-enhanced calcium phosphate cement (Sr-HA/CPC) for increasing bone formation and (2) creating a simvastatin-loaded poly(lactic-co-glycolic acid) (SIM-loaded PLGA) microspheres plus CPC composite (SIM-loaded PLGA + nanostrontium-CPC). The third goal was the extensive assessment of multiple in vitro and in vivo characteristics of the above experimental explorative products in vitro and in vivo (animal and surgical studies). Methods and results pertaining to Sr-HA/CPC Physical and chemical properties of the prepared Sr-HA/CPC were evaluated. MTT assay and alkaline phosphatase activities, and radiological and histological examinations of Sr-HA/CPC, CPC and negative control were compared. X-ray diffraction (XRD) indicated that crystallinity of the prepared cement increased by increasing the powder-to-liquid ratio. Incorporation of Sr-HA into CPC increased MTT assay (biocompatibility) and ALP activity (P \u3c 0.05). Histomorphometry showed greater bone formation after 4 weeks, after implantation of Sr-HA/CPC in 10 rats compared to implantations of CPC or empty defects in the same rats (n = 30, ANOVA P \u3c 0.05). Methods and results pertaining to SIM-loaded PLGA microspheres + nanostrontium-CPC composite After SEM assessment, the produced composite of microspheres and enhanced CPC were implanted for 8 weeks in 10 rabbits, along with positive and negative controls, enhanced CPC, and enhanced CPC plus SIM (n = 50). In the control group, only a small amount of bone had been regenerated (localized at the boundary of the defect); whereas, other groups showed new bone formation within and around the materials. A significant difference was found in the osteogenesis induced by the groups sham control (16.96 ± 1.01), bone materials (32.28 ± 4.03), nanostrontium-CPC (24.84 ± 2.6), nanostrontium-CPC-simvastatin (40.12 ± 3.29), and SIM-loaded PLGA + nanostrontium-CPC (44.8 ± 6.45) (ANOVA P \u3c 0.001). All the pairwise comparisons were significant (Tukey P \u3c 0.01), except that of nanostrontium-CPC-simvastatin and SIM-loaded PLGA + nanostrontium-CPC. This confirmed the efficacy of the SIM-loaded PLGA + nanostrontium-CPC composite, and its superiority over all materials except SIM-containing nanostrontium-CPC