The cement industry is facing numerous challenges in the 21st century due to depleting natural fuel resources, shortage of raw materials, exponentially increasing cement demand and climate linked ...environmental concerns. Every tonne of ordinary Portland cement (OPC) produced releases an equivalent amount of carbon dioxide to the atmosphere. In this regard, cement manufactured from locally available minerals and industrial wastes that can be blended with OPC as substitute, or full replacement with novel clinkers to reduce the energy requirements is strongly desirable. Reduction in energy consumption and carbon emissions during cement manufacturing can be achieved by introducing alternative cements. The potential of alternative cements as a replacement of conventional OPC can only be fully realized through detailed investigation of binder properties with modern technologies. Seven prominent alternative cement types are considered in this study and their current position compared to OPC has been discussed. The study provides a comprehensive analysis of options for future cements, and an up-to-date summary of the different alternative fuels and binders that can be used in cement production to mitigate carbon dioxide emissions. In addition, the practicalities and benefits of producing the low-cost materials to meet the increasing cement demand are discussed.
There are two main models of alkali-activated cements, one is the case of the activation of slag (Si
+
Ca) and the other is activation of metakaolin (Si
+
Al). This paper reviews current knowledge ...about the comparison between alkali-activated slag (Si
+
Ca) and metakaolin (Si
+
Al) cements, including the general properties of slag and metakaolin, hydration products reaction mechanisms, and the role of Ca and Al.
The water industry is facing increasing pressure to replace or renovate aging asbestos cement (AC) pipes due to rising failure rates. While AC pipes have been used since the 1930s, many have already ...exceeded their expected service life. As AC pipe testing requires specialized and certified laboratories due to hazardous friable asbestos material, this paper investigates the potential of using fiber-reinforced cement (FRC) pipes, with cellulose fibers as a substitute for asbestos fibers, as a simulant for deteriorated AC pipes. Material property tests, burst tests, and bend tests were conducted to assess the performance of FRC pipes. Test results revealed that the performance of FRC pipes tested ranged from 20% to 54% of that of AC pipes, as per industry standard minimum values. This provides an excellent case for FRC pipes to be used as a deteriorated AC pipe simulant. In addition, an FRC pipe lined with cured-in-place pipe (CIPP), as an example of a renovation technique for deteriorated AC pipes, was tested under 4-point bending. The findings suggest that FRC pipes can serve as a reliable alternative to deteriorated AC pipes for laboratory testing purposes, and CIPP lining could potentially extend the life of deteriorated AC pipes.
► 15 tropical wood species were examined for manufacturing cementitious composites. ► Paper determined key parameters for hydration and bonding of 15 species with OPC. ► Low molecular weight ...carbohydrates varied considerably among 15 tropical species. ► Compatibility factor of wood-OPC decreased with the increase of solubility content. ► Extracting in H2O, CaCl2, MeO and Ca(OH)2 significantly increased the compatibility.
Compatibility and hydration of Ordinary Portland Cement (OPC) with 15 commercially available tropical wood species were investigated by studying the heat release during cement hydration in various wood species, chemical compositions and microstructure of the hydrated products, and the effects of various solution treatments of wood particles on the compatibility of wood-OPC composites. It was found that (1) low molecular weight carbohydrates and hemicelluloses directly contributed to the inhibition of hydration of cement in wood–cement composites; (2) wood–cement compatibility reduced as the wood content of the mixture increased but the rate of change varying considerably from one to another species; (3) overall ranking order of the wood–cement compatibility at 5% by weight wood content was mouvingui>nkanang>ngollon>sapel>tali>padouk>bibolo>ayous>eyong>frake>bête>bilinga>doussie>iroko>moabi, with movingui having an average compatibility factor 96% even the wood content is greater than 5% while doussie reaching a compatibility factor only 7.7% at 1.8% by weight wood content; (4) X-ray diffractogram analysis indicated that the presence of Ca(OH)2 reduced by 50% for the hydration product in wood–cement composites compared to that in pure cement paste, suggesting the change of structure of hydrated products due to inhibition of wood; (5) wood–cement compatibility was improved significantly by pre-treating wood in solutions with the saturated lime (Ca(OH)2) solution being most efficient and CaCl2 least efficient; and (6) the untreated wood inhibited cement setting by dissolving extractives shortly after the dormant period. The findings of this study provide fundamental and essential database and technologies for exploiting tropical wood species and correctly utilising the 15 tropical wood species with cement as value added commercial products in construction.
Objectives: The aim of this study was to evaluate the amount of the residual cement excess after cementation and cleaning of implant‐supported restorations with various positions of the margins.
...Material and methods: Twenty‐five casts with embedded implant analogs and flexible soft‐tissue imitation were used in the study. Individual abutments with different position of the margin – from 1 mm supragingivally to 3 mm below the gingival level – were modelled and divided equally into five groups. The same amount of polished metal crowns was luted to prosthetic abutments, excess cement was cleaned and the restorations were removed for evaluation of the undetected cement remnants. All quadrants of each specimen were photographed for calculation of the ratio between the cement remnants area and the total specimen area using Adobe Photoshop. Afterwards, cement remnants were cleared from each specimen and weighed with analytical balances.
Results: The measurements in all the groups consisted of (1) the relation between the cement remnants area and the total area of the specimen; and (2) cement excess weight in grams after cleaning: group 1 (0.0111 ± 0.021; 0.0003 ± 0.0001 g); group 2 (0.0165 ± 0.019; 0.0008 ± 0.0003 g); group 3 (0.0572 ± 0.028; 0.0013 ± 0.0005 g); group 4 (0.1158 ± 0.054; 0.0051 ± 0.0013 g); and group 5 (0.1171 ± 0.059; 0.0063 ± 0.0021 g). Results showed significant increase of undetected cement quantity, as the restoration margins were located deeper subgingivally, using weighting (P=0) and calculation of proportion (P=0). There was a significant correlation between evaluation techniques (r=0.889; P=0).
Conclusions: The amount of residual cement after cleaning increased as the restoration margins were located more subgingivally.
To cite this article:
Linkevicius T, Vindasiute E, Puisys A, Peciuliene, V. The influence of margin location on the amount of undetected cement excess after delivery of cement‐retained implant restorations. Clin. Oral Impl. Res. xx, 2011; 000–000.
Recent materials developed and applied for repairing, strengthening, and refining the performance of various structural elements are high-performance fiber-reinforced cement composites (HPFRCCs). ...These materials exhibit appropriate strain-hardening behavior when subjected to tensile loading. Currently, an apparent need is felt for these construction materials in all the world’s countries. The fibers used in HPFRCCs are primarily polyvinyl alcohol (PVA), polyethylene (PE), and high-tenacity polypropylene (HTPP) fibers. Due to the high cost and unavailability of the mentioned fibers, it is not possible to make HPFRCC in many parts of the world. The aim of this study is to achieve HPFRCC constructed from locally accessible ingredients and substances with proper mechanical properties, specifically increasing the tensile strain capacity and being consistent with the environment. For this purpose, 18 mixtures were examined in such a way that the written mix designs included various cases of cement type (ordinary portland cement, limestone calcined clay cement), filler type (silica sand, limestone powder, and their mixture), amount (in two ratio percentages of 0.5 and 1 concerning binders), and cases of water to solid ingredient ratios (0.2, 0.25, 0.3, 0.35, 0.4). The applied fiber in this article was ordinary polypropylene fiber, and in order to investigate the mechanical behavior of the studied mix compositions, compressive strength, direct tensile strength, a three-point bending test, and a scanning electron microscope (SEM) were used. Also, to assess the sustainability of mix designs, material sustainability indicators (MSI) were approved from the perspective of embodied energy and carbon footprint. Finally, it is shown that using local ingredients and ordinary polypropylene fiber, a green composite with a tensile strain capacity of 3.7% is possible. Moreover, replacing ordinary portland cement (OPC) with limestone calcined clay cement (LC3) in mixtures will decrease the compressive strength on average by 20%, increase the tensile strain capacity by 54%, reduce the production of carbon dioxide gas by 34%, reduce energy consumption by 18%, and increase the price by 4%.
This study attempts to correlate the total amount of chloride bound in concrete with the amounts bound by different hydration products. New insights in the quantities of the hydration products formed ...will be used in order to predict the phase assemblage of hardened cement pastes. The two main chloride binding mechanisms are considered - through physical adsorption and through chemical reactions. Chloride binding isotherms are used, taking into account the external chloride concentration and the quantity of each hydration product formed. A distinction is made between the chloride binding capacities of monosulfate and hydroxy-AFm. Two new models for the maximum chloride binding ability of a hardened cement paste are proposed - a basic one, using only AFm and C-S-H isotherms, and an extended one which also considers the ability of portlandite and Friedel's salt to physically adsorb chlorides. Results obtained using these models are within 10% of collected experimental data.
Under the strategies of low-carbon and environmental protection, promoting green technology innovation to achieve carbon neutrality in the construction field has become a universal goal. As the ...building material with the highest consumption, concrete has gradually begun to transform into a multi-functional and intelligent product. Therefore, the research on carbon fiber-reinforced cement-based composites (CFRCs) is of relative interest. It mainly uses carbon fibers (CFs) with high elasticity, strength, and conductivity to disperse evenly into the concrete as a functional filler, to achieve the intelligent integration of concrete structures and function innovatively. Furthermore, the electrical conductivity of CFRC is not only related to the content of CFs and environmental factors but also largely depends on the uniform dispersion and the interfacial bonding strength of CFs in cement paste. This work systematically presents a review of the current research status of the enhancement and modification mechanism of CFRC and the evaluation methods of CF dispersion. Moreover, it further discusses the improvement effects of different strengthening mechanisms on the mechanical properties, durability, and smart properties (thermoelectric effect, electrothermal effect, strain-sensitive effect) of CFRC, as well as the application feasibility of CFRC in structural real-time health monitoring, thermal energy harvesting, intelligent deformation adjustment, and other fields. Furthermore, this paper summarizes the problems and challenges faced in the efficient and large-scale applications of CFRCs in civil engineering structures, and accordingly promotes some proposals for future research.
This paper presents the results of research into the heat of hydration and activation energy of calcium sulphoaluminate (CSA) cement in terms of the dependence on curing temperature and water/cement ...ratio. Cement pastes with water/cement ratios in the range of 0.3–0.6 were tested by isothermal calorimetry at 20 °C, 35 °C and 50 °C, with the evolved hydration heat and its rate monitored for 168 h from mixing water with cement. Reference pastes with ordinary Portland cement (OPC) were also tested in the same range. The apparent activation energy of CSA and OPC was determined based on the results of the measurements. CSA pastes exhibited complex thermal behaviour that differed significantly from the thermal behaviour of ordinary Portland cement. The results show that both the w/c ratio and elevated temperature have a meaningful effect on the heat emission and the hydration process of CSA cement pastes. The determined apparent activation energy of CSA revealed its substantial variability and dependence, both on the w/c ratio and the curing temperature.
CO2 regulation and raw material availability will strongly influence the future cement market and a wider use of composite cements containing limestone and pozzolan or slag is expected.
In the ...present paper, the possibility to combine Portland cements (PCs) with reduced clinker factor with sulfoaluminate cement (CSA), is explored. Low Portland clinker cements are prepared in laboratory using different supplementary cementitious materials (limestone, slag, pozzolan and fly ash) and mixed with a sulfoaluminate cement: the hydration behavior of the resulting binders is investigated up to 90 days through a multi-technique approach involving X-ray diffraction, differential scanning calorimetry and nuclear magnetic resonance spectroscopy. Understanding the interaction mechanisms between SCMs and CSA/PC blends will support the development of innovative high performing binders based on CEM III or CEM V, or even on new standardized CEM II. Results highlight that slag is particularly suitable promoting late strength development.
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