Most concrete produced today includes either chemical additions to the cement, chemical admixtures in the concrete, or both. These chemicals alter a number of properties of cementitious systems, ...including hydration behavior, and it has been long understood by practitioners that these systems can differ widely in response to such chemicals.
In this paper the impact on hydration of several classes of chemicals is reviewed with an emphasis on the current understanding of interactions with cement chemistry. These include setting retarders, accelerators, and water reducing dispersants. The ability of the chemicals to alter the aluminate–sulfate balance of cementitious systems is discussed with a focus on the impact on silicate hydration. As a key example of this complex interaction, unusual behavior sometimes observed in systems containing high calcium fly ash is highlighted.
Supplementary cementitious materials are considered a viable and affordable way to reduce CO
emissions from the cement industry's perspective since they can partially or nearly entirely replace ...ordinary Portland cement (OPC). This study compared the impact of adding spent coffee grounds (SCGs), fly ash (FA), and volcanic ash (VA) to two types of cement: OPC and calcium sulfoaluminate cement (CSA). Cement samples were characterized using compressive strength measurements (up to 210 days of curing), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), attenuated total reflection infrared spectroscopy, and hydration temperature measurements. In all the studied systems, the presence of SCGs reduced compressive strength and delayed the hydration process. CSA composite cement containing 3.5% SCGs, 30% FA, and 30% VA showed compressive strength values of 20.4 MPa and 20.3 MPa, respectively, meeting the minimum requirement for non-structural applications. Additionally, the results indicate a formation of cementitious gel, calcium silicate hydrate (C-S-H) in the OPC-based composite cements, and calcium alumino-silicate hydrate (C-A-S-H) as well as ettringite in the CSA-based composite cements.
The cement sub-sector consumes approximately 12–15% of total industrial energy use. Therefore, a state of art review on the energy use and savings is necessary to identify energy wastage so that ...necessary measures could be implemented to reduce energy consumption in this sub-sector. In this paper energy use at different sections of cement industries, specific energy consumption, types of energy use, details of cement manufacturing processes, various energy savings measures were reviewed and presented. Various energy savings measures were critically analyzed considering amount of energy that can be saved along with the implementation cost. Amount of CO
2 reduction has been presented along with the payback period for different energy savings measures as well.
This study complied a comprehensive literature on the cement industries in terms of Thesis (MS and PhD), peer reviewed journals papers, conference proceedings, books, reports, websites. It has been observed that China producing major share of global cement production. Coal contribute major share of fuel used in cement industries. However, along with conventional fuels, industries are moving towards the use of alternative fuels to reduce environmental pollution. It was reported that cement industries are moving from wet process to dry process as it consume less energy compared to wet process.
Portland cement is one of the principal constituents used as a building material and is responsible for high energy consumption and greenhouse gas (GHG) emissions. Any attempt to reduce cement usage ...would make savings in energy usage and GHG emissions. A case study of Portland cement (CEM-I) replacement using alkali activated soil filter cake as a geopolymer mortar is presented to demonstrate application of a three-stage GHG emission estimation and comparison methodology using a process-based life cycle assessment (LCA) study, with a focus on benchmarking environmental sustainability. Results indicate that the alkali activated soil filter cake reduced total GHG emissions by 31% compared with CEM-I, which equates to 110 kgCO2-eq/m3. Transportation by rail was found to be more sustainable compared with by road, with an overall higher GHG emission reduction of between 5 and 10%. For road transport, heavy goods vehicles (HGV) of between 3.5t and 5.7t recorded the highest GHG emissions whilst articulated lorries recorded the lowest GHG emissions. Furthermore, the results also demonstrated that a bulk carrier is the most environmentally sustainable option for overseas raw material transportation. Monte-Carlo simulations signified the likelihood of achieving lowered GHG emissions when considering commercial production and inventory changes across different countries varies from 18% to 71%. These results highlight the importance of critical analysis of several factors which contribute towards overall environmental sustainability, prior to decision making on sustainable materials. Further research is encouraged on developing processes and methodologies to prioritize selection of sustainable materials to optimize sustainable benefits.
•Addition of alkali activators accounts for 79.13% of the total carbon emissions.•A reduction of 388.85 kgCO2-eq/m3 was achieved through cement replacement.•Europe and USA showed higher likelihoods of achieving carbon savings.•Rail is more sustainable as compared to road for local material transportation.•Using larger ships can potentially lead to carbon emission savings.
The calcium silicate hydrates Richardson, I.G.
Cement and concrete research,
02/2008, Letnik:
38, Številka:
2
Journal Article, Conference Proceeding
Recenzirano
This article is concerned with the calcium silicate hydrates, including crystalline minerals and the extremely variable and poorly ordered phase (C-S-H) that is the main binding phase in most ...concrete. Up-to-date composition and crystal-structure information is tabulated for the most important crystalline calcium (alumino) silicate hydrates and related phases. A number of models for the nanostructure of C-S-H are summarized and compared and it is shown that there is much more of a consensus than might seem apparent at first sight. The value of the recently solved structures of 1.4 nm tobermorite and jennite, together with those of jaffeite and metajennite, for visualizing the nanostructural elements present in the models is demonstrated. The importance of Hal Taylor's contribution to the solution of the structure of jennite is highlighted. The applicability of Richardson and Groves' model is demonstrated using experimental composition-structure observations on the nature of C-S-H in a Portland cement-fly ash blend.
Aim
To assess the extent of gaps between root dentine and titanium or fibreglass post restorations following cementation with a self‐adhesive resin cement.
Methodology
Fourteen root filled maxillary ...central incisors restored with prefabricated posts made of Fibreglass (n = 7) or Titanium (n = 7) and cemented with RelyX Unicem 2 were imaged by rapid, high‐resolution phase contrast‐enhanced micro‐CT (PCE‐CT) in a synchrotron X‐ray imaging facility (ID19, ESRF, 34 KeV, 0.65 µm pixel resolution). Reconstructions were used to measure canal, cement and post perimeters and cross‐sectional areas and interfacial gaps at 0.1 mm increments in the root canal space, along the cervical region of the tooth. Remnants of endodontic sealer (AH Plus), when present, were also quantified. Mann–Whitney and 2‐way ANOVA tests were used to compare findings within slices and between the two post groups. Pearson correlation coefficients (r) were determined between the interfacial gaps and the other measured parameters.
Results
Clearly detectable gaps were found in 45% (±14%) of the interfaces between dentine and cement, along the canal in the cervical area of the tooth beneath the core. The length of interfacial gaps was moderately correlated to the canal cross‐sectional area, to the canal perimeter and to the canal area filled by cement (R = 0.52 ~ 0.55, P < 0.001). There was no significant difference between samples with fibreglass or titanium (P > 0.01). Both post types had defect‐free interfaces with cement. Endodontic sealer remnants were found on ~10% of the canal walls and were moderately correlated to the presence of gaps. Approximately 30% of the sealer‐affected interfaces exhibited no detachment between dentine, sealer and cement.
Conclusions
Self‐adhesive cements had interfacial gaps along substantial regions of the root canal surface, which was not correlated with the amount of cement in the canal. PCE‐CT proved to be an excellent non‐destructive method to study root canal restorations of hydrated samples in 3D.
This study aims to investigate the possibility of using Linz-Donawitz (LD) slag as one of the cementitious materials for preparation of composite slag (having 8 and 15% LD slag), which will ...subsequently be used for manufacturing portland slag cement (PSC). PSC samples (having overall 4 to 9% LD slag) were prepared using LD slag from two sources in a laboratory ball mill. PSC samples were analyzed for various chemical characteristics and physical properties. Studies were conducted on concrete mixtures prepared at water-cement ratios (w/c) of 0.65 and 0.40. Fresh, hardened, and durability properties of concrete mixtures prepared using PSCs made with composite slag having up to 15% LD slag were found to be comparable to their corresponding control mixtures. Based on results, it was observed that composite slag having LD slag up to 15% of total slag can be used up to 60% for manufacturing PSC along with clinker and gypsum. The 3-, 7-, and 28-day compressive strength of PSC samples containing LD slags in different proportions were found to be comparable to control PSC samples and meeting the requirements of IS 455:2015. Even though the free lime content in LD slags was significantly higher (free lime content of 3.03 and 3.48%) in comparison to granulated blast-furnace slag (GBFS), it had almost a negligible effect on the PSC prepared using LD slag and soundness of experimental and control PSC was comparable because the maximum amount of LD slag added in overall PSC was restricted to 9%. The addition of LD slag in different proportions up to 9% in overall PSC does not seem to have any detrimental effect on performance of concrete in terms of sorptivity, carbonation depth, chloride penetration, and diffusion, which indicates its suitability for application in reinforced concrete structures. Keywords: composite slag; durability; granulated blast-furnace slag (GBFS); Linz-Donawitz (LD) slag; portland slag cement (PSC).
The present research compared the behaviours of lightweight mortars based on ordinary Portland cement (OPC), calcium sulphoaluminate cement (CSAC), and calcium aluminate cement (CAC) containing ...expanded perlite and subjected to elevated temperatures. The perlite substituted natural sand in amounts of 25, 50, 75, and 100% by volume. The mortars were subjected to heating at up to 300 °C, 650 °C, and 1000 °C at a rate of 20 °C/min. The consistency and density of fresh mortars, compressive strength and density of hardened mortars after heating and cooling, and absorbability were assessed. Such a holistic testing approach is the main novelty of this research, which is related to the aforementioned mixtures and elevated temperatures. The main contribution of this article is a comparison of various cement types coupled with variations in the level of sand replacement with expanded perlite. In previous studies, comparisons were made in pairs of OPC-CSAC and OPC-CAC for normal-weight concrete. There is a gap in our knowledge of triple comparisons and lightweight cement composites which is filled by the current study. The use of OPC at up to 650 °C is recommended because it is the most common solution, its performance is similar to that of CAC, and it is cheaper than other solutions. Above 650 °C and up to 1000 °C, CAC is the only solution because it performs better than other cements. CSAC is not suitable for use at elevated temperatures because of its poor strength performance, even if it is the best solution from an environmental point of view. Sand replacement with perlite does not increase the strength performance under elevated temperatures, but its efficiency is different for various types of cement.
Stability in the system CaO–Al2O3–H2O Lothenbach, Barbara; Pelletier-Chaignat, Laure; Winnefeld, Frank
Cement and concrete research,
12/2012, Letnik:
42, Številka:
12
Journal Article
Recenzirano
The solubility of AH3, CAH10, C2AH7.5, and C3AH6 was determined experimentally at 7 to 40°C and up to 570days. During the reaction of CA, at 20°C and above initially C2AH7.5 formed which was unstable ...in the long-term. The solubility products calculated indicate that the solubilities of CAH10, C2AH7.5 and C4AH19 increase with temperature while the solubility of C3AH6 decreases. Thus at temperatures above 20°C, C3AH6 is stable, while at lower temperature also CAH10 and C4AH19 are stable, depending on the C/A ratio.
At early hydration times, CAH10 can be stable initially at 30°C and above, as the formation of amorphous AH3 stabilises CAH10 with respect to C3AH6+2AH3. With time, as the solubility AH3 decreases due to the formation of microcrystalline AH3, CAH10 becomes unstable at 20°C and above.
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