Cagla Meral

Bio: Cagla Meral is an academic researcher from Middle East Technical University. The author has contributed to research in topics: Pozzolan & Portland cement. The author has an hindex of 13, co-authored 16 publications receiving 1032 citations. Previous affiliations of Cagla Meral include University of California, Berkeley.

Mechanical properties, durability, and life-cycle assessment of self-consolidating concrete mixtures made with blended portland cements containing fly ash and limestone powder

Abstract: This paper reports the composition and properties of highly flowable self-consolidating concrete (SCC) mixtures made of high proportions of cement replacement materials such as fly ash and pulverized limestone instead of high dosage of a plasticizing agent or viscosity-modifying chemical admixtures. Self-consolidating concrete mixtures are being increasingly used for the construction of highly reinforced complex concrete elements and for massive concrete structures such as dams and thick foundation. In this study, by varying the proportion of portland cement (OPC), Class F-fly ash (F), and limestone powder (L), SCC mixtures with different strength values were produced, and the properties of both fresh and hardened concrete were determined. For a comprehensive analysis and quantification of emissions and global warming potential (GWP) from concrete production, life-cycle assessment (LCA) was employed. We find that high volume, up to 55% by weight replacement of OPC with F, or F and L produces highly workable concrete that has high 28-day and 365-day strength, and extremely high to very high resistance to chloride penetration along with low GWP for concrete production.

High-volume natural volcanic pozzolan and limestone powder as partial replacements for portland cement in self-compacting and sustainable concrete

Abstract: A laboratory study demonstrates that high volume, 45% by mass replacement of portland cement (OPC) with 30% finely-ground basaltic ash from Saudi Arabia (NP) and 15% limestone powder (LS) produces concrete with good workability, high 28-day compressive strength (39 MPa), excellent one year strength (57 MPa), and very high resistance to chloride penetration. Conventional OPC is produced by intergrinding 95% portland clinker and 5% gypsum, and its clinker factor (CF) thus equals 0.95. With 30% NP and 15% LS portland clinker replacement, the CF of the blended ternary PC equals 0.52 so that 48% CO2 emissions could be avoided, while enhancing strength development and durability in the resulting self-compacting concrete (SCC). Petrographic and scanning electron microscopy (SEM) investigations of the crushed NP and finely-ground NP in the concretes provide new insights into the heterogeneous fine-scale cementitious hydration products associated with basaltic ash-portland cement reactions.

Use of perlite as a pozzolanic addition in producing blended cements

Abstract: There are ∼6700 million tons of perlite reserves in the world and two thirds of this amount takes place in Turkey. Although perlite possesses pozzolanic properties, it has not been so far used in producing blended cements. This study focuses on the use of natural perlites in blended cement production. For this purpose, after examining the suitability of the perlites as pozzolans and their ease of grindability, 16 types of blended cements having 320 m 2 /kg or 370 m 2 /kg Blaine fineness were produced by using 20% or 30% perlite additions. Production of the blended cements were accomplished either by intergrinding or separate grinding. The performance of the cements was evaluated by conducting the following tests: particle size distribution by laser diffraction, normal consistency, setting time, soundness and compressive strength. The results showed that perlites possess sufficient pozzolanic characteristics to be used in production of blended cement.

Unlocking the secrets of Al-tobermorite in Roman seawater concrete

Abstract: Ancient Roman syntheses of Al-tobermorite in a 2000-year-old concrete block submerged in the Bay of Pozzuoli (Baianus Sinus), near Naples, have unique aluminum-rich and silica-poor compositions relative to hydrothermal geological occurrences. In relict lime clasts, the crystals have calcium contents that are similar to ideal tobermorite, 33 to 35 wt%, but the low-silica contents, 39 to 40 wt%, reflect Al 3+ substitution for Si 4+ in Q 2 (1Al), Q 3 (1Al), and Q 3 (2 Al) tetrahedral chain and branching sites. The Al-tobermorite has a double silicate chain structure with long chain lengths in the b [020] crystallographic direction, and wide interlayer spacing, 11.49 A. Na + and K + partially balance Al 3+ substitution for Si 4+ . Poorly crystalline calcium-aluminum-silicate-hydrate (C-A-S-H) cementitious binder in the dissolved perimeter of relict lime clasts has Ca/(Si+Al) = 0.79, nearly identical to the Al-tobermorite, but nanoscale heterogeneities with aluminum in both tetrahedral and octahedral coordination. The concrete is about 45 vol% glassy zeolitic tuff and 55 vol% hydrated lime-volcanic ash mortar; lime formed <10 wt% of the mix. Trace element studies confirm that the pyroclastic rock comes from Flegrean Fields volcanic district, as described in ancient Roman texts. An adiabatic thermal model of the 10 m 2 by 5.7 m thick Baianus Sinus breakwater from heat evolved through hydration of lime and formation of C-A-S-H suggests maximum temperatures of 85 to 97 °C. Cooling to seawater temperatures occurred in two years. These elevated temperatures and the mineralizing effects of seawater and alkali- and alumina-rich volcanic ash appear to be critical to Al-tobermorite crystallization. The long-term stability of the Al-tobermorite provides a valuable context to improve future syntheses in innovative concretes with advanced properties using volcanic pozzolans.

Material and Elastic Properties of Al-Tobermorite in Ancient Roman Seawater Concrete

Abstract: This research was supported by Award No. KUS-l1-004021, from King Abdullah University of Science and Technology (KAUST). Data were acquired at beamlines 12.2.2 and 12.3.2 at the Advanced Light Source at the Lawrence Berkeley Laboratories, supported by the Director of the Office of Science, Department of Energy, under Contract No. DE-AC02-05CH11231, and the Advanced Nanofabrication Imaging and Characterization Laboratories at King Abdullah University of Science and Technology. We thank CTG Italcementi researchers and staff, especially B. Zanga, in Bergamo, Italy; G. Vola at Cimprogetti S.p.A., Dalmine, Italy; S. Clark at the 12.2.2 beamline; and N. Tamura at the 12.3.2 beamline; and the ROMACONS drilling program: J. P. Oleson, C. Brandon, R. Hohlfelder. T. Teague, D. Hernandez, C. Hargis, I. A. Delaney, and B. Black provided research support. We thank J. G. Moore, M. Sintubin, G. Sposito, P.-A. Itty, and J. Kirz for critical discussions, and three anonymous reviewers whose comments improved the manuscript.

Image Processing

Abstract: MUCKE aims to mine a large volume of images, to structure them conceptually and to use this conceptual structuring in order to improve large-scale image retrieval. The last decade witnessed important progress concerning low-level image representations. However, there are a number problems which need to be solved in order to unleash the full potential of image mining in applications. The central problem with low-level representations is the mismatch between them and the human interpretation of image content. This problem can be instantiated, for instance, by the incapability of existing descriptors to capture spatial relationships between the concepts represented or by their incapability to convey an explanation of why two images are similar in a content-based image retrieval framework. We start by assessing existing local descriptors for image classification and by proposing to use co-occurrence matrices to better capture spatial relationships in images. The main focus in MUCKE is on cleaning large scale Web image corpora and on proposing image representations which are closer to the human interpretation of images. Consequently, we introduce methods which tackle these two problems and compare results to state of the art methods. Note: some aspects of this deliverable are withheld at this time as they are pending review. Please contact the authors for a preview.

Geopolymers and Related Alkali-Activated Materials

Abstract: The development of new, sustainable, low-CO2 construction materials is essential if the global construction industry is to reduce the environmental footprint of its activities, which is incurred particularly through the production of Portland cement. One type of non-Portland cement that is attracting particular attention is based on alkali-aluminosilicate chemistry, including the class of binders that have become known as geopolymers. These materials offer technical properties comparable to those of Portland cement, but with a much lower CO2 footprint and with the potential for performance advantages over traditional cements in certain niche applications. This review discusses the synthesis of alkali-activated binders from blast furnace slag, calcined clay (metakaolin), and fly ash, including analysis of the chemical reaction mechanisms and binder phase assemblages that control the early-age and hardened properties of these materials, in particular initial setting and long-term durability. Perspectives fo...

Corrosion of steel by concrete

Abstract: The author details the reactions of various concretes on steel reinforcement. Although portland cements, slag cements and high alumina cements are all hydraulic binders, each possess special properties which are examined. The discussion of causes and methods of preventing the corrosion of steel reinforcement covers such aspects as galvanised steel reinforcement, effects of concrete composition, corrosion of steel reinforcments in concrete and prestressed reinforcement. It is concluded that the most significant influences on the corrosion of prestressing wire in concrete are: the presence of chloride; the presence of nitrates; the composition of the concrete; the degree of carbonation of the concrete; concrete compaction and, chlorides and sulphates should be used as far as possible when steel is embedded. (TRRL)

Geopolymers and other alkali activated materials: why, how, and what?

Abstract: This paper presents a review of alkali-activation technology, moving from the atomic scale and chemical reaction path modelling, towards macroscopic observables such as strength and durability of alkali-activated concretes. These properties and length scales are intrinsically interlinked, and so the chemistry of both low-calcium (‘geopolymer’) and high-calcium (blast furnace slag-derived) alkali-activated binders can be used as a starting point from which certain engineering properties may be discussed and explained. These types of materials differ in chemistry, binder properties, chemical structure and microstructure, and this leads to the specific material properties of each type of binder. The secondary binder products formed during alkali-activation (zeolites in low-Ca systems, mostly layered double hydroxides in alkali-activated slags) are of significant importance in determining the final properties of the materials, particularly in the context of durability. The production of highly durable concretes must remain the fundamental aim of research and development in the area of alkali-activation. However, to enable the term ‘highly durable’ to be defined in a satisfactory way, the underlying mechanisms of degradation—which are not always the same for alkali-activated binders as for Portland cement-based binders, and cannot always be tested in precisely the same ways—need to be further analysed and understood. The process of reviewing a topic such as this will inevitably raise just as many questions as answers, and it is the intention of this paper to present both, in appropriate context.