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The history of mineral components in cementitious materials begins with clays and bitumen in the most ancient mortars, followed by gypsum- and lime-based plasters, mortars, and concretes. Romans perfected the fabrication of extremely durable mortars that form the basis of audacious architectural monuments in Rome, massive harbor constructions, and water-proofed cisterns in the Mediterranean region. During the industrial revolution, “natural cements” were developed through the burning of impure limestone or Si- and Al-bearing materials blended with pure limestone. Delving into the past of concrete science and the composition, durability, and resilience of historic binders, mortars, and concretes can inspire the development of modern environmentally friendly cementitious materials.

In this paper, we present a methodology for measuring the reaction degree of ground granulated blast furnace slag (GGBFS) in alkali-activated cements using neural network based image analysis. The new methodology consists of an image analysis routine in which the segmentation of the back scattered electron (BSE) (SEM) images is based on a deep learning U-net. This methodology was applied to and developed for NaOH-activated slag cements and validated against independently measured XRD results. In a next step the developed method was applied to NaOH-Na

Carbonation of alkali activated materials is one of the main deteriorations affecting their durability. However, current understanding of the structural alteration of these materials exposed to an environment inducing carbonation at the nano/micro scale remains limited. This study examined the evolution of phase assemblages of alkali activated slag mortars subjected to accelerated carbonation (1% CO2, 60% relative humidity, up to 28 day carbonation) using XRD, FTIR and 29Si, 27Al, and 23Na MAS NMR. Samples with three water to binder (w/b) ratios (0.35, 0.45, and 0.55) were investigated. The results show that the phase assemblages mainly consisted of C-A-S-H, a disordered remnant aluminosilicate binder, and a minor hydrotalcite as a secondary product. Upon carbonation, calcium carbonate is mainly formed as the vaterite polymorph, while no sodium carbonate is found after carbonation as commonly reported. Sodium acts primarily as a charge balancing ion without producing sodium carbonate as a final carbonation product in the 28-day carbonated materials. The C-A-S-H structure becomes more cross-linked due to the decalcification of this phase as evidenced by the appearance of Q4 groups, which replace the Q1 and Q2 groups as observed in the 29Si MAS NMR spectra, and the dominance of Al(IV) in 27Al MAS NMR. Especially, unlike cementitious materials, the influence of w/b ratio on the crystalline phase formation and structure of C-A-S-H in the alkali activated mortars before and after carbonation is limited.

Materials and structures = Matériaux et constructions 54(2), 87 (2021). doi:10.1617/s11527-021-01658-1, Published by Springer Netherlands, Dordrecht

Materials and structures 53(6), 136 (2020). doi:10.1617/s11527-020-01558-w, Published by Springer, Dordrecht

Gypsum efflorescence on clay brick masonry is a growing problem, leading to a persistent grey-white staining of masonry facades. Gypsum efflorescence has been reported in the United Kingdom, the Netherlands and Belgium, with a specific occurrence on masonry facades erected over the last few decades. This article investigates the origin of this recent occurrence of gypsum efflorescence, with accelerated testing of the gypsum efflorescence sensitivity of separate and combined masonry components. It is demonstrated that both brick and mortar may provide a gypsum source, respectively, via the dissolution of anhydrite and the carbonation of ettringite. Neither does however directly result in gypsum efflorescence, as the released gypsum commonly subfloresces below the brick surface. The efflorescence is instead triggered by mortar admixtures, the application of which has indeed risen strongly in recent decades. Avoiding gypsum efflorescence on clay brick masonry hence requires an inert alternative for the mortar admixtures.

The Boom Clay in northern Belgium has been studied intensively over recent decades as a potential host rock in the context of disposal of radioactive waste. One of the parameters of interest is the cation exchange capacity (CEC) as it is related to the sorption potential of radionuclides to the clay host rock. In the past, the CEC was determined using various methods on a limited number of samples, leading to significant variations. To constrain the CEC of the Boom Clay better, a sample set covering the entire stratigraphy was measured using the quick copper(II) triethylenetetramine method. Part of the sample set was also measured using the cobalt(III) hexamine method, as a quality control for the results of the former method. In addition, the exchangeable cation population of the Boom Clay was quantified systematically for the first time and these results were compared to the {tiin situ} pore-water chemistry, indicating a strong coupling between the pore-water composition and the exchangeable sites of clay minerals.

The origin of recent mud deposits as well as the coastal turbidity maximum in the French-Belgian-Dutch nearshore area of the southern North Sea is still under debate in the literature. Some models favor the erosion of the Cretaceous chalk cliffs along the English Channel and subsequent NE ward directed transport, other models focus on the erosion of Eocene to earliest Oligocene, and Pleistocene to Holocene clays outcropping on the seafloor off the Belgian coast. In order to validate these hypotheses, the detailed qualitative and quantitative clay mineral composition of these sediments was used as a provenance indicator. By comparing the clay mineral composition of the mud deposits and the associated suspended particulate matter (SPM) with the composition of potential nearby and more remote sources such as the present day marine environment, estuaries and rivers, coastal erosion areas and the geological substratum, the origin of the mud deposits and the SPM could be traced. Results showed that only the clay composition of the Scheldt estuary coincides with those of the mud deposits and the coastal turbidity maximum and that all other potential sources could be excluded. Our data suggest that the clay mineral composition of the mud deposits has a similar composition since at least about 100.000 years, indicating that these deposits originate from a paleo-Scheldt river rather than from the recent river system, as the present-day Scheldt estuary is not source of fine-grained sediments. The present-day SPM in the Belgian-Dutch nearshore area originates mainly from the erosion and resuspension of the existing mud deposits situated in the Belgian nearshore. This study demonstrates the value and suitability of quantitative bulk and clay mineralogy techniques in sediment provenance studies and highlights the importance of incorporating the recent geological history in hydrodynamic studies of sedimentary basins.

1. Introduction Halloysite is a dioctahedral 1:1 clay mineral of the kaolinite group frequently discussed in literature because of its potential for nanotechnological applications (Keeling, 2015; Yuan et al., 2015; Yuan et al., 2016). Its geological occurrence has been primarily linked to soil and weathering environments, by the weathering and alteration of volcanic rocks (Vaughan et al., 2002; Velde & Meunier, 2008), the alteration of clay minerals like montmorillonite or biotite (Hill, 2000; Papoulis et al., 2009) or weathering of feldspars (Sheets & Tettenhorst, 1997; Adamo et al., 2001). Halloysite is also a common mineral constituent in karst and paleokarst environments as a result of acid weathering (Polyak & Guven, 2000; Joussein et al., 2005). In Belgium, halloysite was reported in over 30 localities, almost all with a very similar geological setting, i.e. karstified carbonate substrates filled up by Cenozoic sand deposits (Buurman & Van der Plas, 1968; Dupuis & Ertus, 1995; Goemaere & Hanson, 1997; Nicaise, 1998; Kloprogge & Frost, 1999; De Putter et al. 2002; Bruyere, 2004). A similar geological setting is found inside the underground quarries of Hinnisdael, locally known as “mergelgrotten” (“marl caves”), located in Vechmaal, Limburg province, Belgium (Fig. 1). In two of the Hinnisdael underground quarries, dolines filled with marine sand were intersected and an irregular white clay layer occurs at the contact between the karstified top of the Cretaceous calcareni

Metakaolin is one of the most popular solid aluminosilicate precursors for the synthesis of geopolymers. Despite its high reactivity and availability, there is a noticeable move towards the use of other natural clays as alternative precursors, due to their plentiful supply and widespread availability. Natural clays usually consist of a combination of 1:1 and 2:1 layer silicates reactivity of which vary. In this work, four different natural clays (SS, BS, MS and WS) composed of 1:1 and 2:1 clay minerals at different proportions were studied for the synthesis of geopolymers. To increase their reactivity prior to alkali activation, the clays were calcined in a laboratory oven at different temperatures (700, 750, 800, 850, 900 °C) and different holding times (10 seconds to 60 minutes). The reactivity of the calcined clays was assessed by the dissolution test and isothermal conduction calorimetry. NaOH and a mix of NaOH and Na2SiO3 were used as alkaline activators. The results show that the optimum calcination temperature of SS, BS and MS is 800 °C with a holding time of 10 minutes. WS is sufficiently calcined at a higher temperature of 900 °C for 20 minutes. Kaolinite-rich clays (SS) present more reactivity towards alkali activation than clays dominated by smectite or illite.

This study investigates the leaching of main and trace elements from inorganic polymers made with an iron rich, fumed, > 90% amorphous slag. Different inorganic polymer binders were synthesized, varying the amount of the activating solution and the silica over sodium oxide ratio from 1.6, to 1.8, to 2.0, with constant water content of ±63%. Cascade and column leaching tests were performed in combination with geochemical speciation modeling (Visual MINTEQ) with the aim to understand the speciation of the elements in the inorganic polymer and their leaching behaviour as a function of pH. This would allow to identify the elements which would be the major issue with respect to leaching when the slag will be used in a construction material. The formed inorganic polymer was able to immobilize cationic elements such as barium, copper, magnesium, manganese, and zinc, in the pH range 7–12.5 due to adsorption. Elements such as antimony, arsenic, phosphorus, molybdenum, and vanadium were easily leached out in column and cascade leaching tests, because they most likely occurred as anions in the pore solution. Lead, chromium, and titanium were immobilized in the binder or in crystalline phases in the pH range 3.5–12.5. The study shows that there are multiple factors that affect leaching, the most important of which is shown to be the nature (cationic or anionic) of the elements and the morphology of the matrix. Anions that are present as trace elements (

In large parts of the Mediterranean recipes for the earliest man-made glass changed from melting mixtures of crushed quartz pebbles and halophytic plant ashes in the Late Bronze Age to the use of quartz sands and mineral soda during the Early Iron Age. Not much is known about this transition and the experimental materials which would inevitably have been connected to such technological change. In this paper we present a unique snapshot of developments in glass technology in Anatolia during the Middle Iron Age, when glass is still a relatively rare commodity. The present work focusses on black glass beads decorated with yellow trails from eighth to seventh century BCE Sardis, glass beads that are very rare for this period, and on this site. A full elemental analysis of the beads was made, and Sr, Pb and B isotope ratios were determined. This study reveals the use of a combination of a previously unknown source of silica and of mineral soda, giving rise to elevated (granite-like) Sr isotope signatures, as well as high alumina and B concentrations. The yellow trails of glass on the beads consist of lead-tin yellow type II, lead stannate, showing the earliest occurrence of this type of opacifier/colourant so far, predating any other findings by at least four centuries. The production of these glass beads may be local to Sardis and experimental in nature. It is therefore suggested that Sardis may have played its role in the technological development of the glass craft during the Iron Age.

This recommendation is an outcome of the work carried out by a working group within the RILEM Technical Committee 238-SCM “Supplementary Cementitious Materials”. The working group studied the effect of supplementary cementitious materials on the pore solution, the microstructure and the hydration product assemblage of hardened Portland cements blended with common supplementary cementitious materials. The recommendation reflects the results of a round robin test programme on common hydration stoppage methods in 10 participating laboratories. Among four different methods tested, solvent exchange by isopropyl alcohol (isopropanol) gave the best results in terms of preservation of the cement hydrate assemblage and overall reproducibility of the results [1]. The current protocol is developed based on best laboratory practices of the participating laboratories and literature reports [2–4]. The presented hydration stoppage protocol is recommended for the study of Portland cement-based hydrate assemblages by common material characterization techniques such as thermogravimetry and X-ray powder diffraction.

The quantification of the whole rock mineralogical composition of clay-rich sediments can be achieved by quantifying the detailed clay mineralogy in a fraction which concentrates most of the clay minerals (often the fraction

Core-formed glass vessels of Mediterranean Group I were produced in the Mediterranean area between the sixth and fourth centuries BC. Indirect archaeological arguments have pointed to Rhodes as the primary glassmaking centre for these vessels. By comparing the elemental composition of hypothetical glasses produced from sand raw materials collected along the coastline of Rhodes to the reduced base glass composition of the core-formed vessels, it can be suggested that such sands are unsuitable for the production of these ancient glasses. Other locations in the Aegean area, i.e. Crete, Corinthia and central Macedonia, can also be largely excluded. A primary Syro-Palestinian provenance is more likely, based on the similarities in elemental and strontium/neodymium isotopic composition between the Mediterranean Group I glass vessels and raw glass chunks and sand raw materials originating from the Levant.

Mordenite-rich tuff is one of most available zeolitic rocks all over the world. Because of this, the research of natural mordenite as a raw material of geopolymeric materials can provide an almost unlimited source of solid precursor for manufacturing such building materials. Despite efforts to shed light on the behaviour of mordenite-rich tuff during geopolymeric reaction, the performance of these novel materials is barely understood. The aim of this study is to explore the effect of the content of calcium hydroxide, CH, and water-to-solid ratio, W/S, as mixing parameters on compressive strength of mordenite-based geopolymers, MBG, and its thermal conductivity. As solid precursor was used mordenite-rich tuff and mixed with sodium hydroxide (NaOH) at 10M that kept constant during the experiment. Two experimental parameters were selected as independent variables i.e, the content of CH and water-to-solid ratio, and their levels, according to a central composite experimental design. All these designed mixes were characterized by using quantitative X-ray diffraction (QXRD), Fourier Transform Infrared spectroscopy (FTIR), Thermogravimetry and differential scanning calorimetry (TGA-DSC), scanning electron microscopy coupled with energy dispersed spectroscopy (SEM-EDS), in addition thermal conductivity tests were also run according to standard method ASTM C177 at 9, 24, 39°C. The overall results suggested that MBG can be used as building material, however its thermal conductivity was higher than that of commercial isolate building material. The experimental design analysis indicated that the optimum water-to-solid ratio was 0.35, but in the case of the content of CH, the optimum value was not observed on this experimental range because the compressive strength increased as the content of CH increased as well. The compressive strength of MBG was observed in the range between 8.7 and 11.3 MPa. On the other hand, QXRD and FTIR showed that mordenite reacted during the geopolymeric reaction, but instead quartz, also found in zeolitic tuff, acted as inert filler.

GB2018 GEOLOGY SERVING SOCIETY: Conference program & abstract book

For many microstructural studies it is necessary to “stop” cement hydration—to remove free water. This paper describes the results of a round robin test on the impact of hydration stoppage methods on the composition of hydrated cements. A regular and a fly ash blended Portland cement hydrated for 90 days were selected. Ten laboratories participated in the round robin test. Four common hydration stoppage methods were studied: (1) oven drying at 105 °C, (2) solvent exchange by isopropanol, (3) vacuum drying and (4) freeze drying. After the stoppage of hydration powder samples were studied by thermogravimetry (TG) and X-ray diffraction (XRD). Bound water and Ca(OH)2 content were determined based on the TG data. Portlandite and ettringite content were quantified by Rietveld analysis of the XRD data. The goal was to establish interlaboratory reproducibility and to identify the best available protocols for research and standardization purposes. Based on the results of the round robin test three recommendations are made. (1) Oven drying at 105 °C is not recommended. This dehydrates, alters and decomposes calcium aluminate hydrates significantly more than other methods and often produced carbonation artefacts. (2) Isopropanol exchange is the most appropriate hydration stoppage method for the study of the complete hydrate assemblage of cements, including calcium aluminate hydrates such as ettringite and AFm phases. (3) For quantification of portlandite (Ca(OH)2) all tested hydration stoppage protocols are satisfactory, with the exception of oven drying.

The removal of elemental aluminium, sulphate and harmful organics from two types of MSWI ash samples, the sand sized (0.1–2 mm) fraction of MSWI bottom ash from a grate furnace (SF), and boiler and fly ash from a fluidized bed incinerator (BFA), were done to use as fine aggregates in preparation of cement mortar. Results indicate that the chemical treatment by 0.25 M Na2CO3 solution can dissolve the Al and the sulphate bearing minerals from the BFA and therefore enhance its quality to use as a fine aggregate in cement mortar preparation. On the other hand, heat treatment at about 675 °C before Na2CO3 treatment is necessary to improve the quality of SF for using as a fine aggregate. The compressive strengths of mortars improve significantly due to the partial replacement of sand by heat and Na2CO3 treated ash samples. The proposed treatment methods slightly change the toxic element leaching behaviours of the ash samples. The concentrations of toxic elements in the leachates generated from the treated ash samples as well as the leachates generated from the mortars containing these ash samples are well within the regulatory limits.

In the present study, inorganic polymers (geopolymers) were synthesised using volcanic glass, calcined halloysite-rich clay and mine tailings, all from Ecuador. In addition to the possibility of making a geopolymer binder from these materials, the influence of geopolymerisation on the immobilisation of the mine tailings was investigated. The research focused on the effect of synthesis conditions on the strength, microstructure and composition of the geopolymer binder and on the leaching behaviour of heavy metals and Arsenic (As). A water insoluble material with a compressive strength of 30 MPa was synthesised using a Na-silicate activator (composition in wt.%, Na 2 O: 15; SiO 2 : 13; H 2 O: 72) and using 110 kg of activating solution per tonne of raw material. It was shown that incorporation of mine tailings in the geopolymers did not have an effect on the mechanical properties. The production of geopolymer based tailing pastes thus shows potential for use on the mining site, for example as a capping material of tailing ponds. Geopolymerisation influences pH-dependent heavy metal leaching but does not cause a complete immobilisation of heavy metals and As. In general, the leaching of heavy metals is limited, below the regulatory concentrations for using the geopolymers in building materials. An exception on this are Cu and As, which show increased mobility due to the higher pH obtained in the geopolymerisation.

This contribution is the second part of an in-depth study on the hydration and strength evolution of blended cement pastes at a water to binder (W/B) ratio of 0.3, cured by two different methods. The blended cement pastes showed significant hydration up to 7 days, when almost all of the hydration products had already formed; thereafter, carbonation played an important role up to, and possibly beyond, 91 days. Likewise, the hydration of alite (tricalcium silicate, Ca3SiO5, C3S) proceeded up to 14 days and then started to slow down. However, the hydration of belite (dicalcium silicate, Ca2SiO4, C2S) was affected most strongly, as it nearly ceased, under the air-curing conditions. During hydration, some of the blended cement pastes had a larger calcium hydroxide (CH) content than the unblended (plain) ones. The accelerating effects of the addition of supplementary cementitious materials (SCMs), the air-curing conditions and the low W/B ratio may explain these unusual results. Under these experimental conditions, the water incorporated into hydrates was about 50% of the total amount of water used during full hydration of the cement pastes. The pozzolanic reaction predominated during the early ages, but disappeared as time passed. In contrast, the carbonation reaction increased by consuming ∼45% of the total amount of CH produced after aging for 91 days. Only one blended cement paste reached the compressive strength of the plain cements. The blended cement pastes containing 5% of the zeolitic tuffs, Zeo1 or Zeo2, or 10% of the calcareous siltstone, Limo, developed the greatest compressive strength under the experimental conditions used in this study.

This study was carried out to develop geopolymers derived from mordenite-rich tuffs. First the synthesis of mordenite-based geopolymer was explored through the mix design of three chemical reagents: NaOH, Na4Si5O12, and Ca(OH)2 and varying curing temperature. All the types of synthesized geopolymers were characterized by FT-IR spectroscopy, quantitative X-ray diffraction, SEM–EDS, TGA–DSC, compressive strength. The best mix design and curing temperature by means of the highest compressive obtained after 24 h were found as NaOH: 10 M, Na4Si5O12/NaOH ratio: 0.5, Ca(OH)2: 3% (w/w), and 60 °C, respectively, which showed values of compressive strength about 10 MPa. Then early age reaction kinetics was established using Avrami–Erofe’ev model. The carbonation, as side effect of reactive ingredient, was also observed during the experiment seemingly without causing any effect on mechanical properties of geopolymers.

Many factors influence the durability of a building material, such as its mechanical resistance, exposure conditions and the presence of soluble salts in it. Since the latter interact with each other, it is difficult to relate any of them to the specific damage observed. Lubelli et al. [1] have recently summarized the shortcoming of some salt crystallization tests and of the mathematical models based on the accepted salt crystallization theories. The net result is that there is no single salt crystallization test that can provide all answers since crystallization kinetics, depending on specific circumstances, play a critical role in the induced deterioration. Nonetheless, specific tests have been developed which have proved to be practically viable in assessing particular material compatibility or potential damaging sources. Two such tests are described, one using sodium chloride to determine compatibility of restoration mortars, and another where the efflorescence of gypsum for brick masonry is evaluated. These methods have proven their reliability and lead to the conclusion that salt tests should be designed for specific objectives.

Two organic acids were trialled for the extraction of calcium from steelmaking blast furnace slag for the purpose of precipitated calcium carbonate (PCC) production: succinic and acetic acids. While the leaching performance of succinic acid was superior, carbonation of its leachate did not result in the production of PCC, but rather the precipitation of calcium succinate, and only after the use of pH buffering agents (sodium hydroxide or bicarbonate). In contrast, carbonation of the acetic acid leachate resulted in the production of PCC, also with the aid of buffering agents. This discrepancy highlights the need for a combination of chemical, mineralogical and morphological analytical techniques for the accurate characterization of carbonation precipitates for future publications in this field. Additional effects observed in this study were the low atom-efficiency of the acids for calcium leaching, at ~20–30% of the stoichiometric value, the low extraction selectivity but high carbonation selectivity between calcium and magnesium, and the contamination of the formed PCC’s with small amounts of co-leached aluminium and silicon. Further work is warranted on the purification of this PCC synthesis route. ispartof: Hydrometallurgy vol:147 pages:90-94 status: published

A three-stage process was developed to transform blast furnace slag (BFS) into two valuable products: precipitated calcium carbonate (PCC) and zeolitic materials. The conceptualized process aims to simultaneously achieve sustainable CO2 sequestration and solid waste elimination. Calcium is first selectively extracted by leaching with an organic acid, followed by carbonation of the leachate to precipitate CaCO3. In parallel, the hydrothermal conversion of the extracted solid residues in alkali solution induces the dissolution/precipitation mechanism that leads to the formation of micro- and meso-porous zeolitic materials. Leaching selectivity was identified as a key factor in the valorization potential of both products. Acetic acid satisfactorily limited the leaching of aluminium, required for the subsequent synthesis of zeolites, and carbonation of the acetic acid leachate resulted in the production of PCC of varied mineralogy and morphology, depending on processing conditions. In the hydrothermal conversion stage, the formation of zeolitic phases was observed, and their characteristics were found to vary depending on the calcium extraction efficiency in the previous stage, and the alkali (NaOH) concentration. The zeolitic phases produced, in order of increasing valorization potential, were: tobermorite, sodalite, lazurite, and analcime. ispartof: Chemical Engineering Journal vol:249 pages:260-269 status: published

An extensive study in blended cement pastes that comprised two different experimental settings was carried out so as to analyse the hydration process and compressive strength evolution up to 91 days. The aim of this study was to understand the hydration process using zeolite-rich tuffs and siltstone as supplementary cementitious materials at low water-to-binder ratio (W/B =.3) under wet curing condition. It was observed that there were two competing reactions, i.e. pozzolanic reaction and carbonation, during the hydration process, thus leading to a decrease in the content of calcium hydroxide (CH); however, carbonation played a more important role than the pozzolanic reaction in consuming it at the given W/B ratio. The total amount of CH consumed by pozzolanic reaction was likely around 8%, while carbonation transformed around 19% of the total amount of CH at 91 days. Although fully hydrated cement paste incorporates.23 g of water per g of cement, only 60% of this value was used at such a W/B ratio. In addition, the amount of normalised water in hydrates increased as the dosage increased by factor of.158% per 1% of dosage. Finally, the optimal dosages at which Zeo1, Zeo2 and Limo showed the highest compressive strength were in the ranges of 12.5-15%, 17.5-20% and 10-12.5%, respectively. © 2014 Taylor & Francis. ispartof: European Journal of Environmental and Civil Engineering vol:18 issue:6 pages:629-651 status: published

Moisture is known to decrease the mechanical properties of brittle construction materials. The present study focuses on the influence of moisture on the mechanical behavior of ferruginous sandstone in order to understand and quantify this effect. The investigated Diestian and Brusselian ferruginous sandstone have frequently been applied in monumental constructions and many of these monuments presently suffer from material degradation and, in some cases, stability concerns. Experimental analysis is performed on different levels, from micro to macro behavior, in order to obtain a more detailed picture of the acting processes. Therefore, a methodology is proposed which combines established as well as advanced experimental techniques, involving non-destructive testing for pre-classification of the sandstone's quality, mineralogical analysis and investigation of mechanical properties under dry and saturated conditions. It was observed that the decrease of mechanical properties, such as strength and stiffness, is more pronounced for lower-quality ferruginous sandstone. It was also found that water adsorption by the sandstone during acoustic emission-controlled creep tests shifts the specimen's behavior from meta-stable creep damage to accelerated failure. These observations were linked to the results of the mineralogical study, in which the consolidation degree and clay content were analyzed and to the results of the microfocus computed tomography which visualized the fracture progress on a micro scale. © 2013 Elsevier Ltd. All rights reserved. publisher: Elsevier articletitle: Multi-scale analysis on the influence of moisture on the mechanical behavior of ferruginous sandstone journaltitle: Construction and Building Materials articlelink: http://dx.doi.org/10.1016/j.conbuildmat.2013.12.024 content_type: article copyright: Copyright © 2013 Elsevier Ltd. All rights reserved. ispartof: Construction & Building Materials vol:54 pages:78-90 status: published

Natural clay-sized glauconite has the same mineralogical composition as sand-sized glauconite pellets but occurs in

Process limitations have thus far prevented mineral carbonation of alkaline wastes from been widely applied. These barriers are caused by inefficient processing, but also by mineralogical aspects inherent to the materials. Better understanding and predictability of the effects of mineral carbonation on alkaline materials could be obtained by studying the carbonation susceptibility of constituent minerals separately, allowing for detailed and accurate analysis of their reaction kinetics and maximal conversions and of the carbonate products formed. For this purpose, this paper presents the synthesis and carbonation of the seven most abundant alkaline minerals found in AOD, CC and BOF slags, namely: åkermanite (Ca2MgSi2O7), bredigite (Ca7Mg(SiO4)4), cuspidine (Ca4Si2O7F2), β– and γ–C2S (Ca2SiO4), merwinite (Ca3Mg(SiO4)2), and srebrodolskite (Ca2Fe2O5). Two experimental approaches to mineral carbonation of increasing levels of process severity are utilized: (mild) incubator carbonation, and (accelerated) pressurized slurry carbonation. In addition, the slags and two free oxides (CaO and MgO) are equally carbonated and evaluated. Data regarding CO2 uptake, mineral conversion and formed carbonate and non-carbonate products in the samples were obtained through TGA, QXRD (Rietveld refinement) and SEM techniques. Reduction in material basicity and evolution of particle morphology were also assessed. The synthesized mineral purities (> 70 wt% target mineral phase) were found sufficient for more accurate assessment of carbonation behaviour of the individual minerals. Bredigite was found to be the most reactive mineral under all processing conditions; C2S and wollastonite were more reactive under slurry carbonation, while srebrodolskite and calcium monoferrite were found to be more reactive under moist carbonation. Merwinite and diopside had the slowest carbonation conversions. Calcite and aragonite were the dominant carbonate products formed, whereby aragonite formation was promoted in Mg-containing materials. The morphology of aragonite crystals and the packing density of its product layer were found to vary depending on the parent mineral. Characteristic slag carbonation products, not observed as extensively from synthetic mineral samples, were magnesian calcite from slurry carbonation, and monohydrocalcite and vaterite from moist carbonation. Wollastonite was the main crystalline non-carbonate product, occurring predominantly from slag carbonation, while silica-rich amorphous matter formed in all samples proportionally to CO2 uptake. Free lime, when present, controlled material basicity above pH 12, while silicates were found to typically possess pH in the range of 11.3–11.9, and Ca-carbonates eventually controlled the pH of well carbonated samples to values under 10. ispartof: pages:533-549 ispartof: European Journal of Mineralogy vol:25 issue:4 pages:533-549 ispartof: location:GERMANY, Johann Wolfgang Goethe Univ, Frankfurt status: published

Two Ecuadorian zeolite-rich tuffs, coded as Zeo1 (Mordenite) and Zeo2 (Clinoptilolite–Heulandite–Mordenite), were treated and used as supplementary cementitious materials (SCM) so as to study the effect of the thermal and mechanical treatments on pozzolanic reaction in mortars. The treatment was carried out by means of thermomechanical process according to a central composite-blocked cube-star experimental design. In this experimental design as independent factors the milling time (48, 60, 90, 120 and 132 min) and the heating temperatures (559, 600, 700, 800 and 841 °C) were used but keeping a constant heating time (5 h), and zeolite-rich tuffs as experimental blocks. The proportion of SCM was kept constant i.e. 15 %. On the other hand, the compressive strength, fixed lime, normalized water in hydrates and mg Ca(OH)2 per mg Cement at 7, 28 and 45 days, as well as hydration products related to dehydration degree of the zeolitic tuffs (DOD) were used as dependent factors. In addition, Quantitative and High-temperature chamber XRD, TG-DSC, particle size distribution and SEM-EDS were also carried out. The most significant factor was calcination leading to increase in the compressive strength compared to control, but just up to 800 °C because of recrystallization. As a conclusion, a meaningful loss of crystal structure of zeolites was not observed; but instead, the treatment could only lead to removing the water in cages and voids, thus improving the reaction with Ca(OH)2, producing more hydrates. In addition, lime was not only fixed by pozzolanic reaction, but also by carbonation.

Several aspects of ultrasound-assisted mineral carbonation were investigated in this work. The objectives were to intensify the CO2 sequestration process to improve reaction kinetics and maximal conversion. Stainless steel slags, derived from the Argon Oxygen Decarburization (AOD) and Continuous Casting / Ladle Metallurgy (CC/LM) refining steps, were used for assessing the technical feasibility of this concept, as they are potential carbon sinks and can benefit from reduction in alkalinity (pH) by mineral carbonation. Ultrasound was applied by use of an ultrasound horn into the reaction slurry, where mineral carbonation reaction took place at 50 oC for up to four hours; comparison was made to solely mechanically mixed process. It was found that sonication increases the reaction rate after the initial stage, and permits achieving higher carbonate conversion and lower pH. AOD slag conversion increased from 30% to 49%, and pH decreased from 10.6 to 10.1; CC slag conversion increased from 61% to 73% and pH decreased from 10.8 to 9.9. The enhancement effect of ultrasound was attributed to the removal of passivating layers (precipitated calcium carbonate and depleted silica) that surround the unreacted particle core and inhibit mass transfer. Significant particle size reduction was observed for sonicated powders, compared to particle size growth in the case of stirring only; D[4,3] values increased without sonication by 74% and 50%, and decreased with sonication by 64% and 52%, respectively for AOD and CC slags. Considerations on scale-up of this technology, particularly with regards to energy efficiency, are also discussed. ispartof: Applied Thermal Engineering: Design, Processes, Equipment, Economics vol:57 issue:1 pages:154-163 status: published

A comparison was made between the early-age hydration of cements blended with micronized zeolitite and quartzite powders. The Portland cement replacement in the mixes was 30%, and the effect of introducing a superplasticiser to lower the required water to solid ratio was assessed. The cement pastes were hydrated at 40 °C and monitored in situ by time-resolved synchrotron X-ray powder diffraction combined with Rietveld quantitative phase analysis. The quantitative evolution of phase weight fractions showed that the addition of the zeolite tuff accelerated the hydration rate of the main C 3 S cement component. Blending with the quartzite powder of similar fineness did not affect the C 3 S hydration rate. Reduction of the water to solid ratio by introduction of the superplasticiser had a retarding effect on the hydration of the zeolitite-blended cement over the early hydration period up to 3 days. The AFt or ettringite reaction products, formed promptly after the addition of water to the mixtures, underwent a crystal structural modification over the induction period up to 4 to 6 hours of reaction. The continuous contraction of the c -cell parameter and expansion of the a -cell parameter towards the ideal values for AFt or ettringite reflects the structural adaptation of the AFt to the changing availability of sulphate over the course of the first hours of hydration. The observed structural changes were less pronounced in the zeolitite blended cement. This is related to the dilution of the overall sulphate content in the blended cement and highlights the need to control and optimise sulphate additions in blended cements.

Carbonation reaction of lime pastes has been studied with an on-line carbonation set-up combining the measurement of the amount of CO2 consumed by Ca(OH)2 with an in situ XRD analysis monitoring the real-time modification of portlandite and calcite phases. The reaction rates obtained from the net CO2 uptake by Ca(OH)2 and that obtained from the calcite precipitation were compared for lime putty and lime hydrate pastes carbonated in CO2 atmosphere (7, 17 and 33 mol/m3). The results indicate that the carbonation reaction is initially rapid and chemically controlled at the exposed surface with a strong limitation of CO2 diffusion into the sample by the pore water. The reaction proceeds with a chemical-reaction controlled regime at a much higher rate followed by a transition to a CO2-diffusion controlled regime by the carbonated sample depth. Drying and formation of amorphous CaCO3 on the portlandite faces has been found to create a dormant effect for the calcite precipitation at the first stage. Lime putty indicates faster carbonation than lime hydrate due to its small particle size and morphology properties, both at a rate which is independent of the CO2 gas concentration. These results will contribute to the understanding of lime carbonation in lime-based mortars for applications in heritage conservation, in renovation and in modern brick and stone masonry.

Treatment and disposal of Basic Oxygen Furnace (BOF) slag, a residue of the steel production process characterized by high basicity and propensity for heavy metal leaching, is a costly burden on metallurgical plants; a sustainable valorization route is desired. The stabilization of BOF slag utilizing hot-stage carbonation treatment was investigated; this approach envisions carbonation during the hot-to-cold pathway followed by the material after the molten slag is poured and solidified. Three experimental methodologies were employed: (i) in-situ thermogravimetric analyzer (TGA) carbonation was used to assess carbonation reaction kinetics and thermodynamic equilibrium at high temperatures; (ii) pressurized basket reaction carbonation was used to assess the effects of pressurization, steam addition and slag particle size; and (iii) atmospheric furnace carbonation was used to assess the effect of carbonation on the mineralogy, basicity and heavy metal leaching properties of the slag. Free lime was found to be the primary mineral participating in direct carbonation of BOF slag. Initial carbonation kinetics were comparable at temperatures ranging from 500 to 800 °C, but higher temperatures aided in solid state diffusion of CO2 into the unreacted particle core, thus increasing overall CO2 uptake. The optimum carbonation temperature of both BOF slag and pure lime lies just below the transition temperature between carbonation stability and carbonate decomposition: 830-850 °C and 750-770 °C at 1 atm and 0.2 atm CO2 partial pressures, respectively. Pressurization and steam addition contribute marginally to CO2 uptake. CO2 uptake progressively decreases with increasing particle size, but basicity reduction is similar independent of particle size. The solubility of some heavy metals reduced after carbonation (barium, cobalt and nickel), but vanadium and chromium leaching increased. ispartof: Chemical Engineering Journal vol:203 pages:239-250 status: published

Phase and morphology evolution of CaCO3 precipitated during carbonation of lime pastes via the reaction Ca(OH)2 + CO2 → CaCO3 + H2O has been investigated under different conditions (pCO2 ≈ 10−3.5 atm at 60 % RH and 93 % RH; pCO2 = 1 atm at 93 % RH) using XRD, FTIR, TGA, and SEM. Simulations of the pore solution chemistry for different stages and conditions of carbonation were performed using the PHREEQC code to investigate the evolution of the chemistry of the system. Results indicate initial precipitation of amorphous calcium carbonate (ACC) which in turn transforms into scalenohedral calcite under excess Ca2+ ions. Because of their polar character, $$ \left\{ {21\bar{3}4} \right\} $$ scalenohedral faces (type S) interact more strongly with excess Ca2+ than non-polar $$ \left\{ {10\bar{1}4} \right\} $$ rhombohedral faces (type F), an effect that ultimately favors the stabilization of $$ \left\{ {21\bar{3}4} \right\} $$ faces. Following the full consumption of Ca2+ ions and further dissolution of CO2 leading to a pH drop of the pore solution, $$ \left\{ {21\bar{3}4} \right\} $$ scalenohedra are subjected to dissolution. This eventually results in re-precipitation of $$ \left\{ {10\bar{1}4} \right\} $$ rhombohedra at close-to-neutral pH. This crystallization sequence progresses through the carbonated depth with a strong dependence on the degree of exposure to CO2, which is controlled by the carbonated pore structure governing the diffusion of CO2. Both the carbonation process and the scalenohedral-to-rhombohedral transformation are kinetically favored under high RH and high pCO2. Supersaturation plays a critical role on the nucleation density and size of CaCO3 crystals. These results have important implications in understanding the behavior of ancient and modern lime mortars for applications in architectural heritage conservation.

The current widespread use of calcium silicate or aluminate hydrate binder systems in the construction industry finds its roots in the Antique world where mixtures of calcined lime and finely ground reactive (alumino-)silicate materials were pioneered and developed as competent inorganic binders. Architectural remains of the Minoan civilization (2000-1500 BC) on Crete have shown evidence of the combined use of slaked lime and additions of finely ground potsherds to produce stronger and more durable lime mortars suitable for water-proof renderings in baths, cisterns and aqueducts (Spence and Cook 1983). It is not clear when and where mortar technology evolved to incorporate volcanic pumice and ashes as a functional supplement. A plausible site would be the Akrotiri settlement at Santorin (Greece), where archeological indications of strong ties with the Minoan culture were found and large quantities of suitable highly siliceous volcanic ash were present. This so-called Santorin earth has been used as a pozzolan in the Eastern Mediterranean until recently (Kitsopoulos and Dunham 1996). Evidence of the deliberate use of this and other volcanic materials by the ancient Greeks dates back to at least 500-400 BC, as uncovered at the ancient city of Kamiros, Rhodes (Efstathiadis 1978; Idorn 1997). In the subsequent centuries the technological knowledge was spread to the mainland (Papayianni and Stefanidou 2007) and was eventually adopted and improved by the Romans (Mehta 1987). The Roman alternatives for Santorin earth were volcanic pumices or tuff found in neighboring territories, the most famous ones found in Pozzuoli (Naples), hence the name pozzolan, and in Segni (Latium). Preference was given to natural pozzolan sources, but crushed ceramic waste was frequently used when natural deposits were not locally available. The exceptional lifetime and preservation condition of some of the most famous Roman buildings such as the Pantheon or the Pont du …

Mortar samples from the Notre-Dame Cathedral at Tournai in Belgium have been investigated as part of a broader studyconsidering the transition of ancient cities and their rural territories from Roman to late Roman society and the transformation to theearly Middle Ages. Masonry mortars and mortars used for flooring have been studied from the Imperial Roman period, theCarolingian style period and the Romanesque style period (4th–11th century AD).A selected set of samples has been characterised using a combination of mineralogical, chemical and microscopical techniques.This characterisation enabled us to refine our knowledge of the mortar composition, of the original materials and of their provenance.It appears that both chalk and ‘‘hard’’ Tournaisian limestone were used to produce the lime. Both locally available materials can yieldeither hydraulic or non-hydraulic lime. The aggregates have a local origin. Additionally, several microscopical techniques wereapplied to identify the nature of the overburnt particles. The low abundance of this type of Binder Related Particles in the Gallo-Roman and Palaeo-Christian mortars suggests that technological knowledge, be it empirical or theoretical, was available.Key-words: ancient mortars, raw materials, provenance, lime binder, lime burning, hydraulicity, archaeometry.

The stability of pyrochlores as a function of solution composition is relevant in the context of hazardous waste immobilisation as this mineral family comprises minerals that can control actinide solubility in ceramic formulations as well as romeites or calcium antimonates that possibly control the solubility of Sb in cement pastes. However, to date, no thermodynamic model exists that can be used for long-term risk assessment of pyrochlores as stabilising minerals. In this work synthetic romeites were precipitated at pH 6.5 and pH 12 and at varying molar Ca:Sb ratio and analysed by XRD and Rietveld refinement which showed that, like naturally occurring romeites, synthesized romeites have a Ca1+xSb2O6OH2−2x structure with less vacancies and a higher Ca-content as pH and Ca-availability were higher during synthesis. These romeites dissolve incongruently with preferential Ca leaching and antimonate is less soluble from romeites synthesized in alkaline conditions. Batch extractions of romeite in equilibrium with increasing Ca(NO3)2 additions up to 1 mol L−1 showed a minimum equilibrium Sb concentration at [Ca] = 0.01 mol L−1 that could only be explained by assuming the formation of a CaSb ( OH ) 6 + complex. Increasing the Ca concentration in romeite suspensions also resulted in a pH decline in the equilibrium solution, which may be explained by the increasing concomitant uptake of Ca2+ and OH− in the romeite structure as a function of increasing Ca(NO3)2 additions. Thermodynamic modelling supported these assumptions that may explain the incongruent dissolution behaviour of romeite, but the fitting of two equilibrium constants was required. Although the validity of these constants needs more experimental confirmation, this study suggests that despite possible CaSb ( OH ) 6 + formation, the solubility of Ca antimonate in alkaline conditions can be responsible for lower equilibrium Sb concentrations than previously assumed.

The pozzolanic reaction of a natural zeolite-rich tuff and portlandite was investigated by means of IR spectroscopy. The zeolite tuff consisted mainly of Ca-rich clinoptilolite. A detailed analysis of the changes in the bonding environment during reaction presented by the IR spectra showed that the vibrations assigned to the reactant phases were progressively consumed and implied that Si-rich environments were preferentially depleted. The contemporaneous appearance and rise of vibration bands characteristic for calcium-silicate-hydrates and calcium-aluminate-hydrates demonstrated the formation of reaction products. Changes in bonding environment were spatially visualized by means of synchrotron-IR microspectroscopy. Promising results showed the distribution of reactants and reaction products and allowed to analyze spatial trends in IR-vibration frequencies. A shift in calcium-silicate-hydrate mean peak position from 972 to 968 cm −1 indicated a decrease in silicate chain length with increasing distance from the clinoptilolite-matrix interface.

The in situ early-age hydration and pozzolanic reaction in cements blended with natural zeolites were investigated by time-resolved synchrotron X-ray powder diffraction with Rietveld quantitative phase analysis. Chabazite and Na-, K-, and Ca-exchanged clinoptilolite materials were mixed with Portland cement in a 3:7 weight ratio and hydrated in situ at 40 {sup o}C. The evolution of phase contents showed that the addition of natural zeolites accelerates the onset of C{sub 3}S hydration and precipitation of CH and AFt. Kinetic analysis of the consumption of C{sub 3}S indicates that the enveloping C-S-H layer is thinner and/or less dense in the presence of alkali-exchanged clinoptilolite pozzolans. The zeolite pozzolanic activity is interpreted to depend on the zeolite exchangeable cation content and on the crystallinity. The addition of natural zeolites alters the structural evolution of the C-S-H product. Longer silicate chains and a lower C/S ratio are deduced from the evolution of the C-S-H b-cell parameter.

The early pozzolanic reaction in pastes of lime and natural zeolites was studied with time-resolved in situ synchrotron X-ray powder diffraction. For chabazite and Na-, K-, and Ca-exchanged clinoptilolite tuffs, which were mixed with lime and water, the evolution of the quantitative contents of crystalline phases was followed during the early pozzolanic reaction in the first hours and days. The dependence of the rate coefficient on temperature was examined by isothermal curing at 313, 323, and 333 K of lime–chabazite tuff pastes. Kinetic analysis indicates that the reaction rapidly displays a deceleratory character. This is explained by the modified Jander equation as a result of the reaction rate control by diffusion processes through a condensing reaction product boundary layer. The exchangeable cation content of clinoptilolite influences the duration of the initial induction period, the diffusion characteristics of the boundary layer of reaction products, and the structural evolution of the C–S–H reaction product. Alkali-exchanged clinoptilolites show a higher pozzolanic reactivity, a more permeable reaction product layer, and longer silicate chains in the C–S–H phase compared to their Ca-exchanged counterpart. The temperature dependence of the reaction rate coefficients in the lime–chabazite tuff pastes obeys the Arrhenius equation.