Electron tomography requires a wide angular range of specimen-tilt for a reliable three-dimensional (3D) reconstruction. Although specimen holders are commercially available for tomography, they have several limitations, including tilting capability in only one or two axes at most, e.g. tilt–rotate. For amorphous specimens, the image contrast depends on mass and thickness only and the single-tilt holder is adequate for most tomographic image acquisitions. On the other hand, for crystalline materials where image contrast is strongly dependent on diffraction conditions, current commercially available tomography holders are inadequate, because they lack tilt capability in all three orthogonal axes needed to maintain a constant diffraction condition over the whole tilt range. We have developed a high-angle triple-axis (HATA) tomography specimen holder capable of high-angle tilting for the primary horizontal axis with tilting capability in the other (orthogonal) horizontal and vertical axes. This allows the user to trim the specimen tilt to obtain the desired diffraction condition over the whole tilt range of the tomography series. To demonstrate its capabilities, we have used this triple-axis tomography holder with a dual-axis tilt series (the specimen was rotated by 90° ex-situ between series) to obtain tomographic reconstructions of dislocation arrangements in plastically deformed austenitic steel foils.

We review the progress in the electron tomography of dislocation microstructures in the transmission electron microscope (TEM). Dislocation contrast is visible both in conventional TEM and scanning TEM (STEM) modes and, despite the complicated intensity variations, dislocation contrast can be isolated using computational filtering techniques prior to reconstruction. We find that STEM annular dark-field (STEM-ADF) imaging offers significant advantages in terms of dislocation contrast and background artifacts. We present several examples, both in semiconducting and metallic systems, illustrating the properties of 3D dislocations. We present the high-angle triple-axis (HATA) specimen holder where the diffraction condition can be chosen at will and dislocation tomograms of multiple reflections can be combined. 3D dislocations are analyzed in terms of dislocation density and dislocation nodal structures. Several avenues of study are suggested that may exploit the 3D dislocation data.

Concrete and mortar made from limestone cement may exhibit a lack of durability due to the formation of thaumasite. This work deals with the long term behavior of limestone cement mortars in relation to the limestone content, the curing conditions and the type of the sand. Three types of cement were examined: (i) Portland cement (PC), (ii) Portland limestone cement containing 15% w/w limestone and (iii) Portland limestone cement containing 30% w/w limestone. Mortar specimens were prepared using calcareous and siliceous sand. The specimens were immersed in a 1.8% MgSO4 solution and cured at: (i) 5°C and (ii) 25°C. The status of the samples for a storage period of 5years are reported, based on visual inspection, compressive strength, mass measurements, ultrasonic pulse velocity measurements and analytical techniques, including X-ray diffraction, thermal analysis and scanning electron microscopy. It is concluded that mortars containing limestone, either as sand or as a main constituent of the cement, suffer from the thaumasite form of sulfate attack (TSA) at low temperature. In some cases, the TSA leads to almost complete damage of the specimens after only 60months of exposure. At 25°C the specimens do not show any signs of conventional sulfate attack, even after 60months of exposure to sulfate solution.

After previous work producing a successful 3D tomographic reconstruction of dislocations in GaN from conventional weak-beam dark-field (WBDF) images, we have reconstructed a cascade of dislocations in deformed and annealed silicon to a comparable standard using the more experimentally straightforward technique of STEM annular dark-field imaging (STEM ADF). In this mode, image contrast was much more consistent over the specimen tilt range than in conventional weak-beam dark-field imaging. Automatic acquisition software could thus restore the correct dislocation array to the field of view at each tilt angle, though manual focusing was still required. Reconstruction was carried out by sequential iterative reconstruction technique using FEI's Inspect3D software. Dislocations were distributed non-uniformly along cascades, with sparse areas between denser clumps in which individual dislocations of in-plane image width 24 nm could be distinguished in images and reconstruction. Denser areas showed more complicated stacking-fault contrast, hampering tomographic reconstruction. The general three-dimensional form of the denser areas was reproduced well, showing the dislocation array to be planar and not parallel to the foil surfaces.

Concrete and mortar made from limestone cement may exhibit a lack of durability due to the formation of thaumasite. The addition of minerals that improve the concrete durability is expected to slow down the formation of thaumasite. In this work the effect of natural pozzolana, fly ash, ground granulated blastfurnace slag and metakaolin on the thaumasite formation in limestone cement mortar is examined. A limestone cement, containing 15% w/w limestone, was used. Mortar specimens were prepared by replacing a part of limestone cement with the above minerals. The specimens were immersed in a 1.8% MgSO4 solution and cured at 5 and 25°C. The status of the samples after a storage period of 5 years was reported based on visual inspection, compressive strength, mass measurements, ultrasonic pulse velocity measurements and analytical techniques. It is concluded that the use of specific minerals, as partial replacement of cement, inhibits thaumasite formation in limestone cement mortar.

Isothermal conduction calorimetry has been used to monitor the early hydration of Portland–blastfurnace slag (BFS)‐blended cements. Portland:BFS composite cements with ordinary Portland cement replacements from 0 to 90 wt% were studied at curing temperatures from 12° to 90°C. Peak II, principally associated with alite (Ca3SiO5) hydration, was accelerated with increasing temperature for all blends. Peak S, associated with BFS hydration, was particularly noticeable at 40° and 60°C. At higher curing temperatures, peak S merged with peak II, indicating thermal activation of BFS. Novel plots of total heat output against percentage replacement show that BFS contributes to the heat of hydration, even at temperatures below its thermal activation.

The removal of water from hardened cement paste for analysis or to arrest ongoing hydration has been reported to affect the composition of hydrated phases and microstructure. The effect that arresting the hydration of hardened cement paste by replacing the pore water with acetone before drying, and by removing the water by freeze, vacuum and oven drying has on the hardened cement paste has been investigated. Two pastes were studied, a cemented iron hydroxide floc where a high proportion of ordinary Portland cement (OPC) had been replaced by pulverised fuel ash, and a pure hydrated OPC. The results showed that none of the water removal techniques caused any major deterioration in the composition and microstructure of the hardened cement pastes studied, but the pores appeared better preserved after arresting hydration using acetone quenching. Freeze drying appeared to cause more cracking of the microstructure than the other water removal techniques.

A study was carried out into the potential use of slag from the Imperial Smelting Furnace method of zinc production (ISF slag) as a fine aggregate in concrete. One of the main issues associated with the use of ISF slag was that zinc and lead ions are known to cause retardation of the cement setting process. The effect of various inorganic additives to attempt to offset the retardation is reported. The previously favoured explanation for the mechanism of retardation could not fully explain observations made during this and other studies. Based on evidence gathered during this work, a detailed mechanism is proposed for the retardation of setting caused by heavy metal ions such as zinc and lead, involving the conversion of a metal hydroxide to a metal hydroxy-species. This conversion reaction consumes calcium and hydroxide ions from the surrounding solution and delays their supersaturation and hence the precipitation of CSH gel and Ca(OH)2.

Plaster, cement and concrete have been used since antiquity, notably by the Romans. Portland cement was patented by Joseph Aspdin of Leeds in 1824. Since then it has been gradually refined to become the fundamental constituent of modern concrete, familiar to all of us as the major construction material of the past century. Contemporary constructions such as skyscrapers, concert halls, suspension bridges and huge dams testify to the successful use of Portland cement concrete. For routine constructions its compressive strength development and durability are sufficiently well understood for it to be used with confidence in many diverse situations and in locations with widely different climate conditions. Even in the last 30 years, however, unexpected durability problems, such as the alkali silica reaction (ASR), delayed ettringite formation (DEF) and the thaumasite form of sulphate attack (TSA), have emerged. To ensure that the civil engineer can take the necessary steps to avoid their occurrence has required the methods of materials science to be applied to understand the mechanism of these processes. Recent ideas pertaining to the reaction mechanisms underlying DEF and TSA are critically reviewed.

The thaumasite form of sulfate attack (TSA) has been recognised in recent years as a distinct mechanism by which degradation of buried concrete can occur in the presence of an external source of sulfate ions. There is, however, disagreement about the role of pH. It has been proposed that attack by sulfuric acid, produced by oxidation of pyrite, is sometimes the primary cause of deterioration. Others believe that the acid is rapidly neutralised giving a higher concentration of sulfate ions in the ground, hence increasing the extent of attack. The aim of the laboratory study reported here was to understand the role of sulfuric acid in TSA by examining concrete cubes, made from three types of cement and two types of aggregate, immersed at low temperature in two solutions, one alkaline corresponding to BRE Design Sulfate Class DS-3 and the other acidic. It is concluded that the presence of acid does not promote the formation of thaumasite. Although degradation of the concrete was observed in acid conditions, the mechanism was not TSA as observed in alkaline conditions.

This paper presents the findings of a long-term study on the microstructure of Portland cement mortar specimens containing 5%, 15% and 35% limestone filler, as cement replacement, after exposure to a solution of magnesium sulfate at a concentration of 1.44% SO4, for 5 years at 5 °C. The findings are compared to results reported earlier, obtained from the same systems but after 1-year exposure. It was found that the deterioration due to thaumasite advanced with the increased exposure period and limestone content. Thaumasite solid solutions (Tss) formed as the dominant phases within the deteriorated cement matrix and at the paste-aggregate interface resulting in cracks and delamination. Thaumasite was also found as an inner product in various clinker grains. Interestingly, the control specimens, with no limestone filler, were found to exhibit cracks due to the formation of Tss, with atmospheric carbon dioxide being the most likely source for the carbonates.

The hydration of two high replacement composite cements (3:1 blast furnace slag:ordinary Portland cement (BFS:OPC), and 3:1 pulverized fuel ash:OPC (PFA:OPC)) with the addition of both SnCl2 and SnCl4 has been investigated and the results from X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS) are presented. Adding 5 % or 1 % SnCl(2)(.)2H(2)O or SnCl(4)(.)5H(2)O to the mix water resulted in the formation of Friedel's salt, Ca(3)Al(2)O(6)(.)CaCl(2)(.)10H(2)O, and calcium hydroxo-stannate CaSH(OH)(6), which also involved the consumption of calcium hydroxide. After 90 days hydration at lower levels of addition (i.e., 1 %) there was no longer evidence for CaSn(OH)(6), indicating that it too had been consumed in the pozzolanic reaction due to the lack of calcium hydroxide present. Results from SEM and EDS showed that bright regions between the BFS or PFA grains were tin containing and they were incorporated into the hydrated cement matrix. The tin was, therefore, localized rather than spread throughout and intimately incorporated into the microstructure.

Thermodynamic computational packages FactSage and MTDATA have been used to carry out calculations on systems containing 4 to 7 oxide components, i.e. CaO, SiO2, Al2O3 and Fe2O3, the major constituents of the Portland cement, together with MgO, K2O and Na2O, in the temperature range 800 - 1700degreesC. The current coverage of the databases associated with the computational packages is discussed in relation to their application to cement clinker systems. Based on equilibrium and Scheil cooling techniques, the phases present, their distribution and stability range have been determined. The validity of the results is compared with a Bogue calculation and experimental data.

Pastes of neat and blended Portland cement (incorporating either 60% ground granulated blast furnace slag, or 30% pulverised fuel ash, or 22% volcanic ash) were cured for one year at temperatures ranging from 10 to 60 °C. The hydration products were characterised by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The apparent porosity of the pastes increased with increasing curing temperature. Chemical analysis data for the hydration products are presented in ternary composition diagrams, where it is noted that in the presence of the replacement materials the composition of the C–S–H shifted towards higher Si and Al contents, whereas that of Ca was lower.

The development of the thaumasite form of sulfate attack (TSA) has received considerable attention since its discovery in the foundations of motorway bridges in England in 1998. When TSA occurs in siliceous aggregate concrete and mortars, particularly in samples from the field, it is normally assumed that the carbonate source necessary for the formation of thaumasite was either present as a minor component in the aggregate, as a limestone filler in the binder, or from the groundwater. Recent laboratory studies carried out by the authors have identified a further source of carbonate ions, and that is from atmospheric carbonation. However, in other studies, it appears that an initial air cure can improve the resistance of concretes to TSA. This apparent dichotomy suggests that there is insufficient understanding of the relationship between atmospheric carbonation and TSA. The performances of small mortar cubes made using fine aggregates of either high quality silica sand or limestone under different curing regimes have been compared. Detailed analyses of the nature of the thaumasite-ettringite solid solutions that formed have been carried out, and the mechanism of thaumasite formation, in particular, the role of calcium bicarbonate, is discussed in the light of the results obtained. (C) 2004 Elsevier Ltd. All rights reserved.

There is disagreement about the role of sulfuric acid in the thaumasite form of sulfate attack (TSA) of concrete. Some researchers suggest that thaumasite is formed only at pH above 10.5, whereas others report that the primary cause of deterioration in the affected M5 bridge foundations was sulfuric acid attack followed by neutral TSA. The aim of this work is to reconcile these conflicting views by undertaking parallel studies of concrete exposed to aggressive acid and sulfate solutions and concrete/clay interface work using weathered Lower Lias clay.Concrete specimens have been exposed to BRE Digest 363 sulfate class solutions and acidic and acidic-sulfate solutions at 4.5 0.5 degreesC. Selected samples are being characterised at intervals up to 5 years. At this stage, results are reported for 5-month samples. Various binders including Portland cement, Portland-limestone cement, blastfurnace slag cement, pulverized-fuel ash cement and sulfate-resisting Portland cement at water/binder ratios (w/b) from 0.35 to 0.5 have been studied.Initial visual observations and X-ray diffraction analyses have identified thaumasite in some of the systems after 5 months immersion in solution.An overview of the ongoing parallel concrete/clay interaction work is also presented to contextualise the concrete work. (C) 2003 Elsevier Ltd. All rights reserved.

The Portland cement industry consumes large amounts of energy and produces huge quantities of carbon dioxide, which contribute to global warming, the so-called “Greenhouse Effect”. Industrial trials are reported for the production of belite cements (≈3000 t) at lower temperatures and with lower lime saturation factors than for ordinary Portland cement. Belite cements with reasonably good properties have been made on an industrial scale from limestone, burnt clay, volcanic ash, pyrite ash and gypsum. A rapid rate of cooling improves the hydraulic activity, and also the physical–mechanical properties by stabilising reactive forms of belite. Such low energy cements provide a cheap alternative to Portland cement with properties that are acceptable for many applications and the additional benefit of possible improved durability.

Concrete made from limestone cement may exhibit a lack of durability due to the formation of thaumasite. This work deals with the factors affecting thaumasite formation in cement mortars and particularly the limestone content, the curing conditions and the type of sand used. Three types of cement were examined: (i) OPC, (ii) Portland limestone cement containing 15% w/w limestone and (iii) Portland limestone cement containing 30% w/w limestone. Mortar specimens were prepared using calcareous and siliceous sand. The specimens were immersed in a 1.8% MgSO4 solution and cured at: (i) 5 °C and (ii) 25 °C. The formation of thaumasite was checked and confirmed by XRD and TGA. In addition visual inspection, strength tests and ultrasonic pulse velocity measurements were carried out for several months. It is concluded that mortars containing limestone, either as sand or as a main constituent of the cement, suffer from the thaumasite form of sulfate attack at low temperature. At room temperature, no sulfate attack was observed after a year of exposure.

As part of an investigation into the consequences of adding inorganic metal salts to composite cements, based on blastfurnace slag (BFS) and pulverised fuel ash (PFA), the effect on the hydration behaviour of adding AlCl 3 or As 2 O 3 to the mix water of a number of cementitious systems was investigated using isothermal conduction calorimetry (ICC) and x-ray diffraction (XRD). Four cement systems were investigated; ordinary Portland cement (OPC), 3:1 BFS: OPC, 9:1 BFS:OPC and 3:1 PFA:OPC. AlCl 3 ·7H 2 O and As 2 O 3 were added to the mix water at 0.1% and 1% concentrations. Results from ICC indicated that the addition of As 2 O 3 had very little effect on the setting and early hydration of any of the cements. AlCl 3 , however, inhibited the setting of the composite cements at the 1% addition level but accelerated the OPC at 0.1%. The expected hydration products were observed, with the additional observation of Friedel's salt in the presence of aluminium chloride additions and vaterite in both the aluminium and arsenic-containing systems after 180 days hydration.