RILEM TC 247-DTA round robin test: sulfate resistance, alkali-silica reaction and freeze–thaw resistance of alkali-activated concretes

The RILEM technical committee TC 247-DTA ‘Durability Testing of Alkali-Activated Materials’ conducted a round robin testing programme to determine the validity of various durability testing methods, originally developed for Portland cement based-concretes, for the assessment of the durability of alkali-activated concretes. The outcomes of the round robin tests evaluating sulfate resistance, alkali-silica reaction (ASR) and freeze–thaw resistance are presented in this contribution. Five different alkali-activated concretes, based on ground granulated blast furnace slag, fly ash, or metakaolin were investigated. The extent of sulfate damage to concretes based on slag or fly ash seems to be limited when exposed to an Na2SO4 solution. The mixture based on metakaolin showed an excessive, very early expansion, followed by a dimensionally stable period, which cannot be explained at present. In the slag-based concretes, MgSO4 caused more expansion and visual damage than Na2SO4; however, the expansion limits defined in the respective standards were not exceeded. Both the ASTM C1293 and RILEM AAR-3.1 test methods for the determination of ASR expansion appear to give essentially reliable identification of expansion caused by highly reactive aggregates. Alkali-activated materials in combination with an unreactive or potentially expansive aggregate were in no case seen to cause larger expansions; only the aggregates of known very high reactivity were seen to be problematic. The results of freeze–thaw testing (with/without deicing salts) of alkali-activated concretes suggest an important influence of the curing conditions and experimental conditions on the test outcomes, which need to be understood before the tests can be reliably applied and interpreted

Treatment of displaced intra-articular calcaneal fractures by ligamentotaxis: current concepts’ review

Introduction: A large variety of therapeutic modalities for calcaneal fractures have been described in the literature. No single treatment modality for displaced intra-articular calcaneal fractures has proven superior over the other. This review describes and compares the different percutaneous distractional approaches for intra-articular calcaneal fractures. The history, technique, anatomical and fracture considerations, limitations and the results of different distractional approaches reported in the literature are reviewed. Method: Literature review on different percutaneous distractional approaches for displaced intra-articular calcaneal fractures. Results: Eight studies in which application of a distraction technique was used for the treatment of calcaneal fractures were identified. Because of the use of different classification, techniques, and outcome scoring systems, a meta-analysis was not possible. A literature review reveals overall fair to poor result in 10-29% of patients. Ten up to 26% of patients are unable to return to work after percutaneous treatment of their fracture. A secondary arthrodesis has to be performed in 2-15% of the cases. Infectious complications occur in 2-15%. Some loss of reduction is reported in 4-67%. Conclusion: Percutaneous distractional reduction and fixation appears to be a safe technique with overall good results and an acceptable complication rate, compared with other treatment modalities for displaced intra-articular calcaneal fractures. A meta-analysis, based on Cochrane Library criteria is not possible, because of a lack of level 1 and 2 trials on this subject

Impact of Diabetes on Postinfarction Heart Failure and Left Ventricular Remodeling

Diabetes mellitus, the metabolic syndrome, and the underlying insulin resistance are increasingly associated with diastolic dysfunction and reduced stress tolerance. The poor prognosis associated with heart failure in patients with diabetes after myocardial infarction is likely attributable to many factors, important among which is the metabolic impact from insulin resistance and hyperglycemia on the regulation of microvascular perfusion and energy generation in the cardiac myocyte. This review summarizes epidemiologic, pathophysiologic, diagnostic, and therapeutic data related to diabetes and heart failure in acute myocardial infarction and discusses novel perceptions and strategies that hold promise for the future and deserve further investigation

Fly ash geopolymers: effect of admixtures on fresh and hardened properties

One of the most important challenges for the cement industry is to find sustainable solutions to mitigate environmental footprint of its activities. Geopolymers are particularly attractive for this purpose; the use of waste as precursors, along with a room temperature curing, makes these materials low-polluting binders potentially suitable for sustainable building products. The lack of information on effective admixtures is limiting the practical acceptance of geopolymer concrete. The purpose of this paper is to study the influence of different superplasticizers, commonly used in Portland cement concrete technology, on properties of fly-ash based geopolymers. First, second and third generation superplasticizers (i.e., lignin-, naphthalene-, melamine-, polycarboxylic ether, acrylic based superplasticizers) have been used for the preparation of pastes and mortars. Two different amounts of admixture were tested: 0.6wt% and 1.0wt% by mass of binder. Among the investigated admixtures, the polycarboxylic ether based superplasticizer is the most effective. With a dosage of 1.0wt % by mass of fly ash it can be achieved an increase in workability of both geopolymer pastes and mortars without compromising the final strength of hardened material

Thermal properties of fly ash based geopolymers containing refractory powder

Abstract from the Young Researchers\u2019 Forum, XIII AIMAT Congress and SIB Congress - Ischia, Italy, July 2016. Geopolymers are a new class of material synthetized through the alkali activation of a low-calcium aluminosilicate precursor. Several studies highlighted their remarkable thermal stability. However, the majority of the research focus on metakaolin-based geopolymers and, in most of the cases, a thermal curing is performed. This study, instead, aims to investigate the thermal properties of fly ash-based geopolymers containing refractory powder, cured both at room and high (70\ub0C) temperature

Study of the influence of different admixtures on the properties of alkali-activated materials

In the last years many studies have been addressed on the development of new types of cement with the aim to find a sustainable alternative to traditional ordinary Portland cement. Alkali-activated materials (AAM) seem particularly attractive for this purpose, even if effective admixtures such as plasticizers still need to be designed limiting so far the diffusion of AAM for geopolymer concrete preparation. AAM come from the alkali-activation of aluminosilicate powders with suitable amorphous content. Among all the suitable aluminosilicate precursors, great interest is nowadays focused on the possibility to activate industrial waste (e.g., slag or fly ash). The use of waste as precursors, along with a room temperature curing, makes these materials low-polluting binders potentially suitable for green building products. The purpose of this paper is to study the influence of different superplasticizers on the AAM properties. In particular, first, second and third generation superplasticizers (i.e., lignin-, naphthalene-, melamine-, polycarboxylic ether-, and acrylic based superplasticizers) have been used for the preparation of carbon fly ash pastes and mortars in order to improve their physical and mechanical properties at the fresh and hardened state. Different amounts were tested with the aim to determine the best concentration. The results are then compared with those of reference AAM prepared without any admixture addition. Among the investigated admixtures, the mix with the polycarboxylic ether based plasticizer has the best behavior in terms of both fresh and hardened state properties. The optimum amount of SP corresponds to a dosage of 1% by mass of fly ash. Test results show an increase in terms of workability of both geopolymeric pastes and mortars in comparison with AAM samples without any admixture addition. Moreover the use of polycarboxylic ether based superplasticizer does not compromise the final strength of hardened material

Environmentally Friendly La0.6Sr0.4Ga0.3Fe0.7O3 (LSGF)-Functionalized Fly-Ash Geopolymers for Pollutants Abatement in Industrial Processes

Abstract: A ready-to use, highly sustainable solution for large scale exhausts catalytic abatement was developed: the active bricks. An environmentally-friendly composite was synthesized by depositing La0.6Sr0.4Ga0.3Fe0.7O3, by combustion synthesis, on a fly ash-based geopolymer improved to bear the high temperatures (> 900 \ub0C) required for synthesis. The geopolymer was obtained using by-products and was synthesized at RT: its production is sustainable and cost efficient. Prepared composites have been tested for methane oxidation and show good, durable activity above 400 \ub0C. Thermal stability was also proved. Composites are a good solution for oxidation of fuel residues in industrial processes. Graphic Abstract: [Figure not available: see fulltext.]