Influence of Limestone Mineral Addition in Cements on the Efficacy of SCMs in Mitigating Alkali-Silica Reaction Assessed by Accelerated Mortar Bar Test

This study evaluates the effect of limestone mineral addition in cement on the efficacy of supplementary cementitious materials (SCMs) in mitigating alkali-silica reaction (ASR) using the accelerated mortar bar test (AMBT). Mortars with and without SCMs were prepared by substituting portions of 0% limestone general portland (GP) cement with increasing amounts of limestone. Mortars with SCMs (25% fly ash or 65% slag) exhibit negligible expansion regardless of the limestone content in the binder, whereas mortars without SCMs exhibit high and almost identical expansion for all limestone substitutions. The expansion results show that limestone does not aggravate ASR, has no detrimental effect on the efficacy of SCMs in ASR mitigation, and likewise has no observable ASR-mitigating properties under the test conditions. The calcium silicate hydrate (C-S-H) composition is not affected by the amount of limestone, which suggests that limestone has no influence on the alkali uptake in the C-S-H. This is supported by the pore solution analysis results where SCMs (both fly ash and slag) have drastically reduced the pore solution alkali concentration over time, whereas limestone substitution only resulted in an alkali reduction equivalent to the substitution (dilution). Moreover, the carboaluminate phases formed when limestone is present were observed to decompose under AMBT conditions; thus, their influence on ASR mitigation is not possible to discern from this study

The impact of accelerating admixtures on blended cement hydration for early age strength enhancement

With an ever-increasing focus on sustainable concrete, the use of supplementary cementitious materials (SCMs) has grown and, although SCMs provide improved later age properties, their use can result in reduced early age strength. Chemical admixtures, particularly those that accelerate hydration processes, have the potential to address these deficiencies. Examples of these opportunities for greater early age strength systems have been identified in the literature, whether through the development of new research and commercial products, or through the creative application of existing admixtures. Conventional inorganic and organic accelerators can be applied in novel high order combinations that exhibit a synergistic effect on early strength. A major focus in the literature at present is the use of C-S-H seeds in superplasticiser suspensions or composites, which can elicit very early strength improvement. Such nucleating agents provide sites for hydrate product growth, potentially leading to denser microstructures and improved early age mechanical properties. In this paper, key studies from the past decade are reviewed, covering the application of a range of accelerating admixtures to the enhancement of early age strength in blended cements

In vitro assessment of the combined effect of eicosapentaenoic acid, green tea extract and curcumin C3 on protein loss in C2C12 myotubes

EPA has been clinically shown to reduce muscle wasting during cancer cachexia. This study investigates whether curcumin or green tea extract (GTE) enhances the ability of low doses of eicosapentaenoic acid (EPA) to reduce loss of muscle protein in an in vitro model. A low dose of EPA with minimal anti-cachectic activity was chosen to evaluate any potential synergistic effect with curcumin or GTE. Depression of protein synthesis and increase in degradation was determined in C2C12 myotubes in response to tumour necrosis factor-α (TNF-α) and proteolysis-inducing factor (PIF). EPA (50 μM) or curcumin (10 μg ml−1) alone had little effect on protein degradation caused by PIF but the combination produced complete inhibition, as did the combination with GTE (10 μg ml−1). In response to TNF-α (25 ng ml−1)-induced protein degradation, EPA had a small, but not significant effect on protein degradation; however, when curcumin and GTE were combined with EPA, the effect was enhanced. EPA completely attenuated the depression of protein synthesis caused by TNF-α, but not that caused by PIF. The combination of EPA with curcumin produced a significant increase in protein synthesis to both agents. GTE alone or in combination with EPA had no effect on the depression of protein synthesis by TNF-α, but did significantly increase protein synthesis in PIF-treated cells. Both TNF-α and PIF significantly reduced myotube diameter from 17 to 13 μm for TNF-α (23.5%) and 15 μm (11.8%) for PIF However the triple combination of EPA, curcumin and GTE returned diameters to values not significantly different from the control. These results suggest that either curcumin or GTE or the combination could enhance the anti-catabolic effect of EPA on lean body mass

Effect of Carbonation on Compressive Strength Development of High-Slag Mortars

This study investigates the effect of carbonation on the compressive strength development of OPC and OPC+slag mortars (50% and 70% slag replacement) exposed to 2%CO2, 50%RH 23°C as well as the effect of increasing slag replacement level on carbonation resistance. As expected, results showed that OPC has the highest carbonation resistance and that the higher the slag replacement level, the poorer the carbonation resistance. Compressive strength results up to 112 days show that carbonation has no detrimental effect nor benefit to the compressive strength development of high-slag mortars. Mortars cured in accelerated carbonation conditions however show slower strength development than those cured under natural carbonation conditions up to 28 days. This indicates that CO2 curing does not accelerate strength development

Dissolution behaviour of SCMs in alkaline environment and mechanisms behind ASR mitigation

Fly ash and slag are supplementary cementitious materials (SCMs) commonly used to mitigate alkali-silica reaction (ASR). However, future supply of these SCMs is at risk due to a global push to reduce coal-fired energy production and increased steel recycling. Thus, an immediate need to identify alternative SCMs is critical. In order to establish the efficacy of an SCM in its ability to mitigate ASR, an understanding of the chemical processes involved in ASR mitigation is required. This study aims to better understand the mechanisms behind ASR mitigation by comparing the amount of silicon (Si) and aluminium (Al) released by SCMs under AMBT conditions, investigating the interaction of the dissolved SCM species in the system (i.e. formation of reaction products) and how these correlate to explain the differences in SCM dosage requirements for effective mitigation. Results show that the ability of SCMs to release Si is as follows: SF>MK>FA>SL which correlates well with the dosage required to mitigate ASR. This indicates that the efficacy of SCMs in mitigating ASR is primarily due to their ability to release Si in solution. Formation of sodium aluminium silicate hydrate (N-A-S-H) in fly ash and metakaolin and formation of calcium aluminium silicate hydrate (C-A-S-H) in slag post alkali immersion were also observed. This indicates the ability of aluminium to bind silicon and precipate alkali in the process (effectively reducing solution alkali concentration) and highlights its beneficial effect on ASR mitigation. Further, in systems saturated with calcium, Ca is bound instead of Na suggesting the occurence of competitive reactions and subsquent alkali recycling. Calcium, therefore, does not appear to have a beneficial effect on ASR mitigation

Mitigation of ASR using aggregate fines as an alternative for SCMs

The use of supplementary cementitious materials (SCMs) for mitigating alkali-silica reaction (ASR) is the most common and practical approach adopted by concrete producers since the early 1950s [1]. However, with the future supply of commonly available SCMs such as fly ash and ground granulated blast furnace slag set to decline, alternative materials for mitigating ASR needs to be considered. The objective of this experimental work is to investigate the potential of using ground reactive aggregate fines as SCM substitutes to mitigate ASR. The mechanism of mitigation has been investigated using characterization and expansion tests assessed under AMBT conditions. Mortar bars containing 0%, 10%, 25% and 40% ground reactive aggregate fines by mass of cement replacement were prepared for modified accelerated mortar bar testing. The results obtained indicated that a reduction in ASR expansion was achieved with increasing ground reactive aggregate fines content. Further characterization including XRF and ICP-OES analyses were carried out on ground reactive aggregate fines to understand the efficacy of these materials as potential additives for ASR mitigation