Advances in understanding alkali-activated materials

Alkali activation is a highly active and rapidly developing field of activity in the global research and development community. Commercial-scale deployment of alkali-activated cements and concretes is now proceeding rapidly in multiple nations. This paper reviews the key developments in alkali-activated materials since 2011, with a particular focus on advances in characterisation techniques and structural understanding, binder precursors and activation approaches, durability testing and design, processing, and sustainability. The scientific and engineering developments described in this paper have underpinned the on-going scale-up activities. We also identify important needs for future research and development to support the optimal and appropriate utilisation of alkali activated materials as a component of a sustainable future construction materials industry

Electrochemical characterisation of cement hydration and properties by alternating current impedance spectroscopy

The complexity of the chemical and microstructural evolution of cement during the hydration process can be evaluated using many different characterisation techniques. One of these techniques which has been demonstrated to be useful, but not yet fully accepted by the cement research community, is Alternating Current Impedance Spectroscopy (ACIS). However, although ACIS is a non-destructive, rapid, and easily implemented technique, it has been found in the past that it has several limitations such as electrode contact, electrode area dependence, ground coupling effects, complications due to inductance at high frequencies, and a lack of mathematical and physical rigour in much of the data interpretation. Please click Additional Files below to see the full abstract

Differential effects of TFG-β and FGF-2 on in vitro proliferation and migration of primate retinal endothelial and Müller cells

Purpose: During retinal development, the pattern of blood vessel formation depends upon the combined effects of proliferation and migration of endothelial cells, astrocytes and Müller cells. In this study, we investigated the potential for transforming

Evaluation of activated high volume fly ash systems using Na2SO4, lime and quicklime in mortars with high loss on ignition fly ashes

In general, concretes made with blended Portland cement containing high volumes of fly ash provide an alternative to conventional Portland cement concrete to enable carbon footprint reduction. This study evaluates the chemical activation of four fly ashes in blends with Portland cement, by assessing their effects on hydration and compressive strength. In this study, a sieving process is used to regulate the fly ash composition, which has an effect in the chemistry and reaction of the mix. The results show the importance of the amorphous content of the fly ash with respect to achieving a high compressive strength. The effect of sodium sulfate, added as an activator, is significant in terms of compressive strength at early age for two of the fly ashes studied; in this case, the parameter used to correlate with the compressive strength evolution is the amount of portlandite consumed through pozzolanic reactions. However, sodium sulfate does not have the same effect on fly ashes with a high amount of Fe2O3, in which portlandite consumption is much lower

Evolution of phase assemblage of blended magnesium potassium phosphate cement binders at 200 degrees and 1000 degrees C

The fire performance of magnesium potassium phosphate cement (MKPC) binders blended with fly ash (FA) and ground granulated blast furnace slag (GBFS) was investigated up to 1000°C using X-ray diffraction, thermogravimetric analysis and SEM techniques. The FA/MKPC and GBFS/MKPC binders dehydrate above 200°C to form amorphous KMgPO4, concurrent with volumetric and mass changes. Above 1000°C, additional crystalline phases were formed and microstructural changes occurred, although no cracking or spalling of the samples was observed. These results indicate that FA/MKPC and GBFS/MKPC binders are expected to have satisfactory fire performance under the fire scenario conditions relevant to the operation of a UK or other geological disposal facility

Interactions between Simulant Vitrified Nuclear Wastes and high pH solutions: A Natural Analogue Approach

This study details the characterization of a glass sample exposed to hyperalkaline water and calcium-rich sediment for an extended time period (estimated as 2-70 years) at a lime (CaO) waste site in the UK. We introduce this site, known as Peak Dale, in reference to its use as a natural analogue for nuclear waste glass dissolution in the high pH environment of a cementitious engineered barrier of a geological disposal facility. In particular, a preliminary assessment of alteration layer chemistry and morphology is described and the initiation of a long-term durability assessment is outlined

Thermodynamics of calcined clays used in cementitious binders: origin to service life considerations

The use of calcined clays in construction materials has attracted significant attention in the last few years. Based on the continued need for sustainable construction to meet global development challenges, the green transition of the cement industry is an urgent necessity. The use of clay-blended cements will keep increasing to meet the need for mass quantities of materials and the prospect of reducing their embodied CO2, as traditional supplementary cementitious materials are expected to decline in availability. To enable the necessary rapid increase in the fraction of clays that can be used in cements, the use of modeling tools which provide insights into the clays and their reactivity in cementitious systems is of increased interest. The aim is to predict the properties of the calcined clays based on the original rock and calcination conditions, the phase evolution, material properties, and durability of construction materials. This is crucial to reduce the time needed for development and commercialisation, whereas extensive empirical work has been used in the past to achieve material transition in the construction sector, which can be extremely time consuming. This review article therefore aims to provide an overview of available thermodynamic data, issues with database integration, modelling of process parameters, and properties prediction for cementitious materials

Hydration of calcium [alumino] ferrite with limestone

Ferrite has the lowest embodied CO2 among the four major phases found in Portland cement, so increasing the ferrite content of the clinker would improve its CO2 footprint. Ferrite hydration is known to depend on the cooling regime during the production, Al/Fe ratio, and minor element uptake, and thus, their effects have to be fully understood to increase the composition of this phase in the Portland cement and assure their good hydration properties. Here, ferrites with different Al/Fe ratios (0, 0.5, 1, and 2), and minor elements (Zn) has been synthesized at two different burning temperatures, 1250 °C and 1350 °C and hydrated in presence of excess CaCO3 for 1 and 3 days. The ferrite with Al/Fe = 0 did not form any hydration product after 3 days of hydration, while Al-monocarbonate was the only hydration product in the other systems. The hydration kinetics increased with Al/Fe ratio, and when the burning temperature was increased. Comparing XRD and TGA data, the Al-monocarbonate formed from the ferrite with Al/Fe = 2 was found to be more amorphous than other ferrites. ZnO doping up to 2 wt.% had no prominent effect on hydration, implying that raw materials with Zn can be utilised in high-ferrite cement. These results indicate that high-ferrite limestone cement could be a promising solution to reduce cement the CO2 emission