Early-age Reactivity Research Articles

Early age structural build-up and pore stability in raw foam at ambient conditions: Implications for the final properties of glass-ceramic foam

Alkali activation followed by foaming techniques is an effective method for glass-ceramic foam development where early-age reactions in the alkali-activated precursors and the foaming reaction happen simultaneously. Therefore, this early reaction stage must be clearly understood to control the pore characteristic in the glass-ceramic foams. However, correlations between early-age structural build-up and foaming stability and their consequences on the final properties of the sintered glass-ceramic foams have not been investigated. This research aims to examine this relationship. 80–95 wt % of waste glass and 5–20 wt % of slag were used as alkali-activated precursors in this research. Using the alkali activation and combined foaming technique, the raw glass foam was developed and hardened at ambient conditions. The early-age reactivity and structural build-up of the binder and foamed suspension were studied through the rheological parameter and chemical structure analysis over the hardening period. During the hardening process, the percolation effect and development of reaction gels contribute to network formation and stability of the foamed suspension. As the hardening time increases, the matrix strengthens, and the pores stabilise through crosslinking of the gels. After hardening, the raw glass foams were sintered and their properties were evaluated and correlated with early-age structural build-up in fresh glass foam. This study demonstrates that the early-age interaction during matrix development and the foaming process controls the pore stability, connected pore volume, and strength of the final glass-ceramic foams. By understanding these parameters, the properties and pore stability in final glass-ceramic foams can be controlled effectively.

Effect of slag pre-carbonation on its early-age reactivity in alkali activated binder

Early age setting and hardening of alkali activated binders can be influenced by minor variations in the precursor properties. Specifically, in alkali-activated materials based on ground granulated blast furnace slag, the early age behavior can be compromised by processes occurring during handling and storage. This study investigates the impact of pre-carbonation of slag on its reactivity in alkali activated binders using sodium silicate, hydroxide, and/or sulfate. The finding revealed that even low degrees of pre-carbonation could lead to significant delays in slag reaction at early ages. In highly alkaline systems the effect of pre-carbonation was limited due to the high reactivity of the system. However, for systems with lower alkalinities, the delays in slag reaction were notably pronounced, ranging from a few hours up to several days for initially near-neutral activators. Concerning later ages, the effect of pre-carbonation on reaction degree was limited across all studied systems. It is proposed that pre-carbonation might induce a reduction in reactivity by either covering the reactive slag surface with precipitates or modifying the surface chemistry. These findings highlight the importance of proper handling and storage of slag for alkali activated materials and provide insights that may elucidate unexpected behaviours of alkali-activated slags.

Early age reaction of slag in composite cement: Impact of sulphates and calcite

Ground granulated blast furnace slag (GGBS) is an important supplementary cementitious material (SCM) for producing low carbon and durable concrete. There are however questions around the early age reactivity of GGBS and the factors that influence this. To elucidate the fundamental mechanisms controlling the early age reactivity and particularly the influence of anionic species, simplified systems comprising GGBS and calcium hydroxide were examined in the presence of limestone, anhydrite, or both at 4:1 SCM-to-activator ratio. Limestone and GGBS were considered as SCMs, but calcium hydroxide and anhydrite were considered as activators. Multiple techniques, including isothermal calorimetry, thermogravimetry, X-ray diffraction, electron microscopy, mass balance calculation and mercury intrusion porosimetry were used to study hydration and microstructure. The results show that GGBS hydration commences immediately in the alkaline media provided by calcium hydroxide. Sulphates and limestone influence hydration through reactions with aluminates to form ettringite and carboaluminates, but prevalence of macro-capillary pores in sulphate containing binders sustains diffusion-controlled hydration. Consequently, optimization of the alumina to sulphate and carbonate ratios is essential for exploiting the pore solution and space filling effects in composite cements.

Belite clinkers with increasing aluminium content: Effect of calcium aluminates on calcium silicate hydration

Belite cements (BCs) could have advantages over Portland cements concerning durability, low heat development and the use of less demanding raw materials. The activation of BCs by sulfur addition at the clinkering stage and by fast cooling is well established. However, the reaction rates of the calcium silicate phases, mainly belite, are still not fully understood. This is partly due to the interplay between factors including: i) belite activation during clinkering; ii) role of the calcium aluminates at early hydration ages; and iii) role of the sulfates. In the research reported here, three belite clinkers were prepared with constant values of lime saturation factor, and SO3, Fe2O3 and CaF2 contents. The varied parameter was the amount of Al2O3. The resulting clinkers have overall crystalline reactive calcium aluminate contents of 0.4, 7.9 and 16.7 wt%, respectively. Cements were prepared with similar particle sizes and constant anhydrite content. Here, it is shown that calcium silicate reactivities, both alite and belite, strongly depend upon the calcium aluminate contents. As these amounts increase, the degree of hydration of alite at 1 day decreases: 85, 65 and 50 %. Furthermore, the degree of hydration of belite at 7 days was 50, 35 and 0 %. Thus, there is a strong influence of aluminates in calcium silicate rates of hydration. Moreover, comparing the mechanical properties of the cements with 0.6 and 8.2 wt% amounts of calcium aluminates, the improvements due to the higher reactivity of calcium aluminates at very early ages, seem to be counterbalanced by the lower reactivity of the silicate phases. The reported findings may allow further optimization of early age reactivity of active BCs.

Synthesis and hydration of ye’elimite-containing cement (YCC) produced with spent fluid catalytic cracking catalyst

The consumption of petroleum products from fluidized bed catalytic cracking (FCC) units has increased worldwide. One of the primary materials used in this process is the zeolitic catalyst which loses its catalytic capacity over time, generating the spent FCC catalyst – SFCC. This work evaluated the feasibility of using SFCC as raw material for ye'elimite-containing cements (YCC) production. Specifically, six types of clinkers were synthesized in the laboratory, varying the ye’elimite content, with and without SFCC. Powder and in-situ X-ray diffraction (XRD), isothermal calorimetry, and thermogravimetric analysis (TGA) were conducted in anhydrous and hydrated samples. Clinkers with SFCC stabilized more C4AF than those without SFCC; so there was less Fe3+ available in these systems than in the reference systems to stable the pseudo cubic ye'emelite. As a result, the SFCC-containing cements (with more orthorhombic ye’elimite) had higher reaction rates within the first 12–20 h of hydration. In turn, the higher ye’elimite contents in the high- and medium-ye’elimite reference clinkers led to the further formation of hydrated phases at 28 days of hydration on these samples. The equivalent ye’elimite content in low-ye’elimite clinkers led to equivalent cumulative heat and phase assemblage from 48 h to 28 days. Overall, the use of SFCC allowed to incorporate of up to 20.81 wt% of the residue in raw material replacement, resulting in cements with increased early-age reactivity.

Early-age reactivity of calcined kaolinitic clays in LC3 cements: a multitechnique investigation including pair distribution function analysis

Limestone Calcined Clay Cements, LC3, allows CO2 emissions savings up to 40%. The resulting binders have competitive mechanical performances after a week. However, the reactivity of LC3 at early ages is slow and should be improved. Here, we use a multitechnique approach to help in the understanding of early age reactivities which were measured by calorimetry, Frattini assay, and mechanical strengths. The disorder in the kaolinites was quantified by powder diffraction. Some footprints of the local disorder in the resulting metakaolin have been investigated by synchrotron pair distribution function (sPDF). It is concluded that Al-O interatomic correlation position and intensity in the sPDF of the calcined kaolinitic clays could be an additional good descriptor to follow early age reactivity. The results were complemented by 27Al MAS-NMR studies. The rate of the pozzolanic reaction at early ages is governed by the particle size, surface area, and local disorder of metakaolin.

Enhancement of early age cementitious properties of yellow phosphorus slag via CO2 aqueous carbonation

Yellow phosphorus slag (YPS) is an industrial waste by-product and has pozzolanic characteristics. Due to its poor early-age reactivity, this study aims to overcome this limitation via CO2 activation of raw YPS (RYPS) and use as a cement substitute. The experimental results showed that carbonation of RYPS under optimal conditions (liquid to solid ratio of 8 ml/g, temperature of 80 °C, pressure of 0.1 MPa, and for 9 h) can form rich amorphous silica gel and hydro calcite-type CaCO3. As a result, carbonated YPS (CYPS) was utilized as a supplementary cementitious material to improve the early age of pozzolanic characteristics in cement paste. This is because the formation of hemi- and mono-carboaluminates and amorphous silica gel played the important role in early-age strength development in CYPS incorporated cement pastes. Moreover, the presence of CYPS can accelerate the hydration rate of cement clinker, together with the intensification of the alite reaction. The microstructure of composite cement paste containing CYPS was denser compared to that of corresponding samples with RYPS.

Performance of cement-based materials containing calcined coal gangue with different calcination regimes

The storage of coal gangue (CG) takes up a lot of lands and pollutes the environment. Calcined CG has the potential to be used as supplementary cementitious material. In this paper, the CG from Yibin, Sichuan province of China were treated with different calcined temperature, holding times and cooling modes, and the microtopography, phase composition and pozzolanic reactivity of calcined CG were studied. Meanwhile, the fluidity, mechanical properties, hydration products, and pore structure of cement paste and mortar with different calcined CG were analyzed. The apparent color of coal gangue under different treatment methods has also been studied to promote its better application for a wider range in cement-based materials. Results showed that there exists an optimal calcination condition of calcined CG at 800 °C and holding time of 2 h. Rapid cooling and slow cooling reduced the activity of calcined CG. Calcined CG powder would reduce the fluidity of cement mortar. However, proper calcination temperature and sufficient holding time could eliminate it to some extent. It was also found that calcination temperature has a greater impact on the early age reactivity of CG when compared to different temperature treated CG powder, C8T2 sample has the best early activity. Compared to rapid cooling, slow cooling and water-cooling mode, room temperature cooling would result in higher reactive CG. CG powder after proper thermal treatment could refine the pore structure of the hardened cement paste in the later age (28 days), reduce the harmful pores content (>100 nm), and increase harmless pores content (<100 nm) in hardened cement paste. It was found that the CG powder of calcined at 800 °C for 2 h, cooling in water and room temperature might be more suitable as the supplementary cementing material combined the apparent color, pozzolanic reactivity, and preparation process.

On the significance of interfacial chemistry on the strength of fly ash-cement composites

Despite the large number of studies on supplementary cementitious materials, the underlying physicochemical interfacial processes that govern their strength remain obscure. To address this knowledge gap, this paper strives to establish a relation between the chemical composition of fly ash (FA) at the molecular level and the macroscopic compressive strength in cement hydrates-FA composites. We develop a multiscale modeling framework that links the fundamental physicochemical attributes of calcium silicate hydrate (C-S-H)-FA interfaces across molecular (~1 nm), mesoscopic (~100 nm), and microscopic (~10 μm) length scales. We observe that FA's chemical composition affects the interfacial properties across all scales. FAs with higher network-modifier cation concentration show stronger molecular and mesoscale interfacial properties and statistically significant higher macroscopic compressive strength. This is particularly interesting for Class F FA, where early-age reactivity is negligible.

Effect of BaCO3 reactivity and mixing procedure on sulfate-resistant cement performance

The present study focuses on exploring the effects of reactivity and degree of dispersion of BaCO3 additions in the manufacture of sulfate-resistant OPC cements. A new electrochemical deposition method is attempted to effectively disperse BaCO3 particles (studying two different materials with particle size: D50 = 11.45 and 2.37 μm) on cement to enhance their reactivity and favour sulfate immobilisation in the form of BaSO4. The barium carbonate additions, particularly the finest, activate cement hydration to a greater extent. Electrodeposition is also observed to improve early age reactivity (2 d–7 d) in fine BaCO3. Cement paste bearing 15 wt % BaCO3 is more resistant to sulfate attack by a 5% (w/v) solution of Na2SO4 (180 d at 23 °C) than a commercial sulfate-resistant cement, although secondary ettringite and gypsum precipitated in all cases.

Sarooj mortar: From a traditional building material to an engineered pozzolan -mechanical and thermal properties study

Developing new energy efficient building materials to reduce the carbon footprint is now the core of sustainability in construction and an essential factor of life cycle assessment (LCA). The extensive and increasing usage of conventional concrete, mortar, plasters and various cement-based materials is only one of the many factors contributing towards urban thermal discomfort caused by urban heat island phenomena and the poor thermal insulation of ordinary cement mortar. Not only this, the wide use of concrete and mortar in construction increases the consumption of their primary components mainly -Portland cement-requiring a large consumption of energy and causing a significant rise in CO2 emissions.Embedding natural and artificial cementitious/pozzolana materials in today's cement-based building materials has become a common practice. Cementitious and Pozzolanic materials are known to provide an added value to mortar/concrete not only in terms of mechanical and durability properties but also in energy efficiency and enhancing sustainability. Sarooj is a local term describing an artificial cementitious and pozzolana material obtained by traditional calcining of the raw clayey soil. Although its usage is nowadays very limited, Sarooj has been used in Oman and other neighboring countries for centuries, in various buildings and defense structures. The main objective of this research is to transform the traditionally produced Sarooj into an engineered binding material and hence investigating its physico-mechanical and thermal properties. The raw soil used to produce the traditional Sarooj was employed to engineer a modern “Sarooj” under controlled energy processing (grinding and calcination) conditions. The raw clay minded from specific location was ground first to a fine powdered material and then subjected to full characterization. The physical and chemical characterization indicated that the raw soil is suitable for producing a cementitious/pozzolanic calcined clay. The thermogravimetric and differential thermal analysis of the clay used reveal that only a moderate temperature of around 800 °C is required for its calcination which preserves energy and reduces CO2 emissions compared to 1600 °C to produce clinker cement. The strength development showed a slow early-age reactivity but an appreciable enhancement in long-term which demonstrates a remarkable latent hydraulic potential of the clay used. It was also found that adding an optimum amount of the calcined clay enhances the thermal properties. The annual energy performance of a typical housing in the hot climate of Muscat, Oman, was evaluated using DesignBuilder software, a whole-building simulation tool. The simulation results showed insignificant savings in annual energy consumption when the developed mixes are used as plastering materials. The clay alkali-activated with NaOH has, however, showed great potential to enhance the mortar's long-term strength. Using locally engineered cementitious material in a partial replacement of Portland cement can further enhance durability and sustainability by reducing the manufacturing energy of the produced building material such as mortars and plasters.

Ability of the R3 test to evaluate differences in early age reactivity of 16 industrial ground granulated blast furnace slags (GGBS)

Ground granulated blast furnace slag (GGBS) is a glassy by-product of pig iron production and is commonly used in concrete industry to replace cement and thereby lower the carbon footprint of the material. Large variations in reactivity exist depending on the GGBS physical and chemical features. Here we investigate the ability of three rapid calorimetric methods to evaluate the reactivity of GGBS. On a set of 16 industrial GGBS, we show that 24 h heat release, using the R3-protocol, correlates well with 2d compressive strength of standard mortars using 75 wt% GGBS. The correlation of R3-test results (R2 = 0.87) is better than for traditional reactivity indices calculated from chemical composition. Furthermore, we present data on the repeatability of the test protocol and show that the R3-protocol is very sensitive to sample fineness. Finally, XRD patterns show that slight differences in phase assemblage exist between the most and least reactive GGBS.

Retraction

Abstract Original Article Title: Effect of Particle Size of Silica Nanoparticles on Hydration Reactivity and Microstructure of C-S-H Gel Original Authors: U. Sharma,1 L. P. Singh,2 D. Ali,1 and C. S. Poon3 This article has been retracted due to duplicate publication. ASTM International August 2021

Risk and performance assessment of cement made using municipal solid waste incinerator bottom ash as a cement kiln feed

To assess the feasibility of incorporating municipal solid waste incineration (MSWI) bottom ash (BA) as a replacement for traditional raw materials in cement kiln feed, an industrial-scale kiln trial was performed. Leach testing and chemical and physical characterization data from a cement product made at a replacement percentage of 2.8% by mass of kiln feed were comparable to results from ordinary portland cement. The concentrations of constituents of concern in leach tests were generally below risk-based screening levels or of similar or lower magnitude than leachate from control products. Ash-amended cement exhibited greater early age reactivity, and this was reflected in initial mortar compressive strength results; ultimate compressive strength results were higher in the control mortar. The ash-amended and control cements were similar in characteristic, but quantitative x-ray diffraction results reveal differences in alite and aluminate formation during the clinker formation process.

RETRACTED: Effect of particle size of nanosilica on microstructure of C-S-H and its impact on mechanical strength

Abstract The present work is focused on the effect of particle size of silica on its early age reactivity and its impact on C-S-H microstructure and mechanical strength at the early and later ages of hydration. Two different types of commercially available silica i.e. Elk-microsilica (Elk-Si) (100–300 nm) and colloidal nanosilica (CNS) (8–15 nm) were used for the study. The lime silica reaction was carried out with a C/S ratio 2.0 and the reaction was monitored in the first 24 h with a range of instrumentation techniques. The results showed that the CNS had ∼60% higher reactivity than the Elk-nSi. Calorimetric results revealed that in the presence of CNS, the hydration rate and the formation of AFm phase were accelerated. Furthermore, FTIR and NMR results revealed that in the presence of the CNS, the structure of C-S-H gel was also affected. This acceleration and modification C-S-H gel led to the formation of a compact microstructure as the capillary porosity of cementitious system measured by MIP was found to reduce significantly. The formation of a compact microstructure at the early age of hydration improved the early age mechanical strength. However, it hindered the later age hydration and thus more unhydrated cement was observed in the semi-quantitative XRD and BSE/IA analysis, especially in the presence of higher dosages of CNS, which was responsible for the lower long term mechanical strength.

Influence of slag composition on cracking potential of slag-portland cement concrete

Semi-adiabatic calorimetry and a rigid cracking frame were used to compare the effects of five different ground granulated blast-furnace slags with variable Al2O3 and MgO contents, but similar CaO/SiO2 ratios on early-age cracking resistance. While cement replacement with slag significantly reduced concrete temperature rise and delayed the time of cracking compared to the plain concrete, it was observed that stress development varied with the MgO/Al2O3 ratio of the slag. Increasing this ratio reduced the cracking temperature and delayed the time of cracking. The worst performance of the low MgO/Al2O3 ratio slag was attributed to its higher early-age reactivity, which was confirmed by isothermal calorimetry in addition to its higher autogenous shrinkage assessed by free shrinkage measurements.

Rate controls on silicate dissolution in cementitious environments

The dissolution rate of silicate minerals and glasses in alkaline environments is of importance in cementitious systems due to its influences on: (a) early-age reactivity that affects the rate of strength gain and microstructure formation, and/or, (b) chemical durability of aggregates; compromises in which can result deleterious processes such as alkali-silica reaction (ASR). In spite of decades of study, quantitative linkages between the atomic structure of silicates and their dissolution rate in aqueous media (i.e., chemical reactivity) has remained elusive. Recently, via pioneering applications of molecular dynamics simulations and nanoscale-resolved measurements of dissolution rates using vertical scanning interferometry, a quantitative basis has been established to link silicate dissolution rates to the topology (rigidity) of their atomic networks. Specifically, an Arrhenius-like expression is noted to capture the dependence between silicate dissolution rates and the average number of constraints placed on a central atom in a network (nc, i.e., an indicator of the network’s rigidity). This finding is demonstrated by: (i) ordering fly ashes spanning Ca-rich/poor variants in terms of their reactivity, and, (ii) assessing alterations in the reactivity of albite, and quartz following irradiation due to their potential to induce ASR in concrete exposed to radiation, e.g., in nuclear power plants.

Influence of the origin of metakaolin on pozzolanic reactivity of mortars

Cement is one of the main sources of environmental impacts of concrete use. It is thus recognized that the most pragmatic solution for minimizing environmental impacts of concrete is the reduction of the cement content. This could be achieved by replacing a part of cement with mineral additions such as fly ash, blast-furnace slag or metakaolin (MK) during concrete mixing.In recent years, the incorporation of MK in building materials is growing. Metakaolin (Al2Si2O2) is a material obtained by calcination of kaolinite between 500°C and 800°C.In this study, Three MK issued from three different regions in Algeria were tested. The regions are, Jijel, Gulema and Béchar. This study aims to investigate the effects of the origin of MK blended at early age. The chemical and minalorgiques analysis (XRD, BET, SSB and SEM) show a difference in their metakaolinite content. One mortar prepared with 15% substitution rates of cement with different MK. The early-age reactivity of metakaolin-blended cement mortar was investigated. Isothermal calorimetry and compressive strength tests were performed. The hydration rate and the evolution of Ca(OH)2 content of mortars were monitored using thermogravimetric analysis (ATG). The early age reactivity of the three MKs is very different.

Improvement of the early-age reactivity of fly ash and blast furnace slag cementitious systems using limestone filler

This article analyzes the effects of the addition of limestone filler on the hydration rate, setting times and early-age mechanical properties of binary and ternary-binder mortars containing Portland cement, blast furnace slag (BFS) and fly ash (FA), with various substitution rates of cement with mineral additions going up to 50%. Vicat needle penetration tests and measurements of heat flow of reaction, compressive strength and dynamic Young’s modulus were carried out on 14 mortars prepared with binary and ternary binders, at 20°C. The results obtained on the mortars containing binary binders, show that their loss of mechanical strength at early age is not caused by a deceleration of the reactions of cement in the presence of mineral additions, but is mainly explained by the dilution effect related to the reduction in cement content. A moderate addition of limestone filler (8–17%) makes it possible to obtain ternary binders with early-age reactivity equal or even higher than that of Portland cement, and with 28-days mechanical resistance close to those of the binary-binder mortars. This accelerating effect of limestone filler is particularly sensitive in the case of mortars containing FA.

Reducing Thermal and Autogenous Shrinkage Contributions to Early-Age Cracking

Early-age cracking continues to be a significant problem for new concrete construction. Two of the major contributors to such cracking are the heat released by cement hydration during the first few days of curing and the autogenous shrinkage that often occurs during the same time frame. In this paper, three potential alternatives for reducing these contributions by modifying the concrete mixture proportions are investigated, namely increasing the water-cement ratio (w/c), using a coarser cement, or replacing a portion of the portland cement with a coarse limestone powder. Each alternative reduces the heat generated per unit volume by either reducing the volumetric cement content or its early-age reactivity, and reduces autogenous shrinkage by increasing the interparticle spacing between grains in the three-dimensional microstructure. These reductions are quantified for paste and mortar systems by measuring their semi-adiabatic temperature rise and autogenous deformation along with measurements of compressive strength to indicate the strength trade-off that will be experienced in reducing the risk of early-age cracking. These mixtures each have the additional advantage that they should result in a cost savings in comparison with an initial (control) mixture.