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Conventional supplementary cementitious materials (SCMs), such as blast furnace slags or fly ashes, have been used for many decades, and a large body of knowledge has been collected regarding their compositional make-up and their impacts on cement hydration and concrete properties. This accumulated empirical experience can provide a solid, confident base to go beyond the status quo and develop a new generation of low-clinker cements composed of new types and combinations of SCMs. The need for new sources of SCMs has never been greater, as supplies of traditional SCMs are becoming restricted, and the demand for SCMs to reduce CO 2 emissions from concrete production is increasing. In this paper, recent research on emerging SCM sources is reviewed, along with new developments in characterizing and qualifying SCMs for use and improved knowledge of SCMs on long-term concrete performance and durability. [ABSTRACT FROM AUTHOR]

To enable commercial use of alkali-activated fly ash concrete, its durability must be better understood. Alkali–silica reaction is a primary concern since highly alkaline solutions are generally used for activation. This study investigated the effect of NaOH activating solution concentration on pore solution alkalinity and subsequent alkali–silica reaction in alkali-activated fly ash concrete. It was found that pore solution alkalinity increased with increasing activating solution NaOH concentration, and this effect was amplified at concentrations above an optimum, defined as the concentration that resulted in the highest mortar compressive strength. Expansion of concrete prisms containing highly reactive fine aggregate and activating solution concentrations above the optimum concentration was approximately three times that of concrete with optimum activating solution concentrations, but only about 5% of the expansion observed in the ordinary portland cement control. The low expansion may be attributed to the low calcium levels in the alkali-activated fly ash concrete. [ABSTRACT FROM AUTHOR]

This work examined the effects of milling using a gravity ball mill on the reactivity of natural zeolites used as supplementary cementitious materials (SCMs). Six different particle size distributions of zeolites, created by milling the as-received zeolite in a ball mill for a specified amount of time, were characterized using x-ray fluorescence, quantitative x-ray diffraction, particle size analysis, pore size distribution and surface area analysis. Following material characterization, the pozzolanic reactivity of the zeolites was determined by measuring the quantity of calcium hydroxide in paste after 28 or 90 days and by tracking the compressive strength of zeolite-cement mortars. Results showed that a critical milling time exists, corresponding to a d 50 of 7–9 μm, after which reductions in particle size can no longer be achieved and zeolite performance can no longer be improved through ball milling. [ABSTRACT FROM AUTHOR]

This work investigated the use of acid treatment as a method for increasing the reactivity of natural zeolite used as a supplementary cementitious material. The effects of treating a natural clinoptilolite zeolite with nine acid solutions, 0.1 M, 0.5 M, or 1 M hydrochloric or nitric acid or 0.1 M, 0.5 M, or 0.87 M acetic acid, were measured using x-ray diffraction, particle size analysis, pore size distribution and surface area analysis. The zeolite pozzolanic reactivity was determined by measuring the quantity of portlandite in hydrated zeolite-cement paste after 28 and 90 days. Results showed that acid treatment increased zeolite surface area, resulting in increased zeolite pozzolanic reactivity, independent of the solution concentration used. Cement hydration was also increased, evidenced by greater rates of heat evolution from cement-zeolite pastes. Additionally, although reductions of portlandite occurred most quickly in pastes with zeolites treated with strong acids, by 90 days the zeolites treated with acetic acid solutions showed comparable portlandite reductions. [ABSTRACT FROM AUTHOR]

Supplementary cementitious materials (SCMs) are commonly used in concrete mixtures as a replacement of a portion of clinker in cement or as a replacement of a portion of cement in concrete. This practice is favorable to the industry, generally resulting in concrete with lower cost, lower environmental impact, higher long-term strength, and improved long-term durability. SCMs have been used in Portland cement concrete for decades and many of their effects are well-understood. Most recent research on SCMs has focused on a few areas: exploring new materials, increasing replacement amounts, developing better test methods, treating or modifying materials, and using additives (e.g. limestone or nanosilica) to improve performance. The advances in knowledge provided by research in these areas are reviewed in this paper, emphasizing the impact of the research on the field. [ABSTRACT FROM AUTHOR]

Sucrose and zinc oxide (ZnO) are effective cement hydration retarders. The goal of this study was to provide a new look into the ZnO cement hydration mechanism and to investigate impacts of various supplementary cementitious materials (SCMs) on retardation behavior of ZnO and sucrose. Changes in the pore solution composition and reaction kinetics were measured for cementitious systems with ZnO or sucrose that contained rice straw ash (RSA), wheat straw ash, silica fume, metakaolin, and fly ash. Among the SCMs used, RSA dramatically suppressed ZnO and sucrose retardation. Experimental results indicated that the mechanism by which ZnO retards hydration reaction could be nucleation and/or growth poisoning of C-S-H. Reduced retardation of paste samples containing RSA was attributed to the ability of RSA to provide nucleation sites for C-S-H precipitation. This study provides a better understanding of the interaction between SCMs and cement hydration retarders essential in predicting retarder–dose effects. [ABSTRACT FROM AUTHOR]

Abstract: Radon (222Rn) and progenies emanate from soil and building components and can create an indoor air quality hazard. In this study, nine concrete constituents, including the supplementary cementitious materials (SCMs) fly ash and metakaolin, were used to create eleven different concrete mixtures. We investigated the effect of constituent radium specific activity, radon effective activity and emanation fraction on the concrete emanation fraction and the radon exhalation rate. Given the serious health effects associated with radionuclide exposure, experimental results were coupled with Monte Carlo simulations to demonstrate predictive differences in the indoor radon concentration due to concrete mixture design. The results from this study show that, on average, fly ash constituents possessed radium specific activities ranging from 100Bq/kg to 200Bq/kg and emanation fractions ranging from 1.1% to 2.5%. The lowest emitting concrete mixture containing fly ash resulted in a 3.4% reduction in the concrete emanation fraction, owing to the relatively low emanation that exists when fly ash is part of concrete. On average, the metakaolin constituents contained radium specific activities ranging from 67Bq/kg to 600Bq/kg and emanation fractions ranging from 8.4% to 15.5%, and changed the total concrete emanation fraction by roughly ±5% relative to control samples. The results from this study suggest that SCMs can reduce indoor radon exposure from concrete, contingent upon SCM radionucleotide content and emanation fraction. Lastly, the experimental results provide SCM-specific concrete emanation fractions for indoor radon exposure modeling. [Copyright &y& Elsevier]

Abstract: The uptake of pollutants by building surfaces can potentially improve both indoor and outdoor air quality. Cement renders provide a unique opportunity for passive pollutant removal because they can cover large surface areas. This study investigated the passive removal of carbon dioxide and ozone by cement renders having varied binder compositions and curing durations. The results from this study demonstrated shorter curing durations resulted in greater pollutant uptake. However, the use of the supplementary cementitious material, metakaolin, in the cement render increased the carbon dioxide ingress while decreasing the ozone uptake. Therefore, the adaptation of the render composition for the best effective application may result in valuable indoor air quality or carbon savings consequences. [Copyright &y& Elsevier]

Abstract: Owing to concerns about radon exposure, there is a need for understanding risk associated with fly ash in concrete. Monte Carlo simulations were applied, based on the radium specific activity of concrete constituents taken from the literature, to predict probabilities for the radium specific activity and radon exhalation rate. The model was then used to predict the indoor radon concentrations and effective annual doses from two different slab-on-grade concrete floors, one with and one without fly ash, in a typical single-family home in the United States. Due to uncertainty in the literature-reported values, a sensitivity analysis was conducted varying the emanation fraction of the fly ash concrete floors. The results show that concrete floors made without fly ash and a 5% emanation fraction, resulted in 90% of the simulated homes having an indoor radon concentration of less than or equal to 2.3 Bq m−3 and an associated annual dose of less than or equal to 54 μSv y−1. This annual dose represents 4% of the total annual background inhalation dose. A 25wt% fly ash concrete with an emanation fraction of 3% achieved the same exposure probability, but higher assumed emanation fractions raised the exposure probability. In general, the predicted radon exposure from fly ash concrete suggests minimal population health effects. But, given the serious health effects of radon exposure the influence of fly ash on the emanation fraction and radioactive pollution indoors deserves further exploration. [Copyright &y& Elsevier]

Abstract: In recent years, calcium sulfoaluminate-belite (CSAB) cement has been promoted as a sustainable alternative to Portland cement due to lower energy used and less CO2 emitted during production, while providing comparable performance. However, a potential problem facing the widespread adoption and production of CSAB cement is the cost and availability of raw materials and it is therefore desirable to find alternative raw materials to keep costs competitive. In this study, two CSAB cement clinkers with a similar target phase composition were synthesized from combinations of natural and waste materials (coal combustion residuals). The two CSAB cement clinkers were compared against a CSAB clinker made from reagent-grade chemicals, enabling examination of the effects of impurities on performance. Cements made from the clinkers were examined for hydration rate, hydration product formation, dimensional stability, and compressive strength. [Copyright &y& Elsevier]

This paper describes the application of low temperature scanning electron microscopy to the materials science of Portland cement. The details of low-temperature scanning electron microscopy are described, along with a number of specimen preparation techniques. There are three main research topics presented in this paper: (1) ice morphology in entrained air voids, (2) development of air voids during early hydration and (3) progression of hydration in Portland cement. The first research focus examines ice in air voids at freezing temperatures, and various cement paste ages. The second research focus tracks the development of the air voids during the first hour of hydration. In the third research focus, the progression of hydration with and without accelerating and retarding admixtures is described. Each of these research programs demonstrates how low-temperature scanning electron microscopy can be an effective tool in Portland cement research. [Copyright &y& Elsevier]

• Calcination negatively affected zeolite particle size, pore size distribution, and surface area. • Calcination reduced zeolite crystallinity and increased amorphous material quantity. • Zeolites reacted pozzolanically in cement paste, but calcination did not increase reactivity. • Calcining above the zeolite's decomposition temperature reduced pozzolanic reactivity. • Amorphous content did not correlate with zeolite reactivity in cementitious systems. This study examined several sources of natural clinoptilolite zeolite calcined at temperatures of 300 °C-965 °C, tracking changes in phase content, particle size, surface area, and pore size distribution. Changes in pozzolanic reactivity with calcination were measured through calcium hydroxide content of hydrated zeolite-cement pastes and compressive strengths of cement mortars. Calcination increased zeolite particle size and reduced porosity and surface area, resulting in decreased zeolite pozzolanic reactivity despite increased amorphous content in the samples. Overall, in contrast to what has been shown previously in literature, calcination was ineffective in increasing the reactivity of clinoptilolite zeolites for use as SCMs. [ABSTRACT FROM AUTHOR]

Despite the benefits to long-term concrete durability, the use of natural zeolites as supplementary cementitious materials (SCMs) is uncommon due to their high water demand. The motivation of the research presented here was to better understand how the physical and chemical characteristics of natural zeolites influenced the workability of cementitious mixtures and whether those properties could be modified through calcination to mitigate the high water demand of natural zeolites. In this research, three different natural zeolites were characterized in their original and calcined states using x-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) surface area measurements. Rheology experiments were then conducted on cementitious pastes containing these natural zeolites, in their original and calcined states, to assess mixture viscosity and yield stress. Results showed that calcination destabilized the structure of the natural zeolites and reduced their surface area, which led to an improvement in mixture viscosity and yield stress. [ABSTRACT FROM AUTHOR]

Abstract: This study aimed to improve the reactivity of metakaolin-cement mixtures using ZnO additions. Kaolinite samples with 0.1–1wt% ZnO were calcined at temperature intervals of 50°C from 500 to 650°C for 1h. The resulting metakaolins were examined for structural changes after calcination and for their pozzolanic reactivity, influence on the hydration behavior of cement pastes, and impact on the compressive strength of mortar cubes. ZnO behaved as a delayed accelerator for cement paste. However, when ZnO was combined with highly amorphous metakaolin, chemical retardation was eliminated while acceleration was maintained. Such systems also had increased 28-day compressive strengths. ZnO additions did not affect the degree of dehydroxylation or the pozzolanic reactivity of the metakaolin. These results could facilitate the use of less pure calcined clays as SCM by providing a mechanism for improving reactivity and may also impact the ability to use zinc-contaminated materials in concrete. [Copyright &y& Elsevier]

Abstract: Calcium sulfoaluminate–belite (CSAB) cements are promoted as sustainable alternatives to portland cement because of their lower energy and CO2 emissions during production and comparable performance. However, the formation of ettringite, the main hydration product in CSAB cements, can be expansive, sometimes resulting in cracking. The factors controlling expansive behavior in CSAB cements have not been completely elucidated. In this study, three CSAB cements synthesized from reagent-grade chemicals with varied phase compositions were examined for dimensional stability in water and sulfate solutions. The interdependent effects of C4A3Ŝ (Ye''elimite) content, calcium sulfate content, water-to-cement ratio, and particle fineness on CSAB cement expansion were evaluated. The results show that the expansive behavior can be controlled by altering chemical and physical factors in CSAB clinker, cement, and paste. [Copyright &y& Elsevier]

Abstract: A comprehensive approach to qualitative and quantitative characterization of crystalline and amorphous constituent phases of a largely heterogeneous Class F fly ash is presented. Traditionally, fly ash composition is expressed as bulk elemental oxide content, generally determined by X-ray fluorescence spectroscopy. However, such analysis does not discern between relatively inert crystalline phases and highly reactive amorphous phases of similar elemental composition. X-ray diffraction was used to identify the crystalline phases present in the fly ash, and the Rietveld quantitative phase analysis method was applied to determine the relative proportion of each of these phases. A synergistic method of X-ray powder diffraction, scanning electron microscopy, energy dispersive spectroscopy, and multispectral image analysis was developed to identify and quantify the amorphous phases present in the fly ash. [Copyright &y& Elsevier]

Abstract: Recent research has suggested that the shell of an air-entrained void is important for resisting coalescence between air-voids and diffusion of gas from the surrounding fluid. The current paper describes the physical and chemical properties of an air-void shell during the first 2 h of hydration and chemical characteristics at 60 days. Results from this research suggest that the air-void shells found in air-entrained paste have varied physical properties and the crystalline material of these shells is largely made up of fine cement particles during the first 2 h of hydration. Observations of paste at 60 days of hydration suggest that the shell is made up of calcium silicate hydrate (C–S–H) with a morphology different from that in the bulk paste. [Copyright &y& Elsevier]

Abstract: It is commonly accepted that replacement of a portion of cement in mortar or concrete with well-dispersed silica fume reduces expansion caused by alkali silica reaction. Recently there has been much discussion that large, agglomerated particles of silica fume may actually act as alkali silica reactive aggregates, thereby increasing expansion rather than reducing it. The data in the literature, from both field and laboratory studies, are inconsistent. This prompted an extensive laboratory investigation into the alkali silica reactivity of silica fume. Results from accelerated expansion testing and microscopic investigations are presented. It was seen that some agglomerated silica fumes participate in ASR while others do not. Factors determining the reactivity of silica fume agglomerates are suggested. [Copyright &y& Elsevier]

Abstract: Reply to the discussion of the paper “Understanding expansion in calcium sulfoaluminatebelite cements” by G.L. Valenti, M. Marroccoli, M.L. Pace, A. Telesca. [Copyright &y& Elsevier]

This paper investigates the effect of temperature on the composition, solubility, and structure of sodium aluminosilicate hydrate (N-A-S-(H)) and zeolite synthesized using sodium silicate and sodium aluminate solutions across a range of bulk aqueous Si/Al ratios at different temperatures. It was found that temperature had minimal effect on the composition for both N-A-S-(H) and zeolite species. A decrease in N-A-S-(H) and zeolite solubility with increasing temperature was observed and attributed to the temperature-dependent pH. As expected, the solubility of N-A-S-(H) was higher than that of its crystalline counterpart. Estimation of thermodynamic properties also revealed that for both the N-A-S-(H) and zeolite phases, the Van't Hoff expression yielded similar enthalpy and Gibbs free energy of formation data as a three-parameter Gibbs free energy model that includes a heat capacity term. An additional benefit of the Van't Hoff approach is that it obviates the need for estimating the heat capacity from reference reactions. [ABSTRACT FROM AUTHOR]

A critical area overlooked in previous research on pumice is understanding how its physical characteristics influence its behavior as a supplementary cementitious material (SCM). This study investigated three pumices with different particle size distributions to observe whether these porous materials exhibit enhanced nucleation and growth of hydration products, in the same way as non-porous materials, and whether the rate of pozzolanic reaction can be changed through particle size. The effect of particle size on compressive strength, rheology and resistance to alkali silica reaction (ASR) was also evaluated. Results showed that reducing particle size increased the rates of cement hydration, pozzolanic reaction, and compressive strength gain, while also increasing mixture viscosity. Interestingly, particle size did not impact the yield stress of the mixture or the resistance to ASR. These new findings give insight about how the particle size of pumice can be used to overcome drawbacks reported in previous literature. [ABSTRACT FROM AUTHOR]

• Blends of fly ash and milled bottom ash have slower reactivity than fly ash alone. • Reactive crystalline phases in Class C ash reduce sulfate resistance in F ash blends. • Class F-C fly ash blend proportions can be optimized for ASR mitigation. • Class F-C fly ash blends are suitable for use in concrete in non-sulfate environments. The availability of traditional siliceous Class F fly ash, produced when burning bituminous coals, is decreasing around the world as many countries begin to switch to renewable energy sources. Existing coal burning power plants are also starting to convert from bituminous to subbituminous coals, which produce calcareous Class C fly ash, or to a blend of the two to reduce emissions and cost. To prolong the availability of siliceous fly ash, suppliers have started distributing blended coal ashes and have also begun to blend siliceous fly ash with other coal combustion products (CCPs), such as calcareous fly ash or bottom ash, or natural pozzolans. A variety of these blended fly ashes were examined in this study and compared to a traditional siliceous fly ash. Although these fly ashes have similar oxide compositions and physical characteristics to a traditional siliceous fly ash, the crystalline and glassy phases present in the fly ash may differ. This can alter cement hydration and result in failure to mitigate expansion due to sulfate attack. In all other performance and durability tests conducted in this study, all fly ashes performed well in cement-based mixtures. [ABSTRACT FROM AUTHOR]

In an effort to limit the environmental impact of concrete materials, there is increasing interest in the development and use of a wider range of minerals as acceptable supplementary cementitious materials (SCMs). This study investigated calcined blended clays of kaolinite and bentonite, with impurities, to assess their feasibility as SCMs. The combined use of Rietveld quantitative x-ray diffraction (RQXRD) and thermogravimetric analysis (TGA) techniques proved useful in initially gauging amorphous content post-calcination, lending insight into the relationship between calcination temperature and pozzolanic reactivity. The results demonstrated that for the calcined blended clays, as the amorphous content increased, the SCM consumed more portlandite and the compressive strength of cement-SCM mortars increased. Blends of kaolinite–bentonite clays, containing initially 35 wt.% crystalline kaolinite prior to calcination, achieved roughly 10% increase in compressive strength over samples containing 100 wt.% cement, at 90 days. Blended kaolinite SCMs may offer significant advantages as a low-cost alternative binder or cement replacement material, with the ability to maintain or enhance mechanical strength. [ABSTRACT FROM AUTHOR]

The objectives of this study were to use activation treatments on sodium montmorillonite and illite shale, to alter early hydration or later pozzolanic reactivity when used as supplementary cementitious materials (SCMs). For comparison purposes, treatment methods were also applied to the highly reactive pozzolan, metakaolin, and the inert filler, quartz. Activation treatment strategies included the addition of 0.15wt% zinc oxide and the use of thermal treatments to the SCMs at temperatures of 650°C, 830°C and 930°C. The use of zinc oxide additions increased the early hydration rate of SCM-containing pastes, yet introduced a chemical retardation and negatively impacted early compressive strengths. Moreover, the results suggest that retardation was inversely correlated with the pozzolanic reactivity of the SCM used. Thermal treatment methods were effective at influencing the SCM pozzolanic reactivity, with montmorillonite calcined at 830°C and illite calcined at 930°C behaving as late-reacting pozzolans. SCMs calcined at these temperatures resulted in higher 90day compressive strengths compared to mortars containing the quartz filler. Overall, this study provides insight into different strategies that maybe used to enhance the reactivity of impure calcined clays in order to facilitate their acceptance into the concrete industry. [ABSTRACT FROM AUTHOR]

In this study, several tests for supplementary cementitious materials (SCMs) were evaluated to find the best methods to rapidly screen out inert materials, measure overall reactivity, and differentiate between pozzolanicity and latent hydraulicity. The R3 matrix and lime reactivity tests were found to be the most effective at quickly screening out inert materials. However, slow-reacting materials may appear to have low reactivity in both tests and extending the test duration better depicts material reactivity. Additionally, SCMs with higher alumina content perform better in the R3 tests due to the higher heat release and more bound water associated with the formation of calcium aluminate hydrates compared to calcium silicate hydrates, creating reactivity bias when compared to SCMs with lower alumina content. Measuring the calcium hydroxide content of R3 pastes, through thermogravimetric analysis or single point mass loss, can also differentiate between pozzolanic and hydraulic materials. [ABSTRACT FROM AUTHOR]

Zonal isolation by cement barriers can be compromised in many different ways. Among the most important are shrinkage of cementing slurries and contamination of slurries with non-aqueous drilling fluids (NADF) during displacement. Class F fly ash (FA) based alkali-activated materials, referred to as geopolymers, have shown better compatibility with NADFs than ordinary Portland cement (OPC) slurries. This study questioned whether the geopolymer slurries also show enhanced performance with respect to shrinkage behavior compared to OPC slurries, especially at relevant downhole temperatures and pressures. A novel testing technique was developed to measure the autogenous shrinkage of OPC and geopolymer slurries subjected to temperatures and pressures ranging up to 80 °C (175 °F) and 13.8 MPa (2000 psi). The testing demonstrated that the total autogenous shrinkage increased for OPC slurries and decreased for geopolymer slurries with increase in testing temperature from 40 °C (104 °F) to 80 °C (175 °F). In addition, an increase in testing pressure from 1.38 MPa (200 psi) to 13.8 MPa (2000 psi) resulted in a significant increase in the autogenous shrinkage for OPC slurries when tested at 40 °C (104 °F). Furthermore, it was found that the addition of zinc- and aluminum-based expansive agents was effective in mitigating OPC shrinkage. A zinc-based expansive agent was particularly effective at shrinkage mitigation for geopolymers subjected to 80 °C (175 °F) and 13.8 MPa (2000 psi) confining pressure. • New test to measure shrinkage of cement slurry at downhole conditions is developed. • Temperature and pressure have higher effect on shrinkage of OPC than geopolymers. • Pressure has significantly higher effect on OPC shrinkage than temperature. • Expansive agents can mitigate slurry shrinkage at elevated temperature and pressure. [ABSTRACT FROM AUTHOR]

Typical alkali-activated low-calcium fly ash (AAF) geopolymer formulations are yet to deliver acceptable rheologies for applications such as oil and gas well cementing, where the cement slurry needs to be pumped, and few effective superplasticizers have been identified. The work reported here centers on the discovery that the rheological properties (mixability and pumpability) of AAFs can be significantly improved by incorporating an organic-based non-aqueous fluid (NAF). NAFs such as oil-based muds and synthetic-based muds are water/brine-in-oil invert emulsions that are widely used in the oil and gas industry for drilling and completion operations. Adding NAF can significantly improve the rheological properties of AAF geopolymers, to the point where the rheology of the mixture approaches that of a Portland cement slurry. Overcoming the poor pumpability issue of AAF opens up a large variety of well cementing applications for AAF slurries including primary cementation and plug cementing in severe lost circulation zones. To modify the gelation and setting characteristics multiple fly ash sources and activators were considered in this study. The alkali activators tested in this study were sodium hydroxide and sodium hydroxide with addition of liquid or solid form sodium silicates. Sodium hydroxide activated AAFs showed improved rheological properties with the addition of NAFs. The liquid sodium silicate activated AAFs resulted in unfavorable rheology readings, gel strength measurements and accelerated the pumping time in comparison to use of pure sodium hydroxide activator. The addition of NAF further accelerated the pumping time, increased the viscosity of the AAF, leading to an unpumpable slurry with a rapid setting behavior. In contrast, activation with solid sodium silicate did not negatively affect the rheological behavior of AAF in the presence or absence of NAF. The use of a solid activator showed an initial high consistency peak that broke down with continued shearing. This early high consistency behavior may be exploited to combat lost circulation problems on troublesome oil and gas wells. • Addition of non-aqueous fluids to alkali activated fly ashes is termed as AAF hybrid. • AAF hybrid is pumpable and has sufficient compressive strength for well cementing. • Composition of fly ash has a significant impact on the pumpability of AAF hybrid. • Limestone dust can be used as a stability enhancing additive for AAF hybrids. • Silicate activators in solid form offer better rheology than the liquid form. [ABSTRACT FROM AUTHOR]