Blended Portland Cement Research Articles

Porosity and cement controlling the response of artificially cemented tailings under hydrostatic loading to high pressures

Cemented tailings find various applications in mining, such as open-pit and underground backfill, dam decommissioning and filtered tailings stacking. This research investigates the compression behaviour of iron ore tailings (IOT) mixed with distinct amounts of Portland cement and compacted in different conditions through isotropic compression, pulse velocity, and unconfined compression tests. The results show the adequacy of the porosity/cement index (η/Civ) in predicting elastic and plastic characteristics of compacted filtered IOT - Portland cement blends, an original correlation that has not been reported by previous work. This index is useful in selecting the cement content and target density for essential parameters required to design cemented IOT stacks. Besides, both cement addition and compaction have promoted the tailings isotropisation (conversion of an anisotropic system to an isotropic one). The evolution of the Post-Yield Compression Line (PYCL) with cementation is shown. Finally, it is demonstrated that distinct initial (after compaction) porosities of uncemented specimens reach a unique PYCL after isotropic pressures above 100 MPa, and cemented specimens do not reach a unique PYCL even at 120 MPa of isotropic pressures. The results underscore the requirement of rigorous compaction control in the field and offer a methodology for the dosage and technological control of artificially cemented tailings.

Retardation of Chlorine-36 by Cementitious Materials Relevant to the Disposal of Radioactive Wastes

The activation product chlorine-36 (36Cl) is an important radionuclide within the context of the disposal of nuclear wastes, due to its long half-life and environmental mobility. Its behaviour in a range of potential cementitious encapsulants and backfill materials was studied by evaluating its uptake by pure cement hydration phases and hardened cement pastes (HCP). Limited uptake of chloride was observed on calcium silicate hydrates (C-S-H) by electrostatic sorption and by calcium monosulphoferroaluminate hydrate (AFm) phases, due to anion exchange/solid solution formation. Diffusion of 36Cl through cured monolithic HCP samples, representative of cementitious materials considered for use in deep geological repositories across Europe, revealed a markedly diverse migration behaviour. Two of the matrices, a ground granulated blast furnace slag/ordinary Portland cement blend (GGBS–OPC) and an ordinary Portland cement (CEM I) effectively retarded 36Cl migration, retaining the radionuclide in narrow, reactive zones. The migration behaviour of 36Cl within the cementitious matrices is not strictly correlated to the measured sorption distribution ratios (Rd-values), suggesting that physical factors related to the microstructure can also have a distinct effect on diffusion behaviour. The findings have implications when selecting cementitious grouts and/or backfill materials for 36Cl-bearing radioactive wastes.

Life cycle assessment of green binder for organic soil stabilization

Increasing construction on soils with low bearing capacity is a geotechnical challenge currently faced in several parts of the world. Highly compressible organic soils require intervention to improve their mechanical behavior. In this case, mass stabilization with binder is an applicable technique, however the commercial cement used (Ordinary Portland Cement) generates environmental impacts that can be minimized with its replacement by environmentally friendly binders. Blended binders can use secondary materials from the industry (waste or by-products) and promote environmental gains. In this case, this research proposes the use of carbide lime and granulated blast furnace slag with the complement of Portland cement for the stabilization of an organic soil. A comparison of the strength obtained with the blended binder versus Portland cement is analyzed in soil stabilization. A Life Cycle Assessment is performed to verify if the proposed blended binder has environmental benefits in replacing conventional cement. Results show that the blended binder has similar capacity to stabilize the organic clay soil compared to commercial cement. The life cycle analysis showed that the use of secondary materials from industry in the composition of blended binder promotes a significant reduction in environmental impacts assessed.

Low-grade fly ash in portland cement blends: A decoupling approach to evaluate reactivity and hydration effects

Fly ash with low glass content is often prohibited from use in concrete due to the low reactivity and/or the inclusion of contaminants. However, the scarcity of high-quality fly ash promotes the evaluation of the feasibility of using fly ash with low glass content (e.g., low-grade fly ash) in concrete. This study proposes a decoupling method to quantitatively estimate the degree of reaction of fly ash with extremely low glass content, which partially replaces cement, and the degree of hydration of the hosting cement, simultaneously. The estimation is derived from the contents of calcium hydroxide and chemically bonded water in hydrated binary cement pastes, which can be determined by thermogravimetric analysis-based experiments and theoretically validated stoichiometric parameters. The results exhibit that the fly ash tends to retard the early-age hydration of cement but promotes its later-age hydration, resulting in a higher ultimate degree of reaction of cement than the reference paste. The microstructural and porosity evaluation shows that the fly ash, though has relatively low degrees of reaction due to its low glass content, can result in a more tortuous pore network of the hydrated pastes, which could be potentially more resistant to the penetration of water and aggressive chemicals.

Report of RILEM TC 281-CCC: A critical review of the standardised testing methods to determine carbonation resistance of concrete

The chemical reaction between CO2 and a blended Portland cement concrete, referred to as carbonation, can lead to reduced performance, particularly when concrete is exposed to elevated levels of CO2 (i.e., accelerated carbonation conditions). When slight changes in concrete mix designs or testing conditions are adopted, conflicting carbonation results are often reported. The RILEM TC 281-CCC ‘Carbonation of Concrete with Supplementary Cementitious Materials’ has conducted a critical analysis of the standardised testing methodologies that are currently applied to determine carbonation resistance of concrete in different regions. There are at least 17 different standards or recommendations being actively used for this purpose, with significant differences in sample curing, pre-conditioning, carbonation exposure conditions, and methods used for determination of carbonation depth after exposure. These differences strongly influence the carbonation depths recorded and the carbonation coefficient values calculated. Considering the importance of accurately determining carbonation potential of concrete, not just for predicting their durability performance, but also for determining the amount of CO2 that concrete can re-absorb during or after its service life, it is imperative to recognise the applicability and limitations of the results obtained from different tests. This will enable researchers and practitioners to adopt the most appropriate testing methodologies to evaluate carbonation resistance, depending on the purpose of the conclusions derived from such testing (e. g. materials selection, service life prediction, CO2 capture potential).

Recycled Concrete Fines as a Supplementary Cementitious Material: Mechanical Performances, Hydration, and Microstructures in Cementitious Systems

Using recycled concrete fines (RFs) as a supplementary cementitious material in blended cement systems offers potential benefits for the construction industry. This study investigated the mechanical properties, hydration development, and microstructural evolutions of blended Portland cement systems incorporating different particle-size distributions of untreated RFs. The results highlighted that finer RFs improved the compressive strength of mortar and influenced hydration by promoting monocarbonate formation. The incorporation of RFs optimizes the pore structure in the early stage but increases porosity. RFs affected the distribution of capillary pores and created a rougher and more complex surface compared to inert mineral admixtures. Furthermore, the particle size of RFs impacted the fractal dimension of multi-scale pore sizes.

Study on solidified material from dredged sediment, fly ash, and blended Portland cement using the response surface method

Treating dredged sediment is a complex processing and ongoing challenge. To utilize dredged sediment for the landfill or construction purposes, a material fabricated from a mixture of dredged sediment, Portland cement, and fly ash, was cured under room temperature and hydrothermal condition at 180 °C and 0.9 MPa pressure for 16 hours. The response surface methodology was used to evaluate the compressive strength of the material, with the range of factors investigated being the dredged sediments/solid ratio (0.3-0.9), cement/fly ash ratio (2-4), and water/solid ratio (0.45-0.55). The fitting models offered an accurate and reliable match to the actual data. The optimum mix proportions of two curing conditions were obtained using total desirability function, meet multi-objective criteria. This result finger out hydrothermal curing significantly enhances treatment capacity of dredged sediment, with a lower CO2 emission in the mixture compared to ambient curing. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) were used to figure out the difference between the minerals formed in the material under two curing conditions, such as tobermorite.

3D Automated Mineralogical Classification, Characterization and Quantification of Blended Portland Cements using X-ray Microscopy, Deep Learning, and AI

3D Automated Mineralogical Classification, Characterization and Quantification of Blended Portland Cements using X-ray Microscopy, Deep Learning, and AI

Mix and measure II: joint high-energy laboratory powder diffraction and microtomography for cement hydration studies.

Portland cements (PCs) and cement blends are multiphase materials of different fineness, and quantitatively analysing their hydration pathways is very challenging. The dissolution (hydration) of the initial crystalline and amorphous phases must be determined, as well as the formation of labile (such as ettringite), reactive (such as portlandite) and amorphous (such as calcium silicate hydrate gel) components. The microstructural changes with hydration time must also be mapped out. To address this robustly and accurately, an innovative approach is being developed based on in situ measurements of pastes without any sample conditioning. Data are sequentially acquired by Mo Kα1 laboratory X-ray powder diffraction (LXRPD) and microtomography (µCT), where the same volume is scanned with time to reduce variability. Wide capillaries (2 mm in diameter) are key to avoid artefacts, e.g. self-desiccation, and to have excellent particle averaging. This methodology is tested in three cement paste samples: (i) a commercial PC 52.5 R, (ii) a blend of 80 wt% of this PC and 20 wt% quartz, to simulate an addition of supplementary cementitious materials, and (iii) a blend of 80 wt% PC and 20 wt% limestone, to simulate a limestone Portland cement. LXRPD data are acquired at 3 h and 1, 3, 7 and 28 days, and µCT data are collected at 12 h and 1, 3, 7 and 28 days. Later age data can also be easily acquired. In this methodology, the amounts of the crystalline phases are directly obtained from Rietveld analysis and the amorphous phase contents are obtained from mass-balance calculations. From the µCT study, and within the attained spatial resolution, three components (porosity, hydrated products and unhydrated cement particles) are determined. The analyses quantitatively demonstrate the filler effect of quartz and limestone in the hydration of alite and the calcium aluminate phases. Further hydration details are discussed.

Hydration, phase assemblage and microstructure of cementitious blends with low-grade limestone

Limestone of the purity mandated by the standards for use in cement manufacture (as raw material or as performance improver) is only a fraction of the mined material. Sometimes, limestone contains impurities like silica, clay, dolomite etc. beyond the levels specified for use as an additive or for cement production. This limestone, commonly known as low-grade limestone, also may have a potential to be used as a supplementary cementitious material. This paper reports a study conducted to understand the hydration behaviour of ordinary Portland cement in combination with low-grade limestone. Low-grade limestone samples with dolomite, silica and clay impurities were collected from various limestone mines in India and used in cementitious blends at various replacement levels after suitable processing. Reaction kinetics was studied using calorimetry and phase assemblage using techniques like X-ray diffraction and thermogravimetry. Mercury intrusion porosimetry was employed to study the microstructure of cementitious blends. Dilution effect of low-grade limestone was studied by measuring compressive strength of cement mortar cubes for various replacement levels. Shortening of induction period, increased peak heat rate and reduced time to peak were observed in the blends of ordinary Portland cement with low-grade limestone. Carboaluminate formation, ettringite stabilisation and higher bound water content were also seen. The studies showed that low-grade limestone also can be used as a partial replacement for ordinary Portland cement without compromising the strength up to 15% replacement. Higher replacement levels, although showing a reduction in strength due to dilution effect, could still be considered for non-structural applications.

Binary and Ternary Blended Portland Cements Containing Different Types of Rice Husk Ash.

Rice husk ash (RHA) is agricultural waste with high silica content that has exhibited proven technical feasibility as a pozzolanic material since the 1970s. Notwithstanding, its use in mortars and concrete is limited by the standards currently utilized in some countries where RHA production is high and the aforementioned pozzolanic material is not standardized. This is the case in Spain, one of the main rice producers in Europe. Nowadays, the high pressure placed on the Portland cement production sector to reduce its energy use and CO2 emissions has given rise to a keen interest in mineral admixtures for cement manufacturing. In this research, we intended to establish the contributions of different RHA types to the final blended Portland cement properties ("H" is used to identify RHA in standardized cements). The experimental results demonstrated that RHA with good pozzolanic properties (large specific surface and high amorphous silica content) had to be limited to 10% cement replacement because of the severe reduction in workability at higher replacement percentages. RHA with lower reactivity, such as crystalline RHA, or fly ash (FA) can be used to prepare binary and ternary blended cements with reactive RHA. It is possible to design the following cements: CEM II/A-H and CEM II/A-(H-V). It would also be possible to design cement (CEM II/B-(H-V) with replacement values of up to 30% and the same 28-day mechanical performance as observed for the Portland cement without mineral addition.

Thermodynamic modelling of alkali-silica reactions in blended cements

Experiments and field observations have shown that supplementary cementitious materials (SCMs) mitigate the risk of alkali-silica reaction (ASR) in Portland cement blends, but this is difficult to describe thermodynamically due to the lack of appropriate thermodynamic database information, and challenges in defining the kinetic factors. This paper examines how four well-known SCMs (namely ground granulated blast furnace slag, silica fume, metakaolin, and fly ash) mitigate ASR, by using a multi-stage simulation and a newly extended thermodynamic database. Calcium hydroxide consumption by SCM hydration, dilution of available alkalis, and alkali binding in calcium-alkali-aluminosilicate hydrate solid solutions, play pivotal roles in understanding the influence of SCMs in ASRs. Blending aluminium-rich SCMs in ASR-prone systems appears to act by preventing the dissolution of reactive silica in aggregates rather than by suppressing the formation of ASR products. This paper provides new thermodynamic insights into the mechanisms by which SCMs enhance concrete durability against ASR.

How Competitive Hydration between C 3 A and C 3 S in the Fast Dissolution Stage Affects the Hydration of Low-Heat Portland Cement Blended Pastes

How Competitive Hydration between C ₃ A and C ₃ S in the Fast Dissolution Stage Affects the Hydration of Low-Heat Portland Cement Blended Pastes

Encapsulation of iodine-loaded adsorbents in blended Portland cement and geopolymer wasteforms

Capture of radioiodine by solid adsorbents and subsequent cementation is a promising solution to achieve “Near Zero” emissions from nuclear fuel cycles. We investigate cementation of iodine-loaded silica adsorbents in blast furnace slag blended Portland cement (BFS:PC) and metakaolin-based geopolymers, and subsequent leaching in deionised water. Adsorbent encapsulation retarded BFS:PC hydration, but not geopolymer reaction. Phase assemblage was unaffected by adsorbent encapsulation for both BFS:PC and geopolymers, which comprised calcium aluminosilicate hydrate and potassium aluminosilicate hydrate gels, respectively. Adsorbents were encapsulated intact within BFS:PC, whereas adsorbents dissolved in the high pH of fresh geopolymers. BFS:PC exhibited low leaching stability and an alteration layer, however minimal iodine leaching occurred due to intact absorbents. Geopolymers showed high leaching stability, however adsorbent degradation resulted in significant iodine leaching. This evidences potential for cementation of radioiodine-loaded adsorbents under mild conditions, and highlights the importance of synergy when designing adsorbents and wasteforms for radioiodine abatement.

Assessment of mechanical behavior and failure criteria under varied confining pressures in treated calcareous sand

Ensuring project safety for maritime geotechnical structures primarily composed of calcareous sand is crucial. Cement-based reinforcement is a promising strategy to enhance integrity and deformability, especially for overlying infrastructures in high-pressure ocean engineering. Firstly, the specimens are created by blending Portland cement and Gypsum into calcareous sand at contents of 16% and 22% and then subjected to curing periods of 7 and 3 days to explore their resistance to loading. Secondly, a triaxial consolidated drained test is conducted, applying different confining pressures ranging from 100 to 1200 kPa. This test aims to assess the mechanical behavior, strength parameters, failure criteria, and stress dilatancy behaviors of treated specimen. The results illustrating the peak shear strength points of all treated specimens display a concave nonlinear shape sloping downwards. An equation is presented to modify the mean effective stress and accommodate the influence of bonding strength. Finally, A revised criterion is formulated by integrating this equation into the failure criterion. Significantly, this refined failure criterion accurately defines the failure envelopes. An equation was established to reveal the relationship between the brittleness index and confining pressure. Additionally, two stress ratio parameters are defined based on the brittleness index to describe bonding degradation comprehensively.

Performance evaluation of carbonated cement paste derived from hydrated Portland cement based binders as supplementary cementitious material

The production of concrete has gone up from 2.3 billion m3 in 2002 to 14 billion m3 in 2020. At the same time, the amount of construction and demolition waste generated annually has reached levels of 3 billion tons, with concrete rubble making up a major portion of it. This study investigates the performance of carbonated fines derived from hydrated cement paste of different binders. Four cement paste blends, containing Portland cement (PC) and blends of Portland cement with fly ash (FA30), perlite (PL30) and metakaolin (MK30) at a 30 % cement replacement level, were cured for 90 days prior to subjecting them to a carbonation reaction. The R3 test gauged pozzolanic reactivity, while calorimetry, XRD, and TGA studied hydration characteristics. Compressive strength of mortar samples prepared using the same binder composition as paste was also measured at different ages. Carbonated fines exhibited notable pozzolanic activity compared to waste hydrated cement paste. The reactivity of carbonated fines derived from different binders were similar, however slightly higher reactivity was measured for fines comprising of reactive SCM in the precursor material (hydrated paste). Mixes with carbonated fines demonstrated enhanced kinetics, exhibiting over 25 % higher compressive strength at 3 and 7 days compared to the fly ash control mix. Similar compressive strength characteristics were observed in mortar mixes with different carbonated fines, indicating a limited impact of the various binder types from which the fines originated.

Physico-Mechanical Properties and Hydration Processes of Cement Pastes Modified with Pumice, Trass and Waste Chalcedonite Powder.

In this article, the physico-mechanical properties and hydration processes of cement pastes containing three additives are introduced. Cement was replaced with pumice, trass, waste chalcedonite powder at 30% by mass and a combination of pumice or trass and waste chalcedonite powder in the amounts of 15% each. The main aim of this research was to assess the properties of two- or three-component binders to save cement in these binders. Rheological properties such as consistency, yield stress, viscosity and thixotropy were determined, in addition to porosity, 7-day and 28-day flexural and compressive strength and bulk density. Additionally, the heat evolution and degree of hydration of the tested pastes were compared. The use of all additives resulted in a reduction in the consistency of the tested pastes. The highest compressive strength measured after 28 days was observed for the cement paste with a 30% content of waste chalcedonite powder, which is related to it having the best pozzolanic activity of the materials used. The results of this research have confirmed that pumice, trass and waste chalcedonite powder can be used as components of blended Portland cements.

Study of fresh properties of cemented paste backfill material with ternary cement blends

This study is aimed at evaluating the effects of ternary blended Portland cement type I (PCI) with slag and limestone (LS) powder on key engineering fresh properties of CPB: (i) rheological properties and (ii) setting time. CPB samples with PCI/Slag ratios of 50/50 (Group A) and 80/20 (Group B) were considered in this study. The effect of LS in the ternary mix was investigated by replacing the slag with increasing doses of LS (5, 10, and 20 wt%). The specimens were cast and cured over periods of 0, 0.25, 1, 2 and 4 h and tested for rheological properties (yield stress, viscosity). In addition, tests were performed to identify the initial and final setting time of the samples. In addition, microstructural tests, zeta potential and pH measurements, and monitoring experiments (temperature, electrical conductivity) were carried out to better comprehend the underlying mechanisms behind the observed changes in rheological behavior and setting time. The findings have shown that the replacement of slag by a higher dosage of LS in the ternary binder significantly affects the rheological properties of the studied CPB. It reduces the yield stress and increases the viscosity of CPB. The effect of LS on the rheological properties of CPB is mainly attributed to the physical (e.g., filler effect, lubrication, particle size) and chemical (nucleation and changes in repulsive forces between CPB particles) effects of LS in the ternary system. The findings also revealed that increasing the proportion of limestone in the CPB ternary binder system prolonged the setting time (initial and final) of the CPB mixture due to the nucleation and dilution effects of LS. Overall, the synergy between slag and LS was observed; the optimal use of LS and slag in the ternary system can serve as a sustainable alternative to the predominantly used ordinary Portland cement (OPC) or OPC/Slag binary binder, thereby reducing the energy consumption and carbon footprint associated with cement and CPB technology. The results of this research will be valuable for a better comprehension of the impacts of ternary binder with an increasing percentage of LS on the rheology and setting time of the CPB mix, ultimately, the efficient design of the mixing plant, especially the backfill transportation system.

Field and laboratory study of iron ore tailings–Portland cement blends for dry stacking

The dry stacking of filtered tailings has emerged as an alternative way of dealing with the safety-related problems of conventional slurry disposal in reservoirs behind upstream dams. Incorporating a cementing agent into the tailings before compaction can enhance the overall geomechanical behaviour of these structures, giving rise to more stable and safer stackings. However, few dry stacks are in operation worldwide and their field performance needs to be better understood. In addition, the addition of cement provides further challenges to the design of these structures. Obtaining reliable laboratory data for properly designing these tailings storage facilities is thus essential. Accordingly, the mechanical behaviour of artificially cemented iron ore tailings for dry stacking purposes was evaluated, with a focus on comparing the responses between field-compacted samples and laboratory-assembled specimens. To do this, ultrasonic pulse velocity, unconfined compression, split tensile and triaxial compression tests were carried out. Both the stiffness and strength data were well described by the porosity/cement index and, despite minor differences, good agreement was found between the responses of the laboratory-assembled and field-compacted samples. The findings highlight the adequacy of laboratory procedures for reflecting the material's real-field conditions.

Low clinker systems - Towards a rational use of SCMs for optimal performance

Progress in understanding the use of SCMs in blended Portland cement and related effects is reviewed. An optimized use of cement components will avoid wasting unreacted particles that do not contribute to the mechanical and durability performances. The reactivity of cement components increases with fineness and by controlled production processes. Clinker may become a minor component in the cementitious mix due to the optimized particle packing of blended cements. An optimized mineralogy of the clinker coupled to the addition of activators can help to further reduce its use in composite cements while maintaining concrete performance. Other cement constituents introduce different filler and chemical effects to the overall reaction and contributes differently to the performance. Filler and chemical effects influence the hydrates assemblage and in particular C-S-H formation, morphology, and chemical composition. The cement and concrete properties at different ages are tightly linked to these properties. Future approaches could be more technical than simply grinding and blending, allowing a better use of each cement component to achieve a lower CO2 intensity.