Blended Portland Cement Research Articles

Hydration and Microstructure of Ternary High-Ferrite Portland Cement Blends Incorporating a Large Amount of Fly Ash and Limestone Powder

Hydration and Microstructure of Ternary High-Ferrite Portland Cement Blends Incorporating a Large Amount of Fly Ash and Limestone Powder

Competitive Hydration between C3a and C3s in the Rapid Dissolution Stage Affects the Hydration of Low−Heat Portland Cement Blended Pastes

Competitive Hydration between C3a and C3s in the Rapid Dissolution Stage Affects the Hydration of Low−Heat Portland Cement Blended Pastes

Utilization of Phosphorus Slag with Replacement of Fly Ash in Low-Heat Portland Cement Blends: Hydration, Microstructure, and Life-Cycle Assessment

Utilization of Phosphorus Slag with Replacement of Fly Ash in Low-Heat Portland Cement Blends: Hydration, Microstructure, and Life-Cycle Assessment

A practical model to predict the flow of water-powder mixes and its application to mix design of cementitious blends

This paper addresses the prediction of the spread-flow of water-powder mixes, which is of particular interest in the mix design of cementitious pastes, mortar and concrete. The model introduced, splits the total water demand which is necessary to achieve a specific spread of water-powder mixes into three parts: (i) water to fill the voids between the solid particles, (ii) water to reach the onset of flow and (iii) water to reach a specific spread. An algorithm developed allows the systematic calculation of the total water demand of mixes with varying proportions of powders after the individual characterization of the source materials regarding their void volume and spread-flow coefficients (i.e. retained water ratio and deformation coefficient). With this approach it is possible to optimize the proportion of mixture in cement-based binders (blended cements) with regard to a minimum water demand for a target spread. An example for the optimization of blends of ordinary Portland cement (OPC) and supplementary cementitious materials (SCM) in terms of clinker-efficiency is given leading to improved strength with reduced environmental impact in comparison to OPC based mixes.

Microstructure and phase assemblage of low-clinker cements during the early stages of carbonation

Blending Portland cement with fly ash or ground granulated blast furnace slag effectively reduces its carbon footprint. However, these materials hydrate more slowly than Portland cement. Therefore, their early-stage behaviour is of interest.Fly ash- and slag-containing cement pastes were cured for 72 h and 28 days before exposure to ambient air (ca. 400 ppm). Changes in carbonation behaviour at 0%, 30% and 60% replacement and w/b ratios (0.40 & 0.57) were studied. All Ca-bearing hydrate phases carbonated, but portlandite effectively buffered carbonation of other phases. Complete portlandite consumption permitted decalcification of the other phases, with substantial removal of Ca and Al from C-S-H and increased silicate polymerisation. When portlandite was present, monosulfoaluminate transformed to hemi- and monocarboaluminate, but complete decalcification only occurred when portlandite was no longer available. Reduced w/b ratios improved carbonation resistance for materials with moderate substitution but couldn't mitigate the effects of high replacement levels.

Use of clay from a local source for calcination and subsequent preparation of the mixed cement

This paper deals with the use of calcinated clay and micronized limestone as supplementary cementitious materials (SMCs) for preparation of blended Portland cement CEM II/B-M (Q-LL). Clay used in this study was calcinated at 700°C and pozzolanic activity after calcination was assessed using accelerated R3 pozzolanic test and modified Chapelle test. The influence of calcinated clay and limestone addition on mechanical properties and hydration process was investigated and an optimal ratio for 35% clinker replacement was found. Initial decrease of mechanical strength at early ages, caused by SCM addition, was almost compensated during maturation of the binder.

Recent Advances in Magnesia Blended Cement Studies for Geotechnical Well Construction—A Review

The current paper presents a literature review on the studies of incorporation of magnesia (magnesium oxide) into Portland cement material from the geotechnical well construction perspective. Starting with a comparison of application conditions between civil construction and geotechnical well cementing, this work reviewed the Portland cement categorizations, magnesia manufacturing routes at first. Then, the physical-chemical-mechanical properties were investigated which includes the reactivity of magnesia, expansion influence from its hydration, and carbonation/dehydroxylation of magnesia blended Portland cement. The development of cement material hydration modeling methods is also summarized. Moreover, the experimental characterization methods have also been elucidated including composition determination, particle size analysis, volumetric variation measurement, compressive strength testing, shear-bond strength testing, transition state analysis, etc. Meanwhile, the results and conclusions were extracted from the literature. Through this route, a comprehensive understanding of the scientific research progress on magnesia blended Portland cement development for geotechnical well construction is derived. Additionally, it is concluded that incorporating magnesia into Portland cement can provide benefits for this material utilization in geotechnical well constructions provided the reasonable tuning among the characteristics of magnesia, the downhole surrounding conditions, and the formulation of the cement slurry. Satisfying these pre-conditions, the effective expansion not only mitigates the micro-annulus issues but also increases the shear bonding strength at the cementing interfaces. Moreover, the caustic magnesia introduction into Portland cement has the potential advantage on carbon dioxide geological sequestration well integrity compared with the Portland cement sheath without it because of the denser in-situ porous matrix evolvement and more stable carbon fixation features of magnesium carbonate. However, since the impact of magnesia on Portland cement strongly depended on its properties (calcination conditions, particle size, reactivity) and the aging conditions (downhole temperature, pressure, contacting medium), it should be noted that some extended research is worth conducting in the future such as the synchronized hydration between magnesia and Portland cement, the dosage limit of caustic magnesia in Portland cement in terms of CO2 sequestration and the corresponding mechanical properties analysis, and the hybrid method (caustic magnesia, Portland cement, and other supplementary cementitious materials) targeting the co-existence of the geothermal environment and the corrosive medium scenario.

Influence of the amount of calcium sulfate on physical/mineralogical properties and carbonation resistance of CSA-based cements

Binary and ternary binders, Calcium SulfoAluminate (CSA) clinker plus anhydrite (A) and blends of Portland cement, CSA clinker, and A, respectively, are examined in order to understand the effect of the A/CSA clinker ratio (A/CSA) on hydration process, physico-mechanical properties and durability against carbonation. The study revealed that: (i) in binary systems the increase of the A/CSA has a positive influence on the physical performance, but worsens the resistance against carbonation (ii) in ternary systems a non-linear behavior related to the physical aspects is observed, being the system with the intermediate A/CSA the best performer in terms of dimensional stability and carbonation resistance.The effect of carbonation on the hydrate phase assemblage was studied through a multi-technique approach and results were supported by thermodynamic models, indicating that the optimal dosage of sulfates is strictly dependent on the carbonation exposure and the ternary systems are more durable than the binary ones.

Investigating the potential of low-grade calcined clays to produce durable LC3 binders against chloride ions attack

Utilization of limestone calcined clay cements (LC3) as a recently developed ternary blends could be a promising economic approach to reduce the environmental impacts of Portland cement production. This study presents a comparative experimental investigation between LC3 mortars and binary blends, prepared with kaolinitic calcined clays as prominent sustainable resources of supplementary cementitious materials (SCMs). In this regard, four different low to high-grade kaolinitic clays, provided from various resources, were calcined and incorporated in both binary and LC3 blends. Furthermore, the pure Portland cement and limestone Portland cement blends were also prepared to compare the results with calcined clay containing mixtures. Thermogravimetric analysis (TGA) was performed on paste samples to study the phase assemblage of systems. Besides, compressive strength, water absorption and sorptivity, total and free chloride ions penetration profiles, and chloride ions diffusion coefficients of mortar mixtures have been investigated. According to experimental results, the pozzolanic reactivity of calcined clays is not only influenced by the metakaolin content and thermal activation process, but also by the crystallinity of these materials. Besides, although the compressive strength of binary and LC3 mortars may be lower than the control mixture, but the permeability and resistance against chloride ions ingress have been significantly enhanced. Ultimately, low-grade calcined clays have been recognized as a promising resource to produce LC3 blends with adequate durability against chloride ions ingress.

Performance evaluation of limestone-calcined clay (LC2) combination as a cement substitute in concrete systems subjected to short-term heat curing

This paper evaluates the suitability of limestone-calcined clay (LC2) combination as a cement substitute material in concrete systems subjected to steam curing. Concrete with blends of portland cement and LC2 were subjected to short-term heat curing and compared against concrete with plain portland cement and fly ash-based binder (at 30% replacement) for two different concrete systems (a) 400 kg/m3 binder content and 0.40 w/b, and (b) 360 kg/m3 binder content and 0.45 w/b. Several parameters were considered to evaluate the potential of LC2 in such applications, which include - improvements in the 1-day compressive strength, strength gain at later ages, and resistance to chloride-ion penetration. Furthermore, the pore structure, phase assemblage and SEM micrographs were used to assess the alteration in the microstructure at 1-day to elucidate the microstructural development due to steam curing regime.The results show that concrete prepared with LC2 could achieve 1-day compressive strength equal to OPC concrete, which was not achieved with fly ash mixes. The durability performance was similar in both normal and steam-cured concretes across all the binder systems considered in the study. Concrete prepared with LC2 showed significant improvement in 1-day strength due to short-term heat curing. Correspondingly, there was a significant reduction in the porosity and critical pore diameter at 1-day for LC2 systems subjected to steam curing, while fly ash mixes showed almost negligible change in pore structure. LC2 systems could produce a dense microstructure at 1-day, despite the absence of ettringite and carboaluminate phases at elevated curing temperature. The study put forward the beneficial use of LC2 in precast fabrication units with steam-curing requirement for improved early-age strength and durability performance.

Thermal conductivity and shrinkage properties of slag-based cement concretes

The thermal conductivity, specific heat, and total drying shrinkage test of slag blended OPC cement is conducted by using a Hotdisk-2500S thermal conductivity, and non-contact shrinkage deformation measurement apparatus based on ISO 22007-2 and GB/T50082-2009 test standards, respectively. The influence of replacement rates of slag cement (0, 30, 50, and 70%) and high-temperature exposure (21, 200, 400, 600, and 800 °C) on the thermal properties of concrete is analysed. The results show that for all three concretes, the thermal conductivity initially decreases with increasing temperature up to 400 °C, then after it remains almost constant between 400 and 600 °C, and gradually begins to decrease again up to 800 °C. Furthermore, thermal diffusivity of concrete group G-70, shows 21.4, 21.6, and 37.6% increment in 21, 200, and 600 °C temperature exposure respectively compared to concrete group G-0. Though, as the exposure temperature keeps rise to 800 °C, its value starts to decrease. Furthermore, the results indicated that high volume slag cement content in the concrete mix lessen the drying shrinkage of the concrete at later age. Test data is used as a function of temperature and slag replacement to establish high temperature relations for thermal properties. The proposed thermal property relationships can be used as input data for validation in computer programs and to evaluate the response of OPC and slag blended Portland cement concrete structures subjected to fire.

Sulfate and Chloride Resistance Properties of Portland Cement Blends

About 53% area of Bangladesh is alluvial deposited and affected by sulfate, salinity and chloride in water and soil. Existing sulfate and chloride can severely damage the building in coastal regions. In this paper durability of cement is evaluated on the basis of strength of mortar cube, concrete cylinder test. Besides the sulfate resistance is measured by change of length of the mortar bar specimens during exposure to sulfate solution and the attacking chloride properties by Rapid chloride ion penetration test using OPC, PCC, 20% FA, 30% FA and 40% FA. The strength was observed in cube sample about 40.65, 37.2MPa after 13 weeks in sulfate solution and linear expansion was obtained about 0.28% and 0.133% for OPC and PCC cement with reference to the water. The compressive strength of the cylindrical specimens was about 16.96, 18.34 MPa for OPC and PCC, respectively at the age of 28 days. The permeability of chloride ion of OPC sample was 22.8% higher than the PCC at this age.
 Journal of Engineering Science 12(1), 2021, 69-75

Effect of filler particle characteristics on yield stress and viscosity of fresh sulfur composites

The amount and properties of fillers greatly affect the workability of sulfur composites. In addition, modified sulfur has fluidity only above approximately 115 °C, and its rheology may depend on the temperature. This study aimed to mainly quantify the effects of mixing temperature and filler particle characteristics on the yield stress and viscosity of fresh sulfur composites by applying suspension rheology theory. Sulfur composites containing mineral fillers, such as different blends of fly ash and Portland cement, were examined. The test results revealed that the yield stress of the sulfur composites was influenced by both the type and volumetric ratio of fillers, whereas the viscosity was governed by the specific surface area of filler particles. At 140 °C, the sulfur composites attained a higher yield stress and viscosity than at 120 °C. In addition, the intrinsic viscosity of the sulfur composites was dependent on the filler type and not on its volume ratio. The sulfur composites were well described by conventional yield and viscosity models commonly applied for suspension materials, when the filler volume ratio was less than 30%.

Performance of GGBS Cement Concrete under Natural Carbonation and Accelerated Carbonation Exposure

One of the primary problems related to reinforced concrete structures is carbonation of concrete. In many cases, depth of carbonation on reinforced concrete structures is used to evaluate concrete service life. Factors that can substantially affect carbonation resistance of concrete are temperature, relative humidity, cement composition, concentration of external aggressive agents, quality of concrete, and depth of concrete cover. This paper investigates the effect of varying the proportions of blended Portland cement (ordinary Portland cement (OPC) and ground granulated blast-furnace slag (GGBS)) on mechanical and microstructural properties of concrete exposed to two different CO2 exposure conditions. Concrete cubes cast with OPC, and various percentages of GGBS (0%, 30%, 50%, and 70%) were subjected to natural (indoor) and accelerated carbonation exposure. The aim of this paper is to present the research findings and authenticate the literature results of carbonation by using GGBS cement in partial replacement of OPC. The concretes with OPC are compared to concretes with various percentages of GGBS, to assess the carbonation depth as well as rate of carbonation of GGBS-based concretes, under both accelerated carbonation and natural carbonation exposure conditions. Even though GGBS cement increases the carbonation depth, the results are not the same with different GGBS replacement percentages. A correlation is made between concrete samples exposed to 15 ± 2% carbon dioxide (CO2) concentration and those exposed to natural CO2 concentration. The results reveal that the products formed by carbonation are similar under both exposure conditions. The experimental tests also revealed that GGBS cement concrete has a lower carbonation resistance than OPC concrete, due to the consumption of portlandite by the pozzolanic reaction. The combination of 70% OPC and 30% GGBS behaved well enough with respect to accelerated carbonation exposure, the depth of carbonation being roughly equivalent to that of control group (100% OPC). The results also show that rate of carbonation becomes more sensitive as the percentage of GGBS replacement increases (binder ratio), rather than duration of curing. Concretes exposed to natural carbonation (indoor) achieved lower carbonation rates than those exposed to accelerated carbonation.

Exploring Structural Evolution of Portland Cement Blended with Supplementary Cementitious Materials in Seawater.

The present study investigated the structural evolution of Portland cement (PC) incorporating supplementary cementitious materials (SCMs) exposed to seawater. The samples were made with replacing Portland cement with 10 mass-% silica fume, metakaolin or glass powder. The reaction degree of SCMs estimated by the portlandite consumption shows that metakaolin has the highest reaction degree, thus metakaolin-blended PC exhibits the highest strength. The control exposed to seawater exhibited 14.82% and 12.14% higher compressive strengths compared to those cured in tap water at 7 and 28 days. The samples incorporating metakaolin showed the highest compressive strength of 76.60 MPa at 90 days tap water curing and this was 17% higher than that of the control. Exposure to seawater is found to retard the rate of hydration in all SCM-incorporating systems, while the strength development of the neat PC system is enhanced. The main reaction product that forms during exposure to seawater is Cl-AFm and brucite, while it is predicted by the thermodynamic modelling that a significant amount of M-S-H, calcite and hydrotalcite is to form at an extended period of exposure time.

THE MULTIFRACTAL PROPERTY OF HETEROGENEOUS MICROSTRUCTURE IN CEMENT PASTE

Highlights (1) Microstructure of cement paste is acquired through computed tomography. (2) Multifractal property of heterogeneous microstructure is examined. (3) Incorporation of blast furnace slag results in a decrease of singularity width. The microstructure of cement paste is highly heterogeneous in nature that plays a significant role in macroscopic performance. This paper is dedicated to examining the multifractal property of microstructure in cement paste, based on which the microstructural heterogeneity could be quantified meanwhile. In particular, the X-ray computed tomography is adopted to acquire the realistic three-dimensional (3D) microstructure. Then, a thorough examination is performed on the multifractal property with respect to the partition function, the generalized dimension and the multifractal spectrum. Results indicate that the multifractal property in terms of local porosity can be recognized for the heterogeneous microstructure in both ordinary and blast furnace slag blended Portland cement pastes. The multifractal spectrum or singularity width is available to account for the degree of heterogeneity.

Self-healing potential of supplementary cementitious materials in cement mortars: Sorptivity and pore structure

This paper presents the autogenic self-healing potential of Portland cement (PC) blends made with conventional supplementary cementitious materials (SCMs), to improve the water-tightness by reducing the overall pore size. Mortar samples were prepared by mixing PC, sand and water, and partially replacing PC by either silica fume (SF), pulverised fuel ash (PFA), or ground granulated blast-furnace slag (GGBS). Damaged samples were subjected to a water bath to heal microcracks and recover the water-tightness, by further hydration of the starting minerals. Water absorption and density measurements in undamaged, damaged and healed conditions were used to determine the autogenous healing potential of SCMs mixes, showing a post-healing absorption recovery of up to 68% compared to the mix with PC only. Thermal analysis, XRD and MIP measurements confirmed the capability of SCMs to promote the formation of hydrated phases, and reduce the overall pore size by more than 88% compared to PC mixes.

Geopolymer Cement: an Initiative towards the Replacement of Grey Cement by Green Cement in Future

The emissions of greenhouse gases such as carbon dioxide from the production of Ordinary Portland Cement and Blended Portland Cement have widely affected the environment with increase in infrastructure development worldwide. Secondly, due to the continuous mining of limestone for the production of cement there is also simultaneous depletion of natural resources and hardly will it last up to maximum 40 years. Hence we need to switch over to some other alternate binders for constructions purpose in future. Geopolymer Cement is one of the inventions which is produced by a polymeric chain reaction of alkali-activated alumino-silicate materials better known as alkali activator (NaOH/Na2SiO3) binders with the industrial by-product materials such as Fly Ash, Rice Husk Ash, Slag, Crusher Dust etc. and provides high compressive strength which is comparable to BPC and reduces the carbon foot print. The objective of our study is to prepare the low CO2 foot print green Geopolymer Cement which may substitute the Ordinary Portland Cement and Blended Portland Cement in future and will helpful to reduce the greenhouse effect up to some extent and takes an initiative towards the green revolution movement.

Geopolymer Cement: an Initiative towards the Replacement of Grey Cement by Green Cement in Future

The emissions of greenhouse gases such as carbon dioxide from the production of Ordinary Portland Cement and Blended Portland Cement have widely affected the environment with increase in infrastructure development worldwide. Secondly, due to the continuous mining of limestone for the production of cement there is also simultaneous depletion of natural resources and hardly will it last up to maximum 40 years. Hence we need to switch over to some other alternate binders for constructions purpose in future. Geopolymer Cement is one of the inventions which is produced by a polymeric chain reaction of alkali-activated alumino-silicate materials better known as alkali activator (NaOH/Na2SiO3) binders with the industrial by-product materials such as Fly Ash, Rice Husk Ash, Slag, Crusher Dust etc. and provides high compressive strength which is comparable to BPC and reduces the carbon foot print. The objective of our study is to prepare the low CO2 foot print green Geopolymer Cement which may substitute the Ordinary Portland Cement and Blended Portland Cement in future and will helpful to reduce the greenhouse effect up to some extent and takes an initiative towards the green revolution movement.

Long-term cement hydration studies with isothermal calorimetry

The purpose of this study was to investigate for how long the thermal power of hydration can be measured with isothermal calorimetry, which is a general measurement technique with stable properties that, in many cases, can detect low rates of processes. Measurements were conducted for 365 days on cement paste with Portland cement, fly ash blended Portland cement and different water-to-binder ratios. The results showed that all the tested systems still produced a measureable signal after one year. The samples with Portland cement were also analyzed by XRD after 365 days, and phase composition calculations were made with GEMS. Together with the calorimetric results, these results were used to determine the degree of hydration by five methods, the results of which showed good agreement.