Ordinary Portland Cement Content Research Articles

Optimizing compressive strength of quaternary-blended cement concrete through ensemble-instance-based machine learning

Optimizing the composition of concrete, particularly when incorporating ordinary Portland cement (OPC) along with supplementary materials such as ground granulated blast furnace slag (BF), fly ash (FA), and silica fume (SF), poses challenges due to the intricate nonlinearity inherent in concrete properties. Addressing this challenge has urged growing interest in employing Machine Learning (ML) techniques for precise property assessment. In this investigation, various predictive models, encompassing eXtra Gradient Boosting (XGB), random forests (RF), and K-Nearest Neighbor (KNN) algorithms were formulated to predict the compressive strength (CS) of ternary-blended concrete incorporating OPC, BF, FA, and SF. Through comprehensive analysis of an extensive dataset comprising 810 distinct records, the study identifies optimal concrete blends, providing invaluable insights for practical applications. Evaluation of ML models underscores the superior performance of XGB, with a coefficient of multiple determination (R2) values of 0.923 and 0.997 for training and testing datasets, respectively, indicative of exceptional predictive accuracy. Additionally, SHAP values underscore the importance of input age, water–binder ratio, and OPC content. This research enhances understanding of ternary-blended concrete characteristics, offering practical implications for construction practices and laying a foundation for future research endeavors to refine ML models, explore attribute interactions, and optimize concrete constituent proportions for broader civil engineering applications.

Design and Preparation Technology of Green Multiple Solid Waste Cementitious Materials.

For solid waste-based cementitious materials, most scholars focus their research on the hydration reaction of cementitious materials, but there is still a lack of solid waste design that comprehensively considers mechanical properties and durability. Therefore, this article focuses on exploring the mix of design and the microscopic and macroscopic properties of multi solid waste cementitious materials (MSWCMs), namely steel slag (SS), slag powder (SP), desulfurization gypsum (DG), fly ash (FA), and ordinary Portland cement (OPC). According to the orthogonal experimental results, the compressive strength of MSWCMs is optimal when the OPC content is 50% and the SS, SP, DG, and FA contents are 10%, 20%, 5%, and 15%, respectively. The MSWCMs group with an OPC content of 50% and SS, SP, DG, and FA contents of 5%, 15%, 5%, and 25% was selected as the control group. The pure OPC group was used as the blank group, and the optimal MSWCMs ratio group had a 28-day compressive strength of 50.7 megapascals, which was 14% and 7.6% higher than the control group and blank group, respectively. The drying shrinkage rate and resistance to chloride ions were also significantly improved, with maximum increases of 22.9%, 22.6%, and 8.9%, 9.8%, respectively. According to XRD, TG-DTG, and NMR testing, the improvement in macroscopic performance can be attributed to the synergistic effect between various solid wastes. This synergistic effect produces more ettringite (AFt) and C-(A)-S-H gel. This study provides a good theoretical basis for improving the comprehensive performance of MSWCMs and is conducive to reducing the use of cement, with significant economic and environmental benefits.

A New Method for Proportioning Sustainable, Economic, and Resilient Concrete

The ordinary Portland cement (OPC) component of concrete is the highest contributor to concrete’s cost and carbon footprint. Historically, code-writing organizations have required a high volume of paste in concrete mixtures by imposing minimum limits on the OPC content for a given application. However, high paste contents can result in dimensional instability, higher costs, higher carbon footprints, and lower durability. Minimizing the OPC content in concrete can provide economic, durability, and sustainability benefits. This study hypothesizes that the amount of OPC required to achieve some required fresh and hardened characteristics is highly dependent on the aggregate characteristics, supplementary cementing material (SCM) characteristics, and proportions of these. Given this, this research proposes using the amount of voids in the aggregate system (AV), or more specifically the paste volume-to-aggregate void ratio (PV/AV); SCM reactivity; and the SCM replacement level as key parameters to proportion concrete mixtures with minimum OPC contents to meet sustainability, economic, and resilience (SER) requirements. A new mixture proportioning procedure, referred to here as the SER proportioning method, is developed in this study based on assessing AV and identifying an optimal PV/AV that satisfies the required concrete characteristics. The results show that implementing the SER mixture proportioning method and including SCMs, or more specifically off-spec fly ashes (OFAs), can lead to significant reductions in the paste content and associated reductions in the cost and embodied carbon footprint of concrete.

Performance of green high-strength concrete incorporating palm oil fuel ash in harsh environments

Abstract The corrosion of steel reinforcement by chloride is commonly recognized as a key factor that contributes to the degradation of durability in reinforced concreae structures. Using supplementary cementitious materials, such as industrial and agricultural waste materials, usually enhances the impermeability of the concrete and its corrosion resistance, acid resistance, and sulfate resistance. This study’s primary purpose is to examine the effects of replacing ordinary Portland cement (OPC) with ultrafine palm oil fuel ash (U-POFA) on the corrosion resistant performance of high-strength green concrete (HSGC). There were four HSGC mixes tested; the first mix contained 100% OPC, while the other mixes replaced OPC mass with 20%, 40%, and 60% of U-POFA. The performance of all HSGC mixes containing U-POFA on workability, compressive strength, porosity, water absorption, impressed voltage test, and mass loss was investigated at 7, 28, 60, and 90 days. Adding U-POFA to mixes enhances their workability, compressive strength (CS), water absorption, and porosity in comparison with mixes that contain 100% OPC. The findings clearly portrayed that the utilization of U-POFA as a partial alternative for OPC significantly enhances the corrosion-resistant performance of the HSGC. In general, it is strongly advised that a high proportion of U-POFA be incorporated, totaling 60% of the OPC content. This recommendation is the result of its significance as an environmentally friendly and cost-effective green pozzolanic material. Hence, it could contribute to the superior durability performance of concrete structures, particularly in aggressive environmental exposures. Highlights The corrosion resistance performance of high-strength green concrete was investigated. Ultrafine palm oil fuel ash as a partial alternative of cement mass with 20%, 40%, and 60% was used. HSGC performance was evaluated in terms of workability, compressive strength, water absorption, porosity, impact stress testing, and mass loss.

Permeable Blocks with Waste Glass as Coarse Aggregate

In order to reduce the negative impact of waste glass and urban heat on the environment, this research aims to use waste glass cullet as an aggregate in concrete paving blocks. This work aims to produce porous pavement using two sizes of waste glass and ordinary Portland cement (OPC). Two layers of paving blocks with different aggregate sizes were planned. The first part of the work was to determine the best OPC content. The results showed that the largest aggregate-based porous paving block had the highest compressive strength and acceptable permeability. Then, designed porous block (DPB) was designed, which consisted of two layers, with the upper layer consisting of small aggregates and the lower layer consisting of large aggregates, and cement mortar (80 wt% cement powder and 20 wt% glass powder) was used as the binder. Compressive strength and permeability were the criteria. The pavement can release heat better than conventional pavements and is safe because of the skid resistance, which meets the criteria.

Utilization of ground granulated blast-furnace slag and electrolytic manganese residue as a low-carbon cementitious material

Ground granulated blast-furnace slag (GGBS) is a common substitute for ordinary Portland cement (OPC). However, GGBS–OPC lacks early strength when OPC content is low (<50%). A new cementitious material called GGBS–OPC–EMR (GOE) was developed by adding electrolytic manganese residue (EMR) to address this issue. Tests were conducted using XRD, SEM, and TG to analyze the micro-structural mechanisms of strength development in GOE. Environmental and economic evaluations were conducted, including CO2-eq (carbon dioxide equivalent) analysis, leaching tests, and economic analysis. Results showed that mixture of GGBS, OPC, and EMR in a 4:2:1 ratio increased the unconfined compressive strength by 25% after 28 days compared to OPC while reducing cement consumption by 70%. Major hydration products in GOE were C–S–H and ettringite (AFt), with approximately 14% EMR promoting AFt production. GOE reduced CO2-eq emissions by 35.9% and saved $46.6/ton compared to OPC. Leaching tests demonstrated GOE's ability to stabilize heavy metals, sulfate, and ammonia nitrogen.

An Evaluation of the Performance of Lateritic Soil Stabilized with Cement and Biochars to be Used in Road Bases of Low-Volume Sealed Roads

The study investigated the effects of adding Saw Dust Ash (SDA) and Sugar Cane Bagasse Ash (SCBA) on the strength of cement with stabilized lateritic soil. The experiments carried out in both the lateritic soil and stabilized lateritic soil considered Atterberg limits, sieve/hydrometer analysis, compaction, soaked California Bearing Ratio (CBR), and Unconfined Compressive Strength (UCS) at various curing periods. Ordinary Portland Cement (OPC) was introduced into the soil with varying content (0%, 3%, 5%, 7%, and 9%) by weight of the soil sample. The results showed that CBR and UCS increased to 175.7% and 1.999 MPa, respectively, as the OPC content increased to 7%. The optimal OPC content to meet the 1.5MPa UCS requirement for road bases on low-volume sealed roads in Kenya was 7%. The next treatment involved partially replacing the OPC content with SDA and SCBA in different doses (7-0-0%, 5-1-1%, 3-2-2%, 1-3-3%, and 0-3.5-3.5%, respectively) for various curing periods. The results showed that CBR and UCS decreased as the OPC content decreased and SCBA and SDA increased. At a content of 5% OPC, 1% SDA, and 1% SCBA, UCS and CBR were 1.877 MPa and 149%, respectively, suggesting that it was the optimal dosage to meet the 1.5MPa UCS requirement for road bases on low-volume sealed roads in Kenya. The durability test indicated that the specimens treated with 5% OPC, 1% SDA, and 1% SCBA met the 80% durability index mark, as recommended for cement-stabilized soils. Previous studies used SDA and SCBA separately with cement or lime to stabilize the subgrade or subbase of roads, but this study focused on using these materials together as a partial OPC replacement to stabilize lateritic road bases for use in low-volume sealed roads. The goal was to use local agricultural and industrial waste materials in road construction and improve the strength characteristics of road bases while preserving the environment through waste utilization.

Effect of microcapsules on the self-repairing ability of limestone calcined clay cement (LC3) mortar at different temperatures

The fundamental principle of sustainable civil engineering revolves around minimizing energy and resource consumption throughout the entire life cycle of a structure, including raw material production, construction, and maintenance. To achieve this, efficient utilization of raw materials is crucial. LC3, a novel low carbon cementitious material, offers sustainability advantages. In this paper, LC3 mortar was prepared by incorporating limestone, calcined clay and gypsum as supplementary cementitious materials, thereby replacing 50% of ordinary Portland cement (OPC). Additionally, microcapsules, comprising 4% of the total mass of cementitious materials, were introduced. This reduction in OPC content not only decreases energy consumption and CO2 emissions during cement preparation but also capitalizes on the self-repairing ability of microcapsules to mend microcracks that occur within the cement-based material during its service life. Consequently, the durability of cement-based materials is enhanced. To evaluate the effects of self-repairing on mechanical properties, permeability, and maximum amplitude at different temperatures, a comparison was made between OPC mortars and LC3 mortars. Furthermore, the self-repairing ability of surface cracks in microencapsulated mortar was assessed. The findings demonstrate that the mechanical and permeability properties of LC3 mortar (designated as CA2) exhibit no significant deviation from those of OPC mortar (designated as CA0). Moreover, under the same conditions, LC3 mortar containing microcapsules (designated as CA3) displays superior self-repairing ability compared to OPC mortar containing microcapsules (designated as CA1). Additionally, the self-repairing characteristics of microcapsules in LC3 mortar improve with increasing temperature. The self-repair process involving epoxy resin (repairing agent) and 2-ethyl-4-methylimidazole (curing agent) follows a quasi-second-order reaction kinetic model. Surface cracks with an initial width exceeding 0.4 mm in CA3 were entirely repaired within a 72-hour period.

Applicability of the Formation Factor for Different Alternative Binder Types Investigated on Mortars

The high energy demand and associated CO2 emissions to produce ordinary Portland cement (OPC) create the need for alternative types of binders that can be produced in a more environmentally friendly manner. These alternative binders either have a reduced OPC content or can be produced entirely without the use of OPC clinker. To allow their widespread use also in reinforced concrete components, these binders must meet the same durability requirements as types of cement that have already been standardized. This requires a thorough characterization of the materials and, in addition, a verification of the applicability of the evaluation criteria known from the traditional binders. One of the most important factors influencing the transport processes in the material and therefore the durability is the penetration resistance of the pore structure for aggressive species, such as chloride ions. One key parameter for describing the pore structure is the formation factor (FF), which is used for various applications to evaluate durability. It is determined based on the ratio of the electrical resistivity of the concrete and of the pore solution. A high resistivity also influences the corrosion process of depassivated steel reinforcement in concrete or mortar: by inhibiting ion transport, the corrosion rate may be limited. In this study, mortars produced with different alternative binders are characterized in terms of their FF and pore size distribution. In addition, chloride migration coefficients determined by the rapid chloride migration test are related to the FF. The test program includes nine different alternative binders and two reference cements. In addition to a CEM I and CEM III/B, two calcined clays and a modified steel mill slag were investigated as supplementary cementitious materials, as well as a calcium sulfoaluminate () cement and a calcium silicate hydrate (C-S-H) binder. Four materials belong to the group of alkali-activated mortars: Two geopolymers and two alkali-activated slags were investigated here. It is shown that the AC resistances and the conductivities of the pore solutions differ greatly among the mortars investigated. The FF is a suitable parameter for a simplified estimation of the chloride penetration resistance of the investigated alternative binders, provided that realistic values of the pore solution conductivities are determined and used for the calculations.

Experimental study on the fatigue performance of emulsified asphalt cold recycled mixtures

With advantages such as energy saving, environmentally friendliness, green, low carbon emission, and high economic efficiency, emulsified asphalt cold recycled mixtures (CRM) have been used increasingly extensively, and their range of application has also extended from the base layer to the lower surface layer. Thus, studying their fatigue performance is particularly important. The inevitable secondary compaction in the construction process significantly affects the fatigue performance of emulsified asphalt CRM. However, relevant studies concerning the effect of secondary compaction on the fatigue performance of emulsified asphalt CRM are still lacking, and the conclusions of existing studies investigating the effect of emulsified asphalt CRM composition on its fatigue performance are inconsistent. In this study, the effect of emulsified asphalt content, cement type, cement content, and reclaimed asphalt pavement (RAP) content on fatigue performance was investigated through controlled strain four-point bending fatigue tests, and the effect of secondary compaction on the fatigue performance of CRM was comparatively studied by simulating the secondary compaction with indoor wheel rolling tests. The results showed that the fatigue performance of CRM increased significantly with the increase of emulsified asphalt content. With the increase of ordinary Portland cement content, the fatigue performance improved and then degraded. The fatigue performance peaked at the cement content of 1.5% and then decreased sharply. Mixing with high early-strength cement resulted in little improvement in fatigue performance but reduced it at the content of 3%. The fatigue performance increased with the increase of RAP content. Secondary compaction substantially improved the fatigue performance of CRM, and the fatigue performance was underestimated by the existing evaluation methods. This study could provide guidance and reference for the composition design of CRM and the objective evaluation of its fatigue performance.

Engineering behavior of cement-treated stiff clay subjected to freezing/thawing cycles

Deep soil mixing (DSM) with cement has been adopted to enhance soft ground and stabilize problematic soils worldwide. The literature is limited to DSM-treated soft soils with low cement contents, temperate curing conditions, short-term stability, and compressive properties. Due to the increased applications of DSM in cold regions, the study on the mechanical behavior of cemented soils (soilcrete) with high cement content under freezing/thawing (F/T) conditions has become important. In the present study, cylindrical specimens formed by mixing Edmonton stiff clay with high ordinary Portland cement contents (over 20%) were prepared in the lab to examine the mechanical behavior of soilcrete under unexposed and F/T exposed conditions. Unconfined compression and tensile tests were performed to assess changes in the mechanical properties of specimens cured for 1 to 300 days after 1 to 20 F/T cycles at freezing temperatures from −2 to −20 °C. Test results showed that the compressive and tensile strength of soilcrete increased with curing age and decreased significantly with more F/T cycles. Additionally, the mechanical strength loss in the −5 to −10 °C range was more significant than in the −2 to −5 °C range, indicating that the lower temperature caused more severe damage to the samples. Although the mass loss was <5% for most samples, it increased with more F/T cycles and the declining temperature, indicating that the mass loss was able to reflect the impact of F/T cycles.

Study on Mix Proportion Optimization and Microstructure of Coal-Based Solid Waste (CSW) Backfill Material Based on Multi-Objective Decision-Making Model.

The preparation of underground-backfill material from CSW can be used for large-scale disposal of solid waste. The proportion of backfill material plays an important role in transportation and backfilling effect, and the mix-proportion optimization of backfill material is essentially a multi-factor and multi-objective optimization problem. In this paper, to obtain the mix proportion of backfill materials with optimal comprehensive-evaluation indexes, and suitable for the engineering application, the fluidity and strength of backfill material, mainly composed of coal gangue(CG), fly ash (FA), flue gas desulfurization gypsum (FGD gypsum), and gasification coarse slag (GCS), were tested by single-factor transformation method, and the effects of various solid wastes on the slump-flow, bleeding rate and early strength of backfill material were analyzed. The optimal mix proportion of CSW with the slump-flow, bleeding rate, and 3-day and 7-day strengths as the evaluation indicators is FA: GCS: FGD gypsum: CG = 25%:25%:25%:25%, according to the multi-objective decision model. Furthermore, the comprehensive evaluation index that meets the requirements of mine backfilling is obtained by changing the ordinary portland cement (OPC) content, that is, the optimal OPC content is 10% of the total solid waste, and the mass concentration is 78%. Finally, the pore structure, micromorphology, and composition of the backfill material with the optimal mix proportion were studied by Mercury Intrusion Porosimetry (MIP), X-ray Diffraction (XRD), and Scanning Electron Microscope-Energy Dispersive Spectrometer (SEM-EDS). The research results provide a good reference for the field application of CSW for underground backfilling.

ECO2 framework assessment of limestone powder concrete slabs and columns

Producing limestone powder requires comparably far less energy than the production of ordinary Portland cement (OPC), making it a promising sustainable solution for partial replacement of OPC in concrete. Lower production energy could be translated into lower environmental impact and lower cost, which are two pillars of the sustainability of the resulting concrete. However, the question remains if replacing OPC with larger percentages of limestone powder would compromise the performance of the resulting concrete to a level that surpasses the environmental and economic gains. In order to assess the collective impact of these concretes, a performance-based multi-criteria decision analysis framework, ECO2, is used. For that purpose, 26 experimentally verified, concrete mixtures with and without limestone powder were evaluated through potential application in two types of reinforced concrete (RC) structural elements (slabs and columns) under identical environmental condition. The main results of the research showed a clear environmental advantage of concrete with a reduced OPC content, but the relatively higher superplasticizer amount in some cases could affect the final sustainability performance of the resulting mix. In the case of RC slabs, the best ECO2 score was obtained for concrete containing limestone powder. Mixtures with 200–250 kg of cement per unit volume of concrete had the highest ECO2 score for all the considered criteria. In the second case, due to the nature of the structural performance requirements in columns, the crucial influence of the concrete compressive strength is clear. The obtained results have shown approximately equal sustainability potential of OPC and limestone concretes in vertical elements such as columns. However, it seems that a certain improvement in the design of concrete mixtures with a high limestone powder content could make these competitive in all fields.

Characterizing polymer modified Cementations grout for semi-flexible pavement mixtures

In general, injecting grouts into small fractures, cavities, porous soil media, areas of water leakage, fixing cracks or defects in concrete, and filling spaces beneath metal bases or digging anchors are widely applied because of the great strength and workability of the cement in these materials. Furthermore, grout is employed effectively in the manufacturing semi-flexible pavement mixes. The goal of this research is to develop a polymer modified grout that can be used as a flowable grout for semi-flexible pavement mixes. The grout combination was made up of Ordinary Portland Cement (OPC), Acrylic emulsion (ACR), superplasticizer (SP), and water. ACR doses were 0.25, 0.5, 0.75, and 1.0 as a percent of OPC content. Flowability, compressive strength, and flexural strength tests were conducted to characterize the produced grout, with different amounts of the specified components being employed for each test. The results revealed that the flow time rises slightly as the ACR increases. It is also shown that there is an ideal ACR dose based on the compression strength. Where in most cases, the upgrading of the produced grouts was validated by a flexural strength test. As a conclusion, polymer modified grout worthily adds acceptable features to grout mechanical characteristics if the constituents of the grout are optimized.

A study on early age properties of hybrid alkali activated mortars cured under ambient condition

Fly ash based geopolymer can only be used in precast sections because of the need for heat curing. To expand its application beyond precast members, ambient cured geopolymer is required. In this investigation, an experimental study was performed to assess early age properties of ambient cured hybrid alkali activated mortars where the effect of ordinary Portland cement (OPC) content and molarity of NaOH solution on flowability and compressive strength were evaluated. The hybrid alkali activated mortars were prepared from combination of fly ash and ordinary Portland cement (OPC) at different proportions i.e., 90%:10%, 85%:15%, and 80%:20%, and activated with an alkaline solution. Sodium silicate (Na2SiO3) solution and sodium hydroxide (NaOH) solution were mixed to make alkaline solution. The sodium hydroxide solution was prepared with two different molarity i.e. 8 M and 16 M. The flowability was measured in terms of flow percentage and compressive strength was determined at the age of 1 day, 3 days, and 7 days. The obtained results revealed that flow percentage of hybrid alkali activated mortars declined as the OPC content and the NaOH solution’s molarity increased. On the other hand, compressive strength amplified when OPC content and the molarity of the NaOH solution increased. The compressive strength at the age of 7-day was increased from 19.73 MPa to 22.136 MPa i.e., 12.20 % with a rise in ordinary Portland cement content from 10% to 20% for 8 M NaOH solution. Similarly, for NaOH solution of 16 M, the compressive strength at the age of 7-day was increased by 21.62 % with a rise in OPC content from 10% to 20%. The XRD (X-ray diffraction) analysis revealed that in hybrid alkali activated mortars, there is a coexistence of calcium silicate hydrate (C-S-H) gel and geopolymer gels, resulting in a denser microstructure and higher compressive strength.

Characterizing polymer modified cementations grout for semi-flexible pavement mixtures

In general, injecting grouts into small fractures, cavities, porous soil media, areas of water leakage, fixing cracks or defects in concrete, and filling spaces beneath metal bases or digging anchors are widely applied because of the great strength and workability of the cement in these materials. Furthermore, grout is employed effectively in the manufacturing of semi-flexible pavement mixes. The goal of this research is to develop a polymer-modified grout that can be used as a flowable grout for semi-flexible pavement mixes. The grout combination was made up of Ordinary Portland Cement (OPC), Acrylic emulsion (ACR), superplasticizer (SP), and water. ACR doses were 0.25, 0.5, 0.75, and 1.0 as a percent of OPC content. Flowability, compressive strength and flexural strength tests were conducted to characterize the produced grout, with different amounts of the specified components being employed for each test. The results revealed that the flow time rises slightly as the ACR increases. It is also shown that there is an ideal ACR dose based on compression strength. Where in most cases, the upgrading of the produced grouts was validated by a flexural strength test. In a conclusion, polymer-modified grout worthily adds acceptable features to grout mechanical characteristics if the constituents of the grout are optimized.

Improving mechanical properties and shrinkage cracking characteristics of soft clay in deep soil mixing

Deep soil mixing is a ground improvement method that enhances the characteristics of soft soils by mechanically mixing the soil with cementitious binders such as cement and fly ash (FA). The objective of this paper is to investigation the post-treatment mechanical properties and shrinkage cracking characteristics of soft Bangkok clays treated with ordinary Portland cement (OPC) and FA. Unconfined compressive strength, modulus of elasticity, and shrinkage cracking after 7 and 28 days of mixture curing were measured. The effects of wet/dry cycling on the durability of mixtures were examined. Microstructures of treated soft clays were examined using scanning electron microscopy with energy dispersive x-ray analysis (SEM/EDX) techniques. Test results showed that strength and stiffness improvements of stabilised soft clays increased with OPC content but decreased with FA content, while the extent of sample shrinkage decreased with increasing FA content. Based on these results, we propose the preliminary guideline of applying 15% replacement of OPC with FA to obtain the optimal mixture ratios that allows FA to act as a shrinkage-reducing agent for deep soil mixing purposes. By adding OPC and 15% FA at a binder-per-water ratio (B/wc) of 0.4, the stabilised soft clay satisfied both strength and shrinkage cracking criteria for deep soil mixing purposes. SEM/EDX analyses further supported these experiment results. In addition, correlations between the mechanical properties and the chemical compositions of stabilised soft clay were derived and presented.

Recycling of concrete, ceramic, and masonry waste via alkaline activation: Obtaining and characterization of hybrid cements

This research aims to obtain and characterize alkali-activated hybrid cements based on concrete (Co), ceramic (Ce), and/or masonry (M) waste powders from crushed construction and demolition waste (CDW). Hydrated lime (Ca(OH)2) and ordinary Portland cement (OPC) were evaluated as sources of calcium. As an alkaline activator (AA), mixtures of sodium hydroxide and sodium silicate (NaOH + Na2SiO3) were used. The effects of the OPC (0–20%) and AA (0.1–0.4) contents were evaluated. The possibility of combining the Co, Ce, and/or M waste powders (mixed waste) was also studied for a wide range of proportions. The characterization of the hybrid cements included compressive strength determinations at 1, 7, 14, 28, 60, and 90 days of curing (25 °C and 60 °C−24 h), reaction kinetics (setting time) evaluations, and microstructural analysis by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDS). Hybrid cements (10% OPC) based on 90% Co, 90% Ce, and 90% M reached maximum compressive strength values (90 days at 25 °C) of up to 16.9, 36.5, and 25.2 MPa, respectively. The hybrid cement (10% OPC) based on the 30%Co–30%Ce−30%M mixed waste reached a strength of 32.2 MPa at 90 days (25 °C). The results obtained validate the potential of Co, Ce, and M waste powders to be used as geopolymeric precursors, even in scenarios where their separation is not possible (mixed wastes).

Development of a Commercial Screed Mortar with Low OPC Content by Incorporation of Biomass Fly Ash

Substitute Ordinary Portland Cement (OPC) by biomass fly ash (BFA) reduce the environmental impact produced by cement-based materials, and at the same time, decreased the economic and environmental burden associated with the landfilling of this waste. This study aims to evaluate the recycling of BFA as supplementary cementitious materials (SCMs) in a commercial screed mortar formulation. Two BFA varieties, both resulting from fluidized bed combustion of forest residues, were used to replace 17, 50, and 67 wt.% of OPC. The influence of simple pre-treatment processes of the BFA, such as sieving and grinding, in the fresh and hardened state properties of the mortars, was evaluated. The BFAs were characterized in terms of chemical (XRF) and mineralogical (XRD) composition, particle size distribution (laser diffraction-COULTER) and morphology (SEM). The prepared formulations were characterized in terms of workability, mass loss upon curing, bulk density, sorptivity (by immersion and capillary), flexural and compressive strength and durability to 25 freeze–thaw cycles. Both of the BFAs are potential SCMs. Substitution of 17 wt.% OPC with BFA complied with the product technical requirements for compressive and flexural strength (10 and 3 MPa, respectively), with the ground and sieved and just sieved BFAs perform slightly better than the as-received BFA.

Influence of Particle Packing Theories on Strength and Microstructure Properties of Composite Cement–Based Mortars

Supplementary cementitious materials (SCMs) have become a part of cementitious composites in the manufacturing of cement for improved performance and sustainability. Composite cement is one such type of cement in which ordinary Portland cement (OPC) is partially replaced with fly ash and granulated blast furnace slag (GBFS). In this study, the replacement levels of fly ash and GBFS are optimized to 20% and 30%, respectively, with a 50% OPC content. Apart from the superior properties of these binding materials, a better packing of aggregate comes in handy for improved properties. In this study, the modified Taufer model (MTM) and J. D. Dewar (JDD) model of proportioning the fine aggregates are adopted for improved packing density to obtain better mixes, and a comparison is made with proportions recommended by Indian standard (IS) 383 and IS 650. The packing density obtained in proportioning fine aggregates using the MTM, JDD, IS 650:2008, and IS 383:2016 methods are 0.6814, 0.6737, 0.6238, and 0.6008, respectively. The aggregate sizes recommended based on particle packing models (PPM) particularly, the MTM method tends to improve the packing by reducing the voids content. A direct influence of such effective packing can be observed from the microstructure studies conducted on different samples. MTM samples evidenced better packing compared to other methods of proportioning the mixes. The compound phase changes and development of microstructure were examined using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), a back scattered electron (BSE), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Also, the quantification of portlandite and calcium carbonate available in the samples was determined using thermogravimetric analysis (TGA) and differential thermal analysis (DTA) for different proportions. At 28 days, the specimens cast using MTM showed 11.11% and 15.5% higher compressive strength than the specimens prepared using IS 650:2008 and IS 383:2016, respectively. At every stage of curing, MTM mixes exhibited superior compressive strength.