Conventional Ordinary Portland Cement Research Articles

Constitutive model and deterioration mechanisms of uniaxial compressive behavior for calcium aluminate cement-based UHPC under simulated fire temperatures

Conventional ordinary Portland cement (OPC)-based UHPC is vulnerable to explosive spalling and its performance deteriorates significantly under fire temperatures. In this context, the calcium aluminate cement-based UHPC (AC-UHPC) was prepared by combining the calcium aluminate cement (CAC), recycled brick powder (RBP) and refractory steel fiber (RSF) according to the theory of maximum particle packing in this study, aiming at developing a green, economical and high-temperature resistant CAC-based material. This paper mainly investigated the influence of RSF and exposure temperature on the compressive properties of AC-UHPC, and revealed the degradation mechanism at elevated temperature through the analysis of apparent characteristics and microstructure. The results showed that the compressive strength and strain reached the maximum at 400 °C and 1000 °C, which were increased by 27.57–38.34 % and 2.89–3.44 times respectively compared with that at ambient temperature, while the initial elastic modulus gradually decreased. In the range of 20–400 °C, the phase transformation of hydration products mainly determined the strength of AC-UHPC. above 800 °C, the high temperature stability of RSFs has a significant impact on the residual compressive strength and deformation. At 1200 °C, the compressive strength decreased to 38.81–45.32 % and 24.88–30.41 % of the ambient temperature, respectively. Based on the test results, the prediction equations of compressive strength, peak strain and elastic modulus were proposed, and the empirical constitutive model and damage constitutive model of AC-UHPC considering exposure temperature and RSF volume fraction under uniaxial compression were established. This research offers valuable insights for the design and potential enhancement of green, economical and high temperature resistant CAC-based composites to improve the performance under fire conditions.

Sulfate resistance of alkali-activated flyash-slag-lime concrete: comparative study of drying-wetting cycles and conventional exposure

Abstract Sulphate resistance of concrete is a crucial parameter for design of offshore structures. Of late alkali-activated materials are been given due consideration for infrastructure projects. In this context, the present study aims to assess the sulphate resistance of Alkali-Activated Concrete (AAC) with ternary blend of flyash-Ground Granulated Blast furnace Slag (GGBS) and limestone as the principal binder. The first phase of the study includes the optimization of ternary AAC mix with the inclusion of limestone as a potential binder to popularly used flyash slag blends. The inclusion of 5% limestone powder into the binder matrix is found to have beneficial effect on the mechanical properties of the ternary blended AAC. Further, an increase in the limestone powder content is not found to influence mechanical properties positively. The AAC mix with 5% limestone of total binder content was therefore selected for further evaluation of sulphate resistance. The sulfate resistance is evaluated under the alkaline media by subjecting AAC specimens to constant immersion and alternative drying and wetting cycles. The mechanical characteristics and mass reduction of the exposed samples were tested and compared with the conventional Ordinary Portland Cement (OPC) specimens. Evaluations were conducted over periods of 30, 45, 120, and 365 days of exposure. Scanning Electron Microscopy (SEM), and Energy Dispersion Spectroscopy (EDS) were also used to determine the surface morphology and mineral composition of samples after 365 days of exposure periods. The Flyash-Slag-Lime AAC exhibits denser morphology in comparison to OPC-based concrete, which in turn offers enhanced sulphate resistance.

Theoretical investigation on elastic property evolutions of low volume fly ash concrete

AbstractToward expanding the application of fly ash in cement‐based materials, this study proposes a comprehensive study on predicting the elastic properties of low‐volume fly ash concrete, with the replacement levels limited to 30% or less. Unlike conventional ordinary Portland cement concrete, the inclusion of fly ash in concrete brings alterations in properties from both chemical and physical perspectives: (1) the presence of fly ash liberates the alkaline solution that consumes calcium hydroxide to generate secondary calcium silicate hydrate gels; (2) unreacted fly ash particles exhibits a refinement effect on the micropore structure and contributes to forming a denser solid matrix. In order to characterize these effects on the mechanical properties of fly ash concrete, this paper conducts qualitative assessment of hydration reactions and quantitative calculations of volumetric compounds in the material. Utilizing the Mori‒Tanaka scheme, a predictive model is then developed to integrate the hierarchical effects of constituents at multiple scales on the modulus of elasticity of low‐volume fly ash concrete. The reliability of the proposed model is validated through a series of mechanical tests involving various mix designs, as well as comparison with other published test data.

Flexural behaviour of reinforced one-part geopolymer concrete beams

The recent development of “one-part geopolymer” has significantly improved construction safety and convenience, establishing it as a highly promising new type of low-carbon binder with performance comparable to traditional cement. This study investigated the flexural performance of reinforced concrete (RC) beams made from one-part geopolymer concrete (OPGC), in comparison to conventional ordinary Portland cement (OPC) concrete beams. The microstructure of OPGC and conventional concrete were firstly compared. Four-point bending tests were then conducted on nine beams, including three OPC concrete beams and six OPGC beams. The influence of longitudinal reinforcement ratio on the flexural performance of OPGC beams was examined, and the bending performance of OPGC beams and OPC concrete beams was compared. Experimental results revealed that OPGC beams exhibited similar flexural performance to those cast with OPC concrete in terms of cracking development, failure modes, load-deflection curves, and strain distribution. In addition, an analytical model for estimating the flexural capacity of OPGC beams was proposed and validated against experimental results. Finally, the environmental and economic indices between the OPGC and OPC concrete beams were compared and analysed. This research provides valuable insights for the design and analysis of OPGC structural members.

Development of eco-efficient limestone calcined clay cement (LC3) mortars by a multi-step experimental design

Calcined clays and calcium carbonates can be used to reduce clinker factor in blended cements, offering significant economic and environmental benefits. Limestone calcined clay cements (LC3) combine them as supplementary cementitious materials (SCMs) for delivering a sustainable alternative to conventional Ordinary Portland Cement products, with envisioned applications in construction and rehabilitation of historical buildings.This study reports a chemometric approach to the development of LC3 mortars, targeting to minimize clinker content while maintaining or improving the technical characteristics. To evaluate their performance, apparent density, modulus of elasticity, open porosity, water absorption, flexural and compressive strength have been considered as responses. Multiple Linear Regression (MLR) and Principal Component Analysis (PCA) were employed in a three-step mixture-process design allowing to obtain LC3 mixtures with a 21 wt% reduction in clinker while achieving notable enhancements in the physical properties (open porosity −9% and water absorption −10 %), along with commendable increases in compressive strength (+17 %) when compared to benchmark mortars produced without SCMs. The successful integration of multivariate techniques in designing sustainable building materials is showcased, highlighting the potential of chemometric methodologies to reduce the environmental impact as well as to increase the performance of building materials.

Eco-friendly solid waste-based cementitious material containing a large amount of phosphogypsum: Performance optimization, micro-mechanisms, and environmental properties

Reusing phosphogypsum (PG) waste to manufacture eco-cementitious materials is sustainable. However, PG faces the challenge of high stacking volume and low utilization rate, and the low-content PG in eco-cementitious materials currently limits its large-scale potential application. This study provides a solution to use high-content PG to fabricate eco-friendly solid waste-based cementitious material (PBC), associated with ground granulated blast furnace slag (GGBS), fly ash (FA), and hydrated lime. Respond surface methodology (RSM) was undertaken to optimize and discuss the influence of independent design factors of GGBS, FA, and hydrated lime content on the unconfined compressive strength (UCS). Besides, the micro-mechanisms and environmental properties of PBC were also investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and the leachate test. The results indicated that the optimal raw material contents were (by mass): 50.57% PG, 28% GGBS, 20% FA, and 1.43% hydrated lime. The UCS of the optimal PBC mixture is 23.57 MPa at 28 days, which was confirmed via experimental verification (24.65 MPa). Hence, the RSM is an effective method for optimizing PBC's UCS. The micro-mechanisms analysis shows that the ettringite is the primary hydration product within the reaction system of PBC, which is attributed to the substantial amount of PG. The leachate test results indicate that the fluoride ion concentration of the leaching solution of PBC remains below the PG, and the pH value falls within the range of 6–9. The leaching test results meet the Chinese environmental standard of GB 8978-1996. The cost and CO2 emission of the optimal PBC mixture could achieve a reduction of 71.25% and 99.98%, respectively, compared to Ordinary Portland cement (OPC). The findings of this study could serve as a theoretical foundation for the practical implementation of large-scale and efficient utilization of PG waste. The developed eco-friendly PBC has excellent potential to partially substitute conventional OPC binders and reduce engineering project costs.

Why sustainable concrete cannot penetrate concrete markets

Several studies have shown that sustainable concrete mixtures could be a solution to reduce the CO2 emissions of concrete while utilizing supplementary cementitious materials (SCMs) that are waste byproducts, including fly ash, metakaolin, and ground granulated blast furnace slag. However, for these sustainable concrete mixtures to be adopted as a replacement for conventional ordinary Portland cement concrete (OPCC), site engineers, decision-makers, and authorities need to be aware of the mechanical and durability properties of these sustainable concrete mixtures. A brief review of the mechanical and durability properties of both geopolymer concrete and alkali-activated cement demonstrates the objective performance relative to OPCC. Then, the results of a survey targeting researchers, site civil engineers, decision-makers, and employees in governmental agencies are presented. The results indicate that even though the mechanical and durability properties of geopolymer/sustainable concrete are recognized, limited awareness and availability present significant challenges to the adoption of sustainability concrete in infrastructure projects. The survey highlights the need for focused marketing efforts to educate decision-makers on the availability as well as mechanical and durability properties of geopolymer concrete. Additionally, it serves as a call for future research to overcome obstacles such as high initial cost, safety concerns, and limited practical applications.

Effects of biogenic sulfuric acid on simulated concrete septic tanks

Concrete is the major construction material for infrastructure development. Concrete sewer septic tanks are Constructed using the conventional ordinary portland cement (OPC) and the Portland pozzolana cement (PPC). However, OPC based concrete sewer systems are susceptible to biological, mechanical, and chemical degradation. Degradation of the concrete septic leads to their failure hence imposing tremendous environmental problems. The aftermath is the emergence of sanitation-related diseases. The wastewater from failing septic systems leads to contamination of the groundwater or the surface water resulting in the pollution of drinking water. Therefore, the need to explore other possibilities and potential construction materials to achieve sustainable sanitation is inevitable. The use of Limestone Calcined Clay Cement (LC3) in the construction of degradation-resistant concrete sewer septic systems has not been well explored in Kenya. LC3 concrete is resistant to the deterioration effects of aggressive media such as acids, chlorides, and sulfates. This paper presents experimental performance and findings of LC3 in aggressive media vis a vis OPC. The LC3 was formulated by mixing clinker, Calcined clay, limestone, and gypsum at percentages of 50 %, 30 %, 15 %, and 5 % respectively. Compressive strength, Sorptivity, and weight loss during the wet and dry cycles for both LC3 and OPC were evaluated. Simulated concrete septic tanks made of LC3 and OPC were made by casting cubes at water cement ratio of 0.5 and cured in fresh water at ambient temperature for 28 days. These cubes were passed through a regime of W-D cycles in the 3% concentration of Biogenic sulfuric acid. It was observed that after 28 days of curing OPC cubes had slightly higher compressive strength than LC3. However LC3 concrete cubes are expected to have higher compressive strength than the OPC. Cubes curing time increases due to increased pozzolanic activity. Biogenic sulphuric acid attacks on hydrated cement products cause a decrease in compressive strength. The water absorption profile of LC3 cubes was lower as compared to OPC cubes. In conclusion, LC3 cubes had a high potential of resisting degradation as compared to OPC cubes. LC3 show more impressive performance, hence LC3 It’s a potential binder for use in the construction of sewer system.
 Keywords: Septic tank, Sorptivity, compressive strength, wet-dry cycles, biological, mechanical, and chemical degradation, sustainable sanitation, LC3.

Fabrication and Mechanical Evaluation of Eco-Friendly Geopolymeric Mortars Derived from Ignimbrite and Demolition Waste from the Construction Industry in Peru

Ignimbrite rock is a volcanic material located in the Arequipa region (Peru), and for centuries, it has been used as a construction material, giving a characteristic light pastel, white to pink color to the city of Arequipa, with white being the most common. In the present study, the potential use of three types of Arequipa raw materials (ignimbrite rock powder, calcined clay powder, and demolition mortar powder) as the main source of new binders or the manufacture of environmentally friendly mortars, without the addition of ordinary Portland cement (OPC) is discussed. In this work, an in-depth characterization of the materials used was carried out. The proposed fabrication route for geopolymeric materials was considered for the manufacture of binders and mortars using an alkaline solution of NaOH with values between 12 and 18 molar, as a trigger for the geopolymerization process. Geopolymeric mortars were obtained by adding a controlled amount of fine sand to the previously prepared mixture of binder raw material and an alkaline solution. Conventional OPC and geopolymeric mortars manufactured under the same conditions were mechanically evaluated by uniaxial compression tests at a constant compression rate of 0.05 mm/min and under normal conditions of temperature and atmosphere, where the most optimal values were obtained for 15 molar alkaline solutions of ignimbrite without the addition of aggregates, with values of compressive strength of 42 MPa and a modulus elastic of 30 GPa. The results revealed a significant increase in the maximum strength and modulus of elasticity values when the volumetric fractions of OPC are completely replaced with geopolymeric binders in the study conditions of this work, demonstrating the enormous potential of the ignimbrite rock and construction waste studied, as raw material of alternative mortar binders without the addition of OPC. With this work, the ignimbrite rock, of great value in the region and also found in other areas of the Earth’s geography, was characterized and valued, in addition to the calcined clay and demolition mortar of the region.

Unlocking the potential of ordinary Portland cement with hydration control additive enabling low-carbon building materials

Ordinary Portland cement (OPC) is the core ingredient of many construction materials. In 2022, 4.1 billion tons were used worldwide, contributing to ~8% of CO2 emissions ( ~ 3 Gt/year). Nevertheless, the complete strength-generating capacity of OPC remains unrealized due to the restricted conversion of aluminates to ettringite, caused by conventional hydration kinetics. Here we show a hydration control additive that selectively modifies the hydration kinetics, thereby facilitating enhanced dissolution of aluminates (calcium aluminoferrite and tricalcium aluminate) in OPC, which promotes ettringite formation at a desired time. Increasing ettringite content improves packing of the hardened cement, resulting in ~50% higher specific strength and enabling cement reduction. It also increases OPC strength development efficiency, reducing carbon footprint by ~30%. The use of this additive can be combined with methods such as reducing water and/or using supplementary cementitious materials (SCMs) to prepare building materials with significantly fewer CO2 emissions than those from conventional OPC.

Fresh Properties, Strength, and Durability of Fiber-Reinforced Geopolymer and Conventional Concrete: A Review.

Reducing the environmental footprint of the construction industry in general and concrete in particular is essential. The addition of synthetic and natural fibers to concrete mixes at appropriate dosages enhances durability and strength and extends the lifespan of concrete infrastructures. This study reviews the geometric and mechanical properties of selected fibers such as steel, basalt, polypropylene, polyvinyl alcohol, polyethylene, glass, carbon, and natural fibers and their impact on concrete fresh, mechanical, and durability properties when combined in different configurations. The study focuses on the effect of blending fibers with concrete mixes that use alkali-activated binders based on recycled industrial byproducts such as slag and fly ash and thereby contribute to reduction of CO2 contribution through complete or partial replacement of Ordinary Portland cement (OPC). As a result, the effect of binder content, binder composition, alkaline activator concentration, and water-to-binder (w/b) ratio on fresh properties, mechanical strength, and durability of concrete with blended fibers is also evaluated in this study. The properties of fiber-reinforced concrete with alkali-activated binder and conventional OPC binders are compared. Fiber-reinforced concrete with alkali-activated binders that are based on industrial byproducts may represent sustainable alternatives to conventional concrete and offers competitive fresh and mechanical properties when fiber properties, fiber content, w/b ratio, binder type, and dosage are carefully considered in concrete mix design.

Durability assessment of fly ash, GGBS, and silica fume based geopolymer concrete with recycled aggregates against acid and sulfate attack

There is a constant drive to develop high-performance concrete with enhanced mechanical and durability characteristics while incorporating environment-friendly materials. The study investigates the synergistic effects of fly ash (FA), ground granulated blast furnace slag (GGBS), and silica fume (SF) on the durability characteristics of 100 % recycled aggregate (RA) based geopolymer concrete (GPC) against acid and sulfate attacks. Moreover, its relative performance compared to control samples of ordinary Portland cement (OPC) concrete with natural and recycled aggregates was also assessed. The acid and sulfate resistance were determined by submerging the concrete specimens in the 5 % sulphuric acid (H2SO4), 5 % sodium sulfate (Na2SO4), and 5 % magnesium sulfate (MgSO4) for up to 180 days of exposure duration. The specimens' resistance to chemical attack was assessed by visual observation, changes in weight, and the percentage of compressive strength loss at different time intervals. In addition, the changes in the mineralogical and microstructures of the GPC matrix were also examined using X-ray diffraction (XRD), scanning electron microscope (SEM), and mercury intrusion porosimetry (MIP) tests. Results indicated that an increased proportion of GGBS and SF positively influenced the durability of GPC, as revealed by reduced mass loss and compressive strength degradation. In addition, the microstructural, mineralogical, and morphological properties depicted enhanced densification and compactness of the GPC matrix due to the formation of CSH, CASH, and NASH gels. GPC-MG15 (FA:GGBS:SF – 35:50:15) yielded the highest strength and durability performance, compensating for the trade-offs of using 100 % RAs in conventional OPC concrete. So, optimized use of these sustainable materials has depicted promising results in aggressive environments while reducing the need for conventional OPC and natural aggregates.

Enhancement of ductility characteristics of fiber-reinforced ternary geopolymer mortar

There is a need for ambient-cured geopolymer as a potential replacement for conventional ordinary Portland cement (OPC) based concrete. But geopolymers, that belong to the ceramic family, behave in a brittle manner and hence this research focusses on the enhancement of ductility using fibers. Thus, this experimental work was conducted to investigate the performance of polypropylene (PP) and micro steel fiber (MS) of fiber-reinforced geopolymer mortar (FRGM) on the hardened properties. The volume fractions of fiber used were 0%, 0.5%, 1%, and 1.5%. The ternary blended geopolymer mortar consisted of fly ash (FA), ground granular blast furnace slag (GGBS), and palm oil fuel ash (POFA). The hardened properties investigated are compressive strength, splitting tensile strength, modulus of elasticity (MoE), and ultrasonic pulse velocity (UPV). Furthermore, the load-deflection response was investigated in terms of deflection, load, flexural, and toughening mechanisms. The morphology of matrix mortar with the bonding of the fibers was examined through field emission scanning electron microscope (FESEM). The results revealed that the splitting tensile strength was enhanced with the inclusion of 0.5% of PP fibers and up to 1.5% of MS fibers by 27% and 177%, respectively. The enhancements in the ultimate flexural strength with 1.5% fiber were found 173% and 33% higher for MS and PP fibers, respectively compared to the control mixes. The inclusion of both MS and PP fibers showed a significant enhancement in the post-cracking flexural and toughness energy measured at L/150 mm. Furthermore, the addition of fiber volume of 0.5–1.5% enhanced the toughness by 33% (T600), 62% (T150), and 28% (T600), 46% (T150) for MS and PP mixes, respectively.

Self-healing capability of engineered cementitious composites with calcium aluminate cement

The reduced heating temperatures required for producing calcium aluminate cement (CAC) make it highly suitable for reducing CO2 emissions in engineered cementitious composites (ECCs) known with their significant amount of cement. However, it is not clear to what extent this can influence the advanced mechanical and self-healing ability of control ECC, especially with the risk of conversion in CAC reaction products. This study investigates the self-healing capability of ECCs produced using CAC instead of conventional ordinary Portland cement (OPC). It also assesses the impact of incorporating fly ash (FA) into CAC-ECC blends at different FA/CAC ratios. In addition to the mechanical characterisation of sound specimens, flexural properties, cracking behavior, ultra-sonic pulse velocity (UPV) and rapid chloride permeability test (RCPT) were performed on preloaded OPC- and CAC-ECCs. The study also analyzed the microstructural changes of self-healing products associated with the high alumina content of CAC. The results show that CAC can be used to produce high mechanical strengths ECCs, with more than 34% and 7% higher compressive and flexural strengths respectively than those of ECC-CTL at early age, though the addition of FA was important to reach improved patterns of mechanical properties at advanced ages. In addition, significant improvements were recorded for the recovery rates of CAC-ECCs, reaching more than 29% for flexural strengths, 11% for UPV and 75% for RCPT than the ECC-CTL. The self-healing products characterized with SEM-EDS confirmed the occurrence of conversion when FA was not included in CAC-ECCs, nevertheless with limited effect on the self-healing efficiency of these mixtures.

Effect of Activator Concentrations on the Postfire Impact Behavior of Alkali-Activated Slag Concrete

Changing concrete ingredients significantly affects its performance due to changing the type of hydration products formed. The stability of these hydration products will dominate concrete impact behavior before and after exposure to fire. Limited research had explored the role of activators, as the main ingredient of alkali-activated slag concrete (AASC), on impact performance. Hence, this study highlights the effects of activator characteristics on the impact behavior of AASC at an ambient condition (23°C) and after exposure to elevated temperatures (200°C, 400°C, and 600°C). Conventional ordinary portland cement (OPC) concrete was also tested for general performance comparison. Besides the drop weight impact test, compressive and indirect splitting tensile strength, shrinkage, ultrasonic pulse velocity and water absorption tests were conducted to evaluate AASC performance. In addition, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to confirm and analyze findings. Results confirmed the better impact performance of AASC compared to OPC concrete. Activator concentrations showed contrary effects on AASC performance at ambient and elevated temperatures. High activation levels improved strength and impact capacity at ambient temperature, showing lower internal defects and higher hydration product formation. Conversely, lowering the activation level at elevated temperatures was preferable and resulted in a higher residual strength and impact absorption capacity. This was ascribed to the high unreacted slag particle crystallization to akermanite at higher temperatures, leading to strength gain, fewer hydration products to decompose, and high microstructure ductility that accommodated the thermal incompatibility. Hence, designing AASC while focusing only on maximizing strength can be misleading based on the targeted performance and exposure conditions.

Eco-Concrete in High Temperatures.

Concrete technology is becoming more and more sustainable and ecological following more extensive and focused research. The usage of industrial waste and by-products, such as steel ground granulated blast-furnace slag (GGBFS), mine tailing, fly ash, and recycled fibers, is a very important step toward a good transition of concrete into a "green" future and significant improvement in waste management in the world. However, there are also several known durability-related problems with some types of eco-concretes, including exposure to fire. The general mechanism occurring in fire and high-temperature scenarios is broadly known. There are many variables that weightily influence the performance of this material. This literature review has gathered information and results regarding more sustainable and fire-resistant binders, fire-resistant aggregates, and testing methods. Mixes that utilize industrial waste as a total or partial cement replacement have been consistently achieving favorable and frequently superior outcomes when compared to conventional ordinary Portland cement (OPC)-based mixes, especially at a temperature exposure up to 400 °C. However, the primary emphasis is placed on examining the impact of the matrix components, with less attention given to other factors such as sample treatment during and following exposure to high temperatures. Furthermore, there is a shortage of established standards that could be utilized in small-scale testing.

The role of calcium aluminate cement in developing an efficient ultra-high performance concrete resistant to explosive spalling under high temperatures

Conventional ordinary Portland cement (OPC)-based UHPC is vulnerable to explosive spalling under high temperatures. This study aims to classify the role of calcium aluminate cement (CAC) as the substitution for OPC in UHPC under high temperatures and finally develop an efficient UHPC without explosive spalling. It was found that CAC-based UHPC (UHPC-CAC) and OPC-based UHPC (UHPC-OPC) reached their peak strength both at 250 °C, but the peak strength (153.8 MPa) of UHPC-CAC was higher than that (137.5 MPa) of UHPC-OPC. Explosive spalling was found in UHPC-OPC after reaching 500 °C, while no spalling was observed in UHPC-CAC even at 1000 °C. The effectiveness of CAC in reducing the mechanical degradation and preventing the spalling of UHPC was attributed to three potential mechanisms: (1) CAC had less physically bound water to cause the vapor pressure in UHPC; (2) The main hydration product (i.e., calcium aluminosilicate hydrates) decomposed to a lesser extent, compared to the hydration product (i.e., calcium silicate hydrates) of OPC, as proved by X-ray diffraction (XRD) analysis, Thermogravimetric analysis (TGA), and Fourier-transform infrared (FTIR) analysis; (3) there exists pores coarsening in UHPC-CAC, as evidenced by micro-XCT, which could release the water pressure in UHPC and thus prevent the spalling at elevated temperatures.

Synthesis, Stability and Microstructure of a One-Step Mixed Geopolymer Backfill Paste Derived from Diverse Waste Slags

The advent of industrialization has produced an enormous amount of industrial waste slag, which drastically pollutes environmental resources. This study examines the production, stability, and microstructure of a novel backfill geopolymer paste derived from multiple industrial waste slags, including silica-alumina precursors (low-calcium composition) and waste slags (high-calcium composition), as well as two additives. The characteristics of self-hardening were discovered. The effects of low-calcium fly ash, granulated blast furnace slag, red mud, and lime powder on fluidity and compressive strength were then evaluated. To assess the stability, the resistances to drying shrinkage, permeability, and chemical attack by an optimized geopolymer backfill paste were investigated. Furthermore, SEM-EDS, XRD, FTIR, and TG-DSC tests were employed to reveal the microstructures, products, and thermal stability. The results show that the backfill paste hardens well and has no impact on alkalinity dissolution for adjacent soils and water. The optimum sample, P1, had a water-binder ratio of 0.70, resulting in 201 mm fluidity and 2.1 MPa 28-d compressive strength. In terms of drying shrinkage, permeability, and Na2SO4 and NaCl solution attack, sample P1 outperformed the conventional Ordinary Portland cement paste (OPC) for 90 days. The paste P1 containing about 46.0 wt% waste slags meets the fresh and hardened property requirements for goaf backfill, and the chemical binding of P1 is acquired from the mixture of (N,C)-A-S-H, C-S-H, and C-A-S-H gel products. These findings lay the groundwork for the scientific application of a wide range of waste slags in backfill engineering.

A study on development of pavement quality geopolymer concrete for low volume roads

The world's rural roads are extensively interconnected with all conventional OPC (Ordinary Portland cement) concrete roads and with little traffic. The main ingredient in concrete pavements is ordinary Portland cement which has serious environmental issues like CO2 emissions during the production. A replacement for traditional cement-based concrete is available in the form of geo-polymer concrete (GPC). The current work mainly emphasis on the mix development of Fly Ash (FA)-Ground Granulated Blast Furnace Slag (GGBFS) based GPC for rigid pavements application in low volume concrete roads (LVCR). The study consists of preparing GPC mixes with total of 8 combinations comprising GGBFS and fly-ash as binders (GGBFS-40% and 50% replacement to FA), two different alkaline solution/binder ratio (As/Bi = 0.45 and 0.50) and sodium hydroxide (NaOH) solutions of 8 and 10 Molarities with a constant proportion of sodium silicate (Na2SiO3) by sodium hydroxide (NaOH) is 2.5 by 1. All the specimens were kept under outdoor curing only. The guidelines by IRC:SP:62-2014 recommended that the characteristic compressive strength of concrete at 28 days used to pave ruralcountry roads be at least 30 MPa, while the 28 days flexural strength should not be less than 3.8 MPa. From the experimental study it was noticed that, when the GGBFS content and NaOH molarity increases, the mix’s workability is getting reduced and mechanical properties were improved significantly whereas when the As/Bi increases from 0.45 to 0.50, the mix workability increases and also mechanical properties too. And also concluded that, the FA-GGBFS based GPC mix for low volume concrete roads is attained with GGBFS content 40% to 50% replacement for fly ash and NaOH Concentration of 10 M with a binder content of 400 kg/m3 at an As/Bi ratio of 0.45 and 0.50 are adequate to meet the requirements for low volume concrete road standards.

Fundamental design of low-carbon ordinary Portland cement-calcium sulfoaluminate clinker-anhydrite blended system

Calcium sulfoaluminate (CSA) cements have lower carbon dioxide (CO2) emissions during production compared with conventional ordinary Portland cement (OPC). However, the high cost of production is a significant limitation of the application of CSA cements. This paper aims to improve the use efficiency of CSA clinker by adding OPC and anhydrite. The low-carbon OPC-CSA clinker-anhydrite system is expected to contain less CSA clinker while showing excellent performance. A design methodology was developed to optimize the component of the OPC-CSA clinker-anhydrite blended system. The hydration mechanism of the ternary system was investigated using isothermal conduction calorimetry, X-ray diffraction (XRD), and thermogravimetric analysis (TGA), and thermodynamic modelling was used to predict the amount of hydration products. The results showed that ettringite is the main hydration products of the OPC-CSA clinker-anhydrite system, and the addition of OPC provides portlandite for the formation of ettringite. The ternary system is characterized by rapid development of strength and low CO2 emissions. The compressive strength at 4 h and the CO2 emissions are about 10 MPa and 500 kg/t, respectively. In addition, the ternary system, composed of 27.9 wt% CSA clinker, 32.5 wt% anhydrite, and 39.6 wt% OPC has the highest compressive strength at 28 d and the lowest CO2 intensity.