Optimal Design of Ferronickel Slag Alkali-Activated Material for High Thermal Load Applications Developed by Design of Experiment

The development of an optimal low-calcium alkali-activated binder for high-temperature stability based on ferronickel slag, silica fume, potassium hydroxide, and potassium silicate was investigated based on Mixture Design of Experiment (Mixture DOE). Mass loss, shrinkage/expansion, and compressive and flexural strengths before and after exposure to a high thermal load (900 °C for two hours) were selected as performance markers. Chemical activator minimization was considered in the selection of the optimal mix to reduce CO₂ emissions. Unheated 42-day compressive strength was found to be as high as 99.6 MPa whereas the 42-day residual compressive strength after exposure to the high temperature reached 35 MPa (results pertaining to different mixes). Similarly, the maximum unheated 42-day flexural strength achieved was 8.8 MPa, and the maximum residual flexural strength after extreme temperature exposure was 2.5 MPa. The binder showed comparable properties to other alkali-activated ones already studied and a superior thermal performance when compared to Ordinary Portland Cement. A quantitative X-ray diffraction analysis was performed on selected hardened mixes, and fayalite was found to be an important component in the optimal formulation. A life-cycle analysis was performed to study the CO₂ savings, which corresponded to 55% for economic allocation.     

Design of High Volume CFBC Fly Ash Based Calcium Sulphoaluminate Type Binder in Mixtures with Ordinary Portland Cement

Growing concerns on global industrial greenhouse gas emissions have boosted research for developing alternative, less CO₂ intensive binders for partial to complete replacement of ordinary Portland cement (OPC) clinker. Unlike slag and pozzolanic siliceous low-Ca class F fly ashes, the Ca- and S-rich class C ashes, particularly these formed in circulating fluidised bed combustion (CFBC) boilers, are typically not considered as viable cementitious materials for blending with or substituting the OPC. We studied the physical, chemical-mineralogical characteristics of the mechanically activated Ca-rich CFBC fly ash pastes and mortars with high volume OPC substitution rates to find potential alternatives for OPC in building materials and composites. Our findings indicate that compressive strength of pastes and mortars made with partial to complete replacement of the mechanically activated CFBC ash to OPC is comparable to OPC concrete, showing compared to OPC pastes reduction in compressive strength only by <10% at 50% and <20% at 75% replacement rates. Our results show that mechanically activated Ca-rich CFBC fly ash can be successfully used as an alternative CSA-cement type binder.     

Effect of Fibrillated Cellulose on Lime Pastes and Mortars

The use of nanocellulose in traditional lime-based mortars is a promising solution for green buildings in the frame of limiting the CO₂ emissions resulting from Portland Cement production. The influence of the fibrillated cellulose (FC) on lime pastes and lime-based mortars was studied incorporating FC at dosages of 0%, 0.1%, 0.2% and 0.3 wt% by weight of binder. The lime pastes were subjected to thermal and nitrogen gas sorption analyses to understand if FC affects the formation of hydraulic compounds and the mesoporosities volume and distribution. The setting and early hydration of the mortars were studied with isothermal calorimetry. The mechanical performances were investigated with compressive and three-point-bending tests. Furthermore, fragments resulting from the mechanical tests were microscopically studied to understand the reinforcement mechanism of the fibres. It was found that 0.3 wt% of FC enhances the flexural and compressive strengths respectively by 57% and 44% while the crack propagation after the material failure is not affected.     

Effect of Size of Coarse Aggregate on Mechanical Properties of Metakaolin-Based Geopolymer Concrete and Ordinary Concrete

Geopolymer binders are a promising alternative to ordinary Portland cement (OPC) because they can significantly reduce CO₂ emissions. However, to apply geopolymer in concrete, it is critical to understand the compatibility between the coarse aggregate and the geopolymer binder. Experimental studies were conducted to explore the effect of the size of the coarse aggregate on the mechanical properties and microstructure of a metakaolin-based geopolymer (MKGP) concrete and ordinary concrete. Three coarse aggregate size grades (5–10 mm, 10–16 mm, and 16–20 mm) were adopted to prepare the specimens. The microstructure of the concretes was investigated with scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) and mercury intrusion porosimetry (MIP). Results showed an opposite coarse aggregate size effect between OPC and MKGP specimens in terms of compressive strength. SEM/EDS analysis indicated that the MKGP concrete has a weaker microstructure compared to OPC concrete induced by a higher porosity. The differences in mechanical properties and pore structure between the MKGP and OPC concrete are attributed to the greatly differing shrinkages triggered by the large surface area and penny-shaped particles of metakaolin. The findings in this work help tailor the mechanical properties and microstructure of MKGP concrete for future engineering applications.     

Life Cycle Assessment and Impact Correlation Analysis of Fly Ash Geopolymer Concrete

Geopolymer concrete (GPC) has drawn widespread attention as a universally accepted ideal green material to improve environmental conditions in recent years. The present study systematically quantifies and compares the environmental impact of fly ash GPC and ordinary Portland cement (OPC) concrete under different strength grades by conducting life cycle assessment (LCA). The alkali activator solution to fly ash ratio (S/F), sodium hydroxide concentration (C_NaOH), and sodium silicate to sodium hydroxide ratio (SS/SH) were further used as three key parameters to consider their sensitivity to strength and CO₂ emissions. The correlation and influence rules were analyzed by Multivariate Analysis of Variance (MANOVA) and Gray Relational Analysis (GRA). The results indicated that the CO₂ emission of GPC can be reduced by 62.73%, and the correlation between CO₂ emission and compressive strength is not significant for GPC. The degree of influence of the three factors on the compressive strength is C_NaOH (66.5%) > SS/SH (20.7%) > S/F (9%) and on CO₂ emissions is S/F (87.2%) > SS/SH (10.3%) > C_NaOH (2.4%). Fly ash GPC effectively controls the environmental deterioration without compromising its compressive strength; in fact, it even in favor.     

Investigation of Concrete Shrinkage Reducing Additives

This paper analyzes the efficiency of shrinkage reducing additives for the shrinkage deformations of ordinary Portland cement (OPC) concrete and its mechanical properties. OPC concrete was modified with an organic compound-based shrinkage reducing additive (SRA), quicklime, polypropylene fiber, and hemp fiber. It was found that a combination of 2.5% quicklime and 1.5% SRA led to the highest reduction in shrinkage deformations in concrete, and the values of shrinkage reached up to 40.0%. On the contrary, compositions with 1.5% SRA were found to have a significant reduction in compressive strength after 100 freeze-thaw cycles. Hemp fiber did not show a significant shrinkage reduction, but it is an environmentally friendly additive, which can improve OPC concrete flexural strength. Polypropylene fiber can be used in conjunction with shrinkage reducing additives to improve other mechanical properties of concrete. It was observed that 3.0 kg/m³ of polypropylene fiber in concrete could increase flexural strength by 11.7%. Moreover, before degradation, concrete with polypropylene fiber shows high fracture energy and decent residual strength of 1.9 MPa when a 3.5 mm crack appears. The tests showed a compressive strength decrease in all compositions with shrinkage reducing additives and its combinations after 28 days of hardening.     

Influence of Pozzolan,Slag and Recycled Aggregates on the Mechanical and Durability Properties of Low Cement Concrete

The sustainability of the construction sector demands the reduction of CO₂ emissions. The optimization of the amount of cement in concrete can be achieved either by partially replacing it by additions or by reducing the binder content. The present work aims at optimizing the properties of concrete used in the production of reinforced concrete poles for electrical distribution lines, combining the maximization of compactness with the partial replacement of cement by fly ash, natural pozzolans, and electric furnace slags. Natural aggregates were also partially replaced by recycled ones in mixtures with fly ash. Two types of concrete were studied: a fresh molded one with a dry consistency and a formwork molded one with a plastic consistency. The following properties were characterized: mechanical properties (flexural, tensile splitting, and compressive strengths, as well as Young’s modulus) and durability properties (capillary water absorption, water penetration depth under pressure, resistance to carbonation, chloride migration, and concrete surface resistivity). The service life of structures was estimated, taking the deterioration of reinforcement induced by concrete carbonation or chloride attack into account. Results revealed that mixtures with fly ash exhibit higher mechanical performance and mixtures with fly ash or pozzolans reveal much higher durability results than the full Portland cement-based mixtures.     

The Role of Supplementary Cementitious Materials (SCMs) in Ultra High Performance Concrete (UHPC): A Review

Although ultra high-performance concrete (UHPC) has great performance in strength and durability, it has a disadvantage in the environmental aspect; it contains a large amount of cement that is responsible for a high amount of CO₂ emissions from UHPC. Supplementary cementitious materials (SCMs), industrial by-products or naturally occurring materials can help relieve the environmental burden by reducing the amount of cement in UHPC. This paper reviews the effect of SCMs on the properties of UHPC in the aspects of material properties and environmental impacts. It was found that various kinds of SCMs have been used in UHPC in the literature and they can be classified as slag, fly ash, limestone powder, metakaolin, and others. The effects of each SCM are discussed mainly on the early age compressive strength, the late age compressive strength, the workability, and the shrinkage of UHPC. It can be concluded that various forms of SCMs were successfully applied to UHPC possessing the material requirement of UHPC such as compressive strength. Finally, the analysis on the environmental impact of the UHPC mix designs with the SCMs is provided using embodied CO₂ generated during the material production.     

Strength Characteristics of Alkali-Activated Slag Mortars with the Addition of PET Flakes

The production of ordinary Portland cement is associated with significant CO₂ emissions. To limit these emissions, new binders are needed that can be efficiently substituted for cement. Alkali-activated slag composites are one such possible binder solution. The research programme presented herein focused on the creation of alkali-activated slag composites with the addition of PET flakes as a partial substitute (5%) for natural aggregate. Such composites have a significantly lower impact in terms of CO₂ emissions in comparison to ordinary concrete. The created composites were differentiated by the amount of activator (10 and 20 wt.%) and curing temperature (from 20 to 80 °C). Their mechanical properties were tested, and a scanning electron microscope analysis was conducted. Compressive and flexural strengths ranging from 29.3 to 68.4 MPa and from 3.5 to 6.1 MPa, respectively, were achieved. The mechanical test results confirmed that a higher amount of activator improved the mechanical properties. However, the influence of the PET particles on the mechanical properties and microstructure varied with the curing temperature and amount of activator. Areas that require further research were identified.     

The Realization of Clinker-Reduced,Performance-Based Sustainable Concrete by the Micro-Filler,Eco-Filler Concept

In times of climate change, the reduction in embodied greenhouse gas emissions is a premise for sustainable concrete infrastructure. As Portland cement clinker is mainly responsible for the high CO₂ emissions of concrete, its reduction is necessary. In order to be sustainable, the concrete must meet processing, mechanical and durability properties while taking cost aspects into account. The paper presents (i) the “micro-filler/eco-filler concept” for achieving a clinker reduced, optimised binder and (ii) a performance-based approach to put sustainable “Eco-concrete” into practice. Clinker is substituted by locally available inert fillers by at least two different particle size fractions and supplementary cementitious materials. The method is based on particle packing optimisation, reduction in water demand and optimisation of the mix ratio of the binder blend, which allows the performance requirements to be met. The new Eco-concretes deliver the desired performance in terms of processability, strength and durability (water penetration, frost, carbonation and chloride resistance) while lowering the environmental impact in comparison to standard concrete. One of the new mixes was used for a small animal passage tunnel. The direct comparison of the developed Eco-concrete and standard concrete showed a 24% reduction in CO₂, while achieving satisfactory workability, stripping strength and durability performance.     

Mechanical and Durability Analysis of Fly Ash Based Geopolymer with Various Compositions for Rigid Pavement Applications

Ordinary Portland cement (OPC) is a conventional material used to construct rigid pavement that emits large amounts of carbon dioxide (CO₂) during its manufacturing process, which is bad for the environment. It is also claimed that OPC is susceptible to acid attack, which increases the maintenance cost of rigid pavement. Therefore, a fly ash based geopolymer is proposed as a material for rigid pavement application as it releases lesser amounts of CO₂ during the synthesis process and has higher acid resistance compared to OPC. This current study optimizes the formulation to produce fly ash based geopolymer with the highest compressive strength. In addition, the durability of fly ash based geopolymer concrete and OPC concrete in an acidic environment is also determined and compared. The results show that the optimum value of sodium hydroxide concentration, the ratio of sodium silicate to sodium hydroxide, and the ratio of solid-to-liquid for fly ash based geopolymer are 10 M, 2.0, and 2.5, respectively, with a maximum compressive strength of 47 MPa. The results also highlight that the durability of fly ash based geopolymer is higher than that of OPC concrete, indicating that fly ash based geopolymer is a better material for rigid pavement applications, with a percentage of compressive strength loss of 7.38% to 21.94% for OPC concrete. This current study contributes to the field of knowledge by providing a reference for future development of fly ash based geopolymer for rigid pavement applications.     

Effect of Ornamental Stone Waste Incorporation on the Rheology,Hydration, Microstructure,and CO2 Emissions of Ordinary Portland Cement

The ornamental stone industry generates large amounts of waste thus creating environmental and human health hazards. Thus, pastes with 0–30 wt.% ornamental stone waste (OSW) incorporated into ordinary Portland cement (OPC) were produced and their rheological properties, hydration kinetics, and mechanical properties were evaluated. The CO₂ equivalent emissions related to the pastes production were estimated for each composition. The results showed that the paste with 10 wt.% of OSW exhibited similar yield stress compared to the plain OPC paste, while pastes with 20 and 30 wt.% displayed reduced yield stresses up to 15%. OSW slightly enhanced the hydration kinetics compared to plain OPC, increasing the main heat flow peak and 90-h cumulative heat values. The incorporation of OSW reduced the 1-, 3-, and 28-days compressive strength of the pastes. Water absorption results agreed with the 28 days compressive strength results, indicating that OSW increased the volume of permeable voids. Finally, OSW incorporation progressively reduced the CO₂ emission per m³ of OPC paste, reaching a 31% reduction for the highest 30 wt.% OSW content. Overall, incorporating up to 10 wt.% with OSW led to pastes with comparable fresh and hardened properties as comported to plain OPC paste.     

Properties of Light Cementitious Composite Materials with Waste Wood Chips

The CO₂ emissions from the cement industry and the production of waste wood chips are increasing with the rapid growth of the construction industry. In order to develop a green environmental protection building material with low thermal conductivity and up to standard mechanical properties, in this study, pine waste wood chips were mixed into cement-based materials as fine aggregate, and three different kinds of cementitious binders were used, including sulfur aluminate cement (SAC), ordinary Portland cement (OPC), and granulated blast furnace slag (GBFS), to prepare a recycled light cementitious composite material. The mechanical, thermal conductivity, shrinkage, water absorption, and pore structure of a wood chip light cementitious composite material were studied by changing the Ch/B (the mass ratio of wood chip to binder). The results showed that the strength, dry density, and thermal conductivity of the specimens decreased significantly with the increase in the Ch/B, while the shrinkage, water absorption, and pore size increased with the increase in the Ch/B. By comparing three different kinds of cementitious binders, the dry density of the material prepared with OPC was 942 kg/m³, the compressive strength of the material prepared with SAC was 13.5 MPa, and the thermal conductivity of the material prepared with slag was the lowest at 0.15 W/m/K. From the perspective of low-cost and low-carbon emissions, it was determined that the best way to prepare a light cementitious composite with waste wood chips is to use granulated blast furnace slag (GBFS) as the cementitious binder.     

Estimating CO2 Emission Savings from Ultrahigh Performance Concrete: A System Dynamics Approach

Ordinary Portland cement concrete (OPC) is the world’s most consumed commodity after water. However, the production of cement is a major contributor to global anthropogenic CO₂ emissions. In recent years, ultrahigh performance concrete (UHPC) has emerged as a strong contender to replace OPC in diverse applications. UHPC has much higher mechanical strength, and thus less material is used in a structural member to resist the same load. Moreover, it has a much longer service life, reducing the long-term need for repair and replacement of aging civil infrastructure. Thus, UHPC can enhance the sustainability of cement and concrete. However, there is currently no robust tool to estimate the sustainability benefits of UHPC. This task is challenging considering that such benefits can only be captured over the long-term since variables, such as population growth and cement demand per capita, become more uncertain. In addition, the problem of CO₂ emissions from cement and concrete is a complex system affected by time-dependent feedback. The System Dynamics (SD) method has specifically been developed for modeling such complex systems. Accordingly, a SD model was developed in this study to test various pertinent policy scenarios. It is shown that UHPC can reduce cumulative CO₂ emissions of cement and concrete—over the studied simulation period—by more than 17%. If supplementary cementitious materials are further deployed in UHPC and new technologies permit reducing the carbon footprint per unit mass of cement, emission savings can become more substantial. The model offers a flexible framework where the user controls various inputs and can extend the model to account for new data, without the need for reconstruction of the entire model.     

Performance Evaluation of Cementless Composites with Alkali-Sulfate Activator for Field Application

This study analyzed the performance evaluation of alkali-activated composites (AAC) with an alkali-sulfate activator and determined the expected effects of applying AACs to actual sites. Results revealed that when the binder weight was increased by 100 kg/m³ at 7 days of age, the homogel strength of ordinary Portland cement (OPC) and AAC increased by 0.9 and 5.0 MPa, respectively. According to the analysis of the matrix microstructures at 7 days of age, calcium silicate hydrates (C–S–H, Ca_1.5SiO_3.5·H₂O) and ettringite (Ca₆Al₂(SO₄)₃(OH)₁₂·26H₂O) were formed in AAC, which are similar hydration products as found in OPC. Furthermore, the acid resistance analysis showed that the mass change of AAC in HCl and H₂SO₄ solutions ranged from 36.1% to 88.0%, lower than that of OPC, indicating AAC’s superior acid resistance. Moreover, the OPC and AAC binder weight ranges satisfying the target geltime (20–50 s) were estimated as 180.1–471.1 kg/m³ and 261.2–469.9 kg/m³, respectively, and the global warming potential (GWP) according to binder weight range was 102.3–257.3 kg CO₂ eq/m³ and 72.9–126.0 kg CO₂ eq/m³. Therefore, by applying AAC to actual sites, GWP is expected to be 29.5 (28.8%)–131.3 (51.0%) kg CO₂ eq/m³ less than that of OPC.     

Integration of Rice Husk Ash as Supplementary Cementitious Material in the Production of Sustainable High-Strength Concrete

The incorporation of waste materials generated in many industries has been actively advocated for in the construction industry, since they have the capacity to lessen the pollution on dumpsites, mitigate environmental resource consumption, and establish a sustainable environment. This research has been conducted to determine the influence of different rice husk ash (RHA) concentrations on the fresh and mechanical properties of high-strength concrete. RHA was employed to partially replace the cement at 5%, 10%, 15%, and 20% by weight. Fresh properties, such as slump, compacting factor, density, and surface absorption, were determined. In contrast, its mechanical properties, such as compressive strength, splitting tensile strength and flexural strength, were assessed after 7, 28, and 60 days. In addition, the microstructural evaluation, initial surface absorption test, = environmental impact, and cost–benefit analysis were evaluated. The results show that the incorporation of RHA reduces the workability of fresh mixes, while enhancing their compressive, splitting, and flexural strength up to 7.16%, 7.03%, and 3.82%, respectively. Moreover, incorporating 10% of RHA provides the highest compressive strength, splitting tensile, and flexural strength, with an improved initial surface absorption and microstructural evaluation and greater eco-strength efficiencies. Finally, a relatively lower CO₂-eq (equivalent to kg CO₂) per MPa for RHA concrete indicates the significant positive impact due to the reduced Global Warming Potential (GWP). Thus, the current findings demonstrated that RHA can be used in the concrete industry as a possible revenue source for developing sustainable concretes with high performance.     

Alternative Clinker Technologies for Reducing Carbon Emissions in Cement Industry: A Critical Review

Currently, the production of one ton of ordinary Portland cement (OPC) releases considerable amounts of CO₂ into the atmosphere. As the need and demand for this material grows exponentially, it has become a challenge to increase its production at a time when climate-related problems represent a major global concern. The two main CO₂ contributors in this process are fossil fuel combustion to heat the rotary kiln and the chemical reaction associated with the calcination process, in the production of the clinker, the main component of OPC. The current paper presents a critical review of the existent alternative clinker technologies (ACTs) that are under an investigation trial phase or under restricted use for niche applications and that lead to reduced emissions of CO₂. Also, the possibility of transition of clinker production from traditional rotary kilns based on fuel combustion processes to electrification is discussed, since this may lead to the partial or even complete elimination of the CO₂ combustion-related emissions, arising from the heating of the clinker kiln.     

Corn Cob Ash versus Sunflower Stalk Ash,Two Sustainable Raw Materials in an Analysis of Their Effects on the Concrete Properties

The increased CO₂ emissions determined by the cement industry led to continuous and intensive research on the discovery of sustainable raw materials with cementitious properties. One such raw material category is agricultural waste. This study involved research on the effects of corn cob ash and sunflower stalk ash, respectively, on compressive strength measured after 28 days and 3 months, the flexural and splitting tensile strengths, the resistance to repeated freeze–thaw cycles, and on the resistance to chemical attack of hydrochloric acid of the concrete. A 2.5% and 5% replacement of the cement volume with corn cob ash (CCA) of A and B quality was applied, and with sunflower stalk ash (SSA) at A and B quality, respectively. The obtained results revealed that CCA and SSA decreased the compressive and tensile strength, but led to higher resistance of the concrete on repeated freeze–thaw cycles and to hydrochloric acid. The mixes with 2.5% SSA at A quality obtained the best results regarding splitting the tensile strength and resistance to repeated freeze–thaw cycles, the mixes with 2.5% SSA at B quality led to the highest resistance to hydrochloric acid, and those with 2.5% CCA at A quality led to the best values of compressive strength and flexural tensile strength.     

Geopolymer Recycled Aggregate Concrete: From Experiments to Empirical Models

Ordinary cement concrete is a popular material with numerous advantages when compared to other construction materials; however, ordinary concrete is also criticized from the public point of view due to the CO₂ emission (during the cement manufacture) and the consumption of natural resources (for the aggregates). In the context of sustainable development and circular economy, the recycling of materials and the use of alternative binders which have less environmental impacts than cement are challenges for the construction sector. This paper presents a study on non-conventional concrete using recycled aggregates and alkali-activated binder. The specimens were prepared from low calcium fly ash (FA, an industrial by-product), sodium silicate solution, sodium hydroxide solution, fine aggregate from river sand, and recycled coarse aggregate. First, influences of different factors were investigated: the ratio between alkaline activated solution (AAS) and FA, and the curing temperature and the lignosulfonate superplasticizer. The interfacial transition zone of geopolymer recycled aggregate concrete (GRAC) was evaluated by microscopic analyses. Then, two empirical models, which are the modified versions of Feret’s and De Larrard’s models, respectively, for cement concretes, were investigated for the prediction of GRAC compressive strength; the parameters of these models were identified. The results showed the positive behaviour of GRAC investigated and the relevancy of the models proposed.     

Influence of Forced Carbonisation on the Binding Properties of Sludge with a High β-Belite Content

Alternative binders activated by forced carbonisation are regarded as one of the potential solutions to reducing greenhouse gas emissions, water, and energy consumption. Such binders, in particular those based on nepheline sludge (a by-product of alumina production), cured in carbon dioxide with subsequent hydration, are clinkerless building materials. The development of such binders contributes to the involvement of multi-tonnage solid industrial waste in the production cycle. This type of waste is capable of binding man-made CO₂ and transforming it into stable insoluble compounds, having binder properties. The optimum technological parameters of the forced carbonisation of the nepheline slime binder was determined by the mathematical planning of the experiment. The novelty of the research is the expansion of the secondary raw material base that can bind the man-made CO₂ with obtaining the construction products of appropriate quality. It was revealed that the process of active CO₂ absorption by the minerals of nepheline slime is observed in the first 120 min of the forced carbonization. Immediately after carbonisation, the resulting material develops compressive strength up to 57.64 MPa, and at the subsequent hydration within 28 days this figure increases to 68.71 MPa. Calcium carbonate is the main binder that determines the high mechanical properties of the samples. During the subsequent hydration of the uncoated belite, gel-like products are formed, which additionally harden the carbonised matrix. Thus, after the forced carbonisation and the following 28 days of hardening, the material with compressive strength in the range 4.38–68.71 MPa and flexural strength of 3.1–8.9 MPa was obtained. This material was characterised by water absorption by mass in the range of 13.9–23.3% and the average density of 1640–1886 kg/m³. The softening coefficient of the material was 0.51–0.99. The results obtained enables one to consider further prospects for research in this area, in terms of the introduction of additional technological parameters to study the process of forced carbonisation of nepheline slime.