Traditional Portland Cement Research Articles

Study on Impact Resistance of Alkali-Activated Slag Cementitious Material with Steel Fiber

Alkali-activated slag cementitious materials (AASCMs) use alkaline activators to activate blast furnace slag and waste slag to replace traditional Portland cement, which can reduce CO2 emissions. An impact resistance test and scanning electron microscopy (SEM) microscopic performance analysis of alkali-activated slag cementitious material specimens with four different steel-fiber contents are performed. The effects of steel-fiber volume content and strain rate on the dynamic elastic modulus Ed, dynamic compressive strength σd, dynamic peak compressive strain εc, and energy absorption of the AASCM-SS are studied. The results indicate that the dynamic elastic modulus Ed, dynamic compressive strength σd, and energy absorption of the AASCM-SS increase with the increase of strain rate, and the dynamic peak compressive strain εc decreases with the increase of strain rate. The dynamic elastic modulus Ed, dynamic compressive strength σd, and dynamic peak compressive strain εc of the SS-AASCM increase first and then decrease with the increase of steel-fiber content. When the steel-fiber content is 0.5%, the σd and εc of the AASCM-SS are the highest, increased by 9.9% and 19.3%. The energy absorption of AASCM-SS increases with the increase of steel-fiber content. A dynamic constitutive model of the FR-AASCM considering the influence of damage, strain rate, and steel-fiber volume fraction is established. The proposed constitutive model is in acceptable agreement with the experimental AASCM-SS dynamic stress–strain curve, and the correlation coefficient is 0.91.

Study on the Effect of Jute CNFs Addition on the Water Absorption and Mechanical Properties of Geopolymer Concrete

This study investigates the influence of thermoplastic polyurethane (TPU) reinforced with jute cellulose nanofibers (CNFs) on the water absorption and mechanical properties of geopolymer concrete. The integration of TPU/jute CNF nanocomposites into geopolymer concrete is explored as a strategy to enhance both its durability and mechanical performance. Geopolymer concrete, a sustainable alternative to traditional Portland cement concrete, is known for its low carbon footprint, but it suffers from high brittleness and water absorption. The water absorption behavior of the modified concrete was assessed, revealing a significant reduction in water uptake due to the hydrophobic nature of TPU and the reinforcing effect of jute CNFs. Additionally, the mechanical properties, including compressive and flexural strengths, were evaluated to understand the impact of the nanocomposites on the structural integrity of the concrete. The addition of TPU/jute CNFs notably enhanced the splitting tensile strength (63.5%), compressive strength (59%), and water absorption (0.59%) of the composite, indicating a promising route for developing high-performance construction materials. The integration of 6 wt% of TPU/jute CNF nanocomposites was found to be optimal, resulting in a uniform matrix, reduced micro-cracks, and improved compressive strength due to enhanced adhesion between the nanocomposites and the geopolymer matrix. Furthermore, a curing temperature of 100 °C was identified as ideal, minimizing unreacted fly ash and enhancing adhesion strength, while higher temperatures (140 °C) led to material deterioration due to rapid water loss. The findings demonstrate that the addition of TPU/jute CNF nanocomposites not only improves resistance to water penetration but also enhances overall mechanical performance. This supports the development of more sustainable and resilient construction materials, contributing to global efforts to reduce the environmental impact of the construction industry. Future research should focus on the long-term durability of these composites under various environmental conditions to validate their effectiveness in real-world applications.

Investigating the impact of foundry by-product sand as an activator on workability improvement and strength development in alkali-activated blast furnace slag mortar

The substitution of alkali-activated furnace slag significantly reduces the necessity of cement manufacture and mitigates the continuous growth of carbon emissions. In addition, it shows superior mechanical properties compared to traditional concrete materials. However, rapid setting issues hinder its widespread applications. This study investigated the innovative use of zero-carbon waste sodium silicate-bonded sand as a substitute for the fine aggregate and sodium silicate in traditional alkali-activated blast furnace slag mortar. The primary objective is to analyze the impact of waste sodium silicate-bonded sand on the workability and mechanical properties of the mortar. The key properties such as flowability, setting time, temperature measurement, compressive strength, and microstructural were analyzed to determine the improvement in workability and the strength development of alkali-activated blast furnace slag mortar resulting from the use of waste sodium silicate-bonded sand. The research showed the integration of waste sodium silicate-bonded sand results in an eco-friendly and cost-effective material, which addresses limitations in traditional activated blast furnace slag mortars. The finding revealed that substituting fine aggregate and sodium silicate with waste sodium silicate-bonded sand significantly improved the mechanical and workability properties of alkali-activated mortars. Notably, the compressive strength of mortars incorporating waste sodium silicate-bonded sand exceeded that of traditional Portland cement and effectively mitigated rapid setting issues. In addition, this approach led to an environmentally friendly mortar with satisfactory workability. The research emphasizes the practical benefits of utilizing waste sodium silicate-bonded sand and offers new insights into its effects on mortar performance. This has provided more details for future exploration and refinement in the field of alkali-activated materials.

Optimized Machine Learning Model for Predicting Compressive Strength of Alkali-Activated Concrete Through Multi-Faceted Comparative Analysis

Alkali-activated concrete (AAC), produced from industrial by-products like fly ash and slag, offers a promising alternative to traditional Portland cement concrete by significantly reducing carbon emissions. Yet, the inherent variability in AAC formulations presents a challenge for accurately predicting its compressive strength using conventional approaches. To address this, we leverage machine learning (ML) techniques, which enable more precise strength predictions based on a combination of material properties and cement mix design parameters. In this study, we curated an extensive dataset comprising 1756 unique AAC mixtures to support robust ML-based modeling. Four distinct input variable schemes were devised to identify the optimal predictor set, and a comparative analysis was performed to evaluate their effectiveness. After this, we investigated the performance of several popular ML algorithms, including random forest (RF), adaptive boosting (AdaBoost), gradient boosting regression trees (GBRTs), and extreme gradient boosting (XGBoost). Among these, the XGBoost model consistently outperformed its counterparts. To further enhance the predictive accuracy of the XGBoost model, we applied four state-of-the-art optimization techniques: the Gray Wolf Optimizer (GWO), Whale Optimization Algorithm (WOA), beetle antennae search (BAS), and Bayesian optimization (BO). The optimized XGBoost model delivered superior performance, achieving a remarkable coefficient of determination (R2) of 0.99 on the training set and 0.94 across the entire dataset. Finally, we employed SHapely Additive exPlanations (SHAP) to imbue the optimized model with interpretability, enabling deeper insights into the complex relationships governing AAC formulations. Through the lens of ML, we highlight the benefits of the multi-faceted synergistic approach for AAC strength prediction, which combines careful input parameter selection, optimal hyperparameter tuning, and enhanced model interpretability. This integrated strategy improves both the robustness and scalability of the model, offering a clear and reliable prediction of AAC performance.

The influence of mechanochemical activation on the rheological properties and strength development of geopolymer

To address the significant carbon emissions caused by the cement industry and its contribution to the greenhouse effect, there is an urgent need for new construction materials that can substantially reduce the use of traditional Portland cement. Alkali-activated binders, known for their excellent performance and lower carbon footprint, have emerged as a promising alternative. Despite the numerous advantages of geopolymers, their practical application is hindered by challenges in processability required for construction techniques, such as pumping, spreading, and forming. This study focuses on enhancing the rheological properties of geopolymers through mechanochemical activation and exploring the modification mechanisms involved. Slag and fly ash raw materials were processed under different ball milling conditions, specifically varying ball milling rotation speed (BR) and ball milling time (BT). The mechanical properties, workability, and rheological behavior of geopolymer specimens were evaluated to identify the optimal milling parameters affecting these properties. Detailed analysis using XRD, SEM, and heat of hydration tests elucidated the phase composition, microstructural evolution, and thermal characteristics of mechanochemically modified geopolymers, providing insights into the fundamental mechanisms of mechanochemical activation modification. The results indicate a significant correlation between ball milling parameters and the rheological properties of geopolymers. The optimal milling regime was identified as grinding at a speed of 70r/min for 50 min. This specific milling condition imparts ideal properties to the geopolymer, including moderate yield stress (34.353 Pa), low plastic viscosity (0.452 Pa s), good thixotropy, and high 28d strength (53.28 MPa), without any significant shear thickening behavior.

Experimental and thermodynamic investigating of carbonation behavior in Alkali-activated slag-calcined clay materials with different binder constituent

Alkali-activated materials (AAMs) have gained interest as sustainable alternatives to traditional Portland cement in recent years. However, concerns still exist regarding their durability against harsh environments such as carbonation. This study presents an experimental and thermodynamic investigation into the carbonation behavior of alkali-activated slag-calcined clay (AASCC) prepared with varying activator types (sodium hydroxide, sodium silicate, sodium carbonate), slag replacement levels with calcined clay (0 %, 10 %, 20 %), and alkali concentrations represented by the solid part of activator to base material ratio (SPA/B = 0.05, 0.075, 0.1). Furthermore, Portland cement mixtures were also prepared to compare the results with AASCC mixtures. Compressive strength, capillary water absorption, and accelerated carbonation testing were conducted on paste and concrete mixtures over 28–90 days. Thermodynamic modeling accurately predicted the experimental trends, demonstrating that this is a valuable tool for simulating complex processes in AAMs. Results illustrated that AASCC paste mixtures produced with sodium hydroxide demonstrated the best carbonation resistance due to higher pore solution pH (up to 13.74), sodium and alumino-substituted calcium silicate hydrate (CNASH) gels content, and layered double hydroxide phases (Mg-Al-LDH). Increasing alkali concentration further improved durability against the carbonation process by elevating pore solution pH and CNASH content. However, replacing slag with calcined clay reduced carbonation resistance regardless of activator type, attributed to lower pore solution pH, CNASH, and Mg-Al-LDH, although higher alkali concentrations alleviated this impact. In general, the study elucidates key chemical and physical factors regarding the carbonation of these novel materials by utilizing comparative experimental investigation and thermodynamic modeling.

Microstructure development of calcium carbonate cement through polymorphic transformations

This study presents the mechanical properties and polymorphic transformation of pastes made with calcium carbonate cement, where vaterite was the main component. Both laboratory (compression tests, XRD, & SEM) and synchrotron-based techniques (transmission X-ray microscopy and microtomography) were used in the characterization of the pastes. Mechanical properties were developed by controlling the polymorphic transformation of vaterite. When converting to aragonite, calcium carbonate cement exhibited three times greater strength development compared to its conversion to calcite at a water-to-cement ratio of 0.4, which resulted in 42 % porosity. During the conversion to aragonite, the calcium carbonate cement paste develops an interpenetrating matrix of aragonite needles that enhance strength development through interlocking at a low paste bulk density of 1.6 g/cm3. Together the environmental and mechanical properties of calcium carbonate cement suggest its potential as a greener building material compared to traditional Portland cement.

Advances in Geopolymer Composites: From Synthesis to Sustainable Applications

The increasing demand for sustainable construction materials has brought significant attention to geopolymers as a viable alternative to traditional Portland cement [...]

Alkali-Activated Slag as Sustainable Binder for Pervious Concrete and Structural Plaster: A Feasibility Study.

In the realm of sustainable construction materials, the quest for low-environmental-impact binders has gained momentum. Addressing the global demand for concrete, several alternatives have been proposed to mitigate the carbon footprint associated with traditional Portland cement production. Despite technological advancements, property inconsistencies and cost considerations, the wholesale replacement of Portland cement remains a challenge. This study investigates the feasibility of using alkali-activated slag (AAS)-based binders for two specific applications: structural plaster and pervious concrete. The research aims to develop an M10-grade AAS plaster with a 28-day compressive strength of at least 10 MPa for the retrofitting of masonry buildings. The plaster achieved suitable levels of workability and applicability by trowel as well as a 28-day compressive strength of 10.8 MPa, and the level shrinkage was reduced by up to 45% through the inclusion of shrinkage-reducing admixtures. Additionally, this study explores the use of tunnel muck as a recycled aggregate in AAS pervious concrete, achieving a compressive strength up to 20 MPa and a permeability rate from 500 to 3000 mm/min. The relationship between aggregate size and the physical and mechanical properties of no-fines concretes usually used for cement-based pervious concrete was also confirmed. Furthermore, the environmental impacts of these materials, including their global warming potential (GWP) and gross energy requirement (GER), are compared to those of conventional mortars and concretes. The findings highlight that AAS materials reduce the GWP from 50 to 75% and the GER by about 10-30% compared to their traditional counterparts.

Analysis of strength characteristics and microstructure of alkali-activated slag cement fluidized solidified soil

In order to solve such as difficulties in backfilling narrow foundation trenches in engineering, it was proposed to use alkali-activated slag cement (AASC) instead of traditional Portland cement to solidify silt and form AASC fluidized solidified soil. The effect of the content of AASC and the curing period on fluidized solidified soil has been studied by unconfined compression strength test, SEM and EDS. Moreover, the root cause for the improvement of the strength by the microstructure was explored. The results showed that: The fluidity increased first and then decreased with the increase of the content of AASC; 40% was the optimal content; in the same curing period, the unconfined compression strength increased with the increase of the content; 40% was the optimal content; the soil with different contents could reach the most of the 28d strength on Day 7; AASC generated a lot of low-Ca/Si C-S-H gel that consolidated soil particles into a denser structure. These results provide a theoretical basis for the application of AASC in fluidized solidified soil engineering.

Mechanical and Microstructural Analysis of Treated Tuff with Metakaolin Geopolymer Cement for Road Base layers Applications

Traditional road bases materials such as natural gravel and crushed stone are environmentally damaging, and there is a growing need for sustainable and eco-friendly alternatives. One such alternative is using geopolymer cement and tuff as aggregate materials. Geopolymer cement is an innovative and environmentally-friendly alternative to traditional Portland cement, and using locally-sourced tuff as an aggregate material can further reduce the environmental impact of road construction. This article discusses the importance of sustainable road construction practices, particularly in the use of eco-friendly materials for road base layers. It focuses on the treatment of tuff with alkali-activated metakaolin as the geopolymer precursor activated with a mixture of sodium hydroxide and sodium silicate. The effectiveness of treating tuff with metakaolin geopolymer cement is evaluated using several parameters, including dry density, California Bearing Ratio (CBR), shear strength, and microstructure analysis. These evaluations are performed with different NaOH dosages (8, 10, and 12 moles) to determine the optimal molarity for enhancing the material's performance.

Performance Characterization and Composition Design Using Machine Learning and Optimal Technology for Slag-Desulfurization Gypsum-Based Alkali-Activated Materials.

Fly ash-slag-based alkali-activated materials have excellent mechanical performance and a low carbon footprint, and they have emerged as a promising alternative to Portland cement. Therefore, replacing traditional Portland cement with slag-desulfurization gypsum-based alkali-activated materials will help to make better use of the waste, protect the environment, and improve the materials' performance. In order to better understand it and thus better use it in engineering, it needs to be characterized for performance and compositional design. This study developed a novel framework for performance characterization and composition design by combining Categorical Gradient Boosting (CatBoost), simplicial homology global optimization (SHGO), and laboratory tests. The CatBoost characterization model was evaluated and discussed based on SHapley Additive exPlanations (SHAPs) and a partial dependence plot (PDP). Through the proposed framework, the optimal composition of the slag-desulfurization gypsum-based alkali-activated materials with the maximum flexural strength and compressive strength at 1, 3, and 7 days is Ca(OH)2: 3.1%, fly ash: 2.6%, DG: 0.53%, alkali: 4.3%, modulus: 1.18, and W/G: 0.49. Compared with the material composition obtained from the traditional experiment, the actual flexural strength and compressive strength at 1, 3, and 7 days increased by 26.67%, 6.45%, 9.64%, 41.89%, 9.77%, and 7.18%, respectively. In addition, the results of the optimal composition obtained by laboratory tests are very close to the predictions of the developed framework, which shows that CatBoost characterizes the performance well based on test data. The developed framework provides a reasonable, scientific, and helpful way to characterize the performance and determine the optimal composition for civil materials.

Polyaluminum enhanced dehydrated cement paste activated slag: Mechanical performance and microstructural analysis

Dehydrated cement paste (DCP) activated slag offer a promising sustainable alternative to traditional Portland cement, but their inadequate mechanical strength limits practical applications. This study investigates the potential of polyaluminum chloride (PAC) to enhance the performance of DCP activated slags, utilizing multi-scale characterization methods. Results demonstrate that PAC incorporation significantly promotes strength development, enabling the binder to meet requirements for most engineering applications. PAC accelerates Ca(OH)2 consumption, and facilitates additional hydration product formation that refines the pore structure, leading to the densification of samples. These improvements in strength and microstructure are attributed to the modified slag dissolution and the enhanced polymerization of the C-A-S-H gel. Furthermore, the underlying role of PAC on the hydration, mechanical performance and microstructural development of DCP activated slags are discussed.

Experimental study of bond behavior of geopolymer concrete under different curing condition using a pull-out test

Researchers recently have focused on geopolymer concrete as it has several advantages compared to traditional Portland cement, such as lower carbon footprint, high early strength, chemical resistance and long-lasting structural performance. This paper designed 192 pull-out specimens to investigate the influence of factors on the bond-slip behavior between geopolymer and steel bar such as curing condition (ambient and 80 °C for 7 hours), longitudinal rib angle, the position of longitudinal bar, bar diameter (12 mm and 24 mm), stirrup usage (with and without stirrup) and bond length (2d and 4d). The maximum bond strength, bond failure modes, and bond stress-slip relations were discussed. The test results showed that the longitudinal rib angle, and the position of rebar play a vital role in determining the bond strength as well as the bar diameter. In comparison with the specimens without the stirrup, the bond performance of specimens with stirrup increased more significantly, and this phenomenon became even more pronounced as the bar diameter increased. The stirrup usage in samples under ambient and heat cure increased the bond strength by an average of 45 % and %40, respectively. Moreover, it has been determined that the curing conditions have a significant effect on the bond performance, as especially the compressive and tensile strengths of the samples under heat cure improve. In samples exposed to both ambient and heat cure, doubling the bond length increased the bond strength by 70 %. Furthermore, increasing the bar diameter increased the bond strength of the samples exposed to ambient and heat curing by a maximum of 84 % and 79 %, respectively. The findings lay the groundwork for understanding the bond behavior of geopolymer, which is critical for the successful application of geopolymer-bonded rebar.

Review on Research Progress of Geopolymer Concrete

Geopolymer concrete has emerged as a promising alternative to traditional Portland cement - based concrete due to its reduced environmental impact, improved mechanical properties, and potential for sustainable construction practices. This paper presents a comprehensive review of recent advancements in geopolymer concrete technology, focusing on key research findings, innovative materials, and novel applications. A systematic analysis of 40 selected research articles is conducted to elucidate the progress made in the field, covering topics such as material composition, mechanical properties, durability, sustainability, and structural performance. The review highlights the diverse range of materials used in geopolymer concrete, including fly ash, metakaolin, recycled aggregates, and various fibers. Furthermore, it examines the influence of different additives, curing methods, and mix design parameters on the properties of geopolymer concrete. The paper also discusses emerging trends such as the incorporation of hybrid fibers, utilization of waste materials, and development of high - performance geopolymer composites. Finally, future research directions and potential challenges in the widespread adoption of geopolymer concrete are outlined, aiming to contribute to the advancement of sustainable construction practices worldwide.

Properties of one-part CaO–Na2CO3 activated ground granulated blast furnace slag

In this study, the fresh and hardened performance and durability of one-part ground granulated blast furnace slags (GGBFS) activated by solid CaO and Na2CO3 were discussed, and their hydration process and microstructure development were analyzed accordingly. Results showed that when the water-to-binder ratio was 0.32, the alkali-activated slag (AAS) paste exhibited lower flowability, higher yield stress and plastic viscosity. As the content of CaO and Na2CO3 increased, the yield stress, plastic viscosity, and compressive strength of AAS after hardening all increased. For the durability of the hardened sample, AAS with high content of activator have higher shrinkage strain and chloride ion flux. The microscopic analysis results indicated that AAS containing CaO and Na2CO3 exhibited more intense hydration heat release and rapid microstructure development in the early stage, thereby promoting the improvement of strength. The use of CaO and Na2CO3 to activate GGBFS has enormous application potential in solid waste utilization and carbon emission reduction, which can reasonably replace traditional Portland cement (PC) as a new generation of sustainable cementitious materials.

Development of Green Alkali-Activated Mortar Based on Biomass Wood Ash

Portland cement (PC) is the most commonly used binder material for producing concrete. Nonetheless, increasing concerns have been attached to its manufacture which is highly energy-intensive and generates a large quantity of greenhouse gases. Developing cement-free alkali-activated materials as eco-binders is a sustainable replacement for PC, especially the possibility to utilize industrial by-products as precursors significantly reduces the environmental burden due to waste disposal. Many investigations have been reported successfully using coal fly ash, slag, and metakaolin as precursors. However, owing to the low reactivity, studies regarding biomass wood ashes (BWA) in the field of alkali-activated materials are still limited. To produce a green cementless alkali-activated mortar material, in this study, biomass fuel by-products -biomass wood bottom ash (BWBA) at 0, 25, 50, 75, and 100% as well as biomass wood fly ash (BWFA) at 100, 75, 50, 25 and 0%- were binarily used as precursors. Sodium hydroxide (NaOH) at 10 mol/L and calcium hydroxide (Ca(OH)2)at 0 and 20% by binder mass were applied together as alkali activators. Recycled sand, substituting natural sand, was adopted as fine aggregate at an aggregate/binder ratio of 2 to reduce the consumption of non-renewable natural resources. The objective is to investigate the influence of various mix ratios of BWFA and BWBA on the produced alkali-activated mortar, and identify the effects of Ca(OH)2. Compressive and flexural strength were tested to evaluate the evolution of mechanical performance. A cradle-to-gate lifecycle assessment was conducted to analyze the environmental impacts. The results reveal that the alkali-activated mortar has less environmental impact compared to the traditional PC mortar. NaOH solution is the primary source of environmental influence and BWA only contributes to very limited impacts. When 50% BWFA and 50% BWBA are binarily used, the greatest mechanical properties are achieved. The usage of Ca(OH)2 effectively improves the mechanical strength by a maximal 350% (flexural strength) and 320% (compressive strength), but meanwhile increases environmental burdens.

Influences of pretreatment methods on the mechanical and environmental behaviors of PG-GGBS-LM ternary stabilizer.

Phosphogypsum is a kind of acidic industrial byproducts with high content of soluble phosphorus and fluorine pollutants, which requires to be pretreated when used as cementitious material to (partial) replace traditional Portland cement. In this study, five different pretreatment methods were proposed for comparative analysis to examine the pretreatment effect on the mechanical and environmental behaviors of ternary phosphogypsum (PG), ground granulated blast-furnace slag (GGBS), and lime (LM) mixed stabilizer. Series laboratory tests, including unconfined compressive strength (UCS), pH, phosphorus (P)/fluorine (F) leaching, scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests, were conducted to comprehend the macro- and microscopic mechanism. The results show that it is essential to grind raw PG to finer powdered state, so that it reacts more easily and quickly with LM and water. In addition, it was noticed that the UCS and P/F leaching concentration are not only affected by the mixing proportion of the PG-GGBS-LM ternary stabilizer, but also by the curing duration. The UCS increases rapidly from initial curing period and then grows slowly after 28days of curing. From the perspective of strength evolution, mixing proportion of PG: GGBS: LM = 15:80:5 is optimal, but considering the economy and environmental related issues, PG: GGBS: LM = 30:65:5 was regarded as a more attractive choice. The findings can provide a reference for the selection of pretreatment methods and design of PG-based cementitious materials suited for stabilized soils.

Preparation of Geopolymers with Nanosilica and Water-in-Air Pickering Emulsion: Mechanisms Underlying Its Rheology, Polymerization, and Strength.

Geopolymers are alkaline-activated aluminosilicate binders recognized as a promising alternative to traditional Portland cement due to their significantly lower greenhouse emissions, energy consumption, and carbon footprint. However, the challenge is meeting or exceeding the strength of Portland cement concrete while being prepared within a desired setting time and possessing workable rheology. A "water-in-air" Pickering emulsion, also called dry water, was prepared by stabilizing water droplets with hydrophobic nano silica and using them to control the geopolymer's strength, setting time, and workability. The mechanisms that underlie the effects of dry water on the rheology, setting, and strength were studied in detail through a combination of rheological, thermal, morphological, chemical, and microstructural assessments. A reduction in the viscosity and yield shear stress manifests in a higher flow diameter, principally due to the particle size coarsening in the precursor and the flowability of hydrophobic nano silica. There was a rapid rise in temperature during the setting process as the dry water temporarily increased the local alkalinity in the mixture, which boosted the dissolution of the precursor and, hence, the reaction. Outcomes from X-ray diffraction, thermogravimetric analysis, and Fourier-transform infrared confirm the highest degree of polycondensation for the principal N-A-S-H framework in mixtures containing dry water. These eventually correspond to a denser microstructure under scanning electron microscopy and, in turn, a superior mechanical strength. Depending on the unique combination of characteristics, including size coarsening, temporary water encapsulation, microfilling effect, and supplementary silica source, dry water resolves the "trade-off" between geopolymer's fresh and hardened properties when introducing nanoparticles.

Evaluation of long-term properties and life cycle assessment of alkali-activated concrete with varying fiber inclusions

The potential for using alkali-activated concrete (AAC) as a sustainable substitute for Portland cement (PC) concrete is a topic of ongoing research interest. The uncertainties in the raw material composition, the reportedly low tensile strength of AAC, and the lack of relevant standard codes of practice further inhibit wider industrial usage of AACs. Fiber inclusions reportedly enhance the tensile properties of traditional PC concrete. However, there is no long-term data available for fiber-reinforced alkali-activated concrete (FRAAC) mixtures. Hence, the present study is aimed at investigating the long-term mechanical properties of ambient-cured FRAAC with GGBS as the sole precursor. Four different types of fibers, viz., steel (SF), polyvinyl alcohol (PVAF), polypropylene (PPF) and glass (GF) are used in this research as reinforcements in AAC. Tests for compressive strength (fc′), splitting tensile strength (fsp) and flexural strength (fr) are conducted for FRAAC containing varying fiber contents of 0.1–0.3%. The findings demonstrated that fiber additions do not have any noticeable influence on the compressive strength of AAC. However, relative to the plain mix, the fsp and fr of FRAACs were enhanced by up to 32% and 29%, respectively. The formation of the hardened calcium aluminosilicate matrix and evolution of the fiber-matrix bonding over time was evident from the scanning electron microscopy (SEM) images. The related molecular bonds over a period of 7-d to 360-d was identified through mineralogical and chemical analyses. Furthermore, to validate its environmental sustainability, life cycle assessments were conducted. The AACs exhibited at least 43% lesser impacts than PC concrete on the ecosystem. FRAACs had only slightly higher (≤ 7% increase across all fiber types) impacts than plain AAC.