Green Cementitious Material Research Articles

A Review on Research Progress of Corrosion Resistance of Alkali-Activated Slag Cement Concrete.

China is the largest producer and user of Ordinary Silicate Cement (OPC), and rapid infrastructure development requires more sustainable building materials for concrete structures. Portland cement emits large amounts of CO2 in production. Given proposals for "carbon peaking and carbon neutralization", it is extremely important to study alternative low-carbon cementitious materials to reduce emissions. Alkali-activated slag (AAS) cement, a new green cementitious material, has high application potential. The chemical corrosion resistance of AAS concrete is important for ensuring durability and prolonging service life. This paper reviews the hydration mechanism of AAS concrete and discusses the composition of hydration products on this basis, examines the corrosion mechanism of AAS concrete in acid, sulfate, and seawater environments, and reviews the impact of its performance due to the corrosion of AAS concrete in different solutions. Further in-depth understanding of its impact on the performance of concrete can provide an important theoretical basis for its use in different environments and provides an important theoretical basis for the application of AAS concrete, so that we can have a certain understanding of the durability of AAS concrete.

Study on the rheological properties and compressive strength mechanism of geopolymer cementitious materials for solid waste

The large-scale storage of industrial solid waste can cause serious environmental pollution issues. Utilizing industrial solid waste to produce green cementitious materials is an effective alternative to cement. This study utilizes steel slag (SS) and calcium carbide residue (CCR) as alkaline activators, combining them with blast furnace slag (BFS) and fly ash (FA) to create SCBF cementitious materials. Investigate the flowability, setting time, rheological properties, compressive strength, pore structure, and microscopic morphology of SCBF cementitious materials under different conditions and conduct molecular dynamics simulations. The research findings indicate that with an increase in BFS content, the flow performance of SCBF decreases, setting time shortens, plastic viscosity and yield stress gradually increase, UCS increases, and the proportion of harmful pores inside the samples decreases. When SS:CCR:BFS:FA is at a ratio of 25:25:30:20, with an increase in curing temperature, the UCS of samples shows a trend of first increasing and then decreasing. The proportion of harmful pores follows a pattern of initial decrease followed by an increase. When the curing temperature is 30 °C, the proportion of harmful pores is 0.31 %, reaching a local minimum, and the UCS strength reaches 13.83 MPa. In the raw materials, SiO2 and Al2O3 aggregate with Ca2+ in an alkaline environment to form C-(A)-S-H three-dimensional network gel. The potential energy, kinetic energy, non-bonding energy, and total energy of Tobermorite 14 Å crystals gradually increase with higher curing temperatures, with the most intense molecular motion occurring at 60 °C. The research findings are beneficial for promoting the use of industrial solid waste to manufacture green cementitious materials as substitutes for cement-based materials. They also provide a theoretical basis for the industrial application of high-temperature-cured solid waste cementitious materials.

Study on hydration and heavy metal leaching of washed MSWI FA as a green cementitious material

Despite municipal solid waste incineration fly ash (MSWI FA) being classified as hazardous waste, there is a consensus on its significant potential for resource utilization. The high content of soluble chlorides in MSWI FA not only limits its co-disposal in cement kilns but also hinders its application in the field of construction materials. The research aimed to investigate the viability of MSWI FA as a binding material in the construction engineering field. Through examining the impact of liquid/solid ratio and pH levels on the chemical composition of MSWI FA during the washing procedure, the study delved into the mechanisms affecting hydration and the characteristics of heavy metal contamination before and after washing pretreatment. The results indicate the feasibility of developing MSWI FA into construction engineering materials. The liquid/solid ratio is a significant factor affecting the removal of chlorides, with an optimal ratio of 30. pH plays a crucial role in the mineral composition during the water-washing process of MSWI FA. An acidic environment can remove a higher proportion of chlorides, while an alkaline environment can form more calcium salts. The compressive strength of pure MSWI FA at 28 days is 3.92 MPa, which can be increased by 0.99 MPa after washing. The washed MSWI FA not only exhibits heightened reactivity but also demonstrates reduced leaching concentrations of heavy metals, and its leaching toxicity was much lower than the safe landfill threshold. Therefore, MSWI FA, after washing, is a very promising alternative material for construction engineering.

Characterization of mechanical behavior and cementing mechanism of high-strength composites using biomimetic chemically induced calcium carbonate precipitation method

Biomimetic mineralized mortar (BMM) represents a novel green cementitious material, increasingly recognized for its environmental sustainability. In this study, four typical amino acids including acidic amino acids (aspartic acid, glutamic acid), neutral amino acid (threonine), and basic amino acid (arginine), are employed as crystal modifiers to develop the high-strength BMM (HBMM) based on the biomimetic chemically induced calcium carbonate precipitation (BCICP) method. The mechanical properties and failure morphology of HBMM were evaluated through unconfined compressive strength (UCS) test. The microstructure characteristics of HBMM were investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and contact angle test. The results show that amino acid-modified calcium carbonate precipitation can effectively cement loose sand particles and significantly improve the strength of the HBMM. The failure modes of HBMM observed include local failure, vertical splitting failure, shear failure, and splitting-shear mixed failure. Notably, aspartic acid and glutamic acid can induce the formation of vaterite-phase calcium carbonate crystals, while threonine and arginine facilitate the formation of aragonite-phase calcium carbonate crystals. The hydrogen bonding between modified calcium carbonate crystals and silanol groups on the silica surface ensures a tight adhesion of the precipitate to sand surfaces, filling gaps and cementing particles. This study elucidates that using amino acids as modifiers in the BCICP method can significantly enhance the strength of HBMM and influence its microstructure, offering valuable insights for its potential practical applications.

Dynamic mechanical properties and microstructure of ultrafine slag powder cement paste utilizing solid waste industrial tailings powder and fly ash

Ultrafine slag powder cement paste (USP-CP) is a promising green cementitious material with excellent mechanical properties and environmental benefits. In this study, the effects of elemental molar ratios in raw materials (n(Si)/n(Al) ranged from 1.2 to 1.4 with a gradient of 0.1; n(Fe)/n(Al) ranged from 0.15 to 0.21 with a gradient of 0.03; and n(S)/n(Al) ranged from 0.20 to 0.28 with a gradient of 0.04.) on the workability, mechanical properties, and microstructure of USP-CP were investigated. The main products of USP-CP are α-SiO2, AFt, gypsum, and α-C2SH. The molar ratio of Si/Al has the greatest influence on workability, while the molar ratio of S/Al has the greatest influence on setting time. For mechanical property tests, higher USP content can improve the early compressive strength of USP-CP, while its long-term compressive strength is affected by the anhydrous calcium sulfate (CaSO4) content. Specifically, when the molar ratios of Si/Al, Fe/Al, and S/Al are 1.2, 0.21, and 0.24, respectively, the 28-day dynamic and static compressive strengths of USP-CP specimens reach the maximum values, which are 121.3 MPa (321/s) and 42.0 MPa (10-2/s), respectively. Furthermore, the static compressive strength is comparable to that of pure cement of the same grade.The molar ratio of S/Al has a more significant effect on dynamic compressive strength than static compressive strength. The excessive increase of Na and Si elements in the alkaline activator inhibits the dynamic mechanical enhancement performance of USP-CP. This study provides theoretical and practical reference value for the application of USP in impact-resistant structural materials and static load-bearing materials. It also fully utilizes waste materials to reduce the use of cement and achieves environmental benefits of carbon reduction.

Impact of curing conditions on the mechanical properties and micro characteristics of alkali-activated material synthesized from industrial waste soda residue

Alkali-activated materials (AAM) are considered a type of green cementitious material because they are produced without the grinding and calcining required for cement production, significantly reducing carbon emissions. However, their production typically involves the use of commercial alkalis, which are often corrosive, irritating, and expensive. As an industrial waste from sodium carbonate production, soda residue (SR) has a large reserve and is challenging to dewater and utilize, making its disposal a widespread technical challenge. In this paper, considering the alkaline nature and high salt content of SR, a soda residue activated granulated blast-furnace slag cementitious material (SAG) was synthesized directly using undried and unground SR slurry as the alkali activator, with a mass ratio of SR to granulated blast-furnace slag (GBFS) of 30:70. The effects of ambient temperature (AT) curing, water curing, various heat curing temperatures (45°C, 60°C, 75°C, and 90°C), and different heat curing durations (6 h, 12 h, 18 h, and 24 h) on the properties of SAG were investigated. Specifically, the effect of curing conditions on the mechanical properties of SAG was analyzed through unconfined compressive strength (UCS) testing of mortar specimens. The impact of curing conditions on the phase composition and changes in SAG was characterized using XRD, TG, and FTIR, while the effect on the microstructure of SAG was characterized using SEM. The results showed that SAG achieved the highest UCS (3 d/56 d: 28.1 MPa/36.7 MPa) when subjected to heat curing at 75°C for 12 h. The UCS increased significantly by 3022 % and 321 %, respectively, compared to those under AT sealed curing. This was attributed to the fact that SAG under heat curing produced more C-(A)-S-H gels and hydrocalumite crystals, optimizing pore structure and resulting in a denser microstructure. However, exceeding the threshold temperature of 75°C led to an excessively rapid hydration reaction that adversely affected the further dissolution of GBFS and the uniform distribution of hydration products, thereby diminishing the positive effects of heat curing on UCS. In addition, excessively prolonging the heat curing time exacerbated the development of microcracks within the SAG, leading to a deterioration of UCS over age. In this paper, a novel AAM was synthesized using undried and unground industrial waste without the addition of commercial alkali, and the impact of curing conditions on their properties was studied. This broadens the range of applications for SAG, fills a gap in research on the impact of curing conditions on AAM without commercial alkali, and provides a theoretical basis for the low-carbon utilization of industrial waste.

Mechanistic insights into molybdenum immobilization within geopolymer waste form

Molybdenum (Mo) tends to form highly mobile, non-sorbing complex redox species, which complicates its immobilization and encapsulation in cement and glass matrices. This study explores the potential of incorporating Mo into an alternative green cementitious material known as geopolymer (GP). By employing X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), morphological analysis, and nitrogen adsorption-desorption techniques, we obtained comprehensive insights into the chemical behavior of Mo and its impact on the morphology and structure of the GP matrix. XRD and TGA analysis demonstrated that increasing Mo content significantly enhances the crystallinity and thermal stability of the GP matrix, attributed to Mo field effects. High-resolution SEM, TEM, and EDS mapping revealed the structural encapsulation of Mo-rich cavities within the GP waste form. A decrease in leaching rates with higher Mo content, alongside reduced pore volume and pore size, underscores the material's chemical durability. Post-leaching characterizations confirmed that the GP retains excellent structural strength with minimal changes in mesoporosity and surface area. This resilience highlights the effectiveness of GPs in immobilizing non-sorbing species like MoO32−, making them ideal for long-term waste management.

Influence of microwave curing on the early performance of heat-stored LC3 composites

Limestone calcined clay cement (LC3), as a new green cementitious material, has a wide range of functional applications in cement-based composite materials. Heat-stored LC3 effectively achieve energy-saving and carbon reduction in buildings. However, the addition of phase change material (PCM) particles leads to a significant decrease in strength, which imposes higher requirements on early performance. To address this issue, this study adopts microwave curing technology to rapidly enhance the early performance of heat-stored LC3, with a specific focus on the influence of microwave curing on the early mechanical properties, hydration products, and microstructure of heat-stored LC3. The results showed that microwave curing at a power of 320 W for 5 min increased the 3-day compressive strength of heat-stored LC3 by 87.3 %, without adversely affecting the later-stage strength, thus compensating for the deficiency in early strength. Microstructure and pore structure analysis revealed that the enhancement of early strength by microwave curing was mainly attributed to the promotion of early hydration of clinker and the activation of pozzolanic reaction occurred calcined clay. The additional formation of C-(A)-S-H gel reduced the matrix porosity, improved overall integrity, and enhanced the microstructure. Additionally, the temperature regulation capability of heat-stored LC3 was verified, ensuring its auxiliary temperature regulation function while maintaining reliable mechanical properties and excellent early strength.

Preparation and Immobilization Mechanism of Red Mud/Steel Slag-Based Geopolymers for Solidifying/Stabilizing Pb-Contaminated Soil.

Pb-contaminated soil poses serious hazards to humans and ecosystems and is in urgent need of remediation. However, the extensive use of traditional curing materials such as ordinary Portland cement (OPC) has negatively impacted global ecology and the climate, so there is a need to explore low-carbon and efficient green cementitious materials for the immobilization of Pb-contaminated soils. A red mud/steel slag-based (RM/SS) geopolymer was designed and the potential use of solidifying/stabilizing heavy metal Pb pollution was studied. The Box-Behnken design (BBD) model was used to design the response surface, and the optimal preparation conditions of RM/SS geopolymer (RSGP) were predicted by software of Design-Expert 8.0.6.1. The microstructure and phase composition of RSGP were studied by X-ray diffractometer, Fourier transform infrared spectrometer, scanning electron microscopy and X-ray photoelectron spectroscopy, and the immobilization mechanism of RSGP to Pb was revealed. The results showed that when the liquid-solid ratio is 0.76, the mass fraction of RM is 79.82% and the modulus of alkali activator is 1.21, the maximum unconfined compressive strength (UCS) of the solidified soil sample is 3.42 MPa and the immobilization efficiency of Pb is 71.95%. The main hydration products of RSGP are calcium aluminum silicate hydrate, calcium silicate hydrate and nekoite, which can fill the cracks in the soil, form dense structures and enhance the UCS of the solidified soil. Pb is mainly removed by lattice immobilization, that is, Pb participates in geopolymerization by replacing Na and Ca to form Si-O-Pb or Al-O-Pb. The remaining part of Pb is physically wrapped in geopolymer and forms Pb(OH)2 precipitate in a high-alkali environment.

Evaluation of mechanical properties and potential environmental applications of biomimetic mineralized composites

With the growing emphasis on environmental protection, there has been extensive research on new green cementitious materials suitable for different conditions. This study focuses on the influence of key environmental factors on proposed biomimetic mineralized composites (BMC) using polyacrylic acid (PAA) as a modifier, based on the biomimetic chemistry induced carbonate precipitation (BCICP) method. The environmental factors examined include the cementing matrices type, the magnesium ions concentration, and the cementing solution pH. The samples treated under various conditions were evaluated for their unconfined compressive strength (UCS) and calcium carbonate content, and their microstructure was characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results demonstrate that the BMC treatment could achieve high-strength cementation for both Toyoura sand and Fujian quartz sand, with a more pronounced enhancement observed for Toyoura sand. Magnesium ions reduce the cementation effect, and they cannot fully replace calcium ions in participating in the cementation process. Moreover, the cementing solution pH significantly influences the cementation effect, with the best acid-base condition for PAA to modify BMC sand samples found at a pH of 11.5. Overall, the BMC exhibits high performance under various environmental conditions. These findings could provide valuable insights into the influence of environmental factors and the potential applications of BMC in diverse environments.

An investigation on the application of acrylic resin agent for fiber/matrix bond strengthening in green engineered cementitious composites (ECC)

Green cementitious materials are usually developed by the addition of high volumes of mineral fillers. However, the addition of minerals can result in the reduction of mechanical strength. ECCs obtain their superior mechanical behavior from a high volume fraction of fibers. In ECCs, the matrix’s strength and the bond between the fibers and the matrix is a critical parameter, and if it becomes weak, the whole composite becomes weak or fibers may pull out of the matrix. In this study on green ECCs, to increase mechanical strength and also fiber/matrix bonding, the acrylic resin is used in 4 contents (e.g., 0, 2, 4, and 6 % in weight). The tests performed on ECC and plain cement paste (PCP) included tensile, compressive, and flexural. The results show that the acrylic increases the tensile strength, from about 2.0 MPa, up to 20 %, and compressive strength increased from about 88 MPa to 100 MPa. Due to the increase in ductility, the energy-based indexes increase more significantly. Acrylic resin optimum content was measured as 1.5–2.7 % (by weight). The trends show that acrylic resin is more effective for ECCs, because, in addition to enhancing the matrix strength, the resin increases the bonding strength between the matrix and fiber. Seeking the relationship between the results, nonlinear regression was used, and governing equations were presented. Also, using a regression model, the mechanical parameters were predicted successfully using input parameters.

Study on the synergistic effect of calcium carbide residue -fly ash enhanced desulphurisation gypsum under high temperature maintenance condition

The preparation of cementitious materials from bulk industrial solid waste is an effective way to replace cement. Based on the multi-component synergistic coupling effect, the influence law of different dosage of fly ash (FA) and calcium carbide residue (CCR) on the performance of flue-gas desulfurization gypsum (FGDG) slurry was investigated, and the hydration process of composite cementitious materials was discussed through the analysis of hydration products, micro morphology and pore structure by the characterisation methods such as XRD, FTIR, MIP and SEM-EDS. The results show that FA incorporation can improve the flow properties of the slurry, and under the action of CCR and FGDG, the alkalinity of the whole system rises, and the FA vitreous body undergoes dissolution corrosion, releasing reactive SiO2 and Al2O3, and forming C-S-H gel and AFt. In addition, some of the tiny FA particles fill up the pore spaces and microcracks, and the structure becomes denser, and all these effects together contribute to the development of the mechanical properties. This research is conducive to the application of new green cementitious materials and promotes the resourceful use of industrial solid waste.

Preparation of granite powder–based geopolymer by synergistic action of calcination and phosphoric acid

AbstractUsing the solid waste of granite powder (GP) to prepare green cementitious materials is of great significance for the sustainable development of the construction industry. In this study, a phosphoric acid–based geopolymer (PABG) was directly prepared from GP through a combination of phosphoric acid and calcination processes. Reaction mechanism of phosphoric‐activated GP is studied by techniques of X‐ray diffraction, thermal analysis, Fourier transform infrared spectroscopy, SE mode, and mercury intrusion porosimetry (MIP) taking calcination temperature, calcination time, and phosphoric acid as variables. The results indicated that the addition of 15 wt.% phosphoric acid and calcination at the temperature of 200°C for 90 min significantly increased compressive strength from 0.70 to 20.92 MPa. The calcination temperature was the most important factor in the synthesis of PABG using GP. The decrease of the peak value of mineral phase after calcination indicates that high temperature promotes the reaction between phosphoric acid and GP. According to the results of MIP, the gel generated by the reaction of phosphoric acid and GP refines the pore structure, which is conducive to the improvement of geopolymer properties. These research results provide a reference for the preparation of geopolymers directly using low pozzolanic active GP.

Effects of titanium gypsum on high calcium fly ash system: Physical and microscopic properties, hydration, and Fe transformation

Titanium gypsum (TG) is a solid waste generated in the sulfate method of TiO2 production. The stockpiling of TG causes harmful environmental issues, but TG could be reused for manufacturing green cementitious materials with fly ash (FA) and calcium carbide residue (CCR). However, the effects of TG on the high-calcium FA–CCR system and the transformation rule of Fe compound in TG remain unclear. Therefore, FA–CCR and FA–natural gypsum–CCR were used as the control group. The effects of TG on the physical properties, phase composition, and microstructure of the FA–CCR system were studied. Furthermore, the transformation role of Fe in TG was revealed by calculating the thermodynamic properties and performing X-ray photoelectron spectroscopy. Results demonstrated that the appropriate addition of TG was found to shorten the setting time and increase the compressive strength of the FA–CCR system, whereas the excessive addition will cause a negative effect. The small crystal size of TG has a greater contribution to the physical properties compared with the negative effect of iron impurities. The addition of TG can optimize the pore structure of the FA–CCR composites. TG reduced the hydration rate of C-(A)-S-H gels at an early age but promoted ettringite generation and polymerization of C-(A)-S-H at the late stage. Fe(OH)3 in TG plays an insert-filling role at an early age, but this compound could transform into Fe(OH)63− and form ettringite in the late hydration stage, thereby promoting the growth of ettringite crystals. The relative conversion rate of Fe(OH)3 to Fe(OH)63− at 60 days is 11.8%.

Modification mechanism of flue gas desulfurization gypsum on fly ash and ground granulated blast-furnace slag alkali-activated materials: Promoting green cementitious material

Alkali activation and the combination of fly ash (FA) and ground granulated blast-furnace slag (GGBS) has been used for cementitious material, which is seen as an effective method to dispose of industrial solid waste. The GGBS-FA AAMs have the characteristic of drying shrinkage and a large number of tiny pores distributed in the matrix, resulting in strength deterioration. The paper is aimed to optimize the strength property by incorporating another solid waste of flue gas desulfurization gypsum (DG), which could be regarded as a ternary alkali-activated materials (AAMs). The unconfined compression tests are carried out to study the effects of DG content on strength with different curing times, and the effects from the modulus of the alkali activator are also analyzed. Then X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) are performed to reveal the microscopic mechanism of the effects of DG on the mechanical property. Results show that the incorporation of DG can significantly improve the early strength due to the increase of calcium. The SO42- in DG continuously reacts with Ca2+ and active silicate to form ettringite during the curing period, which can fill micro-pores and tiny cracks to form a denser matrix structure. In addition, the presence of SO42- has the effect of secondary enhanced activation, further promoting the polymerization reaction and enhancing the strength, especially for the low alkaline reaction system. These all contribute to the strength improvement. It should be noted that the DG content must be controlled to prevent the volume-filling effect that leads the AAMs matrix to be loose and porous, and the generation of geopolymer gel would also be impeded in a high-calcium reaction system, further influencing the final strength. The results will promote the application of high-performance, cost-saving, and green low-carbon cementitious material based on the synergistic utilization of GGBS, FA and DG.

Understanding the changes in engineering behaviors and microstructure of FA-GBFS based geopolymer paste with addition of silica fume

Geopolymers are attracting attention as a new green cementitious material. However, the severe early drying shrinkage deformation of geopolymers limits the use of geopolymer materials in construction projects. Therefore, this study investigates the effect of silica fume (SF) on the drying shrinkage behavior of geopolymer composite. Fly ash (FA) and granulated blast furnace slag (GBFS) were activated by a combination of sodium hydroxide and water glass solutions to produce geopolymer paste. The modification mechanism of SF content on the drying shrinkage and mechanical properties of FA-GBFS geopolymer paste was studied, as well as the important effect of SF on the internal geopolymerization process of geopolymer composite. The results indicate that the SF changes the binding energy and relative content of Si–O-T (T: Si or Al) structure and tetrahedral coordinated Al–OH bond in FA-GBFS geopolymer composite, delaying the early geopolymerization and calcium silicate hydration reaction in the geopolymer. It diminishes the polymerization degree of gel structure in the geopolymer, which also lowers the early strength of the geopolymer paste. In addition, when the SF content reaches 20%, it not only improves the 28d compressive strength of FA-GBFS geopolymer, but also greatly reduces the relative content of harmful pores inside the geopolymer, which reduces the early drying shrinkage strain by about 50%.

Valorification of Egyptian volcanic tuff as eco-sustainable blended cementitious materials

Rhyolite rocks extend from southern Egypt to northern Egypt in the Eastern Desert, and no effective economic exploitation of them has been discovered so far. The pozzolanic activities of different volcanic tuffs (VT) supplied from the Eastern Desert located in Egypt have been investigated as natural volcanic pozzolan materials to develop new green cementitious materials for achieving sustainability goals in the construction field. Experimentally in this paper, the pozzolanic activities of seven diverse specimens of Egyptian tuffs taken with standardized proportions of 75:25% (Cement: volcanic tuffs) were investigated. Pozzolanic features of such tuffs are examined comparatively via strength activity index (SAI), TGA, DTA, and the Frattini’s test. Chemical composition, petrographic, and XRD analysis were also performed for tuffs samples. The pozzolanic reaction degrees were determined according to the compressive strengths at 7, 28, 60 and 90 days with different replacement ratios (20, 25, 30 and 40%) of tuffs samples. Additionally, the micro-filler effects in mortar and concrete were determined by measuring the heat of hydration in mortar samples and the compressive strength of concrete with different additive ratios for tuffs samples besides, the concrete slump test. The results show that TF6 gives a lower cement heat of hydration value which is less than 270 J/g at 7 days. Also, its performance in concrete is better than silica fume at late strength (28 days) since the concrete index value is 106.2% by compared to the concrete index of silica fume 103.9 and therefore it can be used as an alternative to high price and quality variable silica fume (SF) for producing high-performance green concrete. Due to the good pozzolanic behavior proved by nearly most volcanic tuffs, along with their low cost, this study will be profitable for very auspicious the use of Egyptian volcanic tuffs for developing sustainable and eco‑friendly blended cement.

Effect of steel fibre and manufactured sand on mechanical properties of alkali-activated slag green cementitious material after high temperature

This study investigated the mechanical properties of alkali-activated slag cementitious material (AASCM) after exposure to 20–800 ℃ considering the effect of steel fibre content and aggregate type to promote the use of AASCM in structural engineering. The volume contents of steel fibre were 0%, 0.5%, 1.0% and 1.5%, and the aggregate types were manufactured sand and natural river sand. The residual compressive, tensile strength and mass loss were determined. Besides, the microstructure and phase composition of AASCM before and after high temperature exposure were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the tensile and compressive properties of manufactured sand AASCM were inferior to that of natural river sand after high temperature exposure. Below 600 ℃, steel fibre can improve the mechanical properties of AASCM. Steel fibre oxidation fails and effectively loses its strengthening effect on AASCM with the temperature reaching 800 ℃, resulting in a notable decrease in strength of AASCM. The models for calculating mass loss, compressive strength, and tensile strength of steel fibre reinforced AASCM after high temperature exposure were established.

Prediction of Compressive Strength of Fly Ash-Slag Based Geopolymer Paste Based on Multi-Optimized Artificial Neural Network.

The fly ash-slag geopolymer is regarded as one of the new green cementitious materials that can replace cement, but it is difficult to predict its mechanical properties by conventional methods. Therefore, in the present study, the back propagation (BP) artificial neural network technique is used to predict the compressive strength of the fly ash-slag geopolymer. In this paper, data from the published literature were collected as the training set and the experimental results from laboratory experiments were used as the test set. Eight input parameters were determined, as follows: the percentage of fly ash, the percentage of slag, the water-cement ratio, the curing age, the modulus of alkali activator, the mass ratio of NaOH to Na2SiO3 and the moles of Na2O and SiO2 in the alkali activator. Three multilayer artificial neural network models were constructed using the Levenberg-Marquardt (LM), Bayesian regularization (BR) and scaled conjugate gradient (SCG) algorithms to compare the prediction accuracy of the compressive strength of the fly ash-slag geopolymer paste at different ages (3, 7, and 28 d). It was concluded that the training set error of the BR-BP neural network was the smallest. Ultimately, the hyperparameter optimization of the BR-BP neural network was carried out to compare the training set and the test set errors before and after the optimization, and the results show that the BR-BP neural network model with hyperparameter optimization had the highest prediction accuracy.

Mechanical Performances and Frost Resistance of Alkali-Activated Coal Gangue Cementitious Materials

The coal gangue after composite activation treatment is considered a potential low-carbon and green cementitious material, so the feasibility of employing composite-activated gangue to partially or entirely replace cement for building materials is systematically studied in this paper. The effects of alkali content, slag content, and water-to-binder ratio on the mechanical properties and frost resistance of alkali-activated coal gangue mortar (AACGM) were experimentally investigated. An ESEM was employed to observe the microstructure of the AACGM. Moreover, the microstructure damage to the AACGM was analyzed by a pixel-based image processing algorithm. The research was carried out in accordance with standards JGJ/T70-2009 and GB/T 50082-2009. Experimental results indicated that the mechanical properties and frost resistance of the AACGM were superior to those of ordinary Portland cement mortar (OPCM). Compared with the OPC group, the compressive and flexural strength of the W0.50 group increased by 16.01% and 14.19%. Moreover, the loss rate of mass, flexural strength, compressive strength, and microstructure damage of the AACGM were less than those of the OPCM. Between freeze–thaw cycles 25 and 100, the cracks and pores of specimens gradually grew, and the maximum crack width increased by 277.78%. In addition, the slag was beneficial in improving the flexural strength, compressive strength, and frost resistance of the AACGM. Finally, the freeze–thaw damage mechanism of the CGBG mortar was systematically analyzed.