Mechanical properties and permeability of red mud-blast furnace slag-based geopolymer concrete

Yang Z., Mocadlo R., Zhao M., Sisson R.D., Tao M., Liang J.

• Red mud slurry and fly ash-based geopolymers were successfully synthesized. • The RMFA geopolymer demonstrated strengths high enough for use in structural cement. • The RMFA geopolymer exhibited thermal stability up to 600 °C. • Recrystallization was found to begin above 600 °C, leading to decrease in mechanical strength. This study employed a synthesis method for a geopolymer sourced from red mud (RM) slurry and fly ash (FA) powder. Properties, including mechanical behavior, volume change, weight loss, and microstructural change, of the RMFA geopolymer in the temperature range of room temperature to 1000 °C were investigated. The geopolymer was successfully synthesized at 50 °C for seven days, followed by curing at room temperature and 40% relative humidity for an additional seven days. After curing for fourteen days, the RMFA geopolymer exhibited compressive strengths over 17 MPa. Mechanical tests found the material to retain its strength up to 600 °C. Although the mechanical properties remained relatively stable under 600 °C, weight loss and thermal shrinkage were observed in thermogravimetric analysis and dimensional measurements. These behaviors were attributed to the loss of free and structural water as well as the dehydroxylation reaction under heating. Above 600 °C, the mechanical properties, including compressive strength and Young’s modulus, dropped quickly, and the material showed rapid volume expansion. This observation was associated with the start of the breakdown of the geopolymer matrix, as well as recrystallization, as evident in the X-ray diffraction pattern. The RMFA geopolymer may be explored as an alternative material to ordinary Portland cement, thermal barrier material on substrate metal, thermal insulation material for large equipment, with environmental benefits including red mud and fly ash repurposing.

Hu W., Nie Q., Huang B., Shu X., He Q.

As a toxic industrial waste product, red mud causes severe environmental concern due to its strong alkalinity. In this study, red mud was systematically investigated for beneficial utilization as a raw material for geopolymer production. One type of red mud along with three types of fly ash were utilized to form geopolymers as construction and building materials. Source materials were activated using two types of activator and cured at both ambient and elevated temperatures. The compressive strength, geopolymerization process, and microstructure of the geopolymers were characterized in this study. The geopolymer derived from red mud and class C fly ash obtained a compressive strength of 15.2 MPa under ambient temperature curing at a significantly low NaOH concentration compared to the class F fly ash-based geopolymer. In contrast, the geopolymers derived from red mud and class F fly ash were unable to obtain a serviceable strength when activated with the NaOH solution alone. Elevated temperature curing or using a composite activator proved to be solutions to this issue. This study indicated that the high alkalinity of red mud contributed to geopolymerization, but additional NaOH was necessary to achieve maximum compressive strength.

Gautam M., Agrawal M.

Globally, 120 million tonnes of red mud is generated whose disposal and storage occupy large areas of potentially important arable lands. Red mud dumps are physically, nutritionally and biologically poor in nature. Vetiver (Chrysopogon zizanioides (L.) Roberty), a medicinally important perennial plant, known to control soil erosion, tolerates a wide range of pH and elevated levels of toxic metals. This information prompted to make use of red mud with sewage sludge, a nutrient rich bio-waste for growing vetiver. An experimental study was conducted using red mud at four rates (0, 5, 10 and 15% w/w) in soil amended with sewage sludge (soil: sludge: 2:1 w/w) to evaluate the effects on physico-chemical properties, plant growth performance, biomass and metal contents in vetiver under control (without sewage sludge and red mud) and different soil treatments. Application of red mud with sludge enhanced the levels of organic matter and nutrient status of the soil which offered suitable substrata to support plant growth. Heavy metal contents (Fe, Mn, Mg, Zn, Cu, Ni, Pb, Cd and Cr) increased with increase in red mud levels, however, their phytoavailable contents decreased. Addition of red mud resulted in significant improvement in root-shoot lengths, number of tillers culm− 1, root-shoot ratio and biomass compared to the control. However, maximum improvement occurred in root (125.27%), shoot (79.91%) and total plant biomass (88.07%) under 10% red mud treatment compared to control. Vetiver is found to be a potential metal tolerant plant as tolerance index was > 100%. Based on translocation and bioconcentration factors, the plant was found efficient in translocation of Mn and Cu from roots to shoot, whereas it acted as a potential phytostabilizer for Fe, Zn, Mg, Cd, Pb, Ni and Cr. The study suggests utilization of 10% red mud in sludge amended soil to sustain maximum plant growth coupled with enhanced phytoremediation potential of vetiver.

Li J., Xu L., Sun P., Zhai P., Chen X., Zhang H., Zhang Z., Zhu W.

Originated from the by-product of alumina production, red mud has caused severe impact on environment. To cope with the increasingly urgent environmental issue, red mud has now been utilized for the first time to obtain the hierarchical porous γ-AlOOH/γ-Al 2 O 3 microspheres as high efficient adsorbents for dye removal. The NaAlO 2 leached from the red mud is hydrothermally treated at 150 °C for 6.0 h in the presence of urea, leading to hierarchical porous γ-AlOOH microspheres, with a specific surface area of 76.8 m 2  g −1 , 93% of which have a diameter within the range of 3.5–7.5 µm. The subsequent mild thermal conversion at 600 °C for 2.0 h results in the hierarchical porous γ-Al 2 O 3 microspheres with a specific surface area of 158.6 m 2 g −1 , and ca. 92% of which bear a size of 3.0–7.0 µm. The porous γ-AlOOH and γ-Al 2 O 3 microspheres exhibit excellent adsorption for MB with the maximum adsorption capabilities of 953.0 mg g −1 and 1587.6 mg g −1 , respectively, and the latter is distinctly higher than most of the reported results. The possible formation is proposed, and the adsorption mechanism is discussed. The present work provides a new insight into the comprehensive utilization of the red mud as great potential adsorbents for removal of anionic dyes from mimetic waste water, and also is helpful for the future potential applications of the unique hierarchical porous structures in catalysis and other related fields.

Wei G., Shao L., Mo J., Li Z., Zhang L.

Using molasses wastewater as partial acidifying agent, a new Fenton-like catalyst (ACRM sm ) was prepared through a simple process of acidification and calcination using red mud as main material. With molasses wastewater, both the free alkali and the chemically bonded alkali in red mud were effectively removed under the action of H2SO4 and molasses wastewater, and the prepared ACRM sm was a near-neutral catalyst. The ACRM sm preparation conditions were as follows: for 3 g of red mud, 9 mL of 0.7 mol/L H2SO4 plus 2 g of molasses wastewater as the acidifying agent, calcination temperature 573 K, and calcination time 1 h. Iron phase of ACRM sm was mainly α-Fe2O3 and trace amount of carbon existed in ACRM sm . The addition of molasses wastewater not only effectively reduced the consumption of H2SO4 in acidification of red mud but also resulted in the generation of carbon and significantly improved the distribution of macropore in prepared ACRM sm . It was found that near-neutral pH of catalyst, generated carbon, and wide distribution of macropore were the main reasons for the high catalytic activity of ACRM sm . The generated carbon and wide distribution of macropore were entirely due to the molasses wastewater added. In degradation of orange II, ACRM sm retained most of its catalytic stability and activity after five recycling times, indicating ACRM sm had an excellent long-term stability in the Fenton-like process. Furthermore, the performance test of settling showed ACRM sm had an excellent settleability. ACRMsm was a safe and green catalytic material used in Fenton-like oxidation for wastewater treatment.

Hua Y., Heal K.V., Friesl-Hanl W.

This review focuses on the applicability of red mud as an amendment for metal/metalloid-contaminated soil. The varying properties of red muds from different sources are presented as they influence the potentially toxic element (PTE) concentration in amended soil. Experiments conducted worldwide from the laboratory to the field scale are screened and the influencing parameters and processes in soils are highlighted. Overall red mud amendment is likely to contribute to lowering the PTE availability in contaminated soil. This is attributed to the high pH, Fe and Al oxide/oxyhydroxide content of red mud, especially hematite, boehmite, gibbsite and cancrinite phases involved in immobilising metals/metalloids. In most cases red mud amendment resulted in a lowering of metal concentrations in plants. Bacterial activity was intensified in red mud-amended contaminated soil, suggesting the toxicity from PTEs was reduced by red mud, as well as indirect effects due to changes in soil properties. Besides positive effects of red mud amendment, negative effects may also appear (e.g. increased mobility of As, Cu) which require site-specific risk assessments. Red mud remediation of metal/metalloid contaminated sites has the potential benefit of reducing red mud storage and associated problems.

Geng J., Zhou M., Zhang T., Wang W., Wang T., Zhou X., Wang X., Hou H.

In preparing geopolymer based on red mud (RM), preactivation processes that are generally energy-intensive are employed, including two indispensable steps, namely, calcination and fine grinding. A novel co-grinding preactivation method without calcination was proposed in this study. RM was pretreated by mix grinding with blended coal gangue (CG) (weight ratio of 8:2) for 20 min. The powdered mixture was characterized by alumina silicate dissolution efficiency test, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy. The corresponding geopolymer was also synthesized and characterized by XRD and scanning electron microscopy to assess the mechanical properties and polymerization reaction. Results showed that under co-grinding effect, the main alumina silicates of the RM/CG mixture were transformed into low-coordinated or low-polymerized phases. The phases were then dissolved in alkaline solution and repolymerized. Alkali activation with high compressive strengths completely formed dense amorphous geopolymer matrices. This work demonstrated that CG, as a milled conditioner, could efficiently expedite the preactivation of RM by grinding without calcinations. Moreover, an RM/CG-based geopolymer was successfully synthesized from the preactivated mixture.

Chandrappa A.K., Biligiri K.P.

Pervious concrete (PC) mixtures were designed and prepared to measure and study permeability characteristics at varying head levels using a falling head permeameter. A total of 1092 readings was used to study the permeability properties of eighteen PC mixtures whose porosity was in the range of 15–37%, and permeability in the realm of 0.076–3.5 cm/s. The permeability reduced as the head of water increased, and gradually attained an asymptotic relation with the head. Cement-to-aggregate ratio had largest contribution in controlling permeability of PC mixtures. Nonlinearity in Darcy’s law was observed in respect of permeability of PC mixes, which was modelled using Izbash/power law, and was prominent for gradations consisting of larger sized aggregates due to inconsequential tortuous pore structure. Modified Kozeny-Carman equation was fitted for PC gradations to compare the results with Izbash law, which showed good agreement. This study is deemed to assist in understanding the hydrodynamics of water flow in pervious concrete, which in turn will aid in rational pervious concrete pavement system designs.

Choo H., Lim S., Lee W., Lee C.

Because both fly ash with high unburned carbon particles and red mud are waste materials with very low reuse rates, the reuse of these two waste materials is environmentally and economically beneficial. This experimental investigation aims at developing one-part mix alkali activated materials using only waste materials. Therefore, this study uses fly ash with high unburned carbon particles (or high loss on ignition) as an aluminosilicate precursor and uses red mud as a NaOH supplier in the geopolymerization of fly ash. The results of this study demonstrate that the unconfined compressive strength of the developed one-part fly ash inorganic polymers activated with red mud increases with an increase in red mud content because of the active dissolution of silica and aluminum with an increase in red mud and a consequent promotion of the polycondensation process. The comparison between the inorganic polymers activated with red mud and NaOH pellets reveals that the relation between compressive strength and the Na/Si ratio of the tested inorganic polymers activated with red mud is almost the same as that of the tested inorganic polymers activated with NaOH, reflecting that all solid NaOH (or Na 2 O) in red mud can be dissolved to form highly alkaline solutions. Therefore, one-part alkali activated fly ash can be synthesized using red mud as a solid alkali activator.

Kaya K., Soyer-Uzun S.

The structure and mechanical performance of red mud–metakaolin based geopolymers with varying red mud contents (0–40 wt% red mud in red mud–metakaolin raw material mixture) were investigated by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) Spectroscopy, Scanning Electron Microscopy (SEM) and compressive strength measurements to understand structure–performance relationships in this system. Systematic addition of red mud into geopolymer system resulted in constant loss of intensity and increased broadening of the main features in XRD and FTIR spectra. The compressive strength was at maximum (51.5 MPa) for metakaolin based geopolymer while increasing red mud incorporation in this system resulted in a nearly monotonous decreasing trend in the compressive strength. Iron species originating from red mud were found to be the main factor controlling the evolution of structural characteristics and mechanical performance. The main role of iron species in the system was to prevent dissolution of raw materials in the geopolymer matrix to a great extent. This was supported by diffraction, spectroscopy and microscopy results and was correlated with the decreasing trend in compressive strength with increasing red mud content.

Ye N., Yang J., Liang S., Hu Y., Hu J., Xiao B., Huang Q.

One-part geopolymer was synthesized from alkali–thermal activated Bayer red mud (RM) with addition of silica to optimize its composition. The RM was pretreated through alkali–thermal activation and turned to geopolymer precursor, which could be used by only adding water in blending process. However the long-term strength of the binder with only RM was poor because of the unstable polymerization due to the low SiO 2 /Al 2 O 3 molar ratio (1.41). Silica fume (SF) was chosen to increase the SiO 2 /Al 2 O 3 molar ratio of the geopolymer formulation. By adding 25 wt% of SF, the 28 d compressive strength of the geopolymer with a SiO 2 /Al 2 O 3 molar ratio of 3.45 could reach 31.5 MPa at a water/solid ratio of 0.45. Sodium aluminosilicate in the activated RM dissolved in water and formed an alkaline environment to dissolve SF. The dissolved silica participated in geopolymerization, leading to a satisfactory geopolymer composition. Typical amorphous geopolymer matrices were formed in the binder completely cured.

Díaz B., Freire L., Nóvoa X.R., Pérez M.C.

Red mud, RM, is the main residue generated in the Bayer process for obtaining alumina. This paper gives an assessment on the penetration rate of aggressive substances such as chlorides and CO2 through RM incorporated cement paste. Diffusivity values are significantly reduced in presence of a low RM content, which could contribute to an increase in the service life of the reinforcements. A study based on Mercury Intrusion Porosimetry (MIP) and Differential Scanning Calorimetry (DSC) was performed to clarify the decrease in the penetration rates. This paper emphasizes the relevance of performing an exhaustive microstructural analysis to have a better understanding of the changes induced not only due to the RM incorporation but also those produced after the chloride and CO2 entrance. Regarding the chloride penetration, the high aluminium content of RM, able to trap chlorides to produce Friedel’s salt, is pointed as responsible for the reduction in the chloride diffusivity. On the other hand, the retention in the CO2 penetration is assisted by the larger amount of C-S-H gel developed in the RM-mixtures along with the alkaline nature of the residue. A reasonable prediction of the carbonation progress can be obtained by measuring the weight increment as the experiment advances.

Singh B., Ishwarya G., Gupta M., Bhattacharyya S.K.

An overview of advances in geopolymers formed by the alkaline activation of aluminosilicates is presented alongwith opportunities for their use in building construction. The properties of mortars/concrete made from geopolymeric binders are discussed with respect to fresh and hardened states, interfacial transition zone between aggregate and geopolymer, bond with steel reinforcing bars and resistance to elevated temperature. The durability of geopolymer pastes and concrete is highlighted in terms of their deterioration in various aggressive environments. R&D works carried out on heat and ambient cured geopolymers at CSIR-CBRI are briefly outlined alongwith the product developments. Research findings revealed that geopolymer concrete exhibited comparative properties to that of OPC concrete which has potential to be used in civil engineering applications.

Ke X., Bernal S.A., Ye N., Provis J.L., Yang J.

Ye N., Yang J., Ke X., Zhu J., Li Y., Xiang C., Wang H., Li L., Xiao B.

A composite geopolymeric material was synthesized from Bayer red mud combined with granulated blast-furnace slag. Thermal pretreatment was applied to improve the solubility of red mud in alkaline solution to promote geopolymerization. The dissolution efficiencies of alumina and silica reached a maximum when red mud was calcined at 800°C, resulting in the highest compressive strength of binders. It was demonstrated that a higher solubility of calcined red mud led to a higher strength of the composite binders. The characteristic microstructures of hydration products were studied to illustrate the geopolymerization process by XRD, FTIR and SEM. The results showed that aluminosilicates were dissolved in the alkaline solution to form nanostructural particulates during the early dissolution process, and then accumulated to form highly dense geopolymeric matrices through solidification reaction. The coexistence of geopolymer and C–(A)–S–H is suggested to contribute to the good performance of the composite binders.

Metwally G.A., Elemam W.E., Mahdy M., Ghannam M.

Li P., Luo S., Wang Y., Zhang L., Wang H., Teng F.

Kolade A.S., Ikotun B.D., Oyejobi D.O.

Abstract Geopolymer concrete (GPC) has emerged as a sustainable alternative to conventional Portland cement concrete, which offers notable environmental, technical and economic benefits. At the core of GPC production is industrial symbiosis, where wastes from energy, agriculture and glass manufacturing sectors are repurposed as precursors and alkaline activators. This process exemplifies circular economy principles by transforming waste streams into valuable construction materials to reduce landfill pressure, conserve raw resources and reduce carbon emissions in line with the Sustainable Development Goals. However, GPC’s broader adoption in structural applications is hindered by several challenges, which include variability in waste composition, inconsistent performance and the lack of standardization. This review advances the discourse on GPC by situating its development within an industrial symbiosis framework, focusing on waste-based precursors and alkaline activators, with the latter a critical yet underexplored component in closing material loops. It further evaluates the interplay between precursor and activator variability across GPC chemistry, mix design, structural performance and durability to address practical challenges related to waste stream inconsistencies, toxicity concerns and regional disparities in material availability. Key findings emphasize the urgent need for standardized mix design guidelines tailored to waste variability, scalable production methods and comprehensive life cycle assessments of alternative activators to facilitate GPC’s transition from laboratory research to widespread adoption within a circular and symbiotic construction ecosystem.

Martins J.R., Novais R.M., Hotza D., Labrincha J.A., Senff L.

Abstract Coral reefs are vital to marine ecosystems, providing habitat and protection for marine life and serving as natural barriers against coastal erosion. However, coral degradation due to climate change, coastal development, and marine exploration require alternatives like artificial corals. This study explores the use of geopolymers based on industrial waste, specifically biomass fly ash and red mud, for creating artificial corals. Geopolymers offer an eco-friendly solution by repurposing waste materials and providing resistance to environmental stressors like saline water. This research investigates the mineralogical and mechanical properties of geopolymers formed using 3D printing and casting. The 3D-printed samples exhibited compressive strengths ranging from 4 to 10 MPa, sufficient to withstand marine environmental stresses, although lower than the 20 to 30 MPa observed in cast samples. The mineralogical analysis showed the presence of compatible phases including hematite and calcium carbonate, which enhance environmental compatibility. The study highlights the potential of waste-based geopolymers as sustainable materials for artificial corals, emphasizing the benefits of using 3D printing to generate complex geometries and endow marine integration. Graphical Abstract

Firoozi A.A., Firoozi A.A.

Baki V.A., Ke X.

Raza A., Selmi A., Elhadi K.M., Ghazouani N., Chen W.

Kazemian F., Hassani A.

The prevalent excessive utilization of cement concrete, characterized by energy-intensive processes and notable carbon dioxide emissions, necessitates a shift towards sustainable construction materials. This study addresses the environmental challenges posed by conventional cement concrete by investigating the potential of recycled precursor geopolymer concrete as an environmentally friendly alternative. The research delves into the mechanical and fracture characteristics of ternary blend geopolymer (TBG) concrete incorporating an industrial by-product, red mud (RM), through comprehensive laboratory testing and statistical analysis. The investigation focuses on assessing the impact of varying RM replacement levels (0 %, 8 %, 15 %, 23 %, and 30 %) on mechanical properties and fracture behaviour in both Mode I and Mode II, utilizing semi-circular bend (SCB) specimens for fracture tests. Statistical methodologies, including Weibull fracture failure probability modelling and analysis of variance (ANOVA), were employed to interpret the results derived from 180 SCB test specimens. Furthermore, microstructural analysis through FTIR, SEM, and EDX testing was conducted on the diverse mixes. The outcomes revealed that the incorporation of RM in geopolymer concrete consistently diminished the compressive strength and flexural strength of the geopolymer concrete as the incorporation levels increased. For instance, the compressive strength decreases from approximately 40 MPa in the RM-free sample to about 25 MPa in the sample with 30 % RM. However, statistical analysis revealed that up to 8 % RM inclusion does not significantly affect the compressive strength and, in some cases, may even slightly increase it, highlighting the subtle effect of RM dosage. Additionally, Weibull modelling revealed that the probability of failure for samples with 30 % RM is about five times higher than for samples without RM. The microstructural analysis also depicted that high RM content may lead to decreasing homogeneity and the formation of deep cracks, negatively impacting mechanical properties. Elevated Fe and Al concentrations with higher RM content suggest potential reactions forming stable geopolymer gels and the presence of minerals like katoite.

Frieda F.S., Greeshma S.

The increasing carbon emission by the cement industry has become a serious environmental problem. Geopolymer concrete is an eco-friendly material that is an alternative to conventional concrete. Industrial solid waste and Natural materials are used as precursors in producing geopolymer concrete and are synthesized by alkali reaction. Using material at the nanoscale as an additive to this has proved to enhance the properties of geopolymer concrete. Various nanomaterials yield improved results in the mechanical, durability, and thermal properties of geopolymer concrete. This paper gives a brief overview of geopolymer concrete with nanomaterials, its strength aspects, the response against harsh environments, and a microstructure study to understand how the nanomaterials influence the physical properties and their behavior at elevated temperatures.

Fu J., Chen Y., He J., Zhou H.

Geopolymers derived from solid waste can effectively remediate heavy metal polluted sites, achieving the ideal fusion of solid waste utilization and environmental remediation. Red mud and blast furnace slag were used to develop a geopolymer for the remediation of composite heavy metal-contaminated soils, focusing on Cd(II)-, Pb(II)-, Cu(II)-, and Zn(II)-contaminated soils. Uniaxial compressive strength tests, toxicity characteristic leaching procedures, pH change characteristics, and pH gradient tests were performed on the solidified/stabilized soil. The results showed that increasing the red mud-blast furnace slag content and curing age significantly enhanced the unconfined compressive strength. Furthermore, it suppressed the leaching of heavy metals in the solidified/stabilized soil. Notably, the treatment effectiveness of Cu(II) and Zn(II) was superior to that of Cd(II) and Pb(II). The leaching concentrations of Cd(II), Pb(II), and Zn(II) decreased in acidic to weakly alkaline environments but increased in strongly alkaline environments. However, the impact of curing age and initial heavy metal content on the pH of the solidified/stabilized soil was the opposite. In conclusion, red mud and blast furnace slag exhibited superior solidification/stabilization effects compared to cement. As environmental protection awareness grows and technology continues to evolve, geopolymers derived from red mud and blast furnace slag will play a greater role in pollution control and remediation, showcasing broad application prospects.

Yousaf A., Al Rashid A., Koç M.

Ezzedine El Dandachy M., Hassoun L., El-Mir A., Khatib J.M.

This study aims to investigate the impact of moderate and elevated temperatures on compressive strength, mass loss, ultrasonic pulse velocity (UPV), and gas permeability of mortars made using metakaolin (MK) or Ordinary Portland cement (OPC). The geopolymer mortar comprises MK, activated by a solution of sodium hydroxide (SH) and sodium silicate (SS) with a weight ratio of SS/SH equal to 2.5. For most of the tests, the MK and OPC mortar specimens were cured for 7 and 28 days before exposure to elevated temperatures, ranging from 100 °C to 900 °C in increments of 100 °C. In the permeability tests, conducted at temperatures ranging from 100 °C to 300 °C in 50 °C increments, the results revealed significant findings. When exposed to 200 °C, MK geopolymer mortar demonstrated an increase in compressive strength by 83% and 37% for specimens initially cured for 7 and 28 days, respectively. A strong polynomial correlation between UPV and compressive strength in MK mortar was observed. Prior to heat exposure, the permeability of MK mortar was found to be four times lower than that of OPC mortar, and this difference persisted even after exposure to 250 °C. However, at 300 °C, the intrinsic permeability of MK mortar was measured at 0.96 mD, while OPC mortar exhibited 0.44 mD.

Philip S., Nidhi M.

Fibre reinforcement is essential in the geopolymer concrete (GPC) matrix to enhance deformation resistance and mitigate fracture propagation under tensile and bending stresses. However, a significant challenge is encountered in accurately forecasting the compressive strength of GPC reinforced with fibres. Recently, the application of machine learning (ML) models has proven effective in accurately forecasting GPC characteristics. However, due to its complexity and the scarcity of data available to researchers, developing the strength prediction technique for fibre-reinforced GPC remains in its infancy relative to traditional concrete. Despite the extensive research on estimating compressive strength in GPCs, limited studies are available on fibre-reinforced geopolymer concrete (FRGPC) due to the complex underlying phenomena involved. Therefore, this research evaluates the effectiveness of random forest (RF) and artificial neural network (ANN) algorithms to predict the compressive strength of FRGPC produced using ground granulated blast-furnace slag (GGBS). The study encompasses a detailed dataset of 110 data points with 16 input parameters comprising various mix proportions of GGBS-based GPC and curing conditions with varying types and percentages of reinforcing fibres. The performance of both ANN and RF models is assessed using a range of performance indicators, including MAE, MSE, RMSE, MAPE, and R2, to evaluate their accuracy and generalization capabilities. K-fold cross-validation is applied to both models to prevent overfitting and to optimize their performance for the best output. The results demonstrate that both ANN and RF models exhibit promising performance in predicting the compressive strength properties. These techniques demonstrated strong predictive capabilities across various evaluation metrics. However, the RF algorithm revealed more accurate predictions of compressive strength than the ANN model. The models showed remarkable R2 values of 0.906 and 0.902 and RMSE values of 3.822 and 5.232 for the RF and ANN models, respectively. The specimen’s age, the ratio of alkaline solution to GGBS, and the sodium hydroxide dosage emerged as critical factors significantly influencing compressive strength, as indicated by the sensitivity analysis results.

Su B., Zhang A., Jian H., Chen W., Zhang S.

In response to the problem of high carbon emissions from ordinary Portland cement, this study used red mud base geopolymer (RMG) as cementitious materials to prepare red mud base geopolymer planting concrete (RMGPC). The effects of different particle sizes and dosages of waste glass powder on the flowability, compressive strength, and alkalinity of RMG, as well as the compressive strength, connected porosity, and alkalinity of planting concrete were investigated. The research results indicate that as the particle size of waste glass powder decreases and the dosage increases, the flowability of RMG slurry shows a downward trend. However, the addition of waste glass powder can make the structure of the RMG denser, reduce the shrinkage cracks of the geopolymer, improve the compressive strength of the RMGPC, and make it have appropriate connectivity porosity and soil alkalinity, thereby improving the planting performance of the planting concrete. Finally, planting experiments and slope stability analysis further confirmed that as long as the alkalinity of the geopolymer planting concrete in the red mud base meets the requirements, the geopolymer planting concrete in the red mud base has good planting performance and is suitable for plant growth.

Fu J., Chen Y., He J., Zhou H., Liu W.

Abstract With the development of mining economy and human society, heavy metal pollution incidents have gradually increased while a large amount of mine solid waste has been produced.Red mud (RM) and blast furnace slag (BFS) are common solid wastes in mines with excellent heavy metal adsorption properties. Optimization of geopolymer solidification/stabilization(S/S) materials based on these waste materials is a good way to reduce solid waste and cure heavy metal contaminated soil, and has outstanding environmental protection significance.In this study, RM and BFS were used as geopolymer raw materials, and sodium hydroxide was used as alkali activator to prepare lead nitrate contaminated soil with Pb content of 0.5%. Laboratory tests were conducted to explore the effects of alkali-solid ratio, BFS content on the mechanical strength, toxic leaching characteristics and pH of geopolymer S/S lead contaminated soil. The optimal ratio of geopolymer is obtained. The results show that the S/S soil cured with RM and BFS geopolymer has good mechanical properties and heavy metal adsorption properties, and it has certain scientific research value and utilization prospect for the remediation of Pb contaminated soil.