Ground Granulated Blast Furnace Slag Content Research Articles

Effects of alkaline activators and other factors on the properties of geopolymer concrete using industrial wastes based on GEP-based models

This study aims to develop reliable and practical models for estimating the compressive strength and CO2 emission of geopolymer concrete (GPC) using the Gene-expression programming (GEP) technique. Approximately 274 data points on the strength and CO2 emission of GPC using fly ash (FA) and ground granulated blast furnace slag (GGBFS) were used to generate two prediction models considering the effects of 19 input variables. The research results show that the proposed GEP-based models perform well with high correlation coefficients (R > 0.95) and reasonable errors. The parametric study demonstrates that increasing the GGBFS content, the Na2O (dry) content, and the molarity of NaOH solution, and decreasing the FA content, the FA/GGBFS ratio, and the added water or total water/binder ratio could significantly enhance the strength of GPC. Besides, the proposed GEP-based models were used to optimise the mix proportions of GPC concrete with minimisation of CO2 footprint. The range and reasonable values of the FA and GGBFS contents, the alkaline activators, the aggregates, and other parameters were suggested based on the in-depth analyses. This significant reference data source could promote the use of GPC widely in the construction industry as green construction materials for sustainable development.

Effect of various geopolymerization parameters on poor quality Afşin-Elbistan fly ash-based geopolymer concretes with ground granulated blast furnace slag

AbstractThe utilization of Afşin-Elbistan fly ash (FA), which cannot be used in cement and concrete industry in production of geopolymers, has been studied with some preliminary trials. In this study, FA of Afşin-Elbistan thermal power plant, which does not fit any of FA classes according to ASTM C 618, was used as a geopolymer binder raw material. The main motivation of the study is to investigate the partial usability of this type of FA, which is not sufficient on its own and creates a large amount of waste, as a geopolymer raw material. FA was replaced with ground granulated blast furnace slag (GGBFS) by the ratios of 25% and 50% (by weights) in order to develop the properties of geopolymer concrete. Sodium silicate (SS) and sodium hydroxide (SH) (10 and 14 M) were used as activators. Three different activator to binder ratios (0.45, 0.55 and 0.65) and three SS/SH ratios (0.75, 1.0 and 1.5) were chosen. Unit weight, compressive strength, splitting tensile strength, and ultrasonic pulse velocity tests were performed for 28 and 60 days. In order to investigate the microstructure, scanning electron microscopy (SEM) analyses were performed. As a result, GGBFS incorporation enhanced the properties of Afşin-Elbistan FA-based geopolymer concrete. With the increase of GGBFS content, the compressive strength values increased. The highest strengths were obtained from 50% GGBFS groups. The results revealed that Afşin-Elbistan FA (AEFA), which has the highest waste reserve among the thermal power plant fly ashes in Turkey, could be evaluated as partial geopolymer raw material. Graphical abstract

Compressive Strength, Permeability, and Abrasion Resistance of Pervious Concrete Incorporating Recycled Aggregate

Extensive use of cement in the construction industry increases CO2 emissions and has a negative impact on the environment. In this work, recycled coarse aggregate (RCA) from construction and demolition wastes (C&DW) was used to fabricate sustainable pervious concrete (PC). In order to mitigate the environmental hazards of excess cement waste and to improve the engineering properties of PC, silica fume (SF) and ground granulated blast-furnace slag (GGBS) were added. The effects of SF and GGBS on the compressive strength, permeability coefficient, porosity, and abrasion resistance of recycled aggregate pervious concrete (RAPC) were investigated. The results show that the incorporation of GGBS and SF effectively improves the compressive strength of RAPC but reduces the permeability coefficient and porosity. Moreover, due to the filling effect and pozzolanic activity, the incorporation of GGBS and SF significantly enhances the abrasion resistance of RAPC. Furthermore, the relationships between the compressive strength, permeability coefficient, porosity, and abrasion resistance of RAPC are clarified. The optimum replacement is achieved when the SF content is 7%, and the GGBS content is 20%, respectively, which results in the highest compressive strength (28.9 MPa) and the lowest permeability coefficient (1.2 mm/s) at 28 days, and the lowest mass loss rate (12.1%) after the Cantabro abrasion test.

From cement to geopolymers: Performances and sustainability advantages of ambient curing

The production of Portland cement results in substantial carbon emissions. Geopolymers are regarded as highly promising alternative binder materials to cement due to their low energy consumption and excellent mechanical properties. However, it should be noted that the thermal curing process of geopolymers diminishes their low-carbon advantage. In this study, ground granulated blast furnace slag (GGBS) was used to replace metakaolin (MK) by the ratio of 10 %, 20 %, 30 %, 40 %, and 50 % to produce geopolymers. The aim was to examine the impact of GGBS content on the thermal curing performance of MK-based geopolymers. The microstructure of the specimens was analyzed using SEM and XRD analysis techniques. Lastly, a comprehensive assessment of their sustainability potential was carried out. As a result, slag may increase flow spread, decrease the setting time, and effectively improve the mechanical properties which curing on ambient temperature. The group with 50 % slag content had the highest compressive and flexural strengths, reaching 55.9 MPa and 8.45 MPa at 28 d, respectively. The drying shrinkage of geopolymers increases as the GGBS content goes up. Notably, owing to the evolution of chemical transformation and gel structure, MK exhibits a significant mitigation on shrinkage. Ultimately, with a 50 % slag content, the carbon dioxide emissions of geopolymer can be reduced to 265.36 kg CO2-eq, which is a 43.6 % decrease compared to that of OPC. With a comprehensive consideration of the performance and sustainability potential of geopolymers, it is recommended to introduce GGBS content in the range of 30 %–40 %.

Performance modulation and optimization of PE fiber reinforced 3D-printed geopolymer

This paper aims to develop an environmentally friendly and low-carbon geopolymer for 3D printing, which has excellent mechanical and rheological performance. The effect of ground granulated blast furnace slag (GGBS), NaOH and sand on mechanical strengths, 3D printing performance and rheological behavior was investigated to determine the optimum mix proportion for 3D-printed geopolymer. Moreover, polyethylene (PE) fibers were introduced to reinforce the performance of 3D-printed geopolymer. Results show that when the ratio of GGBS, NaOH and sand is 1:0.13:2.67, geopolymer exhibits superior mechanical, 3D printing and rheological properties. Increasing the dosage of GGBS and sand leads to an overall increase in the yield stress but a decrease in the consistency coefficient, indicating that it benefits the stacking and fluidity performance of 3D-printed geopolymer. However, with an increase of NaOH content, the stacking performance increases while the fluidity decreases. Although increasing NaOH and sand content benefits the viscosity recovery performance, an increase in GGBS content has an opposite effect. Incorporating PE fibers significantly increases the flexural strength with an increase of up to 27.8 % and 21.3 % in 7-d and 28-d flexural strength, respectively, given a PE fiber volume of 0.6 %. Increasing the volume of PE fibers leads to a significant rise in the stacking performance but a reduction in the fluidity. Furthermore, adding PE fibers negatively affects the geopolymerization but benefits the hydration process given an increase of Si/Al and Si/Ca ratio identified in PE fiber reinforced 3D-printed geopolymer.

A comprehensive study on mechanical properties, durability, and environmental impact of fiber-reinforced concrete incorporating ground granulated blast furnace slag

Concrete pavements are integral to sustainable infrastructure, offering longevity and resilience in construction and transportation. This study focuses on optimizing concrete pavements through the incorporation of steel and carbon fibers with Ground Granulated Blast Furnace Slag (GGBS) to enhance mechanical strength, reduce fracture development, and minimize carbon emissions. Utilizing 25 mixing designs with a consistent water-to-cement ratio of 0.40, varying ratios of GGBS, steel fibers, and carbon fibers (0.5 %, 1 %, and 1.5 % based on concrete volume) were explored. A comprehensive evaluation, including slump, compressive strength, flexural strength, split tensile strength, water absorption, abrasion resistance tests, carbon dioxide emissions, and cost analysis, was conducted at different curing stages. Results revealed a decline in compressive strength for all mix designs at 28 days, attributed to reduced cement strength with GGBS substitution. The 1.5 % steel fiber and 50 % GGBS mix demonstrated minimal compressive strength reduction (30.1 MPa, 5.5 % less than control), outperforming other mixtures. Steel fibers surpassed carbon fibers, likely due to \\erior distribution. Notably, 1.5 % steel fibers showed superior results, particularly with 50 % GGBS. Compressive strength generally increased with GGBS content, except for 1 % fibrous samples where 40 % GGBS produced optimal results. At 90 days, compressive strength increased for most designs, with G50S1.5 exhibiting over 38 % growth compared to the control. Steel fiber-containing samples outperformed carbon fiber-containing ones, showcasing the efficacy of steel fibers in enhancing compressive strength. Split tensile strength generally decreased, but steel fibers improved it, emphasizing their positive influence. Flexural strength increased in 28 and 90 days, with steel fiber-containing designs outperforming. G30S1.5 showed the most significant increase (33.3 %) at 28 days, and G30S1.5 exhibited the highest growth (32.22 %) at 90 days. Abrasion resistance tests indicated steel fibers and GGBS positively impacted abrasion reduction. G50S1.5 demonstrated the highest abrasion resistance (25 % increase over control). The environmental evaluation revealed lower CO2 emissions for GGBS-containing designs. G50S0.5 showed a 40.34 % reduction compared to the control sample. Cost analysis showed GGBS reduced costs, but fiber addition, particularly carbon fibers, increased costs. G30C1.5 had the highest cost increase (208.5 %), while G50S1.5 showed a marginal rise (3.9 %) compared to the control. Therefore, steel fibers in concrete pavements offer improved mechanical properties, durability, and reduced environmental impact, making them a viable choice despite a slight increase in cost. Conversely, carbon fibers are cautioned against due to their higher cost and inferior mechanical properties.

Experimental study on performance, hydration, and sustainability of coal gasification coarse slag based geopolymers for sustainable environment

The large-scale application of coal gasification technology generates a large amount of coal gasification coarse slag (CGCS) difficult to treat. In this study, low-carbon geopolymers (CGRC) were produced using CGCS and ground granulated blast furnace slag (GGBS) as precursors, whereas red mud (RM) and carbide slag (CS) served as solid waste activators. The effects of the binder/activator, RM/CS and CGCS/GGBS ratios and the curing age on the compressive strength, setting time, heavy metal leaching, XRD, SEM-EDS, TG-DTG, FTIR, and LF NMR of CGCS-based geopolymers were investigated, and the hydration mechanism of CGRC geopolymer was disclosed. The results showed that the binder/activator ratio had a negligible effect on the ultimate compressive strength (UCS), the RM/CS ratio had a noticeable impact on the compressive strength and setting time, and increasing the GGBS content significantly improved the performance of CGCS-based geopolymers. Therefore, the synergistic effect of RM and CS led to the activation of CGCS and GGBS. The main hydration products were N-A-S-H, N/C-A-S-H, C-A-S-H gel, CH, and CaCO3. Furthermore, the decrease of the RM/CS ratio which promoted the gel transformation from metastable N-A-S-H to N/C-A-S-H configuration and then to stable C-A-S-H state, finally forming a denser gel matrix. The amounts of various heavy metals leached from CGCS-based geopolymers were even lower than those required by the national standards; therefore the material met the requirements for environmental protection. Furthermore, all raw materials belong to solid waste, which reduces carbon emissions.

Capillary water absorption and strength of solidified marine soft soil

In order to reveal the capillary water absorption properties and durability of soft soil solidified with industrial wastes, soda residue (SR), ground granulated blast furnace slag (GGBS), and carbide slag (CS) were used as solidifiers to solidify marine soil. The effects of solidifier content and water absorption path on capillary water absorption properties, strength, and microscopic mechanism were investigated through capillary water absorption, unconfined compressive strength (UCS), X-ray diffraction, and nuclear magnetic resonance tests. And the properties were compared with cement solidified soil. Results showed that capillary absorption parameters, including sorptivity coefficient, capillary coefficient, and diffusion coefficient, decreased with solidifier content and increased with water absorption times. The capillary absorption parameters of SR-GGBS-CS solidified soil were lower than those of cement solidified soil. For samples with 28d-UCS greater than 1390.9 kPa, the UCS after capillary absorption tended to increase up to 1.28 times. With increasing water absorption time, NaCl migrated upward and accumulated, accompanied by the change of hydrated products such as calcium chloroaluminate hydrate and ettringite, which contributed to a decrease in the strength of solidified soil. The carbon emission index of cement solidified soil was approximately 41 times that of SR-GGBS-CS solidified soil, and the soil with SR, GGBS, and CS content of 25%, 10%, and 4% respectively had the lowest carbon emission index.

Application of geopolymer in synchronous grouting for reusing of the shield muck in silty clay layer

This study employs geopolymer as a complete replacement for the cement to solidify the shield muck discharged from tunneling in the silty clay layer, thereby creating an innovative synchronous grouting material. This novel grouting material not only utilizes geopolymer as its primary cementitious component but also incorporates shield muck, promoting the efficient utilization of the shield muck. The cementitious process of the grout is initiated by the principles of geopolymerization. Through a series of laboratory tests assessing grout performance, the new grouting material was developed by further optimizing the grout proportion using the response surface method (RSM). This involves a comprehensive analysis of the impacts of various factors such as muck moisture content, foam injection ratio, ground granulated blast furnace slag (GGBS) content, and sand content, along with their interactions on the key response variables, including consistency, fluidity, 2 h bleeding rate, setting time, and 3 d unconfined compressive strength (UCS). The optimal proportion of the new grouting material is found to be 140% muck moisture, 100% GGBS, and 230% sand. Experimental results reveal that the GGBS content has the most significant effect on various properties of the grout, while the interaction between these factors has distinct effects on different grout properties. This novel synchronous grouting material was subsequently employed in the Nanjing Metro Line 6 project, and it was found that both surface settlement and segment uplift meet the specified requirements.

Concrete containing recycled concrete coarse aggregate and crushed glass sand: Mitigating the effect of alkali–silica reaction

AbstractThe utilization of recycled concrete and glass aggregates in concrete production has emerged as a highly promising method to significantly increase the recycling rate of waste materials. However, the interaction between alkaline environment and silica present in concrete detrimentally impacts mechanical properties and durability of the concrete due to the significant silica content of the aggregates. This study aims to develop a high‐performance and sustainable concrete to resist alkali–silica reaction (ASR). The study focuses on the use of a blend of ground granulated blast furnace slag (GGBS) and fly ash (FA) as binder materials to mitigate negative effects of the ASR on the mechanical properties and and durability of concrete made with crushed glass sand and coarse recycled concrete aggregate (RCA). Various tests, including ASR expansion, flow, slump, density, compression, three‐point bending, water absorption, and chloride attack, were conducted. Furthermore, microanalysis using scanning electron microscopy and energy‐dispersive x‐ray spectroscopy was performed. Based on the results, it is found that the GGBS is less effective than the FA in reducing the ASR expansion of the concrete, with only 3%, 9%, and 12% decreased expansion as a result of the addition of 20%, 40%, and 70% GGBS to the concrete containing 30% FA, respectively. It is also shown that combining 20% GGBS with 30% FA in the RCA concrete containing glass sand develops similar compressive and flexural strengths and water absorption compared to that containing natural sand. This can be related to the pozzolanic reaction of the FA and GGBS, which helps to retain the alkalis for reducing the crack development and propagation in the concrete. However, further GGBS content leads to a decrease in the strengths and an increase in the water absorption of the concrete. The results of this study point to the significant potential of combining FA and GGBS at an optimum ratio to mitigate the ASR effect on RCA concretes containing crushed glass sand. This approach helps in minimizing the emission of greenhouse gases and other pollutants generated during cement production, thereby mitigating environmental pollution. Additionally, it helps the preservation of natural resources by reducing the depletion of natural sand and coarse aggregate.

Compressive strength and chloride permeability of cement-based materials with high-volume compound mineral admixtures

Ground granulated blast-furnace slag (GGBFS) is well known to be capable of improving the performance of cement-based materials, but few studies focus on the impact of its large dosage on concrete containing basalt powder. In this study, the compressive strength and chloride permeability of cement-based materials with compound mineral admixtures (CMAs) containing high-volume GGBFS, basalt powder and desulfurisation gypsum were investigated. The results showed that the mortar strengths at 3, 7 and 28 days decreased with increasing GGBFS content, but that at 56 and 84 days increased with the addition of 45 wt% GGBFS. This is because the activity of GGBFS at an early stage has not been stimulated and the pozzolanic effect is exerted at a later stage. Moreover, cement replacement with up to 55 wt% GGBFS caused a significant decrease in the chloride diffusion coefficient of the mortar and concrete. Furthermore, the incorporation of GGBFS led to a remarkable refinement in pore structure of the hardened paste due to pozzolanic and filler effects. Therefore, the partial replacement of cement with high CMA contents (≥70 wt%) in concrete is desirable for ocean projects requiring low chloride permeability, and significantly reduces carbon dioxide emissions.

Boosting-based ensemble machine learning models for predicting unconfined compressive strength of geopolymer stabilized clayey soil

The present research employs new boosting-based ensemble machine learning models i.e., gradient boosting (GB) and adaptive boosting (AdaBoost) to predict the unconfined compressive strength (UCS) of geopolymer stabilized clayey soil. The GB and AdaBoost models were developed and validated using 270 clayey soil samples stabilized with geopolymer, with ground-granulated blast-furnace slag and fly ash as source materials and sodium hydroxide solution as alkali activator. The database was randomly divided into training (80%) and testing (20%) sets for model development and validation. Several performance metrics, including coefficient of determination (R2), mean absolute error (MAE), root mean square error (RMSE), and mean squared error (MSE), were utilized to assess the accuracy and reliability of the developed models. The statistical results of this research showed that the GB and AdaBoost are reliable models based on the obtained values of R2 (= 0.980, 0.975), MAE (= 0.585, 0.655), RMSE (= 0.969, 1.088), and MSE (= 0.940, 1.185) for the testing dataset, respectively compared to the widely used artificial neural network, random forest, extreme gradient boosting, multivariable regression, and multi-gen genetic programming based models. Furthermore, the sensitivity analysis result shows that ground-granulated blast-furnace slag content was the key parameter affecting the UCS.

Preparation of alkali-activated nickel slag-based cemented tailings backfill: Workability, strength characteristics, localized deformation and hydration mechanism

To solve the problems of high magnesium nickel slag (HMNS) and tailing stacks with large storage and environmental pollution, alkali-activated HMNS-based cementitious materials were prepared by using NaOH, phosphogypsum (PG), HMNS and ground granulated blast furnace slag (GGBFS), and cemented tailings backfill (CTB) was prepared using tailings as aggregates. The workability, strength characteristics, localized deformation and hydration mechanism of CTB were studied. Based on the digital speckle correlation method (DSCM), the localized deformation of CTB was analyzed. The hydration mechanism of CTB was analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetry-differential scanning calorimetry (TGDSC), mercury intrusion porosimetry (MIP) and scanning electron microscopy and energy dispersive spectroscopy (SEMEDS). The results showed that the optimal mix proportions for the cementitious material were 8%, 30%, 6%, and 0.38 for PG content, GGBFS content, alkali dosage, and water/binder ratio, respectively. The best performance of CTB was achieved when the bone glue ratio (BGR) and mass concentration (MC) were 5:1 and 79%, respectively; the slump, slump flow, and consistency of CTB decreased continuously with increasing BGR and MC; the layering degree, bleeding rate, and linear shrinkage of CTB continuously increased with increasing BGR, and decreased with increasing MC; the unconfined compressive strength of CTB increased with increasing maintenance age and MC and decreased with increasing BGR; when the BGR was small (3:1), CTB exhibited shear failure, and when the BGR was large (6:1), CTB exhibited tensile failure. The main hydration products of CTB were C-S-H gel, M-S-H gel, ettringite (AFt), Ca(OH)2 and CaCO3. In the early stage of curing, CTB has more pores, fewer hydration products and a relatively loose internal structure, flocculation, sheet, network and needle rod hydration products coated tailing particles, porosity decreased, and CTB became dense.

Enhancing the Compaction Characteristics of Peat Soil through Ground Granulated Blast Furnace Slag (GGBS) Stabilisation

Peat soil is renowned for its compressibility problem that can give rise to issues such as ground settlement, particularly within the spectrum of construction endeavours. Conversely, the implementation of chemical stabilisation, involving the incorporation of suitable additives, is contemplated prior to commencing construction activities. Ground Granulated Blast Furnace Slag (GGBS), which is a byproduct of the iron and steel industry, stands out as a prominent additive that can augment the engineering attributes of peat soil. This investigation focuses on the compaction characteristics of peat soil treated with varying proportions of GGBS, as evaluated through the Modified Proctor test. It involved examining the impact of diverse GGBS additions on the liquid limit of peat soil. The findings showed that the introduction of GGBS yielded a substantial reduction in the liquid limit of peat soil, signifying an elevated susceptibility to moisture and an increase in plasticity. Moreover, the incorporation of GGBS into peat soil prompted an increase in its Maximum Dry Density (MDD) and a reduction in its Optimum Moisture Content (OMC). Notably, the peak MDD, registering at 1000 kg/m³, was achieved at a GGBS content of 50%, marking the highest value observed in this study. The OMC values further indicated the lowest moisture content, standing at 29%, with the addition of 25% GGBS to the peat soil. These outcomes convincingly advocate that the utilisation of GGBS in treating peat soil engenders positive enhancement in its compaction characteristics, specifically pertaining to MDD and OMC. Such enhancement in engineering properties holds promising implications for potential stability.

Interaction of various parameters on the properties of semi-dry gypsum-based blocks produced by compression forming method

The utilization of hemihydrate gypsum to produce blocks can be a more sustainable alternative to conventional cement concrete blocks. This study explores the fabrication of semi-dry gypsum-based blocks using the compression forming method to address the drawbacks associated with traditional blocks (clay block and cement concrete block) manufacturing processes, including high energy consumption and lengthy production time. However, the low mechanical strength, low water resistance, and high water absorption of gypsum-based blocks limit their application in construction. Therefore, in this study, semi-dry gypsum-based blocks were prepared using the compression forming method by investigating the interactions between the ground granulated blast-furnace slag (GGBS) content (0%, 20%, 45%), water-to-binder (w/b) ratio (0.20, 0.25, 0.30), and compaction pressure (CP) (10 MPa and 20 MPa). The compressive strength, water resistance, mineralogical composition, and microstructure of the produced gypsum-based blocks were investigated and compared with gypsum-based blocks without GGBS. It was found that adding GGBS can lead to formation of AFt and C-S-H gel when the water content reaches the required level for the reaction. These hydration products are beneficial to improve the compressive strength and water resistance. In addition, the porosity of the specimens was examined using water immersion and the mercury intrusion porosimetry (MIP) method. It was observed that when the w/b ratio is 0.25 or 0.30, a lower CP (10 MPa) should be applied. This is because higher CP (20 MPa) caused paste overflow during the forming process, resulting in undesirable pores having an adverse impact on the compressive strength. The optimal performance was obtained with GGBS content, w/b ratio, and CP at 20%, 0.25, and 10 MPa, respectively. In summary, the compression forming method could produce semi-dry gypsum-based blocks with adequate compressive strength (35.3 MPa) and water resistance (softening coefficient of 0.68).

Strength and durability study on alccofine based geo-polymer concrete

Geopolymer concrete (GPC) emerging as the most innovative construction material, which not only reduces the requirement of Ordinary Portland cement (OPC) but also enhances the properties of the concrete as well, and decreases the ejection of harmful gases into the atmosphere like Carbon dioxide (CO2), Nitrogen, and Sulphur, Which is a prime concern for the environment. The need for concrete is raising uncharacteristically and so does for the OPC, to minimize the demand for OPC cementitious materials like Fly ash, Ground Granulated Blast Furnace Slag (GGBS), Silica Fume, Alccofine, Metakaolin, namely mineral admixtures used as partial or full replacements to the OPC. This present paper reports the properties of GPC made with Flyash, GGBS, and Alccofine for Mix M40- grade concrete the outcomes were contrasted with Nominal concrete which is made using 100 percent cement, Fly ash content of 50% was kept constant throughout the investigation whereas GGBS and Alccofine content varied with an interval of 5%. The concrete was tested for workability, strength, and durability aspects, an increment in the slump, and in the strength was noted, and great resistance was observed under the acid attack test for a GPC mixes, a combination of 50% Fly ash, 35% GGBS, and 15% Alccofine GPC mix was shown optimum results.

Preparation and strength formation mechanism of alkali-stimulated spontaneous combustion gangue-granulated blast furnace slag backfill.

Spontaneous combustion gangue (SCG) is often used as aggregate in traditional cemented paste backfill (CPB) for mine backfill, but the activation of SCG is insufficient. To stimulate the activity of SCG for the preparation of spontaneous combustion gangue-granulated blast furnace slag backfill (SGB), a new CPB was prepared by activating SCG via a mechanochemical composite activation method and adding ground granulated blast furnace slag (GGBS) to improve its activity. The mixing ratio was optimized by the response surface method and satisfaction function, and the strength formation mechanism was analyzed by scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) and Fourier transform infrared spectroscopy (FTIR). The results showed that SCG had a certain pozzolanic activity, and the optimal grinding time was 30 min. The optimal mix ratio was 82.58% mass concentration, 2.93% alkali content, 30% GGBS content, and 52.92% fine gangue rate. Calcium silicate hydrate (C-S-H) gel and calcium aluminate sulfate hydrate (C-A-S-H) gel were the main reaction products of backfill, and with increasing curing age, C-S-H gel in the reaction system was gradually converted into C-A-S-H gel. FTIR analysis results showed that there were H-O-H, Si-O, and Si-O-T (T was Si or Al) bonds in the product, indicating that C-S-H gel and C-A-S-H gel were formed in the product. A new damage constitutive model was developed. The damage constitutive model could completely describe the backfill stress-strain curve. The study verified the feasibility of preparing cemented paste backfill with SCG and GGBS, which was beneficial to clean coal mine production and environmental protection.

Influence of ground granulated blast furnace slag on the dispersivity and mechanical property of dispersive soil

This paper focused on the influence of ground granulated blast furnace slag (GGBFS) on the dispersivity and mechanical properties of dispersive soil. Different contents of GGBFS, varying from 1% to 10%, were mixed in dispersive soil and curried for 28 days. Eroded soil weight and flow speed during pinhole test under different water heads were recorded. Dispersivity of soil samples was determined by pinhole test and two kinds of crumb test. Unconfined compression test and splitting test were conducted to determine the compressive and tensile strength of soil samples. Electronic conductivity and pH were also measured during curing time for all soil samples. Microstructural and mineral analyses of soil samples were performed by SEM (with EDS), XRD, and TG/DTG tests. A natural dispersive soil sample was selected to validate the improving effectiveness of GGBFS on the dispersivity and mechanical property of dispersive soil. Experiments show that water stability, compressive strength and tensile strength of dispersive soil are significantly improved with the increase in the mixed content of GGBFS in soil. Results indicate that GGBFS is capable of improving both the dispersivity and mechanical properties of dispersive soil, and this effect is more obvious with the increase in curing time. Appropriate curing time is encouraged during the construction process to intensify the improving effect of GGBFS. Enhancing of water stability of dispersivity soil by GGBFS would ensure the safety and normal operation of soil constructions in geotechnical, agricultural, and hydraulic engineering, which could be a win-win application in the future. The use of GGBFS can effectively reduce the environmental problems caused by the use of traditional high carbon emission materials such as cement and lime.

Microstructural and mechanical properties of a high-strength geopolymer based on coal-based synthetic natural gas slag cured at ambient temperature

In this study, an effort was made to enhance the mechanical properties of coal-based synthetic natural gas slag (CSNGS) geopolymer with curing at ambient temperature by incorporating ground granulated blast furnace slag (GBFS). The effects of GBFS content, activator modulus and alkali content on the compressive strength of CSNGS-GBFS (CG) geopolymers were analyzed, and the microstructural characteristics and the compositional evolution of reaction products were also investigated by X-ray diffraction (XRD), scanning electron microscope-energy dispersive spectrometer (SEM/EDS), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analyzer (TG) tests. It was found that the mechanical properties of CG geopolymers was highly dependent on the of GBFS content. When the GBFS content was 50%, the 1-day and 28-day strengths of the geopolymer were 50.8 MPa and 120.2 MPa, respectively. Increasing alkali content resulted in the strength of geopolymer to increase and then decrease, whereas, the strength of geopolymer increased monotonically with a decrease in activator modulus. The results also showed that with increasing the GBFS contents, the characteristic peaks corresponding to the gels in the XRD patterns became gradually obvious with highly denser microstructures formed by a number of gels in the SEM micrographs, and the Ca/Si ratio and Ca/(Si + Al) ratio of the reaction products were increased, revealing that the gels generated in CG geopolymers was a mixture of N-A-S-H and C-(A)-S-H gels, which corroborated with the observed the stretching vibration of Si–O-T (T = Si or Al) in FT-IR spectrum shifted from 1013 cm−1 to 990 cm−1 and the corresponding temperatures of the mass loss peaks increased form 104 °C–114 °C. In addition, the dissolution of raw materials was promoted owing to the reduction of the activator modulus, but the change of activator modulus had little effect on the thermal stability of the gels. These findings suggest that CSNGS has the potential to prepare high-strength geopolymers at ambient temperature, providing an attractive avenue for reducing the environmental impact of CSNGS and conserving natural resources.

Evaluation of Self-Healing Properties of OPC-Slag Cement Immersed in Seawater Using UPV Measurements

In this study, OPC-slag cement, which partially replaced ground granulated blast-furnace slag (GGBFS), was immersed in seawater at three temperatures and the self-healing effect was evaluated through ultrasonic pulse velocity (UPV) measurement. In addition, test specimens without cracks were immersed and cured in the same seawater environment to compare the characteristics of UPV and crack-healing effects. The results of the study showed that increasing the GGBFS content or immersion temperature improved the healing effect up to 30 days after immersion, but there was no significant effect after 30 days of immersion. In a saltwater environment, a thick layer of brucite was deposited near the crack, blocking the inflow of seawater and impeding the formation of additional healing material. According to visual observation, the crack entrance appears to have been covered and healed by the brucite layer. However, the brucite layer in the crack area increases the UPV in the early stages of immersion, which may lead to a misconception that it is self-healed, and there is a possibility of overestimating the self-healing effect.