Alkali-activated Ground Granulated Blast-furnace Slag Research Articles

Effect of activator concentration on setting time, workability and compressive strength of sustainable concrete with alkali-activated slag binder

The global need to reduce carbon dioxide (CO2) emissions prompted studies on sustainable alternatives to conventional concrete made with ordinary Portland cement (OPC) binders. Alkali-activated ground granulated blast furnace slag (GGBS) is a promising sustainable to OPC in terms of the impact on the environment and reduction of CO2 emissions. Concretes and mortars made with alkali-activated binders demonstrate promising fresh and mechanical properties. This article presents the findings of an experimental study investigating the fresh and mechanical properties of mortar using alkali-activated GGBS binder. The activators used were sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) solution with 6 M, 8 M, 10 M, and 12 M molarities. The study assessed their initial setting time, workability, and 28-day compressive strength. The study evaluated the effect of partial replacement of GGBS with 5 % silica fume. The compressive strength was determined after 28 days of curing in three different environments: 1) ambient air temperature, 2) water submersion, and 3) water immersion for 7 days followed by 21 air curing in ambient temperature. The results showed an increase in compressive strength with higher NaOH concentration but a corresponding decrease in initial setting time and flowability. Depending on the curing method, efflorescence, and blue-green pigmentation were seen during the physical assessment of the samples. The highest 28-day compressive strength was 67.5 MPa when the NaOH activator molarity was 10 mol/L which represents an optimum concentration for strength development. Replacing 5 % of the GGBS binder with silica fume resulted in a decrease in the 28-day compressive strength and workability without affecting the initial setting time.

Investigation on the properties of sustainable alkali-activated GGBS mortar with nano silica and dredged marine sand: Mechanical, microstructural and durability aspects

In recent years, alkali-activated mortar (AAM) has emerged as a promising alternative to ordinary Portland cement (OPC) due to concerns regarding the environmental impact resulting from cement production, which releases carbon dioxide and degrades the quality of the environment. To address these concerns, researchers have explored the addition of supplementary binder materials to enhance cement properties and mitigate pollution. The effectiveness of these binder materials depends heavily on their chemical composition and fineness. Notably, ground granulated blast furnace slag (GGBS) enhances the strength and durability of the cement. In response to the scarcity of river sand (RS), dredged marine sand (DMS) has gained popularity as a potential substitute within the civil engineering field. Furthermore, the integration of nanomaterials has shown promising improvements in the mechanical and microstructural properties of mortar. Therefore, this study aims to investigate the properties of mortar by incorporating nano silica (NS) within the range of 1% to 7%, varying the molarity from 2 M to 8 M, and substituting RS with DMS. The tests carried out encompass a range of evaluations, including compressive strength, flexural strength, SEM-EDS, XRD, UPV, RCPT, and carbonation analysis, to comprehensively assess the properties of the mortar. The study reveals that the AAM demonstrates optimal performance when 50% of RS is replaced by DMS in the absence of NS. Once this optimal point is determined, further analyses are conducted at this value while varying the concentrations of NS from 1–7%. The experimental results indicate that replacing 50% of RS with DMS and incorporating 6% NS leads to maximum compressive strength (49.2 MPa) and flexural strength (9.36 MPa) in the assessed properties. Furthermore, the incorporation of NS in GGBS-based AAM mixes enhances durability by improving resistance against chloride penetration, reducing water absorption, and minimizing carbonation diffusion. Additionally, the microstructural and mineralogical characterization of GGBS-NS-based AAM specimens demonstrates the formation of C-S-H and C-A-S-H gels as the end products of the reactions.

Laboratory Study and Modeling of the Strength Evolution of Dredged Soil Stabilization Using Alkali-Activated Ground Granulated Blast-Furnace Slag

Laboratory Study and Modeling of the Strength Evolution of Dredged Soil Stabilization Using Alkali-Activated Ground Granulated Blast-Furnace Slag

Stabilization of iron ore tailing with low-carbon lime/carbide slag-activated ground granulated blast-furnace slag and coal fly ash

The massive accumulation of iron ore tailing (IOT) results in land resource wastage and increases the possibility of environmental pollution. In this study, the feasibility of using low-carbon alkali-activated ground granulated blast-furnace slag (lime/Carbide slag (CS)-GGBS) and coal fly ash (CFA) instead of portland cement (PC) for solidifying IOT was investigated. The effects of different binders on strength development and durability of cured IOT were analyzed through unconfined compressive strength (UCS), water stability, and dry-wet cycles tests. Furthermore, the microstructure characteristics of cured IOT were conducted by using scanning electron microscope (SEM) method, X-ray diffraction (XRD) analysis, and thermogravimetric analysis (TGA). The results showed that, using the low-carbon material lime/CS-GGBS to replace about 70% of PC (i.e., PC:lime/CS:GGBS=1:1:1) with 9% binder content, the strength and durability of cured IOT were significantly improved compared with using pure PC. The 28d-UCS of cured IOT was 4.86 MPa, which was twice higher than that with pure PC. The 7d-UCS of cured IOT was 8.22 MPa after 12 dry-wet cycles, which was 2.8 times higher than that with pure PC. Moreover, the water stability coefficient of 27 + 1d-cured IOT was 90%. The micro-analysis showed that, the amount of hydration products (i.e., CSH, CAH and ettringite) in IOT cured with low-carbon materials increased significantly, and the structure became denser, resulting in the increase of strength. This study develops a low-carbon binder instead of pure PC to solidify IOT, and the results can provide a theoretical basis and scientific guidance for the comprehensive utilization of IOT as a filler solid waste.

Characterisation of calcined waste clays from kaolinite extraction in alkali-activated GGBFS blends

Metakaolin is a well-studied supplementary cementitious material (SCM) and precursor in alkali-activation. The utilisation of limited kaolinite content clays generated from large-scale industrial activity, denoted as waste clays, in alkali-activation is still largely unexplored. This paper investigates the use of five samples of calcined waste clays from different locations in a kaolinite extraction site as precursors in alkali-activated cements (AACs). Calcined waste clay precursors are blended with ground granulated blast furnace slag (GGBFS) and activated with sodium silicate. The physical and chemical properties of the calcined waste clays are characterised. Both Chapelle and R3 tests for pozzolanic reactivity are examined based on calcined waste clay properties. The R3 test data obtained for sieved particle fractions < 63 µm show marked improvement in the case of C4, elucidating potential calcined waste clay behaviour with prior processing in alkali activated systems. Clay particle size distribution and morphology are identified as key factors to be considered for initial calcination and in mix designs, strongly affecting both the fresh properties and workability of blended pastes. Good workability is highlighted as being crucial for achieving well-behaving calcined waste clay blended binders with resulting dense microstructures and high strength values, comparable with other reported GGBFS systems. Quartz, muscovite, and alkali-feldspar present in the calcined waste clays remain stable throughout alkali-activation. Reaction of the amorphous phase fraction present in the calcined waste clays results in the formation of additional cross-linked gel. A replacement level of up to 20 wt% calcined waste clay is found to exhibit similar compressive strengths to pure GGBFS binders, whilst achieving lower porosity within the bulk. This study provides a methodology for characterising the behaviour of calcined waste clays in alkali-activated systems and a proof of concept in the formulation of novel binders that incorporate waste clays.

Alkali-silica reaction of high-magnesium nickel slag fine aggregate in alkali-activated ground granulated blast-furnace slag mortar

The construction industry is presently encountering a significant challenge regarding the shortage supply of natural sands. The use of metallurgical slags as fine aggregates in building materials presents a solution that not only mitigates the over-exploitation of natural sands, but also provides a sustainable and valuable approach for managing industrial solid wastes instead of traditional landfill disposal. This study investigated the alkali-silica reaction (ASR) of air-cooled and water-quenched high-magnesium nickel slag (HMNS) fine aggregates in alkali-activated ground granulated blast-furnace slag (AAS) mortars. The mortars exhibited satisfactory volume stability and structural integrity throughout the 120 days of accelerated mortar bar test. The lab-simulated dissolution test revealed the formation of a thin precipitate layer of sodium silicate hydrate on the surface of HMNS fine aggregates, which contained a significant amount of Mg with Mg/Si ratios ranging from 0.16 to 0.18. The divalent Mg cations were released from the HMNS fine aggregates and served as the pseudo network former to crosslink the ASR gel instead of Ca. This reduced the moisture adsorption capacity and mitigated the expansion of ASR gel.

Geoenvironmental properties of a Cr(VI)-contaminated soil treated by alkali-activated GGBS under freeze-thaw cycles: Insights into Cr species transformation and microscopic mechanism

Stabilization/solidification is the most frequently used method for treating soils contaminated by heavy metals; however, degradation of the treatment will occur under freeze-thaw (F-T) cycles. In this paper, a low-carbon emission by-product, ground granulated blast furnace slag (GGBS), was adopted as a binder to treat Cr(VI)-contaminated soil after alkali excitation. Built on the usage scenarios of subgrade materials, the impact of F-T cycles and initial water content on the geoenvironmental properties of the treated soils, including leaching toxicity, unconfined compressive strength (UCS), pH, Eh, and permeability, were discussed. To investigate the mechanisms of the changing properties, this study analyzed the chemical morphology of Cr, the micromorphology of the reaction products, and the pore characteristics. The results demonstrated that negative impact of F-T cycles on treatment effectiveness was low at the optimal water content. After 28 F-T cycles, the Cr(VI) component increased by 6.4 %, and the leached Cr concentration showed a significant increase, especially for specimens with low water content. A new solid phase with mixed valence Mn(III/IV), mainly composed of birnessite and manganite, was observed via microscopic analysis. During the first 3 F-T cycles, the content of hydration gel increased by 0.18 %, and the cumulative pore volume decreased such that the UCS increased by an average of 1.2 MPa. This study demonstrated that a few F-T cycles would result in a secondary alkali-activated GGBS reaction, enhancing the treatment effect. However, additional F-T cycles would create an oxidizing environment under which the initially precipitated Cr(III) would react with manganese oxide, resulting in more Cr(VI) released. The degree of reoxidation was closely related to the initial water content of the solidified soil.

Experimental study on solidification/stabilisation of high-salt sludge by alkali-activated GGBS and MSWI bottom ash cementitious materials

This study utilises alkali-activated ground granulated blast furnace slag (GGBS) as the primary method for solidification/stabilisation, with municipal solid waste incineration (MSWI) bottom ash (BA) as an auxiliary precursor to assist in the solidification/stabilisation (S/S) of high-salt sludge. The results show that the alkali-activated GGBS and MSWI BA cementitious material can effectively realize the S/S of high-salt sludge. However, having early strength of the alkali-activated GGBS solidified sludge at low GGBS content is difficult. In comparison, the addition of MSWI BA enhances the unconfined compressive strength (UCS) of the alkali-activated GGBS solidified sludge to reach 6.35 MPa at 3d curing age, whereas the UCS of the alkali-activated GGBS solidified sludge with 20% GGBS achieves only 0.31 MPa at 14d curing age. The MSWI BA significantly improves the effect of S/S on high-salt sludge by alkali-activated GGBS, and the solidified high-salt sludge with 20% alkali-activated GGBS and MSWI BA cementitious material exhibits good water stability, the UCS of which retain 2.33 MPa after 28d water immersion. The analysis of the mineral composition, chemical bond transformation, thermal stability and microstructure of the solidified sludge samples indicates that the geopolymer cementitious material generated by alkali-activated GGBS and MSWI BA can effectively cement and wrap sludge particles and soluble salts, and reduce the strength loss of the solidified samples after water immersion. Moreover, the addition of MSWI BA accelerates the polymerization of alkali-activated GGBS, leading to rapid solidification/stabilisation of high-salt sludge in early curing age and reduction of the consumption of mineral resources. The heavy metal leaching concentration of the solidified sludge is much lower than that of the raw MSWI BA, and can satisfy the pollution control standard limit of landfill. The immobilization efficiency of the heavy metals of the solidified sludge is larger than 89%. By using MSWI BA as an auxiliary precursor in alkali-activated GGBS, the co-disposal of high-salt sludge and MSWI BA can be achieved, providing insights for realizing the energy conservation and environment protection purposes of solid waste reclamation and GGBS consumption reduction.

Enhancement in compressive strength of carbide slag activated ground granulated blast furnace slag by introducing CaCl2 and NaCl

Alkali-activated materials was the green and low carbon cementitious materials. In this study, the calcium chloride (CC) and sodium chloride (SC) were used as accelerator to promote the compressive strength of carbide slag (CS) activated ground granulated blast-furnace slag (GGBFS). The compressive strength of samples was investigated and the related mechanism was comprehensively characterized with hydration heat, XRD, TG-DTG, SEM, 29Si NMR and MIP in details. These results showed that 5% SC and CC significantly improved early strength with an increase of 58.8% and 127.1% at 3 days, respectively. Interestingly, the presence of CC also increased the 28-day and 90-day strength from 16.6 MPa and 30.4 MPa to 50.2 MPa and 70.5 MPa, respectively. These results citified that the addition of CC and SC accelerated the consumption of CS at early age. At late age, the enhancing effect of SC was lower than CC, reflecting the Ca2+ made a greater contribution to strength development than Na+. The addition of CC still accelerated the rapidly precipitation of aluminium phase in the form of hydrocalumite, which could improve further dissolution and hydration of GGBFS at late age. Therefore, the addition of CC produced more hydration products that would refine microstructure and enhance strength at late age. These findings suggested a novel way to improve the mechanical properties of alkali-activated GGBFS.

Novel selection of environment-friendly curing agents for thawing permafrost: Alkali-activated ground granulated blast-furnace slag

Permafrost thawing deformation due to the climate warming has been continuously increasing in the Qinghai-Tibet Plateau, which may influence the stability of local infrastructures and cause frequent subgrade diseases. Although the effectiveness of cement has been certified to solidify thawed permafrost, the usage of cement is gradually limited due to its energy consumption and CO2 emissions. The alkali-activated ground granulated blast-furnace slag (GGBS), as waste by-products, has been widely used in the application of soil stabilization under normal temperature, but there exist few investigations on its application in cold regions, such as permafrost regions. The study aims to investigate the effectiveness of calcium carbide residue (CCR)-GGBS and NaOH-GGBS as curing agents to solidify thawing permafrost cured at low temperature. Simultaneously, the conventional Portland cement (PC) is also selected as the comparison. Laboratory tests, containing the unconfined compressive strength (UCS), pH, electron microscopy (SEM)/ energy dispersive X-ray spectroscope (EDS), X-ray diffraction (XRD), and mercury intrusion porosimetry (MIP) tests, were carried out to investigate the effect of different influence factors including alkali activator types, activator content, and curing time on the strength development. The experiment results showed that alkali-activated GGBS with the optimum activator content can effectively improve the strength of thawing permafrost at low temperature. Furthermore, on the basis of strength difference (ΔUCS) and strength growth rate (UCSgr), it demonstrates that the best approach to development strength is to combine 30% GGBS with 20% CCR or NaOH. The microstructure analysis showed that alkali-activated GGBS is conducive to the polymerization reaction, and the strength development is attributed to the formation of the dense skeleton structure. Finally, the efficacy of alkali-activated GGBS as an alternative and green curing agent to solidify thawing permafrost was confirmed based on the stabilization mechanism and analysis of environmental benefit.

Co-valorization of sediments incorporating high and low organic matter with alkali-activated GGBS and hydraulic binder for use in road construction

This study investigates the valorization of dredged sediments containing high and low organic matter (OM) content with alkali-activated ground granulated blast furnace slag (GGBS) and conventional hydraulic binders (HB). The objective is to develop a sustainable material with the necessary qualities for road construction. Research is conducted on dredged sediments from the French port of Cherbourg (CHER-ALL sediments) and the dam in the Maurienne Valley of France (MOR-ALL sediments), with high and low levels of OM content, respectively. After the determination of physico-chemical and mineralogical characteristics, high organic CHER-ALL sediments were first valorized using conventional HB and then co-valorized using low carbon footprint alkaline activated byproducts (AAB). The alkali activation of the byproduct (GGBS) was performed with a chemical activator named NeoliX. AAB and HB were utilized to treat the dredged sediments to compare their mechanical performances as well as environmental impacts. In terms of mechanical performance, the obtained results revealed that AAB outperformed traditional HB, and concerning the environmental impacts, byproducts have no carbon footprint except for their transportation. As a consequence, AAB has also been utilized to co-valorize the sediments from the Maurienne dam (MOR-ALL sediments) as well. AAB co-valorization of these two sediments (CHER-ALL and MOR-ALL) with varying degrees of OM content facilitates an understanding of the effects of OM concentration on mechanical properties. The high OM content of the CHER-ALL sediment (>17%), regardless of the proposed mixing with traditional HB, proved to impede the valorization, since the 28-day UCS did not exceed 1 MPa. The CBR as well as ultimate tensile strength (UTS) testing confirms the reported trends from the UCS experiments. In addition, the presence of a high OM concentration significantly decreased the mechanical properties of dredging sediments co-valorized with AAB. However, depending on the mass percentage of sediment (wt%) in the mix design, it was achievable to attain the required minimum strength value of 1 MPa with 30% and 70% of CHER-ALL and MOR-ALL sediments, respectively. Even if the OM content of sediments is high, alkaline activation can be employed to co-valorize them, as demonstrated by these encouraging results. The quantity of sediment to be co-valorized is depend upon their OM content.

Quantitative analysis of reaction degrees and factors influencing alkali-activated metakaolin-GGBFS blend

The mechanical properties and durability of an alkali-activated metakaolin (MK)- ground granulated blast furnace slag (GGBFS) blend depend on its reaction degree during the alkali activation process. In the present study, the dissolution ratios of MK and GGBFS and their reaction products in hydrochloric acid with different pH values were investigated. The hydrochloric-acid-insoluble matter of MK and its geopolymers were analysed using an X-ray fluorescence spectrometer, X-ray diffractometry, and Fourier transform infrared spectroscopy. It was found that the MK was mostly insoluble and that the MK-based geopolymer was dissolved completely in the hydrochloric acid solution at a pH of 0, and the GGBFS and alkali-activated GGBFS were completely dissolved in the hydrochloric acid solution at a pH of 0–2. Based on the solubility of the raw materials and the alkali activated products, a quantitative analysis approach for the geopolymerisation degree of MK and an MK-slag blend was developed, and the degrees of reaction of the MK and MK-slag blend under alkali activation conditions were studied. It was found that the degree of geopolymerisation reaction of pure MK increases with the increase in the liquid–solid ratio and decreases with the increase in the activator modulus (molar ratio of SiO2 to Na2O) with an activator concentration of 35%. The addition of GGBFS enhanced the degree of reaction of the MK in the MK-GGBFS blend in most cases, particularly under conditions of a low liquid–solid ratio, a high activator modulus, and a low activator concentration. The degree of reaction of the MK in the blend usually first increases and then decreases with the increase in the GGBFS content, and the 40% and 60% GGBFS contents often correspond to the highest degree of geopolymerisation reaction of the MK. However, the degree of the reaction of the MK will continue increasing with the increase in the GGBFS content when activated by an activator with a low concentration.

Strength development and microstructure of sustainable geopolymers made from alkali-activated ground granulated blast-furnace slag, calcium carbide residue, and red mud

Red mud (RM) and calcium carbide residue (CCR) are waste generated from alumina refining and acetylene gas producing, respectively. This study utilized alkali-activated ground granulated blast-furnace slag (GGBS) and wet-basis CCR stabilized RM to prepare geopolymers material. The alkali activator solution was composed of CCR supernatant, sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). CCR supernatant was used to reduce the amount of strong alkali. The effects of alkali activator on chemical composition and microstructure of geopolymers were studied by X-ray diffraction (XRD), thermogravimetric-derivative thermogravimetric (TG-DTG) analysis, and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). The results show that the utilization of alkali activator improved the compressive strength and especially significantly improved the flexural strength of geopolymers. The strength was negatively correlated with the RM content: the geopolymers containing 30 % RM achieved a maximum 28-day compressive and flexural strength value of 20.3 MPa and 4.3 MPa, respectively. The microstructural analysis revealed that the strength increased due to the formation of calcium aluminate hydrates (C-A-H) and calcium silicate hydrates (CSH). The toxic heavy metals (Cr, Ni, Cu, Pb, Sb, and Zn) from RM formed some complex compounds and were combined in the geopolymers. The 28-day leaching experiment showed that the toxic heavy metals levels were below the test limits. In summary, this study confirmed the safety and feasibility of preparing RM-GGBS-CCR based geopolymers via alkali-activated method.

Advantages and disadvantages of PVA-fibre-reinforced slag- and fly ash-blended geopolymer composites: Engineering properties and microstructure

• Engineering properties and microstructure of the composites are investigated. • The positive and negative roles of PVA fibres in the composites are revealed. • This study promotes the recycling of industrial wastes (GGBFS and FA). • This study serves as an important reference for engineers and designers. Alkali-activated ground-granulated blast-furnace slag (GGBFS) and fly ash (FA) geopolymers are sustainable alternatives to cement. The incorporation of polyvinyl alcohol (PVA) fibres can help minimise their shortcomings, such as drying shrinkage and brittleness, but may lead to other negative effects. Only a few studies have focused on geopolymer composites based on PVA-fibre-reinforced binary phases (GGBFS and FA). The positive and negative roles of PVA fibres in the performance of composites have not been systemically investigated in previous studies. To promote the application of the composites, the mechanical properties, workability, durability, high-temperature resistance, fibre dispersion, phases, and microstructure of composites with 0, 0.3 and 0.6 vol% of PVA fibres were systematically investigated in this study. The results showed that the incorporation of PVA fibres significantly increased the flexural and splitting tensile strengths of the GGBFS- and FA-blended and single FA-based composites at ambient and high temperatures, and the drying shrinkage was significantly reduced. On the other hand, PVA fibre incorporation caused a decrease in the compressive strength, flowability, consistency, sorptivity, and chloride penetration of the composites; however, the values are still acceptable in construction. Compared to the single FA-based composites, the GGBFS- and FA-blended composites showed improved mechanical properties, sorptivity, chloride resistance, and high-temperature resistance owing to their decreased porosity. This study serves as an important reference for engineers and designers for the use of green composites.

Valorization of a Highly Organic Sediment: From Conventional Binders to a Geopolymer Approach

The objective of this research is to investigate the possible reuse of dredged sediments from the port of Cherbourg, France, as an alternative material in road engineering and as a backfill material. These dredged sediments contain high percentages of organic matter (OM), and the presence of OM in the sediment, even in small amounts, can affect the engineering properties of sediments. This research was carried out in two series: the sediment was treated with traditional hydraulic binders (ordinary Portland cement (OPC), calcium sulfo-aluminate (CSA) cement, quarry sand (QS), lime, and a combination of them) in the first series, and with pozzolanic binders in the second series (ground-granulated blast-furnace slag (GGBS) and fly ash (FA)), along with the introduction of an activator. According to French legislation, these two pozzolanic binders (GGBS and FA) have no carbon footprint as they are industrial by-products, and therefore, the second series of this research is considered to be highly eco-friendly and economical. Sediment treated with hydraulic binders yielded a maximum value of unconfined compressive strength (UCS) of 1 MPa at 28 days. Out of eight formulations made using traditional binders, only one formulation barely met the French criteria to be used in the sub-base layer of roads. The development of geopolymer using alkali-activated GGBS and then the incorporation of 30% sediments yielded a UCS value above 2 MPa at 28, 60, 90, and 180 days. Furthermore, the addition of 5% lime and 3% granular calcium carbonate in the same mixture (geopolymer + 30% sediments) increased the UCS by up to 60% and 90%, respectively.

Novel Selection of Environment-Friendly Curing Agents for Thawed Permafrost: Alkali-Activated Ground Granulated Blast-Furnace Slag

Novel Selection of Environment-Friendly Curing Agents for Thawed Permafrost: Alkali-Activated Ground Granulated Blast-Furnace Slag

Continuous Monitoring of the Early-Age Properties of Activated GGBFS with Alkaline Solutions of Different Concentrations

AbstractThis study monitors the early-age reaction kinetics and measures the heat of reaction of alkali-activated ground granulated blast-furnace slag (GGBFS) using an isothermal calorimeter, and t...

Effect of GGBFS on Workability and Strength of Alkali-activated Geopolymer Concrete

This paper focuses on the development of a concrete material by utilizing fly ash and blast furnace slag in conjunction with coarse and fine aggregates with an aim to reduce pollution and eliminate the use of energy extensive binding material like cement. Alternative binding materials have been tried with an aim to get rather an improved concrete material. Alkali-Activated Solution (AAS) made of the hydroxide and silicate solutions of sodium was adopted as the liquid binder whereas, Class F” fly ash and Ground Granulated Blast Furnace Slag (GGBFS) mixed in dry state were used as the Geopolymer Solid Binder (GSB). The liquid binder was used to synthesize the solid binder by thermal curing. The paper investigates the use, influence and relative quantities of the liquid and solid binders in the development of the alkali-activated GGBFS based Geopolymer Concrete (GPC). Varying ratios of AAS to GSB were taken to assess their optimum content. Further, different percentages of GGBFS were used as a partial replacement of Class F fly ash to determine the optimum replacement of GGBFS in the GPC. In order to assess their effects on various properties test samples of cubes, cylinders and beams were cast and tested at 3, 7, and 28 days. Thermal curing of GPC has also resorted for favorable results. It was found that AAS to GSB ratio of 0.5 and GGBFS content of 80% yielded the maximum strength with a little unfavorable effect on workability. The overall results indicated that AAS and GGBFS offer good geopolymer concrete which will find its applicability in water scarce areas. Doi: 10.28991/cej-2021-03091708 Full Text: PDF

Effect of sediment incorporation on the reactivity of alkali-activated GGBFS systems

During the last few years, the valorization of marine sediment has been marked by the incorporation of this material in cementitious matrices. Some studies have depicted, more particularly, the use of the sediment in alkaline activation of Ground Granulated Blast Furnace Slag (GGBFS) for Civil Engineering applications. The objective of this work is to understand the effect of clear sediment incorporation on the reactivity of GGBFS alkali-activation. Two alkaline activators are used, a sodium hydroxide solution (NaOH) and a mixture of sodium hydroxide and sodium silicate solution (NaOH + silicate). The influence of sediment incorporation on the reactivity of Alkali-Activated GGBFS (AAS) is determined through X-ray Diffraction XRD, thermogravimetry TG and Solid State Nuclear Magnetic Resonance (NMR) analyses. Results show that the presence of sediment does not modify the structure of the hydration products formed, neither the proportion of Aluminum atoms incorporated into hydrate chains. The substitution of slag by sediment causes a delay in the initiation of alkaline activation particularly in the short term, but this effect diminishes at 28 days.

Strength evolutions of varying water content-dredged sludge stabilized with alkali-activated ground granulated blast-furnace slag

The variation of water content significantly affects the strength development of stabilized dredged sludge (DS), as well as the rational use of binder. This paper experimentally studies the strength and microstructure evolutions of DS stabilized with alkali-activated ground granulated blast-furnace slag (GGBS) under different water contents, via a range of unconfined compressive strength (UCS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests. The sodium hydroxide (SH) and sodium silicate (SS) were used as single and composite activators for GGBS, and their roles on the stabilization efficacy were mainly focused. The results illustrated that the optimum single activator content tended to increase with the increase of water content. Composite activators were more effective than single activator in activating GGBS for achieving higher UCS of stabilized DS. The optimum mass ratio of SH to SS (H/S) in composite activators was 2/3, 2/3 and 1/4 at water content of 60, 70 and 80%, respectively. The linear empirical equations for predicting 60- and 90-day UCS based on 28-day UCS were proposed. XRD and SEM results confirmed that calcium silicate hydrate and calcium aluminate hydrate were the major hydrations, which undertook the cementation and filling roles. Furthermore, the micro-mechanisms revealing the strength evolutions of stabilized DS were analyzed and discussed. The results recommended that using 20% SH/SS-GGBS binder with optimum H/S of 2/3, 2/3 and 1/4 as the substitute of equivalent PC for stabilizing DS with water content of 60, 70 and 80%, respectively.