One-part Alkali-activated Slag Research Articles

Effects of alkali activator on the chloride-ion permeability of one-part alkali-activated nickel slag concrete

Herein, the effects of the ionic types and content of alkali activator on the chloride-ion permeability of one-part alkali-activated nickel slag concrete were examined. The NT Build 492 method was adopted to measure the Cl− transport performance. In general, the total Cl− concentration in concrete decreases with the increase of penetration depth; however, the enrichment of Cl− concentration in the sample is not obvious. Anions have more effect on 28-d compressive strength, while cations have more effect on chlorine-ion permeability. For the same Na2O content, SiO32−-activator and Na+-activator perform better than other anions and cations, while OH– and K+ perform worse than other ions. The chloride-ion permeability coefficient (DRCM) of concrete with Na2SiO3 is the lowest and that with KOH is the highest. The DRCM of concrete prepared with KOH is 1.93 times higher than that of concrete prepared with Na2SiO3. When the activator is Na2SiO3, the DRCM of concrete decreases with the increase in Na2O content when the Na2O content is less than 7%. However, when the Na2O content exceeds 7%, the DRCM of concrete increases with the increase in Na2O content.

Effect of CaO/SiO2 and Al2O3/SiO2 on the chloride permeability of one-part alkali-activated nickel slag concrete

To study the effect of CaO/SiO2 and Al2O3/SiO2 ratios on the chloride permeability of one-part alkali-activated nickel slag (AANS) concrete, the chloride ion electromigration coefficient and the distribution of total chlorine concentration at different permeability depths of the one-part AANS concrete were investigated. The ratio of CaO/SiO2 and Al2O3/SiO2 of cement were designed in the range of 0.85–1.3 and 0.3–0.75, respectively. The reaction product and pore structure of paste were analyzed. The Results showed that the total chloride ion concentration in concrete first decreased and then increased with CaO/SiO2 and Al2O3/SiO2 ratios increasing. The chloride permeability of the concrete with CaO/SiO2 of 1.0 and Al2O3/SiO2 of 0.45 was the lowest, as the hydration degree of the concrete was the highest, which effectively optimized the pore structure. The chloride ion migration coefficient of concrete decreased with porosity, and an exponential relationship was observed between the chloride ion migration coefficient with porosity.

The Efficiency of the Ordinary Polypropylene Fiber in Producing One-part Alkali-Activated Slag Composites with Strain-Hardening Behavior

The Efficiency of the Ordinary Polypropylene Fiber in Producing One-part Alkali-Activated Slag Composites with Strain-Hardening Behavior

The Effect of Superplasticizers on Eco-friendly Low-Energy One-Part Alkali-Activated Slag

One-part alkali-activated materials (OP-AAM) have become a promising binder with low carbon and energy requirements associated with superior mechanical and durability characteristics. This study aims to employ commercial superplasticizers (naphthalene-based “Nb-SP” and polycarboxylate-based “PCb-SP”), as well as laboratory-prepared one (phenol–formaldehyde sulfanilate “PFS-SP”) in enhancing the properties of OP-AAM. The main problem of superplasticizers (SPs) in the AAM is their hydrolysis in the alkaline activator (NaOH) used in the activation reactions. Therefore, the thermo-chemical treatment process was utilized to mitigate the high activator alkalinity by impeding the NaOH in the aluminosilicate precursor matrix. The OP-AAM was fabricated from thermo-chemical treatment powder (TCT-P) resulting from sintering blast furnace slag (GGBFS) with 10 wt% NaOH at 300 and 500 °C. The XRD-pattern showed that NaOH was impeded in the GGBFS via sodium aluminum silicate phase formation after sintering at 500 °C. The results showed that the admixed OP-AAM prepared from TCT-P at 500 °C greatly enhanced the workability and mechanical properties. The PFS-SP proved its efficiency in improving the properties of OP-AAM prepared TCT-P at 300 and 500 °C, referring to its high stability in an alkaline medium. While PCb-SP reinforced the properties of OP-AAM prepared from TCT-P at 500 °C only, proving that PCb-SP promotes high capability in TCT-P-500 as well as in Portland cement.

Effect of using wastewater from the ready-mixed concrete plant on the performance of one-part alkali-activated GBFS/FA composites: Fresh, mechanical and durability properties

Water scarcity is the world's most pressing issue, as concrete batching facilities and concrete mixer trucks produce massive amounts of wash water every day. Recycling waste water from ready-mix concrete factories' concrete washing water is critical for conserving hundreds of millions of tons of water and preventing water and soil contamination. This study examined the impact of waste washing water on the microstructural, durability, fresh, and mechanical characteristics of one-part alkali-activated ground blast furnace slag (GBFS)/fly as (FA) composites (AAC) containing partial and complete replacement of tap water under ambient conditions. GBFS was used as the main binder in the production of AAC. FA was also used as a binder at 0%, 25%, and 50% instead of GBFS. Sodium metasilicate (MS) was used as a one-part activator at two dosages 7.5% and 15% of the total binder. The fresh properties (setting time and flowability), physical properties, compressive and flexural strength (3, 7, 28, 90, and 180 days) and durability (high-temperature resistance, freeze, and thaw resistance, drying shrinkage, sorptivity, HCl and MgSO4 resistances, NaCl effect and alkali-silica reaction) and microstructure analysis were investigated. The findings showed that the use of wastewater (WW) instead of tap water (TW) contributed positively or had no serious negative effect on the mechanical and durability properties of AAC. Compressive strength of 72.37 MPa and 81.67 MPa was gained with the inclusion of 50%WW at 7.5 and 15 %MS content respectively. The findings showed that WW improved the workability of fresh ACC containing FA, reduced dry shrinkage and sorptivity of ACC with 15%MS content, and refined the pores of hardened ACC. The results also supported that WW contributed to the decrease in expansion due to ASR and sulfate expansion. Using WW improved the high temperature and F-T resistance of ACC mixtures containing 15%MS content.

Utilization of optimized microwave sintering to produce safe and sustainable one-part alkali-activated materials

Sodium hydroxide (NaOH) as an alkaline activator presents a vital limitation in the mass production of alkali-activated binders due to its severe effect on users’ safety. In this study, safe and sustainable one-part alkali-activated slag mixes (OP-AAS) were prepared through an efficient microwave sintering for a mixture of active amorphous ground granulated blast furnace slag (GGBFS) and sodium hydroxide powder (NaOH). Different microwave-sintered powders were prepared using microwave energy of power 900 W for the mixture at different treatment periods (10, 20, and 30 min). Fresh and hardened properties of different OP-AAS mixes were studied. Moreover, the phase composition and microstructure were investigated using X-ray diffraction (XRD) analysis and scanning electron microscope (SEM). Cytotoxicity/viability testing was performed to evaluate the cell death induced by the developed materials to measure their safety for the user. According to compressive strength, cytotoxicity/viability analysis, environmental impact and cost calculation of developed OP-AAS, it is concluded that employing microwave sintering for a short duration is sufficient to produce safe binding materials with adequate mechanical properties suitable for commercial applications in the construction sector.

Effects of chloride salts on strength, hydration, and microstructure of cemented tailings backfill with one-part alkali-activated slag

For mines located in saline areas, the use of mine water containing chloride salts to prepare cemented tailings backfill (CTB) for mined-out area treatment can realize the resource utilization of mine water and save a large amount of precious freshwater. However, the hydration behavior of binder and strength properties of CTB in the presence of chloride salts is still not well understood. This research investigates the effects of NaCl, CaCl2 and MgCl2 with different Cl- concentrations (0.50, 0.77 and 1.0 mol/L) on strength of CTB prepared with one-part alkali-activated slag binder. It analyzes the hydration process of binder and the microstructure of CTB. The results indicated that the decalcification of C-A-S-H (replaced by sodium to create N(C)-A-S-H at high Na+ concentrations) leads to numerous 0.01–0.1 μm micropores within the hardened backfill, increasing porosity while decreasing strength by 3.2–25.0%. Calcium ion (Ca2+) contributes to the formation of dense internal structures and high-strength backfill. Magnesium ion (Mg2+) reduces alkalinity by consuming Ca(OH)2, seriously impacts slag decomposition, but accelerates the dissolution of desulfurized gypsum. The study’s findings will help the application of chloride-containing mixing water in mines situated in saline regions.

Use of Saline Water in Cemented Fine Tailings Backfill with One-Part Alkali-Activated Slag

To evaluate the feasibility of mixing saline underground water (SUW) in the preparation of cemented fine tailings backfill (CFTB), the compressive strength, pore fluid pH, slag hydration degree, hydration phase composition/structure, and pore morphology of CFTB have been tested. The binder used was a one-part alkali-activated slag composed of ground-granulated blast furnace slag (67.8% by weight) as precursor and desulfurized gypsum (25.9% by weight) and hydrated lime (6.3% by weight) as composite activator. The results showed that using SUW instead of deionized water as mixing medium had both negative and positive effects on the strength development of CFTB, depending on the curing time. At the very early ages (1–3 days), mixing SUW resulted in a decrease of the pore solution pH, which is due to the reaction of positive ions in SUW with OH− ions and the decrease of slag hydration rate, leading to a lower strength of CFTB. The positive effects were observed at the later ages (7–28 days). The higher later-age strength of SUW-mixed CFTB is attributed to two factors: (1) a smaller amount of ettringite (AFt) was generated at the very early ages, which reduced the encapsulation-hindering effect on the slag decomposition; and (2) SUW increased the slag hydration rate, promoting the condensation of calcium silicate hydrates, which results in increased formation of a calcium silicate aluminate hydrate [C-(A)-S-H] phase with rigid three-dimensional structure. These findings can provide important information for the use of SUW in CFTB in coastal and arid regions.

Preparation of potassium methylsilicate modified one-part alkali-activated slag grouting material and its effect on adhesion properties of semi-flexible pavement

Because of the opposite polarities of the alkali-activated slag grouting material and the asphalt mixture, their successful combination is challenging. In this study, a small molecular surfactant, viz. potassium methylsilicate (PMS), was used to modify the grouting material. The results showed that PMS is stable in the one-part alkali-activated slag grouting material and can bind to the end of the gel. When 6% PMS was added, the contact angle between the grouting material and SBS-modified asphalt was 55.6°, a 41.60% reduction in contact angle compared with that obtained when unmodified grouting material was used. Moreover, owing to the presence of CH3, there is a complete Interface transition zone (ITZ) between the modified grouting material and the asphalt mixture and the grouting saturation is above 90%. Although PMS modification can reduce the Marshall stability and increase flow value of the SFP, it can still meet the technical requirements of the SFP.

Effect of rice straw powder on properties of one-part alkali-activated slag

One-part alkali-activated slag (AAS) as a binder material has a promising application in the construction industry. The properties of one-part AAS incorporating agricultural wastes have been seldom studied. In this paper, the fresh and hardened properties of one-part AAS with the addition of rice straw powder (RSP) were investigated. The reaction rate in the acceleration period of AAS is reduced by RSP. The compressive strength of the mixture decreases with the introduction of RSP, while the flexural strength increases. The porosity of the hardened mixtures becomes lower when RSP was incorporated. N-(C)-A-S-H gel was detected in the system when 4.2% RSP was present. The RSP reduces the early-age autogenous shrinkage of AAS by providing internal curing to the matrix, but its effect on long-term drying shrinkage is limited.

Characterization of one-part alkali-activated slag with rice straw ash

In this paper, fresh (setting and rheology) and hardened properties (strength and shrinkage) of one-part alkali-activated slag (AAS) with and without rice straw ash (RSA) are comprehensively investigated. The reaction kinetics and microstructure of the mixtures are characterized by a series of experimental techniques. The results reveal that RSA plays dual roles in AAS, as a precursor (though not fully reactive) and an internal curing agent. The reactive K and Si in RSA participate in the formation of C-(A)-S-H gel and the alkaline groups dissolved from the ash facilitate the hydrolysis of slag. Besides, the porous RSA absorbs liquid in the first day and releases it afterwards, thus providing internal curing to the matrix. The consistency index of the paste becomes higher with the incorporation of RSA. Both autogenous and drying shrinkage of AAS, which are considered as two problematic issues for this material, are mitigated by RSA.

One-part alkali-activated slag binder for cemented fine tailings backfill: proportion optimization and properties evaluation.

In this study, a one-part alkali-activated slag (AAS) composed of ground-granulated blast furnace slag, desulfurized gypsum, and hydrated lime is proposed as alternative to cement for the production of cemented fine tailings backfill (CFTB), which is an environmentally friendly binder consisting of 93.72 wt.% industrial solid waste. Results show that AAS with 67.83 wt.% slag, 25.92 wt.% desulfurized gypsum, and 6.25 wt.% hydrated lime yields the highest strength, which is 1.7-3.2 times that of ordinary Portland cement (OPC). Aside from calcium silicate hydrate gel, appreciable quantity of ettringite characterized by interlocking needles structure and high bound water is also produced during the AAS hydration process. In addition, the hydration heat of the AAS binder is 48% less than that of OPC. Moreover, CFTB made of AAS provides better workability than that of CFTB with OPC up to 20h. The findings of this study will contribute to the production of more cost-effective, durable, and environmental-friendly cemented fine tailings backfill.

Incorporation of bioleached sulfidic mine tailings in one-part alkali-activated blast furnace slag mortar

Sulfidic mine tailings are potential waste materials from mining and mineral processing, and they can contain a high content of sulfur and metal(loid)s, even after bioleaching. Due to the large amount of tailings waste from historical mining, it is crucial to find alternative methods for utilizing such waste rather than permanent storage in tailings impoundments. One-part alkali-activated slag mortars are promising co-binder systems for the recycling of sulfidic mine tailings thanks to their practicability, easy transportation, and user-friendly production. In this work, up to 50 wt% mine tailings were incorporated into alkali-activated blast furnace slag mortars. C-(N)-A-S-H gels were formed in all final samples with hydrotalcite zeolites. Tailings hardly participate in alkali activation, but they do have a considerable influence on physical and chemical properties. The 20 wt% tailings-containing sample showed the highest compressive strength of 91.1 MPa after 90 days of curing. The results of isothermal calorimetry indicate that incrementally increasing the percentage of tailings promotes the pre-induction reaction but hinders the slag hydration process. In addition, the results of X-ray microcomputed tomography showed higher porosity when the mortar contains more tailings; thus, the sample with 10 wt% mine tailings showed the lowest porosity. According to the European Union batch leaching test, up to 20 wt% bioleached sulfidic mine tailings can be valorized in a co-binder system while remaining below the nonhazardous waste thresholds.

Effect of fine sand powder on the rheological properties of one-part alkali-activated slag semi-flexible pavement grouting materials

Understanding the rheological properties of one-part alkali-activated slag grouting material(OAASGM) are very significant when it used as a semi-flexible pavement (SFP) grouting material. The fluidity, setting time, rheological properties, mechanical properties, grouting saturation, and Marshall stability of OAASGM with different content of fine sand powder were systematically evaluated. The results showed that fine sand powder can effectively prolong the setting time and improve the rheological properties of OAASGM. When the added amount of fine sand powder was 10% (OAASGM-10), the fluidity was 14 s, the operability time was 45 min, and the initial yield stress and plastic viscosity of OAASGM were 0.699 Pa and 1.997 Pa·s, respectively. Furthermore, it had the characteristics of shear thinning, so it did not bleed water segregation. The grouting saturation of the OAASGM-10 was as high as 91.89%, the Marshall stability of the corresponding composite material was 31.31 kN, and the flow value was 3.055 mm. These results meet the technical requirements of semi-flexible pavement (SFP), which are expected to be an alternative for cement as a SFP grouting materials.

Drying shrinkage of one-part alkali-activated slag concrete

The aim of this study was to evaluate the drying shrinkage of one-part alkali-activated slag concrete (AASC) for up to 180 days that is influenced by mix design parameters. A total of 24 mix designs for AASC and one for OPC concrete were made and cured in two different environments. The impacts of mix design parameters including water to binder ratio, silica fume to binder ratio, alkaline activator to slag ratio, and two curing regimes, in water and sealed plastic bag, on drying shrinkage were investigated, using experimental tests and SEM analysis. The results showed nearly 75% of the 180-day shrinkage was reached within 20 days. The results also revealed that the addition of silica fume considerably reduced drying shrinkage magnitude. AASC samples cured in sealed plastic bags resulted in at least a 5.9% increase in drying shrinkage. The maximum drying shrinkage was observed in a mix design containing the highest water to binder ratio and zero silica fume content regardless of curing type. The results indicated that the application of silica fume as a co-binder led to a considerable reduction in the drying shrinkage.

Preparation of one-part alkali-activated nickel slag binder using an optimal ball milling process

The effects of ball milling processes on specific surface area, particle size distribution, and compressive strength at different curing ages of one-part alkali-activated nickel slag mortar (AASBM) were investigated. Results show that the influence of impact efficiency on nickel slag from mechanical and chemical interaction differs with ball milling process. Reducing ball loading rate and increasing ball material ratio has the highest energy efficiency for improving specific surface area and improving the strength of 28 d of AASBM, respectively. With the extension of ball milling time, the specific surface area of cement can be improved but the strength increase amplitude of the mortar will decrease accordingly. When the ball loading rate is 30%, the ball material ratio is 15, and the undisturbed nickel slag is milled with high speed for 2 h then mixed with solid alkali, the compressive strength of AASBM is optimal.

Preparation of Potassium Methylsilicate Modified One-Part Alkali-Activated Slag Grouting Material and its Effect on Adhesion Properties of Semi-Flexible Pavement

Preparation of Potassium Methylsilicate Modified One-Part Alkali-Activated Slag Grouting Material and its Effect on Adhesion Properties of Semi-Flexible Pavement

Experimental comparisons between one-part and normal (two-part) alkali-activated slag binders

One-part alkali-activated slag (AAS) binders are more promising in large-scale constructions because one-part mixing procedure is safer and easier to handle compared to normal two-part method. Thus, this study aims at investigating different properties of one-part AAS binders and control samples prepared using the two-part method. Experimental results of the former suggested the hardening time was greatly extended, but the workability showed little difference. Besides, compared to the control, one-part AAS binders had similar early compressive strength (within 7 days) and flexural strength in all tested curing stages but lower later compressive strength (from 28 days). The characterisation of the porous structures suggests that there were fewer C-A-S-H gels for one-part binders evidenced by less volume of mesopores but with larger amount of bigger pores. In addition, mineralogical and microstructural analyses imply that there was no hydrotalcite formed in the one-part AAS binders. Moreover, one-part AAS binders are more susceptible to efflorescence, presumably further affecting their surface and long-term durability.

Minimizing energy consumption to produce safe one-part alkali-activated materials

Recently, alkali-activated binders have emerged as a promising sustainable solution in the construction industry. There is great demand to promote the development of one-part alkali-activated materials (OP-AAMs) to overcome the hazardous, irritating, and corrosive nature of alkaline activator solutions while sustaining their superior engineering properties. This study's main objective is to reduce the temperature of the thermochemical treatment process used to produce one-part alkali-activated slag (OP-AAS) by using an amorphous active aluminosilicate precursor. The effect of different treatment temperatures (1000 °C, 800 °C, 500 °C, 350 °C, and 300 °C) on the fresh and hardened properties of OP-AAS pastes was studied. The phase composition and microstructure were investigated using X-ray diffraction analysis and scanning electron microscopy equipped with energy-dispersive X-ray analysis. A viability/cytotoxicity test was performed on selected mixes to investigate the effect of the prepared OP-AAS on the human skin. It is concluded that the optimum treatment temperature to prepare OP-AAS is ranged between 300 °C and 500 °C. Therefore, with low-energy consumption, the production of OP-AAS is accessible, economical, and safe for the commercial application of alkali-activated materials in the construction industry.

One-part alkali activated slag using Ca(OH)2 and Na2CO3 instead of NaOH as activator: more excellent compressive strength and microstructure

In this paper, sodium carbonate and calcium hydroxide instead of sodium hydroxide used as composite activators, and slag are applied to prepare one-part alkali-activated slag. Furthermore, the properties of the slag activated by sodium hydroxide are compared. The compressive strength, XRD, TGA, MIP, and SEM analysis of the two systems are performed. The results show that the one-part alkali-activated slag prepared from sodium carbonate and calcium hydroxide has a superior compressive strength against the slag activated by sodium hydroxide. It is also found that the hydration speed of the sodium hydroxide activated slag is faster, and thus the higher compressive strength of the one-part alkali-activated slag is not caused by the hydration speed. The hydration of one-part alkali-activated slag produces a certain amount of calcium carbonate, resulting in a lower porosity in comparison with the slag activated by sodium hydroxide, which may be the reason for the better compressive strength of one-part alkali-activated slag.