Effects of cation in sulfate chloride and nitrite on Ca(OH)2 activated ground granulated blast-furnace slag (2023)

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Volume 133,

October 2022

, 104648

Abstract

This study explores the effects of the cations in sulfates, chlorides, and nitrites on calcium-hydroxide activated blast-furnace slag. Using several methods, it was demonstrated that the activators investigated could improve early strength development. Compared with chlorides and nitrites, the type of sulfate has a significant influence on slag hydration. Compared with K2SO4 and Na2SO4, the promotion of slag hydration in MgSO4, at an early age, is limited due to the precipitation of gypsum and brucite which retard the formation of hydrates and limits hydration kinetics during the initial stage. The high concentration of sulfate ions in the pore solution causes some ettringite to remain, promoting strength development. It was observed that the mechanism of pH increase in K2SO4 and Na2SO4 is due to the synergistic reactions between the sulfates and Ca(OH)2, while the low pH of MgSO4 due to the low solubility of brucite inhibits slag dissolution. The critical pH for promoting slag hydration was determined to be 13.1.

Introduction

It is known that blended cement formed by combining ordinary Portland cement (OPC) with ground granulated blast-furnace slag (GGBFS) has many beneficial properties, such as increased late strength, good chemical resistance, and long-term durability [1,2], which is why blast furnace slag cement (BFSC) is being used increasingly. BFSC not only exhibits performance that is similar to that of OPC but it also reduces the emission of carbon dioxide by replacing some of the cement with slag [3], which is good for the environment. However, a system containing slag has the problem of lower degree of hydration at early stage and insufficient early strength which seriously restricts the use of slag; however, workability is improved, [4,5]. Previous research concluded that the reaction rate of slag could be improved by changing the reaction environment, that is by adding an additional dosage of activators [6].

Adding chemical activators has some disadvantages, such as making it toxic and environmentally unfriendly as a result of nitrites, and chloride ingress caused by chloride salts [7], sulfate attack caused by sulfates [6], and decrease in workability caused by the increase of Na2SiO3/NaOH ratio [8]; however, chemical additives are a common method of improving the early strength of BFSC. Many studies have shown that alkali-activated systems can obtain strengths equivalent to that of OPC in the early stages and exceed that of OPC in the later stages of hydration [6,[9], [10], [11], [12]]. Thomas et al. [9] reported an improvement in the micro- and macro-properties of BFSC in an alkali-activated BFSC system due to the addition of sodium silicate. Nguyen et al. [10] investigated the effects of sodium sulfate (Na2SO4), gypsum (CaSO4⋅2H2O) and sodium silicate on the early characteristics of BFSC and concluded that Na2SO4 could shorten the setting time and enhance the early strength of BFSC. However, the phase of these systems is too complex to distinguish the effects of individual additivities on the cement and slag. Therefore, many researchers have studied alkali activated slag systems alone [3,12,13]. In an alkali activated slag system, the type and dose of the alkali activator are important factors affecting the strength development [12,13]. Jimenez et al. [14] investigated the effects of sodium hydroxide (NaOH) and sodium carbonate (Na2CO3) on slag hydration and reported that the initial pH and anions of the activator play decisive roles in slag strength development. Song et al. [15] showed the effects of pore solution on an alkali activated slag system; when the pH exceeded 11.5, the hydration reaction of the slag was accelerated. At present, most studies have analyzed the influence of anions in the activators on alkali-activated slag. On the one hand, the mobility of the anions in these systems is much higher than that of cations at the early stage of hydration [2,16]. On the other hand, it is difficult for cations in the pore solution to have specific chemical interactions, and the cations are physically adsorbed on the surfaces of the hydration products to achieve charge neutrality [17]. Depending on the system, some studies have examined the cations in the activator [16,18,19]. Edwards et al. [16] found that the effects of different cations, in soluble inorganic salts, on the early hydration of OPC could be ranked as: Ca2+>Mg2+>Li+>Na+> H2O $\gg$ Zn2+. Myrdal et al. [20] determined similar results. Sun et al. [18] studied the effects of various common cations, in alite pastes mixed with simulated seawater, on the micromechanical properties, and the deleterious effects of Mg2+ on the micromechanical properties were dominant. De Weerdt et al. [21] reported the effect of various cations in chloride salts on the chlorine binding capacity of Portland cement paste. The chlorine binding capacities of Mg2+ and Ca2+ were lower than that of Na+ because of the effects of pH. Sajid et al. [22], showed that the electric charges and sizes of the cations were important for the modification of slag structure. However, few researchers have investigated the effects of cations of various additives on the early hydration of Ca(OH)2 activated slag.

At present, sulfates, particularly Na2SO4, are being widely studied as effective activators of slag hydration [10,[23], [24], [25], [26]]. Na2SO4 mainly increases the pH of the pore solution and promotes slag dissolution, as shown in the following formula [6,24,26]:$N{a}_{2}S{O}_{4}+Ca{\left(OH\right)}_{2}+2{H}_{2}O\to CaS{O}_{4}.2{H}_{2}O↓+2N{a}^{+}+2O{H}^{-}$

Our previous studies concluded that Na2SO4 has a significant effect on the early hydration of the Ca(OH)2 activated slag system [26]. On the one hand, Na2SO4 improves the pH and promotes formation of ettringite (AFt). On the other hand, it is related to the limiting equivalent ionic conductance (LEIC, which indicates ionic mobility in solution) of the sulfate ions (SO42−). The mobility of SO42− in the early hydration of slag is greater than that of other anions, such as NO2−, NO3, and Cl, which may penetrate the hydrates and get exchanged with OH effectively [2]. However, few studies have been reported the effects of other sulfates on the Ca(OH)2 activated slag system. The effects of pH and sulfates on the system remain to be confirmed.$XS{O}_{4}+Ca{\left(OH\right)}_{2}+2{H}_{2}O\to CaS{O}_{4}.2{H}_{2}O↓+X{\left(OH\right)}_{2}$where X represents the corresponding cation.

Kurumisawa [27] reported that in the Ca(OH)2 activated slag system, calcium sulfate (CaSO4) had difficulty influencing the system because the Ca2+ concentration was too high and solubility of CaSO4 was very low. Therefore, this study mainly investigates the effects of different cations in three types of sulfates (K2SO4, Na2SO4, and MgSO4) on slag hydration to fill the aforementioned knowledge gap. In addition, the effects of chlorides (KCl, NaCl, and MgCl2), and nitrites (KNO2, NaNO2, and Ca(NO)2) on strength development, phase assemblage, hydration kinetics, and reaction degree of the slag were also compared.”

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Materials and sample preparation

The Ca(OH)2 activated slag pastes were prepared by mixing commercial GGBFS (40A) provided by Nippon Steel (specific surface area of 4000cm2/g compliant with JIS A 6206) with Ca(OH)2 powder (Kanto Chemical Co., Inc.). The chemical compositions of GGBFS and Ca(OH)2 detected by X-ray fluorescence (XRF) are presented in Table 1. The GGBFS is mainly amorphous with a broad hump between 2 $\mathrm{\theta }$ values of 25° and 35°, as analyzed by X-ray diffraction (XRD) and shown in Fig. 1. Fig. 2 shows the particle

Compressive strength

As an essential part of additive evolution, the influence of different inorganic salts on the compressive strength of mortars was investigated, and the results are shown in Fig. 3. As shown in Fig. 3(a), all the chlorides used in this study could improve the early strength of the mortar. However, after 7d, the improvement was not as evident and was even lower than that of the control group. One phenomenon that could be observed was that although the cations in the chloride were different, the

Conclusions

In this study, the effects of sulfate cations on Ca(OH)2 activated GGBFS were investigated by XRD, isothermal calorimetry, TGA, and thermodynamic modeling. The main conclusions are as follows:

1.

Although all nitrite, chloride, and sulfate activators could improve the strength of slag at an early age, it seems that the types of nitrites and chlorides have little impact on the development of slag hydration.

2.

Sulfate activators with different cations can promote compressive strength and hydration

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This work was supported by JSPS KAKENHI (Grant Number 21K04349) and the Steel Foundation for Environmental Protection Technology.

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FAQs

How does Ggbs affect concrete? ›

Replacing Portland cement CEM I with GGBS reduces the temperature rise and helps to avoid early-age thermal cracking. The higher the percentage of GGBS, the lower the rate of reaction and consequently the slower the rate at which heat is developed.

What is the difference between cement and Ggbs? ›

Concrete containing GGBS cement has a higher ultimate strength than concrete made with Portland cement. It has a higher proportion of the strength-enhancing calcium silicate hydrates (CSH) than concrete made with Portland cement only, and a reduced content of free lime, which does not contribute to concrete strength.

Which of the following constituents is present in the blast furnace slag? ›

Blast furnace slag is a nonmetallic coproduct produced in the process. It consists primarily of silicates, aluminosilicates, and calcium-alumina-silicates. The molten slag, which absorbs much of the sulfur from the charge, comprises about 20 percent by mass of iron production.

What is Ggbs list its advantages? ›

GGBS can be used as a partial replacement of OPC cement in concrete production at batching plants. It is highly cementitious and high in calcium silicate hydrates (CSH) which is a strength enhancing compound which improves the strength, durability and appearance of the concrete.

Why should we use Ggbs in concrete? ›

Durability; GGBS reduces the likelihood of concrete thermal cracking, and it improves concrete's resistance to damage from alkali-silica reaction, sulphates and chlorides. Concrete in aggressive environments is much more durable with the use of GGBS as a partial replacement for the cement.

How is slag formed in a blast furnace? ›

Blast furnace slag (BFS) is a by-product from iron production in blast furnaces, which are fed by a mixture of iron-ore, coke and limestone. In the process, the iron ore is reduced to iron while all remaining materials form the slag, which is tapped off as a molten liquid and cooled.

Which is better flyash or Ggbs? ›

Fly ash is low in calcium oxide content but rich in silica and alumina while GGBS is relatively high in calcium oxide. The combination of these two materials can be more beneficial when used as a stabilizing agent than using them individually.

Why fly ash is used in cement? ›

Fly ash use in concrete improves the workability of plastic concrete, and the strength and durability of hardened concrete. Fly ash use is also cost effective. When fly ash is added to concrete, the amount of portland cement may be reduced.

Which is better fly ash or Ggbs? ›

The reaction heat per unit mass of GGBS is only 16·7% higher than that of fly ash. The main reason for the difference of hydration heats between GGBS binder and fly ash binder is that GGBS shows much higher hydraulic activity than fly ash.

What is the chemical composition of slag? ›

The primary components of iron and steel slag are limestone (CaO) and silica (SiO2). Other components of blast furnace slag include alumina (Alsub>2O3) and magnesium oxide (MgO), as well as a small amount of sulfur (S), while steelmaking slag contains iron oxide (FeO) and magnesium oxide (MgO).

What is meant by ground granulated blast furnace slag? ›

Ground granulated blast-furnace slag, GGBFS, is a by-product of iron in blast-furnace. It mainly consists of silicate and aluminosilicate of melted calcium that periodically needed to be removed from the blast furnace.

Which type of slag is produced in BOF vessel at SMS? ›

Slag in BOF is heterogeneous and always contains some entrained gas bubbles and solid material (either un-dissolved or precipitated). At no stage the slag is 100 % liquid.

What is granulated slag used for? ›

Primarily ground into a cement replacement known as ground granulated blast furnace slag (GGBS) this is used in ready-mixed and precast concrete and masonry, floor levelling compounds and high temperature resistant building products.

GGBS is mainly used as a partial replacement of cement in concrete. When added as an admixture to concrete, it acts as a stabilising agent and improves the quality of concrete. In the production of ready-mixed concrete, GGBS replaces a substantial portion of the Portland cement component, generally about 60-70%.

Is Ggbs a binder? ›

GGBS is primarily a binder used as an addition to cement which uses the latent hydraulic properties of GGBS to produce Portland blastfurnace cement (6-35% of GGBS) or blastfurnace cement (36-90% GGBS) produced by blending at the concrete mixer, or as a factory blend at the cement factory.

What is the maximum percentage of Ggbs in concrete? ›

GGBS is known as Ground Granulated Blast Furnace slag. Use of GGBS significantly reduces the risk of damages caused by Alkali Silica reaction and reinforcement corrosion. The maximum GGBS content which can be used is 25-65 % [11].

What is glass content in Ggbs? ›

All GGBS were considered as almost totally amorphous, with glass content > 99.8%, except for GGBS 14 with a glass content of 98.2% and GGBS13 with 2.6 wt.

What is the difference between Portland cement and slag cement? ›

The content of clinker in slag cement is less than that in Portland cement but the content of granular blast furnace slag is more. Slag cement has the following characteristics compared with Portland cement (see Table 4.6).

What chemical reactions happen in a blast furnace? ›

The reactions of the blast furnace involve 1) combustion of the fuel and its conversion into carbon monoxide, 2) reduction of the ore, and 3) formation of slag. A reaction such as FeO + CO = Fe + CO2 can occur in both the forward and backward direction under conditions existing somewhere in the blast furnace.

What is added in blast furnace charge for forming slag? ›

Limestone is added to blast furnace as flux and sulphur, silicon and phosphorous are oxidized and passed into slag.

How slag is formed? ›

Steel slag, a by-product of steel making, is produced during the separation of the molten steel from impurities in steel-making furnaces. The slag occurs as a molten liquid melt and is a complex solution of silicates and oxides that solidifies upon cooling.

What is the full form of Ggbs? ›

GGBS (Ground Granulated Blast-furnace Slag) is a cementitious material whose main use is in concrete and is a by-product from the blast-furnaces used to make iron. Blast-furnaces operate at temperatures of about 1,500°C and are fed with a carefully controlled mixture of iron ore, coke and limestone.

Is Ggbs a pozzolanic? ›

A GGBS is NOT a pozzolan.

What is in fly ash? ›

Fly ash consists primarily of oxides of silicon, aluminum iron and calcium. Magnesium, potassium, sodium, titanium, and sulfur are also present to a lesser degree. When used as a mineral admixture in concrete, fly ash is classified as either Class C or Class F ash based on its chemical composition.

Is fly ash acidic or alkaline? ›

2.2.

Depending on pH value and calcium/sulfur ratio, fly ashes are classified as acidic ash (pH 1.2 up to 7), mildly alkaline ash (pH 8–9), and strongly alkaline ash (pH 11–13) [23]. Fly ash can be classified according to the type of coal from which the ash was derived.

Is coal ash acidic or alkaline? ›

Coal ash also contains significant concentrations of radioactive materials that can release radon. Whereas bottom ash is typically alkaline (pH > 7), fly ash and scrubber sludge can be acidic (pH < 7), depending upon the concentration of sulfur.

Why gypsum is used in cement? ›

Gypsum is called the retarding agent of cement which is mainly used for regulating the setting time of cement and is an indispensable component. Without gypsum, cement clinker can condense immediately by mixing with water and release heat.

How do you make a geopolymer brick? ›

Geopolymer bricks were prepared by mixing the solid precursors: 50% sand and 50% (WB and GGBFS) with an alkaline solution of silicate and sodium hydroxide. All the formulations prepared in our study contain 50% of sand by weight. The variation is reflected only in the percentages of WB and GGBFS.

What is geopolymer brick? ›

Abstract : Geopolymer bricks is the new innovation in the field of brick industry. Geopolymer bricks contain flayash as the source material and an alkaline activator for the activation of polymerization reaction.

What is the cost of Ggbs? ›

GGBS Granules,Packaging Size- 50 Kg, 500 Kg, 1 Ton at Rs 1950/metric ton in Kolkata.

What is the main disadvantage of using Ggbs in concrete manufacture and when is this relevant? ›

The disadvantage of the higher replacement level is that early age strength development is somewhat slower. GGBS is also used in other forms of concrete, including site-batched and precast. Unfortunately, it is not available for smaller-scale concrete production because it can only be economically supplied in bulk.

What are the disadvantages of slag? ›

Early Strength is low; therefore, it cannot be used in Reinforced Cement Concrete (RCC) works. As the initial setting time is high, this cement is not used for emergency or repair works.

What does fly ash do in concrete? ›

Fly ash use in concrete improves the workability of plastic concrete, and the strength and durability of hardened concrete. Fly ash use is also cost effective. When fly ash is added to concrete, the amount of portland cement may be reduced.

What is Ggbs in civil engineering? ›

GGBS (Ground Granulated Blast-furnace Slag) is a cementitious material whose main use is in concrete and is a by-product from the blast-furnaces used to make iron. Blast-furnaces operate at temperatures of about 1,500°C and are fed with a carefully controlled mixture of iron ore, coke and limestone.

What is the chemical composition of Ggbs? ›

11.2. 2 Ground-granulated furnace slag
Composition (%)Kosmatka and Wilson (2016)El-Chabib (2006)
SiO235.035.0
Al2O312.011.2
Fe2O31.00.5
CaO40.036.1
6 more rows

How Ggbs is produced? ›

Production. GGBS is produced by grinding Granulated Blastfurnace Slag to a controlled fineness. There are a number of different methods of grinding granulated blastfurnace slag. Traditionally, standard ball mills have been used, but since the early 2000s the use of roller presses and vertical mills has increased.

What is glass content in Ggbs? ›

All GGBS were considered as almost totally amorphous, with glass content > 99.8%, except for GGBS 14 with a glass content of 98.2% and GGBS13 with 2.6 wt.

What percentage of slag is added in slag cement? ›

The mixed amount of granular blast furnace slag in cement is 20% ~ 70% by weight. One of the blended materials, limestone, kiln dust, fly ash and volcanic ash, is allowed to replace the slag.

Does slag increase slump? ›

0-slag concrete has 7-cm slump, and it is clear that the addition of slag increases the value of slump up to 6 cm.

Which cement is better OPC or PSC? ›

PPC cement is generally used for plastering, brick masonry and waterproofing works. PPC has a lower heat of hydration and it is prone to fewer cracks compared to OPC. PPC has lower strength than OPC but PPC provides better workability and finishing than OPC.

Why is slag used in concrete? ›

It typically replaces part of the portland cement in concrete mixes. According to the Slag Cement Association, an industry trade group, incorporating slag cement as a supplement in concrete offers higher strength, reduced permeability and improved resistance to chemical attack.

Superplasticizers (SPs), also known as high range water reducers, are additives used in making high strength concrete. Plasticizers are chemical compounds that enable the production of concrete with approximately 15% less water content. Superplasticizers allow reduction in water content by 30% or more.

Is fly ash acidic or alkaline? ›

2.2.

Depending on pH value and calcium/sulfur ratio, fly ashes are classified as acidic ash (pH 1.2 up to 7), mildly alkaline ash (pH 8–9), and strongly alkaline ash (pH 11–13) [23]. Fly ash can be classified according to the type of coal from which the ash was derived.

What is granulated slag used for? ›

Primarily ground into a cement replacement known as ground granulated blast furnace slag (GGBS) this is used in ready-mixed and precast concrete and masonry, floor levelling compounds and high temperature resistant building products.

What is slag powder? ›

h i g h l i g h t s Slag is an engineering waste and by-product in the production of iron in a blast furnace. AAS consists of alumina-silicates and silicates of lime; this makes it suitable for the production of geopolymers.

What is furnace slag? ›

Furnace slag (or ground granulated blast furnace slag, GGBFS) is the granular material formed during the processing of iron blast furnace slag generated from steel manufacturing.

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Phone: +9752624861224

Job: Forward Technology Assistant

Hobby: Listening to music, Shopping, Vacation, Baton twirling, Flower arranging, Blacksmithing, Do it yourself

Introduction: My name is Nathanial Hackett, I am a lovely, curious, smiling, lively, thoughtful, courageous, lively person who loves writing and wants to share my knowledge and understanding with you.