One-part Alkali-activated Slag Research Articles

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.

High strength one-part alkali-activated slag blends designed by particle packing optimization

This paper focuses on the development of high-strength and eco-friendly one-part (i.e., dry-mix) alkali-activated mortar with ground granulated blast furnace slag as the main precursor. In addition to slag, phyllite dust and silica fume were used as co-binders in binary and ternary blends to improve mechanical properties. Particle packing optimization was employed for the mix proportioning to achieve a compact matrix skeleton. The results revealed that a 10% increase in mortar strength was gained after adjusting the particle packing and an additional 20% increment was observed after blending the slag with other mineral admixtures. Ternary blend with all three binders achieved a mortar compressive strength value of 145 MPa (at 28 d age), which is the highest strength reported in one-part alkali-activated materials. Additionally, ternary blends present potential economic benefits because of their ability to replace slag with lower-cost industrial side streams.

Enhancing the mechanical and durability properties of subzero-cured one-part alkali-activated blast furnace slag mortar by using submicron metallurgical residue as an additive

Cold weather (<0 °C) is known for its detrimental impacts on concrete, and thus expensive and energy-consuming heating and insulation systems are used in cold-weather concreting to prevent frost damage. Supplementary cementitious materials are not recommended for use in cold-weather concreting because they slow down the setting time of concrete. In this study, one-part alkali-activated slag (AAS) was presented as an alternative environment-friendly binder for winter construction. The impacts of iron-containing submicron metallurgical residue on the reactivity, hardened properties, and durability of subzero-cured one-part AAS pastes and mortars were comprehensively studied. The incorporation of submicron particles (SMPs) enhanced the reactivity of AAS pastes by increasing the amount of precipitated hydrate phases and developing supplemental hydration products like calcium ferrosilicate hydrate. The positive effects of SMPs were highlighted via the denser microstructure, higher ultrasonic pulse velocity, increased compressive strength, and better durability properties of the AAS mortars. These improvements were attributed to the nucleation and filling behaviors of the added SMPs. On the contrary, decreased subzero curing temperature hindered the reaction progress, which adversely affected the hardened and durability properties of the mortars and limited the SMPs efficiency. With additional above-zero curing, higher compressive strength and lower water absorption and permeable porosity were measured in the AAS mortar cured initially at −5 °C compared to that cured at +20 °C.

Sustainable Design of Pervious Concrete Using One-Part Alkali-Activated Slag with Zeolite and Walnut Shell Activated Carbon to Absorb Runoff Contaminants

Sustainable Design of Pervious Concrete Using One-Part Alkali-Activated Slag with Zeolite and Walnut Shell Activated Carbon to Absorb Runoff Contaminants

Novel procedure of CO2 capture of the CaO sorbent activator on the reaction of one-part alkali-activated slag.

CaO derived naturally from limestone or dolomite is an inexpensive and widely available sorbent. Understanding the mechanisms of CaO carbonation at ambient temperature under the assistance of H2O is important for predicting the reaction of CaO in complex environments and designing novel CaO materials. In this study, we found that the reaction rate of alkali-activated slag is controlled by the CaCO3 layer on a partially carbonized CaO alkali activator. The size of the sorbent increased after the adsorption reaction and the physically adsorbed water in the pores accelerated the carbonation. The carbonation process was governed by CO2 diffusion. When the carbonation conversion rate reached 2–6%, the setting time increased rapidly with the increase in the carbonation rate. This is because the surface of the activator was modified by the thickened CaCO3 product layer, which increased the diffusional resistance and thus prolonged the setting time of the alkali-activated slag.

Sustainable batching water options for one-part alkali-activated slag mortar: Sea water and reverse osmosis reject water.

Concrete production is globally a major water consumer, and in general, drinking-quality water is mixed in the binder. In the present study, simulated sea water and reverse osmosis reject water were used as batching water for one-part (dry-mix) alkali-activated blast furnace slag mortar. Alkali-activated materials are low-CO2 alternative binders gaining world-wide acceptance in construction. However, their production requires approximately similar amount of water as regular Portland cement concrete. The results of the present study revealed that the use of saline water did not hinder strength development, increased setting time, and did not affect workability. The salts incorporated in the binder decreased the total porosity of mortar, but they did not form separate phases detectable with X-ray diffraction or scanning electron microscopy. Leaching tests for monolithic materials revealed only minimal leaching. Furthermore, results for crushed mortars (by a standard two-stage leaching test) were within the limits of non-hazardous waste. Thus, the results indicated that high-salinity waters can be used safely in one-part alkali-activated slag to prepare high-strength mortars. Moreover, alkali-activation technology could be used as a novel stabilization/solidification method for reverse osmosis reject waters, which frequently pose disposal problems.

Effects of mixing water temperatures on properties of one-part alkali-activated slag paste

During hot and cold weather, initial mixing water temperature is a critical parameter in controlling the fresh and hardened properties of cement-based materials. With the advent of Alkali Activated Materials (AAMs), the effectiveness of such a technique becomes questionable as the hydration mechanism differs from that of the ordinary Portland cement (OPC). Therefore, this study focuses on evaluating the effects of initial mixing water temperature on the performance of one-part Alkali Activated Slag (AAS). Various AAS mixtures prepared by different mixing water temperatures (i.e. 0 °C, 10 °C, 20 °C, and 30 °C) were tested. Fresh and hardened properties, including mini-slump, slump loss rate, setting time, the heat of hydration, compressive strength, and shrinkage, were investigated. Results reveal that the initial mixing water temperature plays a dominant role in controlling solubility and dissolution rates for different ingredients (i.e. solid activator and slag). This, in turn, had affected the hydration process and consequently the development of various properties. Slump life and setting time were found to extend as the initial mixing water temperature reduced while the strength was not harmed. Saving energy consumed for warming water during cold weather concreting will also increase concrete sustainability. It is anticipated that these findings will pave the way for a broader implementation of such green sustainable materials in the construction sector.

Alternative alkali-activator from steel-making waste for one-part alkali-activated slag

In this study, the use of desulphurization dust (DeS-dust) generated as a waste material during steel-making process, as an alternative activator to commercial sodium hydroxide in ground granulated blast furnace slag (GGBFS) alkali activation is proposed. The main objective was to decrease the environmental footprint of alkali-activated materials through the reuse of industrial residues. Microsilica was added to increase the amount of soluble silica and enhance the properties of the investigated binders. The results indicate that binders from alternative activator performed better, achieving a 28 days maximum strength of 33 MPa compared to 25 MPa for the sodium hydroxide activated slag. Microsilica addition to the optimum mixes reduces the rate of efflorescence and increases the setting time. Also, microstructural studies using scanning electron microscopy (SEM), x-ray diffraction (XRD) and thermogravimetric analysis (TGA) show both samples having comparable gel formation and structure. Life cycle impact assessment shows significant savings that can be made using alternative activators over sodium hydroxide activated slag. Through the use of this waste material as alternative activator in alkali-activated binders, an environmentally friendly, and cleaner production of alkali-activated binders can be achieved having comparable or superior performance as the reference binder activated with commercial sodium hydroxide.

Environmentally benign production of one-part alkali-activated slag with calcined oyster shell as an activator

This study focuses on an environmental friendly, non-corrosive and non-viscous activator during the production of one-part alkali-activated slag using calcined oyster shell (COS) powder. Test results demonstrate improved mechanical and microstructural characteristics for specimens prepared with COS powder as an activator. The highest increment in the strengths was revealed with a 5% COS addition due to the resulting enhanced pore refinement, whereas an excessive dose resulted in a delayed rate of C-S-H formation and a significant amount of large capillary pores, thus decreasing the strength. The mineralogical and microstructural properties of the paste were also analyzed, and these findings revealed that COS powder is suitable for use as an activator to produce one-part alkali-activated materials.

Durability of the Reinforced One-Part Alkali-Activated Slag Mortars with Different Fibers

This paper investigates the effects of reinforcing one-part alkali-activated slag binders (OAASs) with different types of fiber (steel, polyvinyl alcohol [PVA], basalt, and cellulose) and fiber combinations (single and hybrid) on the mechanical and durability properties of OAASs. All OAASs were reinforced by a 1% fiber volume fraction. Compressive and flexural strengths were the mechanical properties, which were addressed. The durability of the reinforced OAASs was examined based on water absorption by immersion and capillary, acid resistance, high temperature resistance, carbonation resistance, and freeze/thaw resistance. The experimental results showed that the fiber type and combination greatly affects the mechanical and durability properties of OAASs. Moreover, the influence of fiber type and combination on high temperature resistance and freeze/thaw resistance is greater than the influence on acid resistance and carbonation resistance.Graphic

Promoting the performance of one-part alkali-activated slag using fine lead-zinc mine tailings

The feasibility of using fine lead–zinc mine tailings to improve the performance of one-part alkali-activated slag (AAS) with low alkali dosage (1.5 Na2O wt.%) is investigated. The compressive strength of one-part AAS increases with the increase of fine tailings at the early age (≤7 d), and then slightly decreases after 28 d of curing. Two distinguished reaction stages with two dormant periods are identified in all samples, regardless of the content of fine tailings. The incorporation of fine tailings accelerates the second reaction stage, but has little effect on the first reaction stage. The pH value of the pore solution in all samples increases with the reaction time (≤14 d), and those with a high content of fine tailings give relatively high alkalinity values at all curing ages. The incorporation of fine lead–zinc mine tailings enhances the compressive strength of one-part AAS, which is mainly associated with its roles of improving the pH value in pore solutions and accelerating the reaction of binders.

Controlling the setting times of one-part alkali-activated slag by using honeycomb ceramics as carrier of sodium silicate activator

A solid alkali source is a great choice to make one-part alkali activated materials (AAM). Conventional slag-based AAM always suffer from short setting time and unsafe operation with liquid alkaline activators, thus restricting their usage in industry. This study aims to synthesize a new kind of one-part alkali-activated slag cement by using a porous honeycomb ceramic (HCC) as the carrier of sodium silicate activator. The solid activator was produced by making the honeycomb ceramic absorb water glass (Ms = 3.24, 8.21 wt% Na2O, 25.8%wt SiO2), drying for 5 h at 125 °C and then grinding it to powder with particle sizes between 10 and 50 μm. In this study, the result indicates that setting time of alkali activated slag cement (AASC) was successfully extended to at least 5 h by using the solid activator. The maximum compressive strength of the specimens made with 5% NaOH + 40% HCC and 6% NaOH + 40% HCC was ~40 MPa after 28 d of curing time. XRD (X-ray diffraction), FTIR (Fourier Transform infrared spectroscopy), SEM (Scanning Electron Microscope) and linear shrinkage analysis were applied in order to study the hydration product and the effect of the addition of HCC to the AASC. In terms of the strength properties and setting time, this one-part AASC could be classified as a Type 32.5 N and CEM IIIC class cement according to the European standard EN-197.

Effects of Light-Burnt Dolomite Incorporation on the Setting, Strength, and Drying Shrinkage of One-Part Alkali-Activated Slag Cement.

This study investigates the potential of light-burnt dolomite (LBD) as a supplementary cementitious material with ground granulated blast furnace slag (GGBFS) and Ordinary Portland cement (OPC). In this work, LBD was substituted for up to 20% of GGBFS in sodium sulfate-activated slag systems. The effects of LBD incorporation on the flow, setting time, compressive and flexural strength development, and drying shrinkage were explored with, X-ray diffraction and thermogravimetric analyses. LBD incorporation resulted in greater strength development of an alkali-activated slag system. The optimum LBD content for strength development was 10%, regardless of ordinary Portland cement content. In addition, LBD decreased the drying shrinkage, accelerated the hydration process, and induced hydrotalcite formation, which can be attributed to the reactive MgO inside LBD.

Suitability of commercial superplasticizers for one-part alkali-activated blast-furnace slag mortar

Alkali-activated materials are a low-CO2 alternative for Portland cement in construction. However, one major issue in their use is the poor or varying functionality of the currently available commercial superplasticizers. Especially for one-part (‘just add water’) alkali-activated materials, the number of studies is limited. In this study, one-part alkali-activated mortar was prepared from blast furnace slag by using solid sodium hydroxide as an activator and microsilica as an additional silica source. Comparison of commonly used superplasticizer types revealed that lignosulfonate, melamine, and naphthalene-based superplasticizers are more efficient than the currently most used polyacrylate and polycarboxylate-superplasticizers. Lignosulfonate-based superplasticizer was overall best-performing: it improved significantly the workability (+41% spread, −51% yield stress, −27% viscosity), setting time (+70%), and compressive strength (+19%) at a 0.5 wt% dose. When the amount of water and superplasticizer were optimized, compressive strength of mortar could be doubled (from 19 to 40 MPa at 28 d).