Alkali-activated Blast Furnace Slag Pastes Research Articles

Compressive Strength and Microstructure of Carbide Slag and Alkali-Activated Blast Furnace Slag Pastes in China

The alkali-activated blast furnace slag is attracting significant attention in replacing Portland cement due to several characteristics similar to cement hydration. However, there are a few practical problems with commercial alkali activators, such as the fast setting time, relatively high costs, and significant CO2 emissions during preparation. Thus, discovering industrial residues possessing inherent alkalinity are urgent. This study proposes the use of carbide slag at levels of 0%, 5%, 10%, 15%, 20%, and 30% and alkali at levels of 1%, 2%, 3%, 4%, 5%, 6%, 8%, and 10% activated blast furnace slag. The compressive strength and microstructure of carbide slag and alkali-activated blast furnace slag (CAB) pastes were examined using X-ray diffraction analysis (XRD), Differential Scanning Calorimetry/Thermogravimetric Analysis (DSC/TG), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). The results revealed that the addition of carbide slag produced more hydrotalcite-like phase as well as decreased the content of ettringite (AFt) and the calcium–silicate–hydrate (C-S-H) gel, which decreased the compressive strength of the CAB pastes. At the age of 28 days, when the dosage was 5%, 10%, 15%, 20%, and 30%, the compressive strength of CAB mixes decreased by 2.1%, 7.1%, 9.2%, 9.8%, and 28.1%, respectively. The addition of NaOH promoted the formation of AFt, and there was an optimum level of NaOH corresponding to the high compressive strength of paste. At the age of 3 days and 7 days, the compressive strength reached its maximum at the dosage of 6% NaOH, which was 24.8 MPa and 36.3 MPa, respectively. However, at the ages of 14 days and 28 days, the compressive strength increased as the dosage of NaOH increased to 5%, which was 43.3 MPa and 44.5 MPa, respectively. The water curing could both enhance the early and later strength, the compressive strength of 23.3 MPa was gained at 3 days, and this increased by 16.3%, 24.0% and 36.9% at 7 days, 14 days and 28 days, respectively. Therefore, water curing was suitable for the strength development of CAB pastes.

Effect of Waste Ceramic Powder on Properties of Alkali-Activated Blast Furnace Slag Paste and Mortar.

Every year, ceramic tile factories and the iron smelting industry produce huge amounts of waste ceramic tiles and blast furnace slag (BFS), respectively. In the field of construction materials, this waste can be used as a raw material for binders, thus reducing landfill waste and mitigating environmental pollution. The purpose of this study was to mix waste ceramic powder (WCP) into BFS paste and mortar activated by sodium silicate and sodium hydroxide to study its effect on performance. BFS was partially replaced by WCP at the rate of 10–30% by weight. Some experimental studies were conducted on, for example, the fluidity, heat of hydration, compressive strength testing, ultrasonic pulse velocity (UPV), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), electrical resistivity, sulfuric acid attack, and chloride ion diffusion coefficient. Based on the results of these experiments, the conclusions are: (1) increasing the amount of waste ceramic powder in the mixture can improve the fluidity of the alkali-activated paste; (2) adding waste ceramic powder to the alkali-activated mortar can improve the resistance of the mortar to sulfuric acid; (3) adding waste ceramic powder to the alkali-activated mortar can increase the diffusion coefficient of chloride ions; (4) the early strength of alkali-activated mortar is affected by the Ca/Si ratio, while the later strength is affected by the change in the Si/Al ratio.

Preparation and characterization of road alkali-activated blast furnace slag paste

Alkali-activated Materials (AAM) has been applied in road engineering as an environmentally friendly material in recent years. This study prepared road alkali-activated blast furnace slag (AABFS) paste in different mixture ratios based on an orthogonal test scheme. The fluidity, setting time, mechanical strengths, and other properties were systematically evaluated to determine the optimum mixture ratio of paste. Finally, the microstructural characteristics and reaction mechanism of AABFS paste were investigated. The results showed that changes in the mass ratio of sodium hydroxide and blast furnace slag (mSH/mSL) have great influence on the performance parameters, including the fluidity, setting time, flexural strength, and compressive strength. Results at the microstructural level indicated that the structure of the AABFS paste specimen prepared at the optimum ratio is more compact and uniform, and the AABFS paste can be applied effectively in road-grouting reinforcement.

Estudio de la sensibilidad a su propia deformación de escorias de alto horno activadas alcalinamente y reforzadas con fibra de carbono

The addition of carbon fibres is used in cement composite materials with a twofold objective: enhancement of their mechanical performance, and functionalisation of the composite, e.g. as strain sensor. Alkali-activated blast furnace slag pastes were reinforced with carbon fibres, which increased bending and compressive strengths, controlled drying shrinkage, and their resistivity could be related to strains during cyclic compression tests. However, in order to optimise this strain self-sensing property, changes in water saturation of samples are necessary, because fully saturated samples did not work properly as a strain sensor.

알칼리 활성화된 고로슬래그 페이스트의 물리화학적 특성 및 이산화탄소 흡수능 평가

PURPOSES: In this study, alkali-activated blast-furnace slag (AABFS) was investigated to determine its capacity to absorb carbon dioxide and to demonstrate the feasibility of its use as an alternative to ordinary Portland cement (OPC). In addition, this study was performed to evaluate the influence of the alkali-activator concentration on the absorption capacity and physicochemical characteristics. METHODS: To determine the characteristics of the AABFS as a function of the activator concentration, blast-furnace slag was activated by using calcium hydroxide at mass ratios ranging from 6 to 24%. The AABFS pastes were used to evaluate the carbon dioxide absorption capacity and rate, while the OPC paste was tested under the same conditions for comparison. The changes in the surface morphology and chemical composition before and after the carbon dioxide absorption were analyzed by using SEM and XRF. RESULTS: At an activator concentration of 24%, the AABFS absorbed approximately 42g of carbon dioxide per mass of paste. Meanwhile, the amount of carbon dioxide absorbed onto the OPC was minimal at the same activator concentration, indicating that the AABFS actively absorbed carbon dioxide as a result of the carbonation reaction on its surface. However, the carbon dioxide absorption capacity and rate decreased as the activator concentration increased, because a high concentration of the activator promoted a hydration reaction and formed a dense internal structure, which was confirmed by SEM analysis. The results of the XRF analyses showed that the CaO ratio increased after the carbon dioxide absorption. CONCLUSIONS : The experimental results confirmed that the AABFS was capable of absorbing large amounts of carbon dioxide, suggesting that it can be used as a dry absorbent for carbon capture and sequestration and as a feasible alternative to OPC. In the formation of AABFS, the activator concentration affected the hydration reaction and changed the surface and internal structure, resulting in changes to the carbon dioxide absorption capacity and rate. Accordingly, the activator ratio should be carefully selected to enhance not only the carbon capture capacity but also the physicochemical characteristics of the geopolymer.

Effect of Silicate Content on the Properties of Alkali-Activated Blast Furnace Slag Paste

The effect of silicate content (SiO2/Na2O) of an activator on physical and mechanical properties of alkali-activated blast furnace slag paste has been investigated. The paste was produced by activating blast furnace slag with sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) solution. The SiO2/Na2O ratio varied from 0.2 to 1.2. The test specimens were cast and cured in water (fully immersed condition) at room temperature and the direct compressive strength at the age of 3, 7, 14, 21, 28 days were obtained. It has been observed that the compressive strength and ultrasonic pulse velocity of test specimen increases with the increase in silicate content up to a silicate ratio of 0.8. Compressive strength is found to be a maximum 44.53 MPa at 28 days. It is noticed further that the compressive strength increases with age. It is also observed that the silicate ratio has a significant influence on porosity, water absorption and water sorptivity. The mineralogical and micro-structural changes were studied using XRD and SEM/EDX, while porosity, total pore volume, pore-size distribution, etc., were studied using mercury intrusion porosimetry.

Sorptivity Ratio and Compressive Strength of Alkali-Activated Blast Furnace Slag Paste

Abstract The initial/secondary absorption and compressive strength of alkali-activated slag (AAS) paste has been investigated. Emphasis has been given to secondary absorption of AAS paste based on the method described in ASTM C1585-04 [Standard Test Method for Measurement of Rate of Absorption of Water by Hydraulic Cement Concretes, Annual Book of ASTM Standards, ASTM International, West Conshohocken, PA, 2004, pp. 1–4]. The paste was produced by activating blast furnace slag with sodium hydroxide/potassium hydroxide and sodium silicate solution. The major parameters studied were alkali content, silicate content, and the type of activator. Experimental investigation revealed that initial rate of absorption (Si) and secondary rate of absorption (Ss) decreases with increase in alkali and silicate content up to a certain limit with an increase in compressive strength. The maximum compressive strength was found to be 50.40 MPa for the specimens having lowest sorptivity. It was also found that the sorptivity ratio (Si/Ss) plays a significant role on compressive strength in turn on the durability of AAS composites. This paper is an attempt to introduce the simple method of measuring initial and secondary sorptivity described in ASTM C1585-04 to study the strength and durability of AAS. The microstructure study was carried out using SEM/EDAX.