Hydration of alkali-activated ground granulated blast furnace slag

The hydration of ground granulated blast furnace slag (GGBFS) at 25 °C in controlled pH environments was investigated during 28 days of hydration. GGBFS was activated by NaOH, and it was found that the rate of reaction depends on the pH of the starting solution. The main product was identified as C-S-H, and, in the pastes with high pH, hydrotalcite was observed at later stages of hydration. The pH of the mixing solution should be higher than pH 11.5 to effectively activate the hydration of GGBFS. As deduced from very low electrical conductivity measurements, GGBFS pastes had very tortuous and disconnected pores. The effect of the pH of the aqueous solution on the composition, microstructure and properties of alkali-activated GGBFS pastes are also discussed.     

Design of self-compacting concrete with ground granulated blast furnace slag

Ground granulated blast furnace slag (GGBS), due to its pozzolanic nature, could be a great asset for the modern construction needs, because slag concretes can be of high performance, if appropriately designed. The use of GGBS as a cementitious material as well as fine filler is being increasingly advocated for the production of High Performance Concrete (HPC), Roller Compacted Concrete (RCC) and self compacting concrete (SCC), etc. However, for obtaining the required high performance in any of these concrete composites, slag should be properly proportioned so that the resulting concrete would satisfy both the strength and performance criteria requirements of the structure. The present paper is an effort towards presenting a new mix design methodology for the design of self compacting GGBS concretes based on the efficiency concept. The methodology has already been successfully verified through a proper experimental investigation and the self compacting slag concretes were evaluated for their self compactability and strength characteristics. The results indicate that the proposed method can be capable of producing high quality SCC.     

Reaction progress of alkaline-activated metakaolin-ground granulated blast furnace slag blends

Ground granulated blast furnace slag (ggbf slag) and metakaolin were blended and the combination was activated by sodium hydroxide solution. Two mix series were investigated, one with low NaOH concentration (9–16 wt%) and the other with a high NaOH concentration of 25 wt%. The reaction progress of the alkali-activated pastes was indirectly measured by isothermal calorimetry as well as by ultrasonic measurements. Both methods show an acceleration of the condensation reaction of the alkali-activated blends compared to both single phases. The acceleration effect is more considerable at the higher activator concentration related to a higher reaction degree of the metakaolin.     

In situ imaging of ground granulated blast furnace slag hydration

Ground granulated blast furnace slag (GGBFS) reacts with water in the presence of calcium sulfates and alkalis and is frequently used as a partial replacement for portland cement in concrete. The hydration products are known to be slightly different compositionally and morphologically than those of pure portland cement hydration. In this study, a new technique, soft X-ray transmission microscopy, was used to image the hydration of slag in a variety of solutions to investigate the effects of alkali sulfate and hydroxide activators on the morphology of the resulting hydration products. This microscopy method is unique in that it enables high resolution in situ observation and documentation of the formation of hydration products over time in wet samples at atmospheric pressure.

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Mechanical and cementitious characteristics of ground granulated blast furnace slag and basic oxygen furnace slag blended mortar

Reusing waste materials and reducing carbon emissions are crucial environmental concerns. Ground granulated basic oxygen furnace slag (GGBOS) and ground granulated blast furnace slag (GGBS) are the by-products of the steel industry and has positive effects on the environment because it reduces the problems associated waste disposal. This study reused these two products to completely replace cementitious materials, thus contributing to waste recycling, reducing the production demand for cement, and mitigating carbon emissions. Twelve mixture proportions were designed in this study, including an ordinary Portland mortar (OPM) as the control group and 11 steel/iron slag blended mortar (SISBM) experimental groups for the mechanical and cementitious characteristic experiments. The optimal mixing ratio for SISBM compressive strength ranged from GGBOS (steel slag): GGBS (iron slag) = 3:7 to 5:5 (by weight). At the age of 91 days, the compressive strength of SISBM reached 80–90% compared with that of the control group. Based on the pH values, free-CaO, and microanalysis results, the cementitious characteristics were mainly generated because the GGBOS increased the free-CaO or Ca(OH)₂ concentrations in the SISBM curing water and provided alkaline environments for Ca(OH)₂ to engage in the pozzolanic reaction with the SiO₂ and Al₂O₃ in GGBS, forming crystals such as calcium aluminum silicate hydrate, (C–A–S–H), calcium silicate hydrate (C–S–H), and calcium–magnesium–alumina–silicate (C–M–A–S), which generated strength and strengthened microstructure.     

Strength development and microstructural characteristics of barium hydroxide-activated ground granulated blast furnace slag

In this study, barium hydroxide was proposed as a main activator for ground granulated blast-furnace slag (GGBFS) to produce a strong binder, and it was compared to calcium hydroxide in terms of strength development, reaction products, and microstructure. The Ba(OH)₂-activated GGBFS (BHAS) achieved a significantly higher compressive strength than Ca(OH)₂-activated GGBFS (CHAS), except at 3 days, mainly due to (1) the more formation of hydration products, leading to a notable reduction in pore sizes and volume, and (2) the higher solubility of Ba(OH)₂, resulting in a higher dissolution of GGBFS than that of Ca(OH)₂. Although calcium silicate hydrate (C-S-H) was a major reaction product in both mixtures, the Ca/Si ratios were much different. In the BHAS, the presence of barium ions prohibited the synthesis of ettringite and monocarboaluminate, which formed in the CHAS mixtures, but it induced Ba-bearing products, strätlingite, and the hydrotalcite-like phase. The removal of ettringite was the cause of the lower strength of the BHAS at 3 days compared to that of the CHAS.     

Mechano-chemical modification of cement with high volumes of blast furnace slag

The application of chemical admixtures significantly improves the performance of cement-based materials. Some admixtures can also be used to modify the cement grinding process and induce changes in the structure of cement minerals due to mechano-chemical activation. A reactive silica-based complex admixture was developed for the modification of cement grinding. This paper examines the effect of grinding on the strength of a modified cement containing granulated blast furnace slag in high volumes. According to the test results, mortars based on the modified cement possess a compressive strength of up to 91.7 MPa, a 62% increase over the reference.     

Structure characterization of hydration products generated by alkaline activation of granulated blast furnace slag

The hydration mechanism and mineral phase structures by waterglass activation of granulated blast furnace slag (GBFS) are investigated in detail by means of XRD and FTIR. The results show that the network structures of glassy phases are disintegrated and there is not any new material phase formed in the early stage of hydration processes. With evolution of hydration, the polycondensation reaction takes place between [SiO₄]⁴⁻ and [AlO₄]⁵⁻ species and some new mineral phases are produced. A hydration mechanism for the formation of geopolymer by waterglass activation of GBFS is proposed in detail.     

Mechanical properties of reactive powder concrete containing high volumes of ground granulated blast furnace slag

The mechanical properties (flexural strength, compressive strength, toughness and fracture energy) of steel microfiber reinforced reactive powder concrete (RPC) were investigated under different curing conditions (standard, autoclave and steam curing). Portland cement was replaced with ground granulated blast furnace slag (GGBFS) at 20%, 40% and 60%. Sintered bauxite, granite and quartz were used as aggregates in different series. The compressive strength of high volume GGBFS RPC was over 250 MPa after autoclaving. When an external pressure was applied during setting and hardening stages, compressive strength reached up to 400 MPa. The amount of silica fume can be decreased with increasing amount of GGBFS. SEM micrographs revealed the tobermorite after autoclave curing.     

Efficiency of ground granulated blast-furnace slag replacement in ceramic waste aggregate mortar

From our previous findings, the recycling of ceramic waste aggregate (CWA) in mortar has been proved an ecological means plus an excellent outcome against chloride ingress. The CWAs were porcelain insulator wastes supplied from an electric power company, which were crushed and ground to fine aggregate sizes. In this study, to further develop the CWA mortar as an eco-efficient construction material, ground granulated blast-furnace slag (GGBS) was incorporated. The slag (having the Blaine fineness of 6230 cm²/g) was utilized as a supplementary cementitious material (SCM) at three different replacement levels of 15%, 30%, and 45% of cement by weight. The efficiency of the GGBS on enhancing chloride resistance in the CWA mortars was experimentally assessed by using a silver nitrate solution spray method and an electron probe microanalysis (EPMA). The tests were carried out on mortar samples after immersed in a 5.0% NaCl solution for 24 weeks. Another set of the mortar samples was exposed to a laboratory ambient condition for 24 weeks and then followed with a carbonation test. The test results indicated that the resistance to the chloride ingress of the CWA mortar becomes more effective in proportion to the replacement level of the GGBS. In contrast, the carbonation depth of the CWA mortar increases with the increase of the GGBS. The activeness of the GGBS was also evaluated on the basis of the compressive strength development up to 91 days. Due to its high fineness, the GGBS can be used up to 30% while the high relative strength (more than 1.0) is achieved at all ages.     

Properties of lightweight aggregates produced with cold-bonding pelletization of fly ash and ground granulated blast furnace slag

Pelletization is a worldwide process used in producing artificial aggregates although its usage is not common in Turkey. In this study, lightweight aggregates (LWAs) were manufactured through cold-bonding pelletization of ground granulated blast furnace slag (G) and two types of fly ash with different finenesses (Fly ash A and B). Ordinary Portland cement (PC) was used as a binder at varying amounts from 5 to 20 % by weight. A total of 20 cold-bonded lightweight aggregates were produced at room temperature with different combinations of PC, FA and/or G. The hardened aggregates were tested for specific gravity, water absorption, and crushing strength. Thereafter, lightweight concretes (LWCs) were produced with water to cement ratio of 0.50 and a cement content of 400?kg/m³ by using such lightweight aggregates. The hardened concretes were tested for compressive strength at 28 and 56?days to explore the effect of aggregate types on the compressive strength development. Test results revealed that the amount of cement content had a significant effect on the strength of LWAs which in turn governed the variation in compressive strength of the LWCs. The highest 28 and 56-day compressive strengths of 43 and 51?MPa, respectively were achieved for the concretes including LWAs produced from the blend of 40 % slag, 40 % FA-A and 20 % PC.     

Influence of granulated blast furnace slag on the reaction,structure and properties of fly ash based geopolymer

Ground granulated blast furnace slag (GBFS) has been used to alter the geopolymerisation behaviour of fly ash. The influence of varying amount of GBFS (5–50%) on the reaction kinetics has been studied using isothermal conduction calorimetry. It was observed that the reaction at 27 °C is dominated by the GBFS activation, whereas the reaction at 60 °C is due to combined interaction of fly ash and GBFS. The reaction product of geopolymerisation has been characterised using X-ray diffraction and scanning electron microscopy–X-ray microanalysis. Alumino–silicate–hydrate (A–S–H) and calcium–silicate–hydrate (C–S–H) gels with varying Si/Al and Ca/Si ratio are found to be the main reaction products. Coexistence of A–S–H and C–S–H gel further indicates the interaction of fly ash and GBFS during geopolymerisation. Attempt has been made to relate the microstructure with the properties of the geopolymers.     

Effects of granulated blast furnace slag and superplasticizer type on the fresh properties and compressive strength of self-compacting concrete

This paper presents the results of an experimental investigation carried out to study the effect of granulated blast furnace slag and two types of superplasticizers on the properties of self-compacting concrete (SCC). In control SCC, cement was replaced with 10%, 15%, 20%, and 25% of blast furnace slag. Two types of superplasticizers: polycarboxylate based superplasticizer and naphthalene sulphonate based superplasticizers were used. Tests were conducted for slump flow, the modified slump test, V-Funnel, J-Ring, U-Box, and compressive strength. The results showed that polycarboxylate based superplasticizer concrete mixes give more workability and higher compressive strength, at all ages, than those with naphthalene sulphonate based superplasticizer. Inclusion of blast furnace slag by substitution to cement was found to be very beneficial to fresh self-compacting concrete. An improvement of workability was observed up to 20% of slag content with an optimum content of 15%. Workability retention of about 45 min with 15% and 20% of slag content was obtained using a polycarboxylate based superplasticizer; compressive strength decreased with the increase in slag content, as occurs for vibrated concrete, although at later ages the differences were small.     

The role of hydrotalcite in chloride binding and corrosion protection in concretes with ground granulated blast furnace slag

This paper presents an investigation into the extent and reasons of the observed improvement in performance that ground granulated blast furnace slag (GGBFS) contributes against chloride initiated corrosion. Tests conducted on concretes with blended cement included Rapid Chloride Permeability Test (RCPT), long term ponding, corrosion current monitoring, pore size distribution and X-ray diffraction analyses. Values of the RCPT and corrosion current were significantly reduced as the proportion of GGBFS increased. The results showed only small refinements in pore size distribution, as well as indications of the formation of Friedel’s salt. The tests however, revealed the formation of hydrotalcite as a significant hydration product in GGBFS blends. The results further demonstrated the efficiency of hydrotalcite in binding chloride ions. The authors attribute the reduction in corrosion current to the efficient binding of chloride ions by the hydrotalcite that forms in GGBFS hydration products.     

Improvement of ground granulated blast furnace slag on stabilization/solidification of simulated mercury-doped wastes in chemically bonded phosphate ceramics

This paper investigated the effectiveness of (ground granulated blast furnace slag) GGBFS-added chemically bonded phosphate ceramic (CBPC) matrix on the stabilization/solidification (S/S) of mercury chloride and simulated mercury-bearing light bulbs (SMLB). The results showed that the maximal compressive strength was achieved when 15% and 10% ground GGBFS was added for HgCl(2)-doped and SMLB-doped CBPC matrices, respectively. The S/S performances of GGBFS-added matrices were significantly better than non-additive matrices. As pore size was reduced, the leaching concentration of Hg(2+) from GGBFS-added CBPC matrix could be reduced from 697 microg/L to about 3 microg/L when treating HgCl(2). Meanwhile, the main hydrating product of GGBFS-added matrices was still MgKPO(4).6H(2)O. The improvement of S/S effectiveness was mainly due to physical filling of fine GGBFS particles and microencapsulation of chemical cementing gel.