Blast Furnace Slag Mortar Research Articles

Effects of γ-C2S on the Properties of Ground Granulated Blast-Furnace Slag Mortar in Natural and Accelerated Carbonation Curing

γ-Dicalcium silicate (γ-C2S) is known for its strong carbonation reactivity by which it can capture atmospheric carbon dioxide (CO2), thus, it can be used in construction industries. This paper aims to study the effects of γ-C2S on the properties of ground granulated blast-furnace slag (GGBFS) containing cement mortar and paste in natural and accelerated carbonation curing. The compressive strength of 5% γ-C2S (G5) added to GGBFS cement mortar is higher compared with the control one in natural carbonation (NC) and accelerated carbonation (AC) up to 14 days of curing, but once the curing duration is increased, there is no significant improvement with the compressive strength observed. The compressive strength of AC-cured mortar samples is higher than that of NC. The scanning electron microscopy (SEM) images show that the AC samples exhibited compact, uniform, and regular morphology with less in porosity than the NC samples. X-ray diffraction (XRD) and Fourier transform infra-red (FT-IR) results confirmed the formation of calcium carbonate (calcite: CC) as carbonated products in paste samples, which make the surface dense and a defect-free matrix result in the highest compressive strength. The decomposition of AC samples around 650–750 °C revealed the well-documented and stable crystalline CC peaks, as observed by thermogravimetry analysis (TGA). This study suggests that γ-C2S added to concrete can capture atmospheric CO2 (mostly generated from cement and metallurgy industries), and make the concrete dense and compact, resulting in improved compressive strength.

Influence of low-temperature curing on the mechanical strength, hydration process, and microstructure of alkali-activated fly ash and ground granulated blast furnace slag mortar

Alkali‑activated concrete, a green building material with excellent mechanical properties and durability, is the most promising building material for use in the continuously increasing number of infrastructure construction projects in cold regions. However, at present, there are few studies evaluating the performance of alkali‑activated concrete cured in a low-temperature environment. In the present work, 50% fly ash (FA) and 50% ground granulated blast furnace slag (GGBFS) were used as composite cementitious materials to prepare four groups of alkali‑activated mortar samples, which were cured at −5 °C, 0 °C, 5 °C and 20 °C. The effects of low curing temperature (−5 °C, 0 °C, and 5 °C) on the mechanical properties, hydration process, hydration products, pore characteristics and microstructure of alkali‑activated FA and GGBFS (AAFG) mortar were investigated with uniaxial compressive strength tests, resistivity measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). The results indicated that low-temperature curing reduced the compressive strength of the alkali‑activated mortar. The resistivity curves of the four groups of samples well reflected the influence of different curing temperatures on the early hydration process of the alkali‑activated binder. A low curing temperature delayed the hydration process and showed an obvious “hysteresis effect”. The lower the curing temperature was, the more significant the effect. The hydration reaction was not stopped when the sample was cured at −5 °C. Low curing temperatures did not change the type of hydration products but changed their amount. Low-temperature curing resulted in the formation of harmful pores.

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.

The curing times effect on the strength of ground granulated blast furnace slag (GGBFS) mortar

This research aims to study the effects of setting times and soundness of the GGBFS cement for various fineness of ground granulated blast furnace slag (GGBFS) as partial replacement ordinary Portland cement (OPC) at 20 wt%, 40 wt% and 50 wt%, on the compressive and flexural strength of GGBFS mortar. A total of 54 test samples and 9 controlled samples of prisms were cast and cured for 7, 28 and 90 days before compressive and flexural strength test. However, the setting times and the soundness test results of GGBFS cement and controlled OPC were investigated. The results showed that GGBFS cement with higher Blaine’s fineness with 40 wt% replacement had the highest compressive strengths of 57.29 MPa and 69.70 MPa at 28 and 90 days of curing duration respectively. Moreover, outperformed OPC with compressive strengths of 55.67 MPa and 61.49 MPa at 28 and 90 days of curing duration, respectively. Setting times decreased with a higher fineness of GGBFS cement, but increased with greater percentages of GGBFS cement, while the average expansion of soundness test is within acceptable limits. Therefore, it can be concluded from this study that curing duration increases the strength of mortar and GGBFS cement is useful for partial replacement of OPC.

Effects of Mineral Admixtures on Pore Structure and Compressive Strength of Mortar Contaminated Chloride

This study evaluates the mechanical properties of performance fly ash, silica fume, metakaolin and blast furnace slag mortars due to contaminated chloride. The compressive strength and pore structures at water-to-binder ratios of 0.4, 0.5 and 0.6 are investigated. The result, in general, showed mineral admixtures mortar contaminated chloride improved compressive strength and porosity but different rates depending on their binder type.

One-part blast furnace slag mortars activated with almond-shell biomass ash: A new 100% waste-based material

The use of almond-shell biomass ash (ABA) as an alkali source in one-part blast furnace slag (BFS) mortars activation was investigated for the first time. The chemical composition of ABA revealed high alkalinity ash to be composed mainly of K2O and CaO. The one-part 100% waste-based mortars and pastes were studied by mechanical and thermogravimetric tests. The compressive strength values of the newly designed materials were higher than the mortars fabricated with commercial products (36.4 versus 21.2 MPa). The formation of C-S-H/(C,K)-A-S-H gels took place in the thermogravimetric studies. The use of ABA in mortars proved an interesting alternative to chemical reagents in alkali activated cements.

Synthesis of Alkali-Activated Binary Blended Silico-Manganese Fume and Ground Blast Furnace Slag Mortar

This study was aimed at developing novel and sustainable alkali-activated binder of silico-manganese fume (SMF) and ground blast furnace slag (BFS) at room temperature. The level of BFS substitution was varied from 0 - 50% and activation was done using 10 M NaOH and Na2SiO3 of an initial silica modulus of 3.3. The Na2SiO3/10MNaOH ratio was kept constant at 2.5. The setting time, flow and compressive strength were evaluated and complemented with the microstructural and bond characteristics of the product. A 28-day strength of 45 MPa was achieved with the base materials ratio (BFS/(BFS+SMF)) of 0.3. The activation of SMF resulted in the formation of glaucochroite and nchwaningite minerals (C-Mn-S-H) while the inclusion of BFS influenced the formation of potassium feldspar (K-A-S-H), gehlenite hydrate (C-A-S-H) and additional C-S-H due to later-age contribution of hydration of BFS. The Manganese in SMF contributed significantly to the consistency of the mixture while lime in BFS improved the microstructure thereby enhancing strength of the developed alkali-activated binder.

Influence of sodium silicate powder silica modulus for mechanical and chemical properties of dry-mix alkali-activated slag mortar

Sodium silicate powders with different SiO2/Na2O (silica modulus) were characterized by solubility rate, pH, and chemical structure (by 29Si MAS-NMR) and compared in the preparation of one-part (or dry-mix) alkali-activated blast furnace slag mortar. The low SiO2/Na2O indicated the beneficial presence of less-polymerized silica (Q1 and Q2 Si environments) and thus faster dissolution. Consequently, using sodium silicates with SiO2/Na2O of 0.9, 2.1, and 3.4 resulted 28 d compressive strengths of 103, 80, and 2 MPa, respectively, with increasing setting time and decreasing heat release in isothermal calorimetry. Adjustment of activator SiO2/Na2O from 2.1 or 3.4 to 0.9 by adding NaOH powder resulted increased or decreased mechanical properties of mortar, respectively, depending on the initial silica modulus. These properties were not, however, similar to those obtained with sodium silicate having SiO2/Na2O of 0.9 originally. Depending on the case, the added NaOH can be consumed for dissolving sodium silicate activator, slag, or the forming (C,N)-(A)-S-H gel.

Alkali silica reaction of waste glass aggregate in alkali activated fly ash and GGBFS mortars

This paper evaluates the alkali silica reaction (ASR) susceptibility of waste glass aggregate in alkali activated fly ash and ground granulated blast furnace slag (GGBFS) mortars as compared to that in ordinary Portland cement (OPC) mortars. In accelerated mortar bar tests, glass fine aggregate showed much lower expansions in alkali activated fly ash and GGBFS blended mortars than in OPC mortars or alkali activated neat fly ash or GGBFS mortars. Glass aggregate was classified as non-reactive with alkali activated fly ash and GGBFS blends according to 10-day and 21-day expansion limits of the Australian Standard. Microstructural studies revealed that glass aggregate produced typical ASR products in OPC mortars and alkali activated neat GGBFS mortars due to the presence of high calcium. However, alkali activated fly ash and GGBFS blended mortars produced reaction products of low Ca/Si and high Al/Si ratios that reduced the dissolution of reactive silica present in glass aggregate causing less expansions. The observed expansion of the alkali activated neat fly ash mortar is attributed to the analcime phase found in the X-Ray diffraction of this mortar.

Carbon Dioxide Absorption by Blast-Furnace Slag Mortars in Function of the Curing Intensity

Climate change is one of the most important issues affecting the future of the planet. Then, a lot of resources are being used to actively work on climate change issues and greenhouse gas reduction. Greenhouse gas (GHG) emissions are monitored by each country and reported yearly to the United Nations Framework Convention on Climate Change (UNFCCC). The Intergovernmental Panel on Climate Change (IPCC) published the document entitled “2006 IPCC Guidelines for National Greenhouse Gas Inventories” to provide the calculation rules and the way to inform the UNFCCC of the national GHG emissions. Currently, this document does not give a procedure to calculate the net carbon dioxide emissions to the atmosphere due to the Portland cement clinker production. The purpose of this paper is to get reliable relationships to better calculate the CO2 uptake by ground granulated blast-furnace slag (GGBFS) mortars. The application of this material cured under controlled conditions could help minimize environmental impact. Carbonation coefficient versus 28-day compressive strength relationship of mortars elaborated with GGBFS and cured underwater for 0, 1, 3, 7, 14, or 28 days were obtained. The main finding is the extreme sensitivity of the GGBFS mortars to the curing intensity and, therefore, they can be used cured under controlled conditions to minimize carbon footprints.

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).

Mechanical and microstructural properties of alkali-activated slag and slag + fly ash mortars exposed to high temperature

In this study, changes in the mechanical and microstructural properties of alkali-activated blast furnace slag (BFS) and BFS + fly ash (FA) blended mortars exposed to 25, 400, 600 and 800 °C temperatures are investigated. The alkali-activated mortars using the replacement ratios of 0, 25 and 50% FA by weight of BFS together with the activators are produced in addition to the control mortars produced by only cement. Three different optimum Ms (SiO2/Na2O ratio of activators) values of 0.50, 0.75 and 1.00 are determined for the alkali-activated mortars. The FA substitution by BFS increases the high temperature resistance of alkali-activated BFS mortars.

Alkali Activated Slag Mortars Provide High Resistance to Chloride-Induced Corrosion of Steel

The pore solutions of alkali-activated slag cements and Portland-based cements are very different in terms of their chemical and redox characteristics, particularly due to the high alkalinity and high sulfide content of alkali-activated slag cement. Therefore, differences in corrosion mechanisms of steel elements embedded in these cements could be expected, with important implications for the durability of reinforced concrete elements. This study assesses the corrosion behaviour of steel embedded in alkali-activated blast furnace slag (BFS) mortars exposed to alkaline solution, alkaline chloride-rich solution, water, and standard laboratory conditions, using electrochemical techniques. White Portland cement (WPC) mortars and blended cement mortars (white Portland cement and blast furnace slag) were also tested for comparative purposes. The steel elements embedded in immersed alkali-activated slag mortars presented very negative redox potentials and high apparent corrosion current values; the presence of sulfide reduced the redox potential, and the oxidation of the reduced sulfur-containing species within the cement itself gave an electrochemical signal that classical electrochemical tests for reinforced concrete durability would interpret as being due to steel corrosion processes. However, the actual observed resistance to chloride-induced corrosion was very high, as measured by extraction and characterisation of the steel at the end of a 9-month exposure period, whereas the steel embedded in white Portland cement mortars was significantly damaged under the same conditions.

Influence of alkali ions on the efficiency of shrinkage reduction by polypropylene glycol in alkali activated systems

Alkali-activated materials, especially when activated by water glass, exhibit substantial drying shrinkage that hinders their broader industrial application. The effect of shrinkage-reducing admixtures (SRA), based on polypropylene glycol, on drying shrinkage of alkali-activated blast furnace slag (BFS) mortars was examined. The determination of SRA efficiency and the influence of potassium alkali activators with varying silicate modulus on drying shrinkage characteristics were studied. It was observed that a high amount of alkalis positively affected the effect of SRA. The higher the amount of alkalis was, the lower was the drying shrinkage. The paper further discusses and underlines the role of the amount of alkali ions on the properties of alkali-activated BFS systems.

Olive-stone biomass ash (OBA): An alternative alkaline source for the blast furnace slag activation

Alkali activated materials (AAM) are being investigated as an alternative binder that could be more eco-efficient than Portland cement. The effect of olive-stone biomass ash (OBA) on the activation of blast furnace slag (BFS) was studied. The mechanical behaviour of mortars in which OBA was replaced, or added to, BFS were compared to those found for BFS mortars activated with potassium hydroxide (KOH) and sodium hydroxide (NaOH) solutions in the range of 4–12 mol·kg−1. The results showed the high efficiency of OBA as activating reagent because it provided similar, or higher, strengths when compared to the alkali hydroxide activating solutions. The microstructural characteristics of the new binding OBA/BFS systems were assessed by X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM) and mercury intrusion porosimetry (MIP). These systems showed lower mean pore diameter and scarcer formation of zeolite structures when compared to KOH/BFS systems. These promising results demonstrated the viability of the use of these type of ashes as activating reagents in AAM.

Effect of curing time on granulated blast-furnace slag cement mortars carbonation

Currently, ground granulated blast-furnace slag cements use in cement-based materials is being increasing because perform well in marine and other aggressive environments. However, mortars and concretes made of this type of cement exhibit high carbonation rates, particularly in badly cured cement-based materials and when high blast-furnace slag contents are used. Concrete reinforcement remains passive but can be corroded if the pore solution pH drops as a result of the carbonation process promoting the reinforced concrete structure failure during its service life. Results show the very sensitive response to wet-curing time of slag mortars with regard to the natural carbonation resistance. Then, a minimum period of 3–7 days of wet curing is required in order to guarantee the usual projected service life in reinforced concrete structures. In this work, estimation models of carbonation depth and carbon dioxide diffusion coefficient in ground granulated blast-furnace slag mortars as a function of the curing period and the amount of ground granulated blast-furnace slag are proposed. This information will be useful to material and civil engineers in designing cement-based materials and planning the required curing time depending on their ground granulated blast-furnace slag content.

Comparison of alkali and silica sources in one-part alkali-activated blast furnace slag mortar

Abstract Alkali-activated materials (AAMs) are one of the alternative low-CO2 binders. One-part AAMs, (that is, mixing a solid precursor with a solid alkali activator and adding water) have recently attracted increasing interest. The purpose of this study is to examine if fast-dissolving solid synthetic sodium metasilicate could be replaced by a combination of sodium hydroxide and slow-dissolving silica derived from rice husk ash or microsilica in the preparation of one-part alkali-activated blast furnace slag mortar. The replacement would improve the carbon footprint and the cost efficiency of the binder. The results demonstrate that silica availability significantly affects compressive strength development as a function of time or mixture composition. The highest compressive strength (107 MPa, 28 d) was obtained with fast-dissolving silica. Furthermore, setting times could be adjusted based on the mix composition, and the durability of mortar remained good after 120 freeze–thaw cycles. The results highlight the overall effect of silica availability on the fresh and hardened properties of one-part AAMs.

Influence of Calcined Mine Tailings on the Properties of Alkali Activated Slag Mortars

Influence of copper mine tailings on properties of soda activated ground granulated blast furnace slag mortars and pastes was investigated. Calcination of copper mine tailings was found to be a method of increasing their pozzolanic activity. Material calcined at 750°C possessed highest pozzolanic activity. So obtained material can be used as a partial substitution of ground granulated slag in soda activated blends. Introduction of calcined copper mine tailings decrease strength up to 28 days, but after 56 days strength results are similar or even higher comparing to control samples. Phase composition of hydrated material is not affected significantly by the presence of calcined copper mine tailings.

Experiments on Tensile and Shear Characteristics of Amorphous Micro Steel (AMS) Fibre-Reinforced Cementitious Composites

Amorphous micro-steel (AMS) fibre made by cooling of liquid pig iron is flexible, light and durable to corrosion, then to be compatible with high flowable and disperable states of mixing as well as high ductile post-cracked performances to apply in fibre-reinforced cementitious composites. In the current research, AMS fibre-reinforced cementitious composites based on cement and alkali-activated ground granulated blast furnace slag mortars were newly manufactured and evaluated for the strength and ductile characteristics mainly by direct tensile and shear transfer tests in the variation in the volume of AMS fibres with two different lengths of 15.0 and 30.0 mm. As a result, it was found that 1.0–1.25% fibre volume fractions were recommendable for AMS fibre-reinforced cementitious composites to maximize direct tensile strength, ductile tensile strain, and shear strength of the composites. However, a further fraction of AMS fibre lowered these mechanical characteristics. Simultaneously, it could be said that AMS fibre-reinforced cementitious composites exhibited up to about 3.7 times higher in direct tensile strength and up to 2.3 times higher in shear strength, compared to AMS fibre-free specimens.

Evaluation of the combined deterioration by freeze–thaw and carbonation of mortar incorporating BFS, limestone powder and calcium sulfate

The durability performance of cementitious material is traditionally based on assessing the effect of a single degradation process. However, this study investigates the coupled deterioration properties of mortar incorporating industrial solid waste—ground granulated blast furnace slag (BFS) and different mineral admixtures, such as calcium sulfate (CS) and limestone powder (LSP). The combined deterioration properties caused by carbonation and frost damage in the mortar sample were experimentally investigated with respect to accelerated carbonation and freeze–thaw tests. Different degrees of deterioration, i.e. after subjected to 12, 30 and 60 freeze–thaw cycles, were induced in the freeze–thaw tests. The experimental investigation of single degradation revealed that the compressive strength, frost resistance and carbonation resistance decrease as the BFS replacement ratio increases by weight from 0 to 45%. The less amount of CH in the BFS cement leads to the carbonation progress more easily. Moreover, to achieve the same strength as ordinary Portland cement, 2 wt% CS and 4 wt% LSP in the BFS mortar are required. However, the data shows that incorporating LSP into the BFS mortar produces a lower frost resistance. The combined damage tests revealed that different deterioration degrees resulting from 12, 30 and 60 freeze–thaw cycles slightly decreased the carbonation resistance, which is related to the decrease in the inkbottle pore volume due to its water retention characteristics. Simultaneously, the pre-carbonation deterioration could effectively decrease the surface mass scaling of the freeze–thaw and the pore structure undergoes densification due to pre-carbonation.