Ground Granulated Blast Furnace Slag Mortar Research Articles

Alkali-Activated Binders as Sustainable Alternatives to Portland Cement and Their Resistance to Saline Water.

Alkali-activated binders have emerged as promising alternatives to Ordinary Portland Cement (OPC) due to their sustainability features and potential advantages. This study evaluates the durability properties of heat-cured fly ash (FA) and ground granulated blast-furnace slag (GGBFS) geopolymer mortars activated with sodium hydroxide, which were subjected to wet-dry cycling in saline environments. Three series of FA, a FA/GGBFS blend, and GGBFS mortars previously optimized on a compressive strength basis were investigated and compared against two control OPC mixes. Performance indicators such as the water absorption, porosity, flexural strength, and compressive strength were analyzed. The results demonstrate that geopolymer mortars have significantly reduced water absorption and porosity with increasing wet-dry cycles. The compressive strength of the FA/GGBFS mortars also increased from 66.5 MPa (untreated) to 87.9 MPa over 45 cycles. The flexural strength remained stable or improved slightly across all geopolymer mortars. The control OPC specimens experienced significant deterioration, with compressive strength in CEM I 42.5R dropping from 51.8 to 17.1 MPa. These findings highlight the superior durability of geopolymer mortars under harsh saline conditions, demonstrating their potential as a resilient alternative for coastal and marine structures.

Investigation on the properties of sustainable alkali-activated GGBS mortar with nano silica and dredged marine sand: Mechanical, microstructural and durability aspects

In recent years, alkali-activated mortar (AAM) has emerged as a promising alternative to ordinary Portland cement (OPC) due to concerns regarding the environmental impact resulting from cement production, which releases carbon dioxide and degrades the quality of the environment. To address these concerns, researchers have explored the addition of supplementary binder materials to enhance cement properties and mitigate pollution. The effectiveness of these binder materials depends heavily on their chemical composition and fineness. Notably, ground granulated blast furnace slag (GGBS) enhances the strength and durability of the cement. In response to the scarcity of river sand (RS), dredged marine sand (DMS) has gained popularity as a potential substitute within the civil engineering field. Furthermore, the integration of nanomaterials has shown promising improvements in the mechanical and microstructural properties of mortar. Therefore, this study aims to investigate the properties of mortar by incorporating nano silica (NS) within the range of 1% to 7%, varying the molarity from 2 M to 8 M, and substituting RS with DMS. The tests carried out encompass a range of evaluations, including compressive strength, flexural strength, SEM-EDS, XRD, UPV, RCPT, and carbonation analysis, to comprehensively assess the properties of the mortar. The study reveals that the AAM demonstrates optimal performance when 50% of RS is replaced by DMS in the absence of NS. Once this optimal point is determined, further analyses are conducted at this value while varying the concentrations of NS from 1–7%. The experimental results indicate that replacing 50% of RS with DMS and incorporating 6% NS leads to maximum compressive strength (49.2 MPa) and flexural strength (9.36 MPa) in the assessed properties. Furthermore, the incorporation of NS in GGBS-based AAM mixes enhances durability by improving resistance against chloride penetration, reducing water absorption, and minimizing carbonation diffusion. Additionally, the microstructural and mineralogical characterization of GGBS-NS-based AAM specimens demonstrates the formation of C-S-H and C-A-S-H gels as the end products of the reactions.

Alkali-silica reaction of high-magnesium nickel slag fine aggregate in alkali-activated ground granulated blast-furnace slag mortar

The construction industry is presently encountering a significant challenge regarding the shortage supply of natural sands. The use of metallurgical slags as fine aggregates in building materials presents a solution that not only mitigates the over-exploitation of natural sands, but also provides a sustainable and valuable approach for managing industrial solid wastes instead of traditional landfill disposal. This study investigated the alkali-silica reaction (ASR) of air-cooled and water-quenched high-magnesium nickel slag (HMNS) fine aggregates in alkali-activated ground granulated blast-furnace slag (AAS) mortars. The mortars exhibited satisfactory volume stability and structural integrity throughout the 120 days of accelerated mortar bar test. The lab-simulated dissolution test revealed the formation of a thin precipitate layer of sodium silicate hydrate on the surface of HMNS fine aggregates, which contained a significant amount of Mg with Mg/Si ratios ranging from 0.16 to 0.18. The divalent Mg cations were released from the HMNS fine aggregates and served as the pseudo network former to crosslink the ASR gel instead of Ca. This reduced the moisture adsorption capacity and mitigated the expansion of ASR gel.

Fracture toughness evaluation of ground granulated blast furnace slag concrete using experimental study and machine learning techniques

The relationship between mix design and fracture properties of ground granulated blast furnace slag (GGBFS) concrete is complex and influenced by many factors, such as mixture composition. This study evaluates the fracture toughness under mode-I, mode-II, and mixed-mode, performed on centrally straight-notched Brazilian discs. An experimental program generated an extensive database of the fracture toughness of GGBFS mortar, consisting of 143 specimens with different mix designs under different loading angle conditions. Then, a combination of support vector regression (SVR) algorithm and genetic algorithm (GA) as hyperparameter tuner was conducted to develop models for fracture toughness. The SVR algorithm was trained with Radial Basis Function (RBF), polynomial, sigmoid, and linear kernel functions. Based on the Taylor diagram, the models demonstrated robust performance in predicting fracture toughness. The performance metrics indicate that the RBF function is the most reliable model, with R2-score 0.95 and 0.94 for KIC and KIIC, respectively. The importance score of input features was determined with the permutation importance function. The angle between the crack and loading direction is the most influential parameter in the models.

Experiment on the Properties of Soda Residue-Activated Ground Granulated Blast Furnace Slag Mortars with Different Activators.

Soda residue (SR), a solid waste generated in the production of Na2CO3 during the ammonia soda process, with a high pH value of 12, can be used as an activator of alkali-activated ground granulated blast furnace slag (GGBFS) cementitious materials. Three groups of experiments on SR-activated GGBFS mortars were designed in this paper to assess the role of the dominant parameters on fluidity and compressive strength of mortars. The results indicate that for fluidity and mechanical properties, the optimal scheme of SR-activated GGBFS mortars is 16:84–24:76 S/G, 0.01 NaOH/b, 0.05 CaO/b, and 0.50 w/b, with fluidity and compressive strength (28 d) of the mortars being 181–195 mm and 32.3–35.4 MPa, respectively. Between 2.5–10% CaCl2 addition to CaO (5%)-SR (24%)-activated GGBFS mortar is beneficial to the improvement of the compressive strength of C2, whereas the addition of CaSO4 is harmful. The main hydration products of mortars are ettringite, Friedel’s slat, and CSH gels. The results provide a theoretical basis and data support for the utilization of SR.

Experimental investigations on durability characteristics of ground granulated blast furnace slag mortar

Ground Granulated Blast furnace Slag (GGBS), a waste product from steel plants, can be effectively utilized as a pozzolanic material and can be used as a partial replacement to cement leading to sustainable construction practice. Mortar is usually used as a binding and plastering material; hence the chances of exposure to a damaging environment are high than concrete. GGBS mortar should be examined for durability from weathering action, chemical attack, and abrasion to ensure a long-life cycle and less repair and replacement in structures. The present paper is an experimental investigation of the durability properties of GGBS mortar by considering the parameters like water absorption, effective porosity, sorptivity, chemical attacks, abrasion resistance, and chloride ion resistance. This study involves the replacement of Ordinary Portland Cement (OPC) with GGBS in 10%, 20%, 30%, 40%, 50%, 60% and 70%. The test results are compared with OPC mortar and observed a significant enhancement in the durability characteristics of GGBS mortar. Also, it is observed that 50% replacement of cement with GGBS gives an optimum mix considering the strength and durability characteristics.

Hydration-drying interactions in a high-volume ground granulated blast-furnace slag mortar

An experimental study of interactions between hydration and early drying was carried out on a mortar with a GGBFS volume as high as the OPC volume. 1 day after casting, the mortar was subjected to 6-month unidirectional drying in natural surrounding conditions in laboratory. At the end of the exposure period, Portlandite content, water porosity and pore size distribution were found to be not uniform along the material. When approaching the exposed surface, due to the early drying, the material gradually becomes less hydrated, more porous, and less dense. This causes strong gradients of transfer properties between the exposed surface and the core of the material, which facilitates exchanges with the surrounding environment near the surface and lowers the resistance against the penetration of aggressive agents. For instance, it was shown that considering properties only within the core of the material, sheltered from drying, significantly underestimates the risk of carbonation, and thus the risk of corrosion of reinforcement in concrete.

The role of recycled waste glass incorporation on the carbonation behaviour of sodium carbonate activated slag mortar

This study investigates the influences of recycled waste glass powder (RGP) on the carbonation behaviour of sodium carbonate activated ground granulated blast furnace slag (GGBS) mortars. The effect of activator dosages, types and RGP addition on resistance to carbonation are evaluated. The results indicate a high dosage of sodium carbonate or water glass combination as activator always can enhance the ability of resistance to carbonation. Furthermore, the addition of 30% RGP in the GGBS binder system seems to significantly improve the resistance to carbonation of mortars. The carbonation shrinkage is reduced after RGP incorporation; at the same time, a higher strength performance is observed. The RGP in sodium carbonate activated GGBS blends shows no influence on the species of reaction products. However, after carbonation, the sample containing RGP promotes the formation of nahcolite, while less bound water loss and calcium carbonate formation are identified. A high volume of gel pores (<10 nm) is formed in the RGP sample compared to specimens only containing GGBS. These properties contribute to a better resistance to carbonation for RGP containing sodium carbonate activated GGBS mortars.

Impact of sodium silicate solution chemistry on product formation and jelly hardening of alkali-activated GGBS mortars

This study investigated the effect of silicate modulus (M = silicon dioxide (SiO2)/sodium oxide (Na2O) by mass) and activator content S (mass proportion of sodium oxide and silicon dioxide to ground granulated blast-furnace slag (GGBS)) of sodium silicate (SS) solution on the compressive strength of alkali-activated GGBS (AAS) mortars. At a given solid content, the specimens activated by SS with modulus of 1.0 and 1.5 had the highest compressive strength. In the case of the same modulus of SS, the compressive strength of the AAS mortars rose linearly and then remained unchanged or declined slightly with the increase in S. The mechanism of the action of SS on AAS was studied using backscattered electron (BSE) and energy-dispersive spectroscopy (EDS). The BSE image of AAS shows that GGBS particles are tightly bonded to the surrounding hardened, jelly-like slurry, and that the structure of the GGBS particles in the AAS slurry is intact without an apparent hydrating layer around it. EDS analysis revealed that only active materials in the GGBS, mainly calcium, are dissolved to participate in reaction, and that dissolving these materials does not damage the GGBS structure. S is solidified by these active materials, which embed the GGBS particles therein to form a whole.

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.

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.

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.

Evaluation of the eco-friendly crushed waste oyster shell mortars containing supplementary cementitious materials

The ever-increasing demand for natural aggregates in the concrete industry has resulted in substantial consumption of a dwindling supply of natural resources, leading to irreversible environmental damage. One solution to solve this problem is through the use of waste materials as alternatives to natural aggregates. In this study, 30% of natural river sand was replaced by crushed waste oyster shells (WOS). Full cement (control), different proportions (20%, 30%, and 40%) of cement replaced by fly ash (FA), and ground granulated blast-furnace slag (GGBS) were used. The hardened densities, mechanical properties, durability-related properties, microstructures, and sustainability of the WOS–Control, WOS–FA, and WOS–GGBS mortars were investigated. The test results indicated that, because of the low pozzolanic reaction activity, the inclusion of FA and GGBS decreased the hardened densities and mechanical properties of early-age crushed WOS mortars. Scanning electron microscopy with energy dispersive X-ray spectroscopy analyses indicated low hydration degrees of FA and GGBS in the early stage. These reductions decreased with increasing curing time. The secondary hydration products generated by supplementary cementitious materials considerably filled and compacted the microstructures of the WOS mortars in the later stage. The crushed WOS mortars with FA and GGBS had approximately identical hardened densities and mechanical behaviors to the control mortar. The chloride ion penetration of these blended samples decreased rapidly. The use of these waste materials would offset the demand for natural fine aggregate and cement, decreasing both CO2 emissions and associated costs. A greener mortar with adequate engineering properties could be produced by incorporating FA and GGBS and crushed WOS in limited quantities.

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.

Activated slag as partial replacement of cement mortars: Effect of temperature and a novel admixture

Abstract This paper, from the perspective of the precast industry, reports on a study into the activation of mortar mixes with ground granulated blast furnace slag (GGBS) (0, 30, 50, 70%) and cement (CEM I 42.5R) using temperature (ambient (20 °C) and moderate (35 °C)) and accelerating admixtures (a novel chloride free activator and a commercial admixture) to enhance very early age strength. The discrete temperature activation is found to provide larger improvements in early age strength compared to the use of admixtures. However, irrespective of temperature activation, the novel admixture, in absolute terms, provides greater benefit in strength activation of GGBS mortars compared to the existing commercial admixture. Further, most of the GGBS mortar mixes equalled or surpassed the 28-day strength of the control mixes without any cross-over effects.

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.

Drying shrinkage and microstructure characteristics of mortar incorporating ground granulated blast furnace slag and shrinkage reducing admixture

This paper presents an experimental study of the effects of cement type, ground granulated blast furnace slag (GGBFS) fineness, curing age, and use of shrinkage reducing admixture (SRA) on the drying shrinkage property and microstructure in mortar. The relationship between drying shrinkage and the microstructure characteristics is determined, and an equation that can reasonably predict the drying shrinkage behavior is also proposed according to the dependent variables. The test results revealed that the drying shrinkage evolution can be significantly affected by the GGBFS powder fineness, the cement type – ordinary Portland cement (N), moderate heat Portland cement (M), and low heat Portland cement (L), and the SRA dosage and pore volume of the mortar, but not the curing age (7 and 28days). For mortar samples without GGBFS, the N and L mortar samples exhibited greater shrinkage strain evolution compared to the M sample. For the case of mortar samples incorporating GGBFS, the L mortar sample exhibited the greatest drying shrinkage strain among the investigated mortar mixes. In addition, the drying shrinkage increased significantly with the increase in the GGBFS fineness for the M and L Portland cement mortars. Moreover, the addition of SRA could effectively reduce the drying shrinkage, which is mainly controlled by the pore size distribution and mass loss. In the case of mortar without and with SRA, the drying shrinkage was found to have a high correlation with the pore size ranges of 6–30nm and 0–20nm in diameter, respectively. As a result of the high correlation of pore volume and mass loss observed in this study, the prediction equation for the drying shrinkage of GGBFS mortar is proposed, which verifies good accuracy compared to the test results.

A ternary optimisation of mineral additives of alkali activated cement mortars

The effects of binary and ternary combinations of ground granulated blast furnace slag (GGBFS), fly ash (FA) and silica fume (SF) on compressive strength, flexural strength, water sorptivity, permeable voids and drying shrinkage of steam cured alkali-activated cement (AAC) mortars were investigated within the scope of this study. Also, three-level full factorial experimental design and response surface method were used for the optimisation of the amount of mineral additives by maximising compressive and flexural strengths while minimising drying shrinkage, water sorptivity and permeable voids. The use of ternary blends in AAC provided significant decreases in drying shrinkage, water sorptivity and permeable void content. However, the mechanical performance of ternary blended AAC has been negatively affected compared to GGBFS mortar. Nevertheless, compressive strength values of all binary and ternary blends of AAC were higher than conventional Portland cement mortar. The optimum AAC composition was obtained with a ternary mixture containing 20.3% FA, 18.9% SF and 60.8% GGBFS.

The influence of high-temperature curing on the hydration characteristics of a cement–GGBS binder

The influence of high temperature curing at early ages on the hydration characteristics of a complex binder containing ground granulated blast furnace slag (GGBS) was investigated. High-temperature curing at early ages promotes the early hydration of cement, but it hinders the later hydration, and leads to large pores in the microstructure. So the long-term strength of cement mortar cured under high temperature at early ages is lower than that cured at under 20°C. The hydration of a cement–GGBS complex binder is more sensitive to temperature than is cement, and the strength gain rate of a cement–GGBS mortar is higher than that of cement mortar under high temperature curing at early ages. After high temperature curing at early ages, the later hydration of the cement fraction of the complex binder is hindered, but the later reaction of GGBS fraction is not influenced. The further reaction of GGBS increases the C–S–H gel quantity and improves the pore structure. Therefore, the cement–GGBS mortar gains a high early strength under high temperature curing at early ages, and its strength has a considerable increment at later ages due to the contribution of the reaction of GGBS.

Hydration products and strength development of calcium hydroxide-based alkali-activated slag mortars

To strengthen the practical application of the Ca(OH)2-based alkali-activated (AA) ground granulated blast-furnace slag (GGBS) system, the hydration products, microstructural characteristics and compressive strength development of the AA GGBS mortars were examined for 3 pastes and 21 mortar mixes according to the different auxiliary activators and curing conditions. 7.5% Ca(OH)2 was used for the main activator and either 1% Na2SiO3 or 2% Na2CO3 was added for an auxiliary activator. Test results revealed that the diffraction peaks and molar Si/Ca ratio of the calcium silicate hydrate (CSH) gels were higher for water curing than for air-dried curing and with the addition of auxiliary activators than with the use of the single Ca(OH)2. Furthermore, the addition of auxiliary activators contributed to the stabilization of CSH gels at a long-term age, showing that the molar Si/Ca ratio in CSH gels increased with the hydration time. These growth and intensity of CSH gels were consistent with higher strength development. The strength gain ratio of water-cured mortars was lower at the early ages but higher at the long-term ages than that of the companion air-cured mortars. This trend was independent of the mixing proportions of the mortars and the type of auxiliary activators. Simple equations were also proposed to predict the strength development of Ca(OH)2-based AA GGBS mortars considering the influencing parameters including the curing condition, the type of auxiliary activators and the mixing proportions. The predicted compressive strength of Ca(OH)2-based AA GGBS mortars at different ages was in good agreement with the test results, though the 3-day compressive strength was underestimated.