scholarly journals Strength, Shrinkage and Early Age Characteristics of One-Part Alkali-Activated Binders with High-Calcium Industrial Wastes, Solid Reagents and Fibers

2021 ◽  
Vol 5 (12) ◽  
pp. 315
Author(s):  
Dhruv Sood ◽  
Khandaker M. A. Hossain
Keyword(s):  
Fly Ash ◽  
Sodium Metasilicate ◽  
Cementitious Materials ◽  
Industrial Wastes ◽  
Supplementary Cementitious Materials ◽  
Powder Form ◽  
High Calcium ◽  
Dry Mixing ◽  
Alkali Activated Binders ◽  
Alkali Activated

Alkali-activated binders (AABs) are developed using a dry mixing method under ambient curing incorporating powder-form reagents/activators and industrial waste-based supplementary cementitious materials (SCMs) as precursors. The effects of binary and ternary combinations/proportions of SCMs, two types of powder-form reagents, fundamental chemical ratios (SiO2/Al2O3, Na2O/SiO2, CaO/SiO2, and Na2O/Al2O3), and incorporation of polyvinyl alcohol (PVA) fibers on fresh state and hardened characteristics of 16 AABs were investigated to assess their performance for finding suitable mix compositions. The mix composed of ternary SCM combination (25% fly-ash class C, 35% fly-ash class F, and 40% ground granulated blast furnace slag) with multi-component reagent combination (calcium hydroxide and sodium metasilicate = 1:2.5) was found to be the most optimum binder considering all properties with a 56 day compressive strength of 54 MPa. The addition of 2% v/v PVA fibers to binder compositions did not significantly impact the compressive strengths. However, it facilitated mitigating shrinkage/expansion strains through micro-confinement in both binary and ternary binders. This research bolsters the feasibility of producing ambient cured powder-based cement-free binders and fiber-reinforced, strain-hardening composites incorporating binary/ternary combinations of SCMs with desired fresh and hardened properties.

scholarly journals Fresh State, Rheological and Microstructural Characteristics of Alkali-Activated Mortars Developed Using Novel Dry Mixing Technique under Ambient Conditions

2021 ◽  
Vol 11 (19) ◽  
pp. 8920
Author(s):  
Dhruv Sood ◽  
Khandaker M. A. Hossain
Keyword(s):  
Yield Stress ◽  
Microstructural Analysis ◽  
Supplementary Cementitious Materials ◽  
Powder Form ◽  
Microstructural Characteristics ◽  
Setting Times ◽  
Slump Flow ◽  
Fresh State ◽  
Dry Mixing ◽  
Alkali Activated

Ambient cured alkali-activated mortars (AAMs) are developed through the activation of supplementary cementitious materials (SCMs) by powder form reagents with silica sand using a novel dry-mixing method. The fresh state, rheological, compressive strength and microstructural characteristics of eight AAM mixes are comprehensively investigated. The effects of binary/ternary combinations/proportions of SCMs, different combinations/dosages of powder form reagents and the fundamental chemical ratios (SiO2/Al2O3, Na2O/SiO2, CaO/SiO2 and Na2O/Al2O3) present in the precursors and the reagents are investigated. The AAM mixes obtained compressive strengths ranging from 34 to 42.6 MPa with initial and final setting times between 122 and 458 min and 215 and 483 min, respectively. The yield stress and viscosity of the mixes decreased with the increase in the slump flow spread. All the mixes demonstrated pseudoplastic behavior. The microstructural analysis revealed the formation of more longer polymeric chains comprising Si-Al linkages in N-C-A-S-H/N-A-S-H gels for reagent one (calcium hydroxide:sodium metasilicate = 1:2.5) mixes, which resulted in a lower slump flow, higher yield stress, higher plastic viscosity and quicker setting times compared to their reagent two (calcium hydroxide:sodium sulfate = 2.5:1) counterparts.

scholarly journals Effects of Curing Method on Properties and Salt-Scaling Resistance of Concrete under Lab Testing

2021 ◽  
Author(s):  
Greg Richards ◽  
Medhat Shehata
Keyword(s):  
Fly Ash ◽  
Cementitious Materials ◽  
Supplementary Cementitious Materials ◽  
Alkali Concentration ◽  
Salt Scaling ◽  
High Calcium ◽  
Curing Methods ◽  
Curing Method ◽  
High Alkali ◽  
Scaling Resistance

This paper presents a study of the effect of curing on the salt-scaling resistance of concrete containing supplementary cementitious materials (SCMs) under lab conditions. Two curing methods were examined: moist curing and wrapping in a tight plastic sheet. Wrapping concrete slabs in plastic was adopted to represent curing methods that do not supply the concrete with additional water. The two curing methods produced different scaling results; however, the outcomes did not change in terms of meeting or failing the acceptance limit. Curing in plastic wraps produced higher carbonation depth prior to exposing the sample to the salt solution. This could have contributed, partly, to the higher scaling obtained in wrapped samples, other than the sample with 40% high-calcium fly ash. For this sample, there is evidence that curing using plastic wraps maintained high alkali concentration in the surface concrete, which could have enhanced the pozzolanic activity of the fly ash at the surface.

scholarly journals Strength, Fracture and Durability Characteristics of Ambient Cured Alkali—Activated Mortars Incorporating High Calcium Industrial Wastes and Powdered Reagents

Crystals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1167
Author(s):  
Dhruv Sood ◽  
Khandaker M. A. Hossain
Keyword(s):  
Elastic Modulus ◽  
Fly Ash ◽  
Calcium Hydroxide ◽  
Ultrasonic Pulse ◽  
Industrial Wastes ◽  
Freeze Thaw ◽  
High Calcium ◽  
Alkali Activated ◽  
Ambient Curing ◽  
Class F

Alkali-activated mortars (AAMs) are developed incorporating binary/ternary combinations of industrial wastes comprising of fly ash class C (FA-C), fly ash class F (FA-F) and ground granulated blast furnace slag (GGBFS) with alkaline reagents and silica sand. The use of high calcium precursors, calcium-based powder form reagents, dry mixing method, and ambient curing with performance characterization based on chemical ratios and fracture properties are some novel aspects of the study. The mechanical (dry density, compressive strength, ultrasonic pulse velocity, elastic modulus, fracture/crack tip toughness and fracture energy), durability (shrinkage/expansion and mass change in water and ambient curing conditions, water absorption and freeze-thaw resistance) and microstructural (SEM/EDS and XRD analyses) characteristics of eight AAMs are investigated. The binary (FA-C + GGBFS) mortars obtained higher compressive strengths (between 35 MPa and 42.6 MPa), dry densities (between 2032 kg/m3 and 2088 kg/m3) and ultrasonic pulse velocities (between 3240 m/s and 4049 m/s) than their ternary (FA-C + FA-F + GGBFS) counterparts. The elastic modulus and fracture toughness for mortars incorporating reagent 2 (calcium hydroxide: sodium sulphate = 2.5:1) were up to 1.7 and five times higher than those with reagent 1 (calcium hydroxide: sodium metasilicate = 1:2.5). This can be attributed to the additional formation of C-S-H with C-A-S-H/N-C-A-S-H binding phases in mortars with reagent 2. Ternary mortars exhibited comparatively lower shrinkage/expansion and initial sorptivity indices than their binary counterparts due to the lower geopolymerisation potential of fly ash class F that facilitated the reduction of matrix porosity. All mortar specimens demonstrated 100% or more relative dynamic modulus of elasticity after 60 freeze-thaw cycles, indicating the damage recovery and satisfactory durability due to probable micro-level re-arrangement of the binding phases. This study confirmed the viability of producing cement-free AAMs with satisfactory mechanical and durability characteristics.

scholarly journals Effect of High Calcium Fly Ash, Ladle Furnace Slag, and Limestone Filler on Packing Density, Consistency, and Strength of Cement Pastes

Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 301
Author(s):  
Eleftherios K. Anastasiou
Keyword(s):  
Fly Ash ◽  
Cementitious Materials ◽  
Supplementary Cementitious Materials ◽  
Strength Development ◽  
Ladle Furnace ◽  
Limestone Filler ◽  
Cement Pastes ◽  
High Calcium ◽  
High Calcium Fly Ash ◽  
Furnace Slag

Environmental considerations and technical benefits have directed research towards reducing cement clinker content in concrete, and one of the best ways to do this is to replace cement with supplementary cementitious materials. High calcium fly ash, ladle furnace slag, and limestone filler were investigated as supplementary cementitious materials in cement pastes, and binary mixtures were produced at 10%, 20%, and 30% cement replacement rates for each material. The water requirement for maximum packing and for normal consistency were obtained for each paste, and strength development was determined at 3, 7, 28, and 90 days for the 20% replacement rate. Furthermore, two ternary mixtures at 30% cement replacement were also prepared for maximum packing density and tested for compressive strength development. The results showed that high calcium fly ash decreased cement paste packing and increased water demand but contributed to strength development through reactivity. Ladle furnace slag and limestone filler, on the other hand, were less reactive and seemed to contribute to strength development through the filler effect. The ternary paste with 70% cement, 20% high calcium fly ash, and 10% limestone filler showed equivalent strength development to that of the reference cement paste.

scholarly journals Effects of Curing Method on Properties and Salt-Scaling Resistance of Concrete under Lab Testing

2021 ◽  
Author(s):  
Greg Richards ◽  
Medhat Shehata
Keyword(s):  
Fly Ash ◽  
Cementitious Materials ◽  
Supplementary Cementitious Materials ◽  
Alkali Concentration ◽  
Salt Scaling ◽  
High Calcium ◽  
Curing Methods ◽  
Curing Method ◽  
High Alkali ◽  
Scaling Resistance

This paper presents a study of the effect of curing on the salt-scaling resistance of concrete containing supplementary cementitious materials (SCMs) under lab conditions. Two curing methods were examined: moist curing and wrapping in a tight plastic sheet. Wrapping concrete slabs in plastic was adopted to represent curing methods that do not supply the concrete with additional water. The two curing methods produced different scaling results; however, the outcomes did not change in terms of meeting or failing the acceptance limit. Curing in plastic wraps produced higher carbonation depth prior to exposing the sample to the salt solution. This could have contributed, partly, to the higher scaling obtained in wrapped samples, other than the sample with 40% high-calcium fly ash. For this sample, there is evidence that curing using plastic wraps maintained high alkali concentration in the surface concrete, which could have enhanced the pozzolanic activity of the fly ash at the surface.

Effects of Curing Method on Properties and Salt-Scaling Resistance of Concrete under Lab Testing

2021 ◽  
Author(s):  
Greg Richards ◽  
Medhat Shehata
Keyword(s):  
Fly Ash ◽  
Cementitious Materials ◽  
Supplementary Cementitious Materials ◽  
Alkali Concentration ◽  
Salt Scaling ◽  
High Calcium ◽  
Curing Methods ◽  
Curing Method ◽  
High Alkali ◽  
Scaling Resistance

This paper presents a study of the effect of curing on the salt-scaling resistance of concrete containing supplementary cementitious materials (SCMs) under lab conditions. Two curing methods were examined: moist curing and wrapping in a tight plastic sheet. Wrapping concrete slabs in plastic was adopted to represent curing methods that do not supply the concrete with additional water. The two curing methods produced different scaling results; however, the outcomes did not change in terms of meeting or failing the acceptance limit. Curing in plastic wraps produced higher carbonation depth prior to exposing the sample to the salt solution. This could have contributed, partly, to the higher scaling obtained in wrapped samples, other than the sample with 40% high-calcium fly ash. For this sample, there is evidence that curing using plastic wraps maintained high alkali concentration in the surface concrete, which could have enhanced the pozzolanic activity of the fly ash at the surface.

scholarly journals Influence of Asphalt Emulsion Inclusion on Fly Ash/Hydrated Lime Alkali-Activated Material

Materials ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7017
Author(s):  
Thanon Bualuang ◽  
Peerapong Jitsangiam ◽  
Teewara Suwan ◽  
Ubolluk Rattanasak ◽  
Weerachart Tangchirapat ◽  
...  
Keyword(s):  
Fly Ash ◽  
Construction Material ◽  
Hydrated Lime ◽  
Cementitious Materials ◽  
Supplementary Cementitious Materials ◽  
Asphalt Emulsion ◽  
Structural Formation ◽  
Road Base ◽  
Alkali Activated ◽  
Road Bases

Supplementary cementitious materials have been widely used to reduce the greenhouse gas emissions caused by ordinary Portland cement (OPC), including in the construction of road bases. In addition, the use of OPC in road base stabilization is inefficient due to its moisture sensitivity and lack of flexibility. Therefore, this study investigates the effect of hybrid alkali-activated materials (H-AAM) on flexibility and water prevention when used as binders while proposing a new and sustainable material. A cationic asphalt emulsion (CAE) was applied to increase this cementless material’s resistance to moisture damage and flexibility. The physical properties and structural formation of this H-AAM, consisting of fly ash, hydrated lime, and sodium hydroxide, were examined. The results revealed that the addition of CAE decreased the material’s mechanical strength due to its hindrance of pozzolanic reactions and alkali activations. This study revealed decreases in the cementitious product’s peak in the x-ray diffraction analysis (XRD) tests and the number of tetrahedrons detected in the Fourier transform infrared spectroscopy analysis (FTIR) tests. The scanning electron microscope (SEM) images showed some signs of asphalt films surrounding hybrid alkali-activated particles and even some unreacted FA particles, indicating incomplete chemical reactions in the study material’s matrix. However, the H-AAM was still able to meet the minimum road base strength requirement of 1.72 MPa. Furthermore, the toughness and flexibility of the H-AAM were enhanced by CAE. Notably, adding 10% and 20% CAE by weight to the hybrid alkali-activated binder produced a significant advantage in terms of water absorption, which can be explained by its influence on the material’s consolidation of its matrices, resulting in significant void reductions. Hence, the outcomes of this study might reveal an opportunity for developing a new stabilizing agent for road bases with water-prevention properties and flexibility that remains faithful to the green construction material concept.

scholarly journals Long-Term Strength Development of Fly Ash-Based One-Part Alkali-Activated Binders

Materials ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4160
Author(s):  
Sani Haruna ◽  
Bashar S. Mohammed ◽  
Mubarak M. A. Wahab ◽  
Mubarak Usman Kankia ◽  
Mugahed Amran ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Water Absorption ◽  
Sodium Metasilicate ◽  
Strength Properties ◽  
Experimental Result ◽  
Term Strength ◽  
Alkali Activated Binders ◽  
Alkali Activated

This research aims to study the effect of the dosage of anhydrous sodium metasilicate activator on the long-term properties of fly ash-based one-part alkali-activated binders (OPAAB) cured at ambient conditions. Powdered sodium metasilicate activator was utilized in the range of 8–16% by weight of the fly ash in producing the OPAAB. The properties examined are hardened density, compressive strength, flexural strength, water absorption, efflorescence formation, and microstructural analysis. The experimental result revealed that the binders exhibited excellent long-term strength properties. The compressive strength of the OPAAP is well correlated with its hardened density. The pastes were found to exhibit good soundness characteristics over the long-term. The absorption of water decreases with an increase in the activator dosage from 8–12%, and beyond that, the water absorption relatively remains the same. Field emission scanning electron microscope (FESEM) micrograph revealed uniformly formed solid matrices with the micro-crack present were observed in the samples. The larger pore size promotes the crystallization of the resulting hydrate substances (N, C)-A-S-H gel. The initial dissolution of the OPAAP occurred within the first 30 min. At longer age of curing, mixtures with a higher dosage of powdered activator tend to absorb less water. Strength properties beyond 28 days are considered as the long-term strength.

Effect of ground granulated blast funrnace slag and fly ash on strength, permeability, and under-water abrasion of fine-grained concrete

2020 ◽  
Vol 71 (7) ◽  
pp. 775-788
Author(s):  
Quyet Truong Van ◽  
Sang Nguyen Thanh
Keyword(s):  
Fly Ash ◽  
Concrete Strength ◽  
Cementitious Materials ◽  
Supplementary Cementitious Materials ◽  
Chloride Permeability ◽  
Cement Replacement ◽  
Fine Grained ◽  
Granulated Blast Furnace Slag ◽  
Compressive Strength Test ◽  
Economic Ground

The utilisation of supplementary cementitious materials (SCMs) is widespread in the concrete industry because of the performance benefits and economic. Ground granulated blast furnace slag (GGBFS) and fly ash (FA) have been used as the SCMs in concrete for reducing the weight of cement and improving durability properties. In this study, GGBFS at different cement replacement ratios of 0%, 20%, 40% and 60% by weight were used in fine-grained concrete. The ternary binders containing GGBFS and FA at cement replacement ratio of 60% by weight have also evaluated. Flexural and compressive strength test, rapid chloride permeability test and under-water abrasion test were performed. Experimental results show that the increase in concrete strength with GGBFS contents from 20% to 40% but at a higher period of maturity (56 days and more). The chloride permeability the under-water abrasion reduced with the increasing cement replacement by GGBFS or a combination of GGBFS and FA

scholarly journals A Review of the Mechanical Properties and Durability of Ecological Concretes in a Cold Climate in Comparison to Standard Ordinary Portland Cement-Based Concrete

Materials ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 3467
Author(s):  
Ankit Kothari ◽  
Karin Habermehl-Cwirzen ◽  
Hans Hedlund ◽  
Andrzej Cwirzen
Keyword(s):  
Carbon Dioxide ◽  
Portland Cement ◽  
Ordinary Portland Cement ◽  
Cementitious Materials ◽  
Cold Climate ◽  
Supplementary Cementitious Materials ◽  
Short Exposure ◽  
Chemical Admixtures ◽  
Composite Cements ◽  
Alkali Activated

Most of the currently used concretes are based on ordinary Portland cement (OPC) which results in a high carbon dioxide footprint and thus has a negative environmental impact. Replacing OPCs, partially or fully by ecological binders, i.e., supplementary cementitious materials (SCMs) or alternative binders, aims to decrease the carbon dioxide footprint. Both solutions introduced a number of technological problems, including their performance, when exposed to low, subfreezing temperatures during casting operations and the hardening stage. This review indicates that the present knowledge enables the production of OPC-based concretes at temperatures as low as −10 °C, without the need of any additional measures such as, e.g., heating. Conversely, composite cements containing SCMs or alkali-activated binders (AACs) showed mixed performances, ranging from inferior to superior in comparison with OPC. Most concretes based on composite cements require pre/post heat curing or only a short exposure to sub-zero temperatures. At the same time, certain alkali-activated systems performed very well even at −20 °C without the need for additional curing. Chemical admixtures developed for OPC do not always perform well in other binder systems. This review showed that there is only a limited knowledge on how chemical admixtures work in ecological concretes at low temperatures and how to accelerate the hydration rate of composite cements containing high amounts of SCMs or AACs, when these are cured at subfreezing temperatures.

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