Alkali-activated Mortars Research Articles

Carbonation Resistance of Mortar Mixed with Electrolysis Alkaline Aqueous Solution and Blast Furnace Slag

Cement production is the primary source of global CO2 emissions in the construction industry. Blast furnace slag (BFS) has been examined as a potential substitute for cement to reduce CO2 emissions. In addition, this substitution increases the long-term strength and improves the chemical resistance of mortar. However, a glassy film is formed on the surface of BFS while it is generated as a byproduct, lowering the initial strength of mortar. Notably, this film is destroyed in an alkaline environment. Thus, several studies have used solutions with various alkali activators. However, alkali activators are unsafe, as they are strong alkaline materials, and have low economic efficiency. This study experimentally improved the initial hydration reactivity of a mortar containing BFS as a substitute for cement, thereby improving its initial strength. We observed an increase in carbonation resistance. In addition, this study focused on evaluating the compressive strength and carbonation resistance of mortar prepared using BFS and alkaline water obtained from the electrolysis of a K2CO3 electrolyte. Results show that alkali-activated mortar using an electrolyzed alkaline aqueous solution has higher strength and contains more hydration products than that using conventional mixing water.

Utilization of Ultra-Fine Dredged Sand in Alkali-Activated Mortar: A Case Study in the Lower Reaches of Yangtze River

Utilization of Ultra-Fine Dredged Sand in Alkali-Activated Mortar: A Case Study in the Lower Reaches of Yangtze River

The Effect of Nano-Silica and Nano-Alumina with Polypropylene Fiber on the Chemical Resistance of Alkali-Activated Mortar

This study investigates the simultaneous effect of nano-silica and nano-alumina with and without polypropylene fiber on the chemical-resistant of alkali-activator mortar (AAM) exposed to (5% Sulfuric Acid, 5% Magnesium Sulphate, and 3.5% Sodium chloride) attack. Design-expert software provided the central composite design (CCD) for mixed proportions. Nano-silica (NS) and nano-alumina (NA) at 0, 1%, and 2%, and with polypropylene fiber (0, 0.5%, and 1%) were used in the production of AAM. The alkali activator mortar mixes were created using an alkaline activator to binder ratio of 0.5. The binder materials include 50% fly ash Class F (FA) and 50% ground granulated blast furnace slag (GGBS). A sodium silicate solution (Na2SiO3) and sodium hydroxide solution (NaOH) were combined in the alkaline activator at a ratio of 2.5 (Na2SiO3/NaOH). The mechanical properties of AAM were tested via compressive strength and flexural strength tests. The results show that the acid attack, more than the sulphate and chloride attacks, significantly influenced the AAM. The addition of both nanomaterials improved the mechanical properties and chemical resistance. The use of nanomaterials with PPF showed a superior effect, and the best results were indicated through the use of 2%NA–1%PPF.

The Effect of Superabsorbent Polymers on Mechanical Characteristics and Cracking Susceptibility of Alkali-Activated Mortars Containing Ground Granulated Blast-Furnace Slag and Copper Slag

In an attempt to increase sustainability of construction materials, both ground granulated blast-furnace slag (GGBS) and, less popular, copper slag (CS) can be used in alkali-activated composites. However, such composites are often more susceptible to cracking, triggered by the self-desiccation processes. The addition of superabsorbent polymers (SAP) may enable internal curing of concrete and prevent excessive cracking. Thus, this paper aims to evaluate the effectiveness of SAP as an internal curing agent for alkali-activated slag mortars containing GGBS and CS. The samples were activated by sodium silicate using 6.5% Na2O by mass of precursor. The evaluation was based on the analysis of mechanical properties, autogenous shrinkage, and water absorption capacity of two types of SAPs. Depending on the type of polymer, a higher alkali concentration in SAP solutions speeds up early age reactions up to 7 days. After this period, SAP collapses and reactions follow at the same pace as the reference sample. In the presence of CS, SAP with higher absorption and smaller particles well-distributed in the mix leads to a higher extension of reactions, observed in higher values of autogenous shrinkage (AS). This results in increased compressive strength of GGBS-CS mortars, achieving values 8.8% greater than the reference sample (without SAP) at 6 months. Although its leads to higher cracking susceptibility, SAP can improve mechanical properties and promote new applications for sustainable material containing copper slag.

Optimizing piezoresistivity of alkali-activated mortar using carboxylated multi-walled carbon nanotubes/basalt fibers

• MWCNTs-COOH were electrostatically adsorbed onto the surface of basalt fibers to fabricate conductive MWCNTs-COOH/BFs. • CBFs improve the flexural strength of AAM. • The addition of CBFs optimizes the piezoresistivity of the AAM. Carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) were modified using KH550 and electrostatically adsorbed onto the surface of basalt fibers (BFs) to fabricate conductive MWCNTs-COOH/BFs (CBFs), which were then added to an alkali-activated mortar (AAM) to produce AAM health monitoring sensors. KH550 is a commonly used silane coupling agent that can promote the electrostatic adsorption of MWCNT-COOH and BFs. The CBFs were characterized using FTIR and SEM, and the mechanical and piezoresistive properties of the samples were investigated. The results showed that the addition of CBFs can improve the flexural strength of AAM by up to 10.8% and affect its compressive strength to a certain extent. When using a small amount of MWCNTs-COOH, the CBFs in the AAM overlap more easily, forming conductive paths and tunneling under cyclic loading; this optimizes the piezoresistive performance of the AAM. The absolute value of the minimum value of the fractional change of resistance (FCR) increased by 86.93%.

Potential of industrial waste as alternative alkaline activator for development of eco-efficient mortars

The alkali-activated materials (AAMs) design can be viewed as one of the most investigated fields in building materials engineering. However, despite numerous studies aimed at the utilization of various precursors, very limited attention is paid to the utilization of waste alkali sources as an alternative to commercial activators. In this regard, this study provides a novel approach to the utilization of industrial waste alkalis as a replacement for commercial alkali activators to reduce costs and reduce the environmental burden. The main innovation consists in the utilization of a waste-cleaning solution (SWCA) as an alternative alkaline activator for blast furnace slag to improve the environmental and economic efficiency and preserve functional properties. The functional properties of designed alkali-activated mortars are described by the setting time, pore size distribution, and mechanical strength. To comply with sustainable measures, the carbon dioxide emissions and costs analysis associated with the material production are carried out. The obtained results reveal the great potential of waste alkaline sources as a replacement for commercial activators. The increase in the applied SWCA concentration induced a shortening in the initial setting time from 240 to 120 min and the final setting time from 480 to 245 min. The designed mixtures reached a satisfactory level of mechanical strength (25 MPa) in comparison to low-grade cement mortars together with a substantial reduction in environmental burden excluding the avoided production. Specifically, a carbon footprint of 75 kg/m3 CO2 equivalent was achieved which represents 5 times lower values compared to low-grade concrete and even better value than AAMs based on a commercially-produced activator. Significant improvements were achieved also in cost efficiency per cubic meter as it was dropped to approx 40 €/m3, thus designed alkali-activated mortars provide better cost efficiency per cubic meter over traditional binders. The findings show that AAMs based on waste alkaline activator should of particular attention to materials science as lowers the consumption of energy-intensive sources and represent a valuable step toward a circular economy.

Chemical resistance of alkali-activated mortar with nano silica and polypropylene fiber

In this study, the mechanical and long-term performance of alkali-activated mortar (AAM) were investigated. In the fresh phase, the flow table and fresh density were evaluated. The compressive and flexural strengths were investigated at 28 and 56 days. In addition, the water absorption, sorptivity, and chemical resistance (sulfuric acid, magnesium sulfate, and sodium chloride) of AAM were investigated after 56 days of exposure Nano silica with and without polypropylene fiber was added to the AAM mixtures and cured at ambient temperature (23 ± 2 °C). Sodium silicates (Na2SiO3) and sodium hydroxide (NaOH) were used as alkaline-activated solution with a ratio of 1.5 to 2.5. The results show that the workability, water absorption, and sorptivity were better, with a ratio of 2.5 (the ratio of sodium silicates to sodium hydroxide). Nevertheless, the simultaneous use of fiber and nano-silica was adversely influenced. On the other hand, better hardened performanc was achieved with the ratio of 1.5. Moreover, the together use of fiber and nano-silica were reduced the flexural and compressive strengths when exposed to sulfuric acid, magnesium sulfate, and sodium chloride. In contrast, an increment of compressive strength was recorded for sodium chloride exposure.

Blending Plastics Waste with Highly Available Jordanian Kaolin for Preparation of Alkali-Activated Mortars

Due to their lower energy demand, alkali-activated materials or geopolymers (GPs) are strong candidates to replace ordinary Portland cement binders in some applications. The present article attempts to investigate the possibility of incorporating plastics waste in place of silica sand filler in the GP mortars. The compressive strength, density, FTIR, XRD, BET and SEM of the prepared mortars were evaluated. Satisfactory compressive strength was achieved for metakaolin (MK)-based GP mortars containing plastic fillers (polyvinylchloride (PV), polystyrene (PS), polypropylene (PP) and polyethylene (PE)) which was dependent on the nature of plastic incorporated in the GP matrix: MKPV (30.3 MPa) > MKPS (15.8 MPa)~MKPP (15.9 MPa) > MKPE (9.1 MPa). The 28-day compressive strength of GP containing polyvinyl chloride was almost equivalent to that containing silica sand. Much lower values were obtained for the corresponding kaolin-based GPs (2.5, 2.8, 1.8 and 2.2 MPa, respectively). As reflected by FTIR absorption bands at 1447 and 1400 cm−1, the addition of plastic filler reduces absorption of CO2 from the atmosphere which enhanced dissolution of Al species from metakaolin. The morphology of GPs containing plastic fillers exhibited amorphous tissue-like structure compared to crystalline structure in the case of GP containing silica sand. However, both types of GPs exhibited lower porosity than previously prepared metakaolin-based GPs. Remarkably, poor adhesion of plastic filler to the GP binder was observed due to the inertness of plastic fillers toward alkali activators.

Revealing corrosion parameters of steel in alkali-activated materials

The long-term corrosion behaviour of reinforcing steel embedded in alkali-activated mortars (AAMs) prepared with three different binder compositions was monitored over a 360-day period by cyclic wetting/drying and spraying with chloride solution. Corrosion potential and polarisation resistance were determined by linear polarisation, individual resistance of mortar and steel by electrochemical impedance spectroscopy, and Tafel slopes by potentiodynamic anodic polarisation. The results were validated by correlating the electrochemical mass losses with the gravimetric mass losses. Based on the time evolution of the corrosion parameters, the study proposes new limits for passive and active corrosion conditions for reinforcing steel in AAMs.

Performance Evaluation of Hybrid One-Part Alkali Activated Materials (AAMs) for Concrete Structural Repair

Alkali-activated materials (AAMs) have been widely used as an alternative to Portland cement. This production of AAMs emits lesser carbon dioxide by utilizing industrial waste products to make this cement binder technology greener and more sustainable. The conventional two-part system comprises solid aluminosilicate precursors with an alkali solution to activate the AAMs. However, higher alkalinity of the liquid activator is required to complete the geopolymerazation process, making the cementitious materials costly and sticky, and thus not convenient to handle on the construction site, affecting the worker’s safety. A one-part AAMs system was introduced to overcome the two-part system’s shortcomings. The alkali solution is now replaced with a solid alkali activator which is easier and more practical to apply at construction sites. This study was carried out to evaluate the mechanical performance of one-part alkali AAMs in the form of mortar by conducting compressive and flexural strength, modulus of elasticity, and tensile strength tests at 28 days of curing age under laboratory experiments in the tropical climate of Malaysia. A drying shrinkage test was also performed to detect its durability. Three types of solid admixtures were added to complete the composition of the novel mix design formulation. According to the results obtained, the mechanical strength of one-part alkali-activated mortar achieved the minimum requirement for Class R3 structural concrete repair materials as per EN1504-3 specifications. This eco-friendly cement binder has excellent potential for further engineering development, particularly to become a new concrete repair product in the future.

Microstructure as a key parameter for understanding chloride ingress in alkali-activated mortars

This study aims to evaluate the influence of microstructural properties on the chloride diffusion resistance of alkali-activated materials (AAMs) based on blast furnace slag and/or fly ash, with variable activator doses (represented as Na2O%). Resistance to chloride penetration was tested using accelerated chloride penetration (NT BUILD 443) and chloride migration (NT BUILD 492) tests. Addition of slag to alkali-activated mortars mainly based on fly ash reduced porosity and chloride permeability. Chloride penetration decreased with increasing Na2O%, but porosity and pore structure did not follow the same trend. The pore threshold (dth) and critical pore radius (rcrit) determined by mercury intrusion porosimetry had a good correlation with the chloride diffusion coefficient. Both the quantification of reaction products and the correlation between chloride penetration and pore surface area indicated that physical chloride adsorption on the C-A-S-H/N-A-S-H gel surfaces predominated over chemical chloride binding.

Efficacy of pond ash (PA) combined with ground granulated blast furnace slag (GGBFS) in producing cement-less mortar

In this research, an attempt has been made to produce cementless construction materials utilizing industrial wastes, e.g., pond ash (PA) and ground granulated blast furnace slag (GGBFS) as binder materials, followed by alkali activation using a mixture of sodium hydroxide (NaOH) and sodium metasilicate (Na2SiO3) solution. In this study, two types of samples, i.e., alkali-activated paste (AAP) and alkali-activated mortar (AAM) were prepared. The AAP samples were prepared to evaluate the setting times, hydration behavior (by monitoring hydration temperature as the function of time), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Analyzing the results, it is revealed that AAP samples sets within the standard time range (initial and final setting times are 55 and 105 min, respectively). The compressive strength analysis of the AAM sample (prepared using the same binder composition with a binder to fine aggregate ratio = 1: 3) is measured to be ∼12 MPa after 28 days of ambient curing. The setting and the hardening ability of AAP and AAM samples appear to be due to the pozzolanic reaction of PA and GGBFS with alkali activators, which is verified by the formation of hydrated products as demonstrated by the FTIR, XRD, and SEM analysis. Finally, a comparative study has been done to assess the reduction of CO2 emission for the use of PA-GGBFS binary mixture in the construction sector replacing the cement.

The potential of one-part alkali-activated materials (AAMs) as a concrete patch mortar

One-part alkali-activated materials (AAMs) are developed to improve conventional two-part systems. One-part AAMs technology has been used in cement binders to produce concrete, mortar, and paste. Current research mainly focuses on synthesizing raw materials obtained from industrial and agricultural waste as the main aluminosilicate precursors of the cement binder for a concrete application. The one-part AAMs were reported to have higher early compressive strength at 7 days of age, contributed by its fast-setting time, mainly when the binder activates by a higher dosage of alkaline activator and containing OPC-rich. Due to bonding issues, single or combination, FA/GGBFS/MK precursors were reported as unsuitable for use as a concrete repair material. They were the reason for the lack of one-part AAMs application of mortar compared to concrete usage. This study was conducted to determine the potential of one-part AAMs used as concrete patch mortar by investigating its rheology and mechanical properties. The compressive strength of the mortar was tested under lab ambient temperature in the tropical climate country of Malaysia. The setting time of fresh mortar and bonding strength were set under controlled lab temperature. The one-part alkali-activated mortar was composed of hybrid aluminosilicate precursors between fly ash (FA), Ground Granulated Blast Furnace Slag (GGBFS) and ordinary Portland cement (OPC). A low alkaline activator of solid potassium carbonate was used for the geopolymerization process. Three types of solid admixtures were added to complete the composition of the new mix design. The experiment's outcome showed that the mortar composed with the combination of conventional Portland cement and industrial waste products has compressive and pull-off adherence strength that meets with Class R3—EN1504-3 standard for structural concrete repair materials requirement.

Influence of superplasticizer on workability and strength of ambient cured alkali activated mortar

Alkali activated materials contain aluminosilicates, which can be used for building with a low environmental impact by repurposing waste resulting in cost-effective construction. The impact of nature and superplasticizer dosage on fly ash slag-based ambient cured mortar activated with sodium silicate and sodium hydroxide is not yet definitive. This paper studies the influence of various superplasticizers on fly ash-based ambient cured mortar activated with sodium silicate and sodium hydroxide. The effect of superplasticizers was evaluated by adding various superplasticizers including melamine, polycarboxylate ether and naphthalene-based superplasticizers in different dosages from 0 to 3% at 0.5% intervals. Fresh properties of alkali-activated mortar with various percentages of superplasticizer were tested using flow table apparatus and compared with mortar without superplasticizer. The hardened property of the alkali-activated mortar was tested by checking the compressive strength of the mortar cube. From the test results, naphthalene and polycarboxylate ether-based superplasticizers are compliant with alkali-activated mortar. Melamine-based superplasticizer shows a slight reduction on strength of alkali-activated mortar. In the ambient cured mortar, the optimum concentration for naphthalene and polycarboxylate ether-based superplasticizers is 2.0 percent, whereas melamine-based superplasticizer exhibits maximum strength for 2.5 percent. Even though naphthalene and polycarboxylate-based superplasticizers are effective for alkali-activated mortar, the most efficient type is the polycarboxylate ether-based superplasticizer.

Evaluation of the mechanical properties and durability of self-compacting alkali-activated mortar made from boron waste and granulated blast furnace slag

The production of high-strength alkali-activated mortar and concrete by using waste materials instead of cement in order to reduce the amount of carbon dioxide released to nature in cement production is an important study that attracts the attention of researchers. In this study, self-compacting alkali-activated mortar samples were produced using boron waste (BW) and granulated blast furnace slag (GBFS). Prismatic samples of 40 × 40 × 160 mm and cubes of 50 × 50 × 50 mm were produced, in which 0%, 5%, 10%, 15%, 20%, 25% of BW were used. To achieve self-compacting alkali-activated mortar (SCAAM) slump-flow test method was conducted by per The European Federation of Specialist Construction Chemicals and Concrete Systems (EFNARC) guidelines. The samples prepared using Na2SiO3 (NS)/NaOH (NH) = 3.0 were exposed to oven curing at 60 °C and 100 °C for 3 days. The flexural and compressive strength (CS) values of 3, 28 and 90 days were obtained for the samples whose curing period was completed. According to the mechanical strength results, influence of capillary water absorption, porosity, water absorption and density and freeze-thaw from durability tests were carried out. After experimental tests, Scanning Electron Microscope (SEM) and Energy-dispersive X-ray Spectroscopy (EDS) images were utilized to determine microstructures of the samples. As a result of the study, it was determined that the highest strengths were obtained at the curing temperature of 60 °C. Also, it was seen that mechanical strengths and durability decreased with the increase in the BW ratio in the mixtures.

Development of eco-friendly GGBS and SF based alkali-activated mortar with quartz sand

Development of eco-friendly GGBS and SF based alkali-activated mortar with quartz sand

Properties and microstructure of lime kiln dust activated slag-fly ash mortar

Commercially available alkali activators such as sodium hydroxide and water glass are widely used in the formulation of alkali-activated binder (AAB) to activate ground granulated blast furnace slag (GGBS) or fly ash (FA). However, the production of the commercially available alkali activators yields high carbon dioxide (CO 2) emission results in the same environmental impact as cement production. The present study aimed to develop an alternative alkali activator with low embodied CO 2 for the sustainable production of AAB. In this study, the FA/GGBS blend was activated by 5–30% by lime kiln dust (LKD), an industrial by-product from lime production. The resulting binder was used to produce alkali-activated mortar (AAM) to evaluate mechanical, durability and microstructure properties. The increased of LKD replacement level from 5% to 10% was found to improve both the mechanical performance by around 30% and durability performance of alkali-activated mortar (AAM) by 50% as shown by the optimum mix design, L10G36F64. The best ratio of FA to GGBS was for optimal alkali activation was established as 3:2, by binder weight. A further increase in replacement level and GGBS content beyond the stipulated contents reduced the overall performance of the AAM from the optimum level. The main hydration products of LKD activated FA/GGBS were C-A-S-H and C-S-H. The SEM investigation revealed that the best sample with the composition mentioned had dense microstructure and dense foil-like C-S-H gel. LKD was established to be an effective alkali activator for GGBS-FA to yield AAB with the desired mechanical and durability properties due to its inherent quicklime composition.

Influence of Silica Fume Additive and Activator Ratio on Mechanical Properties in Slaked Lime-Based Alkali-Activated Mortars

Influence of Silica Fume Additive and Activator Ratio on Mechanical Properties in Slaked Lime-Based Alkali-Activated Mortars

Multicomponent Low Initial Molar Ratio of SiO2/Al2O3 Geopolymer Mortars: Pilot Research.

Alkali-activated binders have the potential to consume various types of waste materials. Low initial molar ratios of SiO2/Al2O3 geopolymer mortars were considered in this article. Here we studied alkali-activated binders produced with photovoltaic glass powder in 5%; kaolin clay in 15%; ground granulated blast furnace slag in 30%; alumina-lime cement in 30%; and, interchangeably, fly ash from coal combustion in 5%, fly ash from biomass combustion in 5%, or granulated autoclaved cellular concrete in 5%. The influence of clay dehydroxylation, curing conditions, glass presence, and a kind of waste material was investigated. According to the experimental results, strength (compressive and tensile) gradually increased with increasing time and with the use of calcined clay. Significant improvement in compressive strength was seen with the additional 3 days curing time in 105 °C when non-sintered clay was used. The presence of photovoltaic glass in alkali-activated mortars immobilised mercury and arsenic but released zinc, chromium, and sulphates. The microscopic observations confirmed the greater densification of the microstructure of the binder made of calcined clay due to its greater surface development and dehydroxylation. The binder of non-calcined clay was granular, and the interfacial transitional zone was more porous. The C–A–S–H gel seemed to be the main phase. XRD examination confirmed the presence of C–A–S–H, C–S–H, zeolites, and many other phases in minor amount. The presented research was a pilot study, and its main goal was to develop it further.

Durability and fire-resistance performance of slag-based geopolymer composites

The fresh and durability properties of alkali-activated mortar were investigated in this study. Ground granulated blast-furnace slag was used as a binder material. Both carbon fibres (CFs) and polypropylene fibres (PPs) were added at ratios of 0, 0.75, 1.00 and 1.25% by weight of the binder. Simultaneously, hybrid fibres were also used (CF 1.0% and PP 0.25%, CF 0.5% and PP 0.5%, and CF 0.25% and PP 1.0%). The fresh properties of the composite were investigated by performing a flow test. Durability properties such as fire resistance, water sorptivity, water absorption, density, porosity, efflorescence and sulfate attack were also investigated. According to the findings, increasing the fibre content reduces the flowability of the mixture. Simultaneously, the best fibre content studied was 1%, which significantly enhanced durability properties. Also, both fibres achieved excellent improvement. However, CF had more influence than PP on durability properties.