Liquid Alkaline Activator Research Articles

Compressive strength and gel structure improvement in the high-volume calcium carbide residue activated-blast furnace slag system combined with sodium carbonate and silica fume

Calcium carbide residue (CCR) with high alkalinity favorably corresponds to the alkaline activator in the alkali-activated materials (AAMs) production. Its utilization could reduce the carbon footprint and facilitate cast-in-situ applications compared to traditional liquid alkaline activators. A high-volumed CCR from 10 % to 25 % as alkaline activators in an alkali activated-blast furnace slag system was investigated, in which sodium carbonate (Na2CO3) and silica fume were used to improve the mechanical properties of CCR-activated blast furnace slag (CCR activated-BFS) pastes. Isothermal Calorimetry, X-ray diffraction (XRD), 29Si nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM) were used to characterize the reaction process, phase transformation, and gel structure. The results show that the highest compressive strength of CCR activated-BFS pastes was obtained when the CCR proportion was 20 %. Na2CO3 addition significantly improved the compressive strength, especially at the CCR to Na2CO3 mass ratio at 1:1.5. However, the compressive strength deterioration appeared at 28 d because of the gel structure decomposition in CCR activated-BFS pastes. The silica fume addition inhibited the structure decomposition, improved the connectivity of gel structure, favored the formation of gel, and thus suppressed the compressive strength deterioration. The study established a sustainable waste recycling from acetylene gas production by using CCR as feedstock to mitigate carbon emissions from AAMs production.

Evaluation of Amended Black Cotton Soil Using Bagasse Ash with Liquid Alkaline Activator for Sustainable Pavement Subgrade Performance

Evaluation of Amended Black Cotton Soil Using Bagasse Ash with Liquid Alkaline Activator for Sustainable Pavement Subgrade Performance

Evaluating the Performance of Expansive Soil by Using Rice Husk Ash and Liquid Alkaline Activator

Evaluating the Performance of Expansive Soil by Using Rice Husk Ash and Liquid Alkaline Activator

One-part alkali-activated soil stabilization with sodium metasilicate: Mechanical-geochemical-mineralogical characterization

A shift towards environmental sustainability is an emerging trend in the modern construction industry, and soil stabilization is no exception. Environmental and economic constraints associated with traditional cement have led to a renewed research focus, particularly on the development of alkali-activated materials (AAMs), a cost-effective and environmentally sustainable stabilization method. Traditional AAM synthesis involves the activation of industrial byproducts in an alkaline solution, which poses challenges in transporting, storing, and handling large quantities of liquid alkaline activators in the field. To address these challenges and enable the large-scale application of AAM-based soil stabilization, a one-part alkali-activation method is proposed, utilizing a dry powdered alkaline activator. This study aims to evaluate the potential of dry sodium metasilicate (SM), used in conjunction with Class C fly ash, Class F fly ash, and ground granulated blast-furnace slag, to stabilize weak clayey soils with medium-to-high initial moisture content. Towards that end, five stabilizer mixes with and without SM were designed to stabilize natural soil at different initial moisture states. The engineering properties of these blends were assessed through unconfined compressive strength (UCS) testing, and a relationship between the initial water content of the soil, stabilizer dosage, and the desired UCS for the alkali-activated mixtures was developed. Furthermore, the microstructure of these blends was characterized through geochemical and mineralogical analyses, including pH measurement, X-ray diffraction (XRD) analysis, thermogravimetric analysis (TGA), and scanning electron microscope (SEM) imaging. This study demonstrates the feasibility of using dry SM to create one-part AAM, which holds promise for stabilizing weak soils in various transportation infrastructure systems, including roadways, airfield pavements, and railways.

The effect of fly ash to alkaline activator ratio to the mechanical properties of stabilized lateritic soil using fly ash based geopolymer

Stabilization of fill soil improve its physical and mechanical properties and led to better load carrying capacity and enable steeper temporary slope to be formed during construction period. In this study an industrial by-product, fly-ash (FA), was used as precursor to produce geopolymer as chemical stabilizer to improve the physical and mechanical properties of fill soil. Sodium silicate solution (Na2SiO3) and sodium hydroxide (NaOH) at a concentration of 15 molars were combined as the liquid alkaline activator (AA). The effect of different fly ash to alkaline activator ratio (0, 1.0, 1.5, 2.5 and 3.0) on the physical and mechanical properties of treated fill soil were measured using Atterberg limit test and unconfined compressive strength (UCS) test. All sample were tested at 1 day and 3 days of curing period under room temperature. The result indicates that the highest compressive strength is obtained with fly ash to alkaline activator ratio of 2.5 for both 1 day and 3 days of curing. In addition, the plasticity index of the treated sample for all fly ash/alkaline activator were lower than that of the untreated fill soil.

Structure–function relationship during the early and long‐term hydration of one‐part alkali‐activated slag

AbstractUnderstanding the mechanisms controlling the early (fresh) and long‐term (hardened) hydration of one‐part alkali‐activated slags (AAS) is key to extend their use as low CO2 substitutes for ordinary Portland cement (OPC). Their “just add water” use makes them easier and less hazardous to manipulate than the more studied two‐part ones. This is due to the absence of liquid alkaline activators, which are environmentally and energy demanding. In this work, numerous experimental techniques have been linked to obtain a comprehensive physico‐chemical characterization of a one‐part AAS activated with Na2CO3 and Ca(OH)2 powders at several water to solid ratios (w/s). Calorimetry and pH/conductivity measurements describe the functioning of the activators immediately after contact with water. Early reactivity is characterized through in situ X‐ray powder diffraction (XRPD) and small amplitude oscillatory shear (SAOS) rheology, which reveal a rapid precipitation of nanometric hydration products (nano‐C‐A‐S‐H), which results in a continuous increase in the paste cohesivity until setting. Moreover, SAOS shows that rejuvenating the paste by means of shearing (performed externally to the rheometer in this study) is enough to restore the initial cohesion (i.e., workability) for long time spans until setting occurs. The long‐term hydration is characterized by ex situ XRPD on aged AAS pastes, in parallel with mechanical testing on AAS mortar. A correlation can be observed between the amount of nano‐C‐A‐S‐H and the increase in compressive strength. Overall, this formulation shows satisfactory fresh and solid properties, demonstrating suitability for low‐ and normal‐strength applications.

Influence of Recycled Glass on Strength Development of Alkali-Activated High-Calcium Fly Ash Mortar

This article presents the development of green and sustainable mortars using alkali-activated high-calcium fly ash (AAFA) and recycled glass (RG) as part of the fine aggregate. RG was used to replace river sand at dosages of 0%, 25%, 50%, 75%, and 100% by weight. Sodium hydroxide (SH) and sodium silicate (SS) solutions were used as liquid alkaline activators in all mixtures. The AAFA samples were prepared with different liquid-to-binder ratios of 0.6 and 0.7, and the ratio of SS-to-SH was fixed at 2.0. Compressive and flexural strengths were determined at the ages of 7, 28, and 60 days. Test results showed that the compressive and flexural strengths of AAFA mortars declined as RG replacement increased; nevertheless, they increased with curing time. The high Na2O concentration derived from RG and the weak interfacial transition zone of RG are reasons for the decrease in strength development. The optimum percentage replacement of fine aggregates with RG was found at 25%. The 28-day compressive strength of AAFA with 25% RG was 32.5 MPa for L/B ratios of 0.6 and 29.5 MPa for L/B ratios of 0.7, which resulted in a strength index higher than 75% while releasing low CO2.

Evaluation of Expansive Soil Amended with Fly Ash and Liquid Alkaline Activator

Evaluation of Expansive Soil Amended with Fly Ash and Liquid Alkaline Activator

Preparation and Characterization of the Functional Properties of Synthetic Aggregates from Silico-Manganese Slag.

A large number of natural aggregates are used in the field of construction materials, resulting in the exhaustion of natural aggregates. Therefore, looking for an alternative will slow down the consumption of natural aggregates. The sintering method not only consumes a lot of energy to prepare aggregates but also produces a lot of pollutants. In this study, silico-manganese (SM) slag was dried, ground into powder, and used as raw material. Solid and liquid alkaline activator methods were used to prepare SM slag non-burning aggregate (SMNA) by the cold bonding method. The effects of grinding time, amounts of solid and liquid alkaline activators, curing temperature, and the amount of added fly ash on aggregate properties were investigated. The aggregate microstructure was characterized by XRD, SEM, and FTIR methods, and the toxic leaching analysis of aggregate was performed. The results showed that with a fixed amount of liquid activator (16.2% wt.) and solid activator (15% wt.) and fly ash (20% wt.), respectively, and curing was performed at room temperature, the aggregate properties were optimal: the bulk density of 1236.6–1476.9 kg/m3 and the water absorption lower than 4.9–5.5%. The apparent density was 1973.1–2281.6 kg/m3, and the bulk crushing strength was 24.7–27.9 MPa. The XRD, SEM, and FTIR results indicated that amorphous gel could be formed from SM under an alkaline activator, improving the aggregate strength. The results of toxic leaching showed that the aggregate prepared from SM exhibited environmentally friendly characteristics. The SMNA was obtained via the simple and low-energy consumption production process, paving the new way toward large-scale utilization of SM.

Mitigation of Expansive Soil by Liquid Alkaline Activator Using Rice Husk Ash, Sugarcane Bagasse Ash for Highway Subgrade

Mitigation of Expansive Soil by Liquid Alkaline Activator Using Rice Husk Ash, Sugarcane Bagasse Ash for Highway Subgrade

Strength and Microstructure of Clay Geopolymer Non-Load-Bearing Masonry Units Using Fine-Clay Brick Waste and Palm Oil Fuel Ash

This research studies the applicability of alkali-activated cement with a mixture of fine-clay brick waste (FCBW) and palm oil fuel ash (POFA) to manufacture environmentally friendly masonry units. FCBW and POFA were used as a precursor, while a dredged soft clay (SC) was used as aggregate. Sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) solutions were used as the liquid alkaline activator. Effects of NaOH concentration, initial SiO2/Al2O3 mole ratio, Na2SiO3/NaOH ratio, and curing conditions on the strength and microstructure of the FCBW-POFA-SC geopolymers were evaluated. The FCBW-POFA-SC geopolymers had a lower total unit weight than compacted SC because NaOH in the geopolymer binder caused a flocculated soil structure. It was found that Na2SiO3/NaOH=70/30, 10 M NaOH, and FCBW/POFA=70/30 were the best ingredients providing the rigid network of the geopolymer structures. The suitable heat duration of 48 h at 80°C accelerated the dissolution rate of the Si and Al and polycondensation in the geopolymer structure, resulting in denser geopolymer gels and early strength gain. With this optimum ingredient and suitable heat condition, 7-day unconfined compressive strength (UCS) of the FCBW-POFA-SC geopolymers achieved the requirement of the Thailand industrial standard for non-load-bearing masonry units (UCS>2.5 MPa). The geopolymer products were found to be sodium aluminum silicate hydrate (N─ A─ S─ H) and calcium aluminum silicate hydrate (C─ A─ S─ H). The research outcome will promote the usage of waste materials for manufacturing environmentally friendly infrastructure in Thailand and other countries.

Multi-walled carbon nanotube dispersion methodologies in alkaline media and their influence on mechanical reinforcement of alkali-activated nanocomposites

The focus of present research is the establishment of a practical procedure for effective incorporation of multi-walled carbon nanotubes (MWCNTs) into alkali-activated materials (AAMs) with the aim of mechanical reinforcement. Investigated composite in this work was an alkali-activated matrix composed of fly ash (FA) and ground-granulated blast furnace-slag (GGBS) as solid aluminium-calcium-silicate precursors along with highly concentrated sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) as liquid alkaline activators. Na2SiO3, NaOH, and a combination of them were used for dispersion of MWCNTs. An anionic surfactant, naphthalene sulfonate (NS), and ultrasonication were applied to assist in the preparation of nanofluids. Optical microscopy, integral light transmission (ILT), and Fourier-transform infrared spectroscopy (FTIR) were performed to assess the colloidal behaviour of MWCNTs in the nanofluids. The possible dispersion mechanisms were furthermore hypothesised for each alkaline medium. Based on the outcomes, MWCNTs had the best dispersion performance in the Na2SiO3 based nanofluids. The relevant nanocomposites accordingly, in comparison to the other preparation methodologies in this research, indicated the highest improvements in flexural (65%) and compressive (30%) strengths as a consequence of 0.050 wt% MWCNT incorporation. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) further clarified the reinforcement functionality and microstructure refinement of the MWCNTs dispersed in the Na2SiO3 based nanofluids. Altogether, this paper represents a broad insight concerning a better understanding of MWCNTs’ interactions in alkaline activators, i.e. dispersion media, and AAMs, i.e. host matrices, to obtain the highest possible mechanical and microstructural performance of reinforced nanocomposites.

Evaluation of polyvinyl alcohol and high calcium fly ash based geopolymer for the improvement of soft Bangkok clay

Soft Bangkok clay (SC) is recognized as a problematic soil in Thailand. This research investigates the possibility of using polyvinyl alcohol (PVA) and high calcium fly ash (FA) geopolymers to improve the strength of SC in deep soil mixing applications. The liquid alkaline activator (L) was composed of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH). The studied influence factors included FA content, water content, L content, Na2SiO3/NaOH ratio, PVA concentration, PVA content, and curing time. Strength development and microstructure in the PVA-FA geopolymer stabilized SC were evaluated via the unconfined compressive strength (UCS) test and scanning electron microscope (SEM) test. The optimum ingredient considering workability and cost of FA geopolymer stabilized SC was found to be at a mix design of 1.0LL, Na2SiO3/NaOH = 1, FA = 40% and L/FA = 0.6, whereby a 28-day UCS of 1026 kPa was attained. The optimum PVA content and PVA concentrations were found at 15% and 4%. The 7-day and 28-day UCS values were improved by PVA up to 40% and 42% compared to those of the specimen without PVA, respectively. The outcome of this research will promote the usage of PVA-FA geopolymer as an alternative green soil stabilizer alternative to Portland cement for a DM improved soft Bangkok clay.

Compressibility and strength development of geopolymer stabilized columns cured under stress

The objective of this study was to evaluate the effects of geostatic stresses on the compressibility and strength development of submerged geopolymer stabilized columns. In this research study, modified 1D consolidation cells were developed to replicate deep mixed columns in the field when subjected to varying stresses at various depths. Various combinations of fly ash (FA) and slag (S) precursors were used and activated with a liquid alkaline activator (L) to form the geopolymer binder. Soil-column samples were cured under vertical stresses of 0, 50, 100 and 200 kPa for up to 28 days. The results indicated that by increasing the curing stress, the vertical strain and constrained modulus of soil-column composite increased. Moreover, by increasing the binder content, the vertical strain and stiffness of the composites were decreased and enhanced, respectively. The permeability of the composites decreased by increasing the curing stress. The results indicated that addition of the FA+S up to 25% resulted in an increase of permeability and further addition of binder content resulted in insignificant changes in the permeability values. For all the tested geopolymeric binder contents, increasing the curing stress resulted in the enhancement of strength development of stabilized columns. The rate of strength development was enhanced with curing time at an increasing rate, up to 28 days.

Durability analysis of eggshell powder–flyash geopolymer composite subjected to wetting–drying cycles

PurposeThe purpose of this study is to investigate the effect of various heat conditions on the durability of eggshell powder (ESP)–flyash (FA) geopolymer subjected to wetting–drying cycles.Design/methodology/approachIn this study, two waste materials, ESP and FA, which are destined for landfills, were used as precursors to produce geopolymers in a sustainable manner. The mixture of Na2SiO3and NaOH was used as a liquid alkaline activator in geopolymerization. The ESP and FA content were varied as 30, 50 and 70% and Na2SiO3/NaOH ratios were varied as 0.5, 1 and 2. Geopolymer samples were cured at three heat conditions: 25°C (ambient temperature), 50°C and 80°C for seven days prior to durability tests.FindingsThe results of this study revealed that the strength loss of the geopolymer decreases with an increase in curing temperature up to 50°C and then increases for higher temperature up to 80°C. Further, the strength loss of the geopolymer decreases with an increase in FA replacement and Na2SiO3/NaOH ratio. Geopolymer composites exhibited early strength development because of the inclusion of calcium-rich ESP. The weight loss of the ESP–FA geopolymer follows a similar pattern of strength loss. Geopolymer samples previously cured at optimum heat condition of 50°C for seven days exhibited higher durability.Originality/valueThe inclusion of calcium-rich ESP in FA-based geopolymer is novel research. As ESP–FA geopolymer composites show higher mechanical strength and higher durability compared to Indian standards, the potential use of this geopolymer can be in road subbases/subgrades.

Microstructural Properties of Alkali-Activated Metakaolin and Bottom Ash Geopolymer

This paper presents a study on the use of alkali-activated metakaolin (MK) and Bottom Ash (BA) blend in geopolymer concrete. A preliminary attempt was made on alkali-activated metakaolin and bottom ash-based geopolymer (MK–BA-GPM) mortar with river sand as fine aggregate to find a suitable mix to produce geopolymer concrete (GPC). The liquid alkaline activator is a combination of sodium silicate and sodium hydroxide solution. The molarity of NaOH was 8 M. Molar ratio of Na2O and SiO2 was 2, and ambient curing mode was selected. Also, M30 grade control concrete was made using OPC and cured in water. Further, GPC and control concrete specimens were tested for compressive strength, split tensile, flexural strength and modulus of elasticity. Also, XRD, SEM and EDAX studies were carried out to analyse element/mineral compounds present and the microstructure and morphological characteristics of GPC to substantiate the strength development. MK–BA GPC demonstrated 49% higher compressive strength than that of control concrete at 28 days. More so, the early as well as later strength gain of GPC was remarkably higher than that of OPC. Strength was due to densification of microstructure over a period of time and due to the formation of additional crystalline phases in geopolymer concrete.

Bagasse ash–fly ash-geopolymer-treated soft Bangkok clay as subgrade material

A geopolymer was investigated as a low-carbon dioxide emission binder for soft Bangkok clay improvement. Bagasse ash (BA), an industrial by-product, was used as the main precursor, while fly ash (FA) was used as a supplementary to develop a geopolymer. A mixture of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) was used as a liquid alkaline activator. The unconfined compressive strength, q u, of the geopolymers was found to be directly dependent on the precursor (BA and FA) to liquid alkaline solution (P:L) ratio, sodium hydroxide concentration, FA:BA ratio and curing time. The geopolymer binder with P:L = 55:45, BA:FA = 70:30, sodium silicate:sodium hydroxide = 2:1 and sodium hydroxide concentration = 16 M was selected to treat Bangkok clay based on engineering and economic perspectives. The q u improvement with geopolymer content was divided into active and inert zones. The 10% geopolymer content was found to be the threshold limit. Beyond this limit, the q u improvement was insignificant. The 5% geopolymer content could improve the q u of soft Bangkok clay to meet the minimum requirement for subgrade according to the local road authority. The outcome from this research will promote the BA–FA geopolymer as a cleaner binder by using recycled waste materials in ground improvement applications.

Controlling the setting times of one-part alkali-activated slag by using honeycomb ceramics as carrier of sodium silicate activator

A solid alkali source is a great choice to make one-part alkali activated materials (AAM). Conventional slag-based AAM always suffer from short setting time and unsafe operation with liquid alkaline activators, thus restricting their usage in industry. This study aims to synthesize a new kind of one-part alkali-activated slag cement by using a porous honeycomb ceramic (HCC) as the carrier of sodium silicate activator. The solid activator was produced by making the honeycomb ceramic absorb water glass (Ms = 3.24, 8.21 wt% Na2O, 25.8%wt SiO2), drying for 5 h at 125 °C and then grinding it to powder with particle sizes between 10 and 50 μm. In this study, the result indicates that setting time of alkali activated slag cement (AASC) was successfully extended to at least 5 h by using the solid activator. The maximum compressive strength of the specimens made with 5% NaOH + 40% HCC and 6% NaOH + 40% HCC was ~40 MPa after 28 d of curing time. XRD (X-ray diffraction), FTIR (Fourier Transform infrared spectroscopy), SEM (Scanning Electron Microscope) and linear shrinkage analysis were applied in order to study the hydration product and the effect of the addition of HCC to the AASC. In terms of the strength properties and setting time, this one-part AASC could be classified as a Type 32.5 N and CEM IIIC class cement according to the European standard EN-197.

Synthesis and characterization of fly ash and slag based geopolymer concrete

This paper presents the formulation and characterization of composite fly ash and slag based geopolymer concrete. Potassium hydroxide (KOH) and potassium silicate (K2SiO3) liquid alkaline activators were used in the preparation of the geopolymer concrete. The mechanical response of the best recipe was investigated through compressive, tensile and flexural strength tests after 3, 7 and 28 days of curing. One batch was tested for compressive strength after 16 and 32 weeks of curing. The microstructure of the concretes was characterized using scanning electron microscopy (SEM). The testing results are compared with a reference ordinary portland cement-based concrete. After 28 days of curing, test results showed that the geopolymer concretes can approach the compressive strength of the reference ordinary concrete. Moreover, the tensile strength and flexural strength attained reached up to 68% and 80% of the reference cement, respectively. The results indicated the potential application of geopolymer that can satisfy the standard strength requirement. After longer time of curing, 32 weeks, some of the geopolymer preparations exhibited 111% compressive strength, compared to the ordinary cement reference.

Solidification and stabilisation of metal plating sludge with fly ash geopolymers

The disposal of metal plating sludge (PS) to landfills is an increasingly common practice in developed and developing countries. This paper presents a novel PS stabilisation technique using fly ash (FA)-based geopolymers as a waste management option. Strength and microstructural evaluations were carried out on PS-FA geopolymers at various values of factors, including liquid alkaline activator (L = sodium silicate (Na2SiO3)/sodium hydroxide (NaOH) ratio), L/FA ratios, FA/PS ratios and curing time. Increasing the amount of PS in PS-FA geopolymers reduced the total porosity, subsequently resulting in higher unconfined compressive strength (UCS) values. The main geopolymerisation product of the FA-based geopolymer was sodium aluminosilicate hydrate (N-A-S-H) gel. Since PS had a high calcium content, it would react with the high amount of silica and alumina present in FA to generate calcium aluminosilicate hydrate (C-A-S-H) gel in PS-FA geopolymers. This C-A-S-H gel coexisted with the N-A-S-H gel from FA-based geopolymers and hence significantly accelerated UCS development of PS-FA geopolymers over time. The UCS values of PS-FA geopolymers were found to meet the US Environmental Protection Agency requirement for disposal to landfills. The outcomes from this research can be translated into a regulatory framework for managing PS and diverting this industrial waste from landfills.