Geopolymer Content Research Articles

Materials design and strength development of a novel cold recycled mixture with asphalt emulsion and geopolymer

ABSTRACT Cold recycling of asphalt pavement with asphalt emulsion is an important approach for achieving low-carbon and sustainable development in road engineering. Enhancing the performance of cold recycled mixtures has become a key research focus. The objective of this paper is to develop a novel cold-recycled asphalt mixture stabilised with asphalt emulsion and geopolymer (CRM-GE). Firstly, the effects of mixing sequence, geopolymer content, asphalt emulsion content and curing conditions on the strength of the mixture and its time-dependent law are studied. Then, the microstructure and composition of the mixture are analysed by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The results show that the optimum amount of asphalt emulsion is different under different geopolymer contents. The indirect tensile strength of the mixture specimen increases with the increase in the curing time and curing temperature. The microstructure analysis indicates that geopolymer reaction and asphalt emulsion demulsification in CRM-GE with 7-day curing are relatively limited, while asphalt film and the geopolymer reaction products are intertwined to achieve a denser microstructure in CRM-GE with 28-day curing. In addition, the element analysis further verifies the result of materials design and micromorphology analysis.

Optimization of geotechnical characteristics of clayey soils using fly ash and granulated blast furnace slag-based geopolymer

In this study, the effects of fly ash and granulated blast furnace slag based geopolymer on the mechanical properties of high plasticity clayey soils were investigated. For this purpose, experimental studies were carried out using the Taguchi Method. The Taguchi L16 orthogonal array was used with various amounts of class F fly ash (12 %, 16 %, 20 %, and 24 %), granulated blast furnace slag (8 %, 10 %, 12 %, and 14 %), and alkaline hydroxide solution NaOH molarity (6, 8, 10, and 12). After 7 and 28 days of curing, unconfined compressive strength (UCS) and California bearing ratio (CBR) were carried out. Permeability test was carried out as well after 28 days of curing. The effects of the variables on the experimental results were determined using S/N and variance analyses (ANOVA). The microstructure and phase composition of geopolymer samples were identified via scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The findings indicate that the strength of geopolymer-stabilized soil is significantly affected by the stabilizer content, fly ash–slag ratio, and molarity of alkaline activator (M). The optimal mix proportions for geopolymer-stabilized high plasticity clayey soil were found to be as follow: 38 % geopolymer content (24 % fly ash, 14 % slag) and an alkaline activator content of 25.75 % with a molarity of 12 M.This study concluded that fly ash and granulated blast furnace slag based geopolymer can serve as a feasible alternative material to cement, being sustainable and applicable. It could be utilized to enhance the strength characteristics of high-plasticity clay soil, while simultaneously, reducing permeability.

Strength and durability characteristics of geopolymer treated pond ash as pavement material

This study evaluated the strength and durability characteristics of pond ash (PA) treated with geopolymer (3%, 6%, 9%, 12%, and 15%, by dry weight of PA) and compared them with Portland cement and hydrated lime stabilizations at same additive contents. Unconfined compressive strength of specimens was evaluated at curing durations of 1, 3, 7, 28, and 90 days. The durability of 28-day cured stabilised specimens against wet-dry cycles, freeze-thaw cycles, water slaking cycles, water immersion, capillary action, and dispersion was assessed. Geopolymer-stabilized PA achieved higher strength and durability than cement and lime-stabilised PA. It is due to the formation of a dense microstructure with significant reaction products. PA stabilised with 3% geopolymer and 15% cement satisfies the strength properties of the cementitious subbase in flexible pavements. Whereas, 6% geopolymer content fulfils the requirements of the cementitious base in flexible pavements and the cementitious subbase in rigid pavements as per IRC: 37-2018 and IRC: 59-2015, respectively.

Mechanical Response and Deterioration Mechanisms in Freeze–Thaw Environments for Crushed Stone Stabilized with Industrial Solid Waste

The conflict between industrial solid waste treatment and environmental protection in Inner Mongolia is becoming increasingly prominent. Using industrial solid waste such as mineral powder, fly ash and wet calcium carbide slag as raw materials, using the alkali excitation method to prepare geopolymer, and replacing part of the cement for pavement base can effectively absorb industrial solid waste and realize the dual goals of waste utilization and environmental protection. Through mechanical properties tests before and after a freeze–thaw cycle and micro tests such as scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP), the strength variation rule and mechanism of geopolymer-cement stabilized aggregate under freeze–thaw cycles were deeply investigated. The relationship between different porosity indexes and mechanical properties in mercury intrusion porosimetry (MIP) was established by grey relation analysis. The results prove that a mixture with impaired properties after freeze–thaw cycles and the anti-freezing performance of the mixture with 20% geopolymer content are better than that of the mixture with no geopolymer content and 40% geopolymer content. The loss rates of unconfined compressive strength (UCS) after 5, 10 and 20 freeze–thaw cycles were 9.5%, 27.6% and 36.4%, respectively. The appropriate addition of geopolymer can enhance the anti-freezing performance of a stable aggregate. Following freezing and thawing cycles, the unconfined compressive strength (UCS) damage of the mixture is mainly influenced by a rise in total porosity, and the grey correlation degree is 0.75. The increase in more harmful pores and total porosity mainly results in an indirect tensile strength (ITS) loss. The grey correlation degree is 0.91. The compressive rebound modulus (CRM) is not affected by the change in pores but decreases with a rise in the geopolymer dosage.

Investigation on strength characteristics and mechanism of cold mix based on geopolymerization reaction

Cold mix asphalt is an energy-efficient and eco-friendly pavement material, yet its early strength is deficient. This study investigated the strength augment of cold mix asphalt through modification with geopolymer additives. Macro-strength was assessed via Marshall stability testing under varied geopolymer contents, curing durations, and water immersion conditions. Microscale analysis encompassed fluorescence microscopy to discern geopolymer-asphalt interactions and discrete element modeling to simulate the compression process. Results showed that stability rose and then fell as geopolymer content increased, with an optimal ratio of 4:3 between base asphalt and additive. Stability increased rapidly in the first 3 days of curing and accumulated at a slower rate afterwards. Fluorescence microscopy revealed that geopolymer bonded the asphalt to the aggregate surfaces. Modeling exhibited geopolymer resisted vertical loads and confined the aggregate. In summation, geopolymerization enhances cold mix strength by improving adhesion and generating a rigid 3D network encompassing aggregate particles. The discoveries provide guidance on formulating durable cold mix asphalt utilizing geopolymer additives.

Impact of crushing shape and geopolymerization on reclaimed concrete aggregate for recycling in the flexible pavement: an enhanced circular economy solution

This study evaluates the quality and mechanical performance of various shapes of reclaimed concrete aggregates (RCAs), including elongated, cone-shaped, angular, and ordinary mix, in comparison to fresh aggregates (FAs). The RCAs are treated with fly ash-based geopolymer, and the effects of various percentages of geopolymer content on the geotechnical properties of the modified RCAs are investigated. The study finds that the angular shape of an RCA exhibits more strength than other shapes, and the use of fly ash-based geopolymer significantly improves the mechanical characteristics of the modified RCAs by up to 10%. The research also shows that the use of fly ash-based geopolymer-treated RCAs in the subbase layer of flexible pavements can lead to a reduction in the required thickness of the base layer, resulting in significant cost savings and curtailment of CO2 emission compared to the use of FAs. Abbreviations: AASTHO: American association of state highway and transportation officials; A: Area of cross-section of flexible pavement; ACV: Aggregate crushing value; AIV: Aggregate impact value; BS: British standard; ASTM: American society for testing and materials; Cc : Co-efficient of curvature; CO2: Carbon dioxide; Cu : Co-efficient of uniformity; D50 : Mean grain size; DCW: Demolished concrete waste; CBR(s): Soaked California bearing ratio; FA: Fresh aggregate; FI: Flakiness index; EI: Elongation index; GC: Geopolymer content; GSD: Grain size distribution; k: Co-efficient of permeability; LAAV: Los Angeles abrasion value; m: Drainage co-efficient; m2 : Drainage co-efficient of base layer; m3 : Drainage co-efficient of subbase layer; ma : Dry mass of additive; MR : Resilient modulus; MR(B) : Resilient modulus of base layer; MR(SB) : Resilient modulus of subbase layer; MR(SG) : Resilient modulus of subgrade layer; mRSM : Dry mass of reclaimed subbase material; NAOH: Sodium hydroxide; Na2SiO3: Sodium silicate; PKR: Pakistani Rupees; R: Reliability; RCA: Recycled concrete aggregate; So : Overall standard deviation; SN: Structural number; USCS: Unified soil classification system; NCHRP: National cooperative highway research programme; NHA: National highway authority; W18 : 18-kip equivalent single axle loads; US$: US Dollars; ξOGC : Optimum geopolymer content; wopt : Optimum moisture content; γdmax : Maximum dry unit weight; a: Structural layer co-efficient; a1 : Structural layer co-efficient of asphalt concrete; a2 : Structural layer co-efficient of base layer; a3 : Structural layer co-efficient of subbase layer; ΔPSI: Present serviceability index; tb : Thickness of base; tsb : Thickness of subbase; δ: Total material weight

Mechanics, durability, and microstructure analysis of marine soil stabilized by an eco-friendly calcium carbide residue-activated coal gangue geopolymer

Constructing infrastructure on soft soils demands the implementation of ground improvement. This study proposed an eco-friendly method of stabilizing marine soil using a calcium carbide residue (CCR)-activated coal gangue (CG) geopolymer derived from industrial waste. Laboratory experiments were conducted to investigate the mechanical properties, durability performance, and stabilization mechanisms of stabilized marine soils under multiple wetting-dry cycles. The results highlighted the effectiveness of CG-CCR geopolymer by a content of 15% to achieve satisfactory strength gain over the engineering requirements. However, the largest decrease in strength (71.89%) was observed when the initial water content was beyond 1.5 times the liquid limit (LL). The optimum solution was proposed to have a geopolymer content of 15% or an initial water content of 1.25·LL to exhibit the highest resistance to strength decay after 12 cycles. Compared with water intrusion, mass loss had a more significant effect on soil strength deterioration. The formation of noncrystalline or amorphous-phase reaction products effectively filled intergranular pores and reduced the void space between soil particles, improving the mechanical properties. The CG-CCR geopolymer was demonstrated to offer a promising solution for soil improvement in geotechnical engineering and waste reduction in industry as a soil stabilizer.

Stabilization of Lead and Zinc Nitrate-Contaminated Low Plasticity Clayey Soil Using Metakaolin Geopolymer

ABSTRACT Contamination of soil threatens the environment and can have a negative effect on soil strength parameters. Soil stabilization is one way to address this issue. In the present study, metakaolin geopolymer was used to stabilize contaminated clay. Initially, the effects of the concentration on the soil parameters was investigated. A combination of lead nitrate and zinc nitrate at a 1:1 ratio was used to contaminate the soil by introducing 1000, 5000 and 10,000 ppm of contaminants. The samples were subjected to a 7-day curing period after which the Atterberg limits, compaction, unconfined compressive strength (UCS), California bearing ratio (CBR) and pH tests were conducted. The results showed that the addition of 10,000 ppm of contaminant to the base soil decreased the CBR, UCS and pH by 21.07%, 23.37% and 15.51%, respectively. The most critical contaminant concentration was found to be 10,000 ppm. Next, soil samples contaminated with 10,000 ppm of lead and zinc nitrates was stabilized with 5%, 10% and 15% metakaolin geopolymer at curing times of 7, 14 and 28 days. After stabilization, the tests initially conducted on the contaminated samples without stabilizer were performed on samples stabilized with metakaolin geopolymer. The outcomes revealed that the soil strength parameters increased significantly with increases in the metakaolin geopolymer content and curing time. An increase in the curing time was shown to increase the UCS. The findings demonstrated that, after 28 days of curing, the soil pH of the stabilized samples with 5%, 10% and 15% metakaolin geopolymer increased by approximately 43.4%, 49.2% and 50.65%, respectively, in comparison with the soil containing 10,000 ppm of contaminants without stabilizer.

Mechanical Properties and Microscopic Study of Steel Slag–Fly Ash-Solidified Loess under Alkaline Conditions

To address the geological hazard posed by unstable loess slopes prone to collapse and landslides, a high-strength geopolymer cementing material was developed utilizing green steel slag–fly ash as its primary constituent and activated through the application of sodium silicate alkalinity. The mechanical properties and microstructure changes of loess under varying dosages of steel slag–fly ash geopolymers and curing age were investigated through a series of tests, including unconfined compressive strength, direct shear, disintegration, electron microscope scanning, and X-ray diffraction. The findings indicate that the incorporation of geopolymers can significantly enhance the internal friction angle, cohesion, and unconfined compressive strength of loess, while mitigating the disintegration quantity and rate of stabilized soil. When 20% geopolymer is mixed into the solidified soil and cured for 28 days, the resulting solidified soil exhibits an internal friction angle of 31.12°, a cohesion of 81.09 kPa, and an unconfined compressive strength of 570.86 kPa. These values are 1.62 times, 1.76 times, and 3.36 times higher than those of loess, respectively. Moreover, the solidified soil shows minimal disintegration within 1800 s, with only 1.97% disintegration. The curing age of solidified soil has a significant impact on its curing effect. Enhancing the curing time can considerably enhance the mechanical properties of solidified soil. When the geopolymer content is 20% and the curing time is extended to 28 days, the internal friction angle, cohesion, and unconfined compressive strength increase by approximately 0.23 times, 0.48 times, and 1.61 times, respectively, compared to a curing time of 7 days. By analyzing SEM and XRD, it was found that the hydration of steel slag–fly ash geopolymer produces C-S-H and C-A-S-H cementing materials, which effectively fill the gaps between soil particles and enhance the mechanical properties of solidified soil. The research findings can serve as a theoretical foundation for the consolidation of loess subgrade utilizing steel slag–fly ash geopolymer.

Mechanical and environmental properties of geopolymer-stabilized domestic waste incineration slag in an asphalt pavement base

Domestic waste incineration slag (WIS) includes fly ash and slag. Fly ash is classified as hazardous waste because it contains heavy metals. Most of slag are directly stacked or landfilled due to problems such as large output and low utilization rate. Harmless treatment is imminent. If WIS is used effectively in the road engineering, which can realize the high-quality and high-efficiency recycling of WIS, and it is of great significance to save resources and protect the environment. This study applies a geopolymer prepared from WIS fly ash as a stabilizing agent in WIS blending macadam for use as a pavement base mixture, and reports the mechanical properties (unconfined compressive strength, splitting strength, and resilience modulus) of the geopolymer-stabilized WIS blending macadam (GeoWIS). The leaching concentrations of harmful heavy metals of GeoWIS soaked in water were also investigated. Finally, the strength formation and heavy metal stability mechanisms were explored. The unconfined compressive strength, splitting strength, and compressive resilient modulus of GeoWIS all increased with increasing geopolymer content and decreasing WIS content. The strength of GeoWIS was derived from its geopolymerization and hydration products (C-S-H gel, N-A-S-H gel, and AFt). When the geopolymer content reached 12%–14%, the GeoWIS without natural macadam met the strength criterion of the asphalt pavement base. Through physical adsorption and chemical bonding, the geopolymer significantly reduced the leaching of harmful heavy metals. In GeoWIS with 50% WIS and stabilized with 10% geopolymer, the Cr, Ni, Cd, and Pb concentrations met the grade Ⅲ groundwater standard. Concentrations of heavy metals leached from GeoWIS are low and exert little impact on environment.

Mechanical characteristics and solidification mechanism of slag/fly ash-based geopolymer and cement solidified organic clay: A comparative study

Geopolymers have recently received intensive research interests in the solidification of various soft soils due to their low-carbon footprint and environmentally friendly. However, understanding of the solidification characteristics of geopolymers in organic clay is still limited. In this study, a range of unconfined axial compression, pH value, moisture content, phase analysis, micromorphology, element composition and pore structure tests was conducted to comparatively investigate the physical properties and micromechanism of slag/fly ash-based geopolymer solidified organic clay (GSO) and cement solidified organic clay (CSO). Furthermore, the reinforcement effect of different parameters (geopolymer content and alkali-activator content) on the mechanical characteristics of GSO in the presence of humic acid was also investigated. The results show that the moisture content of CSO and GSO gradually increases with the content of humic acid, but the pH value and strength gradually decrease. Sustainable geopolymer is proven to be superior to cement in improving the physical-mechanical properties of organic clay. The unconfined compressive strength (UCS) of 28-day cured GSO2 containing 6% humic acid can reach 1.31 MPa, about 1.96 times of CSO1 containing 3% humic acid. The UCS of GSO can be significantly increased by the reasonable content of geopolymer and alkali-activator. Specifically, the 28-day UCS of GSO6 containing 20% geopolymer is 1.92 times and 2.68 times that of GSO2 (15%) and GSO5 (10%), respectively. The analysis of microscopic characteristics confirms that the strength formation of CSO and GSO is mainly affected by the number of cementitious products and the cementation degree of clay particles, which is attributed to the compactness of the matrix structure. The research results provide insights for a more comprehensive understanding of the application potential of geopolymers in organic clay solidification.

Enhancing Rutting Resistance in Bituminous Concrete: A Response Surface Methodology Approach for Optimizing Bitumen and Hydrochar-Based Geopolymer Content

In recent time, there has been a wave in concern in enhancing the durability and performance of bituminous pavements, particularly considering rising traffic volumes and environmental concerns. Thus, modifying bitumen with biowaste materials such as hydrochar-based geopolymer composites is one new technique for resolving these challenges. Thus, this study investigates how the bitumen and hydrochar-based geopolymer composites (HBGC) affect the rutting resistance (RR) of bituminous pavements, utilizing an optimization known as the Response Surface Methodology (RSM). Three main design factors were investigated: asphalt binder content, hydrochar content, and geopolymer content. The asphalt binder content varied from 4% to 6%, whereas the biochar and geopolymer content ranged from 0% to 4%. The RSM technique was used to analyze the interplay between various design elements and develop a prediction model for optimizing the RR. The ANOVA analysis demonstrated strong statistical performance, indicating a high link between actual and projected outcomes. Notably, the synergistic effect of increasing bitumen content and the use of a hydrochar-based geopolymer composite modifier resulted in improved RR in bituminous concrete. Furthermore, the study indicated ideal input content of 5.75% for bitumen, 3.4% for hydrochar, and 3.24% for the geopolymer modifier for improve RR. Also, the model has a 5% percentage error, showing a significant correlation between predicted and actual data. This study demonstrates the effectiveness of using RSM to optimize and predict HBGC bituminous concrete RR, by providing durability and sustainability through HBGC utilization in bituminous concrete

Fabrication of B4C hardened body using geopolymer binder with cold reaction sintering and application to neutron shielding

Boron carbide (B4C) is widely used as a neutron shielding material, but it is known to be difficult to sinter. Typically, B4C is sintered at ultra-high temperature (>2000 °C) and high pressure, or hardened using an organic binder such as silicone rubber. In this study, hardening by an inorganic binder, that is, a geopolymer binder was investigated. The raw materials for the binder were fly ash, sodium metasilicate anhydride (Na2SiO3) and sodium metasilicate 9-hydrate (Na2SiO3·9H2O), with the B4C being hardened at only 130 °C by novel “cold reaction sintering” using a warm-pressing device. The process involves a simultaneous reaction involving geopolymer formation (geopolymerization) and solidification. The effects of the geopolymer content and the mixing ratio with B4C powder with different particle sizes on the compressive strength and density of the B4C were investigated. When coarse B4C particles (∼100 μm), and fine B4C particles (∼1 μm) were combined, the fine B4C particles and the binder filled the voids between the coarse B4C particles. As a result, it was found that when appropriate pressure was applied to the raw materials, the binder was completely geopolymerized, and a strong hardened body was formed. The compressive strength of the hardened body exceeded 50 MPa when the content of fine B4C particles was 30 wt% and the content of the geopolymer binder was 20 wt%. Furthermore, neutron transmission test of the hardened bodies were conducted to evaluate their neutron shielding properties, and it was confirmed that the geopolymer-based B4C composites achieved a B4C volume occupancy of more than 70%, which is unreachable for commercial rubber-based B4C composites.

Research on the Pavement Performance of Slag/Fly Ash-Based Geopolymer-Stabilized Macadam

The substitution of slag-based geopolymer materials for cement-stabilized macadam in road bases is in line with the demand for green and sustainable development in the transportation industry. Thus, slag/fly-ash-based geopolymer materials were prepared to stabilize macadam of road bases in this study. The mechanical properties, freeze-thaw resistance, and dry shrinkage durability of slag/fly-ash-based stabilized macadam materials were studied to analyze the influence of geopolymer dosage on these properties of stabilized macadam. Microscopic tests such as XRD, FITR, and SEM were carried out to explore the formation mechanism of strength and the characteristic of interface transition zone (ITZ). Results show that the 28 d compressive strength, compressive elastic modulus, and tensile strength of slag/fly-ash-based stabilized macadam increase linearly with the increase of geopolymer content. When the dosage of slag-based geopolymer is 4%, the 7 d unconfined compressive strength of slag/fly-ash-based stabilized macadam reaches 8.76 MPa, and the strength still reaches 14.84 MPa after five freeze-thaw cycles (28 d), which satisfy the application requirements of expressway and first-class highway base (JTG/T F20-2015). The dry shrinkage property of slag/fly-ash-based stabilized macadam is better than that of cement-fly-ash-stabilized macadam. When the amount of geopolymer is 3%, the dry shrinkage strain of slag/fly-ash-based stabilized macadam is 231.2 με, which is smaller than that of cement-fly-ash-stabilized macadam (261.3 με). No obvious porosity around the ITZ was detected, indicating good binding between the geopolymer and the aggregate.

Compressed Earth Blocks Using Sediments and Alkali-Activated Byproducts

Sediment dredging is necessary and vital to preserve maritime activities and prevent floods. The management of these sediments represent an environmental challenge for many countries all over the world. This study focuses on evaluating the feasibility of using dredged sediments for the manufacturing of compressed earth blocks (CEB). The alternative construction material has the potential of reducing the need for dredged sediment onshore storage or ocean dumping. Several experimental tests have been conducted on two geopolymer types, which were obtained by mixing sediments from the northern region of France, fly ash (FA), and grounded blast furnace slag (GBFS). The geopolymers, which were activated using an eight-molar concentrated sodium hydroxide solution (NH), were cured at a temperature of 50 °C. The results have shown that a geopolymer content of 36% of FA and 10% of GBFS along with (NH) alkaline solution has significantly improved the mechanical properties of CEBs, which have outperformed those of Portland Cement-stabilized traditional blocks. The use of NH has resulted in the formation of crystalline calcium silicate hydrate (C-S-H) amorphous gel. Adding GBFS to the mix has enhanced the geopolymer paste compressive strength and microstructure because of the formation of additional C-S-H. The valorization of dredged sediments in CEB based on geopolymer stabilization can contribute to the reduction of the CO2 footprint of the construction industry.

Experimental Investigation of Unconfined Compression Strength and Microstructure Characteristics of Slag and Fly Ash-Based Geopolymer Stabilized Riverside Soft Soil.

To solve the issues of insufficient early strength of cement stabilized soil and high resource cost, high reduction cost, and high environmental cost induced by the application of cement, the slag and fly ash-based geopolymer was adopted as the stabilizer to treat riverside soft soil. This study mainly investigated the effects of stabilizer content, slag-to-fly ash ratio, and alkaline activator content on the strength of geopolymer stabilized soils with different curing ages. Unconfined compressive strength (UCS), scanning electron microscope (SEM), and X-ray energy spectrum analysis (EDS) tests were carried out. The results show that the stabilizer content, slag–fly ash ratio, and alkaline activator content have a decisive influence on the UCS of geopolymer-stabilized soil. The mix-proportions scheme of geopolymer stabilized riverside soft soil, with a geopolymer content of 15%, a slag–fly ash ratio of 80:20, and an alkaline activator content of 30%, is considered optimum. It is proven by SEM that the uniformly distributed gelatinous products formed in the geopolymer-stabilized soil bind the soil particles tightly. Moreover, the EDS analysis confirms that the gelatinous products are mainly composed of C-S-H gel and sodium-based aluminosilicate (N-A-S-H).

Strength and Durability of Granular Soil Stabilized with FA-GGBS Geopolymer

Granular soils are sensitive to internal erosion due to the presence of lesser fines and need to be stabilized to improve their geoengineering properties. An investigation is made to explore the efficacy of fly ash-slag (FA-GGBS) geopolymer in stabilizing granular soil through a set of experimental studies. The experimental program focused on compaction characteristics, unconfined compressive strength, bearing resistance, and durability of geopolymer stabilized granular soil to assess its suitability as a construction material. Microstructural analysis has been carried out and correlated with strength development. Based on the test results, a maximum unconfined compressive strength of about 7 MPa and California bearing ratio (CBR) ranging from 52% to 416% is obtained. The geopolymer stabilized soil showed excellent stability against wetting–drying and freezing–thawing cycles, slaking water, and aggressive chemical environments. The microstructural developments are greatly influenced by the geopolymer content and curing period, indicating the formation of hydration and geopolymeric reaction products.

Influence of Various Types of Steel Fibre on the Mechanical and Physical Characteristics of GGBS Based Geopolymer Concrete

This study provides experimental investigation of the mechanical and physical properties of reinforced geopolymer concrete based on Ground Granulated Blast Furnace Slag (GGBS). This research demonstrates the influence of various types of steel fibre on compressive, split tensile, flexural strengths and elastic modulus of hardened GPC, workability of reinforced geopolymer concrete and also analyzed the workability, setting time and flow test of fresh geopolymer concrete. Additionally, corrosion test was conducted on reinforced geopolymer concrete. Mixtures of alkaline liquid to GGBS ratio of 0.5 with steel fibers had been added to the mixture of 0% volume fractions (Vf %), 0.5%, 1.0%, and 1.5% concrete amount. Based on the result of the experiments, the presence of steel fibres enhanced the compressive and tensile strength of the SERGPC, in terms of volume fraction of steel fibres as compared to the regular GPC without fibres. It was observed that there was a significant improvement in GPC's mechanical characteristics and corrosion rate as the lifespan of concrete increased. The incorporation of steel fibres resulted in increased compressive and flexural strengths in the early age and consequently tensile splitting power was increased. The increase in concrete geopolymer content improved the rate of corrosion over time.

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.

Evaluating Fly Ash‐Based Geopolymers as a Modifier for Asphalt Binders

Severe Canadian winter conditions and growing traffic volumes are vital factors resulting in a reduction of the service life of flexible pavements. Researchers and engineers strived to develop several additives to develop balanced asphalt mixers capable of resisting distresses that caused deterioration of flexible pavements in Canada. In this study, a critical literature review regarding the use of geopolymers and their application in construction materials is provided. Moreover, an experimental matrix of laboratory testing was conducted to study the rheological and microstructural properties of the PG 58‐28 asphalt binder, with different percentages (0%, 3%, 6%, and 9%) of geopolymer. The effect of geopolymer‐curing time on rheological properties was investigated. Rotational viscometer, dynamic shear rheometer (DSR), and environmental scanning electron microscopy (ESEM) imaging devices were used to compare the performance of control binder with a binder with different percentages of geopolymers. Results indicated that the increase in the geopolymer content and the curing time affect the rheological behavior of the asphalt binder by increasing its viscosity, complex shear modulus, and failure temperature. Samples with higher geopolymer percentage exhibited better performance in terms of rutting resistance. Moreover, an increase in the failure temperature of modified asphalt binder with 9% geopolymer is recorded as 8.58%, 14.2%, and 15.2% for curing times of 2, 7, and 14 days, respectively, compared with virgin asphalt. Furthermore, the nanoparticles appear to be well dispersed in the binder, and increasing the percentage of the geopolymer does not seem to affect the microstructure of the binder. Overall research conclusion is that geopolymer application resulted in a potential enhancement of some of the properties of the asphalt binder.