Engineered Geopolymer Composites Research Articles

Axial behavior of concrete cylinders retrofitted with a hybrid system of CFRP textile grid and engineered geopolymer composite

Fiber-reinforced polymer (FRP) textile grid-reinforced engineered cementitious composites (ECCs) are effective in strengthening concrete structures. Considering environmental interest, engineered geopolymer composites (EGCs) have been employed as an alternative to ECC. In this study, we present a retrofit scheme for CFRP textile grid-reinforced EGC matrix composites for concrete cylinders and compare the axial behavior of strengthened concrete cylinders with a conventional FRP-reinforced ECC strengthening system. Axial compressive specimens were tested for various parameters, including the number of FRP textiles, original concrete strength, and damage level of the original concrete cylinder. The results indicated that the strengthened concrete cylinders failed in a ductile manner owing to the progressive rupture of the CFRP textile grids. The CFRP-EGC strengthening layers improved the axial bearing capacity, stiffness, and ductility of the concrete cylinders. The axial bearing capacity increased by 89.4%–170.4 %; therefore, the contribution of enhanced confinement effect was 36.7–113.6 %. The confinement effect provided by the grids ranged from 0.805 to 1.958 MPa and played a major role in the CFRP-EGC strengthening layers. Comparatively, the CFRP grid utilization is more efficient in the EGC matrix than in the traditional ECC matrix. Moreover, the influence of the pre-damage on the behavior of the concrete cylinders was compensated for by the strengthening layers.

Pozzolanic potential of sustainable precursors for engineered geopolymer composites (EGC)

Confirming the pozzolanic activity is crucial to ensure their compatibility and performance in geopolymer composite (GC) applications, as it improves the geopolymerization process and optimizes the strength characteristics of GCs. This work evaluates the pozzolanic properties of Fly ash (FA), Basic Oxygen Furnace (BOF) slag, and Iron Ore Tailings (IOT) for their potential use in the development of Engineered Geopolymer Composites (EGC). IOT partially substitutes fine aggregate, while FA and BOF slag are the major precursors. Pozzolanic properties of the aforementioned materials were assessed through the Frattini, saturated lime test (SLT), and strength activity index (SAI). The Frattini test values recorded were 90, 47, and 30% of CaO removal, denoting their degree of pozzolanicity respectively for BOF Slag, FA, and IOT. In the SLT, the formation of stable calcium silicate hydrates and aluminates are verified by the reaction of the test pozzolans with lime, thereby conforming their pozzolanicity. The results from the Frattini and SAI tests showed a significant correlation, indicating an effective pozzolanicity measure of the test materials. However, the results from the SLT did not align with the outcomes from the Frattini and SAI tests. This contradiction suggests that the SLT is ineffective compared to the other two test methods in measuring the pozzolanic activity of the test materials. The research findings provide valuable insights into the potential usage of these materials (pozzolans) as sustainable building materials in the construction industry.

Bond properties of steel bar with engineered geopolymer composites under monotonic load

AbstractEngineered geopolymer composites (EGC) featuring extraordinary tensile ductility are a potential alternative to engineered cementitious composite. In this study, the local bonding properties of steel bars in EGC were investigated. Monotonic loading tests of the 120 specimens were performed using the pullout test method. The study examined the ultimate tensile strain of EGC, diameter and anchorage length of the steel bar on bond performance. The results showed that the EGC, with an ultimate tensile strain of 4.57%, had the highest peak bond strength. By comparing the test results of rebar to ordinary concrete bond performance provided in several previous literature, it was demonstrated that EGC has superior bond performance with rebar compared to ordinary concrete. Based on this, suggestions were provided for the design of rebar anchorage length in EGC. Finally, a mathematical model suitable for determining the bond–slip curve between EGC and steel bars is proposed.

Comprehensive Analysis of Mechanical, Economic, and Environmental Characteristics of Hybrid PE/PP Fiber-Reinforced Engineered Geopolymer Composites

Engineered Geopolymer Composites (EGCs), known for their excellent tensile properties and lower carbon emissions, have gained widespread attention in the field of fiber-reinforced concrete. However, the high cost of high-performance synthetic fibers, a crucial component of EGCs, limits their practical engineering applications. In this study, by using low-cost PP fibers hybridized with PE fibers and adjusting the fly ash/ground granulated blast furnace slag (FA/GGBS) ratio, cost-effective, high-performing hybrid PE/PP-reinforced engineered geopolymer composites (H-EGCs) were developed. This study conducted axial compressive and tensile tests on H-EGCs with different FA/GGBS ratios (7:3, 6:4, and 5:5) and PP fiber replacement ratios (0%, 25%, 50%, 75%, and 100%), investigated the influence of FA/GGBS and PP fiber replacement ratio on static mechanical behavior, and evaluated the economic and environmental benefits based on mechanical performance indicators. The result indicated that the compressive strength of H-EGCs can reach 120 MPa when the FA/GGBS ratio is 5:5; however, an increase in FA/GGBS and PP fiber replacement ratio leads to a loss in compressive strength and elastic modulus. The incorporation of PP fibers in moderate amounts enhances ultimate tensile strain by reducing crack control ability, and the maximum tensile deformation capacity (7.82–9.66%) was obtained for H-EGCs with a PP fiber replacement ratio of 50%. The optimal economic and environmental benefits of H-EGCs are observed when the FA/GGBS ratio is 5:5 and the PP fiber replacement ratio is set at 50%.

Investigation of dynamic compression properties of lightweight engineered geopolymer composites containing different ceramsites (LW-EGC)

Lightweight engineering geopolymer composites (LW-EGC) can contribute to green building materials products by taking advantage of the advantages of man-made ceramsite and geopolymers. In this paper, an active "sacrifice" method was proposed, which is based on the idea that low elastic modulus ceramsites are preferentially damaged or ruptured during the impact loading process, thus absorbing and dissipating the impact energy. LW-EGC was enhanced by PVA fiber with volume fraction of 2% and multi-walled carbon nanotubes with mass fraction of 0.15%. The dynamic compression properties of LW-EGC containing different ceramsites were studied by using Φ100 mm split Hopkinson pressure bar (SHPB) test device. The compression characteristics of the LW-EGC under an impact load were evaluated, including the strain rate, dynamic stress–strain relationship, elastic modulus, dynamic increase factor (DIF), energy absorption, and failure patterns. The results showed that the dynamic peak stress, dynamic peak strain, DIF, energy absorption and damage degree of LW-EGC all increased with the increase of strain rate, showing obvious strain-rate sensitivity. At high strain rate, the dynamic elastic modulus mainly showed softening effect. At the same strain rate, the impact resistance of LW-EGC-1 containing fly ash ceramsite was the best, and the damage degree of LW-EGC-3 containing shale ceramsite was the lowest. Empirical DIF formulas of the LW-EGC was proposed; the DIF increased approximately linearly with the strain rate in a logarithmic manner.

Development of engineered geopolymer composites containing low-activity fly ashes and ground granulated blast furnace slags with hybrid fibers

Engineered geopolymer composites, a green version of engineered cementitious composites, replace the cement by industry byproducts such as ground granulated blast furnace slag and/or fly ash with alkaline activators. However, fly ashes largely available in Kazakhstan termed here as low-activity fly ash, do not meet ASTM standard in terms of the particle size distribution and strength activity index due to lack of quality control during collection. Therefore, this paper aims to develop an engineered geopolymer composite containing low-activity fly ash and ground granulated blast furnace slag with hybrid fibers. Different combinations of fibers including polyvinyl alcohol, polypropylene, and steel fibers were investigated. The developed composite is targeted for multi-functional retrofitting on unreinforced masonry structures which requires high strain hardening capacity and low thermal conductivity. To achieve this target, the workability, dry shrinkage, compressive strength, tensile strength, strain hardening capacity, and thermal conductivity were examined through extensive experimental studies. From test results, it has been found that the geopolymer composite containing low-activity fly ash with a proper fiber combination can exhibit desirable mechanical and thermal properties with more than 20 MPa compressive strength, more than 2% of the tensile strain hardening capacity, and less than 0.25 W/mK thermal conductivity. Based on test results, micromechanical models were also developed for the composite to identify suitable fiber combinations for required strain hardening capacities.

Effects of PVA fibers and multi-walled carbon nanotubes reinforcement on uniaxial compression fatigue properties of Engineered geopolymer composites

As a new type of green and environmentally friendly cementing material, engineered geopolymer composites (EGC) have broad application prospects. In this study, uniaxial compression fatigue tests were conducted to investigate the fatigue properties of geopolymer material. A total of 137 samples were tested to investigate the effects of carbon nanotubes content, polyvinyl alcohol (PVA) fibers volume content, and maximum stress level on the fatigue life and deformation of geopolymers. The results showed that the fatigue life of geopolymers obeys Weibull distribution, and PVA fibers and multi-walled carbon nanotubes (MWCNTs) achieved multiscale enhancement of the fatigue life by up to 16.34 times. The total strain accumulation, residual strain, and fatigue stiffness of the geopolymers under fatigue loading exhibited a three-stage evolution rule, with stability within the secondary creep branch. In the process of EGC production, the innovative adoption of optimized MWCNTs surface modification and dispersion strategies improved the uniformity of MWCNTs distribution in the matrix. Scanning electron microscopy (SEM) confirmed the hybridization of MWCNTs and PVA fibers at the microscopic level, which can achieve multi-scale enhancement of geopolymers. This study successfully optimized the content of MWCNTs and PVA fibers, further expanding the application range of composite materials.

Sustainable engineered geopolymer composites: A study on the potential of fly ash, BOF slag, and iron ore tailings

Sustainable engineered geopolymer composites: A study on the potential of fly ash, BOF slag, and iron ore tailings

Fly ash-dominated High-Strength Engineered/Strain-Hardening Geopolymer Composites (HS-EGC/SHGC): Influence of alkalinity and environmental assessment

In this study, fly ash (FA)-dominated High-Strength Engineered Geopolymer Composites (HS-EGC) were designed and developed. The influence of alkalinity and the underlying mechanism on the mechanical performance and microstructures were investigated through a systematic study. The developed HS-EGC presented high compressive strengths (over 100 MPa) and high tensile ductility (over 4%). Specifically, results showed that HS-EGC with 6% alkalinity possessed the highest compressive strength of 122.7 MPa, the largest tensile strain capacity of 8.0%, and the highest tensile strength of 12.9 MPa. Tensile over-saturated cracking was observed for HS-EGC with alkalinities of 6% and 8% through crack analysis. Back scattering electron and nanoindentation further confirmed that higher alkalinity resulted in higher reaction degrees, but a strength loss was observed at an alkalinity of 8% due to the deterioration of the reaction product. From the comprehensive review of high-strength Engineered Cementitious Composites (ECC) with similar compressive strength and the existing FA-dominated EGC/ECC, it was found that the developed HS-EGC recorded the lowest embodied carbon, embodied energy, and material cost per MPa compared to all the counterparts. Notably, the HS-EGC with 6% alkalinity in this work pushed the performance envelope of FA-dominated EGC. The findings of this study provided useful knowledge for the design and development of HS-EGC for sustainable and resilient infrastructure.

Mechanical and environmental performance of engineered geopolymer composites incorporating ternary solid waste

In order to reduce the utilization of cement and promote the low-carbon development of construction materials, engineered geopolymer composites (EGC) offer an alternative to engineered cement composites (ECC). In this study, slag, fly ash and steel slag were innovatively combined as precursor materials to prepare EGC. The focus was laid on the influence of sodium silicate modulus (Ms) and alkali content on the mechanical and tensile properties of ternary solid waste based EGC. Four levels of Ms (1.2, 1.5, 1.8, and 2.1) and three groups of alkali content (6 %, 8 %, and 10 %) were designed in the experiments. The flowability, setting time, compressive strength, flexural strength, uniaxial-tensile performance, and carbon emissions were comprehensively studied. Results revealed that as the Ms decreased and the alkali content increased, the setting time and flowability showed a decreasing trend. With an increase in Ms, the compressive strength and flexural strength initially increased and then decreased, indicating an optimal dosage of sodium silicate modulus. Moreover, alkali content showed a positive correlation with compressive strength and flexural strength. At Ms 1.5 and alkali content 8 %, the 28-day compressive strength reached a maximum of 83.9 MPa, the 28-day flexural strength was 14.7 MPa, and the ultimate tensile strain reached 11.31 %. The environmental benefit analysis indicated that compared with high-ductility cement-based materials, EGCs had lower carbon emissions and energy consumption, and the carbon emissions of EGCs were approximately 50.6 % lower than that of ECC.

Effect of mix proportion parameters on chloride erosion resistance of fly ash/slag-based engineered geopolymer composites

The incorporation of ground granulated blast furnace slags (GGBS) into fly ash-based engineered geopolymer composites (EGC) was explored to enhance their resistance against chloride-induced erosion. An investigation was conducted to understand how variations in the slag content, the water-to-binder ratio, the quantity of alkali activator, and the inclusion of polyethylene fibers affect the EGC's ability to resist chloride erosion. The study found an enhancement in the chloride erosion resistance with an increase in the water-binder ratio from 0.32 to 0.38. Conversely, the resistance decreased when the proportion of slag was raised from 40% to 100%, when the alkali activator content went up from 4% to 6%, and when the percentage of polyethylene fibers grew from 1.0% to 2.0%. Microstructural analyses revealed that a higher water-binder ratio of 0.38 reduced the peak intensity of calcium aluminate silicate hydrate, increasing the porosity and, thereby, compromising the chloride erosion resistance of the EGC. In contrast, increasing the slag content, alkali activator, and polyethylene fiber percentage generated the reverse effect, reinforcing the material's resistance to chloride penetration. The optimized EGC demonstrated promising chloride erosion resistance with a low chloride diffusion coefficient of 0.0661 × 10−12 m2/s, paired with robust mechanical properties including compressive strength ranging from 70 to 80 MPa, ultimate tensile strength between 5 and 6 MPa, and ultimate tensile strain reaching up to 8%.

Evaluation of Mechanical and Microstructural Properties of Engineered Geopolymer Composites with Construction and Demolition Waste-Based Matrices

Evaluation of Mechanical and Microstructural Properties of Engineered Geopolymer Composites with Construction and Demolition Waste-Based Matrices

Engineered geopolymer composite (EGC) with ultra-low fiber content of 0.2%

Engineered cementitious composite (ECC) features with excellent tensile performance. However, two major drawbacks, including the high environmental impacts associated with high content of cement and the high cost caused by high fiber content, impede the wide application of ECC. This study designs and successfully develops a high ductile cement-free engineered geopolymer composite (EGC) with ultra-low content of fibers (0.2% by volume, EGC-0.2%). EGC-0.2% exhibits a tensile strain capacity above 4% and a controllable crack width around 200 µm. The compressive strength reaches 39 MPa and the density is below 1200 kg/m3, showing an excellent specific strength (the ratio of the compressive strength-to-density) of 37 kPa/(kg/m3). The matrix fracture toughness of the developed EGC is low to facilitate the high ductility of the EGC-0.2% by such low fiber content. In addition, EGC-0.2% presents extremely low environmental impacts and cost. The embodied energy and embodied carbon decrease by 23% and 67% than conventional concrete, respectively, and the cost is only 21% of the classic M45-ECC with similar mechanical performance. The current findings provide valuable references for the future advancement of ECC towards high sustainability and cost effectiveness.

Magnesium Sulfate Resistance of Strain-Hardening Fiber Reinforced Slag and Fly Ash-Based Engineered Geopolymer Composites

Magnesium Sulfate Resistance of Strain-Hardening Fiber Reinforced Slag and Fly Ash-Based Engineered Geopolymer Composites

Optimisation Investigation and Bond-Slip Behaviour of High Strength PVA-Engineered Geopolymer Composite (EGC) Cured in Ambient Temperatures

Engineered geopolymer composite (EGC) is becoming an uprising product in the civil industry as a substitute and solution for conventional geopolymer concrete (GPC) as GPC exhibits brittleness and has poor cracking resistance. In this paper, we explored high strength engineered geopolymer composite (EGC) made of polyvinyl alcohol (PVA) fibre and without coarse aggregate constituents characterised as high-performance geopolymer concrete. Varying alkaline solution to fly ash ratio (AL/FA) was investigated. Bond-slip behaviour and the mechanical properties, including compressive, tensile, and flexural strengths, were studied. PVA-EGC mix designs in this research was optimised using response surface methodology (RSM). Various parameters, including the amount of ground granulated blast slag (GGBS) and silica fume, were included in the parametric and optimisation study. Based on the RSM study, the use of quadratic studies found the responses to be well-fitted. Next, the optimised mix design was utilised for the casting of all the samples for the mechanical and bond-slip tests in this study. The main parameters of bonding behaviour include multiple embedment lengths (7 d, 10 d, 12 d and 15 d) and various sizes of rebar diameter used for pull-out tests. Moreover, the mechanical properties and bond behaviours of EGC were compared with those of conventional geopolymer concrete (GPC). The compressive strength of EGC and GPC at 28 days were designed to be similar for comparison purposes; however, EGC shows higher early compressive strength on day 1 compared to GPC. In addition, results indicate that EGC has superior mechanical properties and bond performance compared to GPC, where EGC is approximately 9 and 150% higher than GPC in terms of flexural and tensile strength, respectively. Pull-out tests showed that EGC samples exhibited higher ductility, as evidenced by the presence of multiple cracks before any exhibited failure in tension and flexure. Ductile failure modes, such as pull-out failure and pull-out splitting failure, are observed in EGC. In contrast, GPC specimens show brittle failure, such as splitting failure.

Fly Ash and BOF Slag as Sustainable Precursors for Engineered Geopolymer Composite (EGC) mixes: A Strength Optimization Study

Fly Ash and BOF Slag as Sustainable Precursors for Engineered Geopolymer Composite (EGC) mixes: A Strength Optimization Study

Feasibility study of engineered geopolymer composites based high-calcium fly ash and micromechanics analysis

Engineered geopolymer composites (EGC) have attracted much attention as green construction materials, characterized by strain-hardening behavior and multiple cracking capabilities. Nevertheless, the current utilization of low-calcium fly ash in EGC preparation poses a challenge in terms of long hardening time, which substantially affects the feasibility of applying EGC in engineering projects. The purpose of this study is to assess the potential for developing EGCs using high-calcium fly ash (HFA), explore the impact of sodium silicate (SS)-to-sodium hydroxide (SH) ratio on material properties, and perform a comparative analysis between EGCs fabricated with low-calcium fly ash (LFA) and HFA. SEM analysis elucidates that an increase in the SS-to-SH ratio exerts a favorable influence on matrix density, thereby augmenting overall strength. Nevertheless, this enhancement is accompanied by a notable reduction in tensile strain capacity. It was observed that EGC based on HFA (HFA-EGC) outperforms LFA-based EGC (LFA-EGC) in various aspects of mechanical properties. The effects of SS-to-SH ratio, LFA, and HFA on the mechanical properties were analyzed at the microscale using XRD and SEM, and combined with micromechanical parameters, establishing a multi-scale connection for material performance. The study offers a comprehensive analysis of how varying precursor and activator compositions affect the tensile properties.

Effect of Curing Age on Tensile Properties of Fly Ash Based Engineered Geopolymer Composites (FA-EGC) by Uniaxial Tensile Test and Ultrasonic Pulse Velocity Method

Effect of Curing Age on Tensile Properties of Fly Ash Based Engineered Geopolymer Composites (FA-EGC) by Uniaxial Tensile Test and Ultrasonic Pulse Velocity Method

Micromechanical and mineralogy analyses on extremely ductile engineered geopolymer composites with different activator pretreatments

In this study, the effects of activator pretreatments on properties of fly ash-based extremely ductile engineered geopolymer composites (ED-EGCs) were investigated. Two ED-EGC mixtures were designed using the same binder system and polyethylene fiber reinforcement, but different pretreated activators. A sequence of experiments including mechanical testing, micromechanical analysis, and chemical characterization was performed. The test results indicate that ED-EGCs were lightweight with density values lower than 1.7 g/cm3, had moderate compressive strengths over 21 MPa, and exhibited extremely ductile behavior with tensile strain capacities over 11 %. Overall, the warming pretreatment was beneficial to improve strengths but less effective to enhance tensile ductility of ED-EGCs. In contrast, the ED-EGC mixture adopting the cooling pretreatment showed tensile strain capacity up to 18.6 %, which has been unprecedented in the literature. The micromechanical analysis explained the extremely ductile behavior of ED-EGCs. SEM observation also confirmed that the fibers were robustly embedded into the geopolymer matrix. Through chemical analysis using EDS, it was found that N-A-S-H gel was the dominant geopolymeric product of ED-EGCs.

Bond stress–slip constitutive relationship between engineered geopolymer composites (EGC) and rebar under cyclic loading

This study investigated the performance of the bonding between engineered geopolymer composites (EGC) and rebar under cyclic loading. A total of 120 specimens were designed for the study. EGC ultimate tensile strain, rebar diameter, and anchorage length were selected as variables, and the bond slip data under cyclic loading were collected using the pull–out method. These variables and data were used to study the failure mode, energy dissipation and bond strength degradation of the specimens. The results showed that the bonding between EGC and rebar is good under cyclic loading, EGC with a high ultimate tensile strain effectively reduce the bond stress degradation. In the range of 0.03% – 6.24%, the higher the EGC ultimate tensile strain is, the stronger the energy dissipation capacity of the sample. Whereas increasing the rebar diameter and anchorage length has a negative impact on bonding. Finally, a slip analysis model was established for the bond stress between EGC and rebar under cyclic loading. The prediction results showed that the proposed model accurately reproduces the bond degradation under cyclic loading.