Ambient Cured Geopolymer Concrete Research Articles

Influence of alkaline activators on mechanical properties of environmentally friendly geopolymer concrete under different curing regimes.

Previous studies highlighted the significance of tailoring alkaline activators (AA) to specific fly ash (FA) sources for optimal properties of geopolymer concrete (GPC). This study examines the influence of various AA's properties on mechanical properties and microstructures of local low-calcium FA-based GPC under varying curing conditions. A comprehensive investigation consists of several factors such as NaOH molarities (10M, 12M, 14M, 16M), ratios (1.5, 2.0, 2.5) and ratios (0.5, 0.6). The results reveal a complex relationship, demonstrating that NaOH molarity positively influences compressive strength up to a threshold of 14M, beyond which an adverse effect was observed while, the flexural strength was increased up to 16M. Moreover, the study highlights the complex relationship between ratios and mechanical strengths. Notably, these properties exhibited an increase as the ratio rose up to 2.0, but a subsequent decrease was observed when the ratio reached 2.5. Moreover, proposed regression equations predict the compressive and flexural strengths of both ambient-cured GPC and heat-cured GPC with marginal statistical errors. The optimal GPC mix exhibited 49% lower embodied emissions than the corresponding OPC concrete. GPC has higher cost, but it exhibited lower cost-to-strength ratio compared to OPC concrete.

Mechanical, microstructural, and durability assessment of ambient cured geopolymer concrete

Mechanical, microstructural, and durability assessment of ambient cured geopolymer concrete

Durability Studies and Stress Strain Characteristics of hooked end steel fiber reinforced ambient cured geopolymer concrete

Abstract For conventional concrete, the use of fibers has proven to improve the strength properties of the material. However, in the case of ambient cured geopolymer concrete, there are limited studies that explore the application of fibers, in particular, the use of hooked end steel fibers. Further, it is important to study the durability properties of geopolymer concrete with fibers, since it will influence the service life of the structures in practice. Therefore, in the present study, fiber-reinforced geopolymer concrete was synthesized using fly ash, GGBS, hooked end steel fibers, and alkaline solution made with Na2SiO3 and NaOH. The percentage of steel fibers varied in the range of 0.5% to 2% with an increment of 0.5% by volume fraction of the binder. The precursor materials were characterized using techniques such as X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscope (SEM). Durability studies like water absorption, drying shrinkage, sulphate attack were studied. In addition, the elastic constants were determined through stress strain behaviour of geopolymer concrete in uniaxial compression. The results of the experimental study showed that the addition of hooked end steel fibers influences the strength of geopolymer concrete up to an optimal percentage, which was found to be 1%. Furthermore, in terms of durability properties, the addition of fibers exhibited better results in terms of resistance to water absorption and chemical attack, and this was validated by the microstructural studies, where the specimens with hooked end steel fibers revealed much denser hardened geopolymer matrix when compared to the mixes without fibers.

Fatigue analysis of ambient-cured geopolymer concrete for high-traffic pavements.

The building sector is growing at a rapid rate, leading to an increased demand for construction materials. Concrete made with Ordinary Portland Cement (OPC) has long been the preferred choice due to its excellent bonding properties and versatility as demanded by construction process. However, the manufacturing of Ordinary Portland Cement (OPC) leads to negative impacts on the environment, with the cement sector responsible for around 5-8% of global CO2 emissions. In addition, the manufacture of OPC necessitates significant amounts of natural raw materials and energy. Contrastingly, using geopolymers promises to save substantial amounts of energy and reduce CO2 emissions. This potential has sparked growing interest in the application of geopolymers within transportation infrastructure. For pavements, the workability requirement is less, and hence, geopolymer concrete (GPC) is a viable option, but fatigue-resistance of GPC is not seen reported in literatures. This article evaluates the properties of geopolymer concrete with low-calcium fly ash partially replaced with ground granular blast furnace slag (GGBS) with 8M NaOH alkaline solution and cured under ambient atmospheric conditions to evaluate its usage in pavements and develop an environmentally sustainable and durable GPC capable of withstanding heavy traffic. The study involves adjusting the pavement quality concrete (PQC) mix design; evaluating the mechanical characteristics, abrasion resistance, and shrinkage strain of the GPC; and analyzing its microstructure. Additionally, the study compares the fatigue life of GPC to that of PQC using various Weibull distribution approaches. The results showed that GPC4 (70% Fly ash and 30% GGBS) mix achieved best results at 28days, with a compressive strength of 45.68MPa, split tensile strength of 3.76MPa, and flexural strength of 4.62MPa. Also, shrinkage strains were nearly 31% lesser than PQC at 90days. In addition, developing GPC needs 27% lesser embodied energy than PQC. Fatigue analysis prove that ambient cured fly ash-GGBS based geopolymer concrete with 8M NaOH exhibits less stress development than PQC at medium loads, even though it is brittle. Thus, the study proves that it is suitable as a material for pavements to resist medium-loaded traffic-resisting pavements.

Comparative fracture properties of ambient-cured geopolymer concrete containing four different fibers in mono and hybrid combinations using digital image correlation

This paper presents an investigation on the effects of four different fibers (polypropylene (PP), polyvinyl alcohol (PVA), recycled polypropylene (RPP), and steel (S) fibers) on the fracture behaviour of ambient-cured fly ash geopolymer concrete (GPC). The four fibers were added into GPC by both mono at 1.0% volume and hybrid combinations with steel fiber at 0.5% of each other type of fiber. The full-field strain distribution and the crack mouth opening displacement (CMOD) were monitored by digital image correlation (DIC) technology. The results reveal that adding fibers was effective in enhancing the fracture performance and hindering the cracking behaviour of GPC. Furthermore, 1.0% volume steel fiber exhibited to be most advantageous in enhancing the flexural strength by 100%, flexural toughness by 4000%, fracture energy by 3897%, and critical stress intensity factor by 98.8%. GPC with 1.0% volume PP fiber exhibited a characteristic length of 7909 mm, improving the characteristic length of GPC by about 2925%. Additionally, the CMOD was found to have a strong linear relationship with deflection which is unaffected by other factors. The presence of fibers significantly enhanced the ultimate strain. The steel fibers exhibited better performance in hindering the crack propagation. The fracture process zone (FPZ) characteristics differed between specimens with non-metallic and steel fibers, with the latter exhibiting more tortuous shapes and multiple cracks. Notably, a hybridization of steel and non-metallic fibers proves better than mono non-metallic fibers in improving strength, toughness, and ductility. This research provides valuable insights for concrete design and the selection of appropriate fibers based on specific requirements.

Synergistic use of nano-silica to enhance the characterization of ambient-cured geopolymer concrete

Synergistic use of nano-silica to enhance the characterization of ambient-cured geopolymer concrete

Influence of Discrete Basalt Fibres on Shrinkage Cracking of Self-Compacting Ambient-Cured Geopolymer Concrete

Short basalt fibres (BFs) have recently gained significant interest in the building materials sector due to their superior mechanical characteristics and cheaper manufacturing cost than other fibre types. Drying shrinkage and the early-age cracking of concrete are the root cause of many durability issues in the long run. Including small dosages of fibres within concrete composites has been shown as an effective technique to minimise drying shrinkage rates and reduce the crack widths developed due to plastic shrinkage cracking. Nevertheless, limited research studies have investigated the influence of short and long BFs with different dosages on the drying shrinkage rates and early-age cracking of geopolymer composites. In the present study, self-compacting geopolymer concrete (SCGC) using fly ash and slag as the binder is mixed with anhydrous sodium metasilicate powder as an alkali-activator. The study aims to investigate the influence of short (12 mm), long (30 mm) and hybrid-length (1:3 (short/long)) BFs with 1%, 1.5% and 2% dosages on the drying shrinkage properties and plastic shrinkage cracking of SCGC. The study results showed that adding BFs to SCGC reduces the drying shrinkage rates compared to plain SCGC, and SCGC reinforced with a 2% dosage of hybrid-length BFs recorded the lowest drying shrinkage rate. Two methods were used to measure crack widths: manual measurement (crack width gauge) and image analysis. No plastic shrinkage cracks were identified in mixes reinforced with 12 mm (1.5% and 2% dosages), 30 mm and hybrid-length BFs.

Effect of hooked end steel fibers on strength and durability properties of ambient cured geopolymer concrete

Growing carbon emissions in the construction industry have warranted the use of alternative materials such as geopolymer concrete. At the same time exposure of concrete material to harsh environmental conditions has compelled to design of durable geopolymer concrete. The use of hooked-end steel fibers in conventional fiber-reinforced concrete has proven to improve its crack resistance, and thus, positively influence the durability properties of concrete structures. Nevertheless, limited studies explore the effect of hooked-end steel fibers on the strength and durability properties of ambient cured geopolymer concrete with a low NaOH content (i.e., 8 M concentration). In this study, ambient cured geopolymer concrete was prepared by fly ash, ground granulated blast furnace slag (GGBS), NaOH, Na2SiO3, manufactured sand, and natural coarse aggregates. Additionally, hooked-end steel fibers with an aspect ratio of 67 were added to the mix by volume fraction in dosages of 0 %, 0.5 %, 1 %, 1.5 %, and 2 %. The experimental results showed that the addition of fibers reduced the workability with a minimum slump of 70 mm and a maximum Vee Bee time of 8 s for mixes with 2 % steel fibers. The addition of fibers improved the compressive strength, split tensile strength, and flexural strength of geopolymer concrete, with a maximum strength of 41.44 MPa, 4.28 MPa, and 5.23 MPa at an optimum fiber dose of 1 %, respectively. Above the optimum dose, the strength of the steel fiber-reinforced geopolymer concrete (SFRGPC) was reduced. The depth of water penetration reduced in SFRGPC when compared to GPC. Moreover, the resistance to chloride ion penetration was not significantly affected by addition of steel fibers till optimum dose of 1 %. The scanning electron microscopic results revealed the positive effect of steel fibers in restricting the progression of cracks. This has resulted in smaller crack width in the SFRGPC when compared to GPC. Overall, steel fibers in optimum dose have improved the performance of geopolymer concrete and this will contribute towards low carbon material.

Water absorption of ambient-cured geopolymer concrete

This study aims to determine the effect of the activator-binder ratio on the water absorption of ambient-cured geopolymer concrete. Class F fly ash from Mpanau power plant was used as precursor. This raw material was activated by a mixture of sodium silicate and sodium hydroxide solution, with an activator-binder ratio of 0,45; 0,50; 0,55; 0,60. Five percent replacement of fly ash by slaked lime was added to achieve ambient curing. The test specimen for the absorption test is made in the form of a cylinder with a size of 100 mm dia x 100 mm height. The absorption test used ASTM C642-06, and the test was conducted at the age of 28 days. The test results show that the geopolymer concrete with the largest activator/binder ratio has the lowest absorption, and volume permeable of voids. In this research, it was found that for the geopolymer concrete, activator-binder ratio of 0.60 has the lowest absorption and volume of permeable voids but gave the highest compressive strength. In addition, the test results show that normal concrete has the highest absorption and volume permeable of voids compared to the geopolymer concrete

Engineering behavior of ambient-cured geopolymer concrete activated by an alternative silicate from rice husk ash

Manufacturing of commercialized silicate is a highly polluting source in geopolymer production. To reduce these emissions, rice husk ash has been considered as an option for synthesizing alternative silicate. However, available research has been focused on the study of geopolymer pastes and mortars, but unknowns remain on its reliability to manufacture plain geopolymer concrete, motivating this research. Goals were synthesizing an unfiltered-alternative sodium silicate from rice husk ash at room conditions (21 °C − 65 ± 5%RH − atmospheric pressure) for manufacturing plain ambient-cured geopolymer concrete and assess its engineering properties. Results shown that the proposed concrete reached 21 MPa, 17959 MPa, 0.183, and 2.13 MPa for 28-day compressive strength, modulus of elasticity, Poisson’s ratio, and splitting tensile capacity, respectively. Results also portrayed that all these properties of the proposed concrete were comparable to those of geopolymer concrete with commercial silicate and traditional Portland-cement concrete. Its elasticity modulus was 44% higher than that of the geopolymer concrete with commercial silicate, which is considered as serviceability proxy. Based on the results, three equation models were developed to predict the engineering properties of the proposed concrete. Results demonstrate that the use of alternative silicate from rice husk ash provides an innovative-cheaper and eco-friendlier geopolymer concrete exhibiting suitable properties for structural applications. HIGHLIGHTS Alternative sodium silicate from rice husk ash has not been assessed in geopolymer concrete An alternative sodium silicate from rice husk ash was prepared at room temperature Geopolymer concrete shows 44% higher modulus of elasticity with alternative silicate Empirical models were developed to predict the engineering properties of the geopolymer concrete with alternative silicate Geopolymer concrete with alternative silicate is reliable for structural applications

Properties of blast furnace slag geopolymer concrete

Cement being the most consumed commodity after water contributes about 8% CO2 to the total amount of CO2 emitted. Therefore, alternate binders are being explored to make concrete production more sustainable. Geopolymer an inorganic polymer is being projected as one of the potential alternatives. However, most of the published literature recommend the use of highly concentrated alkali hydroxides of sodium or Potassium as alkali activator or a combination of alkali hydroxide with silicates for geopolymer synthesis, which are unsafe for workers. Furthermore, heat curing regimes of 24 to 120 h at temperature ranging 60 to 85 °C are also recommended. However, heat curing of structural components in a building is not possible in most of the in-situ construction projects, except for the production of prefabricated structural components. Furthermore, the silica and alumina rich wastes are preferred choice as the precursor for geopolymer synthesis. Therefore, an experimental study is carried out to produce blast furnace slag based geopolymer concrete using sodium silicate as the alkali solution. The geopolymer concrete was cured for 7, 14 and 28 days at ambient temperature to assess the mechanical properties of the developed concrete. The results of compressive and flexural strength test indicate the possibility of making ambient cured geopolymer concrete using sodium silicate and granulated blast furnace slag for structural application.

Influence of Hybrid Basalt Fibres’ Length on Fresh and Mechanical Properties of Self-Compacted Ambient-Cured Geopolymer Concrete

Recently, short basalt fibres (BFs) have been gaining considerable attention in the building materials industry because of their excellent mechanical properties and lower production cost than their counterparts. Reinforcing geopolymer composites with small volumes of fibres has been proven an efficient technique to enhance concrete’s mechanical properties and durability. However, to date, no study has investigated the effect of basalt fibers’ various lengths and volume content on self-compacted geopolymer concrete’s fresh and mechanical properties (SCGC). SCGC is prepared by mixing fly ash, slag, and micro fly ash as the binder with a solid alkali-activator compound named anhydrous sodium metasilicate (Na₂SiO₃). In the present study, a hybrid length of long and short basalt fibres with different weight contents were investigated to reap the benefits of multi-scale characteristics of a single fibre type. A total of 10 mixtures were developed incorporating a single length and a hybrid mix of long (30) mm and short (12) mm basalt fibres, with a weight of 1%, 1.5% and 2% of the total binder content, respectively. The fresh and mechanical properties of SCGC incorporating a hybrid mix of long and short basalt fibres were compared to plain SCGC and SCGC containing a single fibres length. The results indicate that the hybridization of long and short fibres in SCGC mixture yields better mechanical properties than single-length BF-reinforced SCGC. A hybrid fibre coefficient equation will be validated against the mechanical properties results obtained from the current experimental investigation on SCGC to assess its applicability for different concrete mixes.

Flexural Behavior of Fly ash and GGBS Based Ambient Cured Geopolymer Concrete Beams

Abstract: Concrete is the world’s most versatile, durable and reliable construction material. Next to water, concrete is the most used material, which required large quantities of Portland Cement. Ordinary Portland Cement production is the major generator of carbon di oxide, which polluted the atmosphere. In addition to that large amount energy was also consumed for the cement production. Hence, it is essential to find an alternative material to the existing most expensive, most resource consuming Portland Cement.The study describes experimental investigation on flexural behavior of reinforced GPC. A total of eighteen beams were tested. From this, nine were of M20 mix, i.e., conventional concrete beams while nine were of geopolymer concrete,from this nine beams, three beams with the ratio of binder i.e., flyash:GGBS ratio as 75:25, other three with 70:30 while remaining three beams with 65:35. Also, 12 cubes & 12 cylinders were also casted and tested for compressive strength and split tensile strength respectively. From them, three were of conventional concrete while other nine of GPC with three different ratios as mentioned above. The reinforcement was designed considering a balanced section for the expected characteristic strength. All the beam specimens were tested under two point static loading. The studies demonstrated, the study of conventional and geopolymer concrete beams related to deflection, first load at which crack appeared and their crack patterns.

Enhancing the Durability Properties of Sustainable Geopolymer Concrete Using Recycled Coarse Aggregate and Ultrafine Slag at Ambient Curing

This study aimed at investigating the durability characteristics of the ambient-cured geopolymer concrete (GPC) developed using recycled coarse aggregate (RCA) and ultrafine slag (UFS). Two series of mixes were prepared. Natural aggregates (NAs) were replaced by RCA at different volume levels of 0, 25, 50 and 100% in both series. Meanwhile, UFS was added as a replacement by volume of fly ash at varying levels of 0, 15, and 30% in the first series, while UFS was used in addition to fly ash by percentage weight of fly ash at the levels of 0, 15, and 30% in the second series. The compressive strength, water absorption, chloride ion penetration, and carbonation depth of the developed ambient-cured GPC were studied. In addition, creep and drying shrinkage of the specimens were also examined. It was found that the compressive strength increased with the UFS content, while the opposite trend was observed with increasing RCA%. The highest compressive strength obtained with 100% RCA was 40.21 MPa (at 90 days), when 30% UFS was used in addition to fly ash. The addition of UFS not only helped in improving the strength characteristics but also provided an alternative to heat curing, which is a major drawback of GPC. Furthermore, the negative effects of RCA can also be minimised by adding UFS, which can be used as a compensator to RCA to improve the durability characteristics. The experimental results prove that susceptibility to chemical, water and chloride attacks can be mitigated by incorporation of UFS, and durable GPC can be produced by using RCA and UFS.

Effect of fibre addition on the static and dynamic compressive properties of ambient-cured geopolymer concrete

This paper presents an experimental study on the static and dynamic compressive properties of ambient-cured fibre reinforced geopolymer concrete (FRGPC) containing mono steel, mono polypropylene (PP) or hybrid steel-PP fibres. A Split Hopkinson Pressure Bar (SHPB) was used to carry out dynamic compressive tests under different strain rates up to 130.5 s−1. The effects of fibre addition on static compressive strength, splitting tensile strength, dynamic failure process and damage mode, dynamic compressive strength, specific energy absorption and dynamic increase factor (DIF) were investigated and analysed. The results revealed mono steel fibre as the most effective in improving static compressive and splitting tensile strengths, which increased by 21.92% and 21.05% respectively, compared to plain geopolymer concrete (GPC). The dynamic compressive strength of both plain GPC and FRGPC increased with the increase of strain rate. There is a positive relationship between DIFs of compressive strengths and strain rates for all GPC and FRGPC samples. The samples containing mono PP fibres showed the most strain rate sensitivity with respect to compressive strengths and specific energy absorption within the tested strain rates. Furthermore, empirical formulae are proposed accordingly to predict the DIFs and specific energy absorption of ambient-cured GPC and FRGPC.

Test of Dynamic Mechanical Properties of Ambient-Cured Geopolymer Concrete Using Split Hopkinson Pressure Bar

The application of geopolymer concrete (GPC) in construction could reduce a large amount of carbon dioxide (CO2) emission, which is greatly beneficial to environmental sustainability. Structures made of GPC might be subjected to extreme loading such as impact and blast loads. Therefore, a good understanding of the dynamic properties of GPC is essential to provide reliable predictions of performance of GPC structures subjected to dynamic loading. This study presents an experimental investigation on the dynamic compressive and splitting tensile properties of ambient-cured GPC using split Hopkinson pressure bar (SHPB), with the strain rate up to 161.0 s−1 for dynamic compression and 10.3 s−1 for dynamic splitting tension. The failure mode and damage progress of GPC specimens, energy absorption, and dynamic increase factor (DIF) were studied. Test results showed that ambient-cured GPC exhibited strain rate sensitivity. The compressive and splitting tensile DIFs increased with the strain rate and the ambient-cured GPC with lower quasi-static compressive strength exhibited higher DIFs under both dynamic compression and splitting tension. Empirical formulas were proposed to predict the DIF of ambient-cured GPC. Furthermore, the specific energy absorption of ambient-cured GPC under dynamic compression increased approximately linearly with the strain rate.

Strength and toughness of ambient-cured geopolymer concrete containing virgin and recycled fibres in mono and hybrid combinations

This paper presents an investigation on the workability and mechanical properties of ambient-cured fly ash geopolymer concrete (GPC) containing four different fibres, namely steel (S), polyvinyl alcohol (PVA), polypropylene (PP) and recycled polypropylene (RPP) fibres at 1% volume of concrete. The influences of hybrid S-PVA, S-PP and S-RPP on GPC at 0.5% of each type of fibre were also studied. In the mono fibre reinforced GPC (FRGPC) series, steel fibre showed the most effective role in improving the mechanical properties which were 4.0% in compressive strength, 74.3% in splitting tensile strength and 65.3% in flexural strength. In the hybrid FRGPC series, mixing of steel and RPP fibres was found more effective than the other combinations. The improvements by S-RPP were 15.5% in compressive strength, 48.9% in splitting tensile strength and 60.0% in flexural strength. The highest toughness was achieved for the S-RPP hybrid fibres following by mono steel fibres. A net deflection equal to 1/75 of the span could be regarded as the end deflection point to calculate the total flexural toughness of FRGPC according to quantitative analysis of toughness enhancement. There is a strong positive correlation between the total toughness and stress at the limit of proportionality (LOP) point.

Zero Cement Concrete with Self-Curing Technology: An Overview

Geopolymer concrete is the concept of environmental friendly construction material which helps in reducing the greenhouse gas emission, however it cannot be applied directly on field due to its steam curing process. To overcome this defect various researcher have found self-curing or ambient curing process to achieve same strength as in steam curing process for geopolymer. This paper presents an over review about self-cured or ambient cured geopolymer concrete produced by various methods.

Shear behaviour of ambient cured geopolymer concrete beams reinforced with BFRP bars under static and impact loads

The use of fiber reinforced polymer (FRP) bars in GeoPolymer Concrete (GPC) structures has drawn increasing attention in recent years. The application of GPC with basalt fiber reinforced polymer (BFRP) reinforcements in replacing Ordinary Portland cement Concrete (OPC) and steel reinforcements leads to green and sustainable constructions. Currently, very limited studies have been conducted to investigate the performance of GPC beams reinforced with BFRP bars under static loads, but no study on their performance under impact loads has been reported yet in open literature. In this study, ambient-cured GPC beams reinforced with BFRP bars were designed, cast and tested under static and impact loads. The damage mode and quantitative results such as midspan deflection, reinforcement strain, and impact and reaction forces were recorded and analysed. Test results showed that spiral stirrups led to superior performance of the beams under both static and impact loads as compared to conventional rectangular stirrups. The commonly used concrete material model *Mat_072R3 in LS-DYNA was modified based on test data to model GPC material. With the modified GPC material model, numerical models were developed and calibrated against the impact test results. Parametric studies were carried out to investigate the influences of GPC material strength and longitudinal and stirrup reinforcement ratios on the performance of beams subjected to impact loads. It was also found that using steel bars as the compression reinforcements led to better performance because BFRP bars under shear and compression were vulnerable to splitting damage subjected to impact loads.

Influence of alkaline activators on the mechanical properties of fly ash based geopolymer concrete cured at ambient temperature

In this study, cement-free geopolymer concrete (GPC) mixes are prepared using locally produced fly ash with varying NaOH concentrations (8 M−16 M), Na2SiO3/NaOH ratios (1.5–2.5) and alkaline activator to fly ash (AA/FA) ratios (0.4–0.6) to investigate the influence of alkaline activators on the mechanical properties of GPC cured at ambient temperatures. The optimum compressive strength (21.5 MPa) of ambient-cured GPC was attained with NaOH concentration of 14 M, Na2SiO3/NaOH of 1.5 and AA/FA of 0.5. The optimum flexural strength (5 MPa) of ambient-cured GPC was attained with NaOH concentration of 16 M, Na2SiO3/NaOH of 1.5 and AA/FA of 0.5.