Fly Ash Geopolymer Concrete Research Articles

Effect of coarse aggregate size on the compressive behaviour of geopolymer concrete

The utilisation of ordinary Portland cement not only consumes significant amount of natural resources but also causes pollution to the environment due to Carbon emission. As a result, a replacement material for cement including the use of fly ash becomes a solution to this environmental concern. Accordingly, the compressive strength of cement-based concrete depends primarily on several factors such as the size of gravel. Therefore, it is worth studying to find out whether this factor likewise influences the compressive behaviour of geopolymer concrete. This study experimentally investigated the effect of the particle size of coarse aggregate on the compressive behaviour of fly ash geopolymer concrete. Compressive tests have been carried out on a 100 mm × 200 mm cylindrical specimen using a compression testing machine. The results showed that the fly ash geopolymer concrete specimens exhibited brittle failure mode characterised by splitting, shear, columnar and conical type of failure. It was found that the size of the coarse aggregate that offered a maximum compressive strength is in the range of 12.5–25 mm. Furthermore, the size of the coarse aggregate does not affect the trend results on ambient vs. oven-cured specimen, as well as the days of curing.

Deterioration and Microstructural Evolution of the Fly Ash Geopolymer Concrete against MgSO4Solution

Fly ash geopolymer concrete (FAGC) and ordinary Portland cement concrete (OPCC) specimens were immersed in 5% MgSO4solution undergoing 32 wetting-drying and heating-cooling cycles. Their compressive behavior was investigated after every 8 cycles. Several microstructure analysis techniques were applied on the samples to identify the materials formed due to magnesium sulfate attack, including XRD, FTIR, SEM, and EDS. Experimental results elucidated that the compressive strength loss ratio in the heating group of FAGC was 12.7%, while that of OPCC was 17.8%, which means that FAGC had better magnesium sulfate resistance than OPCC. The compressive strength loss of OPCC was due to the formation of gypsum under the magnesium sulfate attack exposed to wetting-drying and heating-cooling cycles. The deterioration mechanisms of FAGC against MgSO4solution were discovered to be that sodium aluminum silicate hydrate (N-A-S-H) gels reacted with MgSO4, leading to the creation of low strength magnesium aluminum silicate hydrate (M-A-S-H) gels.

Review on Various Types of Geopolymer Materials with the Environmental Impact Assessment

The development of green technology in the construction industry since 10 years ago is something to be proud of Malaysia. Several alternative geopolymer materials were invented in Malaysia such as fly ash, POFA, kaolin, metakaolin, and dolomite based geopolymer materials to achieve sustainable development especially in the building and construction sector. Those alternative materials are very important to replace the application of OPC, which is said to be the main cause of global warming. A review on the content of the chemical differences with the environmental impact resulting from the production of geopolymer is carried out in this study. In conclusion, fly ash based geopolymer material showed the best performance in terms of aluminosilicate content and also it is the best practice in the environmental protection applications for the moment. However, when compared with the OPC, fly ash geopolymer concrete was still able to reduce the effects of global warming potentials, but it is rather gave a negative impact on some aspects of the environment such as abiotic depletions, human toxicity, freshwater ecotoxicity, terrestrial ecotoxicity and acidification.

Carbonation of a low-calcium fly ash geopolymer concrete

The carbonation resistance of a blended slag and low-calcium fly ash (FA) geopolymer concrete was investigated. The geopolymer binder studied was composed of 90% low-calcium FA and 10% ground granulated blast-furnace slag. The alkalinity of the pore solution plays a pivotal role in carbonation progression and subsequent corrosion initiation. pH profiles were measured to assess the pore solution alkalinity. Phenolphthalein indicator was used to measure the carbonation depth. X-ray diffraction (XRD) and quantification were carried out to identify and quantify the carbonation products. The obtained pH profiles illustrated a wider semi-carbonation zone in the geopolymer specimens, although the pH drop was insignificant in most cases. XRD analysis revealed that nahcolite mainly formed at 3% carbon dioxide concentration and led to a significant drop in pH values. The results further demonstrated that 1% accelerated carbonation replicated the natural carbonation process well, with only natron identified as a carbonation product. This work contributes to the assessment of the risk of carbonation-induced reinforcement corrosion in low-calcium FA geopolymer concrete.

Chloride ingress and steel corrosion in geopolymer concrete based on long term tests

Alkali activated binders (geopolymer) is an emerging technology to produce concrete without the use of any Ordinary Portland Cement (OPC) by alkali activation of alumino-silicate source materials such as fly ash and/or slag. Limited knowledge on durability issues like corrosion behaviour of reinforced geopolymer concrete impedes the usage of this technology in structural applications.This study explored the chloride permeability and initiation of chloride induced corrosion of geopolymer concrete in accelerated chloride environment using longer test period. Corrosion initiation was also monitored in embedded rebar in 2% chloride contaminated concrete. Corrosion state of the rebar was monitored using non-destructive test method using Cu/CuSO4 reference electrode.The results showed that the apparent chloride diffusion coefficient of blended fly ash and slag geopolymer concrete is lower than that of OPC concrete. The diffusion coefficient also decreased with the increase of slag content in the binder. Blended fly ash and slag geopolymer concrete also exhibited higher aging factor than OPC concrete indicating improved resistance to chloride ingress with time. The study also showed that the embedded rebar in fly ash and slag based geopolymer concrete has higher protection against corrosion than a rebar in OPC concrete even when the concrete is contaminated with significant levels of chloride.

Flexural strength and elastic modulus of ambient-cured blended low-calcium fly ash geopolymer concrete

Fly ash geopolymer is an emerging alternative binder with low environmental impact and potential to enhance sustainability of concrete construction. Most previous works examined the properties of fly ash-based geopolymer concrete (GPC) subjected to curing at elevated temperature. To extend the use of GPC in cast-in-situ applications, this paper investigated the properties of blended low-calcium fly ash geopolymer concrete cured in ambient condition. Geopolymer concretes were produced using low-calcium fly ash with a small percentage of additive such as ground granulated blast furnace slag (GGBFS), ordinary Portland cement (OPC) or hydrated lime to enhance early age properties. Samples were cured in room environment (18–23°C and 70±10% relative humidity) until tested. The results show that, density of hardened GPC mixtures is similar to that of normal-weight OPC concrete. Inclusion of additives enhanced the mechanical strengths significantly as compared to control concrete. For similar compressive strength, flexural strength of ambient cured GPC was higher than that of OPC concrete. Modulus of elasticity of ambient cured GPC tend to be lower than that of OPC concrete of similar grade. Prediction of elastic modulus by Standards and empirical equations for OPC concrete were found not conservative for GPC. Thus, an equation for conservative prediction of elastic modulus of GPC is proposed.

Use of Recycled Concrete Aggregate in High-Calcium Fly Ash Geopolymer Concrete

The comparison results of using crushed limestone (NA) and recycled concrete aggregates (RCA) as coarse aggregates in high-calcium fly ash geopolymer concrete with and without temperature curing are presented. Local river sand with a fineness modulus of 2.1, sodium hydroxide solution concentrations of 8, 12, and 16 Molar, and sodium silicate were used to produce geopolymer concrete (GC). The curing was separated in two conditions: the first was cured at ambient temperature (AT) and another was cured at temperature of 60°C for 48 hrs. (CT). The compressive strength, thermal conductivity, and ultra pulse velocity of GC were investigated at age 7 days. The results found that RCA could be use as coarse aggregate in GC. The thermal conductivity increased with the increasing of compressive strength. Curing at 60°C yielded compressive strength about 3 times higher than that of AT. However, both AT and CT curing, GC containing RCA had thermal conductivity and ultra pulse velocity lower than those of containing NA.

Strength and Behaviour of Small-Scale Reinforced High Calcium Fly Ash Geopolymer Concrete Beam with Short Shear Span

The small-scale reinforced high calcium fly ash geopolymer concrete beams with short shear span were studied in this research. Reinforced concrete beams with 150x150 mm2 cross-section and 530 mm in length were used for tests. Conventional reinforced Portland cement concrete beams (RC) with designed concrete compressive strengths of 35, 45 and 55 MPa and high-calcium fly ash geopolymer reinforced concrete beams with similar strength were tested. The geopolymer concretes (GC) were designed with alkaline liquid to fly ash ratio (L/A) of 0.5, sodium silicate to sodium hydroxide (S/H) ratio of 1.0 and two sodium hydroxide (NaOH) concentrations of 10M and 15M. Two temperatures of 23 and 60 °C were used for curing geopolymer reinforced concrete (GRC) beams for 24 hr, while RC beams were moist cured at 23 °C. The maximum sustained moment and shear were compared with the predicted values from the RC-design standard. The results showed that the failure patterns of small GRC beams were different to that of normal RC beam. The small GRC beams failed in flexure whereas the similar small RC beams failed in shear. However, the GRC beams were able to sustain higher shear and moment than the values obtained from the design code. The different in failure mechanism was probably due to the different in modulus of elasticity of geopolymer concrete and normal concrete.

Steel Reinforcement Corrosion in a Low Calcium Fly Ash Geopolymer Concrete

Geopolymer concrete (GPC) has significant potential as a more sustainable, low-embodied carbon alternative for ordinary Portland cement concrete (PCC). However; as a rather new engineering material, there are some concerns over the durability aspects of geopolymeric binders. In this study, performance of chloride contaminated reinforced GPC specimens manufactured using low calcium fly ash is investigated by long-term monitoring of corrosion parameters such as free corrosion potential and polarization resistance. It was found that low calcium fly ash GPC can perform as well as PCC during the propagation phase of corrosion; although, some conventional reference values of corrosion parameters which are indicative of severity of the steel corrosion in PCC are not suitable for GPC. Additionally, commonly used electrochemical test methods are successfully employed to assess the degree of reinforcement corrosion in geopolymeric binders within an acceptable level of accuracy.

Utilisation of steel furnace slag coarse aggregate in a low calcium fly ash geopolymer concrete

This paper evaluates the performance of steel furnace slag (SFS) coarse aggregate in blended slag and low calcium fly ash geopolymer concrete (GPC). The geopolymer binder is composed of 90% of low calcium fly ash and 10% of ground granulated blast furnace slag (GGBFS). Mechanical and physical properties, shrinkage, and detailed microstructure analysis were carried out. The results showed that geopolymer concrete with SFS aggregate offered higher compressive strength, surface resistivity and pulse velocity than that of GPC with traditional aggregate. The shrinkage results showed no expansion or swelling due to delayed calcium oxide (CaO) hydration after 320days. No traditional porous interfacial transition zone (ITZ) was detected using scanning electron microscopy, indicating a better bond between SFS aggregate and geopolymer matrix. Energy dispersive spectroscopy results further revealed calcium (Ca) diffusion at the vicinity of ITZ. Raman spectroscopy results showed no new crystalline phase formed due to Ca diffusion. X-ray fluorescence result showed Mg diffusion from SFS aggregate towards geopolymer matrix. The incorporation of Ca and Mg into the geopolymer structure and better bond between SFS aggregate and geopolymer matrix are the most likely reasons for the higher compressive strength observed in GPC with SFS aggregate.

Bond Slip Models for Uncorroded and Corroded Steel Reinforcement in Class-F Fly Ash Geopolymer Concrete

AbstractGeopolymer concrete is an innovative construction material that utilizes industrial by-product waste materials to form a cement replacement for concrete manufacture. In order to simulate the behavior of reinforced concrete at all load levels, an understanding of the bond between the reinforcement and the concrete is required. That is, at the serviceability limit state, the bond between the reinforcement and the concrete controls the formation of cracks, crack widening, and tension stiffening. Similarly, adequate bond between the reinforcement and the concrete is required at the ultimate limit state to ensure the full capacity of the reinforcement is obtained. Over time, the bond between the reinforcement and concrete can deteriorate due to corrosion, thus impacting the overall performance of a structure. This paper presents a wide-ranging study of the bond between reinforcement and geopolymer concrete including an investigation of the influence of corrosion. This study involved 102 pull-out test s...

Long term permeation properties of different fly ash geopolymer concretes

Geopolymer is a sustainable construction material produced by the activation of fly ash using a high concentration alkali to initiate a polymerisation reaction. A key parameter in determining the potential adoption of geopolymer concrete in the construction industry is the long term durability of the material. To determine the durability characteristics a detailed investigation of the permeation properties of four different fly ash geopolymer concretes was carried out up to one year of age. An improvement in the durability properties is observed for all geopolymer concretes with time. This is attributed to an on-going geopolymerization which results in continuing gel formation leading to a more densely packed microstructure, with an associated reduction in meso-pores and macro-pores. The packing density coupled, with the pore size distribution, were observed to determine the permeation and diffusion characteristics of the concrete. The increased in meso-pores represents the increase in the gel of the matrix and in turn this affect the increase of water absorption. On the other hand, a high quantity of macro-pores leads to an increase in the water and air permeability of geopolymer concrete. A large quantity of coarse particles in fly ash results in an uneven gel distribution which reduces pore-filling ability, while the presence of a high quantity of CaO was observed to contribute to a densely packed microstructure. Notably the initial chloride diffusion coefficients are analogous to those observed in Portland and blended cement concretes and also decrease with the age in a similar manner.

Mechanical and durability properties of fly ash geopolymer concrete containing recycled coarse aggregates

Abstract This paper presents mechanical and durability properties of geopolymer concrete containing recycled coarse aggregate (RCA). The RCA is sourced from local construction and demolition (C&D) waste in Perth, Australia. The RCA is used as a partial replacement of natural coarse aggregate (NCA) in geopolymer concrete at 15%, 30% and 50% by wt. which corresponds to series two, three and four, respectively, while the geopolymer concrete containing 100% NCA is control and is considered as the first series. Class F fly ash is used as the source material for the geopolymer and 8 M sodium hydroxide and sodium silicate alkali activators are used to synthesise the fly ash geopolymer in this study. In all four series a constant alkali activator to fly ash ratio is used. Compressive strength, indirect tensile strength and elastic modulus of above geopolymer concrete are measured at 7 and 28 days, while sorptivity, immersed water absorption and volume of permeable voids of above geopolymer concrete are measured at 28 days. Relevant Australian standards are used to measure all the above properties except the sorptivity which is measured according to ASTM standard. Results show that the compressive strength, indirect tensile strength and elastic modulus of geopolymer concrete decrease with an increase in RCA contents, which is also true for both 7 and 28 days. Excellent correlations of compressive strength with indirect tensile strength and elastic modulus are also observed in geopolymer concrete containing RCA. Existing empirical models for cement concrete and geopolymer concrete containing NCA underestimate and overestimate the indirect tensile strength and elastic modulus, respectively of geopolymer concrete containing RCA. The measured durability properties such as sorptivity, water absorption and volume of permeable voids of geopolymer concrete were also adversely affected by the incorporation of RCA and these properties increase with an increase in RCA contents. The effects of RCA on the measured mechanical and durability properties of geopolymer concrete follow similar trend in cement concrete. Very good correlations of compressive strength with volume of permeable voids and water absorption of geopolymer concrete containing RCA are also observed, while the correlation between the compressive strength and the sorptivity is not that strong.

Properties of lightweight fly ash geopolymer concrete containing bottom ash as aggregates

In order to evaluate the utilization of waste from coal combustion thermal power plant, the properties of lightweight geopolymer concrete (LWGC) containing fly ash as geopolymer binder and bottom ash as aggregates were studied. Sodium silicate solution (NS) and 10M sodium hydroxide (NH) were used as alkali activators. The NS/NH ratios of 0.5, 1.0, and 1.5 with liquid/ash (L/A) ratios of 0.70, 0.75, and 0.80 were used. The compressive strength, splitting tensile strength, surface abrasion resistance, density, thermal conductivity, and ultrasonic pulse velocity (UPV) of concrete were tested. The results indicated that fly ash and bottom ash could be used to produce LWGCs with compressive strengths of 14.3–18.1MPa, splitting tensile strengths of 1.2–2.0MPa, and densities of 1661–1688kg/m3. Theirs thermal conductivity coefficients of 0.43–0.47W/mK were lower than those of the geopolymer concrete containing natural aggregate. LWGCs in this study could thus be used for moderate strength concrete and thermal insulation concrete.

Acoustic emission and microstructural changes in fly ash geopolymer concretes exposed to simulated fire

Two fly ash-based geopolymer concretes with quartz aggregates or with expanded clay (lightweight) aggregates were exposed to the ISO 834-1 standard fire curve in a small-scale fire test set-up. Acoustic emission measurements during fire exposure and subsequent cooling were employed to study spalling events and cracking during the tests. Optical microscopy and additional acoustic measurements were conducted after the testing to better understand the crack propagation in the samples. The testing revealed that neither of the concretes were susceptible to spalling, which is particularly notable for the concrete with quartz aggregates, as it is a high-strength concrete. This behavior is attributed to the relatively high permeability of the concretes and their low amount of chemically bound water. Significant crack formation was detected only around the temperature of the α–β quartz transition (573 °C) and on cooling. Because of aggregate deformations at the quartz transition temperature, deterioration after heating was more significant in the geopolymer concrete with quartz aggregates. Crack formation also occurred in the concrete with expanded clay aggregates, caused by shrinkage of the geopolymer paste on cooling. Acoustic emission measurements proved to be a valuable tool to investigate processes during high temperature exposure.

Effect of Natural Clay and M-Sand on the Strength and Chemical Attack of Fly Ash Geopolymer Concrete

This paper reports the achievements of using the stable form of the natural clay, locally available in Coimbatore, Tamilnadu, India, as a base material of geopolymer concrete with flyash. The laboratory and field study shows the strength development and acid resistant of Clay-Fly ash geopolymer mortar and concrete with dissimilar ingredients, specimen sizes and heating temperature. A silty natural clay without calcination is used as a pozzolanic component with low calcium Class F-flyash brought from Mettur Thermal Power Unit, Tamilnadu as well as fine aggregate with manufacturing sand in different combinations. The moisture content in the clay is adjusted with the total volume of liquid used for geopolymer manufacturing. The considered factors are FA/Clay ratio, Alkaline activator ratio, M-Sand/Clay ratio, molding moisture content, specimen sizes, curing temperature, rest period and NaOH concentration. Alkali solution for this study is prepared with the mixture of Sodium silicate and different molarities of Sodium hydroxide solution with the proportion ratio 1. The mortar test specimens were 70x70x70 mm cubes, 50x 100 mm cylinders and concrete test specimens were 150x150x150mm cubes, 100 x 300 mm cylinders heat cured at 600C/800C in an oven. The grades selected for the experimental investigation were M 25, M 30 and M 40 and the mixes were designed for the molarity of 8M, 10M and 12M.

Theoretical and experimental study on mechanical properties and flexural strength of fly ash-geopolymer concrete

In this paper, evaluation of the mechanical properties of heat-cured low-calcium fly-ash geopolymer concrete and the behavior of geopolymer concrete beams are reported in detail. The mechanical properties are evaluated using the modulus elasticity, Poisson’s ratio, stress–strain relation, and indirect tensile strength. Behavior of the geopolymer beam is determined using a flexural test with four-point bending, elastic theory, and a finite element model (FEM). The measured modulus elasticity values of geopolymer concrete are lower than those calculated using current standards for normal concrete. The Poisson’s ratio is from 0.16 to 0.21, which is similar to the values of conventional concrete. The stress–strain relation in compression matches well with the formulation designed for Portland cement concrete. The indirect tensile strength is a fraction of the compressive strength but it is higher than the calculated value using an expression designed for normal concrete. The deflections at mid-span, and the crack patterns of the geopolymer concrete beam determined from FEM, are better matched with the experimental results than with the elastic theory results.

Influence of recycled aggregate on fly ash geopolymer concrete properties

Geopolymer binder and recycled aggregate are environment friendly products and is thus considered as part of sustainable development. This paper presents a study of the effect of recycled aggregate on strength and durability of fly ash based geopolymer concrete. Geopolymer concrete samples were prepared from high calcium fly ash, sodium silicate solution, sodium hydroxide solution, fine aggregate from river sand, and two types of coarse aggregate viz., recycled concrete aggregate and crushed limestone coarse aggregate. Test results indicated that recycled concrete aggregate can be used as a coarse aggregate in high calcium fly ash geopolymer concretes with the 7-day compressive strengths of 30.6–38.4 MPa which were slightly lower than those of high calcium fly ash geopolymer concretes containing crushed limestone. The use of high sodium hydroxide concentrations of 12 and 16 M resulted in better performances both in strength and durability than that of 8 M.

Properties of lightweight high calcium fly ash geopolymer concretes containing recycled packaging foam

In this research, the properties of lightweight geopolymer concretes containing recycled packaging foam were studied. The recycled foam was crushed to sizes of 2.35–4.75mm and used as lightweight aggregate. Compressive strengths and densities with liquid alkaline/ash ratios of 0.5–1.0, sodium silicate/NaOH ratios of 0.33–3.0, NaOH concentrations of 5–15 molars, curing temperatures at 25 and 60°C, and foam contents of 0.85–1.05%wt. were tested. In addition, the thermal conductivities of geopolymer blocks were determined. Results showed that the lightweight geopolymer blocks of densities of 1000–1300kg/m3, with satisfactory strength and low thermal conductivity can be made. This gave a twofold advantageous viz. the use of low carbon footprint fly ash geopolymer and the reuse of packaging foam.

Bond strength between blended slag and Class F fly ash geopolymer concrete with steel reinforcement

Abstract In this paper, geopolymer concrete bond with both deformed and smooth reinforcing steel bars is investigated using the standard RILEM pull-out test. The geopolymer binder is composed of 85.2% of low calcium fly ash and 14.8% of ground granulated blast furnace slag (GGBFS). The tests were aimed to assess the development of the bond strength from 24 h to 28 days after casting, with different heat curing conditions. The results show that 48 h of heat curing at 80 °C is required in order to obtain similar or better performances to those of the reference 45 MPa OPC concrete. The 28-day bond strength and the overall bond stress–slip behaviour of the geopolymer concrete were similar to those previously reported for OPC-based concretes. Providing intensive heat curing, high early bond strength can be achieved showing that Class F fly ash geopolymer concrete is well suited for precast applications.