Behavior Of Geopolymer Research Articles

Influence of the nature and concentration of alkali cations in silicate solutions on the behavior of MK-CaCO3 based geopolymers at 600–1150 °C

The objective of this work is to study the effect of the nature (potassium or a mixture of potassium and sodium) and concentration of alkali cations on the behavior of geopolymers at a high temperature (1150 °C). First, the physico-chemical characteristics of the different geopolymers, such as the initial viscosity, the density of the mixture and structural data (Raman spectroscopy), are presented. Then, thermal analysis, dilatometry and mercury porosity are conducted, as well as the mechanical behavior and X-ray diffraction after 1150 °C. The different formulations display different trends depending on the concentration and the nature of the alkaline cations. In comparison to the use of a potassium cation, the addition of sodium leads to an increase of the viscosity and a decrease of the onset temperature of the viscous flow. The potassium-based formulations show better behavior after treatment at high temperature (1150 °C). The improvement in the mechanical properties after thermal treatment is controlled by the different crystalline phases formed, such as leucite and anorthite.

ENHANCING OF FLEXURAL STRENGTH OF WEB OPENING REINFORCED GEOPOLYMER BEAMS BY USING FRP STRIPS

This study is devoted to inspect the flexural behavior of Geopolymer reinforced concrete beams with “large” web transverse opening and strengthened by three kinds of Fiber Reinforced Polymer materials. The implemented experimental program comprised casting eight beams under static and “one stage” repeated load, two of these are normal concrete beams and the others are Geopolymer beams. These beams are divided into two groups, the first comprised four beams of solid and beams “with transvers web opening” under static load for normal and Geopolymer concrete beams. The second group are of four Geopolymer beams that one of them is “un strengthened and having transvers web opening” while the others are also have transvers web opening but strengthened by different kinds of Fiber Reinforced Polymer materials sheets that installed vertically aligned and accompanied with the 90mm diameter large circular web opening. The strengthening materials included are Carbon Fiber Reinforced Polymer, Glass fiber Reinforced Polymer and Hybrid (one layer of Glass + one layer of Carbon) reinforced polymer sheets. The results showed that for the ultimate load capacity was decreased by 9.96% for holed normal concrete beam if compared with solid normal concrete solid beam while such capacity was decreased 2.25% and 11.89% for solid and holed Geopolymer beams respectively. In addition to that, the maximum load capacity is also decreased by 8.16%, 10.20% and 12.25% for Glass, Carbon and Hybrid fiber reinforced polymer strengthened beams if compared with reference beams “holed un strengthened beam” subjected to cyclic load.

Behavior of geopolymer concrete‐filled circular steel tube members

AbstractBehavior of geopolymer concrete‐filled circular steel tube members was experimentally investigated. Four column specimens and one beam specimen were prepared using fly‐ash based geopolymer concrete. The material properties for both circular steel tubes and the geopolymer concrete infill were measured. The column specimens were tested under concentric and eccentric compression while the beam specimen was tested under three‐pointing bending, aiming to investigate the behavior of the structures subject to compression or combined loading. The load‐deformation behavior, compressive and bending strengths and failure mode of the specimens observed through the experiments are also reported in this paper. The compressive load and moment interaction relationship was developed using the experimental results. The measured ultimate compressive loads and ultimate moment capacity were also compared with the predictions obtained based on European and American Standards. It shows through the comparison that the predictions based on the standards are conservative. Therefore, the European and American Standards can be applied to safely design the structures.

Thermal Characteristics of Geopolymer from Co-combustion Residuals of Bamboo and Kaolin

Geopolymer, inorganic polymer with Si-O-Al bonds, can be utilized as Portland cement substitute. Resistance to fire or high temperature is one of the characteristics that should be possessed by building materials. In this paper, the behaviour of geopolymer from co-combustion residuals of bamboo and kaolin when exposed to high temperature was studied from thermogravimetric, derivative thermogravimetric, and differential scanning calorimetry analysis. The result showed that geopolymer from co-combustion residuals of bamboo and kaolin underwent dehydration, densification by viscous sintering, and further densification processes with mass loss of 19.5 % after exposure to temperature of 1000 °C.

Importance of rheology in the prediction of structural transition phenomena in geopolymer matrices loaded with phosphogypsum

Through a purely experimental approach, we proceed here to the description of the rheological behavior of the geopolymer matrices in the fresh state according to one or other of the parameters characterizing their formulation. This consolidates the different physicochemical techniques usually used for their characterization. This comes to allow us especially the definition of drafts for the implementation of empirical laws ensuring a better follow-up in the elaboration of these materials or even more optimization in their formulation. This description also allows us to follow the structural transition phenomena from the fresh state to the hardened state. We are particularly interested in demonstrating the impact of the addition of Phosphogypsum on the rheological behavior of geopolymers or on their kinetics of setting.

Water content and porosity effect on hydrogen radiolytic yields of geopolymers

The behavior of geopolymers under irradiation is a topic that has not been thoroughly investigated so far. However, if geopolymers are considered to be used as radioactive waste embedding matrices, their chemical and mechanical stability under ionizing radiation as well as low hydrogen production must be demonstrated. For that purpose, a particular focus is put on water radiolysis. Various formulations of geopolymers have been irradiated either with γ-rays (60Co source) or 95 MeV/amu 36Ar18+ ions beams and the hydrogen production has been quantified. This paper presents the results of radiolytic gas analysis in order to identify important structural parameters that influence confined water radiolysis. A correlation between geopolymers nature, water content on the one side, and the hydrogen radiolytic yield (G(H2)) on the other side, has been demonstrated. For both types of irradiations, a strong influence of the water content on the hydrogen radiolytic yield G(H2) is evidenced. The geopolymers porosity effect has been only highlighted under γ-rays irradiation.

Behavior of geopolymer and conventional concrete beam column joints under reverse cyclic loading

An experimental investigation was carried out on the strength and behavior plain and fiber reinforced geopolymer concrete beam column joints and the results were compared with plain and steel fiber reinforced conventional concrete beam column joints. The volume fraction of fibers used was 0.5%. A total of six Geopolymer concrete joints and four conventional concrete joints were cast and tested under reversed cyclic loading to evaluate the performance of the joints. First crack load, ultimate load, energy absorption capacity, energy dissipation capacity stiffness degradation and moment-curvature relation were evaluated from the test results. The comparison of test results revealed that the strength and behavior of plain and fiber reinforced geopolymer concrete beam column joints are marginally better than corresponding conventional concrete beam column joints.

Tensile behaviour of geopolymer-based materials under medium and high strain rates

Geopolymers are a promising class of inorganic materials typically obtained from an alluminosilicate source and an alkaline solution, and characterized by an amorphous 3-D framework structure. These materials are particularly attractive for the construction industry due to mechanical and environmental advantages they exhibit compared to conventional systems. Indeed, geopolymer-based concretes represent a challenge for the large scale uses of such a binder material and many research studies currently focus on this topic. However, the behaviour of geopolymers under high dynamic loads is rarely investigated, even though it is of a fundamental concern for the integrity/vulnerability assessment under extreme dynamic events. The present study aims to investigate the effect of high dynamic loading conditions on the tensile behaviour of different geopolymer formulations. The dynamic tests were performed under different strain rates by using a Hydro-pneumatic machine and a modified Hopkinson bar at the DynaMat laboratory of the University of Applied Sciences of Southern Switzerland. The results are processed in terms of stress-strain relationships and strength dynamic increase factor at different strain-rate levels. The dynamic increase factor was also compared with CEB recommendations. The experimental outcomes can be used to assess the constitutive laws of geopolymers under dynamic load conditions and implemented into analytical models.

A Study on Flexural Behaviour of Geopolymer Based Ferrocement

Portland cement production is under critical review due to the high amount of carbon dioxide gas released to the atmosphere. But at the same time, disposal of huge quantity of fly ash generated from the power plants is also becoming a big burning problem. This is detrimental to animal and plant life, since it pollutes the environment as well as it requires large area for its disposal, when availability of land get scarce day by day. Most of the plants now are facing shortage of dumping space of these waste materials. Most of this by product material is a currently dumped inland fill, thus creating a threat to the environment. In recent years attempts to increase the utilization of fly ash to partially replace the use of Portland cement in concrete are gathering momentum. Efforts are urgently underway all over the world to develop environmentally friendly construction materials, which make minimum utility of fast dwindling natural resources and help to reduce greenhouse gas emissions. In this connection, Geopolymers are showing great potential and several researchers have critically examined the various aspects of their viability as binder system. Geopolymer concretes (GPCs) are new class of building materials that have emerged as an alternative to Ordinary Portland cement concrete (OPCC) and possess the potential to revolutionize the building construction industry. Considerable research has been carried out on development of Geopolymer concretes (GPCs), which involve heat curing. A few studies have been reported on the use of such GPCs f or structural applications. An experimental investigation was carried out to study the material and mixture proportions; the manufacturing processes, the fresh and hardened state characteristics of fly ash based geo polymer concrete are evaluated. In the present study the flexural behavior of geo polymer concrete was assessed and the behavior was found to be considerably more than that of conventional concrete.

Alkali–silica reaction in metakaolin-based geopolymer mortar

This paper assesses the behaviour of metakaolin-based geopolymers in the presence of alkali-reactive aggregates. Geopolymer mortars were made with flash metakaolin and sodium waterglass solution in presence of six different aggregates, each having different levels of reactivity to alkali–silica reaction (ASR). The behaviour of geopolymer in presence of such reactive aggregates was investigated by monitoring the dimension changes and the dynamic modulus of the specimens placed in accelerated conditions at 60 °C and 95 % RH for up to 250 days. SEM and EDX analyses were also performed at 170 days to visualize the newly formed products. A comparison with an ordinary Portland cement (OPC) was made for all aggregates in order to evaluate how strongly geopolymers were affected by ASR, if at all. Results showed that geopolymers, although they contained high concentrations of alkalis, were more able to resist ASR than OPC was, and no characteristic swelling or any significant loss of rigidity was observed for the geopolymer specimens. An exception was nevertheless noted for the mortar made with crushed glass sand, where a significant drop in rigidity was found, with the presence of a gel layer at the surface of the glass grains but without any swelling.

Investigation into the Effect of the Duration of Exposure on the Behaviour of GPC at Elevated Temperatures

Ordinary Portland Cement (OPC) Concrete has long been used in the construction industry as a primary material owing to its versatility, superior performance, low cost, easy workability and availability of accepted standards of practice. The readily available raw materials for the manufacture of cement, and subsequently for concrete itself, have been a driving force for the acceptance of concrete as a construction material worldwide. Recently however, OPC concrete has come under scrutiny over its large carbon footprint. This is largely due to the energy intensive manufacturing process of cement and the extensive use of virgin material in cement production. Focus is therefore shifting to engineer new construction materials that offer similar advantages to that of OPC concrete while being environmentally friendly. Geopolymer Concrete (GPC) is such a material. It has emerged during the last decades, and has been found to possess excellent engineering properties as well as enormous benefits on the sustainability front. The current study is conducted to investigate the compressive strength of GPC up to temperatures of 1000 o C for varying duration of exposure time. It was found that when tested at temperatures of 600 o C, 800 o C and 1000 o C, the GPC samples exhibited a higher compressive strength (8-18%). However, the samples tested after cooling recorded a residual compressive strength 25-50% lower than the ambient strength. Yet, the residual strength of GPC is significantly higher than that of OPC. The duration of exposure time was found to have an insignificant effect on the strength properties of GPC, especially at higher temperatures. Scanning Electron Microscopy (SEM) was used to reveal the changes to the micro-structure that took place after exposure to high temperatures and to get a useful insight into the behaviour of geopolymers.

Influence of Curing Temperature on Metakaolin-Based Geopolymers

Geopolymers, also known as inorganic polymers, are aluminosilicates with cementing characteristics that have great application potential. They are produced by the alkaline activation of aluminosilicates precursors such as industrial wastes, calcined clays, natural minerals, among others and have their properties intimately associated to characteristics of the precursor materials and curing conditions. In this sense, this study aims to evaluate the mechanical behavior of geopolymers obtained from metakaolin according to the curing temperature. The geopolymerization was reached by the mixture of metakaolin with NaOH and the curing of the specimens was held at room temperature, 60°C and 100°C. The specimens were characterized by X-ray diffraction, mercury intrusion porosimetry, and SEM. The mechanical strength was determined by flexural test. The results show that the process of geopolymerization suffers a direct influence of the curing temperature used.

Synthesis, Rheological Behavior and Mechanical Characterization of Structural Fast-Setting Geopolymers

Geopolymers are inorganic materials with ceramic characteristics that can be synthesized at room temperature from the setting of slurries. Their structure consists of aluminosilicate units that polymerize in alkaline environment. The setting rate and mechanical behavior of geopolymers strongly depends on the SiO2:Al2O3 molar ratio, polymeric precursor and polymerization cation. The present work reports the synthesis and characterization of 3.5:1 (SiO2:Al2O3) structural geopolymers prepared using either metakaolin (GPMK) or kaolin (GPK) as geopolymeric precursor in potassium hydroxide solution. GPMK depicted quick setting whereas GPK set only after 4 hours. The rheological characterization of the slurries revealed that plastic viscosity and yield point of GPK were 0.40 Pa.s and 14.2 Pa, respectively, whereas GPMK set instantly. The compressive strength of both geopolymers were measured after 24 hours and resulted in similar results, i.e., 4.6 MPa for GPMK and 4.4 MPa for GPK. The strength of both geopolymers was compatible to values typical of structural materials.