Table of Contents

1. Introduction

2. Literature Review

2.1 Geopolymer Cement/Concrete

2.1.1 General

2.1.2 Constituents

2.1.3 Mechanical Properties

2.1.4 Environmetal impact of Geopolymer Concrete

2.1.5 Application of Geopolymer Concrete

2.2 Fibre-reinforced Plastic

2.2.1 General

2.2.2 Repair Concept

2.3 Numerical Analysis

2.3.1 General

2.3.2 Finite Element Modelling

3. Conclusion

Reference

List of Figures

Figure 1:  Schematic Chemical reaction of fly ash and akaline activator(Xu and Van Deventer, 2000)

Figure 2: Example of Aggregate Grading Curve (Wardeh et al, 2018)

Figure 3: Strength gain of ordinary Portland cement concrete and fly ash concrete (Tafheem Et.al, 2011)

Figure 4: Compressive Stenght of Geopolymer Concrete after exposure of Sulfuric Acid with respect to time (Wallah and Rangan, 2006)

Figure 5: Fly ash production (million tonnes/year) among different countries (Jain and Dwivedi, 2014)

Figure 6: Pavement plan for BWWA (Glasby et al, 2015)

Figure 7: Example of 3D model of a rectangular concrete beam (Tejaswini and Rama Raju, 2015)

Figure 8: Comparison of numerical and experimental result of crack pattern (Nguyen et al, 2016)

List of Tables

Table 1: Chemical Composition of Raw Fly Ash from two different power stations (Yu et al., 2012)

Table 2: Design mix for OPC and GPC (Mustafa Al Bakri et al., 2013)

Introduction

The demand of housing has been continuously increased due to the global growth of population. Concrete as an accomplished construction material has been used extensively in every construction building while it is a mixture of cement, water and aggregates. Traditionally, Ordinary Portland cement (OPC) is used as the hydraulic binder in order to produce concrete. Meanwhile there is a major drawback of using OPC with respect to its sustainability. Hence, Geopolymer Concrete (GPC) has been introduced to as a much more environmental friendly construction material. This material used fly ash as partial or complete replacement of ordinary Portland cement.

The main purpose of this project is to investigate the strength and toughness of a notched geopolymer concrete beam reinforced with fibre-reinforced plastic (FRP) sheet. Since concrete is the major material involved in almost every civil engineering building. Engineers are interested on repairing defective concrete in different levels of damages.  The notched concrete beam is referring to a real life scenario as it has been damaged with cracks. In order to recover its strength. Fibre-reinforced plastic is used to composite to the concrete beam.  This process increased the overall strength, stiffness, crack resistant as well providing a quality corrosion protection. 

1.    Literature Review

1.1 Geopolymer Cement/Concrete

2.1.1 General

Concrete is the most widely used material in civil engineering due to its versatility and durability. The most common applications of concrete are foundation, retaining walls, highway, pavement, bridge and architecture buildings. Research shows that an estimate of 260,00,00,000 tons of cement required on demand every year while researchers belief the number is going to increase by 25% within the coming decade. (Abdul Aleem and Arumairaj,2012) Traditional concrete is a composite material with three major components: water, fine & coarse aggregate (e.g sand, gravel) as well as Ordinary Portland Cement. Cement experiences a chemical reaction with water called hydration in order to form a paste. In this process the paste is harden and bind the aggregate together that eventually turned into concrete. (Portland cement concrete materials participant notebook, 1995). However, production of Portland cement requires enormous amount of energy. This energy-intensive process generates large amount of greenhouse gases (CO₂). Hence, geopolymer concrete is introduced to reduce the pollution to the atmosphere by large reducing the greenhouse gases emission. Fly ash is the new constituents used in concrete as partially or completely replacement of cement. This material is a fine solid waste produced by coal-fired power plants during the combustion of coal process. This material utilized wasted material and require less energy which significantly reduce the environmental impact. Moreover, this new material also obtains a higher compressive strength and chemical resistance compare to Portland cement concrete.

2.1.2 Constituents

2.1.2.1 Fly ash

Fly ash is a powder like material which is generated by coal-fire station. Thermal industry generates electricity through combustion of fossil fuel such as coal or natural gas while Fly ash is the by-product generated in this process. Standard fly ash is made of silt-sized spherical particles with a range of size between 10-100 micron. Spherical particles within fly ash presents fluidity as well as workability to the geopolymer concrete. (Fhwa.dot.gov, 2018) Typically, it consists primary of Silicon oxides (SiO₂), Aluminum Oxide (Al₂O₃), Iron(III) Oxide (Fe₂O₃₎, Calcium Oxide (CaO), Sodium Oxide (Na₂O), Magnesium Oxide (MgO) as well as Sulfur Trioxide (SO₃).  Table 1 (Yu et al., 2012) is from a research paper which investigated the chemical composition produced by different power station. This result indicates that the chemical composition of fly ash depends on the coal used by the power station. Some power station added extra material within the coal to increase efficiency to generate power.

Table 1: Chemical Composition of Raw Fly Ash from two different power stations (Yu et al., 2012)

Reducing the amount of Portland cement within concrete and replace it with fly ash provide several benefits. For fresh concrete, the water demand is decreased for a given slump. This highly improves the paste flow behaviour by improving its pumpability. When it is added to the concrete mix, the silt-sized spherical particles within the fly ash behave as miniature ball bearing, thus lubricant effect was introduce causing improvement of concrete workability.

2.1.2.2 Alkaline Liquid

Alkaline liquid is a solution added to fly ash which carries a chemical reaction call geo-polymerization. This process transforms fly ash from an amorphous and metastable material into a strong and solid composite material.  Sodium Hydroxide (NaOH) and Sodium Silicate are mostly used as the alkaline solution with an alternative choice of Potassium Hydroxide and Potassium silicate. (Joshi and Kadu, 2012) Exothermic process of dissolution takes place while fly ash is added into alkali solution. Throughout this reaction, the microstructure within fly ash breaks down as the covalent bonds between Si-O-Si as well as AI-O-AI are yielded. Therefore, the silicon ions and aluminium ions are capable to combine with the alkali solution to from a compact and condensate material. This kind of concrete obtains a high ultimate compressive strength but bad order structure appearance. (Palomo, Grutzeck and Blanco, 1999)  Figure 2 shows the schematic chemical formula which present the two reaction paths.

Figure 1:  Schematic Chemical reaction of fly ash and akaline activator(Xu and Van Deventer, 2000)

Further research has been done in order to investigate the compressive strength of concretes between using NaOH and KOH as the alkaline solution. The result indicates that extend of dissolution of silicon ions and aluminium ions had a direct relationship with the product compressive strength. (Xu and Van Deventer, 2000) clearly states that mineral tend to obtain a better performance under compressive loading with a higher extend of dissolution during geopolymerisation. In this paper, 15 natural Al-SI mineral were tested with both NaOH and KOH medium solution to fabrication geopolymer. The result indicates that in general, by using KOH in the geopolymerisation process achieved a higher compressive strength. The highest compressive strength by KOH was up to 18MPa. 

2.1.2.3 Aggregates

Just like traditional concrete, coarse and fine aggregates are both required for geopolymer concrete fabrication. The aggregate grading curve that has been used nowadays by the concrete industry is still capable to use in geopolymer concrete. (Rangan, 2008). Geopolymer paste binds both the coarse and fine aggregates together to provide the overall strength to the material. Same as traditional concrete, 70-80% of the total volume is aggregates. (Hardjito, et al, 2005)

Figure 2: Example of Aggregate Grading Curve (Wardeh et al, 2018)

2.1.3 Mechanical Properties

2.1.3.2 Chemical resistance

It is the primary characteristic of concrete that engineer interested in. Numbers of research show that fly ash based geopolymer concrete obtain a higher compressive strength than Portland cement concrete. In 2009, a research paper compared the compressive strength of geopolymer concrete to Portland cement concrete. Total of 8 samples were made based on different ratio between fly ash and Portland cement to aggregate. Table 2 shows the detail of each sample which include the ratio of Portland cement and fly ash to aggregates. For ordinary Portland cement concrete, the sample with 50% cement and 50% aggregate achieved the highest compressive strength at about 31MPa. Meanwhile the highest compressive strength that geopolymer concrete achieved was at 49.3 MPa with a ratio of 30% fly ash and 70% aggregate. (Mustafa Al Bakri et al., 2013) This result indicated two main facts of concrete. Firstly, although aggregate normally provide the overall strength to the concrete, increasing the content of aggregate does not ensure a higher compressive strength. Concrete made with 80% of aggregate did not achieve the highest compressive strength. Secondly, there was a 37% different difference between both concretes’ compressive strength. This result indicates that replacing fly ash as the source material provides a higher compressive resistance to the concrete.

Table 2: Design mix for OPC and GPC (Mustafa Al Bakri et al., 2013)

This phenomenon was explained in other research paper.  The major effect of replacement of cement with fly ash is to allow it to obtain chemical reaction with alkali and lime. This process produces addition binder with the concrete which eventually allow the concrete to gain strength throughout the aging stage. (Tafheem Et.al, 2011) Figure 4 compares the difference of ultimate strength between fly ash concrete and plain cement concrete. The graph shows that the compressive strength between geopolymer and Portland cement concrete were relatively similar at early stage before 28days. However, the difference between them started to increase after 28 days while fly ash concrete obtains a much higher compressive strength.

Figure 3: Strength gain of ordinary Portland cement concrete and fly ash concrete (Tafheem Et.al, 2011)

2.1.3.2 Chemical resistance

It is an important properties for concrete since this material is often been used in application requiring exposure to the environment. Studies shows that geopolymer concrete obtain a relatively higher acid resistant than Portland cement concrete. Portland cement concrete obtains an extremely low chemical resistance because of limestone as the source material for Portland cement is extremely reactive with acidic solution. Research that was done by Davidovits in 1994 shows that Portland based concrete did not perform well when exposed in acidic environment. Destruction due to chemical attack was significant with 30-60% weight loss. Meanwhile, geopolymer concrete did not experience any major destruction and a much lower weight loss at approximately 5-8%. (Davidovits, 1994) In 2006 Wallah and Rangan did similar test to investigate the chemical resistance of geopolymer concrete. Comparing both research, Wallah and Rangan focused on the resistance from sulfate acid. Geopolymer concrete specimens were soaked into different amount of sodium sulfate acid for an entire year. After that all specimen were tested for compressive strength and visual appearance. Figure 4 shows the result that the concrete compressive strength decreases as the concentration of the acid increase. 

Figure 4: Compressive Stenght of Geopolymer Concrete after exposure of Sulfuric Acid with respect to time (Wallah and Rangan, 2006)

2.1.4 Environmetal impact of Geopolymer Concrete

Reducing environmental impactis the major advantage of using geopolymer concrete over ordinary Portland cement concrete. This material utilized fly ash generated by thermal industry as a partial or fully replacement of Portland cement. Manufacturing Portland cement requires intensive-energy process. During this process, the raw materials such as limestone are heated in the kiln. This caused a chemical reaction called thermal decomposition of calcium carbonate. (Huntzinger and Eatmon, 2009) Research shows that global anthropogenic CO₂emitted by cement industry while manufacturing Portland cement is estimated at about 2% of the global primary energy consumption, or almost 5% of the total global industrial energy consumption (Omer, 2014). However, Portland cement only has a minor portion within the concrete sitting at approximately 7-15%. The other constituents such as aggregate and water require much less or no energy to obtain. Hence, by reducing the amount of Portland cement used can efficiently reduce the energy needed to produce concrete. In addition, coal is the primary fossil fuel source for electricity generation. Research shows that in 2015, an estimate of 39.3% of the world’s electricity is generated by combustion of coal. (IEA, 2017) As coal being the major source of generation of electricity, over 300 million tonnes of fly ash is produced by the coal-fired stations worlwide. 10-30 % of the fly ash wastes is utilised to produce geopolymer concrete instead of deposit into the pond or ocean. (Joshi, 2010). Figure 1(Jain and Dwivedi, 2014) shows the estimated number of the total fly ash produced in different country per year. India, China and USA are the top 3 countries in terms of fly ash production. These three countries contributed 78% of the total world fly ashes. The reason causing that is because these three countries are also the top 3 countries with the highest population. Geopolymer concrete utilized this by-product to produce construction material which effectively reduce the environment impact.

Figure 5: Fly ash production (million tonnes/year) among different countries (Jain and Dwivedi, 2014)

2.1.5 Application of Geopolymer Concrete

Geopolymer concrete has the potential to be used to fabricate bridges. Since geopolymer concrete works perfectly with plastic fibre. Geopolymer-fiber composites can be used to produce precast structural elements or decks. This technology is suitable for precast application use because of the need on handling alkaline solution. Both NaOH and KOH are high-alkali activating solution with extreme sensitivity. Furthermore, fabricating geopolymer concrete requires a high temperature curing environment

Wangers is a company in Australia which has a large interest on geopolymer concrete. They believed that with benefit of geopolymer concrete, this new material can be used to replace traditional concrete. This company is also known as “Earth Friendly Concrete (EFC)’’. This company understand that this new class material not only is environment friendly, but also obtain a high flexural tensile strength, low shrinkage as well as well workability characteristic.  In 2014, they have officially announced that Brisbane West Wellcamp Airport (BWWA) was fully operated. This project indicated the development of geopolymer concrete technology since this airport was by far the largest project base on the use geopolymer concrete. Throughout this project, an estimate of 100 000 tons of geopolymer concrete was involved for heavy duty use such as turning node ,apron  as well as taxiways. (G0lasby et al, 2015) This successful project is an important milestone for this new material technology which is capable to encourage future project using this technique.

Figure 6: Pavement plan for BWWA (Glasby et al, 2015)

1.2 Fibre-reinforced Plastic

1.2.1        General

Due to the intensive of concrete in civil engineering, researchers and civil industry are interested in repairing concrete structure. Traditional, damaged civil infrastructures were replaced instead of repaired. About 30 years ago, a new effective reinforcement technique was introduced based on the use of fibre-reinforcement polymer (FRP). FRP is a convenient composite material  made of polymer matrix that is reinforce using fibre. Various types of fibre can be used in this material, generally glass, carbon and aramid are mostly used. This composite material is perfect for modern construction used mainly due to its corrosion resistance and high strength to weight ratio.               FRP is often compared to the use of steel. Studies shows that strength of FRP can be 2-10 times higher than steel with only 1/5 of the weight of steel. High specific strength leads to ease installation in site as well as reducing the construction cost. (Teng et al,2002). This material more often used as external reinforcement for concrete due to its numerous resistances to the environment. Composite material of concrete with external boned FRP leads to significant improvement of resistance to UV radiation, temperature, humidity and air pollution. Furthermore,  Portland concrete are known with relatively low tensile strength and corrosion resistance due to limestone as the source material is highly reactive with acid. Hence , externally boned FRP reinforcement is used very often to composite with Portland concrete.

2.2.2 Repair Concept

This reinforcement technique can be used for both indoor and outdoor applications. It is an efficient and effective technique to improve material performance typical in damaged civil infrastructures. The first ben Tensile strength is known as the major weakness of concrete. Generally crack is formed on the tensile side of concrete beam. FRP plate of sheet can be used to bond to the tensile face of the structure in order to recover the flexural strength. (Rougier and Luccioni, 2007) There are three main types of FRP repairing method that is commonly used in civil industry. a) Wet lay-up technique is a moulding process that positions the FRP sheet into or against a mold (Concrete beam) in layers. In this process, liquid resin is used to improve the quality of laminate. This method is convenient for low-volume reinforcement with simple instalment and low cost. b) Pre-cured FRP composite method involves laminates in different form such as plates or strips. Structure and FRP sheet are combined using a layer of epoxy.  This process has a fast installation times since curing time only require a few hours and limited labour. (Mirmiran, 2004) c)Near surface mounted method is where a reshaped grooved is placed into the concrete cover of an reinforcement concrete structure. After that, FRP is booded with an groove filler. This technique reduce the installation time because there is no other in site preparation except  grooving. (De Lorenzis and Teng, 2007)

1.3 Numerical Analysis

2.3.1 General

Finite element is a convenient method to solve different numerical static problem for given boundary condition. Abaqus is a software to carry out finite element analysis which is about to predict the behaviour of a product (material) affected by various type of physical effects. This software is capable to simulate various physical effects such as point load, vibration, heat transfer stress and fatigue etc. (Hibbit et al., 2012).

2.3.2 Finite Element Modelling

Tejaswini and Rama Raju, (2015) developed finite element analysis to investigate the steel reinforcement concrete beam under 3 point bending test. This paper illustrated every aspect of performing FEA in quality. In order to generate a three dimensional finite element model, a cross-section sketch of each element (concrete and steel) has to be made followed by extrusion in a certain direction. Figure 7 is a screenshot of the 3D finite element model generated. This element has 8 nodes and each with 3 degrees of freedom. The steps of achieving a quality finite element model are as followed.

. :

Figure 7: Example of 3D model of a rectangular concrete beam (Tejaswini and Rama Raju, 2015)

Nguyen et al , (2016) used experimental and numerical analysis to investigate the mechanical properties of steel reinforced geopolymer concrete beams. Four point bending tests were carried out numerically and experimentally. Three dimensional finite element models were generated using ABAQUS/CAE modelling tools in order to simulate the four point bending experiment. Crack pattern was generated in FEA model and compared it to the experimental result. Result obtained in both analysis were relatively similar. Both results shows that at early stage there were flexural crack occurred at bottom and midspan of the beam. Number of vertical cracks formed and spread across the beam as the load increased.               

Figure 8: Comparison of numerical and experimental result of crack pattern (Nguyen et al, 2016)

Lu et al (2005) used meso-scale finite element model to analysis FRP reinforced concrete. Generally, failure of FRP reinforced concrete structure was caused by debonding of the FPP and concrete. Numerical anlaysis was carried out in order to understand the FRP to concrete interface behaviour under pull test. A new finite element approach was used in this paper which is called fixed angle crack model. This approach allows the model to appropriately represent the entire debonding and separation process in a pull tests. Since it could be difficult to model such complicated structure, this study simplify it and set it as a plane stress problem with 4-nodes isoperimetric elements, thus to reduce the computational effort.

2.    Conclusion

This report has provided a literature review of geoploymer concrete, fibre-reinforced plastic as well example of numerical amylases. The mechanical properties and environmental impact for geopolymer concrete are studied in great detail.  Generally, researchers obtained similar result for relatively high compressive strength of geopolymer concrete. Majority of the researches compared both type of concrete with same constituent ratio. Meanwhile research that is done by Mustafa Al Bakri et al was discussed in detail is included in this review. Unlike other papers, it compared the compressive strength between geopolymer concrete and normal concrete with different constituent ratio with comparison on the highest value obtain. In my opinion, it is more realistic since geopolymer and Portland cement used different source material during fabrication.

The background fibre-reinforced plastic is included in this report especially on the external boned reinforcement. The advantages, application and repair concept of this technology is briefly covered.

In the final part of this literature review, a brief overview of numerical analysis using ABQUAS is provided. Since there is limited studies specifically on ‘’FRP reinforced geopolymer concrete’’. Instead, examples of finite element analysis of ‘’geopolyer concrete’’ and ‘’FRP reinforced concrete’’ are discussed. Combining and learning from all adjustments and techniques provided during the FEA are profoundly useful and essential to carry out quality numerical analysis.

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