3.1APPLICATION OF GEOPOLYMER CONCRETE IN CONSTRUCTION
Application of geopolymer concrete is almost the same to the ordinary cement concrete. However, this material is not popular to be used in various applications. According to expert, there are a few advantages of geopolymer concrete compare to ordinary cement such as require lower cost. Here are some example of construction that used geopolymer concrete:-
In preparation of the pavement project, it was tested and construction trials were undertaken to ensure that geopolymer concrete would meet the performance criteria for the best pavement. It must overcome some challenges to have specifications. If the trial success, engineers will approve and will start doing their construction using this concrete. As example one project that were carried at Brisbane West Wellcamp Airport is Australia which also the first greenfield public airport. The project was considered succeed.
Retaining walls are rigid walls used for supporting the soil mass laterally so that soil can be retained at two levels in different site. It is the wall that is designed to restrain soil to a slope that it would not naturally keep to. Experts has found that the ordinary cement that is used to build this retaining wall can be replaced with other better material which is the geopolymer concrete. Swan Street Bridge over the Yarra River was one of the retaining walls that use geopolymer concrete in its construction. The construction was undertaken utilising conventional techniques for formwork construction, concrete placement by pumping, finishing, curing, with polyethylene plastic. For long term performance, it was tested in the laboratory so that the performance meet the require specifications. Using geopolymer concrete in construction of retaining wall is a good idea as a result the built wall was very strong and stay still now.
31060572610576Usage of geopolymer concrete in the making of boat ramp is invented by an extreme innovator under R&D project by QLD Transport and Main roads, Department of Maritime Safety. The slab of the ground was made on ground to the ramp and was made from site cast of geopolymer concrete and similarly reinforced with GFRP. The precast ramp unit were manufactured at Wagners precast facility in Toowomba, while the site cast were batched in Toowomba, trucked to site with 6.5 hour transit time and then were activated with chemical activator. The entire batch constituent can be mixed in a truck bowl and remain completely dormant until activator chemicals are added.
3.1.4Precast Bridge Decks
This is a composite bridge structure made from pultruded fibreglass girders acting compositely with a Grade 40 geopolymer bridge deck. One of the earliest bridge was prefabricated at Wagners Toowoomba CFT factory and was installed at site 2009. The bridge has been successfully in service since that date with continual concrete agitator truck. Next one which is one of the bridge that using geopolymer concrete in its construction is the Bundaleer Road bridged, West Moggill, Brisbane was constructed. The geopolymer deck act as compression flange to the bridge as we as providing a serviceable wearing deck.
3.2CHEMICAL COMPOUND IN GEOPOLYMER CONCRETE
Production of geopolymer concrete requires an aluminosilicate precursor material such as matakaolin or fly-ash which is a user friendly alkaline reagent. Unlike ordinary portland cement, geopolymers do not form calcium-silicate-hydrates (CSHs) for matrix formation and strength, but utilise the polycondensation of sililica and alumina precursors to attain structural strength. The hardening process are more ready in room process to be achieved with some addition of calcium cations. Concrete is the composite material resulting from the mixing and hardening of cement with water and stone aggregates.
3.2.1User-friendly alkaline reagent
Geopolymerization only rely on water, but geopolymerization also need chemical ingredients which is require safety procedures as it is dangerous. Safety rules can be classified into two that are corrosive and irritant. They can be recognize from their logo.
Gloves, glasses and mask must be used during handling material that is corrosive. It cannot be implemented without appropriate safety procedures as it is user hostile. This geopolymer alkaline reagents are actually user-friendly although it us irritant and has its risk if inhaled of powder. It also require selection and use of appropriate personal active equipment although in any situation.
Alkali-activated-cement or alkali-activated geopolymer that are found in literature and on the internet such as fly ashes that uses alkali silicates that has molar ratio of SiO2:M2O which is below 1.20 (pure NAOH 8M/12M). These conditions are actually not user-friendly for normal labor force, it requires careful consideration of personal protective equipment if are used in field.
In a nutshell, geopolymer concrete recipes that are used in the field generally that involve alkaline soluble silicates with molar ratios starting from 1.45 to 1.95, particularly, 1.60 to 1.85 that is user-friendly conditions.
3.2.2Geopolymer concrete categories
126.96.36.199Slag based geopolymer cement
The components are metakaolin (MK-750) + blast furnace slag + alkali silicate (user-friendly). Geopolymeric make-up are Si:Al = 2 , solid solution of Si:Al, Ca-poly(di-sialate)(anorthite type) + Si:Al = 3, K-poly(sialate disiloxo) (orthoclase type) and C-S-H Ca-silicate hydrate
188.8.131.52Rock based geopolymer cement
Certain amount MK-750 are been replaced but only with selected volcanic stuffs yields geopolymer cement with better properties but the CO2 must be less emission than simple slag based geopolymer concrete
The components are metakolin MK-750, blast furnace slag, volcanic stuffs either calcined or not calcined, mine tailing and alkali silicate but the user-friendly one
Geopolymer make-up are Si:Al = 3 and the solid solution of Si:Al = 1 Ca-poly (di-sialate)(anorthite type) + Si:Al = 3-5(Na,K)-poly(silicate-multisiloxo) and C-S-H Ca-silicate hydrate
184.108.40.206Fly ash based geopolymer cement
1) Alkali activated fly ash geopolymer (user-hostile)
It requires heat curing around 60-80°C; not manufactured separately as a cement that ratherly produced directly as a fly-ash based concrete. NaOH (user-hostile) + fly-ash;
Particles that are embedded in an alumino-silicate gel with Si:Al = 1 or 2, zeolitic type
2) Slag or fly ash based geopolymer (user-friendly)
At room temperature is the hardening and user-friendly silicate solution + blast furnace slag + fly ash: fly particles that are embedded in geopolymeric matrix with Si:Al = 2 (Ca,K) poly (sialate-siloxo).
3) Ferro sialate based geopolymer cement
This properties are almost similar to the rock based geopolymer cement but this one is involved geological elements with higher iron oxide content.
Geopolymeric make up are poly(ferro-sialate)(Ca,K)-(-Fe-O)-(Si-O-AO).
3.3PROPERTIES OF GEOPOLYMER CONCRETE
Geopolymer concrete normally can be manufactured to look dan perform physically like the Ordinary Portland Cement (OPC) concrete. Some of the chemical and the physical properties of the geopolymer concrete are similar to the OPC concrete. However, the chemical resistance of the geopolymer concrete is much higher than OPC concrete.
3.3.1Compressive strength and the strength development
The behaviour in compressive of the geopolymer concrete is normally represented by compressive strength, strength developement and the stress-strain relationship. The behavior in compressive of the geopolymer concrete is similar to that of the OPC concrete.
Geopolymer concrete have been found that its compressive strength can up to 70 MPa. The geopolymer concrete gains its compressive strength faster than the OPC concrete. It is found that the compressive strength of the geopolymer concrete is larger than 25 MPa after 24 hours.According to the test results by SERC Chennai, the compressive strength of geopolymer concrete have been found to be 60 to 70 MPa after 28 days.
The curing process is affected the compressive strength development of the geopolymer concrete significantly. The geopolymer concrete obtain the full compressive strength through curing since there is no increase in compressive strength after one day. The geopolymer concrete will achieve almost 90% of the final compressive strength if it cure at 80 to 90?. All curing regimes produce similar strength results, it only affect the time to reach the ultimate compressive strength.
It is an inverse relationship between the water to geopolymer concrete ratio and the compressive strength of the concrete. It is similar to the relationship betwwen water/cement ratio and the compressive strength of OPC concrete. The geopolymer concrete is mixed with fly ash and slag to obtain a higher compressive strength. For optimum compressive strength of geopolymer mix, the ration of slag to fly ash by mass is 35: 65.
3.3.2 Tensile strength
Tensile strength of geopolymer concrete usually measured using some indirect tensile strength such as splitting tensile test, flexural tensile test and modules of rupture. The tensile strength of geopolymer concrete is higher than that of OPC concrete with the same compressive strength for both.
3.3.3 Elastic Modulus
Elastic modulus is a function of the aggregates and the cement matrix and their relative proportions. The geopolymer concrete has a greater elastic modulus compared to OPC concrete with the same coarse aggregates since the matrix of geopolymer concrete is denser. However, geopolymer concrete shows a lower elastic modulus than OPC concrete with the similar compressive strength in the experimental results.
There is two phase model which was developed by Setunge and purposed by Nd and Foster for calculating the elastic modulus of geopolymer concrete which is using the function of elastic modulus of coarse aggregates and geopolymer mortar. These two model give the observation that geopolymer concrete has an lower elastic modulus than OPC concrete.
The model developed by Setunge is given as:
Where V is volume proportion of coarse aggregate Ea is elastic modulus of coarse aggregateEm is elastic modulus of mortar
The model purposed by Ng and Foster is given as:
Where fmm is the mortar peak stress
3.3.4 Creep and shrinkage
The type of geopolymer materials, curing regime and the activation process would affect the creep and shrinkage of geopolymer concrete. The shrinkage of geopolymer concrete can be 100 micro strain if it is a heat cured while the drying shrinkage value can be 1200 micro strain if the concrete cure at low maturuty. The drying shrinkage of geopolymer concrete is much less compared to cement concrete. This makes geopolymer concrete suitable for thick and heavily restrained concrete structure.
The magnitude of creep of slag based geopolymer concrete is similar to the OPC concrete while the creep of heat cured fly ash based geopolymer concrete is only about 50% to the magnitude of that in OPC concrete.
3.3.5 Thermal expansion and fire resistance
The thermal expansion of geopolymer concrete is less than OPC concrete under a normal temperature. Geopolymer concrete has a better fire resisitance compared to OPC concrete, it can be melt ultimately at 1200? without spalling. However, there is some uncertainty about the behaviour in thermal expansion of some geopolymer concrete. It is because there is an incompatibility of the expansion between geopolymer matrix and coarse aggregates which is geopolymer matrix contracts about 1% while the coarse aggregates expand about 2.5% at 800?. This situation will affect the fire resistance of geopolymer concrete.
3.3.6 Chemical resistance
Geopolymer concrete has a high acid resistance when it is testing by exposed to 2% and 10% sulphuric acids which means it has a better resistance to sulphate attack compared to OPC concrete. The OPC concretes are defenceless against the decay under acid attack, sulphur exposure and ingress of chloride ions.
The choride permeability of geopolymer concrete is very low as per ASTM 1202C. Geopolymer concrete has a higher resistivity to against the corrosion of reinforcing steel compared to OPC concrete which is due to the non-porosity and high pore soulution ionic strength of geopolymer concrete. This gives a better protection to the reinforcing steel from corrosion than the OPC concrete.
The workability of geopolymer concrete can be tested by slump test. The slump loss of geopolymer concrete with fly ash is equal or less than that of OPC concrete. The workability of geopolymer concrete can be increased by adding naphthalene based superplasticiser with the amount of 2% of the mass of fly ash.
3.3.8 Heat of hydration
Geopolymer concrete has a low heat of hydration compared to OPC concrete. Geopolymer concrete does not show an exothermic reaction during the first 25 hours, it is because the heat of the curing usually adopted in geopolymer concrete.
3.4ADVANTAGES AND DISADVANTAGES OF GEOPOLYMER CONCRETE
The main advantages and disadvantages of geopolymer concrete are listed here:
It has a high compressive strength that showed higher compressive strength than that of ordinary concrete. It also has rapid strength gain and cures very quickly, making it an excellent option for quick builds.
Geopolymer concrete has high tensile strength. It is less brittle than Portland concrete and can withstand more movement. It is not completely earthquake proof, but does withstand the earth moving better than traditional concrete.
220.127.116.11Very Low Creep and Shrinkage
Shrinkage can cause severe and even dangerous cracks in the concrete from the drying and heating of the concrete or even the evaporation of water from the concrete. Geopolymer concrete does not hydrate; it is not as permeable and will not experience significant shrinkage.
The creep of geopolymer concrete is very low. When speaking of creep in concrete terms it means the tendency of the concrete to become permanently deformed due to the constant forces being applied against it.
18.104.22.168Resistant to Heat and Cold
It has the ability to stay stable even at temperatures of more than 2200 degrees Fahrenheit. Excessive heat can reduce the stability of concrete causing it to spall or have layers break off. Geopolymer concrete does not experience spalling unless it reaches over 2200 degrees Fahrenheit.
As for cold temperatures, it is resistant to freezing. The pores are very small but water can still enter cured concrete. When temperatures dip to below freezing that water freezes and then expands this will cause cracks to form. Geopolymer concrete will not freeze.
It has a very strong chemical resistance. Acids, toxic waste and salt water will not have an effect on geopolymer concrete. Corrosion is not likely to occur with this concrete as it is with traditional Portland concrete.
While geopolymer concrete appears to be the super concrete to take the place of traditional Portland concrete, there are some disadvantages such as:
22.214.171.124Difficult to Create
Geopolymer concrete requires special handling needs and is extremely difficult to create. It requires the use of chemicals, such as sodium hydroxide, that can be harmful to humans.
Geopolymer concrete is sold only as a pre-cast or pre-mix material due to the dangers associated with creating it.
126.96.36.199Geopolymerization Process is Sensitive
This field of study has been proven inconclusive and extremely volatile. Uniformity is lacking.
While the idea of geopolymer concrete seems ideal and could be the best thing to come along since Portland concrete, there are still too many unstable issues that can cause major hiccups in the mixing and application process of the concrete.
3.5GEOPOLYMER CONCRETE VS PORTLAND CEMENT
White fly ash and slag have been widely used throughout the world, as additional cementing materials in Portland cement concretes. This is because the fly ash and slag reaction in the Portland cement system is generally slower than the cement reaction itself. This means that the cement mixed with high fly ash or slag content will show lower initial strength, but better late strength development than Portland cement. Geopolymer based on fly ash and slag will use a non-water-based alkaline activation solution, to compensate for this tendency for a slower reaction. This activation blend is used to expedite the dissolution and subsequent reactions of ash and slag particles. Among the techniques used to study the formation of kinetic geopolymers are spectroscopic, calorimetric and rheological techniques, and a more detailed mechanical description of the interconnected dissolution-gel dissolution processes has been developed based on these data. The increased strength in the well-designed portland cement concrete mix will survive over the months to the year as the microstructure continues to grow. The appropriate geopolymer concrete mix design can build high strength at acceptable rates when healed at temperatures as low as 10-15?C.
Within the portland cement concrete, many admixtures are used either unnecessary, ineffective or both in the geopolymer system. Furthermore, commercially available superplasticisers have been insulted by alkaline activation solutions used in geopolymer synthesis, this is not necessarily true as there is some evidence that conventional spreading agents such as superplasticisers will act on binders if added before the alkaline activator is added to the mix. Different geopolymer chemistry is due to the different additive mixtures, this is useful in controlling geopolymer properties. Additionally, standard accelerator, retarder and viscosity transformer used in portland cement are not necessarily useful. This is because, Research over the last few decades has led to the development of specific admixtures toolkit to geopolymer systems and which provide an ever-expanding level of rheological control, setting time and strength.
Although the geopolymer control level has not been able to compete with portland cement in terms of its ability to control the design and development of strengths, which have been developed in nearly 200 years of research, the rapidly developing scientific understanding of developing geopolimer chemistry continues to provide advancement in this field.
While the durability of fly ash- derived geopolymers has obviously not yet been extensively proven, as these materials were first introduced and studied in 1993, there do exist extensive data regarding the performance and durability of the cements generated by alkaline activation of slags. These tests have shown excellent resistance to ageing, freeze-thaw cycling, salt scalling and carbonation. Testing of geopolymer cements in each of these areas is ongoing, but initial results generally appear very promising. The aluminosilicate geopolymer phase is inherently quite highly resistant to acid attack due to the high degree of crosss-linking present and the formation of an acid-resistant leached silica phase. The strong binding of the gel phase to aggregate particles enhance flexural and tensile strength, which are particularly valuable in aiding freeze-thaw resistance. While some early and poorly-designed geopolymer concrete formulations were found to be susceptible to efflorescence as the excess alkali present was gradually released from the pore solution and reacted with atmospheric CO2 to form sodium carbonate crystals, this problem is readily able to be overcome with accurate its proportioning and adequate curing.
The existing Portland cement and concrete control levels have been developed over a period of nearly 200 years of worldwide use, and as comparison between fly ash and slab-based geopolymers have been studied at global number of laboratories in worldwide for less than two decades, and just starting to meet commercial use. Furthermore, the development of geopolymer technology continues, but with more mature technology to the point where geopolymer concrete can now be produced on a commercial scale with full confidence that it will implement specifications, will not be fixed gradually or too slowly, and will develop its design strength. The fly ash precursor, in particular, is a volatile material, the chemical understanding of ash in geopolymerization has reached the point where small rectifiers can be made in mixed designs to account for direct any deficiencies or changes in ash properties, providing a geopolymer product that can reliable.
3.5.6Problem of Liquids Activators
One of the main difficulties associated with geopolymer technology is, the use of liquid alkali activation solutions, which are classified as highly corrosive materials. In terms of operations, occupational health and safety problems are extremely difficult and expensive to handle. Additionally, alkali solutions are used more than 1 million tonnes annually in Australia each year, indicating that its uses are everywhere in many processes and industries where, the problems have been mitigated by proper procedures and operations. Use of geopolymer concrete, pure liquids need to be mixed with aggregates and binders to form pre-mixed concrete or other aggressive per-cast products will drastically decrease. Nevertheless, the use of geopolymer concrete should be learned and trained with appropriate handling of precautionary measures and safety procedures, as the new geopolymer concrete is still much more aggressive than traditional OPC concrete. This is because the pH of the geopolymer is almost 14 compared to the pH of OPC 13.