A critical review of slag and fly-ash based geopolymer concrete

Portland cement concrete is a world-wide used construction material. However, when Portland cement concrete is exposed to fire, its mechanical properties are deteriorated. The deterioration of concrete is generally caused by the decomposition of the Portland cement hydrate or the thermal incompatibility between cement paste and aggregate. Spalling, which is a violent or non-violent breaking off of layers or pieces of concrete from the surface of a structural element, may also occur when the concrete is exposed to rapidly rising temperatures. It is generally believed that spalling is influenced by the build-up of pore water pressure and thermal gradient in the concrete when exposed to elevated temperatures. Geopolymer is an alternative cementitious material which has ceramic-like properties. Geopolymer belongs to the family of inorganic polymers. The chemical composition of geopolymer is similar to natural zeolite, but the microstructure is amorphous. It is suggested that geopolymer processes a potential superior fire resistance due to its amorphous and ceramic-like properties. The objective of this thesis is to study the fire resistance of geopolymer material and to explore the spalling behaviour of geopolymer material when exposed to elevated temperatures. In this thesis, a method was presented to carry out spalling test in small scale specimen with exposure to rapid temperature rise using a commonly available electric furnace. Hydrocarbon fire and standard fire exposure can be simulated by manipulating the exposure location of the surface of the concrete cylinder. Ordinary Portland cement concrete cylinders with different strengths were tested. The results demonstrated that this method was an effective and convenient technique to predict the spalling risk of a concrete. The spalling behaviour of geopolymer concrete by using the surface exposure test and standard gas furnace fire test was studied. It was shown that 100% fly ash based geopolymer concrete had a better spalling resistance to rapidly rising temperature exposure than that of Portland cement concrete. The study of sorptivity test of geopolymer concretes results showed that the geopolymer concrete specimen's structure is more porous and more continuous pore structure than Portland cement concrete specimen. The more porous structure of geopolymer than OPC concrete facilitates the release of the internal steam pressure during heating. Hence, less tensile stress is imposed in the geopolymer concrete than Portland cement concrete during heating, reducing the geopolymer's risk of spalling. When slag was used as a replacement to fly ash in the geopolymer binder, geopolymer paste and concrete specimens developed considerably high strength at room temperature. It was showed that the magnitude of shrinkage of fly ash and slag based geopolymer is significantly higher than that of 100% fly ash based geopolymer and Portland cement concrete. The residual strength of fly ash based geopolymer concrete with slag replacement after exposure to elevated temperature was studied. It was found that the residual strength of 100% fly ash based geopolymer concrete after elevated temperature exposure increased in the temperature range of 200~500°C compared with OPC concretes. Fly ash based geopolymer concrete with slag replacement experienced a strength loss at the temperature range of 200~300°C, then followed by a strength gain at 300~400°C, and another strength loss after 500°C. When slag was used as an additive to fly ash based geopolymer concrete, the overall strength loss of geopolymer concretes with slag replacement after exposure to elevated temperatures ranging from 200~800°C was higher compared with 100% fly ash based geopolymer concrete, however, it was significantly lower than that of the Portland cement concrete specimens. The investigation of fire resistance property of fly ash and slag based geopolymer material when exposed to hydrocarbon fire was followed. After hydrocarbon fire, no spalling was observed on geopolymer concretes when using varying factors as binder, slag replacement, cation type of alkaline liquid activator, room temperature and elevated temperature curing. Residual strength testing of geopolymer concretes after hydrocarbon fire exposure showed a similar residual strength percentage compared with the result of Portland cement concrete. However, it is noted that high strength Portland cement concrete spalled, while high strength geopolymer concrete still had a considerably high residual strength after fire exposure.

Geopolymer is a new trend in cement industry, traditional cement has prompted several problems related to health and environment due to cement dust and carbon dioxide. Geoplymer, however, has attenuated such problems due to the method of manufacturing and low emission of carbondioxide. This paper examines the ability to form geopolymer cement and the ability to use this cement in the formation of geopolymer concrete in the field. Various papers have been published with concern to the geopolymer cement set the curing in an oven is constraint to the geopolymer cement formation. During this paper are studied in air without any types of curing. Also the improvement of cement by meta koline as a source of aluminium and silica are studied. geopolymer cement based on the slag has been improved as it has been replaced with 10% metakoline. After optimizing the best mix of cement (slag and metakoline). The effect of geopolymer cement content is studied. Results have shown variation in compressive strength related directly to content of geoplymer strength. Water in geopolymer cement is not included in the reaction. So, throughout the paper the sea water is used as an alternative to fresh water. Results have shown an improvement in the compressive strength as compared to the presence of fresh water.

Geopolymers are produced by alkali activation of aluminosilicate raw materials (fly ash or metakaolin), which are transformed into reaction products by polymerisation in a high pH environment and hydrothermal conditions at relatively low temperatures (up to 120°C). In the past decade, much experimental work has focused on the mechanical properties of geopolymer based materials subjected to static loading, covering Young's modulus, Poisson's ratio, compressive strength, splitting tensile strength, fracture energy, fire resistance and sulphate resistance. It has been shown that geopolymers can provide comparable performance to traditional cementitious binders in a range of applications, with the added advantage of significantly reduced greenhouse emissions. However, there are few published studies of damping properties and strain rate effect on geopolymers under dynamic loadings. Structural engineers routinely need to make assumptions about the dynamic properties (damping and impact resistance) of a building to simulate its response to dynamic loads such as strong winds, earthquake ground motions, and even impacts. To address this gap, this thesis explores both the damping property and strain rate effect of geopolymers as construction materials. The critical damping value (ζ) is the main parameter in relation to vibration reduction. In this study, free vibration tests and the traditional logarithmic decrement technique were used to measure the ζ of geopolymers. Geopolymers were prepared by activating fly ash using alkali solutions with different Si02/Na20 ratios. The results show that the ζ of the geopolymers is similar to that of the Ordinary Portland Cement (OPC) counterpart. The effect of strain rate on the compressive behaviours, the critical strain and the splitting tensile strength of geopolymer concrete and mortar are presented under a wide range of strain rate loadings. A Shimadzu AG-X 300 kN testing machine was adopted to measure the compressive behaviours at a quasi-static strain rate and low strain rates, and split Hopkinson pressure bar (SHPB) techniques were used at high strain rates. The dynamic increase factors for compressive strength (DIFfc), the dynamic increase factors for splitting tensile strength (DIFft) and the critical strain (DIFec) were measured and compared with results of OPC concrete and its empirical equations. The results show that the coarse aggregates in geopolymer concrete mixes play an important role in the increase of compressive strength and that the viscous effect and crack inertia are responsible for the improvement of splitting tensile strength. Furthermore, the existing formula for OPC concrete underestimates the DIFft of geopolymer concrete and therefore new empirical equations are proposed. In the initial stage of the candidature, the topic of carbon nanotube reinforced OPC paste was explored. However, due to occupational health and safety issues, it was not permitted to conduct SHPB tests on OPC pastes containing carbon nanotubes (CNTs) in the laboratory conditions. Preliminary research on Molecular Dynamics (MD) simulations of the energy absorption properties of CNTs was conducted and the relevant research findings are presented in the Appendix.

Corrosion of concrete sewer pipes by sulfuric acid attack is a problem of global scope. The current paper aims at evaluating two supplementary cementing materials metakaolin and geopolymer cement as partial cement replacements for improving the ability of concrete to resist severe sulfuric acid attack. Both, metakaolin and geopolymer cement were found to significantly improve the resistance of concrete made to Type 10 and 50E cements to 3% and 7% sulfuric acid solutions (pH of 0.6 and 0.3, respectively). Maximum weight loss reduction with respect to the control for specimens made of modified Type 50E cement ranged between 20 and 37%, depending on the additive and the concentration of the acid. Maximum weight loss reduction for specimens made of modified Type 10 cement range between 10 and 42%, depending on the additive and the concentration of the acid. For this test Type 10 cement was found to perform best in the presence of geopolymer cement while the performance of the Type 50E cement was best when metakolin was used as partial replacement for cement. The results emphasize the important role that the nature and composition of hydration products and the completeness of the hydration process play in improving concrete resistance to acid attack.

Concrete infectious together with normal Portland cement (PC) is notable on the planet for its reliability, durability, and versatility. PC concrete is the second most used material next to w Concrete infectious together with normal Portland cement (PC) is notable on the planet for its reliability, durability, and versatility. PC concrete is the second most used material next to water. Even though OPC is so popular in construction, it is not ecofriendly due to enormous energy consumption in its production and due to emission of enormous CO2.This is a serious challenge to sustainable development. Endeavors are expected to build up a natural amicable structural designing development material for limiting the emission of greenhouse gases to the environment. The Endeavour to develop an environment friendly concrete had offered many alternatives. One eminent among them is zero cement concrete. Zero Cement Concrete is an improved version of Geo-polymer Concrete wherein the thermal activation of the binding materials such as GGBS and FA are done with the help of alkaline solution namely (NaOH) and (Na2SiO3). Contrasting to (PC), the creation of geopolymers has a relatively higher quality of strength, durability, and workability. This current paper is a review on geopolymer concrete properties. ater. Even though OPC is so popular in construction, it is not ecofriendly due to enormous energy consumption in its production and due to emission of enormous CO2.This is a serious challenge to sustainable development. Endeavors are expected to build up a natural amicable structural designing development material for limiting the emission of greenhouse gases to the environment. The Endeavour to develop an environment friendly concrete had offered many alternatives. One eminent among them is zero cement concrete. Zero Cement Concrete is an improved version of Geo-polymer Concrete wherein the thermal activation of the binding materials such as GGBS and FA are done with the help of alkaline solution namely (NaOH) and (Na2SiO3). Contrasting to (PC), the creation of geopolymers has a relatively higher quality of strength, durability, and workability. This current paper is a review on geopolymer concrete properties.

The main challenge for concrete industry - and in general for construction materials - is to serve the two major needs of human society, the protection of the environment, on one hand, and the requirements of buildings and infrastructures by the world’s growing population, on the other. In the past concrete industry has satisfied these needs well. However, for a variety of reasons, the situation has changed dramatically in the last years. First of all, the concrete industry is the largest consumer of natural resources. Secondly, Portland cement, the binder of modern concrete mixtures, is not as environmentally friendly. The world's cement production, in fact, contributes to the earth's atmosphere about 7% of the total CO2 emissions, CO2 being one of the primary greenhouse gas (GHG) responsible for global warming and climate change. As a consequence, concrete industry in the future has to face two antithetically needs. In other words, how the concrete industry can feed the growing population needs being - at the same time - sustainable? The answer to this question is represented by the “3R-Green Strategy” widely discussed in the first chapter of this PhD thesis: Reduction in consumption of gross energy for construction materials production, Reduction in polluting emissions and Reduction in consuming not renewable natural resources. In particular, this thesis is focused on the alternative binders to Portland cement such as alkali-activated slag cements and calcium sulphoaluminate cement-based binders in order to manufacture sustainable mixtures for special applications such as repair mortars, lightweight reinforced plasters and concretes for slabs on ground. The experimental results show the feasibility of manufacturing both EN 1504-3 R3 class mortars and Portland-free concretes for jointless slabs on ground with calcium sulphoaluminate cement, supplementary cementitious materials (fly ash, ground granulated blast furnace slag) and hydrated lime instead of Portland cement. Moreover, alkali-activated mortars and concretes seem to be a reasonable alternative to natural hydraulic lime-based and/or traditional Portland cement-based mixtures for rehabilitation or restoration of ancient masonry buildings and existing concretes structures. Finally, a new sustainability index was developed taking into account the environmental impact, the performances and the durability of mixtures. In particular, in the environmental impact section, the natural raw materials consumption, the greenhouse gas emissions and the energy consumption have been considered. Furthermore, depending on the applications and the environments, design parameters and properties related to durability have been assigned to each mixture.

Mineral admixtures have been widely used to produce concrete. Pozzolans have been utilized as partially replacement for Portland cement or blended cement in concrete based on the materials' properties and the concrete's desired effects. Several environmental problems associated with producing cement have led to partial replacement of cement with other pozzolans. Furnace slag and fly ash are two of the pozzolans which can be appropriately used as partial replacements for cement in concrete. However, replacing cement with these materials results in significant changes in the mechanical properties of concrete, more specifically, compressive strength. This paper aims to intelligently predict the compressive strength of concretes incorporating furnace slag and fly ash as partial replacements for cement. For this purpose, a database containing 1030 data sets with nine inputs (concrete mix design and age of concrete) and one output (the compressive strength) was collected. Instead of absolute values of inputs, their proportions were used. A hybrid artificial neural network-genetic algorithm (ANN-GA) was employed as a novel approach to conducting the study. The performance of the ANN-GA model is evaluated by another artificial neural network (ANN), which was developed and tuned via a conventional backpropagation (BP) algorithm. Results showed that not only an ANN-GA model can be developed and appropriately used for the compressive strength prediction of concrete but also it can lead to superior results in comparison with an ANN-BP model.

Geopolymer results from the reaction of a source material that is rich in silica and alumina with alkaline liquid. It is essentially cement free concrete. This material is being studied extensively and shows promise as a greener substitute for Ordinary Portland Cement concrete in some applications. Research is shifting from the chemistry domain to engineering applications and commercial production of geopolymer concrete. It has been found that geopolymer concrete has good engineering properties with a reduced global warming potential resulting from the total replacement of Ordinary Portland Cement.In this work, low-calcium fly ash-based geo-polymer and cement is used as the binder to produce concrete. The fly ash-based geo-polymer and cement paste binds the loose coarse aggregates, fine aggregates and other un-reacted materials together to form the cement added geo-polymer concrete, with or without the presence of admixtures. The manufacture of geo-polymer concrete is carried out using the usual concrete technology methods. To evaluate whether cement added geopolymer concrete can be cured as a normal concrete or not. The present study is about finding optimum percent of cement to be added to know the compressive strength. To study the microstructure of Cement added Geopolymer Concrete (XRD analysis)

This study investigated the mechanical strength and durability of alkali-activated binders composed of blends of fly ash (FA) and ground granulated blast furnace slag. Five samples with FA/slag ratios of 100/0, 75/25, 50/50, 25/75, and 0/100 by mass were employed to prepare alkali-activated FA/slag (AAFS) concrete. Sodium oxide (Na_2O) concentrations of 6% and 8% of binder weight and activator modulus ratios (mass ratio of SiO_2 to Na_2O) of 0.8, 1.0, and 1.23 were used to prepare alkaline activators. Test results revealed that higher slag contents, Na_2O concentrations, and activator modulus ratios increased the compressive strength and splitting tensile strength of AAFS concrete. The total charge passed through AAFS concrete was between 2500 and 4000 C, higher than that passed through reference ordinary Portland cement (OPC) concrete. However, AAFS concrete demonstrated higher performance than that of OPC concrete when exposed to sulfate. According to scanning electron microscopy observations, the main hydration products of AAFS concrete were amorphous alkaline aluminosilicate and low-crystalline calcium silicate hydrate gel. As the slag content increased, the amount of C-S-H gel increased and that of A-S-H gel decreased. According to the results, 100% slag-based AAFS concrete with a Na_2O concentration of 8% and activator modulus ratio of 1.23 offers superior performance.

A cost-effective bacteria-based self-healing cementitious composite for low-temperature marine applications

This paper deals with the performance of semi-lightweight concrete (sLWC), prepared by using calcite powder pellets as coarse aggregates which was improved by partial replacement of cement with UFGGBFS (ultrafine ground granulated blast-furnace slag). Cement could be replaced by UFGGBFS as 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, and 70% to enhance the strength and durability properties of concrete. High-range water-reducing admixtures (HRWA) were used in these mixes which were dosed up to 1.5% weight of the total cementitious material content. It also develops the weaker transition zone into more impermeable layers. Specimens were subjected to accelerated curing (AC) method as well as conventional curing method. Experimental results were compared and reported that a maximum 28th-day compressive strength of 32.6 MPa has achieved at 30% replacement level with a density of 2200 kg/m3 in conventional curing, while in AC, the maximum compressive strength of 29.5 MPa has achieved at 40% replacement level. From the experimental results, the conventional curing method shows the better compressive strength when compared with the AC method. Therefore, rapid chloride penetration test (RCPT) was conducted on conventional cured specimens. The RCPT test results show that the replacement level at 70% gives the charge passed of 545.6 coulombs which comes under “very low” category of penetration of chloride ions when compared with 0% replacement level of 3296.7 coulombs which comes under “high” category. From the test results, it was concluded that the increase of UFGGBFS percentage improves the resistance of sLWC against aggressive chloride ions.

This study deals with the different properties of Geo Polymer concrete using fly ash and pebbles as coarse aggregate. Potassium hydroxide and sodium hydroxide solution are used as alkali activators. The strength is compared with Geo polymer concrete and conventional concrete. Fly ash-based Geo polymer concrete is a new material that does not need the Portland cement as a binder. There are two main constituents of geo polymers, namely the source materials and the alkaline liquids. The source material for geo polymers is based on alumina-silicate which should be rich in silicon (Si) and aluminium (Al). These could be natural minerals such as kaolinite, clays, etc. Alternatively, by-product materials such as fly ash could be used as source materials. Fly ash is a by-product from the coal industry, which is widely available in the world. Fly ash is rich in silicate and alumina, it reacts with alkaline solution to produce alumino silicate gel. This gel binds the loose aggregates and other unreacted materials in the mixture to form the geo polymer concrete. Hence, fly ash-based geo polymer concrete is a good alternative to overcome the abundant of fly ash. They have very high earlier strength. Fly ash based geo polymer also provided better resistance against aggressive environment and at high temperature compared to normal concrete

Every 1 ton of concrete leads to CO2 emissions which vary between 0.05 to 0.13 tons. About 95% of all CO2 emissions from a cubic yard of concrete are from cement manufacturing. It is important to reduce CO2 emissions through the greater use of substitute to ordinary Portland cement (OPC) such as fly ash, clay and others geo-based material. This paper, report on the study of the processing of geopolymer using fly ash and alkaline activator with geopolymerization process. The factors that influence the early age compressive strength such as molarity of sodium hydroxide (NaOH) have been studied. Sodium hydroxide and sodium silicate solution were used as an alkaline activator. The geopolymer paste samples were cured at 70°C for 1 day and keep in room temperature until the testing days. The compressive strength was done at 1, 2, 3 and 7 days. The result showed that the geopolymer paste with NaOH concentration of 12 M produced maximum compressive strength. Key words: Green polymeric concrete, fly ash, molarity, compressive strength.

Among the construction materials; concrete, steel, timber and glass, concrete has gained popularity all over the world due to its durable properties in normal environment and easiest construction procedure. Compare to others constituent, cement performs a vital role for the production of concrete. Due to continuous increasing demand and the cost of cement, recently, the utilization of supplementary cementing materials such as industrial by-product (fly ash, silica fume and slag) and agricultural wastes (rice husk ash, palm oil fuel ash, bagasse ash and ash from timber) has become an important issue for the researchers in concrete industry. Fly ash (FA), one of these valuable industrial wastes, is generated as by-product from power generating industry. The production of FA increases every year, it is disposed for landfills without any commercial gain and now becomes a trouble. It contains a non-crystalline silicon dioxide with high specific surface area and high pozzolanic reactivity. Huge researches have been carried out for the use of pozzolans, mainly waste pozzolans such as FA, slag and rice husk ash, as a supplement of ordinary portland cement (OPC). Test results of compressive strength and durability of concrete from those previous researches ensured the use of FA as a pozzolanic material for cement replacement in concrete. In this paper, a critical review on the strength development of concrete as influenced by the use of FA as a supplement of cement in concrete has been presented on the basis of available information in the published literatures of utilization of FA in blended cement and concrete. The compressive strength of mortar and concrete as varied by the percent replacement and fineness of FA is discussed here. Physical and chemical properties, pozzolanic activity, normal consistency and setting time, strength activity index, advantages and disadvantages of using FA in concrete are also pointed out. Proper consumption of FA as pozzolanic material in concrete would be a useful step for the production of cost effective and more durable concrete. Besides, utilization of FA in cement and concrete could reduce negative environmental effect, and also would be the appropriate solution for the disposal of this waste. Key words: Fly ash, mortar, concrete, compressive strength.

The alarming rate of depletion of natural stone based coarse aggregates is a cause of great concern. The coarse aggregates occupy nearly 60-70% by volume of concrete being produced. Research efforts are on to look for alternatives to stone based coarse aggregates from sustainability point of view. Response surface methodology (RSM) is adopted to study and address the effect of ferrochrome slag (FCS) replacement to coarse aggregate replacement in the ordinary Portland cement (OPC) based concretes. RSM involves three different factors (ground granulated blast furnace slag (GGBS) as binder, flyash (FA) as binder, and FCS as coarse aggregate), with three different levels (GGBS (0, 15, and 30%), FA (0, 15, and 30%) and FCS (0, 50, and 100%)). Experiments were carried out to measure the responses like, workability, density, and compressive strength of FCS based concretes. In order to optimize FCS replacement in the OPC based concretes, three different traditional optimization techniques were used (grey relational analysis (GRA), technique for order of preference by similarity (TOPSIS), and desirability function approach (DFA)). Traditional optimization techniques were accompanied with principal component analysis (PCA) to calculate the weightage of responses measured to arrive at the final ranking of replacement levels of GGBS, FA, and FCS in OPC based concretes. Hybrid combination of PCA-TOPSIS technique is found to be significant when compared to other techniques used. 30% GGBS and 50% FCS replacement in OPC based concrete was arrived at, to be optimal.