Type Of Alkaline Activator Research Articles

Review of Recent Developments in Tensile Properties of Engineered Geopolymer Composites

Engineered Cementitious Composite (ECC) is a type of highly ductile cementitious material. However, due to its characteristics of high energy consumption and high carbon emissions, it is necessary to seek a new type of low-carbon and environmentally friendly substitute. Engineered Geopolymer Composite (EGC), as a promising construction material for replacing ECC, has broad application prospects. Through visual analysis of the relevant literature in Web of Science, it was discovered that the research on EGC mainly concentrates on aspects such as the types of precursors, the chemical composition of the alkali-activated solution, and the related parameters of fibers. This paper mainly combines the relevant experimental research data on the tensile properties of EGC conducted by scholars at home and abroad, and focuses on analyzing the influence of precursor types, the chemical composition of the alkaline activator, and fibers on the tensile properties of EGC. The statistical results indicate that fly ash and ground granulated blast-furnace slag (GGBFS) are the most commonly used precursor materials. Replacing an appropriate amount of fly ash in the precursor with GGBFS can significantly enhance the tensile strength of EGC. The type of alkaline activator and its molarity have a relatively obvious influence on the tensile properties of EGC. An increase in the molarity of NaOH within a certain range can enhance the tensile strength of EGC. Furthermore, the incorporation of fibers, especially synthetic fibers such as polypropylene (PP) and polyvinyl alcohol (PVA) fibers, as well as inorganic fibers such as glass fibers (GF) and carbon fibers (CF), can effectively enhance the tensile strength and tensile strain capacity of EGC. The use of hybrid fibers may further improve the tensile properties.

The Effect of Recycled Citrogypsum as a Supplementary Mineral Additive on the Physical and Mechanical Performance of Granulated Blast Furnace Slag-Based Alkali-Activated Binders

In the last decades, gypsum-bearing industrial wastes become one of the common globally produced industrial and domestic wastes that are currently recycled and further utilized. In this study, the gypsum-bearing waste citrogypsum was used as a Ca2+-containing component to modify the properties of alkali-activated cement (AAC) based on granulated blast-furnace slag (GBFS). Citrogypsum was used in different AAC mixes activated with three different alkaline components: Na2CO3, NaOH, and Na2SiO3. Laser granulometry was applied to assess the granulometric characteristics of citrogypsum and GBFS. Specific gravity (SG), compressive strength, and water resistance were tested to evaluate the effect of citrogypsum on the physical and strength performance of AAC. Experimental results obtained over 4-day to 28-day time periods for the studied AACs showed that the addition of citrogypsum had a detrimental effect on the properties of AAC mixes, where decreases in compressive strength between 1 and 100%, decreases in specific gravity between 4 and 30%, and decreases in water resistance between 12 and 100% were observed. It was determined that AAC mixes modified with citrogypsum cured in ambient conditions had compressive strength values 61% to 90% lower than those cured in hydrothermal conditions. In terms of strength performance, specific gravity and water resistance, citrogypsum showed the greatest effect on AAC mixes activated with NaOH, and to a lesser extent, on mixes activated with Na2CO3. The highest water resistance value of 0.77 was observed for the AAC mixes activated with Na2CO3 cured in ambient conditions, and when cured in hydrothermal conditions, the highest water resistance reached up to 0.84 for the AAC mixes activated with NaOH. It was observed that the type of alkaline activator and curing conditions are both crucial factors that govern the response of citrogypsum as a supplementary mineral additive in GBFS-based AAC mixes in regard to compressive strength, specific gravity and water resistance.

Evaluation of mechanical and microstructural properties of eggshell lime/rice husk ash alkali-activated cement

Searching for innovative solutions to produce alternative construction materials using residues is a need to reduce the exploitation of natural resources. Alkali-activated cements (AACs) have been studied in recent years and pointed out as a possible alternative to Portland cement (PC). AACs can still be produced from waste and/or by-products from different sectors of the economy. In this sense, this research proposes the development of an alkali-activated binder produced from rice husk ash (RHA) and eggshell lime (ESL), activated with NaOH or KOH. A dosage study using a second-order composite design sought to evaluate the influence of parameters such as ESL/RHA ratio, alkali content (%Alk), water-binder ratio (w/B), curing temperature (TEMP) and type of alkaline activator (TYPE). Specimens were produced, thermally cured for 24 h and tested at 3 days of age. Unconfined compression strengths (UCS) and ultrasonic pulse velocities (UPV) were determined. Results indicated the ESL/RHA 30/70 ratio, 3 % alkali content, and curing temperature of 60 °C as optimal parameters, with the mixture reaching UCS of 18 MPa at 3 days of age. XRD and FTIR results show that CSH gel formation increases when increasing ESL/RHA ratio up to 30 %, alkaline content up to 3 %, and curing temperature up to 60 °C. Above these values, the formation of CSH tends to decrease. Binders activated by KOH obtained UCS results on average 10 % higher than those activated by NaOH.

Geopolymer Synthesis and Alkaline Activation Technique of Fly Ash and Slag Source Material: A Review

The advent of geopolymer and its synthesis from industrial waste rich in silicon and aluminum activated by an alkaline solution has proven a viable alternative to ordinary Portland cement. This review presents background on alkaline activation, geopolymerization technology as well as industrial aluminosilicate-based geopolymeric products produced from a range of low to high calcium fly ash, and metallurgical slags in different combinations. Important synthesis conditions, such as the nature of the source material, the type of alkaline activator, the curing condition, and the mixing procedure were effective determinant factors for desired properties in products. The significance of these parameters on the mechanical performance of products relative to each other is discussed. Advances in synthesis, material processing, and production, such as solid-state mechanism and one-part activation are also presented. Future recommendations on other aluminosilicate sources to be considered are highlighted.

A study on the setting and flow behaviour of alkali activated slag/fly ash composites in ambient condition

Alkali-activated binders (AAB) are considered as a promising sustainable future construction material, and promoted as an environmentally beneficial option when compared to Ordinary Portland Cement (OPC). Portland cement-based concrete is the most used material in the construction industry. In the production of OPC, harmful gasses like CO2, NO2, SO2 and specks of dust are discharged into the atmosphere due to calcination of limestone and combustion of fossil fuel. Hence in the present scenario, it has become an emphatic necessity to replace Ordinary Portland Cement based concrete with AAB based system (geopolymer) which is more sustainable. The characteristics of geopolymer composites are predominantly influenced by some of the variables such as temperature and time of curing, alkaline solution to solid binder ratio, water content, type of alkaline activators used, molarity of alkaline solution, chemical composition of aluminosilicate precursors etc. Although geopolymer systems are good in terms of durability and strength, the main issue faced for its less popularity in the field application is its low workability, poor slump retention and too fast setting.The aim of this experimental study is to investigate the compatibility between modern generation superplasticizers (SP) and various alkali activated binder systems prepared using industrial wastes and the evaluation on the effect of alkali binder ratio (a/b) on the fresh properties of alkali activated binder (AAB) systems. Considering the practical implications, it is the need of the hour to develop a geopolymer mix setting in ambient condition. This study focuses on setting and flow behaviour of the alkaline activated composites of slag and fly ash in ambient condition only. The slag/fly ash ratios of 100/0, 75/25, 50/50 and 25/75by mass and alkali-to-binder ratios of 0.4 to 1 with an increment of 0.1 were used for the study. The type of superplasticizer used for the study is Sulphonated Naphthalene Formaldehyde (SNF) with dosages of 0%, 1%, 2% and 3%. The setting time and the flow of the paste were determined using vicat apparatus and mini slump cone respectively. The penetration resistance of the setting paste was also measured using vicat apparatus. The test results revealed that even though the setting time increase marginally with SP dosage, the use of SNF was not much effective in prolonging the setting time of alkali activated pastes. There was tremendous increase in the initial and final setting time for pastes with an increase in a/b ratio.

A factorial experimental analysis of using wood fly ash as an alkaline activator along with coal fly ash for production of geopolymer-cementitious hybrids

Alkaline activated materials such as geopolymers and cementitious materials derived from pozzolanic reactions offer several advantages over the currently widely used Portland cement, especially in terms of environmental sustainability and physiochemical properties. However due to the need of an alkaline activator, such as NaOH or KOH, which result in high production cost and requires skilled personnel, they have not been deeply explored and put to use. Here in this study, wood fly ash, a by product of wood combustion is used as an alternative source of alkaline activator for producing such alkaline activated materials along with coal fly ash, where the resulting geopolymer–cementitious hybrid (GCH) was characterized physico-chemically through electron microscopy, BET, FTIR, XRF & XRD. However, the leaching of heavy metals from the wood fly ash could potentially pose an environmental concern. Therefore, the focus of this study is to reduce the leachability factor of wood fly ash involved in the alkaline activated process and to understand the effects of various factors (i.e. water-to-ash ratio (w/a), method of curing, type of alkaline activator and ash sieving) on the leaching process, through factorial experimental analysis. The leaching patterns of various elements such as Pb, Zn, Cr, As. Hg, Se were studied along with the contributing factors and results showed that the dominant factor was the type of alkaline activator (i.e. Wood Fly Ash versus Na2SiO3). By comparing the leaching data to Denmark’s leaching criteria, the best performing GCH sample was found to be 0.3DI_p_s (0.3 represents the w/a ratio, “p” denotes that samples were precured and “s” denotes sieving).

Effect of activators on hybrid alkaline binder based on tungsten mining waste and ground granulated blast furnace slag

This article illustrates the effects of different combinations of alkaline activator solutions (sodium silicate “SS”, sodium hydroxide, potassium hydroxide and dissolved waste glass powder in sodium hydroxide) as well as their concentrations and the Solid/Liquid ratios on the compressive strength development, and the microstructure of hybrid alkaline binder. The current study used a combination of tungsten mining waste mud (TMWM) (90 vt.%) and ground granulated blast furnace slag (GGBFS) (10 vt.%) as precursors. The obtained hybrid alkaline binder specimens were submitted by compressive strength tests. It was found out that the alkaline activator (KOH when mixed with SS) improves the compressive strength of the hybrid alkaline binders compared to the alkaline activator (NaOH mixed with SS), which depends on the presence of alkali metal K+ and Na+ cations. Moreover, the samples prepared by the alkaline activator (dissolved waste glass powder in NaOH mixed with SS) giving the highest compressive strengthof about 32.8 MPa at 28 days. From the results of XRD, TGA-DTGA, FTIR analyses, and the obtained microstructures of the hybrid alkaline binders it indicates the existence of a different reaction product formed during the alkaline activation such as C-S-H, N-A-S-H, C-A-S-H, and K-A-S-H type cementitious gels. In addition to these conventional gels, there was a formation of a complex mixture of (C, M)-A-S-H cementitious gels were (M = K, Na). The pore structure of hybrid alkaline binder was evaluated through mercury intrusion porosimetry (MIP). The pore structure of specimens was characterised by the total porosity, average pore diameter, pore size distribution as well as characteristic pore sizes. The MIP results indicate that the type of alkaline activators, solid/liquid ratios and the alkaline activators’ concentration have a specific impact on all characteristics of the pore structure of all the hybrid alkaline binders. Finally, the cost impact on the compressive strength for different activators was also analysed.

Factors Affecting Compressive Strength Development in Alkali-activated Slag Concrete

Studies show that the production and use of ordinary Portland cement (OPC) is responsible for more than 5% of the global CO2 emission. Alkali-activated slag (AAS) has been studied for decades as potential alternative to OPC. Engineers are interested in understanding and quantifying the fresh properties, mechanical properties, and durability of concrete made used AAS as sole binder. This paper reviews some of the literature highlighting the factors affecting compressive strength development in AAS slag. These include water-binder-ratio, temperature, humidity, and amount of Na2O, molarity of the alkaline activator solution, and type of alkaline activator. For instance, certain studies reported that AAS concrete activated using sodium silicate solution (water-glass) produce higher 7-day and 28-day compressive strength compared to similar concrete that use 100% OPC, concrete activated using sodium hydroxide (NaOH), or concrete activated using potassium hydroxide (KOH). When NaOH is used as activator, mechanical properties of concrete improved with increase in molarity of the alkaline activator solution. Compressive strength of concrete cubes increases with increase in the amount of Na2O supplied by the activator solution but to an optimum beyond which further increase in Na2O results in decrease in compressive strength. However, the optimum amount of Na2O, often reported as percentage of total slag content, varied from one study to another, probably dependent on the type of activator used as well as the water-to-binder (w/b) ratio.

Geopolymers and polymers in the conservation of tile facades

The most commonly used materials to fill gaps/lacunae in glazed tiles are lime mortars or organic resins, which have some disadvantages regarding their compatibility and durability, failing to guarantee the desired characteristics. Therefore, there is a need to develop new materials with compatible characteristics, able to withstand exposure to variations in climatic conditions. This scientific work focuses on the possibility of using geopolymers, aiming to evaluate the possibility of the use of these materials in the intervention process of historic tiles conservation as compatible materials that may be used to fill gaps. Different geopolymer pastes were developed changing the source of aluminosilicates, the type of alkaline activators and the pH. To evaluate the geopolymers, polymers and tiles, several tests were carried out. The results suggest that the geopolymers are a possible option for the filling of tile gaps, given the characteristics that can be achieved, ensuring compatibility and durability properties.

A review of recent developments in geopolymer concrete

Geopolymer concrete is proved to have high strength, lesser shrinkage, resistance against reinforcement corrosion, acid and sulphate resistance, freeze-thaw resistance, fire resistance and resistance to alkali-aggregate reaction. There are many parameters which influence the strength characteristics of Geopolymer Concrete. They are types and fineness of Source alumino silicate material used, concentration and type of alkaline activators used, curing temperature and curing time, utilization of M-sand etc. High performance characteristics could be achieved through the correct choice of these parameters. This review paper focuses on the influence of different variables on the properties of geopolymer concrete and the progress in the field of geopolymer concrete. Consequently many research papers pertaining to the geopolymer have been reviewed in this state of art paper.

The Effect of Corrosive Environment on Geopolymer Concrete Tensile Strength

This study has the purpose to explore the potential of geopolymer concrete tensile strength in particular on the effects of corrosive environments. Geopolymer concrete, concrete technology used no OPC that has advantages, one of which is durability, especially for corrosive seawater environment. In addition, geopolymer concrete with polymerization mechanism does not require large energy consumption or an environmentally friendly concept. Geopolymer concrete in this study is using a type C fly ash from PT. International Power Mitsui Operation & Maintenence Indonesia (IPMOMI) Paiton. The type of alkaline activator used NaOH (14 molar) and Na 2 SiO 3 . Coarse and fine aggregate used are local aggregate. Geopolymer concrete molded test specimen with dimensions of (10 × 20) cm cylinder, further heating and without heating, then maintained at room temperature and seawater up to 28 days. Then to determine the mechanical properties, the tensile strength testing is done with reference. This result of study indicates the curing of geopolymer concrete at 60 ° C for 24 hours to raise the tensile strength of geopolymer concrete.

Hydration kinetics in hybrid binders: Early reaction stages

Activated blends of Portland cement and fly ash with a high ash content (>70%) are a new alternative to traditional OPCs. A number of papers have been published on C–S–H and N–A–S–H, the two gels that constitute the main cementitious products generated by the alkaline activation of these cements, and the elements that may be taken up into their structure. Very little is known about the kinetics of these systems, however, particularly during the early stages of the reaction. The present study used isothermal conduction calorimetry to explore hydration kinetics during the first 72h in a cement containing 30% OPC and 70% fly ash. Two activating solutions were used: a mix of NaOH+Na2SiO3 and a Na2CO3 solution. The findings showed that hydration kinetics were substantially modified by the type of alkaline activator used, particularly with respect to the secondary phases generated. In both cases the main reaction product appeared to be a mix of C–A–S–H and (N,C)–A–S–H gels, whose proportions were clearly impacted by the type of activator used.

Statistical Study of the Effect of the Composition on the Strength of Supersulphated Cements

ABSTRACTSupersulphated cements (SSC) are environmentally friendly binders that incorporate several raw materials, including byproducts. A systematic study was considered opportune considering the wide range of formulations found in the literature. The effect of the type and proportioning of components in the strength of SC was investigated using the Taguchi method to optimize the experimental work and to define the optimal conditions. The factors were: [A] %blast furnace slag (82.5-90%), [B] CaSO4 - alkaline activator ratio (1:0, 3:1, 1:1, 1:3 and 0:1), [C] type of CaSO4 (5 types) and [D] type of alkaline activator (portland cement, Ca(OH)2, KOH and NaCO3 and 2 combinations of these). Pastes were prepared and characterized for up to 28 days at 20°C. In general, for all values of [A] the best strength was for levels of [C] at 3:1, followed by the 1:1 and 1:0 ratios. The optimal conditions using the 28 day strength consisted of [A]= 82.5%, [B]= 3:1, [C]= flyorgypsum and [D] = portland cement, which developed excellent strength from day one and 35MPa. X-ray diffraction showed ettringite and C-S-H formation from the early ages. The microstructures showed dense matrices of reaction products well bonded to partially reacted slag grains, which in some cases showed rims of hydration products.

Effect of the Combined Using of Fly Ash and Granulated Blast Furnace Slag on Properties of Cementless Alkali-Activated Mortar

This paper examines the effects of the mixture ratio of fly ash/slag, the type of alkaline activators and curing conditions on the workability, compressive strength and microstructure of cementless alkali-activated mortar. The investigation showed that the mixture ratio of fly ash/slag and the type of alkaline activator have significant influence on the workability and strength, whereas the curing temperature has relatively poor effect. An alkali-activated mortar using a binder composed of 50% of fly ash and 50% of granulated blast furnace slag and alkaline activator made of 9M NaOH and sodium silicate in proportion of 1:1 is seen to be able to develop a compressive strength of 65 MPa at age of 28 days even when cured at ambient temperature of 20°C.

Hydration of alkali-activated slag: thermodynamic modelling

The composition of solid and liquid phases of alkali-activated slag systems was investigated by thermodynamic modelling. The calculations predict the formation of C(–A)–S–H, stratlingite and hydrotalcite in different alkali-activated slag systems, which agrees well with experimental findings. In addition traces of FeS and ettringite are predicted to precipitate. The type of alkaline activator (Na-silicate, NaOH) has no influence on the type of hydrates formed but influences the Ca/Si ratio of the C–S–H. The addition of sodium silicate leads to the formation of C–S–H with a higher Ca/Si ratio (1.1–1.2), whereas NaOH results in a Ca/Si ratio of 0.8to1.1. In contrast, the kind and concentration of the activator has strong influence on the composition of the pore solution. Low concentrations of the alkaline activator result in lower Na, Si and Al concentrations and lower pH values. In all pore solutions a high concentration of sulphide (HS–) is expected to be present.

Factors affecting the strength of alkali-activated slag

The effect of several factors on the strength of alkali activated slags has been investigated. The most important factors were found to be: the type of alkaline activator, the means of adding activator, the dosage of alkali, the type and fineness of slag, SiO 2/Na 2O ratio (modulus, Ms) when using waterglass solution, curing temperature, liquid/slag or water/slag ratio and additive. Some of these factors are interdependent and the effect of changing more than one is usually not additive. The optimum range for each factor is suggested through reviewing previous work and our recent results of a full factorial range strength study. The interaction of factors is considered and discussed throughout the paper, hoping to gain a better understanding of the processing of alkali-activated slag (AAS) cement and concrete.