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Article

Innovative Retarders for Controlling the Setting Characteristics of Fly Ash-Slag Geopolymers

by
Shaise Kurialanickal John
1,
Alessio Cascardi
2,*,
Madapurakkal Nandana
3,4,
Femin Kurian
3,4,
Niyas Aruna Fathima
3,4,
M. Muhammed Arif
5 and
Yashida Nadir
3,4
1
Department of Innovation Engineering, University of Salento, 73100 Lecce, Italy
2
Department of Civil Engineering, University of Calabria, 87036 Cosenza, Italy
3
Department of Civil Engineering, College of Engineering Trivandrum, Thiruvananthapuram 695016, India
4
APJ Abdul Kalam Technological University, Thiruvananthapuram 695016, India
5
Department of Chemistry, Government College Attingal, Thiruvananthapuram 695016, India
*
Author to whom correspondence should be addressed.
Eng 2025, 6(12), 366; https://doi.org/10.3390/eng6120366
Submission received: 14 October 2025 / Revised: 29 November 2025 / Accepted: 11 December 2025 / Published: 15 December 2025
(This article belongs to the Special Issue Emerging Trends in Inorganic Composites for Structural Enhancement)
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Versions Notes

Abstract

Geopolymers, as sustainable alternatives to traditional cementitious materials, offer superior mechanical and durability properties; however, they face challenges with rapid setting, particularly in fly ash–slag systems. Retarders play a crucial role in tailoring the setting behavior and workability of geopolymers, especially in applications where extended setting time or placement under challenging conditions is required. Geopolymers, unlike traditional Portland cement, undergo a rapid alkali-activation process involving dissolution, polymerization, and hardening of aluminosilicate materials. This can lead to very short setting times, particularly at elevated temperatures. In this scenario, the present study investigates the effect of different retarders-including cellulose, starch, borax, and their different combinations the setting time. The effectiveness of a retarder depends on the geopolymer formulation, including the type of precursor, activator, and curing conditions. The initial and final setting times improved by the addition of retarders, whereas most of the retarders had a negative effect on compressive strength. The optimum retarder combination was starch and borax, with a remarkable improvement in setting time and a positive result on the compressive strength, while maintaining reasonable workability. The retarder was equally effective under both ambient and oven-cured conditions and for different mix proportions of fly ash (FA) and slag, indicating that its effectiveness depends only on the type of precursors used. The study reveals the use of borax along with cellulose- or sugar-based compounds, which balances the reaction kinetics, resulting in balanced mechanical characteristics.

1. Introduction

Geopolymers are low-carbon cementitious materials derived from aluminosilicate sources, offering a more sustainable alternative to conventional Portland cement, particularly in the form of one-part systems with significantly reduced energy consumption and global warming potential [1,2]. Geopolymer cementitious products are derived from aluminosilicate minerals through their reaction in an aqueous alkaline medium, forming an amorphous three-dimensional polymer structure [3,4,5]. Despite their superior mechanical and durability properties, challenges remain in controlling their setting characteristics. The setting time of geopolymers depends on the aluminosilicate source materials involved in their synthesis. Fly ash (FA)–based geopolymers generally exhibit setting characteristics comparable to those of ordinary Portland cement; however, they often require high-temperature curing, which poses challenges for practical applications. In high-calcium FA systems, the presence of calcium oxides leads to a high pH value in geopolymers, resulting in rapid setting, and the readily available calcium ions form calcium silicate hydrate (CSH) gels through reaction with silicates [6,7]. The CSH gel precipitates rapidly at an early stage of reaction, and some of the calcium hydroxide remains intact due to the reduction in solubility and the common-ion effect [8]. Ground Granulated Blast Furnace Slag (GGBFS) is an aluminosilicate mineral rich in calcium oxides, which is often blended with low-calcium FA geopolymer to accelerate geopolymerization and hydration reactions, resulting in superior mechanical properties. The calcium oxide in GGBFS is known to accelerate geopolymerization due to the formation of calcium aluminon silicate hydrate (CASH) and hybrid CASH/sodium aluminon silicate hydrate (NASH) gel phases [9]. The increased GGBFS content in fly ash geopolymer results in reduced setting time due to early precipitation of the calcium-rich gel phases that act as the nucleation sites for enhanced geopolymerization due to greater dissolution of aluminosilicates. However, this accelerated reaction comes at the cost of a significantly reduced setting time, which becomes a major drawback [10]. Additionally, the rapid setting leads to poor workability of the mixture, which hampers its practical application [8]. Retarders are added to slow down this reaction, allowing more time for mixing, transport, or placement. They significantly extend the initial and final setting times, which is critical in hot climates or when using highly reactive precursors like slag or metakaolin [11,12].
Commonly used retarders in cement composites include lignosulfonates, hydroxylated carboxylic acids, polyhydric alcohols, and different sugar–based compounds. However, geopolymer chemistry is different from that of ordinary Portland cement, rendering cement retarders ineffective. Efforts to enhance the setting time of geopolymer have led to the exploration of various additives. Different additives like calcium chloride, calcium sulfate, sodium sulfate, and sucrose have minimal impact on compressive strength, and calcium–based additives accelerate the setting of geopolymer [7]. Due to the high mobility of chlorine ions in calcium chloride, the early-formed gel tends to be more open and porous, resulting in more gel formation. Unlike calcium sulfate, sodium sulfate significantly delays the initial setting time, due to the formation of ettringite around FA particles, preventing leaching of alumina and silica. The addition of sugars like glucose, fructose, lactose, and sucrose improves both the initial and final setting time of geopolymer [13]. Attempts to reduce the pH of the mix through acid addition, aimed at extending the setting time, have proven ineffective and even detrimental [14,15].
Borax, a well–known additive in geopolymers, improves the initial and final setting times of fly ash–slag geopolymers by approximately 2.25 and 1.25 times, respectively, with a 10% addition [16]. The addition of borax reduces the affinity of aluminosilicates in the precursor and the silicates in the activator, thereby delaying the setting and enhancing workability. Antoni et al. [17] observed that the addition of borax delays the setting of fly ash geopolymer, although the improvement is marginal even at a dosage of 7%. In a subsequent study, Antoni et al. [18] found that a high dosage of borax (20% by weight of binder) could improve setting time by 75–90 min, compared to the flash setting of the control mix. However, this was accompanied by a 30% reduction in compressive strength. Various other retarders have also been explored in the literature, including sodium lignosulfonate, borax, citric acid, sucrose, sodium gluconate, sodium pyrophosphate, sodium hexametaphosphate, sodium tripolyphosphate, calcium sulfate, anhydrous sodium sulfate, anhydrous calcium chloride, barium chloride, and boric acid [19,20]. While some of the retarders have negative effects, and some have marginal effects in improving the setting characteristics, borax has emerged as the most effective; a dosage of 8% improves the initial and final setting time by 307.5% and 268%, respectively [20]. It should be noted that the use of borax is effective only at high dosages [16,18].
The addition of cellulose and starch as retarders in geopolymer is a novel concept. Ferreira et al. [21] employed microcrystalline cellulose (MCC) as an additive in geopolymer and found improvement in the mechanical properties. It was reported that the addition of MCC has resulted in accelerated setting of geopolymer in 36 min (15% faster) and delayed setting time of cement pastes in 97 min (40% slower). Hoyos et al. [22] reported the delay in hydration reaction in cement-based composites by the addition of MCC, due to the formation of a waterproofing barrier on the anhydrous particles of cement. On the other hand, cellulose addition results in a reduction in the setting time of geopolymer, possibly due to the heat generated during cellulose degradation, causing an enhanced polymerization reaction [23].
Investigating the effect of a retarder on the setting time and curing of geopolymers is crucial for both scientific understanding and practical application. First, geopolymers often have rapid setting behavior, which can be challenging in large-scale or complex construction projects. By studying retarders, researchers can better control setting time, allowing more time for placement, finishing, and adjustments on-site. In addition, the rate of setting and curing can directly impact the development of mechanical strength and durability. A well-tailored setting profile can improve long-term performance and resilience of geopolymers. Thus, the present study deals with the evaluation of the setting characteristics of different retarders, including cellulose, starch, borax, and their combinations. The effects of the retarders on workability and mechanical performance are also analyzed. The effect of temperature curing on the mechanical properties of geopolymer with the retarder additives is also evaluated.

2. Experimental Program

2.1. Materials

The geopolymer binder materials used in the study were FA and GGBFS, procured from the Tuticorin coal-fired thermal power plant and JSW Cements in India. Low-calcium FA with higher silica content that conforms to Class F as per IS 3812-1 [24] was used. The physical properties and chemical composition of FA and GGBFS are given in Table 1. The fine aggregate used in the study was graded sand with a maximum particle size of 4.75 mm. A combination of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) solutions was used as alkali activators for binders. Industrial-grade NaOH flakes, white in color and with 98% purity, were used to prepare the NaOH solution. Industrial-grade Na2SiO3 solution, bluish gray in color with 14.7% Na2O, 35% SiO2, and 50.3% H2O by weight, was used in the study. The chemicals used as retarders included carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), starch, and borax in powder form. All the additives were in powder form, with CMC and HEC having a mean particle size of 150 μm, and borax and starch having mean particle sizes of 30–75 μm and 20–35 μm, respectively. CMC and HEC are commercially available cellulose powders; both are water-soluble and derived from cellulose, a natural polymer found in trees and plants. Borax is a colorless, crystalline water-soluble salt, a hydrated borate of sodium. Starch, derived from grain flour, was also used in the study.

2.2. Mix Proportion and Sample Preparation

FA and GGBFS were used as the binders in a 60:40 proportion for the evaluation of the effect of retarders. The alkali activators Na2SiO3 solution and 10M NaOH solutions were mixed 24 h prior to casting in a 2:1 ratio. The retarder dosage selected was 3% by weight of the binder, based on previous studies [20] and on a median dosage [13]. This optimum dosage may vary depending on the precursors and should be evaluated parametrically. The retarder dosage was fixed as 3% to collectively analyze and study its primary effects on the setting time, and consequently on the strength. Cellulose and starch were used in solution form, prepared by dissolving each additive in water at a 1:1 ratio (additive/water). Since borax is a salt and is readily soluble, it was added in powder form. The combinations of retarders used and their proportions are listed in Table 2. For retarder combinations containing cellulose or starch with other additives, the additives were mixed in a 1:1 ratio. In these cases, borax was dissolved in the 1:1 cellulose or starch solution before blending.
A geopolymer paste was prepared to evaluate the standard consistency and setting time. The binder content for the geopolymer paste was 1350 kg/m3. The solution-to-binder ratio for the setting time measurements was selected based on the standard consistency. Geopolymer mortar samples were prepared to evaluate the compressive strength of the mixes with retarders, with a binder-to-sand ratio of 1:2 [25]. For the preparation of geopolymer mortar binder content in the mix proportion was selected as 630 kg/m3, and the alkali solution-to-binder ratio was fixed at 0.5. The setting time of FA–GGBFS geopolymer is dependent on the percentage by weight of GGBFS in the mix. As the GGBFS content increases, the setting time is drastically affected by the increased geopolymerization reaction due to the presence of calcium oxide. After choosing a suitable retarder, the effectiveness of the combination was tested for different GGBFS contents in geopolymer mixes. Two different mixes of geopolymer with the optimum retarder containing FA/GGBFS in the ratio 50:50 and 40:60 were analyzed and compared with the 60:40 mix.

2.3. Test for Setting Time, Workability, and Compressive Strength

The setting time of the geopolymer was measured using the Vicat apparatus as per [26]. The Vicat apparatus is a fundamental tool in construction materials testing, used primarily to measure the setting time and consistency of cement-based pastes, including emerging materials like geopolymers. It functions with a vertical rod that holds different types of needles or plungers, depending on the specific test being conducted. This rod is carefully lowered into a standardized mold filled with the test paste, and the depth to which it sinks is measured using a graduated scale. To determine the standard consistency of a paste, a plunger is used. The amount of water in the mix is adjusted until the plunger penetrates the paste to a specific depth—typically from 33 to 35 mm. This consistency is important because it provides a baseline for further testing. For setting time measurements, different needle configurations are employed. The initial setting time is recorded as the duration from the moment water is added until the needle fails to penetrate to a point 5 mm from the bottom of the mold. To find the final setting time, a needle with an annular attachment is used, and the test ends when the needle marks an impression on the specimen surface and the annular attachment fails to do so.
Flow workability of the geopolymer mortar with additives was measured using a mini-slump flow test with modified ASTM C1611 [27]. A mini slump cone was employed, having a bottom diameter, top diameter, and height of 38.1 mm, 19.05 mm, and 57.15 mm, respectively [28,29]. Flow workability of the mortar was expressed in terms of relative slump [30]. The slump cone was filled in three layers and compacted thoroughly to remove any air voids, and the cone was lifted, and the flow diameter of the mortar on a glass plate is measured after 60 s. The flow in percentage was expressed in terms of the bottom diameter of the cone [31], the relative slump (r0) given in Equation (1).
r 0 = d d 0 2 − 1
where d is the average of three diameters of mortar flow, and d0 is the bottom diameter of the mini slump cone.
The compressive strength of geopolymer mortar was evaluated according to ASTM C873 [32]. Cylindrical specimens of 50 mm in diameter and 100 mm in height were cast as per the standard, maintaining a height-to-diameter ratio of 2. The specimens were cast in three layers and were demolded the next day and ambient cured for 28 days at 29 ± 3 °C and relative humidity of 70 ± 10%. After the curing period, the specimens were tested in a compression testing machine of 3000 kN capacity, at a displacement-controlled loading rate of 1 mm/min. To study the effect of temperature curing, some of the specimens were left at room temperature for 24 h and demolded and cured in a hot air oven at a temperature of 60 °C for 7 days and further kept at ambient conditions until 28 days of aging were achieved. At an early stage, heat curing has a positive effect on the strength of FA–GGBFS geopolymer, and the curing temperature of 60 °C was employed for a prolonged curing of 7 days [33,34,35].

3. Results and Discussion

3.1. Setting Time

For the measurement of setting time, the alkali solution to binder ratio was fixed as 0.35 based on the standard consistency of binder with the alkali solution, for an FA to GGBFS ratio of 60:40. The results of setting time characteristics of the mixes are given in Figure 1. The letter ‘C’ stands for the control mix, followed by the mixes with different retarder combinations.
The final setting time of geopolymers is a critical parameter that must be optimized for practical applications. The preferred final setting time should be more than 350 min, while the minimum initial setting time is at least 60 min [36]. In the present study, a combination of starch and borax was found to be the most suitable retarder combination for geopolymers with the FA/GGBFS ratio of 60:40, yielding the longest setting time while still meeting the mechanical properties. The setting time of the geopolymer reduces with increasing GGBFS content as the calcium oxides in GGBFS accelerate the geopolymerization reaction. The combination was also selected based on the compressive strength, which is discussed further. Borax is known to complex with alkaline ions (Na+), thereby reducing the availability of free alkali ions and thus suppressing the dissolution of silicates from aluminosilicate precursors, delaying nucleation and polycondensation [37,38]. However, higher dosages of borax have a detrimental effect, since it complexes with the Al and Si ions, delaying gel formation. This is evident from the studies by He et al. [39] on the microstructural analysis through SEM. Unreacted fly ash particles and a porous gel structure were observed when the borax dosage was increased from 2 to 6%. Additionally, borax can adsorb on particle surfaces, limiting nucleation and growth of the gel phase [40]. The addition of cellulose resulted in an increased final setting time. Cellulose is known for its impact on cementitious materials, causing delayed setting, evident from the lower heat of hydration, and may affect hardening. Natural polysaccharides, such as cellulose and starch, form a diffusion barrier around the unreacted precursors or absorb free water, affecting the mobility of ions [41]. Starch, in contrast, is a polysaccharide that can absorb water, physically delays gelation by hindering molecular mobility through creating a viscous medium [42]. Additionally, both can interact with the activating solution; their hydroxyl groups undergo ring-opening reactions, forming low-molecular-weight acids that reduce the pH of the activating solution. The hydroxyl ions will then enhance the interconversion of the sugars in the solution, leading to the opening of the sugar ring molecules. Thus, cellulose and starch sugars form organic acids in the solution, and the strong alkali degrades them [13]. Cellulose/starch with borax shows synergistic effects, combining the chemical (via complexation and acidification) and physical hindrance, allowing better control of setting time.
In order to evaluate the effectiveness of the starch and borax retarder combination in mixes containing higher GGBFS content, the authors evaluated mixes with the FA/GGBFS proportion of 50:50 and 40:60. The results for setting time are given in Figure 2. The initial setting time gradually reduces as the GGBFS content increases, but remains within limits. However, the final setting time is not affected.

3.2. Workability

The workability of the geopolymer mortar was measured using a mini slump flow test. The mini slump flow test is a compact and efficient method used to evaluate the flowability and consistency of fresh cement pastes, including those used in geopolymer systems. It involves a small, cone-shaped mold, essentially a scaled-down version of the traditional slump cone, placed on a flat, non-absorbent surface like a glass or plexiglas sheet. Once the mold is filled with paste and carefully lifted, the material spreads out under its own weight. The key measurement in this test is the diameter of the spread, which reflects the material’s fluidity. A larger spread indicates a more workable or flowable mix, while a smaller spread suggests a stiffer consistency. The results of the workability properties of geopolymer mortar with additives are given in Figure 3. The retarders, in addition to their effect on setting time, also acted as fluidizing agents, thus improving the workability of the mix. The addition of starch compounds has already been proven effective in improving the workability of geopolymers [43]. Similar liquefaction behavior of the geopolymer was observed in both rheological and mini-slump tests, confirming the adequacy of evaluating workability through the slump flow test. Moreover, starch or CMC is considered a rheological agent in geopolymer [44]. However, future scope lies in the exploration of different retarder combinations for the rheological properties. The results indicate that more fluidizing properties are imparted by cellulose and starch addition. Significant improvement in workability was obtained by the addition of HEC. The exact mechanisms can be evaluated only through rheological studies. The addition of borax did not cause any significant influence on the workability. However, a slight improvement was observed. This can be attributed to the chemical retardation effect of the borate compound, which increases the availability of free water molecules and imparts fluidity to the mix.

3.3. Compressive Strength

The compressive strength of geopolymer with different retarders is given in Figure 4. The geopolymer mortars were cured in both ambient conditions and in an oven at 60 °C, to evaluate the effect of retarders on the compressive strength development. The mix with starch alone as a retarder and with starch and borax had a positive impact on the compressive strength. All other retarders resulted in a decrease in compressive strength after 28 days for both ambient and oven curing. For FA–GGBFS systems, an improvement in 28-day strength is generally observed under oven curing due to enhanced geopolymerization [34]. The oven curing significantly contributes to the early strength of FA–GGBFS geopolymer. In the present study, this improvement in early strength is outside the scope of this study, and the 28-day strength was unaffected by the addition of different retarders. The retarders do not undergo any type of degradation in oven curing and are stable at the curing temperature of 60 °C. As already mentioned, borax can form complexes with oxide ions, leading to a delay in setting. When borax delays setting too much, preventing polymerization, and traps unreacted alkalis, it affects strength development [45]. Research also reports the influence of borax involving the interruption of the reaction involving Ca2+ in high-calcium geopolymer mix [46,47]. The borax could react with Ca2+, forming a calcium borate layer, hindering the formation of CASH gel, which is important for ambient-cured geopolymer. Thus, the reaction could be partially interrupted, leading to lower hardening and thereby strength. Cellulose interferes with gel packing or introduces microvoids during degradation, which affects the microstructure and strength [21]. The glucose in the starch may have transformed into acid complexes in an alkaline environment, which can chelate the Na+ ions in the system and delay the formation of geopolymer [11]. In the presence of borax, cellulose/starch chars form an insulating layer, which participates in the geopolymerization reaction and forms boron-modified aluminosilicate hydrates. The tetrahedral boron directly participates in geopolymerization, resulting in enhanced polycondensation [48]. Starch alone, while it delays setting, may not promote strength unless it is used with another agent that balances the reaction kinetics. Starch and borax have a balanced retardation, providing controlled geopolymerization, avoiding flash setting, and allowing complete reaction. In addition, the slower and uniform gel formation may have resulted in a denser and more homogenous gel network, which improves the compressive strength.

3.4. Compressive Strength of Geopolymer with Varying Binder Proportions

The compressive strength of geopolymer with different FA/GGBFS ratios and starch and borax as the retarders is given in Figure 5. The percentage replacement of fly ash by slag from 30% to 60% is generally considered in the literature, beyond which the setting time is severely affected. A clear trend is observed wherein the compressive strength increases with higher GGBFS content due to the formation of additional CASH gel phases. GGBFS provides readily available calcium ions, which accelerate the polycondensation process and promote early and higher strength development. The selected retarder combination remains effective across all mix proportions, demonstrating its compatibility with aluminosilicate precursors. The retardation mechanism is not significantly disrupted by the GGBFS content; the reaction kinetics are maintained without impeding the strength development. Setting time and strength development are governed by the calcium content, and the compressive strength is least affected by the optimum retarder combination. The system achieved balanced retardation, enabling extended workability and consistent strength, without significantly affecting the mix proportions.

4. Conclusions

The present study aimed at improving the setting time of FA–GGBFS geopolymer using cellulose, borax, and starch as retarders, and the following conclusions are drawn.
  • Among the different retarders, CMC, HEC, and a combination of CMC, HEC, and starch with borax were found to be effective in improving the initial and final setting time. Starch was found to be ineffective as a retarder. However, in combination with borax, it improved the initial and final setting times to 129 min and 360 min, respectively, complying with the standards. Cellulose forms a waterproofing barrier that hinders the setting time of the geopolymer. Cellulose/starch with borax shows synergistic effects combining the physical and chemical retardation mechanisms, delaying setting time.
  • The compressive strength at 28 days improved for the starch and borax retarder combination compared with the negative effect for all other retarders. Even though starch was ineffective in improving setting time, it did not have a negative effect on compressive strength. The optimum retarder, a combination of starch and borax, has complementary effects that lead to controlled geopolymerization and a complete reaction. The starch and borax as the retarder maintained the compressive strength, even with a slight improvement, indicating that it is effective in improving setting time without negatively impacting strength development.
  • The retarders were equally effective from the results of oven-cured specimens compared to ambient-cured ones. For all the oven-cured specimens, a slight improvement in the 28-day strength was obtained; the strength improvement generally observed in FA–GGBFS geopolymers was unaffected by the addition of the retarders. In addition, the retarder worked well for different mix proportions of FA and GGBFS. The retarder works well in calcium-rich geopolymer with aluminosilicate precursors.
While this study focused on a fixed dosage of retarders to identify an effective combination, future research should investigate the optimal dosage levels of each retarder, their influence on mechanical properties, and their performance across varying proportions of GGBFS incorporation. The effects of retarders should also be further examined through microstructural analyses, and the durability of the retarder-modified systems will be addressed in future studies.

Author Contributions

S.K.J. conceptualized the research methodology, analyzed the data, and wrote the original draft. A.C. validated the analysis, reviewed, and edited the original draft. M.N., F.K., and N.A.F. collected the resources, investigated, and performed the formal analysis. M.M.A. conceptualized, designed the research work and supervised. Y.N. developed the methodology, supervised and reviewed, and edited the original draft. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author. The data will be made avaliable on request for pushing discussion and collaborations.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported.

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Eng 06 00366 g001
Figure 1. Initial and final setting time of geopolymer paste with additives.
Figure 1. Initial and final setting time of geopolymer paste with additives.
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Figure 2. Initial and final setting time of geopolymer with different FA/GGBFS ratio.
Figure 2. Initial and final setting time of geopolymer with different FA/GGBFS ratio.
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Figure 3. Flow workability of geopolymer with retarders.
Figure 3. Flow workability of geopolymer with retarders.
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Figure 4. Compressive strength of geopolymer with retarders.
Figure 4. Compressive strength of geopolymer with retarders.
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Figure 5. Compressive strength of geopolymer with different FA/GGBFS ratios.
Figure 5. Compressive strength of geopolymer with different FA/GGBFS ratios.
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Table 1. Physical properties and chemical composition of FA and GGBFS.
Table 1. Physical properties and chemical composition of FA and GGBFS.
FAGGBFS
Physical propertiesBAT fineness (m2/kg)365382
Specific gravity (g/cc)2.972.91
Mean particle size (µm)2415
Chemical composition (wt.%)SiO261.5333.81
Al2O325.1919.52
Fe2O35.390.49
CaO1.3135.22
MgO0.636.68
SO30.821.4
Na2O0.390.34
TiO20.650.94
MnO0.3-
K2O0.230.44
LOI *0.950.11
* Loss on ignition.
Table 2. Retarder combinations and proportions for geopolymer paste and mortar.
Table 2. Retarder combinations and proportions for geopolymer paste and mortar.
RetarderQuantity (kg/m3)
Geopolymer PasteGeopolymer Mortar
Carboxymethyl celluloseCMC powder4019
Water4019
Hydroxyethyl celluloseHEC powder4019
Water4019
StarchStarch powder4019
Water4019
Borax-4019
Hydroxyethyl cellulose + boraxHEC powder209.5
Water209.5
Borax209.5
Starch + boraxStarch powder209.5
Water209.5
Borax209.5
Carboxymethyl cellulose + boraxCMC powder209.5
Water209.5
Borax209.5
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MDPI and ACS Style

John, S.K.; Cascardi, A.; Nandana, M.; Kurian, F.; Fathima, N.A.; Arif, M.M.; Nadir, Y. Innovative Retarders for Controlling the Setting Characteristics of Fly Ash-Slag Geopolymers. Eng 2025, 6, 366. https://doi.org/10.3390/eng6120366

AMA Style

John SK, Cascardi A, Nandana M, Kurian F, Fathima NA, Arif MM, Nadir Y. Innovative Retarders for Controlling the Setting Characteristics of Fly Ash-Slag Geopolymers. Eng. 2025; 6(12):366. https://doi.org/10.3390/eng6120366

Chicago/Turabian Style

John, Shaise Kurialanickal, Alessio Cascardi, Madapurakkal Nandana, Femin Kurian, Niyas Aruna Fathima, M. Muhammed Arif, and Yashida Nadir. 2025. "Innovative Retarders for Controlling the Setting Characteristics of Fly Ash-Slag Geopolymers" Eng 6, no. 12: 366. https://doi.org/10.3390/eng6120366

APA Style

John, S. K., Cascardi, A., Nandana, M., Kurian, F., Fathima, N. A., Arif, M. M., & Nadir, Y. (2025). Innovative Retarders for Controlling the Setting Characteristics of Fly Ash-Slag Geopolymers. Eng, 6(12), 366. https://doi.org/10.3390/eng6120366

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