Effect of cement kiln dust and lignosulfonate on cement paste: a rheology and hydration kinetics study

This research provides a comprehensive analysis of the influence of cement kiln dust (CKD) and lignosulfonate (LS) on the rheology and hydration kinetics of cement paste. The interaction effect, dispersion potential, and adsorption kinetics of LS on the cement/CKD paste were obtained using UV spectroscopy and zeta potential measurements. The results indicate that the addition of LS reduces the yield stress and plastic viscosity through the dispersion effect of LS, which alters the adhesion of the particles and improves the rheology of the CKD/cement paste. The competing adsorption of LS by the cement and CKD particles increased the flowability of the cement paste and a maximum was obtained due to the stable combined action of two different mechanisms of steric hindrance and electrostatic repulsion by LS. The X-ray Diffraction analysis performed to evaluate the hydration response of cement with LS and CKD showed greater conversion potentials of SiO2 to stable CSH.


Introduction
Utilizing wastage and by-products, eco-efficient cement composites are made, and recently, the addition of CKD as a binder substitute has garnered a lot of interest.Due to the application of CKD, the rate of noxious ion penetration into the cement paste was considerably reduced, and resistance to chloride penetration was also greatly enhanced (Kunal et al 2015).CKD is said to be a calcium-rich source and a non-toxic substance that may be used in the production of concrete (Kunal et al 2012, Saleh et al 2020).The use of fly ash to swiftly generate high-quality CSH gels often complements the use of CKD as a cement substitute material (Chaunsali andPeethamparan 2013, Abdalla andSalih 2022).Due to the variable quality of CKD, it is a material of questionable suitability for use in high-performance cementitious materials (Alnahhal et al 2018, Baghriche et al 2020).
When ultrafine CKD is obtained by milling at different parameters and utilized as a cement substitute, it generates a cement paste with high compressive strength (Alnahhal et al 2017).Najim et al 2016 are the only people who have looked into the rheological properties of self-compacting cement concrete made with CKD as a partial substitute instead of cement.In the construction industry, various ultra-fine additives have been utilized to improve the strength and longevity of cementitious components (Liu et al 2000, Kumar et al 2018).It has also been discovered that chemical admixtures, such as retarders (Guoju and Zhang 2020), viscosity-modifying agents (Bouras et al 2012, Fares et al 2022), accelerators (Leinitz et al 2019), and water-reducing agents (Varela et al 2021), improve the rheology of cement paste.Table S1 depicts the summary of previous research works on cement/mortar involving Rheological parameters.Even though CKD as a supplementary cementitious material has produced encouraging results, no research has been conducted on the rheological characteristics of CKDcontaining cement paste using dispersion agents.Unless a suitable dispersion agent is employed, the full potential of CKD cannot be realized.
In cementitious systems, the most prevalent plasticizers are polycarboxylate (Barneoud-Chapelier et al 2022), naphthalene (El Gindy et al 2022), melamine, and lignosulfonate-based (Colombo et al 2017).Utilizing steric hindrance and electrostatic repulsion mechanisms, superplasticizers impart a dispersion impact on the cementitious system (Flatt et al 2000).Evidence from the past shows that the resistance to clumping is caused by the steric force, which in turn depends on the thickness of the adsorption layer.The dispersion effect of the superplasticizers is caused by the amount of adsorption on the cement grains (Yoshioka et al 2002).Lignosulfonates are water-soluble polymers that can be used as a dispersing agent in cement composites and can enhance the stability of the cementitious mixtures (Yoshioka et al 2002).The superplasticizer lignosulfonate works as a dispersant by attaching the positively charged cement particles and generating a repulsive force between them (Colombo et al 2018, Kalina et al 2022).By inhibiting cement particle agglomeration, lignosulfonates in concrete lower the system's overall water demand (Arel and Aydin 2017).Literature from the past says that the lignosulfonate mechanism for slowing things down is supported by a number of important processes (Singh et al 2002).The calcium ions in the pore solution interact with the polymers in the superplasticizers, which causes calcium complexation.Calcium complexation is the process by which calcium ions interact with the functional group of lignosulfonate.It is this interaction that leads to the formation of clusters on the surface and in water.Additional calcium complexation would lead to calcium supersaturation, which would postpone cement's hydrate nucleation.Conversely, the setting time was not significantly slowed by low lignosulfonate amounts (Ouyang et al 2006).This shows that calcium complexation is not the main reason for the slowing effect.The second type of retardation mechanism is known as nucleation poisoning.This type of retardation occurs when the superplasticizer molecule poisons the CH nuclei, preventing them from forming and staying together.This, in turn, prevents CSH from forming and C3S from dissolving, hence extending the duration of the induction process (Thomas et al 2009).The final mechanism of retardation is surface adsorption, which inhibits clinker dissolving, hence delaying the synthesis of hydration products and extending the induction duration (Zhang et al 2022).The hexose in the superplasticizer sticks to the dry phases of the cement, and this slows down the acceleration period and the production of CH (Wu et al 2021).

Research significance
Some researchers attempted to use lignosulfonates as a dispersing agent due to their ability to prevent the agglomeration of cement particles.The research on the dispersing ability of lignosulfonates is sparse, and no study has attempted to report the effect of lignosulfonates on the rheology of cement paste, particularly when finer materials are employed as cement substitutes such as ultrafine CKD.This research focuses primarily on the fresh state behavior and rheological properties of cementitious composites, including ultrafine CKD as a partial cement substitute and lignosulfonate as an additive, without modifying the water-binder (w/b) ratio.Using rheological testing and UV spectral analysis, the ability of the lignosulfonate to get absorbed and disperse CKD in the cement paste was evaluated.The goal of this research is to use lignosulfonate as a dispersion agent in CKDsubstituted cement paste and to conduct micro-scale research such as dispersion characteristics and rheological qualities.This will allow researchers and builders to follow a strategy for making modified cement paste with nano and micro additions with the use of dispersants.

Materials and mix proportion
Ordinary Portland cement (53 grade) is used as the main binder, and CKD was collected from the Indian Cement Plant, India, which is used as a cement replacement material.The chemical composition of the raw material is presented in table 1. Figure 1 shows the grain size distribution curves of cement and CKD.Calcium lignosulfonate, which is 98% to 98.5% water soluble and collected from Astraa Chemicals, India, has been employed as a self-curing agent.Table 2 lists the chemical properties of the lignosulfonate that was used in the present study.The cement-CKD blended pastes were prepared using a w/b ratio of 0.35 and the CKD was used as cement replacement in varying proportions of 5, 10, 15, 20, and 25% by weight of cement.The dosage levels of lignosulfonate (LS) carried out in the present study were about 0% to 1.25% with 0.25 increments.The mix proportion details of the casted samples are presented in table 3.

Methodology
The flowability of the cement paste was measured using a mini-slump flow test, and the spread diameter was measured in two perpendicular directions.The average of the two values is recorded as the flowability value.An isothermal calorimeter was used to measure the heat of hydration of the cement paste for 100 h at a temperature of 23±1 °C.The heat measurements were then standardized with regard to the weight of the cement.The adsorption characteristics of the cement paste containing LS and CKD were measured using UV-visible spectroscopy, and the amount of LS adsorbed by the cement paste and CKD was measured.After 30 min of hydration, the LS concentration was measured using UV-visible spectroscopy by extracting the pore solution from the cement and CKD mixture (Colombo et al 2017).The extraction of the pore solution was accomplished by centrifuging the mixture at 4000 rpm for approximately 5 min.Since the lignosulfonates exhibit a dominant absorbance peak at approximately 280-284 nm, the extracted pore solution was then analyzed using a UV spectrophotometer in the wavelength range of 280 nm.The UV-visible absorbance test was carried out from 200-700 nm to attain the maximum absorbance.The absorbance values were subsequently acquired using a calibration curve, and the amount of LS absorbed by the cement CKD system was calculated using the formula shown in equation (1): where 'abs' means lignosulfonate consumed, 'total' means the total amount of lignosulfonate added and 'free' means amount of free lignosulfonate.Chemical shrinkage measurement is regarded as more significant than total shrinkage because it may qualitatively reveal the hydration behavior and pore refinement properties of the admixtures utilized in the cementitious system.Chemical shrinkage is a measurement of the volume reduction of cement paste as the  hydration reaction proceeds.In order to investigate the early volume change of cement paste and gain a better understanding of the variables affecting chemical shrinkage with the goal of reducing or eliminating cracking in cement-based materials, precise measurement of chemical shrinkage is done as per ASTM C1608.In order to accurately assess chemical shrinkage, it is necessary to ensure that water is available throughout the system and that hydration is unimpeded in order to prevent self-desiccation.According to ASTM C1608, it is best to keep the cement paste thickness between 5 and 10 mm.Three 200 ml containers containing cement paste were filled with deionized water to a depth of 12 mm, and a 1 ml pipette filled with water was inserted via a hole in the rubber stopper.By putting the setup in an environmental chamber, the temperature is kept at 21.5 ± 0.5 °C and the relative humidity is kept at 95%.The amount of water in the drop indicates the chemical shrinkage per gram of cement, given in milliliters.The LS solution was prepared by mixing varying concentrations of LS (0 to 1.5%) with cement and CKD.The mixture was centrifuged at 3000 rotations/min for about 7 min and the amount of LS in the supernatant solution was measured using 1CP OES and UV analysis.The cement paste's zeta potential was measured using Zeta PALS (Zeta Phase Analysis Light Scattering), which relied on a laser source emitting light at 633 nm and setting the scattered angle to 130 degrees.The zeta potential measurement is carried out using a solution of LS with the mixture of cement and CKD (15 g cement + 5 g CKD) with distilled water and stirred for about 5 min.The rheology of the cement paste with different dosages of CKD and varying LS dosages is evaluated using DHR 3 (Discovery Hybrid Rheometer).The fresh cement paste was pre-sheared at the rate of 100 s −1 for about 80 seconds and then rested for a period of 30 seconds to allow for the dissipation of stresses.
The shear rate was decreased from 100 s −1 to 1 s −1 at a rate of 20 s −1 as shown in figure 2. Each stage was maintained for about 30 seconds to attain a steady state for the estimation of the shear stress values under each shear rate.Yield stress is a measure of the resistive force offered by the fluid to withstand against movement whereas the inner failure degree of any fluid is measured through plastic viscosity.The Rheometer readings were processed and fitted with the Bingham and Modified Bingham model to obtain yield stress values and plastic viscosity values of the cement samples.The cement paste's diffraction patterns were measured to determine the amount and calibre of the hydration products.The primary crystalline phases of cement paste were examined using X-ray diffraction analysis and Cu-Kα radiation (Xpert Pro, PANalytical).

Setting time and flowability
To investigate the influence of CKD and LS on the fresh cement paste, the setting time and flowability of the cement paste containing varying proportions of CKD and LS at 0.35 w/b ratio were investigated, and the results are presented in figure 3. The CKD is more effective in affecting the setting time of the cement paste, and the higher specific surface area of the CKD enhances the solid/liquid ratio, leading to reduced setting time values.The reactivity of the cement increased significantly and the setting time was further decreased by around 4 min, whereas the LS additions delayed the setting time of the cement/CKD paste by around 30 seconds for a 1% LS addition.The flowability of the cement paste as observed through flow diameter measurements showed that the CKD has a direct negative influence on the flowability of the cement paste due to its ultra-fine nature, causing agglomeration and aggregation of the CKD particles with themselves and with the cement paste.As can be seen, the flowability decreased as the CKD dosage increased, whereas the opposite performance was observed when the LS was used as an additive.The increasing dosage of LS up to 0.5% showed negligible influence on the flow increment due to the CKD addition, whereas beyond 0.5% additions of LS, the effect was more pronounced.This shows that the flowability enhancement of the cement paste is dependent on the dosage of LS added to the composite as an effective dispersing agent.The higher affinity of CKD to water also affected the flowability of the cement, which was mitigated by the amount of lignosulfonate adsorbed by the CKD and cement grains, as evident from the adsorption measurements done using UV-visible spectroscopy.

Heat of hydration
The hydration curve of cement can generally be classified into two distinct stages of an exothermic peak, the first of which corresponds to the hydration of silicate phases in the cement paste and the second to the formation of mono-sulfate from ettringite until gypsum is depleted.While the first peak is sharp and distinct, the second peak is broad and extends over a period of time.The heat of hydration curves of cement paste, including CKD with and without LS, as well as the total quantity of heat evolved, are shown in figure 4. The hydration curves were recorded for the first 40 hours immediately after water was added to the cement.The w/b ratio adopted was 0.35 and the peak flow of heat was increased as the CKD was added to the cement and the dormant phase of cement hydration was shifted to the left, indicating the accelerating effect of the CKD on cement hydration.The higher  fineness of the CKD also creates additional formation of CSH by functioning as a nucleating site.Due to the calcium oxide hydration, CKD particles can also function as seeding agents for the hydration process to occur.It can also be seen that the heat of hydration of CKD mixes is higher than plain cement hydration, which is mainly related to the presence of CaO content in the CKD.However, the induction period and the shape of the hydration curve were not much affected due to CKD additions.The humps in the hydration curves were almost similar in all the mixes, accompanied by a significant amount of heat evolution.The curves also clearly show that the rapid increase in hydration is caused by the CKD's larger specific surface area and that increased heat evolution does not guarantee faster strength attainment.The accelerated effect of CKD on cement can also be explained by the increased alkalinity, which reduces the calcium ions liberated by gypsum, hence boosting the hydration of C The effect of LS on the hydration of cement has been studied in the past, but its effect on ultrafine CKD with high alkali content has not been investigated.This variation can be explained by the fact that the water used by the CKD in the presence of LS was merely a physical absorption and therefore contributed less to the evolution of heat.Another explanation may be the existence of sulfates in LS, which may undergo endothermic reactions, resulting in less heat being produced.The acceleration effect of CKD was reduced with increasing LS additions, which is manifested through the decreased heat flow peak when compared to the mixes without CKD.Recent studies on LS also showed that the addition of LS delays the setting and hydration of cement (Colombo et al 2017) due to the presence of hydroxyl and carboxyl groups that get absorbed into the cement grains.In this study, the LS molecules get absorbed onto the CKD surfaces, thereby minimizing the nucleation sites and exerting a retardation effect on the cement/CKD paste.Furthermore, the effect of LS on the alkali content of the CKD influenced the hydration behavior of cement, resulting in a lower amount of heat release.The alkali groups are highly positively charged, which binds effectively with the carboxyl groups of LS, thereby minimizing their adsorption on the cement surface.Hence, the CKD dominates the competitive adsorption of LS rather than cement, which is further confirmed through an adsorption measurement test.(The balancing of the negative changes of LS by the positively charged alkali ions of CKD may also further cause an acceleration effect on the cement paste.Thus, two important mechanisms that affect the hydration of cement can be stated as (i) Cement acceleration by CKD particles with a nucleation effect due to their larger surface area, (ii) Competitive LS adsorption by CKD, which neutralizes the LS retardation effect on cement.

Adsorption characteristics
Studies are done on the LS suspensions with CKD to observe its effect on the dispersion and absorbance.The maximum absorbance was observed at a wavelength of 228 nm and the next absorbance occurred around 320 nm.Hence, the absorbance tests were conducted at 228 nm with different concentrations of LS.Initially, the absorbance test was conducted on a cement paste with LS at varying proportions (0%-1.5% by wt.) and the comparative analysis was performed between cement and CKD at different proportions (5 to 25% wt. of cement).The adsorption amount of CKD-incorporated cement pastes at various LS dosages is presented in figure 5.It can be seen that the adsorption amounts of LS with cement increased with increasing dosage and reached a maximum value at a certain dosage (1.25% LS).This shows the stronger adsorption capacity of the cement paste towards the lignosulfonate particles.By observing the values, it can also be obtained that the absorbance values of LS were much higher with the CKD additions, indicating that the dispersion of CKD was more uniform and homogenous with LS.

Zeta potential values
The measured zeta potential values of the fresh cement paste with CKD and LS are shown in figure 6.Previous studies have shown greater zeta potential values for LS due to their higher electrostatic repulsion mechanism, and this study also showed greater zeta potential values with increasing LS content in the cement (Peng et al 2015).It can also be seen from the decreasing zeta potential values as CKD was added to the cement mix, indicating the flocculation of the CKD particles, but the effect of LS in the cement paste made their zeta potential values higher by causing mutual repulsion between the ultrafine CKD particles.This shows that the greater charge densities of the LS are easier to absorb on the CKD particles thereby hindering their flocculation.

Rheology measurements
The rheology of the mixes containing CKD and LS increased linearly with shear rate and followed the Bingham and modified Bingham model as expressed in the equations (2) and (3) respectively:  In these models, τ, τ 0, μ p, γ, and C are shear stress, yield stress, plastic viscosity, shear rate and a regression constant, respectively.The data obtained from the rheological study was fitted with the modified Bingham model as presented in table 4. The 'C' value in the modified Bingham model represents the shear thinning behavior (C=0) and shear thickening behavior (0 < C > 0) of the cement paste.The C values in the CKD samples ranged between 0.003 and 0.005, indicating shear thickening behavior.The increase in values as LS content grew and the decrease in values as CKD increased suggests the shear thickening effect.The yield stress values of the cement paste increased as the LS content increased in the presence of CKD, and the values were highly significant at 1% LS additions.The decreasing yield stress values reflect the ease with which the cement paste can flow while resisting decrement owing to CKD.This may be attributed to the morphology and particle size distribution of CKD being smaller than the average size of the cement particles, resulting in a decrease in free water.As shown by smaller particles and less flowability loss, CKD may also cause the mixtures to be more difficult to work with.The shear rate plotted against the shear stress of developed cement pastes is presented in figure 8.The shear rate versus shear stress curves displayed nearly identical flow curve profiles with increasing CKD proportions, whereas the addition of LS had a significant effect on the shear stress.The CKD proportion maintained a condition in the cementitious system where the attractive forces between the CKD particles were sufficient to keep the cement and CKD particles in a clustered state, whereas the addition of LS resulted in a significant viscosity decrease with increasing shear rate, reaching a linear relationship between shear rate and shear stress.At higher shear rates, the viscosity of the CKD-cement system increased slightly, particularly at higher LS proportions.This fascinating phenomenon is primarily the result of LS molecules forming clusters at higher shear rates, thereby impeding flow, and CKD, which increases viscosity.The greater potential of hydrodynamic forces to overcome the repulsive effect of LS, thereby producing hydro-clusters of CKD and cement particles, may also contribute to the increased viscosity at higher shear rates and a higher proportion of LS.However, the incorporation of LS decreased the cement-CKD system's viscosity, thereby reducing the shear rate required to achieve a higher shear  stress.The incorporation of LS decreased inter-particle contact, thereby decreasing the shear energy necessary to disrupt CKD particle interactions and cluster formations.

Yield stress
The yield stress calculated using the Bingham and modified Bingham model, with different contents of CKD and LS, is shown in figure 9.The CKD is more effective in affecting the rheology of the cement paste, and the higher specific surface area of the CKD enhances the solid/liquid ratio, leading to increased yield stress.The yield stress increment with CKD can be mainly related to the increment in the particle surface area that eventually requires more water to wet the surface, causing agglomeration and shrinkage of the water layer around the cement surface (Li et al 2020).The next series of the cement blends containing CKD and LS showed increased shear stress and yield stress, however, the values were lower than the mixes with CKD alone even at higher dosages of CKD in the presence of LS.This contentious behavior can be attributed to the synergistic effect of CKD and LS; while the former acted as filler and occupied the voids in the cement paste, the latter acted as a water releasing agent, resulting in higher viscosity and lower yield stress.In addition to increasing the paste's volume, the LS also improves its lubrication, which may lower its yield stress.The addition of LS promotes the production of negative charges, while during cement hydration, the cement particles become positively charged due to the adsorption of calcium ions.Because of the LS's air-entraining action, cement particles might be drawn together  to build bridges.Because of this bridging effect, the yield stress of the mixtures can be raised.The shearthickening behavior of concrete can be easily and effectively mitigated by increasing the LS to a level that generates a minor air-entraining effect.

Plastic viscosity
The viscosity measurements obtained for the developed cement pastes containing CKD and LS are presented in figure 10.The reduced viscosity of the cement paste is essentially a result of the water releasing effect of LS, but this phenomenon can be found negligible in the cement pastes containing lower amounts of LS due to the dominating effect of water absorbance by CKD.The CKD, due to its extreme fineness, can function as a thickening agent in the cement paste and absorb more water.The increased surface area of the total cement system containing LS and CKD reduces the spacing between particles in the system, hence increasing viscosity.The thickening effect of the CKD can be seen with the increased plastic viscosity of the cement paste with increasing CKD, and the critical amount of CKD required for thickening can be noted as 7.5% of the plastic viscosity values.The finer particle substitution in cement paste can be viewed through the lens of two competing factors: dilution and thickening.Initially, the dilution effect of the finer CKD particles in the cement paste was observed up to a 2.5% concentration, beyond which the thickening effect was dominant.This shows that the rheology of the cement paste mainly depends on the surface area of the particles, and this supports the result of  the previous study conducted on the use of micro fillers as plastic viscosity-enhancing agents in cement which showed that the surface area of the system influence the yield stress and plastic viscosity, and they are indirectly proportional (Damineli et al 2016).The effect of LS additions into the cement system with CKD showed a nonlinear relationship, and this may be due to the modification of the surface area of the cement and CKD particles by the adsorption of LS on their surface.

Compressive strength
Figure 11 is a graphical representation of the compressive strength of cement pastes that contain varying concentrations of CKD and LS.Every newly created cement paste has a rise in compressive strength as the curing period accumulates.However, with CKD concentrations up to 5%, there was a minor decrease in the compressive strength of the material.Above this percentage, the compressive strength dropped out significantly, and the point at which it reached its lowest point was at 25% CKD.The decrease in compressive strength can be attributed to a decrease in the cement content as well as a rise in the free lime content in cement dust; the greater amount of Ca(OH)2 degraded the cement matrix.Additionally, the rise in the water-to-cement ratio contributed to the decrease in compressive strength.In addition, the development of chloro and sulfo-aluminate phases causes the hydration products to become more malleable and expand in volume.The decrease in strength could be attributable to the high chloride and sulphate content of the CKD, which in turn leads to an increase in the number of pores present in the cement matrix.As a result of the synthesis of these products, the crystallization of hydration products is facilitated, which in turn leads to an expansion of the pore system.It is possible that the crystallization of hydration products will be accompanied by an increase in the pore size as a result of a change in the packing among the crystals.This will result in a decrease in the strength of the product.The strength declination has been slightly improved by adding LS to CKD-substituted cement pastes, but not enough to make it stronger than the reference compressive strength.The strength of the LS dosage mixed with CKD was higher than that of CKD mixes used by themselves, but the strength value went down as replacement amounts went up.

X-Ray diffraction studies
To describe the involvement of CKD and LS in the hydration of cement, a slow scan XRD analysis was conducted on the cement paste, and the spectral curves are presented in figures 12(a) and (b).The slow scan XRD was performed on the cement samples at an angle (2ϴ) 25 to 35°, which shows the characteristic SiO 2 (quartz) peak and CSH phase.It is interesting to note that the CSH peak in the cement paste was higher in the presence of CKD and this is in agreement with the results obtained from the previous experiments.The influence of LS-modified CKD additions on the mineral admixture of the cement paste was identified through XRD analysis and the CSH peaks were evident in all the mixes with major intensity variations.The silica peak reduction is an indicator of the consumption of silica by the hydration reaction.As the CKD content increases, the formation of SiO 2 peaks reduces, and with LS addition, comparatively less consumption of SiO 2 is evident.

Conclusions
An experimental program has been done to evaluate the dispersing effect of LS on cement paste containing ultrafine CKD as filler.The study successfully employed LS as a practical material for the dispersion of ultrafine CKD in cement systems.The flowability results showed that at a definite w/b ratio, the addition of CKD significantly reduced the spread diameter due to their extreme fineness and higher water demand.However, the flowability of the cement paste increased when LS was added and it can be inferred that the LS exerts its effect on workability through its electrostatic repulsion mechanism.The rheology results clearly reveal that the addition of CKD increased the yield stress and plastic viscosity at a definite w/b ratio.The addition of LS reduced the yield stress and apparent viscosity at larger proportions.The electrostatic repulsion aided by the LS was sufficient to achieve an effective dispersion of CKD in the cementitious matrix.The zeta potential studies showed that the additions of water further aggravated the aggregation phenomenon necessitating the use of dispersants to ensure homogeneous dispersion of the CKD.The LS ratio magnified the volume stability at higher CKD contents indicating prevention of agglomeration of ultrafine CKD particles leading to minimal voids that can be filled with water.The LS dosage combined with CKD was more potent than the CKD mixes used alone, although the value decreased with increasing levels of replacement.Thus, from the limited experimental studies conducted in the present study, the mixture comprising 1% LS and 20% CKD demonstrates the optimal proportions for use in cementitious composites with less interference with the hydration reaction, flowability, improved volume stability, and desirable shrinkage resistance.

Direction for future work
This article presented an experimental analysis of the influence of CKD and LS on cementitious systems.In this investigation, LS was found to be effective as dispersion agents in cement containing CKD, where they are typically employed as water-reducing agents.It has been discovered that CKD enhances the cement's flocculation and structural development, resulting in enhanced yield stress and plastic viscosity values.As a cement replacement, the ultrafine CKD addition affected the cement's hydration behavior.However, there is a need for improvement in our understanding of hydration, particularly in its early stages, and its effect on the construction process of cement structures must be researched.In addition, unambiguous links must be made between the physical and chemical characteristics of CKD and the rheology of cement by assessing flow behavior (coagulation and flocculation) in relation to hydration patterns.Due to their performance, availability, and capacity to customize the rheological properties of cement by incorporating ultrafine elements, lignosulfonate has potential advantages over other HRWRA.There is more room for research into other properties of durability, like fire resistance, thermal stability, AAR, and chemical attacks.The threshold level of CKD that has been reached due to dispersion concerns found in the use of ultrafine CKD is determined by the present investigation.In this work, the use of LS as a dispersion agent has been suggested.Also comparable to the LS dispersing agent are improved dispersion techniques, such as mechanical and physical, or a combination thereof.Other practical considerations include mixing the LS in a solid/slurry state to prevent the aggregation effect of ultrafine CKD, thereby minimizing cement paste shrinkage and optimizing mechanical strength.Adding a mix of admixtures, both synthetic and natural, can also make the characteristics better.

Figure 1 .
Figure 1.Particle size distribution curve of raw materials.

Figure 3 .
Figure 3. Setting time and fluidity results of developed cement pastes.

Figure 4 .
Figure 4. Heat flow results of CKD and LS substituted cement paste mixes.
3 A (Siddique 2006, Kunal et al 2012).The addition of LS altered both peaks of the hydration curve, and a 5 to 10-minute delay in the creation of peaks was noted.Several previous studies have shown that LS can act as pseudo retarders by suppressing topo-chemical hydration on the surface of cement grains by absorbing (Grierson et al 2005, Topçu and Ateşin 2016, Colombo et al 2017, Colombo et al 2018, Leonavičius et al 2020).

4. 5 .
Chemical shrinkage testChemical shrinkage is calculated by adding self-desiccation and hydration volume changes.As the cement's CKD percentage increased, its chemical shrinkage values climbed fast throughout the first 10 hours.The shrinkage values of mixtures including CKD were lower than those of mixtures containing LS which can be evident from figure 7 (a) and (b).Accelerated hydration has high shrinkage values.In this investigation, mixes with CKD had higher shrinkage values due to altered hydration rates.The Afm phase of the cement reacted with the CaO of CKD, creating more Afmc (mono carboaluminate) phases that are denser and cause shrinkage.No matter the amount of CKD in the combination, shrinkage was practically comparable.CKD may modify cementitious system hydration chemicals, causing maximum shrinkage.A slight reduction in chemical shrinkage due to LS can be attributed to the expansion of cement paste resulting from the reaction of sulfate components in LS with calcium-rich components of CKD to create Aft (alumina-ferric-oxide-tri-sulfate) and Afm (alumina-ferric-oxide-monosulfate) phases.As a result, CKD inclusion mitigated the unfavorable attribute of excessive shrinkage by increasing the volume stability of cement-LS composites.

Figure 5 .
Figure 5. Adsorption amount of CKD substituted cement pastes at various LS dosages.

Figure 6 .
Figure 6.Zeta potential measurements of plain cement and CKD substituted cement pastes at various LS dosage.

Figure 8 .
Figure 8. Shear rate versus shear stress of developed cement pastes.

Figure 9 .
Figure 9. Yield stress of CKD substituted cement pastes with and without LS dosages.

Figure 10 .
Figure 10.Plastic viscosity of CKD substituted cement pastes with and without LS.

Figure 11 .
Figure 11.Compressive strength of developed CKD and LS substituted cement pastes.

Figure 12 .
Figure 12.(a) XRD results of CKD substituted cement paste without LS.(b) XRD results of CKD substituted cement paste with LS.

Table 3 .
Mix details of casted samples.

Table 1 .
Chemical composition of raw materials employed.

Table 4 .
Data obtained from rheological study.