Hydroxyl Group-Dependent Effects of Alkanolamine Additives on Rheology, Hydration, and Performance of Early-Strength Cement Slurries

Abstract

Alkanolamine additives play a critical role in enhancing the early process performance of cement slurries, thereby improving construction efficiency and structural durability. This study systematically evaluates the effects of ethanolamine (EA), diethanolamine (DEA), and triethanolamine (TEA) on cement slurry properties, including the thickening time, rheology, density, shrinkage, and hydration kinetics. Clear structure–activity relationships are established based on the findings. The experimental analysis demonstrated that increasing the hydroxyl group count in the alkanolamines significantly accelerated cement hydration. At a dosage of 1.0%, the thickening time of the cement slurry was significantly shortened to 125 min (EA), 15 min (DEA), and 12 min (TEA), respectively. Concomitantly, a reduction in fluidity was observed, with flow diameters measuring 15.8 cm (EA), 14.6 cm (DEA), and 14.1 cm (TEA). The rheological analysis revealed that the alkanolamine additives significantly increased the consistency coefficient (K) and decreased the flowability index (n) of the slurry, with TEA exhibiting the most pronounced effect. The density measurements confirmed the enhanced settlement stability, as the density differences diminished to 0.1 g/cm³ at the optimal dosages (0.6% TEA and 0.8% DEA). The hydration degree analysis indicated a hydration rate acceleration of up to 32% relative to plain slurry, attributed to the hydroxyl-facilitated promotion of Ca(OH)₂ formation and C₃S dissolution. The XRD analysis confirmed that the alkanolamines modified the reaction kinetics without inducing phase transformation in the hydration products. Crucially, the hydroxyl group count governed the performance: a higher hydroxyl density intensified Ca²⁺/Al³⁺ complexation, thereby reducing ion mobility and accelerating setting. These findings establish a molecular design framework for alkanolamine-based additives that balances early process performance development with practical workability. The study advances sustainable cement technology by enabling targeted optimization of rheological and mechanical properties in high-demand engineering applications.

1. Introduction

Optimizing the early-age performance of cement-based materials is critical for enhancing construction efficiency and structural durability, as early-strength accelerators—as primary chemical additives—address time-sensitive demands in rapid construction, low-temperature operations, and specialized engineering by significantly shortening the setting times and accelerating early-strength development [1,2,3,4,5]. These accelerators are primarily categorized into three classes based on their chemical composition: inorganic salts (e.g., chlorides, sulfates, nitrates, and carbonates), organic compounds (primarily alkanolamines and organic acid salts), and hybrid systems (achieving synergy through inorganic–inorganic/organic compounding) [6,7]. Of these, alkanolamine-based additives uniquely integrate amine (-NH₂/-NR_x) and hydroxyl (-OH) functionalities, enabling the dual chemical behaviors of amines and alcohols. Within cement hydration environments, they enhance early strength by promoting silicate mineral dissolution and hydration product crystallization, thus serving as widely adopted accelerators [8,9,10]. Mechanistic studies have revealed that their inherent strong polarity and cationic traits (from nitrogen’s lone electron pair) drive selective adsorption onto cement particles and chelation with ions like Ca²⁺/Al³⁺. This process accelerates ion migration while optimizing spatial distribution of hydration products (e.g., C-S-H gel, ettringite) via electrostatic dispersion, thereby synergistically refining cement slurry microstructure.

As versatile chemical compounds, alkanolamines have been extensively studied and applied as cement production additives since the mid-20th century, with triethanolamine (TEA) being the most thoroughly investigated variant [11,12,13,14,15,16]. In studies examining the effects of triethanolamine (TEA) as a standalone additive on the age-dependent strength of cement-based materials, it has been demonstrated that TEA forms complexes (TEA-Ca²⁺) via chelation between the oxygen atoms in TEA molecules and the calcium ions (Ca²⁺) in cement slurry. This process promotes the development of distorted and radiating Ca(OH)₂ crystals with reduced dimensions, thereby enhancing early strength [17]. The rapid early-stage setting has been primarily attributed to accelerated C-S-H formation, with observations indicating that varying TEA/C₃A ratios generate two distinct ettringite morphologies: TEA–ettringite and conventional ettringite [18]. For cement formulas with TEA as the sole additive, Ramachandran et al. observed that low TEA dosages (e.g., 0.25%) slightly retard setting. This retardation intensifies at a 0.5% dosage, whereas 1.0% induces flash setting [19]. Compressive strength tests revealed an 11.6% increase at 1 day but reductions of 3.3% and 0.5% at 3 and 28 days, respectively, with 0.02% TEA in the mortar [20]. Enhanced Al³⁺ chelation has been correlated with high TEA dosages (0.02–6%), a process shown to accelerate C₃A hydration. The resulting products (e.g., C₂AH₈, C₄AH₁₉) form coatings on the C₃S surfaces, inhibiting C₃S hydration—particularly C-S-H formation—and consequently reducing the early strength. This negative effect escalates with an increasing TEA content [21]. Experimental studies have confirmed that TEA·HCl exhibits cement-setting acceleration and early-strength enhancement comparable to TEA at optimal dosages (~0.02%), suggesting its viability as a TEA alternative [22]. Notably, amine adsorption by nascent C-S-H gels under a low TEA dosage prolongs the hydration induction period, a process that consolidates particle bonding and boosts early-age strength development [23].

The current research on the alkanolamine-mediated regulation of cement slurry properties exhibits a pronounced imbalance: an excessive focus on the hardened-state strength evolution and mechanical performance has overshadowed the mechanisms governing their effects on the rheological behavior and workability of fresh mixtures [24,25,26]. Concurrently, rigorous investigations into structure–property relationships remain inadequate, particularly regarding the quantitative correlations between the molecular structural parameters (e.g., hydroxyl group count/carbon chain length) and macroscopic performance. While prior studies have established alkanolamines’ acceleratory mechanisms individually (e.g., TEA by Ramachandran [9]; EA/DEA by Heren [8]), they have omitted comparative analyses of hydroxyl group dependency and its tradeoffs between hydration acceleration and rheological detriment. Unlike this fragmented approach, our work fills two critical gaps: (1) the quantitative linkage of hydroxyl stoichiometry to macroscopic performance, demonstrating a near-perfect correlation with thickening time reduction and hydration acceleration; and (2) a first-principles reconciliation of rapid setting (kinetics) with workability loss (rheology) through gradient dosage experimentation across EA, DEA, and TEA. This establishes a predictive framework where the molecular structure dictates cement slurry behavior. This study employs a gradient dosage design to systematically examine the integrated regulation mechanisms of EA, DEA, and TEA in cement slurries. We characterize evolution patterns of thickening time, fluidity, density, and hydration degree in fresh slurries, while investigating the structure–activity relationships and mechanistic actions of alkanolamine additives. This work ultimately establishes the theoretical foundations for molecular design of early-strength cement slurry additives and facilitates innovative applications of alkanolamines in low-carbon building materials.

2. Materials and Methods

2.1. Materials

EA, DEA, TEA, and anhydrous ethanol were procured from Tianjin Fuyu Fine Chemical Co., Ltd. in Tianjin, China. Portland cement (Type PI) was supplied by Qingyun Kangjing Building Materials Co., Ltd. in Dezhou, China, with its chemical composition comprising 64.9% CaO, 21.7% SiO₂, 4.8% Al₂O₃, 3.7% Fe₂O₃, 2.8% MgO, 0.6% Na₂O, 0.3% SO₃, and 1.3% minor oxides by mass. All chemicals were used without further purification.

2.2. Preparation of Cement Slurry

The cement slurry was prepared using a multi-speed mixing process: First, the PI cement and solid additives were dry-mixed according to the designed proportion. The deionized water and liquid additives were measured based on a water–cement ratio of 0.44 and then poured into the mixing cup. The dry mixture was uniformly added within 15 s under a low speed of 4000 ± 200 rpm. Subsequently, the mixture was stirred at a high speed of 12,000 ± 500 rpm for 35 s to obtain a homogeneous slurry.

2.3. Measurement of Cement Slurry Thickening Performance

The thickening performance was measured using an Atmospheric Consistometer (Model: 2001, Qingdao Chuangmeng Instrument Co., Ltd., Qingdao, China). Freshly mixed cement slurry was slowly poured into a standard slurry cup along the wall. The cup was manually shaken to eliminate entrained air bubbles. The sealed cup was placed into the preheated chamber of the consistometer. After setting the test temperature and starting the motor, recording commenced once the consistometer pointer rotated smoothly.

2.4. Measurement of Cement Slurry Rheological Properties

A total of 300 g of cement was weighed and poured into a mixing bowl. The recommended dosage of additives and 105 g of water were added to the mixing pot and automatically mixed using a cement slurry mixer. Upon completion, the mixture was poured into a slurry cone mold placed on a cement slurry fluidity tester to assess fluidity.

(1)

The rheological properties were measured using a ZNN-D6S six-speed rotational viscometer (Qingdao Haitongda Special Instrument Factory, Qingdao, China). For viscometer testing: Freshly mixed cement slurry was placed in the atmospheric consistometer and allowed to stand for 20 ± 0.5 min at ambient conditions. It was then poured into the viscometer cup. The torque values were measured sequentially at rotational speeds of 600 r/min, 300 r/min, 200 r/min, 100 r/min, 6 r/min, and 3 r/min. The measurements were first taken in increasing order of rotational speed, then repeated in a decreasing order. The arithmetic mean of the readings at each corresponding speed (ascending/descending) was calculated. The rheological parameters were determined by substituting these values into Equations (1) and (2).

$$\mathrm{n}=2.092 \lg \left({\displaystyle \frac{{\mathrm{\theta }}_{300}}{{\mathrm{\theta }}_{100}}}\right)$$

(1)

$$\mathrm{K}=0.511{\displaystyle \frac{{\mathrm{\theta }}_{300}}{{511}^{\mathrm{n}}}}$$

(2)

$\mathrm{n}$: Flow index;

$\mathrm{K}$: Consistency coefficient.

(2)

Truncated cone fluidity test: The glass base plate was wiped with a damp, lint-free cloth to ensure a moist, water-free surface. The truncated cone mold was positioned on the glass plate. The mold was rapidly filled with cement slurry and the top surface was leveled in a single pass using a spatula. The cone mold was lifted vertically and a stopwatch was started simultaneously. After 30 s, the maximum spread diameter of the cement slurry in two perpendicular directions was measured using a digital vernier caliper. The average of these two values was recorded as the fluidity of the cement slurry.

2.5. Measurement of Cement Slurry Density

The cement slurry density was measured using a density meter (Model: M392121, Qingdao Haitongda Special Instrument Factory, Qingdao, China). Prior to measurement, the prepared cement slurry was thoroughly stirred to remove air bubbles and then poured into the pressurized density cup. The cup lid was tightly sealed. Water was used to rinse the exterior of the density meter, which was then dried. The pressurized density meter was placed on a support stand. The rider on the balance beam was adjusted to achieve equilibrium (indicated by the bubble in the beam level stabilizing at the center position). The value displayed on the left side of the rider was read as the cement slurry density.

2.6. Measurement of Cement Slurry Shrinkage

Slurry specimens (40 × 40 × 160 mm) were prepared according to GB/T 17671-2021 [27], “Method of testing cements-Determination of strength”. Specimens were cured under standard conditions: temperature (20 ± 2) °C and humidity (95 ± 5)%. At designated curing ages, specimen dimensions were measured and substituted into Equation (3) to calculate drying shrinkage rate.

$${\mathrm{S}}_{\mathrm{t}}={\displaystyle \frac{(L_0-L_t)\times 100}{160}}$$

(3)

S_t: Shrinkage of cement slurry at curing age t (days);

L₀: Initial length of cement slurry;

L_t: Length of cement slurry at curing age t.

2.7. Determination of Cement Hydration Degree by Chemically Bound Water Method

(1)

Determination of Loss on Ignition (LOI): Approximately 1~2 g of cement paste powder (weighed to an accuracy of 0.0001 g) was placed into a pre-ignited and constant-weight porcelain crucible. The lid was placed askew on the crucible, which was then transferred into a muffle furnace. The temperature was gradually increased to and maintained at 950 ± 25 °C for 15 min~20 min. The crucible was removed, placed in a desiccator to cool to room temperature, and weighed. This process was repeated until a constant weight was achieved. The LOI of cement was calculated using Equation (4).

(2)

Removal of Non-Combined Water: The hardened cement samples were cured to the required test age. The samples were broken into small pieces, immersed in anhydrous ethanol to stop hydration, ground into powder, and dried in an oven at 60 °C until a constant weight was achieved. This process removed the non-chemically bound water from the sample.

(3)

Determination of Bound Water: A total of 1~2 g of the treated cement powder (weighed to an accuracy of 0.0001 g) was placed into a pre-ignited, constant-weight porcelain crucible. It was ignited following the LOI determination method until a constant weight was reached. The chemically bound water content (×1) of the tested cement sample was calculated using Equation (5).

(4)

Calculation of Hydration Degree: Based on the chemically bound water content measured at various ages and the chemically bound water content at complete hydration determined using the above methods, the hydration degree (α) at each age was calculated using Equation (6).

$$\mathrm{L}={\displaystyle \frac{m_0-m_1}{m_0}}\times 100\%$$

(4)

$$x_1={\displaystyle \frac{m_1-m_2}{m_2}}\left(100-L\right)-L$$

(5)

$$\alpha ={\displaystyle \frac{x_1}{x_2}}\times 100\%$$

(6)

L: Loss on ignition of fresh cement;

m₀: Mass of fresh cement before ignition;

m₁: Mass of fresh cement after ignition;

m₂: Mass of hydrated specimen after ignition at specified age;

x₁: Chemically bound water content at specified age;

x₂: Chemically bound water content of fully hydrated specimen;

α: Degree of hydration at specified age.

2.8. XRD Test

The mixed cement paste was cured to the required test age. The hardened cement sample was removed, broken into pieces, immersed in anhydrous ethanol to stop hydration, ground into powder, and dried in an oven at 60 °C until a constant weight was achieved. The XRD analysis was performed using a D8 ADVANCE X-ray diffractometer (Bruker, Karlsruhe, Germany) in reflection mode. Instrument specifications: Maximum output power: ≥3 kW; rated voltage: 60 kV; rated current: 60 mA. The data were collected with a 2θ range of 5–80°, a step size of 0.02°, and a scanning speed of 2°/min.

3. Results and Commentary

3.1. Effect of Alkanolamine Additives on Cement Slurry Thickening Behavior

The thickening curves of cement slurry incorporating EA, DEA, and TEA at varying dosages (0.2%, 0.4%, 0.6%, 0.8%, and 1.0%) are shown in Figure 1, Figure 2 and Figure 3. For EA, the thickening curve morphology remained similar to that of the control group (plain cement slurry) at dosages below 0.8%. However, when the dosage reached 1.0%, the curve exhibited a pronounced upward trend after 90 min. In contrast, both DEA and TEA induced distinct alterations to the thickening behavior even at the lowest dosage (0.2%). At dosages exceeding 0.2%, these additives triggered a significant transformation of the curve morphology, characterized by a rapid near-vertical rise in the consistency within a short timeframe. This demonstrates that DEA and TEA substantially accelerate cement hydration, particularly at higher dosages where they dramatically reduce the thickening time.

A comparative assessment of Figure 1, Figure 2 and Figure 3 reveals a hierarchical acceleration efficacy governed by the hydroxyl group count: TEA demonstrates the most profound impact, reducing the thickening time to 12 min at a 1.0% dosage (vs. 180 min control). This represents a 93% reduction, significantly exceeding that of DEA (92%) and EA (31%). DEA shows intermediate potency, triggering near-vertical consistency rises at ≥0.4% dosage (Figure 2). EA exhibits minimal influence below 0.8%, with only marginal curve morphology changes (Figure 1). In conclusion, based on the thickening curves in Figure 1, Figure 2 and Figure 3, TEA exhibits the most pronounced accelerating effect.

The effects of alkanolamine additives on the initial consistency and thickening time of cement slurry are shown in Figure 4 and Figure 5, respectively. As observed in Figure 4, the initial consistency increases progressively with a higher additive dosage. At a 1.0% dosage, ethanolamine (EA), diethanolamine (DEA), and triethanolamine (TEA) elevate the initial consistency to 20 Bc, 18 Bc, and 19 Bc, respectively. This indicates a marginal enhancement in the initial consistency within the tested dosage range, with no statistically significant differences observed among the three additives. Figure 5 demonstrates a dosage-dependent reduction in the thickening time. Ethanolamine exhibits negligible acceleration effects. In contrast, both DEA and TEA significantly shorten the thickening time at a 0.4% dosage—to 31 min (DEA) and 22 min (TEA), corresponding to 82% and 87% reductions compared to plain cement slurry, respectively.

3.2. Effect of Alkanolamine Additives on Rheological Properties of Cement Slurry

The rheological parameters of cement slurry incorporating EA, DEA, and TEA at dosages of 0.2%, 0.4%, 0.6%, 0.8%, and 1.0% are presented in

Table 1. Effect of EA on the rheological properties of cement slurry at a curing temperature of 35 °C.

Dosage, %	θ600	θ300	θ200	θ100	θ6	θ3	n	K
0	150	120	96	79	36	30	0.3805	5.3540
0.2	150	124	99	80	37	30	0.3989	4.9328
0.4	152	125	98	81	36	31	0.3949	5.0980
0.6	156	124	99	81	36	31	0.3876	5.2932
0.8	155	128	100	84	37	31	0.3834	5.6091
1.0	158	130	102	85	38	30	0.3868	5.5793

,

Table 2. Effect of DEA on the rheological properties of cement slurry at a curing temperature of 35 °C.

Dosage/%	θ600	θ300	θ200	θ100	θ6	θ3	n	K
0	150	120	96	79	36	30	0.381	5.3542
0.2	159	122	99	81	37	30	0.373	5.7111
0.4	163	125	100	83	38	29	0.373	5.8550
0.6	168	128	102	85	38	29	0.373	5.9991
0.8	170	129	103	86	39	28	0.369	6.1822
1.0	172	131	105	88	40	28	0.362	6.5543

and

Table 3. Effect of TEA on the rheological properties of cement slurry at a curing temperature of 35 °C.

Dosage, %	θ600	θ300	θ200	θ100	θ6	θ3	n	K
0	150	120	96	79	36	30	0.381	5.3541
0.2	155	120	95	80	38	29	0.369	5.7502
0.4	159	122	93	82	39	30	0.362	6.1230
0.6	162	123	92	83	38	29	0.358	6.3146
0.8	168	123	90	84	39	28	0.347	6.7588
1.0	170	125	90	86	39	29	0.340	7.1634

. Under 35 °C curing conditions, the alkanolamine additives reduced the flow index (n) while significantly increasing the consistency coefficient (K). Figure 6 shows the influence of additive dosage on the slurry fluidity. Increasing the alkanolamine content progressively decreased the fluidity, with DEA and TEA exhibiting more pronounced effects. At a 1.0% dosage, the flow diameters for the EA-, DEA-, and TEA-modified slurries were 15.8 cm, 14.6 cm, and 14.1 cm, respectively. These results demonstrate that alkanolamine additives reduce cement slurry fluidity and enhance consistency, with their efficacy following the order TEA > DEA > EA.

3.3. Effect of Alkanolamine Additives on Cement Slurry Density

The density measurements of cement slurry incorporating ethanolamine (EA), diethanolamine (DEA), and triethanolamine (TEA) at dosages of 0.2–1.0% are summarized in

Table 4. Density difference in EA cement slurry.

Dosage, %	Density (g/cm3)			Density Difference (g/cm3)
	Upper	Center	Below
0	1.80	1.82	1.83	0.3
0.2	1.80	1.81	1.83	0.3
0.4	1.81	1.82	1.84	0.3
0.6	1.82	1.82	1.84	0.2
0.8	1.82	1.82	1.84	0.2
1.0	1.83	1.83	1.85	0.2

,

Table 5. Density difference in DEA cement slurry.

Dosage, %	Density (g/cm3)			Density Difference (g/cm3)
	Upper	Center	Below
0	1.80	1.82	1.83	0.3
0.2	1.80	1.80	1.82	0.2
0.4	1.81	1.82	1.83	0.2
0.6	1.81	1.81	1.83	0.2
0.8	1.82	1.82	1.83	0.1
1.0	1.82	1.82	1.83	0.1

and

Table 6. Density difference in TEA cement slurry.

Dosage, %	Density (g/cm3)			Density Difference (g/cm3)
	Upper	Center	Below
0	1.80	1.82	1.83	0.3
0.2	1.80	1.81	1.82	0.2
0.4	1.81	1.81	1.83	0.2
0.6	1.81	1.81	1.82	0.1
0.8	1.82	1.82	1.83	0.1
1.0	1.83	1.83	1.84	0.1

. Increasing the alkanolamine content elevated the slurry density while reducing the density differential, indicating enhanced sedimentation stability. To achieve a critical density differential of 0.1 g/cm³, the required dosages were as follows: >1.0% for EA, 0.8% for DEA, and 0.6% for TEA. Thus, the efficacy for improving the sedimentation stability is as follows TEA > DEA > EA.

3.4. Effect of Alkanolamine Additives on Shrinkage and Hydration Degree

The shrinkage behavior of cement slurries (formulation: cement + 1.0% alkanolamine + 44% water) was evaluated. As shown in Figure 7, the shrinkage progressively increased with the curing time across all groups. During the initial 9 days, the shrinkage differences between the alkanolamine-modified slurries and the control were negligible. However, upon extending curing to 14 days, the DEA-modified slurry exhibited a 6.7% lower shrinkage versus the control. The TEA-modified slurry showed a 5.6% reduction, demonstrating the superior shrinkage suppression efficacy of hydroxyl-rich additives at later stages. This behavior can be attributed to two factors. First, hydroxyl groups accelerate hydration to form more C-S-H gel, refining capillary pores and reducing capillary tension (diminishing the shrinkage driving force). Second, hydroxyl groups promote ettringite network formation, restricting water evaporation.

As shown in Figure 8, all the additives increased the degree of hydration relative to the control, though their effects differed significantly. DEA and TEA induced substantially higher hydration degrees, demonstrating their role in accelerating cement hydration. The hydration degree reached 62% in the DEA-modified slurry, representing a 32% increase over the plain slurry control (47%). This acceleration mechanism may originate from the positively charged, highly polar alkanolamine molecules adsorbing onto the cement particles and forming calcium complexation zones that promote dissolution and hydration product formation.

3.5. XRD Analysis

As shown in Figure 9, the phase composition of hydration products in the alkanolamine-modified cement slurries remained consistent with those of the control group, whereas significant variations in their relative abundance were observed. This indicates that alkanolamines modulate the formation ratios of hydration phases without altering their mineralogical identities. The XRD analysis revealed a graded increase in the Ca(OH)₂ diffraction peak intensity following the order EA < DEA < TEA, directly corroborating that higher hydroxyl group content enhances the degree of cement hydration. The semi-quantitative XRD analysis revealed a distinct hydroxyl-dependent acceleration of cement hydration. Compared to the control, TEA induced the most pronounced changes: a 23.1% increase in the Ca(OH)₂ content accompanied by an 8.2% reduction in the residual C₃S. DEA exhibited intermediate effects, with an 18.3% Ca(OH)₂ elevation and a 6.5% C₃S consumption, while EA showed modest alterations (+7.7% Ca(OH)₂, −2.7% C₃S). These result demonstrate that hydroxyl groups enhance Ca²⁺ complexation, reducing ionic mobility barriers, while simultaneously strengthening nucleation to accelerate crystallization.

3.6. Mechanism of Alkanolamine Additives on Cement Slurry

The molecular structures of the alkanolamine additives and the thickening times and fluidity of the cement slurry at a dosage of 1.0% are presented in

Table 7. Effect of alcohol amine additives on the thickening time and flowability of cement slurry.

Alcoholic Amine Type	Thickening Time (min)	Fluidity (cm)
	125	15.8
	25	14.6
	15	14.1

. As the number of hydroxyl groups increases from ethanolamine to diethanolamine to triethanolamine, the cement slurry thickening time progressively decreases. This occurs because the hydroxyl groups in the alkanolamine molecules accelerate the formation of Ca(OH)₂, thereby promoting the hydration of C₃A and accelerating the reaction between sulfates and aluminates. This reaction consumes significant free water, increasing the slurry viscosity and reducing the fluidity. Furthermore, increasing the alkanolamine dosage enhances the complexation of hydroxyl groups with the alkanolamines, lowering the concentrations of Ca²⁺ and Al³⁺ ions in the liquid phase. This reduction further promotes the hydration of C₃S, accelerating cement slurry setting and shortening the thickening time.

Figure 10a–c illustrate the initial, mid-term, and final stages of cement hydration, respectively. Figure 10a depicts the initial hydration stage (induction period): The mineral phases rapidly dissolve, releasing ions (Ca²⁺, Al³⁺, OH⁻, and SiO₄⁴⁻), while the initial hydration products form. Macroscopically, slurry fluidity loss occurs (initial setting). Figure 10b represents the mid-term hydration stage (acceleration period): The hydration reaction accelerates, generating fibrous C-S-H gel and plate-shaped CH crystals that fill the pores and form crystal networks. Macroscopically, the slurry hardens (final setting) with rapid strength development. Figure 10c illustrates the final hydration stage (stabilization period): The residual unhydrated particles become encapsulated by the hydration products. The hydration rate decreases significantly, though C-S-H and CH generation persist. Continuous C-S-H growth fills the capillary pores, reducing the porosity and densifying the crystal networks. Macroscopically, strength development continues while moisture evaporation increases the capillary tension, inducing shrinkage.

4. Conclusions

This study systematically evaluated the comprehensive effects of EA, DEA, and TEA on cement slurry properties. The results demonstrate that as the number of hydroxyl groups increases (EA → DEA → TEA), the cement slurry thickening time significantly decreases (125 min, 15 min, and 12 min, respectively, at a 1.0% dosage), accompanied by a concurrent reduction in the fluidity (corresponding flow diameters of 15.8 cm, 14.6 cm, and 14.1 cm). The analysis of hydration degree revealed a 32% acceleration in the hydration rate compared to that of plain slurry. This phenomenon is attributed to the hydroxyl groups accelerating Ca(OH)₂ nucleation, thereby promoting C₃A hydration and enhancing the sulfate–aluminate reaction. This process consumes the free water and increases the slurry viscosity. Simultaneously, the complexation of alkanolamines with Ca²⁺/Al³⁺ ions reduces their concentration in the liquid phase, further promoting C₃S hydration. These combined mechanisms induce accelerated setting. Furthermore, DEA and TEA, at dosages ≤ 1.0%, effectively control density differences within 1.0 g/cm³, exhibiting superior performance compared to EA. This study achieves a molecular design-enabled precision control of cement performance by establishing a quantitative hydroxyl performance relationship, which defines the efficacy hierarchy as TEA > DEA > EA and resolves the empirical selection challenges for alkanolamine additives. Mechanistically, hydroxyl groups enhance hydration through the following: (1) complexation-mediated reduction in ionic mobility barriers, (2) C-S-H gel refinement of capillary pores, and (3) ettringite network suppression of moisture evaporation. Environmentally, alkanolamine additives provide a sustainable alternative to traditional calcium chloride accelerators by eliminating Cl⁻-induced steel corrosion. For engineering applications, this work establishes fundamental principles for construction in extreme cold regions and rapid repair projects.