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Strength Enhanced White Portland Cement Through the Reactive Release of Ions from Potash Alum Solution for Hydration Performance

This study demonstrates that incorporating a saturated potash alum solution into White Portland Cement enhances early-age strength and long-term durability by accelerating hydration kinetics through ion release, which promotes the formation of ettringite and C-S-H gel while refining the microstructure to reduce porosity.

Original authors: SHIVANI PANDEY, SACHIN VERMA, RAUSHAN KUMAR, KANHAYA LAL, SUNANDA DAS, ANIL KUMAR SHUKLA

Published 2026-07-23

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CC BY 4.0

Original authors: SHIVANI PANDEY, SACHIN VERMA, RAUSHAN KUMAR, KANHAYA LAL, SUNANDA DAS, ANIL KUMAR SHUKLA

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the world of construction as a giant, slow-motion kitchen where the main ingredient is cement. When you mix cement with water, it doesn't just dry out; it wakes up and starts a chemical party called "hydration." During this party, tiny crystals dance together to form a super-strong glue called C-S-H gel, which holds our buildings together. However, sometimes this party starts too slowly, or the crystal structure ends up with too many empty spaces (pores), making the final concrete a bit weak or prone to cracking. Scientists have been looking for a way to invite the right guests to this party to make the glue stronger and the structure tighter, all while keeping the cement looking bright and white for fancy architectural designs.

Enter the "saturated solution of potash alum" (SPA). Think of potash alum not as a solid rock, but as a pre-dissolved, super-charged energy drink for cement. When you add this clear liquid to the cement mix, it instantly releases a trio of ions: potassium, aluminum, and sulfate. You can imagine these ions as tiny, hyper-active construction workers. The aluminum and sulfate ions rush in to build a specific type of crystal called "ettringite," which acts like a scaffolding network, while the potassium ions help the whole process start faster. The big question researchers asked was: If we swap some of the mixing water with this special alum solution, will it make White Portland Cement (the kind used for beautiful, bright buildings) stronger and more durable without ruining its color?

This study by Shivani Pandey and her team at the University of Allahabad dives into exactly that. They took White Portland Cement and replaced small amounts of the mixing water with their saturated potash alum solution. They didn't just guess; they mixed up five different batches, ranging from no alum at all to adding 17 ml of the solution to 250 grams of cement. They then put these samples through a rigorous workout: checking how fast they set, measuring the chemical soup inside the liquid, testing how hard they got over 28 days, and even peering at them under powerful microscopes to see the tiny crystal structures.

The results were quite promising, especially for the batch with 10 ml of the alum solution. The researchers found that this specific mix didn't just set; it set faster than the control. The paper explicitly notes that the 10 ml sample exhibited an "accelerated setting time," which is advantageous for applications requiring rapid workability, whereas higher amounts of alum actually delayed the setting process. The alum solution helped the cement form a denser, tighter network of crystals. Under the microscope, the control samples (just plain cement) looked a bit like a room with scattered furniture and empty gaps. In contrast, the alum-blended samples looked like a fortress where needle-like ettringite crystals had grown and interlocked perfectly with the glue-like C-S-H gel, filling in the gaps and creating a much stronger bridge between particles.

In terms of strength, the 10 ml blend was the star of the show. After 28 days of curing, this sample reached a high compressive strength, with the study noting that "SPA modified WPC" achieved a value of 41.6 MPa, outperforming the control. The study also noted that the alum solution helped "eat up" some of the free lime (a byproduct that can sometimes cause issues) and reduced the amount of expansion or swelling that often happens in cement as it hardens. While adding too much alum (like 15 ml or 17 ml) actually slowed down the setting time and lowered the strength, the 10 ml dose seemed to hit the sweet spot. The authors suggest that this method offers a cost-effective and environmentally friendly way to boost the performance of white cement, making it stronger and more durable for decorative and architectural uses, all while keeping that pristine white color intact.

Technical Summary: Strength Enhanced White Portland Cement Through the Reactive Release of Ions from Potash Alum Solution

Problem Statement
White Portland Cement (WPC) is a specialized material valued for its aesthetic qualities and low iron content, yet it faces distinct hydration challenges compared to Ordinary Portland Cement (OPC). Due to its reduced ferrite phase ( $C_4AF$ ), WPC exhibits altered sulfate balance and aluminate reaction kinetics, which can hinder early strength development and microstructural densification. Furthermore, the industry seeks sustainable, cost-effective hydration activators that do not compromise the color or durability of the cement. Conventional activators often introduce color-imparting ions or corrosion risks, creating a need for a color-neutral, chemically effective alternative to optimize WPC hydration without disrupting its unique mineralogy.

Methodology
The study investigated the use of a Saturated Potash Alum (SPA) solution as a partial replacement for mixing water in WPC. Potash alum ( $K_2SO_4 \cdot Al_2(SO_4)_3 \cdot 24H_2O$ ) was selected for its ability to dissociate into $K^+$ , $Al^{3+}$ , and $SO_4^{2-}$ ions in an aqueous environment.

Materials: Birla White Cement (IS-8042:2015) was used as the base binder. Potash alum was dissolved in distilled water to create a saturated solution.
Sample Preparation: Five sample sets were prepared with a constant cement mass of 250g. The SPA solution replaced mixing water in varying volumes (0, 10, 12, 15, and 17 ml), corresponding to a chemical additive weight percentage of approximately 0.25% for the 10ml sample. The water-to-solid ratio varied between 0.3 and 0.4.
Testing Protocols:
- Setting Time: Measured via Vicat apparatus (EN 196-3) to determine initial and final setting times.
- Liquid Phase Analysis: Concentrations of $Ca^{2+}$ and $OH^-$ ions were quantified at various intervals using EDTA and acid-base titration methods.
- Free Lime: Determined using the Franke extraction method to assess the consumption of uncombined calcium oxide.
- Compressive Strength: Tested on 5x5x5 cm cubes at 1, 3, 7, 15, and 28 days (IS 4031).
- Microstructural Analysis: X-ray Diffraction (XRD) was performed on 28-day hydrated samples to identify crystalline phases. Scanning Electron Microscopy (SEM) analyzed surface morphology and pore structure.
- Expansion: Measured using length comparators on mortar rods to assess dimensional stability.

Key Results

Setting Time: The incorporation of SPA generally delayed setting times as the concentration increased, a behavior noted as potentially beneficial in hot climates. However, the 10 ml SPA sample exhibited accelerated setting characteristics, attributed to the rapid formation of an ettringite network by the $Al^{3+}$ and $SO_4^{2-}$ ions reacting with tricalcium aluminate ( $C_3A$ ).
Hydration Kinetics: Liquid phase analysis revealed that blended WPC samples maintained lower concentrations of $Ca^{2+}$ and $OH^-$ ions compared to the control. This indicates that the ions were actively consumed in secondary hydration reactions, specifically the formation of Calcium Silicate Hydrate (C-S-H) gel and the consumption of portlandite ( $Ca(OH)_2$ ).
Compressive Strength: The 10 ml SPA-blended sample demonstrated the highest compressive strength at 28 days (41.1 N/mm²), surpassing the control sample (37.2 N/mm²). The strength gain is linked to the increased formation of C-S-H gel and a denser microstructure.
Free Lime and XRD: Free lime percentages in the blended samples were consistently lower than the control, confirming the effective consumption of portlandite through pozzolanic reactions facilitated by $Al^{3+}$ . XRD analysis of the 28-day samples showed a significant reduction in silica and portlandite peaks in the blended samples, correlating with the formation of ettringite, monosulphate, and C-S-H.
Microstructure (SEM): SEM imaging of the 10 ml SPA sample revealed a highly densified microstructure characterized by acicular (needle-like) ettringite crystals that were intimately interlocked within the C-S-H gel. This "micro-reinforcement" effect reduced capillary porosity compared to the more porous structure of the control sample.
Expansion: The SPA-blended cement exhibited lower expansion (9.7% at 5 days) compared to the control (11.4% at 7 days), suggesting improved dimensional stability.

Key Contributions and Significance
The study establishes that a saturated potash alum solution acts as an effective hydration activator for White Portland Cement. The primary contribution is the demonstration that the reactive release of $K^+$ , $Al^{3+}$ , and $SO_4^{2-}$ ions can synergistically enhance early-age strength and long-term durability without compromising the aesthetic whiteness of the cement.

The research claims that the SPA modification leads to:

Microstructural Densification: The formation of interlocking ettringite needles and increased C-S-H gel creates a refined pore structure.
Chemical Efficiency: The accelerated consumption of free lime and portlandite indicates a more complete hydration process.
Sustainability and Cost-Effectiveness: The method offers a low-cost, environmentally benign approach to producing high-performance cementitious composites. It utilizes readily available materials and avoids the use of corrosive or color-altering additives.

The authors conclude that this approach bridges a research gap regarding liquid-phase activators for WPC, providing a viable pathway for creating high-performance, eco-friendly cementitious materials suitable for precast architectural elements and decorative concrete.

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