Shreesh A Khadilkar outlines that by integrating controlled specialty additives at the manufacturing stage, cement plants can deliver consistent, high-performance concretes tailored to specific environmental and structural challenges.

The water repellent cement (PPC based) was first launched in the Indian market in 2013, The cement was developed by the ACC R&D team, the specialty of the cement was that during hydration the cement sand mortar / concrete the cement particles reacts with water and also repel the permeation of water even at early ages. The cement was developed using alkoxy /alkyl silanol based emulsions with an aqueous / oil based property. Subsequently from 2017/18 many different brands of such cements became available in the different markets of the country. These cements which possess the water repellent properties alike hydrophobic cements but these cements are not actually hydrophobic and do not float on the water. These cements react with the water to fill the pores and capillaries of the cement and reacts with the calcium hydroxide of cement to form a hydrophobic resin within the capillary pores of the concrete, significantly reducing water absorption and permeability.
These studies carried out to explore the potential benefits of the water repellent cement on the mortar and concrete properties by assessing the Water Permeability Tests, which affects the overall durability of concrete. The results demonstrated that the water repellent PPC cement (flyash based) substantially reduced water permeability by up to 70 per cent, compared to normal PPC and water sorptivity by up to 50 per cent in both mortar and concrete cubes due to improved impermeability of the concrete made with water repellent cement and its effect on the hydration mechanism. This water repellence effect achieved without compromising the properties of the cement like compressive strength, setting time, expansion etc. of the mortar and concrete, which remained similar to the normal PPC cement.
Through the use of similar special cement additions (with small tweaking of the additives) we could have a water repellent / permeability resistant PSC (Portland Slag Cement) and PCC (Portland flyash slag composite cements. Thus, this niche property of water repellence makes the resultant concretes more durable.

Biocidal cement
Biocidal cements prevent mold, bacteria, algae, and fungi from growing on or inside the concrete. Types of Biocidal Additives for Cement:

1. Silver-based biocides – Silver ions disrupt microbial cell membranes, kills bacteria/fungi. Best for: Hospitals, water tanks, sewage systems. Dosage: 0.1 per cent to 0.5 per cent by weight of cement (often pre-dispersed in powder or liquid).
   Pro: Long-lasting, broad-spectrum, non-toxic to humans at low doses. But Expensive, may stain concrete slightly.
2. Copper-based biocides – Copper ions inhibit enzyme activity in microbes. Best for: Marine structures, cooling towers, wastewater plants – Dosage: 0.2 per cent to 1.0 per cent (depends on environment). Very effective against algae and fungi, durable in wet conditions. However, it can accelerate corrosion of steel reinforcement need to e used with caution.
3. Zinc-based biocides – Interferes with microbial metabolism. Best for: Interior walls, plaster, stucco – Dosage: 0.5 per cent to 2.0 per cent it is odorless, non-staining, less effective in alkaline environments (cement is highly alkaline pH).
4. Quaternary ammonium compounds (Quats) – Disrupts cell membranes. Best for: Indoor concrete, flooring, sanitary areas – Dosage: 0.2 per cent to 0.8 per cent, Odorless, colorless, compatible with most admixtures, its use can reduce early strength if overdosed.
5. Titanium dioxide (TiO2) – Photocatalysts UV light activates TiO2 ? generates reactive oxygen species ? kills microbes + breaks down organic stains., – Best for: Exterior facades, pavements, self-cleaning concrete – Dosage: 1 per cent to –5 per cent (often nano-sized for better dispersion), self-cleaning, eco-friendly, long-term durability, needs UV light to work, less effective indoors.

Photocatalytic cement
Types of photocatalysts used:

1. Titanium dioxide (TiO2) – Most Common Form: Anatase (best photocatalytic activity), sometimes mixed with rutile for stability, Dosage: 2 per cent to 10 per cent by weight of cement (often 3 per cent to 5 per cent). Highly effective, non-toxic, stable, FDA-approved for food contact. The cement needs UV light (but newer versions work under visible light).
2. Zinc oxide (ZnO) – Pros: Works under visible light, antibacterial, UV- blocking, Cons: Less stable in high pH (cement is alkaline), can
   leach zinc.
3. Modified TiO2 (visible-light active) – Doped with metals (Ag, Cu, Fe), works under indoor/ambient light. Great for indoor applications (hospitals, offices).
   The Photocatalytic Cement react in presence of sunlight (UV or visible light) to break down organic and inorganic pollutants in the air and on the surface of cement, thus it results in self-cleaning walls, smog-eating streets, stain-resistant pavements.
   The mechanism of action is as follows:
4. Sunlight hits TiO2 excites electrons, creates electron-hole pairs.
5. Holes react with water, produce hydroxyl radicals (OH), super strong oxidisers.
6. Radicals attack organic dirt, bacteria, NOx, VOCs, soot breaks them down into harmless stuff like CO2, H2O, nitrates
7. Rain washes away residue ? surface stays clean!
   Where it can be used:
   Applications Benefits
   Façade Panels Self-cleaning, anti-algal and anti-fungal
   Roads and Side walks Reduces NOx pollution, stays white longer
   Tunnels and Bridges Cuts maintenance, improves visibility
   Parking Garages Less cleaning cost, healthier air
   Hospitals and Schools Reduces microbial load, improves IAQ

In a similar manner as above, we could have Cements with niche properties tailored to achieve specific performance in concretes.

Corrosion inhibiting cements
Types of corrosion inhibitors, which could be a part of the cements are:

1. Calcium nitrite based inhibitors – Dosage: 2 per cent to 4 per cent by weight of cement (often 10–30 L/m3), anodic inhibitor forms a protective oxide film on steel surface, blocks chloride ion attack. Works even in cracked concrete.
2. Organic compounds like amino alcohol based (e.g., triethanolamine, amino carboxylate) ? Phosphate-based ? Carboxylate based , less toxic than nitrites (some are non-hazardous) can be used in potable water structures for existing structures or low cover the cements would be applied as surface treatment or added to repair mortars the inhibitor component, migrates to steel, forms protective layer. The cements could have multifunctional combo additive, these additives also enhance the concrete performance besides the inhibition effect

ASR resistant cements
In certain regions of the country the aggregates available locally are reactive aggregates. For use of such aggregates, in say concrete road and other infra structural concretes the cements can be used, which would resist ASR reactions in resultant concrete, such cements could be either

1. Low alkali cement
2. PPC with class F flyash — 20 per cent to 30 per cent replacement or with ground granulated blast furnace slag (GGBS) — 40 per cent to
   60 per cent replacement , or use of 5 per cent silica fume or 10 per cent to 15 per cent Metakaolin (The SCMs bind the alkalis ad prevent
   ASR reaction)
3. Cements with lithium nitrate (LiNO3) — 0.5 per cent to 1.5 per cent by weight of cement Lithium ions compete with sodium/potassium ? suppresses formation of expansive gel, proven to stop ASR even in highly reactive system. Doesn’t affect strength or setting time significantly.
   Thus, depending on the additive used we could have shrinkage compensating cements, fragrant cements (cements with fragrance) etc.
   Lastly it could be stated here that having such cements with niche properties would have a consistent performance in concrete as these cements would be manufactured in plants, the active compound would be monitored and controlled effectively thus, the performance concrete would be ensured.

This is concluding part of the series.

About the author:
Shreesh Khadilkar, Consultant & Advisor, Former Director Quality & Product Development, ACC, a seasoned consultant and advisor, brings over
37 years of experience in cement manufacturing, having held leadership roles in R&D and product development at ACC Ltd. With deep expertise in innovative cement concepts, he is dedicated to sharing his knowledge and improving the performance of cement plants globally.