Economy & Market

Benefits of gypsum capping

Published

5 years ago

October 14, 2021

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Taiwan Capstone, the sole promoter of the new gypsum capping method, demonstrates to ICR how the technology works and why is it better than conventional methods.

The most important property of concrete for an engineer is its compressive strength. But are you testing for it in the right way? Several factors influence the measurement process. The flatness of the surface, its horizontal level does have a huge impact on the measurement outcome. To ensure that such anomalies are ruled out, conventionally the concrete specimen block is ground to get a flat surface. This method however, has several shortcomings and which can be overcome with the new gypsum capping method.

Capping is the process of leveling the ends of cylindrical concrete specimens to ensure that the test cylinder or core has smooth, parallel, uniform bearing surfaces that are perpendicular to the applied axial load during compressive strength testing. This is done to ensure that the specific criteria for flatness and perpendicularity of the ends are in accordance with the applicable standards specified.

Importance of capping

ASTM C39 requires that the ends of compressive test specimens be plane to within 0.002 inch (0.05 mm) and that the deviation of end faces from being perpendicular to the specimen axis is less than 0.5Â° (0.12 inch in 12 inches or 1 mm in 100 mm). Similar requirements are stated in ASTM C42 for testing cores. Irregular end surfaces or when the specimen axis is not perpendicular to the end-faces will cause stress concentrations within the test specimen and reduce the measured strength. Since the end-faces of most test specimens will not meet these requirements, procedures in ASTM C617 or C1231 for capping hardened concrete cylinders are used. This ensures that the compressive load is applied evenly and consistently for every strength test.

Capping process

ASTM C617 is the standard practice for capping cylindrical concrete specimen. Cores should be cut or ground to meet the end condition requirements or they may be capped in accordance with ASTM C617. Unbonded caps are currently not permitted when testing cores but may be permitted in the future. ASTM C617 permits a bonded cap to be applied to freshly molded cylinders using high strength gypsum plaster or sulfur mortar are permitted as bonded capping materials for hardened concrete cylinders.

Comparison

There are two ways to get the ends of the concrete specimen flat and horizontal. One is grinding the concrete surface and other is using capping material. Let’s review each one.

Grinding

Grinding is a very common and standard surface treatment method but the user must spend huge capital for the machine and also has to do periodic maintenance to ensure that ground surface remains evenly flat.

Capping material

There are three capping materials, which are qualified for this as per the IS 516 standard.

Neat cement.
Sulphur.
Hard plaster.

Those are also qualified in the ASTM C617 standard.

Neat cement capping

Mix the cement with water in the desired water-cement ratio. A two to four hour additional waiting time is required before it can be pasted on the concrete surface. The waiting period is important as the mixed pastes tend to bleed, shrink and make unacceptable caps.

Sulphur capping

Sulphur capping requires a heater for melting the capping material first. It also generates toxic gas and bad odour in the process. Sulphur capping needs two hours of hardening time before testing. For concrete strengths of 350 kg/cm2 or greater, sulphur caps must be allowed to harden for at least 16 hrs before use. Besides, sulphur caps cannot be reused.

Hard plaster capping

The strength of the plaster material is a critical property for its use as capping material. Ordinary plaster of Paris will not serve the purpose of the capping material due to its low compressive strength. Taiwan Capstone manufactures extraordinary high strength gypsum for use as capping material in concrete compression strength testing. Generally, the common gypsum hardens to with stand 1000 psi more or less. However, our products in the Capstone series can reach 5,000-9,000 psi (350-630 kgf/cm2), 30 minutes after mixing with water. It is fast, more efficient, highly reproducible, health friendly to the user, easy to stock, no costly apparatus needed and follows IS 516 Indian Standard and ASTM C617 regulation. There is another material which is also used in the concrete compressive strength test. It is Neoprene pad capping. The major advantage is the convenience. But often the test results are not completely reliable. The users have to prepare different types of caps for variety of concrete specimen.

Gypsum capping vs grinding

The two methods can be compared on the basis of following characteristics:

Surface flatness.
Pressure uniformity.
Sample applicability.

Surface flatness Gypsum

Gypsum shows better flatness after capping. The complete smooth surface is an outcome of the flowing gypsum slurry and the thick glass plate placed on it while the gypsum sets. After covered by the glass, the gypsum surface will become flat just like the glass surface on top of it.

Grinding

Grinding merely reveals the surface beneath the top with all its imperfections. In this process the concrete surface is treated by the grinding knife. It is difficult to get a completely smooth surface. Without the periodic maintenance, the knife frequently gets damaged and eventually leads to uneven concrete surface.

Pressure uniformity

Here, a pressure-sensitive paper is used to check the surface smoothness. As you can see from the diagram, there is a significant difference between the flatness of gypsum capped and ground surface.

Comparison of capping materials

If we compare gypsum capping, sulphur capping and the neoprene pad, it becomes obvious that gypsum has several advantages over the other two. It provides the best pressure uniformity and data accuracy. That is clear from the comparison chart below.

As the data shows, gypsum capping renders the surface extremely smooth and also makes it perfectly horizontal. Therefore, it can reach the highest compressive strength value and retain stable data at any time. From the operational point of view, gypsum only needs water for the reaction. It provides a safe working process and also increases the efficiency of the sample preparation. Sulfur has characteristics similar to those of gypsum for capping applications, but it takes a very long time to harden, with very bad odours and toxic gases let out during the process.

Neoprene pads have lower compressive strength and a higher SD value since they are often not perfectly horizontal. Furthermore, neoprene pads show higher and higher variation as the pads get reused. It is a convenient but inaccurate capping material.

Capstone compressive test data

Established in 1981, Taiwan Capstone is based in Taiwan and is the sole supplier of high strength gypsum for capping in the country. Sulfur capping is prohibited for safety reasons and rubber is banned by the market for the unstable performance.

They started their international business in April 2013 and since then, have expanded the market with competent local agent partners in India, Thailand, Singapore, Indonesia, USA, Mexico, Columbia, Canada and Israel. Now they are looking for more partners worldwide, to grow further. High-strength gypsum is absolutely the revolutionary capping material, especially considering its environment friendliness.

For more information, contact: Shailesh Chauhan Tel: 00-91-9377458606, E-mail: shailesh@itlneels.com Website: www.twcapstone.com

Economy & Market

TSR Will Define Which Cement Companies Win India’s Net-Zero Race

Published

4 days ago

April 27, 2026

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Jignesh Kundaria, Director and CEO, Fornnax Technology

India is simultaneously grappling with two crises: a mounting waste emergency and an urgent need to decarbonise its most carbon-intensive industries. The cement sector, the second-largest in the world and the backbone of the nation’s infrastructure ambitions, sits at the centre of both. It consumes enormous quantities of fossil fuel, and it has the technical capacity to consume something else entirely: the waste our cities cannot get rid of.

According to CPCB and NITI Aayog projections, India generates approximately 62.4 million tonnes of municipal solid waste annually, with that figure expected to reach 165 million tonnes by 2030. Much of this waste is energy-rich and non-recyclable. At the same time, cement kilns operate at material temperatures of approximately 1,450 degrees Celsius, with gas temperatures reaching 2,000 degrees. This high-temperature environment is ideal for co-processing, ensuring the complete thermal destruction of organic compounds without generating toxic residues. The physics are in our favour. The infrastructure is not.

Pre-processing is not the support act for co-processing. It is the main event. Get the particle size wrong, get the moisture wrong, get the calorific value wrong and your kiln thermal stability will suffer the consequences.

The Regulatory Push Is Real

The Solid Waste Management (SWM) Rules 2026 mandate that cement plants progressively replace solid fossil fuels with Refuse-Derived Fuel (RDF), starting at a 5 per cent baseline and scaling to 15 per cent within six years. NITI Aayog’s 2026 Roadmap for Cement Sector Decarbonisation targets 20 to 25 per cent Thermal Substitution Rate (TSR) by 2030. Beyond compliance, every tonne of coal replaced by RDF generates measurable carbon reductions which is monetisable under India’s emerging Carbon Credit Trading Scheme (CCTS). TSR is no longer a sustainability metric. It is a financial lever.

Yet our own field assessments across multiple Indian cement plants reveal a sobering reality: the primary barrier to scaling AFR adoption is not waste availability. It is the fragmented and under-engineered pre-processing ecosystem that sits between the waste and the kiln.

Why Indian Waste Is a Different Engineering Problem

Indian municipal solid waste is not the material that imported shredding equipment was designed for. Our waste streams frequently exceed 40 per cent to 50 per cent moisture content, particularly during monsoon cycles, saturated with abrasive inerts including sand, glass, and stone. Plants relying on imported OEM equipment face months of downtime awaiting proprietary spare parts. Machines built for segregated, low-moisture waste fail quickly and disrupt the entire pre-processing operation in Indian conditions.

The two most common failures we observe are what I call the biting teeth problem and the chewing teeth problem. Plants relying solely on a primary shredder reduce bulk waste to large fractions, but the output remains too coarse for stable kiln combustion. Others attempt to use a secondary shredder as a standalone unit without a primary stage to pre-size the feed, leading to catastrophic mechanical failure. When both stages are present but mismatched in throughput capacity, the system becomes a bottleneck. Achieving the 40 to 70 tonnes per hour required for meaningful coal displacement demands a precisely coordinated two-stage process.

Engineering a Made-in-India Answer

At Fornnax, our response to these challenges is grounded in one principle: Indian waste demands Indian engineering. Our systems are built around feedstock homogeneity, the holy grail of kiln stability. Consistent particle size and predictable calorific value are the foundation of stable kiln combustion. Without them, no TSR target is achievable at scale.

Our SR-MAX2500 Dual Shaft Primary Shredder (Hydraulic Drive) processes raw, baled, or loosely mixed MSW, C&I waste, bulky waste, and plastics, reducing them to approximately 150 mm fractions at throughputs of up to 40 tonnes per hour. The R-MAX 3300 Single Shaft Secondary Shredder (Hydraulic Drive), introduced in 2025, takes that primary output and produces RDF fractions in the 30 to 80 mm range at up to 30 tonnes per hour, specifically optimised for consistent kiln feeding. We have also introduced electric drive configurations under the SR-100 HD series, with capacities between 5 and 40 tonnes per hour, already operational at a leading Indian waste-processing facility.

Looking ahead, Fornnax is expanding its portfolio with the upcoming SR-MAX3600 Hydraulic Drive primary shredder at up to 70 tonnes per hour and the R-MAX2100 Hydraulic drive secondary shredder at up to 20 tonnes per hour, designed specifically for the large-scale throughput that higher TSR ambitions require.

The Investment Case Is Now

The 2070 Net-Zero target is not a distant goal for India’s cement sector. It starts today, with decisions being made on the plant floor.

The SWM Rules 2026 are already in effect, requiring cement plants to replace coal with RDF. Carbon credit markets are opening up, and coal prices are not going to get cheaper. Every tonne of coal a cement plant replaces with waste-derived fuel saves money on one side and generates carbon credit revenue on the other. Pre-processing infrastructure is no longer just a compliance requirement. It is a business investment with a measurable return.

The good news is that nothing is missing. The technology works. The waste is available in every Indian city. The government has provided the policy direction. The only thing standing between where the industry is today and where it needs to be is the commitment to build the right infrastructure.

The cement companies that move now will not just meet the regulations. They will be ahead of every competitor that waits.

About The Author

Jignesh Kundaria is the Director and CEO of Fornnax Technology. Over an experience spanning more than two decades in the recycling industry, he has established himself as one of India’s foremost voices on waste-to-fuel technology and alternative fuel infrastructure.

Concrete

WCA Welcomes SiloConnect as associate corporate member

Published

3 weeks ago

April 13, 2026

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The World Cement Association (WCA) has announced SiloConnect as its newest associate corporate member, expanding its network of technology providers supporting digitalisation in the cement industry. SiloConnect offers smart sensor technology that provides real-time visibility of cement inventory levels at customer silos, enabling producers to monitor stock remotely and plan deliveries more efficiently. The solution helps companies move from reactive to proactive logistics, improving delivery planning, operational efficiency and safety by reducing manual inspections. The technology is already used by major cement producers such as Holcim, Cemex and Heidelberg Materials and is deployed across more than 30 countries worldwide.

Concrete

TotalEnergies and Holcim Launch Floating Solar Plant in Belgium

Published

3 weeks ago

April 13, 2026

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TotalEnergies and Holcim have commissioned a floating solar power plant in Obourg, Belgium, built on a rehabilitated former chalk quarry that has been converted into a lake. The project has a generation capacity of 31 MW and produces around 30 GWh of renewable electricity annually, which will be used to power Holcim’s nearby industrial operations. The project is currently the largest floating solar installation in Europe dedicated entirely to industrial self-consumption. To ensure minimal impact on the surrounding landscape, more than 700 metres of horizontal directional drilling were used to connect the solar installation to the electrical substation. The project reflects ongoing collaboration between the two companies to support industrial decarbonisation through renewable energy solutions and innovative infrastructure development.