Concrete

Making Concrete in Cold Conditions

Published

8 years ago

February 28, 2017

admin

Cold weather is defined as a period when the average daily temperature falls below 4?C for more than three successive days. These conditions warrant special precautions when placing, finishing, curing and protecting concrete.

Concrete production always faces a problem during cold weather. There are two main problems associated with cold weather. The general rule is that the concrete has to gain strength till about 500 psi (35 kg per cm2).

Concrete can freeze before it gains strength which breaks up the matrix;
Concrete sets more slowly when it is cold – very slow below 6? C; below 4? C, the hydration reaction basically stops and the concrete doesn’t gain strength.
But these are concrete temperatures, not air temperatures. So when it’s cold, the concrete has to be protected until it can handle the cold on its own. The general rule is that the concrete has to gain strength till about 500 psi (35 kg per cm2). Almost the same time that the concrete achieves 500 psi compressive strength, hydration of the cement consumes enough of the water in the original mix so that even if it does freeze, there’s not enough water left in the pores to damage the concrete. With most concrete, even at 6?C, this happens during the second day.

To help it reach that 500 psi strength, the mix can then be changed to get it to set more quickly or protect the concrete from the cold – or more likely do both.

Changes to Concrete Mix during Cold Weather
Many of the problems with cold weather can be overcome by the ready mix producer. Here are a few things to keep in mind:
Hot water: A ready mixed concrete producer will usually have, and use, hot water in the concrete when the weather turns cold. Most producers will try to have the concrete be at least 180C when it leaves the plant, which is generally good enough depending on air temperature and thickness of the concrete element. The slump has to be specified at less than 100 mm and air-entrained concrete should be used to reduce bleeding.

Accelerators: Since colder weather leads to colder concrete, the set time can be delayed. Accelerators added to the concrete can keep it on schedule. Addition of 2 per cent (by weight of cement) of calcium chloride is the traditional way to accelerate the hydration reaction – it is very effective and reasonably cheap. But – a big but -that much chloride can lead to corrosion of any steel embedded in the concrete (like rebar) and can lead to a mottled surface appearance with coloured concrete.

Non-chloride accelerators are also widely available and are very effective. They won’t discolour the concrete, but they are a bit expensive. Accelerators are not anti-freeze agents – they simply increase the rate of the hydration reaction.

Fly ash: Producers should typically stay away from using fly ash or slag cement in cold weather, since those materials set more slowly and generate less internal heat; slag can cause the same effect.

To make the reaction a bit hotter, the ready mix producer can add some extra cement (typically 60 kg per cubic metre) or can use Type III (high-early strength) cement, which hydrates more rapidly.

Producers have to be careful with water reducers in cold weather, since they can slow the set time. Besides, cooler concrete seldom needs water reduction since the cooler temperatures prevent slump loss. For admixtures added at the job site, they shouldn’t be used if they have frozen. The chemicals may have separated.

Precautions before Placing Concrete in the Cold
When cold weather comes on unexpectedly, the following tips will help:
Frozen ground: Concrete should be never placed on frozen ground or onto ice or snow. There are a couple of problems with this. First, frozen ground will settle when it thaws, cracking the concrete. Second, when the ground is cold, the concrete in contact with it will be cold and will set more slowly. Crusting might also occur, with the top part of the concrete set and the bottom still soft. If the ground is frozen, it can be thawed using hydronic heat pipes and blankets (such as those from ground heaters), or electric blankets.

Anything that will come in contact with the concrete should be warmed up, including forms and any embedment, to at least 00C. If it’s not too cold and everything is covered with tarps the day before the pour, it will stay dry and warm enough.

Concrete

Ador Welding Limited and Ador Fontech announce merger completion as a strategic move towards strengthening Global Leadership in Welding Solutions

Published

3 days ago

October 18, 2024

Roshna

Ador Welding Limited, India’s leading manufacturer of welding products announced the merger completion of Ador Fontech Limited with Ador Welding Limited. The merger will facilitate the creation of a more efficient and integrated business structure with an aim to consolidate the company’s market position, expand its domestic and international reach, and foster stronger research and development capabilities. The operating management teams of both companies will remain the same.

Aditya Malkani, Managing Director of Ador Welding Limited shares “We are excited about the potential opportunities that this merger presents. It will enable us to leverage the benefits of scale, revenue and cost synergies, cross sell combining the customer base, and tap into best practices from both organisations. With this, we are poised to expand our product and service offerings to our customers and accelerate our growth in both domestic and international markets. Most importantly, with our combined strengths, including a stronger manufacturing presence and a more resilient workforce, we are better equipped to Make, Research & Create in India.”

Following the merger, J B Advani and Co Pvt Ltd (JBA) will hold 44.83% of the shares, other promoters will hold 8.24%, and the public will hold 46.93%. Ador also plans to restructure its divisions to focus on two distinct verticals – Products and Services. This will enable the company to optimise its operations and better serve the diverse needs of its customers.

With its origin and base in India as the quintessential ‘Make in India’ brand, Ador has created an indelible global footprint by providing exceptional, cutting-edge welding solutions. With a rich experience of over seven decades, the company has been dedicated to creating the best welding experience for its customers, investing in people, technology, research and development.

Having made great strides in R&D and innovation, Ador’s Research and Development Center is recognised by the Department of Scientific and Industrial Research and has developed groundbreaking solutions such as the Rhino E, India’s first battery-powered electric welder. Ador’s dedication to excellence is reflected in its numerous international awards and research papers which have been presented at many international forums.

Concrete

Festive optimism

Published

4 days ago

October 17, 2024

admin

As we transition into the festive season, it is crucial to take stock of the current state of India’s key infrastructure sector. August saw a 1.8 per cent contraction, largely attributed to excessive rainfall in many parts of the country, impacting several industries, including cement. The cement sector registered a 3 per cent decline in August 2024, compared to the same period last year, which had seen robust growth of 19.7 per cent, leading to what analysts call a high base effect, as per news reports. Despite this, there remains optimism as we approach the latter part of the year, with industry players anticipating demand revival by the end of Q3.
The evolving dynamics of the cement industry paint an interesting picture. Once dominated by regional and local players, the market has seen significant consolidation, with large companies taking the lead. These larger corporations, with their extensive reach and deep pockets, are strategically shifting focus toward non-trade segments, specifically targeting bulk buyers such as large contractors and infrastructure projects. This shift underscores the importance of India’s infrastructure-led growth focus, further solidified by government-backed projects.
However, the road ahead isn’t without challenges. While non-trade demand is expected to rise after the monsoon, it brings the dilemma of lower margins, potentially putting pressure on cement prices. We witnessed a price hike of Rs.10-20 per bag across regions in August, with more hikes expected in October, ranging from `5-15. Yet, there is uncertainty about whether these increases will hold, especially as market dynamics continue to evolve.
As we celebrate Diwali, I wish all our readers prosperity and success in navigating these changing tides. The coming months will be pivotal, and we look forward to a promising revival across the sector.

Concrete

Holcim for decarbonisation

Published

4 days ago

October 17, 2024

admin

Holcim has invested in Sublime Systems to expand its range of solutions to decarbonise the construction industry. The partnership will advance Sublime’s first commercial manufacturing facility in Massachusetts, US, giving Holcim a large share of Sublime Cement produced there through a binding offtake reservation. Sublime’s first commercial-scale plant is set to start production in 2026 with a capacity of 30,000t/yr.