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Hence it is very essential during the concreting in cold weather conditions to ensure that the concrete will not undergo freezing in its plastic state.

There are two methods for carrying out cold weather concreting:

1. Provision of normal ambient temperatures for the concrete. This can be done through the heating of the concrete ingredients or bley providing heating enclosures.
2. The addition of chemical admixtures.

Conventional Chemical Admixtures in Cold Weather Concrete

 

Conventional concrete used calcium chloride as accelerating admixtures to offset the retarding effects of slow hydration of concrete in low temperatures. This admixture is not effective below the freezing temperatures.

This is found to be a drawback in the conventional form of admixtures. Hence, for arctic weather conditions, special admixtures are necessary. One such is antifreeze admixtures.
Antifreeze Admixtures for Concrete

The antifreeze admixtures affect the physical condition of the mix water used in the concreting. These can depress the freezing point of the water to a large extent and can be used in temperatures lesser than -30 degrees Celsius. This can enable the extension of the period of the construction activity.

Chemical Composition and Action of Antifreeze Admixtures

There are two groups of antifreeze admixtures that provide the characteristics of antifreeze and the accelerated setting and hardening properties.

They are:

1. First Group

This includes chemicals, weak electrolytes, sodium nitrite, sodium chloride and non-electrolytic organic compounds which lower the freezing point of the water used in the concrete. But these group acts as weak accelerators to promote the setting and hardening.

2. Second Group

These include binary as well as ternary admixtures which contains potash and additives based on calcium chloride, sodium nitrite, calcium chloride with sodium nitrite, calcium nitrite -nitrate-urea and other chemicals.

These have effective antifreeze properties and accelerating property to promote the setting and hardening. These are used in larger dosages compared to that of conventional admixtures.

One such example is the use of 8% of sodium nitrite to keep the liquid at a temperature of -15-degree Celsius.

These admixtures function by lowering the liquid phase freezing point and by accelerating the cement hydration at the freezing temperatures.

Based on the dosage in the mixture, the non-chloride admixture enables the mix (concrete or the mortar) to be placed at sub-freezing temperatures. This hence reduces the need of protective measures required during the cold weathering works.

The method improves the quality of the concrete and as it facilitates early setting, early stripping of formworks can also be carried out. This helps in the reuse of the form within a small duration and hence speed up the construction.

The table-1 shows the significant difference is strength gain at 3, 7 and 28 days for plain concrete and antifreeze admixture used concrete.

Table.1: Concrete Compressive strength with and without antifreeze admixture

 

(As per Ratinov and Rosenburg)

Property	Plain Concrete	Freeze-protection Admixture
Set time (-4 degree Celsius)	–	–
Compressive strength (MPa)
-4 degree Celsius (3 days)	3.4	9.24
-10 degree Celsius (7 days)	8.3	39.3
-10 degree Celsius (28 days)	18.1	49.9

It is possible for the incorporation of other admixtures that contains superplasticizers to be incorporated with the antifreeze admixtures. The main advantage of such combination is that in totality there will be a reduction of water.

The water reduction will reduce the freezable free water content in the mix. This freezable water content is the one that serves as the heat sink for the heat liberated by the initial hydration reactions. This will hence reduce the number of antifreeze admixtures.

Selection of Antifreeze admixtures

The factors based on which the selection of antifreeze admixtures is carried out are:

1. The type of structure
2. The operating Conditions
3. Protecting methods employed in winter concreting
4. Cement brand and aggregate types

A laboratory test must be carried out with the operating materials and the dosage of antifreeze admixtures that are intended to be used in the field.

The incorporation of other admixtures like retarders, superplasticizers with antifreeze admixtures is not restricted in cold weather concreting. The dosage of all the admixture that are used must be established experimentally.

Application and Advantages of Antifreeze admixtures

The antifreeze admixtures are technologically simple and beneficial for cold weather concreting. The admixture helps in improving the cohesiveness, cold joint minimizations, sand streaking, and plasticity. These are estimated to provide large cost saving than other methods of steam curing or concrete enclosures.

The combination of antifreeze agents with water reducing agents or air-entraining agents will help in increasing the resistance of concrete towards the frost action and corrosion.

All of us have seen heat sinks in one form or another, from the ones used in old desktop computers to the high-end specially engineered ones in power plants. Their purpose is to use Heat transfer through convection to help cool a certain high-temperature part or piece of equipment. What if these heat sinks could be used to solve an age-old problem of cooling homes? This is exactly what Miguel Nino and Johanna Navarro from Colombia aim to achieve. Their company named Smart Design and Architecture SAS has made several amazing designs to help cool the house with the help of bricks designed like heat sinks.

 

 

The  BT – Bloque Termodisipador Heatsink Brick as they are calling it is a clay brick designed with an irregular cross-section on the inside and a long angular face from the outside. The face makes it possible to deflect as much solar radiation as possible as it is the primary source of heat transfer from the Sun. The internal vent-type arrangement allows the brick to get rid of any kind of radiation converted into heat through natural convection. Additionally, the porous structure of these bricks allows the wind to pass through these bricks and create a cooling effect by helping in the dissipation of heat from the wall. They can also muffle sounds from the outside by deflecting and breaking up sound waves coming from the outside. So, it could work really well in an urban environment.

But, what I can think right now is that this kind of building will also create a strong cooling effect in winters. We know that in tropical areas and even in deserts, winters can become very cold. Would a structure made of these bricks continue to dissipate heat in the winters or do these Navarro and Nino have some counter measure for winters? I guess only they can answer that! Nevertheless, it is a great design that will help the thermodynamics of the house in hot countries and reduce needless power consumption that is associated with modern housing. 

 

This is the story of a small building in Ohio that was one of the first, if not the first, substantially green or high-performance buildings on a college campus. It spans the decade between 1995 and 2005. In that time, Americans impeached a president, balanced the federal budget and then unbalanced it again, witnessed the largest corporate bankruptcy ever, opted out of the Kyoto treaty, suffered a major terrorist attack, fought wars in the Balkans, Afghanistan, and Iraq, evacuated a major city, and became acutely aware of our vulnerability to malice, the forces of nature, and incompetence and malfeasance in high places. Ostensibly the story is about the art and science of ecological design, a specific building, a particular college, and education of the higher sort. But it is also a thread in the larger narrative of our time and the uncertain struggle to calibrate global civilization with the realities and limits of the biosphere. We are not faring particularly well in that effort and the stakes are rising. For Americans, with our SUVs, sprawling suburbs, and peculiar blend of manifest destiny, religiosity, militarism, and consumerism, larger connections are sometimes hard to see. Yet see them we must. We might have had an easier path to walk had we had the good sense to pay serious attention to the problems of energy, the environment, and security put before the public by the Carter administration in The Global 2000 Report (1980). Instead, we did the national equivalent of a quarter-century Australian walkabout, mostly ignoring energy efficiency, solar energy, the preservation of natural systems, and the national remodeling implied by the necessities of sustainability and resilience. Ronald Reagan’s “morning in America” is ending in the twilight of terrorism, war, debt, inequity, ecological decline, greater oil dependency, and national division some twenty-five years later. And we still have no adequate national strategy to move the nation toward energy efficiency and solar energy, preserve farmland and forests, restore our lakes and rivers, eliminate waste and pollution, and build a society secure by design, and hence little capacity to truly honor our children and their future. The story told here, however, is not so much about politics but about a college building and its wider implications.

Many sustainable design approaches and technologies are discussed in this versatile magazine.The international community has made great strides in sustainable endeavors throughout the past decade. Some might say that the U.S. has chased (and continues to chase) countries in Europe.

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