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Cold Weather Concreting 101

Cold Weather Concreting Is Possible When Certain Precautions Are Taken

Construction doesn’t stop–it’s a year-round industry. This means concrete mixes, pours and placements are needed all year and cannot come to a halt due to less-than-ideal weather conditions.

While concrete can be mixed and poured during the cold weather, there are many things to keep in mind which we plan to detail throughout this blog.

  • First, we’ll explain what can go wrong while pouring concrete in cold weather conditions.
  • Then, we’ll discuss how your ready mix provider can help you overcome the problems associated with cold weather concreting.
  • Finally, we’ll warn you of the mistakes we frequently see when it comes to cold weather concrete pouring and tips to avoid making those mistakes.  

Before we start, we feel it’s important to all get on the same page as to what exactly “cold weather” is considered.

The ACI or American Concrete Institute says in their ACI 306R-10 “Guide to Cold Weather Concreting that “cold weather exists when the air temperature has fallen to, or is expected to fall below 40℉ during the protection period*.” So if you find yourself grabbing a jacket on your way out the door, consider the air temperature before mixing, pouring, or placing concrete.

*The “protection period” is defined as the time required to prevent concrete from being affected by exposure to cold weather.

The Two Biggest Problems Cold Weather Concreting Creates

Now, there are two big problems you’ll face when pouring concrete in cold weather.

Problem #1

Concrete must be protected from freezing at an early age. If concrete freezes prior to reaching an initial strength of 500 psi it will not achieve its intended strength.

A general rule to keep in mind is that once the concrete has gained a strength of about 500 psi, it can withstand the effects of one freezing-and-thawing cycle. Exterior concrete should be air entrained and at the minimum required strength prior to exposure to multiple freezing-and-thawing cycles.

Problem #2

Concrete sets more slowly when it is cold but especially slow when temps are below 40℉. Below 40℉ the hydration reaction basically stops and the concrete will gain strength at a very slow rate.

To help your concrete reach that 500 psi strength ASAP, your ready-mix provider can add to (or change-up) the mix in ways that will get it to set more quickly. Those mix add-ins and changes are explained further below.

Mix adjustments alone can only do so much and its possible additional precautions are required to provide temporary heat prior to, during and after a concrete placement to aid in maintaining the concrete temperature once in place.

Mix Changes Your Ready-Mix Supplier Can Make To Help Your Cold Weather Concrete

Many of the problems experienced with cold weather concrete pouring can be overcome with an experienced ready-mix producer’s assistance. A concrete mix can be manipulated in ways that allow it to set and strengthen quickly.

  • Hot water – As temperatures get colder most producers can start using hot water in the mixing process when requested to meet a minimum placement temperature.
  • Slump – The slump required from any ready-mix is dependent on a variety of things. A slump that is less than 4 inches can reduce bleeding. Since the concrete sets slowly in the cold, bleeding starts later, lasts longer, and you’ll see more bleed water.
  • Accelerators – Accelerators keep setting on a somewhat predictable schedule. Often times you’ll see the use of calcium chloride to speed up the hydration reaction. But consider this–calcium chloride can lead to corrosion of any steel embedded in the concrete and it can lead to a streaked and spotted surface appearance with colored concretes.
  • Non-chloride accelerators – Non-chloride accelerators are readily available and must be used any time there are embedded metals such as reinforcing steel. Non-chloride accelerators are also appealing because they don’t discolor concrete.

*Please note that accelerators should not be considered antifreeze agents. They work to increase the rate of the hydration reaction–not prevent freezing.

  • Fly ash –  Fly ash or slag cement may cause the mix to set slower and generate less heat compared to a straight cement mix. Your ready-mix producer will have straight cement options available upon request.
  • More internal heat – To make the reaction hotter, mixes with higher cement contents can be requested. You may consider ordering a concrete that is one or two classes higher in strength. The use of Type III cement may also be an option based on availability which is typically limited to larger metropolitan areas. Your mix’s internal heat can be used to your advantage, and you’ll see why a little later on in this article.

A quality concrete mix design is crucial for success in construction. At Concrete Supply Co. we believe in our ready-mix designs and their ability to help you achieve a successful cold weather concrete placement.

Avoid These Common Mistakes with Cold Weather Concreting

1. Placing concrete on a frozen ground

measuring ground temp

Concrete should not be placed on ground that is frozen or covered with ice or snow as it will have an immediate and long-term impact on the performance of the concrete. A frozen or cold subgrade will slow the set by lowering the in place concrete temperature reducing the effect of the hot water and/or accelerating admixtures when used. Frozen ground may also settle once thawed leading to potential settlement cracks.

2. Allowing concrete to freeze

Think about it this way, water takes up more space in its ice phase than it does in its liquid phase. So when the water used in your mix freezes, it expands, causing damage to the concrete. Do what you can to ensure your pour sets fast enough to prevent freezing. Additional precautions to prevent the in place concrete from freezing may be needed during the protection period.

3. Not taking advantage of heating techniques (or using them incorrectly)

Many times, heating techniques are used to prevent concrete from freezing (mistake #2). When it comes to flatwork, the best way to protect concrete from the cold is to cover it with blankets after it’s been finished. This is where you should take advantage of the heat concrete generates on its own. Blankets will keep your concrete warm even if the temperature goes below 20℉. Use layers of blankets at corners and edges that could freeze.

If blankets aren’t enough, try laying heating blankets on top of the slab or using hydronic heating pipes to keep the slab from freezing.

Still not enough? Enclose and heat the air with a temporary enclosure. While this option comes with its own problems and can run a pretty penny, it is sometimes your only option if the concrete pour has to happen. Be especially careful when using fuel-fired heaters. If your enclosure isn’t properly ventilated, carbon dioxide can build up and react with the concrete, causing the surface to become weak and dusty.

These same blankets used to protect the in place concrete after the placement can also be used to prevent the subgrade from freezing the day or night before the placement providing a warmer subgrade leading to faster set times.

4. Using cold materials

Not only is it important to ensure your mix, the ground, and the air are warm enough, the materials (forms, embedments, and tools) you use for cold weather concrete pouring should also be above freezing and close to the delivered concrete temperature if possible.

At Concrete Supply Co., we have experience with all types of ready-mixes, even mixes that will stand up to freezing conditions. If you need to pour concrete this winter, download our Get The Best Mix For Your Project Concrete Checklist, and be sure to specify that you’ll be looking to pour your mix during cold temperatures.

And remember, concrete can be poured during cold weather and develop sufficient strength and durability to satisfy requirements when the proper precautions are taken. A mix that is properly proportioned, produced, placed, and protected will survive the cold weather.  

cold weather concrete site
2019-02-11T10:40:24+00:00

How CarbonCure Technology Is Taking The Concrete Industry From Gray To Green

The Impact CarbonCure Technology is Having on the Concrete Industry

Seven percent of the world’s carbon dioxide (CO2) emissions come from cement production. One US Government agency revealed that global cement production was responsible for about four billion pounds of CO2 emissions last year alone.

Cement is the primary–and most widely used–ingredient in concrete. As a result, these emissions are often blamed on the concrete industry.

The government endorsing environmental stewardship programs encourages architects and designers to reduce both the operational and embedded footprint of buildings. While this is a great step towards change, there’s still more that can be done! There are options for designers and architects that don’t just benefit the environment but the structure itself too. 

During a United Nations summit on Climate Change in 2007, Rob Niven saw a global need for less carbon emissions.

Rob Niven said, “The scientific community understands that CO2 can be chemically converted to a mineral within concrete. So why can’t we find a way to use CO2 in every-day concrete and help concrete producers respond to the demand for green building products?”

That same year, Rob Niven founded CarbonCure with a goal of reducing the carbon footprint of the concrete industry.

Today, CarbonCure is at the forefront of a movement to turn carbon dioxide into a valuable commodity–concrete!

The progress CarbonCure has made over the last ten years will change the concrete industry as we know it. We like to say, CarbonCure is taking the industry from gray to green–not literally, but definitely for the better!

How CarbonCure Recycles Co2 to Make Better Concrete

CO2 utilization is an innovative process in which industrial CO2 is captured and used to manufacture valuable products. CarbonCure is the only commercial CO2-utilisation technology currently serving the concrete sector.

CarbonCure’s CO2 utilization technology injects a precise dosage of carbon dioxide (generally between 1-5 fl oz/cwt is recommended) into ready-mix concrete and concrete masonry products, where it chemically converts into a mineral.

The use of CO2 in concrete shows no effect on the mix’s fresh properties–set-time, slump, workability, pump-ability, air content, temperature, and finishing. Or on the hardening properties of the mix–pH, freeze-that, density, color, texture, and durability.

Sourcing CO2

Sourcing CO2 is not the hard part. Third party gas suppliers collect CO2 from industrial emitters then purify, liquefy, and distribute it.

Ready-mix producers are able to store CO2 necessary for production at their plant in a refrigerated, pressurized tank which is refilled regularly by the gas supplier. When discharged, the CO2 is a mixture of gas and a solid white powder.

The Reaction

When CO2 is injected into a ready-mix, it reacts with calcium ions in the cement. Eventually this forms a nano-sized calcium carbonate mineral that becomes permanently embedded in the concrete.

This answers most people’s biggest question about CarbonCure: “Will the CO2 ever escape?” Once the CO2 is converted into a mineral, it cannot escape because it no longer exists.

This permanence is a huge sustainability advantage for CarbonCure technology. With almost all other applications, CO2 makes its way back into the atmosphere. CarbonCure will never be released into the atmosphere as a greenhouse gas.

As we said, the concrete industry’s future just went from gray to green!

See the reaction explained in the diagram below.

CarbonCure_ConcreteIndustry

The Green Future With CarbonCure

The CarbonCure vision is to “make the introduction of CO2 into concrete standard for all concrete production across the globe”.

A world in which CO2 is sourced from cement plants and used by concrete producers to create stronger and greener concrete is now the biggest goal.

The beneficial reuse of CO2 industry is expected to become a $1 trillion industry by the year 2030 according to The Global CO Initiative (GCI).

CO2 utilization products for the concrete sector alone have the potential to reduce up to 1.4 gigatonnes of annual CO2 emissions by 2031. A greener concrete industry is possible.

Concrete Supply Co. is onboard with the change CarbonCure is helping the concrete industry achieve, now what about you? CarbonCure provides FAQ pages to answer all of your questions–whether you are a contractor, engineer, or designer.

Is being eco-friendly a concern of yours when ordering a ready-mix from your supplier? Check sustainability on our Concrete Checklist: Get The Best Ready-mix For Your Project, and plan to use CarbonCure technology with your next mix.

carbon cure technology
2019-02-18T15:59:43+00:00

Concrete Basics: Essential Ingredients For A Concrete Mixture

Concrete is and has been for thousands of years, a very popular building material.

Made up of just a few basic ingredients, concrete is the most widely used man-made material on the planet. Humans use more concrete than all other building materials combined.

So what is concrete exactly?

What goes into the most commonly used building material?

Concrete is a mixture of cement, air, water, sand, and gravel–it’s as simple as that!

Not exactly. The typical concrete mix is made up of roughly 10% cement, 20% air and water, 30% sand, and 40% gravel. This is called the 10-20-30-40 Rule–though proportions may vary depending on the type of cement and other factors.

Now let’s discuss each ingredient and the important role they play in your mix.

Concrete mix ingredients and their important roles:

Cement

Though cement makes up the smallest percentage of the mixture, it’s an essential ingredient in concrete. Cement serves as the glue that keeps everything else together. It’s also what allows the ready mix to harden once it’s placed. There are five different types of cement depending on what kind of concrete you’re looking to make:

  • Type I is used for most residential work
  • Type II is used in moderate sulfate conditions
  • Type III is used in climates where freezing is a risk
  • Type IV is used for special orders like industrial placements
  • Type V is used in extreme sulfate conditions

Types I and II are the most widely used residentially in the United States due to the relatively moderate climates we experience here.

Air and Water

For a mixture to be effective, some amount of air entrainment (tiny air bubbles) is needed in the concrete. Air-entrained cement ensures that excess water has a chance to expand when it moves through the freeze-thaw cycle. These air bubbles, however, must be microscopically small or else the ‘entrained’ air will turn into ‘entrapped’ air which leads to shrinkage and cracking.

Amongst all of the other essential ingredients involved in creating a mixture, water tends to have the largest impact. As a rule of thumb, the more water that you put into the mixture, the less strength the hardened mixture will have. Shrinkage and cracking are also probable when too much water is involved. Excess water will eventually evaporate out of the hardened concrete, causing the concrete to shrink and eventually crack.

An ideal amount of water can be measured by water to cement ratio, which should vary between .4 and .6. The higher the ratio, the weaker the concrete. A good way to test the solubility of your concrete is to perform a slump test. This will help to determine whether or not your mixture contains too much water.  

Gravel and Sand

As you can see, gravel and sand aggregates make up about 70% of the mixture. This high percentage makes the mixture more economical–as gravel and sand are both stronger and more cost-effective than the cement. A good ready mix will include proportionate amounts of both large (gravel) and small (sand).

The reason for this is that the gravel makes up the majority of the ready-mix and the smaller sand particles do a good job of filling in any extra spots that could otherwise be filled by unwanted air pockets.

Well there you have it, the ingredients that combine to create the most widely used building material in the world–concrete. As you can see, each ingredient and its ratio impacts the final ready mix’s quality and type. It’s important that you get the best ready mix for your specific job. That’s why we’ve created this Ready Mix Checklist to help you and your ready mix supplier create just what you need. Download your Ready Mix Checklist now.

Concrete supply co mixing truck in front of plant
2019-02-11T10:32:10+00:00

The Importance of Concrete Mix Design

Why a good ready-mix concrete design is necessary

A good concrete mix design creates the foundation of a sound infrastructure.

Concrete mix design involves a process of preparation in which a mix of ingredients creates the required strength and durability for the concrete structure. Because every ingredient in the mix consists of different properties, it’s not an easy task to create a great concrete mix. It is imperative that all ingredients be tested to determine their physical properties and the bearing capacity of the project location.

The ingredients to be tested: water, fine aggregate (sand), coarse aggregate, cement, chemicals, reinforcement, and soil.

The values of the physical properties obtained after testing will be used as the basis for all concrete mix design considerations. This will ensure the structure will be sound and prevent failure of the mix. It is important to note that the ingredients for the mix might vary from one project location to another, so the physical properties must be tested for the requirements specified for each location.

Types of concrete mix

The two types of concrete mix are normal performance concrete and high-performance concrete, and they’re characterized by their compressive strength:

Normal Performance Concrete

A normal performance concrete mix has a performance strength ranging between 20 and 40 MPa. It is the more used mix of the two. Normal performance concrete has good workability if all of the mix ingredients are in accurate proportions. When freshly mixed, the concrete must be plastic or semi-fluid so that it can be molded.

High-Performance Concrete

A high-performance concrete mix has a performance strength above 40 MPa. The main purpose of using high-performance concrete is to reduce the weight, creep or permeability issues, and to improve the durability of the structure. Like the normal performance concrete mix, this mix must be plastic or semi-fluid when freshly mixed so that it can be molded.

Because high-performance concrete has a high cement content, it is often sticky and hard to be handled and placed. However, this does not cause the cement to bleed, an issue that normal performance concrete might run into.

Factors affecting concrete mix design

Strength and durability of the concrete mix design are dependent upon the following factors:

Grade designation: Concrete’s strength is measured in N/mm2 when subject to test after curing in any curing medium. The choice of concrete grade depends on its usage.

Choice of cement: Cement choice varies depending on usage. The cement should be tested for performance required by their usage before being tested in the design mix.

Choice of aggregate size: Aggregates needed for each mix is dependent upon the physical properties needed for the design. All aggregates must be quality sized before use.

Type of water: Any water used for concrete mix design should be tested before use to ensure it is within the range of water required for concrete. Most all consumable water is good for concrete work, but should still be tested.

Water to cement ratio: The ratio of water to cement should be tested for consistency, initial and final setting, soundness of the cement, workability, slump of the concrete and compacting factor.

Workability: This is the measure of ease of mixing concrete without segregation or bleeding. It mostly depends on the designed slump of the concrete.

Durability: This is the measure of the required strength (N/mm2) of any concrete grade after 28 days of curing. Durability should be control tested on site.

A quality concrete mix design is crucial for successful construction. At Concrete Supply Co., we sleep better at night knowing our end-to-end ready mix concrete solution meets the highest quality performance in concrete, and our integrity in doing so is unparalleled.

We offer a guide to help you find your perfect read mix. If durability and quality are what you’re looking for in a concrete mix, take a look at our guide and we’ll be sure to help you create the best mix for your project. 

Contact us if you’re in need of a supplier or if you have questions about our mixes.

concrete supply mixing plant
2019-02-11T10:29:36+00:00