Concrete Curing Time

Waiting for the curing of concrete can easily test patience, especially when you’re ready to move on to the next step of a project. However, it’s important to remember that quality is the end goal, not quickness. Rushing ahead and not allowing enough time for concrete to properly cure before allowing foot traffic or heavy machinery to travel across your newly placed cement can seriously compromise the integrity of a concrete slab.

 

Cement Curing Factors

Several factors influence concrete slab cure time, including:

 

Typical Concrete Setting Time

Typically, concrete is recognized to have reached full strength 28 days after placement; however, this does not mean you need to wait 28 days to walk, or even continue construction on newly placed concrete. After placement, concrete increases in strength very quickly for 3-7 days, then gradually for the next 3 weeks. This means that concrete hardening time is typically 24-48 hours, at which point it’s safe for normal foot traffic. After one week, concrete is typically cured enough to handle continued construction including heavy machinery.

The “70 in 7” Rule

When in doubt, remember the “70 in 7” rule: Most concrete mixes will have reached 70% of specified compressive strength after 7 days. At this point, it’s ready for exposure to normal traffic.

Concrete Curing Blankets

Unfortunately, cold weather during winter months can seriously slow down concrete cure time and significantly hold up construction projects. Luckily, solutions, such as concrete curing blankets that maintain optimum temperatures during cure time, are available. Concrete Blankets are an effective option that cure concrete 2.8 times faster than a typical insulated blanket and properly maintain moisture throughout the hydrating process. Concrete Blankets are easily transported and installed and maintain ACI compliance for cold-weather concreting. If you’re looking for a solution to maintaining optimum concrete cure time during cold winter

How Cold is Too Cold to Pour Concrete?

What Temperature is Too Cold to Pour Concrete?

Experts agree that the best temperature to pour concrete is between 50-60 °F. The necessary chemical reactions that set and strengthen concrete slow significantly below 50 °F and are almost non-existent below 40 °F. Even when daytime temperatures are within the satisfactory range, winter concrete setting creates risks that could result in weak, inadequate concrete. If nighttime temperatures are below freezing, the water in the concrete will freeze and expand, causing cracks. Additionally, if temperatures reach below 40 °F (but not freezing) during set time, concrete will take much longer to reach required strength. However, if the correct measures are taken, concrete can still be successfully placed during even the coldest months of the year.

Things to Consider with Cold Weather Concreting

Before embarking on a cold weather concrete project, it’s important to determine any special strength requirements or considerations. This will help as you schedule your pouring and determine which strategies you will use to keep your surroundings and materials warm. The predominant challenge you will face during a winter concrete project is ensuring that the concrete sets before it is exposed to freezing temperatures. You might take the following suggestions into consideration as you plan your upcoming project:

  • Use heaters to thaw frozen ground, snow or ice.
  • Use hot water to mix cement.
  • Keep dry materials in a dry, warm location.
  • Use products designed to set quickly. During cold weather, these products will not set as quickly as the instructions may indicate, but will set faster than conventional materials.
  • Use additives that accelerate set time. Use caution; if additives contain calcium chloride, any rebar or metal wire mesh in concrete will rust and cause concrete to crack.
  • Use extra cement (typically 100 lb/ cubic yard) to make the reaction hotter and cause concrete to hydrate more rapidly.
  • Remember that you still need to wait for bleed water to evaporate. Incorporating the water into the surface during finishing will weaken the surface. Bleeding starts later and takes longer during cold weather; you can use squeegees or a vacuum to remove water quickly.
  • Wait until concrete has reached desired strength to remove any framework. If the framework is removed too early, the concrete will be damaged and the surface could collapse.

Maintaining Ideal Temperature

After implementing the above suggestions, It’s important to consider how you will keep concrete at the correct temperature during the curing process. Concrete must maintain a temperature above 50 °F for approximately 48 hours for the correct chemical reactions to take place. Two popular options used during cold weather concrete curing are heated enclosures and insulated blankets. If using an enclosure, ensure that the structure is both wind and waterproof. Additionally, ensure that there is proper ventilation for the space heater. Heaters cause an increase in carbon dioxide that could cause carbonation in the surface of the concrete.

Powerblanket Concrete Blankets

Powerblanket® concrete blankets are an extremely effective option for attaining and maintaining the correct temperatures for concrete pouring and setting. Powerblanket® concrete blankets can be used to thaw ground before pouring concrete and again after finishing to keep concrete from freezing. Utilizing Powerblanket® concrete blankets will ensure that concrete is kept at the correct temperature for the necessary reactions to happen quickly and the desired strength to be reached.

What Temperature is Too Cold to Pour Concrete?

What Temperature is Too Cold to Pour Concrete?
What Temperature is Too Cold to Pour Concrete?

What Temperature is Too Cold to Pour Concrete?

Experts agree that the best temperature to pour concrete is between 50-60 °F. The necessary chemical reactions that set and strengthen concrete slow significantly below 50 °F and are almost non-existent below 40 °F. Even when daytime temperatures are within the satisfactory range, winter concrete setting creates risks that could result in weak, inadequate concrete. If nighttime temperatures are below freezing, the water in the concrete will freeze and expand, causing cracks. Additionally, if temperatures reach below 40 °F (but not freezing) during set time, concrete will take much longer to reach required strength. However, if the correct measures are taken, concrete can still be successfully placed during even the coldest months of the year.

Before embarking on a cold weather concrete project, it’s important to determine any special strength requirements or considerations. This will help as you schedule your pouring and determine which strategies you will use to keep your surroundings and materials warm. The predominant challenge you will face during a winter concrete project is ensuring that the concrete sets before it is exposed to freezing temperatures. You might take the following suggestions into consideration as you plan your upcoming project:

  • Use heaters to thaw frozen ground, snow or ice.
  • Use hot water to mix cement.
  • Keep dry materials in a dry, warm location.
  • Use products designed to set quickly. During cold weather, these products will not set as quickly as the instructions may indicate, but will set faster than conventional materials.
  • Use additives that accelerate set time. Use caution; if additives contain calcium chloride, any rebar or metal wire mesh in concrete will rust and cause concrete to crack.
  • Use extra cement (typically 100 lb/ cubic yard) to make the reaction hotter and cause concrete to hydrate more rapidly.
  • Remember that you still need to wait for bleed water to evaporate. Incorporating the water into the surface during finishing will weaken the surface. Bleeding starts later and takes longer during cold weather; you can use squeegees or a vacuum to remove water quickly.
  • Wait until concrete has reached desired strength to remove any framework. If the framework is removed too early, the concrete will be damaged and the surface could collapse.

After implementing the above suggestions, It’s important to consider how you will keep concrete at the correct temperature during the curing process. Concrete must maintain a temperature above 50 °F for approximately 48 hours for the correct chemical reactions to take place. Two popular options used during cold weather concrete curing are heated enclosures and insulated blankets. If using an enclosure, ensure that the structure is both wind and waterproof. Additionally, ensure that there is proper ventilation for the space heater. Heaters cause an increase in carbon dioxide that could cause carbonation in the surface of the concrete.

Powerblanket® concrete blankets are an extremely effective option for attaining and maintaining the correct temperatures for concrete pouring and setting. Powerblanket® concrete blankets can be used to thaw ground before pouring concrete and again after finishing to keep concrete from freezing. Utilizing Powerblanket concrete blankets will ensure that concrete is kept at the correct temperature for the necessary reactions to happen quickly and the desired strength to be reached. With Powerblanket, it’s almost never too cold to pour concrete!

Compressed Gas Sizes

How long does concrete take to set

How long does concrete take to set?

If you really want to know the truth, concrete never stops curing; it continually hardens forever.  However, for practical purposes, it reaches a point where further hardening will be so slow it becomes unnoticeable.  In this article, we cover the basics of what you need to know about “how long does concrete take to set.”

 

Concrete Never Stops Curinghow long does it take concrete to set

The continual hardening occurs because cement particles react with the water in the mix (hydration), and as long as cement is in contact with moisture, even miniscule bubbles, it will continue to form bonds.  This is minimal after “full strength” is achieved, but it is continual.  

 

Curing Time for Concrete

In standard industrial cases, full strength concrete is recognized at 28 days.  At seven days, you should have concrete that is cured to 70% full strength or greater.  But to answer the question of, “How long does concrete take to set?”, concrete setting time is generally 24 to 48 hours.  At this point the neighborhood dog will not leave his footprints in it, but you should keep it clear of heavy equipment during this time period. Most mixes are cured at 28 days.

 

Factors Affecting Concrete Setting Time

  • Moisture plays a critical role in curing time for concrete.  If there is not sufficient water in the mix, the concrete will cure too fast, resulting in weaker overall strength.  Too much moisture, often used in the finishing step will weaken the top layer and cause flaking.
  • Hot ambient temperatures and wind accelerate the evaporation of moisture–speeding concrete setting time.
  • The mix design has a lot to do with concrete setting time.  Some jobs will require accelerants because the area needs to be usable as soon as possible.  The accelerant will do its job and speed up the concrete setting time.  Accelerant mixes will show a weaker overall strength in the end, but will still meet strength requirements.

 

Powerblanket Concrete Blankets

If you are wondering about how long does concrete take to set, Powerblanket has a solution for your concrete setting needs.  If you are dealing with HOT conditions and your concrete setting too quickly, consider Powerblanket ICE.

Powerblanket ICE is portable cooling equipment that will keep newly poured concrete safe from heat, regulating concrete setting time in both regular and hot conditions.

The Powerblanket ICE Circulation Blanket is combined with either a cooler or chiller to achieve optimum results. The Circulation Blanket draws heat to the blanket in order to cool the concrete.

  • Use Powerblanket’s patented heat-spreading technology in reverse–the cooling blanket draws heat away and lowers the temperature of the concrete.
  • Take it with you on every jog.  It is easily portable.
  • Blanket cover and insulation are the same as the robust system used in Powerblanket heating products
  • Control the curing speed of newly poured concrete even in hot conditions

If conditions are cold, Powerblanket concrete curing blankets provide a manageable way to cure concrete effectively and confidently. Powerblanket curing blankets increase production by rapidly curing with consistent, even heat.

  •  Cure concrete 2.8 times faster than conventional, insulated blankets
  •  Maintain moisture throughout hydrating process
  •  Easily installed and removed
  •  Produce cold weather concreting strength of up to 3,925 psi in 72 hours
  •  Prevent a freeze cycle
  •  Thaw ground and frost from job site before you pour
  •  Reduce downtime & increase profitability
  •  Maintain ACI compliance for cold weather concreting

Powerblanket ICE

 

Concrete Curing Temperature Makes a Difference

How Warm Does it Have To Be To Pour Concrete?

Whether the conditions are hot or freezing, the ideal concrete curing temperature should be maintained at about 55°F to achieve the optimum concrete strength.

Curing the Hoover Dam

At its completion in 1935, the Hoover Dam was the largest dam in the world and a marvel of labor and engineering.  The first pour began on June 6, 1933. Rather than being a single block of concrete, they built the dam as a series of individual columns. The trapezoidal columns rose in five foot lifts. This method allowed the tremendous heat produced by the curing concrete to dissipate. If the dam were built in a single continuous pour, the concrete would have gotten so hot that it would have taken 125 years for the concrete to cool to ambient temperatures. The resulting stresses would have caused the dam to crack and crumble away (The Story).  

The heat and dryness of Nevada posed additional complex problems with the pour and concrete curing temperature.  When the concrete was first poured, river water circulated through cooling coils of 1″ thin-walled steel pipes. Once the concrete had received a first initial cooling, chilled water from a refrigeration plant on the lower cofferdam circulated through the coils to finish the cooling (The Story).

Concrete Curing is an Art

We live in a world where faster always seems better; however, concrete that cures too quickly or under hot concrete curing conditions can actually result in weak or unstable concrete.  If concrete is cured in cooler ambient  temperatures (32°F to 50°F) with moisture continually present, strength gain will be slow but the concrete will eventually reach a high strength. Concrete should not be allowed to get hotter than 90°F or to dry out during the curing period.

Best Concrete Curing Temperature

By “best” we mean “most thoroughly,” not the fastest.  High temperatures mean faster curing, but fast curing equates to weaker strength in the end.  The following study by Paul Klieger in the Portland Cement Association Research Bulletin 103 illustrates this concept.

concrete cure time chart with concrete curing temperature

Concrete Cure Time Chart with Temperature

At an age of 1 day the 120°F concrete was strongest and the 25°F concrete was weakest. By 7 days the high-temperature cured concretes had no more strength than the 73°F concrete or even less. By the age of 28 days the high-temperature concretes were weaker than the 73°F concrete. From 28 days to 1 year the 55°F concrete was considerably stronger than the 73°F concrete. All of this suggests that, provided there is continuous curing, concrete cured at about 55°F for the first 28 days ultimately reaches the highest strength (Concrete).

Hot Weather Concrete Temperature Limits

Hot weather concreting doesn’t simply involve temperature.  High ambient temperatures, winds, and relative humidity all play a role in “hot weather.”  Under hot heather conditions, the primary curing issue is having the top of the slab of concrete dry much faster than the bottom. As concrete dries it shrinks. This means that the top will be shrinking while the bottom is not. This creates internal problems with the concrete that will result in a damaged slab. The top and the bottom of the pour need to cure at the same rate (Placing).

Concrete Curing Temperature Solutions

Is it too HOT?

Powerblanket ICE is portable cooling equipment that will keep newly poured concrete safe from heat.  Portable, insulated, and efficient, Powerblanket ICE effectively regulates the temperature of concrete under both regular and hot conditions.

The Powerblanket ICE Circulation Blanket is combined with either a cooler or chiller to achieve optimum results. The Circulation Blanket draws heat to the blanket in order to cool the concrete.

  • Use Powerblanket’s patented heat-spreading technology in reverse–the cooling blanket draws heat away and lowers the temperature of the concrete.
  • Blanket cover and insulation are the same as the robust system used in Powerblanket heating products
  • Portable
  • Control the curing speed of newly poured concrete even in hot conditions

Is it too COLD?

Powerblanket concrete curing blankets provide a manageable way to cure concrete effectively and confidently in the cold weather months. Even in warm weather, Powerblanket curing blankets increase production by rapidly curing with consistent, even heat.

  •   Cure concrete 2.8 times faster than conventional, insulated blankets
  •   Produce cold weather concreting strength of up to 3,925 psi in 72 hours
  •   Maintain moisture throughout hydrating process
  •   Easily installed and removed
  •   Prevent a freeze cycle
  •   Thaw ground and frost from job site prior to pour
  •   Reduce downtime & increase profitability
  •   Maintain ACI compliance for cold weather concreting

 

Concrete Curing Temperature

Works Cited

Concrete Construction Staff.  “Best Curing Temperatures”. Concrete Construction Magazine. 16 May 2017. http://www.concreteconstruction.net/how-to/best-curing-temperatures_o

“Placing Concrete in hot or cold weather”. Sakrete Blog. 16 May 2017. http://www.sakrete.com/media-center/blog-detail.cfm/bp_alias/Placing-Concrete-in-hot-or-cold-weather

“The Story of Hoover Dam – Essays”. Bureau of Reclamation. 16 May 2017. https://www.usbr.gov/lc/hooverdam/history/essays/concrete.html

 

Hot Weather Concreting Made Easier

Hot Weather ConcretingHot weather concreting

Hot weather concreting problems are most often encountered in the summer; however, any condition that increases curing rates and strips the concrete of moisture is considered hot weather concreting.

Pouring Concrete in Hot Weather

With temperatures rising and summer approaching, attentions shift from protecting concrete from the cold to concreting in hot conditions.  When pouring concrete in hot weather, special procedures should be followed for proper mixing, placing, finishing, and curing.  High ambient temperatures, high concrete temperatures, low relative humidity, and/or high winds impair the quality of freshly mixed and recently placed concrete (Hot).  Pouring concrete in hot weather affects laboratory test results, showing that higher temperatures affect the compressive strength gain of hardened concrete. Even though concrete poured in hot weather will produce higher early strength but as time goes by, the ultimate strength will be lower than expected (Rodriguez).

Water Loss

Hot weather concreting causes increased setting rates and rapid water loss.  Shrinkage and cracking are usually associated with hot windy weather.   The major side effect of faster curing and water loss is decreased overall concrete strength.  It is critical to prevent moisture from evaporating from the concrete surface. The evaporation rate removes surface water necessary for hydration , and thermal cracking may result from rapid changes in temperature, ie. pouring concrete on a hot day followed by a cool night (CIP 12). Proper mix design can compensate for these conditions, and in combination with protective measures to prevent rapid evaporation, quality concrete can be poured in hot temperatures (Rodriquez).

Adding water can increase concrete workability. However, adding water beyond the amount required by the approved mix design increases the water to cement ratio. This, in turn, can result in decreased compressive strength and an increased chance of cracking (Hot).

Recommendations for Hot Weather Concreting

Preparation is key and there are several basic precautions that can reduce the damaging effects of hot weather on concrete:

  • Use mix designs that are less susceptible to the effects of hot weather. The use of low-heat-of-hydration cement and certain admixtures (such as hydration retarding and/or water-reducing admixtures) are two standard approaches.
  • Keep concrete as cool as reasonably possible. ACI 305R does not state a maximum “as-placed” or “as-delivered” concrete temperature, but 90° F is commonly used. Substituting chilled water or shaved ice for a portion of the required mix water can help.
  • Limit the amount of time between loading the concrete at the plant and placement/finishing at the site.
  • Limit water addition at the job site, except to adjust slump upon arrival (when permitted by mix design).
  • Avoid or limit hydration accelerating admixture use.
  • Schedule large concrete pours in the early morning or evening when temperatures are cooler and have the manpower available to complete the job as quickly as possible.
  • Use temporary wind screens and water misting nozzles to reduce surface moisture loss (Hot).
  • Consider using a concrete cooling blanket to both retain moisture and protect the concrete’s surface from high ambient temperatures.

Powerblanket ICE Concrete Cooling

Powerblanket ICE® is portable cooling equipment that will keep newly poured concrete safe from heat.  Portable, insulated, and efficient, Powerblanket ICE effectively regulates the temperature of concrete under both regular and hot conditions.

The Powerblanket Ice Circulation Blanket is combined with either a cooler or chiller to achieve optimum results. The Circulation Blanket draws heat to the blanket while also cooling the concrete.

  • Blankets use Powerblanket’s patented heat-spreading technology in reverse–the cooling blanket draws heat away from the drum and lowers the temperature of the concrete.
  • Blanket cover and insulation are the same as the robust system used in the Powerblanket heating products
  • Powerblanket Ice industrial cooling systems are portable (120VAC required)
  • Control the curing speed of newly poured concrete even in hot conditions

Hot Weather Concreting

 

Works Cited

“CIP 12 Hot Weather Concreting”. NRMCA. 5 May 2017. www.nrmca.org/aboutconcrete/cips/12pr.pdf

“Hot Weather Concrete”. Engineering Consulting Services.  5 May 2017. www.ecslimited.com/blog/hot-weather-concrete

Rodriguez, Juan. “Pouring Concrete in Hot Weather: Tips and Tricks”. The Balance.  5 May 2017. www.thebalance.com/pouring-concrete-in-hot-weather-845030

 

Process Heating Engineering: Heat Tape

Process Heating Engineering:  Heat Tape

Powerblanket makes industrial heating blankets; however, for this process heating project, we skipped the outer jacket and went straight for the heat tape on the inside.

Upgrade Your Security Clearance

For the third installment of Powerblanket Engineer Favorites, we delve (really only dip our toes) into the world of defense contracting.  

The Heating Dilemma

This company needed to cure carbon fiber reinforced polymer composites.  They were on a very tight timeline and their current suppliers were unable to react quickly enough to meet their needs. This became a custom project because the composites had a complex geometry that could not be evenly heated/covered with a standard industrial heating blanket.

The Powerblanket Custom Solution

Powerblanket recognized that a standard blanket could not meet the process heating needs of these complicated composites.  So we offered them the electrical heating tape normally used inside PB400 blankets that would adhere directly to the surfaces they wanted to heat.  In addition, we built them a custom power cord and wiring harness to power several pieces of heat tape at once.  

They had their own temperature control system, so our offering was incredibly simple: a plug, a cord, and a wiring harness used to power several pieces of adhesive-backed high-temperature heat tape (300 F°/149°C rated).  We designed the heat tape to be one-time-use disposable and the power cord and wiring harness to be reusable and easily be disconnected.

Powerblanket Custom Team

Powerblanket’s custom engineering team prides itself on creativity and out-of-the-box thinking, quickly dreaming up a solution that met all of the customer’s technical requirements.  Despite this being a new product category for Powerblanket, we provided a quote within 24 hours of the initial conversation, and built and shipped the process heating product within a week of receiving the PO.

When you purchase a Powerblanket custom process heating solution, you will enjoy quick turn-around times and the ability to choose from varying levels of customization. Our products are certified to universal safety standards and are easy to install, use, and store.

So whether you need a heat solution for complicated composite curing, tank heaters for your three phase horizontal separator used during drilling operations, or process heating temperature control on your assembly line, our custom approach can provide you with the perfect custom process heating solution. Powerblanket has you covered.