Concrete Curing Case Study The Ultimate Custom Heating Solution
Concrete Curing Case Study Those in the concrete industry know that cold weather can have detrimental effects on the concrete curing process. In the winter, concrete cures more slowly, unless of course, the fresh concrete is protected and perhaps heated externally to create an environment for the concrete to cure faster.
Concrete Curing Case Study Background Information Concrete hardens, gains strength, and attains desirable properties at a rate proportional to the temperature at which it is cured. The Cold Weather Concreting Committee (ACI 306) defines cold weather as “when the air temperature has fallen to, or is expected to fall below 40 ºF (4.5 ºC)”. When the temperature reaches this point, concrete should be protected from freezing.
Concrete Curing Case Study Experimental Setup The purpose of this experiment was to learn how concrete would cure underneath three different blanket types. The three types were (A) Powerblanket® Curing Blanket with the heat turned ON, (B) Powerblanket® Curing Blanket with the heat turned OFF, and (C) standard curing blankets.
Concrete Curing Case Study The concrete temperature was recorded over a period of approximately 72 hours. A sensor was also placed inside an extra test cylinder, which was then placed inside a heated cure box that was on site. For reference, ambient temperatures were recorded during the testing period.
Concrete Curing Case Study Method The temperature inside the concrete was sampled and recorded once every 10 minutes for a period of 72 hours. There were sensors placed inside each of the three sections of the slab, corresponding to the three variables: Powerblanket® heated, Powerblanket not heated, and standard blanket. Another sensor was placed inside a test cylinder and yet another measured ambient temperature at the jobsite.
Concrete Curing Case Study Temperature Results Ambient conditions for this test were consistent with Cold Weather Concreting as defined by ACI 306. Ambient Record 72 Hrs TEMPERATURE °C °F 43 110 38 100 32 90 26 80 21 70 16 60 10 50 4 40 -1 30 -7 20 09:00 14:00 20:00 02:00 08:00 14:00 20:00 02:00 08:00 TIME The Ultimate Custom Heating Solution 14:00 20:00 02:00 Total Time: 2.9 days Max Temp: 38.6 °F 3.6°C Min Temp: 22.3 °F -5.
Concrete Curing Case Study Section A: Heated Powerblanket External heat was applied from above using a Powerblanket® heated curing blanket. Note gradual rise in temperature after heat was turned on at approximately 9:00 p.m. Heat was maintained above 100 ºF (38 ºC) for approximately 2 of the 3 days.
Concrete Curing Case Study Section B: Unheated Powerblanket A Powerblanket® concrete curing blanket was again used, but this time no external heat was applied. The maximum temperature attained was just over 80 ºF (26.5 ºC), simply due to the heat released by the concrete. The blanket did a good job of trapping the heat from the hydration reaction.
Concrete Curing Case Study Section C: Standard Curing Blanket This section used a standard construction insulating blanket and no external heat was applied. The temperature attained is consistently about 10 ºF (-12 ºC) lower than the adjacent section of concrete covered by the unheated Powerblanket® . Note that the temperature of the slab dropped noticeably over the last 8 hours of curing time, likely due to the cold rain that fell at the jobsite. Upon arrival at the jobsite at 6 a.m.
Concrete Curing Case Study Test Cylinder All the cylinders were placed in a heated cure box, but it should be noted that at some point in the evening of February 6th, it appears that the cure box heater malfunctioned. Upon arrival at the jobsite, it was observed that the cure box temperature was 50 ºF (10 ºC) as displayed by the high-low thermometer inside the cure box. The temperature of the cylinders reflects that drop in temperature.
Concrete Curing Case Study Strength Results Each slab of concrete was cured for a period of 2.8 days, and the maturity at 2.8 days was compared to an equivalent age of laboratory curing. The equivalent age was how long it would take a slab to reach that level of maturity in a laboratory setting. Section Strength Equivalent Age at 2.8 days A. Heated Powerblanket 3,925 PSI 7.0 days B. Unheated Powerblanket 2,642 PSI 3.3 days B. Standard Blanket 2,162 PSI 2.5 days Test Cylinder 2,415 PSI 2.
Concrete Curing Case Study Implications It was established that the concrete under the heated blanket would cure significantly faster than the unheated concrete, and the heat-spreading technology contained inside the Powerblanket® heater would create a better curing environment than the industry-standard curing blankets. The task at hand was to measure the differences. Heated Powerblanket The heated Powerblanket accelerated the curing rate approximately 2.
Concrete Curing Case Study Unheated Powerblanket The unheated Powerblanket® section cured 1.3 times faster than the area under the standard blanket. When this rate of strength gain is projected over time, the unheated Powerblanket section will attain “design strength” (4000psi) in only 53⁄4 days. (This is determined by dividing the actual age at which design strength is attained in the laboratory by the “equivalent age-to-actual age ratio” at the moment. For this mix design, that is assumed to be 7.
Concrete Curing Case Study Test Cylinder For this test, the test cylinders were cured under mostly ideal laboratory conditions, but that would mean that they would attain higher strengths than the in-place concrete under the standard blankets. That difference would get even greater once the blankets are removed and the concrete equilibrates to ambient conditions after a few days. Higher cylinder vs. in-place strengths can lead to construction disasters, so caution is urged.
Concrete Curing Case Study Conclusion Powerblanket® cures concrete 2.8 times faster than conventional insulated blankets, and produced a cold weather concreting strength of 3,925 in 72 hours. Powerblanket allowed the work to get done faster and the concrete to become stronger, reducing the amount of downtime and lost profits due to cold weather. Don’t let the elements get the best of you. Contact Powerblanket to get started on a heating solution for your business.
