By Chuck Fifelski, Contributing Author
Latex Modified Concrete (LMC) is used in infrastructure across the country to rehabilitate old and worn-out concrete bridge deck overlays, parking decks, and other roadway surfaces.
This fact is especially important as we begin 2023. Thanks to the Infrastructure Investment and Jobs Act (IIJA), America is finally beginning to grapple with infrastructure repairs amid increases in traffic and vehicle weight loads, which increase stress on older roads and bridges.
Studies have shown that improved infrastructure is a competitive advantage for any country. For the health of our country and its citizens, American infrastructure needs to give a positive impact on the quality of daily life. LMC can assist in guaranteeing that roads and bridges across the U.S. do just that by remaining sound.
LMC offers lower maintenance and total costs over the expected lifetime compared to other concrete repair alternatives. LMC overlays provide more than 25 years of maintenance free service life to a bridge deck and an expected service life of 30 plus years.
This performance is contingent on proper bridge deck preparation and installation practices. Contractors have proven that properly installed LMC overlays have superior durability and long-term performance. For more than 50 years, LMC has outperformed Portland cement concrete and alternative technologies, delivering outstanding compressive strength, bond strength, flexural strength, and chloride ion penetration resistance.
For most concrete systems, the installation period is seasonal and restrained by ambient temperature variations. Low temperatures during early spring and late fall months, particularly in the northern American states, can shorten the pour season for LMC, as most state departments of transportation (DOTs) require bridge deck overlays to be installed and cured within a temperature range of 50 to 85 degrees Fahrenheit.
Historically, when it drops below 50 degrees Fahrenheit, installers have used insulated blankets to maintain required cure temperature. Prior research confirmed that the use of curing blankets had no negative effects on curing at 50 degrees, showing excellent compression strength and chloride ion penetration resistance development.
However, a new study by researchers sought to determine if LMC can be installed and cured under lower temperature conditions without compromising its performance and overall quality.
The team examined the development of compressive strength, bond strength by slant shear, and ability to resist chloride ion penetration over a six-month period when LMC is cured at 35, 40, 45, 50, and 72 degrees.
Compressive Strength
Compressive strength is a key indicator of strength development and durability. For LMC overlays, compressive strength is used to determine when a roadway is suitable for opening to traffic.
LMC cylinders were cast in triplicate and cured at the targeted temperatures for 180 days. Compressive strength was measured at multiple intervals for each temperature. The compressive strength for all temperature systems increased from two days to 180 days, with LMC cured under lower temperature conditions exhibiting excellent strength development over time.
After five days of curing, all systems achieved the 3,000 PSI minimum requirement for opening a roadway to traffic.
In addition, the LMC systems cured under the lowest temperatures of 35 and 40 degrees ultimately developed higher compressive strength than the systems cured at higher ones. This supports the historical evidence that a “low-and-slow” curing process results in outstanding mechanical strength.
Bond Strength by Slant Shear
LMC used for bridge deck overlays is known for its exceptional bond strength, which, at times, exceeds the strength of the concrete deck. Excellent bond strength is a key contributor to long-term durability, leading to minimal maintenance requirements over the life of the overlay.
When testing bond strength by slant shear, results show that bond strength for each cure temperature increased from 28 days to 180 days. Samples maintained at lower temperatures developed higher bond strength compared to higher temperature systems at every testing interval.
The samples maintained at 40 degrees had higher bond strength at 28- and 180-day intervals than the other temperature systems. Slant shear testing demonstrates how LMC delivers excellent bond strength performance when poured and cured at lower temperatures.
Chloride Ion Penetration Resistance
The ability to resist chloride ion penetration is important to minimize deck and rebar deterioration due to corrosion. LMC is known for its low permeability due to the latex developing barrier properties within the concrete matrix, reducing moisture and chloride ion penetration.
LMC develops improved chloride ion penetration resistance over time, even when it is cured under low temperatures. Samples cured at lower temperatures began in the moderate range of penetrability and continued to decrease to the low range.
Chloride ion penetration resistance improves over time due to polymer film formation and coalescence, which is time and temperature dependent. Low-temperature curing is not expected to negatively impact LMC’s chloride ion penetration resistance performance.
Future Implications
Study results showed that LMC cured under low temperature conditions and developed exceptional mechanical properties as shown in compressive strength and bond strength performance. Additionally, chloride ion penetration resistance improved over time and is not impacted by low temperature curing.
Knowing that LMC can be poured at lower temperatures without compromising performance, installers and DOTs alike should consider extending their pour season to months previously deemed unworkable. Installers could extend their pour season, and DOTs could benefit from an extended installation window to complete infrastructure projects.
The industry should continue to evaluate the implications of pouring in lower temperatures to further understand the capabilities of LMC. Doing so may open the possibility of expanded uses of the concrete known for its quality performance and reliability. R&B
Chuck Fifelski is a Senior Technical Specialist for R&D, Latex Binders, Trinseo
