Best Practices for Protecting Fresh Concrete
Freshly poured concrete needs protection from the elements, pedestrians, damage, debris, and vehicles shortly after pouring. This usually entails a combination of physical barriers, signage, and curing/sealing compounds after the fact. Following a pour, concrete can be susceptible to damage such as physical damage, improper curing, and precipitation such as rain or hail.
There are various means and methods to protect freshly placed concrete from damage, read on for details.
TABLE OF CONTENTS
Temperature Guidelines for Curing Concrete
Curing and Sealing Compounds
Special Admixtures / Curing Accelerators / Hardening Accelerators
How to protect fresh concrete from rain?
Protecting Against Physical Damage
Other Curing Tools
Protecting Concrete Against Freezing
Summary
Temperature Guidelines for Curing (fresh concrete)
Temperatures of at least 10 degrees Celsius and up are best for pouring and curing concrete.
Anything below that could freeze the moisture in the concrete. The freezing of the water/moisture in concrete means there can be inadequate mixing of the concrete/cement ingredients with water, making a weaker bond in the mixture, and overall less MPa(megapascal) strength at desired curing periods such as 7, 14, and 28 days for instance in a typical curing/testing guideline.
Inadequate temperatures can lead to issues with curing and hardening of concrete making the surface of the concrete impossible to walk on or permit vehicle traffic longer than typical.
Curing and Sealing Compounds
It is a good practice to utilize a curing or sealing compound on top of the slab or concrete element once poured. This will provide a better curing/setting of the concrete, trapping moisture within the concrete itself, preventing excess evaporation, almost acting like a mini-wet cure.
You also get the added benefit of protection against the elements with the right curing or sealing compounds. Some products can be sprayed/applied after the concrete has been poured or placed, alternatively, other products are utilized as a concrete admixture itself within the concrete mix.
This sort of product functions similarly, akin to hardeners, crystalline waterproofing products etc.
Most typically though a surface applied acrylic or penetrating sealer is going to be utilized. This will protect concrete but may require application up to 12 hours or more after placement (after the concrete is hardened). These compounds can affect the look and feel of concrete itself too so can be beneficial from an aesthetic perspective.
Special Admixtures / Curing Accelerators / Hardening Accelerators
Special compounds:
Some specific compounds / admixtures like curing accelerators and set accelerators could aid a contractor in setting fresh concrete, when trying to avoid the rain with tight schedules in fast-paced projects.
These mixes increase curing strength in shorter periods so theoretically, a concrete element will gain more strength faster, and this can help to circumvent negative weather conditions in forthcoming days.
A hardening accelerator can also be utilized to decrease the time to where concrete is unworkable. This in theory makes a the finished surface quicker to harden, but doesn’t necessarily increase the actual strength of the concrete for the curing process. A hardener applied as an admixture is ideal as this type of product is already in the mix design, rather than having to wait 6 – 12 hours to apply a spray on product, can be used immediately with the finishing/plpacing process.
A concrete hardening accelerator is probably the most beneficial for quick setting concrete when physical damage is a concern.
How to protect fresh concrete from rain?
How to protect fresh concrete from rain:
One common issue with pouring concrete is precipitation. The advent of precipitation in the form of rain, snow, or even hail can have a negative effect on freshly poured concrete.
Ideally, follow local building standard guidelines on temperature requirements for pouring fresh concrete. Temporary provision such as polyethylene covers and temporary hoarding structures can aid in the protection of fresh concrete against the rain.
Another common method is just to align the date of your pour with a day that doesn’t have rain in the forecast. Allowing a day or even 12 hours of curing is going to allot to ensure that the the physical impact of rain and other precipitation does not affect the quality of the finish on the concrete. After a day of curing the surface of the concrete in most instances is already ready for walking. Albeit, the utilization of moisture in curing means some rain after this fact of the concrete hardened surface, is not necessarily going to damage the concrete.
In summary, try to schedule pours appropriately around rain events, but with fresh concrete, right after a pour and during placement, utilize temporary hoarding measures and covers to protect against the impact of rain droplets or hail for instance.
Alternatively, with practice for wet curing, using a cover such as polyethylene sheeting or burlap could pose as a defense against rain impact damaging a freshly troweled or finished surface of fresh concrete.
Water content with concrete:
Obviously the water content of concrete is a vital determining factor in the structural mix design requirements and subsequent suitability for the structure. Do not exceed specified mix design water contents without authorization from a structural engineer in the event of a heavy rainfall for instance. The added moisture from rain will affect the slump of the concrete and can affect strength, dispersion of aggregates, finishing, and general suitability of the concrete.
Protecting Against Physical Damage
Protect your concrete from physical damage from pedestrians, site foot traffic, vehicle traffic and more… with simple barriers, flagging and tape, create a barrier to entry onto fresh concrete for up to a whole week after pouring.
Signage and general notices to those who may damage the concrete are warranted.
Other curing tools
Remote monitoring of concrete curing and quality of setting is also an option. Sensors embedded in concrete can be monitored from a smart phone or computer to observe the conditions of the concrete curing, typically related to temperature in the slab or concrete element. This gives a reasonable understanding of the progress of curing for the concrete.
Protection Against Freezing
One of the ways to pour in winter, and protect fresh concrete against freezing is through the utilization of heating and hoarding. Heating and hoarding, such as a small tent structure, with propane heaters for instance, and general tarps, can keep the internal temperature surrounding a concrete element quite toasty.
The goal is ensure the moisture in the concrete does not freeze and prevent the proper mixing of the cement/concrete elements for adequate compressive strength and standard curing times. Freezing can not only increase curing times, but in drastic circumstances, actually totally reduce the effective strength and structural suitability of concrete in general.
Heaters, and even in-slab heating in theory, are both methods that could be utilized. Monitoring of the internal temperatures of a concrete heating and hoarding setup are still critical though, as too high of temperatures could also pose an issue, that, or, pockets of heat and pockets of cold. Even heating is critical to ensure a consistent structural stable cure throughout freshly poured concrete.
Summary
Overall protecting freshly poured concrete is not too difficult. Basic common sense, like pouring after rain events for the best finish possible, scheduling accordingly, working with the right surface protections, and utilizing concrete sealers or admixtures is a great way to protect freshly placed concrete!
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