When does Concrete Reach Maximum Strength?
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.
After concrete is placed, the concrete increases in strength very quickly for a period of 3-7 days. Concrete which is moist cured for 7 days is about 50% stronger than uncured concrete.
The entire curing period of concrete takes about a month, but your concrete will be ready for use sooner. Each project will vary slightly due to differences in the weather, concrete mix and placement and finishing techniques.
When waiting for concrete to dry, keep these timeframes in mind:
- 24 to 48 hours – after inital set, forms can be removed and people can walk on the surface
- 7 days – after partial curing, traffic from vehicles and equipment is okay
- 28 days – at this point, the concrete should be fully cured
Why Concrete Strength Is Important?
Careful control of moisture and temperature of your in-situ concrete during curing is an essential part of quality control and quality assurance of your concrete structure. Proper curing techniques will prevent in-situ concrete from drying, shrinking, and/or cracking, and ultimately affecting the performance of your structure, particularly at the cover zone. Curing of concrete should occur as soon as it has been placed. It is also essential that continuous monitoring of concrete curing conditions be carried out for seven days. If water evaporates from the concrete before it has attained its maximum strength, there will not be enough water remaining in the concrete to fully hydrate the cement and achieve maximum compressive strength. This is especially true during extreme weather conditions when your concrete slab is subjected to various environmental elements, and the strength development of your concrete can be compromised.
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3 Techniques for Efficient Concrete Curing
Many factors affect the rate at which water evaporates from freshly placed concrete. This includes air temperature, humidity, concrete temperature, and wind speed. As a result, many techniques have been developed to help concrete retain moisture at the early ages. These methods are used to:
- Maintain the presence of water in the concrete during the early hardening period,
- Reduce the loss of water from the surface of the concrete, and
- Accelerate concrete strength gain by supplying heat and additional moisture.
1. Maintaining Moisture
Ponding and Immersion
Ponding is typically used to cure flat surfaces, such as pavements and floors, as earth and sand around the perimeter of the concrete surface can retain a pond of water. Ponding is an ideal method for preventing loss of moisture from the concrete; it is also effective for maintaining a uniform temperature throughout the concrete. Immersion of a finished concrete element is commonly used for curing test specimen.
Spraying and fogging
Spraying and fogging are used when the ambient temperatures are well above freezing, and the humidity is low. Fog mist is applied through nozzles or sprayers to raise the relative humidity of the air over flatwork, thus slowing evaporation from the surface. Fogging is used to minimize plastic shrinkage cracking. If sprinkling is done at intervals, the concrete must be prevented from drying between applications of water by using burlap or similar materials; otherwise, alternate cycles of wetting and drying can cause surface cracking.
Saturated wet coverings
Wet coverings saturated with water, such as burlap, cotton mats, rugs, or other moisture-retaining fabrics, are commonly used for curing. The materials should be placed as soon as the concrete has hardened enough to prevent surface damage. They should be kept constantly wet so that a film of water remains on the concrete surface throughout the curing period.
Left-in-place forms
Left in place forms usually provide satisfactory protection against moisture loss for formed concrete surfaces. The forms are usually left in place as long as the construction schedule allows. If the forms are made of wood, they should be kept moist, especially during hot, dry weather.
2. Reducing Loss of Water
Covering concrete with impervious paper or plastic sheets
Impervious paper and plastic sheets can be applied on thoroughly wet concrete, such as polyethylene film. This material is a lightweight, effective moisture retarder that is easy to apply. During placement, the concrete surface should be hard enough to prevent surface damage.
Applying membrane-forming curing compounds
Membrane-forming curing compounds are used to retard or reduce evaporation of moisture from concrete. They can be clear or translucent and white pigmented. White-pigmented compounds are recommended for hot and sunny weather conditions to reflect solar radiation. Curing compounds should be applied immediately after final finishing and must comply with ASTM C3094 or ASTM C13155.
3. Accelerating Concrete Strength Gain
Live Steam
Live steam and high-pressure steam are the two methods of steam curing. The temperature for live steam should be kept at about 140 degrees Fahrenheit or less until the desired concrete strength is achieved.
Heating coils
Heating coils are usually used as embedded elements near the surface of concrete elements. Their purpose is to protect concrete from freezing during cold-weather concreting.
Electrical heated forms or pads
Electrical heated forms or pads are primarily used by precast concrete producers.
Concrete blankets
Concrete insulation blankets are used to cover and insulate concrete surfaces subjected to freezing temperatures during the curing period. When using concrete blankets, make sure that the concrete is hard enough to prevent surface damage.
Process To Get Concrete Cost Estimate Report
Here I am going to share some steps to get your concrete cost estimate report.
