The Roman Empire started using concrete about 2000 years ago. It was used in monuments such as the Pantheon and Colosseum in Rome, which has survived for centuries. Surprised? Not really. After all concrete is the material of choice in wharves, breakwaters and other harbor structures. We all know that concrete structures are meant to last a lifetime. Usually concrete structures have a design life of 50 or 100 years.
While concrete is highly durable, you will want to do everything you can to stop the premature deterioration of concrete structures. Here’s how:
Mix Design
Durability starts with a concrete mix design suitable for the service conditions that the concrete will be exposed to. The amount of water specified may be the single most important component of the mix design. A low water-cement ratio between 0.40 and 0.50 is normally recommended for concrete frequently subjected to severe exposure. Do not add extra water on site. Additional water will lower strength and increase permeability and the likelihood of scaling.
Other important components of the mix design are the aggregates. Contaminated aggregates can cause pop-outs or alkali silica reactivity (ASR), and off-spec cement can cause finishing problems with inconsistent setting times.
Construction Joints
Construction joints are a common weak point in the structure where water will often find its way in and through it. Corrosion of the reinforcing steel from water penetrating through the joints can cause damage to your structure. Planning for and using control joint locations can help avoid random cracking. Just make sure that each joint employs a reliable waterproofing system of its own. The best long-term protection at joint locations is due to a joint waterproofing system that includes crystalline technology, which self-seals random cracking and thus provides added reliability and protection.
Prevent Premature Moisture Loss During Placing
Keeping the concrete moist and at an adequate temperature helps to provide proper hydration of the cement for maximum strength, increased density, lower permeability, and greater resistance to scaling. Pay special attention to placing and finishing. Often excessive or premature finishing can lead to blistering and reduce surface air content and durability. Adding water to concrete during toweling, increases the probability of surface scaling and spalling. The increase in the water-cement ratio at the surface weakens the concrete at the near-surface wear zone. It is better to use an evaporation retardant in rapid moisture loss conditions to prevent surface crusting, plastic shrinkage or cracking.
Low Permeability
You may have to adjust the mix designs to match the conditions, but there is one factor that is common to all good concrete and that is low permeability. For lower permeability good mix proportioning by reducing the amount of free water in your mix and using water reducing admixtures or plasticizers is essential. A waterproofing admixture should be used to protect concrete from water intrusion.
Proper Curing
Curing means maintaining conditions that will allow the concrete to harden and gain strength optimally and this step is central to extending the life of your concrete. Proper temperature and humidity are most important. The temperature should be above 10°C for strength development to proceed at a reasonable pace. It is critical to maintain proper moisture levels the first few days for cement hydration and also to keep the concrete from drying, shrinking and cracking.
Protect Concrete From De-icing Salts After Curing
Frequent wetting and drying during the early age of concrete will cause crazing, scaling, lower concrete strength, and increase the possibility of scaling. It is essential that concrete be protected from freezing temperatures during the first days of hydration; when its low strength and high moisture content make it most susceptible to freeze/thaw damage. Where the presence of deicer agents cannot be eliminated, treat the surface, with something like Aquapel, to prevent the migration of nearly 90 percent of deicer salts and effectively repel a high percentage of the moisture that will cause deterioration.
Concrete Placement
Concrete must be placed properly and consolidated into a solid mass that is free from any voids or rock pockets. Avoid voids below or behind reinforcing steel bars and vibrate all concrete with special attention around congested reinforcement. There should be no standing water prior to concrete placement.
You can create durable concrete structures that will guard against corrosive conditions and other deteriorating mechanisms by ensuring the right mix design, reducing permeability, and paying attention to good jointing, placing and curing practices.
At Davis Concrete, our expertise in concrete building solutions is unmatched in the West Central Florida area. If you have any questions about any concrete jobs, give us a call at 800 -910-6928. We take pride in our legacy of outstanding work and satisfied clients.
