The old adage time is money certainly applies to the construction industry. Delays waiting for materials to arrive or properly cure have been the headache of contractors for decades. Time is of the essence on many concrete projects, but contractors can't sacrifice quality, durability, or cost savings simply to reduce construction time. That is why many concrete contractors are turning to rapid-hardening hydraulic cement to meet tight schedules. Rapid-hardening hydraulic cement is not only a more durable alternative to portland cement on many projects, but its rapid-setting properties make it an ideal solution for today's schedule-and budget-driven projects.
Benefits over portland cement
The need for a more durable cement drove the research and development that produced CTS Cement Mfg. Corp. Rapid Set cement. Although portland cement has been successfully used for many years, it is not without limitations. Portland cement concrete is prone to drying shrinkage cracking. It is susceptible to attack by sulphates and has an undesirable reaction with certain aggregates (ASR). Generally, when one accelerates the gain in strength of portland cement concrete through finer grinding or chemical additives, there is a significant increase in drying shrinkage.
Rapid-hardening hydraulic cement offers reduced shrinkage and superior resistance to chemical attack. It achieves strength much faster than portland cement and many installations can be put into service in as little time as one hour. Compared to portland cement, rapid-hardening hydraulic cement reaches typical compressive strengths in a few hours that an equivalent portland cement mix would require one month to achieve.
Rapid-hardening hydraulic cement has been used for both concrete repair and new construction, wherever superior durability and rapid strength gain are required. It is blended and packaged into a wide range of high-performance products including nonshrink grout, structural repair mortar, concrete, exterior plaster, and other cementitious products.
Rapid-hardening hydraulic cement is manufactured with similar raw materials, equipment, and processes used to make portland cement, but that is where the similarities end. The chemistry of rapid-hardening hydraulic cement, which differs from portland cement, is composed primarily of hydraulic tetracalcium trialuminate sulphate (CSA) and dicalcium silicate (C2S). C2S is the most durable compound found in portland cement. The CSA compound, often referred to as calcium sulfoaluminate, hydrates to form ettringite-a strong needle-like crystal that develops quickly to give rapid-hardening hydraulic cement its high performance. Another significant aspect of this product's chemistry is the absence of tricalcium aluminate (C3A), which makes a cement susceptible to sulfate attack. Because rapid-hardening hydraulic cement has little or no C3A, it is very durable in sulfate environments.
As a viable alternative to portland cement, rapid-hardening hydraulic cement offers several advantages including durability, versatility, speed, and ease-of-use, as well as cost benefits and environmental considerations.
- Durability. The amount of mixing water in concrete is a major factor in its durability. With portland cement concrete, the mixing water needed to make it fluid enough for placement is in excess of the water needed to hydrate the cement. This excess water, often called water of convenience, evaporates over time leaving voids or pores in the concrete and causes drying shrinkage. In a typical portland cement concrete mix, the excess water of convenience amounts to about 50% of the water in the mix.
In rapid-hardening hydraulic cement, the water required to hydrate the CSA compound is several times greater than that required to hydrate typical portland cement compounds. In a typical rapid-hardening hydraulic concrete mix, nearly all of the water used in the mix is used up in the hydration process resulting in a dense concrete with very low drying shrinkage.
Voids or pores in concrete, along with drying shrinkage cracks, provide routes of entry for substances that attack the concrete and reinforcing steel. With fewer pores and less drying shrinkage, rapid-hardening hydraulic concrete is more durable than portland cement concrete.
- Versatility. Rapid-hardening hydraulic cement can be formulated for a wide range of applications. Various properties, such as setting time, fluidity, air content, and color are adjusted easily by using commercially available additives. Rapid-hardening hydraulic cement is highly resistant to freezing and thawing, and can, due to its rapid hydration, be used in cold weather conditions that are not possible with portland cement.
- Speed. Today's schedule-driven projects require quick construction solutions. One such example is the Hyperion Sewage Treatment Plant in Los Angeles. Serving more than four million residents, the city's oldest and largest wastewater treatment facility has an average capacity of 450 million gallons per day. The general contractor for the project, Kiewit, Santa Fe Springs, Calif., opted to use the product to reduce the construction time and ensure high durability. Ten pallets of the Mortar Mix were used for full-depth repairs on sewage containment tanks. The original specifications allowed for 28 days for the repair process and the use of rapid-hardening hydraulic cement enabled the project to be complete in a mere three days.
- Ease-of-use. As much of the infrastructure in the U.S. is wearing out, repair work becomes a necessity both for safety and aesthetic reasons. The higher durability of rapid-hardening hydraulic cement offers a real solution for repair work, not just a temporary, short-lived Band-Aid.
Restoration projects are extremely complex as design and construction teams have the added challenge of matching an older look. First opened in 1910, the historic Hotel Shattuck in downtown Berkeley, Calif., is one of the premier structures in the area. Although they had never used the product, BPR Properties, Palo Alto, Calif., chose to use Cement All for grouting the concrete repairs. Eighteen different types of repairs had to be used on the project and the contractor was able to use Cement All for all of the repairs, which allowed the project to be completed faster.
- Cost benefits. Although portland cement is less expensive on a first-cost basis than rapid-hardening hydraulic cement, its durability, rapid cure time, reduced shrinkage, and resistance to chemical attack outweigh the cost differentials, especially when the cost of time is added to the equation. For a contractor or owner, the value of time for a repair delay that results in the late opening of a parking garage, an airport runway, or a retail center often are much greater than the premium paid for rapid-hardening hydraulic cement. On many jobs, bonuses offered for getting a job done on time or a project completed earlier is money well spent.
Superior Wall Systems, Fullerton, Calif., selected WunderFixx-a durable, fast-setting, one-component concrete patching material formulated with a premium-grade hydraulic cement, high-performance polymers, and a finely ground aggregate-for a project at Sony Picture Studios. For this project, it was critical that an ultra-smooth finish was achieved on the plaster system. The contractor for the project learned about the product at a trade show and thought it would be the best application for this job as opposed to an acrylic system. WunderFixx required fewer coats because it had a much larger spread than the acrylic system, so the contractor was able to provide a tremendous cost savings by using less material. A scratch coat, brown coat, two coats of base material, and then the rapid-set product served as the final coat on the plaster. The owner liked the smooth and fine spreadability of the product, the elimination of chatter marks, as well as the fact the product is engineered for sandability.
Yet another example of the cost savings rapid-set hydraulic cement can provide is found on the Highway 23 project in California. Security Paving, Sun Valley, Calif., the contractor for the project, used 20 pallets of the DOT Repair Mix for road and bridge repair work. Some of the work performed was vertical in nature but the majority was flatwork that was 1 to 8 inches in depth. They were able to use one-third less material, which saved a great deal of money.
- Environmental responsibility. Rapid-hardening hydraulic cement has a much smaller carbon footprint than portland cement. During the production process, rapid-hardening hydraulic cement reduces CO2 emissions by 32% to 36% over conventional portland cement manufacturing procedures. This is because rapid-hardening hydraulic cement is produced at lower temperatures, so less fossil fuel is required. It also requires less limestone per ton, further reducing CO2 emissions.
Rapid-hardening hydraulic concrete is much more durable than portland cement, and has a greater resistance to sulfate and other types of chemical attack. Due to chemical formulation, lower porosity and subsequent internal self-desiccation, rapid-hardening hydraulic cement is extremely impervious to carbonation, freeze/thaw susceptibility, and acid rain leaching. Rapid-hardening hydraulic cement has a proven record of field performance that exceeds the normal useful lifespan of portland cement concrete.
A proven technology
Contractors across the country have realized the benefits of using rapid-hardening hydraulic cement products on a diverse range of projects for nearly three decades. Compute the cost of durability and time, and it is apparent that rapid-hardening hydraulic cement is a viable, cost-effective alternative to portland cement. No special equipment is needed to mix rapid-hardening hydraulic cement, and it can be put into service in as little as one hour, which allows contractors to complete work faster. Rapid-hardening hydraulic cement can obtain the same strength in just six hours, as the 28-day strength of an equivalent portland cement mix.
Frank Senatore is vice president of packaged products for CTS Cement Mfg. Corp.