|This article was written before Hurricane Maria hit Puerto Rico in September 2017. The author has since been able to verify all the repairs mentioned withstood the ferocity of Hurricane Maria without any deterioration.|
by Guillermo E. Alvarez Cartañá, PE
When it comes to concrete construction and repair, use of fast-setting cementitious materials is often the best way to ensure crews can work around the weather and more conventional challenges like traffic. The key to success often lies in specifying rapid-hardening, durable cement products that are easy to mix and place. These should be formulated to set fast, minimize shrinkage, maintain strength—even when submerged in water—and resist chemical attack.
Whether Hawaii, Southern Florida, or Puerto Rico, a tropical climate brings a host of unique construction challenges. In Puerto Rico, the focus of this article, the average temperature hovers near 27 C (80 F), with humidity varying by region, and strong easterly trade winds pass across the island year-round. A rainy season also stretches from late April through November, not to mention hurricane season from June through November. Even after construction is completed, the built environment is susceptible to corrosion brought on by salt-infused sea breezes from the surrounding ocean.
The following case studies show how rapid-hardening cement-based products have been used to speed construction and fortify structures and infrastructure against corrosion in the harsh climate of the island. The projects address corrosive environments, windy and wet conditions, and hot-weather concreting methods.
Working around the wind
National University College has five campuses located throughout Puerto Rico. The Arecibo campus sits just 15 m (50 ft) from the Atlantic Ocean, which means the facility is subjected to strong winds and corrosion. As a result of these factors, the campus parking structure was in dire need of structural repairs.
In April 2016, the university contracted a San Juan company to repair the 8-m2 (86-sf) covered parking lot. The owner wanted a durable solution able to withstand the corrosive seaside environment and be installed within five months.
The contractor used high-performance, rapid-hardening cement products to provide full- and partial-depth repairs with rebar replacement for the structure’s beams and columns. All materials were one-component mixes, which were combined with water onsite via barrel mixer. The fast-setting materials enabled the contractor to perform the bulk of repairs before daily high-wind conditions set in. Further, because the repair materials can be applied at thicknesses up to 152 mm (6 in.), the crew was able to achieve full depth in a single coat, completing repairs more quickly.
For partial-depth repairs, the crew removed the top third of damaged slabs and replaced it with a corrosion-resistant material. The polymer-modified blend of rapid-hardening cement, additives, and specially graded fine aggregates is fortified with a corrosion-inhibitor and fibers. Designed for vertical/overhead (V/O) repair and resurfacing applications, it bonds well with existing concrete and achieves rapid strength gain, high durability, and low shrinkage.
The contractor also employed a multipurpose mortar for all full-depth repairs. Like the cement product mentioned previously, this mortar mix is designed for V/O applications. This combination of rapid-hardening cement and quality sand is durable in wet environments, sets in 15 minutes, and is ready for traffic in one hour. As work took place during temperatures that ranged in the high-20s C (mid-80s F), the crew added one packet of a powder-based, set-retarding additive and three packets of a powder-based flow-enhancing additive to every 25 kg (55 lb) of the mortar mix to keep the material from setting too fast. The set-control additive effectively slowed setting times, while the flow-control additive increased the fluidity of the mixture. Additionally, by replacing water in the mix with the flow enhancer, the contractor was able to increase concrete strength and further reduce shrinkage.
The crew’s biggest challenge was the need to work around sea breezes and strong ocean winds threatening to blow around the material. For example, while performing partial-depth repairs, the crew mixed and placed the V/O repair material during the early morning hours, when wind conditions were most favorable. It was placed by 9 a.m. each morning, when the wind typically changed directions and grew stronger.
The V/O repair mix contains self-curing technology, which means it does not need to be wet-cured in most applications. This enabled the material to set
in 45 minutes and achieve structural strength in two hours, well before the intense mid-morning sea breeze. Repairs were completed months ahead of schedule, which resulted in profits for the contractor as well as cost savings for the owner. As an example, early completion allowed the university to save two months of payments on a rented parking lot for students and staff during construction.