Vietnam’s construction material producing company Thach Anh has successfully invented a technology to make concrete from salt water and sea sand, and the invention will be donated to the Ministry of Defense for building infrastructure on remote islands.
Applications of the technology will help facilitate soldiers on the Truong Sa (Spratly) archipelagos with the construction of architectural structures, foundations, sea walls, pavements, bridges, runways and reservoirs.
In addition, costs will be cut to a third of previous projects, when the Navy had to transport everything from cement, sand, fresh water and aggregates from the mainland to the islands.
Tran Minh Chi, chairman of the board of directors of Thach Anh company, said his staff began researching the idea of producing concrete from sea water and sand last year when Tuoi Tre newspaper launched the fund-raising “Let’s Build Truong Sa” campaign in May.
After over six months, several solid samples from trial production were sent for technical tests to the Quality Assurance and Testing Center 3 (Quatest 3), and gained satisfactory results, according to Chi.
The average compressive strength of the samples reaches 89.9 MPa — much higher than normal concrete, with 30 MPa. Water absorption is 3.1 percent and corrosion is 215 mm3, which meet and even better quality standards for concrete.
Chi said Thach Anh has registered for a patent and copyright.
Nguyen Minh Luan, the firm’s vice director and head of the research, revealed that the main composition to produce the samples of concrete includes gravel, sea sand, coral, cement P40, sea water, and glue additive.
Salt water is not used for mixing concrete as it can lead to corrosion of reinforcement and thus degradation of concrete and steel inside.
A cubic meter of normal concrete of 30 MPa requires 472 kg of cement. But with sea sand and salt water, only 350 kg of cement is needed to create a cubic meter of concrete of 50 MPa thanks to the use of a special additive made by Thach Anh, he added.
With the dosage of the additive around 1 percent by mass of cement, it helps Thach Anh concrete solidify compressive strength, limit its water absorption and corrosion, and block the air entrainments of tiny air bubbles in the concrete, which will reduce damage during freeze-thaw cycles and increase its durability.
“The additive speeds up the process of hydration, so making concrete with sea water and sand with Thach Anh’s technology takes only four hours for concrete to hydrate, while normal concrete takes 24 hours.
“This property permits concrete construction projects near the sea shore to be undertaken during ebb tide, and it will harden before the water rises,” Luan said.
A technological secret to make concrete with sea water lies at the heart of the additive, he added.
The additive fills voids within concrete, pushes salt water out, and helps particles of a fresh concrete batch quickly clump and glue the aggregate together. Forcing voids and salts out yields a stronger and more durable concrete and steel framework inside.
The concrete can be made manually at the sea shore, Luan noted.
The samples of concrete taken for tests to Quatest 3 were mixed with sea water and sea sand directly taken from Truong Sa and sealed by the Navy.
During mixing, the Navy’s technical unit sent their staff to witness the process. When it hardened, Admiral and Deputy Defense Minister Nguyen Van Hien came to inspect the sample batch of concrete.
“We carefully tested and verified the result of the research,” the Admiral told Tuoi Tre.
“We highly appreciate the transfer of the technology to the Ministry of Defense and consider this a gift to Truong Sa. It is a significant development as the Navy need not transport fresh water and sand from the mainland for construction on Truong Sa.”
Concrete from sea water made 10 years ago
Ph.D. Nguyen Hong Binh, vice chief of the HCMC Construction Science and Techniques Association, said he had studied and successfully applied salt water and sea sand to make concrete ten years ago.
The pier at Hon Ngoc Phuong Nam resort in Can Gio District was made by that kind of concrete and it has been in use in the last 10 years.
“The concrete there had compressive strength of 20-250 MPa,” Binh confirmed.