Many highways and key road links around Vietnam have traditionally been built on embankments, as this is perceived to entail lower initial costs. However, numerous new projects, especially expressways in the Mekong Delta, have encountered formidable challenges due to a severe shortage of suitable roadbed materials. By 2025, the Delta plans to implement 16 projects, with critical phases already underway. While total demand for roadbed sand is estimated at 63 million cu m, according to the Ministry of Transport (MoT), as of the end of May, 26 million cu m remains unallocated.

Beyond the scarcity of sand, these expressway initiatives must also contend with geological complexities and landscapes fragmented by canal networks, creeks, and rivers. Addressing weak ground conditions can often extend construction timelines by 12 to 18 months, resulting in project delays. Experts therefore advocate for the construction of reinforced concrete causeways as a partial substitute for embankments, in order to mitigate the challenges posed by the shortage of construction sand.

Options needed

The current approach to designing causeways typically involves simple span configurations using precast beams, commonly referred to as Super-T beams. However, many experts and engineers argue that in the more than 15 years that these beams have been used in Vietnam, they have exhibited certain limitations and many projects have failed to meet design lifespan requirements in subsidence-prone areas.

Various advanced structural solutions for bridge beams are being implemented around the world. These include wavy-edged reinforced concrete beams, High-Strength Concrete or High Performance Concrete (HPC) beams, and Ultra-High Performance Concrete (UHPC) beams cast in shapes such as wide-flange I, inverted T, and U. Countries like Japan, South Korea, Germany, and the US have already adopted and are integrating these hybrid beam solutions in their construction projects. While these new solutions promise greater efficiency, their widespread adoption in Vietnam has been hampered by a number of obstacles.

At a recent introduction of UHPC technology for large-span causeway beams, Dr. Tran Ba Viet, Vice President of the Vietnam Concrete Association (VCA), underscored its effectiveness in the construction of causeways in weak land areas and how it can address the shortage of construction sand while meeting government-mandated timelines. UHPC causeways and bridges offer a host of advantages: rapid construction independent of weather conditions, the elimination of the need for sand filling, superior quality, longer lifespans, low maintenance costs, and a significant reduction in site clearance costs, by up to 25 per cent compared to conventional methods, thereby conserving land resources.

In particular, comparative analyses indicate that the overall investment required for large-span causeways utilizing U-UHPC beams in deep, weak land areas, with sand filling depths of around 4 meters, is only 25-35 per cent higher than traditional sand filling methods, representing substantial savings compared to the construction of causeways using Super-T beams.

Indifference to new technology

U-HPC concrete beams fully meet both economic and technical criteria, ensuring reliability, and have been quality-proven through nationwide projects since 2017 and also globally. Despite their significant advantages, the widespread use of U beams in causeway projects is currently limited to privately-funded initiatives and provincial investments, rather than being integrated into high-speed projects overseen by the MoT.

Mr. Nguyen Trong Nghia, CEO of the Synectics Consulting Corporation, explained the barriers to the broader implementation of such methods in new projects. Firstly, consulting units under the MoT consider U beams impractical due to their perceived higher cost, with the Ministry continuing to favor Super-T beams for its projects. Secondly, concerns about quality control for high-strength concrete abound but have been disputed, as concrete strengths ranging from 50-80 MPa (megapascals) have long been produced in Vietnam, particularly by precast concrete factories. Thirdly, the notion of requiring new equipment is also unfounded, as U beams can be handled using existing cranes and beam launchers used for Super-T beams.

“In discussions with various consulting firms, especially major players like Transport Engineering Design Inc. (TEDI), it is clear they are accustomed to Super-T beams and lack sufficient time to explore alternative beam types,” Mr. Nghia continued. “This highlights a reluctance among consulting firms to embrace advanced applications. I have reviewed numerous projects where design consultants did not conduct thorough comparisons of different options and provided recommendations quite hastily.”

Dr. Ngo Chau Phuong from the University of Transport and Communications has similar concerns, noting limitations in the research and consulting phases. Additionally, initial cost estimates for manufacturing U beams are often inflated due to the need for new formwork, which complicates cost comparisons. “Most consulting firms are hesitant to adopt new technologies due to difficulties in persuading investors and stakeholders,” he explained. “Typically, implementing new technologies in Vietnam encounters many barriers, with at least ten years required before successful adoption.”

Cost of investment

The MoT asserts that building causeways costs approximately three times more than sand filling, resulting in higher project investment costs in the Mekong Delta compared to other regions. This core issue has been pivotal in its reluctance to approve causeway construction plans. However, others argue that, in many scenarios, utilizing U-UHPC beams for causeway construction presents a financially-viable option, with costs only 25-35 per cent higher than sand filling, rather than the three-fold increase claimed by the MoT. But what is the reality?

Dr. Viet said the challenge is that the MoT’s cost benchmarking is based on the Ho Chi Mnh City - Trung Luong Expressway, where causeway investments have been deemed to be three-times as costly as sand filling, thus impeding wider adoption. It is worth noting, however, that this expressway involved complex terrain and geological challenges, including sections with unstable ground conditions. To address the resulting bottlenecks, some 13 km of causeways were built along the route using Super-T beams.

Nevertheless, Dr. Viet contends that employing advanced solutions like U beams instead of Super-T beams could significantly lower investment costs. For instance, in Section 3 of the Chau Doc - Can Tho - Soc Trang Expressway, the cost for causeway construction using UHPC beams is VND256 billion ($10.04 million) per km compared to VND304.5 billion ($11.92 million) per km for Super-T beams.

He explained that UHPC beams require only four beams compared to seven Super-T beams. Additionally, the longer length of U-UHPC beams (50 meters vs. 38 meters for Super-T beams) reduces the number of bored piles required by approximately 20 per cent. Regarding Section 3 of the Chau Doc - Can Tho - Soc Trang Expressway, the cost of investing in causeway construction using U-UHPC beams is almost equivalent to the sand filling option (97.8 per cent), whereas in Section 1 the investment in causeway construction is 1.25 times higher than sand filling.

“In general, clearing land for 1 km in Section 3 and Section 1 typically requires approximately 68 ha and 65 ha, respectively,” he emphasized. “However, using causeways only involves clearing about 16 ha of land. A saving of up to 75 per cent of land resources is critical in these projects.”

Thus, in many instances, the overall investment cost for causeway construction using UHPC beams, including consulting fees, surveying, design verification, project management, and site clearance costs, is lower than for Super-T beams and sand filling.

In addition to financial considerations, there is also a strong argument for a comprehensive comparison of all factors, as causeways remain a viable option that minimize resource exploitation and environmental impact. The VCA points out an unquantified impact in expressway and highway construction, particularly concerning environmental effects such as soil filling, flood prevention, and sediment distribution. Importantly, the use of sea sand in the Mekong Delta entails significant, difficult-to-determine impacts and requires environmental trade-offs.

Box:

Dr. Tran Ba Viet, Vice President of the Vietnam Concrete Association (VCA)

In terms of criteria for constructing causeways, I advocate their application in regions characterized by weak soil, requiring underpasses for residential use, and where embankments exceed 3 meters. These areas often experience shortages of sand, leading to increased sand prices ranging from approximately VND250-300,000 ($9.8-$11.76) per cu m, sourced from Cambodia, while bidding prices are around VND170-180,000 ($7) per cu m, with mines yet to be allocated. Market rates can go up to VND270-280,000 ($11.2) per cu m. Causeways are also well-suited for deployment in areas where embankments hinder flood drainage and feature large intersections spaced 70-100 meters apart. Furthermore, the investment costs for causeway projects in Mekong Delta expressways are comparable to high sand filling options, and the cost-effectiveness of using large-span UHPC beams is superior to Super-T beams in regions with high sand filling.