Integrating Concrete Protective Liner in Micro-Tunneling

Over the last few decades, micro-tunneling technology has gained significant popularity as an effective alternative to conventional construction approaches, especially in densely populated urban city areas where minimal disturbance to the flow of traffic and the local economy is targeted (1). However, several drawbacks represented by the resistance of the utilized pipes to aggressive environmental actions, their long-term strength capacity, and their expected service life are currently rising concerns of decision-makers in the industry (2–4). Thus, this article discusses certain shortcomings of the traditional practice involved in micro-tunneling and suggests an efficient, yet feasible solution based on concrete protection liners.

Resistance to Aggressive Environmental Actions

While concrete pipes readily have the strength to support the jacking forces and burial loads the ability of concrete pipes to withstand the surrounding actions of aggressive media is a critical issue for ensuring efficient long-term functionality. The abrasion resistance of pipes constructed from concrete materials is one point of weakness, making concrete pipes vulnerable to abrasion in aggressive sites. Acid environments also contribute to elevated abrasive wear compared with the neutral settings, which raises concern for applications in such an environment. Applying high-density polyethylene liners to the inner surface of the pipes mitigates these issues (5).

On the other hand, wastewater chemical concentrations expose sewage pipes to degradation by attacking their surfaces through biogenic sulfuric acid corrosion (6). This attack starts when the sulfuric acid reacts with the calcium hydroxide in the cement matrix to produce a calcium sulfate compound that hydrates to form gypsum. In a continuing chemical attack, the resulting gypsum reacts with the calcium aluminate hydrate to form ettringite in the deep layers of the concrete. Finally, the ettringite causes extensive damage to the structure by expanding the elements from the surface to the inner core (7). Indeed, the lack of corrosion resistance is a massive threat responsible for a significant reduction in the projected life of concrete pipes but using concrete pipes with a plastic liner eliminates the problem of biogenic sulfuric acid corrosion (8).

In addition to the durability mentioned above, designing engineers tend to control thermal actions by improving the resistance of concrete pipes using insulation materials. A study about this issue shows that polyethylene liner is an easy-to-apply material that can sustain most acids and alkalis at a moderate temperature, making such applications suitable for micro-tunneling activities (9).

Long-term Strength Capacity of Concrete Pipes

One of the main advantages of concrete pipes over other options is their high strength and rigidity, allowing utilization when extensive loads and stresses are acting on the pipes (10). However, the long-term serviceability performance of the pipes is a factor in the concrete mixture’s permeability. Improving the pipe’s surface resistance to external actions is vital to ensure the system’s long-term integrity. Presently, using concrete protective liners significantly enhance the capability of concrete pipes to preserve their strength properties at a later age. They also improve the surface resistance to acid, abrasions, and other aggressive attacks that tear the pipe’s surface and drop the life span of the structural element (11).

Life Cycle Cost Optimization

Multiple factors play a vital role in selecting pipes material for micro-tunneling applications. Among them, decision-makers consider the life cycle cost as an essential parameter. Generally, using concrete pipes in micro-tunneling is an economical option from a construction engineering point of view, owing to the low materials and labor cost requirements at the manufacturing stage and its high rigidity. Moreover, concrete pipes have the least global warming potential compared to ductile iron, cast iron, PVC, and high-density polyethylene (12). Nevertheless, the pipes’ life is typically a function of the durability of the concrete mixture. Accordingly, applying concrete protective liners to concrete pipes extends their life span, reduces the system’s construction and maintenance cost, and permits more controlled life cycle cost optimization.

Concrete Protection Liner: A Solution for Risk Mitigation in Concrete Pipes

One of the advantages of concrete pipes over other alternatives is their high strength development at a low manufacturing cost. However, several aggressive environmental actions impact the long-term serviceability performance of such rigid pipes, decrease their inherent strength and robustness, and reduce their estimated life (13). This is why AGRU developed a concrete protective liner (CPL) technology, known as AGRU-ULTRA GRIP®, made of chemically resistant thermoplastics that, when integrated with the micro-tunneling applications, can increase the resistance of the concrete pipes to aggressive environmental attacks. Thus, the Ultra Grip liner extends the pipes’ life and reduces the life cycle cost of the project.