Bentonite to Polymer Slurry, the Sustainable Route to Building Reinforced Concrete Diaphragm Walls

Bentonite has been a crucial construction element in building reinforced concrete diaphragm walls for deep basement structures. But over the years, civil construction companies have started using polymer in their excavation fluids and slurry.

Read on to understand the importance of both the materials in constructing concrete diaphragm walls, the differences between them, and how polymer is growing as a more sustainable option in excavation activity while bentonite remains the foolproof back plan for civil engineers.

What are Bentonite and Polymer Slurries?

Bentonite clay is formed by the alteration and weathering of volcanic ash and is abundant in the clay mineral montmorillonite, which swells when mixed with water and possesses exchangeable irons on the surface that produce thixotropic suspensions. Typically mined in Rajasthan India, it is extensively used in diaphragm wall construction as an excavation fluid. Bentonite clay (in powder form) is combined with water in a colloidal mixer where the clay particles bond with one another to form a gel-like texture.

The mixing process continues till the standard quality is achieved for the slurry.

Polymer slurry is prepared with the combination of water and hydrophilic superabsorbent polymers like polyethylene glycol, polyvinyl alcohol, or carboxymethylcellulose to form a thick, viscous mix. These water-soluble polymers have been used to stabilise deep excavations for reinforced concrete diaphragm wall trenches. When compared with conventional bentonite slurries,this engineered fluid is known to offer a variety of advantages including smaller site footprint and lesser environmental impact.

How is a bentonite slurry or polymer slurry prepared?

The slurry is prepared with the aim of attaining maximum hydration of bentonite clay or polymers. Hence, it must be slowly added into the mixing water to ensure all particles are irrigated and do not get lumped. Potable fresh water should be used in the mixing process to obtain the best results. Alongside this a chemical analysis, as listed out by the Indian Standard Code of Practice for Construction of Diaphragm Wall, must be conducted to ascertain the suitability of water. If needed, chemical treatment is given to the water before its usage.

The preparation of the slurry is done either in batches or in a continuous process, depending on the type of equipment used. The components are added in a high shear mixer through a simple venturi-hopper. To assure the dispersion of all the individual particles in the mixing water, the mixing equipment must generate sufficient shear. Once prepared, it is moved to storage tanks, and from there they are supplied to the excavation point, to be filled into the cavity of the soil. This entire process, including the testing is done on-site by the civil construction company assigned to build the diaphragm wall.

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Everything You Need To Know About Building Concrete Diaphragm Walls

Right from metro rail construction to new age super structures like towering residential and commercial complexes, building of concrete diaphragm wall has become a common practice and projects are now seeking only the best diaphragm wall company, like HIPL, to be building these D-Walls. But, what exactly is a diaphragm wall, and how does it help building structures? Here’s everything you need to know.

What is a concrete diaphragm wall?

Diaphragm walls or slurry walls are generally reinforced concrete walls, constructed in the ground using an under-slurry technique developed in Europe. This technique involves excavating a narrow trench that is kept full of an engineered fluid of slurry. This way, walls with thickness ranging between 300 mm to 1200 mm can be formed as deep as 45 metres underneath. Inclined rock or soil anchors are used for this purpose. Diaphragm walls are commonly used while constructing structures with deep basements in congested areas, as they can be installed in close proximity to the existing structures.

Previous history of diaphragm wall being used in construction in India

The earliest recorded use of diaphragm wall technology is said to be during the excavations for the construction of Milan Metro in Italy back in the 1950s. In India, this technique can be traced back to the construction of metro rail stations and tunnels, Kolkata Metro being the first ones.

This is a civil engineering technique of construction, pioneered by Heritage Infraspace in deep basement diaphragm walls in India.

Now, in metro construction, D-walls ranging between 800 to 1200 mm are built. But while constructing deep basements for residential and commercial complexes, there are varying sizes used, they are as follows:

• For a single basement construction, we build 300 mm diaphragm walls
• For a double basement construction, we build a minimum 400 mm diaphragm wall
• For a 3-basement construction, we build a minimum 500 mm diaphragm wall
• And for a construction of 4-basement or more, we build diaphragm walls starting at 600 mms.

But here’s a crucial point to remember, all the above depends majorly on the soil strata. For a D-wall to do its job perfectly, the soil must not be loose. D-wall construction makes it cost effective compared to the other older, traditional methods like Piling. The major challenge with Piling, apart from being costly and time consuming, is that it doesn’t maintain the verticality.

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