Roman secret to durable architecture? Self-healing concrete

Subject: Science & Tech

Section :Msc

Roman architecture:

For many years, researchers assumed the key to the ancient concrete’s durability was based on one ingredient: Pozzolanic material, such as volcanic ash from the area of Pozzuoli on the Bay of Naples.

Recent findings:

Under closer examination, the researchers found the ancient samples also contain small, distinctive, millimetre-scale bright white mineral features, which have been long recognised as a ubiquitous component of Roman concretes.
These white chunks often called “lime clasts,” originate from lime, another critical part of the ancient concrete mix.
The relict lime casts were earlier thought of as evidence of sloppy mixing practices or poor-quality raw materials.
On close examination, they found the Romans employed a hot mixing method and used quicklime in conjunction with, or instead of, slaked lime for producing concrete.
Hot mixingwas actually the key to the super-durable nature.

What is Self healing concrete?

It will biologically produce limestone to heal cracks that appear on the surface of concrete structures.
Bacterial concrete or self healing concrete fills up the cracks developed in structures by the help of bacterial reaction (produce limestone) in the concrete after hardening.

Hot mixing process:

During the hot mixing process, the lime clasts created a brittle structure with a reactive calcium source.
The calcium would travel through the lime clasts, react with water and quickly fill any cracks.

Schematic of the proposed mechanism for self-healing within ancient Roman mortars

The calcium-saturated solution could also react with pozzolanic materials to further strengthen the composite material.
These reactions take place spontaneously and automatically heal the cracks before they spread.