Self-Healing Properties of Bioinspired Amorphous CaCO3/Polyphosphate-Supplemented Cement.

Emad Tolba,Xiaohong Wang,Meik Neufurth,Heinz C Schröder,Bothaina M Abd El-Hady,Maximilian Ackermann,Shunfeng Wang,Werner E G Müller,Rafael Muñoz-Espí

doi:10.3390/molecules25102360

Abstract

There is a strong interest in cement additives that are able to prevent or mitigate the adverse effects of cracks in concrete that cause corrosion of the reinforcement. Inorganic polyphosphate (polyP), a natural polymer that is synthesized by bacteria, even those on cement/concrete, can increase the resistance of concrete to progressive damage from micro-cracking. Here we use a novel bioinspired strategy based on polyP-stabilized amorphous calcium carbonate (ACC) to give this material self-healing properties. Portland cement was supplemented with ACC nanoparticles which were stabilized with 10% (w/w) Na–polyP. Embedding these particles in the hydrated cement resulted in the formation of calcite crystals after a hardening time of 10 days, which were not seen in controls, indicating that the particles dissolve and then transform into calcite. While there was no significant repair in the controls without ACC, almost complete closure of the cracks was observed after a 10 days healing period in the ACC-supplemented samples. Nanoindentation measurements on the self-healed crack surfaces showed a similar or slightly higher elasticity at a lower hardness compared to non-cracked surfaces. Our results demonstrate that bioinspired approaches, like the use of polyP-stabilized ACC shown here, can significantly improve the repair capacity of Portland cement.

Highlights

Concrete has proven to be an excellent building material since a few thousand years, like in the Ancient Rome or in the German city of Trier, the Roman “Augusta Treverorum”, with the Basilica of Constantine which was built at the beginning of the 4th century [1]
We show that addition of amorphous calcium carbonate (ACC), amorphous CaCO3, added to the cement starting material, substantially induce the self-healing process in microcracks
The present study shows that addition of the bioinspired amorphous calcium carbonate, ACC, stabilized with Na–polyP of a chain length of 40 Pi units (“ACCP10”), substantially increases the self-healing property of Portland cement (“hCEM”)

Summary

Introduction

Concrete has proven to be an excellent building material since a few thousand years, like in the Ancient Rome or in the German city of Trier, the Roman “Augusta Treverorum”, with the Basilica of Constantine which was built at the beginning of the 4th century [1]. Cement is the binder that adheres to other materials and binds them together [1]. It is an exceptional construction material since it withstands environmental stress and compression but is prone to cracking. Molecules 2020, 25, 2360 common cause for early cracks in concrete is plastic shrinkage. Before hardening concrete is in a plastic state and full of water

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