Our bridges, motor­ways, tun­nels, and dams, and all the build­ings that make up our infra­struc­ture are vital to our soci­ety and eco­nom­ic growth yet we take them for grant­ed. The shock­ing truth is that our infra­struc­ture is crum­bling beneath our feet. And this is cost­ing us dear­ly, both in terms of mon­ey and carbon. 

Now, most of our infra­struc­ture is actu­al­ly made up of a remark­able con­struc­tion mate­r­i­al, con­crete. But con­crete dete­ri­o­rates, and for decades we have been neglect­ing its upkeep. It is now reach­ing a state of cri­sis. It will require huge amounts of mon­ey to upgrade it. 

And we use so much con­crete, around three tons for every per­son on the plan­et, per year. It is the second-most used sub­stance on earth after water. It con­sumes huge quan­ti­ties of nat­ur­al resources, and the pro­duc­tion of its cement com­po­nent alone emits about 8% of all man-made CO2, rough­ly one ton per ton.

The sta­tus quo does not make any eco­nom­ic or envi­ron­men­tal sense. Which begs the ques­tion, can we design our con­crete struc­tures to look after them­selves? This way, they could last so much longer, we would use far less con­crete, slash­ing expen­di­ture, car­bon emis­sions, and envi­ron­men­tal damage.

Looking to nat­ur­al sys­tems for inspi­ra­tion, the con­cept of self-healing mate­ri­als emerged. So, can we turn the non-living con­crete all around us into liv­ing sys­tems? Wee see advances in oth­er sec­tors. Self-healing paints for our cars, and self-healing asphalt for our roads are becom­ing a reality.

But con­crete is a far more com­plex mate­r­i­al. It is a multi-component, multi-layered sys­tem, and dam­age occurs at dif­fer­ent length and tem­po­ral scales. As pat of a nation­al team, our inspi­ra­tion came from the sim­i­lar­ly com­plex way in which our skin deals with dam­age at dif­fer­ent levels.

So for small-scale dam­age, my team at Cambridge has been devel­op­ing tiny cap­sules which we felt with a heal­ing agent and we mixed with­in the con­crete. They then remain dor­mant until the con­crete is attacked. A crack would them rup­ture the cap­sules, releas­ing the heal­ing agent, which fills the crack, seal­ing it. 

Similar to the for­ma­tion of a blood clot, the whole of the self-healing process has to be com­pat­i­ble with a con­crete matrix and to restore func­tion­al­i­ty, and we have been able to deliv­er a sim­i­lar func­tion using min­er­al com­pounds. Some strains of bac­te­ria that pro­duced lime­stone, which is a nat­ur­al cement, is anoth­er good contender. 

For large-scale dam­age, we are employ­ing shape-memory poly­mers, the same mate­ri­als used in med­ical sutures or shrink-wrap. These are plas­tic rods placed strate­gi­cal­ly with­in the con­crete, and they shrink when large cracks form, there­by clos­ing them, and the cap­sules can actu­al­ly fin­ish their seal­ing process.

Now dam­age is some­times recur­rent. And like our cir­cu­la­to­ry blood sys­tem, we are devel­op­ing flow net­works using small inter­con­nect­ed tubes. Through these, we can con­tin­u­ous­ly cir­cu­late a heal­ing agent with­in the con­crete so that it’s avail­able when it’s need­ed again and again. So, we have made sig­nif­i­cant advances on the per­for­mance of indi­vid­ual self-healing com­po­nents, and are col­lec­tive­ly work­ing on the more chal­leng­ing inte­grat­ed configurations. 

There is also the chal­lenge of longevi­ty and resilience, as well as of course min­i­miz­ing any addi­tion­al cap­i­tal cost of the con­crete. Together with our indus­tri­al part­ners, we have con­duct­ed full-scale field tri­als through which we’re demon­strat­ing some of the devel­oped self-healing sys­tems, and we are mon­i­tor­ing those in the real world. We are test­ing both con­crete repair appli­ca­tions as well as new con­crete construction.

We are also impact­ing on oth­er sec­tors where con­crete and oth­er sim­i­lar mate­ri­als like grouts and mor­tars play a key role. Our focus is on extreme and inac­ces­si­ble envi­ron­ments, for exam­ple under­ground nuclear repos­i­to­ries, or in oil well cement­ing appli­ca­tions, where safe­ty is paramount.

Self-healing con­crete can deliv­er a low-carbon infra­struc­ture by poten­tial­ly elim­i­nat­ing inspec­tion, repair, main­te­nance, and replace­ment, and build­ing the future with a much low­er whole-life cost. We can trans­form our land­scapes and our every­day lives.

We are con­fi­dent we can pro­duce self-healing con­crete, but it’s going to take a lot more than that to make it into a com­mer­cial real­i­ty. We are also explor­ing self-sensing, self-reporting, and self-immunity in concrete. 

So my ques­tion to you is, how can we all work togeth­er to trans­form this remark­able con­struc­tion mate­r­i­al all around us into a far more remark­able liv­ing sys­tem? Thank you.

Further Reference

The con­crete that heals its own cracks ” by Abir Al-Tabbaa, at the World Economic Forum site.

Faculty page at the University of Cambridge.