Materials, Design, Technologies and Zero Risk – Let us take our future back

Lately, there have been several talks by some opinion leaders on the building safety, with reference to the acceptability of the risk of collapse, either for new buildings or for maintenance and structural restoration of the existing building heritage. However, these remarks cannot refer exclusively to engineering design in the strict sense (use of codes and regulations for structural purposes) but must include innovative technologies and new materials used in a manner equivalent to calculation.
And starting from the materials (whether new or not) we would like to make our own contribution to the ongoing debate.

Zero Risk

To date, the structural reliability of a reinforced concrete or masonry depends on the mandatory design codes, materials and application technologies validated, making the probability of a negative event low but certainly such as not to exclude the probability of collapse (zero risk). Therefore, it should be noted that only the validity of design codes, the service life reliability of materials, the expertise of both designer and materials technologist, are the only tools to reduce (unfortunately not to eliminate!) the risk of collapse of building structures.
And it is in this general context in which we discuss design codes, new plant engineering and application technologies that we need to approach the materials from a different vision, so that the PROJECT of a building is the hybridization of different skills and not simply the result of a calculation.

Materials

At the beginning of the 90s, at the invitation of a Japanese company, I visited a precast company, accompanied by some Italian entrepreneurs of the same sector.The first thing we noticed was the scrupulous attention to the choice of materials.All metal reinforcements, from cables to nets, were entirely treated with epoxy resin to avoid corrosion during the lifetime of the structural element. Beams, slabs, panels and pillars, after the formwork removal, were placed in water pools for aging for up to 28 days. Asking  why this treatment was necessary, the answer was as simple as ingenious: they could not afford to carry out an effective programmed maintenance, in case of deterioration due to corrosion of the reinforcement or not perfect aging of the cement paste, on structural elements located in buildings of more than 5 floors!
…..We are talking about the ’90s!
We noticed that already at that time they were producing curtain panels, safe concrete barriers like new jersey walls, with structural polymeric fibers, completely eliminating any metal reinforcement. If we then think about the development of FRP systems by Mitsubishi at the end of the 90s and the subsequent development of new polymeric fibers (carbon,aramid, PBO, etc.), I have the clear feeling that the Japanese approach to the construction sector is that the durability of the materials used prevails over the calculation and architectural aspects of the work.
Unfortunately, this sensitivity to the durability of building materials in Italy is not sufficiently perceived for both a lack of teaching at university level and a cultural approach that sees structural and architectural design (calculation and aesthetics) prevail over the reliability of materials used.
The unfortunate events of recent years – earthquakes included – of collapsed, degraded and out of order infrastructure, of hundreds of thousands of bridges whose structural safety is unknown but they are still in service, of thousands of school and hospitals just to name a few types, cannot but make us reflect on the fact that most, if not all, of these emergency situations are due to the unsuitable construction materials.
I am reminded of what has been done in terms of restoration work on the Polcevera viaduct, which has been maintained since its construction, continuing over the years with repair projects  that seemed to pursue, without ever achieving the complete reliability of restoration. The latter could never be achieved, because the materials and technologies used complied with the regulations in force but were not sufficiently suitable for service life .
Until we find a zero-porous structural binder to replace the concrete characterized by macro and micro porosity, we cannot avoid the phenomena, more or less accentuated, of corrosion of the metal reinforcements used in reinforced concrete.
However, we can attempt to start a technical-scientific and regulatory process aimed at developing METAL FREE building technologies. While the design codes -the calculations- can be verified as they are based on mathematics and physics to substantiate even bold architectural solutions, there is no “scientific” – physical or mathematical – basis, on materials, according to the variable environmental conditions and exposure time, cannot be traced back to mathematical or physical models but to chemical-physical processes that can change over the time and are not predictable today.

… What to do then? First, we try to eliminate from the beginning the corrosion of the reinforcements, moving towards a Metal Free Approach.

Proposals
Precast Sector

Although there are already small infrastructures built without metal reinforcements (Metal Free) and hoping that they can continue to be built, I would advise to start, at the prefabrication plants, studies and constructions of structural and non-structural elements, totally free of metal elements, using nets, cables and composites with polymeric fibers of glass, aramid, carbon, PBO, etc.
The consequent reduction of the concrete cover, combined with a correct structural design, could reduce the weight of the building by as much as 40% (according to some constructions already carried out in the United States) and a consequent saving of cement (Green Economy).
At this point the Nominal Life of the building with these “Metal Free Elements” would be lightened by the maintenance costs due to the corrosion of the reinforcements and the consequent positive effects on the structural fatigue phenomena, giving a significant contribution to maintain the initial performance levels over time.
The precast manufacturer will of course continue to make the traditional elements but will start a line of new technologies that will replace the traditional production line in the future, even for events that are currently unforeseeable but probable.
This process will necessarily involve structural engineers, materials experts and academics for the validation of new processes and for the regulatory acceptance by the MIT [Italian Ministry of Infrastructure and Transport].

Structural restoration, improvement and seismic retrofitting.

This sector has been the one that has suffered the most in recent years from significant innovations, aimed at implementing long-lasting repair restoration.
Just to point out a few examples, the develop of FRP systems (late ’90s) that have replaced almost entirely the technology of beton plaquèfor reinforced concrete repair.
In the same period (early 2000) the first patents were filed and several pioneering repair projects were carried out (shear reinforcement of the beams at the San Siro Stadium in Milan, retrofitting of the Cathedral of Noto, etc.) with FRCM composites, in which the epoxy resin is replaced as a binder, by an inorganic, non-flammable, breathable and durable material in operation even at temperatures and relative humidity at which the epoxy resins lose their effectiveness due to the glass transition temperature.
The next step, in my opinion, will be to complete the scientific, technological and regulatory process for the total elimination of metal elements, such as welded steel  mesh with metal inserts and connectors, discrete metal fibers, replacing the latter with repair mortars with polymeric fibers able to create composites with hardening properties, covering all areas of application of the traditional mortars with steel fibers.
Some of these composites have already been development and marketed; it is a matter of changing mentality and forgetting the “metal” to start, without preconceptions, a wide-ranging study involving the academic world and at the same time to gather a host of experts (Italian Ministry of Infrastructure and Transport, Academics, Companies) for the preparation of standard and immediately usable regulations.

At the end of these talk I would not want anyone to think that these are “the usual good intentions”; for more than 35 years I have been involved in developing materials and technologies for construction, thinking about their durability in operation, there is a strong determination to continue in this direction. I believe, however, that only through the hybridization of different skills, it will be possible to start an innovative phase for the constructions in our country.

Giovanni Mantegazza
Technical Director and Co-Founder -MAHAC srl