A special concrete was used to erect the MAXXI building in Rome designed by Zaha Hadid and her team with long, inclined, curvilinear walls. Due to the very congested reinforcements, the original concrete issued by Zaha Hadid and her team was self-compacting concrete (SCC). However, irregular cracks -caused by the restrained drying shrinkage- appeared on the surface of this concrete a few days after removing the formworks. On the other hand, due to aesthetic reasons, neither saw cuts in the hardened concrete to produce regular contraction joints -carried out to avoid the irregular cracks caused by a restrained drying shrinkage- were accepted by the Architects. Therefore, a special 3-SC mixture was developed and used; it is characterized to be: - a self-compacting concrete based on the use of an acrylic superplasticizer, a viscosity modifier to avoid the bleeding risk, and a special particle size distribution of the aggregates; - a self-compressive concrete due to the use of a CaO-based expansive agent; - a self-curing concrete based on the use of a shrinkage-reducing admixture (SRA). This concrete called 3-SC, because it is 3 times “self”, was very successful in producing a crack-free concrete surface even in the very long, curvilinear, and inclined walls: after 18 years of building the long, inclined, curvilinear walls of the MAXXI museum have been carefully examined and during the last inspection their surface resulted to be still sound and crack-free. However, just before the building’s inauguration in 2009, in very few areas some micro-cracks were observed on the concrete surface and considered to be dangerous for the future of the building. Therefore, the concrete surface was treated with a transparent varnish in order to avoid the ingress of the aggressive humid air to protect the steel reinforcements from the corrosion promoted by the carbonation process.

The application of a novel superabsorbent polymer (SAP) as a multifunctional chemical admixture for concrete properties is expected to contribute to the overall durability and sustainability of concrete structures. SAPs are well known to quickly absorb and retain a significant amount of water within the concrete matrix as a means of providing internal curing. However, the rate of water uptake can significantly affect the rheology of fresh concrete such as reduced flowability. This paper introduces a novel SAP that features slow water absorption and swelling behavior, and its resulting impact on both fresh and hardened concrete properties. The novel SAP has been shown to delay swelling for several hours in cement filtrate, followed by a predictable absorption of water over a 24-hour period comparable to conventional SAP. The delayed swelling effect observed with the novel SAP eliminates the need for additional water to obtain a similar flowability, but with a very slight increase in viscosity, compared to a concrete mixture without SAP. Moreover, the internal curing capability of the novel SAP can result in an increase in both early age and long-term compressive strengths, improved freeze-thaw resistance, and a reduction in autogenous shrinkage under sealed and air curing conditions.

The present paper shows the study of a mixture design of the concrete used in the reinforced foundations of the bridge on the Straits of Messina in Italy. A cube compressive characteristic strength of 35 MPa (5,075 psi) is required for the foundation concrete. Due to the peculiar shape of the concrete foundations (completely embedded in the excavated ground), the damages caused by the thermal stress, the steel corrosion, and the alkali-silica reaction cannot be monitored and repaired. Therefore, a concrete structure must be designed without any damage for at least 200 years due to the very important role of this structure from a social point of view. In order to guarantee this long-term durability, there are two problems to be faced and solved: 1) the heat of cement hydration could cause cracks inside the foundation due to thermal gradients between the hotter nucleus of the massive structure and the colder peripheral areas; 2) the corrosion of the metallic reinforcements caused by the reaction between the metallic iron and the oxygen (O₂) present in the air to an extent of about 20%; 3) the alkali-silica reaction causing a local disruption in the concrete. All these problems can be solved using a blast-furnace slag cement such as CEM III B 32.5 R characterized by a very small heat of hydration and adopting a ground coarse aggregate with a maximum size as large as 32 mm (1.28 in): the choice of this aggregate produces a reduction in the amount of mixing water and then of the cement content and reduces the volume of the entrapped air at about 1.3% by concrete volume. This amount of O₂ would cause the corrosion of a negligible amount of iron corresponding to only 10 to 13 g (0.4 to 0.5 oz) of steel in 1 m³ (1.31 yd³) of concrete of each foundation. In order to prevent any ingress of air from the environment, the top of the foundation should be protected by self-compacting, self-compressing, and self-curing concrete.

The use of recycled aggregates allows for reducing the environmental impact of concrete materials, by reducing the amount of waste and limiting the consumption of natural resources. Recycled asphalt pavement (RAP) is a granular material that comes from the milling of road pavements whose size and distribution make it suitable as aggregate for concrete. The environmental benefits of the replacement of natural aggregate with RAP need to be assessed with a better understanding of the long-term behavior of RAP concrete, considering the evolution of its performance in time and its ability to guarantee an adequate service life when exposed in operating conditions. This note presents the preliminary results of research on the effect of RAP on concrete properties. The addition of RAP aggregate affects concrete properties in a fresh and hardened state. Some parameters showed clear trends with the percentage of RAP, however, also other factors (e.g. w/c ratio and curing time) seem to play a role. Compressive strength and dynamic modulus of elasticity of RAP concrete were always lower compared to reference concrete, while the electrical resistivity did not show a clear trend. Further investigations will be carried out to clarify the role of RAP aggregate.

The use of recycled concrete aggregate (RCA) from construction and demolition waste (CDW) in new concrete production is a promising solution to reduce the exploitation of non-renewable resources and landfill waste. Nowadays, only a small part of RCA is recycled due to severe regulatory restrictions in this field. Specifically, Italian Standards enable the use of solely coarse RCA and limit by 30% its substitution ratio to natural aggregate for structural concrete >C20/25 and ≤C30/37. In the present paper, concrete waste resulting from selective demolition was fully characterized and the high potential to develop green structural concrete using high RCA content was outlined. Substitution ratios of 30, 60, and 90vol% of natural aggregates were evaluated. Special attention was paid to the concrete mix design depending on the peculiar properties of RCA. Compressive strength tests at 3, 7, and 28 days of curing outlined the possibility to develop highly sustainable concrete of strength class C25/30. Thus, a viable and sustainable valorization of all particle size fractions was suggested, as well as the necessity of more permissive regulations based on the quality of the RCA used.