International Concrete Abstracts Portal

The development of low carbon footprint and high initial compressive strength binders for the precast industry is presented. Binders with a substitution of up to 75% of a normal Portland cement (CEM I) with a mixture of metakaolin and two different limestone additions were developed on mortars. Water/binder ratio reduction (down to 0.25) and thermal treatment (up to 50°C) have been applied to improve initial compressive strength (> 14 MPa at 8 hours). Pozzolanic reaction improved 28 days compressive strength (> 50 MPa). The most technically and environmentally performant binders have been applied to concrete. Concretes with low clinker contents have been produced to achieve the C25/C30 and C40/50 strength classes. Durability performances corresponding to XC4 were assessed via a performance approach (FD P 18-480). A wall with integrated formwork has been industrially manufactured which allowed a carbon footprint reduction of around 30% over its whole life cycle.

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.

This research focused on concrete beams with voids simulating beams with fully corroded steel that were repaired with CFRP laminates. The experimental program included testing five, approximately one-third-scaled simply supported rectangular concrete beams. In three beams, the oiled steel rebars for flexure and shear were safely pulled out of the formwork after the concrete had cured for six hours, leaving voids. This technique was used to represent an extreme case of corrosion, albeit non-realistic, that is even worse than being exposed to the most corrosive environment. The aim was to investigate the extent of improvement by CFRP to flexural and shear capacity of beams that contain fully corroded steel bars, simulated by voids. The first specimen was with voids representing completely deteriorated steel. The second was a plain concrete beam without voids. The third beam was a typical code-designed reinforced concrete (RC) beam, that represented the “original undeteriorated” beam. The two remaining deteriorated beams were repaired by externally bonding one and two layers of CFRP. Load carrying capacity, deflection, and ductility were measured and compared. The novel results of this investigation were that test results showed that one layer of CFRP increased the load capacity to slightly higher than the RC beam, and two layers of CFRP increased it by a factor of two. Finally, a computer model was created to estimate the performance of the tested beams and to carry out a parametric study to investigate the effects of CFRP longitudinal reinforcement ratio and CFRP transverse confinement ratio on the flexural performance of CFRP-repaired concrete beams. The predicted contribution of CFRP to flexure and shear capacities was in good agreement with test results.

Insulated concrete sandwich panels are composed of two concrete wythes separated by an insulation layer and connected by shear connectors. This paper develops a multifunctional photovoltaic (PV) integrated insulated concrete sandwich (PVICS) panel, which can act as a passive energy system through the insulation layer and an active energy system by harvesting the solar energy using attached thin-film solar cells. The panel features an innovative co-curing scheme, where solar cells, Fiber-Reinforced Polymer (FRP) shell, and polymer concrete are manufactured together to act as a formwork for the sandwich panel. The objective of this paper is to prove the concept of PVICS based on bending test, Finite Element (FE) analysis and analytical study. It can be concluded that the test results correlate well with those from the FE and analytical models. FRP shell can act as both shear connectors and reinforcement. The panel achieved 82% Degree of Composite Action, which can provide enough strength and stiffness. Solar cells worked properly under service load. Shear-lag effect was observed for the strains along the width of the panel.

The results of an experimental campaign on the thermal conductivity of a mortar (cement + sand) containing various amounts of steel fibers are presented in this study. Increasing the amount of steel fibers (from 0 to 6% by volume) is shown to reduce the thermal conductivity of SFRC, by the extra porosity induced by the fibers and contact thermal resistance. To show the possible benefits coming from the use of SFRC, the case of SFRC formworks is presented, as these formworks may be used in the fire protection of R/C members, as expendable permanent formworks. To this purpose, the finite-element analysis of an R/C member protected by a SFRC formwork is presented, to assess the effectiveness of this kind of fire protection