Comparison between the environmental performance of buildings made of reinforced concrete and timber

In order to reduce the environmental impact of the construction industry, the case of natural material (such as timber) is pursued. However, is the use of low-impact materials sufficient to decrease the overall environmental impact of a building? The answer is not trivial, because there are many parameters that affect sustainability, in addition to the unitary environmental impact of the building materials. Through this article, an evaluation of the total CO2 emission in buildings made of reinforced concrete and CLT panels is carried out. The entire life cycle (LCA) of the materials is considered, as well as the CO2 emissions derived from heating and chilling. The relationship between CO2 emissions and building height is also taken into account along with weather conditions.The structures and envelopes of a three - storey family house and of a multi-storey residential building are designed from a structural and thermal point of view, respectively. In order to consider the climatic effects, three locations with very different weather conditions are assumed (i.e. Catania, Turin, Oslo). The carbon footprint of three different structures is considered, namely RC frame made with cast-in-situ structural elements, precast RC panels and timber CLT structure.The quantification of the carbon footprint allows to notice how the overall structural and thermal performances, including the thermal mass, affect the environment performance

New eco-mechanical index for concrete structures

A new eco-mechanical index (EMI) has been introduced with the aim of quantifying the environmental impact of concrete structures. From a general point of view, this indicator represents the amount of carbon dioxide released to produce certain mixtures of pre-established strength and ductility. Both for normal strength and high strength concrete, with and without steel fibers, these mechanical properties are summarised by the work of fracture under tensile actions. If also structural durability has to be taken into account, the maximum crack width of reinforced concrete structures must be computed. This is possible by using a tension-stiffening model, here applied to reinforced concrete elements in tension. However, with or without the evaluation of crack width, the concrete with the best EMI releases the highest fracture energy. For this reason, the work of fracture represents also a durability parameter, and therefore it can be used to tailor cement-based composites with the highest strength, ductility, and durability, and the lowest environmental impact

Multiple cracking and strain hardening in fiber-reinforced concrete under uniaxial tension

Fiber-reinforced concrete (FRC) showing strain hardening after cracking is commonly defined as High Performance Fiber Reinforced Cementitious Composite (HPFRCC). In the post cracking stage, several cracks develop before complete failure,which occurs when tensile strains localize in one of the formed cracks. As iswell known,multiple cracking and strain hardening can be achieved in cement-based specimens subjected to uniaxial tension by increasing the volume fraction of steel fibers with hooked ends, or by using plastic fibers with and without steel fibers, or bymeans of high bond steel fibers (e.g., twisted fibers or cords). To better understandwhy, in such situations, highmechanical performances are obtained, an analyticalmodel is herein proposed. It is based on a cohesive interface analysis,which has been largely adopted to investigate themechanical response of FRC or the snubbing effects produced by inclined fibers, but not the condition ofmultiple cracking and strain hardening ofHPFRCC. Through this approach, all the phenomena that affect the post-cracking response of FRC are evidenced, such as the nonlinear fracture mechanics of the matrix, the bond–slip behaviour between fibers andmatrix, and the elastic response of both materials. The model, capable of predicting the average distance between cracks as measured in some experimental campaigns, leads to a new design criterion for HPFRCC and can eventually be used to enhance the performances of cement-based composites

Optimal calculation of reinforcement in tunnel segmental lining

The capability of steel fiber-reinforced concrete to carry tensile stresses, also in the presence of wide cracks, allows designers to reduce the area of steel reinforcing bars. This aspect has been taken into account in a new design procedure of concrete segmental linings, capable of computing the behavior of ordinary reinforced cross-sections subjected to bending moment and normal forces. Accordingly, a practical formula to quantify the possible reduction of steel rebars in fiber-reinforced concrete is proposed in the present paper. This formula, which is in accordance with code rule requirements, has been used to optimize the reinforcement of prefabricated concrete linings

Steel fiber-reinforced self-compacting concrete subjected to concentrated loads

To model the behavior of precast segmental tunnel linings under thrust jack loading, cylindrical concrete columns, subjected to concentrated loads, are investigated. Specifically, uniaxial compressive tests have been performed on specimens made with self-compacting concrete and reinforced with two different amounts of steel fibers (0, 30 kg/m3, respectively). In addition, to measure concrete properties, three point bending tests have been carried out in accordance with code rules. As a result, not only the fracture toughness of concrete in compression is improved, but also the ultimate and the maximum splitting loads are remarkably increased by the presence of long fibers. Accordingly, a new formulation of the classical Leonhardt's approach is eventually proposed. Finally, based on the results of the present research, it seems reasonable to replace reinforced concrete with SFRSCC in structures subjected to high concentrated loads