Structural Concrete Prepared with Coarse Recycled Concrete Aggregate: From Investigation to Design

An investigation of mechanical behaviour and elastic properties of recycled aggregate concrete (RAC) is presented. RACs were prepared by using a coarse aggregate fraction made of recycled concrete coming from a recycling plant in which rubble from concrete structure demolition is collected and suitably treated. Several concrete mixtures were prepared by using either the only virgin aggregates (as reference) or 30% coarse recycled aggregate replacing gravel and by using two different kinds of cement. Different water-to-cement ratios were adopted ranging from 0.40 to 0.60. Concrete workability was always in the range 190–200 mm. Concrete compressive strength, elastic modulus, and drying shrinkage were evaluated. Results obtained showed that structural concrete up to C32/40 strength class can be manufactured with RAC. Moreover, results obtained from experimentation were discussed in order to obtain useful information for RAC structure design, particularly in terms of elastic modulus and drying shrinkage prediction

a variational model for determining fracture modes in frcm systems

Abstract: The bond strength at the yarn to matrix interface is one of the key factor affecting the FRCM mechanical behavior. The interaction between multi-filament yarn and cementitious matrix, governed by complex mechanisms, determines the behavior and failure mode of this composite system. An experimental campaign comprising of 20 pull out tests on multifilament carbon yarns embedded in a cementitious matrix was carried out. Different bond lengths have been analyzed, equal to 20 and 50 mm. Failure modes observed were different depending on the bond length: slippage of the yarn for a bond length of 20 mm and failure of the external filaments when the bond length was increased to 50 mm. The maximum load recorded at fibers breakage was lower than the tensile strength of the yarn, confirming the fact that only the external filaments of the yarn are engaged in the load transfer mechanism and the effective area is only a portion of the total area. This work aims to propose a variational model to reproduce the behavior and possible failure modes of multifilament carbon yarns embedded in a cementitious matrix. Smeared crack terms are incorporated into the energy functional of the model to account for possible fracture in the yarn and in the matrix, and for debonding at the yarn-matrix interface. The evolution problem is formulated as an incremental energy minimization problem, and discretized by finite elements. Numerical simulations are able to accurately describe the composite behaviours and to reproduce experimental results

Early-Age Behaviour of Fiber Reinforced High Performance Concretes

The aim of this experimental activity was to study the early-age behavior of several Fiber-Reinforced Concretes (FRCs) containing expansive agent. The investigation concerned the evaluation of the influence of different amounts of fibers (dosages of 2.0%, 1.75% and 1.5% by volume of FRCC) on the mechanical performance of FRCs. In particular, hooked brass-coated fibers were used and dead-burnt calcium oxide based expansive agent was employed at a dosage of 40 kg/m3. The attention was focused on the strength development at early ages. Mechanical tests were carried out at 0.25 (i.e. 6 hours, that is time of demolding), 1, 2, 7 up to 28 days of curing. The properties of FRCs were characterized at the fresh state, by measuring flow ability and consistency as well as at hardened state by measuring compressive and flexural strength up to 28 days. Flexural strength was measured on prismatic specimens according to the procedure described in EN 12390-5. The different dosage of fibers did not influence the values of compressive strength, while there is a significant difference in terms of 28-day flexural strength between the several mixtures depending on the different amount of fibers. In all cases at least 20 MPa of 28-day peak flexural strength were achieved

Reusing and Recycling C&D Waste in Europe

Proceedings of the International Conference on "Sustainable Waste Management and Recycling: Challenges and Opportunities", held at Kingston University, London, U.K., September 14-15, 200

Recycled demolition wastes for concrete and mortar

Two-Day International Seminar on "Sustainable Development in Cement and Concrete Industries", Milan, Ital