Reinforced concrete slab optimization with simulated annealing

Flat slabs have several advantages such as a reduced and simpler formwork, versatility, and easier space partitioning, thus making them an economical and efficient structural system. When producing structural components in series, every detail can lead to significant cost differences. In these cases, structural optimization is of paramount relevance. This paper reports on the structural optimization of reinforced concrete slabs, presenting the case of a rectangular slab with two clamped adjacent edges and two simply supported edges. Using the yield lines method and the principle of virtual work, a cost function can be formulated and optimized using simulated annealing (SA). Thus, the optimal distribution of reinforcing bars and slab thickness can be found considering the flexural ultimate limit state and market materials costs. The optimum result was defined by the orthotropic coefficient k = 8, anisotropic coefficient g = 1.4, and slab thickness H = 11.8 cm. A sensitivity analysis of the solution was developed considering different material costs

Waste tire rubber particles modified by gamma radiation and their use as modifiers of concrete

En este trabajo se produjo concreto añadiendo hule de llantas de desecho, posteriormente se irradió con rayos gamma, para finalmente evaluar sus propiedades mecánicas. Los efectos de la radiación en el hule de llanta se evaluaron con diferentes técnicas analíticas.in this work, cement concrete specimens were produced with cement, water, rock crushed and sand; this last was partially substituted by particles of waste tire rubber. Then the compression properties of the specimens were evaluated following the experimental parameters: a) gamma irradiation dose (200, 250 and 300 kGy), b) particle size of tire rubber (0.85 and 2.8 mm), and c) particulate concentration of tire rubber (1, 3 and 5 wt. %). In addition, the mechanical compression results were related with the changes on the physicochemical properties of the irradiated tire particles, which were analyzed by FT-IR, Raman, UV–vis, SEM, XRD, TGA and DSC

Sensitivity analysis of a stress strain model for steel fiber reinforced concrete plates

p. 2941-2954This article deals with the sensitivity study of a given model for the behavior of thin laminar elements of SFRC (steel fiber reinforced concrete). In order to carry out this analysis, a brief description of the model used for the behavior of the SFRC in laminar elements is presented. The analysis was made by means of ABAQUS finite element software with a particular model for the behavior of SFRC. The limit of the fragile-plastic behavior of SFRC plates has been established as an outcome of the analysis. The results of test performed on plates were compared with the numerical simulation. Good correlation between experimental results and those obtained in the numerical simulation was observed as an adequate support for the model.Lopez-Gayarre, F.; Serrano, MA.; Lázaro Fernández, CM.; Domingo Cabo, A.; Pelufo Carbonell, MJ. (2009). Sensitivity analysis of a stress strain model for steel fiber reinforced concrete plates. Editorial Universitat Politècnica de València. http://hdl.handle.net/10251/668

A study on drying shrinkage and creep of recycled concrete aggregate

p. 2955-2964Although it is not a new material, in the last years the recycled aggregates of concrete RCA have had a great progress and are highly valued because of being friendly with the environment, multiple studies find feasible their use in structural concrete but when it is intended to be used in singular structures or prefabricated pieces that require high performance levels an exhaustive evaluation of its properties dealing with deformation and durability are needed. The paper presents an experimental study on drying shrinkage and creep of recycled concrete at constant standard ambient conditions, 8 concrete mixtures with 2 water/cement ratio (0,5 and 0,65) and 4 substitution levels of natural coarse aggregates by recycled concrete aggregates (0%, 20%, 50% and 100%) were used and the influence on this two important time-dependent deformations of recycled concrete were examined in conformity the ASTM C 512 for creep and UNE 83-318-94 for shrinkage. The effects of recycled concrete aggregates on the mechanical properties were analyzed and coefficients and recommendations to fit design are provided. The experimental results showed that the recycled aggregate have a significant effect on the overall elastic properties of concrete, the creep and drying shrinkage increases considerably, as the substitution level increases, without a lineal relation with the elasticity modulus variation when high performance concrete is used.Castaño, JO.; Lopez-Gayarre, F.; Lázaro Fernández, CM.; Domingo Cabo, A. (2009). A study on drying shrinkage and creep of recycled concrete aggregate. Editorial Universitat Politècnica de València. http://hdl.handle.net/10251/670

Model for the behavior of steel fibers reinforced concrete in plates elements

p. 2965-2981This article presents and develops a model for the behavior of steel fibers reinforced concrete (SFRC) for its use in plates elements. In order to carry out the present investigation, a series of laboratory tests were made for the mechanical characterization of SFRC. Additionally, a set of plates elements were tested in the laboratory of Construction Engineering at the Technical University of Valencia, with different fiber contents and load conditions. These plates elements were tested to their fracture, and the obtained results were verified experimentally with the implementation of the given model in a program of finite elements, where the tested plates were modelized. The obtained results show a satisfactory adjustment of the given model for its application in nonlinear calculation of plates elements made with steel fibers reinforced concrete.Lopez-Gayarre, F.; Lopez-Colina, C.; Lázaro Fernández, CM.; Pelufo Carbonell, MJ.; Domingo Cabo, A. (2009). Model for the behavior of steel fibers reinforced concrete in plates elements. Editorial Universitat Politècnica de València. http://hdl.handle.net/10251/670

Use of Mining Waste to Produce Ultra-High-Performance Fibre-Reinforced Concrete

This research work analyses the influence of the use of by-products from a fluorite mine to replace the fine fraction of natural aggregates, on the properties of Ultra-High-Performance Fibre-Reinforced Concrete (UHPFRC). Replacing natural aggregates for different kinds of wastes is becoming common in concrete manufacturing and there are a number of studies into the use of waste from the construction sector in UHPFRC. However, there is very little work concerning the use of waste from the mining industry. Furthermore, most of the existing studies focus on granite wastes. So, using mining sand waste is an innovative alternative to replace natural aggregates in the manufacture of UHPFRC. The substitutions in this study are of 50%, 70% and 100% by volume of 0–0.5 mm natural silica sand. The results obtained show that the variations in the properties of consistency, compressive strength, modulus of elasticity and tensile strength, among others, are acceptable for substitutions of up to 70%. Therefore, fluorite mining sand waste is proved to be a viable alternative in the manufacturing of UHPFRC

Paving with precast concrete made with recycled mixed ceramic aggregates : a viable technical option for the valorization of Construction and Demolition Wastes (CDW)

This research aimed to prove the feasibility of producing two types of precast elements widely used in construction, such as curbstones and paving blocks, using recycled concrete made with a 50% substitution of the natural gravel by recycled mixed aggregates with a significant ceramic content (>30%). In order to prove the quality of such mass concrete recycled precast elements, two different mixes were used: the first one was a conventional concrete mix provided by Prefabricados de Hormigon Pavimentos Paramo S.L., one of the collaborating companies in this study, and the other was a mixture in which wt 50% of the natural coarse aggregates were substituted for recycled mixed aggregates ceramic (RMAc). This recycled aggregate is a heterogeneous mixture of unbound aggregates, concrete, ceramic, etc., used as a secondary recycled aggregate and commonly produced in a lot of recycling plants in many European countries. This material was supplied by Tecnologia y Reciclado S.L., the other collaborating company. Both mixtures were representative in order to establish the comparative behavior between them, taking into account that smaller percentages of replacement of the natural with recycled aggregates will also produce good results. This percentage of substitution represents a high saving of natural resources (gravel) and maintains a balanced behavior of the recycled concrete, so this new material can be considered to be a viable and reliable option for precast mass concrete paving elements. The characterization of the recycled precast elements, covering mechanical, microstructural, and durability properties, showed mostly similar behavior when compared to the analogous industrially-produced pieces made with conventional concrete