# A Novel Artificial Neural Network to Predict Compressive Strength of Recycled Aggregate Concrete
###### Abstract  
Most regulations only allow the use of the coarse fraction of recycled concrete aggregate (RCA) for the manufacture of new concrete, although the heterogeneity of RCA makes it difficult to predict the compressive strength of concrete, which is an obstacle to the incorporation of RCA in concrete production. The compressive strength of recycled aggregate concrete is closely related to the dosage of its constituents. This article proposes a novel artificial neural network (ANN) model to predict the 28-day compressive strength of recycled aggregate concrete. The ANN used in this work has 11 neurons in the input layer: the mass of cement, fly ash, water, superplasticizer, fine natural aggregate, coarse natural or recycled aggregate, and their properties, such as: sand fineness modulus of sand, water absorption capacity, saturated surface dry density of the coarse aggregate mix and the maximum particle size. Two training methods were used for the ANN combining 15 and 20 hidden layers: Levenberg-Marquardt (LM) and Bayesian Regularization (BR). A database with 177 mixes selected from 15 studies incorporating RCA were selected, with the aim of having an underlying set of data heterogeneous enough to demonstrate the efficiency of the proposed approach, even when data are heterogeneous and noisy, which is the main finding of this work. construction and demolition waste; recycled concrete aggregate; compressive strength; artificial neural networks +
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transition zone [7; 8] than natural aggregate. The mortar paste also shows tiny cracks that develop during the crushing process. Most of the studies relate the worst physical-mechanical and chemical properties of RCA with the presence of attached mortar paste [9]. RCA show a lower density, higher water absorption and less resistance to fragmentation than the NA [10]. From a chemical point of view, RCA show a higher number of sulfates and soluble salts than natural aggregates [11]. Most regulations only allow the use of the coarse RCA fraction for the manufacture of concrete [12]. The substitution of NA by RCA normally leads to a reduction in the mechanical properties of concrete (compressive and tensile strength, modulus of elasticity and abrasion resistance). Compressive strength at 28 days is the most representative property for evaluating the mechanical performance of concrete [5]. The compressive strength of concrete has been used in models to predict the modulus of elasticity and its evolution over time [13]. Additionally, the elastic modulus plays a significant role in the dynamics of Reinforced and Prestressed Concrete structures [14]. The increase in RCA content and water-to-cement ratio impairs the durability properties of concrete, such as water absorption by immersion and water absorption by capillarity, chloride penetration resistance, carbonation depth, frost resistance and acid resistance. From a rheological point of view, the shrinkage and creep increase [15; 16]. The compressive strength is one of the parameters to be considered by the RILEM Technical Committee TC-242-MDC to predict creep, drying shrinkage and autogenous shrinkage of normal and high-strength concrete with multidecade applicability [17]. In order to produce a more durable recycled aggregate concrete it is suggested to use pozzolanic materials and CO\({}_{2}\) treatment prior to use in concrete [15]. The compressive strength of concretes made with recycled aggregates is closely related to the dosage of its constituents. The compressive strength of concrete depends mainly on the amount of cement, the water-to-cement ratio, the amount of sand and coarse aggregates, the use of additives and additions, the percentage of incorporation and the moisture conditions of the RCA [18]. The quality of the primitive concrete (high, medium or low strength) determines the water absorption capacity and the density of the RCA particles, which affects the compressive strength of the new concrete [19].