Mohamed Elchalakani

Mechanical properties of rubberised concrete for road side barriers

Abstract This paper presents the mechanical properties of rubberized concrete for roadside barriers with the intent to reduce injuries and fatalities during crashes. The test programme involved the preparation of normal strength concretes made out of recycled waste tire rubber. The tire–rubber particles composed of a combination of crumb rubber and fine rubber powder were used to replace 10, 20, 30 and 40% of the total weight of the fine aggregate. The test results indicated considerable reductions in compressive and flexural strengths, and tangential modulus of elasticity. New design guidelines in accordance with the Australian Bridge Design Code AS 5100 for strength and serviceability of rubberized concrete roadside barriers were derived based on the test results. New moment-thrust interaction curves and shear strength equations were derived for the rubberized concrete. It was found that the shear strength is critical compared to the combined moment and axial thrust and the maximum rubber content was 17% max for rubberized concrete.

Green Concrete with High-Volume Fly Ash and Slag with Recycled Aggregate and Recycled Water to Build Future Sustainable Cities

AbstractBuilding sustainable green cities for the future can be difficult or highly challenging as such cities need to reduce their environmental footprint through eco-friendly materials, resource and energy conservation, as well as renewable energy generation. A recent paper by the first author has proposed sustainable concrete with 80% ground granulated blast furnace slag (GGBFS) to build Masdar City in the UAE with a 153  kg/m3 carbon footprint. This paper proposes three new types of sustainable concretes in an attempt to further reduce the carbon footprint. In Type I, a total of 4 concrete mixes were made with a high volume GGBFS with 60, 70, 80, and 90% replacement of ordinary portland cement (OPC), 100% recycled water (RW), and 100% recycled aggregate (RA). The same replacement ratios were used in Type II but with only 100% RA. In Type III, a total of four concrete mixes made with a high volume fly ash (FA) cement with 40, 50, 60, and 70% replacement of OPC. The paper provides information on the mix...

Lattice Finite Strain Theory for Non-hydrostatically Compressed Materials

The purpose of this paper is to describe the nonlinear behaviour of geomaterials within the principles of thermodynamics. The main components of this contribution are (1) a new method to estimate the properties of minerals subjected to the non-hydrostatic compression in diamond anvil cell using the finite strain theory is introduced and (2) a proper measure of deformation that applies to a wide range of minerals is identified. This research work shows that the logarithmic (Hencky) strain produces a good agreement with experiments for a wide range of materials.

Energy Dissipation and Storage in Underground Mining Operations

In this paper, we focus on the energy alteration during longwall mining in an attempt to mimic the conditions of a coal mine in Western Turkey. We verify the proposed model using existing analytical and numerical solutions in terms of stress components. Based on the verified numerical model, the energy balance during longwall retreat is studied rigorously. It is found that excavation-induced increment of external work increases linearly with time, while the stored strain energy increment is quadratic. Meanwhile, the strain energy increment rate gradually decreases with longwall progress because of excavation-induced higher stored energy within the adjacent coal block. The energy dissipation process during lonwall mining, corresponding to crack propagation, is divided into four stages, namely initiation stage, steady growth stage, sharp increment stage, and stabilisation stage. Our results provide new insights into energy evolution during longwall mining both from the reversible and irreversible points of view. The current paper shows, for the first time, that the extended finite element method is suitable to describe the crack propagation during longwall mining. The excavation induced crack propagation in the roof strata predicted by the model is in agreement with the “arch-shaped” patterns obtained using laboratory tests and Discrete Element numerical simulations.

Axial impact behavior and energy absorption of rubberized concrete with/without fiber-reinforced polymer confinement

This study investigates the axial impact resistance and energy absorption of rubberized concrete with/without fiber-reinforced polymer confinement. The impact tests were carried out using an instrumented drop-weight testing apparatus. The experimental results have shown that rubberized concrete significantly reduced the maximum impact force of up to 50% and extended the impact duration. These characteristics make rubberized concrete a promising material for protective structures and particularly for future sustainable construction of rigid roadside barriers. Glass fiber–reinforced polymer confinement is a very effective method to improve the impact resistance for both conventional concrete and particularly for rubberized concrete. It was found that the rubberized concrete reduced the maximum impact force so that it transferred a lower force to a protected structure as well as a lower rebound force, which is desirable for protection of passengers in an incident of vehicle collision. Interestingly, the rubberized concrete showed a lower energy absorption capacity as compared to conventional concrete, where the exact reason for this is unknown to the authors. Therefore, further research is sought to provide more understanding of the response of rubberized concrete under impact and improve its energy absorption. This study explored experimentally the use of rubberized concrete as a promising sustainable construction material for applications to construction of columns in buildings located in seismic active zones or subjected to terrorist attack, security bollards and rigid road side barriers.

The prediction of ultimate pure bending moment of concrete-filled steel tubes by adaptive neuro-fuzzy inference system (ANFIS)

Abstract In this study, different modelling techniques such as multiple regression and adaptive neuro-fuzzy inference system (ANFIS) are used for predicting the ultimate pure bending of concrete-filled steel tubes (CFTs). The behaviour of CFT under pure bending is complex and highly nonlinear; therefore, forward modelling techniques can have considerable limitations in practical situations where fast and reliable solutions are required. Linear multiple regression (LMR), nonlinear multiple regression (NLMR) and ANFIS models were trained and checked using a large database that was constructed and populated from the literature. The database comprises 72 pure bending tests conducted on fabricated and cold-formed tubes filled with concrete. Out of 72 tests, 48 tests were conducted by the second author. Input variables for the models are the same with those used by existing codes and practices such as the tube thickness, tube outside diameter, steel yield strength, strength of concrete and shear span. A practical application example, showing the translation of constructed ANFIS model into design equations suitable for hand calculations, was provided. A sensitivity analysis was conducted on ANFIS and multiple regression models. It was found that the ANFIS model is more sensitive to change in input variables than LMR and NLMR models. Predictions from ANFIS models were compared with those obtained from LMR, NLMR, existing theory and a number of available codes and standards. The results indicate that the ANFIS model is capable of predicting the ultimate pure bending of CFT with a high degree of accuracy and outperforms other common methods.