M. Iqbal Khan

Production of Recycled Plastic Aggregates and Its Utilization in Concrete

AbstractPlastic represents an environmental issue, as only 7% of it is recycled. The plastic remaining is either burned, disposed of in an uncontrolled manner, or landfilled. Thus, to reduce the qu...

Optimized Fresh and Hardened Properties of Strain Hardening Cementitious Composites: Effect of Mineral Admixtures, Cementitious Composition, Size, and Type of Aggregates

AbstractThe present paper thoroughly investigates the effects of mix design with various water-to-binder (W/B) ratios, types of mineral admixture and types and sizes of local sands on the tensile d...

Flexural Behavior of Beams Reinforced with Steel Bars Exceeding the Nominal Yield Strength

If steel manufactures usually comply with the minimum code specifications, the nominal yield strength of rebar can however be significantly exceeded in many countries, depending on the steel manufacturing processes. Such an increase in yield strength can have negative effects on the flexural behavior of beams designed as tension controlled, and reduce their ductility, an essential property in seismic resisting structures. An experimental and analytical study of the flexural behavior of reinforced concrete (RC) beams was conducted through the investigation of the Moment-Curvature relationships and the ultimate steel strains. The main variable was the level of the actual steel yield stress as compared to the nominal value. It was found that unexpectedly high values of steel yield stress reduce the beam ductility and violate the tension-control condition which was enforced in the design stage. Appropriate design corrections are proposed to account for high yield stress values in order to achieve the desired ductility of beams while maintaining the moment capacities.

Influence of Fiber Properties on Shear Failure of Steel Fiber Reinforced Beams Without Web Reinforcement: ANN Modeling

IN THIS PAPER, AN ARTIFICIAL NEURAL NETWORK (ANN-10) MODEL WAS DEVELOPED TO PREDICT THE ULTIMATE SHEAR STRENGTH OF STEEL FIBER REIN-FORCED CONCRETE (SFRC) BEAMS WITHOUT WEB REINFORCEMENT. ANN-10 IS A FOUR-LAYERED FEED FORWARD NETWORK WITH A BACK PROPAGATION TRAINING ALGORITHM. THE EXPERIMENTAL DATA OF 70 SFRC BEAMS REPORTED IN THE TECHNICAL LITERATURE WERE UTILIZED TO TRAIN AND TEST THE VALIDITY OF ANN-10. THE INPUT LAYER RECEIVES 10 INPUT SIGNALS FOR THE FIBER PROPERTIES (TYPE, ASPECT RATIO, LENGTH AND VOLUME CONTENT), SECTION PROPERTIES (WIDTH, OVERALL DEPTH AND EFFECTIVE DEPTH) AND BEAM PROPERTIES (LONGITUDINAL REINFORCEMENT RATIO, COMPRESSIVE STRENGTH OF CONCRETE AND SHEAR SPAN TO EFFECTIVE DEPTH RATIO). ANN-10 HAS EXHIBITED EXCELLENT PREDICTIVE PERFORMANCE FOR BOTH TRAINING AND TESTING DATA SETS, WITH AN AVERAGE OF 1.002 FOR THE AVERAGE OF PREDICTED TO EXPERIMENTAL VALUES. THIS PERFORMANCE OF ANN-10 ESTABLISHED THE PROMISING POTENTIAL OF ARTIFICIAL NEURAL NETWORKS (ANNS) TO SIMULATE THE COMPLEX SHEAR BEHAVIOR OF SFRC BEAMS. ANN-10 WAS APPLIED TO INVESTIGATE THE INFLUENCE OF THE FIBER VOLUME CONTENT, TYPE, ASPECT RATIO AND LENGTH ON THE ULTIMATE SHEAR STRENGTH OF SFRC.

Optimized Fresh and Hardened Properties of Strain-Hardening Cementitious Composites: Effect of Sand Size and Workability

AbstractThe feasibility of the preparation of strain-hardening cementitious composites (SHCC) relies to a great extent on the properties of one of its main constituents, quartz sand. The particle size distribution (PSD) of such sand should satisfy certain criteria specifically for SHCC to deliver quasi-static responses under tensile stress. The successful use of naturally available sand helps preparation of a cost-effective SHCC. The aim of the current paper was to evaluate the potential use of white quartz sand that is naturally available in the Arabian Gulf with different PSDs to produce different mixtures of SHCC. These mixtures were prepared with different ranges of workability to obtain optimized fresh and hardened properties with improved strain-hardening response. The effect of workability on the compressive, flexural and tensile properties has shown that there is an optimal workability range among the defined ranges that provided improved strain-hardening responses under tensile stress. The mode o...

Fiber-Matrix Interfacial Behavior of Hooked-End Steel Fiber-Reinforced Concrete

AbstractConcrete has inherent low tensile strength and fails at low tensile strains. These drawbacks have been bypassed by the introduction of discontinuous randomly distributed fibers to the concrete. The fiber-matrix interfacial behavior is of critical importance to the properties of fiber-reinforced concrete (FRC), which is usually assessed by fiber pullout tests. In this paper, a rigorous pullout test setup was developed with 50-mm-diameter × 100-mm-height cylindrical concrete specimens and utilized to investigate fiber-matrix interfacial behavior of hooked-end steel FRC with two fiber sizes and various embedment depths. The relation of fiber pullout load-end slip displacement and its average curves established the efficiency of the utilized fiber pullout test setup concerning the repeatability and reliability. Four components of the fiber matrix interactions were observed for hooked-end steel fibers. These include the elastic fiber-matrix bond, partial fiber-matrix debonding, full fiber-matrix debond...

HPC Composites Formulated to Counteract Early ASR Expansion

AbstractThe authors investigated the ability of different high-performance concrete (HPC) composites to restrain an alkali-silica reaction (ASR) in the presence of reactive aggregates. They evaluated the effectiveness of different binary and ternary blended cementitious systems comprising optimized contents of pulverized fly ash (PFA) and silica fume (SF) in suppressing ASR expansion. They assessed different mortar mixtures made of different contents of PFA (up to 40%) and SF (up to 15%) with water-to-binder (W/B) ratios of 0.27 for ASR expansion according to standard procedures for accelerated mortar bar test. The results showed a given pessimal combination among the ternary mixtures in which there was an obvious synergistic interaction where ASR expansion was at its minimum level.

Nanosilica/silica fume

Abstract Sustainability in concrete construction necessitates exploration of waste product materials as primary examples of renewable resources for use as fine powders in concrete construction. In addition, deterioration, long-term poor performance, and inadequate resistance to the hostile environment, coupled with greater demands for more sophisticated architectural form, led to development of new materials and composites. The present state of the art in concrete research has demonstrated the benefits of silica fume (SF) and nanosilica (NS) as cementitious partial replacements. Their use has not only become an increasingly accepted practice in such structures but also has contributed to energy conservation and provided a major solution to the disposal of industrial by-products. In this chapter, the production process, the availability and handling, physical and chemical properties, strength and durability issues of SF and NS are described in detail. The role of SF and NS in green and sustainable construction, codes and standards implementation, health and safety issues, cost–benefit analysis, and leachate analysis are discussed. SF is a very reactive pozzolanic material and it modifies transition phase in mortars. It densifies the matrix which results in reduction in ingress of moisture and penetration of aggressive chemicals. SF enhances corrosion resistance, alkali-silica expansion, however, it tends to increase the carbonation depth. The application of NS in concrete is dependent upon the chemical and physical nature of its particles, and well-dispersed NS demonstrates its promising effect in improving the macro-, micro-, and nanocementitious properties. Development of new family of nano-superplasticizers and understanding the reaction mechanism may be very useful for extracting maximum benefits by using NS.