Study of Topology Optimized Hammerhead Pier Beam Made with Novel Preplaced Aggregate Fibrous Concrete

This study aims to study topology Optimized Hammerhead Pier Beam (TOHPB) designed with a density-based technique. TOHPB is made with Preplaced Aggregate Fibrous Concrete (PAFC), which comprises two main preparation processes. First, the fibers and coarse aggregates filled into empty formwork to develop a skeletal system. Second, voids in the skeletal system are filled with cement grout; hence a type of PAFC was obtained. Besides, alleviating the self-weight of the concrete beam is a top priority of design engineering without compromising its strength and durability. The effect of topology optimization in association with the safety of factors and elastic design case is considered in this study. Explicitly, (i) compliance is scaled down to a minimum under a perimeter on the utilized material (ii) the principle Drucker-Prager is employed to impose the stress limitations even though utilization of material is minimized. The problem is designed with imposed stress limitation and generates keys that involve an essential part of post-processing before fabrication. In total, ten TOHPB were prepared with and without the combined shape of crimped-hooked end steel fiber. Two different types of fiber reinforcement schemes were used; first, the fibers were reinforced to full beam cross-section; then, the fibers were reinforced to the top half of the beam cross-section. Results revealed that the TOHPB beam reinforced full cross-section exhibited better ultimate load performance than that of the beam with half reinforced cross-section

Short-term deflection of RC beams using a discrete rotation approach

Quantifying the deflection of RC beams has been performed traditionally using full-interaction moment–curvature methods without considering the slip that takes place between the reinforcement and the surrounding concrete. This was commonly carried out by deriving empirically based flexural rigidities and using elastic deflection equations to predict the deformation of RC structures. However, as flexural and flexural/shear cracks form in RC beams with increase in applied load, the reinforcement steel begins to slip against the surrounding concrete surface causing the cracks to widen and ultimately increasing the deflection at mid-span. Current design rules cannot cope directly with the deformation induced by the widening of cracks. Because of that, this study focused on predicting the non-time dependent deflection of RC beams at both service and ultimate limit states using a mechanics-based discrete rotation approach. The mechanics-based solution was compared with experimental test results and well-established code methods to which a good agreement between the results was observed. The method presented accounts for the non-linear behavior of the concrete in compression, the partial-interaction behavior of the reinforcement, and the deflection was computed while considering the rotation of discrete cracks. Due to its generic nature, the method presented does not require any calibration with experimental findings on the member level, which makes it appropriate to quantify the deflection or RC structures with different types of concrete and novel reinforcement material

PERFORMANCE OF SUSTAINABLE GREEN CONCRETE INCORPORATED WITH FLY ASH, RICE HUSK ASH, AND STONE DUST

The performance of a sustainable green concrete with fly ash (FA), rice husk ash (RHA), and stone dust (SD) as a partial replacement of cement and sand was experimentally explored. FA and RHA have a high silica content, are highly pozzolanic in nature and have a high surface area without any treatment. These by-products show filler effects, which enhance concrete’s density. Results showed that the FA and RHA materials have good hydration behaviour and effectively develop strength at an early age of concrete. SD acts as a stress transferring medium within concrete, thereby allowing the concrete to be stronger in compression, and bending. Consequently, water absorption capacity of the sustainable concrete was lower than that of the ordinary one. However, a little reduction in strength was observed after the replacement of the binder and aggregate using the FA, RHA and SD, but the reduction was insignificant. The reinforced structure with sustainable concrete containing the FA, RHA, and SD generally fails in concrete crushing tests initiated by flexural cracking followed by shear cracks. The sustainable concrete could be categorized as a perfect material with no significant conciliation in strength properties and can be applied to design under-reinforced elements for a low-to-moderate service load

The effect of POFA-gypsum binary mixture replacement on the performance of mechanical and microstructural properties enhancements of clays

Soft clay is categorized as problematic due to its weak and dispersive properties which requires stabilization. In Malaysia, there is another challenge, the increment of palm oil waste productions to meet the global demand for food oil. These two concerns motivate engineers to develop novel strategies for exploiting palm oil waste in soil stabilization. Utilizing POFA as a soil stabilizing agent is an economical and sustainable option due to that POFA contains high pozzolanic characteristics which make it more suitable and reliable to treat soft soil. This study uses the replacement portion of the soil with stabilizing agents -POFA and Gypsum; aiming to achieve Malaysia green technology goals by the balance of the economic expansion and environmental privilege. However, the aim of this study is to determine the effect of POFA-gypsum binary mixture replacement on the performance of mechanical and microstructural properties en-hancements of clays. Kaolin S300 is the control sample whereas POFA and gypsum are the used binders. The mechanical properties and shear strength with the curing period were tested. Results showed that treated clay marked increment of optimum water contents and reduction of maximum dry densities, a clear 200% of enhancement of treated clay’s compressive and shear strength with curing period as well as the amount of stabilizing agent to less than 15% of POFA and 6% of POFA. It is also found that as gypsum contains a high amount of lime (CaO), the results illustrate that strength raises significantly even with less curing time due to its high reactivity compared to silica and alu-mina. Overall, the results show an enhancement of mechanical and shear strength properties of treated kaolin supported by microstructural SEM imaging

Properties and applications of FRP in strengthening RC structures: a review

In civil and structural engineering, building structures with robust stability and durability using sustainable materials is challenging. The current technological means and materials cannot decrease weight, enlarge spans, or construct slender structures, thus inspiring the exploration for valuable composite materials. Fiber reinforced polymer (FRP) features high-strength and lightweight properties. Using FRP motivates civil engineers to strengthen existing RC structures and repair any deterioration. With FRP, a system that can resist natural disasters, such as earthquakes, strong storms, and floods, can be developed. However, deterioration of structures has become a critical issue in modern construction industries worldwide. This paper reviews the FRP design, matrix, material properties, applications, and serviceability performance. This literature review also aims to provide a comprehensive insight into the integrated applications of FRP composite materials for improving the techniques of rehabilitation, comprising the applications toward the repair, strengthening, and retrofit of concrete structures in the construction industry today

Response of precast foamed concrete sandwich panels to flexural loading

This paper presents the results of an experimental and analytical investigation of a total of six precast foamed concrete sandwich panels (PFCSPs) as one-way acting slabs tested under flexural loads. Foamed concrete of 25.73 MPa was used to produce the PFCSP concrete wythes. The results obtained from the tests have been discussed in terms of ultimate flexural strength capacity, moment-vertical deflection profile, load–strain relationship, strain variation across the slab depth, influence of aspect ratio, cracking patterns, and ultimate flexural load at failure. An analytical study of finite element analysis (FEA) as a one-way slab model was then conducted. The increase in aspect ratio (L/d) from 18.33 to 26.67 shows a reduction of 50% and 69.6% on the ultimate flexural strength capacity as obtained experimentally and in FEA models, respectively. Theoretical analyses on the extremes of fully composite and non-composite actions were also determined. The experimental results showed that cracking patterns were observed in one direction only, similar to those reported on a reinforced concrete solid slab, as well as precast concrete sandwich panels, when both concrete wythes act in a single composite manner. The experimental results were compared with FEA model data, and a significant degree of accuracy was obtained. Therefore, the PFCSP slab can serve as an alternative to the normal concrete slab system in buildings

Structural behavior of axially loaded precast foamed concrete sandwich panels

This paper presents results from an experimental and analytical study of precast foamed concrete sandwich panels (PFCSPs). Full-scale experimental tests of six PFCSPs were conducted to study the behavior of the panels under axial loads. Foamed concrete (FC) was used to cast PFCSP concrete wythes. The axial load-bearing capacity, load–deflection profiles, load–strain relationships, slenderness ratio, load–displacement, load–deformation, failure and collapse modes, cracking patterns, and propagations under constant increments of axial loads were recorded and discussed. The properties and use of FC were briefly reviewed. Results of the experimental test and finite element analysis were compared with the theoretical values calculated based on the American Concrete Institute (ACI) design equation for a solid concrete wall and other empirical formulas developed by antecedent researchers which might be applicable to predict the ultimate load-bearing capacity of sandwich panels. A semi-empirical formula was proposed based on the laboratory test and finite element analysis results

Fiber-reinforced alkali-activated concrete : A review

Alkali-activated materials (AAMs) received broad recognition from numerous researchers worldwide and may have potential applications in modern construction. The combined use of AAM and steel fibers are superior to typical binder systems because the matrix and fibers exhibit superior bond strength. The results obtained by various authors have shown that good dispersion of the fibers ensures good interaction between the fibers and the AAM matrix. The tensile strength of FR-AAC is superior to that of Ordinary Portland cement (OPC)-based materials, with the addition of silica fume (SF) being particularly remarkable. However, the tensile strength of fiberreinforced alkali-activated concrete (FR-AAC) decreases with increasing fiber length. The bond strength increases with the increasing grade of concrete, the roughness of interface, and the solution’s strength activated by alkalis. Regardless of fiber type, AAC’s modulus of elasticity is linearly correlated with compressive strength. Fibers can affect the modulus of concrete due to the stiffness of the fiber and the porosity of the composite. Poisson’s ratio for AAC corresponded to the ASTM C469-14 standard (about 0.22) and decreased to about 0.15–0.21 with silica fume addition. There are limited resources for the experimental Poisson’s ratio and it is only estimated using the predictive equations available. Therefore, it is necessary to conduct additional experimental studies to estimate Poisson’s ratios for FR-AAC composites. Retention of 59% and 44% in flexural strength during exposure at 800 ◦C and 1050 ◦C was observed in the FR-AAC stainless steel composite, and the chopped alumina fibers achieved higher yield strength at these temperatures. For FA-based AAC mortars with 1% SF with a hooked end, activated with a solution of NaOH and sodium silicate, an increase in the number of bends increased the bond strength, load pull-out and maximum pull-out strength. Autogenous shrinkage and drying shrinkage increase with higher silicate content, while shrinkage decreases with higher NaOH concentration. Relatively little research has been completed on FR-AAC in terms of durability or different environmental conditions. In addition, trends of development research toward the broad understanding regarding the application possibilities of FR-AAC as appropriate concrete materials for developing robust and green concrete composites for modern construction were extensively reviewed