The review outlines modern trends in theoretical developments, novel designs and modern applications of sandwich structures. The most recent work published at the time of writing of this review is considered, older sources are listed only on as-needed basis. The review begins with the discussion on the analytical models and methods of analysis of sandwich structures as well as representative problems utilizing or comparing these models. Novel designs of sandwich structures is further elucidated concentrating on miscellaneous cores, introduction of nanotubes and smart materials in the elements of a sandwich structure as well as using functionally graded designs. Examples of problems experienced by developers and designers of sandwich structures, including typical damage, response under miscellaneous loads, environmental effects and fire are considered. Sample applications of sandwich structures included in the review concentrate on aerospace, civil and marine engineering, electronics and biomedical areas. Finally, the authors suggest a list of areas where they envision a pressing need in further research.

Review of current trends in research and applications of sandwich structures

Disposal of waste tire rubber has become a major environmental issue in all parts of the world. Every year millions of tires are discarded, thrown away or buried all over the world, representing a very serious threat to the ecology. It was estimated that almost 1000 million tires end their service life every year and out of that, more than 50% are discarded to landfills or garbage without any treatment. By the year 2030, there would be 5000 million tires to be discarded on a regular basis. Tire burning, which was the easiest and cheapest method of disposal, causes serious fire hazards. Temperature in that area rises and the poisonous smoke with uncontrolled emissions of potentially harmful compounds is very dangerous to humans, animals and plants. The residue powder left after burning pollutes the soil. One of the possible solutions for the use of waste tire rubber is to incorporate into cement concrete. This paper presents an overview of some of the research published regarding the fresh and hardened properties of rubberized concrete. Studies show that there is a promising future for the use of waste tire rubber as a partial substitute for aggregate in cement concrete. It was noticed from literatures that workable concrete mixtures can be made with scrap tire rubber and it is possible to make light weight rubber aggregate concrete for some special purposes. Rubberized concrete shows high resistance to freeze-thaw, acid attack and chloride ion penetration. Use of silica fume in rubberized concrete enables to achieve high strength and high resistance to sulfate, acid and chloride environments.

A comprehensive review on the applications of waste tire rubber in cement concrete

Seismic Design and Retrofit of Bridges

Workability and mechanical properties of alkali-activated fly ash-slag concrete cured at ambient temperature

Waste tyres and their accumulation is a global environmental concern; they are not biodegradable, and, globally, an estimated 1.5 billion are generated annually. Waste tyres in landfill and stockpiles are renowned for leaching toxic chemicals into the surrounding environment, acting as breeding grounds for mosquitoes, and fuelling inextinguishable fires. The properties of waste tyre rubber and engineering applications have been previously reported in a range of publications with respect to the environmental, economic, and technical factors. This study compiles and reviews this research with a focus on geotechnical engineering applications, such as earthworks and infrastructure construction. The applications of waste rubber in construction materials includes cementitious concrete, asphalt concrete, and granular materials for earth structures. Crumb rubber, when used as a sand replacement in flowable concrete fill, improved ductility and strength-to-weight ratio. A 40 MPa concrete mix with 0.6% rubber crumb content exhibited optimal strength and air entrainment capabilities, displaying minimal damage after 56 freeze/thaw cycles. Rubber, as a partial replacement for aggregate in road base and sub-base layers, adversely affected the California Bearing Ratio (CBR) of the graded aggregate base course. Rubber-soil mixtures as the interface of foundation and structure yielded a 60–70 % reduction in vertical and horizontal ground accelerations when subjected to earthquake simulation modelling. There is concern regarding the toxicity of waste rubber incorporated products due to leachates of heavy metals and other chemicals common in tyres. Further comprehensive studies in this area are needed. Leachate studies should be conducted under different pH and liquid to solid ratios.

Recycling waste rubber tyres in construction materials and associated environmental considerations: A review

Latex-modified concrete overlays using waste paint

Shear behaviour of ultra-high performance concrete beams with openings

Out-of-Plane Flexural Behavior of Reinforced Masonry Walls Strengthened with Near-Surface-Mounted Fiber-Reinforced Polymer

This study investigated retrofitting measures for improving the seismic performance of rectangular columns in existing bridges. Experimental tests were conducted on 0.4-scale column specimens which incorporated details that were selected to represent deficiencies present in older bridges in Washington State. Two unretrofitted specimens were tested to examine the performance of the as-built columns incorporating lap splices at the base of the columns and deficient transverse reinforcement. Five columns were retrofitted with carbon fiber reinforced polymer (CFRP) composite wrapping and one specimen was retrofitted with a steel jacket. The specimens were subjected to increasing levels of cycled lateral displacements under constant axial load. Specimen performance was evaluated based on failure mode, displacement ductility capacity and hysteretic behavior. For retrofitting of rectangular columns, it is recommended that oval-shaped jackets be used whenever possible. Column specimens with oval-shaped jackets of steel and CFRP composite material performed similarly, both producing ductile column performance. Failure in these specimens was due to flexural hinging in the gap region between the footing and retrofit jacket, leading to eventual low-cycle fatigue fracture of the longitudinal reinforcement. Details and procedures for the design of oval-shaped steel jackets are provided in FHWA Seismic Retrofitting Manual for Highway Bridges (2006). Design guidelines for oval-shaped CFRP jackets are given in ACTT-95/08 (Seible et al., 1995). Oval-shaped jackets designed according to these recommendations can be expected to prevent slippage of lapped bars within the retrofitted region. Design guidelines for rectangular-shaped retrofitting using CFRP composite materials are proposed for application to columns with cross-section aspect ratios of 2 or less. While no slippage of the lap splice was observed, it is conservatively recommended that rectangular-shaped CFRP wrapping be used only for the situation where controlled debonding of the lap splice is acceptable.

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Mohamed A. ElGawady

Papers

Latex-modified concrete overlays using waste paint

Shear behaviour of ultra-high performance concrete beams with openings

Out-of-Plane Flexural Behavior of Reinforced Masonry Walls Strengthened with Near-Surface-Mounted Fiber-Reinforced Polymer

Retrofit of rectangular bridge columns using cfrp wrapping

Behavior of high strength concrete – filled hybrid large – small rupture strains FRP tubes