Investigation of the deterioration of blended cement concrete under sulfate attack in terms of interfacial transition zone

The importance of the porous interfacial transition zone to the chemical aggression of concrete is obvious when one considers the relations existing between porosity, permeability, chemical composition and the sulfate attack. In this study, the effect of ITZ quantity through varying aggregate content on the deterioration of blended cement concrete under sulfate attack, was determined to understand better the relationship between sulfate ions and concrete microstructure. The ITZ quantity was directly proportional to the aggregate volume fraction. Therefore, the effect of ITZ on sulfate resistance ability of concrete made with pure OPC and blended binders was evaluated by a comparison among mortars with systematically varied aggregate volume fraction. The porosity distribution with the ITZ was determined by using a quantitative backscattered electron microscopy (BSE) image analysis. It was found that the incorporation of moderate amount of Limestone filler is able to compact the microstructure of both ITZ and bulk matrix by filling effect and nucleation sites effect. The effects of slag on the porosity of ITZ were dependent on the replacement rate. The degree of deterioration had a slight tendency to increase for the samples prepared with higher aggregate volume content, which means high ITZ volume fraction. For the sulfate to reach the interior of the samples, it must move through the bulk cement matrix. The effect of aggregate and ITZ can only be notable when the interior structure was exposed to the sulfate ions. The presence of ITZ was normally accompanied by a denser bulk cement matrix. This could limit the ingress of sulfate ions and delay the formation of expansive products in initial stage. After the sulfate penetrates into the interior of the samples, the inner structure was expected to exert more significant influences on the deterioration

Viscoelastically prestressed polymeric matrix composites: An overview

Elastically prestressed polymeric matrix composites exploit the principles of prestressed concrete, i.e. fibres are stretched elastically during matrix curing. On matrix solidification, compressive stresses are created within the matrix, counterbalanced by residual fibre tension. Unidirectional glass fibre elastically prestressed polymeric matrix composites have demonstrated 25–50% improvements in impact toughness, strength and stiffness compared with control (unstressed) counterparts. Although these benefits require no increase in section dimensions or weight, the need to apply fibre tension during curing can impose restrictions on processing and product geometry. Also, fibre–matrix interfacial creep may eventually cause the prestress to deteriorate. This paper gives an overview of an alternative approach: viscoelastically prestressed polymeric matrix composites. Here, polymeric fibres are subjected to tensile creep, the applied load being removed before the fibres are moulded into the matrix. Following matrix curing, viscoelastic recovery mechanisms cause the previously strained fibres to impart compressive stresses to the matrix. Since fibre stretching and moulding operations are decoupled, viscoelastically prestressed polymeric matrix composite production offers considerable flexibility. Also, the potential for deterioration through fibre–matrix creep is offset by longer term viscoelastic recovery mechanisms. To date, viscoelastically prestressed viscoelastically prestressed polymeric matrix composites have been produced from fibre reinforcements such as nylon 6,6, ultra-high molecular weight polyethylene and bamboo. Compared with control counterparts, mechanical property improvements are similar to those of elastically prestressed polymeric matrix composites. Of major importance, however, is longevity: through accelerated ageing, nylon fibre-based viscoelastically prestressed viscoelastically prestressed polymeric matrix composites show no deterioration in mechanical performance over a duration equivalent to ∼25 years at 50℃ ambient. Potential applications include crashworthy and impact-absorbing structures, dental materials, prestressed precast concrete and shape-changing (morphing) structures

Study of changes in properties of solar sail materials from radiation exposure

Techniques for monitoring changes in preparation of solar sail materials resulting from space radiation simulation, stressing (e.g., thermal, mechanical) and exposure to terrestrial environments are developed. The properties of interest are: metallic coating deterioration, polymeric film deterioration, interfacial debonding and possible metallic coating diffusion into the polymeric film. Four accelerated tests were devised to simulate the possible degradation processes mentioned above. These four tests are: a thermal shock test to simulate the wide variation of temperature expected in space (260 C to -100 C), a cyclic temperature test to stimulate the 6 minute temperature cycle anticipated in space, a mechanical vibration test to simulate mechanical bonding, folding and handling, and a humidity test to simulate terrestrial environment effects. The techniques for monitoring property changes are: visual and microscopic examination, ellipsometry, surface potential difference (SPD), photoelectron emission (PEE), and water contact angles

Interfacial strength in fibre reinforced thermoplastics

There has been a rapid growth in the development and application of fibre-reinforced thermoplastic polymer composites in recent years. Parallel to this growth has been the increasing recognition of the need to better understand and measure the micro-mechanical parameters which control the structure-property relationships in such composites. The properties of thermoplastic composites result from a combination of the fibre and matrix properties and the ability to transfer stresses across the fibre-matrix interphase. Optimization of the stress transfer capability of the fibre-matrix interphase region is critical to achieving the required performance level in thermoplastic matrix composites

Material and the Arts Research Facilities Booklet

A booklet to demonstrate the MATAR equipment which is now available for use at London College of Communication and Camberwell College of Arts. The booklet was created for, and launched at, The MATAR Open Day in May 2010, and is now used to advertise the facilities available

Dry sliding wear properties of Jute/polymer composites in high loading applications

In the last few decades natural fiber composites has gained its importance due to its low cost and their availability as additives with minimal processing. Amongst the various natural sources the Jute fiber is chosen in the present research due to its fiber structure and good physical and mechanical properties. In this background natural fiber composites of unsaturated polyester were reinforced with jute fibers. While most research on green composites focuses on the structural characteristics, the present work investigates the suitability of the material to be used as a tribocomposite. Tailor made hybrid composites were made with chemically treated (NaOH) jute fiber and 2 wt % PTFE filler (tribo lubricant) to obtain the better tribological characteristics in high loading condition. Tribotests were performed on flat on flat configuration where 100Cr6 steel was used as counterface material. A pv limit of 400 MPa-mm/s (10KN and 100 mm/s) was attainedin a flat-on-flat configuration for studying the tribological properties. The static and dynamic coefficient of friction was found to be 0.15 and 0.07 respectively.An exponential increase in temperature was observed throughout the test. The material failure was observed within 500 m of sliding distance where pulverization of matrix due to thermal degradation is evident. Wear mechanisms such as fiber breakage, polymer degradation, fiber thinning and fiber separation was observed. From the present investigation the low cost Jute fabric composites havinglow frictional coefficient seemed to be a alternative to the bearing materials working at higher contact pressure and low velocity

Structure – Property relationships for nanofluids

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Nanofluids refer to dilute liquid suspensions of nanoparticles in commonly used heat transfer liquids. They triggered much excitement since mid 1990s mainly owing to the claims of anomalous enhancement of thermal conductivity even at very low nanoparticle concentrations. There have been numerous attempts to interpret the mechanism(s) that drive the displayed enhancement. A long debate within the research community supported by experimental and theoretical evidence has highlighted the nanoparticle structuring as the dominant underlying mechanism. On the other hand the viscosity increase as a result of nanoparticle structuring raises concerns about their suitability for certain applications. This paper mainly discusses the structure – property relationship for nanofluids in microscopically static conditions

A review of conducting polymers in electrical contact applications

A review of recent developments in fretting studies in electrical contacts is presented, focusing on developments in conducting polymer surfaces. Fretting is known to be a major cause of contact deterioration and failure; commonly exhibited as the contact resistance increases from a few milliohms, in the case of a new metallic contacts, to in excess of several ohms for exposed contacts. Two technologies are discussed; firstly extrinsically conducting polymer (ECP), where highly conductive interconnects are formed using metallized particles embedded within a high temperature polymer compound, and secondly; intrinsically conducting polymers (ICPs) are discussed. These latter surfaces are new developments which are beginning to show potential for the application discussed. This paper presents the work on the ICPs using poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT /PSS) and its blends from secondary doping of dimethylformamide (DMF)PEDOT/PSS. Two different processing techniques namely dropcoating and spin coating have been employed to develop test samples and their functionality were assessed by two independent studies of temperature and fretting motion. The review leads to a number of recommendations for further studies into the application of conducting polymers for contacts with micro-movement.<br/