Tigger paper : integration

The process of architecture will always be holistic. As long as it is taught in segments, its educational structure will always run the risk of failing to meet this primary educational aim, and be continually shooting itself in the foot. The pedagogical and professional advantage to breaking the perceived lack of integration between studio and subject classes is I believe a fundamental imperative, to recognise that every part of the architectural process is not in contradiction but has equal value, and to realise the added value that integration would bring to all parts of the educational process, to staff and student alike

Effect of temperature on RC elements strengthened with CFRP

The strengthening of RC elements with CFRP is a technique that has been acquiring more and more potential. The bond between the CFRP reinforcement and the concrete support is usually made with epoxy adhesives. However, it is here that the integrity of the system can be affected, namely by exposure to high temperatures. In order to study the effect of an increase of air temperature on the behaviour of the epoxy adhesive, CFRP strengthened RC and reference RC specimens were tested. After cyclical thermal exposures, with temperatures rising between 20ºC and 80ºC, specimens were subjected either to compressive shear tests or bending tests. The results demonstrated that epoxy adhesive exhibits poor behaviour when subjected to increased temperatures, causing important bond deterioration. The improvement achieved with the CFRP reinforcement tends to disappear with an increase of the environment temperature. So, the thermal resistance of this strengthened system can not be considered very high. However, the inclusion of insulating materials can be a good solution to protect the strengthened RC elements. Among tested materials, the foamed polyurethane showed the best behaviour

Aggregate effect on the concrete cone capacity of an undercut anchor under quasi-static tensile load

In the last decades, fastening systems have become an essential part of the construction industry. Post-installed mechanical anchors are frequently used in concrete members to connect them with other load bearing structural members, or to attach appliances. Their performance is limited by the concrete related failure modes which are highly influenced by the concrete mix design. This paper aims at investigating the effect that different aggregates used in the concrete mix have on the capacity of an undercut anchor under tensile quasi-static loading. Three concrete batches were cast utilising three different aggregate types. For two concrete ages (28 and 70 days), anchor tensile capacity and concrete properties were obtained. Concrete compressive strength, fracture energy and elastic modulus are used to normalize and compare the undercut anchor concrete tensile capacity employing some of the most widely used prediction models. For a more insightful comparison, a statistical method that yields also scatter information is introduced. Finally, the height and shape of the concrete cones are compared by highly precise and objective photogrammetric means

The effect of polypropylene fibres within concrete with regard to fire performance in structures

Purpose – The purpose of this paper is to examine the effect of various polypropylene fibre additions (types and volume) to concrete with regard to explosive spalling when subject to high temperatures similar to those experienced in building or tunnel fires. Design/methodology/approach – Medium strength concrete was manufactured with varying proportions of polypropylene fibres. Plain control samples were used to determine the original concrete strength and this was used as a benchmark following high temperature heat tests to evaluate the surface condition and final compressive strength. A pilot study was used to determine an appropriate heat source for the test. This was three Bunsen burners, however sufficient heat could not be generated within 150mm concrete cubes and the concrete was shown to be a significant insulator and fire protection for structural members. The concrete test cubes were tested in a saturated condition which may reflect conditions where concrete is used in an external environment and thus is subject to soaking. Findings – One hundred and fifty millimetre concrete cubes with and without fibres were placed into a furnace at 1,000°C. Explosive spalling was shown to be reduced with the use of polypropylene fibres but the final compressive strength of concrete was significantly reduced and had little residual structural value after a two hour period of heating. Research limitations/implications – As the concrete tested was saturated, this condition provided a worst case scenario with regards to the build up of hydrostatic and vapour pressure within the cube. A range of percentage moisture contents would produce a more evenly balanced view of the effects of fibres in concrete. A single grade of concrete was used for the test. As the permeability of concrete influences the rate at which steam can escape from the interior of a saturated concrete cube, testing a range of concrete strengths would show this aspect of material performance with regard to spalling and final residual strength. Further research is recommended with regard to moisture contents, strengths of concrete and a range of temperatures

Environmentally Friendly Pervious Concrete for Treating Deicer-Laden Stormwater: Phase I

A graphene oxide-modified pervious concrete was developed by using low-reactivity, high-calcium fly ash as sole binder and chemical activators and other admixtures. The density, void ratio, mechanical strength, infiltration rate, Young’s modulus, freeze-deicer salt scaling, and degradation resistance of this pervious concrete were measured against three control groups. The test results indicate that graphene oxide modified fly ash pervious concrete is comparable to Portland cement pervious concrete. While the addition of 0.03% graphene oxide (by weight of fly ash) noticeably increased the compressive strength, split tensile strength, Young’s modulus, freeze-deicer salt scaling, and degradation resistance of fly ash pervious concrete, it reduced the void ratio and infiltration rate. The fly ash pervious concrete also showed unfavorable high initial loss during the freeze-deicer salt scaling test, which may be attributed to the low hydration degree of fly ash at early age. It is recommended that durability tests for fly ash concrete be performed at a later age

Bond–slip Behavior of Fiber-reinforced Polymer/concrete Interface in Single Shear Pull-out and Beam Tests

It has been assumed that the fiber-reinforced polymer/concrete interface is subjected to in-plane shear condition when intermediate crack debonding failure occurs. Therefore, the single shear pull-out test results are often used to predict the intermediate crack debonding failure in beams. In this study, the behavior of fiber-reinforced polymer-strengthened concrete beams and single shear pull-out specimens were studied experimentally and numerically. The bond–slip behavior of the fiber-reinforced polymer/concrete interface was obtained by single shear pull-out and beam tests. In all beam specimens, a concrete wedge located at the edge of the notch detached with the fiber-reinforced polymer debonding failure. This phenomenon shows that the initiation of debonding is due to a diagonal crack formation close to the major flexural/shear crack inside the concrete. The diagonal crack formation is due to a local moment at the tip of the notch. This causes the different stress state and slip of the fiber-reinforced polymer/concrete interface of beam specimens from that of the pull-out specimens. It is found that the bond–slip relation obtained from the pull-out test does not represent the bond–slip relation of the fiber-reinforced polymer/concrete interface in the fiber-reinforced polymer-strengthened concrete beams, and it cannot be directly used for predicting the load capacity of the fiber-reinforced polymer-strengthened concrete beams

Top Bar Effects in Prestressed Concrete Piles

The top bar effect in reinforced concrete is a widely recognized phenomenon. Currently, the ACI Building Code prescribes a 30% increase in the development length of top cast reinforcing bars. No such provision is required for strands in prestressed concrete members. In this paper, the top bar effect for prestressing strands is introduced. Parameters affecting top bar phenomena in prestressed concrete piles are identified, and strategies for reducing this effect are presented. Finally, for the first time, the application of a top bar effect factor for prestressed concrete development length calculations, similar to the one applied in reinforced concrete structural elements, is proposed

Strength and water absorption rate of concrete made from palm oil fuel ash

Concrete is one of the most important materials for construction industry. The material in the mixture of concrete includes cement, sand and coarse aggregate. Production of cement causes the air pollution from the emission of carbon dioxide to the air. This research studies the replacement of cement with palm oil fuel ash (POFA) in the concrete mixture. The objective of this research is to investigate the compressive strength of concrete and water absorption rate of concrete made from POFA and to compare the strength and absorption rate between conventional concrete and concrete made from POFA. This is to indicate whether the compressive strength and absorption rate are equivalent to the strength of conventional concrete. The methodology used in this research is experimental method and the palm oil fuel ash was taken from palm oil mill in Cha’ah, Johor, Malaysia. The results of this research are the specimens which contain 20% POFA has a compressive strength and water absorption rate comparable to conventional concrete

Sustainable Concrete for the 21st Century Concept of Strength through Durability

The world is passing through difficult and troubled times, and we live in a rapidly changing world. The construction industry is facing many challenges – global warming, climate change forces, and the capability to achieve sustainable development and economic progress without damaging our environment. The concrete industry in particular faces further challenges. There is extensive evidence to show that concrete materials and concrete structures all over the world are deteriorating at a rapid rate, and that we are unable to ensure their long-term durable service life performance. To confound this situation, we are also faced with an urgent need to regenerate our infrastructure systems if we are to eradicate poverty and provide a decent Quality of Life for all the peoples of the world. This paper shows that the current emphasis on high strength and very high strength, and the design philosophy of Durability through Strength for concrete materials and concrete structures is fundamentally flawed. It is this misleading concept and vision that is primarily responsible for the lack of durable performance of concrete in real life environments. To change this scenario, this paper advocates that concrete materials must be manufactured for durability and not for strength. It is shown that this concept of Strength through Durability can be achieved through careful design of the cement matrix and its microstructure. If concrete is to be an eco-friendly, and sustainable driving force and construction material for social change, the need is to produce durable concrete with strengths of 30 to 60 to 80 MPa rather than very high strength concrete without an assured durable performance