Applied Mechanics and Materials Vol. 802

Abstract: Drying shrinkage in mortar produces cracks and micro-cracks which affect the durability of a structure. The effects of seawater as a substitute to freshwater and fly ash as a partial replacement for cement were investigated in this study in order to address the predicted water shortage by 2025 and the increasing carbon footprint from carbon dioxide emissions worldwide. Moreover, these materials are also more economical alternatives to freshwater and cement. Rectangular prism specimens with varying fly ash content (10%, 15%, 20%, 25%, and 30%) were cast to measure the drying shrinkage in mortar while 50-mm cube mortar specimens were prepared to determine the compressive strength. This study investigated whether the addition of fly ash and seawater reduced the drying shrinkage of mortar. From the results, it was found that mortar specimens with 20% fly ash replacement achieved the highest early and late strengths. Partial substitution of fly ash would result to shrinkage in mortar while substitution of seawater to freshwater counteracts the effects of fly ash, thus producing less shrinkage. Fly ash content between 20%-25% combined with seawater produces the least shrinkage value without compromising the minimum required compressive strength.

Abstract: In Malaysia, more than 50,000 tons of used automobile tyres are stockpiled annually. This subsequently causes a major threat to the environment. This article focus on the durability of mortar with treated crumb rubber (TCR) as partial replacement for fine aggregate (FA) and addition of oil palm fruit fibre (OPFF) in the mix. For every 0.5% OPFF additions, there were 10% TCR replacements up to 30%, resulting in 16 different mixes with constant water cement ratio. The specimens were cured either by water ponding or water sprinkling for 28 days, after which they were preconditioned and subsequent carbonation depth measurement was made. The results showed that the carbonation depth lies between 2.5mm to 6.7mm. These confirmed that rubberised fibre mortar achieved carbonation depth of less than 15mm, the tolerable limit.

Abstract: Concrete-filled double skin steel tubular (CFDST) columns with three different diameters were exposed to fire following ASTM E-119 fire curve. The temperature was kept constant for 60 minutes after reaching 600°C. After the cooling down process, the columns were tested under concentric axial load condition until failure. Maximum loads, displacement and strain were recorded during testing. Failure patterns were observed. In this paper, failure patterns, increment or reduction of residual strength, ductility and stiffness are reported and discussed in details. All tested CFDST columns failed by local buckling and crushing of concrete. As expected, residual strength index (RSI) decreased with increased fire exposure time. Whereas, larger diameter heated specimen retain more than 50% of it corresponding room temperature secant stiffness. In addition, ductility index (DI) of larger diameter specimen shows an enhancement after fire exposure. Highest enhancement in DI was observed in 90 minutes fire exposure.

Abstract: This paper presents the outcomes of investigating the dynamic behaviour experienced by composite footbridges and concrete footbridges when subjected to footfall induced vibration incurred by walking pedestrians. The study focuses on three set of varying parameters including bridge’s deck thickness, span length and width of footbridge. Models are generated and analysed using finite element method. Dynamic responses obtained from the footfall analysis are expressed in term of vertical displacements and accelerations. Data are tabulated and evaluated based on different parameters incorporated; meanwhile comparisons are made between concrete and composite footbridges. It was found that for both composite and concrete footbridges, the displacement and acceleration decrease exponentially with the increase of deck thickness. They also show decreasing trend with the increase of span length. Besides, an increase in displacement and acceleration is observed with the increase of footbridge width.

Abstract: The article reports a laboratory experimental programme that investigated effect of ground granulated blast furnace (GGBS) on compressive strength of POFA ternary concrete. Compressive strength tests were performed at a range of cements combinations, including 100%PC, two POFA levels for binary concrete, 35% and 45%, and 15%GGBS inclusion for POFA ternary concrete. The compressive strength results were examined in comparison to PC only and equivalent POFA binary concretes for up to 28 days. Results show that the reduction in compressive strength is greater with the higher cement replacement level for all concretes particularly for POFA binary concretes. However, 15%GGBS in POFA blended concrete has a comparable compressive strength compared to PC concrete at both, 35% and 45%, cement replacement levels except for ternary concrete at 0.65 w/c. In addition, the compressive strength of ternary concrete is slightly higher compared to binary concrete for all concrete combinations. Although there is no significant noticeable influence on strength development, the presence of GGBS did not adverse the strength development of POFA blended concrete. Thus, it can be concluded that GGBS compensates the adverse effect of POFA at early strength development.

Abstract: The possibility of utilizing treated coal bottom ash as a partial replacement of Portland cement was examined through compressive strength test on mortar samples. A total of 16 batches of mortar mixtures with cement:sand ratio of 1:2.5 and 1:2.75 were prepared using two types of treated coal bottom ash. The chemical compositions including the unburned carbon of coal bottom ash were also analyzed. In order to remove the excess unburned carbon which will affect the potential pozzolanic properties, the coal bottom ash was heated at 550 ± 50oC and 700 ± 50^°C for 60 min in an electrical furnace.The results showed that compressive strength of mortar mixtures with cement:sand ratio of 1:2.5 and 1:2.75 containing treated coal bottom ash which was heated at 550oC results in an increase in compressive strength. At 10% and 20% of treated coal bottom ash replacement levels to Portland cement, the compressive strength of the mortar mixture was significantly improved at the age of 28 days. The compressive strength of the mortar mixtures at early ages gives lower strength as compared to the plain Portland cement mortar. However, the effect of treated coal bottom ash that was heated at 700°C is to reduce the compressive strength of the mortar mixtures except for mixture with cement:sand ratio of 1:2.5 containing 10% coal bottom ash at 56 days.

Abstract: This paper investigates the effects of footfall induced vibrations on the floors of a 3-storey sub-frame structure. Composite and concrete floors were examined. Variables involved are floor widths, floor thicknesses, floor aspect ratios and column heights. Models are generated and analysed using the finite element method. The vibration responses were represented in terms of displacements and accelerations. Results show that higher vibration responses occurs on longer floor widths, thinner floor slabs and higher floor aspect ratios for both composite and concrete floors.

Abstract: Abstract: Two groups of rectangular beams, comprising of six specimens, the first group (L) were provided with four longitudinal bars, one at each corner while the second groups of beams (S) were fully reinforced with longitudinal bars and transverse reinforcement. Each group consisted of three beams. Two beams have been strengthened with ultra high performance fiber concrete (UHPFC) on four sides having a thickness of (15mm - 25mm) and one control beam. The variables considered in the experimental study include the transverse reinforcement ratios and the effect of thickness of UHPFC wrap. Experimental results show the effectiveness of the proposed technique at ultimate torque for strengthening beams and behavioral curves. Strengthened RC beams fully wrapped with a thin layer of UHPFC exhibit an enhanced torsional strength when compared to control beam. Results reveal that the transverse reinforcement ratios by 0.66%, increases the UHPFC contribution to torsional strength of strengthened beams with a 15 thick UHPFC; and by up to 7% for strengthened beams with a 25 thick UHPFC, respectively when compared to same strengthened beams without stirrup. It is found that the ultimate torque of beams with a 25 mm thin layer UHPFC is greater than beams with 15 mm by (28% and 28.3%) for the groups L and S, respectively.

Abstract: The design of the concrete mixtures of Ultra High Performances Fibre Reinforced Concrete (UHPFRC) is related to a densely compacted cementitious matrix and has outstanding material characteristics involving workability and high mechanical properties. Generally it is a combination between high strength concrete and fibres. UHPFRC offers high compressive strength which is higher than a normal concrete. The application of POFA as a cement replacement enhances the transport properties of concrete and contributes to a sustainable environment. The utilization of 50% UPOFA in mix design leads to develop a new class of concrete designated as GUSMRC. GUSMRC mixtures enhance the mechanical behaviour of concrete. GUSMRC with 50% replacement of the total binder content by ultrafine palm oil fuel ash (UPOFA) could contribute sustainability of environmental. The development of UHPFRC and its application in the field may contribute a good bonding strength at interface as a repair material between a new and old material. However, complex properties of materials can change dramatically when exposed to the elevated temperatures and adversely affected. The physical and chemical will change when occurred to heat. This paper investigates the change in mechanical properties of UHPFRC at elevated temperature and to determine the bonding strength between two layers which is overlay and concrete substrate

Abstract: The northwest coast of Peninsular Malaysia had suffered various extents of structural damage and loss of 68 lives in the unprecedented 2004 Indian Ocean tsunami. Since then, the government of Malaysia concerns about the safety of civil engineering structures and human lives in coastal area. An experimental study was embarked on the formulation of tsunami force for onshore buildings in Peninsular Malaysia. Four downscaled rigid building models with various heights were subjected to probable tsunamis with three nominal wave heights and flow velocities. The wave pressures at front and back faces of building model were measured. The findings show that the front face wave pressure measured from the experiment is in good agreement with the wave pressure predicted using the equation proposed by Japanese researchers. The back face wave pressure distribution is found to be slightly higher than the hydrostatic pressure. The pressure distributions at the front and back faces were then proposed for the estimation of tsunami force on buildings in the northwest coast of Peninsular Malaysia.