Roszilah Hamid

Dynamic Stress-Strain Behaviour of Steel Fiber Reinforced High-Performance Concrete with Fly Ash

The addition of steel fibers into concrete mix can significantly improve the engineering properties of concrete. The mechanical behaviors of steel fiber reinforced high-performance concrete with fly ash (SFRHPFAC) are studied in this paper through both static compression test and dynamic impact test. Cylindrical and cube specimens with three volume fractions of end-hooked steel fibers with volume fraction of 0.5%, 1.0%, and 1.5% (39.25, 78.50, and 117.75 kg/m3) and aspect ratio of 64 are used. These specimens are then tested for static compression and for dynamic impact by split Hopkinson pressure bar (SHPB) at strain rate of 30–60 s−1. The results reveal that the failure mode of concrete considerably changes from brittle to ductile with the addition of steel fibers. The plain concrete may fail under low-strain-rate single impact whereas the fibrous concrete can resist impact at high strain rate loading. It is shown that strain rate has great influence on concrete strength. Besides, toughness energy is proportional to the fiber content in both static and dynamic compressions.

Strength and Microstructure of Mortar Containing Nanosilica at High Temperature

The effect of high temperature on the mechanical properties and microstructure of nanosilica-incorporated mortars has been studied. Results show that the incorporation of nanosilica increases both compressive and flexural strengths significantly at both ambient and after a 2-hour exposure to 752°F (400°C) temperatures; the strengths increase with the increase of nanosilica content. A significant decrease in strength was recorded for all control and nanosilica-incorporated mortar specimens after a 2-hour exposure to 1292°F (700°C) heat; however, nanosilica-incorporated specimens show higher residual strength than those without nanosilica. Microstructural analysis shows that nanosilica reduces the calcium hydroxide crystals to produce more calcium silicate hydrate, the process that contributes to the strength and the residual strength of the material. In addition, the material exhibits a stable structure state up to 842°F (450°C), while exposure to higher temperatures results in a decomposition of hydration products.

Dynamic Properties of High Volume Fly Ash Nanosilica (HVFANS) Concrete Subjected to Combined Effect of High Strain Rate and Temperature

The study aims to determine the dynamic properties of high volume fly ash nanosilica HVFANS concrete exposed to strain rates between 30.12 to 101.42 s‐1 and temperatures of 25, 400, and 700 oC by using split Hopkinson pressure bar SHPB machine. The static and dynamic compressive strengths of HVFANS concrete were slightly lower than plain concrete PC at room temperature, while its values were higher at 400 and 700 oC. The results proved that the CEB model of dynamic increase factor is more reliable to estimate the behaviour of HVFANS concrete at studied temperatures. The toughness, critical strain, and damage of HVFANS concrete recorded a superior performance than PC under studied strain rates and temperatures that would reflect the possibility of use HVFANS concrete in structures to improve its resistant of fire and impact loads, as well as to decrease the demand on Portland cement which could lead to restrict the risks of liberated gases during cement production. Furthermore, equations were proposed to estimate the dynamic increase factor, toughness, and critical strain of both concretes under investigated conditions.

Influence of Micro Steel and Polypropylene Fibres on the Dynamic Properties and Porosity of Ultra High Performance Concrete

Ultra-high Performance Concrete (UHPC) is a special type of concrete with extraordinary potentials in terms of strength and durability performance. This paper aims to determine the dynamic properties and porosity of fibre reinforced UHPC (FRUHPC). Two types of fibres were used: micro steel (MS) and polypropylene (PP) fibres, with three volume fractions of 0.5%, 0.75% and 1.0%. A total of 54 specimens were prepared and tested after 28 days of wet curing for static compression and flexural strengths; dynamic stress and strain; and porosity. The dynamic properties were determined using split Hopkinson pressure bar (SHPB) and porosity by mercury intrusion porosimeter (MIP). The optimum static compressive strength of UHPC is at 0.75% PP fibre inclusion at 150.2 MPa. UHPC with 1.0% MS fibre inclusion exhibits highest flexural strength at 14.2 MPa. PP fibre reinforced UHPC recorded highest value of pore at 15.51% compares to normal UHPC. The ultimate dynamic stresses are between 140 – 160 MPa, ultimate dynamic strains between 0.0006 – 0.002 mm/mm and the ultimate strain rates in the range of 100 s-1 and 230 s-1. The highest DIF value is 1.34 for 5% MS fibre reinforced UHPC.

Preliminary study of neutron absorption by concrete with boron carbide addition

Concrete has become a conventional material in construction of nuclear reactor due to its properties like safety and low cost. Boron carbide was added as additives in the concrete construction as it has a good neutron absorption property. The sample preparation for concrete was produced with different weight percent of boron carbide powder content. The neutron absorption rate of these samples was determined by using a fast neutron source of Americium-241/Be (Am-Be 241) and detection with a portable backscattering neutron detector. Concrete with 20 wt % of boron carbide shows the lowest count of neutron transmitted and this indicates the most neutrons have been absorbed by the concrete. Higher boron carbide content may affect the concrete strength and other properties.

Blast damage assessment of symmetrical box-shaped underground tunnel according to peak particle velocity (PPV) and single degree of freedom (SDOF) criteria

This study aimed to determine the reliability of the damage criteria that was adopted by the peak particle velocity (PPV) method and the single degree of freedom (SDOF) approach to assess the damage level of a box-shaped underground tunnel. An advanced arbitrary Lagrangian Eulerian (ALE) technique available in LS-DYNA software was used to simulate a symmetrical underground tunnel that was subjected to a surface detonation. The validation results of peak pressure into the soil revealed a good consistency with the TM5-855-1 manual within differences that were much less than previous numerical studies. The pressure contours revealed that the blast waves travelled into the soil in a hemispherical shape and the peak reflected the pressure of the tunnel that occurred immediately before the incident pressure reached its highest value. The assessment results proved that the criteria of the above methods could efficiently predict the damage level of a box-shaped tunnel under different circumstances of explosive charge weight and lining thickness at a depth of 4 m within slight differences that were observed during van and small delivery truck (SDT) explosions. However, the efficiency of both the methods was varied with the increase of burial depth. Whereas, using the PPV method significantly underestimated or overestimated the damage level of the tunnel, especially during SDT and container explosions with a lining thickness of 250 mm at burial depths of 6 and 8 m, respectively, the damage level that was obtained by the SDOF method greatly matched with the observed failure modes of the tunnel. Furthermore, new boundary conditions and equations were proposed for the damage criteria of the PVV method.

Influence of Morphology of Cathode-Ray Tube Glass as Coarse Aggregates on Compressive Strength and Water Absorption of Concrete

The study on the substitution for natural coarse aggregates using waste CRT funnel glass in spherically shapes is still limited. In this paper, the waste CRT glass has been processed to form a spherical CRT glass (GS) and crushed CRT glass (GC), which were used as a coarse aggregate in concrete production. Results indicated that the inclusion of GS and GC has lower the compressive strength and decreased the rate of capillary water absorption of concrete. It was demonstrated that the morphology properties of GS and GC (shape, surface texture, size, grading) is significantly affected the concrete properties.

Physical Damages Effect on Residential Houses Caused by the Earthquake at Ranau, Sabah Malaysia

Earthquake, the destructive natural disaster had recently stormed East Malaysia. This study aims to identify the physical effects of the earthquake to the building that occurred in Sabah, Malaysia. A survey method had been conducted among 221 citizens in the affected area to meet the requirements of this research objective. The result shows that 68% responded that building cracks had formed on the wall, 48% cracked floor, 23% cracked columns, 10% damages on roof and 8% responded no damages at all while only 2% stated the total collapse of the houses’ structures. Researchers have also identified that the impact of the earthquake towards their house yards shows that 55% and 12% responded experienced cracks on ground and landslide respectively, 25% with flood occurrence and 1% are caught with fire. Finally, almost 90% of the respondents are ready to upgrade their house structures. Thus, this research will be continued by developing the retrofitting and strengthening methods for the low rise buildings.

Elevated Temperature Performance of Multiple-Blended Binder Concretes

Concretes that contain binary-blended binders (BBB) and ternary-blended binders (TBB) incorporating thermally activated alum sludge ash (AASA), silica fume (SF), ground-granulated blast-furnace slag (GGBS) and palm oil fuel ash (POFA) are exposed to temperatures as high as 800 °C. The water-binder ratio of the multiple-blended binder (MBB) concretes was 0.30, and the total binder and polypropylene (PP) fibre contents were 493 and 1.8 kg/m3, respectively. The elevated temperature performance of the MBB concretes is evaluated in terms of the mass loss, compressive strength, ultrasonic pulse velocity (UPV) and surface cracks. The concrete strength deteriorated significantly due to elevated temperature up to 800 °C, but the residual strength of the BBB containing 15 % AASA was higher than that of the control and 20 % AASA concretes. Hightemperature exposure decreased measured UPV values. The concrete weight loss was more pronounced for TBB concretes. The elevated temperature performance of all of the TBB concretes was better than that of the BBB concretes with the same AASA replacement levels. It was observed that PP fibres help reduce spalling. BBB concrete containing 15 % AASA combined with either SF or GGBS or POFA exhibits superior performance at elevated temperature than Portland cement concrete at the same mix design proportion.

Dynamic increase factor of high strength concrete with silica fume at high strain rate loading

The dynamic mechanical properties (stress-strain diagram, ultimate stress, ultimate strain and strain rate) and of high strength concrete (HSC) with 5% and 10% silica fume (SF) addition at high strain rate of 10 s-1 to 102 s-1 (3.8 MPa, 4.1 MPa and 4.8 MPa) are determined using Split Hopkinson Pressure Bar equipment. The compressive strength of the HSC at design strength of 80 and 90 MPa is also determined. Results show that the compressive strength of the 5%SF and 10%SF HSC are 83 MPa and 92 MPa, respectively. The dynamic stress-strain diagrams show that the higher the pressure load, the higher the values of ultimate dynamic stress, σu and the ultimate strain rate, ἐu for both percentages of SF addition concrete. The ultimate dynamic stress, σu are between 200 – 250 Mpa and the ultimate strain rate, ἐu is in the range of 95 s-1 and 160 s-1. The ultimate dynamic strain, εu between 0.005-0.008 mm/mm. The dynamic increase factors (DIF) of the HSC are more than 2 compare to normal strength concrete.