Mechanical properties of old concrete—UHPFC interface

The uniqueness of Ultra-High Performance Fiber Concrete (UHPFC) is its extremely low porosity gives its low permeability and high durability, making it potentially suitable for rehabilitation and retrofitting reinforced concrete structures or for use as a new construction material. This experimental study was performed to assess the bond strength between UHPFC as a repair material and Normal Concrete (NC) substrate as an old material; split tensile strength and slant shear tests were performed to quantify the bond strength in indirect tension and shear respectively, also the correlation between split tensile strength and slant shear were studied. The result showed that UHPFC has been cured by steam, gives high bond strength at the early age of the repair process, and interacts well with the surface of NC, as a result the failure occurred mostly in the NC substrate. A good correlation between the slant shear test results and the split tensile test results has been observed

The relationship between substrate roughness parameters and bond strength of ultra high-performance fiber concrete

The bonding that exists between the old concrete and the new concrete depends largely on the quality of substrate surface preparation. The accurate representation of substrate surface roughness can help determine very precisely the correct bonding behavior. In this work, an experimental investigation was carried out to quantify the normal concrete (NC) substrate roughness parameters and evaluate their relationship with the bonding performance of ultra high-performance fiber concrete (UHPFC), used as a repair material. The bond strength was quantified based on the results of the pull-off test, splitting cylinder tensile test, and the slant shear test. Three types of NC substrate surface preparation were used: as-cast (without surface preparation) as reference, wire-brushed, and sand-blasted (SB); the roughness of which was determined using an optical three-dimensional (3D) surface metrology device (Alicona

Compressive Stress-Strain Behavior of Composite Ordinary and Reactive Powder Concrete

The deterioration of reinforced concrete structures is a major social problem. To minimize this problem and ensure effective structural management, the number and extent of repair interventions must be kept at the lowest probable level. Good bond is one of the main requirements for successful repair. The main aim of this study was to investigate the compressive stress-strain behaviour of the composite specimens consist of ordinary concrete (OC) substrate as old concrete and reactive powder concrete (RPC) as a retrofitting material, by using different types of OC substrate surface preparation methods. The results showed that the composite OC/RPC specimens were able to behave closely to individual OC, in the case of using OC substrate with surface prepared by sand blasted

Thermal Model of Rotary Friction Welding for Similar and Dissimilar Metals

Friction welding is one of the foremost welding processes for similar and dissimilar metals. Previously, the process has been modeled utilizing the rudimentary techniques of constant friction and slip-stick friction. The motivation behind this article is to present a new characteristic for temperature profile estimation in modeling of the rotary friction welding process. For the first time, a unified model has been exhibited, with an implementation of the phase transformation of similar and dissimilar materials. The model was generated on COMSOL Multiphysics® and thermal and structural modules were used to plot the temperature curve. The curve for the welding of dissimilar metals using the model was generated, compared and analyzed with that of practical curves already acquired through experimentation available in the literature, and then the effect of varying the parameters on the welding of similar metals was also studied

Utilization of ultra-high performance fibre concrete (UHPFC) for rehabilitation–a review

Under normal circumstances, reinforced concrete structures (RCS) show excellent performance in terms of durability and structural behaviour except for the zones that are subjected to severe mechanical or cyclic loading and aggressive environmental conditions. Therefore the methods of rehabilitation or strengthening of these zones should be reliable, effective and economical. Today, many scientists, academics and engineers understood the extremely low porosity and low permeability characteristics of ultra high performance fibre concrete (UHPFC) giving its enhanced durability over high performance concrete (HPC), thus making it potentially suitable for rehabilitation and retrofitting problematic RCS. The advantages of utilising the technology of UHPFC in repairing works includes (i) decrease the working time needed for the rehabilitation works; and (ii) increase the serviceability and durability to an extent where

Evaluation on the Preference of Coffee Shop among the Undergraduate Students with Analytic Hierarchy Process Model

Emergence of coffee shop in recent years has proven the demand of coffee shop in modern lifestyle. Nowadays, visitation to coffee shop has become a common trend for most of the undergraduate students for group discussion or chatting. This study aims to evaluate the preference of undergraduate students from Universiti Tunku Abdul Rahman in selecting the coffee shop based on multiple criteria. There are 19 respondents participating in this study who have visited all the 4 selected coffee shops which are Simple Coffee, Bean Caf, Starbucks and Old Town White Coffee. An Analytic Hierarchy Process (AHP) model is proposed to determine the weight of criteria, priority of coffee shop selection in terms of each criterion and the overall performance of the coffee shop. The findings show that the most important criterion is cleanliness, followed by flavor, store atmosphere, sales promotion, speed of service, price and location. Starbucks is the most preferred coffee shop while the followings are Simple Coffee, Bean Caf and Old Town White Coffee. The significance of this study is to propose a conceptual framework to identify the most preferred coffee shop and the most important criteria in coffee shop selection among the undergraduate students by using AHP model

Flexural Strength Behavior of Composite UHPFC-Existing Concrete

Article Preview Article Preview Ultra high performance fiber concrete (UHPFC) is an advanced formula concrete that is proven to be more superior than conventional concrete because it embrace the qualities of steel and concrete. Therefore UHPFC properties which include high durability and strength are fully exploited in the research of rehabilitation and strengthening in concrete and even non-concrete structures. This article presents the findings of an experimental study carried out to examine the bonding strength behaviour between normal concrete (NC) substrate and UHPFC as a repair material, under flexural strength test by using third-point loading beam test method. Three types of NC substrate surface preparation were used: as-cast (without surface preparation) as a reference, wire-brushed, and sand-blasted. The flexural test results clearly indicated that all failures occurred through the NC substrate and no

Retardation of heat exchanger surfaces mineral fouling by water-based diethylenetriamine pentaacetate-treated CNT nanofluids

Mineral scale deposition on heat exchanging surfaces increases the thermal resistance and reduces the operating service life. The effect is usually intensified at higher temperatures due to the inverse temperature solubility characteristics of some minerals in the cooling water. Scale formation build up when dissolved salt crystallize from solution onto the heated surface, forming an adherent deposit. It is very important for heat transfer applications to cope with the fouling problems in industry. In this present study, a set of fouling experiments was conducted to evaluate the mitigation of calcium carbonate scaling by applying DTPA-treated MWCNT-based water nanofluids on heat exchanger surfaces. Investigation of additive DTPA-treated MWCNT-based water nanofluids (benign to the environment) on fouling rate of deposition was performed. 300 mg L−1 of artificially-hardened calcium carbonate solution was prepared as a fouling solution for deposit analysis. Assessment of the deposition of calcium carbonate on the heat exchanger surface with respect to the inhibition of crystal growth was conducted by Scanning Electron Microscope (SEM). The results showed that the formation of calcium carbonate crystals can be retarded significantly by adding MWCNT-DTPA additives as inhibition in the solution

STUDI KOMPARASI SISTEM PENDIDIKAN DI MADRASAH IBTIDAIYAH MUHAMMADIYAH (MIM) KAHUMAN NGAWEN DAN SEKOLAH DASAR ISLAM TERPADU (SDIT) MUHAMMADIYAH AN NAJAH JATINOM TAHUN 2017/2018

This research aims at describing: 1) How education system applied at MIM Kauman Ngawen is, 2) How education system applied at SDIT Muhammadiyah An Najah Jatinom is, 3) What the similarities and the differences of education system applied at MIM Kauman Ngawen and SDIT Muhammadiyah An Najah Jatinom are. This research used qualitative method and was conducted at MIM Kauman Ngawen and SDIT An Najah Jatinom from December 2017 to January 2018. Method of collecting data used interview, documentation, and observation. Informants were the Principal, the teachers and the students. Technique of data analysis used comparative descriptive method. Method of descriptive was applied to describe education system of each school in detail, while method of comparative was used to compare the similarities and the differences of education system. The conclusions of this research are: 1) Education system at MIM Kauman applies both School curriculum and alliance curriculum, also provides additional extracurricular activities dealt by the agreement of parents, School Committee and alliance Board. The learning system is classic means that only guided by one class room teacher for the first and the second grade. Meanwhile, subject teachers are for other classes. The learning is conducted at 7 am – 1.50 pm, except on Friday, 2) SDIT Muhammadiyah An Najah Jatinom applies curriculum of Department of Education and Culture, alliance curriculum and Integrated Islamic School curriculum enriched with some specific programs and extracurricular activity. The learning system at SDIT Muhammadiyah An Najah Jatinom is also classic with double class room teachers for the first and the second grade, except for sport subject and special program, also the system of subject teachers for other classes. The learning is implemented by applying full day school concept, from 7 am until 02.40 pm everyday including on Friday, 3) Education system applied at MIM Kauman and SDIT Muhammadiyah An Najah Jatinom substantially are similar, including vision, mission, and objective. The difference is in pertaining to editing and showing school’s characteristics. Keywords: Comparison of Education Syste