Khalifa S. Al-Jabri

Use of Copper Slag and Cement By-Pass Dust as Cementitious Materials

Copper slag (CS) and cement by-pass dust (CBPD) are by-products of the production of copper and cement, respectively. In the Sultanate of Oman, large quantities of copper slag (60,000 tons/year) and cement by-pass dust (25,000 tons/year) are produced every year, most of which is not effectively utilized and disposed on-site without any reuse. The main objective of this research is to investigate the potential use of copper slag and cement by-pass dust in concrete as partial replacements for Portland cement. The physical and chemical properties of both slag and cement by-pass dust were determined. Mortar samples were prepared using different proportions of slag, cement by-pass dust and lime, which was used as an activating material. Proportions up to 15% of Portland cement replacement were used. In addition, a control mixture containing 100% Portland cement was prepared for comparison. Results obtained indicated that the increase in the proportions of copper slag and cement by-pass dust alone resulted in a decrease in the compressive strength of mortars compared with the control mix. The highest compressive strength was achieved in samples containing 5% CBPD + 95% cement, which was 41.7 MPa after 90 days. The optimum copper slag and cement by-pass dust to be used is 5%. In addition, it was determined that using cement bypass dust as an activating material will work better than using lime. Additional studies should investigate the strength and durability when copper slag and cement by-pass dust are used in concrete mixes.

Prediction of the degradation of connection characteristics at elevated temperature

Abstract This paper describes a simple procedure developed to predict the moment–rotation response of connections at elevated temperatures. It is based on the actual degradation of connection rotational stiffness and strength based on results obtained from the experimental tests. These tests were conducted on a range of connection sizes and types. The rate of degradation of connection characteristics is compared with the strength reduction factors of structural steel according to the EC3: Part 1.2 recommendations. This procedure predicts with reasonable accuracy the degradation of stiffness and the strength of bare-steel connections, but it overestimates to some extent the rate of degradation of strength of composite connections.

Effect of organic fibers on open-graded friction course mixture properties

Open-graded friction course (OGFC) or porous asphalt mixtures are special mixes used for improving the surface friction, increasing surface permeability, and reducing pavement noise. The mix consists mostly of coarse size aggregate with little fines. This study was conducted to evaluate the effect of two types of organic fibers: date-palm fibers and textile fibers, in combination with styrene butadiene rubber (SBR) polymer on the properties of OGFC mixes. A total of six different mixes were evaluated. Mix designs were performed according to the design procedure proposed by the National Center of Asphalt Technology (NCAT) for a range of 4.5–6.5% asphalt content. One-way ANOVA using the Tukey method of multiple comparisons was used to test the effect of the modifier and/or stabilizer on abrasion as an indication of raveling potential as well as draindown. The results indicated that the asphalt mix containing date-palm fibers and SBR polymer at 5.0% and the asphalt mix containing textile fibers and SBR polymer at 6.5% asphalt content satisfied the mix design criteria. The asphalt mixes at optimum asphalt content were evaluated for moisture susceptibility using the indirect tensile strength.

Recycling of waste spent catalyst in road construction and masonry blocks

Waste spent catalyst is generated in Oman as a result of the cracking process of petroleum oil in the Mina Al-Fahl and Sohar Refineries. The disposal of spent catalyst is of a major concern to oil refineries. Stabilized spent catalyst was evaluated for use in road construction as a whole replacement for crushed aggregates in the sub-base and base layers and as a partial replacement for Portland cement in masonry blocks manufacturing. Stabilization is necessary as the waste spent catalyst exists in a powder form and binders are needed to attain the necessary strength required to qualify its use in road construction. Raw spent catalyst was also blended with other virgin aggregates, as a sand or filler replacement, for use in road construction. Compaction, unconfined compressive strength and leaching tests were performed on the stabilized mixtures. For its use in masonry construction, blocks were tested for unconfined compressive strength at various curing periods. Results indicate that the spent catalyst has a promising potential for use in road construction and masonry blocks without causing any negative environmental impacts.

Use of Cement By-pass Dust in Flowable Fill Mixtures

Flowable fill is a self-compacted, cementitious material used primarily as a backfill in lieu of compacted fill. It is generally a mixture of sand, small amount of cement, fly ash, and water. Sand is the major component of most flowable fill mixes. Waste materials such as fly ash, ground granulated blast furnace slag, and foundry sand are commonly used to ensure low maximum compressive strength. Cement by-pass dust (CBPD) is considered a waste material of the production of cement. An estimated 25,000 tons of CBPD are produced annually in the Sultanate of Oman by Oman Cement Company alone. Most of this material is not effectively used and is disposed of on-site without any reuse causing environmental concerns. The main objective of this research is to investigate the potential use of CBPD in flowable fill mixtures as an alternative to fly ash and as a partial substitute for cement. The physical and chemical properties of both CBPD and cement were determined. Cube and cylindrical samples were prepared using different proportions of CBPD and water-to-cement ratios in order to select the optimum mixes that can be used in flowable fill applications. The optimum mixtures were cured in air and covered in plastic bags in order to study the effect of curing method on the compressive strength of flowable fill mixtures. Promising results were obtained with respect to the use of CBPD as a partial or full substitute for cement in flowable fill mixtures. Results also demonstrated that air cured samples gave a higher compressive strength than samples cured in the plastic bags for the mixes where CBPD was used as a partial substitute for cement. However, in mixes where CBPD was used to fully replace cement, samples that were cured in plastic bags produced higher strength than air cured samples at longer curing periods.

Finite Element Analyses of Flush End-Plate Connections between Steel Beams and Columns at Elevated Temperatures

This paper presents a finite element analysis procedure developed to study the behaviour of a flush end-plate connection between steel beams and a column at elevated temperatures and generates temperature-rotation diagrams that describe the behaviour of the connection. The analysis uses a highly detailed three dimensional finite element model that is created using the commercial ANSYS software. The steel connection properties are selected in a way that reflects commonly used connections in steel framed buildings. The results of the finite element model are calibrated and compared to the results of experimental fire tests conducted on similar connections. This comparison shows a deviation of about 12% which is reasonable considering the complexity and the nonlinear nature of the analysis. Furthermore, the same methodology used to create the finite element model of isolated steel connections is then used to create a sub-frame constructed with similar connections. Both the applied loads and the dimensions of the model represent a part of a typical steel framed building that is subjected to a fire outbreak in one of its bays. The results indicate that at low temperatures, the main beam is snugly fixed and the joints at both sides provide full rigidity whereas at elevated temperatures the central deflection is rapidly increased because of plastic hinge formation. Although this frame has not been tested in reality, the finite element model gives a prediction of the failure mechanism of such a frame under fire loads without the use of expensive full scale testing facilities.

Modelling and simulation of beam-to-column joints at elevated temperature: A review

Abstract This paper presents an overview of the modelling and simulation methods, which have recently been developed in the literature to simulate the behaviour of the beam-to-column joints at elevated temperature. These include curve-fit models, component-based models, finite element models, and artificial neural network models. The study concluded that the various numerical modelling methods can be used reliably to predict the behaviour of joints at elevated temperature to an acceptable degree of accuracy.

An advanced ANN model for predicting the rotational behaviour of semi-rigid composite joints in fire using the back-propagation paradigm

This paper describes an artificial neural networking (ANN) model developed to predict the behaviour of semi-rigid composite joints at elevated temperature. Three different semi-rigid composite joints were selected, two flexible end-plates and one flush end-plate. Seventeen different parameters were selected as input parameters representing the geometrical and mechanical properties of the joints as well as the joint’s temperature and the applied loading, and used to model the rotational capacity of the joints with increasing temperatures. Data from experimental fire tests were used for training and testing the ANN model. Results from nine experimental fire tests were evaluated with a total of 280 experimental cases. The results showed that the R2 value for the training and testing sets were 0.998 and 0.97, respectively. This indicates that results from the ANN model compared well with the experimental results demonstrating the capability of the ANN simulation techniques in predicting the behaviour of semi-rigid composite joints in fire. The described model can be modified to study other important parameters that can have considerable effect on the behaviour of joints at elevated temperatures such as temperature gradient, axial restraints, etc.

Efficiency of horizontal-to-vertical spectral ratio (HVSR) in defining the fundamental frequency in Muscat Region, Sultanate of Oman: a comparative study

Muscat region is the most important political, economic, and densely populated region in the Sultanate of Oman. The proximity of Muscat region to the Oman Mountains and Makran subduction zones controls the earthquake hazard for Muscat. Evidences indicate the occurrence of a nearby historical earthquake with moderate magnitude MS = 5.5 in 1883. This event led to the damage of some villages near Nizwa City. The main objective of the current study is to compare the site characteristics of the region of interest in terms of the fundamental frequency using microtremors measurements with the numerical analysis results using one-dimensional (1-D) shear wave profiles. The microtremor measurements were performed at 99 sites distributed over the study region in order to calculate the horizontal-to-vertical spectral ratio (HVSR). The numerical modeling of horizontal shear (SH) waves in soil at the selected 99 sites are assessed by carrying out 1-D ground response analysis using the program SHAKE91. The required shear wave velocity profiles for the numerical modeling of SH-waves were derived using multichannel analysis of surface waves profiles. The amplification spectra have been evaluated for the soil column at each site location and the fundamental frequency obtained using SHAKE91 and HVSR are compared. Results were found to be compatible with the general surface geology of the region of interest and in most cases the HVSR is proved to be suitable for calculating the fundamental frequency in Muscat region.

The Influence of Connection Characteristics on the Behaviour of Beams in Fire

Publisher Summary Steel is seriously affected by fire, losing strength and stiffness leading to large deformations and often collapse. Using applied fire protection remains the most common way of satisfying structural fire resistance requirements, despite its cost. Parametric studies are conducted to investigate the effect of connection characteristics on beam response in fire. This effect is considered by incorporating the moment–rotation characteristics for flush and flexible end-plate connections within both bare-steel and composite sub-frame analyses. The Ramberg–Osgood expression is adopted to represent the connection characteristics at elevated temperature. The analyses are conducted using the finite element code, VULCAN. The connection characteristics incorporated to simulate the connection response are obtained from a series of beam-to-column connection tests. These tests are conducted in a portable junction furnace to study the moment–rotation characteristics of typical connections. The results show that the structural connections could have considerable influence on the behavior of beams at elevated temperatures.