Ramzi Taha

A comparative evaluation of various additives used in the stabilization of expansive soils

This paper looks at the effectiveness of using cement by-pass dust, copper slag, granulated blast furnace slag, and slag-cement in reducing the swelling potential and plasticity of expansive soils. The soil used was brought from a location where structural damage was observed. The experimental program first dealt with determination of the chemical, mineralogical, and geotechnical characteristics of the untreated soil. The soil was then mixed with stabilizers at 3, 6, and 9% of the dry weight of the soil. The treated samples were subjected to liquid limit, plastic limit, swell percent, and swell pressure tests. Furthermore, the cation exchange capacity, exchangeable cations, and pH of the treated samples were also measured. This work showed that copper slag caused a significant increase in the swelling potential of the treated samples. Other stabilizers reduced the swelling potential and plasticity to varying degrees. The research further indicated that cation exchange capacity and the amount of sodium and calcium cations are good indicators of the effectiveness of chemical stabilizers used in soil stabilization.

Causes, Effects, Benefits, and Remedies of Change Orders on Public Construction Projects in Oman

Change orders are usually issued to cover variations in scope of work, material quantities, design errors, and unit rate changes. This paper discusses variations in public construction projects in Oman by investigating causes of variations, studying their effects on the project, identifying the beneficial parties, and suggesting remedies to alleviate related problems. Tasks included an analysis of four actual case studies and conducting a field survey via a questionnaire. It was determined that the clients additional works and modifications to design were the most important factors causing change orders, followed by the nonavailability of construction manuals and procedures. The most important effects of change orders on the project were found to be the schedule delays, disputes, and cost overruns. The contractor was found to be the party most benefiting from the change orders followed by the consultant and then the client. A set of remedial actions were suggested and respondents viewed that the revision of registration of consulting offices would be the most important action followed by establishing standard documents for design procedures and building a national database about soil conditions and services.

Evaluation of Reclaimed Asphalt Pavement Aggregate in Road Bases and Subbases

Recycling of pavement materials has become a viable alternative to be considered in road maintenance and rehabilitation. Conservation of resources, preservation of the environment, and retention of existing highway geometrics are some of the benefits obtained by reusing pavement materials. In the United States of America, more than 50 million tons (45.36 million Mg) of asphalt paving material are milled annually; recycling into new asphalt paving mixtures is the predominant application. However, large quantities of reclaimed asphalt pavement (RAP) aggregate remain unutilized and further uses should be explored. In the Sultanate of Oman, recycling of pavement materials is not practiced; this study presents a first attempt at evaluating RAP aggregate. The reuse of RAP aggregate could be economically attractive in Oman because certain regions of the country experience virgin aggregate shortage. Furthermore, rehabilitation of the road network would provide a valuable resource to be considered in highway construction. A laboratory evaluation of RAP and RAP-virgin aggregate mixtures as road base and subbase materials is described here. Physical, compaction, and California bearing ratio tests were conducted on the following RAP/virgin aggregate blends: 100/0, 80/20, 60/40, 40/60, 20/80, and 0/100 percent. Initial results indicate that RAP could be expected to replace virgin aggregate in the pavement subbase structure with satisfactory results if the RAP material were mixed with virgin aggregate. Best results were obtained for the 60/40, 40/60, 20/80, and 0/100 percent RAP/virgin aggregate blends. Higher dry density and CBR values are obtained as virgin aggregate content is increased. Based on a comparison with standard paving materials used in the Sultanate of Oman roads, the stabilized RAP material appears to be able to function as well as a conventional subbase material. However, only minimal use of RAP (about 10 percent) can be expected in road bases.

Use of Reclaimed Asphalt Pavement as an Aggregate in Portland Cement Concrete

The main objective of this research is to investigate the potential use of reclaimed asphalt pavement (RAP) as an aggregate in portland cement concrete (PCC). RAP aggregate finer than 4.75 mm (#4) sieve was treated as fine materials while those particles passing 19.05 mm (3-quarters of an inch) and retained on #4 sieve were treated as coarse aggregates. One set of concrete cylinders was prepared using 100, 75, 50, 25, and 0 percent RAP as coarse aggregate while fine aggregate was 100 percent RAP. Another set of samples was made using 100, 75, 50, 25, and 0 percent RAP as fine aggregate while coarse aggregate was 100 percent RAP. Samples were prepared using water-cement ratios of 0.40 and 0.50. In addition, control mixtures containing 100 percent conventional aggregate were made for comparison purposes. Higher compressive strength was obtained as the percentage of RAP aggregate was decreased for all mixtures. The control specimens yielded the highest compressive strength. However, the strength was sufficient to qualify the use of RAP aggregate in concrete applications such as barriers, sidewalks, driveways, pipes, curbs, and gutters. Furthermore, mixtures containing RAP aggregate had enhanced ductility and showed excellent shatter resistance properties. Additional studies should investigate the use of additives and admixtures with RAP aggregate.

Effect of cement kiln dust (CKD) on mortar and concrete mixtures

Abstract The aim of this study was to investigate the use of cement kiln dust (CKD) as a cementitious material in concrete and mortar. CKD was added to concrete and mortar mixtures to study its effect on the strength and on the ability of the cover zone to absorb water, an important factor in the deterioration process. Experimental results on compressive strengths, flexural strength and toughness of concrete samples containing CKD are reported. The sorptivity and the initial surface absorption tests (ISAT) of mortars were used to measure the absorption characteristics for different mortar samples containing CKD. It was found that substitution of cement with CKD does not lead to strength gain for all samples studied and proper addition of CKD has no negative effects on strength properties. It is also shown that mortars prepared using suitable amounts of CKD have better absorption characteristics. However, above certain limits, the water absorption of the mortar increased with increasing CKD contents and decreasing mortar strengths.

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.

EVALUATION OF CEMENT KILN DUST-STABILIZED RECLAIMED ASPHALT PAVEMENT AGGREGATE SYSTEMS IN ROAD BASES

Road rehabilitation and reconstruction generate large supplies of reclaimed asphalt pavement (RAP) aggregate, and recycling into asphalt paving mixtures is the predominant application. Cement kiln dust (CKD), also known as cement bypass dust, is a by-product material generated during production of portland cement. In Oman, where recycling of pavement materials is not practiced, a first attempt was made at combining two by-product materials for use in road construction. Conservation of natural resources and preservation of the environment are two benefits that could be gained by reusing waste materials. The potential use in road bases of CKD-stabilized RAP and RAP with virgin aggregate mixtures was investigated. Physical, compaction, and unconfined compressive strength tests were conducted on RAP and virgin aggregate blends of 100% to 0%, 90% to 10%, 80% to 20%, and 0% to 100%. Samples were prepared using CKD at 0%, 3%, 5%, 7%, 10%, 15%, and 20% and were cured for 3, 7, and 28 days in plastic bags at room temperature. Results indicate that the maximum dry density and unconfined compressive strength of RAP generally increase with addition of virgin aggregate and CKD. The moisture content-dry density curves for CKD-stabilized RAP aggregate mixtures did not show a distinctive peak similar to that of the 100% virgin aggregate blend. Longer curing periods will produce higher strength values. CKD content of 15% seems to be the optimum for achieving maximum strength.

Stabilization of oil‐contaminated soils using cement and cement by‐pass dust

Purpose – To investigate the effect of cement and cement by‐pass dust (CBPD) as a stabilizer on the geotechnical properties of oil‐contaminated soils resulting from leaking underground storage tanks, or soils surrounding petroleum refineries and crude oil wells.Design/methodology/approach – Oil‐contaminated soil (untreated soil) and a soil treated by bio‐remediation (treated soil) as well as a natural soil were obtained from Northern Oman. These soils were stabilized with cement and cement by‐pass dust at 0, 5, 10, 15 and 20 percent, by dry weight of the soil, and cured for seven, 14 and 28 days. Compaction, compressive strength, direct shear, permeability and leaching tests were carried out on the stabilized soils.Findings – The results indicate that cement and cement by‐pass dust improve the properties of oil‐contaminated soils. Traces of arsenic, barium, cadmium, chromium and lead were found in the oil soils, but none of them exceeded the EPA limits.Practical implications – Reuse in construction applic...

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.

MEASUREMENT, ANALYSIS, EVALUATION, AND RESTORATION OF SKID RESISTANCE ON STREETS OF MUSCAT

This research was undertaken to study the problems of skidding, particularly during the wet season. Thirty-nine typical street sections of known service age and traffic were selected from the Muscat area for field investigation. Six age groups were used, ranging from ⩽0.5 to >10 years, with five to eight road sections in each group. Traffic-level categories were low, medium, and high. Field measurements of dry and wet friction coefficients were undertaken for 6 months using a pendulum skid tester and a motometer decelerometer mounted on a test car. Site measurements included surface temperature, length of skidding, texture depth, and assessment of pavement condition. Cored samples 100 mm in diameter were visually evaluated and laboratory tested. The experimental work included determination of asphalt mix content and gradation, Los Angeles abrasion, and acid-insoluble residue of the extracted aggregates. Various relationships between friction coefficient and the relevant independent variables were developed. A predictive relationship between the friction coefficient and the skid length was obtained. Minimum required values of friction coefficient were recommended for safe performance. On the basis of criteria such as those proposed in this study, recommendations were made to immediately maintain eight streets to increase their skid resistance followed by others with different maintenance priorities to improve skid resistance. Open-graded friction courses are strongly recommended to reduce wet-weather skidding. The results of this research will have a positive effect on constructing and maintaining roads to reduce skidding accidents.