Bilal S. Hamad

EFFECT OF CONFINEMENT OF BOND STRENGTH BETWEEN STEEL BARS AND CONCRETE

*ACI COMM 408, 1990, 4081R90 ACI; Darwin D, 1996, ACI STRUCT J, V93, P347; Eligehausen R, 1983, UCBEERC8323 U CAL; Esfahani MR, 1998, ACI STRUCT J, V95, P272; Filippou F, 1983, UCBEERC8319; HAMAD BS, 2002, IN PRESS ACI STRUCTU; Harajli M, 2002, J MATER CIVIL ENG, V14, P503, DOI 10.1061-(ASCE)0899-1561(2002)14:6(503); HARAJLI M, 2002, BOND CONCRETE RES ST, P570; HARAJLI MH, 2004, J MAT CIVIL ENG ASCE, V16; HARAJLI MH, 1995, ACI MATER J, V92, P343; Harajli MH, 2002, ACI STRUCT J, V99, P509; Orangun C, 1975, 1543F U TEX AUST CTR; Orangun C. O., 1977, ACI J, V74, P114; Zuo J, 2000, ACI STRUCT J, V97, P630

Effect of Fiber Reinforcement on Bond Strength of Tension Lap Splices in High-Strength Concrete

This research evaluates the effect of steel fiber reinforcement on the bond strength and ductility of the mode of bond failure of tension lap splices anchored in high-strength concrete (HSC) test specimens. 12 full-scale HSC beam specimens were tested. Each beam was designed with bars spliced in a constant moment region at midspan. Test results indicated that the use of steel fibers in the splice region increased the bond strength and the ductility of the mode of failure of the beam specimens.

Effect of used engine oil on properties of fresh and hardened concrete

Abstract There is a current trend all over the world to investigate the utilization of processed and unprocessed industrial by-products and domestic wastes as raw materials in cement and concrete. This has a positive environmental impact due to the ever-increasing cost of waste disposal and stricter environmental regulations. Historically, reference books on concrete technology and cement chemistry indicate that the leakage of oil into the cement in older grinding units resulted in concrete with greater resistance to freezing and thawing. This effect is similar to adding an air-entraining chemical admixture to the concrete. Such information is not backed by any research study reported in the literature. The objective of the research reported in this paper was to investigate the effects of used engine oil on properties of fresh and hardened concrete. The main variables included the type and dosage of an air-entraining agent (commercial type, used engine oil, or new engine oil), mixing time, and the water/cement ratio of the concrete. Results showed that used engine oil increased the slump and percentage of entrained air of the fresh concrete mix, and did not adversely affect the strength properties of hardened concrete.

Bond strength improvement of reinforcing bars with specially designed rib geometries

The objective of the research program was to evaluate the effect of rib geometry on bond-slip characteristics of deformed bars in reinforced concrete structures. In one phase of the study, 56 specially machined bars were tested in rectangular eccentric pullout specimens. The bars were hot-rolled carbon-steel Grade 60 plain round bars with a diameter of 0.811 in. (20.6 mm) and were machined to simulate No. 6 American bars with parallel or bamboo deformation pattern and with different deformation properties. The variables were the bar rib face angle, rib spacing, rib height, and concrete strength. Failure of the pullout specimens wa governed by splitting of the concrete cover over the anchored bar. In the second phase of the study, 13 beams were tested in positive bending with two splices of 0.811-in. (20.6-mm) Grade 60 bars in a constant moment region at the center of the span. The splice length was selected so that the bars would fail in bond, splitting the concrete cover in the splice region. The bars were machined along the splice length to different deformation patterns identical to those investigated in the first phase. No transverse reinforcement was provided in the splice region. Variables in the beam splice tests included the bar rib face angle, rib spacing, and rib height. Test results indicated that the bond strength and bond-slip resistance of the specially machined bars varied with the bar rib face angle, rib spacing, and rib height. The trends of the results were independent of concrete strength. Using the results, design recommendations were made concerning optimum rib geometries of deformed bars with superior bond-slip characteristics

Investigations of chemical and physical properties of white cement concrete

Abstract To address questions concerning the behavior and performance of white cement concrete, a research program was designed to conduct comparative studies of type I gray and white portland cements. Different properties of cement paste and cement mortar, made with the two different cements, were measured and compared. Test results indicated shorter setting time of white cement paste and greater ultimate tensile and compressive strength for its mortars than the corresponding values for the gray cement. Results of tests on samples of fresh concrete indicated greater slump and shorter times of initial and final set of mixes prepared with the white cement. Tests conducted on samples of hardened concrete indicated greater ultimate compressive strength of the white cement cylinders. Finally, full-scale companion reinforced concrete beams, identical except for the type of cement, were designed to fail in shear or in flexure. Test results indicated no difference that could be attributed to the type of cement used. Advanced Cement Based Materials 1995, 2, 161–167

Bond strength of noncontact tension lap splices

The subject of transverse spacing between two reinforcing bars lapped in a noncontact or spaced tension splice is addressed in the ACI Building Code (ACI 318-89). The code provisions are based on monotonic tests performed before 1957 of pullout specimens, beam-end specimens, and small-scale beam specimens, where the clear splice-bar spacing was small (less than 3 d b or 50 mm). Tests reported in 1991 of full-scale flat plate specimens subjected to monotonic and repeated inelastic loading in direct tension did not check splice-bar spacings beyond the ACI Code limit of one-fifth of the required lap length. The study reported in this paper provides data on 17 full-scale slab specimens, each reinforced with three lap splices, loaded in flexure, and designed to fail in a splitting mode. Splice-bar spacings below and above the ACI limit were checked. The objective was to check the validity of the ACI provisions based on the results of this study and other studies of noncontact lap splices.

STRENGTH OF EPOXY-COATED REINFORCING BAR SPLICES CONFINED WITH TRANSVERSE REINFORCEMENT

This study determined the effect of epoxy-coated transverse reinforcement on the strength of epoxy-coated bar splices. Existing recommendations for design of splices and anchorage of epoxy-coated reinforcement were reviewed and modifications are suggested. Test results show that the presence of transverse reinforcement in the splice region increased deformation capacity of the beams and improved anchorage strength of epoxy-coated bar splices relative to uncoated bar splices. The improvement was independent of the number of splices, bar size, or bar spacing. Using results of this study and results of other tests on epoxy-coated bar splices in the literature, a comprehensive review of the effect of epoxy coating on structural aspect of epoxy-coated bar splices was performed. Design equations are recommended, and modifications to the ACI Building Code (ACI 318-89) development and splice length provisions are suggested.

Effect of used engine oil on structural behavior of reinforced concrete elements

Abstract This paper reports on the second phase of a research program started at the American University of Beirut (AUB) to study the effects of used engine oil on concrete properties and concrete behavior. In the first phase, the effect of used engine oil on properties of fresh and hardened concrete was investigated. Results indicated that used engine oil acted as an air-entraining agent by improving the slump and fluidity of the concrete mix, and enhancing the air content of fresh concrete. Reductions in the strength properties of hardened concrete due to the incorporation of oil were not as significant as when a commercial chemical air-entraining admixture was used. Results of the first phase of the AUB study instigated further investigation reported in this paper. The objective was to evaluate the effect of used engine oil on structural behavior of reinforced concrete elements. Six full-scale beam specimens were tested in three sets. The difference between the three sets was the mode of failure of the beams: flexure; shear; or bond. The two companion beams in each set were identical except for the use of engine oil in one of them. The beams were tested in positive bending. Results showed that regardless of the mode of failure, used engine oil did not have any significant effect on the ultimate load or load-deflection behavior of the beams.

Experimental and Analytical Evaluation of Bond Strength of Reinforcement in Fiber-Reinforced Polymer-Wrapped High-Strength Concrete Beams

[Anonymous], 2002, 440 ACI COMM; [Anonymous], 2002, 318 ACI COMM; AZIZINAMINI A, 1993, ACI STRUCT J, V90, P554; Azizinamini A, 1999, ACI STRUCT J, V96, P826; Darwin D, 1996, ACI STRUCT J, V93, P347; Hamad BS, 2004, J COMPOS CONSTR, V8, P14, DOI 10.1061-(ASCE)1090-0268(2004)8:1(14); Hamad BS, 2001, ACI STRUCT J, V98, P638; Hamad BS, 2002, MATER STRUCT, V35, P219, DOI 10.1007-BF02533083; Orangun C. O., 1977, ACI J, V74, P114; SOUDKI K, 1997, INT C REH DEV CIV EN, V2, P1270

Effect of Steel Fibers on Bond Strength of Hooked Bars in Normal-Strength Concrete

This study investigates whether steel fibers improve the bond performance of hooked-bar anchorages and the ductility of the failure mode of beam-column connections. Twelve beam-column-type specimens that simulated the rigid connection of a vertical cantilever beam to a base column were tested. The tensile beam reinforcement consisted of two bars anchored in the column outside the column reinforcement cage using hooked-bar anchorages. The variables were the beam tensile bar size and percentage of steel fibers by volume of concrete. The results showed that all specimens showed similar crack patterns. The steel fibers increased the anchorage capacity and the ductility of the load-deflection history of specimens. The optimum steel fiber content in the study was 1.0% for the mixture proportion and ingredients in this study. Research directions for future studies are discussed.