International Concrete Abstracts Portal

Presents information regarding highly confined, high-strength lightweight aggregate (LWA) concrete specimens, tested as part of a proprietary research program for which Phase I results have recently been released. The program specifically investigated the ultimate and post-ultimate behavior of members designed to resist high-intensity bending/punching shear loads, such as those imparted by massive ice features against offshore oil/gas platforms. Two special steel confining systems were utilized to confine the high-strength (compressive strengths nominally between 8000 and 9000 psi) LWA concrete; these were T-headed stirrup bars for use in reinforced concrete, and overlapping button-headed studs for use in plate-steel/concrete/plate-steel sandwich composites. These two confining systems both allowed the LWA concrete to exhibit extreme ductility prior to failure. Flexural, deflection, and ductility factors of over 40, and axial compressive strains of over 8 percent, were achieved, while maintaining essentially 100 percent of the ultimate capacity of the test specimens The tests were performed on 1- to 3.5-scale specimens, using a 4 million-lb capacity testing machine. Three approximately 16 x 16 x 42-in. prisms--two of reinforced concrete and one of sandwich composite concrete--were tested in axial compression. Also, four continuous beam specimens (one reinforced concrete and three sandwich composite concrete) were tested in bending/punching shear. These beam specimens were approximately 153 in. long, 36 in. wide, and had effective depths of approximately 13 in. Nonlinear finite element analyses of the beam specimens were also performed as part of the study.

This experimental investigation was aimed at gathering information on flexural properties, including ductility, of high-strength lightweight concrete members (concrete with a dry unit weight of approximately 120 lb/ft 3 and with compressive strength approaching 9 ksi at 56 days) under reversed cyclic loading. Two sets of six specimens each were manufactured using lightweight aggregate concrete having compressive strengths of 5 ksi at 28 days and 9 ksi at 56 days. The test variables were concrete strength, amount of longitudinal reinforcement, and spacing of ties. The test results, including hysteretic load-deflection curves, for specimens representing columns under zero axial load are reported.

Presents results of an experimental investigation to determine the flexural fatigue strength of lightweight concretes made with expanded shale aggregates. Six mixtures were investigated. A total of 120 prisms (20 prisms measuring 76 x 102 x 406 mm for each mixture) were tested in flexural loading of 20 cycles per sec, Hz. The prisms that survived 2 million cycles of fatigue loading were tested in static flexure to determine their residual strength (modulus of rupture). The static flexural strength (modulus of rupture) ranged from 3.04 to 4.91 MPa. The fatigue strength varied from 2.2 to 3.0 MPa. The endurance limit (ratio of the fatigue strength to modulus of rupture) ranged from 0.55 to 0.72. The wet specimens tested at earlier ages had higher strength values (both fatigue strength and modulus of rupture), whereas the endurance limit was higher for dry specimens tested at later ages. There was an increase in the residual static flexural strength for the prisms previously subjected to 2 million cycles of fatigue stress.

First of a three-part paper presents the results of a joint industry project to develop high-strength lightweight aggregate concrete for use in the Arctic. Lightweight aggregate selection tests, high-strength mixture development with the selected aggregates, batching procedures, unhardened properties of the 110 batches made during the program, and the temperature development of the mixtures in large concrete sections are described. Both crushed and pelletized lightweight aggregates were used with supplementary cementing materials and high-range water reducers to produce concretes with compressive strengths from 8000 to 11,000 psi (55 to 76 MPa). Also evaluated was the influence of pumping on the aggregate moisture content, slump, unit weight, air content, and concrete strength. The effects of the air void system in the hardened pumped concrete with respect to freezing and thawing durability and the drying behavior of a large concrete section were also evaluated.

Second of a three-part paper presents the results of a joint industry project to develop high-strength lightweight aggregate concretes for use in the Arctic and describes the mechanical properties of those concretes. Both crushed and pelletized lightweight aggregates were used with supplementary cementing materials and high-range water reducers to produce concretes with compressive strengths from 8000 to 11,000 psi (55 to 76 MPa). Other properties evaluated included modulus of elasticity, Poisson's ratio, splitting tensile strength, modulus of rupture, drying shrinkage, creep, seawater absorption, chloride ion permeability, thermal properties, air-void systems, freezing and thawing behavior, ice abrasion resistance, and adfreeze bond behavior. The effects of low temperatures on many of these properties were also evaluated. Special tests were developed to approximate Arctic conditions for freezing and thawing behavior, ice abrasion, and adfreeze bond strength.