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.

The problem of concrete deterioration and its durability has become a matter of great concern to everyone involved in the construction industry. Carbonation and chloride ingress are the two major sources of deterioration, and the penetration of both is influenced by the pore structure of the concrete. Paper presents data on pore structure, carbonation depths, and the interrelationship between the two in structural lightweight concrete after 10 years' outdoor exposure in an industrially polluted area. The concrete was made with expanded slate aggregate using either all lightweight aggregates or with part of the lightweight fines replaced by sand. Both cement content and water-cement ratios were varied. The results showed that the total pore volume was influenced by both the water-cement ratio and fine aggregate content of the concrete. The total pore volume was higher for concretes containing all lightweight fines than for concrete with part replacement of fines by sand. However, for a given pore volume, carbonation was higher for the concretes containing sand than for concrete containing all lightweight aggregates. This phenomenon is explained in terms of the pore structure of the concrete, and a pore structure characteristics parameter is introduced to correlate carbonation with pore volume.

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.

During the past three decades, lightweight aggregate concrete has emerged as an important sector of the structural concrete industry. It possesses unique properties, similar in some ways to those of normal weight concrete, but differing in significant aspects. Difficulties experienced with lightweight concrete in some projects appears to be caused by a lack of understanding of the differences between normal weight concrete and lightweight concrete as materials and differences in production technologies. It is most wisely used when treated as a material in its own right, with its special properties fully considered in design and construction. A three-phase model of lightweight concrete and its effect on durability are discussed as they relate to selection of materials, concreting and curing technology, control of in-service distress due to freezing and thawing, and corrosion of reinforcing steel. ased on the observed performance of bridge and marine structures built over the past four decades, the author presents a series of generalized observations applying to durability of lightweight concrete that provide a fair cross section of the entire experience. Paper concludes that, with proper selection of materials and design, and good construction practices, lightweight concrete offers an excellent solution to the problem of durability in severe environment.