International Concrete Abstracts Portal

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.

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.

Final part 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 determination of selected structural parameters for 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). Structural parameters evaluated were the stress-versus-strain behavior of concrete, multiaxial stress behavior, beam shear strength, shear friction capacity, bearing strength for post-tensioning operations, and reinforcing bar development length. Where possible, the test results were compared to ACI 318 provisions. In almost all instances, the ACI code requirements were satisfactory for use with these types of concrete.

Project consists of a 15-story office tower and a 4-level parking structure. The advantages of lightweight concrete over other structural materials for this particular project, and the process followed for its selections, as well as different types of structural systems, are evaluated. The length of spans in both structures was a determining factor in the selection of the floor system. Lightweight concrete, 4000 psi, was chosen for the floors, and 6000-psi normal weight concrete was selected for the columns. As a first step of the design process, economic comparisons were made between concrete and structural steel. After determining that concrete was more economical, alternate floor systems were studied for constructability, function, economy, and availability of materials. Lightweight concrete was preferable for all floor systems, even though a premium cost of nearly 10 dollars per yd 3 is common for this geographic location.