The structural permeability of concrete at cryogenic temperatures

The thesis describes a programme of research designed to identify concretes for application at cryogenic temperature, in particular for storage of Liquefield Natural Gas which is maintained at a temperature of -165oC. The programme was undertaken in two stages. Stage 1 involved screening tests on seventeen concrete mixes to investigate the effects of strength grade (and water/cement ratio), air entrainment, aggregate type and cement type. Four mixes were selected on the basis of low temperature strength, residual strength after thermal cycling and permeability at ambient temperature. In Stage 2 the selected mixes were subjected to a comprehensive range of tests to measure those properties which determine the leak tightness of a concrete tank at temperatures down to -165oC. These included gas permeability; tensile strength, strain capacity, thermal expansion coefficient and elastic modulus, which in combination provide a measure of resistance to cracking; and bond to reinforcement, which is one of the determining factors regarding crack size and spacing. The results demonstrated that the properties of concrete were generally enhanced at cryogenic temperature, with reduced permeability, reduced crack proneness and, by virtue of increased bond to reinforcement, better control of cracking should it occur. Of the concretes tested, a lightweight mix containing sintered PFA aggregate exhibited the best performance at ambient and cryogenic temperature, having appreciably lower permeability and higher crack resistance than normal weight concretes of the same strength grade. The lightweight mix was most sensitive to thermal cycling, but there was limited evidence that this behaviour would not be significant if the concrete was prestressed. Relationships between various properties have been identified, the most significant being the reduction in gas permeability with increasing strain capacity. The structural implications of the changing properties of the concrete have also been considered

Early age thermal cracking in concrete

SIGLELD:8677.29(ICT-TN--2) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

M56 Hapsford to Lea-by-Backford contract M56/11 PFA concrete trials: addendum to main report; long term in-situ deformation of concrete containing fly-ash

Available from British Library Lending Division - LD:84/33215(M56) / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

M56 Hapsford to Lea-by-Backford contract M56/11 Assessment of the performance of concrete containing fly-ash by in-situ measurement of early age temperatures and strains and laboratory tests to measure the properties of hardened concrete

Available from British Library Lending Division - LD:84/33214(M56) / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

A testing methodology for performance-based specification

Satisfactory guidelines for ensuring adequate reinforced concrete durability can only be developed by monitoring concrete performance under a range of field exposure conditions over an extended period of time. Only then can there be a move from prescriptive durability specifications (minimum grade, maximum water-binder ratio, and minimum cement content) to performance-based methods. The situation is also made more complex by the range of cements now available – BS EN 197 defines a total of 27 products in the family of common cements. Implementation of both design for durability and performance-based standards and specifications are limited by the lack of rapid, simple, science-based test methods for characterizing the transport properties and deterioration resistance of concrete. This paper presents an overview of performance-based specification and developments in the application of electrical property measurements as a candidate testing methodology in evaluating the relative performance of concrete mixes. The technique lends itself to in situ monitoring, thereby allowing measurements to be obtained on the as-placed concrete