THE INTRODUCTION OF BS EN 450 FLY ASH AND MITIGATING THE RISK OF ASR IN THE UK

摘要

The addition of BS 3892: Part 1 pulverized-fuel ash (BS 3892-1 pfa) to concrete has been successfully used as a method to minimize the risk of deleterious alkali-silica reaction (ASR) in the UK. The corresponding European Standard BS EN 450 "Fly ash for concrete", specifies a significantly different quality of ash. Accelerated prism testing of concretes containing these ashes was conducted at the Building Research Establishment with one primary objective: to determine the changes to specifications necessary to allow comparable protection from the risk of damaging ASR, as is obtained with BS 3892-1 pfa, when using BS EN 450 fly ash. The programme studied the ASR mitigation behaviour of BS EN 450 fly ash compared to BS 3892-1 pfa, when added to concrete as a supplementary cementitious material or Type II addition. The experimental programme included different addition levels of ash and different cement alkali contents in the concrete. The research indicates that both ashes are equally effective in suppressing deleterious ASR, irrespective of their coarseness, but that insufficient additions of either ash will increase the risk of deleterious ASR occurring. The alkali content of the ash has more influence on the degree of ASR expansion than the coarseness of the ash. The results of the research leads to recommended additions of 25% BS 3892-1 or BS EN 450 ash with normal reactivity aggregates, and 40% BS 3892-1 pfa or BS EN 450 ash with high reactivity aggregates.