BRE IP4/11 PDF

INTRODUCTION

Alkali-activated binder concretes consist of a predominantly alumino-silicate mineral binder which is activated with a highly alkaline metal solution (generally sodium silicate). The alkaline environment breaks down the Si–O chemical bonds in the glassy component of the binder. These phases then become available for reaction with the alkaline species in the solution to form an ‘inorganic polymer' comprising molecular chains and networks. The liquid activator is consumed in the reaction. The chemistry of the reaction depends on the composition of the binder, which is usually an industrial by-product, most commonly fly ash conforming to BS EN 450. The use of additional components such as ground granulated blastfurnace slag (ggbs) in addition to fly ash is generally needed to produce formulations that set and harden at room temperature.

The commercial materials supply chains for alkaline ash binders such as fly ash and ggbs are well established, but in the UK, a significant proportion of fly ash is stockpiled or landfilled due to the absence of buoyant markets and high value end uses. Such surplus materials could, however, be suitable for use in alkali-activated systems. Some materials that may be suitable for alkaline activation are listed in Table 1