Philip J. Nixon

Aspects of the pore solution chemistry of blended cements related to the control of alkali silica reaction

Abstract The effects of four pulverised fuel ashes (PFA) and three ground blastfurnace slags (GBFS) on the alkalinity of the pore solution phase of hardened cement pastes has been studied. It has been found that the total alkali content of a PFA is an important factor, but not the only one, determining its effectiveness in reducing the hydroxyl ion concentration of the pore solution. For GBFS, however, there was found to be no direct correlation between the total alkali content of the slag and the composition of the pore solution. Implications regarding the roles of PFA and GBFS in reducing expansion associated with alkali silica reaction (ASR) are discussed.

Alkali metal sulphate — a factor common to both alkali aggregate reaction and sulphate attack on concrete

Abstract Cases of deterioration of concrete in which evidence of both sulphate attack and alkali aggregate reaction has been detected are described and a possible connection between these two mechanisms of attack on concrete is discussed with reference to theories of the enhancement of alkali hydroxides in the pore solution of concrete. It is suggested that sulphate attack on concrete by alkali metal sulphates may promote alkali aggregate reaction.

The concentration of alkalies by moisture migration in concrete - a factor influencing alkali aggregate reaction

Abstract The concentration of alkali metal ions caused by the movement of moisture in concrete has been examined by chemical analysis and X-ray microprobe analysis. It has been found that there is a significant increase in the concentration of these ions close to the surface from which moisture is evaporating with local very high concentrations which have been shown to be due to the crystallisation of alkali sulphates. The significance of this effect in promoting alkali aggregate reaction is discussed.

RILEM Recommendations for the Prevention of Damage by Alkali-Aggregate Reactions in New Concrete Structures

This book contains the full set of RILEM Recommendations which have been produced to enable engineers, specifiers and testing houses to design and produce concrete which will not suffer damage arising from alkali reactions in the concrete. There are five recommended test methods for aggregates (designated AAR-1 to AAR-5), and an overall recommendation which describes how these should be used to enable a comprehensive aggregate assessment (AAR-0). Additionally, there are two Recommended International Specifications for concrete (AAR-7.1 & 7.2) and a Preliminary International Specification for dams and other hydro structures (AAR-7.3), which describe how the aggregate assessment can be combined with other measures in the design of the concrete to produce a concrete with a minimised risk of developing damage from alkali-aggregate reactions

RILEM Recommended Test Method: AAR-4.1—Detection of Potential Alkali-Reactivity—60 °C Test Method for Aggregate Combinations Using Concrete Prisms

This is a method developed by RILEM in the light of the results of an international trial. This trial showed that the method can reliably differentiate reactive and non-reactive combinations for a range of aggregate compositions from around the world.

Alkali–silica reactivity of some common rock types. A global petrographic atlas

The correct identification of potentially alkali–silica reactive aggregates is important for the prevention of alkali–silica reaction (ASR) in concrete. Although a number of standards for assessment of concrete aggregate by petrography are available, distinction of potentially deleterious from innocuous rock types can be problematic. The application of geological nomenclature alone is insufficient, as the geological history and hence mineralogical texture of a given rock type may strongly influence its performance in concrete. One of the goals of RILEM TC 219-ACS is to develop a worldwide photo atlas as a guide for petrographers in the identification of the mineral compositions and textures that are characteristic of alkali-reactive rocks. The atlas is based on micrographs of rock types recognized as potentially deleterious by field performance and/or laboratory expansion testing. It is intended to serve as an independent reference work and aims to unify rock terminology so as to improve the petrographic characterization of aggregates. The mission of RILEM, the International Union of Laboratories and Experts in Construction Materials, Systems and Structures (Réunion Internationale des Laboratoires et Experts des Matériaux), is to advance scientific knowledge in the field of construction. Its Technical Committee TC 219-ACS focuses on alkali reactions and their effects on concrete.

RILEM Recommended Test Method: AAR-5—Detection of Potential Alkali-Reactivity—Rapid Preliminary Screening Test for Carbonate Aggregates

The accelerated mortar-bar test (AAR-2) has been widely and successfully used as a screening test to identify aggregates that are potentially alkali-reactive. However there are some aggregates that, though alkali-reactive according to both field experience and concrete prism test results, do not show as such in the mortar-bar test.

RILEM Recommended Test Method: AAR-2—Detection of Potential Alkali-Reactivity—Accelerated Mortar-Bar Test Method for Aggregates

This draft method was originally prepared by RILEM TC 106-AAR (Alkali-Aggregate Reaction—Accelerated Tests) as TC 106-2, and has been revised by RILEM TC 191-ARP

RILEM Recommended Test Method:AAR-1.1—Detection of Potential Alkali-Reactivity—Part 1: Petrographic Examination Method

Petrographic analysis should always be the first step in the assessment of the potential alkali- reactivity of concrete aggregates as stated in RILEM AAR-0 (Outline guide to the use of RILEM methods in assessments of aggregates for potential alkali-reactivity).

RILEM Recommended Specification: AAR-7.2—International Specification to Minimise Damage from Alkali Reactions in Concrete—Part 2: Alkali-Carbonate Reaction

Carbonate rocks containing finely divided inclusions of silica. These may be termed siliceous limestones and can be very reactive towards alkalis. Because of the finely disseminated nature of the silica it can be difficult to detect by conventional optical petrography.