Tag Archive for Tag: Aggregate

Tag: Aggregate Concrete and aggregate Specification issues in Standard EN 206-1

The prescriptive approach to durability in EN 206-1 maintains the durability grade principle of Deacon and Dewar (1982) that underpins the advice in concrete design standards such as those published in the UK since the 1980s. This approach is based on the principle that a clear relationship exists between durability expectation and minimum concrete grade, minimum binder content and maximum

View Article...

Tag: Aggregate Concrete and aggregate specifications

Specification of freeze-thaw resistant concrete is exemplified by European practice outlined in the primary specification documents for concrete and aggregates for concrete, EN206-1 and EN 12620 respectively. The former sets out a comprehensive framework for integrating specific concerns in a prescriptive approach to durability. These concerns include provision for freeze-thaw resistance, where applicable. The latter provides guidance to specifiers where

View Article...

Tag: Aggregate Use of non-reactive aggregate (or exploitation of the ‘pessimum’ effect)

Although the use of aggregates that are not susceptible to ASR would be the most obvious option for avoiding the problem, non-reactive aggregates are unavailable in many locations, and importing non-reactive material may not be economically viable. Furthermore, ASR has occurred in a number of cases where prior testing of the aggregate indicated the aggregates were not deleter- iously reactive.

View Article...

Tag: Aggregate Test methods for identifying aggregate reactivity

The first step in assessing the potential of an aggregate for AAR expansion and cracking is the performance of a petrographic analysis by a trained petrographer, the methodology being as recommended by a RILEM technical committee (Sims and Nixon, 2003). However, a petrographic analysis may not identify certain reactive materials (some may not be readily identified by optical microscopy), and

View Article...

Tag: Aggregate Introduction Alkali-aggregate reaction (AAR)

Alkali-aggregate reaction (AAR) is a reaction between the alkali hydroxides present in the pore solution of concrete and certain constituents of some aggregates; under certain conditions the reaction may produce deleterious expansion and cracking of the concrete. There are two distinct types of alkali-aggregate reaction in concrete; these are (i) alkali-silica reaction (ASR), which involves the reaction of certain silica minerals

View Article...

Tag: Aggregate Harmful constituents and impurities in aggregates

The presence of even small amounts of harmful constituents and impurities in aggregates can have a major impact on concrete performance and thus it is important to be able to identify the type and amount of these undesired materials. Table 7.1 provides a broad overview of the various harmful con- stituents of concern and their potential effects on concrete (Kosmatka

View Article...

Tag: Aggregate Identification of frost-susceptible aggregates

A key step in designing durable concrete in cold weather applications is to identify whether an aggregate of interest may be susceptible to frost damage, which may manifest itself as internal distress within concrete or surface damage, such as D-cracking (especially for pavements) and pop-outs. The process of identifying salt-susceptible aggregates may involve a review of past field performance or,

View Article...

Tag: Aggregate Factors affecting frost resistance of aggregates

Air-entrainment is an accepted method of ensuring durability of concrete in a cold environment, with regard to both internal distress and external damage from salt scaling (see also Chapter 9). However, even when concrete is properly air-entrained, certain types of coarse aggregates can cause distress. The mechanisms responsible for this distress are discussed next. Frost damage in hydrated cement paste

View Article...

Tag: Aggregate General requirements of aggregates for use in concrete

In most cases, aggregates perform very well in Portland cement concrete. Aggregates, because they occupy about 60 to 80% of the total volume of  concrete, affect many key fresh and hardened concrete properties and also contribute to the long-term performance of the concrete structure, including its long-term durability and resistance to cracking. Aggregates also allow for the overall cost of concrete

View Article...

Tag: Aggregate Concrete aggregates and the durability of concrete Introduction

Aggregates are the major constituents of concrete and typically occupy between 60% and 80% of the concrete volume. Properties of both fresh and hardened concrete are influenced by the quality of aggregates and yet their role is often overlooked. This chapter provides a brief review of the general requirements of concrete aggregates; the main focus concerns how aggregates can affect

View Article...