ASTM M295
Full Name
ASTM M295 – Coal Ash and Raw or Calcined Natural Pozzolan for Use in Concrete
Scope
In the world of concrete construction, supplementary cementitious materials (SCMs) play an important role in enhancing concrete properties and promoting sustainability. Coal ash and natural pozzolans are two such SCMs, and their quality is paramount for achieving desired concrete performance. AASHTO M295 serves as an important standard to ensure these materials meet the necessary requirements.
Developed by the American Association of State Highway and Transportation Officials (AASHTO), AASHTO M295 outlines specific requirements and test methods to evaluate these materials, ensuring they contribute positively to concrete strength, durability, and workability.
Key provisions of AASHTO M295:
- material classifications – the standard classifies coal ash into two types:
- Class F: fly ash with pozzolanic properties and low calcium oxide content.
- Class C: fly ash with both pozzolanic and cementitious properties, generally having higher calcium oxide content.
Natural pozzolans are categorized as raw or calcined, depending on their processing.
- chemical requirements – AASHTO M295 specifies limits on various chemical components, including:
- sulfur trioxide (SO3): to control expansion and potential sulfate attack.
- loss on ignition (LOI): to assess the presence of unburned carbon and organic matter.
- available alkalies: to mitigate alkali-silica reaction (ASR) risk.
- physical requirements – the standard includes requirements for:
- fineness: measured by specific surface area or residue on a No. 325 sieve, influencing the rate of pozzolanic reaction and water demand.
- soundness: evaluated by autoclave expansion, ensuring dimensional stability and preventing cracking.
- water requirement: to assess the impact on concrete workability.
- pozzolanic activity index: to determine the strength contribution of the material.
Significance of AASHTO M295:
- quality assurance: by adhering to AASHTO M295, producers and users of coal ash and pozzolans can ensure consistent material quality and performance.
- performance prediction: the standard’s requirements and test methods enable the prediction of the material’s influence on concrete properties, aiding in mix design and construction planning.
- durability and sustainability: using AASHTO M295 compliant materials promotes the development of durable concrete structures, contributing to sustainable construction practices.
Resources
Keywords
coal ash; fly ash; pozzolan; concrete; supplementary cementitious material; class f; class c; calcium oxide; sulfur trioxide; loss on ignition; fineness; soundness; water requirement; pozzolanic activity index; alkali-silica reaction