Better Roads Digital Magazine
Issue link: https://read.dmtmag.com/i/85926
plutonic or sedimentary origin, crushed and screened to spec in quarries, while gravel has a more rounded shape, produced by weathering and erosion (unless crushed), and is extracted from fluvial or glacial deposits or "pits". Sand also is extracted from pits but manufactured sand is produced in quarries construction aggregates. Crushed stone is an angular rock of Image Credit: Bill Bradley Crushed stone (shown) and sand and gravel constitute the major types of Lightweight aggregates comprise a ceramic material produced by expanding and vitrifying select shales, clays and slates in a rotary kiln. This pyroprocessing produces an aggregate that is structurally strong, durable, environmentally inert and low in density Image Credit: Expanded Shale, Clay and Slate Institute The condition of an aggregate impacts its performance. Dusty aggregates – in which aggregate dust coats either coarse or fine aggregate – can contribute to stripping in asphalt pavements, as the liquid asphalt binder coats the dust and not the aggregate surface. But moisture used to clean the aggregate can cause stripping as well Image Credit: Caltrans Aggregates are the component of a composite material – such as bituminous asphalt or portland cement concrete – which resists compressive stress. Aggregates in asphalt or concrete will have a wide variety of sizes, from coarse material to sand, bound in a matrix by a cementing medium the SYNAG process, coal combustion fly ash is cold-bonded chemically to produce a hardened product that can be crushed and sized for construction applications, with properties specified by ASTM and AASHTO. The chemistry of reclaimed asphalt pavement (RAP) and recycled concrete aggregate (RCA) as construction aggregates will be discussed in September materials. For example, in from recycled Piezoceramic-based devices – smart aggregates – someday may monitor dynamic seismic response and perform structural health monitoring for large-scale concrete structures Image Credit: Western Research Institute Image Credit: Gu, Moslehy, Sanders, Song and Mo Water-proof coating Electric wires Piezoceramic patch aggregates can be made Synthetic ASR is a chemical reaction that occurs between alkalis contributed primarily by cement, and a reactive form of silica from reactive aggregate, which form an alkali/silica gel. Under the right conditions – particularly enough available moisture – the gel will expand and produce stresses and damage in the concrete Image Credit: Portland Cement Association Better Roads July 2012 17