Chert
Chert is a type of fine-grained and silica-rich sedimentary rock. It often contains microfossils and/or macrofossils, and can be found in a great variety of colours. It is often confused with flint which is a particular type of chert.
Chert occurs in geology as nodules, concretionary masses and layered deposits, and is characterised by its hardness and conchoidal fractures that create sharp edges. It was these properties that meant chert was used in early human civilisations for creating tools and weapons.
Chert is often used as an aggregate and as a material for road surfacing. It is particularly suited to road surfacing as rainwater firms and compacts it rather than making it 'muddy' like some other fill materials.
However, there can be problems when is used as an aggregate in concrete, such as the development of surface pop-outs as a result of freezing and thawing. This is due to the high porosity of weathered chert. In addition, some kinds of chert can undergo an alkali-silica reaction (ASR) when they come into contact with high-alkali cement which can lead to cracking or expansion.
[edit] Find out more
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
The UK's Modern Industrial Strategy: A 10 year plan
Previous consultation criticism, current key elements and general support with some persisting reservations.
Building Safety Regulator reforms
New roles, new staff and a new fast track service pave the way for a single construction regulator.
Architectural Technologist CPDs and Communications
CIAT CPD… and how you can do it!
Cooling centres and cool spaces
Managing extreme heat in cities by directing the public to places for heat stress relief and water sources.
Winter gardens: A brief history and warm variations
Extending the season with glass in different forms and terms.
Restoring Great Yarmouth's Winter Gardens
Transforming one of the least sustainable constructions imaginable.
Construction Skills Mission Board launch sector drive
Newly formed government and industry collaboration set strategy for recruiting an additional 100,000 construction workers a year.
New Architects Code comes into effect in September 2025
ARB Architects Code of Conduct and Practice available with ongoing consultation regarding guidance.
Welsh Skills Body (Medr) launches ambitious plan
The new skills body brings together funding and regulation of tertiary education and research for the devolved nation.
Paul Gandy FCIOB announced as next CIOB President
Former Tilbury Douglas CEO takes helm.
UK Infrastructure: A 10 Year Strategy. In brief with reactions
With the National Infrastructure and Service Transformation Authority (NISTA).
Ebenezer Howard: inventor of the garden city. Book review.
The Grenfell Tower fire, eight years on
A time to pause and reflect as Dubai tower block fire reported just before anniversary.
Airtightness Topic Guide BSRIA TG 27/2025
Explaining the basics of airtightness, what it is, why it's important, when it's required and how it's carried out.
Construction contract awards hit lowest point of 2025
Plummeting for second consecutive month, intensifying concerns for housing and infrastructure goals.
Understanding Mental Health in the Built Environment 2025
Examining the state of mental health in construction, shedding light on levels of stress, anxiety and depression.