Other specialty admixtures include shrinkage-reducing admixtures and alkali-silica reactivity inhibitors. The shrinkage reducers are used to control drying shrinkage and minimize cracking, while ASR inhibitors control durability problems associated with alkali-silica reactivity. Cement Industry Annual Yearbook U.
Greg Halsted, P. Joshua Gilman, P. Chemical Admixtures.
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Chemical admixtures are the ingredients in concrete other than portland cement, water, and aggregate that are added to the mix immediately before or during mixing. Producers use admixtures primarily to reduce the cost of concrete construction; to modify the properties of hardened concrete; to ensure the quality of concrete during mixing, transporting, placing, and curing; and to overcome certain emergencies during concrete operations.
Successful use of admixtures depends on the use of appropriate methods of batching and concreting. Most admixtures are supplied in ready-to-use liquid form and are added to the concrete at the plant or at the jobsite. Certain admixtures, such as pigments, expansive agents, and pumping aids are used only in extremely small amounts and are usually batched by hand from premeasured containers. This timescale contrasts starkly with the life spans of contemporary buildings. Steel is often perceived to be inert and resilient too. If construction steel is visible, it can be maintained — for instance, when the Sydney Harbour Bridge is repeatedly painted and repainted.
However, when embedded in concrete, steel is hidden but secretly active. Moisture entering through thousands of tiny cracks creates an electrochemical reaction. I suggest that we need to change our thinking, to recognise concrete and steel as vibrant and active materials. This is not a case of changing any facts, but rather of re-orientating how we understand and act on those facts. Avoiding waste, pollution and needless rebuilding will require thinking well beyond disciplinary conceptions of time , and this is especially true for the building and construction industries.
The collapsed civilisations of the past show us the consequences of short-term thinking. We should focus on building structures that stand the test of time — lest we end up with hulking, derelict artefacts that are no more fit for their original purpose than the statues of Easter Island. Screen music and the question of originality - Miguel Mera — London, Islington. UEA Inaugural lecture: Alternative performance measures: do managers disclose them to inform us, or to mislead us?
Edition: Available editions United Kingdom. The cracks are starting to show.
Dean McCartney , Author provided. Old bridges need new money to replace. Cheap and effective, in the short term at least. The environmental costs of rebuilding This has serious repercussions for the planet. Rebar reclamation: an expensive job. Concrete cancer: not pretty. Highton Shopping Village in Geelong. Liu, J.
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