Editing Concrete (section)

===Mixing===
{{See also|Volumetric concrete mixer|Concrete mixer}}

Thorough mixing is essential to produce uniform, high-quality concrete.

{{em|Separate paste mixing}} has shown that the mixing of cement and water into a paste before combining these materials with [[Construction aggregate|aggregates]] can increase the [[compressive strength]] of the resulting concrete.<ref>{{Cite web |title=Concrete International |url=https://www.concrete.org/publications/concreteinternational.aspx |access-date=2022-08-13 |archive-url=https://web.archive.org/web/20070928092034/http://www.concreteinternational.com/pages/featured_article.asp?ID=3491 |archive-date=28 September 2007|website=concrete.org|date=1 November 1989}}</ref> The paste is generally mixed in a {{em|high-speed}}, shear-type mixer at a [[Water-cement ratio|w/c]] (water to cement ratio) of 0.30 to 0.45 by mass. The cement paste premix may include admixtures such as accelerators or retarders, [[Plasticizer|superplasticizers]], [[pigment]]s, or [[silica fume]]. The premixed paste is then blended with aggregates and any remaining batch water and final mixing is completed in conventional concrete mixing equipment.<ref>{{cite web | title=ACI 304R-00: Guide for Measuring, Mixing, Transporting, and Placing Concrete (Reapproved 2009) | url=https://www.concrete.org/store/productdetail.aspx?ItemID=30400}}</ref>

Resonant acoustic mixing has also been found effective in producing ultra-high performance cementitious materials, as it produces a dense matrix with low porosity.<ref>{{Cite journal |last=Vandenberg |first=Aileen |last2=Wille |first2=Kay |date=2019-06-02 |title=The Effects of Resonant Acoustic Mixing on the Microstructure of UHPC |url=https://www.iastatedigitalpress.com/uhpc/article/id/9636/ |journal=International Interactive Symposium on Ultra-High Performance Concrete |volume=2 |issue=1 |doi=10.21838/uhpc.9636 |issn=0000-0000|doi-access=free }}</ref>