Self-consolidating concrete or self-compacting concrete (SCC)
selfconsolidatingconcrete.org
National Ready Mixed Concrete Association is a concrete
Concrete is a composite material composed of aggregate bound together with a fluid cement that cures to a solid over time. It is the second-most-used substance (after water), the most–widely used building material, and the most-manufactur ...
mix which has a low yield stress
In materials science and engineering, the yield point is the point on a stress–strain curve that indicates the limit of elasticity (physics), elastic behavior and the beginning of plasticity (physics), plastic behavior. Below the yield point ...
, high deformability, good segregation resistance (prevents separation of particles in the mix), and moderate viscosity
Viscosity is a measure of a fluid's rate-dependent drag (physics), resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for e ...
(necessary to ensure uniform suspension of solid particles during transportation, placement (without external compaction), and thereafter until the concrete sets).
In everyday terms, when poured, SCC is an extremely fluid mix with the following distinctive practical features – it flows very easily within and around the formwork
Formwork is Molding (process), molds into which concrete or similar materials are either precast concrete, precast or cast-in-place concrete, cast-in-place. In the context of concrete construction, the falsework supports the shuttering mold ...
, can flow through obstructions and around corners ("passing ability"), is close to self-leveling (although not actually self-levelling), does not require vibration or tamping
A tamping machine or ballast tamper, informally simply a tamper, is a self-propelled, rail-mounted machine used to pack (or tamp) the track ballast under railway tracks to make the tracks and roadbed more durable and level. Prior to the intr ...
after pouring, and follows the shape and surface texture of a mold (or form) very closely once set. As a result, pouring SCC is also much less labor-intensive compared to standard concrete mixes. Once poured, SCC is usually similar to standard concrete in terms of its setting and curing time (gaining strength), and strength. SCC does not use a high proportion of water to become fluid – in fact SCC may contain less water than standard concretes. Instead, SCC gains its fluid properties from an unusually high proportion of fine aggregate, such as sand (typically 50%), combined with superplasticizer
Superplasticizers (SPs), also known as high range water reducers, are Concrete additive, additives used for making high strength concrete or to place Self-consolidating concrete, self-compacting concrete. Plasticizers are chemical compounds enabli ...
s (additives
Additive may refer to:
Mathematics
* Additive function, a function in number theory
* Additive map, a function that preserves the addition operation
* Additive set-function see Sigma additivity
* Additive category, a preadditive category with fin ...
that ensure particles disperse and do not settle in the fluid mix) and viscosity-enhancing admixtures (VEA).
Ordinarily, concrete is a dense, viscous material when mixed, and when used in construction, requires the use of vibration or other techniques (known as compaction) to remove air bubbles (cavitation
Cavitation in fluid mechanics and engineering normally is the phenomenon in which the static pressure of a liquid reduces to below the liquid's vapor pressure, leading to the formation of small vapor-filled cavities in the liquid. When sub ...
), and honeycomb
A honeycomb is a mass of Triangular prismatic honeycomb#Hexagonal prismatic honeycomb, hexagonal prismatic cells built from beeswax by honey bees in their beehive, nests to contain their brood (eggs, larvae, and pupae) and stores of honey and pol ...
-like holes, especially at the surfaces, where air has been trapped during pouring. This kind of air content (unlike that in aerated concrete
Autoclaved aerated concrete (AAC) also referred to as autoclaved cellular concrete (ACC) or simply autoclaved concrete is a lightweight, Prefabrication, prefabricated concrete building material. Developed in the mid-1920s, it is an alternat ...
) is not desired and weakens the concrete if left. However it is laborious and takes time to remove by vibration, and improper or inadequate vibration can lead to undetected problems later. Additionally some complex forms cannot easily be vibrated. Self-consolidating concrete is designed to avoid this problem, and not require compaction, therefore reducing labor, time, and a possible source of technical and quality control issues.
SCC was conceptualized in 1986 by Prof. Okamura at Kochi University, Japan, at a time when skilled labor was in limited supply, causing difficulties in concrete-related industries. The first generation of SCC used in North America
North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
was characterized by the use of relatively high content of binder as well as high dosages of chemicals admixtures, usually superplasticizer to enhance flowability and stability. Such high-performance concrete had been used mostly in repair applications and for casting concrete in restricted areas. The first generation of SCC was therefore characterized and specified for specialized applications.
SCC can be used for casting heavily reinforced sections, places where there can be no access to vibrators
Vibrator may refer to:
Technology
* Vibrator (sex toy), a device for massage or sexual pleasure used by both men and women
* Vibrator (mechanical), a class of devices which create mechanical vibrations for uses such as signaling annunciators, d ...
for compaction and in complex shapes of formwork which may otherwise be impossible to cast, giving a far superior surface than conventional concrete. The relatively high cost of material used in such concrete continues to hinder its widespread use in various segments of the construction industry
Construction are processes involved in delivering buildings, infrastructure, industrial facilities, and associated activities through to the end of their life. It typically starts with planning, financing, and design that continues until the ...
, including commercial construction, however the productivity economics take over in achieving favorable performance benefits and works out to be economical in pre-cast industry. The incorporation of powder, including supplementary cementitious materials and filler, can increase the volume of the paste, hence enhancing deformability, and can also increase the cohesiveness of the paste and stability of the concrete. The reduction in cement
A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel ( aggregate) together. Cement mi ...
content and increase in packing density of materials finer than 80 μm, like fly ash
Coal combustion products (CCPs), also called coal combustion wastes (CCWs) or coal combustion residuals (CCRs), are byproducts of burning coal. They are categorized in four groups, each based on physical and chemical forms derived from coal combust ...
etc. can reduce the water-cement ratio, and the high-range water reducer (HRWR) demand. The reduction in free water can reduce the concentration of viscosity-enhancing admixture (VEA) necessary to ensure proper stability during casting and thereafter until the onset of hardening. It has been demonstrated that a total fine aggregate content ("fines", usually sand) of about 50% of total aggregate is appropriate in an SCC mix.
There are many studies on different types of SCC which address its fresh properties, strength, durability and microstructural properties. Types of self-consolidating concrete include low-fines SCC (LF-SCC) and semi-flowable SCC (SF-SCC) etc.
SCC can be produced using different industrial wastes as cement replacing materials. They can be used for pavement construction <2-6>.
Reference:
https://doi.org/10.1016/j.conbuildmat.2022.130036
Overview
* SCC is measured using the flow table test (slump-flow test) rather than the usual concrete slump test, as it is too fluid to keep its shape when the cone is removed. A typical SCC mix will have slump-flow of around 500 – 700 mm.
* SCC is weakened, not strengthened, by vibration. As vibration is not needed for compacting the mix, all that it achieves is to separate and segregate it.
See also
* Concrete slump test
* Flow table test
References
2. Low-fines self-consolidating concrete using rice husk ash for road pavement: An environment-friendly and sustainable approach
https://doi.org/10.1016/j.conbuildmat.2022.130036
3. Kannur, B., Chore, H.S. Utilization of sugarcane bagasse ash as cement-replacing materials for concrete pavement: an overview. Innov. Infrastruct. Solut. 6, 184 (2021).
https://doi.org/10.1007/s41062-021-00539-4
4.Strength and durability study of low-fines self-consolidating concrete as a pavement material using fly ash and bagasse ash
Bhupati Kannur &H. S. Chore.
https://doi.org/10.1080/19648189.2022.2140207
5.Bhupati Kannur, Hemant Sharad Chore. Semi-flowable self-consolidating concrete using industrial wastes for construction of rigid pavements in India: An overview. https://doi.org/10.1016/j.jtte.2023.01.001
6.B Kannur, HS Chore. Assessing Semiflowable Self-Consolidating Concrete with Sugarcane Bagasse Ash for Application in Rigid Pavement. Journal of Materials in Civil Engineering 35 (10), 04023358, 2023.
https://doi.org/10.1061/JMCEE7.MTENG-16355
External links
Proportioning of self-compacting concrete – the UCL method
– paper summarizing common mixes, uses, choices of additives, properties, and extensive information on SCCs.
Working With SCC Needn’t Be Hit or Miss
– precast concrete makers' experience is SCC / what to do and not do.
{{Concrete navbox
Concrete