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29 Some of the following definitions are general and apply to con- ventional concrete, while others are specific to self-consolidating concrete. Some of these definitions are based on definitions given in American Concrete Institute (ACI) and Precast/Prestressed Concrete Institute (PCI) technical documents. AdmixtureâA material, other than water, aggregates, hydraulic ce- ment, and fiber reinforcement, used as an ingredient of a cementi- tious mixture to modify its freshly mixed, setting, or hardened properties and that is added to the batch before or during its mix- ing (ACI 116). Autogenous shrinkageâThe shrinkage occurring in the absence of moisture exchange due to the hydration reactions taking place in- side the cement matrix (ACI 209). BinderâA cementing material, either a hydrated cement or reaction products of cement or lime and reactive siliceous material; also, materials such asphalt, resins, and other materials forming the matrix of concretes, mortars, and sanded grouts. Bingham fluidâA fluid characterized by a yield stress and a constant plastic viscosity, regardless of flow rate (PCI 2003). Bleed waterâThe water that rises to the surface subsequent to the placing of the concrete. The rise of mixing water within, or its emer- gence from, newly placed concrete, caused by settlement and con- solidation of the plastic concrete (PCI 2003). Bleeding testâThe standard test for determining the relative quantity of mixing water that will bleed from a sample of freshly mixed con- crete (ASTM C 232). BlockingâThe condition in which coarse aggregate particles combine to form elements large enough to obstruct the flow of the fresh con- crete between the reinforcing steel or other obstructions in the concrete formwork (PCI 2003). CohesivenessâThe tendency of the SCC constituent materials to stick together, resulting in resistance to segregation, settlement, and bleeding (PCI 2003). ConsistencyâThe relative mobility or ability of freshly mixed concrete or mortar to flow (ACI 116). ConsolidationâThe process of inducing a closer arrangement of the solid particles in freshly mixed concrete or mortar during place- ment by the reduction of entrapped voids (ACI 116). In SCC, con- solidation is achieved by gravity flow of the material without the need of vibration, rodding, or tamping. CreepâTime-dependent deformation due to sustained load (ACI 209). DeformabilityâThe ability of SCC to flow under its own mass and fill completely the formwork. Drying shrinkageâShrinkage occurring in a specimen that is exposed to the environment and allowed to dry (ACI 209). FillersâFinely divided inert material, such as pulverized limestone, sil- ica, or colloidal substances, sometimes added to portland cement paint or other materials to reduce shrinkage, improve workability, or act as an extender or material used to fill an opening in a form (ACI 116). Filling abilityâThe ability of SCC to flow into and fill completely all spaces within the formwork, under its own weight, also referred to as deformability or non-restricted deformability (ACI 237). Filling capacityâThe ability of SCC to flow into and fill completely all spaces within the formwork. FlowabilityâThe ability of fresh concrete to flow in confined or un- confined form of any shape, reinforced or not, under gravity and/or external forces, assuming the shape of its container (PCI 2003). FluidityâThe ease by which fresh concrete flows under gravity (PCI 2003). Fluidity is the reciprocal of dynamic viscosity. Fly ashâThe finely divided residue that results from the combustion of ground or powdered coal and that is transported by flue gasses from the combustion zone to the particle removal system (ACI 116). Because of its spherical shape and fineness, fly ash can im- prove the rheology of SCC. Formwork pressureâLateral pressure acting on vertical or inclined formed surfaces, resulting from the fluid-like behavior of the un- hardened concrete confined by the forms (ACI 116). Ground granulated blast-furnace slag (GGBFS)âA fine granular, mostly latent hydraulic binding material that can be added to SCC to improve workability of the material (PCI 2003). GGBFS is also referred to in some cases as slag cement (a waste product in the manufacture of pig iron and chemically a mixture of lime, silica, and alumina). High-range water-reducing admixture (HRWRA)âA water-reducing admixture capable of producing large water reduction or greater flowability without causing undue set retardation or entrainment of air in mortar or concrete (ACI 116). J-Ring flowâThe distance of lateral flow of concrete using the J-Ring in combination with a slump cone (ASTM C 1621). J-Ring testâTest used to determine the passing ability of SCC, or the degree to which the passage of concrete through the bars of the J-Ring apparatus is restricted (ASTM C 1621). Glossary
30 L-box testâTest used to assess the confined flow of SCC and the extent to which it is subject to blocking by reinforcement (ACI 237). MetakaolinâMineral admixture used as binding material (supple- mentary cementitious material) in concrete (PCI 2003). Mixture robustnessâThe characteristic of a mixture that encompasses its tolerance to variations in constituent characteristics and quan- tities, as well as its tolerance to the effects of transportation and placement activities (PCI 2003). Passing abilityâThe ability of SCC to flow under its own weight (with- out vibration) and completely fill all spaces within intricate form- work, containing obstacles, such as reinforcement (ASTM C 1621). Paste volumeâProportional volume of cement paste in concrete, mor- tar, or the like, expressed as volume percent of the entire mixture (ACI 116). Plastic viscosityâThe resistance of the plastic material to undergo a given flow. It is computed as the slope of the shear stress versus shear rate curve measurements. Mixtures with high plastic viscos- ity are often described as âstickyâ or âcohesive.â Concrete with higher plastic viscosity takes longer to flow. It is closely related to T-50 and V-funnel time (higher plastic viscosity: higher T-50 and V-funnel time). Powder (also referred to as graded powder)âIncludes cement, fly ash, GGBFS, limestone fines, material crushed to less than 0.125 mm (No. 100 sieve), or other non-cementitious filler (ACI 237). Powder-type SCCâSCC mixtures that rely extensively on the amount and character of the fines and powder included in the mixture for meeting workability performance requirements (stability) (PCI 2003). PumpabilityâThe ability of an SCC mixture to be pumped without significant degradation of workability (PCI 2003). Rheological propertiesâProperties dealing with the deformation and flow of matter (PCI 2003). RheologyâThe science of dealing with flow of materials, including studies of deformation of hardened concrete, the handling and placing of freshly mixed concrete, and the behavior of slurries, pastes, and the like (ACI 116). In the context of SCC, rheology refers to the evaluation of yield stress, plastic viscosity, and thixotropy to achieve desired levels of filling ability, passing ability, and segregation resistance. SegregationâThe differential concentration of the components of mixed concrete, aggregate, or the like, resulting in non-uniform proportions in the mass (ACI 116). In the case of SCC, segregation may occur during transport, during flow into the forms, or after placement when the concrete is in a plastic state. This results in non-uniform distribution of in-situ properties of the concrete. Segregation resistanceâThe ability of concrete to remain uniform in terms of composition during placement and until setting (PCI 2003). Segregation resistance encompasses both dynamic and static stability. Self-consolidating concrete (SCC) (also self-compacting concrete)âA highly flowable, non-segregating concrete that can spread into place, fill the formwork, and encapsulate the reinforcement without any mechanical consolidation (ACI 237). Service lifeâThe time during which the structure performs its design functions without unforeseen maintenance or repair. SettlementâThe condition in which the aggregates in SCC tend to sink to the bottom of the form resulting in non-homogeneous concrete (PCI 2003). Surface settlement can also be caused by bleeding of free water and loss of air as well as movement of aggregate particles within fresh concrete (consolidation). Shear stressâThe stress component acting tangentially to a plane (ACI 116). Silica fumeâVery fine non-crystalline silica produced in electric arc furnaces as a byproduct of the production of elemental silicon or alloys containing silicon (ACI 116). Silica fume can be added to SCC to improve the rheological properties. Slump flowâTest method used (upright or inverted) to measure mix- ture filling ability (ASTM C 1611). Slump flow retentionâThe ability of concrete to maintain its slump flow over a given period of time. Slump flow spreadâThe distance of lateral flow of concrete during the slump-flow test (ASTM C 1611). Slump flow spread is the numer- ical value in inches (mm) of flow determined as the average diam- eter of the circular deposit of SCC at the conclusion of the slump flow test. StabilityâThe ability of a concrete mixture to resist segregation of the paste from the aggregates (ASTM C 1611). Stability, DynamicâThe resistance to segregation when external en- ergy is applied to concrete, namely during placement. Stability, StaticâThe resistance to segregation when no external en- ergy is applied to concrete, namely from immediately after place- ment and until setting. T-50 measurement (also referred to as the T-20 in. time in North America)âThe time for the concrete to reach the 500 mm (20 in.) diameter circle drawn on the slump plate, after starting to raise the slump cone (ASTM C 1611). TextureâThe pattern or configuration apparent in an exposed surface, as in concrete and mortar, including roughness, streaking, striation, or departure from flatness (ACI 116). ThixotropyâThe property of a material that enables it to stiffen in a short period while at rest, but to acquire a lower viscosity when me- chanically agitated, the process being reversible, a material having this property is termed thixotropic or shear thinning (ACI 116). Thixotropy indicates formwork pressure and segregation resistance of SCC. TransportabilityâThe ability of concrete to be transported from the mixer to the placement site while remaining in a homogeneous condition (PCI 2003). V-funnelâDevice used to determine the time for a given volume of concrete to flow out through a funnel opening (PCI 2003). ViscosityâThe resistance of a material to flow under an applied shearing stress (ASTM C 1611). Viscosity-modifying admixture (VMA)âAn admixture used for en- hancing the rheological properties of cement-based materials in the plastic state to reduce the risk of segregation and washout (ACI 237). Visual Stability Index (VSI)âA test that involves the visual examina- tion of the SCC slump flow spread resulting from performing the slump flow test (ACI 237). Water-cementitious material ratio (w/cm)âThe ratio of the mass of water, exclusive only of that absorbed by the aggregate, to the mass of cementitious material (hydraulic) in concrete, mortar, or grout, stated as a decimal (ACI 116). WorkabilityâThat property of freshly mixed concrete or mortar that determines the ease with which it can be mixed, placed, consoli- dated, and finished to a homogenous condition (ACI 116). For SCC, workability encompasses filling ability, passing ability, and segregation resistance, and it is affected by rheology. Yield stressâThe minimum shear stress required to initiate (static yield stress) or maintain (dynamic yield stress) flow (ACI 237). The yield stress is closely related to slump flow (lower yield stress re- sults in higher slump flow); it is calculated as the intercept of the shear stress versus shear rate plot from rheometer flow curve measurements.