Workability of concrete refers to the effort (or energy) required to manipulate a freshly mixed quantity of concrete with minimum loss of homogeneity. The manipulation may refer to pumping, placing, consolidation and/or finishing of the concrete. Workability of concrete is quantified in terms of “slump” or “slump flow”. The slump flow test has been standardized as ASTM C 1611, “Slump Flow of Self-Consolidating Concrete.” Slump and slump flow are measurements of concrete rheology and is determined using a slump cone. A slump cone is standardized measurement cone having a predefined volume and angle. FIG. 1A illustrates a standard slump cone 100 which includes a top opening 102 and a bottom opening 104.
The slump cone 100 is used by placing the slump cone 100 on a flat surface and filling the slump cone 100 with fresh concrete through the top opening 102 as shown in FIG. 1B. The slump cone 100 is completely filled and any excess concrete at the top of the slump cone 100 is scraped off. The slump cone 100 is lifted directly upwards. The concrete 110 slowly spreads out over the flat surface without the support of the slump cone 100 to hold the concrete 110 in place. The spreading action causes the height of the concrete 110 to decrease to a height 112 from an initial height 116 corresponding to the height of the slump cone 100. The distance 114 represented by the change in height of the concrete 110 is referred to as the “slump”. The “slump” is indicative of the yield value of the concrete. The concrete 110 ultimately spreads out over the flat surface to form a crude disc or pancake shape as shown in FIG. 1C. The diameter 118 of the disc formed by the concrete 110 is referred to as the “slump flow”.
Another measurement of the workability of the concrete is the T50 test. The T50 test quantifies the viscosity of the concrete 110 and measures the amount of time in seconds for the concrete in the slump flow test to spread to a diameter of 50 cm or 500 mm). The T50 test has been standardized as ASTM C 1611. The T50 time is indicative of the viscosity of the concrete. The slump, slump flow and T50 are used to assess the rheological properties of the concrete and predict how it will flow or move under the force of gravity or positive force into a desired shape or position.
Conventional concrete has a slump flow of 80 mm to 120 mm. The placement and finishing of concrete floors in residential and commercial applications using a conventional concrete is difficult, labour intensive and time consuming due to this low slump. Conventional concrete having a minimum compressive strength of 25 MPa is typically designed to have a maximum slump flow of 100 mm; however, water is added in the field to raise the slump flow to 200 mm to improve the workability of the concrete, and in particular the placeability of the concrete. The consequences of adding extra water to increase the water/cement ratio, is to decrease ultimate strength and increase shrinkage.
SCC is a type of concrete characterized by a low yield, moderate viscosity which can be used to ensure a uniform suspension of aggregate during transportation, placement and finishing until the concrete sets. SCC has properties which are desirable in the construction of the concrete floors in residential and commercial applications; however, known SCC compositions are more costly to produce than conventional concrete and provide a surface which is prone to tearing and peeling in response to mechanical working/finishing (smoothing and/or hardening) such as when power troweled. This results in surface defects such as blisters and delaminations which are unacceptable for most applications.
Accordingly, a SCC mixture is desired which is comparable in cost to conventional concrete used in residential and industrial floor construction but which requires less time to place and finish, thus increasing the productivity of the concrete supplier and user.