Mix design proportioning methods for Roller Compacted Concrete RCC:Mix design proportioning methods for no slump concrete applicable for Roller Compacted Concrete.
Materials Used in RCC mix designa) Cementitious materials: Cement content is generally low (typically 70 to 130 kg/m3). Any kind of Portland Cement (but low heat cement is a preferred type when its is available) Fly Ash: Class F pozzolans are preferred. When used pozzolans, may replace up to 80 % of cement content. b) Aggregates: Selection of aggregates and control of aggregates quality is essential. Aggregates shall meet ASTM C33 standard.
- Coarse aggregates: Most of project use a coarse aggregates with a Nominal Maximal Size Aggregate (NMSA) between 37.5 and 75mm. The thickness of placement layer shall be more than 3 times the NMSA.
- Fine aggregates: The grading of fine aggregates strongly influence paste requirements and compatibility of RCC. It also affects water and cementitious material requirements needed to fill the aggregates voids and coat aggregate particles.
- Other aggregates: Fines (crusher fines): In low cement content mixtures, supplements fines (material passing 0.075 mm sieve) are usually required. Fines quantities is generally 5% of total aggregates
Mix design considerations:a) Workability / Consistency: Measured with a Vebe vibrating table (ASTM C 1170). The test principle is to measure the time for the concrete to be consolidated by vibrating in a cylindrically shaped mold. The longer the time, the drier/lesser workable is the concrete. Vebe times of RCC mixtures is generally from 10 to 40 seconds. Comparison of concrete consistency measured by slump and Vebe apparatus. ACI 211.3R.
|Consistency||Slump (mm)||Vebe (s)|
|Extremely dry||-||32 to 18|
|Very stiff||-||18 to 10|
|Stiff||0 to 25||10 to 5|
|Stiff plastic||25 to 75||5 to 3|
|Plastic||75 to 125||3 to 0|
|Very plastic||125 to 190||-|
- Vebe Consistency Test
- Density and air voids tests.
- Moisture/water content tests.
- Cement content evaluation
- Temperature monitoring
- Using modified Vebe apparatus (generally for mix with Vebe up to 20 seconds),
- Using of special vibrating hammers