Influence of Additives on Flexural Strength of Roller Compacted Concrete
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-08-21 |
| Journal | Journal of Cement Based Composites |
| Authors | Saad Issa Sarsam |
| Institutions | University of Baghdad |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study investigates the optimization of Roller Compacted Concrete (RCC) flexural strength through the partial replacement of Portland cement with three common additives: Hydrated Lime, Fly Ash, and Fumed Silica. The research compared performance across two aggregate gradations (Dense and Gap) and two standard testing modes.
- Optimal Additives: Hydrated Lime and Fly Ash are strongly recommended for improving RCC flexural strength. Hydrated Lime yielded the highest gains, increasing strength by up to 109% (Gap graded, 10% replacement).
- Fly Ash Performance: Fly Ash replacement also provided significant benefits, increasing flexural strength by up to 99.7% in Gap graded mixtures (10% replacement).
- Fumed Silica Impact: Fumed Silica replacement consistently resulted in a decline in flexural strength (up to 77% loss). This is attributed to its extremely high specific surface area (up to 230,000 m2/kg), which absorbs water necessary for cement hydration.
- Gradation Effect: Dense graded mixtures generally exhibited higher flexural strength than Gap graded mixtures for control samples, but Gap graded mixtures showed greater percentage strength improvements when optimized with Hydrated Lime or Fly Ash.
- Testing Mode Discrepancy: Flexural strength measured under the Four-Point loading mode was significantly lower than that measured under the Three-Point loading mode, ranging from 0.787 to 0.732 times the 3-point strength value.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Optimum Cement Content | 12 | % | Control RCC Mixture (by weight of aggregate) |
| Beam Specimen Dimensions | 38 x 10 x 8 | cm | Flexural Testing Sample Size |
| Fumed Silica Specific Surface Area | 170,000 - 230,000 | m2/kg | Material Property |
| Hydrated Lime Specific Surface Area | 4,404 | m2/kg | Material Property |
| Fly Ash Specific Surface Area | 650 | m2/kg | Material Property |
| Max Strength Gain (Hydrated Lime) | 109 | % | Gap Graded, 10% cement replacement |
| Max Strength Gain (Fly Ash) | 99.7 | % | Gap Graded, 10% cement replacement |
| 4-Point Strength Ratio (Dense) | 0.787 | Folds | Relative to 3-Point Loading Strength |
| 4-Point Strength Ratio (Gap) | 0.732 | Folds | Relative to 3-Point Loading Strength |
| Coarse Aggregate NMS | 25.4 | mm | Nominal Maximum Size |
| Curing Age | 28 | Days | Standard Testing Age (ASTM C-78, C-293) |
Key Methodologies
Section titled âKey MethodologiesâThe experimental procedure followed a modified Proctor standard (ASTM D-1557) for mixture preparation and utilized a three-stage rolling compaction process to achieve target density.
- Material Preparation: Fine and coarse aggregates were oven-dried, sieved, and recombined to meet the requirements for Dense (Iraqi SCRB) and Gap (British Standards B.S. 882) gradations, both with a 25.4 mm Nominal Maximum Size (NMS).
- Mixture Design: Mixtures were prepared at the optimum cement content (12%) and at levels 2% and 4% above and below optimum. Additives (Hydrated Lime, Fly Ash, Fumed Silica) were incorporated as partial cement replacements at specified percentages.
- Slab Compaction: The mixture was placed in a 38 x 38 x 10 cm mold and subjected to initial compaction via a vibrating table (3 cycles of 30 seconds).
- Roller Compaction (3 Stages): A 36 kg roller (16 cm diameter) applied 10 passes per direction in each stage:
- Stage 1 (Primary): 1.1 kg/cm width load.
- Stage 2 (Breakdown): 3.2 kg/cm width load.
- Stage 3 (Final): 5.3 kg/cm width load.
- Curing: Slabs were covered for 24 hours at room temperature (30 ± 2°C), then immersed in a water bath for 27 days (30 ± 2°C).
- Specimen Extraction: Beam specimens (38 x 10 x 8 cm) were sawed from the cured slabs using a diamond saw (per ASTM C78/C293).
- Flexural Testing: Flexural strength was determined after 28 days using two distinct testing modes: Three-Point Loading and Four-Point Loading.
Commercial Applications
Section titled âCommercial ApplicationsâThe findings regarding optimized RCC mixtures are highly relevant for infrastructure projects requiring enhanced durability and load-bearing capacity, particularly in pavement design.
- Rigid Pavement Construction: Implementing optimized RCC mixtures for high-volume traffic roads, highways, and airfields where flexural strength is the primary design parameter.
- Sustainable Infrastructure: Utilizing high percentages of industrial byproducts (Fly Ash and Hydrated Lime) as cement replacements to reduce carbon footprint and material costs in mass concrete applications.
- Industrial and Heavy-Duty Flooring: Construction of durable floors in warehouses, ports, and manufacturing facilities that must withstand high concentrated loads and repetitive fatigue.
- Dam and Hydraulic Structures: Application of RCC in gravity dams and roller-compacted concrete dams, where material optimization ensures structural integrity and cost efficiency.
- Material Specification Development: Providing quantitative data to inform engineering standards regarding the use of additives and the selection of appropriate flexural testing methodologies (3-point vs. 4-point loading) for quality control.
View Original Abstract
Roller compacted concrete is considered as a sustainable solution. In the present investigation, three types of additives namely (fly ash, fumed silica, and hydrated lime) are implemented as partial replacement of Portland cement for preparation of roller compacted concrete slab samples using dense and gap aggregate gradation. The slab samples were prepared at optimum cement requirement of 12 % and at (2 and 4) % cement below and above the optimum. Beam specimens of (38 x 10 x 8) Cm were extracted from the slab samples using diamond saw. The specimens were subjected to flexural strength determination using two testing modes, the three and the four points loading. It was noticed that the flexural strength under four-points loading mode is lower by a range of (0.787 to 0.732) folds than that under three-points loading mode for dense and gap graded mixtures respectively. It was concluded that the flexural strength increases by (96.2, 84, and 17.2) % and (109, 86, and 9.3) % after replacement of (10, 12, and 15) % of cement by hydrated lime while it declines by (50, 64.6, and 77) % and (0.1, 30.8, and 63.5) % after replacement of (5, 7, and 10) % of cement by fumed silica for dense and gap graded aggregates respectively. The flexural strength of dense graded mixtures increases by 63 % at 20 % replacement by fly ash, however, it increases by (99.7, 53.8, and 1.0) % after replacement of (10, 12, and 15) % of cement by fly ash for gap graded aggregates respectively.