Mohammed, Haneen Adil
(2018)
Design and evaluation of two-layer roller compacted concrete.
PhD thesis, University of Nottingham.
Abstract
Roller Compacted Concrete (RCC) is a mixture of well graded aggregates, cement and water. It is placed with a high compaction asphalt type paver and compacted to high density by vibratory rollers to provide a high strength and durable pavement structure. RCC requires no formwork, surface finishing, dowelled joints or reinforcement. These characteristics make RCC simple, fast and economical. However, it also presents difficulties with high-speed applications related to surface texture and surface evenness. These difficulties have so far restricted the use of RCC to the lower layers of normal roads.
A two-layer RCC pavement system is a type of composite pavement consisting of two concrete layers. The two layers are paved in either a “wet-on-wet” technique or ”wet-on-dry” technique. The bottom layer serves as the main bending-resistant component of the composite slab, while the top lift is generally constructed with higher-quality constituent materials for improved surface characteristics such as noise and skid resistance.
The aim of this research is to evaluate and design two-layer RCC systems with different aggregate sizes and types and different placement conditions in order to expand the application of RCC in pavements. Mechanical properties, bond strength properties, durability characteristics, surface properties, fatigue damage, joint deterioration and pavement design are the main. A range of testing equipment, methodologies and tools have been used in this investigation.
The findings of this study showed that a two-layer RCC system can achieved good strength and stiffness for each of the mixtures in the two layers. Also, the inter-layer bond was found to be strong when the two layers were placed within one hour, but weaker when the upper layer was placed three hours after the lower layer. Moreover, the durability of the two-layer RCC system was found to be acceptable, especially when the upper layer was placed within an hour of the lower layer. The surface characteristics for the upper layer of RCC showed that the minimum requirement for skid resistance and texture depth have been achieved. However, it is suggested that further investigation is needed, particularly into the evenness of RCC.
The investigation into the effect of dynamic load on the two-layer RCC system demonstrated a good fatigue strength for each RCC mixture and for the two layers together, compared to conventional concrete pavements. Also, the results of load transfer stiffness and joint deterioration showed acceptable performance with regard to crack or joint width, shear stress and placement conditions. The effect of other parameters such as moisture and differential temperature requires a separate investigation and is recommended for future work.
The results of the design and analysis of two-layer RCC using KENSLAB, a finite element program, indicted that RCC could perform successfully in pavements with a long service life.
In conclusion, the results obtained show that the two-layer RCC are a valid alternative for pavements. On one hand, the use of a harder and more resistance aggregate at the top layer guarantees higher skid resistance and durability, while limiting for the use of high quality aggregate. On the other hand, the results show that adequate construction techniques can alleviate the problems arising from the lack bond between layers.
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