CHAPTER ONE
1.0 INTRODUCTION TO SCC
Self-Compacting Concrete (SCC), a relatively new category of high performance concrete, is proportioned in such that the concrete freely passes around and through reinforcement, completely fills the formwork and consolidates under its own weight without segregation. The high flowability of SCC makes it possible to fill the formwork without vibration
[Khayat, 1999; Khayat et al., 2004].
Developed in Japan in the late 1980’s [Ozawa, et al., 1989], SCC has been a topic of research and development in many locations, especially in Japan and Europe [Ouchi, et al., 2003]. SCC has been successfully used in numerous applications where normal concrete is difficult to place and consolidate due to reinforcement congestion and difficult access. Precast, prestressed bridge elements, such as AASHTO Type III girders, have congested reinforcement and tight dimensional geometry, and therefore can benefit from the use of SCC.
Three basic characteristics are required to obtain SCC: high deformability, restrained flowability and a high resistance to segregation [Khayat, et al., 2004]. High deformability is related to the capacity of the concrete to deform and spread freely in order to fill all the space in the formwork. It is usually a function of the form, size and quantity of the aggregate, and the friction between the solid particles, which can be reduced by adding a high range water-reducing admixture (HRWR) to the mixture. Restrained flowability represents how easily the concrete can flow around obstacles, such as reinforcement, and is related to the member geometry and the shape of the formwork.
Segregation is usually related to the cohesiveness of the fresh concrete, which can be enhanced by adding a viscosity-modifying admixture (VMA) along with a HRWR, by reducing the free water content, by increasing the volume of paste, or by some Combination of these factors.
Two general types of SCC can be obtained:
(1) Concrete with a small reduction in the coarse aggregate, containing a VMA.
(2) Concrete with a significant reduction in the coarse aggregate content without any VMA.
SCC has been claimed to offer many advantages for the precast, prestressed industry including elimination of noise and problems related to concrete vibration, lower labor cost per member, and faster casting, thereby increasing productivity. Due to the low water-cement ratio, SCC should have improved to durability and strength.
Generally, SCC contains a higher cementitious materials and lower water-cement ratio than conventional concrete, and so can provide relatively high strength. The paste usually includes fly ash, slag, silica fume, or other supplementary cementitious materials, or an inert filler such as limestone powder. The paste content of SCC is also relatively high, with a reduction in the size and quantity of coarse aggregate. These factors are typically associated with increased creep and shrinkage, and may be related to a reduction in elastic modulus.
WHAT IS SELF-COMPACTING CONCRETE (SCC)?
It is a concrete that can be compacted by its own weight and fills every corners in the formwork and the placing can be done without vibrating compaction. In the plastic state it is very homogenous, cohesive and very flowable.
1.1 WHY IT IS NEEDED?
Concrete is a versatile material extensively used in construction applications throughout the world. Properly placed and cured concrete exhibits excellent compressive-force-resisting characteristics and engineers rely on it to perform in a myriad of situations. However, if proper consolidation is not provided, its strength and durability could be questionable. To help alleviate these concerns, Japanese researchers in the late 1980’s developed a concrete mixture that deformed under its own weight, thus filling around and encapsulating reinforcing steel without any mechanical consolidation.
Self-Compacting Concrete offers new possibilities and prospects in the context of durability and strength of concrete. As a result of the mix design, some properties of the hardened concrete can be different for SCC in comparison to normal vibrated concrete. Mix design criterions are mostly focused on the type and mixture proportions of the constituents. Adjustment of the water/cement ratio and super plasticizer dosage is one of the main key properties in proportioning of SCC mixtures.
1.2 AIM AND OBJECTIVES
The aim of this study of self-compacting concrete using Plantain leaf ash as partial replacement of ordinary portland cement is to obtain self-compacting concrete satisfying EFNARC guidelines and make comparison of self-compacting concrete to normally compacted concrete in terms of workability and compressive strength.
The above aim will be accomplished by fulfilling the following research objectives:
Determining the effect of Plantain leaf ash as partial replacement of cement on the properties of SCC in FRESH STATE (Filling ability and Passing ability) HARDENED STATE (Compressive strength) Obtaining specific experimental data to understand fresh and hardened properties of self-compacting concrete.
Developing SCC using Plantain leaf ash as partial replacement of cement in varying dosages satisfying European standards and to study their behaviour.
Determining whether the properties observed in
(1) are structurally sufficient for its application according to relevant standard as a construction material.
Assessing the implication of its usage as a construction material in the built environment
1.3 SCOPE OF STUDY
For this study, concrete with varied percentages of Plantain leaf were used in producing self-compacting concrete in terms of filling ability and passing ability and were compared with normally compacted concrete.. The key parameter in the study is:
i. The workability characteristics using slump flow test, V-funnel test, L-box test and compressive strength characteristics at 14, 21 and 28 days using 45 cubes of 150mm X 150mm X 150mm were determined.
1.4 SIGNIFICANCE OF STUDY
To produce concrete of high and significant strength and durability to be used for all construction structures. To effectively utilize and solve the problem of the storage and disposal of plantain leaf ash. To minimize maintenance, labour cost, and cost due to the vibrators required.