COMPARATIVE ANALYSIS OF THE STRENGTH OF CONCRETE MADE FROM VARIOUS AGGREGATE
ABSTRACT
The importance of studying the behavior and properties of concrete can be highlighted by considering the fact that concrete is the most used man-made material in the world. The very first step in making concrete is its mix design and deciding the type and amount of constitutes used in the production of concrete which should fulfil the requirements of the final product. Mix design models are commonly used for the purpose of proportioning concrete ingredients while anticipating the properties of the final product.
The current document deals with the commonly used principals in mix design models namely particle packing theory and excess water/paste layer theories. The conducted studies includes an investigation on accuracy of particle packing models (Toufar, 4C, CPM) and also tries to address the issue with measurement of specific surface area of particles as an essential input to water/paste layer theories.
It has been observed that the particle packing models can predict the packing density with acceptable margin. However, it should be mentioned that the particle packing models by themselves are not mix design models but should be rather used as a part of a mix design. In addition, it was found that the accuracy of calculating the specific surface area of particles based on their size distribution curve can be further improved by assuming angular platonic solids as uniform shape of aggregate instead of traditional approach of assuming spheres for aggregates’ shape.
1. INTRODUCTION
1.1. Background
Historical evidences indicate that cement was first used by ancient Macedonians around eighth century. The knowledge of making hydraulic cement was later on documented by French and British engineers in the 18th century. Construction with cement and also usage of reinforcement in the structural design eventually led to making concrete the most used man made material. As the fundamental knowledge of making cement and concrete developed and was able to cover the basic questions about constitutes of concrete, researchers have been continuously working with the ways of optimizing mix design recipes. Optimization can be achieved by means of studying the ingredients of concrete mixes with the aim of maximizing the performance of concrete in both fresh and hardened state while keeping a low cost of production and limiting the pollutants released in the air due to cement production. As a result, several attempts have been made on formulating the mix design of concrete. Understanding the role of constitutes in fresh concrete is fundamental to the production of high quality concrete at fresh state, during hardening and as a hardened structural material. Fresh concrete can be characterized by several aspects among which workability is the most important one and is chiefly influenced by the water requirement, which in turn is a function of aggregates’ shape, grading, and fine content. As for the performance of the hardened concrete, the crucial factors are water to cement ratio which influences strength and permeability and cement characteristics and performance.